Mustang Gear Doors and Flaps, the eternal debate

I recall reading years ago -- probably in one of Merle Olmstead's accounts -- that it was common practice among ETO Mustang crews to hand-close and spring-lock the inner doors, purely to keep them out of the way when performing maintenance functions underneath the aircraft.

There certainly are quite a few photos showing this configuration, and that's usually how I've modeled mine over the years without photo sources to the contrary.

Thanks, John. I wish I could remember where I read what I posted about the landing gear doors and flaps on the Allison Mustangs. It's just that all the photos I've see of Allison Mustangs show the flaps and gear doors up so that's the way I built my kits.

Ooops. Except this one:

It has been several months since I worked on a P-51, but IIRC, the inboard side of the flaps have a step on them.  The P-51s wing is pretty high off the ground, so the step on the flap makes it a lot less of a high jump to get on the wing.  Of course, when working on it, we always covered the wing and used a step ladder instead of the flap step.  Couldn't say how any of the mechanical components work, as that's not my field (mine is avionics), but the flaps have always been down, and I think its because of the flap step.

Ta John, I expected as such. same as on the T6, exept the T6has a slider pushrod that actuates pushrods to the flaps

If you’ve ever seen footage of a P-51 starting it’s engine, you can see the clamshell doors snap closed as the system gains hydraulic pressure.

Theunis, both flaps on the P-51 are connected via a torque tube to a single hydrulic actuator that moves them. 

What John is saying is correct. I work on NA T-6 Harvards and whan on the ground they all droop their flaps over time, atleast the ones I see. Unlike the P51 they dont have clamshell geardoors but the down lock on the T5 is somewhat more elabotare and very fiddly to work on believe me, I had to replace on a few years ago and it is NOT a fun job.

On the T6, the main gear , as it pivots down has a metal lockbar ontop of the gearleg. This engages a triangular lockblock (also springloaded) in the top section of the outer centre wingsection, you may have seen the small pannel that allows access and inspection of this lock setup. It actually works in exactly the same way a door in your house does, but there is an overly complex system of small pushrods and belcranks that will pull the lockpin aft as the gear "up" lever is selected before the hydrolics are activated. I am sure on the P51 is had to work basically the same way jusy not through links and rods.

The reason you will see the clamshelldoors at different angles is because the way hydrolics work. Each door has its own ram that wil retract or lower it when the selector pushes oil in either end of the piston. Fluid dynamics will tell you that it will always take the path of least resistance and therefore one piston may be "favored" over the other untill pressure in the system is equalised.

That is why, upon gear retraction on older craft like T6, P51, P40, c47 ect you see one gearleg almost always retracts before the other one does, it is easier for the oil to flow to one piston and fill it first before the other one untll the piston in the ram is under so much pressure that it then diverts oil to the non -up piston and retracts that one.

As for the flaps  on the P51 being in the same "amount" of down, I can only asume that the flaps must have some form of mechanical link between them to stop assymetrical deployment in flight and as the pressure bleeds off both droop at the same rate.

Granted some may say the pilots select down flap  and leave then there but this, to me atleast is a strange thng to do. I know  on the Spitfire and Hurricaine the flaps were retracted as soon at they were on the ground because it desturbed theairflow throught radiators. On the P51 this is not an issue but flaps in the fully down position are prone to be damaged with debris from the wheels being kicked up so my locic tell me they would have retracted them also  on the way back to the apron....I stand to be corrected on this issue though

Theuns