Apply brakes before gear retraction

Jacko wrote:

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.

FYI, the C182RG manual has the same sentence in it and also mentions it in the ‘normal’ take-off checklist. I don’t have the C172RG manual to hand right now, but IIRC it contains wording to the same effect.

I always dab the brake before retraction for the simple reason that in the event of some unintended contact between the wheel and some other component, the risk of consequential damage from a stationary wheel is far less than rotating one. A loose brake line or wiring are possible in the well of my aircraft if their security fails.

I shamefacedly admit that, while being taught exactly that, I don’t do it…

I picked up the bad habit in the Turbo Saratoga, which needs a good boot-full of rudder to keep straight with the ball in the middle in the climb. I never managed to apply the brakes without causing yaw excursions. And using the parking brake to stop the wheels, tempting as it may be, is a big no-no, it NEVER gets touched in flight.

Transport jets have snubbers which ensure the wheels stop rotating when they enter the well. Slinging crud into the well and freezing it at FL370 might be the reason for the snubbers for the nosewheel?

The main gear on these jets automatically brakes when gear is selected up, this for gyroscopic forces and to ensure a burst tyre doesn’t damage hydraulics.

Some fast jet pilots mention gyroscopic forces, so it maybe an airforce thing. Precession may be causing some unhelpful torque on the gear leg and they don’t have automatic braking when selecting gear up?

There is a contrary argument that pressurising brakes in some GA types during retraction may cause problems, so the POH/AFM should apply.

Regarding the C172RG, I can see why gyroscopic forces might be a major factor.

The same might be said of the Twin Commander and P40, where the wheel also performs pirouettes in the sky before settling, but they both have chunky solid-state legs, whereas the Cessna ones are designed to be springy.

Most of the airliners that I have flown put a small amount of hydraulic pressure in to the brake system as the gear is retracted, this is largely to prevent water and ice/snow being flung into the gear bay and then freezing.

The secondary reason is in case of a tyre burst on takeoff the flailing tyre won’t damage the systems that are in the gear bay. The B737 is especially critical in this because the hydraulic system and aileron PCU’s are in the gear bay so the Aircraft is fitted with a flailing tyre detection system that prevents the gear retracting in the case of a severe tyre burst.

For me the most important reason to tap the brakes on a light Aircraft is to prevent water, snow & ice entering the gear bay re-freezing and jamming the gear.

I have just taken this high definition high quality video of a Piper Cub wheel. I would say it takes about 20 seconds for it to completely stop turning after takeoff:

Years ago I shot a video of the C172RG gear retraction from the bottom rear of the a/c. If I can find it (not sure). I’ll post it. The dance the Cessna gear does is quite impressive and centrifugal forces may really be an issue in addition to what has already been said. Meanwhile, have a look at the C210 retraction in this video. While the subject matter is a fly-off between a Bonanza and a C210, there is the ‘tap the brakes’ call at 1:02 followed by a great shot of the Cessna undercarriage during retraction. Note, however, that most Cessnas do not have the MLG doors anymore. They were / are prone to failure (and existed only on the 210) and were removed from most of the fleet, e.g. the one I fly.

I guess the real question is “why wouldn’t you?”

How many man-minutes have been invested in this thread? How many 250ms toe-dabs could have achieved in the same time?

Who wants to argue for not doing it? With all respect to Cobalt, it can be done while remaining in balance in most aircraft.