Hot answers tagged

46

Yes, otherwise airplanes would be unable to go upwards into the sky.


42

Yes, a wing can (given sufficient forward speed and angle of attack) generate lift greater than the weight of the aircraft. As with any "unbalanced" force, this will result in an acceleration of the airplane in the direction of the lift, according to Newton's Second law. $$\mathbf F=m~\mathbf a$$ Please note, the entities in bold face are vector quantities....


41

Their primary wing feathers have an unusual structure incorporating a fringed, comblike leading-edge, which reduces wind noise. The wing feathers also have an overall softness or flexibility. The trailing-edge of the wing is also dominated by soft, fringed edges. Even the underwing lining (covert) feathers have an unusual softness that plays a role in ...


40

You can get negative load factors (g forces) in different ways than just flying upside down: Change in pitch: When you push on the control column, the pitch will start to decrease. Depending on how fast you do this, the load factor can even become negative from this. Some aircraft do this intentionally to reduce the g force to exactly zero: (image source: ...


37

In addition to quiet flyer's excellent answer: Owls have large wings in relation to their body size and weight. One might think that no, their bodies are quite large, but actually owls are kind of fluffy flying feather balls: what you percieve as their bodies, is mostly air. This leads to two things: Low wing loading. Their large wings do not need to ...


31

Actually, in aircraft construction tension is preferable to compression: aeroplanes are thin walled structures, and compression forces introduce buckling. In a low wing aircraft, the fuselage is pressing downwards on the top half of the wing, the bit that is under compression. In fact, quite complicated frame structure members are required for the fuselage/...


30

Stealth aircraft are built to reduce their observability in 3 main areas, with the goal of reducing the warning time an enemy has: radar optical and IR sound This is in order of detection range: Radar can find an aircraft potentially at hundreds of km, optical systems go to a few tens of km, and sound becomes a factor only when the aircraft is very near (...


30

The Auxiliary Power Unit (APU) exhaust (Source) The item 72 is what you are looking for and it is labelled "APU exhaust". The black residue is soot from incompletely burned fuel. The Eurofighter Typhoon can use its APU to start the main engine or to provide power when on the ground. From airvectors.net: The Eurofighter is also fitted with an auxiliary ...


26

Interestingly, I couldn't find an answer to this question on the website, but I've found an answer of Peter Kämpf on Quora. He brings forth the same arguments I wanted to mention, so I'll repeat them here. Elliptical wings are very good - aerodynamically. If you want to minimize induced drag for a given lift requirement, you end up with an elliptical wing. ...


22

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


19

I'm haven't flown them but am very familiar with them and the reflex wing controversy because I was interested in getting into the sport (I normally fly power and gliders). A reflex wing when in "reflex mode" offloads the aft part of the wing and shifts the pressure distribution forward. Effectively, the rear part of the wing is being allowed to "trail", ...


18

Furthermore to @Zeiss' answer, whenever an aircraft is steady-state banked, the lift will be greater than its weight. However, its speed will be constant; instead, the acceleration is centripetal and results in a circular turn. Edit, clarification on pull up maneuver: When an aircraft is pitched up via pitch control, and after the short-period mode settles ...


17

I can give you two theories. One is it's a very very mild case of "overcontrolling" of the autopilot roll servo as it chases a perfectly wings level condition and continuously applies a teeny bit too much left, ooops, then a teeny bit too much right, oops, and back and forth. The aileron control circuit is cables running to hydraulics at the ailerons, ...


15

It‘s a BV-347 technology demonstrator: In 1969, the Army and then-Boeing Vertol entered into a partnership to improve upon their cargo helicopter fleet, and thus the BV-347 was borne from a CH-47A Chinook that was provided by the Army as a technology demonstrator, according to retired CW5 Jim Kale, who now serves as a tour guide for the U.S. Army Aviation ...


14

Yes, and it has been done. In 2010, the first human-powered ornithopter recorded its first flight. It took a very light aircraft and a lot of power from the pilot, about 650 W, so the flight only lasted 20 seconds. It only sustained level flight, requiring assistance to take off. To put this into perspective, a good power target for cyclists is 250 W. A ...


13

Well the short answer is the elliptical wing was used on a lot more aircraft than this article lets on. The following all used an elliptical wing and there are others too: German Heinkel 112 fighter German Heinkel 111 bomber German Heinkel 70 US P35 US P43 Italian Reggiane 2000 Japanese Aichi D3A "Val" dive bomber British Hawker Tempest


12

The flaps and ailerons are "reflexed" on this glider. They have been raised to a setting above the normal zero position, above the airfoil's normal chord line. A number of flapped gliders have this feature. Two main benefits are a reduction in pitching moment as the pressure distribution on the wing is moved forward, so less downforce work for the tail, ...


11

It's because leading edge devices allow a higher Angle of Attack. The four types of leading edge devices work by pointing the nose of the wing downwards so that at higher AoA there is no flow separation at the upper surface near the nose. Deflecting the slats does not increase $C_L$, the aeroplane must increase AoA to do that. Lower stall speed comes with ...


10

Maybe wings never mattered... Altitude: The answer depends a bit on the design of the craft in terms of control surfaces/wings. Atmospheric reentry begins at the Karman line at an altitude of 100 km (62.14 mi / ~ 54 nautical mi) (327,360 feet) above the surface. Which is generally when air resistance starts to matter but that does not mean control surfaces ...


10

Quoting the F/A-18A,B,C,D Flight Manual A1-F18AC-NFM-000, I-2-42 2.8.2.8 Control Augmentation System (CAS) [...] The lateral control system uses ailerons, differential trailing edge flaps, differential leading edge flaps, differential stabilator, and rudders to achieve the desired roll characteristics. Scheduled air data roll rate feedback is used ...


9

Short answer: Elliptical wings are too expensive to manufacture. A trapezoid wing with a defined geometric or aerodynamic twist can get very close to an elliptical lift distribution (optimal lift distribution over the wingspan, therefore the primary goal of the wing design).


9

the tensile-versus-compressive stress issues have been worked out to a satisfactory degree many years ago, meaning that the loadpaths for high-versus-low wing aircraft really aren't design differentiators- but there are other issues, as follows. Low wings furnish a natural location for a wide-stance main landing gear, making for stable landings and easy ...


9

That'd be a roughly 1 meter stick you've got to beat that other aircraft with, at most. Not a long stick at all. By the time the other aircraft got that close a collision would be unavoidable. Not only would momentum carry them closer, but the banging would likely not even be heard by the crew of the other aircraft. Remember they'd be wearing headphones, ...


8

According to Wikipedia, the Grumman X-29 had washed-in wings, as its considerable forward wing sweep gave it a strong tendency to stall at the roots. As the wing roots on a forward-swept-winged aircraft are located aft of the wingtips, a root stall on such an aircraft would cause a strong pitch-up tendency, so the X-29's wings were washed in to mitigate the ...


8

The leading edges are roughened to improve the stall characteristics. Typically vortex generators are used for this purpose nowadays. The 5 and the 5a were used by the RAF for pilot training and the nose strakes were fitted to improve the spinning characteristics - the leading edges of the wings had a roughened paint finish to improve the stall ...


8

Five short, generic reasons (i.e., not specific to the Weedhopper): Fatigue reduction: some highly stressed parts of the airframe (particularly mainspars and engine mounts) are susceptible to fatigue failure from cyclic loading. The key word here is 'cyclic'; a spar which is subjected to loads between (say) -5g/+5g will fail faster than one which is ...


7

Indeed, it is due to resemblance with Greek letter 'lambda', though not the capital one ($ \Lambda $), but the small one: $ \lambda $. I am attaching a pic of X-45 with me drawing a lambda over it. Typically, the wing has two taper ratios. The inboard wing tapers heavily, corresponding to legs of small lambda, and the outboard wing tapers slightly or do not ...


7

That looks close but I think there is too much camber in it as depicted above, and that is only the root airfoil. There are significant changes along the span. I used to jokingly call it my 'Lie Back' airfoil because I usually design things at night in bed :) At some point I hope to get a 3D CAD model published of the whole Lazair series of aircraft but I ...


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