Brakes on before gear retraction?

[Chadzat]

After getting good responses in my multi-engine runups thread, I thought I might see what responses this query gets.
I currently fly 210's and I was talking with another pilot about different techniques for this and that, and it came up that one contentious point of difference between the way we fly the aircraft was that he never touches the brakes before gear retraction, whereas I always do.
Here are the two arguments:
No brakes before retraction:
He reckons that because the wheels obviously have enough room to be able to stow without hitting anything in the wheel well/gear leg bay then what difference does it make if the wheels are still spinning or not when they finally stow- also he pointed out that a mechanic had told him when you put on the brakes on the wheels- they are not under any friction with the ground- so stopping the wheels will be instantaneous and possibly cause tyre creep around the wheel from the sharp decelleraton forces.
Brakes before retraction:
I was always taught (and after thinking about what goes on in the wheel wells) that you should always tap the brakes to stop the wheels before retraction. This way in case the tyres do come in contact with anything they do not rub and possibly burst. Also with operating off of dirt strips- they are not going to fling mud and dirt everywhere in your wheel well's.
I would be keen to read other peioples views- and if there any mechanics on here, their opinions on the tyre creep 'issue'.

[Atlas Shrugged]

Oh goodie, this little chestnut again.

I've never done it. Can't see the point really. It only stops the main gear from spinning whilst the nosewheel still goes 'round. :suspect:

[Richo]

Another good question chadzat.

This is my 2 bobs worth, I expect some others will help as well.
There are of course many "reasons" why we do many things. Unfortunatley some are 'Myths" and some mostly correct. Remembering that you can't neccesarily apply one rule to all aircraft types.

The problem with most LIGHT retractable aircraft, when retracting the gear, is the rotational 'Gyroscopic" effect that the wheels have on the light support structure. Not discounting the wheel spining into the well idea, but this is more correct in my eyes. Both are good reasons to use the brakes. Unfortunately I don't belive that your friends information to be the most correct.

1. When either locked up or down the undercarriage leg has some form of strength within its supporting structure Ie it is locked with cams, pins, overcenters or other such engineering bits. Obviously when down the structure can support the weight of the aircraft plus the worst sort of touchdown. Light aircraft manafacturers do MOSTLY try to keep these structires to the minimum design strength to keep weight down.

2. When moving between up or down the sturcture is significantly weaker as the brace or locks are removed, during this time the structure is suseptable to damage by forces working against the drives. (electric motors , cogs, rods or Hyd fluid) A good example is that most light aircraft have a maximum airspeed for gear retraction as well as for extended. this is due to the load on the U/C motors ect, by airflow over the doors which do create thier own local forces.

3. The worst sort of Gyscopic effect is in aircraft where the wheels retract at right angles to the plane of rotation of the wheels. ie B55/58, A36, most piper retracts ect. The force used to move the rotating wheel is transfered to the U/C structure as a twisting moment. Over a long period of time these forces may/can/have caused damage to the internal components and structure.

4. As Atlas has pointed out (in his own elquant style) , the nose wheel does not have brakes, but the nose wheel in almost all light aircraft retract in the fore/aft plane, therefore the twisting moment is minimal on this structure. Also nose wheels are provided with "dampners" to prevent "Shimmy" during spin up and spin down.

The C210 wheels actualy move in several different planes of rotation during retraction. Just have your friend watch the wild gyrations of this type of cessna U/C. even do a test, watch one takeoff with brakes used to stop the wheels and then the other. let us know the results, if any.
Some one else may be able to provide more info, but I beleve that there have been several failures of the internal cog drive in this type of cessna undercarriage.


richo

[kingtoad]

I was taught that its to save the bearings - not just the spinning on them but the excessive wear caused by the gear leg retracting while the wheel is still spinning on the bearing. If you can grab a bicycle wheel (not attached to the bike) and set it spinning while holding it vertical (like it is on the bike). While it is spinning, rotate it so that it is horizontal. Do the same while the wheel is not spinning. Notice the difference. This is the gyroscopic effect (which acts at 90 degrees to the direction of motion) and puts torque/strain on the bearings and the undercarriage leg. This doesn't apply to most nosewheels, in that they retract inline with the rotation.

There is also the centrifugal effect which will enlarge the diameter of the tyre and it may rub against something until it stops spinning and reduces to its "normal" size.

Richo is right about the failure of the actuators in the cessna single retractable system - and its an expensive failure. Each actuator (one for each MLG) is about $15,000.00.

The system works in a similar way to the rack and pinion steering system in a car. The cog is on the end of the MLG leg and the rack is part of the hydraulic actuator that moves back and forth, rotating the whole gear leg - but you knew that anyway from when you studied the C210 aircraft systems before you flew it, right?

Yep - I reckon its a good idea to tap your brakes before retraction!:ok:

[OH410E]

Another wank

A large percentage of noobies couldnt co-ordinate well enough to dab the brakes after lift off and chew gum

Theyd be smoking the tyres during the take off roll

Leave the brakes for what they was designed to do
Stop the plane on the ground

Whats next boys asking your pax "Clear right?" :rolleyes:

[nig&nog]

Not an engineer or anything but all heavy turbine and middle size jets that I have flown up to 50 tonne, have automatic brakes on retraction to help stop wheel spin, so maybe its just a couple of old airliner types doing a bit of instructing and teaching younger people what they do at present.
Otherwise there are alot of pros & cons from the previous posts that all have good merit.

Nog

[disco_air]

Not a retractable, and havent noticed as much with other types but the Airvan definately has a noticeable gyroscopic effect from wheels spinning after lift off.

Sometimes makes a shudder thru the airframe that maybe the pax notice (never asked) so I used to tap the brakes to prevent it.

...disco

[Lasiorhinus]

Somehow I doubt that the forces involved in stopping a wheel in the air are anywhere near significant to move the tyre relative to the rim. The same force happens on touchdown, when the wheel is accelerated from stopped to touchdown speed in a very short amount of time. The wheel is under more stress on landing because, in addition to this quick speed-up, suddenly the tyre is now load-bearing as well.

I can see no reason to deliberately not stop the wheels after takeoff. If you forget, fine, its probably not going to damage the aircraft, but stopping them before retraction removes the gyroscopic forces, potential rubbing on the wheel well, mud flinging etc, and even on a fixed, it eliminates the vibrations caused by slowing down.

I always tap the brakes after liftoff. No need to slam them on hard - remember, the wheel will stop with very little pressure, as there is no resistance other than inertia. A quick tap, and onward and upward.

[ScottyDoo]

he pointed out that a mechanic had told him when you put on the brakes on the wheels- they are not under any friction with the ground- so stopping the wheels will be instantaneous and possibly cause tyre creep around the wheel from the sharp decelleraton forces

Which do you think is more likely to result in the tyre "creepnig" around the rim:

Stopping the tyre in the air with no pavement dragging against the rubber in the opposite direction to the braking force, or

Braking on the ground with a tonne and a half or whatever of aircraft load trying to push the machine and the tyres in the opposite direction?

A mechanic told you that???

[disco_air]

yes methinks the mechanic needs a lesson on inertia and friction :=

[flyby_kiwi]

I was never taught it. I have never done it. I have never heard anyone convince me on the merits of doing it. I have never had a major u/c problem (touch wood).

Lets face it, if it was that important/of any importance there would be words to that effect in the flight manual.

Prehaps a thread on old wives tales could be interesting. Can only imagine what myths are out there! ie Never taxi faster than walking pace :ugh:

[ForkTailedDrKiller]

Taught to do it as a young fella. Always do it - second nature. Too old to change now!

Dr:cool:

PS: I also tap the brakes before retracting the gear!

[VH-XXX]

I suspect many of you may have underestimated the vibrations and shuddering of a poorly balanced wheel.

From an engineer, tap the brakes. No harm done, miniscule brake wear, less torsional loads and less wear and tear.

If you forget or you aren't coordinated enough to do it, don't lose sleep over it, however it's a good idea.

[squawk6969]

Whoever the engineer was that told VH-XXX that stuff is spot on!

SQ6969

[chode1984]

I have to agree with whoever mentioned the gyroscopic effect. I thought this was one of the main reasons. In the Baron anyway.

[Pinky the pilot]

Taught to do it as a young fella. Always do it - second nature. Too old to change now!

Likewise! Once knew a CP who absolutely insisted on the procedure in his 402s. Used to get a bit 'narky' if you forgot!

[muddergoose]

In light of suggested tyre creep and gyroscopic forces, don't ever land your C210 @1600 KG (thereabouts) in the 80 knots vicinity because those impact forces will really root your bearings:8
The 172 was notorious for wheel shake during slowdown after liftoff. Touching the brakes prevented the shudder.
Does it really matter? :hmm:

[Capt Wally]

.......there are more pro's than cons in touching the brakes after T/Off by the sounds of things here, so it's down to personal choice as PIC, I was taught to do it too many years ago to remember but have done it from C172RG thru to Jets. We learnt about aviation from the Wright Brother days onwards & we are still learning.

Capt Wally

[ScottyDoo]

We learnt about aviation from the Wright Brother days onwards & we are still learning.


Not all of us were around back in those days....


Just tap the brakes. If you do it firmly and quickly enough, you'll feel and hear the wheels *thunk* to a stop.

The grinding noise you may be able to faintly discern will be the mechanic's teeth.




Disclaimer:
I take no responsibility for the results of any advice given out anonymously on the internet regarding the operation of an aircraft.

If in doubt, always consult the POH or your C.P. before operating an aircraft or a plane.

[Cloud Cutter]

As flyby mentioned, if it was that important it would be in the flight manual.

Also a major point has been missed: When you decelerate a spinning wheel in a split second like this, all that kinetic energy is absorbed by the hub, and can cause it to crack sooner than it otherwise would. I know of one very experienced operator years ago who prohibited his pilots from touching the brakes after takeoff for this reason.

The well well is designed to take a spinning wheel, and if any damage is done, there must be a problem to start with. The gyroscopic force in a wheel with such a small diameter as a light aircraft is minimal compared to the side loads the bearing normally copes with, so that's not a good enough excuse, and if you take a spinning bicycle wheel and move it to simulate a typical light twin main wheel retracting, you'll note a twisting force at your hands, but little resistance to the general motion that would be powered by the gear motor. Conversely, tire creep will not be a problem as the inertia of a tire when stopped suddenly is minuscule when compared to the force between the hub and the tire during even light braking on the ground.

This is just one of the many things that someone in there infinite wisdom has invented over the years, and it's plausible enough to have stuck.

[VH-XXX]

"When you decelerate a spinning wheel in a split second like this, all that kinetic energy is absorbed by the hub, and can cause it to crack sooner than it otherwise would."


Are you for real?

Do you think there is more load on a wheel / hub when stopping in a nil weight condition versus the aircraft landing with say a couple of tonnes on it? It's no different to locking up the brakes.

That is just a wank sorry.

[ScottyDoo]

Agreed VH-XXX...

And while you're at it, CCutter, thanks for re-iterating the same thing which was pointed out already on the previous page.

[Cloud Cutter]

Tell me where on the previous page this point was stated? I can't find it. You may be confusing it with what someone said about tire creep, which, if you read my post, I disagree with.

I said nothing about load, I was talking about shock energy absorption. Like hitting something with a hammer compared to resting a mass on it that way's many times more than the hammer.

You won't get a wheel to stop spinning as quickly by locking up the brakes on the ground, yes the wheel will stop turning, but it won't happen anywhere near as quickly, and you won't (I hope) do it on every single flight. Similarly the wheel won't spin up anywhere near as quickly on even the most firm touchdown. Simple physics. If you don't agree, that's fine, it's only a theory and I invite you to disprove it.

[Lasiorhinus]

Similarly the wheel won't spin up anywhere near as quickly on even the most firm touchdown. Simple physics. If you don't agree, that's fine, it's only a theory and I invite you to disprove it.

With respect, Cloud Cutter, that is how religion works, not science. If you postulate a theory, the burden of proof is on you to prove, not on anyone else to disprove.

[RENURPP]

Disclaimer:
I take no responsibility for the results of any advice given out anonymously on the internet regarding the operation of an aircraft.

If in doubt, always consult the POH or your C.P. before operating an aircraft or a plane.

You will not get better advice than that.

When you move on to bigger and better (oppinion only) things, you will be expected to operate the aircraft as per the aircraft flight ,manual and the company SOP's approved by CASA and generally based on information by the aircraft manufacturer.

Do yourselves a favour and begin that practice now and forget what your mate down the pub told you unless he can substatiate it with evidence from one of the above. i.e. aircraft POH/Flight manual or company SOP's. (company SOP's in light aircraft tend to be based on personal preference)

[pig dog]

Boeing and Airbus go to a lot of trouble designing their undercarriage so that the brakes automatically activate and stop wheel rotation during retraction. The main reason for this is to prevent damage to the vital components in the wheel well from a delaminated tyre tread and to a lesser extent foreign objects such as mud and slush.
In the wheel well of aircraft types that I have flown there is hydraulic lines and reservoirs, fire extinguisher bottles, flight control cables and wiring looms. All would be damaged if a spinning delaminated tyre tread entered the wheel well.
I guess if there are any vital components in your wheel well it is a good idea to tap the brakes prior to retraction.

[Capt Fathom]

Boeing and Airbus go to a lot of trouble designing their undercarriage so that the brakes automatically activate and stop wheel rotation during retraction.
Mainly to do with the shape/size of the spinning tire, fitting into the wheelwells.

The main reason for this is to prevent damage to the vital components in the wheel well from a delaminated tire tread and to a lesser extent foreign objects such as mud and slush.
More chance of a tire delaminating, and damage from foreign objects as the wheel is decelerated by the brakes.
Just a thought!

[Jamair]

I have no strong views either way; although I do apply brakes as part of the process before the gear comes up. In at least one turboprop I used to fly, failure to apply brakes before retraction resulted in a very distinctive burning rubber smell as the tyres rubbed on parts of the wheel well.:yuk:

[ScottyDoo]

very distinctive burning rubber smell as the tyres rubbed on parts of the wheel well.:yuk:

Tell us about your systems:

If it burnt as a matter of course, maybe it was a brake pad in the wheel-well that caused the smell.

Maybe it was the designer's intent.

What type was it?

[YesTAM]

Wot Pig dog daid is correct.

Wot VH - XXX said is correct.

A simple calculation will show you that the your wheels are turning at around 2000 rpm after liftoff and perhaps slightly less on landing..

Forget about grass and mud sticking to the wheel at that speed - its gone in an instant. The tire of course will "grow" slightly at that RPM.

I am not sticking anything into my wheel wells thats turning at 2000 rpm, except the nose wheel, period. If the tire is on its last legs and deflating, if it took a stone fracture or something, if a bearing has decided to go at the wrong time, I do not want that much kinetic energy dissipating itself in my wheel well.

And having watched an engineer replace Arrow and similar cracked metalwork over time, I have great respect for the gyroscopic forces of retracting a spinning wheel as well.

Gentle tap after takeoff is always part of my routine on anything.

[18-Wheeler]

There's almost no negatives to a gentle tap before retraction, and plenty of positive factors.
And as mentioned, the larger aeroplanes do it automatically for you anyway.

[Ethel the Aardvark]

172 RG manual directs you to momentarily apply brakes before retraction,
They say that centrifugal force caused by the rapidly spinning wheel expands the dia of the tire, if there is an accumulation of mud or ice in the wheel well, the rotating wheel may rub as is it retracted into the wheel well.
I think this would apply to all retractables.

[puff]

In my experience in PN68s and Cessnas where you can see the wheel all of them seem to drag the brakes even slightly. When i've been a pax onboard a 172 i've watched the wheel and I reakon most of the time it stops spinning in less than 20 seconds, and even then it's not that quick. Esp in singles when your waiting until there is no runway left for retraction in RGs surely it's not that big of an issue. That being said it was taught and always did touch the brakes, but seriously have a watch of the wheel when your not flying, they do seem to slow up pretty quickly.

[Fragnasty]

It's very simple - read the Aircraft Flight Manual (AFM). If the AFM says apply the brakes before retracting the gear, apply the brakes!!!

If it doesn't. don't!!!!

Choice Bro'!

[SOPS]

I agree with Frag. When I fly my Boeing I ask "What does Mr Boeing say?" when I fly my Cessna I ask "What does Mr Cessna say?". Just keep it simple:)