P-51 doors and flaps

[mhorina]

During Jan's gorgeous build. He did a great job on everything, no question about that. However during the build

he used AM and did a great job on the wheelwells. Then he was told that while beautiful and well done, its a shame you have to close them up because the gear doors should be up. Then he was told thats not right they should be down,find this on his '

'Ready for inspection' post, it was said no they should be down. Jan's model now has doors up and flaps down So my question is if the doors are

down do the flaps have to be down or is it both down or both up ? Help me please help me. Thanks

 

Mike Horina

Edited April 12, 2018 by mhorina

[D Bellis]

After engine shutdown, the normal procedure was to fully lower the flaps. On Merlin-engined P-51s that relieved the pressure in the hydraulic system, thus the inner doors would bleed down because there were no positive up-locks on the inner gear doors.

 

Yes, there are photographs of Merlin-engined P-51s with the inner gear doors up, but either those photos were taken immediately after shutdown, or the ground crew pushed the door closed for whatever reason. Inner doors closed on the ground was not the 'normal' position.

 

Allison-engined P-51s had positive up-locks on the inner gear doors, so those were normally up when parked. 

 

HTH,

D

[Gigant]

Here is my position on that kind of thing:

 

A Man and his son were once going with their Donkey to market. As they were walking along by its side a countryman passed them and said: “You fools, what is a Donkey for but to ride upon?â€

So the Man put the Boy on the Donkey and they went on their way. But soon they passed a group of men, one of whom said: “See that lazy youngster, he lets his father walk while he rides.â€

So the Man ordered his Boy to get off, and got on himself. But they hadn't gone far when they passed two women, one of whom said to the other: “Shame on that lazy lout to let his poor little son trudge along.â€

Well, the Man didn't know what to do, but at last he took his Boy up before him on the Donkey. By this time they had come to the town, and the passers-by began to jeer and point at them. The Man stopped and asked what they were scoffing at. The men said: “Aren't you ashamed of yourself for overloading that poor donkey of yours and your hulking son?â€

The Man and Boy got off and tried to think what to do. They thought and they thought, till at last they cut down a pole, tied the donkey's feet to it, and raised the pole and the donkey to their shoulders. They went along amid the laughter of all who met them till they came to Market Bridge, when the Donkey, getting one of his feet loose, kicked out and caused the Boy to drop his end of the pole. In the struggle the Donkey fell over the bridge, and his fore-feet being tied together he was drowned.

“That will teach you,†said an old man who had followed them:

 

“Please all, and you will please none.â€

 

IMHO, from my experience, unfortunately, you post your WIP stuff at your own risk.

 

Listen to the "Monday morning quarterbacks", and their often conflicting and contradicting advice can get frustrating enough where even a statue would explode.

 

Personally, if the modeler wants certain flaps and doors down and open as well, or some open and others closed, I feel that is the builders' prerogative.

Edited April 12, 2018 by Gigant

[Kagemusha]

It might be the builder's prerogative, but I think it wise to consider what would the donkey do?

[mhorina]

Since these are models yes you can do whatever you wish. To answer D's reply and thank you but. There is a 355 FG site with many war time

photos that I went through. As I was going to do my buid with the doors up and the flaps down. You can fing doors up and flaps up,

you can find doors down with flaps down. But after going through many photos I couldn't find any with one up and one down. So I thought

I'd ask if anyone knows for sure if that could happen.

Mike Horina

[Plasto]

How long does it take after engine shutdown for the hydraulic pressure to bleed off and the inner doors to drop down to the lowered position?

 

Also after start up and with the engine running as hydraulic pressure builds up do the doors then close up??

[Gigant]

Here we go again!

 

And while we are at it, why not the debate whether the wheel wells were zinc chromate green or yellow?

 

I have instruction sheets telling me green, while I also have actual WWII color footage where the fighter aircraft had a camera in it's wheel-well, and everything painted was painted yellow!

 

Personally, unless someone is/was an actual P-51/47/38, etc., pilot or technician, not just another armchair expert, I would not let them influence my decided preferences based on my personal research and experience as a now retired engineer.

[Gigant]

It might be the builder's prerogative, but I think it wise to consider what would the donkey do?

 

You might try that yourself and see if your luck was better then Balaam's. If you remember, he didn't like what he was told by his.

[Juggernut]

When the engine has been shut down after a flight, the hydraulic system will remain charged at 1000-1150 psi until either the gear ,brakes or flaps are exercised until pressure is zero (not practical).  Hydraulic system leaks notwithstanding (and not common) the landing gear inner fairing doors (aka inner doors) will remain closed as long as there is sufficient pressure in the system. Only when there is insufficient pressure in the hydraulic system will the inner doors free fall to their fully down position (gravity works).  Exercising the flaps and/or landing gear as I said, is hopelessly impractical to bleed off hydraulic pressure.  The only other way to dump the pressure is with the emergency hydraulic release in the cockpit.  I have not yet been able to confirm this but in my considered opinion, ground crew could pull the emergency hydraulic release in the cockpit to dump all hydraulic pressure.  This may cause the flaps to drop and will cause the inner fairing doors to drop over time.  Again, gravity works.  Ground crews may also have lowered the flaps using residual hydraulic pressure then pulled the emergency hydraulic release which would seem like a better option to me.  I haven't found any documentation about standard practices of the ground crews (aka service manuals) but that's what i've deduced from reading the manuals.  I suppose it would be possible that the pilot would drop the flaps on returning from a sortie at the hardstand but I've not seen photographic evidence (and it's hard to tell at best) of the practice occurring and I've been unsuccessful at locating the procedure in the pilot's flight manual.  I'm more inclined to think the ground crew dropped the flaps while rearming the aircraft and dumping the hydraulic pressure via the emergency hydraulic release.  in short, this is a summary of some of the possible combinations of flaps and inner fairing doors:

 

Yes, you can build the aircraft with the flaps down and the inner fairing doors up (pressure in hydraulic system, flaps selected down).

Yes, you can build the aircraft with the flaps down and the inner fairing doors down (no pressure in hydraulic system, emergency release pulled).

Yes, you can build the aircraft with the flaps down and the inner fairing doors in any position between fully up and fully down (emergency released pulled, zero pressure in hydraulic system).

Yes, you can build the aircraft with flaps and inner fairing doors up. (hydraulic pressure present)

Flaps up and inner fairing doors down should not normally be possible unless there were a problem somewhere in the hydraulic system or the flaps are stuck in the up position or my belief that the flaps would bleed down with zero hyrdaulic pressure is false (and that's entirely possible but gravity really works and flaps aren't balanced like primary control surfaces are). 

 

EDIT: I need to study the hydraulic schematics and system documentation some more to answer questions I have and time will tell if I'm correct or not.

 

 

REFERENCES: P-51D Mustang Pilot's Manual & P-51D, K, Mustang IV Erection and Maintenance Manual.

Edited April 13, 2018 by Juggernut

[D Bellis]

I also have actual WWII color footage where the fighter aircraft had a camera in it's wheel-well...

No great secret. The "Special Project" stencil on Lou IV's data block denotes that the airframe was altered. And, there are period, color photographs of the camera opening installed forward of Lou IV's tail wheel well (certainly not "in" it).

 

From the Roger Freeman Collection:

 

And, a cropped, lightened close-up of that area:

 

Never quite understood why anyone would rail against wanting to get things right. 

 

D

Edited April 13, 2018 by D Bellis

[Juggernut]

I think he was referring to the gun camera.

[D Bellis]

I think he was referring to the gun camera.

If so, that's even more bizarre since all P-51B/C/D/K variants had a gun camera installed in the left main wheel well with the opening visible on the leading edge... 

 

D

[BiggTim]

Here's another opinion you probably won't hear from anyone else:

 

I have no freaking idea!!!!! ðŸ˜

 

Tim

[Gerhard]

So is it yellow or green chromate?

[Jan_G]

that's so much valuable information in this thread (one of the reason I like LSP so much), pity that I knew about it before

however when I decided to keep main gears doors up and flaps down I was inspired mainly by this pic of that particular airframe (main doors closed, flaps looks to be down and engine turned off)

HTH

jan