If "all flying rudders" for LSA aircraft need up to 40% less area, what about "all flying elevators (stabilators)"? If "all flying rudders" for LSA aircraft need 33%-40% less area than a typical vertical tail (stabilizer and rudder) ( subject to final stability analysis), what about "all flying elevators" (stabilators) with:

anti-servo trim tab?
no anti-servo trim tab?

I understand anti-servo tabs add stability to "all flying rudders/elevators" by auto-centering.
According to a design guide from Zenith: Flying on Your Own Wings, by Chris Heintz, pg 229:

The vertical tail area should be 12 to 15% of the wing area (15% if the rear fuselage has a small rounded section, and 12% if the rear fuselage has large flat sides). These percentages may be reduced to 7% and 10% for an "all flying rudder".

A wing is a wing, no matter what attitude, whether it be horizontal or vertical. So I should be able to reduce my horizontal tail area by roughly 33-40% when using only a "all flying elevator" (stabilator) (subject to final stability analysis).  Is this correct?
My personal view is that a Zenith can fly a lot slower with an all flying rudder, 39 mph or slower, and that is why Heintz recommends that based on the type of aircraft he manufactures: basically LSA types, @ 1320 lbs MTOW, 39-4 5mph stall speed. Somewhere I read that a Zenith 701 won a STOL competition in Australia with a 25' takeoff, and  that a 3 second takeoff is common and by the time you reach full throttle, you're aloft albeit still in ground effect.
I understand the Zenith CH200 had a classic vertical tail, but that most or all current designs use an all flying rudder.
Summary:
So I assume that Heinz's above recommendation is for sizing a rudder at a 39mph stall speed which would need to be bigger for slow speed handling than for a plane that stalls at 60mph.
Revised question: at 39 mph would an "all flying" elevator be more efficient, thus letting it be 33% to 40% smaller?

Zenith gets away with the little All Flying Rudder without an anti-servo tab because the fuselage itself is used to provide sufficient fixed fin area for acceptable passive weathervaning. If you look at their designs they all have slab sided fuselages that are quite deep all the way back.  So there is a kind of "fin" with the rudder; it's just built into the fuselage.  I got to fly the Zenith 750 demonstrator once in Mexico Missouri and I recall that its yaw stability was perfectly acceptable even though the rudder just wanted to trail if if left it to do its own thing.

Horizontal tails have more work to do and horizontal surface area of the fuselage aft won't cut it without a fixed stabilizer surface; unless you use a stabilator/anti-servo tab. If you wanted to use an all-flying surface without an anti-servo tab, you have to have a means to "fix" the surface to provide stick free static stability.  If you're in an F-86, the all flying tail is hydraulically powered and can be fixed easily with a bungee that controls where the hydraulics wants to center the surface when you're not applying force.  Some gliders use all flying tails with no tabs of any kind, and they depend on bungee springs in the pitch control circuit to provide a tendency of the surface to want to hold a certain angle if you aren't hanging on to it.

You could design your ultralight with an all flying tail with no anti-servo tab by using a fairly stiff spring bungee as your "stick free" stabilization device, and for trim. You may find the anti-servo tab method provides better handling characteristics however and if it was me I would go that way.

Note that airplanes sometimes use bungee springs in the rudder control circuit to provide a passive centering force that has the effect of increasing the fin area to improve passive weathervaning. Cessna 180/185s do this to improve yaw stability so that when fitted with floats they don't need extra ventral fins.  Problem is, it makes the rudder unpleasantly heavy.


Does low pressure induces high velocity or high velocity induces low pressure? Does low pressure induces high velocity or high velocity induces low pressure? I am wandering what is the cause and what is the result. I mean i.e. Bernoulli principle or situation in the core of a vortex.

Neither! The cause is wing moving through the air, and the effect is a fairly complex flow pattern around it that produces lift (and wake vortex).
We know that the flow obeys certain laws (that are largely averaging of the microscopic laws governing individual molecules). One of them is law of conservation of energy, which for fluids is known as Bernoulli's equation. But that's just one equation with many free variables, so alone it is not enough to explain anything. You need the complete set of Navier-Stokes equations to be able to describe the flow.
The equations are partially differential, and need to be evaluated for every point in space and time, which can only be done approximately and requires a computer.
There is only a few conclusions that can be made using conservation laws without this, the most important probably is the existence of downwash. The third law of motion tells us that if upward force, lift, is applied to the wing, downward force is applied to the air, and second law of motion tells us that this force accelerates the air downward. The boundary between downward moving air behind the wing and the still air outside the span is the wake vortex.
But again, neither is cause and effect. The laws of physics work both ways. They just tell us that these phenomena always occur together. But the cause is the situation. We just know that both or neither will occur.


why do wings have high aspect ratios on commercial airliners? On the Boeing 777x they have made the wing span large to increase area and therefore lift. why don't they change the aspect ratio so that the wings don't have to be that long but maintain the same area and therefore lift? this would mean there is no need for the hinge and therefore less complex. Wouldn't this also mean the wings are less of a lever so less force so their could be lighter (proportionally less strong) joint to the plane? To be clear I am not talking about a blende wing body. The wing would be no thicker than normal. Is there a name for this?

Aerodynamically, you want the aspect ratio to be as high as it can be (for a given wing area). You want infinite wingspan, because that results in no induced drag. But that is not very practical at airports, and a bit heavy.

Structurally, you want short stubby wings because they have a very low bending moment. In fact structurally, you want zero wing span. But that is not very practical at take-off time.

As always, aerodynamic desirability implies structural objections, and vice versa. The aerodynamicists need to strike a deal with the structures engineers: a balance needs to be found. As long a wing span as possible, with as thick a profile as possible, using a material that is as light as possible. So a long wingspan is desirable and is only limited by structural constraints: as you say, at a certain point the longer wing span's increased weight will offset any aerodynamic advantages.

In aluminium, the optimum was reached over the course of a few decades. But now there is a new material with a better strength/weight ratio: composite carbon fibre. Carbon is much stronger than aluminium, and it is woven in a matrix of resin, with most wires running in the direction of highest stress. With carbon fibre, even the direction of material strength can be optimised. And the B787 and A350 have even higher aspect ratios than the B777.


What is the upper deck on converted freighter long-hump 747s used for? All 747s1 have an upper deck directly behind the elevated cockpit, a legacy of the 747’s genesis as a design for a strategic-airlifter competition (the upper deck and elevated cockpit were partly to allow the use of a swing-up nose for easier cargo loading without having to disconnect and reconnect all the wiring and control cables and whatnot every time the nose was opened, and partly to keep the main-deck cargo from crushing the flightcrew in the event of an accident);2 this gives the 747 its distinctive hump and unmistakeable silhouette.  There are two 747-upper-deck major versions:

The original-length, short upper deck, used on almost all first- and second-generation 747s (the 747-100, -200, and -SP) and on all 747s built as freighters, has one emergency exit per side, and the hump begins to taper down almost immediately; as a result, the rear end of the hump ends forward of the wings (except on the -SP, whose shorter fuselage brings the hump’s rump rearward over the wing roots, even with the original short hump).  On passenger aircraft, the upper deck was originally used for a first-class lounge, but was later replaced with a few extra rows of passenger seating; on freighters, it contains a few rows of seats for crew rest and carriage of supplementary/supernumerary crew, cargo-handling personnel, and nonrevenue passengers.
The later, stretched upper deck, available as an option on the very last passenger -100s and late-model passenger -200s, and used on all -300s3 and passenger -400s and -8s,4 has two exits per side, and produces a hump that extends well back over the wing roots; it provides a considerable increase in passenger capacity for the 747s so equipped.

As even relatively-new 747s become increasingly uneconomical to operate as passenger aircraft in a world of rising fuel prices and big, efficient, ETOPS-300+-certified twinjets, many long-hump 747s are being converted for freighter service; the conversion process for these aircraft (known as Boeing Converted Freighter, or BCF, 747s) involves stripping out the main-deck seating (and ancillaries like lavatories, galleys, overhead bins, etc.) for cargo rails and tiedowns and cutting main-deck cargo doors into the fuselage.  It does not, however, involve cutting the upper fuselage down to a short-hump configuration (which would be a far more involved piece of surgery than the other BCF modifications), and, as such, leaves the BCF aircraft with an upper deck that is all wrong for its new role; it can’t be used for large, containerised cargo á la the main-deck and lower-lobe5 compartments (the upper-deck fuselage profile doesn’t leave enough space, and there’s no upper-deck cargo door), and, yet, it’s far too large for carrying any reasonable amount of supernumeraries, cargo-handlers, or would-be jumpseaters.

What do operators of long-hump 747-BCFs do with the upper deck?  Do they leave the seats in, on the off chance that they have to transport something that requires a LOT of handlers/escorts/whatnot?  Use it for small bulk cargo (mail, parcels, checked baggage that didn’t make its owners’ flights, etc.)?  Tear out everything but the front few seats and just haul it around empty?

1: ...well, except for these ones, but those are a very special case.

2: The proto-747 lost out to the Lockheed C-5, which has a full-length upper deck used for personnel transportation.

3: The -300 had no dedicated freighter version, although many passenger -300s were eventually converted to carry freight.

4: The -8’s upper deck is slightly longer than that used on earlier long-hump 747s, due to the 747-8’s stretched fuselage.

5: The space (divided by the wing centre box into separate forward and aft compartments) below the main-deck floor, which, in the aircraft’s previous passenger-carrying life, was known simply as the “cargo hold”.

They have seats for couriers, same as factory freighters, but roomier.

Note: From the -400BCF type certificate:

  There are no provisions for the carriage of passengers. A maximum of 19 couriers can occupy the aft cabin of the upper deck as defined in AFM.

  Source: airplane-pictures.net

Above is the upper deck of a -400BCF (converted freighter).

And below on the left is an -8F. Also, note the foldable yellow ladder for access to/from the main deck.

  Sources: left: pbase.com; right: pinterest.com (original source unknown)


Is the shape of the Bell X-1 wing on Virgin Galactic's VSS Unity's artwork correct? This answer to the Space SE question What do these patterns on Virgin Galactic's VSS Unity represent, and how are they applied? indicates that one of the aerospacecraft representations on the Unity is the Bell X-1, and comments there suggest that the shape of the wing might not be completely accurate.

It may be possible that the shape evolved during development, but I'd like to ask;
What is the shape of the Bell X-1 wing, and is the representation of it in the artwork on Virgin Galactic's VSS Unity correct?

above: Screen shot from the Virgin Galactic YouTube video VSS Unity | Third Rocket Powered Flight.

above: from this answer and Virgin Galactic.

According to this NACA (now NASA) Technical Report [Wing Loads on the Bell X-1 Research Airplane (10 Percent Thick Wing) as Determined by Pressure-distribution Measurements in Flight at Subsonic and Transonic Speeds], the wings look a bit different to the one used by Virgin.

But there might be different versions of the wing, since there were multiple versions of the X-1.

The wikipedia article shows yet another wing geometry.

Below is a composition of 3 different drawings I found via google, which show that at least there exist various different drawings of the wing


On Airbus aircraft, can the pilot control the aircraft when the autopilot is active? I am looking at the schematics of computerized control for Aibus aircraft and I do not understand the relation between the various control law and the autopilot.

Under "normal law" can the pilot control the aircraft while the autopilot is engaged, or will control input from the pilot disconnect the autopilot automatically?

What is the meaning of "alternate law" for the autopilot? Will the autopilot be disconnected when shifting to alternate law?

Moving the flight controls above a certain threshold will disconnect the autopilot.
From the A320 FCOM (1.22.30 Auto Flight - Flight Guidance, emphasis mine):

AP DISENGAGEMENT
AP1 or 2 disengages when:

The pilot presses the takeover pushbutton on the sidestick.
The pilot presses the corresponding AP pushbutton on the FCU.
The pilot pushes on the sidestick harder than a certain threshold or moves on the rudder pedals above a threshold.
The pilot moves the pitch trim wheel beyond a certain threshold.
The other AP is engaged, except when localizer/glideslope modes are armed or engaged, or when the rollout or go-around mode is engaged.
Both thrust levers are set above the MCT detent and the aircraft is on the ground.
The aircraft reaches the MDA-50 feet (MDH-50 feet), or 400 feet AGL if not MDA/MDH, with APPR mode engaged and a non-ILS approach selected.
One of the engagement conditions is lost.

Furthermore, in normal law with all protections available, the AP will disconnect if:

High speed protection is active;
Angle-of-attack protection is active (α prot +1° is reached);
Pitch attitude exceeds 25° up, or 13° down, or bank angle exceeds 45°;
A rudder pedal deflection is more than 10° out of trim.

The different control laws act in the F/CTL COMPUTER in the following diagram:

(source: FCOM 1.27.10 Flight Controls - Description)
They are independent of the autopilot and the protections are available regardless of whether or not the autopilot is engaged.


Why has the rest of the world gone after delta wings while not the USA? JAS Gripen, Eurofighter, HAL Tejas, Mirages, all are delta winged fighter jets.

We don't see any delta-winged fighter jets in the US inventory.

Why is that difference?

The Gripen and Eurofighter are canards with a delta wing (as is the J-37 Viggen). This, coupled with relaxed stability, gives the first two unmatched maneuverability, and good transsonic and short-field performance. While the Viggen is a stable design, it too has very good short-field performance.

The Mirage III (and the F-102, F-106, B-58, J-35 Draken and Concorde) were first-generation Deltas from the mid-1950s which were optimized for supersonic speed. By using a highly swept delta wing, low supersonic drag could be combined with short take-off and landing distances.

So it is not true that the US "never went after delta wings"; they just outgrew that configuration when they shifted their priorities away from high supersonic performance.

Note that the more modern Mirage F1 is an unstable conventional configuration while the last Dassault design is also an unstable canard.

Regarding the Tejas: It is designed for the specific requirements of the Indian Air Force. One of the unusual design requirements was the low vulnerability to bird strikes, because Indian airfields have a high birdstrike rate. Therefore, no leading edge devices were allowed, and to give the Tejas still a respectable short-field performance, a delta wing was the best choice. Full disclosure: This was actually the requirement which led to the LCA having a delta wing, and the Tejas, which resulted from the LCA, does have leading edge flaps after all.


What does BUS mean in the startup procedure? I noticed the term BUS in the startup procedure of a 737. What do BUS on, off and transfer mean and what is their significance?

A bus is a strong connection that distributes current. It's not limited to the conductive part, it is usually understood as including the switches and relays that manage its connection to the rest of the wiring.

(Keep in mind that with AC, when two different sources are used to feed the same component, frequency and phase need to be adjusted and must coincide, else energy would be lost, and voltage increased / decreased, possibly to a dangerous level.)

The transfer buses in that case have a logic detecting multiple current sources, e.g. battery and ground supply, and selecting which one to use to feed the bus. The crew has some authority on this process, using switches:

(Source)

There is one transfer bus on each side of the aircraft. They feed other buses, like galley and main buses, with energy, typically from the engine generators.

They are connected by the tie bus (between BTB1 and 2 on the image, it's name doesn't appear), for redundancy purposes.

Boeing 737 NG, modified (source)

Before the two engines are running (and their generator supplies current), the tie bus allows the ground power, or the APU, or a single engine to feed the whole aircraft.

Transfer buses can be disconnected from the tie bus for normal use, each engine generator providing energy to different smaller buses, creating a redundancy.

If one source fails, the other can feed the whole aircraft by connecting the tie bus. Another connection can be used on the DC part (cross-bus tie relay). This mode is useful and required when performing an approach with the autopilot (e.g. ILS cat III).

Conversely if one transfer bus creates a security problem, it can be switched off.


Why isn't runway 4L/22R at KMDW available as an emergency runway? Chicago-Midway (MDW/KMDW) has five runways, oriented along the diagonals of the square airport.  The longest two (13C/31C [1988 x 46 m] and 4R/22L [1964 x 46 m]) are ILS-equipped, and serve as the airport's primary air carrier runways; the other three (4L/22R, 13L/31R, and 13R/31L) are used primarily for small general-aviation operations.  Of the three, 13L/31R and 13R/31L are available for use by larger aircraft in case of emergency:

  Chicago Midway International Airport covers just over one square mile (650 acres or 260 hectares) [...] and has five runways: [...]

  13C/31C: 6,522 ft × 150 ft (1,988 m × 46 m), air carrier runway, ILS-equipped.
  4R/22L: 6,445 ft × 150 ft (1,964 m × 46 m), air carrier runway, ILS-equipped.
  4L/22R: 5,507 ft × 150 ft (1,679 m × 46 m), general aviation and air taxi.
  13L/31R: 5,141 ft × 150 ft (1,567 m × 46 m), general aviation and air taxi. Used as an Emergency Runway for commercial aircraft.
  13R/31L: 3,859 ft × 60 ft (1,176 m × 18 m), light aircraft only. Used as an Emergency Runway for commercial aircraft.

4L/22R, however, is apparently not available for use by air carrier aircraft even in an emergency, despite being longer than either of the other two general-aviation runways (and also twice and half again as wide as 13R/31L, the smallest runway at the airport), and the only one of the three to be useable when the winds are blowing along a northeast-southwest axis (the two designated emergency runways are both oriented northwest-southeast).

Why are Midway's two smallest runways available as emergency runways for large aircraft, but not the larger 4L/22R?

EDIT: As @RonBeyer suggests in his comment, one potential reason a runway of sufficient size might be unuseable for large aircraft could be if its bearing strength were insufficient (such that the pavement could collapse under the weight of a heavily-loaded jetliner).  However, to hear it straight from the horse's mouth, 4L/22R is rated for aircraft imposing pavement loads of up to 30 short tons per single wheel, or 60 short tons per two-wheel bogie; although not up to the standards of the airport's two air carrier runways (each rated to 47.5 short tons per single wheel, 82.5 short tons per two-wheel bogie, or 125 short tons per four-wheel bogie) or emergency runway 13L/31R (rated to 40 short tons per single wheel, or 62.5 short tons per two-wheel bogie), it far surpasses the mediocre strength of runway 13R/31L, which is rated for a mere 6.25 short tons per single wheel... and is, nevertheless, a designated air-carrier emergency runway!

Prologue: the quote in the question is from Wikipedia, and the parts there that mention the designation to commercial aircraft emergencies have later been marked as "citation needed". Therefore, for as long as an authoritative source can not be verified, it might well be that in reality there is no such designation.

Actually, should the nature of the emergency require, any runway (or even taxiway) on any airport is available for any aircraft if the crew so wishes. Some more or less famous examples of such situations (Air Safety Network):

Air Canada flight 143 (The Gimli glider, fuel starvation)

United Airlines flight 232 (Sioux City, total loss of hydraulics)

Air Astana flight 1388 (Portugal, reversed aileron cables)

If you are out of fuel or experiencing severe control issues or something of such magnitude, regardless of what you are flying there is no way ATC is going to tell you "sorry you can't land on the 4L, turn to heading..."

This might seem like splitting hairs, but that's how it is. To state that some runway is (or is not) available for emergencies of a certain aircraft type, is somewhat of a moot point.

After you've spoken the three magic words, the ATC has to, and more importantly, they want to do everything they possibly can and more to help you out. You are finally free as a bird, if only you did't have an emergency to deal with...

Speaking of splitting hairs, Gimli glider did not land in an airport at all, but it's the most famous case of the sort...


Will dual-learning in a glider make my airplane learning safer? This question got me thinking, would attending gliding lessons at the same time as my airplane training make me safer in a small plane or microlight?

Yes learn both, but... not at the same time.  As Dave says, there are too many differences to be absorbing simultaneously.  It's like a new airline pilot taking a type course on a Dash 8 and an RJ at the same time.  It'll burn you out.

If all this is a hobby activity in the first place with no urgent time lines, drop the power training for now and go take a glider course.  When you have your glider license, resume the power course (in most jurisdictions you get a bit of credit you can apply to the power license).

Absolutely no question that a power pilot who learned to fly gliders first, and especially if they became proficient in soaring, will be a superior power pilot.  Without the engine there, you learn fine motor skills, control coordination, energy management and speed control, and the ways of the atmosphere, to a degree that a power student doesn't and simply can't.  It also helps to remove a lot of the terror at the thought of dealing with engine failures.  I learned power in 1975 and gliders in 1993, and wish I'd started on gliders first.

And you may just discover that soaring is the sport for you.  You have to try it and get into it, and experience the incredible rush of climbing at 500 fpm in a thermal without an engine, that you found by trolling the sky, or spotting a hawk and joining him (and seeing him just look at you and carry on as if you weren't there), that may be a struggle to stay in or may be an easy elevator ride, maybe for 30 minutes in the air or 4 hours. No two flights are ever the same.  The private owners at my club, on a good day, launch at noon or a little after, and come back at 3 or 4 or 5 pm.

Power flying is mostly enjoying operating a machine that takes you from A to B, or to go sight seeing, in really fun and novel way.  Soaring is flying as pure sport; a game you play with the atmosphere. Like sailing a catamaran times ten, vertically.  It may not be for you, but if you get into the game, it's like nothing else and it's worth going to find out.

Plus since you're aviating largely on solar energy and at non-profit clubs the instruction is free, it's somewhat cheaper lol.


Do autopilot headings consider the earth's shape? How do you set correct heading while cruising across latitudes?

On a flat map, point A might be to point B at, say, heading 060 (intentionally no cardinal headings taken for example, as they don't create this situation). But on a curved surface, like spherical earth, the heading doesn't remain constant- it keeps changing as you move away from or toward the equator, sending aircraft miles off-target over long distances, as a result of pole-bound spiraling of the path.

Is there a formula to determine the optimum heading at the outset (even though it may not 'seem' correct), thereby, reaching the desired point B on the globe at the end of the cruise?

Yes, almost all modern computer navigation systems take this into account.

The track between two points along the "spherical" earth is called the great-circle track. Except for a N/S heading (or a E/W heading at the equator), the heading will vary along the track. Ed Williams has compiled a formulary for great circle navigation here, mostly derived from the Haversine formula. The formula you are interested in is "Course between points" for calculating the initial heading to fly from point A to point B.


Are modern airliners still stressed-skin aircraft? Can modern airliners still be seen as stressed-skin aircraft?

i.e. is the skin, whether it be aluminium or composites, still an integral structural member of the airplane?

Yes, absolutely. The skin transfers shear stresses between the stringers or longerons which run lengthwise along the fuselage and transmit tensile or compressive stress. Cutouts and openings (for doors and windows) need special local reinforcements, so the reduced structure can still withstand the loads.

Equally, the wing skin is the main element for the transmission of torsional loads. In today's airliners, the spar is part of the skin, but the wing skin ahead and aft of it is also a part of the primary structure.

Generally, stress follows stiffness. When a structure is loaded, it will deform, and those parts which withstand deformation most will carry most of the load. In the end, all parts which have similar stiffness will carry loads in proportion to their cross section. Since most of an airliner's structure is made from aluminum, it has the same stiffness.

See this question for one example clearly showing fuselage skin deformation.


Has Jeppesen announced plans to stop supporting the Microsoft platform for Flight Deck Pro? I heard a rumor around the water cooler recently that Jeppesen plans to drop support for Microsoft and have continued development of Flight Deck Pro EFB software only available on Apple. Has anyone seen anything that could confirm or refute this?

Only 6 months ago Jeppesen announced a common interface for iOS 9 and Windows 10.
And why would they deliberately lose their airline customers that use Windows? The integrated Class 3 EFB's on Boeing planes for example, run Windows.

The open architecture of the EFB
Class 3 system will allow airlines
(or third-party suppliers) to develop
software for the Microsoft Windows
processor using a software development kit provided by Boeing and
Jeppesen.

Regarding the FliteDeck, only a couple of weeks ago:

ForeFlight and Jeppesen Announce Strategic Alliance
Jeppesen and ForeFlight will work together on a next-generation release of FliteDeck Pro for both iOS and Windows that will deliver a combination of the familiar capabilities in FliteDeck Pro and significant features and functionality from ForeFlight Mobile.


Why is a control surface that allows two sides of airflow better than those that allow one? For example, ailerons allow air to flow past both the top and bottom surfaces, which makes it more aerodynamic than speedbrakes. Also, plane rudders have air flowing on both sides, which is apparently mote efficient than a spoiler. Why does this happen?

For low drag, you want to minimize the surface changes presented to the air flow. Large changes in the surface will create turbulence and pressure changes that contribute to drag. Small changes will minimize these sources of drag.

When you move a control surface like an aileron or elevator, air is flowing past both sides of the airfoil. Although this changes the direction of the flow, which gives the control force as well as some drag, the air can still flow past both sides.

In the case of a spoiler, the air cannot flow past both sides. This increases the frontal area presented to the flow, and creates a low pressure area behind the deployed surface. Creating a low-pressure area behind an object is a big contributor to drag, which is why aerodynamic bodies tend to have a teardrop shape.

Spoilers on the wing also have the effect of reducing lift. By disrupting the smooth low-pressure flow over the upper surface of the wing, they reduce the effectiveness of the wing, effectively stalling the affected portion.

For an illustration of both principles in action, see this video of a speed brake on a Mooney. This shows how even a relatively small object, when disrupting the air flow, can add a significant amount of drag.


How and why can multiple people control the Boeing B-29? I am making a down-to-the-1/128th-inch (literally, to the 1/128th inch) model of the Boeing B-29 Superfortress in SketchUp. Starting from zero, I had to make the entire plane up, and to be honest it looks exactly like the real thing at this point. I went down to copying every detail in even the dials and switches and levers, and realized something.
I saw that the pilot can control each of the 4 engines independently. Now, that isn't exactly the problem. The problem, is that the Pilot, "Second Pilot", and Flight Engineer can all control each of the 4 engines. And I can't figure out how that's supposed to work! I mean, can the flight engineer just turn up the throttle whenever? But what if the Pilot is going to speed up so that he/she can reach a higher altitude, but the flight engineer doesn't know that and so he turns the throttle down to decrease engine heat because the cowl flaps are at max degrees for stable flight?
Then there's the issue: If the flight engineer turns the throttle down at the same time that the pilot turns it up, what will the engines do? And I doubt the pilot would speak his every move to the "Second Pilot" and the Flight Engineer to prevent a mix-up. So, does the Flight engineer have to literally request permission and state his/her reasoning to the Pilot before changing the throttle?
And then I thought some more, and realized that the "Second Pilot" also has a "steering wheel", which I know for a fact that other co-pilots have in other planes, but I never knew why. The Pilot can handle the plane's steering by himself/herself, can't they? And even if they couldn't, giving the "Second Pilot" a steering wheel too... well, I can't see how that fixes anything. And if the "Second Pilot" turns the steering wheel at the same time that the pilot does, what does the plane do?
Same thing for the pedals I realized that the Pilot and "Second Pilot" both have. It makes no sense. I get that the "Second Pilot" could take control of the plane if needed because of these duplicate control instruments, but what would happen if they were (accidentally) used a the same time as another? And I also don't get why the Flight Engineer would need to be able to change the throttle. The Flight Engineer literally sits in the opposite direction of the front windows, so it isn't like Boeing wanted the Flight Engineer to be able to fly the plane.
Any suggestions would be very helpful. And, sorry about the gigantic question.

In aircraft of this vintage, all the controls are mechanically interconnected.  If the left-hand pilot's control yoke/ wheel moves, so does the right-hand pilot's.  Likewise for the rudder pedals.  And if a pilot or the flight engineer moves a throttle lever, the other throttle lever for that engine will also move.
If several people are exerting different inputs on the same control, then-- "strongest man wins!"
But normally the crew would have an understanding, at any given time, as to which pilot would be flying the plane, and who (which pilot, or the flight engineer) would be controlling the throttles.  Standard protocols would be established, and reinforced via training.  Normally only one pilot would be "flying", i.e. handling the primary aerodynamic controls (aileron, elevators, and rudder, via the control wheel and the rudder pedals), at any given time.  Normally the flight engineer would handle the throttles on this aircraft, in accordance with whatever requests the pilot flying the plane made via the intercom.


Is the size of hail on the ground any indication of the winds and updrafts of a thunderstorm? Is there any rule of thumb or way to estimate the wind speeds or up and down drafts inside a storm by the size of hail that reaches the ground?

The October 2018 issue of AOPA's "Flight Training" magazine provided the following illustration and comments.

A 24mph updraft will form ~1/4" hail, while a 98mph updraft will form
4" hail.
Down drafts are usually about 1/2 the speed of the updraft
(due to a larger outer core area).
When a pilot encounters a
downdraft, expect an updraft twice the speed to soon follow.
The change will be a quick dramatic shear.
Only about 10% of thunderstorms produce hail.


When taxiing a taildragger across a kerb, is it best to cross straight-on or at an angle? The grass taxiways at my local aerodrome are sometimes crossed by hard surfaces. Where they cross, the levels don't quite match, so there's a bump as you cross: not quite a pavement kerb, but still a sudden change in surface height.

What's the best way to cross these safely? Crossing straight-on carries the risk that the mainwheels will both stick against the ledge, lifting your tail and in extreme cases maybe causing a prop strike; like trying to cycle up a kerb and going over the handlebars. Crossing at an angle makes sticking less likely, but it rolls the aircraft slightly, and in a low-wing airplane you risk touching a wing-tip.

What's the best way to balance these risks and safely cross the kerb?

The rule I was always taught is to cross any 'step' - up or down - at an angle with the elevator full back:

It minimizes the chance of a prop strike, which is much more expensive than a wingtip strike
When going 'up', you avoid having both wheels up against the step at the same time, which usually means you need a burst of power to get over it, which could lead to sudden acceleration and sharp braking
When going 'down' you avoid the aircraft dropping down suddenly, with the same risks of strikes or an increase in speed
Lifting the elevator reduces the chance of it striking

There may be some differences for specific aircraft types, but I've always followed that advice and never had a problem. I've also never seen an aircraft get close to a wingtip strike doing this, but I suppose it could happen if the step is large enough. Although in that case you might want to just find another taxi route.


What makes inertial guidance unsuitable for auto-land? Above shows the performance of a Lockheed Martin civilian landing system developed in the mid-90s. It works by using the weather radar in SAR mode to update the INS, and the final 100 ft are flown by inertial guidance only.

There was interest from American and European carriers, and certification was underway, the rest is unknown. (Rumor has it, an export-embargo was placed due to the sensitivity of the SAR technology.)

Why can't the inertial guidance on its own fly an automatic landing the last 200 ft, thereby saving the CAT II/III installment?

Flying the final 200 ft in 20-30 seconds should have a maximum worst case scenario error of 3-4 m on a 45-60 m wide runway. It should even be better with today's GPS-coupled INS.

The final update before lock-on can happen either via an ILS CAT I or GNSS/SBAS. With a cross-check against stored runway track heading and glide-path angle. Thus eliminating the need for the weather radar and the runway specific SAR data.

RE comments:

LM, as shown, has done it in 1996 for the last 100 ft. It was for civilian application.
Initialization/alignment is not required, just a position update/check.

Suitability for CAT III autoland requires much more than just accuracy. A big factor is system integrity which involves fault detection and alerting. Fault detection in autoland approved ILS/MLS/GLS receivers dual channel processing (command and monitor) with continuous cross-checking and required detection and alerting response times. In the multi-mode receivers (MMR) I've worked on, the monitor tripped if the two channels disagreed by more than 0.0065 DDM for a period of 350 milliseconds. Total time to alert has to be less than 1 second.

To my knowledge, as a result of that requirement GLS has not been approved for less than CAT I approaches as they have not been able to demonstrate the necessary integrity and time to alarm.

I don't know of any method for monitoring an INS system that would be able to meet the requirements. The FMS I work with is capable of detecting and excluding an IRU from the nav solution, but the tolerances are much larger than what would be required for approach and it requires much more than 1 second.

The best reference for what is needed is AC 120-28D. Section 5 covers the Airborne Equipment requirements.

Ultimately, it not only has to work, you have to be able to get it approved. That is not a trivial or inexpensive process, even with published standards. Doing something new, without industry standards, is significantly more difficult. Can you make a business case that would show a long term savings?


What would they call the US President's personal plane? Air Force One is called that because it is operated by the Air Force.  The President's personal helicopter is called Marine One because it is operated by the Marines.

What would the President's personal aircraft be called?

I'd expect Executive One:

  Executive One is the call sign designated for any United States civil aircraft when the President of the United States is on board.