Warbird Information Exchange

I have had this question asked of me dozens of times and I truely do not know the answer...........nor have I found anyone that does.

Why is the rudder on the P-51D (maybe the others too) the only dope and fabric part of the entire aircraft?

Help me out here, so I can answer truthfully instead of making things up (they don't know the answer so they believe anything told to them ).

It has always been my impression that it was due to control surface balance. Most aircraft up to that time had fabric control surfaces. The rudder is the most critical (flutter) and is balanced during the silver dope application. Checked, rechecked and final check before painting.

Sully

And you left out a final balance after paint application as this is the most important step.

All flight control surfaces are (should be) removed from the aircraft during painting and balanced before re-installation.

I wasn't going to go that far but yes.

Sully

All Mustangs up to and including the early D models had fabric elevators as well.
They were later replaced with metalized units as the fabric would induce pitching of the nose up and down at high speeds.
Rich

You beat me to it.

I also seem to recall some experiments with metalized rudders in the 50's?.

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That still begs an answer to the original question.

Why is the rudder left as being the only dope and fabric part on the airplane?

Rudder is a lot longer. Maybe it required too much weight to balance (overloaded the existing hinge design)?

It seemed to be the design philosophy of that time to have the controls be fabric covered. They were light, easy to repair and didn't use critical materials (alum) for the covering.
Different companies had there own ways. Republic and Lockheed metalized. NAA, Grumman, Vought used fabric or a combination of materials. Corsair ailerons were fabric covering over a wooden structure on all models as I recall.
As the speeds increase the next generation moved to all metal.
I believe Cavalier had an STC to metalize the P-51 rudders. I think it was only done to one. The H model had a metal rudder. I believe Whittington's Precious Metal had a H vertical and a metal Rudder on a D.
Rich

The farther away weight is from the Centre of Gravity the more profound its effect on Weight and Balance and therefore handling.
And range is better with "lighter" anywhere you can ADD it.
I always thought that was the whole reason for staying fabric.
Interesting about the elevators starting out fabric, but being changed to metal later.

And I could ALMOST buy the theory on strategic material shortages keeping the rudder fabric, but not the elevators due to flight characteristics.

Dang you guys is purty durned bright! Or good BSers!
SPANNER the humbled

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Support Your Local Warbirds! KBO!
The only reasons the airplanes matter is what the veterans did with them... and why.

This is a no BS zone.

Even the last of the WWII Navy fighters had fabric all around including the flaps. That being the Bearcat.
As to weight difference between fabric and Alum I don't think it is much. The USAAC Tech Order which pertains to changing the elevators on the P-51 has you remove the balance weight from the fabric elevator and install it on the metal one. The TO doesn't specify a rebalance though IIRC.
Rich

The overbalance and underbalance limits are spelled out in the SRM.

If I remember correctly, Twilight Tear (TFC's version) has fabric covered elevators.

Is there a STC to metalise the fabric ones. I assume they are approved for use today.

George

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BURMA! Sorry, I panicked

I believe some of the structure is shared between both types. You make or purchase whatever is different (ribs, trailing edge and skins) and rebuild them. You need a fixture to keep it straight. You also should have the blue prints so the completed part matches the original design.
As the parts are already a part of the original design and listed in the manuals it is not a modification of the aircraft. An STC shouldn't be needed but probably a Form 337 would.
There is the Type Certificate which specifies the aircraft should incorporate all the Tech Order changes. Technically for a Limited Category registered P-51 they should have metal covered elevators.
Fabric elevator P/N is 73-22001, metal is 122-2201. They fit either side. Same balance weight and trim tab is used.
Rich