Difference in P-51B/C Landing Gear vs P-51D/K

[Matt Gunsch]

Matt - are you sure it wasn't pure 'aero' cause, basically same at the ammo access door? How would they suspect or prove gear leg 'play' as the cause? Then, if true what did NAA do to prevent play in the gear leg?

IIRC all the aforementioned failures due to clam shell opening at very high speed - normally near compressibility. I know there was a dive test at RAE in which the test pilot observed the 'bulge'/deflection on the ammo access door in a .82-85. Ultimate dive test... but that was on the Mustang IV, after they beefed up the door from the B to D/K[/quote]


there was a story in air comics that detailed the problem and how it was detected. as far as the ammo bay, the forces are different. Being on top of the wing, the bay doors are subject to a low pressure area that can suck the doors open, the clam shells are in a high pressure area.

[drgondog]

Matt - are you sure it wasn't pure 'aero' cause, basically same at the ammo access door? How would they suspect or prove gear leg 'play' as the cause? Then, if true what did NAA do to prevent play in the gear leg?

IIRC all the aforementioned failures due to clam shell opening at very high speed - normally near compressibility. I know there was a dive test at RAE in which the test pilot observed the 'bulge'/deflection on the ammo access door in a .82-85. Ultimate dive test... but that was on the Mustang IV, after they beefed up the door from the B to D/K

there was a story in air comics that detailed the problem and how it was detected. as far as the ammo bay, the forces are different. Being on top of the wing, the bay doors are subject to a low pressure area that can suck the doors open, the clam shells are in a high pressure area.[/quote

In a near terminal dive with shock turbulence, the 51 and 47 and 38, for different reasons, increased the negative pitching moment causing the nose to tuck and decrease the relative AoA of the wing, causing the bottom surface to have more 'lift contribution' on the lower surface than it had before.

Remember there is negative pressure on both sides of the wing relative to free stream pressure, just that the airfoil will cause the top side to have more 'lower pressure' than the bottom. When you invert the ac, you turn the tables, put forward pressure on the stick and change the AoA - and what was the bottom surface is now creating the greatest 'suction' and the airplane continues flying

[Matt Gunsch]

the article detailed the problem and it was not ammo door related. The brake lines were wrapped around the gear, showing the gear deployed and was twisted around in flight, cause the gear to be torn from the wing, that caused the wing to be torn from the plane. They redesigned the landing gear uplocks after the discovery.

[drgondog]

the article detailed the problem and it was not ammo door related. The brake lines were wrapped around the gear, showing the gear deployed and was twisted around in flight, cause the gear to be torn from the wing, that caused the wing to be torn from the plane. They redesigned the landing gear uplocks after the discovery.

The issue with the gear popping out is not in question - that is pure fact.

Ammo door issue is at very high speeds/low pressure over the top surface of the wing - that is a pure fact.

Negative pressure relative to free stream "Q" on both surfaces of a wing - that's a fact.

Improved door uplocks solving the issue - that's fact..Wheel tapping in my opinion is speculation- if that was the cause, what did NAA do to stop it.

I feel it is more reasonable to speculate that the wheel door opened for same aerodynamic (i.e negative pressure distributiion over the door) reasons - causing the door to deflect enough to be ripped open... and yes the uplocks solved it.. as the stiffened ammo door solved that problem.

Look, I could be wrong, but I do know a lot about fluid mechanics and aerodynamics and a fair amount about the 51 - enough so that the 'wheel' tapping sounds fishy - that's all I meant to say.

We can agree to believe what we wish to believe and not be bothered by an opposing opinion?

[Matt Gunsch]

the way they fixed it was to install gear up locks, the problem was early D models that had no uplocks. I have 40+ years of air classics here, if I can find it, I will, I think the story was in the 80s, so that narrows it down to only 120 issues

[51fixer]

. I have 40+ years of air classics here, if I can find it, I will, I think the story was in the 80s, so that narrows it down to only 120 issues

Air Classics as a source isn't the most true and believable information on record. The filter it went through to get printed there wasn't the greatest. They do have some good info but it isn't the leading source of factual information.
There is a reason they are referred to as Air Comix.
Rich

[mlenoch]

pressure-schmesser...........

Wasn't the fact that in the early D models, no mechanical landing gear uplocks were installed relying completely on hydraulic pressure to keep the landing gear retracted. When the pilot would apply back stick with the resulting high G, the landing gear would sag out of the gear wells....the hydraulic pressure was not able to keep the gear fully retracted. With the gear sagging under the high G load, the free stream airflow would simply tear either the clam doors or landing gear or both from the wing with resulting wing failure.

....Wasn't the above discussed before?.....Wasn't this the history of why mechanical gear uplocks are installed? Nothing to do with 'air pressure' in regards to the landing gear..........just checking.
Thx,
VL

[Matt Gunsch]

pressure-schmesser...........

Wasn't the fact that in the early D models, no mechanical landing gear uplocks were installed relying completely on hydraulic pressure to keep the landing gear retracted. When the pilot would apply back stick with the resulting high G, the landing gear would sag out of the gear wells....the hydraulic pressure was not able to keep the gear fully retracted. With the gear sagging under the high G load, the free stream airflow would simply tear either the clam doors or landing gear or both from the wing with resulting wing failure.

....Wasn't the above discussed before?.....Wasn't this the history of why mechanical gear uplocks are installed? Nothing to do with 'air pressure' in regards to the landing gear..........just checking.
Thx,
VL

You got it Vlado, that is what I was saying. As far as aircomics, if it was a story by O'leary, I would be leary, but this was not, it was by someone that had photos to back up the story.

[51fixer]

pressure-schmesser...........

Wasn't the fact that in the early D models, no mechanical landing gear uplocks were installed relying completely on hydraulic pressure to keep the landing gear retracted. When the pilot would apply back stick with the resulting high G, the landing gear would sag out of the gear wells....the hydraulic pressure was not able to keep the gear fully retracted. With the gear sagging under the high G load, the free stream airflow would simply tear either the clam doors or landing gear or both from the wing with resulting wing failure.

....Wasn't the above discussed before?.....Wasn't this the history of why mechanical gear uplocks are installed? Nothing to do with 'air pressure' in regards to the landing gear..........just checking.
Thx,
VL

The actual retainment of the MLG wasn't just hyd but the locks they built into the inner doors on the -D. That was the major change in design in regards to the door.
Earlier (B,Cs) there was a single latch at the rear of the inner door. It rotated by spring pressure into the lock position and was pushed into unlock by a push rod which ran outboard to the MLG actuator.
It is behind the inner door micro switch on the far right of the photo.

I think the engineers figured with hyd and the inner door latched front and rear that it would work and eliminate complexity and save weight. Quote from March 11th weekly NAA Service News (Which introduced the P-51D) states that "Uplocks eliminated and the weight of the MLG is carried by the retracting strut (actuator) and the fairing doors (inner doors)." It goes on "The latch (inner doors) also insures the doors will be positively held closed at high airspeeds, thus eliminating any possibility of excessive drag by the doors partially opening". I paraphrased a bit to reduce typing.
I guess it wasn't as successful. The hyd system was redesigned as well.
Rich

[mlenoch]

Rich:
Does Princess E have mechanical landing gear uplocks? Did I miss the pix with that view?
Thx,
VL

[drgondog]

pressure-schmesser...........

Wasn't the fact that in the early D models, no mechanical landing gear uplocks were installed relying completely on hydraulic pressure to keep the landing gear retracted. When the pilot would apply back stick with the resulting high G, the landing gear would sag out of the gear wells....the hydraulic pressure was not able to keep the gear fully retracted. With the gear sagging under the high G load, the free stream airflow would simply tear either the clam doors or landing gear or both from the wing with resulting wing failure.

....Wasn't the above discussed before?.....Wasn't this the history of why mechanical gear uplocks are installed? Nothing to do with 'air pressure' in regards to the landing gear..........just checking.
Thx,
VL

This Does make sense

[51fixer]

Rich:
Does Princess E have mechanical landing gear uplocks? Did I miss the pix with that view?
Thx,
VL

Vlado,
The pic I posted is PE. The silver hook in the middle is the uphook. It is to the left of the inner door plunger. The linkage runs off of a torque tube on the spar to the right. It is similar to a T-6 system in its design.
Rich

[mlenoch]

Thanks Rich. Now I see. Thanks for pointing that out.
The sun is in the window, its a warm afternoon and my eyes are almost at half-staff.
VL

[Matt Gunsch]

Thanks Rich. Now I see. Thanks for pointing that out.
The sun is in the window, its a warm afternoon and my eyes are almost at half-staff.
VL

and you without a Mustang to fly,

make the oil companies happy and take the T-bird up.....................

[51fixer]

Thanks Rich. Now I see. Thanks for pointing that out.
The sun is in the window, its a warm afternoon and my eyes are almost at half-staff.
VL

If it helps you feel better Jim just took PE down to a beach show in Ocean City MD and Dan Friedkin flew along in his TF with Ed Shipley in the back seat.
Rich