Question/request: Gear handling on take off

There is a passage in Pierre Clostermann's book "The Big Show" where he flies the Hawker Typhoon for the first time:

"I retracted my undercart but forgot to put the brakes on. A terrific vibration which shook the whole plane from stem to stern reminded me that my wheels had had gone into the cavities in the wings still revolving at full speed. I only hoped the tyres hadn't been ruined."

This leads me to the following two questions:

1. Is this a "feature" of all WW 2 planes (and maybe later as well) that you have to manually brake the wheels before retracting them?

2. If this is the case, could this behaviour be implemented in the DCS modules that it corresponds to? (Ie. P-51, Dora, Kurfürst etc.)

For me such a "basic" handling requirement would add even more to the immersion, especially if both the vibration and the possible damage to the wheels was included as well. :)

(By the way, PC's whole recapitulation of this first flight makes me feel a little bit better about my horrible first attempts in any of the WW 2 planes until now. ;) )

At least for the Mustang, you should never use the brakes after takeoff.

(From the original manual, pg. 18 )

After takeoff, never brake the wheels to stop them from turning. If the brakes are hot from excessive ground use, they are likely to freeze.

Thank you Nirvi.

It was exactly that kind of information I was looking for.

So it seems that the requirements in this aspect differs from plane to plane.

Would be interesting to check it for other planes as well.

I was actually thinking that the problem for a heavy and fast plane like the Typhoon might be, that the wheels are so heavy and fast rotating that you would need to use the brakes, while on smaller planes this might not be necessary.

It's interesting to hear of the restriction in the Mustang. Back in the sixties the standard "Vital Actions" on takeoff in the N.A.Harvard (T-6) started with "Brakes", "Undercarriage", etc. and definitely involved using the toe-brakes to stop the wheels spinning before raising the undercarriage, and was strictly enforced by the Air Force Instructors in training flights.

It's interesting to hear of the restriction in the Mustang. Back in the sixties the standard "Vital Actions" on takeoff in the N.A.Harvard (T-6) started with "Brakes", "Undercarriage", etc. and definitely involved using the toe-brakes to stop the wheels spinning before raising the undercarriage, and was strictly enforced by the Air Force Instructors in training flights.

Ok. Interesting.

There goes my theory about "heavier and faster planes".. ;)

Then I think it is something that should be looked into on a plane by plane basis.

I tried looking through original Bf 109 manuals, but I could find no mention about how to handle the brakes on take off.(*)

But I think it would be interesting to have implemented on the planes that require it.

Even for the P-51 it could be fun if you risk freezing your brakes on that particular plane. :)

Of course to the extent that ED and the other developers can implement it.

Edit: *A possibility could be, that this was "common knowledge" back in the day, so that the manuals would only mention it if there was deviations, like in the case of P-51?

I've asked one of our warbird pilots if he has any input, will be interesting to find out

Pman

On any complex, high performance aircraft.....

Application of the brakes before retracting the gear is a good idea. It prevents the tires from scrubbing in the wheel well which can lead to the gear failing to extend, blown tires, and excessive wear.

On any complex, high performance aircraft.....

 

Application of the brakes before retracting the gear is a good idea. It prevents the tires from scrubbing in the wheel well which can lead to the gear failing to extend, blown tires, and excessive wear.

The tires are spinning that fast that they expand like on fuel drag car?

Think about it.

100 mph unstick speeds...relatively small diameter tire... :thumbup:

Aircraft tyres that expand due to centrifugal forces at take off speeds? Really?

The Mustang manual clearly says that the brakes can lock if you use the brake after take off due to the excess heat generation. Might make for some spectacular landing runs! I wonder if it is modelled?

Hi! I might be of some assistance!

My day job involves working on these type of aircraft (warbirds).

In a modern world this is indeed a SOP, including the Mustang that we operate in the collection

There are several reasons, the first one is the obvious one. If a tyre is damaged on take off, if it is spinning when it enters the wheel well. You can imagine the damage it would cause.

Even if you did retract with hot brakes; I would be far more concerned with brakes that are hot enough to seize, in a wheel well; around flammable liquids. I cant imagine a time you would excessively heat the brakes enough during a taxi to cause this while operating the aircraft correctly.

A side note to this; is most brakes that are used on Warbirds today are from modern material. Modern steel disks and modern wear material, heat dissipation rates etc are all far far better than they were. But still even then; I cant imagine any reason for an war time operational aircraft ever having issues with brakes on the ground.

The second and often missed reason is gyroscopic precession, a wheel spinning whilst being retracted puts huge load strains on the undercarriage and retraction mechanism through precession loads. There is a surprising amount of force generated by even a small wheel spinning at 90 knots.

Typical after take-off checklist is to indeed touch the brakes before retraction. Its a touch not hold the brakes on, then retract the gear.

Most large modern airliners; as soon as the gear starts its retraction cycle, an automatic brake system stops the wheels before the gear even starts moving. For both the above reasons, blown tyre damage and precession loads.

Hope that helps

Aircraft tyres that expand due to centrifugal forces at take off speeds? Really?

Maybe Milo can PM you and explain that theory he came up with. The tires expand from heat and so does the air inside them.

The Mustang manual clearly says that the brakes can lock if you use the brake after take off due to the excess heat generation. Might make for some spectacular landing runs! I wonder if it is modelled?

My mustang POH is not available as I am not at home. Your quote specifies after use during excessive taxi. Many aircraft can do this...the one I fly at work actually has a Brake Temperature Monitoring System (BTMS) as do many modern large transport category aircraft.

"Excessive use" is the key to understanding the Instructions!

Excellent, some useful first hand information is always welcome.

My question regarding excessive expansion still however remains. In any design study, surely the expansion factors would always be taken into consideration when a. designing the fabric of a tyre, and it's expected operation parameters. And b. the design of a wheel well ought surely to allow extra clearance to accommodate any expansion. Damage to a tyre would of course be understood as a reason for issues, but surely not simple standard expansion due to heat/centrifuge, which must surely be mitigated for?

Also, the DCS P-51D manual, as provided, has a highlighted box, that simply states "Do not apply brakes after takeoff to stop rotation of the wheels to prevent the brakes from seizing."

There is no ambiguity in this statement, and it is written as a clear instruction, and mentions nothing about excessive anything as a pre-requisite. Modern practice aside.

I've asked one of our warbird pilots if he has any input, will be interesting to find out

 

Pman

Pman, thank you for looking into it. :)

Hi! I might be of some assistance!

 

My day job involves working on these type of aircraft (warbirds).

 

In a modern world this is indeed a SOP, including the Mustang that we operate in the collection

 

There are several reasons, the first one is the obvious one. If a tyre is damaged on take off, if it is spinning when it enters the wheel well. You can imagine the damage it would cause.

 

Even if you did retract with hot brakes; I would be far more concerned with brakes that are hot enough to seize, in a wheel well; around flammable liquids. I cant imagine a time you would excessively heat the brakes enough during a taxi to cause this while operating the aircraft correctly.

 

A side note to this; is most brakes that are used on Warbirds today are from modern material. Modern steel disks and modern wear material, heat dissipation rates etc are all far far better than they were. But still even then; I cant imagine any reason for an war time operational aircraft ever having issues with brakes on the ground.

 

The second and often missed reason is gyroscopic precession, a wheel spinning whilst being retracted puts huge load strains on the undercarriage and retraction mechanism through precession loads. There is a surprising amount of force generated by even a small wheel spinning at 90 knots.

 

Typical after take-off checklist is to indeed touch the brakes before retraction. Its a touch not hold the brakes on, then retract the gear.

 

Most large modern airliners; as soon as the gear starts its retraction cycle, an automatic brake system stops the wheels before the gear even starts moving. For both the above reasons, blown tyre damage and precession loads.

 

Hope that helps

This is very interesting information, thank you for that. :)

That was exactly what I hoped for.

I guess, in the case of a partly damaged tyre, the damage could be even worse if the tyre explodes in the closed wheel well?

Not a very nice thing to imagine.

Now my hope is just that the developers can implement this procedure in the modeling of the different aircraft. :)

At least for the Mustang, you should never use the brakes after takeoff.

 

(From the original manual, pg. 18 )

After takeoff, never brake the wheels to stop them from turning. If the brakes are hot from excessive ground use, they are likely to freeze.

:thumbup:

Every aircraft have their differences about this. I never worked on older aircraft , but from a modern aircraft stand point they can have differences. Looking at two modern ones I work on, the F-117 uses brakes to slow down the main tires but nothing about the nose tire. It does this by applying lower brake pressure ( around 700psi IIRC, when landing gear handle is placed on the up positions) The F-16, does the same for the main tires but the nose tire is stop by rubber pads. They are two rubber pad installed in the nose wheel well and this go against the nose tire rim/wheel and stop it after retraction. Its a simple thing, so I wonder if other aircraft may have the same. May be the reason the P-51 or other might not need to stop the main wheels by applying brakes.

Every aircraft have their differences about this. I never worked on older aircraft , but from a modern aircraft stand point they can have differences. Looking at two modern ones I work on, the F-117 uses brakes to slow down the main tires but nothing about the nose tire. It does this by applying lower brake pressure ( around 700psi IIRC, when landing gear handle is placed on the up positions) The F-16, does the same for the main tires but the nose tire is stop by rubber pads. They are two rubber pad installed in the nose wheel well and this go against the nose tire rim/wheel and stop it after retraction. Its a simple thing, so I wonder if other aircraft may have the same. May be the reason the P-51 or other might not need to stop the main wheels by applying brakes.

The nose wheel does not have a brake. The only way to stop the tire from spinning before the gear uplock is with a scrubber block.

Most commonly you will find a system to stop the wheel from spinning before the gear retracts on the landing gear without a brake system. It is just too easy and saves weight to just tap the brakes after take off and then retract the gear.

Nose wheel brakes can be fitted on some aircraft when operating in snow and slushy conditions aka 737. Not a normal fit though. Some aircraft disable the air ground sensor temporarily on lift off to apply de spin brake pressure then remove all brake pressure till the squat switches are made again. The rubber pads mentioned are pretty common though.

Mustang Manual Misquoting

Please - drop the "excessive". It is a misquote - it's not in the manuals, P-51D or F-51D, even though the wording of the caution changed a bit. If it was in a DCS manual, it was probably under artistic license. It does not seem to be mentioned in the early manuals, so it was possibly a lesson learned the hard way while operating the aircraft.

If you have a brake dragging by even an unnoticeable amount, things will be hot regardless of the amount of taxiing performed.

Shredded Tyres

It is true that you do not want to retract a spinning shredded tyre, as the rubber shreds can wreak havoc on the electrickery and hydraulics inside the wheel well. I wouldn't rule out denting a bit of structure either. On a big plane with several wheels per landing gear, it is a real risk. On a Mustang, or other WWII fighters with one wheel per landing gear, the likelihood of you shredding a tyre during the takeoff roll without noticing it is... let us say somewhat reduced. In theory you could hit a rare (and endangered) Southern Rebar Hedgehog just as you take the weight off the wheels and not notice that your tyre was ripped apart, but...

Precession

The gyroscopic forces are real, but nothing the torque links can't handle. Compare the precession loads with the punishment the gear has to take on the ground, and it'll be completely marginal. You'll find that some of the automated systems will apply brakes during the retraction, not prior to it. In other words, only once the gear is moving and the precession loads are already in place. Red herring/OWT.

It's Getting Creepy

Applying brakes after take off can lead to the tyre creeping on the rim. For this reason, and as mvsgas pointed out earlier, the automatic systems apply a limited amount of brake pressure (at times even on separate actuators, hooked up to the retraction system). Moderating the brake pressure finely is not an easy thing to do well manually every time as you're busy flying the departure.

For tubeless tyres, tyre creep is merely bad. For tyres with inner tubes, you'll end up shearing a valve stem and find a completely flat tire upon landing. Not a good day in the office.

Terminology

Snubbers is the term I'm familiar with for the rubber pads braking mainly nose wheel tyres. 'Scrubber block' was a new one to me, and to Google it would seem. Where is that one found?

Final Words

As always: Go by the book. If you think the book is in error, get engineering to change the book and then continue to go by the book. In the meantime - and this may be surprising - you should go by the book.

Cheers,

/Fred