Must RAIM be checked in flight before every GPS approach or is a preflight check acceptable? My instructor has been teaching me to run a RAIM check for each RNAV approach we do.  For some flights this can be 4 or more RAIM checks for the various airports/approaches and adds significantly to the workload.

I started doing some research and I think I've gathered a few things. First RAIM applies over large areas, not singular GPS points (makes sense), the FAA provides a tool to determine RAIM availability from the ground as part of preflight, and last that a RAIM check while briefing the approach seems Like it might not be necessary since the GPS is required to run a RAIM check 2 miles prior to the FAF.  Additionally since the GPS has no way to know about unexpected NOTAM announced outages the 430 RAIM precalculation is a bit less reliable.

Is it a requirement to run the manual RAIM check in flight or is it more appropriate to use the FAA tools and determine it as part of preflight preparation?

The FAA website predicts pre-flight whether RAIM will be available

The RAIM algorithm will tell you during your flight if GPS is working correctly.

The pre-flight FAA website check is not a substitute for the use of the RAIM function during flight. It will only show whether the RAIM function is available during flight.

RAIM stands for Receiver Autonomous Integrity Monitor. It is a part of aviation graded GPS receivers that checks consistency of all used GPS satellite signals in order to raise an alert if the GPS system is not working correctly.

For RAIM to work, there must be at least 5 usable satellites in view of the GPS receiver. For GPS without RAIM, at least 4 satellites are needed. If there are only 4 satellites visible, or more than 5 but with an unfavourable geometry, RAIM cannot work and therefore the GPS receiver cannot be certain that the produce position fix is correct.

The FAA website predicts the availability of RAIM; based on the constellation of GPS and the health status of its satellites, the route and the time of flight it is possible to calculate  whether RAIM is available for your flight. This can be done before you take-off.

If there is no RAIM available during part of your flight, you can't rely on GPS during that part. The GPS may still work fine, but there is no way to check its integrity. A single fault in a GPS satellite or, more likely, a corruption in the downlinked GPS satellite almanac will cause the position fix to be off. You must use alternative navigation means if GPS RAIM is not available.

The FAA website does not say anything about the actual quality of the GPS system during your flight. This is what RAIM does. It continuously monitors all satellite signals for consistency and flags any inconsistencies.  There are various categories of RAIM such as Fault Detection and Fault Detection & Exclusion but all RAIM algorithms will give you a containment radius.

The containment radius is the maximum size that a position error can grow due to a fault in the GPS system without the RAIM algorithm being able to detect it. The value of the containment radius depends on the geometry of the satellites.

The requirements for the value of the containment radius depend on the flight phase. For En-Route mode the RAIM containment radius value should be under 2 NM, terminal mode under 1 NM, and approach mode 0.3 NM.


What is the explanation of this airfoil phenomenon? Why the air from below the leading edge's tip deflected up? I have difficulties to understand this air phenomenon, why the air from below the leading edge's tip (from below the horizontal line) is deflected up and not just follow the bottom wing's surface? What is the physics explanation of it?

The short answer is: because not all of the incoming air can fit under the airfoil, so some of it gets pushed up and above the leading edge. This air could also fit under the airfoil by other means like becoming denser (compressing), but that requires more energy, so it mostly flows around.

In your image, the effect is exaggerated by the closeness of the ground, which places the entire airfoil in ground effect. In normal flight conditions, without the ground blocking it, more air would be able to flow underneath the airfoil.

The longer answer has to do with the speed of sound, which is the speed at which pressure waves propagate through a fluid. If the free stream is subsonic, pressure waves generated by an object can flow upstream and alter the flow ahead of any disturbance.

This is exactly what is happening here: the airfoil is affecting the pressure field, specifically by creating an area of high pressure underneath. This affects the incoming flow, deflecting it upwards ahead of the airfoil.

If this experiment were performed in supersonic conditions, you would not see any disturbance in the incoming airflow until it hit the bow shock wave of the object, after which it would become locally subsonic and be abruptly deflected to flow around the airfoil.


Could a private pilot violate 'commercial' rules if there is no compensation or expense sharing at all? How might a private pilot run into regulatory trouble by flying a passenger if they don't receive any compensation at  all? I'm interested in some specific scenarios. In all of these cases, let's assume the pilot receives no compensation of any kind, and pays all costs himself. The passenger makes no contribution whatsoever. There are no exchanges of services, no favours, no under-the-table deals. Also assume that none of the activities mentioned are in any way concerned with the employment or other business activities of either pilot or passenger.

The pilot flies the passenger somewhere the passenger wasn't planning on going, but nonetheless enjoys. I'm assuming this is not a problem, and happens most days
The pilot flies the passenger to visit a family member, one they wouldn't have visited otherwise.
The pilot flies the passenger to a recreational event, which they are attending.
The pilot flies the passenger to a recreational event, which only the passenger is attending.

Again, no money changes hands, no compensation of any kind, pilot pays all the costs.
US regulations. And please, specific citations of cases or regulations.
EDIT: Since this appears to be a source of confusion, let me repeat for the third time in the question: there is no compensation or expense sharing and nothing of value changes hands. The pilot pays all costs, at exactly the same rate as he would if he was flying alone. There is no 'goodwill' expected, no future business deals, nothing.

Yes.  Without compensation, a private pilot can violate 'commercial' rules.

For starters, the FAA considers the ability to log flight time as compensation.  A legal interpretation to John Harrington issued October 1997 clarifies that point.  The regulation that you are asking about is quoted below.

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

  (a) Except as provided in paragraphs (b) through (h) of this section, no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft.

An interpretation to Mike Sommer in part says

  The FAA construes the terms “compensation for hire” very broadly. It does not require a profit, profit motive, or the actual payment of funds. Instead, the FAA views compensation as the receipt of anything of value. In an interpretation letter to John W. Harrington, from Donald Byrne, Assistant Chief Counsel, October 23, 1997, it is stated that, “any reimbursement of expenses (fuel, oil, transportation, lodging, meals, etc.), if conditioned upon the pilot operating the aircraft,’ would constitute compensation.”

In 1985 the FAA chief counsel determined that there had to be a bona-fide common purpose in conducting the flight.  See the Chero Interpretation from December 1985.

  Section 61.118(b) allows a private pilot to share the operating expenses of a flight with his or her passengers. Additionally, the FAA has interpreted 61.118(b) so that the only allowable share-the-costs operations are those which are bona fide, that is, joint ventures for a common purpose with the expenses being defrayed by all passengers and the pilot. Nor does Section 61.118 permit pilots who want to build up time toward their commercial pilot certificates to carry expense sharing passengers to a destination at which they have no particular business. (emphasis added)

To answer your question.

The pilot flies the passenger somewhere they weren't planning on
going, but nonetheless enjoy. I'm assuming this is not a problem,
and happens most days.

There is no problem here.  The pilot would pay for the expenses of the flight anyway so taking a passenger is OK.
The pilot flies the passenger to visit a family member, one they wouldn't have visited otherwise.

This is only legal if the pilot pays for all expenses.  Since the FAA has determined compensation quite broadly I would expect they would also consider food and lodging as compensation as stated previously in a legal interpretation.  The pilot would, for all practical purposes, pretend the passenger was not there and make their own arrangements.
The pilot flies the passenger to a specific recreational event, which they are attending.

This is legal and the pilot can share the costs with the passenger.
The pilot flies the passenger to a specific recreational event, which only the passenger is attending.

This goes back to #2 above.  The pilot does not have a bona-fide common purpose for making the flight.  They cannot accept any compensation in any form for the flight to be legal.


Why does the LP compressor rotate in the opposite direction of the HP compressor? Why does the LP compressor rotate in the opposite direction of the HP compressor in some multi-spool turbine engines?

Contra-rotating spools are a very recent development, apart from the Bristol-Siddeley (later: Rolls-Royce) Pegasus engine for the Harrier. The Rolls-Royce Trent 900 started the trend when its high pressure spool was made to rotate in the opposite direction to the other two spools. From Wikipedia:

  It is also the first member of the Trent family to feature a
  contra-rotating HP spool

Next was General Electric with the GEnx, a two-spool design with a high pressure compressor rotating clockwise while the low pressure compressor rotates counterclockwise.

Contra-rotation means that the relative speeds between the spools are increased, increasing the bearing losses between them. However, contra-rotation helps to increase efficiency - now the stator between the last low pressure stage and the first high pressure stage of the compressor and the stator between the last high pressure turbine stage and the first low pressure turbine stage can be left away which reduces parts count, engine length, engine mass and friction.

Again Wikipedia:

  Counter-rotating spools for the reaction turbines to reduce load on
  guide vanes.


How did Airbus fit 6,340 gallons more fuel into the A359? Bloomberg posted an article that says, among other things, the A350 ULR variant increases range by utilizing "additional space already available in the existing tanks to carry an extra 6,340 gallons of fuel."

What is the deeper technical explanation, or why not use this space in the regular A359 variant?

Bloomberg says minor changes to "piping and venting" made the capacity available. It came from previously unused space in the center fuel tank.

The a359 center tank filling point is not at the highest point in the tank, so it needs a vent in order to use that space. Without the vent, the tank airlocks and no more fuel will flow in.
Piping refers to changes to that tank's inerting system, designed to prevent explosion of fuel vapor in the tank. Inerting has been required for wingbox center tanks ever since TWA800. See Leeham for more detail, search the page for Update2.

As to why this is not part of every a359, it is operating cost. The regional variant has a 260t MTOW and therefore lower landing and navigation fees. The 280t MTOW needed for the ULR will be available from 2020 on the standard model, so there is very little difference otherwise. If you order the ULR you can paper change it to a regional, though I don't know anyone who would.

Leeham also has an interesting article on how seating (passenger weight) has to be limited to get maximum range from the ULR.


What is the benefit of a curved up flight deck? A Russian aircraft carrier Admiral Kuznetsov has an interesting aspect: the edge of the runway is raised, which “pushes” the plane in the air during the takeoff. Looking at takeoff videos, the curved edge seems very natural.

All USA aircraft carriers I can think of have an absolutely flat deck, similarly to, for instance, USS Abraham Lincoln:

The Admiral Kuznetsov's curved deck provides benefits, so why were most carriers not built the same way?

Because the method of launching aircraft are completely different in these carriers. Carriers with ski-jump, initially designed for RN Harriers (as @Simon already has explained), requires that the aircraft take-off under its own power.

On the other hand, large aircraft carriers having flat decks have their aircraft launched by catapults (with a notable exception) which basically throw the aircraft from the deck. Though this system is heavy, expensive and complicated, it brings significant advantages to the table:

It allows aircraft with higher t/o weight to operate from the carriers. USN operates F/A-18E/F Super Hornets, which weigh ~30 tons from its carriers (they even operated the heavier F-14 Tomcats). The ski jumps, on the other hand restrict the aircraft t/o weight (which means less ordnance), as the Chinese are finding out. Indian Navy operates Mig-29Ks from its carrier, but they are lighter (~25t).
The catapult launch offers more options - it can operate in wider range of sea conditions compared to the ski-jump and can even launch aircraft even if one of the engines fail during the launch, a feat usually not possible for the aircraft in ski-jump.
The catapult allows for a significantly higher takeoff rate, which means a higher sortie generation. As rusnavy.com notes:

  With its four catapults, a US carrier is capable to shoot one aircraft in every 15 seconds. Kuznetsov has only three takeoff tracks. Moreover, two bow tracks are not intended for fully-loaded aircrafts! They can take off Kuznetsov only from one track which starts far behind the midship, i.e. an aircraft must run almost the whole flight deck! Comparing to catapult, takeoff rate of ski-ramp is at least twice lower.

The catapult allows the launching of support aircraft (like AWACS), which have low thrust-weight ratio and would not be able to take off under their own power.
The ski jump takes up space in two ways- physically, it occupies front deck space (on the other hand, aircraft can be parked over catapults when not in use), while the take off run required by the aircraft (greater with more gross weight) eats up more space, leading to limitations of the number of aircraft on the deck.

As for the exception, the USN operates carriers without ski-jumps, but these are not called as such- they are called amphibious warfare ships an operate only VTOL aircraft like the F-35 Lightening II and V-22 Osprey.


How can I isolate altitude as a specific range variable on a Sporty's electronic e6b? So, I'm trying to understand the specific range calculation on my Sporty's E6B electronic calculator. The manual gives two examples.

In one, the assumption is 150 Ground Speed, 24 Gallons of fuel per hour and 140 gallons of fuel on board. It also assumes 12000 MSL. The answer is 875 miles.

Then there is another example: 160 GS, 27 G/Hr, 140 gallons on board, and MSL is 8000. The range changes to 855.6.

The problem is: the altitude is not an enterable variable (those others are). Entering it and adjusting in different parts of the calculator does nothing. Does anyone know how to isolate MSL as variable in this device?

TL;DR; You need to look up the burn rate in your POH.

I think you are misunderstanding the examples...

Your fuel burn rate is determined by your power setting and altitude from your charts in your POH. You need to look that up, so to calculate the range, here is what you do:

First, use your POH to look up your fuel burn for a specific power setting/manifold pressure/altitude, here is an example from a Cessna 172 POH:

You can then you can use that fuel burn rate in your calculations. A range calculation is simply:

$$
Range = {Fuel \above 1pt BurnRate} GS
$$

So using the table above, if we are cruising at 6000 feet @ 2200 RPM on a standard day we are burning 7.7 GPH. The 172 has a capacity of 53 gallons. If we are indicating 100 knots ground speed on a GPS (1knot = 1 nautical mile per hour), we can calculate our rate as:

$$
Range = {53 \above 1pt 7.7} 100 = 688
$$

The result would be 688 nautical miles (this is burning every drop of usable fuel, not taking into account VFR or IFR reserves).


Where do standard torque values in maintenance manuals come from? Maintenance manuals of today's civil aviation aircraft (from both Boeing (e.g., B-737) and Airbus (e.g., A320)) have special chapter to describe "standard torque value" for fasteners and connections. These values are determined by material, size, etc.

I wonder where and how these values come from. Could anyone provide me with detail about this?

The standardized values are related to the yield strength and elasticity of the fastner.  Bolts in normal tolerance holes are effectively spring clamps (bolts in close tolerance holes can be better thought of as spring clamps + shear pins) and when you are tightening a bolt you are using a spiral wedge, the threads, to force the bolt to stretch to clamp the parts together.

You want to be able to stretch the bolt to apply as much clamping force as possible without exceeding its yield, or permanent deformation threshold.  It's like stretching a spring too far, so that when unloaded, it is longer than before.  You would say that the spring is ruined if that happens.  Same with a bolt. If you overtorque it and exceed its yield strength, it will be a bit longer than before when loosened and will have lost some of its ultimate strength after being permanently elongated.

So the standard torque tables are limits on how much the bolt can be stretched, converted to the equivalent rotational force applied to the spiral wedge of the threads.  The values are those that keep the axial tension force below the yield threshold, with some safety margin.  The standard limits are a function of the material strength and elasticity of the material that a particular bolt is made from.

A lot of the time torque values are given that differ from the standard values because the designer wanted to customize the clamping force for some other purpose, such as to limit clamping force on the base material or gasket or washer, or limit shear loads on parent material threads (like a steel bolt in an aluminum casting).  The normal engineering practice is to quote a torque value on the engineering drawing (and hence in the Maintenance Manual procedure) when it differs from the standard tables.

So as a general rule, when a torque value is from the standard torque tables, it's a limit for the bolt itself and is related to its tensile yield limit.   When a special torque value is given, it's a limit to control force applied to something other than the bolt itself for various other reasons.


How to determine the thickness of an airfoil? In calculation or designing, how to determine the airfoil thickness? What is the guideline or consideration in designing airplane's wing? We all know that the bulge (the ticker in the airfoil) is required to apply Bernoulli principle, to create low pressure above the wing. But how to bind the round nose shape requirement to the design requirement. In this case, to make the airplane to be efficient (especially related to the power consumption).

This airfoil is required for an airplane as I explained here. Maximum weight will be 400kgs, and the maximum speed will be 200km/h.

Factors for determining the wing thickness during the aeroplane design procedure:

Determine the required structure height, which follows from the aspect ratio determined by the aerodynamicists: the cantilever ratio, which is the structural wing semi-span divided by maximum root thickness. Statistical analysis has found that transport aircraft usually have a ratio between 18 and 22, lower means a lighter wing but more drag.
Stall behaviour: for thin wings the leading edge stall dominates, for thick wings trailing edge stall which is more gradual. This imposes a minimum thickness.
For aircraft cruising at M > 0.5: the wing thickness must be such that dive Mach number remain subcritical. Imposes a maximum thickness.
For good max $C_L$ a value from the sweet spot between 12 and 15 should be selected, see below = fig 7-9 from Torenbeek.

Torenbeek then concludes:

It is concluded that the root section thickness of transport aircraft should be chosen such that a good cantilever ratio is obtained. For a given taper ratio this implies that the thickness ratio at the root will increase proportionally to the aspect ratio. A thickness ratio of between 15 and 20 percent is in the interest of good performance when using relatively simple trailing-edge high-lift devices and provides adequate room for retracting the undercarriaqe. Thickness ratios above 20 percent may show diminishing returns due to the increasing profile drag and the relatively low maximum lift and this, in turn, limits the aspect ratio to a maximum of approximately 13 for cantilever wings.
Tip sections (without flaps) should be between 10 and 15 percent in order to attain a high maximum lift. This reduction relative to the root is also in favor of low structural weight.


How to Tell Flight Following You Want to Change Your Destination? I want to fly the LAX Coastal VFR Transition Route northbound, and I want to do the whole thing with flight following.  When I get near Van Nuys airport, I'll need to tell ATC (flight following) that I want to change my direction and head eastward to a different airport.  How do I do this?  And more broadly, how do I tell flight following radar services that I want to change my destination?  For some routes it seems easier for me to have them follow me with radar services to a certain airport that I don't intend to land at, then ask them to change as I fly to a different airport.

Just tell them.  Like you told us in the question.  Seriously, plain old English works just fine on the radio.

Don't get all chatty, and be professional, but don't overthink things and feel you need to use a bunch of radiotelephony code words to get a simple point across.

The most important thing is to clearly communicate intentions.  Don't tell them you are going one place and then "change" it when you actually planned on going there all along.  That's phony and unnecessary, and could confuse things if there any sort of emergency where knowing your planned route of flight or destination would be useful.

Simply tell them you plan to fly VFR up the coast to VanNuys, then turn Eastward and proceed to destination XYZ.  Or, more briefly:  "destination XYZ, via Van Nuys".  It's just that simple.

And consider filing a flight plan.


Why the 747 testing GE-9X doesnt have a winglet? News says it is a 747-400, but it doesn't have a winglet.

That's because its been removed for testing. The aircraft used in for flight testing the GE-9X belongs to GE and is a modified JAL 747-400.

  The aircraft, a former Japan Airlines -400, was acquired by GE in 2010 and
  following maintenance and interior modification in Xiamen, China,
  by Taikoo Aircraft Engineering, was delivered to Evergreen Aviation
  Technologies in Taiwan for installation of data racks and instrumentation.

For carrying out the testing, GE has carried out a number of modifications for maintenance and testing:

  ... modifications are also planned to reduce the chances of aero
  elastic interaction between the extended wing of the 747-400 and the
  GE9X mounted on the inboard left strut. GE has already removed
  the standard winglets because these add unnecessary weight and a
  maintenance burden to the aircraft’s flight-test role. Later this year,
  the outer 6 feet of each wingtip also will be removed, ... Designers say the stiffer wing will reduce potential exposure to limit cycle oscillation and maintain an unrestricted test envelope.

Quotes from archive.org. Original ariticle appears to be from aviationweek.


Are commercial aircraft designed with a shared data network? In modern airliners, do systems like the in-flight entertainment system (IFE) share the same physical and/or logical network as the flight management systems (FMS)? Is there any communication between the IFE and the FMS? Also, is there any Airbus training or procedure that might deal with what to do if flight systems were being tampered with?

I'm asking because an information security researcher named Chris Roberts is in a bit of trouble with the FBI after claiming he hacked into the entertainment systems on Airbus and Boeing airliners and used the access to tamper with the airplanes' flight control systems. Apparently he would connect into a Seat Entertainment Box (SEB) and hack the IFE system. I am an information security professional myself and I have no reason to disbelieve this part given my personal experience.

What I am initially skeptical about is that he has claimed to have successfully tampered with flight control systems using the access gained from the compromised IFE. Specifically listed in this document he has allegedly claimed that he issued a climb command to one of the engines through the thrust management computer, causing it to spool up and temporarily cause the aircraft to yaw. This would only be possible if the IFE were able to communicate somehow with the FMS.

Aircraft do have LAN Networks for their sensors to minimize wiring (and consequently weight), however I would assume these are closed circuit networks and NOT connected to the IFE system.

In terms of the FMS system on aircraft according to this they do have databases however I dug into it a bit and it seems that based on this walk through on updating you need to physically connect to the device to change that database (for Rockwell Collins Equipment). It also seems that the Honeywell FMS computers have a similar way of updating via USB. While I cant say for certain it does not seem the FMS is on any kind of network aside from its own.

The big question is autopilot/FBW systems and can they be overridden or tampered with. It seems that Boeing-Honeywell has a patent on some remote flying systems but has not yet implemented it on any aircraft. I am still looking for some solid evidence that the systems have a point of access on the network. It is clear that they can be altered if you can physically connect to them for update purposes. Keep in mind you would have to load them with false data.

This seems to be the autopilot for the 777 however Rockwell Collins does not seem to allow you to get the info on it very readily. Maybe someone else on here can comment on how its set up.

This nice paper overview of FBW systems on a 777, in section 11.4.4 lists the connections the FBW system has to other systems on the plane. While this is by no means an official document (at least I don't think so) it does not list the IFE system as a connection and is pretty clear on the fact that everything connects over the ARINC 629 style data busses.

Edit:

It does appear that ethernet technology is making its way onto aircraft however it seems that the tech still uses ARINC Specification 664. However page 2 of this spec documents seems to imply that through a "gateway" the system is connected to the "internet". However Page 38 clearly states

  Although AFDX/ARINC 664 is a closed network, UDP port numbers
  should be selected from the Dynamic/Private range of numbers. The reason
  for this is that there could be potential conflicts with the standard port
  number assignments when a gateway is used to communicate between the
  AFDX network and the Internet

So it is connected to the internet but the flight control systems are on a closed network. They also advise you to use the private range of ports to avoid any possible conflicts. Here is another good paper on the technology. It does seem that they are moving towards some internet like devices on aircraft but it also seems that they will remain closed networks. Companies are looking to consume some modern tech for an age old application as its simpler and easier to use existing high speed bus technology than reinvent the wheel and make a new custom bus. Just because something has a router and ethernet cables does not mean its connected to the internet!


How do I calculate the heading to steer in this example? At 1415 an aircraft was overhead a VOR maintaining radial 215°, en
  route for B, heading 210°(M). At 1430, the pilot decides to return to
  the VOR. The heading to steer is...

The answer is given as 040°(M), I'd just like to know the steps to calculate the answer.

You are holding 215 by compensating for a crosswind using 5 degrees of heading change.

The opposite of 215 is 035.

You must compensate by holding 5 degrees of heading change past 035.

Presumably, the fact that you're 30 minutes flight time away from the VOR when you turn gives the pilot sufficient time to reestablish themelves on course. Thanks @MichaelHall!


How is shear stress distributed on an airfoil? I know the pressure distribution on an airfoil but not shear stress. How is shear stress distributed on an airfoil?

Shear stress is proportional to the speed gradient at the wall. This means:

A thin boundary layer produces more shear than a thick one. The boundary layer is thinnest right next to the stagnation point and grows in thickness downstream.
A turbulent boundary layer will create much more shear stress than a laminar one. Most of the shear on an airfoil happens past the transition point.
Higher speeds cause higher shear stresses. Therefore, the suction area on the upper side of the airfoil produces more shear stress than the pressure area on the lower side. In a separation bubble with speed reversal at the wall you will even get a small amount of "shear thrust".

The shear acts along the local flow direction, so it is mostly front-to-back. Only near the wingtips, where lateral flow becomes non-negligible, will a lateral shear component become noticeable.

Friction drag over chord for an E502mod airfoil at 3° AoA. Blue: Top surface, Red: Bottom surface. Source: XFOIL 6.97. The transition points are clearly visible: It is where shear shoots up again at mid-chord. Note the separation bubble ahead of the transition point on the bottom side: It is marked by negative values of shear.


Why do we no longer have a navigation officer on modern commercial flights? In the olden days there used to be a navigation officer in commercial airlines who had the tasks of navigation and radio communication. But, in modern commercial airliners there is no navigation officer.

Do the pilot(s) take the additional responsibility of radio communication and navigation? Or is the navigation part now done by onboard computers and systems?

If the electronic navigation system fails, are there any backup plans? Are physical maps and a compass then used to determine the direction and position?

Navigation has gotten much simpler over the years.  Initially, navigation would be done by a combination of dead reckoning, looking out the window for landmarks, and for night or long-distance flights, by celestial navigation (many old airplanes have a window at the navigator's station specifically to let the navigator see the stars).  This took quite a bit of time and effort, so the pilot couldn't do it and also fly the airplane.

In the 1920s, radio navigation was added to the navigator's toolkit, but finding bearings to beacons and calculating a location was still an entirely manual process.  Additionally, radio beacons didn't cover the entire world, so older navigation techniques were still needed for most flights.

In the 1950s, fully-automatic radio direction finding systems became common and navigation beacons were available across most of Europe and North America.  At this point, the workload involved in navigation dropped to the point that the pilot could also navigate: plot out the sequence of NDBs to follow ahead of time, then tune the radio and follow the navigation display.

Very recently, navigation has been integrated with the autopilot to the point that the pilot can punch in a sequence of waypoints and have the airplane fly the route entirely on its own.

And yes, even today if the electronic navigation system fails, the fallback is map, compass, and slide rule.


How many pilots do long flights need? Under normal 2 pilot part 121 ops I could only be scheduled to fly 8 hours in a given day.  This is plenty for the routes we flew (longest leg around 4 hours) so I never encountered the rules for longer flights.

For flying beyond 8 hours -- long haul international ops -- what determines how many pilots must be on board?  Is only flight time taken into account or is the number of timezones crossed also a factor?

The regulations for this are in 14 CFR 121 Subpart R—FLIGHT TIME LIMITATIONS: FLAG OPERATIONS.

In short, flight time limits within a rolling 24 hour period depend on the number of crew members assigned to the flight:

One or two pilot crews - 8 hours max
Two pilots and one additional flight crewmember: 12 hours max
Three or more pilots and an additional flight crewmember: More than 12 hours, but "adequate sleeping quarters on the airplane" will be provided

However, they may also implement a "Fatigue Risk Management System" which allows them to exceed these limits if they are found to be safe and approved by the FAA.  This system would most likely address the number of timezones crossed but is optional.

A particular airlines pilot contract may also have more restrictive limitations (like considering the number of timezones crossed) that are negotiated by the union, but this is not required by the regulations.

  §121.481   Flight time limitations: One or two pilot crews.

  (a) A certificate holder conducting flag operations may schedule a
  pilot to fly in an airplane that has a crew of one or two pilots for
  eight hours or less during any 24 consecutive hours without a rest
  period during these eight hours.

  ...

  §121.483   Flight time limitations: Two pilots and one additional flight crewmember.

  (a) No certificate holder conducting flag operations may schedule a
  pilot to fly, in an airplane that has a crew of two pilots and at
  least one additional flight crewmember, for a total of more than 12
  hours during any 24 consecutive hours.

  ...

  §121.485   Flight time limitations: Three or more pilots and an additional flight crewmember.

  (a) Each certificate holder conducting flag operations shall schedule
  its flight hours to provide adequate rest periods on the ground for
  each pilot who is away from his base and who is a pilot on an airplane
  that has a crew of three or more pilots and an additional flight
  crewmember. It shall also provide adequate sleeping quarters on the
  airplane whenever a pilot is scheduled to fly more than 12 hours
  during any 24 consecutive hours.

  ...

  §121.495   Fatigue risk management system.

  (a) No certificate holder may exceed any provision of this subpart
  unless approved by the FAA under a Fatigue Risk Management System.

  (b) The Fatigue Risk Management System must include:

  (1) A fatigue risk management policy.

  (2) An education and awareness training program.

  (3) A fatigue reporting system.

  (4) A system for monitoring flightcrew fatigue.

  (5) An incident reporting process.

  (6) A performance evaluation.


Is it illegal to fly a Cessna 172S under day VFR with an inoperative vacuum gauge? Let's say my vacuum gauge is not working on my C172S and I want to go day VFR flying.  There is no MEL.  14 CFR 91.213 details procedures for inoperative instruments, and I think the following paragraph applies to my operation, so let me go through these one by one:

  (d) Except for operations conducted in accordance with paragraph (a) or (c) of this section, a person may takeoff an aircraft in operations
  conducted under this part with inoperative instruments and equipment
  without an approved Minimum Equipment List provided -

  ...

  (2) The
  inoperative instruments and equipment are not -

  (i) Part of the VFR-day type certification instruments and equipment
  prescribed in the applicable airworthiness regulations under which the
  aircraft was type certificated; (N/A, vacuum gauge not part of TOMATO FLAMES)

  (ii) Indicated as required on the aircraft's equipment list, or on the
  Kinds of Operations Equipment List for the kind of flight operation
  being conducted; (not sure here*)

  (iii) Required by § 91.205 or any other rule of this part for the
  specific kind of flight operation being conducted; (N/A, not conducting flight at night or IFR)

  (iv) Required to be operational by an airworthiness directive; (N/A, let's assume no applibale ADs)

*This is interesting language: "Indicated as required on the aircraft's equipment list".  AFAIK, to determine if the vacuum gauge fits this description, I should consult the equipment list in the POH, which reads:

Ok, so I now assume any instrument with a number ending in "-R" is "required" for the purposes of complying with the above regulation.  Locating the vacuum gauge in the equipment list, I see it indeed has a suffix "-R", indicating it is a "required item for FAA certification":

Thus I am led to conclude that the vacuum gauge is "indicated as required on the aircraft's equipment list", and hence continuing my flight would be in violation of 14 CFR 91.213.

Is my reading of the regulation and my interpretation of "required item" accurate here?

Your reading is correct: a Cessna 172 with an inoperative vacuum gauge is not airworthy.
Type Certificate Data Sheet No. 3A12, Revision 85 shows how Cessna 172 models meet FAA airworthiness requirements. Section XII, “Model 172S, Skyhawk SP, 4 PCLM (Normal Category), 2 PCLM (Utility Category), Approved May 1, 1998,” contains

Equipment
The basic required equipment as prescribed in the applicable airworthiness regulations (see Certification Basis) must be installed in the airplane for certification …
NOTE 2: Pilot’s Operating Handbook and FAA Approved Airplane Flight Manual (POH/AFM):  part number 172SPHUS-00 (or later approved revision) is applicable to the Model 172S. The airplane must be operated according to the appropriate POH/AFM …

The Comprehensive Equipment List in Section 6 of the POH/AFM gives the Combination Vacuum Ga[u]ge/Ammeter the R suffix, meaning required.
FAR 91.213(d)(2)(ii) reads

(d) Except for operations conducted in accordance with paragraph (a) or (c) of this section, a person may takeoff an aircraft in operations conducted under this part with inoperative instruments and equipment without an approved Minimum Equipment List provided -
  (2) The inoperative instruments and equipment are not -
    (ii) Indicated as required on the aircraft's equipment list, or on the Kinds of Operations Equipment List for the kind of flight operation being conducted;

But the equipment list does indicate the gauge as required, so this exception does not apply.
To fly the airplane to a repair station to fix the vacuum gauge, apply for a Special Flight Permit (or “Ferry Permit”) with your geographic region’s Flight Standards Office, as provided in FAR 21.197.


Is it safe to fly if the flaps won't retract on ground? The Piper Archer (PA-28) i had this morning had issues returning flaps to normal after being fully extended ON THE GROUND. It required a non trivial amount of push on the air-frame itself to restore the flaps to the original position after having retracted the flaps using the stick in the cockpit.
I was told that "this is normal" and that the spring might be a little worn but that it wouldn't cause any safety issues, but none of the other Piper Archers I've flown have had this issue. I would add that it was a cold day (just above freezing) but the plane fully fully de-iced.
Is it reasonable the fly the plane?
Would you be worried? If you refused to fly the plane in that condition despite booking, would you accept the rental to be charged partially?

The main thing to be concerned with, is that the spring tension is important for keeping the bicycle chain segment secure on the eccentric sprocket (item 17 below) that drives the torque tube.  If there are issues with spring tension in the return spring (item 32), I'd be concerned that slack could result in the chain potentially coming off, but that would require the tension spring on the bottom (item 22) to be not doing its job.
The top return spring should be a fair bit stronger than the tension spring, which is only there to keep the chain from going slack when the cable from the cockpit lever is slack.  There is likely a combination of a weakened return spring and some binding in the bushing blocks for the torque tube.
There isn't any risk of flap asymmetry unless the torque tube itself breaks or a control rod lets go, so a problem with the chain arrangement where it jams up or disconnects will, in a worst case scenario, just leave you stuck with flaps partially extended or at zero.
So what to do about it?  Depends.
I'm assuming they went almost fully up and you had to push them a bit to get them to move the last little bit.  If I knew the plane well, and if the panels came up almost all of the way and just needed a little nudge to overcome some friction, and they stayed up after the nudge, and every thing otherwise felt smooth and solid (when you do a walkaround, you shouldn't just be looking at stuff; you should be gently tugging and moving bits as part of your inspection to detect unusual play), it should be ok and air loads will do the job fine at retracting them as soon as you are moving with some speed, although I would snag it and expect it to be fixed the next time I saw it.
On the other hand, technically it shouldn't be doing that and if there is significant friction, or slop, or you are just uncomfortable with it, you should refuse it and shouldn't be charged for it.  A weak return spring and/or binding in the mechanism that prevents retraction on the ground is still a "defect" and needs to be rectified.
If you have access to the A&P that maintains the airplane it might be a good idea to mention it.  They may not be aware of the problem.


Is there a difference in landing fees for charter and scheduled flights? Is there a qualitative difference for landing fees/charges between charter and scheduled flights at a particular airport?

This is almost completely dependent on the airport but we can talk somewhat generally.

For what its worth airlines (scheduled carriers) can often negotiate lower landing fees by being able to guarantee a specific amount of flights into an airport. Charter companies don't have this luxury since it can be hard for them to predict where and when they are going. On the other hand some fees are set by the local government, for example here in Philadelphia any airport in the city (KPHL and KPNE) has landing fees set by the city. You can find the official legislation here and I assume thats non negotiable but I cant be sure.

There is also a bit of a discrepancy due to the type of planes. Landing fees are often charged by weight and in most cases charter planes are flying smaller stuff than the scheduled carriers and their fees may be lower as a result (even though the scheduled carrier has a lower rate). If we look again at Philadelphia we can see that they have fees for both weight and passengers which generally go hand in hand however a charter company may be flying a big RJ for just one guy while a scheduled carrier may be operating the same plane at its maximum seating arrangement.

Charter carriers may also have the luxury of flying into smaller satellite airports where the fees may be lower or structured differently. Since some of these airports could potentially be private or private/public they have the ability to charge what they chose. Some will even have no fee if you buy a pre prescribed amount of fuel.

For other points of reference you can check out the

New York Landing Fees
Miami Landing Fees


What is this object in the cockpit of an ultralight? This is a tool (probably) in on an ultralight airplane. Initially I guessed that it is a tilting meter (to level between right and left), but seems it is not as it just a vertical tube filled up with something like liquid.

So, what is that and how does it work?

It's an airspeed indicator for ultralights.  The pitot inlet is at the bottom and the pitot air pushes a little red plastic disc up and down on a central rod, with a calibrated clearance between the edge of the disc and the walls of the tube.  They are very sensitive and are good down to 10 MPH or less.  You'll also see them on hang gliders.

See here:
https://www.aircraftspruce.com/catalog/inpages/hallwindmeter.php?clickkey=5468


How do one day simulator courses work? There are companies such as this that offer one day full simulator experiences where you take several attempts at landing a 747 or something similar. Some people report success after a couple of attempts.

In this question, asked recently here on ASE, it was generally agreed upon that no-one could land such an aircraft without many hundreds of hours of training.

So how do these day-courses/experiences work? Do they somehow 'dumb down' the simulator, automating most or all of the process'?

Side-note: I am asking, because I am interested in learning the basics of flying, but could only afford simulator training, the actual school in my real country offers block bookings for a reasonable price.

I’ve done one of these before (not with that company). It literally used the Microsoft FSX game engine but with an A320 cockpit. You have an instructor guiding you and I got to fly around my local airport, land at Kai Tak at night (nailed my first attempt), and because I was in real-world training at the time I shot an ILS approach in zero visibility (definitely did not nail that one).

These simulators are usually aimed at people with little to no piloting experience who want some fun (and they are, I enjoyed mine and my dad has done it 3 or 4 times). If you’ve used FSX you know that you can adjust the realism settings to make it easier to fly so, with help from the instructor a novice can probably land it. At the very least you will learn about basic procedures, flaps etc, and what the cockpit looks like.

It will definitely not make you ready to land the real thing though. These things are designed for fun, not realism.


What is the proper procedure for a piston engine fire on the ground (e.g. during engine starting)? I am wondering what is the correct sequence of action if there is a fire e.g. during engine starting. Of course I know that there are emergency procedures in each AFM and every single plane is different etc. but I am thinking about "general" set of actions.
Let's say that an aircraft has a fuel shut off valve and mixture control - like a little Cessna. What should we do if an engine catches fire during start-up - shut off the fuel valve and mixture to idle cutoff, or remain mixture and cut off fuel valve (and still try to start the engine)?
Please help me out what are the correct steps.

As you said, the "proper" procedure is whatever is in the aircraft's operating handbook. Having said that, there is a general pattern, at least based on a few POHs I have to hand. Note that they all list the procedure as "engine fire on startup"; there's no general "engine fire on the ground" procedure.
The 'generic' steps are:

Continue cranking as usual to pull the fire and fuel into the engine
If the engine starts: let it run for a few minutes then shut down as normal and inspect the aircraft for damage
If the engine doesn't start: open the throttle, cut off the fuel (mixture, fuel pump, and/or fuel cutoff as applicable), and evacuate the aircraft

Here's an example from a Cessna 172S POH (Lycoming IO-360-L2A engine); bold items are memory items:

Ignition Switch -- START, Continue Cranking to get a start which would suck the flames and accumulated fuel into the engine.

If engine starts:

Power -- 1800 RPM for a few minutes.
Engine -- SHUTDOWN and inspect for damage.

If engine fails to start:

Throttle -- FULL OPEN.
Mixture -- IDLE CUT OFF.
Cranking -- CONTINUE.
Fuel Shutoff Valve -- OFF (Pull Full Out).
Auxiliary Fuel Pump Switch -- OFF.
Fire Extinguisher -- ACTIVATE.
Engine -- SECURE.   a. Master Switch -- OFF.   b. Ignition Switch -- OFF.
Parking Brake -- RELEASE.
Airplane -- EVACUATE.
Fire -- EXTINGUISH using fire extinguisher, wool blanket, or dirt.
Fire Damage -- INSPECT, repair damage or replace damaged components or wiring before conducting another flight.


Why would my transponder interfere with my ADF? The ADF in my plane works very well until I switch the transponder to ALT. At that moment, the ADF needle is stuck in a random position and will not show the direction to the selected NDB anymore (the transponder works flawlessly).

Where is the interference coming from? Is it because the two boxes sit on top of each other on the dashboard? Or is it due to a bad placement of their respective antennas on the fuselage? Would seem strange to me, as their respective frequencies are far apart (kHz vs. MHz).

Any norm / guidance on how to install these two systems so that they do not interfere with each other?

ADFs and transponders are often right next to each other in the dashboard, it's not the placement that's the issue. The two systems work on different sets of frequencies, so antenna placement shouldn't be an issue. If the ADF is being getting interference from the transponder in ALT mode the most likely issue is that one or the other is malfunctioning, or there is a short in the wiring between the two systems.


What is the influence of yaw on P-factor? From William Kershner's “The Advanced Pilot’s Flight Manual”- page 2-17, P-Factor:

If the airplane is yawed, the P-factor effect is encountered. A left
yaw would mean a slight nose down tendency and a right yaw a slight
nose up tendency (you can reason this out).

Unfortunately, I couldn’t reason this out :(
Anyone care to explain?
Thanks!

As a starting point, you need to thoroughly understand why P-factor tends to make a left yaw torque (in the case of a clockwise-rotating prop, as viewed from behind) when an aircraft flies in a nose-high "angle-of-attack".  Note that by the aircraft's "angle-of-attack", we mean the aircraft's pitch "attitude" in relation to the flight path, not in relation to the ground.  Do you see how this increases the lift or thrust generated by the down-going half of the prop disk, and decreases the lift or thrust generated by the up-going half of the prop disk?  Thus creating extra thrust from the right side of the prop disk and making the aircraft tend to yaw to the left, in the case of a clockwise-rotating prop (as viewed from behind)?  If not, you might benefit from reading the section entitled "P-factor" from John Denker's "See How It Flies" on-line tutorial website.
Once you've digested that, you'll observe that for a mental "shortcut", we can model the effect of P-factor as follows:  think of the spinning prop as a solid disk.  Pick the point on the disk that is "tilted backwards" in relation to the actual flight path.  This would be the top of the disk in the case of an aircraft flying at a high angle-of-attack.  Now rotate your chosen point 90 degrees in the direction that the prop is rotating-- which for this explanation we'll assume to be clockwise, as viewed from behind.  So now you are looking at a point on the right edge of the prop disk, as viewed from behind.  P-factor can be modeled as an extra forward "thrust" or "push" applied to the prop disk at this point.  This will tend to make the aircraft yaw to the left.  Note that this has nothing to do with gyroscopic precession-- it's a purely aerodynamic effect.  This mental shortcut isn't meant to explain why P-factor occurs, just to quickly determine in which direction it acts.
Once you are comfortable with this "shortcut" for figuring out which part of the prop disk will be "loaded up" by the P-factor effect, consider that sideslip tilts the prop disk in relation to the direction of the flight path, just as flying at a high angle-of-attack does.  In a sideslip with the nose pointing to the left of the flight path (ball to the right, yaw string to the left), which part of the prop disk is "tilted backwards" in relation to the direction of the flight path?  The left-hand side.  So if the prop is rotating clockwise as viewed from behind, the P-factor effect can be modeled as an extra forward "push" on the top of the prop disk, and a decreased forward "push" on the bottom of the prop disk.  This will create a nose-down pitch torque.
Kershner could have been more clear in his language here, particularly in relation to his use of the word "yaw".  It's critical to note that we are actually talking about the sideslip angle here, not an actual yaw rotation rate.1  An actual non-zero yaw rotation rate creates a pitch torque in the opposite direction, through gyroscopic precession -- yawing to the left will pitch the nose up.  Just as flying at a high angle-of-attack creates a left yaw torque through P-factor, while pitching the nose down (as when a tail-wheel aircraft lifts the tail during the take-off roll2) creates a left yaw torque through gyroscopic precession. One effect is related to the aircraft's attitude in the relation to the direction of the flight path, and the other effect is related to the direction and rate of change of the aircraft's attitude in space.
Footnotes--

Clearly, the word "yaw" is often used in several different ways in aviation.  Most correctly, it refers to an actual rotation about the aircraft's vertical axis, but it's not uncommon to use it to mean essentially the aircraft's "yaw attitude" in relation to the "relative wind" or actual direction of the flight path though the surrounding airmass-- which is exactly the same thing as the "sideslip angle".  (The term "yaw string" is a classic example of this usage-- and the "yaw string" is sometimes also called the "slip string".)  When Kershner says "if the aircraft is yawed", you should read "if the aircraft is yawed into a sideslip or skid and then held there", or "if the aircraft is allowed to fly in slipping or skidding attitude".

Harvey S Plourde's book "The Compleat Taildragger Pilot" contains a great graph showing the individual and combined effects of all the different factors that contribute a left-yawing tendency during the takeoff roll in a tailwheel aircraft, from the start of the takeoff roll all the way to the moment of liftoff.  Different factors are dominating at different points in the takeoff roll.


What does it mean to have a SIC limitation on your medical class 1 Is there anyone who knows what a SIC limitation on your medical would mean? I found out on the EASA documents that it stands for "Specific medical examination pilot". But what exactly would a SIC change for someone (if anything).

This EASA document Easy Access Rules for Medical Requirements explains what the Specific Medical Examination (SIC - Medical Certificate Limitation Code) is and how it applies to medical qualifications for pilots/crewmembers). An explanation of what it means is found in the EASA document referenced above on page 52, item 8:
(8) SIC   Specific regular medical examination(s)   contact the medical assessor of the licensing authority.
This limitation requires the AeMC, or AME to contact the medical assessor of the licensing authority  before  embarking  upon  a  revalidation  or  renewal  aero-medical  assessment. The  limitation  is  likely  to  concern  a  medical  history  or  additional  examination(s)  which the AeMC or AME should be aware of prior to undertaking the assessment.
Apparently it means that when you go to revalidate or renew your medical certificate the AME will have to contact the medical assessor of the licensing authority and you will have undergo some additional testing or the AME will be made aware of some specific medical history or issue that needs to be considered prior to renewal or recertification of your medical certificate. Perhaps similar to having a non-obstructing kidney stone reevaluated or a blood sugar evaluation. This would depend on the medical reason the SIC notation (limitation) was placed on your medical certificate.
The EASA linked document (above) provides additional information relating to the SIC Limitation Code on a Medical Certificate.


What is the maximum crosswind component for large airliners? For smaller aircraft like Cessnas, the demonstrated crosswind component is something like 12 knots but they can land up to 20 to 25 knots. For bigger jets, such as the Boeing 737 and 777, what is the maximum crosswind component?

From this site:

  During the type certification process, the FAA requires the manufacturer to demonstrate that its airplane can be controlled in 90° crosswinds up to 20% of VS0.


How can we recover from a tailplane stall? I was studying for icing and a tailplane stall. I have looked up some internet pages and instrument flying handbook, and found the procedure below.

raise flaps to the previous setting. (To reduce down wash from the main wing so that reducing negative angle of attack of the tail and break the stall)
apply nose up elevator pressure (I don't get it. The nose up pressure will make the elevator to go up and wouldn't this increase the negative angle of attack and worsen the stall?)
do not increase airspeed unless it is necessary to avoid a wing stall. (Why shouldn't we increase airspeed?)

So now I'm trying to understand the reason why should a pilot do such actions. Can you help me out?

Lets start with the very basic concepts....

In most aircraft, the Centre of Gravity (cg) is somewhat forward of the wing or mainplane Centre of Pressure. The exact distance between the cg and the Centre of pressure will depend on aircraft loading, configuration, thrust setting and drag. However, cg forward of the Centre of Pressure produces a nose-down pitching moment. The horizontal stabilizer, or tailplane, then provides a downward force to overcome this normal, nose-down, pitching moment.
The tailplane behaves as an ‘upside down’ wing and operates with negative Angle of Attack (AOA) as shown in Figure 1

Positive and Negative Angle of Attack

Figure 1 - Positive and Negative Angle of Attack

If the horizontal stabiliser becomes contaminated with ice, airflow separation from the surface can prevent it from providing sufficient downward force or negative lift to balance the aircraft and a nose-down pitch upset can occur.

When compared to an aircraft's mainplane, the horizontal stabiliser normally has a thinner aerofoil with a sharper leading edge. Differences in the ice collection efficiency or catch rate between the two surfaces means ice accumulates faster on the horizontal stabiliser and may form before any ice is present on the aircraft's mainplane.

Tailplane stall can occur at relatively high speeds, well above the normal 1G stall speed of the mainplane. Typically, tailplane stall induced by icing is most likely to occur near the flap limit speed when the flaps are extended to the landing position, especially when extension is combined with a nose down pitching manoeuvre, airspeed change, power change or flight through turbulence. Aircraft stall warning systems provide warnings based on an uncontaminated mainplane stall so during a tailplane stall induced upset there will be NO artificial stall warning indications, such as a stick shaker, warning horn or the mainplane or flap buffeting normally associated with a mainplane stall.

Tailplane Stall Aerodynamics

The horizontal stabiliser, or tailplane, of an aircraft is an aerofoil that provides a downward force to overcome the aircraft's normal nose-down pitching moment. The further forward the Centre of Gravity is from the Center of Pressure, the greater the nose down moment and, thus, the greater the amount of down-force that must be generated by the tailplane. This, in turn, requires a greater negative tailplane angle of attack (AOA). angle of attack (AOA).
[As shown in Figure 1, The tailplane is effectively an upside down aerofoil so an increase in negative tailplane AOA occurs with UP elevator movement or when the aircraft is pitching nose down.]
Accumulation of ice on the tailplane will result in disruption of the normal airflow around that surface and will reduce the critical (or stalling) negative AOA of the horizontal stabiliser.
Ice can accumulate on the tailplane before it begins to accumulate on the mainplane or other parts of the aircraft.
Flaps extension usually moves the mainplane Centre of Pressure aft, lengthening the arm between the Centre of Pressure and the cg and increasing the mainplane nose down moment. More down force is required from the tailplane to counter this moment, necessitating a higher negative tailplane AOA.
Flap extension, especially near the maximum extension speed, increases the negative tailplane AOA due to the increase in downwash, as shown in Figure 2
Increasing the power setting on a propeller driven aircraft may, depending on aircraft configuration and flap settings, increase the downwash and negative tailplane AOA.
When the critical negative AOA of the horizontal stabiliser is exceeded causing it to stall.
Tailplane stall drastically reduces the downward force it produces, creating a rapid aircraft nose-down pitching moment.

Effect of mainplane flap on downwash

Figure 2 - Effect of mainplane flap on downwash

On aircraft with reversible (unpowered) elevator, tailplane airflow changes caused by ice accretion may lead to an aerodynamic overbalance driving the elevator trailing edge down and pitching the aircraft nose down. This can occur separately from or in combination with the nose down pitching moment caused by tailplane stall. The yoke may be snatched forward out of the pilot’s hands and the control force required for the pilot to return the elevator to neutral or to a nose-up deflection can be significant and potentially greater than the pilot can exert.

now match with your recovery actions

You have no doubt with your 1st point.
The second point: You have to resist the nose down elevator movement. Once the tailplane is already stalled then you have to assume the elevator has already gone in down position to make your ac nose down. So you have to apply nose up elevator pressure.
You should not increase the airspeed cause it might make the situation worse. Cause in dive with increased airspeed is always difficult to maintain the aircraft control. And you might end up with overstressing the elevator which is not good at all in such condition.


Why is vertical take-off restricted to lighter weight aircraft? Vertical take off is a big advantage, but why it is only limited to low weight?

For example, fixed wing like An225 can lift more than hundred tonnes of payload, while the biggest helicopter is 25 tonnes. Why there is no effort to build a helicopter can lift 50 - 100 tonnes. What limits them? Economic or technical problem? I guess it is a technical problem because even the heaviest helicopter is just an experiment, but what is it?

Essentially it comes down to supersonic rotor tips

With a plane, in theory you can make it pretty much as big as you like - as long as you have strong/light enough materials, and can keep adding power, an aeroplane design scales pretty well. Bigger wing = more lift. As long as you can make the wing bigger without it breaking, and as long as you can add enough power to overcome the extra drag, there aren't many fixed limits

With a helicopter, we're limited by the rotor tips: once they go supersonic, they cause a lot of problems.

So how does a helicopter produce lift? By using rotors to push air down within a kind of circle. To add more lift we can do (essentially) three things.

Make the rotor spin faster, so it pushes more air down in the circle it already uses. Obviously this makes the tips spin faster, so we can only do it to a certain extent. We've already hit this limit.
Make the rotor blades longer, so they push a bigger circle of air. Again, though, due to the nature of a circular blade, the outside of a blade is moving faster than the inside. For a certain rotor speed, there's a fixed limit to how large the blades can be. Again, we've already hit this limit
Add more blades, so there are more blades producing lift. This works to an extent (hence why smaller helicopters may have two rotor blades, but larger ones have 4, 5 or more. Again, though, this doesn't scale indefinitely - each rotor interferes with the next, you can't just keep adding more

There are other slight modifications we can make, such as the airfoil of the rotor, but they don't add significant gains

So, basically, we've hit the limit of what we can lift with a single rotor, The only real way to add more lift now is to add more rotors: doing that would be far less efficient than simply using an aeroplane.

Which brings me to the final point - helicopters are very inefficient and pretty slow... We simply don't need, except in a few niche circumstances, to carry more weight with them.


Is there any equation on propeller thrust that takes into account the number of blades I had a look at both

What is the equation for calculating static thrust?

and

Is there any equation to bind velocity, thrust and power?

However, it does not mention how much would the thrust be affected by the amount of blades. e.g if it was a 20 blade propeller with a given RPM, how much would it affect the amount of thrust

Could you please kindly help me with this? Thank you

The most simple propeller thrust equations replace the propeller with an abstract disk in which the flow is accelerated. How this disk is composed in detail does not matter. However, more elaborate codes which also model the helical wake of each blade will use blade count specific algorithms.

So the answer is yes, there are algorithms which account for the number of blades, but they are more complex than a single equation.

This answer shows how the number of blades of the propeller for the Supermarine Spitfire grew with engine performance, and this answer sheds light on the number of blades of helicopter rotors.


If commercial airliner cabin is depressurized, are pilots protected against it in any ways? Basically, if the cabin in a large air liner is depressurized, are pilots protected in any way, specifically:

Is the cockpit separately pressurized from the rest of the cabin?
Can they keep consciousness if sudden depressurization happens?

No, the cockpit is not separately pressurized. That would be impractical and not particularly useful.

However, pilots do have oxygen masks, just like the passengers. Unlike the passenger masks, these masks are generally designed to be donned extremely quickly, with one hand (they tend to have automatic straps that clamp on without needing to be manually adjusted). The masks also have a separate oxygen supply from the passenger masks, and have much more oxygen available for each mask, and have other nice features. Furthermore, when one pilot is off the flight deck, the other wears an oxygen mask that's either releasing oxygen or set to automatically do that if the plane depressurizes.

If sudden depressurization happens, there are still a few seconds of useful consciousness for most people. That time is enough for airline pilots to put on their masks. Once the crew has on oxygen masks, they can control the depressurized plane just fine (depending on how it depressurized, of course: if the tail broke off, there's not much that can really be done).


What is the difference between ILS and VOR/DME? I have wondered many times about the difference between VOR/DME and ILS and which one is better for carrying out approaches. Why do pilots use VOR/DME when the ILS is a better option because it is precise and VOR/DME is a non-precision approach?

Which one is better for carrying out approaches?
An ILS approach is more precise for two reasons:

The ILS localizer is more sensitive than a VOR radial, therefore providing more accurate lateral guidance.
The ILS has a glide slope providing vertical guidance. A VOR approach does not have any vertical guidance (although with a VOR/DME one can at least determine the exact point at which to start a CDFA (continuous descent final approach) and regularly crosscheck the altitude with the DME).

Why do pilots use VOR/DME when the ILS is a better option?
Pilots fly a VOR/DME approach when they are cleared for the VOR/DME approach by ATC. Why would ATC provide a VOR/DME approach clearance when the runway also has ILS? This is usually due to ongoing maintenance of one of the ILS antennas. When an antenna is not available, you obviously cannot fly the ILS approach (although it may be possible to fly a localizer approach, if only the glideslope antenna is unavailable).
A pilot can also request the VOR/DME approach for various reasons, e.g.:

It could also be that the aircraft is not equipped with an ILS receiver antenna and is therefore unable to fly an ILS approach, but at least for an airliner that would be quite unusual.

For training the specific approach type or to maintain proficiency (thank to StephenS for pointing this out).

Sometimes flying the VOR approach might actually be more convenient if the VOR approach has different approach transitions available compared to the ILS. In Jersey (EGJJ) for example, the VOR is not co-located with the aerodrome and therefore allows an IAF further to the east compared to the ILS approach, which begins at the NDB (which is co-located):


Does a Boeing 737 NG have Air Data Modules for the standby Pitot probe and static pressure port? In other words, how does the ISFD calculate the air data and IR parameters? Or is the ISFD an ADM by itself?

Standby instruments provide a critical backup function and are totally independent from the primary air data system. The dedicated standby probes are connected directly to the standby display unit which is capable of converting the pressure inputs into airspeed and altitude. They only require a 28V DC input from the EMER/BATT power bus to operate.

Here's the description diagram from the Boeing maintenance manual:


How was this old beacon used? I saw this beacon at an old airport; how and in what situations was it used?

It's the airfield identification beacon.

  An aerodrome beacon or rotating beacon is a beacon installed at an
  airport or aerodrome to indicate its location to aircraft pilots at
  night.

  An aerodrome beacon is mounted on top of a towering structure, often a
  control tower, above other buildings of the airport. It produces
  flashes not unlike that of a lighthouse.

  Airport and heliport beacons are designed in such a way to make them
  most effective from one to ten degrees above the horizon; however,
  they can be seen well above and below this peak spread. The beacon may
  be an omnidirectional flashing xenon strobe, or it may be an
  aerobeacon rotating at a constant speed which produces the visual
  effect of flashes at regular intervals. Flashes may be of just a
  single color, or of two alternating colors.


Is Qantas holder of the world’s longest commercial non-stop flight? Is it Singapore Airlines or Qantas that is currently holding the record for the world longest non-stop commercial flight?

I assume you are referring to the recent Qantas flight from New York to Sydney:

Australian carrier Qantas has completed a test of the longest non-stop commercial passenger flight as part of research on how the journey could affect pilots, crew and passengers.
The Boeing 787-9 with 49 people on board took 19 hours and 16 minutes to fly from New York to Sydney, a 16,200-km (10,066-mile) route.

(BBC)
This flight was primarily a test flight to study impacts of ultra-long haul flights on passengers:

Qantas has announced three ultra long-haul research flights to gather new data about inflight passenger and crew health and wellbeing.

(Qantas News Room)
Because it was just a test flight, this does not count as regular service, which would not make sense with the current aircraft anyway:

No commercial aircraft yet has the range to fly such an ultra-long haul route with a full passenger and cargo load, Reuters news agency reports.
To give the plane sufficient fuel range to avoid re-fuelling, the Qantas flight took off with maximum fuel, restricted baggage load and no cargo.

(BBC)

The current record for longest regularly scheduled flight is indeed Singapore Airlines flight SQ21 between Newark and Singapore according to the Wikipedia List of longest non-stop flights (retrieved 2 Nov 2019, based on great circle distance, thanks to Michael Seifert for pointing this out).

The record for the longest ever flight with a commercial airliner however is still held by a Boeing 777-200LR:

In a trip that included two sunrises, a new long-range Boeing 777 flew more than halfway around the world nonstop on Thursday, breaking an aviation distance record set by a B-52 bomber 43 years ago.

New York Times
This flight was primarily a publicity stunt resulting in a Guinness World Record. It was never meant to be used commercially since they intentionally flew a longer route.


What is the function of this fixed protrusion on the tail? (wikimedia.org)

Above you can see a small fixed (?) part on the Embraer 190, just above the KLM logo. It is on both sides of the tail. What is the function of this part?

That is almost certainly a navigation antenna.

From the E190 AOM (Airplane Operations Manual):

You can see the VOR2/LOC2 antenna rather more clearly in this photo:

(The VOR1/LOC1 and VOR3 antennae are embedded within the tailfin.)

Similar nav antennae are used on many smaller aircraft such as (more modern) light aircraft, utility aircraft, business jets and some regional jets.


Checklists before take off - how often must they be performed? Friday I was on a plane from MXP to Prague, should have been a 737-400, and the take off was preceded by something I'm not sure what it was: probably a pre-flight checklist, but it's the first time I see something like this:

The plane got pushed back by a tractor from ramps to apron - at least, I think it was the apron- and turned (still by the tractor) in the right direction for the taxiway
Engines thrust was increased and decreased a few times, keeping them at "high" levels for a bit
Control surfaces were checked as usual

I'm used to pilots checking control's surfaces either while still at ramps or on the taxiway while waiting for their turn to take off, or just at the beginning of the runway, but never seen anything different and never seen "testing" the engines that way, and it got me wondered about check list frequencies.

Was that routine some kind of checklist? And if so, is there a specific regulation about how often it must be performed? (and, by the way...I know that it's possibile to load fuel even with passenger on board, but...testing engines with plane full loaded? Isn't it a bit too dangerous?)

For an airline crew, the Before Takeoff Checklist is performed once before every takeoff.  There is normally no "run up" associated with such a checklist for jet aircraft.

Depending on what else is going on, there are reasons that engine power might be advanced then reduced, and it would be speculation as to what the reason for that was on your particular flight.


Why does the Pilatus PC-24 have such a large "Airplane Support"? The PC-24 has, under the fuselage, a kind of huge support to hold the wings.

If we compare with the Citation CJ4 or the Phenom 300, this difference is quite significant. Why??

To add to the other answer...

The Pilatus PC-24 is billed as a business jet that can operate out of rough airfields. Comparing the pictures of the PC-24 to the Phenom 300 or CJ4, you can see that there is quite a bit of extra ground clearance. You can also see that the rear landing gear on the PC-24 are much more robust (dual wheels, longer travel length) than the other two aircraft.

If you look at this picture:

Source: Wikipedia

You can see that the wheels also retract into that area. They probably wanted to keep the wing low to take advantage of ground-effect to improve short-field performance. So having a higher-up fuselage allowed them to put the engines up higher and avoid FOD damage, while the low wing allowed them an impressive short field take-off performance. The PC-24 can operate out of a field just 2,800 feet long. The Phenom 300 takes 3,200 feet and the CJ4 takes about 3,500.

So the "bump" is there to be able to handle additional loads, elevate the fuselage, and store the gear. I can't find any diagrams of the fuel system, but it's possible that it also houses fuel tanks or baggage.


How are modern jets modified to takeoff/land on a dirt runway? I've been reading a lot about the Soviet and Russian military aircraft, and it seems a lot of them are built to work on dirt runways, or modified to do so.

How is this accomplished? Is it a simple thing to modify aircraft in this way? Is it just a matter of strengthening the undercarriage and upgrading the tires for more stress? Or is something harder involved, like maybe strengthening the fuselage frame?

NOTE: let's exclude worries about foreign objects going into the engines. Right now I'm only interested in the difference between paved and dirt runways as far as landing gear and strength are concerned.

Just to roll around on "unimproved" airfields (grass/dirt/gravel strips), the biggest thing planes need is simply a decent set of tires:

This MiG-29UN trainer shows off the fairly beefy main tires put on these planes specifically to allow them to more easily roll over minor imperfections in the runway/taxiway surface, including dirt/gravel/grass strips (though here it's landing on a traditional asphalt/concrete surface). Compare these to the relatively small gear wheels and low-aspect rubber on the similarly-sized F-16:

(source: f-16.net)

Now, your question oversimplifies things, because "foreign object debris" or FOD is in fact a primary danger of unpaved airstrips for jets, and this danger has to be accounted for in the design. Here's the main reason the MiG-29 can take off from dirt:

MiG-29s and similarly-minded Su-27s, and their variants, have special doors to close off the lower intakes normally used in flight, instead drawing in air through the gill-like ports over the top of the wing strakes. This prevents the engine from ingesting dust, rocks, birds, rodents, etc on takeoff and landing.

This engine protection system, while effective, adds mechanical complexity and weight which U.S. designers and military brass have generally thought unnecessary given that requirements rarely include the ability to operate from unimproved strips. Most U.S. fighters in the jet age, therefore, have had to operate from airbases with some form of paved runway surface (and the U.S. military actually has higher standards for runway surface quality than most international airports). The U.S. arsenal does, however, have several aircraft that are specifically designed to operate from rudimentary airstrips at forward bases. These designs avoid FOD damage primarily by keeping the engines up as high as the design will allow. For instance, the A-10's two engines are on pods angled up on the fuselage between the wings and tail for a variety of reasons including FOD avoidance:

Most of the other designs in the Western arsenal that can do this are high-wing designs with wing-mounted engines, which keep them out of the dust produced by takeoff and landing in a similar fashion. Here are a C-130 and C-17 landing at an Afghanistan forward base:

The Harrier is a notable exception to this general strategy by Western designers of just keeping the engines out of any debris cloud. While it's probably not done routinely, a Harrier can set down just about anywhere, and as this picture shows, it ingests no small amount of dust in the process:


Why do winglets reduce maneuverability (of fighter jets)? In this answer Ethan makes the following statement concerning winglets on fighter jets:

  [Winglets] reduce maneuverability which is why you don't see a winglet on a fighter jet

I could image that adding more weight at the end of the wings increases inertia, reducing maneuverability, but I'm not sure if this is the only reason.

Perhaps there is some aerodynamic phenomenon at play as well?

Your observation about roll inertia is correct: Winglets add proportionally more roll inertia for their small increase in L/D, and this increase exists only for the higher range of lift coefficients. At low lift coefficients (think cruise), when the induced drag is low, they add more friction drag and reduce the L/D overall.

There are three aspects to maneuverability:

How quickly can you accelerate into a roll? Here the added inertia of winglets reduces roll acceleration
How high is the maximum sustained turn rate? This is determined by the maximum lift at zero sink rate, and here winglets are helping. Especially when mounted to low aspect ratio wings.
How high is the maximum turn rate? Now only lift counts, and the increased drag is compensated by an increased sink rate. Again, winglets help a little, but less than with the sustained turn rate.

Now look at the time any fighter will spend around 1g (hint: Something close to 100%) and how much is spent at high lift coefficients, like when turning tightly in air combat. Winglets would help in the turn (and I think Ethan's opinion is wrong), but be a source of drag for the rest of the mission. Adding winglets would require to increase the fuel volume to prevent a reduction in flight time and range.

Normally, winglets are only used on highly loaded, high-aspect ratio wings when their L/D at a rather high lift coefficient needs to be pushed up even more. Highly maneuverable configurations are less concerned with single-percentage increases in L/D for a small part of the flight, and in order to improve turn performance, increasing wing span is much more effective. But that increases roll inertia and roll damping, so fighters use low-aspect ratio wings and compensate their higher drag in a turn with more powerful engines. Note that the trend in fighter aspect ratios went down with the improving thrust-to-weight ratio of jet engines.

Now that is the reason why you don't see winglets on fighter jets: They would lower L/D for most of the flight. To perform the same mission, the fighter without winglets can be made smaller.

But let's make no mistake: Low aspect ratio configurations gain the most from winglets: They were essential on the Hermes re-entry vehicle project to give it enough L/D for a successful flare.


Where can I find the latest METAR and TAF for RPVK / Kalibo International Airport? What website holds the latest METAR and TAF for RPVK / Philippine weather?
In aviation weather the information does not exist at all times.

Could you suggest an other website that provides the required information.

Thanks for the help!

You can find the latest METAR for RPVK here: https://tgftp.nws.noaa.gov/data/observations/metar/stations/RPVK.TXT and TAF here: https://tgftp.nws.noaa.gov/data/forecasts/taf/stations/RPVK.TXT

Remember to look at the publication date/time, since it may not be very recent.


Burdens of working as an airline pilot Every job in every industry has some "pressure", "stress", or "burdens" for that job. Being a PPL feels free, but I'm paying for flying. Working as a pilot, I get paid for flying. BUT, before I decide I want to join this industry, what are the burdens that an airline pilot has to face routinely? Does it vary if you're working for a small regional airline vs major international airlines?

This is a very broad topic and is heavily opinion based.

Vast majority of commercial pilots do love flying and that's the reason they go through the abuse by airlines. All GA pilots also love flying but either cannot afford the abuse or don't have time for it, so they just pay to satisfy this hobby.

So to answer your question, some of the burdens are:

High costs of training
Waiting a long time (2 years or more on occasions) before getting hired by an airline
Very low salaries in the beginning (several years)
Losing seniority (very often) when you go to another carrier
Staying away from home a lot
Very unstable industry
Many pilots eventually get bored and frustrated (regardless of initial enthusiasm)

Having said that, there are many many great benefits, too. The bottom line is that people only get into this career if they love it deeply.

The question you have to ask yourself is: Am I willing to undergo this trouble for my passion?

P.S.: The above holds true for the airlines and pilots in the US.


Should depressurization be considered in the event of an inflight cabin fire? Uncontrolled cabin fires only need a few minutes to spread throughout the cabin of an aircraft, killing everyone onboard and destroying the airframe.

Now, we all know that depressurization and fire do not combine; the lack of oxygen will eliminate one of the elements necessary to keep the fire alive. So if an aircraft had a way to depressurize the cabin and eliminate oxygen in the event of a fire, the fire would be extinguished, saving lives. Of course this applies to flights above 14,000 ft. I know that depressurization is dangerous but there is a better chance of surviving a depressurization than surviving flames.

Does a mechanism exist to depressurize the aircraft in case of uncontrolled fire in the cabin? If so, under what circumstances would it be used?

Some aircraft do have a manual decompression button which can be used by the pilot in a situation like this.  Keep in mind however that it will only help until the pilot descends (which you will want to do asap in order to land) and the air isn't as thin.

It is very important for the crew to get on the ground as rapidly as possible, and simultaneously attempt to put out the fire in order to minimize the amount of damage that can be done.  The single biggest factor in an aircraft fire is how much time elapses before they land and can evacuate.

Also, if the cabin depressurizes, typically the oxygen masks deploy automatically which when combined with a fire can have even more disastourous results.


Is it true that the pilot and co-pilot are required to eat different meals? I was watching a documentary about a Lufthansa A380, and they said that the pilot and co-pilot are required to eat different meals; why is that?

Is it a country-specific requirement, or airline-specific?

It is a company specific rule found in the Flight Operations Manual so is airline specific.  There is usually a statement that goes along with it which also says to avoid foods with a higher than typical rate of food poisoning, such as raw fish before and during the Flight.  In the US, the FOM is submitted to, and accepted by the FAA so the procedures become required.


How do airlines and airport exchange data? I was just waiting for a flight, when the airline’s app sent me a push notification; my gate was changed to 12 in the same moment that the airport notified passengers about that the gate was changed to 15. So I started wondering how airlines and airports exchange this information?

Is it a central IT system? Run e.g. by IATA? Or do the alliances (star alliance etc) have central systems for that and they connect to airports? Or are there individual contracts between airlines and airports they go to? Does everyone use the same protocol / standard? Or is it more chaotically?

Additionally, flightradar24 recently started including gate & baggage belt information in their service – do they get it (likely) from the airports? Or do the airlines provide that data? Or how does that work?

Introduction : determining which gate is assigned

I assume we are talking about IFR flights with the purpose of passenger travel.

An aircraft, in order to be assigned to a gate, has to be planned and to arrive at an airport.
So let's look at the breakdown of arrival of an aircraft.

First, the airline (operator) has filled a flight plan before the flight occurred and submitted it to the legal authority managing flights in the airspace (Aeronautical Navigation Services -ANS- typically) in order to have clearance to enter the airspace, getting navigation informations and accessing the airport (more on this matter). At this moment, the airport gets informations about the next aircrafts (operator, type of aircraft, passenger, cargo etc.), which will be managed upon arrival.

Secondly, after being handled by Area Control Center (ACC) ATCO (en route flight), the aircraft is routed towards the airport by Approach controllers (APP) which manage the airplane when it flies from en route (high altitude) to the airport (ground); when the aircraft is lined up with the runway a few miles from the airport it is transfered to the tower which manages the operations from this moment (given no go around has been initiated due to runway incursion, landing mishaps etc.) and will most importantly manage ground operations (taxiing, handling take-off and landing sequences etc.).

Once the aircraft has landed and starts taxiing, the tower (TWR) will give directions to the gate it would be assigned, depending on various factors:

Negotiations with the operator : location of the aircraft at the airport has a price, aprons are more costly than parking the aircraft further from the terminal and being handled by a bus for example.
Destination and origin of the aircraft : international and regional flight can be handled in different terminals: e.g. in Europe, Schengen area flights are usually handled separately from outside the Schengen area.
Size of the aircraft : for example A380 are notable for being difficult to maneuver around airports and need specific aprons and some airport have only a few gate that can be assigned to such specific aircraft.
Available spots : the airports are incredibly busy around noon every day (look at the traffic at a major airport like Heathrow around that time), which means that some spots might be taken and the airport has to accommodate the aircraft at an available gate.

Information exchange

The tower exchange directly with the aircraft (crew or the aircraft itself) via radio or data-link, they give directions and update the gate according to the current available spots. It seems (so I might need more information with somebody more familiar with the matter) that data-link is use in most cases to share informations regarding flight details between ground and aircraft.

All in all, the airport tower decide and manages the gate. The information are stored in an operational database (at the tower or the ANS provider) and are provided to aircrafts, operators and passenger (terminals and online).

Generally speaking, the data is provided to operators via the database and a technical overlay, this can vary depending on the regions. In Europe, operators  rely on Eurocontrol Network Manager Operations Centre to exchange informations regarding flight plans, updates of flight plans and different informations regarding operations. I don't have information regarding other regions like North America.

Airport-Collaborative Decision Making

A big topic at the moment for the European airports is the principle of Airport Collaborative Decision Making (ACDM for short) which should improve the quality and reliability of these informations, by sharing information directly from the airport and the NMOC of Eurocontrol.

Though this topic is to large to cover here, it would improve such information being shared between operators, airports, aircrafts etc. and normalise the way information is shared.

Flightradar24

As for Flightradar as I pointed out in the comments, they have an explanation of how they work with data.

A final word, it seems that airport API are usually not public, and it can be expected that for examples airlines do not have other's flight information (and gate per se).


Why can such a small difference in thrust make such a big difference in maximum speed? I was recently comparing two aircraft, and, although I feel stupid asking this question, I wondered why one had a maximum speed of M2.2 compared to M0.94, when both have similar weight, both are supersonic capable and both have similar thrust.
Compare for example the Hawker Hunter F.6 which has:

Empty weight 6,406kg
Max speed M0.94 (>M1.0 In a dive)
Engine thrust 10,145lbf
Climbrate 17,200ft/min

And the Mirage F.1:

Empty weight 7,050kg
Max speed M2.2
Engine thrust 13,700lbf (WET)
Climbrate 16,400ft/min

As you can see, both have similar rates of climb, similar empty weights, and both are aerodynamically supersonic capable. Only major difference being the the F.1 has ~35% more thrust- yet, with this extra thrust and weight, it is able to go over twice as fast? How does this work?
As I write this the only thing I can think is that wave drag plays a part, and the afterburner is required to give it that extra boost to break through the transonic barrier?
If the above is the case, then does this mean that all aircraft that can supercruise require the use of afterburner to get there, but can then hold it in mil power? And, if so, could this mean theoretically you could use a rocket booster of some form to push the Hunter F.6 through the transonic region and hold a supersonic speed, or, is there a minimum thrust to weight ratio in mil power required to achieve supercruise, or do more special aerodynamics need to be involved to keep wave drag down to make it possible?

and both are aerodynamically supersonic capable

No, not really.

The blunt nose and rather thick wing with not all that much sweep of the Hawker Hunter are not suited for supersonic flight.

The engine inlets of the Hunter lack the (movable) shock cones like the Mirage, which are needed for flight at higher Mach numbers (either a movable shock cone or a variable inlet vane are needed above around M1.6), and the shape is generally not suited for supersonic flight. Supersonic inlet needs to create an orderly pattern of shock waves inside to maintain smooth air flow and the triangular shape does not look like it would do that.

Also the Hunter engine probably has lower exhaust velocity, which makes it more efficient, but limits the maximum power at which it can still produce thrust.


Does Raymer's installed engine equation include the weight of the pylon? I am currently modelling an aero engine and require the weight breakdown of the individual components, I have the dry weight of the engine and need to verify the pylon and nacelle weight.

Raymer has presented an equation for the weight of the installed engine in his book
$$W_{InstalledEngine} = 2.575 *(W_{Engine})^{0.922}*N_{engine}$$

Does this include the pylon?

No, it doesn't include the pylon. If you think about it, the engine is installed on the pylon, which is part of the aircraft's fuselage or wing structure and not part of the engine.

You can see what I mean by watching this video of the replacement of an engine on an American Airlines 777.

Raymer's equation does include the nacelle and other auxiliary equipment installed on the engine.


Why are thermal switches connected in parallel to each others? Why are thermal switches fire detection system connected in parallel to each others?

Thermal switches, here, are indeed connected all in parallel (Fig. 17-1).

Wiring so allows to trigger the response if any of the switches closes in response to high temperature. This should allow to detect small initial fires that trigger only a single switch, or maybe a couple of them.

The switches are a simple computing machine that performs the logical disjunction.

In the same article you can see thermocouples connected sequentially (Fig 17-2). Thermocouples are not switches, they produce voltage in response to heating, and wiring two of them sequentially in the opposite directions produces the signal proportional to the temperature difference between them. The pair alerts when one thermocouple is heated significantly more than another.


Is a safety pilot required to share costs? Where I fly, it is customary for a pilot maintaining instrument currency to pay all the costs associated with the training flight while a safety pilot volunteers their time in exchange for the opportunity to log PIC. I personally don't disagree with this arrangement, since it encourages pilots to help each other out.

The FAA has repeatedly taken the position that building up flight time is considered compensatory in nature when the pilot does not pay the costs to operate the aircraft (see Harrington 1997, Lincoln 1990, and Howell 2013).

So, in this case, is the safety pilot being "compensated" by logging PIC? I vaguely remember seeing something saying that the FAA did NOT consider this compensation, but I can't remember where I saw that...

This actually came up in chat recently -- the answer (if only the two pilots are on board) is a qualified "No", not because the time isn't "compensation" but because the safety pilot is a required crewmember for simulated instrument flight.
Since both pilots are required crewmembers the safety pilot is not acting as a PIC of a flight carrying passengers as long as they are only acting as the Legal PIC while the other pilot is under the hood.
(Note however that while neither pilot is in simulated instrument conditions the safety pilot is not required crew, and therefore someone is PIC of a flight carrying at least one passenger - so log your time carefully and try to wrap your head around a "pro rata share" of that mess.)

This is further addressed (more directly) in the interpretation issued to Roberts, July 11, 2012.

Note that if we're talking about a flight with more than the two pilots on board (carrying someone who is NOT a required crewmember, like a friend in the back seat) then the whole thing goes out the window: No matter who is acting as the Legal PIC for the flight they're "PIC of a flight carrying passengers", and you're back to pro rata share territory.