P51 gear doors

[V1650]

Can anybody shed some light on the purpose of the polished inner section of the P51 main gear clam shell doors.

[barit1]

V1650:

inner section

: I presume you mean the inner skin panel, with spanwise "corrugations". This is a stiffener inner skin, riveted to the smooth outer skin, which maintains the shape of the door against air loads. Not unlike corrugated cardboard; It's typical of lightweight stiffening techniques used in aircraft structures.

polished

: Restorers like to display pride in their handiwork.

[V1650]

That's the section I'm talking about. I thought it may have also been used to snub the mains on retraction.

[clunckdriver]

No "snubing" should be required, the pilot is suposed to brake the wheels before retraction, its all to do with gyroscopic forces and not getting a nasty smell should the tires {tyres?} indeed "snub" somthing in the gear well. Anyone who forgets to do this on one of the aircraft I fly is rewarded with a fairly load screeching noise, not audible to the pilot but all the folks on the ground hear it.

[Old Photo.Fanatic]

P51 Photos. of main gear closing up on take off

In anticipation that these photographs illustrate the door panel in question.

Taken at Duxford Legends in 2010.





Taken at Oshkosh in 2011.




Taken at Duxford Legends 2010.




Close up from Pic. 3
Good view of the construction of this door panel. (Painted)









OPF

[barit1]

Great shots!

Also readily seen on parked aircraft after the hydraulic system has bled down.

[mightyauster]

The purpose of the polished stainless steel section on the inner surface of the wheel doors is for the tyres to slide on during emergency extension of the undercarriage. For an emergency extension, a "T" handle is pulled on the lower sub panel below the instrument panel which releases the hydraulic system pressure and, IIRC, also releases the wheel door latches. The gear lever is then selected "down", releasing the uplocks and both the mains and tailwheel extend under gravity, hence the tyres sliding on the wheel doors, pushing them out of the way. It is ops normal, after engine shut down on the ground, to pull the "T" handle to to relieve the hydraulic system pressure and consequently the reason why you will normally see a P-51 with the wheel doors open when parked.

[Vzlet]

To hopefully add to the interesting pieces of information already in this thread, here is a retraction shot with unbraked wheels, and a video of the gear doors closing immediately upon engine start.

[clunckdriver]

When I went through training on various North American products, if the "Eagle Eyed "duty pilot in the shack half way down the runway saw your wheels still rotating at high RPM on retraction it would cost one a contribution to the "Rumble Fund" on return from the flight, for a second incident one would be sent out to the duty pilot shack for a few days to be the "spotter" for gear-up approaches and unbraked retractions along with other student foul ups, both far more effective than a "bolicking" from some senior officer I found! {dont ask how I know}

[Vzlet]

Googling turned up a P-51 (D & K models) flight manual that states "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."

[clunckdriver]

Well, only about 150 hours on type, but have never been told or read that, I do remember however that when picking up T6s South of the border the Americans were suprised we used the brakes after T/O, they didnt, however now they are all owned by very rich guys , let them worry about it.

[barit1]

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.

Rather an overblown academic point of view; possible, not so likely. It would take a lot of aggressive taxiing to get brakes that hot, and the kinetic energy in the wheels after takeoff is quite low compared to braking during landing.

[Vzlet]

Brake Or Not?

I don't mean to come across as defending the "don't brake" method (especially as I have "about 150 hours on type" less than clunkdriver!), but it's interesting that there are two such diametrically opposed views. Could the pilot's manual be based on the assumption of much heavier operating weights than is typical today?

[mightyauster]

Part of the retraction test on the P-51 is to ensure there is a minimum clearance of 1/2" between the tyre and any components and/or structure in the wheel well to allow for tyre "growth" due to a spinning wheel.