How to figure unusable sectors if the VOR is not colocated at/near an airport? Stemming from Why am I not getting the "TO" VOR flag as I think I should?
If a VOR is not colocated at an airport (i.e. not in that airport's chart supplement page), how does one figure out the unusable sectors if they plan to use said VOR for off-airway (IFR or VFR) navigation?
I don't think it's been asked before.
Optional: Given that it's very common, why aren't those sectors just depicted on the charts?

The US Chart Supplement will give you the necessary information you seek. The supplement lists a plethora of information on airports, airfields, heliports, NavAids, Flight Service Stations, ATC facilities, other aviation facilities, preferred routes, TEC routes, etc. You will find the useful and usability information for all of the NavAids listed in the entry for that particular NavAid. Regardless of if the same information is listed in the entry for an associated airport.
The US Cart supplement is generally organized in the following hierarchy:

Geographical region
State
City center
Facility name

I would imagine this is done to put the facilities in the same general geographical vicinity of each other grouped together in the supplement for ease of use when navigating in that area.
You can get the facility name from the either the VFR or the IFR sectional charts. Reviewing the information for the NavAid would be a good idea if you intend to use it for navigation. Similar to reviewing the information for the airfields of intended use.
As to why the unusable sectors of a NavAid are not depicted on the sectional chart? I would imagine it is just a matter of ease of use. The sectional chart is already cluttered with invaluable, important, critical information. Putting more information would get it to the point of overload and unusability as a navigation resource. Keeping it as an overview works well. Hence, the Chart Supplement is necessary to provide targeted information for your particular flight.

The unusable “sectors” of the VOR are not based on track, bearing, course or heading. They are based on the radials of the VOR. If you are on a radial depicted in the NavAid, airfield, or other facilities information, you must consider its usability.
If you are dialing/tuning into a specific radial, or if you are located on a specific radial (extended out to depict capturing the radial with a centered CDI regardless receiving thee signal) it does not matter where on the radial you are located.
Case in point. KLOL lies roughly on the 155 Radial of the LLC VOR. Yet, the airport lies on a 171° True Course from the LLC VOR with a 16° magnetic variation. The Wind Correction Angle will determine your Magnetic Heading. If the magnetic variation changes (which it does), but the VOR is not updated to the change, the radial will stay the same even though the Magnetic Course will be different.


Can I Return Back to the Destination Airport after I Diverted to the Destination Alternate? Can I Return Back to the Destination Airport after I Diverted to the Destination Alternate (while enroute to the destination alternate)?
I highly appreciate an answer with reference please.

There are no regulations in the US that state you must land at a particular airport. It will be even more difficult to find one that says you can return to your original destination after announcing or performing a diversion. There are only regulations stating that you have to list a destination airport on an IFR flight plan. And, that there are certain situations when you must list one or more alternate destinations on an IFR flight plan.
VFR flight plans are not required in the US. Even if you file a VFR flight plan, ATC will not be made aware of your flight plan unless it is not closed prior to half an hour after your ETA. In which case, only VFR aircraft on VFR Flight Following will be tracked by ATC. The pilot can cancel a flight plan (IFR or VFR) or flight following at any time that the pilot is in VMC, entering Class G airspace or landed. Otherwise, you must fly your filed IFR flight plan all the way to your clearance limit or your alternate (once you have informed ATC of your diversion). But, you may also amend your flight plan or Flight Following at any time.
Case in point. I have diverted to an airport just to take an unplanned bathroom break. Before diverting, I informed  ATC of the diversion as well as requesting to keep my flight plan and transponder (squawk) code. When returning to controlled airspace, I was able to continue onto my original destination.
Another example of continuing on to your original airport after diverting is when the diversion airport is en route to your original airport. Having an alternate airport planned that is halfway to your original airport gives the pilot a convenient out or Plan B if the weather ahead starts turning hazardous. If the weather improves before you reach your alternate, you can continue onto your original (after informing ATC if on an IFR flight plan or Flight Following).


Does the yaw damper require manual activation on modern airliners? Modern commercial aircraft are equipped with yaw dampers. This post explains the feature. Now I was wondering if there is a button to manually activate and deactivate it (e.g., on a Boeing 787) or if the yaw damper is automatically activated when the autopilot is engaged?

787
On the 787 there is no activate/deactivate button for it. Yaw damping and turn coordination are always active as long as the flight controls law is in primary mode. In secondary or direct modes, yaw damping becomes degraded.
Primary being the fly-by-wire's fully functional mode. Source: 787 FCOM.

MD-11
On an older generation plane, for example the MD-11, there are buttons for the yaw damper, 4 in fact for the 4 channels, they are rarely used (always on) unless there's a fault and after troubleshooting you want to take a channel out.
(airliners.net) Four yaw damper buttons on the MD-11's overhead panel.

737 Next Generation
On a 737, after a flight is completed and the IRS knobs are moved to the off position, the yaw damper switch automatically goes to the off position.
I suspect the rationale back then (carried over from earlier 737 variants) was you can't have the switch on the "on position" and the fault light illuminated when there was no fault. (The yaw damper needs a functioning ADIRU, which needs input from the IRS.)

(airliners.net) Yaw damper and IRS controls on the 737 overhead panel.

Autopilot and yaw damper
In most (if not all) planes that come with a yaw damper (YD), engaging the autopilot (A/P) is not needed to enable the YD, i.e., you can hand fly and still have the YD on, whether there's a switch for it (737) or not (787).
In the MD-11 if all four channels failed, the A/P can only be used in cruise. So as you can see, you need the YD for the A/P in the MD-11, not the other way around. Source: MD-11 QRH.


What about the DC-9's wing makes wingletting it so difficult? A common way of making older airliners more efficient without increasing their wingspan is to add winglets, either as a retrofit for existing aircraft or as a new, wingletted derivative of a preexisting non-wingletted model.

One particular older airliner for which this doesn't work, however, is the DC-9; winglets for the DC-9 have been studied, but never made it into production.  One of the main reasons for this (alongside the relative smallness of the benefit that could be gained by wingletting a DC-9, compared to that gained by wingletting other types of airliner, and the increasing smallness of the world's DC-9-classic1 fleet) is that the DC-9's wing structure makes it unusually difficult to safely and successfully winglet:

  APB has investigated a retrofit design for the DC-9 family. Those design studies have not been successful in creating a viable business case. Projected block fuel burn reductions of less than 2 percent are offset by substantial modification costs. The limited potential for the DC-9 is a result of the existing wing structure, which hinders installation of a large winglet, as was possible on the Boeing 737 family. Since the DC-9 has been out of production since the early 1980s, the fleet size has shrunk and the fleet has aged, making the business case for a retrofit winglet or wingtip not as attractive as that for the Boeing 737 and 757 families.  [Emphasis added.]

What is it about the DC-9's wing that makes it so hard to winglet, compared to (say) a 737?

1: The DC-9-10 through DC-9-50, but not the DC-9-80 or DC-9-90.

I do not know, and I have looked for answers for a little bit. Interesting question. I have seen it said that the DC-9 has a high aspect ratio, which may be a factor -- resisting a wing-axial torque is easier with a longer chord, which all things being equal, would be a lower aspect ratio.  Still, a split winglet (part up, part down) or tip fence like on the A320 could mitigate that particular torque. Ground clearance comes into play then, with the low wing and very low dihedral.

So, my other suspicion is that resistance to flutter might be an issue -- podded engines (podded correctly) combat flutter. Rear-mounted engines do not. If the winglet tended to induce flutter, it might be tougher to suppress. Nobody wants to re-engineer the spar box for the scanty gain offered.


Can anyone help me with the Make, Model (version), and Unit of this WWII army trainer. Appears to be an AT-6 version Location: Madison, WI Municipal Airport on May 21, 1939.
Notice the straight bottom on the vertical stabilizer, crest emblem, pitot tubes, landing gear, exhaust location, antenna, etc.
I have two photos of this plane, the 2nd photo is from the front, but I don't know how to add a second photo to this post.

That is a North American NA-36, BC-1, a North American NA-16 derivative, the predecessor of the  North American T-6 Texan

Source: nationalmuseum.af.mil
Some observations that helped to determine the precise model:

The fuselage is covered with fabric. Later models used metal

The trailing edge of the rudder is rounded, later models had a straight rudder

The bottom corner of the rudder is squared, some other models are rounded (e.g BT-9)

The fuselage shows the crest of the USAAF's Technical Training Command:

Source: Picturing Meteorology. The text "Sustineo Alas" is latin for: "I sustain the wings", or more loosely translated: "I keep em flying"
The aircraft belonged likely to Chanute Field Technical Training Command (Illinois), located some 200 miles south of Madison.


What are typical insurance premium reductions for renters and owners as they earn instrument and commercial tickets? I hear general claims that insurance companies dislike VFR-only pilots and that premiums fall as airmen move up in hours, ratings, and certificate levels.

What are the hard data from the actuarial tables? How do the profiles compare for owners versus renters?

(This is a US-based answer.)

There's no statistical information that I could find out there about this, but aircraft type, total hours, hours in type, age, previous claims etc. are all factored into the premium as well, so it's hard to make a simple comparison based on one variable. And as AOPA says:

  Not all carriers have the same guidelines for when they will offer a
  premium reduction.

But having said all that, it looks like an instrument rating is the key qualification to get. AOPA's insurance FAQ recommends it:

  Typical actions you can take to reduce your rates include:

  [...] Obtain an instrument rating.

I guess you could go through AOPA's quote process multiple times with different data to see what premiums come out, but just calling them is probably easier.

Avemco is a well-known aviation insurer and they're more specific. The wording is bit awkward but it looks like an instrument rating reduces your premium with them by 10%:

  Q: Is there any type of additional training that would lower my premiums?
  A: [...] obtain an upgraded certificate or Instrument
  Rating and you become eligible for the full 10% savings.

They don't say what an "upgraded certificate" means, but if you're one of the few people who have a commercial certificate but no instrument rating then perhaps that would count. Other insurance companies also say that advanced ratings can reduce your rates (here, here).

Finally, I can add a couple of comments from personal experience. I have AOPA renter's insurance and it's flat rate: your certification and experience don't matter at all. Second, when I was looking for life insurance, having an instrument rating cut my premiums a lot but it was a while ago and I can't remember the exact numbers. I do remember that they were reluctant to even consider me without it.


How do I use the takeoff and landing distance charts in the C172 POH? Can anyone explain how to calculate takeoff and landing distances using the chart for C172s, and please give me an example?

There are many ways to calculate aircraft performance. Some ways are entirely manual through the use of formulas. Some ways use electronic means like apps and special calculators. Some ways use pre-calculated Tables. Then there are ways that use graphs and charts. Let’s tackle the charts way.

First, remember one thing. These charts are made from data obtained using highly experienced and skilled test pilots using brand new airplanes with ideal performance and under ideal conditions. Since you probably meet none of these parameters (most of us don’t), it is best to add as much as 50% fudge-factor to your results as a safety buffer.

Think of the Takeoff and the Landing Performance Charts as each being a combination of 4 separate charts.

The Pressure Altitude to Density Altitude conversion chart.
The effect of Density Altitude on weight chart.
The effect of wind on distance chart.
The additional distance needed to clear an obstacle chart.

To start your calculations, read any associated text on the chart. It will give you parameters that must be met in order to make the chart as accurate as possible. They may also give you factors to consider and/or adjust in your calculations.

The Pressure Altitude to Density Altitude conversion chart.

Next, find out the Pressure Altitude and Temperature at Field Elevation for your point of departure. You may have to obtain the Pressure Altitude by calculating it using your Field Elevation and Atmospheric Barometric Pressure reading. Another chart may be handy for this.

Start your graph entering at the horizontal Temperature axis at your Field Elevation Temperature. Follow the graph line vertically up to where it intercepts the line representing your Field Elevation Pressure Altitude. Follow the graph line horizontally to the right until it intercepts the Reference Line for the next section of the chart.

The effect of Density Altitude on weight chart.

Enter the next section at the point where your drawn graph line from the previous section intercepts the Reference Line. Draw a line that roughly parallels the diagonal lines immediately above and below your drawn line. Find the point at which your drawn line intercepts the vertical graph line representing the actual total weight of your aircraft at the point the performance data would be used (takeoff weight or landing weight). Draw another line horizontally from the point of interception, to the next Reference Line.

The effect of wind on distance chart

Enter the next section at the point where your drawn graph line from the previous section intercepts the Reference Line. Draw a line that roughly parallels the diagonal lines immediately above and below your drawn line. Find the point at which your drawn line intercepts the vertical graph line representing the actual Wind Component at the point the performance data would be used (takeoff or landing). Draw another line horizontally from the point of interception, to the next Reference Line. If the winds are calm, use the 0 wind graph line that coincides with the Reference Line. Your drawn line would then be an individual horizontal line from the reference line to the next Reference Line.

The additional distance needed to clear an obstacle chart.

Enter the next section at the point where your drawn graph line from the previous section intercepts the Reference Line. Draw a line that roughly parallels the diagonal lines immediately above and below your drawn line. Find the point at which your drawn line intercepts the vertical graph line representing the actual obstacle height AGL you would have to navigate/avoid at the point the performance data would be used (takeoff or landing). Draw another line horizontally from the point of interception, to the vertical axis on the right. If there is not an obstacle, use the 0 height graph line that coincides with the Reference Line. Your drawn line would then be an individual horizontal line from the reference line to the vertical axis.

Results.

The value you read on the y-axis of the chart is the minimum distance you need to accomplish the stated phase of flight under the given conditions. As a reminder, there will be different charts for different phases of flight. A phase of flight may have multiple charts. An example of this is a chart with flaps and a chart without flaps. Make sure you are using the correct charts and conditions for your aircraft and situation.


What is wing trammelling? What is wing trammelling and how does it affect wing stability and performance?

It's just making sure the rectangle formed by the spars, compression tubes and cross bracing is square.  It's done using a trammel bar, which is just a stick (which the guy in the picture is holding) with a metal point at each end that is used to make sure diagonal reference points along the spar beams are the same distance apart when set across one leg of the X formed by the cross bracing, then the other leg.  The effect on stability and performance is indirect insofar as you don't want a rectangular wing to be trapezoidal (swept - unless the sweep is part of the design like the upper wings of some biplanes, in which case you trammel to that requirement), as well as the fact that parts won't fit if things aren't square.


What is this racetrack-shaped Special Use Airspace, and why isn’t it on the VFR sectional? What type of SUA is AR633A, the cyan racetrack-shaped SUA north of Knoxville, Tenneessee (KTYS) depicted below on sua.faa.gov?

Why doesn’t it correspond to anything on the VFR sectional?

This is indeed a designated air refueling track used by military tanker aircraft (all AR-nnn SUA areas are, and they all share that same general racetrack shape).

The reason why it isn't on a sectional is because it's simply not a concern to anyone who isn't in a high-performance, high-altitude airplane -- air refueling (of fixed-wing birds at least) typically takes place well into the FLs (FL280-FL330 is typical, although it may be lower or higher depending on what the tanker is gassing up), and doesn't bother anybody below.


Is it possible to lift a ship sized vehicle into the sky by following modern day aerodynamics and aircraft design? Is it is possible in real life to make a aircraft carriers size ships to fly in the sky like the flying things we seen in avengers movie?

Possible: Yes

You can in theory lift anything. To do this you will simply need to generate an equal or exceeding amount of lift than the weight of the object. You will also need to generate enough thrust to achieve said situation. The closest thing I can think of to this was Howard Hughes Spruce Goose which did actually fly. If you are talking about the kind of vertical hovering that the ship in the movie does you would need to generate an amazing amount of thrust to achieve that. A US Nimitz-Class aircraft carrier displaces 100,000 long tons (224,000,000 LBS) so you would need to generate at least that much thrust but in reality you would need to generate more to overcome drag and to actually accelerate the craft vertically. For a point of comparison the Saturn V rocket weighed 3270 tons (6,540,000 pounds).

If we work through a quick example (these are very very lose numbers), lets take the Nimitz at 224,000,000LBS and the GE90 jet engine (currently the biggest turbo fan jet). The GE90 generates about 115,000 lbf of thrust. So it would take just under 2000 GE90s to generate enough thrust. But lets round it off at 2000 for ease of use and a bit of extra power. The diameter of the engine is 3.429m and the Nimitz is 332.8m long. You would need arms with 10 engines a piece just to make all 2000 engines fit down the length of the side. If they were stacked directly next to each other the arms would be about 35m in length. The bigger issue here is fuel flow/mass. You would need to lift enough fuel to actually power these engines for a useable amount of time.

On the more sifi side of things, you could use the Nimitz's nuclear reactor to power ducted fans which overcomes the fuel problem to an extent but I dont have any numbers on that.


Principle of aerodynamic lift: are misconceptions also taught in flight schools? Describing lift as the result of "equal transit time" on both sides of an airfoil is a fallacious theory widely found in technical books and articles for general public (see below for details about this explanation).

But such explanation is also found in aviation books, in spite being identified by NASA as an incorrect theory (NASA explains that if lift is computed from fluid laws, based on airspeed on both sides of the airfoil, the result will not be in line with what is observed in real life).

Question

Is this very popular theory also taught this way in flight schools? (please note the question is about pilot teaching, not about what is lift.)

Annex: Popular explanation of lift from equal transit time:

Supporters of this theory explain aerodynamic lift results from the differential of pressure between lower and upper sides of a wing created by Bernoulli principle. They say:

Air has to move a longer distance on the upper side because of the curve of the profile (not correct for all wing profiles).
Both sides must be traveled in an equal amount of time so that air molecules that were nearby ahead of the wing, will meet again behind it (may be right or wrong.)

By Bernoulli's principle accelerated airflow has lower pressure. Pressure is then lower on top of the wing, and higher on bottom. Hence the wing receives a force which has a vertical component upward. This component balances the weight of the aircraft, and allows to stay aloft.

I am a CFI who teaches at a large (+200 students) flight school in the United States.  You might be surprised to hear this, but...
We really don't worry about how a wing works that much.
As far as I'm concerned, the technical explanation for how a wing works is a subject for the engineers who build and design such things.  Private pilot applicants (at least all of the ones that I have met) are more concerned with things like "How do I get the plane into the air??" and "What do I do if it starts coming back down again in a hurry?"
In fact, Van Sickle's Modern Airmanship starts off the chapter on aerodynamics by saying (paraphrased):

Some of the concepts presented in this chapter are wrong, but they are useful illustrations.

So, to answer your question, we teach that:

The alignment of the wing to the relative wind displaces air downward, which creates lift.
Because of the shape of the airfoil, air on top of the wing has a lower pressure than air below the wing, which also causes lift.

And unless a student asks us for more information, we leave it at that.
If you hope to become an aircraft designer or research fluid dynamics, you'll quickly be corrected of any misconceptions you may have about Mr. Bernoulli and his asymmetric wing.  Most student pilots, however, are satisfied with a pre-discussion "What we'll talk about today isn't technically correct, but you'll find it a lot easier to understand the necessary concepts this way."

Peter Kämpf made a worthwhile comment:

It is really not so hard to understand aerodynamics correctly, and you
make it sound as if you prefer a short term gain over a profound basis
which could help pilots to really understand what happens with their
plane and to select the most appropriate action.

Which is very true - it's not difficult to understand aerodynamics correctly.  I'll defend my viewpoint with an analogy:  Consider a store where you are shopping with a child who doesn't yet understand decimal addition.  You have two purchases, one costing $5.08 and one costing $3.99.  The child adds the big numbers and tells you that the final price will be $8. You now have (at least) two choices: you could begin a discussion of significant figures and fractional multiplication (can't forget tax!), or you could praise the child for applying the skills they do have and getting an answer which is pretty close.
Is it better if the child eventually understands how to calculate tax rather than simply trusting what the cashier reads off the screen?  Of course.  But at the stage where most of my students are, it's much more valuable to their development as pilots to simply praise them for being close enough.
As regards JAL123, I am in 100% agreement with you.  By the time you as a pilot have progressed sufficiently in your development to be flying something with a turbine pushing it, you should certainly know the principles and concepts of your machine to the highest degree of accuracy.


How does a mechanic determine if a repair or alteration requires a Supplemental Type Certificate? How does a mechanic know when they have exceeded what 14 CFR Part 43 allows for a repair or alteration to an aircraft? They have thus entered an area where the repair/alteration is so significant that the Type Design has been changed, requiring a Supplemental Type Certificate (STC). Do aircraft maintenance manuals give the mechanic some limits to what he can do, or is AC 21.101 all they have to go on?

Repairs and alterations are defined at FAR 1.1, FAR 43 App(A)(a)(1-4), FAR 43 App(A)(b)(1-4)

"Major alteration means an alteration not listed in the aircraft, aircraft engine, or propeller specifications - (1) That might
appreciably affect weight, balance, structural strength, performance,
powerplant operation, flight characteristics, or other qualities
affecting airworthiness; or (2) That is not done according to accepted
practices or cannot be done by elementary operations."
Minor alteration means an alteration other than a major alteration.
Major repair means a repair: (1) That, if improperly done, might
appreciably affect weight, balance, structural strength, performance,
powerplant operation, flight characteristics, or other qualities
affecting airworthiness; or (2) That is not done according to accepted
practices or cannot be done by elementary operations.
Minor repair means a repair other than a major repair.

In the US, to be airworthy (FAR 21.183) all aircraft must "conform to type design and condition for safe flight". To "conforms to type design" there must be some type of approved authorization for every piece on the airplane. There are several ways to do this.

The manufacture may have pre-approved the equipment you wish to install. Under CAR 1,2, & 3 (~prior to 1958) regulations a separate document for the aircraft called a "data sheet" showed approved equipment. After 1958 aircraft where certified under FAR's and used a "Equipment List". The "Equipment List" for light aircraft is usually found at the back of the Pilot Operating Handbook (POH). An example for a 1978 C152 is shown below.

If a manufacture did not approve the equipment than it may be installed under the authority of a "STC" (equipment pre-approved by the FAA).

...or an "alteration" that a AI (Authorized Inspector) gets approval from the local FAA FSDO office by filling out Form 337 and have it field approved.

The owner is required to keep a copy of either a "STC" or Form 337 "alteration" to show the equipment is legal for each annual inspection. If an aircraft has equipment installed that is not authorized by a Data Sheet, Equipment List, STC, or Form 337, the aircraft is un-airworthy and illegal to fly.
There are three small exceptions:

The FAA provides an alternate approval for small common parts (FAR 21.303-4 and Court Order 8110-42A)
such as wheel bearings, chemicals i.e de-iceing fluid, etc via a "PMA" authorization.

The FAA approves replacement of some parts that meet industry
standards (AC 20-62e) without need of authorization for parts such as sheet metal,
electrical components, minor hardware, etc.

In certain circumstances (FAR 21.303-2 and AC 20-62e) the owner may have a part built or manufactured that is no-longer available for purchase. This provision is often used for old bi-planes and war birds.


What is the use of this object in the cockpit of a Bombardier Dash 8 Q400? What is the use of this object in the  cockpit of a Bombardier Dash 8 Q400?

It is a mechanical checklist where each item on the list can be flipped to indicate that is has been checked. You can see it in operation in this YouTube video (which I believe is where you got the image from). Each of the 6 stacks can be extended to check the items and then collapsed again in order to not obstruct the pilot's view.

It is not a default part of the Dash-8 Q400. As far as I know, Qantas is the only airline using it.


Why would a Su-25, which has more power and is much lighter than an A-10, only fly half as high? On the web, on several sites, the A-10 is listed with a ceiling of 14 km, the Su-25 with 7 km, although there is data that puts the height for the Su-25 at 10 km.

Nevertheless, why would the Su-25 fly only half as high as the A-10 knowing that the Su-25 has more engine power and is much lighter?

Just look at the wing loading: The Su-25 has between 585 kg/m² (regular Su-25) and 691 kg/m² (Su-25TK) when fully loaded, whereas the A-10 has a wing loading of 316 kg/m². This alone should explain why the Su-25 cannot climb as high.

Even when flying at minimum mass, the Su-25 has still 309 kg/m² (345 kg/m² for the Su-25TK), and the A-10 is almost a glider by comparison, having just 208 kg/m² at minimum mass.

Since both are subsonic designs, they have a strict limit on maximum speed. With that, wing loading and the airfoil determine their ceiling if thrust is sufficient.

Another limiting factor is the cockpit: Since the Su-25 was designed for ground attack, it has an unpressurized cockpit. This detail limits the certified envelope, even though a lightly loaded Su-25 can climb higher than 7000 m.


How to read representations of pressure around an airfoil? Actual representations found online

I selected 6 online representations of pressure around an airfoil, mostly using inconsistent symbolization of the pressure field.

Source of the individual pictures: Fig 1, fig 2, fig 3, fig 4, fig 5, fig 6

As visible, arrows can be found in nearly every combination of directions. On figure 4, pressures are about 2 hPa (200 Pa) and 5 hPa, which is not really understandable when pressure at sea level is about 1,000 hPa.

Last figure shows the pressure field in the cross-section, not only at the surface of the airfoil (which I believe is the case for the other figures).

Assumptions made to read the figures

By following the answers on this site, I know that the pressure on the lower side of the airfoil is greater than the pressure on the upper side. I also assume that the pressure on the upper side is lower than the ambient pressure, and the pressure on the lower side is greater than it. I believe the drawings are trying to depict these two aspects, but using different (and unspecified) conventions.

Probably the clearer convention is the one used on fig 6: Yellow is likely the ambient pressure, orange would be greater, green lower, blue even lower.

Questions

What are the usual pressures found around an airfoil, e.g. in cruise, at mid-span of a A320 wing (compared to the ambient pressure).
What is the most correct representation of the pressure field in the figures above?
Is there some conventional way used by engineers to depict the pressure field without ambiguity?

The arrows are more for the "gee wiz" factor - while they help to show in which direction which pressure is acting, the regular way of depicting pressures is using the pressure coefficient.

Now to your figures:

This probably tries to illustrate the fact that there is air pressure all around the airfoil, and less on top than on the bottom. But the length of the arrows does not correspond to any real pressure distribution. Please do not use this plot to learn aerodynamics.
This one tries to be more realistic, but gets the pressure distribution around the nose totally wrong. While better than 1, it is still not recommended.
This one is clearly the best of the bunch. Here you have a small but intense overpressure region at and near the stagnation point and suction on both sides, as would be the case at small and medium angle of attack if the airfoil has some thickness. The displacement effect will cause the flow on both sides to accelerate to a speed above flight speed, but camber and angle of attack make this effect much more pronounced on top. At the trailing edge you will find a small overpressure on top and a little suction at the bottom when the flow negotiates around the trailing edge because the boundary layer on the upper surface is much thicker than on the lower surface.
Here you see absolute pressure difference numbers, which is unusual. While the figures look realistic, this plot is also not really helpful because it omits the pressure distribution in the forward part of the airfoil where most of the action takes place. I think this is another special plot to illustrate one specific aspect. The numbers are the pressure difference to ambient pressure.
This one just tries to show how the pressure varies along one streamline. But the streamline has a constant distance from the airfoil, which is wrong, because it would normally come closer to the airfoil surface in proportion to the local speed increase. Also, the stagnation area is stretched out too far backwards.
This is a typical plot from a Euler or Navier-Stokes code where the space around the airfoil is panelled instead of only the surface as is customary for potential flow. The plot looks credible, but without a legend you do not learn much about the pressures around the airfoil. Your assumption about the colours is correct.

Please note that 1 tries to show absolute pressure while the others show the pressure difference to ambient.

To answer your question: Most of the plots suck and it would be a waste of time to "read" them because of their limited truthfulness. Maybe this would improve when you read the accompanying text as well, but it would be even better if all plots were like number 3.

What helps most when reading pressure plots is consistency - here all 6 plots fail. The proper way is to plot the pressure coefficient as explained in the linked answer. Only then can you gain some familiarity with the representation and make meaningful comparisons among different airfoils or flow conditions. Negative values of the pressure coefficient $c_p$ denote suction and positive ones overpressure, all relative to ambient static pressure.


What is the difference between ground effect for an infinite wing and for a finite wing? A question about ground effect  has just reappeared.

I think one needs to differentiate between ground effect for a finite wing (3D flow) and ground effect for an infinite wing (2D flow).

What are the differences?

That wingspan is used as a measure of distance to the ground to indicate the presence or strength of ground effect leaves me with the impression that there is a 3D aspect to ground effect. Ignoring maneuvering a long wing for the moment.

I haven't fully grasped the importance or unimportance of the trailing vortices yet.

Ground-effect analysis is generally completed using the method of images, where we imagine an opposite geometry providing a flow that interacts with the original geometry.

The 2D case

Katz and Plotkin have a good explanation; here is their diagram for the 2D case:

For a flat-plate airfoil, the math works out to
\begin{equation}
C_\mathrm{l} =\frac{\pi  \alpha  \left(c^2-8 \alpha  c h+16 h^2\right)}{2 h (4 h-\alpha  c)}
\end{equation}
where $c$ is the chord, $\alpha$ is the angle of attack, and $h$ is the height above the ground.

The 3D case

In the 3D case, we model the entire wing (or aircraft) as mirrored. The math here gets quite a bit more complicated, but I can summarize Phillips and Hunsaker, who provide the following figure and equation:

For an untapered flat wing with small $\alpha$, the lift coefficient in ground effect $C_\mathrm{L_G}$ is about
\begin{equation}
C_\mathrm{L_G}\approx\left(\left(\frac{261.562}{\left(\frac{b}{c}\right)^{0.882}}-\frac{1.944}{\left(\frac{b}{c}\right)^{0.165}}\right) \left(\frac{h}{b}\right)^{0.787} e^{-9.14 \left(\frac{h}{b}\right)^{0.327}}+1\right)C_\mathrm{L}
\end{equation}
where $C_\mathrm{L}$ is the lift coefficient in the absence of ground effect, $h$ is the height above the ground, $c$ is the chord, and $b$ is the wingspan.

Comparing the two

I plotted the 2D equation for an airfoil with $c=1$ along with the 3D equation with $C_\mathrm{l}=C_\mathrm{L}$ for a wing with $c=1$ and $b=10$ (for any reasonable aspect ratio, this trend is similar):

As expected, far away from the ground and very close to it the 2D and 3D cases converge. The 3D case gets a bit more help from the ground in the intermediate range. Because we have only considered inviscid flows in the mathematical analysis, we know that the induced drag is the major difference between the 2D and 3D cases.


Can wind shear conditions be identified visually? Without relying on winds aloft or LLWS data, can pilots identify wind shear conditions visually, by watching clouds or otherwise?

Can you see wind shear?  Nope, but you can sometimes see indications of it.  According to Airbus, windshear is usually associated with the following weather situations (photos found on Google images by me and are clickable to take you to the source):

Jet streams

Mountain waves

Frontal surfaces

Thunderstorms and convective clouds (and I added virga here too)

Microbursts.

Avoid these at all cost!  Actually, that's the easy part.  The windshear without the visible signs is more the issue, and csatlos's answer does a good job of telling you what to look for during flight (especially takeoff and landing when you are low and slow).


Why we had two empty rows on busy Ryanair flight Boeing 737-800 and no one was allowed to seat there? Back in 2012 I flew from Tenerife South airport to London Stansted with Ryanair airline. All the tickets for this flight were sold out. But 3rd and 4th row on this Boeing 737-800 were empty (12 empty seats) 1 & 2 row are for customers who paid for the seats. The interesting think that no one was allowed to seat there. One lady before departure occupied one of the empty seat in the 4th row. Cabin Crews told her that aircraft will not depart unless she will go back to her seat. At first lady refused to go back and started complaining. We were waiting for her to change the seat and then we departed.
I did ask the steward why is there two empty rows but had no clear explanation from him

Were these emergency exit rows?

Seat pitch on low cost airlines is too small to allow an emergency evacuation within the required 90 seconds with regular seat pitch in the exit rows. Therefore, the seat pitch is larger there, which makes a world of a difference for tall people. Low cost airlines have decided to monetize those few more inches of leg room and charge extra for sitting there.

If no passenger on that flight was willing to pay the extra fee, those airlines which pride themselves on treating their passengers with the utmost contempt keep these emergency exit row seats free even if the plane is fully booked on all other seats.


Are “Kennedy Steve’s” various jokes allowed in ATC communications? Forgive me if there is an obvious answer to this, but I was just listening to this “Kennedy Steve” playlist, and he seems to joke a lot more than most ground controllers I’ve listened to.

I have three questions about this.

Is it legal for air traffic controllers to joke on the air at all, and definitely this much?
Are Ground controllers held to the same rules regarding communication as Tower, Approach/Departure, or Center?
Is it more serious for a pilot to start joking on ATC, or for a controller to, in terms of consequences?

(US-based answer)

Yes, it's legal. Yes, everyone - including pilots - is held to the same standard of professionalism. And there are no real consequences for anyone (usually). The simple fact is that we're all human beings and humor, slang and jokes are all part of how we communicate and even handle stress.

Legally, the FAA doesn't regulate radio communication, the FCC does. Of course, the FAA has aviation regulations and guidelines that apply, but they're very general (as they should be). Using standard phraseology is strongly encouraged at all times for clearer, quicker communication. The ATC orders 2-4-14 say:

  Use the words or phrases in radiotelephone and interphone
  communication as contained in the P/CG or, within areas where
  Controller Pilot Data Link Communications (CPDLC) is in use, the
  phraseology contained in the applicable CPDLC message set.

In other words, stick to standard phrasing. But there's nothing in there about avoiding humor or jokes.

As for different controllers, they all follow the same standards for radio use no matter where or on which frequency they're working. In my experience, the quieter the frequency the more likely it is that someone - controller or pilot - will joke or even have a brief conversation. I was once taxiing a C172 to the far end of a 12,000ft runway - which takes some time - and the tower controller asked me a few short questions about my accent, where I was from etc. But I was the only aircraft on his frequency at the time and I'm sure he wouldn't have done it if it would have impacted operations or safety in any way.

Which brings me to your final point. In normal circumstances, no one cares about this stuff at all because a) it has no significant impact on anything, and b) it makes life a little more interesting for everyone. It's practically impossible to fly cross-country for more than half an hour without hearing someone make a joke, chat with someone else (briefly), or even complain about something. And again, in normal circumstances that's completely fine: no one expects pilots and ATC to act like robots with a limited vocabulary.

But, if a joke or non-standard phraseology causes offence or a misunderstanding or - in the worst case - an incident of some kind then the FAA or NTSB could be interested. This column from NASA's ASRS team has some examples of reports of problems causes by non-standard phraseology, including this one:

  "I called for clearance to St. Louis as follows: 'Clearance delivery,
  company ident, ATIS info, federal aid to St. Louis.' Federal aid was
  meant to mean FAA clearance in a joking fashion. The Controller
  misinterpreted this to mean that we were being hijacked and called the
  FBI and airport police...I used no 'standard' phraseology to indicate
  nor was it my intent to indicate we had a hijacking...I will use
  absolutely standard phraseology in the future..." (# 248982)

And this incident got quite a lot of attention, even outside the aviation press. I don't think it makes sense to say that it's 'more serious' for ATC to make jokes than pilots because every incident is different anyway.

All in all, joking on the radio is like joking in any professional context: if it doesn't disrupt your work or other people's work, if you're not insulting people or wasting their time, and if you're not saying anything stupid or dangerous then no one really minds.


What are these hooks on the A320's wing used for? I was flying on an A320 (equipped with sharklets) the other day, and I found these hooks on the wing's surface:

Note that the single hooked attachment is outside the wing's "DO NOT WALK OUTSIDE THIS AREA" line. What are these hooks used for? Why is the single hooked attachment outside the "safe" walking area line?

In the event of a water evacuation, there is a line associated with each overwing exit that is extended, and clips to that yellow bracket, as a guide to get everyone out on the wing.

From Wikipedia, these are for overwing exits.

  The use of overwing exits in a ditching varies from airline to
  airline. On aircraft fitted with overwing exits, there is typically a
  raised escape rope bracket (about a third of the way from the door)
  attached to the wing's upper surface and typically painted yellow.
  This is accompanied by an escape rope found in the frame of the exit
  after opening the hatch. Once this rope is attached to the escape rope
  bracket, it will aid passenger evacuation onto the wing to await
  rescue or to enter the water (depending on the airline's procedures).
  On aircraft with life rafts to be launched via the overwing exit, the
  wing will be used to provide a boarding platform onto the life raft.
  On certain regional aircraft, the overwing exits are the only escape
  route in the event of a ditching.


How are wooden aircraft protected from lightning strikes? A wooden aircraft is not conductive and if a lightning hits the wood it will instantaneously ignite. How would you protect a wooden aircraft from this occurrence?

By not flying through thunderstorms. For a small aircraft, the lightning is not the most hazardous part of a cumulonimbus (Cb) cloud system. Mature Cb clouds have huge updrafts underneath them, which can cause enough turbulence to upset most aircraft. Heavy rain and hail is also commonplace underneath Cb clouds. Even the rain can be heavy enough to damage wooden propellers and any components on your leading edge (such as the leading-edge slats found on the Tiger Moths I fly). Hail can put holes in your canvas, which are expensive to repair - if you manage to get the aircraft home at all. This turbulence and rain persists for a much longer period and across a wider area than the thunderstorm itself.

For these reasons, the chief protection against thunderstorms is by training and procedure: student pilots are taught to avoid Cb clouds when they're visible, and to plan flights to avoid areas where Cb are forecast. Weather forecasts and reports specially call out Cb clouds to help with this, and ATIS messages often warn of "cumulonimbus cloud in the vicinity of the aerodrome".

Protecting a wooden aircraft specifically against lightning is not hugely worthwhile, because it's unlikely to be able to stay in the vicinity of the Cb cloud for long enough to be at risk of a lightning strike. It just wooden happen.


How much safer does painting prop tips make a plane? While re-reading one of my earlier questions, the answers left me wondering how much good painted tips on props actually does.  I did some searching for statistics but didn't come up with much.  Are there any published statistics about how much safer it is to have painted prop tips specifically in military planes (although civil aviation stats would also be nice)?

An FAA study looked into that, it's titled: A Review of Civil Aviation Propeller-to-Person Accidents: 1980-1989.

This part stands out:

  While propeller and rotor paint schemes may reduce the number of propeller-to-person accidents, there is little information available regarding the various circumstances surrounding the accidents that do occur.

So there is little information. Their summary is:

  Persons most at risk for a propeller-to-person accident are deplaning passengers and passengers attempting to assist the pilot. That finding clearly assigns considerable responsibility to pilots to ensure safety of their passengers in this regard.

As you see, they did not stress on the paint, they also highlight that since the past, propeller driven aircraft are no longer the most popular type [for civil air transport].

An older study but relevant was conducted by the US Army. The document does not list accidents or statistics, so it's safe to assume it's a precaution. Better safe than sorry.

And in an environment such as an aircraft carrier's deck at night, it most certainly helps (but that's my opinion), there isn't a control set for a scientific assessment (as far as I can tell).


How much is a swashplate system more energy efficient than a fixed blade system for the same load When reading about the lifting capacity of swashplates (as found in helicopters) vs fixed blade systems (as found in e.g. DJI drones), I read a lot of comments about the fact that the bigger rotors of a helicopter are more efficient. But how does that link to the system (fixed vs swashplate) and how much efficiency are we talking about? Now, I know that the question is way too simple for the complexity of the problem, also after reading these questions 1, 2, 3
The factors that influence this problem is also part of the 'quest' and I hope to reach a ballpark figure. It also links to the complexity of the use of a swashplate or even a virtual one. A very complex system can be more efficient in the long run, but is it worth it. That is the underlying question.
If possible could you explain formula's? I had math and physics back in the day until the age of 18 (VWO for the dutchies), so it is rather rusty.
edit: the core of the question is the system efficiency vs 1 or multirotor

The question does not really make sense: a helicopter is a kind of aircraft, a drone is a mode of how a vehicle is controlled.
I can rip the seats and controls out of a helicopter and put some clever software, some cameras, and some transmitters inside, and boom: I have a drone that can carry exactly as much as it could before – probably even more because humans and safety systems are heavy, and we got rid of both of those.
In fact, that's exactly what some companies are doing. The Northrop-Grumman MQ-8C Fire Scout is literally just a Bell 407 with some added electronics and software. And while this particular drone is designed for combat, there are others which are designed for cargo delivery. For example, two uncrewed Kaman K-MAX were deployed to Afghanistan already in 2011.
Here is a video about the Office of Naval Research's Autonomous Aerial Cargo/Utility System AACUS program. The goal of this program is to have a software/hardware package that can be installed in any helicopter to make it fully autonomous. There is no reason you couldn't install it in a Mil Mi-26, for example.
So, in short: by turning an existing helicopter into a drone, a drone can by definition lift just as much as a helicopter. By designing a helicopter specifically as a drone, you could potentially lift even more, because you can get rid of all the weight for the cockpit, seats, life support, safety systems, controls, etc. You could also remove a lot of redundancy, if you consider occasional crashes acceptable when no humans are on board.


Has anyone attempted to board a flying aircraft mid-air? A few movies (e.g. Air Force One, Executive Decision) feature a story where people board a flying aircraft from another flying aircraft.

Has anyone ever attempted, either via docking two aircraft together, using cables, parachuting on top etc., to get from one flying aircraft to another mid-air?

Sure. It was regularly done by the aerialists or barnstormers of flying circuses during their heyday in 1920s.

  Barnstormers performed a wide range of stunts. Although many of them handled all their own tricks, others became specialists, either stunt pilots or aerialists. Stunt pilots performed daring spins and dives with their planes, including the well-known loop-the-loop and barrel roll maneuvers. Aerialists, on the other hand, performed such feats as wing walking, soaring through the air with winged costumes, stunt parachuting, and midair plane transfers.

These were mostly done using army surplus biplanes after WWI. The performers boarded aircraft from a variety of vehicles, from cars to speedboats. This ticket for one of the performances clearly mention the midair plane transfers.

Ticket for a flying circus; Image from all-things-aviation.com

As time went by, lack of cheap aircraft and tightening federal regulations put an end to barnstorming. I'm not aware of anything like that in modern times. Anyway, mid-air transfers are not easy and are quite dangerous, as Simon Crane found out while shooting for Cliffhnager.


What is the Hot Air Pressure Regulating valve and what's its purpose? What does the hot air pressure regulating valve do, yes I know that it regulates hot air pressure but what does that do, create hot air? How does it regulate hot air pressure?

I have a picture of the valve here at page 3. It's an Airbus A320
http://www.smartcockpit.com/docs/A320-Air_Conditioning_and_Pressurization.pdf

The valve regulates the pressure of hot air from the engine bleed system that bypasses the airconditioning packs. This hot air is then fed to the trim air valves to adjust cabin temperature.


Can you verify that this aircraft is not a variant of the T-34 Mentor? On this page, near the bottom, the aircraft below is identified as a T-34. I'm wondering if that's correct, but before I contact them to point out a possible mislabeling, I'd like to find out what it is or is not.

UPDATE -- I sent en email to The Catalina Island Conservancy, and they have changed the image to correctly show it as a Nanchang CJ-6.

Looks like a CJ-6. Popular as an affordable "warbird" type of aircraft, without the rarity.

Various other images of the CJ-6 that seem to match up to what you posted.


Can a door be shut while in flight? What is the best way to shut a door that has popped open in flight?

I had a door on a Cessna 172 pop open shortly after takeoff and was unable to get it closed, but I was fortunate enough to be able to quickly circle around and land. I tried reaching across with my right hand, but I was unable to push the door open enough to pull it quickly enough to latch. Is there a way to shut a door?

Source

In this accident of a Cirrus SR22 the pilot became disorientated by an open door and crashed. What procedure should be used for an open door?

I've had this happen a few times on aging C152's and in all cases I have been able to simply push it against the airflow enough to pull it closed. On a PA28 with the door the other side of the cabin from the pilot seat, this wouldnt be possible. Not that I have experienced it in a PA28, but I might ask a passenger to attempt the same (hard push followed by a hard pull).

Some things to note:

There's no massive danger of a door slightly ajar, so waiting until  out of a critical phase of flight is advisable (ie, climbed to cruise, clear of any ATZ)
In all but one time I had another competent pilot sitting next to me who can keep an eye out and even hold the controls for a few seconds. Just one reason flying with other pilots is nicer than flying alone.

However, I would suggest that every situation is different. The most important thing is, as always, Aviate first. A light aircraft is unlikely to be critically unable to continue flying with a door ajar. Don't get distracted by something like an ajar door - fly the aircraft.

If in any doubt, land as soon as possible and fix the problem. It would, I think, be acceptable to call "Pan Pan" if you feel you need to expedite a landing.


In a turbofan, why are there no stators behind the fan? Why are there no stators behind the fan? At least, I've never seen any turbofan design that has stators right behind it. (Here is the latest turbofan I've looked at, the CFM56. Cutaway part starts around 00:35.)

The purpose of stators is to redirect the airflow to be mostly axial. Without them, the air would be spiralling too much.

The fan is the biggest compressor so I would think stators are needed there more than any other place, but apparently that's wrong. I just do not know why it's wrong.

Edit: Yep, there are stators there after all. Just because they're not shown in a video doesn't mean they aren't there. Oh well.

Right behind the fan you can see the stators.

Here they are from behind.

Here is the fan removed, with the (1) fan stators (outlet guide vanes), and (2) inlet guide vanes for the compressor (booster).

Just like I wrote here:

  On the funny side, here's a thumbnail from RR's own YouTube channel, absolutely bonkers exhaust. Don't trust illustrations.

(CFM56-5A manual)

You can watch the fan removal here: CFM56 7B Fan Blade Removal

Below is the stator assembly for the GE90:

Image sources:

https://commons.wikimedia.org/wiki/File:The_CFM-56_(3852495197).jpg
https://commons.wikimedia.org/wiki/File:Airbus_A319-114,S7-_Siberia_Airlines_AN1710042.jpg
https://c2.staticflickr.com/4/3194/2378036305_e14dab2949_b.jpg
http://memberfiles.freewebs.com/70/53/41845370/photos/GE90-BUILDUP/Image678.jpg


Does the Cessna 152 or 172 have emergency door cable releases? Is there such a thing as an emergency cable release inside the cockpit of 152 or 172, to remove the door hinge pins in an emergency?

The Cessna 150 Aerobat and 152 Aerobat both have jettisonable doors.

I don’t believe any version of the Cessna 172 does as there in no aerobatic C172 versions.

This Photo shows two “D” rings which are pulled to jettison the doors.


Are 'climb via a SID' instructions actually used in the US? In the USA, a departing aircraft is instructed to climb:

to flight level and maintain, or
via standard instrument departure (SID)

That's according to US Aeronautical Information Publication (AIP). But pilots say they never hear climb via SID. Can anybody clarify if climb via SID instruction is really used by ATC?

In my experience, I've received a climb via SID many times at airports like Las Vegas and Teterboro.

This is common at certain airports, but a lot of airports don't use it because the procedures aren't designed that way.

I think that a lot of pilots, especially those flying smaller non-turbine powered aircraft, don't receive this type of clearance because:

They are flying at smaller airports that don't have a SID which uses it, or
They are not assigned the SID's which do have it because the SID is only assigned to turbine-powered aircraft or aircraft capable of flight above a certain speed or altitude.

It is also a relatively new procedure in the US.  They were originally going to start using it in 2014, but it got delayed and was finally implemented a year or two ago (I don't remember exactly when).  For a while, the US was only using "descend via" clearances, and not "climb via" clearances.

Here are a couple of resources about this:

NBAA PBN site
FAA Climb Via/Descend Via Speed Clearances
Frequently Asked Questions
FAA “Climb Via” and “Descend Via” Procedures and Phraseology Air Traffic Policy Notice


Why does the B-52 outboard engine nacelle have a sharp change in shape? The outboard engine nacelle of a B-52 appears to have a change of shape too extreme for just blending to the center-line of the engine pod. Why is the B-52 outboard engine nacelle shaped the way it is?

The B-52 was build in different versions (A-H) and the engines and their installation differ between these version1.

The image in the question most likely shows the engine configuration of a B-52H.

The following drawings suggest that this also changed the inlet design2.

There seem to be different engine-designations depending on the application. For the B-52H, JT3Ds (TF33-P-3) were used3.

Pictures of the TF33-P-3 inlet show they are symmetrical. (While the question is focused at the outboard engine-inlet, this question can only be answered taking the other engine and the placement relative to the wing into account as well).

At the symmetry-plane the TF33-P-3 inlet-section extends further than the rest of the inlet-lip.

I would guess that there are multiple reasons and considerations which led to this design. Three of which will most likely have been:

Basic aerodynamic considerations like stagnation-point and pressure distribution will prefer a sharp/point nose over a flat area. Especially since the air needs to be diverted from the engine-pylon.
The cruise speed of the B-52H is Mach 0.914 which means the nose could also be some kind of anti-shock-body reducing wave-drag by applying the area-rule.
The nose between the two engines prevents aerodynamic interaction of the two engines, for example during cross-wind operation.

The negative aspects of placing two jet-engines close to each other were also discussed in another SE-question with respect to commercial airliners.

[1]:www.airpowerstrategy.com/
[2]:http://www.afwing.com/
[3]:en.wikipedia.org/wiki/Pratt_%26_Whitney_JT3D
[4]:www.globalsecurity.org/wmd/systems/b-52.htm


What is MCAS' purpose? In a recent question, one of the answers states:

MCAS has nothing whatsoever to do with stall recovery or stall behaviour.

It was implemented strictly to make the MAX's pitch stick force response in certain regimes match older 737s, to avoid an additional training requirement necessitating Sim time.

But after reading this article, I'm confused about what exactly MCAS was intended for, as I thought it was stall recovery.

This website has a very comprehensive description and analysis of MCAS: http://www.b737.org.uk/mcas.htm
I find it to be the most accurate of all the various sources often quoted.
Here is a small quote from that website:

MCAS is a longitudinal stability enhancement. It is not for stall prevention (although indirectly it helps) or to make the MAX handle like the NG (although it does); it was introduced to counteract the non-linear lift generated by the LEAP-1B engine nacelles at high AoA and give a steady increase in stick force as the stall is approached as required by regulation.
The LEAP engine nacelles are larger and had to be mounted slightly higher and further forward from the previous NG CFM56-7 engines to give the necessary ground clearance. This new location and larger size of nacelle cause the vortex flow off the nacelle body to produce lift at high AoA. As the nacelle is ahead of the C of G, this lift causes a slight pitch-up effect (ie a reducing stick force) which could lead the pilot to inadvertently pull the yoke further aft than intended bringing the aircraft closer towards the stall. This abnormal nose-up pitching is not allowable under 14CFR §25.203(a) "Stall characteristics". Several aerodynamic solutions were introduced such as revising the leading edge stall strip and modifying the leading edge vortilons but they were insufficient to pass regulation. MCAS was therefore introduced to give an automatic nose down stabilizer input during elevated AoA when flaps are up.


At which point in scale reduction do slats and flaps become unnecessary? Imagine some Fi-156 Storch, and reduce its scale down gradually to 10cm span. Let's assume full scale Fiesler Storch is 100% efficient at, for example, minimizing stall speed.

During this reduction process, if every dimensional element is scaled down perfectly, except airfoil shape, slats airfoil shape, flaps airfoil shape, and slats and flaps relative gap width between them and the wing, how would these (allowed to vary along vertical axis) parameters roughly evolve during scaling down process, so that this aircraft ability to minimize stall speed remains close to 100%? Is there in this case some linear pattern along Reynolds number variation?

Putting slats and flaps on a 10 cm model is extreme, but would add a touch of realism for the serious hobbyist.

  At which point in scale do slats and flaps become unnecessary?

We turn to the lift equation:

$Lift$ = Air density x Area x Lift Coefficient x Velocity$^2$

$Weight$= $Lift$ for steady state flight so we derive:

$Weight/Area$ = Rho x Lift Coefficient x Velocity$^2$

In terms of considering the need for slats and flaps, the primary factor is the difference in landing and cruising speed.  In an airliner, the difference can be 350 knots! (Maybe a little less, considering Rho at higher altitudes, indicated airspeed).  For a Storch, around 60 knots,  for a tiny model with light wing loading:  maybe 7 knots.

When we compare $Kinetic$ $Energy$ = 1/2mV$^2$, one sees a scaled down model with low airspeed and very little mass makes for a landing roll-out of only a few feet, whereas the 400 ton airliner at 150 knots needs over a mile to stop.  The faster, heavier plane needs to slow down as much as it can before touchdown.

Also from the lift equation we can derive that increasing coefficient of lift, by increasing AOA, or by reconfiguring the wing, only increases lift in a linear fashion, whereas lift increases with the square of velocity.

The need for slats and flaps really depends on how slow you need to get to land safely.
So does greater runway length, which allows for a slightly faster approach speed.

Further more, we find one aspect of the Fi 156 Storch rarely discussed, its 240 hp Argus AS 10 V8 and it's variable pitch prop.

This shows the designers went to great lengths to provide adequate power to keep flying in spite of the tremendous drag the slats and flaps create.  It was a price to pay for increasing STOL performance, and illustrates why aircraft perform far better "cleaned up" at Vy.

Note of interest:  the same engine was used with the Bf 108 "Taifun", resulting in a cruise speed 50 knots faster, landing around 45 knots.  Both planes were of similar weight.


What's the meaning of underlined frequency in sectional chart nav aid box? There is a statement to describe the underlined frequency in legend, it says:

  Underline indicates no voice on this frequency.

What does this mean? We still need to ident the Morse code, doesn't it? So what's the "no voice" referring to?

Navigation receivers can be used as a fall back for regular VHF/HF radio transceivers

Before data links, there were essentially two types of radio receivers in the flight deck, and this is still the case for most GA aircraft: "COM" used for voice communication, and "NAV" used to receive navigation signals. When COM transceivers fail, the pilot is left without information from ATC, and will follow their current flight plan and clearances.

However ATC may try to send additional information and new clearances using the NAV radios. In that case this is a one way communication, as NAV aboard the aircraft have no transmitting capability.

Information provided to ATCO by FAA in JO 7110.65:

  a. In the event of lost communications with an aircraft under your
  control jurisdiction use all appropriate means available to
  reestablish communications with the aircraft. These may include, but
  not be limited to, emergency frequencies, NAVAIDs that are equipped
  with voice capability, FSS, Aeronautical Radio Incorporated (ARINC),
  etc.
  [...]

  b. Broadcast clearances through any available means of communications
  including the voice feature of NAVAIDs.

The voice feature is present on all navaids, except TACAN. It may also be used to transmit ATIS when no communication emergencies are going on.

Pilot has also instruction to use NAV receivers, e.g. in AIM 6-4-1. Two-way Radio Communications Failure, 6-4-3. Reestablishing Radio Contact:

  a. In addition to monitoring the NAVAID voice feature, the pilot
  should attempt to reestablish communications by [...]

Audio mixer, source

Navaids without voice capability

No voice or underlined frequency indicates ATC can't use this navaid for to transmit voice messages.

Such navaids have a class code W (without), e.g. CHANDLER NDB in Arizona:

Source: AirNav

Source: SkyVector

See also:

NORDO.


Why don't combat aircraft have rear-facing weapons? This excellent question addresses the role of dogfighting in modern aerial warfare. However it seems that most ACM concentrate on maneuvering into shooting position. Why don't combat aircraft have rear-facing weaponry?

Even WW-II bombers had rear-, side-, and downward cannons, albeit manned. Could a small electronically-controlled cannon be added to the stern dorsal part of a combat aircraft, for shooting rearward? I've personally seen remote-operated FN MAGS on vehicles, the whole system seems to weigh on the order of 100-150 KG including hundreds of rounds. The vehicle-mounted systems took up about a cubic meter or so of space, but a purposed-designed system could probably take up less than half that, and probably shave off a good portion of the weight as well.

Could a computer not point a barrel at a vehicle with a relative velocity approaching 0 and shoot, even in a +Mach 1 wind in the direction of the target? It may be enough to just get a few bullets in, shotgun style. The Uzi rifles famously don't shoot straight, they make a cone of bullets. Perhaps this cone, if aimed in the general direction of an aggressive aircraft, might be enough to either disable it or get it off your tail. A short barrel will make a wider cone, perhaps the rear-facing weapon could have an very short barrel. ACMs such as the Cobra maneuver seem to imply that there are a finite number of angles from which attack is most likely, the weapon could be limited in angular range to those angles.

I'm sure that piloting an aircraft while trying to avoid being shot is difficult enough, so I wouldn't assume that such a system would be of much help on a single-seat aircraft. However, in a dogfight presumably the ROI or navigator could operate the guns while the pilot does the aviation.

If your opponent is directly behind you, you have lost the fight. The point of basic fighter maneuvering, or BFM, is to keep your opponent off your tail and hopefully get on his. Everything you would learn as a fighter pilot centers around ensuring you would never have to use a rear-firing weapon.

In addition, visibility directly behind the pilot is typically poor; humans can't turn our heads 180 degrees, and if we could we'd be staring at the headrest behind us. A few fighters have had rear-view mirrors, typically ones with a two-piece canopy including the Eurofighter, F-15C and F-14 among others, but the one-piece bubble canopy on fighters like the F-16 and F-22 give no good place to put a mirror that wouldn't further interfere with the pilot's forward vision. Rear-view cameras would be laughed at by pilots as a waste of an MFD.

A cannon firing backward would also be a pretty single-purpose weapon; in a multirole fighter you might get a chance to use it to add insult to injury when pulling out of a ground run, but in all likelihood you'll either have peeled off to one side as soon as you pickled your bombs, or you'll be toss-bombing and not even overfly the target. The only real reason you'd ever fire it would be to keep someone directly behind you on their toes.


How did Wilbur Wright create and use the formulas he mentions in his letter to Octave Chanute? In a letter written by Wilbur Wright and addressed to Octave Chanute, dated 1903/06/18, I have found two things that I do not quite understand.

  Our engine develops at the brake 15.6 horse power and we are convinced that this is very close to what we will be able to reach as a maximum. It furnishes in foot pounds at the brake, energy equivalent to 23 percent of the heat units
  contained in the fuel, so its efficiency is some twenty percent higher than the usual efficiency of gasoline engines which ranges from 14 to 18 percent of the total power contained in the fuel.

How did the two brothers make such a revolutionary improvement?
Modern gasoline engines have a maximum thermal efficiency of about 25% to 30%. The Wright brother's motor had an efficiency of 23% in 1903.

  The Dumont motor may develop more than 10 horsepower but it is with me a case of seeing before believing. The screw of the airship was 4 meters in diameter and had a pitch of 4 meters, and the engine at 1200 revolutions (which is the speed of maximum power of motors of this size) drove it 200 turns per minute and gave a thrust of 154 to 165 lbs. Now if you multiply the thrust, by the pitch divided by the circumference of the screw, and multiply this by the travel per minute of the center of pressure (which is about 5/6 of the circumference of the screw) you will find that the result is about 10 horse power.”

It is evident that the Wrights used the relation:

Power = Thrust x (5/6) x pitch x (RPM/60 sec)

Where does this formula come from?

What exactly is that "center of pressure (which is about 5/6 of the circumference of the screw)"?

I do not have first-hand knowledge of this formula, so what I write below is speculation. But the Wrights used sound physical reasoning, and I will try do do the same.

Power in physics is the product of force and speed. The formula does indeed contain a force (thrust) and a speed (pitch times rotation speed) if the terms used by Wilbur are interpreted in a certain way. Pitch today is an angle, but I would think Wilbur meant with pitch what is termed distance D in the picture below.

Propeller advance ratio (picture source)

This is consistent with his earlier sentence where he gives a length for the term pitch. The term pitch * RPM/60 is actually the flight speed in m/s.

Now to the term 5/6: I would expect that Wilbur calculated the pitch from the incidence of his propeller. Since the propeller blade needs some angle of attack to produce thrust, the actual distance traveled through air is a little smaller than what Wilbur got. Therefore, I think the term 5/6 accounts for that slippage and had been determined empirically.

Now for the revolutionary increase in efficiency: I do not know what engines Wilbur used for comparison, but the low number he cites suggests that he used exceptionally poor specimens .


How can I determine the quality of training provided by a CFI at a local flying club? I'm considering getting a private pilot license, but considering that it is more dangerous than driving a car (with pilot error being a large factor of that), I want to make sure I train with a CFI and aircraft that are safe, and also ensure that I learn the habits necessary to become a safe pilot.

Are there any objective (or fairly reliable subjective) ways to determine the quality of training provided by CFI at a local flying club?

Jeff, I really appreciate that you ask for safety before asking for the price. Unfortunately it takes some experience and time at a school to say if the equipment and teaching methods are safe or not, but I'll try my best to provide you with some of my insights into flight training.

I personally tend to the bigger flight schools. Having a strict training concept and standardized methods is a huge benefit in safety. If the same teachers also do more advanced training like IR or MEP your PPL training will most probably also be more intense. Your training should concentrate on learning to fly not flying the nicest routes but of course you should also enjoy your time. That's why you should of course also have a look at the people who are there. They should not only be friendly, but also be professional and well organised. The most annoying thing during flight training is bad organization and the changing of schedules due to absolutely avoidable reasons.

Good maintenance is key for safety. Here again, a big flight school that can do it's own maintenance has a lot of advantages. Often it happens that there are minor problems which should be fixed before the next flight without being a big safety hazard. It's better to squawk this and wait ten minutes until maintenance has fixed it, rather then flying without having it fixed, or cancelling the lesson. If the flight school has its own maintenance and they are happy with their work they will tell you and also show you around. Honestly the only thing you can do is to look if the hangar looks clean and tidy. If you decide for a smaller school without its own maintenance, it should at least be done at the same airport. Otherwise this could cause regular delays in your training.

Also think of yourself. During your solos and later when having your license you are allowed to and you will fly alone without an instructor. Be motivated to learn more than you have to. Know your aircraft and ask your questions. RTFM should not be the general answer of your flight school but you should spend some time doing it.

I made a list with all my questions before visiting different flight school so I don't forget to ask them. I would sugest you to do the same before getting there. If you for example ask for some more detailed information how many flight time you have to do with an instructor before flying solo and what exercises and maybe progress checks you'll have to do prior to it, you'll get a good insight how structured the flight training is. Also don't forget to ask about the theoretical part. That's really dependent on your self if you prefer to learn with books or with a teacher in front of you.


Why is thrust said to be constant over speed for a jet engine? I'm just interested in some basic facts regarding flight. On reading the rather "low level" book "Understanding Flight, David F. Anderson, Scott Eberhardt), I recently came up to the following diagram:

Why is thrust approximately constant with speed for a jet engine? Everything gets mixed up in my head as follows:
Thrust is approximately $F_t=\dot m \cdot \left( v_{gas}-v_a\right) $, where the speeds are outlet speed on the nozzle and true airspeed, respectively.
https://en.wikipedia.org/wiki/Turbojet#Net_thrust
So there are really a lot of parameters. What of them are assumed to kept constant in the right diagram and what are changing? Without that information, the diagram seems meaningless for me. For my naïve opinion, a change of thrust is controlled by changing the thrust lever and thereby changing the fuel content within the combustion chamber. Lets say the lever is at its max or a fixed position (whatever this means). Then while increasing speed the factor $v_{gas}-v_a$ gets smaller, assuming the outlet speed is constant.
So to have still the same thrust there are three possibilities':

outlet speed increases
mass stream increases
both of them increase

I can imagine that mass stream increases "somehow" with airspeed (keeping fuel injection constant), so there might be some cancellation of the speed factor. .But is this the whole story? Why is it canceling completely?
On writing this question another question arises:
Considering an ideal engine without losses, total power is
$P_{tot} = \frac{1}{2} \dot m \cdot (v_{gas}^2-v_a^2) = \frac{1}{2} \dot m \cdot (v_{gas}-v_a)(v_{gas}+v_a) = \frac{F_t}{2}\cdot (v_{gas}+v_a)$
Lets say, the power lever is on a fixed position. Is this position an indicator for the total power of the engine? In other words: is total power to the engine constant, when the lever is on a fixed position? I ask, because when assuming constant thrust this formula would mean, that total power (as well as propulsive power) must also increase, because at higher TAS of the plane, gas outlet speed would (up to my poor understanding) rather increase instead of decrease. So what happens, when the thrust lever is on a fixed position? Could it be, that there is a governor behind, taking control of thrust? In this case the right picture has no meaning at all, because while increasing TAS the governor automatically injects more fuel.
There are so many questions and in fact no understanding of anything...

There are several effects which in combination make constant thrust a good approximation at subsonic speed.
Thrust is created by accelerating a working mass in opposite direction. Net thrust is the difference between the impulse of the air flowing towards the engine and the combined impulse of burnt fuel and the air exiting the engine (and propeller, if one is fitted), derived after the time. Since that impulse is the product of mass and speed, you can either accelerate a large mass by a small speed difference, like a propeller does, or a small mass by a large speed difference, like a turbojet does.
When flying faster, the entry impulse of a propeller quickly grows large relative to the exit impulse, so thrust goes down with the inverse of speed. On the other hand, the high exit speed of a turbojet results only in a small increase of the entry impulse relative to the exit impulse while speed increases.
But if that were all, even the thrust of a turbojet engine would drop when speed increases. But there is a second effect which helps to let thrust grow with speed. With the square of speed, to be precise. That is the ram effect which helps to precompress the air entering the engine. At subsonic speed, this just about compensates for the loss of thrust: At low speed, the growing entry impulse lets thrust drop a bit but at higher subsonic speed the ram effect becomes larger and raises thrust again, such that a constant thrust becomes a good approximation. However, at supersonic speed the ram effect becomes dominant and thrust grows with speed squared – until the absolute internal pressure becomes too high so the engine must be throttled (or the aircraft needs to fly higher) or the shock losses in the intake become too large and thrust drops again.


Why is 51,000 ft a common service ceiling for business jets? According to this article on aerospace-technology.com, many of the larger business jets seem to have a service ceiling of 51,000 feet. Other sources verify this trend.

What is the reason for this, if anything specific can be named? Some possibilities that I came up with are:

engineering considerations (limitations of materials, pressurization, systems capabilities etc.)
safety, i.e. time of usefull consciousness getting too short higher up (being less than 10 s @ 50,000ft)
too little to be gained going higher (no congestion anymore at that alt anyway)
an industry agreement (based on any of previous and/or other factors), in the same manner as european automakers' pact to limit the max speed of cars to 250km/h (excluding some model)
regulatory factors

Other common "steps" appear to be 45,000 ft and 41,000, with smaller models. Nice round numbers all, but surely there has to be some reason for the magical 51,000 ft figure. Interestingly, the Learjet 85 was designed to have a service ceiling of "only" 49,000 ft, and the program got cancelled at least partially due to poor sales. It seems it was simply lacking the last 2000 ft...

Examples of business jets with 51000ft service ceiling:

Cessna Citation X

Falcon 7X, 8X

Global  5000, 6000 and 7500

Gulfstream G550, G600, G650 ER

Learjet 40, 45, 60, 70/75

etc...

If for no other reason, its likely because there is a practical maximum descent speed for a given airframe and aircraft must be able to descend from their maximum cruising altitude to 10,000 ft. in 10 minutes or less. Although under part 135 (how many of these planes are likely flown) the regulations have a few variations you can have less oxygen on board if you can descend in 4 minutes.

At 51,000 ft. you would need to lose 41,000 ft in 10 minutes or even 4 minutes. That is a descent rate of either 4100 ft/min or a blistering 10,250 ft/min which likely yields a speed at or near Vne for most of these airframes.

This Gulfstream pilot discusses a bit of it from a practical standpoint here.


Why is the PIC position for helicopters the right seat, rather than the left seat as in airplanes? So far as I am aware, in a fixed wing aircraft having side-by-side seating and  dual controls but only a single set of instruments, those instruments are always positioned in front of the left seat. Even when an aircraft (such as commercial air transport) is fitted with dual instruments, the left seat is designated as the "pilot-in-command" or "captain's" position. This "left-seat as principal" designation appears to hold true for any fixed wing aircraft from a Cessna 152 to a Boeing 747, in all jurisdictions of manufacture and operation.

For a helicopter, the situation appears to be reversed - the "pilot in command" appears to always occupy the right seat.

Is this true, always, or is it an observational bias? Is this simply convention or is it specified by regulation? What would account for exceptions, if any?

The reason is both historical and operational.

The first mass produced helicopter was the Sikorsky R-4.  It had a single collective located between the two pilot seats, so by necessity, the person on the right would control the cyclic with their right hand, and the person on the left would control the cyclic with their left (because their right is needed on the collective).  The cyclic in the R-4 was very difficult to manipulate and required a lot of strength and coordination.  Since the vast majority of student helicopter pilots were right handed, they sat in the right seat, allowing them to use their dominant hand on the cyclic.  Thus, the first generation of helicopter pilots all sat in the right seat, since they all learned on the R-4 (or the R-6).  That's how traditions begin.

The operational applications of sitting in the right seat relate to the inherent instability of a helicopter. A helicopter pilot rarely wants to let go of the cyclic, as it often requires continuous control inputs, especially when hovering. The collective, on the other hand, does not need to be monitored as closely and can be held steady with a friction adjustment, so that hand is occasionally free to manipulate things like radios and other equipment, which are located in the center of the cockpit.

Most helicopters these days have a collective for each seat, located on the left, so the pilot wants to use the hand in the middle of the cockpit to work the radios and things.  Hence, they sit on the right side, which places the collective hand in the middle of the cockpit.

You can read a longer article about this: Why do helicopter pilots sit in the right seat?


Which engine type requires the shortest take-off run: a turboprop or a turbofan? If two fixed-wing aircraft almost identical except for the engines, one turbofan and one turboprop, which one would need less runway to take off?

Even with similar weight, turboprop and turbofan aircraft will have different design characteristics. A turboprop will fly at lower altitudes and airspeeds, resulting in different aerodynamic designs. A turboprop also burns less fuel per hour, so it will need less fuel capacity.

That being said, we can look at some aircraft to get an idea of what the trends might be. The best example is probably the Dornier 328. It's a turboprop aircraft that seats about 30 passengers. There also happens to be a version of the plane with jet engines. This is probably about as similar as you can get in both weight and aerodynamics. According to Skybrary, the figures are as follows:

Dornier 328
MTOW 13990 kg
Distance 1000 m

Dornier 328JET
MTOW 15200 kg
Distance 1382 m

You can see the the jet derivative is a bit heavier but requires a much longer takeoff distance.

The trend is similar between other aircraft.

Dash 8-300 Turboprop
MTOW 18600 kg
Distance 1085 m

ERJ-135 Jet
MTOW 20000 kg
Distance 1580 m

CRJ-200 Jet
MTOW 21523 kg
Distance 1527 m


Can the acting PIC sit in the back? For a planned ferry flight under FAA Part 91, this is the scenario:

Two of us, let's call us A and B (rated pilots for that airplane), want to sit in front and do the flying.
A highly experienced pilot, C, will accompany and supervise the flight, sitting in the back seat.

Insurance insists that C be acting PIC throughout the flight.
At the same time, insurance has explicitly said that C can sit in the back while doing so.

This doesn't accord with C's own understanding of what is legal in an airplane that only requires one crew member. My own reading of who can be PIC doesn't say anything about where in the plane they have to sit.
So the question is: Can someone act as PIC while sitting in the back seat in a single-pilot airplane?
Relatedly, if the answer to the above is Yes:

Suppose B is a CFI
A manipulates the controls.
Can all 3 pilots log PIC time?

A is sole manipulator of the controls;
B provides instruction;
C is acting PIC?

Can the acting PIC sit in the rear seat?
There's no regulation or FAA interpretation I can find that requires the acting PIC to sit in a seat with access to the controls. For flight instruction specifically, 14 CFR 91.109(a) requires dual controls (usually) and the instructor must be at a "pilot station" (14 CFR 61.195(g)(2) and Williams interpretation, 2018). So no instructing from the rear seat.
Of course there's also 91.13 (careless and reckless operation). That's a deliberately broad regulation and I have no idea how risky your operation might be considered. If A and B already have experience in the aircraft and they'd be fine to fly it without C anyway (from the FAA's point of view), then arguably there's nothing careless or reckless happening. On the other hand, if something goes wrong and lawyers get involved to determine liability then it's anyone's guess what could happen.
Can all three pilots log PIC time?

A: yes, as sole manipulator of the controls (61.51(e)(1)(i))
B: yes, if they're giving instruction (61.51(e)(4)). That means A and B need to log it as instruction time in their respective logbooks (61.51(h)); they can't just say "let's call this instruction so we can both log PIC".
C: no, acting as PIC doesn't automatically allow you to log PIC time. 61.51(e)(1)(iii) doesn't seem to apply here because in your scenario neither the aircraft type nor the operation require a second pilot


What's the difference between Free-Flight and Free-Route? I have been reading documents about the concepts of Free-Flight and Free-Route that are being implemented (or being simulated to be implemented in the future) in Europe since 2012 by the initiative Single European Sky, that aims to provide a safer and more efficient airspace.

I have noticed that the concept is similar but it is treated differently, and I am wondering what's the main difference between these two concepts. Also, is it a safe concept? (It involves more possible conflicts in the airspace, if not carefully implemented).

The difference is between the definition itself.

  Free Flight : Free flight is a developing air traffic control method that uses no centralized control (e.g. air traffic controllers). Instead, parts of airspace are reserved dynamically and automatically in a distributed way using computer communication to ensure the required separation between aircraft. This new system may be implemented into the U.S. air traffic control system in the next decade.[citation needed] Its potential impact on the operations of the national airspace system is disputed, however.

This effectively means that, if a part of space is reserved for free flight, you can effectively do anything with your flight plan. Moreover this reserved space would change dynamically, so if there is an approaching aircraft nearby., your free flight space changes to accommodate free flight space for the other flight as well. Both of the planes would have DIFFERENT free flight space, and they can adjust their flight plan just in their own flight space. This eliminates the need for ATC completely.

  Free Route Airspace : Free Route Airspace (FRA) is a specified airspace within which users may freely plan a route between a defined entry point and a defined exit point. Subject to airspace availability, the route can be planned directly from one to the other or via intermediate (published or unpublished) way points, without reference to the ATS route network. Within this airspace, flights remain subject to air traffic control.

Here, the Airspace allotment remains under the control of the ATC, which allocates single space to multiple planes, and there one can decide which path to take. Here, inherently there is a possibility of overlapping routes (Because of the same airspace being allotted to multiple planes), and thats why, some routes are allowed in this space, and some are not.


How much does the swirl of engine exhaust affect aircraft performance? Most multi-engine aircraft have engines that rotate the same direction on both sides of the fuselage (e.g. the GEnx rotates clockwise, as viewed from the front, there is no 'mirrored' version).

What would the effect (drag, stability, turning performance) be, if an aircraft were to have oppositely-turning engines on each side of the aircraft (especially if the engines were rotating counter to the wingtip vortices)?

Note that propeller and jet engines may have significantly different answers!

More of a comment than a complete answer, but  the losses caused by swirl are not really on drag, stability, and turning performance. The swirl represents is a loss in total pressure in the axial direction, and so is a loss in shaft power extracted by the power turbine, or thrust provided by the engine if it’s a turbofan. This won’t reduce drag at the same aircraft velocity one iota, but does enable you to go faster if you reduce the swirl, due to the higher power (in a turboshaft) or thrust (in a turbofan). How much effect swirl has, I am not sure. I think it’s pretty small, because some engines have vanes at the turbine exit to remove, and others don’t bother, and instead choose to save the weight of these vanes.

Fairly obviously, extra power or thrust will help the vehicles turning performance, but I think it’s clearer to state this is due to extra power or thrust, rather than imply it’s a direct effect.


What is the relation of AIR BLEED IN message with the pack system on an Airbus A320? Before the power-up, if the pack switches are set to the ON position and the aircraft is powered up with the APU bleed off, is there a chance that the AIR BLEED IN maintenance message comes up on Lower ECAM page?

On A320, if the BLEED P/B are still pushed ON, it will not be a reason from the FWC to get a an error message on the ECAM in phase 1, 2 or 10 (Elec power, 1st Eng Start and 2nd eng shutdown) But you definitely will have the FAULT in amber on the P/B itself until there is bleed from APU or Engine coming up.


Force Balance in Wind Tunnel I am considering a model wing inside a wind tunnel supported from underneath from its center of mass.
Two load cells can be used, when properly oriented, to measure the lift force and the drag force. How can two load cells be arranged to also measure the pitching moment and specifically the constant aerodynamic moment I discussed in other threads?

Thank you!

I had imagined simply mounting your lift and drag sensors on a simple (HO gauge model railroad) track for a DIY homebuilt wind tunnel.

Pitching moments for your wing could be done as a separate experiment.  Your could pivot on your aerodynamic center (as an axle) and measure pitching torque moments with the load cell attached to the end of the fuselage.  Once these moments are established, you can then design the H stab based on area and distance from your wing.  Ideally, the H stab will keep your pitching moments zero through all angles of attack (including stall), leaving pitch control to the pilot (with the elevator).

Similar study can be done with you center of pressure (center of all lifts), once you establish it in your planform design.


How does an aircraft derive winds aloft on its own? The G1000 has a feature where it can put up a winds aloft arrow/speed in the PFD.  I've been sort of wondering how exactly this is determined.  My guess is that the aircraft (or the G1000) knows your airspeed via the pitot/static system and heading via the fluxgate/mag compass.  Then, it uses your GPS position to figure out where you should be every X seconds given the airspeed and heading.  Any difference must be attributable to winds aloft.  Does this make sense?

Yes, you are correct. You need three pieces of information:

airspeed
true compass heading (considering magnetic variation)
multiple absolute position fixes (eg. from gps)

The aircraft heading has to be measured by a compass within the aircraft (it can't be derived from the gps track), and the gps position can be used to look up the local magnetic variation. The difference between the speed/heading and the ground track (in straight and level flight, anyway) is attributable to winds aloft.


What are the flying accommodations in Silicon Valley for private pilots? What are the flying accommodations in Silicon Valley for private pilots? I notice there are two pretty sizable airports: Moffett Airfield and Mineta San Jose. Do both accept GA flights and have landing fees below $50?

What about instruction? Where do pilots generally go for instruction in the San Jose-Palo Alto area?

Moffett Field is still primarily a Federal airfield. They'll take some corporate jets, but not GA, and prior permission is required. All requests go through Planetary Ventures LLC, which owned by Google.

San Jose is a large international airport, but it appears to have no landing fee, though you'll pay a ramp fee unless it's waived. Some AirNav reviews of the FBO give you an idea of what to expect, and you could contact them for further information.

There are a number of GA airports to choose from though. Including:

Reid-Hillview
Palo Alto
San Carlos

All of these airports have flying clubs and should offer instruction.

Along with others somewhat further away (a few examples include Half Moon Bay to the Northwest, San Martin to the south, Hayward Executive and Oakland International to the east), depending on where exactly you'd like to be.