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Apply brakes before gear retraction

Most of my instructors have been strict about making sure the brakes are ‘tapped’ before the gear if retracted. I recently did 5 days of training at Diamond in Austria, there was no mention of applying brakes before gear retraction (I also can’t find any mention at all in the POH). So, is it necessary?

I can understand that you don’t want to spray the inside of the wheel well with water and debris but is there another valid reason to apply brakes? I’ve heard the gyroscopic effect arguments but find it hard to believe that the forces are sufficient to cause any issue, after all the aircraft’s undercarriage can take far greater forces (even if the angles are different).

I haven’t been tapping the brakes but would love to know if there’s a good reason why I should start being more vigilant about it

EGTR

I have also been taught this by different instructors in different countries flying different retractable gear aircraft, with the arguments mentioned, but I can’t assess if it makes sense on all models. But it certainly doesn’t hurt either.

There are a few microswitches for gear up/locked position and other hoses and clamps in the wheel well close to the retracting wheel that will be thankful in terms of lifetime if you avoid those vibrations caused by a fast (e.g. 70kt) rotating wheel in their immediate vicinity.

Last Edited by nobbi at 20 Dec 15:28
EDxx, Germany

I always do it (having been taught that also). One of the reasons is that the rapidly rotating tire may scrape the wheel well and gets damaged (and damages the microswitches, hydraulic lines, etc in there). From the C210 POH:

Before retracting the landing gear, the brakes should be applied momentarily to stop wheel rotation. Centrifugal force caused by the rapidly-spinning wheel expands the diameter of the tire. If there is an accumulation of mud or ice in the wheel wells, the rotating wheel may rub as it is retracted into the wheel well.

I don’t think it’s anything to do with wheel rotation.

Admittedly these are slightly bigger wheels than some RG airplanes, but in this video rotation stops at 0:12 seconds (i.e. 3 seconds after take-off, or 9 seconds after start of take-off roll):



Is anyone really that quick with the gear switch?

I wonder whether a better reason for tapping the brakes shortly after departure might be to free the pads and squeeze any slush out from between disc and pads so that they won’t freeze up while cruising at flight levels. I guess most of us tap the brakes before landing, but at that point we can’t be sure that the pads aren’t frozen solid.

Glenswinton, SW Scotland, United Kingdom

Jacko wrote:

Admittedly these are slightly bigger wheels than some RG airplanes, but in this video rotation stops at 0:12 seconds (i.e. 3 seconds after take-off, or 9 seconds after start of take-off roll):

Looks to me like he hit the brakes, the wheels don’t spin down but stop rapidly. Not sure you’d want the relatively big mass of Tundra tires spinning away down there. In any case, I go by the POH…

Cool video, btw.

I would find it hard to believe that the rotating (and slightly larger) wheel would damage microswitches etc because that would be a really totally crappy design, since it is only a matter of time before somebody forgets to apply the brakes.

My take on it (without knowing any manufacturer’s actual thinking*) is that it is

  • to reduce the amount of mud flying off the wheel as it goes up into the wheel well (which is much worse after a grass departure)
  • to reduce scraping between the wheel and airframe parts, in designs where the wheel itself rests against a rubber bung or some such “stop” device

On a TB20 the rubber bung does not touch the wheel; it instead touches the landing gear leg, so point 2 should not apply, but I think there can be contact as I recall reading a report by another TB20 owner who rebuilt his wheel wells which got scraped right through by the wheel rotating. Obviously I won’t post his name. The Socata wheel wells are made of vacuum moulded plastic…

* manufacturers almost never reveal the reasons for putting something into their POH

Nice video Jacko I hope he puts a lot of ACF50 inside his elevator

Administrator
Shoreham EGKA, United Kingdom

172driver’s quote from a Cessna manual should obviously be followed, but I doubt that a C210 wheel spins “rapidly” for more than a few seconds. A video like the one above would prove or disprove this, if someone would be kind enough to lend me a C210.

Glenswinton, SW Scotland, United Kingdom

Looks to me like he hit the brakes, the wheels don’t spin down but stop rapidly.

Yes, they stop remarkably quickly, but “he” was me, and I’ve never thought of dabbing brakes on take-off – until now. In any case, as you see from the video I’m busy with the flap handle until long after the wheels have stopped and dabbing brakes at that point would be too much like walking and chewing gum for me…

Last Edited by Jacko at 20 Dec 17:26
Glenswinton, SW Scotland, United Kingdom

Jacko wrote:

Yes, they stop remarkably quickly, but “he” was me, and I’ve never thought of dabbing brakes on take-off – until now.

Ha! Gotcha! Cool flying there !!! As for the C210 – you’d have to come to L.A., I’d be happy to take you flying

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