Hit brakes after takeoff
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As has been said, retraction braking on a fixed gear aircraft just makes you feel more in control, but has no engineering reason behind it.
On transport category aircraft, most type have a feature called retraction braking, that applies the brakes to stop rotation before the wheels are fully up. Typically, the de-rotation happens over 2s or so whilst the gear is travelling. The principle reason for this feature is to prevent a burst tire retracting into the bay whilst spinning and allowing the tire to damage hydraulic lines, fuel tank walls and anything else in proximity etc. Gyro effect is also a consideration but given the wheels are still spinning at the start of retraction this feature does not help so much.
The reason the brake application is limited in torque (typically to a reduced psi for hydraulic brakes), is to reduce the loads on the gear during the braking itself. These cycles have to be taken into account when calculating the fatigue spectrum for the gear. High loads = lower total gear cycles or beefier gear.
For the nose, a snubber may be used to stop the wheels in the bay or they are left to spin down naturally - there are less critical systems in the NLG bay compared with the mains.
Alex
On transport category aircraft, most type have a feature called retraction braking, that applies the brakes to stop rotation before the wheels are fully up. Typically, the de-rotation happens over 2s or so whilst the gear is travelling. The principle reason for this feature is to prevent a burst tire retracting into the bay whilst spinning and allowing the tire to damage hydraulic lines, fuel tank walls and anything else in proximity etc. Gyro effect is also a consideration but given the wheels are still spinning at the start of retraction this feature does not help so much.
The reason the brake application is limited in torque (typically to a reduced psi for hydraulic brakes), is to reduce the loads on the gear during the braking itself. These cycles have to be taken into account when calculating the fatigue spectrum for the gear. High loads = lower total gear cycles or beefier gear.
For the nose, a snubber may be used to stop the wheels in the bay or they are left to spin down naturally - there are less critical systems in the NLG bay compared with the mains.
Alex
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I agree it is a waist (sic) of time.
Gyro effect? Negligible.
Increased drag? Mental drag maybe.
Fixed gear? Only if the rotating wheel is out of balance and that bothers you. Risk of creep if you hit the brakes while the wheels are spinning fast (tire will rotate on wheel and if tubed might pull the tube stem out, and the tire will go flat).
Retractable? Follow the POH. Most airplanes will not require it, because the tire bay is large enough to take the spinning wheel and many have automatic brakes/snubbers anyway. If not, the POH will specify the procedure.
Some airplanes take off so fast that the wheels are really really spinning and will have a bigger diameter while doing so. If you find yourself flying a jet fighter, check the book and follow the recommended procedure.
If you misjudge your height above the runway, you could touch down with the brakes on during the retract process, which will spoil your whole day I guarantee it.
Letting the wheels spin for a while before retraction will throw off water, mud, ice etc. Applying the brakes too soon could stop this crud from being removed and you could face extension problems after a long flight, or the prox/micro switches could be contaminated.
Sounds a lot like downwind turns, turning into the dead engine, and other urban legends many otherwise smart pilots believe without verification.
Gyro effect? Negligible.
Increased drag? Mental drag maybe.
Fixed gear? Only if the rotating wheel is out of balance and that bothers you. Risk of creep if you hit the brakes while the wheels are spinning fast (tire will rotate on wheel and if tubed might pull the tube stem out, and the tire will go flat).
Retractable? Follow the POH. Most airplanes will not require it, because the tire bay is large enough to take the spinning wheel and many have automatic brakes/snubbers anyway. If not, the POH will specify the procedure.
Some airplanes take off so fast that the wheels are really really spinning and will have a bigger diameter while doing so. If you find yourself flying a jet fighter, check the book and follow the recommended procedure.
If you misjudge your height above the runway, you could touch down with the brakes on during the retract process, which will spoil your whole day I guarantee it.
Letting the wheels spin for a while before retraction will throw off water, mud, ice etc. Applying the brakes too soon could stop this crud from being removed and you could face extension problems after a long flight, or the prox/micro switches could be contaminated.
Sounds a lot like downwind turns, turning into the dead engine, and other urban legends many otherwise smart pilots believe without verification.
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I can see itnow. Pilot loses control of aircraft doto gyroscopic precession of retracting landing gear
. One gear would not retract and the effect ofthe retracting gear caused the aircraft to spiral out of control. He should have tapped the brakes
. A good script for a lousy movie
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If your CFI insists that you tap the brakes, do it, but please don't pass on the misinformation he has given you.
The spinning wheels don't produce any drag that I've ever noticed. In addition, if you're flying a Cessna, look at the wheels and see how long they spin. Within a few seconds of leaving the ground, they are stationary.
The spinning wheels don't produce any drag that I've ever noticed. In addition, if you're flying a Cessna, look at the wheels and see how long they spin. Within a few seconds of leaving the ground, they are stationary.
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Tyre Creep .......you have to be joking !
Just think about the inertia load that the mass of a spinning tyre stopping will apply as torque between the tyre and the wheel when you stop it by braking in the air.
Now think about the torque loading that is applied when stopping the aircraft even at a low speed.
Who thinks up with this tyre creep rubbish !?
Lancman as well as being short of things to think about you also seem to be short of a SoH.
Now think about the torque loading that is applied when stopping the aircraft even at a low speed.
Who thinks up with this tyre creep rubbish !?
Lancman as well as being short of things to think about you also seem to be short of a SoH.
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So what do you do in an aeroplane with no brakes?
If you can feel vibration due to an unbalanced wheel, go ahead.
Otherwise, don't sweat it. I've never seen any reference to doing so in a POH.
If you can feel vibration due to an unbalanced wheel, go ahead.
Otherwise, don't sweat it. I've never seen any reference to doing so in a POH.
Avoid imitations
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Risk of creep if you hit the brakes while the wheels are spinning fast (tire will rotate on wheel and if tubed might pull the tube stem out, and the tire will go flat).
Now, on the other hand...if the aircraft were to be landed on a conveyor belt....
An ex-colleague of mine was told off in the air by his Jet Provost QFI for allegedly dabbing the brakes at the point of take-off. He swore blind he hadn't done so. And he was later found to be correct by the groundcrew, who were asked to check for tyre flat spotting.
What he'd actually done was to press the undercarriage up button too early during a final runway "bounce", which defeated the WOW switch and allowed the bay doors to touch the runway during retraction. There was half an inch of metal missing from the ends of each main gear door
Last edited by ShyTorque; 27th Oct 2012 at 15:46. Reason: repetition, repetition..
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Hi, didnīt care to read the whole thing, and probably someone already mentioned this...but I 'll just say it.
if the POH, flight manual, FCOM, etc instructs you to apply brakes after takeoff, do it, otherwise itīs not required and might not be desired.
rgds.
sw.
if the POH, flight manual, FCOM, etc instructs you to apply brakes after takeoff, do it, otherwise itīs not required and might not be desired.
rgds.
sw.
If you pick up a spinning bicycle wheel, you'll find that the gyroscopic forces seem greater than the weight of wheel itself. Not that gyroscopic forces would have an effect on aircraft handling, but they could matter during gear retraction, when the mechanism otherwise has to deal with mostly with the weight of the wheel itself. (OK -- I guess "mostly" is an exaggeration; the weight of the non-rotating components and the drag on everything are bound to be quite significant.)
Or maybe it's to stop running up the odometer.
Or maybe it's to stop running up the odometer.
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I'm with zonda in this one, i was taught since day one of training, that on single engine airplanes to slightly brake after airborne to avoid the vibration on out of balance wheels, which you will normally find in used and abused trainers and small airplanes flown by too many people.
Never used this technique in anything else but Small SEL up to C-207.
Never used this technique in anything else but Small SEL up to C-207.
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Gyroscopic effect is the reason behind Automatic braking on large aircraft after takeoff.
Most Large aircraft apply braking through the Autobrake system once the gear handle is selected up. If the Autobrake system is inop or one brake is deactivated, then the landing gear has to be left down for 2 minutes after takeoff.
All this is due to the gyroscopic effects because they are too great and might cause a twist in the landing gear strut, hence damaging the strut and preventing the wheels from fitting in the landing gear bay.
The nose wheel will not experience those gyroscopic effects, thats why only brake pads are fitted in the nose wheel bay to stop the spinning once the nose gear is fully retracted.
Now with regards to light aircraft with retractable landing gear some don't have the Autobrake feature, so thats why Instructors get into the habit of teaching this technique.
But for non retractable landing gear ?? it is a useless procedure
Most Large aircraft apply braking through the Autobrake system once the gear handle is selected up. If the Autobrake system is inop or one brake is deactivated, then the landing gear has to be left down for 2 minutes after takeoff.
All this is due to the gyroscopic effects because they are too great and might cause a twist in the landing gear strut, hence damaging the strut and preventing the wheels from fitting in the landing gear bay.
The nose wheel will not experience those gyroscopic effects, thats why only brake pads are fitted in the nose wheel bay to stop the spinning once the nose gear is fully retracted.
Now with regards to light aircraft with retractable landing gear some don't have the Autobrake feature, so thats why Instructors get into the habit of teaching this technique.
But for non retractable landing gear ?? it is a useless procedure
Last edited by SURGEBLEEDVALVE; 28th Oct 2012 at 02:07.
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Just a 'for info'; many transport aircraft (737, BAe146 to name but a few) use the landing gear UP hyd pressure to operate an auxiliary set of pistons (146 anyway) on the brake units. Usually operation of the gear handle also disables the anti skid to allow the brakes to work.
After a 146 brake change, it's gear pins IN, hydraulics on, then gear UP to check for leaks. I always dread that 'clack clack' as the downlocks release and the gear actuators try to break the gear pins!
After a 146 brake change, it's gear pins IN, hydraulics on, then gear UP to check for leaks. I always dread that 'clack clack' as the downlocks release and the gear actuators try to break the gear pins!
Last edited by itsresidualmate; 28th Oct 2012 at 21:40.
Just noticed that the video posted in this thread
http://www.pprune.org/passengers-slf...ml#post7493102
has a good illustration of the brake snubbers in a 747 NLG bay (at around 11:00).
http://www.pprune.org/passengers-slf...ml#post7493102
has a good illustration of the brake snubbers in a 747 NLG bay (at around 11:00).
