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Lordbutter4
03-27-2006, 03:25 PM
Just got done reading an article in Air Classics about an american pilot who loved flying 39's. Reading this article brought up an interesting find.

"For those of you who dont know the airplane, the cockpit controls actually flew the trim tabs which in turn moved the controls. This made control movement almost effortless. Contrary to all other fighters of the time, where you had to rapidly move all three trim tabs as well as the controls in a hard dogfight, you could do Cuban Eights all day long in a P-39 with your feet on the floor and one finger on the top of the control stick. I would come down after dogfights in p-40s, p-47s, p-51s, etc., wringing wet and totally pooped. With the p-39 I was nice and dry and ready to party. This might account for my infatuation with this plane."

The man was Elden E. Williams, the article was from Air Classics Volume 41.

So the 39 should trim itself with control movements? Anyone have any good info on this?

Lordbutter4
03-27-2006, 03:25 PM
Just got done reading an article in Air Classics about an american pilot who loved flying 39's. Reading this article brought up an interesting find.

"For those of you who dont know the airplane, the cockpit controls actually flew the trim tabs which in turn moved the controls. This made control movement almost effortless. Contrary to all other fighters of the time, where you had to rapidly move all three trim tabs as well as the controls in a hard dogfight, you could do Cuban Eights all day long in a P-39 with your feet on the floor and one finger on the top of the control stick. I would come down after dogfights in p-40s, p-47s, p-51s, etc., wringing wet and totally pooped. With the p-39 I was nice and dry and ready to party. This might account for my infatuation with this plane."

The man was Elden E. Williams, the article was from Air Classics Volume 41.

So the 39 should trim itself with control movements? Anyone have any good info on this?

Tully__
03-28-2006, 04:41 PM
No.

What the guy is saying is that the joystick moves the ailerons and elevator by actuating the trim tabs instead of by direct mechanical connection. He would still need to adjust the trim tab offset to fly hands off (trimmed) so it doesn't mean trim is automatic.

I also suspect it's at least partly in error as the trim tabs alone would not give you full control authority at low speed when you most need to be able to make large but precise control movements. Without actually researching it I'd suspect that what happens is the trim tabs are actuated in conjunction with the primary controls to reduce required pilot forces at high speeds. Again you would still need to use the trim controls to adjust the "neutral" position of the trim for hands off flight as speed/power/load conditions change.

NonWonderDog
03-28-2006, 07:36 PM
What Tully said.

Also, this system is not uncommon. Many planes had their flettner tabs rigged to the control stick to reduce control forces -- even if there was no trim control for the surface in question. The control stick still moves the surface itself in this config, but the tab is rigged to move in opposition at the same time.

Fly an IL2 and look at the ailerons, you'll see the system in action.