Tapping the Brakes

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Colin
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Tapping the Brakes

Post by Colin »

I know that I already asked this, but I can't find the thread. Even searching.

In any case, when you take off, before you raise the gear, you tap the brakes to keep the wheels from being rubbed against the inside of the gear housing when you pull up the gear. That's on the checklist.

When I asked before, some people did it, some people did not, stating that they were sure the wheels didn't keep spinning. Yesterday when pre-flighting and looking for evidence that neglecting to tap the brakes in the first few weeks of flying might have rubbed a spot (nope), I was looking in the nose gear well and then realized: no brake on that wheel.

If it is important to do, what about the nose wheel?
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CFIDave
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Re: Tapping the Brakes

Post by CFIDave »

Just a guess (and only a guess) is that when retracted, the nose wheel has sufficient room to keep spinning without hitting anything, whereas the main gear wells are much tighter (there's only a 4mm or 0.16" gap between the retracted main tires and the gear wells). This is why you need to be careful about installing tires of the correct size.

It does bother me that I have to temporarily stop applying right rudder during the initial climb (right before gear retraction) in order to hit the brakes on top of the rudder pedals, and then re-apply right rudder to keep the "ball" centered during the climb.
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Karl
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Re: Tapping the Brakes

Post by Karl »

The main wheel tyres shouldn't touch the structure when retracted. If you see any signs of rubbing best to get it checked out. Tyres touching structure has caused more than a few gear up incidents on the DA42.

I always touch the brakes just after take off even on fixed gear, most light aircraft wheels are not balanced the way they are on a car. Just seems to make sense to me to stop them spinning.

Random thought, I wonder if they generate any lift when spinning?
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Steve D
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Re: Tapping the Brakes

Post by Steve D »

I believe the reason for tapping the brakes has nothing to do with fitting the wheel in the well. You stop the mains spinning because the gyroscopic effect of the wheels turning adds tremendously to the work the retraction gear has to perform to get the wheels up.

IFRC This doesn't apply to the nose wheel because the arc it travels is not fighting against (precession?)
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Steve
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Re: Tapping the Brakes

Post by Steve »

Steve D wrote:I believe the reason for tapping the brakes has nothing to do with fitting the wheel in the well. You stop the mains spinning because the gyroscopic effect of the wheels turning adds tremendously to the work the retraction gear has to perform to get the wheels up.

IFRC This doesn't apply to the nose wheel because the arc it travels is not fighting against (precession?)
Exactly correct. Think of the forces generated when retracting a large gear assembly like on a B52...
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TimS
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Re: Tapping the Brakes

Post by TimS »

Steve D wrote:I believe the reason for tapping the brakes has nothing to do with fitting the wheel in the well. You stop the mains spinning because the gyroscopic effect of the wheels turning adds tremendously to the work the retraction gear has to perform to get the wheels up.

IFRC This doesn't apply to the nose wheel because the arc it travels is not fighting against (precession?)
I have read over on BeechTalk and a few other places that the habit of stopping the wheels dates to WW2. The problem was not the gyroscopic forces on the gear, the problem was the wheels expand/grow in size when spinning at 100+ MPH. With the low quality rubber in use at the time, the larger diameter caused by the spinning caused many tires to hit he gear wells on retraction which caused all sorts of problems.

Now, since I read all this on the internet. take it as unconfirmed and with a huge pile of salt.

In the mean time, no I do not tap the breaks and never have. There is no brake on the nose wheel...

Tim
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