Could deflating an airliner's tyres once the gear up button is activated then re-inflating them for landing once gear down is set in motion, reduce the weight of the aircraft and subsequently the fuel consumption? Is it feasible, is it safe?
So the plan is to take an aircraft in perfectly good condition, deflate all the tires to save a few pounds of weight, and hope that everything works right to re-inflate the tires later. It would only take one failure of the re-inflation hardware, and the subsequent damage caused by landing on all flat tires, to erase the $ saved from decades of fuel savings from this scheme. And that not even considering if the vented air outweighs the re-inflation pumps and pipes. Don't see this one happening, sorry.
Air is 1.2kg/m3 and charged to 13atm that's 15kg/m3. Say a tire is roughly 2 cubic meters, and main landing gear has 8 wheels and that's 250kg. Roughly it's safe to say air in the tires are "hundreds of kilos" on a large jet. But "subsequently"? Not likely. Feasible or safe? Not likely, either. Online inflating systems are only widely used for tires below 150kph and airplanes would need to run above 300kph so your wheel hub with integrated online inflating mechanism would be quite a piece of high-tech precision machinery.
@user3528438: The internal tire volume is maybe a tenth of what you estimated. If I remember correctly, all the air in the tires of a 747 weighs less than one passenger (80 kg).
This got me thinking... If tyres store too little air then how about cabin? There are those oxygen masks, so passengers don't need air, right? If we could evacuate air from cabin, how much weight could we save? /s
You would save more weight and make more money by convincing passengers that there was a safety or security reason they needed to dump all their pocket change into a donation bin before boarding. Also you could accomplish the same end by inflating tires with helium.
@RalphJ Just as ridiculous a plan it is to take an aircraft in perfectly good condition, retract all the landing gear to save a bit of drag, and then hope that everything works right to expand the landing gear later, right? (Not saying that it would be a good idea, but outrightly rejecting something just because it sounds crazy isn't that good either)
@DanielJour. The fuel savings from retracting the landing gear are many orders of magnitude greater than any possible savings from this deflation scheme. For a 30% fuel burn savings, plenty of things are reasonable that wouldn’t be considered for a 0.03% savings.
@Harper . If you're going that far, you might as well just use Hydrogen in the tires. It's half the weight, so it's twice as good, and what could go wrong?!
@DanielJour "take an aircraft in perfectly good condition, retract all the landing gear to save a bit of drag, and then hope that everything works right to expand the landing gear later" That's why gravity-drop landing gear extension systems is a thing on airplanes. It's not ideal, which is why the normal systems (e.g. using hydraulics) are there, but if the main fails, it's a backup that relies on little more than gravity and simple mechanics. If you can't assume that those work the way you're used to, then you're probably out of luck either way long before the plane is even on final...
Aren't most aviation tires filled with an inert gas, such as nitrogen? If so, you'd either have to store the gas somewhere on the aircraft, or bring a machine that allows you to pull nitrogen out of the air.
Discussion on question by securitydud…
Discussion on question by securitydud…