Braking forces on front wheels
Paxing All Over The World
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Braking forces on front wheels
Non-pilot question: When braking a motor vehicle, the weight is shifted forward onto the front wheels and their associated assembly and they have to be strong enough to handle that.
For an a/c, my guess is that the same physics apply! Yet the front assembly looks fairly frail and only has two wheels.
What are the effects on the front OLEO(?) although I realise that it is strong enough to pull the rest of the a/c, so is that the answer to my question?
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"I tell you, we are here on Earth to fart around, and don't let anybody tell you any different." Kurt Vonnegut, Jr.
For an a/c, my guess is that the same physics apply! Yet the front assembly looks fairly frail and only has two wheels.
What are the effects on the front OLEO(?) although I realise that it is strong enough to pull the rest of the a/c, so is that the answer to my question?
--------------------
"I tell you, we are here on Earth to fart around, and don't let anybody tell you any different." Kurt Vonnegut, Jr.
Last edited by john_tullamarine; 19th Oct 2004 at 12:09.
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Big difference for most a/c is that the front wheels typically only carry about 10% of the total weight (or less) statically; your car is more like 50-50 usually.
Then the long "arm" to the wheel means that any pitching down caused by braking on the mains can be resisted with proportionally less load on the nose.
A very few aircraft have used brakes on the front wheels (SAAB Gripen is one IIRC) but most don't bother.
Think of it as a similar case to a drag racer - small spindly front wheels because all the weight is near the back wheels.
Then the long "arm" to the wheel means that any pitching down caused by braking on the mains can be resisted with proportionally less load on the nose.
A very few aircraft have used brakes on the front wheels (SAAB Gripen is one IIRC) but most don't bother.
Think of it as a similar case to a drag racer - small spindly front wheels because all the weight is near the back wheels.
very few aircraft have used brakes on the front wheels (SAAB Gripen is one IIRC) but most don't bother.
Also, the un-braked nosewheel assembly will only really have purely vertical forces acting on it under braking, so they don't need a lot of fore-aft support compared to the main gear.
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To add a few comments to Mad (Flt) Scientist's
wise words -
The stresses upon the nosewheel assembly, including the compression forces upon the oleo, are well within the design limits for the assembly. Viewing manufacturer's tests of Vmbe (mbe = Maximum Brake Energy), where brake capability is taken all the way to the limit (very graphic pictures) reveal an 'unconcerned' nosewheel sitting there whilst all hell breaks loose with the main gear and tyres.
The B727 did have nosewheel braking available as an option, my old company did opt for it but progressively removed it in the '80s due to negligible performance gain Vs weight / maintenance cost. I recall that it only added about 500 Lb (227 Kg) to the Accelerate-Stop performance limit.
wise words -
The stresses upon the nosewheel assembly, including the compression forces upon the oleo, are well within the design limits for the assembly. Viewing manufacturer's tests of Vmbe (mbe = Maximum Brake Energy), where brake capability is taken all the way to the limit (very graphic pictures) reveal an 'unconcerned' nosewheel sitting there whilst all hell breaks loose with the main gear and tyres.
The B727 did have nosewheel braking available as an option, my old company did opt for it but progressively removed it in the '80s due to negligible performance gain Vs weight / maintenance cost. I recall that it only added about 500 Lb (227 Kg) to the Accelerate-Stop performance limit.
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B727 Nosewheel Brakes & Baking Forces
Yes, indeed they did John T, , and if you went beyond a 'tad too much' to maximum effort, HalesAndPace's baking forces became all too evident.
Maybe with 2 second deltas between Vef and V1 now, we'll see the re-emergence of Nosewheel Brakes as manufacturers rediscover old ways to increase Accelerate-Stop performance limiting weights.
Yes, indeed they did John T, , and if you went beyond a 'tad too much' to maximum effort, HalesAndPace's baking forces became all too evident.
Maybe with 2 second deltas between Vef and V1 now, we'll see the re-emergence of Nosewheel Brakes as manufacturers rediscover old ways to increase Accelerate-Stop performance limiting weights.
