Why increase the number of cylinders in an engine instead of increasing their volume? I've been reading about WW2 planes lately. Some of them have 12 or even more pistons in their engines.

But if your goal is to increase power, why would you add more pistons instead of simply increasing the size of the cylinders?

Example: The P-51 Mustang had a V12 engine with a total displacement of 27 liters. So that's 2.25 L per cylinder. Instead, why not have a V4 engine with the same total displacement, which would have been 6.75 L per cylinder?

Correct me if I'm wrong, but...

Such "collectivizing" of the cylinders would be more efficient for a number of reasons. The friction of piston rings scraping the cylinder would be less, meaning less oil and more power. The crankshaft and related things could be shorter. I believe it would be lighter for another reason too: the surface area goes up less than the volume (squared versus cubed). Probably the engine as a whole would be simpler.

I believe this concept can be applied to radial engines as well as inline engines. I made an assumption that 4-stroke engine needs a minimum of 4 cylinders. Today that is not true but during WW2 with the technology of the time, I'm not sure. There were radial engines with 3 cylinders. I'm unaware of any 4-stroke engines with 2 or less cylinders in that era.

Anyway, why not just make the cylinders bigger?

Constraints
Different applications have different constraints:

Aviation: very light weight, highly reliable
Marine: very high endurance
Automotive: moderately light weight, responsive
Motorcycle: very light weight, very compact, very responsive

Different technology ages yield different solutions due to additional constraints, always limited by the then contemporary technology:

Pioneer era: make it work
World War I/II era: as fast as possible
Post-war era: further, faster, better
Fuel crisis era: as efficient as possible

Aircraft Engines
The question is about the optimization of number of cylinders versus displacement volume per cylinder for engines used for aviation. This narrows the scope to “internal combustion reciprocating piston engines” (plus the Wankel engine as a very special case).
Obviously, rockets, pulse jets, turbine-powered,  and electric engines have no cylinders, and steam engines were never  (successfully) used in aircraft.
Number of cylinders and the cylinder displacement are two out of countless parameters that go into the design of any engine. Both may be used to increase the power output.
Power Increase
The power output of an engine may be increased either through the number of cylinder or through increasing the cylinder displacement (or both).
Each change of parameters causes the gain or loss of certain wanted characteristics. These are listed further below under (N), (n), (D), and (d).

Increasing the number of cylinders means gaining (N) and losing (n)
increasing the cylinder displacement means gaining (D) and losing (d)

Adding cylinders is easier than increasing the size of the cylinder. The cylinder geometry does not change. Identical engine parts can be used multiple times in the same engine design (cylinder banks, cylinder heads, or complete engine blocks).
Tradeoff shift
Starting from one engine configuration, the same power output may be achieved by

gaining (N) and (d), and losing (n) and (D)
or
gaining (n) and (D), and losing (N) and (d).

Reasons to increase the number of cylinders (N)

Torque directly scales with the number of cylinders
Increasing the surface-to-volume ratio is advantageous for air-cooled engines
Increase the power: Adding cylinders is easier than increasing the size of the cylinder. The cylinder geometry does not change. Identical engine parts can be used multiple times in the same engine design (cylinder banks, cylinder heads, or complete engine blocks)
Improve balancing of forces and momenta
Reduce the time between power strokes
Decrease the impact of a failing cylinder
Improve the flatness of the torque distribution over revolution speed.
Enable more flexible and more distributed form factor

 Pratt & Whitney R-4360 Wasp Major, 28-cylinder, 28 l, 3500 hp, 2700 rpm, built 1944-1955.
Reasons to decrease the number of cylinders (n)

Simplicity: less moving parts improve robustness,  decrease the need for service, thereby increase the availability.
Enable a more compact form factor

Mercedes 1 cylinder, 1.5 kW, 720 rpm, 84 kg, built 1888.
Reasons to increase the cylinder displacement (D)

Increase power through torque

BMW IIIa, 6-cylinder, 19.1 l, 200 hp, 1400 rpm, built 1917.
Reasons to decrease the cylinder displacement (d)

Smaller displacement means smaller pistons, shorter rods, or both. Either way,  smaller displacement allows for higher revolution speed, and higher acceleration.
Smaller combustion chamber will decrease the time required for the flame expansion (gasoline only, not diesel). This allows for higher revolution speed.
The valves are limiting the gas stream into and out of the cylinder. The valves are subject to the surface-volume ratio. Smaller cylinders are easier to fill and empty through the valves, allowing for higher revolution speed.
At a given compression rate, smaller cylinders have to withstand less total force, allowing for a lighter engine structure (less weight).

JPX PUL 212, 1 cylinder, 212 cm³, 11 kW, 6000 rpm.

Notes

Radial engines belong to the WW I/II era. Most of them were air-cooled. For air-cooled engines, the surface-to-volume ratio matters. Therefore increasing the number of cylinders instead of the displacement per cylinder is obvious.

Aircraft during WW I/II had to be as fast and powerful as possible to attack and defend. There was no good reason to go for less than 6 cylinders.

Four-stroke engines perfectly work with 1, 2 and 3 cylinders. They are used powered paragliders respectively ultralight aircraft.

Certain cylinder numbers are more preferable to due symmetry reasons

6, 8, 4 for in-line engines
odd numbers (per row) for radial engines

Building radial engines with an even number of cylinders is well possible, albeit an even number in one row us not preferable. Multi-row radial engines with even cylinder number have been flown in many aircraft.

Automotive engine developers prefer 0.5 l per cylinder as ideal trade-off.

A high cylinder count would be necessary to build high power piston engines, but this segment is now occupied by jet engines.

Radial engines with less than 5 cylinders exist. Here is a radial 3-cylinder, built 1930 in the USA:


What is the aerodynamic motivation behind vortex generators? An airplane's wing creates lift efficiently when the airflow is parallel to the chord of the wing. Vortex generators twist the airstream on the wing surface.

Doesn't this kind of twisted airflow cause lift inefficiency?

You are correct that vortex generators create drag, so a successful installation depends on reducing some other drag even more. Airflow separation causes significant drag that vortex generators can reduce. The energy consumed by vortex generators making drag is injected into the boundary layer, delaying airflow separation and the eventual stall, which might be of even more value. Correcting poor flight characteristics on an existing design is often where they are used. The illustration of a wing stalling is easy to understand but may not be the best use of VGs since few wings fly continuously on the brink of separation.


Why is this airfoil curved upwards on the bottom part of the airfoil? Image source datawiki.net

Is this to slow down airspeed. I know that the high pressure and low pressure above and below the wing both contribute to downwash, but how does this airfoil form downwash?

Downwash is simply the deflection of air due to airfoil (or wing etc.)

Symmetric airfoils don't produce downwash (or lift) at zero angle of attack.

Source: oppositelock.kinja.com

However, as the angle of attack is increased, the (symmetric) airfoil produces both.

Source: Effect of angle of attack on flow field and body forces by Paul Nathan from youtube.com

Symmetrical airfoils are used in rotary wing applications, vertical tail (and rudder) etc.


Is there a difference between altitude and flight level? I came across a question in Quora asking the difference between altitude and flight level. One of the answers said that anything above the transition altitude is referred to as a flight level. So suppose an aircraft is flying at 35,000ft, it is flight level 350. Is this correct? Can we not refer to altitude as flight level below 18,000ft (the transition altitude)?

Yes, altitude is below transition level, flight level is above transition altitude.

Altitude is referencing to actual (local) air pressure, while flight level is against standard pressure 2992 / 1013.

The transition altitude is dependent on the location and are definded so both will not mix up.

When climbing through transition altitude, pilots set their QNH to 2992 - and so no longer need to set it to changes due to local weather.

When decending through transition level they set it back to the local QNH - as they are close enough to ground the real altitude (above ground...) is getting important.


What does it cost to get an ATP certificate from scratch? If someone decides to become a professional pilot - meaning an airline or business jet pilot in the USA - what does it cost to get the certifications and ratings and build enough hours to become employable? Let's assume that the person is starting from scratch and works through private, instrument, commercial and ATP qualifications.

I'm thinking of a scenario where someone already has a career and income but decides to change to flying and is able to invest the necessary time and money. Of course this could include other commercial flying jobs along the way - like crop dusting or banner towing - but the idea would be to eventually reach a position that pays a decent salary. "Decent" isn't very precise but I mean something much higher than the low regional salaries mentioned in this question.

The cost from 0 to ATP can be highly variable.  An easier number to quantify is 0 - Commercial/CFI.

Even the cost of 0 - Comm/CFI can vary, but there are a few accelerated programs that offer this.  One service (I'm not advertising, so I'm not naming them) offers a program that lasts 150 days and costs $65,000* + checkride expenses.  You start with nothing and end up with single/multi commercial, an instrument rating and your CFI/MEI/II along with 100 hours multi-engine time.  This particular program (and others like it probably) hires their instructors from within, so there is a possibility for multi-instruction -- but you won't be making much money for it.

The cost of commercial to ATP is harder to nail down because of the possibilities that open up post-commercial.

On the high end, you could just rent or buy time to ATP mins, but that could cost a fortune.
On the low end you could work to ATP mins and make some money.

A good way to make money with a fresh commercial/cfi ticket is to instruct. There are also jobs like banner towing or pipeline/powerline patrol you could do, but you probably still need to build time beyond commercial mins to be competitive for those jobs.  You also mention cropdusting, but keep in mind many of those ops are turbine powered ag-cats and you won't be competitive there with a fresh commercial ticket.

*You can do it cheaper but I'm giving these numbers because a fast but expensive program may appeal to a career changer.


What steps are needed to communicate with ATC on an A320? In the description to this video, Captain Joe says that it took this inexperienced person 20 minutes to establish radio contact with ATC (in an A320 simulator).

This seems like an awful lot of time just to find and push the "push-to-talk" button. So, is there something more to it, like having to enter the right frequencies or something?

In the hypothetical case described in the video (passenger having to fly the plane), would it be enough to push the PTT button to establish contact with ATC, or are there other steps that need to be taken?

You need to even realize that you have to push a button to talk. Not everyone grew up with ham radio, CB radio, or walkie-talkies, especially nowadays where everybody has a mobile phone.
You need to find the PTT button.
You need to select where you want your headset to be routed: you can talk to your co-pilot, you can talk to ground crew, you can talk to the cabin crew, or you can talk to you radios.
Note the plural above: the plane has multiple radios. You need to select the right one.
You need to know the frequency of the ATC entity you want to talk to.
You need to tune the radio (the right radio) to that frequency.
Every radio has an active frequency and a standby frequency. You need to make sure that you change the right one. (Either change the active one, or if you change the standby one, you need to make that one active.)
You need to realize that radio is a shared medium, and that only one person can talk at any one time, and that you need to wait for a break.
Depending on how busy the frequency is, you might not even recognize where the pauses are, or you might not be able to squeeze yourself in because you are not used to talking that fast and efficient.

I consider myself technically adept, and I used to do a little bit of CB radioing in my youth, but I'm not sure if I could figure all that out in 20 minutes.


How heading bug is calculated during cross wind and tail wind? From this question, it is been suggested to ask different question, rather than keep discussing it under comment section.

How is the heading bug calculated and used for navigation when there is a cross wind?
… when there is a tail wind?
Will the heading bug matter for navigation when there is wind correction required?
What role does the heading bug play in autopilot mode?

First thing first, let's go over some concept: heading is which way the plane's nose is pointing at, track is which way the plane is travelling on the ground. E.g. if your heading is 360 (North), and the wind is blowing from 090 (blowing East to West), the plane's track may be 350 (slightly left of North).

With that in mind, it's not hard to deduce most of the time pilots want to fly track, rather than heading. The purpose is to navigate from point A to point B on the ground. In our example, you have to turn the plane slightly to the right to compensate for the crosswind. To figure out exactly how many degrees to turn, you will first need to decide how fast you want to fly. After that, it's simple geometry.

A mechanical flight computer can be used to calculate the drift angle easily. Using it is a matter of marking dots on a transparent disc, then sliding and rotating it to the correct position and read off the pre-calculated figures below.

If you are flying manually, or flying a plane with an elementary autopilot, you will need to calculate the drift angle, then add (or minus) that to your desired track to get the heading. You will then set the heading bug to that value. Theoretically, that heading should compensate just enough crosswind that you stay on your desired ground track. In practice minor adjustments are often necessary. Provided that the numbers you use are not awfully off, you should end up with an estimation good enough for the safety of your flight.

If you are flying a plane with an advanced flight computer which has the ability to detect winds aloft, your autopilot will fly the track you dial in and automatically compensate for crosswind.

So to answer your questions:

You will use simple math or tools to compute the heading which will let you fly the desired track.
It does not matter when you have an exact headwind or tailwind.
Heading bug denotes the desired heading, not track. You always turn your plane towards the heading bug.
Advanced autopilot fly track, fundamental ones fly heading. Some autopilots can read the heading bug position on the instrument, others must be set explicitly on another panel.


Is a dancing crew dangerous? Recently, the crew of an Indian airline performed a short choreographed dance sequence mid-flight on the occasion of Holi. This is, a not so rare practice amongst low-cost Indian carriers, who organize such dance sequences to celebrate special festivals (since festivals are a huge part of Indian culture, plus publicity for the airline afterwards).
Here is a YouTube video.

One of the pilots can be seen recording the dance on his camera.

SpiceJet specially planned this event, and had extra cabin crew on-board the flight as a precaution. Also, during the dance, one of the pilots was in the cockpit while the other one was outside, following standard regulations.
DGCA however, got wind of this, and turned out to be not in a very festive mood.

Mid-air Holi celebrations aboard eight flights have cost SpiceJet heavily, with the DGCA issuing show cause notice to the airline and suspending two of its pilots.

Here's another news link.
One of the arguments made by the DGCA was that this was dangerous to flight operations, and could have resulted in disaster had there been any emergency on-board during the event. Also, that this could result in an unruly cabin environment where in-flight safety of the crew and passengers would be affected.
Were the actions (suspension of pilots and showcause notice to the airline) justified? Is a dancing cabin crew dangerous to flight operations?

Well I suppose the answer depends on whether or not the flight crew are good dancers: If my uncoordinated self was trying to bust a move in an airline cabin I'd probably wind up kicking someone in the face, but these folks seem to be doing OK.
I can only assume dance lessons are part of SpiceJet's crew training program :-)

Alright, in all seriousness - there is increased risk any time every person onboard isn't securely strapped into their seats. There have been incidents (recent ones) where flight crew walking about the cabin have been injured due to unexpected turbulence, and those same unrestrained people can essentially become human projectiles to injure others onboard.
That said I personally don't think the cabin crew doing a mid-flight dance routine poses a significant safety risk.

The fact that one of the pilots was out of the cockpit recording it is slightly more questionable, and may be what has the DGCA upset in this situation. While there are procedures for having one pilot off the flight deck those provisions are generally for necessary things (like a trip to the bathroom, or investigating a systems fault). The intent is for the cockpit to be manned by two qualified pilots at all times.
If an emergency were to have happened during this dance routine the pilot we see in the video would have had to get back to the cockpit, strap in, and put on a headset (& possibly an oxygen mask) before being of much use.


Why most military transport aircrafts use turboprop engines? What is the reason behind that most (or many) military transport aircraft use turboprop engines?

It depends on the main purpose of the mission.
For example, for long haul flights, carring many pallets, they will use probably the turbo jets, because they have more endurance, and normally they will land on longer runways.


How does the idle mixture adjustment in a Stromberg NA-R9B float-type carburetor work? At what temperature should idle mixture adjustments be made in Stormberg NA-R9B float-type carburetor?

The temp is nominally 68F, but the acceptable range is 40 to 80 ambient, by practice.

I can't say about that specific carb, but generally in the Stromberg and the SUs, there is a needle, which can be raised and lowered, which changed the metering.  By changing the taper of the needle, you can also change the mixture profile through the venturi flow rates.

We used to use a manometer to get the vac reading, and then look at EGT to make a decision on mixture.

The needle height will impact the overall mixture, and the shape of the needle will impact the mixture through the flow range.

What aircarft is this on?  I know some of the J-3s had Stromberg carbs, but this specific carb model is not ringing any bells on aircraft.


How do I know if an arrival procedure (STAR) clearance includes altitudes? Air traffic control (ATC) can issue a standard terminal arrival route (STAR) to aircraft entering the terminal environment. The STAR usually communicates a predefined route of flight (fix1, fix2, fix3, etc.). The STAR procedure usually includes altitudes too.
What will I hear from a controller when I am to follow the vertical guidance on the STAR vs. waiting for assigned altitudes?

In the U.S., the phrase "Descend via the (arrival)" means that you are cleared to the altitudes as published.  Without that phrase, simply cleared for the ___ arrival, then your clearance is the fixes, but ATC will assign your altitude explicitly. In this case, the published altitudes may later be assigned, so descent planning should still be based on making the next fix at its altitude. You just don't go below your assigned altitude until cleared lower.

FAA Explanations:
Starting on page 8 for "descend via" clearances: http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/afs400/afs470/pbn/media/rnav1_rnp1_rnav2/climb_descend_via_faq.pdf

More succinctly: https://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/info/all_infos/media/2014/InFO14003.pdf


Did the cusp in the Boeing 377/C-97/KC-97’s fuselage structure cause fatigue problems? The Boeing 377 Stratocruiser - a civilian adaptation of the C-97, a military transport which would also later be developed into the KC-97 - were derived from the B-29/B-50 family by grafting a large, bulbous passenger/cargo compartment onto the B-29/50 fuselage; this created a sharp cusp in the fuselage cross-section, as can be seen in this photo of a half-built Stratocruiser:

(Image source)

Such a sharp discontinuity in the fuselage profile would be expected to serve as a stress concentrator in a pressurised aircraft, like the 377/C-97/KC-97 series, and cause accelerated fatigue cracking in and around the cusp, shortening the lifespan of these fuselages; did these aircraft, in fact, experience fatigue problems emanating from the fuselage cusp, and, if so, how were they dealt with?

You can actually see the same effect happening with soap bubbles when they touch and form a flat film connecting them. You can actually still see this type of fuselage in use in the Boeing 717 (Douglas/McDonnell Douglas DC-9). A lot of other narrowbody airliners also have it, but the outer panels fair over the intersection between the two fuselages.


Learn in-depth about airplane operations Currently seeking a book or manual that teaches a civilian how a cargo aircraft operates and what it's pilots do, say a 787. Preferably a high-level overview at a per flight phase:

Pre-flight: Flight planning, aircraft checkout (airworthiness), maintenance checking, taxing, ATC communication, etc
Take-off: What do pilots look at during take-off: engine parameters (torque?), airspeed, etc.
Cruise: What do pilots moderate during cruise? What are they doing to prepare for landing?
Landing: Again, what parameters are they looking at, and how often are they looking down? How and what are they communicating to ATC?
Post-flight: What happens to the aircraft? What maintenance is done on the aircraft? What are they doing while they await instructions from ATC? What reports are looked at.

I understand that this is a lot of information to ask for from one book but I am willing to do a lot of reading, from various sources. Any help in answers these questions would be greatly appreciated as well. Young engineer in the aerospace industry and I'd like to learn more.

I'm not aware of any official resources which present all that information in a concise way, but to get a general idea of the operation of a modern civil passenger aircraft you can refer to the manuals provided with flight simulation add-ons. As opposed to the standard aircraft contained in most flight simulators, these payware models are very accurate and highly complex.

Next to the complete manuals, each aircraft typically also contains a tutorial flight manual, where all the steps necessary for the operation are shown in detail (100+ pages each). Here are a few examples:

787: http://qualitywingssim.com/files/ultimate_787_collection/docs/QualityWings%20-%20Ultimate%20787%20Collection%20Tutorial.pdf
A320: https://www.aerosoft2.de/downloads/a318-a319/Aerosoft-Airbus-A318-A319-Vol6-StepbyStep-EN.pdf
Some other Boeing aircraft (PMDG): https://www.precisionmanuals.com/pages/downloads/documentation.html

If you're specifically interested in ATC communications, you can for instance refer to the IVAO documentation about IFR phraseology: https://www.ivao.aero/training/documentation/books/DOC_IFR_phraseology.pdf

Remember that these are NOT official documents, so they are not suitable for any real world use. But in my opinion they are the easiest way to get an idea of aircraft operations. At least that's how I learned it! It has helped me a lot in my Aerospace Engineering studies.


Could modern unmodified Airbus aircraft be used for zero-G flight? ESA operates a mostly-stock A310 for their zero-G science flights, which doesn't have the flight envelope protection of more modern planes. Even then, a third pilot is required to monitor warnings to sort out the ones normally encountered in the parabolic maneuvers from unusual ones. If this aircraft were replaced with a modern Airbus (newer than A300/A310), would it be possible to fly these parabolic maneuvers without going into alternate law or doing other modifications to the control system?

According to this source and this source, the relevant A320 control laws (CLAWS) limitations are:

Normal load factor limitation in clean configuration down to -1g
Nose down pitch attitude down to -15deg
High Speed Protection (HSP) to prevent exceeding VD/MD

The problematic one would be the pitch attitude limiting. Since the pitch attitude will keep decreasing at zero G, the limiting function will pull the aircraft up and increase the load factor after some point. This could limit the time in zero G below the requirement.

Given the constraints and objective, more analysis would be needed to ascertain whether aircraft in Normal Mode is acceptable.


USB interface for FDR? Currently I am investigating the feasibility of transmitting a limited amount of FDR data via radio link for domestic flights within continental USA. I am working on building a prototype system in which I need to connect the FDR with a computer. USB interface is the most appealing one. I am using a small Flight data recorder (FDR) which has a USB interface. However, it is for hobby planes. Is there a USB interface for FDR's in the passenger planes? Or something that converts between ARINC and USB?

Certified FDR's for commercial aircraft don't have USB ports. They have interface ports because you obviously need to be able to extract data, but they are usually proprietary and each one uses a specific cable for the FDR you want to talk to. To do what you want to do you'd have to design a device that talks to FDR units to download and decompress the data. There are commercial test set units out there that can do this. They are not cheap. As was mentioned in a comment, to do this while in flight will require an STC from the FAA. Also, converting between ARINC and USB doesn't make sense. ARINC is a company, USB is a computer interface specification.

That said, I don't think connecting to the FDR is the best way to do this. As was mentioned, ACARS may already do part or all of what you are interested in doing.


Which authority regulates airliner design? To which regulating authority's regulations and standards are large sub-sonic transport aircraft (passenger or cargo) designed? The FAA's, or EASA's, or both?

The safe operations of an aircraft is called airworthiness. It is the standard by which an aircraft is determined fit to fly. Responsibility of airworthiness lies with national aviation regulatory bodies, manufacturers, as well as owners and operators. International standards are dictated by ICAO during the aircraft design process:

  The International Civil Aviation Organization sets international
  standards and recommended practices for national authorities to base
  their regulations on

FAA has regulations governing all aviation activities in the US. EASA also has airworthiness regulations.

The answer to your question is:

  The aircraft manufacturer makes sure that the aircraft meets existing
  design standards, defines the operating limitations and maintenance
  schedules and provides support and maintenance throughout the
  operational life of the aircraft.


How many displays does an ARTCC Air Traffic Controller view and what is displayed on each? I am trying to figure out the relation between the data sent to a center (ARTCC = Air Route Traffic Control Center) air traffic controller and the displays they view. Did the workstation change when En Route Automation Modernization (ERAM) was implemented?

I am really just looking for a general description of a center air traffic control workstation (if it varies based on the type of controller I would like to know any significant differences).

Although your question is specifically about the USA, I thought an insight into a typical European setup would be interesting as well. I imagine it will be very similar to what you find in many American centers.

The image is from Copenhagen Area Control Centre (Denmark) and shows a normal controller working position. You will notice five screens in total.

The largest screen, immediately in front of the controller, is the main situational display. It is essentially the radar screen, showing different aircraft in their geographical position in relation to airspaces and other traffic. Typically, the situational display will also, depending on the specific system, enable the controller to interact with aircraft labels, for instance to enter notes about clearances and instructions and show them directly on the display.

To the left is a secondary screen which also shows information about traffic in the area. Here, the traffic is presented in text lists, which allows the controller to get a thorough overview of what is currently going on, and what is coming. This is basically a replacement for old fashioned paper flight strips (which are being phased out across the world). In this example, it also features the arrival management (AMAN) system.

Below the main situational display there are three screens. From left to right, the first one is a telephone panel, which gives the controller easy access to all relevant phone communication lines. It is a touch screen, and by pressing any button on the screen, the controller can call adjacent ATC sectors, control towers, emergency services, the meteorological office etc. to coordinate.

The lower middle screen can show a lot of different information. On the image above, it is set up to show the frequencies of other ATC sectors in the area along with any active military areas. It can also be used to retrieve meteorological information or anything else that might be relevant.

Finally, in the lower right corner is the voice communication system (VCS) interface. Also a touch screen, here you have control buttons for the VHF radio equipment, used to communicate with aircraft. The controller will be able to toggle which radio frequencies are used to transmit and receive, and will receive information about any radio equipment that might not be working as it should.

Apart from the actual computer screens, you will notice the backup phone to the left and a clock above it. There is also a backup VHF radio in the upper right of the console, but that cannot be seen on the above image.


How does turning Errors in the Air Driven Artificial Horizon work? Turning through 90°, 180°, 270° & 360°, the error is different. I can understand what is turning error and pitch error individually.

But why turning through different degree, the resulting error is different?

Rapidly becoming a nonfactor as electronic systems replace vacuum driven gyros:

https://www.flyingmag.com/g00/how-it-works-attitude-and-heading-reference-system?i10c.ua=1&i10c.encReferrer=aHR0cHM6Ly93d3cuZ29vZ2xlLmNvbS8%3d&i10c.dv=2

How It Works: Attitude and Heading Reference System

Attitude and heading reference systems (AHRS) have been providing heading and attitude information with greater accuracy and reliability than traditional mechanical gyros for years now. But how do these solid-state systems deliver this information, and how do they do so using increasingly smaller and lighter equipment?

Micro Electronics

An AHRS’s key features include micro-electronic mechanical gyros, accelerometers and a magnetometer or flux valve. The micro-electronic mechanical gyros are responsible for capturing motion data as an aircraft moves about all three axes. They do this by using vibrating components. As an aircraft changes direction, these vibrations deviate, and these deviations can be measured and used to calculate directional change data.

Gyro Drift

In order to account for gyro drift, which can produce erroneous data, an AHRS must also rely on accelerometers as well as a magnetometer or flux valve. The former uses gravity to serve as both an initial attitude reference as well as an inflight reference, whereas the latter uses Earth’s magnetic field to provide heading information.

The AHRS aggregates all the information from these different components and conducts complex algorithms and calculations to provide highly reliable attitude and heading data.

Side Note: Previously out of reach for private aircraft owners due to high costs, AHRS prices dropped remarkably as the result of the use and advancement of AHRS technology in the automotive industry. An AHRS today can be as small as a coin.


How does Bernoulli's principle contribute in lifting airplane? I have searched if any explanation that bind Bernoulli's principle in lifting airplane. There is one here which receive many appreciations, but still did not answer the question. So far, it was taught, explained, or mentioned in any aerodynamic or airplane principle, but never bound the Bernoulli's formula to the lift formula. As we know, there are pressure conservation as below:
$$\mathrm{P}_{1}+\frac{1}{2} \rho \mathrm{V}_{1}^{2}+\rho \mathrm{gh}_{1}=\mathrm{P}_{2}+\frac{1}{2} \rho \mathrm{V}_{2}^{2}+\rho \mathrm{gh}_{2}$$

Due to height is considered are same below and above the wing (the different are very small), then the third part of the equation will cancel one each other. Then left only part one and part two of each side of the equation. As the velocity above (considered as V1) is said will be different below the wing which wind is faster in above, then pressure above the wing will be lower, which will lift the wing. Thats is commonly taught in every explanation. Then, the

$$V_{2}=\sqrt{\frac{2\left(P_{1}-P_{2}\right)-\rho V_{1}^{2}}{\rho}}$$
Meanwhile, lifting formula is expressed as below:
$$L=\frac{1}{2} \rho v^{2} S C_{L}$$
V here is the airplane velocity, which is the wind hit the airfoil. Thence, V=V2 of the Bernoulli's equation above. V1 that hit upper side of the airfoils/wing, which is said faster than below, is unknown.

So, where is the Bernoulli's principle contributes in this case? How actually we calculate the lift force of an airplane?

If I understand correctly you want to know how to get from the first formula to the second one. If that is the case, the answer is simple: you don't :)

The lift formula is a simplified one, which considers the wing as a whole. It doesn't use velocities on different points of the wing, it uses the speed of the airplane. All the factors such as profile, wing shape, etc are included in the lift coefficient. This formula is useful when you already know the behavior of the wing in different situations (the behavior is determined in wind-tunnel tests or with numerical methods).


Why is bleed air taken from some stage of the compressor used for de-icing? Why not e.g. exhaust gas? In the answers to this question, it is said that

  The de-icing system on most turbine aircraft (including MD-82 involved in that accident) uses bleed air from the engines, that is it extracts some air from behind the (low pressure stage of the) compressor. This air is therefore not ejected from the nozzle and not producing thrust, so the thrust is reduced.

My question is:

Why is bleed air taken from some stage of the compressor used? Why not e.g. exhaust gas?

For de-icing, the temperature of the used medium must be above 0°C (melting ice), while the environmental temperature usually is far below.
So the engine has to invest energy to generate bleed air with reasonable temperature, the air cools down to still >0°C during de-icing, and is then vented out to the environment.
There, it expands and cools down far below the environmental temperature.
This expansion means that energy is wasted, and also, when the bleed air is cooled down / expanded before inserting it into the de-icing system (I don't know if this is done), energy would be lost.
In addition, air/pressure is lost in the compressor stage, which makes the combustion less effective. (Again, I don't know how much air is taken, and how big the effect is)

On the other side, the exhaust gas of the engine is very hot due the combustion and could be used without the need of extra compression. So, using some exhaust gas, one would not waste so much energy. If it's too dirty, heat exchangers could be used to heat fresh air.

I would think of this reasons

Bleed air is anyway used for many purposes in an aircraft, so this is more economic than a completely separated system
De-icing is not used for long time during flight, so again no need for a dedicated system

EDIT:

I'd like to expand the question to explain what makes me curious. In the comment, the correctness of this sentence is challenged:

  There, it expands and cools down far below the environmental temperature.

This is a simple thermodynamic process. The air is compressed adiabatically, i.e. without adding heat to it. The heat comes from the thermal energy of the air, now also compressed to a lower volume.
De-icing cools down the air, and when releasing the air to the environment, it expands to the orignal pressure. As thermal energy has been removed during de-icing, the temperature drops below environmental temperature.

Here is the math behind:

The relation of pressure and temperature in this case is:

$$ p_1^{1-\gamma}\cdot T_1^\gamma=p_2^{1-\gamma}\cdot T_2^\gamma\qquad \gamma
\approx 1.4$$

Let's assume a pilot switches on de-icing during flight at 11km altitude. There, environmental pressure is 0.25bar (atmospheres) and temperature is -50°C (223K). It was also said here in the answers that it's possible that the bleed air has about 200°C (473K).
The formula now gives a bleed air pressure of 3.47 bar, so a pressure ratio of about 14. The air is now cooled down while the pressure is maintained by the engine. I assume de-icing will be effective for bleed air temperatures above 0°C. So if the air is released at this temperature, the temperature will fall down to -144°C (128K). Another number: If releasing at 100°C, the temperature will drop to -97°C (175K).

(Of course, the air will mix with the environmental air immediately)

In principle, one can play with the numbers, increase/decrease altitude / temperatures and discuss how adiabatically this (de)compression processes are.

Anyway, this is a big air conditioner, using the thermal energy for de-icing and wasting the cooled air. If one only needs hot air, something coming from the exhaust system would always be more efficient.

This is not really efficient. May be the bleed air behind the de-icing system can still be used for other purposes, as it still has the pressure?

Using air from the exhaust section either for anti-ice directly, or using a heat exchanger, would create many problems.

The air must first be used to burn fuel before reaching a turbine bleed location. Air taken from the compressor section hasn't required any fuel to be burned (other than to compress that air of course).
The air will be much, much hotter than air from the compressor. Turbines, especially in the high pressure section, are made of specialized alloys and can be additionally actively cooled to prevent them from melting. This means more specialized, and therefore more expensive and/or heavy material must be used for the whole anti-ice system.
Components must also be designed for the case of this bleed air leaking. Hotter turbine air would be a huge problem for this.
The air will have the combustion byproducts in it. This can coat the insides of the anti-ice system, reducing its effectiveness, and possibly requiring it to be disassembled and cleaned periodically.
If there is some type of engine fire, the fire typically goes downstream, which would send it into this anti-ice system as well.
In the case of using a heat exchanger, this would be yet another component to fit into spaces that are already very full, and yet more weight on the airplane.

The air from the compressor is already plenty hot. Take a look at the diagram in this answer. Notice that all the compressor bleed air goes through the precooler before going to cowl or wing anti-ice. This means that the compressor air is already hotter than is required. So taking air from the turbine provides no benefit for creating the problems listed above.

Also, taking air from the compressor does reduce engine efficiency, but you are going to have to get that energy from somewhere.

To address your points about the thermodynamics:

Assuming your numbers are correct, what is wrong with that scenario? Releasing air at -97°C that was initially at -50°C means that you extracted 47°C of energy from it to use for anti-ice, using the systems already available on the aircraft (bleed air, precooler). Kind of like a heat pump, but just using air? Wouldn't it be less efficient to burn fuel to heat this air, which would then leave the aircraft at a higher temperature, and therefore throwing away more energy?

  In principle, one can play with the numbers, increase/decrease altitude/temperatures and discuss how adiabatically this (de)compression processes are.

(Emphasis added) I'm not convinced that your assumption that these processes are adiabatic is a good basis for your model, since that is an idealization (though your initial bleed numbers do seem to match here and here). An important point is the way the air is used. A typical installation uses piccolo tubes. Small holes along the tubes release the air onto the leading edge. This whole leading edge cavity then vents to the environment. (This doesn't seem to match your assumption that the air is cooled at constant pressure) In order for this air to be useful any further, you would have to somehow return this air to for reuse. This adds more complication, when there is already an abundant supply of compressed bleed air available.

Another option would be to somehow maintain the pressure behind the surfaces with ice protection. This may be feasible for the engine inlet, but not for wing leading edges that include moving slats.

Even assuming you can somehow recover this air for use, that would be another system and more complication added to the aircraft. And you can't rely on this system, because anti-ice is not always in use. You have to provide a pretty large gain in efficiency to justify adding weight and complexity to the airplane.

Maybe you would like to see proof that most the work done on the air is used in the anti-ice process, and adding heat from combustion is not necessary. We may need to get someone like Peter Kämpf in here to run some numbers.


What's the MTOW I can fly with a PPL? I thought there was a limit but I can't remember and can't find it anymore.

So with an US PPL, what would be the maximum takeoff weight that an aircraft would be allowed to for me to still fly it?

It'd be great if anybody could point out the appropriate FAR, too!

There are no explicitly regulated MTOW limits for a private pilot with a valid medical but extra certifications/training may be required to fly heavier aircraft.

The often cited number is 12,500 but this is somewhat incorrect depending on how you look at it. You will need a Type Rating to fly anything over 12,500 but strictly speaking those can be added to a private pilots license.

If you are a PPL flying under Basic Med you are limited to 6000 LBS MTOW

  14 CFR § 61.113 - Private pilot privileges and limitations: Pilot in command.

  (i) A private pilot may act as pilot in command of an aircraft without
  holding a medical certificate issued under part 67 of this chapter
  provided the pilot holds a valid U.S. driver's license, meets the
  requirements of § 61.23(c)(3), and complies with this section and all
  of the following conditions and limitations:

  (1) The aircraft is authorized to carry not more than 6 occupants, has
  a maximum takeoff weight of not more than 6,000 pounds, and is
  operated with no more than five passengers on board; and

Just a note on practicality, even if you don't get into the 12,500 range you are likely to need high performance and complex ratings to fly anything much bigger than a 172. While there are some big fixed gear aircraft out there most of your common 6 seat planes (Saratoga, Bonanza, etc) are retracts.


Why isn't the V flight formation being used for commercial purposes? The V Flight Formationhas been found to be helpful in achieving greater fuel efficiency and range. Though it is currently used mostly for military purposes, what restricts it from being used for commercial purposes?

This possibility has actually been studied and discussed (e.g. here, here, here) as a way to save fuel costs, but there are several issues with implementing it today:

You need to schedule a number of aircraft all flying the same route at the same time for a significant amount of time
If different, competing airlines should participate in one formation then they have to cooperate and be satisfied that no one is at a commercial (dis)advantage
A lot of work would need to be done on procedures and training (how does the formation form up, who takes the lead, how/when does the formation leader change, how are emergencies handled, what flight levels are used, what separation is required between formation and non-formation flights etc.)
Autopilots, software and other equipment would need major updates, which in turn requires re-certification
All relevant regulations on separation, formation flying and so on would need to be reviewed and changed which in most countries means changing the aviation laws, and changing any law is usually a long, slow process

Having said all that, you'll notice that most of those issues are procedural, not technical. In theory it's a viable approach, but turning that theory into reality would require a lot of work.


Where can I listen online to live VOLMET broadcasts? Are there sites that stream live VOLMET broadcasts? I need to listen to the format but haven't have the time to put together an amateur radio.

The Globaltuners site will allow you to tune their UK radios (subject to them being online) to the UK VOLMET frequencies if you really wanted. Whether this is technically "legal" or not is for you to decide ... it's not in the UK, but it's not enforced either.


Is there a graph that shows the thrust required for a given airspeed? I would like to see the graphical relationship between thrust required and airspeed for a typical general aviation aircraft, e.g. C-150 or C172 series.

For horizontal flight, thrust required is the same as drag.  Go to the specific graph referenced in this answer How close is the air resistance or drag force to be proportional to the speed squared?, and you'll have your answer, or close to it.

The specific graph referenced here is for "a conceptual two-seat light sport aircraft (LSA) designed to cruise between 80 and 100 kts".  A Cessna 150 or 172 might need somewhat more power for the same cruise speed.


Is there a special ULD to be loaded at the main cargo door? Watching this video, it appears that the hydraulic ram intrudes into the cargo space and would run into the Unit Load Device (ULD) that was stowed there.

Is there a special ULD that is loaded on each flight to clear the ram, or is there enough clearance that any ULD will fit in this spot?

No, the container near the door is the same as the others. The containers do not fill the entire cabin all the way around, which leaves enough space above for things like the door hydraulics. The containers on the upper cargo area below are all 88" x 125", which corresponds to a standard LD7 container.

Source


What are some ways to decrease turbulence? I know there are ways turbulence can be reduced, but what are these ways that keep the ride comforting and also with better stability.

There is no way to really decrease turbulence per-se since its a factor of the air around you. There are ways to mitigate its effects and some are.

Climb: In some cases the air higher up is less turbulent or you can climb over the weather system causing the turbulent air. In this case climbing to a higher altitude may help
Divert: Similar to the climb situation you can divert around the turbulent air if you know where its occurring.
Timing: This is the one you may have the least control over if you are talking about commercial flying and its not always true but generally speaking the winds and thermal activity tend to be calmer in the early morning and evening. Flying around these times may allow you to find smoother air.
Size: Again this one is hard to control but there is some truth to the fact that big planes will be less effected by turbulent air than small planes. By this I mean that a 777 is going to bump around less than a Piper Cherokee. But it holds more or less true across the board.


Space Catapault Model A secretive space catapault is said to be in progress.  For the sake of mathematical simplicity, assume the launch vehicle is one kilogram point-mass and to be placed in geosynchronous orbit.

What quantitative forces (impulse?) and energy necessary to accelerate said vehicle into geosynchronous orbit?  Feel free to make any assumptions necessary to facilitate an answer.

I won't be displaying mathematics or even a guesstimate here because this subject is somewhat beyond my scope of competency. However:

To shoot something into orbit with a catapult from ground level is not feasible, as the object would immediately burn to ashes, no matter what the material would be. The required velocity to reach orbit is about 40 000km/h, and to make things worse, you'd have to reach that speed at basically zero altitude, with a very dense atmosphere creating friction.

See this question and answers from physics stack exchange for further information.


How is a fly-by-wire system realized in big planes? For example if whole system is build on CAN protocol that give maximum rate of 9000 messages per second with IMHO is quite low number for big plane.

Can you give me any example how this problem was solved?
Do they divide system into subsystem or use protocols like Ethernet IP?
Or maybe that number of messages is enough because they're sending only critical information?

In fact, ARINC 429 is used in the "federated" avionics, this is the "old" system used in many aircraft like A320, B737, ...

Federated avionics require a lot of wires which generates a lot of weight. In ARINC we have approximately one wire per device, so the speed (100Kbps or 12,5Kbps depending on the selected mode) is sufficient.

ARINC 429 Architecture :

In "new" aircraft like A350 or B787 the industry use the Integrated Modular Avionics in order to reduce weight and reduce the number of S/N to stock.

In this kind on avionic all computers are merged in a couple of "cabinet" composed of multiple core processor units, shared ROM, shared RAM, shared graphic cards.
All these cards are linked, in the cabinet, with the Backplane BUS (ARINC 659), which operates at 60Mbps as a commercial aviation bus
All cabinet are linked ,each other and with actuators, using AFDX (ARINC 664) who look like Ethernet protocol and work at the speed of 100Mbit/s.

There is a lot of different IMA architecture with the same principle, but some differences. This is one on them, in this picture you can replace PCI Ex. by ARINC 659 :

Regarding CAN bus, Airbus use in in this A380 (http://www.aviationtoday.com/av/issue/feature/can-bus-in-aviation_31468.html)

Sources :

http://www.interfacebus.com/Design_Connector_Avionics.html

http://www.modern-avionics.com/

https://en.wikipedia.org/wiki/Avionics_Full-Duplex_Switched_Ethernet


Why do I get an overspeed warning at 250kts below 10,000ft in Microsoft Flight Simulator? I'm flying the Cessna CJ4. I get overspeed warnings at 250kts when below 10,000ft, and the speed indicator has red lines at 300kts. Are these warnings triggered because it'll damage the plane to go that fast, or because it's illegal to go that fast that low? What's the distinction between 250kts and 300kts?

Most likely Cessna introduced a speed switch that is controlled by an aneroid.  Anytime you are below 10,000 FT MSL, the aneroid activates that switch.  If you go above 250 knots, the overspeed warning will sound.
As far as why that is the case, in the United States you are limited to a speed of 250 KIAS below 10,000 FT.  I would imagine this is also the case for most other countries.  The FAA realizes that most small airplanes with a much slower airspeed travel only below 10,000 FT MSL so the FAA is providing a safety margin to prevent in-flight collisions.
The structural limit of the airplane would not be a factor at 250 KIAS hence the red line at 300 KIAS.  I would imagine 300 KIAS deals more with structural stability than anything else.
My question... can a slow-tation go that fast?  :-)


What is "company compensation fuel" and "pad fuel"? I tried to find the definition of these fuels but I could't.

Does anyone know about company compensation fuel or pad fuel?
In which document can I find the definition of these fuels?

Company Compensation Fuel
This is a term, which seems to be used by Korean Air. They define it on their website:

▶ Company Compensation Fuel
fuel to minimize abnormal flight occurred. Based on this, fuel consumption performance is modeled for a certain period of time, and based on this, the amount of fuel repeatedly consumed excessively compared to the flight plan is added.

(koreanair.com, translated by Google)
So this is fuel added based on the airline's experience (hence company) for typical fuel use on a given route.
Pad Fuel
I have never heard this term and Google also does not find anything related to aviation. Is it possible this was a translation? If so, could you add the original term and where you heard about it?


Is it common for aircraft tugs to work from under the aircraft? I came across this photo showing a tug attached in a way I have never seen before. I assume it was used to allow the aircraft closer to the terminal.

Did this require special equipment or modifications to the aircraft?

Was it a common practice before terminals were redesigned to accommodate large aircraft and large tugs.

Source: wikipedia.org

Yes, this is a perfectly normal practice, still used, especially for tight spaces, as seen in this video moving a 747 into the hangar for service. And no, it doesn't require any special equipment - the nose gear attachment is designed to be used either way.

A still from the video:


Wheel or skid? Which advantages does each one have when used as the landing gear system compared to the other one? I would like to discuss this topic in depth, as I have not found a clear answer yet.
Which are the advantages of using skids instead of wheels (or viceversa) for the following considerations?:

-As the nose landing gear (case: Dream Chaser)

-As the whole landing gear (case: Eurocopter HH-65 Dolphin (wheels) VS. Bell 205A-1 (skids)

It really depends on how you intend on landing the vehicle, how you intend on using the vehicle, and generally any design limitations that may come into play.

For fixed wing aircraft that need to land with a forward velocity you can chose either skids, wheels or a combination of both.

Skids are beneficial as they are, simple, light and take up less space than conventional wheels as discussed in reference to the X-15

  The aft landing skids have been questioned many times. But if you can
  figure out how to put a conventional gear into a 5-percent-thick wing
  and struts long enough to reach the ground in the landing attitude
  without losing the back end of the fuselage, be my guest! The current
  skids were located, as you will note on other figures, as the best
  solution to a difficult problem from a weight, temperature, and
  simplicity point of view.

However with a front skid you lose the ability to have nose gear steering and must resort to differential braking (assuming rear tires). With skids all around you lose ground steering and may possible damage the runway. For space craft this is typically not an issue as they are usually towed off the runway anyway. In the case of the Dream Chaser their may have not been enough space to stow a nose wheel.

Skids generally dont allow for any mechanical braking method to be applied. This means that you need to rely on aerodynamic braking like a drogue chute or reverse thrust.

Below certain airspeeds, with only skids you also lose all ground steering which can be an issue.

Wheels preserve steering and generally allow the craft to be moved off the runway easily. However this comes at the cost of added complexity, added weight, and generally added size. Since the space shuttle we have gotten pretty decent at putting landing gear on orbiters and at this point we know how to do it. While the tires need to be a bit different than your average car tire many aircraft tires are highly specific anyway. This question may also be of interest on the topic.

Spinning wheels, generally speaking also allow for braking to slow the aircraft after touch down. For short runway operations this is a must, since rolling to a stop is often not an option.

Wheels are generally beneficial for your average powered aircraft since ground maneuverability is needed to get around the airport and tires allow good braking ability.

Helicopters are a bit of a unique case, since they have the ability to hover and land vertically they don't really need any landing gear beyond a flat bottom. Wheels make it easier to push or tow a helicopter around the ramp while skids are simple and require little service on a helicopter.


Is altitude information included in filed flight plan? When the dispatcher produces and files the flight plan for a scheduled flight with ATC, are the determined optimal cruise altitudes part of the flight plan, or does the flight plan only contain lateral route information?

The flight plan contains the requested cruise flight level, as well as step climbs or level changes along the route in the route field.

Example 1:

(Image Source: skybrary.aero)

Example 2:

  SAM UN621 BASIK/N0412F330 UZ150 BADUR/N0426F340 UN472 ARE/N0424F350 UN864 PIMOS

Fxxx being the requested flight level.


Why doesn't a wing in supersonic flow produce a shock that results in flow parallel to the leading edge? When we look at a wedge in supersonic flow, a shock emanates from the leading edge such that the flow after the shock is turned and is parallel to the airfoil surface.

The shock angle is based on the flow turning angle (wedge angle) and can be found using the chart below:

I was wondering why a wing in supersonic flow would not have the same behavior (see image below). That is, why wouldn't there be a shock emanating from the apex of the wing (which depends on the sweep angle much like the wedge angle ($ \theta $)? If this were to occur, there would be no component of the flow perpendicular to the wing (as the shock would turn the flow parallel to the surface). I know this doesn't occur physically because there is always a component of flow perpendicular to the wing, but this confused me because the wing seems exactly like a wedge (if we look at a wedge from the top instead of the side).

Air needs to make way for the approaching airplane. For that, it takes the route of least resistance, which is above and below the wing. This is shown in your first picture which is valid for a supersonic leading edge. Your top view shows a different cross section through a three-dimensional shock at a much lower speed. The vector M$_2$ is wrong and does not correspond to what is really happening.
If X is in flow direction, Y is sideways and Z is down, picture 1 shows a cut in the X-Z plane for a supersonic leading edge. Picture 3 shows a cut in the X-Y plane for a subsonic leading edge. Here, air does not flow sideways but continues past the shock along the direction of the vector M$_1$.


Is it unprecedented for an F-16 to get hit by its own bullet(s)? According to Dutch state broadcaster NOS, an F-16 was hit by its own bullet(s) in a training exercise:

  De F-16 die in januari aanzienlijke schade opliep tijdens een oefening boven Vlieland blijkt geraakt te zijn door zijn eigen munitie.

My translation:

  The F-16 that in January suffered considerable damage during a training exercise above Vlieland turns out to have been hit by its own ammunition.

They also added a picture of the damage:

Image attribution: originally by Inspectie Veiligheid Defensie, taken from nos.nl.

Comparing that picture with the following stock photo, it looks to me like the bullet that caused the damage entered from the front. Of course it could also be due to the aircraft flying at a high velocity.

Image attribution: "F-16 Cockpit (J-513)" by Gerard van der Schaaf // CC BY 2.0

Is this unprecedented? Or are there any records of other F-16 jets getting hit by or collide with their own bullets?

I can find no record of an F-16 shooting itself down prior to the Dutch incident. There is certainly nothing on the wikipedia page for aircraft shootdowns or anywhere else I can find.

However its not the first aircraft to manage the feat. In 1956 a US Navy F-11 Tiger became the first aircraft to shoot itself down, whilst testing its cannons on a test flight. The pilot fired a long burst of cannon fire then entered a shallow dive and hit the afterburner, shortly after the aircraft was hit by its own bullets.


How to do the base turn course reversal? Can anyone tell me how to do the base turn course reversal? Please. I'm afraid it might be asked of me in my Checkride and my instructors haven't taught me that. Please.

If your worried something will be on the checkride (which is practical) you need to seek out more practical instruction on the maneuver.

Procedurally this site offers a good explanation:

  Base turn consists of:

  a specified outbound track and timing or DME distance from a facility; followed by
  a turn to intercept the inbound track

  The outbound track and/or the timing may be different for the various
  categories of aircraft. Where this is done, separate procedures are
  published.


How are horsepower and standard displacement for a rigid airship calculated according to this book? This is a follow-up based on a question posted here. I updated my initial question but came to the conclusion that a new post might be more manageable. For bibliographic reference(s) and/or getting a copy please refer to the linked question. Be that as it may, this is my current issue:
Having had some time at hand, I went back to the book. The solution of the problem set above continues like this:

Assuming the weight of the power plant and its cars to  be 8.lbs/Hp. and the weight
of the fuel and the fuel system to be .6 lb. per horsepower hour, the total weight
of power plant, fuel system and fuel is

[8 + ( .6 x 60 ) ] Hp. = 44 (Hp.)

combining this with the military load,

15,000 + 44 (Hp.) = .357

No issue so far, I was also able to compute this formula:

However, I cannot make heads or tails of the next part

Combining equations (1) and (2)

My question is how did the author arrive at equation (3)? Where does the value 48D(2/3) come from and how were these formulae combined.
When using the previously computed value of .0357 for D, I am not getting the result of 42,000.
Apart from the "actual" math involved, I fail to see the meaning of the components involved in equation (3):
Could someone help me out here and maybe translate that formula into English sentences?

The book author just eliminated Hp from 1 by the formula 2.
$$ 15000 + 44(.39D^{2/3}) = .357 D$$
Do arthitmatic and rearrange:
$$.357 D -17.16 D^{2/3} = 42000$$
Divide by the .357 to get
$$ D- 48.067 D^{2/3} = 42016.8 $$
Then round off because he used a slide rule not a calculator.


Was the P-82 twin Mustang better than the P-51D? The P-82 twin Mustang was made to replace the P-51D in the escort role. It was faster, and had two engines with two pilots. It also had a better armament but wasn't as maneuverable as the P-51D. Which would usually win in a dogfight and what plane did pilots prefer?

The two planes serve very different roles. The 82 was a long distance aircraft first and foremost, and everything else was secondary to that goal. The 51 was a fighter, and its excellent range was not a specific design criterion, but the result of several unrelated design decisions that worked in happy concert.
So, based on that alone, I think the answer is clear.
But the real issue with this comparison is the time dimension, the 82 saw combat when it was already outdated, whereas the 51 saw combat when it was the pinnacle of performance. Jets were already the hotness when the 82 was on the front line, and I doubt anyone looked favorably on being assigned to them when the alternative was an 84 or 86.


How does wind affect the airspeed that I should fly for maximum range in an airplane? I have heard that wind affects the actual airspeed that I should fly for maximum range in an aircraft.

I understand that wind will not affect the airspeed that I should fly if I am looking for maximum endurance, but what about maximum range?

How (and how much) should airspeed be adjusted for wind in order to get maximum range?

My answer was rather concise first, and I got the impression that I need to elaborate the question first. The question is about the best airspeed for maximum range. With wind. Best range means you cover the most distance while the wind is carrying the plane with it. If you have a headwind, the longer you stay aloft, the more you are carried back, so you better hurry up. With a tailwind, it helps to slow down because now the wind is helping you to cover even more distance.

But how much? We need to pick that particular speed where the change in fuel consumption just balances the change in speed over ground. I always found that easier to explain with gliders, and there you can really observe which polar point is best. Just picture yourself as an observer on the ground who sees the plane fly by in the distance. If you plot a line with the combination of positions and altitude, there must be one flight speed that produces a line where the flight path angle is the shallowest. This is the desired optimum. That has only little to do with optimum L/D - this is just one other point you can find with a sink speed polar. And it happens to be the point for best glide in still air. But there is so much more that humble polar will tell you, if you look at it the right way.

With powered aircraft you need to pick the polar point where your fuel flow is lowest for the given speed over ground. Basically, you fly like the glider and add enough power to stay at the same altitude. That is all the difference. User2168 has answered that part already with a graphical solution.

OK, now back to gliders. Please look at the plot below which shows airspeed on the X axis and sink speed on the Y axis.

The solution is graphical: You start on the X-axis at the point which corresponds to the wind speed and put a tangent on the sink speed graph. Where the tangent touches the sink polar (blue line), the plane flies at the best L/D for that given wind speed. Move the starting point to positive speeds for headwind and to negative speeds (not shown here) for tailwind. If the term "best L/D" is already reserved in your mind, please read this as the "best polar point". It is really the same.

Since User2168 has beaten me to the graphical solution, I will add an analytical solution.

For powered flight things become more tricky, because thrust changes with speed. To simplify things, we can say that thrust changes over speed in proportion to the expression $v^{n_v}$ where $n_v$ is a constant which depends on engine type. Piston aircraft have constant power output, and thrust is inverse with speed over the speed range of acceptable propeller efficiencies, hence $n_v$ becomes -1 for piston aircraft. Turboprops make some use of ram pressure, so they profit a little from flying faster, but not much. Their $n_v$ is -0.8 to -0.6. Turbofans are better in utilizing ram pressure, and their $n_v$ is -0.5 to -0.2. The higher the bypass ratio, the more negative their $n_v$ becomes. Jets (think J-79 or even the old Jumo-004) have constant thrust over speed, at least in subsonic flow. Their $n_v$ is approximately 0. Positive values of $n_v$ can be found with ramjets - they develop more thrust the faster they move through the air.

Now for fuel flow: This goes up and down with the power output of the engine. Again a simplification, but it helps to get to grips with the problem and gives useful results. This lets us re-formulate the problem as: At what airspeed do I have the best ratio between power and ground speed?

Mathematically, we want to fly with $\frac{P}{v_w+v}$ at the lowest possible value. $P$ is the power, $v_w$ is the wind speed and $v$ the airspeed. To express the thrust behavior over speed, I break P up into a product of a constant $K_S$, the throttle setting $\delta$ and the speed like this: $K_S\cdot\delta\cdot v\cdot v^{n_v}$. Here is the general solution, pasted as a PNG to save me all the typing in the editor:

Please note that implicitly the lift coefficient is on both sides of the equation. To solve it, you need to do it recursively, until speed and lift coefficient match. I took this form because of the similarity to the general form at still wind which can be found in many performance books. This here I didn't find anywhere, and it took me a while to figure it out. Thank you, Lnafziger, for the excellent question! It gave me a chance to learn something.

Now I have put the results into a plot. In order to eliminate the aircraft-specific parameters, it shows the ratio of $c_L$ with wind over $c_L$ without wind. The plot is metric, but will work for all units if you use the same units for wind speed and air speed.

To give an example for the application of the correction factor: If you are flying in a 20 m/s headwind and your best range speed at still wind is 50 m/s (approx 97 kts), the $c_L$ needs to be 70% of the $c_L$ at still wind for piston-powered aircraft. This makes your corrected airspeed 60 m/s (v is proportional to $\sqrt{c_L}$), and now the recursive nature of the formula rears its ugly head. At 60 m/s, the correction is only 77.5%, so we need to do a few loops until we arrive at a point where the airspeed and the correction factor match. In this example, this would be 57 m/s or 110 kts in case of a piston-powered aircraft.


What valve would be the best for a model rocket with a hybrid engine? I am planning on building a model rocket with a hybrid engine. I am trying to find the best valve that could be used for the MOV, main oxygen valve. I plan to use gaseous oxygen and would like the valve to be electrically actuated, and have the ability to throttle. Does anybody have any recommendations for a good valve to use? Thank you.

It depends on a lot of factors.
Most valves with the specs you need will work really, but you'll have to carefully determine your specs. There's not really a single answer.
What kind of thrust are you designing your engine for? This (amongst other things) will determine your minimum needed flow rate, and will determine the pressures this valve will need to be able to cope with. These things will be the most important valve specs you'll be considering.
I don't know where exactly your valve will be in your engine, but make sure it can withstand the heat its exposed to.
On the flipside, knowing you'll be using GOX, you'll probably just use the pressure from your oxygen tank to power your engine. As the oxygen will be expanding, the MOV might tend to freeze up and lock itself in place. Beware of that as well when choosing a valve.
Not all valves will be able to safely operate in a pure oxygen environment. However, as we're talking model rockets here (the operating time of your engine is quite short I suppose) it'd surprise me if that would turn out to be an issue.
To end with, although maybe not directly related to your question about the valve, make sure you understand hybrid engine throttling. It can get more complicated than you might anticipate.


Do Air Passenger Number statistics on a route refer to both directions of flight? Looking at the air passenger data for specific routes, I was wondering if this data referred to just one direction of the route, or both directions?
For example (see link below), Philadelphia's most served route is to Orlando, flying 548,320 passengers last year. Is that number referring only to PHL-MCO, or is that cumulative of PHL-MCO and MCO-PHL?
Thanks!
https://en.wikipedia.org/wiki/Philadelphia_International_Airport#Top_destinations
https://www.transtats.bts.gov/airports.asp?pn=1&Airport=PHL&carrier=FACTS

By looking through the BTS website you linked (and is cited in the Wikipedia listing), you can find the answer.
The first 3 sections on the infographic; Summary Data, Carrier Shares, and Total Passengers include both departure and arrival passengers totaling about 14 million passengers.
The fourth section Top 10 Destination Airports (US Only) is less clear and you can't cross-check to the other totals because it is limited to only the top 10 airports. But it is a clue that the title says Destination Airports which implies departures only.
But there is a potential check. At the top, you can select the airport. By selecting Orlando, FL: Orlando International from the pulldown, you can see the data from there. That shows in the Top 10 Destination Airports that PHL is number 3 and the total number of passengers is 539,900. Since this is different than the 548,320 PHL-MCO number, it would appear that section references departures only.


Why do we have to check the speed brakes during GPWS memory items on an A320? Just out of curiosity, I want to ask why do we have to check that the speed brakes lever is retracted during a GPWS (Ground Proximity Warning System) maneuver using the A320 memory items?

It clearly says in the F/CTRL SYS that the SPD BRK is inhibited if the thrust levers are above the MCT detent.

Because that is how American Airlines Flight 965 went down.

Long story short, the pilots deployed the speed brakes to increase descent rate during approach, and did not notice they were off course. The GPWS warning sounded. The pilots reacted within one second. They did everything they could - except they did not retract the speed brakes. They crashed.

Why is it a memory item? Because GPWS means imminent terrain contact. You don't want to wait around for some automatic mechanism to retract the speed brakes for you. Let alone take the chance of that mechanism failed. You do it. NOW.


Why do we still use pilots to fly airplanes? With the recent advances in drone and remote control technology, why are there still commercial and military pilots?

I understand that there can be some serious tactical advantages to human pilots in military operations, but for patrol and commercial flights what are the advantages of a human pilot in the aircraft as opposed to a drone or a remotely controlled airplane?

That's a good question, and brings up a joke that many pilots know well:

  "What's going to be in the cockpit of the future?"

  "A dog and a pilot."

  "A dog?  Why a dog?"

  "Well, the dog is there to keep the pilot from touching anything."

  "Ummm, why have the pilot then?"

  "Well, someone has to feed the dog! "

Technology has improved to the point where airplanes can pretty much fly and even land themselves.  They are even getting pretty good at handling "normal" emergencies like engine failures and depressurizations.

Where pilots really shine though are the type of abnormal and emergency situations that aren't "in the book".

When an engine flies apart and shreds the hydraulic lines on all three redundant hydraulic systems, a computer will be out of options because it was never programmed to handle that (because it was considered "virtually impossible" when it was designed).  A pilot on the other hand can analyze and experiment until he finds enough of a solution to keep the airplane in the air as he works through other issues.

During a total electrical failure, the computers won't be much good.  Sure, you can design redundant systems and make it so that it "can never happen", but what about when it does?

There are also all of the little things that a pilot is constantly making decisions on how to handle.  Some examples could include:

Can the airplane fly with a particular feature inoperative?
What about multiple features inoperative?
How do they interact with each other?
What do you do when the passengers take too long to board and you are going to miss your departure slot?
What do you do when the ground crew forgets to close a door?
What about when the tug driver doesn't push you back quite far enough?
Or ATC wants to change you to a different runway?
Or you ask ATC to change you to a different runway because it might save a few minutes and that will keep you from having to deice again?
Or another airplane unexpectedly pulls out in front of you while taxiing?
A pilot can see "ugly" clouds off the end of the runway and decide that it would be better to wait a bit before taking off.
What happens when a flock of birds suddenly appears during the takeoff roll?
What happens when a passenger gets sick or unruly?
When do you need to divert and when can you continue?

On a typical flight, a pilot will make hundreds of small decisions that can make a big difference in the flight.  Any one of these (or one of the tens or hundreds of thousands of other things that could happen) could trip up a computer.

The pilot is also there as the "final authority".  If a hacker were to somehow hack into the automated systems, a pilot can always disconnect them and fly the airplane manually.  He can turn off systems, he can be...  Well, the pilot can be creative and a computer can only do what it was programmed to do.

Right now when a drone crashes it isn't such a big deal because nobody was on board.  If an airliner with a load full of paying passengers crashes it is a big deal.  Even just one.

Many of these problems can be overcome.  Some of them already have been.  Some of them may never be fully handled in an automatic way but maybe we could still do automated flights with an acceptable level of safety.  Some automation is actually better than some pilots in certain areas.

However, the biggest reason that we don't have fully automated passenger airplanes is because the general public feels comforted by a person being up front who can take over and carry them to safety if needed.  Even if the technology were 100% ready for automated passenger flights, I think that the number of people willing to purchase a ticket would be so low that it would be financially unfeasible for an airline to deploy it.


What is the reason to have LOC/VNAV landing method? What is purpose of mixing LOC/VNAV in this landing method?

A VNAV with localiser approach is normally a backup to a regular ILS should there be a glide slope unserviceability. The use of VNAV  to manage the vertical portion of the approach would allow the use of APV minima which are normally lower than using a vertical speed mode.

VNAV is a better mode when conducting non-precision approaches as the aircraft is still following a defined glideslope - albeit derived from a database - which is more accurate than trying to follow a tabled set of heights and distances using vertical speed.


What is the difference between the red and black box identifiers on UK airport charts? On UK airport charts like the one below for Manchester (EGCC), what is the difference between an identifier with white lettering on a red square and one with yellow lettering on a black square with a yellow outline?

(eurocontrol.int)

(UK AIP GEN 2.3)

Both are holding position signs. Both reflect the physical sign color the pilot would see, below is the red J2 and black J1 as seen from the cockpit (YouTube):

Red J2

Black J1

The red is for intermediate holding positions:

  Where it is considered necessary to locate taxi-holding positions other than at runway/taxiway intersections – for example at taxiway/taxiway intersections in order to protect a priority route – the holding position should be identified by a single sign located wherever practicable on the left side of the taxiway. The sign consists of a combination of the letter designating the taxiway and a number identifying the hold position e.g. A1, A2, B2 etc. in white on a red background.

(CAP 168 Licensing of Aerodromes)


Why is dropping off passengers on the ramp by bus not more common? Even at remote terminals as discussed in this answer it seems there's a preference for using a jet bridge to get passengers to and from the aircraft.

Can't the passengers just be bussed directly to the aircraft rather than the remote terminals?
Why the use of a jet bridge here if they can use stairs at other times?

The use of a jet bridge has several major advantages over loading passengers from the ramp via portable staircases or built-in "air stairs", among them:

Boarding of handicapped passengers
Not all passengers can use stairs: a jet bridge allows passengers with limited mobility, particularly those confined to wheelchairs, to board and disembark from the same level as the passenger deck.
Accommodating these passengers from the ramp would require some kind of lift mechanism to raise them to the passenger deck of the aircraft - this is typically accomplished elsewhere in the terminal when a jet bridge is used, e.g. via passenger elevators in the ticketing area, or in the type of design shown in your question, via an elevator in each "mini-terminal".
Passenger shelter
Boarding from the ramp may work well on a beautiful spring day, but in less favorable conditions (rain, snow, temperature extremes) most passengers would not find the experience to be enjoyable. The jet bridge provides an enclosed and relatively climate-controlled route from the terminal to the aircraft.
Passenger Safety
Airport ramps are inherently dangerous places: Aircraft are starting their engines, being pushed back for departure, etc. and ground support vehicles are moving at all times carrying luggage, cargo, catering supplies, etc. to and from the aircraft. In addition to the ongoing movement there is a great deal of noise from these operations.
Bringing passengers into this environment represents an inherent liability risk: Someone could be struck by a support vehicle, or injured by jet blast. A jet bridge is an enclosed area away from these dangers, providing an improvement in passenger safety.
Airport Security
A great deal of effort goes into ensuring that unauthorized persons do not have access to the airside facilities at an airport. Bringing passengers into this area represents a security risk, as even a ticketed passenger could be intent on causing disruption or damage once airside.
A passenger wandering off on the ramp would represent both a safety hazard (as the passenger could be injured) and a security hazard (as the passenger could perform any number of malicious acts before they are located).


Where can I find information about Boeing delivery history? Where can I find the records of which airplane model and creation number was delivered to which airline in which year for Boeing (Like B737-300 number 32 was delivered to Lufthansa in 1980)?

Planespotters.net also has a nice list. It has a good layout, and has pictures.


Where can I get a reliable and a updated Airport API or Airport Database, and I also want to know the charges for the API? Kindly guide me where can I get a reliable and updated airport Master API. The airport API should have all the information about all the airports in the world and I also want to know how much do they charge for the API.

Location Identifiers & Airline Designators data files available with daily updates
The perfect solution to feeding your coding database. These files (more information in right hand column) are available as a 12 month subscription or a one-time web download. For the subscription, you will be granted access to the password protected extranet site upon purchase where you can retrieve the data files update daily.

http://www.iata.org/publications/Pages/coding.aspx


Is there any Class G airspace south of Portage Bay in Seattle? I would like to apply for a waiver to fly a UAS to take pictures over the campus at Seattle Pacific University that is located just south of Portage Bay in Seattle but I'm told that can only be done in Class G airspace.  Is there any Class G airspace in that area?  Thanks.
Alan Rither

It appears that Seattle Pacific University is located 14NM north of the SEA VOR on the 350° radial.  This puts the university under class B airspace.

Over the university, class G airspace starts at the surface and extends upwards to 700 FT AGL, class E airspace extends from 700 FT AGL up to 3,000 FT MSL and class B airspace extends from 3,000 FT MSL to 10,000 FT MSL.

From a regulatory standpoint the FAA has a set of guidelines that are found in 14 CFR Part 107.

There are rules stating you cannot fly an UAS over persons who aren't part of the flight or with the traffic area of airports.  You also cannot operate in areas where class B, C, D or E extends to the ground but that appears not to be the case here.


Why does ADS-B broadcast velocity? I just read on opensky-network (scroll down to the section "facts") that ADS-B transmits roughly as many velocity as position messages.

Since the velocity of an aircraft can be computed from two successive position  broadcasts, why is the velocity transmitted directly?

The "position" and "velocity" include more than what the title would suggest.

Airborne position gives you:

Latitude/longitude
Altitude

Airborne velocity gives you:

Horizontal ground speed vector
Vertical rate
Air speed (when ground speed not available, can be true or indicated)
Heading (when ground speed is not available)

Together these two message types give you all the basic information you need about an aircraft's location and velocity. You are correct that given two lat/lon/altitude points, you can calculate the average horizontal speed, heading, and vertical rate. Keep in mind that ADS-B is already using the Compact Position Reporting format which calculates position with either two sequential messages or a reference position.

In addition to the additional computation cost, the measurement accuracy also needs to be considered. ADS-B broadcasts a "Navigation Integrity Category" or NIC, which expresses the accuracy of the GPS position. In terminal airspace, ADS-B is required to have about +/-300 feet in positional accuracy. While this is sufficient for giving general position and providing separation, it would create a lot of error in computing velocity. In reality the positions are fairly consistent but data errors still happen.


How are aircraft depainted? There are several questions about livery changes and livery in general on this website. Yet, I fail to find information about paint removal.

As a routine maintenance for an airframe that can live for up to 30 years, livery is redone several time as explained here. When changing painting, it should be preferable to remove the old one (I'm mostly thinking about weight as a big airliners has a lot a surface to paint). Moreover, I imagine that for military aircraft changing their operation theater, paint must be redone to adapt camouflage, and thus accumulating many layers of paint may have consequences.

Given material and other aviation-specific constraints, I also imagine there are special techniques to handle any intervention on the airframe.

Is this paint removal done and if so, how?

Paint stripper. Lots of paint stripper.
(originally I said thinner, but I have been corrected, it's more accurately called stripper)

Seriously though, it's actually not too different to other things that you paint. You need to spray on paint stripper. But, just like when painting the aircraft, it's imperative that you cover up all the delicate systems on the aircraft fuselage.

See here:

Also, I think it would be rare to paint a new livery over and existing one without first removing the old paint (maybe only if you were just changing small details), because covering an aircraft in paint weighs A LOT. For a 747 or 777 sized aircraft the paint job can weigh over 1000lbs

Carrying that around costs fuel and fuel costs a lot!


Crop dusting regulations in the US What are the regulations regarding crop dusting and flying low over private property. Do they have to file a flight plan and is there a way to make your private property a no fly zone?

To answer your questions:

A crop duster does not have to file a (normal) flight plan. They do have to file a special "operations" plan if they are going to be spraying chemicals. Notice of the intended operation must be given to the public by some effective means, such as daily newspapers, radio, television, or door-to-door notice. A plan for [the spraying] operation must be submitted to, and approved by appropriate personnel of the FAA Flight Standards District Office having jurisdiction over the area where the operation is to be conducted. The plan must include consideration of obstructions to flight; the emergency landing capabilities of the aircraft to be used; and any necessary coordination with air traffic control.

All aircraft must maintain a height of at least 500 feet above ground or objects on the ground, like a house. (Minimum Safe Altitude) A crop duster can go below this height only to operate to apply chemicals and for no other reason. The exact text of the exception reads as follows: "No person may operate an aircraft over a congested area below the altitudes prescribed in part 91 of this chapter except during the actual dispensing operation, including the approaches and departures necessary for that operation."

You cannot prevent someone from flying over your house.

If someone is flying over your house at less than 500 feet, you can file a complaint with the FAA by calling (703) 230-7664. Please observe the following:

• Identification - Can you identify the aircraft? Did you record the registration number which appears on the fuselage or tail? (On U.S. registered aircraft, that number will be preceded with a capital "N".)

• Time and Place - Exactly when did the incident(s) occur? Where did this happen? What direction was the aircraft flying?

• Altitude - How high (low) was the aircraft flying? On what do you base your estimate? Was the aircraft level with or below the elevation of a prominent object such as a tower or building? Did you obtain photographs? Are there any witnesses who could confirm your estimate - do you have their names, addresses, telephone numbers?

• Supporting Evidence

• Witnesses, Police

• Photographs


How does banner tow attach and release work? Planes can sometimes be seen towing banners around large cities or events.

How is the banner attached for takeoff?

How does the plane land after towing a banner?

There are actually a couple of different towing mechanisms out there. You've got your traditional banner pick, with the ropes and the hooks and all that, but there's also a new type of billboard mechanism that allows a tow aircraft to take off with the billboard already attached; it unfurls as the aircraft gains altitude, and can eliminate a potential inefficiency in the process (some days are worse for banner picks than others due to high winds, turbulence, etc.), but it limits the tow aircraft to some pretty small billboards and letter banners are pretty much a no-go.

Talking about the traditional method of banner towing, there are a couple of things to cover.

The banner/billboard setup on the ground - they will be attached to a tow rope (usually about 200 feet long) with a loop at the end. This loop is strung out between two poles a small distance apart. The goal of a banner pick is to have the hook pass between the poles, thru the loop; do that and you will be able to pick the banner off the ground. The banner or billboard will be laid down upwind of the poles (with the tow rope fully extended), so that the pick takes place into the wind; the lower ground speed will help with timing and allow the banner or billboard to come off the ground more smoothly. A small windsock is a common addition next to the poles to make it easier for the pilot to spot them and to give some local wind information. The banners and billboards may be set up parallel to a runway (usually the active runway), or there may be a designated spot elsewhere on the field.
The hook itself is attached to aircraft with a tow hitch and it is possible to have multiple hitches on the same aircraft (highest number i ever saw was 4 on a Piper Pawnee); they get used sequentially i.e. drop the hook, pick up the banner, fly the banner, drop the banner, drop the next hook, pick up the next banner, fly said banner, and so on until you run out of hooks. Most of the time, hooks that are not in use will be tied down somewhere accessible to the pilot who will drop them manually. That Pawnee I mentioned earlier, however, had the hooks attached to hitches on the aircraft's belly, from where they would be released with a switch, so there's more than one way to skin a cat. The hooks are normally attached prior to engine start and the pilot needs to make sure there is no slack in the line, to avoid it becoming entangled in rudder or elevator cables (more on that later), or other assorted bits and pieces of equipment.
Banner tow procedures

Take off is normal, but depending on your hook and cockpit setup, you may have to hold the hook in your throttle hand as you're taking off (this was the case with the Husky I towed in). Be careful not to hit anything with it.
After climbing through about 50 feet AGL, side-step the runway, and drop the hook. Procedure varies depending on your setup, but we used to extend the arm holding the hook as far out the window as we could get, give a gentle tap on the rudder to kick the tail out of the way and toss the hook outwards and away from the airplane. Kicking the rudder was important due to the way the rudder control cables ran in the Husky; we had one pilot who didn't and nearly wrecked when the rope got fouled around the cables, forcing a rudder hard-over once there was tension in the line after the pick - fortunately he was a big guy and the runway was sufficiently long that he was able to overpower the rudder and make a safe landing. Tossing the hook outwards is important lest it get caught up in the propwash and bang against the skin of the aircraft. Again, this happened (wasn't me though).
Coming around for the banner pick - depending on where the banners are set up, you may end up flying almost a regular traffic pattern, but it usually happens at much lower altitudes (5-600 feet) and the banner tow waiver may require that you avoid flying over populated areas to do so, so you may end up flying, say a right-hand pattern instead of your regular left. Either way you end up doing it, you want to end up downwind of the poles, similarly, if you will, to coming in for landing.
The actual banner pick - this is where you'll see a lot of variation. Some outfits will come in flat, just above the poles and pull up once they pass them (unusual, but some do it that way), others will come in high and dive towards the poles, and pull up once past them (it's very pretty and dramatic, but not a lot of room for error IMO). We used to be a bit more sedate about it, and came in as if for a landing, with the goal of touching down at the top of the banner (i.e. the end nearest to you). Obviously, you have to correct for crosswind, which you can do by shifting your line left or right depending on wind direction; the goal is to place the hook, which is trailing behind you and getting blown about by the wind, between the poles. Either way you do it, once you pass the poles, you pitch up immediately to at least 45 degrees or so, and apply full throttle. You zoom climb to about 200 feet AGL and then reduce the pitch angle to be able to maintain a slow-speed climb. Do this right and the banner or billboard will come smoothly off the ground; you may feel a slight tug as tension is applied through the towline if you haven't been smooth enough and ended up yanking the banner off the ground. Continue to climb to whichever altitude you've planned for and, when stabilized in the climb, try to take a look behind you (if you can) to make sure you've picked successfully and that the banner didn't get damaged or something. If you can't look behind you, you can check during a turn, or have your ground crew radio/text and let you know.
Fly the banner - you want to fly slow enough to avoid stressing the engine, airframe, tow rope and banner, but not quite so slow that the engine can't get enough airflow to cool down (remember, on the backside of the power curve, power required increases the slower you try to fly). Watch your altitude and distance from people and objects (the powers that be are quite serious about it), look out for towers (especially those that come with guide cables and the like), high rise buildings, and other traffic, and try not to get too bored flying in circles for hours.
Drop the banner - when you come back in to drop the banner, the goal is to drop it low enough to the ground that the wind won't have time to blow it away onto  active runways (or into the trees - I had to help pull somebody else's banner out of the trees once, not fun). Ideally, you might want to drop it as close as you can to where the ground crew has their bags and everything setup to spare them having to haul heavy banners and billboards over long distances. You release the hook using a lever bolted onto the floor of the aircraft and then apply power, climb out, and come around for another pick or a landing, whatever the case may be.

Hope this helps, let me know if you'd like to know more about any of this.