102
votes
Could airline tires be deflated in mid-flight to reduce weight?
You want to reduce weight by removing a few kilos of air, and adding an equal, if not greater, amount of kilos of pumps needed to reflate the tires (see David Richerby's answer for details), not to ...
- 32.4k
82
votes
Accepted
How are brakes cooled on heavy aircraft?
Summary
The order of magnitude of brake energy after a rejected takeoff (RTO) for a very heavy aircraft is 1 GJ, or 100 MJ per wheel brake.
Aircraft brakes are cooled with ambient air, either ...
- 10.7k
75
votes
Accepted
What is the purpose of the extra wheel on the XB-70 main gear?
It is a sensing wheel that is part of the antiskid braking system. It contains an electronic sensor to measure the true groundspeed of the airplane. See NASA Technical Note D-4836, Landing Loads and ...
- 2,468
66
votes
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What operation is this aircraft performing?
The flight in question is most probably an evaluation/calibration flight for radio navigation systems at Ust-Kut. The aircraft is a Yak-40 special version designated for such tasks:
Aviamuseum - Yak-...
- 27.2k
60
votes
Accepted
Why does the 767’s main landing gear appear spaced considerably farther apart than airplanes of a comparable size?
The Boeing 767 main landing gear is not actually spaced further apart than other twin-engine wide-bodies:
Aircraft
Wingspan
Gear Spacing
Fuselage Width
Gear Spacing:Fuselage Width
B767
48 - 52 m
9.3 ...
- 54.3k
56
votes
Accepted
Why would one plane in this picture not have gear down yet?
Why does the 747 not have its gear down yet?
Based on the image it is hard to say how far these aircraft are from the runway. The 747 could still be be quite far from the runway and thus does not ...
- 54.3k
55
votes
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Can the landing gear be pulled up while the plane is on the ground?
There is a weight sensor which senses if the plane is on the ground. This sensor prevents gear retraction while the plane is still on the ground. Failure of this sensor would prevent gear retraction ...
- 39.7k
54
votes
How are brakes cooled on heavy aircraft?
Hot brakes are normally cooled by natural convection, but in extreme cases the fire fighters will cool overheated brakes. Some designs use brake fans. From the linked page:
Brake fans reduce brake ...
- 230k
51
votes
Accepted
What is the purpose of the Dash 8’s “TOUCHED RUNWAY” warning light?
The light is a tail-strike indicator.
Touched Runway system
The Touched Runway system provides a warning light in the flight compartment. It illuminates when the aft fuselage ...
- 1,244
50
votes
Accepted
Why did the space shuttle use bias-ply tyres instead of radials?
Simply put, for the weight bearing factor bias-ply is a lighter tire, and when building a spaceship weight is the top concern.
The reason they were thin and single use also had to do with weight, ...
- 100k
49
votes
Accepted
How can the landing gear fit in the small room in the engine bay on the Tupolev Tu-144?
The Tu-144 uses much smaller wheels than comparably-sized subsonic aircraft. This makes it possible to rotate the gear bogie sideways towards the middle of the aircraft, so it can be stowed vertically ...
- 230k
48
votes
How can the landing gear fit in the small room in the engine bay on the Tupolev Tu-144?
The Tu-144 landing gear rotates 90 degrees when retracted up between the engines.
Source: Tu-144 Landing Gear Retraction
Source: Tu-144 Landing Gear Retraction
- 37.5k
44
votes
Why do landing gear tires smoke upon touchdown?
Because the tires are momentarily skidding on the pavement as they rapidly spin up from standstill to the jet’s touchdown speed. It’s just a puff of burnt rubber but the tire tread itself becomes ...
- 72.8k
44
votes
Accepted
Do military bases still employ wheel watchers?
No
They do not continue this practice anymore. This is likely because landing gear are more reliable now than they were in the 70's. There is also the practice of Air Traffic Control prompting ...
- 2,409
42
votes
Accepted
Do commercial aeroplanes use ABS to brake?
Yes, they do. They are called Anti-Skid and they go from Mark I of 1948, with simply an on-off switch triggered by wheel lock, till Mark V (or at least that's the last I've seen), with quite complex ...
- 32.4k
37
votes
Could airline tires be deflated in mid-flight to reduce weight?
Some military transport aircraft can indeed adjust tire pressure from the cockpit for soft field operations. The Antonov An-22 would be one example. A central tire inflation system is a standard ...
- 230k
35
votes
Accepted
Is there a landing gear system that extends automatically to prevent belly landing?
The simple fact is that an unintended gear deployment could be catastrophic, as it has a profound impact on the flight dynamics of the aircraft (one of the reasons there are warnings for both ...
- 3,676
35
votes
Accepted
Why was the nose gear of Concorde located so far aft?
In a conventional "tricycle arrangement", placement of the nose landing gears is normally chosen to respect three basic requirements:
nose landing gear should carry 10 to 15% of the total ...
- 9,598
34
votes
Could airline tires be deflated in mid-flight to reduce weight?
Along with the pump (and such) involved, it should be noted that inflating the tires of a large aircraft is a fairly non-trivial undertaking from a safety point of view.
In particular, when you're ...
- 3,157
33
votes
Why use an airplane with non-retractable landing gear for aerobatics?
As you mentioned, drag is one of the reasons why retractable landing gears are used in the first place. But in order to use it, there are way more considerations than just drag.
Scale: Size of the ...
- 441
33
votes
Accepted
Why do aircraft sometimes bounce while landing?
The FAA covers this in the airplane flying manual quite nicely:
Bouncing During Touchdown
When the airplane contacts the ground with a sharp impact as the result of an improper attitude or an ...
- 100k
33
votes
Accepted
Why should an overheated wheel be approached from the front/back and not in line with the axle?
Besides staying clear of the fuse plug in the rim, it's partly because the sidewall of the tire is the weakest part of the carcass, so that a rupture from overpressure from overheating means most of ...
- 126k
31
votes
Is there a landing gear system that extends automatically to prevent belly landing?
It has been tried before. Piper's PA-28R and PA-32R aircraft were equipped with an automatic landing gear extension system which would automatically extend the landing gear below 85kts regardless of ...
- 72.8k
31
votes
Accepted
Why complex landing gears are used instead of simple, reliable and light weight muscle wire or shape memory alloys?
Shape-memory alloys change their shape with temperature, with control usually achieved with electric heating in one direction, and back with convective heat transfer to the environment. There is one ...
- 56.2k
31
votes
Are there any aircraft with a 4-wheel nose landing gear and a 16-wheel main landing gear?
The Il-76:
4 main bogies with 4 wheels each, nose gear with 4 wheels.
this one has a better view of the wheels, but it's a CGI:
4-wheel nose gear is rare, 16-wheel mains are more common: Boeing ...
- 10.2k
30
votes
Accepted
What causes a Cessna 172 and its gear to shake violently after landing and braking?
I'm pretty sure you have encountered "nose wheel shimmy".
For reference, see this video on Youtube: c172 M Nose wheel shimmy [sic].
The shimmy can occur for a variety of reason, most likely ...
- 27.2k
29
votes
Do commercial aeroplanes use ABS to brake?
It is not called ABS but Anti-Skid, but the principle is similar. All large aircraft have it.
The purpose is however slightly different. In aircraft the nose wheel has relatively little weight on it ...
- 56.2k
28
votes
Could airline tires be deflated in mid-flight to reduce weight?
You simply wouldn't save any weight.
One of Goodyear's largest commercial aviation tyres is the 54x21.0–23 Flight Leader,* used on Airbus A330s and A340s. That is, outside diameter 54 in, ...
- 11.9k
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