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 ...
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86 votes
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Why do planes always land on rear wheels instead of the nose wheels?

Aircraft land on the main wheels. For aircraft with nose wheel it is the back ones, but for aircraft with tail wheel (also called “tail-draggers”) it is the front ones. In either case the main wheels ...
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81 votes
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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 ...
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75 votes
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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 ...
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  • 2,418
66 votes

Why are aircraft tires not pre-spun prior to landing to preserve them?

This has been researched over the years, but it seems that the solutions did not find wide application. The oldest I could find is from 1941 (see page 112 in the September 1941 issue of Popular ...
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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-...
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  • 20.8k
56 votes

Is there a good reason why modern airliners can't have conventional landing gears (vs. tricycle landing gears)?

Short answer: Yes. Not one, but several. A taildragger configuration for modern airliners comes with several disadvantages: Visibility during taxiing is much worse. Visibility while taxiing is a ...
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56 votes
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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 ...
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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 ...
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  • 39.2k
53 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 ...
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51 votes
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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 ...
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  • 1,244
50 votes
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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, ...
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  • 96k
49 votes
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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 ...
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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
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45 votes
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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 ...
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  • 2,379
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 ...
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43 votes
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How are modern jets modified to takeoff/land on a dirt runway?

Just to roll around on "unimproved" airfields (grass/dirt/gravel strips), the biggest thing planes need is simply a decent set of tires: This MiG-29UN trainer shows off the fairly beefy main tires ...
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  • 22.2k
42 votes
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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 ...
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41 votes
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Why don't modern aircraft have landing gear that can swivel to compensate for crosswinds?

There is one aircraft I know of that can do exactly what you state, the B-52: This plane has steerable dual-bicycle gear which allows the crew to point the gear along the runway while the fuselage is ...
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  • 22.2k
38 votes

Why does the landing gear control have 3 positions (up/down/off) on Boeing 737-800?

With the gear handle in the UP position, the retraction side of the landing gear actuators remain pressurized. The gear will stay in the full up position, however they will not be hanging on the ...
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  • 1,030
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 ...
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35 votes
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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 ...
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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 ...
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  • 2,927
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 ...
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33 votes
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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 ...
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  • 96k
32 votes

Why do planes always land on rear wheels instead of the nose wheels?

Jan Hudec already gave an excellent description of why the gear configurations are designed as they are. Another important thing to note, though, is that because aircraft are designed to land on their ...
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  • 18.9k
32 votes
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Why does the landing gear control have 3 positions (up/down/off) on Boeing 737-800?

When UP or DOWN is selected, the hydraulics pressurize in the appropriate direction. Once the gear is up and the mechanical locks are keeping the gear locked in place, OFF can be selected to ...
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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 ...
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31 votes
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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 ...
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