So if the pilots braked immediately, with only the back wheels down, and nose wheel still up, would the force from braking cause the front wheel to come slamming down?
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asked Dec 13, 2019 at 1:24
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3$\begingroup$ Not in most aircraft. For the braking force to be high, there needs to be a substantial load on the mains, so the nosewheel is close to settling. Also, generally technique on mid to small sized aircraft is to hold the nose off until the speed is lower, where it will more naturally drop. For max braking, many aircraft will use the technique of copious rear elevator (nose up pitch) which transfers weight to the mains. Different aircraft have different design trades, different tail clearances, and different operational recommendations. $\endgroup$– mongoDec 13, 2019 at 1:54
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1$\begingroup$ If you're a reasonably skilled pilot, you adjust your braking effort and elevator so that that doesn't happen. Same as you generally don't slam on the brakes when you're driving a car. $\endgroup$– jamesqfDec 13, 2019 at 2:36
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$\begingroup$ It would be nice if an answer addressed the general case, rather than transport aircraft. There are lots of utility aircraft, and light aircraft and even military and cargo aircraft with different brakes, different aerodynamics, different braking systems, and of course different recommended techniques. Having answers which are focused on transport aircraft with highly specialized systems to manage secondary effects tends to obscure the underlying understanding of how the brakes, the aircraft mass distribution and the underlying issues the OP appears to be seeking to address. $\endgroup$– mongoDec 17, 2019 at 3:45
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3 Answers
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If you get on the brakes hard after main touchdown, once the anti-skid is active following wheel spin-up (you can't land with brakes applied on any airliner with anti-skid - brakes are depressurized until after the main wheels start to spin and/or you are weight-on-wheels for a minimum time) and don't apply any additional compensating elevator, the nose will come down faster than if just hold the existing elevator input, and will contact a bit harder, but "slamming down" would be a bit extreme unless you also relieved some of the control back pressure as you did so. Then it would be a bit firm and if you were reckless enough you might blow the nose tires, and somebody would have a chat with you.
In practice though, on most jets you land the mains, then the nose in two separate actions and during that "second phase" you are applying elevator to modulate the sink rate of the nose to make it touch down reasonably gently for that "2nd landing". If you were on the brakes hard at that point you would normally just compensate instinctively with extra elevator input to get a gentle landing of the nose.
You would certainly have enough tail power available to counteract the nose down torque of the braking at high speed. But you would probably get scolded for getting on the brakes before nose wheel contact anyway, and a lot of pilots will keep their feet low on the pedals to avoid applying brake, then move them up once the nose wheel is down.
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Yes. Hammering on the brakes right at touchdown will apply a torque to the airplane which will tend to rotate the fuselage "nose down".
answered Dec 13, 2019 at 1:53
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Yes, it would. In the case of the A320, you would actually put the nose down smoothly (fly it down). If you hold the nose up and apply harsh brakes (or have Med autobrake set), then the nose wheel will slam down eventually.
