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GOT: The Curtiss-Wright XP-55 Ascender


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#31 Wuzak

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Posted 20 January 2017 - 05:34 AM

Interesting - so they are not elevators, but flaps. 

 

My mistake.



#32 Wuzak

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Posted 20 January 2017 - 05:36 AM

In the case of the XP-55 the foreplanes were elevators.

 

But they had very restricted movement, more one way than the other - I have to look it up tonight. They were also all moving, And free floating , when not being activated.



#33 GregP

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Posted 20 January 2017 - 05:40 AM

I keep wondering what "the elevators were free to rotate somewhat when the pilot wasn't using them" means ... that has never been very well explained, unless it means the could freely rotate with the relative wind whenever some sort of "brake" was not engaged, and that doesn't make sense for a control surface.

 

I've never seen a coherent explanation of it yet ...

 

If anyone knows, could you share?  What about you, Wayne? Know what it means?

 

The only thing I can think is they were tab-controlled, like the surfaces on the Spruce Goose. In that plane, the pilots could never hope to control the elevators due to forces involved, and the control cables were connected to the servo tabs instead of the elevator. If that's what it means, why don't they just say it was servo tab controlled? The everyone would understand.

 

Most in here know the differences among servo, anto-servo, trim, and spring tabs.

 

I'm assuming a very poor description of servo tabs.



#34 Wuzak

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Posted 20 January 2017 - 08:52 AM

I keep wondering what "the elevators were free to rotate somewhat when the pilot wasn't using them" means ... that has never been very well explained, unless it means the could freely rotate with the relative wind whenever some sort of "brake" was not engaged, and that doesn't make sense for a control surface.

 

I've never seen a coherent explanation of it yet ...

 

If anyone knows, could you share?  What about you, Wayne? Know what it means?

 

The only thing I can think is they were tab-controlled, like the surfaces on the Spruce Goose. In that plane, the pilots could never hope to control the elevators due to forces involved, and the control cables were connected to the servo tabs instead of the elevator. If that's what it means, why don't they just say it was servo tab controlled? The everyone would understand.

 

Most in here know the differences among servo, anto-servo, trim, and spring tabs.

 

I'm assuming a very poor description of servo tabs.

 

It means that the elevator can move independently of the stick.

 

Somehow when the pilot performs a pitching movement with the stick the elevator engages and is under hos control. At othe times it can have a mind of its own.

 

The example given in the book is that if the nose pitches up without pilot input the elevator will pitch down relative to the fuselage. If the nose is pitched up 4° the elevator is pitched down 5° relative to the fuselage. At 12° nose up the elevator is pitched down 7°.

 

I'm not sure, but I think that is opposite what they would do for a commanded pitch up?

 

Apparently when the elevator was fixed to the stick the aircraft was unstable in pitch, but when it was allowed to free-float the aircraft was stable.

 

The elevator travel was 70° (60° on first prototype) trailing edge up to 17° trailing edge down.



#35 GregP

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Posted 20 January 2017 - 10:19 AM

Sounds like an anti-servo tab.

 

A servo tab helps the pilot move the surface in the directikon he wants it to go. An an anti-servo tab opposes that. So it SOUNDS as if the XP-55 Ascender had a very strong anti-servo tab. There is no other way of controlling the pitch wth a direct connection as far as I know, at that time.

 

It would be nice to know, though.



#36 Wuzak

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Posted 20 January 2017 - 12:43 PM

No, it had tabs as well.

 

170231-ascender_aug06.jpg



#37 GregP

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Posted 22 January 2017 - 03:30 AM

Most servo tabs I have seen serve to reduce the control forces. The aileron or elevator or rudder are moved by the stick with the tab being cam-driven. Perhaps this one has no pilot control over the front part of the elecator, and all depends on the tab, with the stick connected only to the atb, as in the Spruce Goose and a few other planes. Perhaps that is how it is "free floating."



#38 USAF Steve

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Posted 25 July 2017 - 06:13 PM

Not that this adds anything useful to the discussion of this particular aircraft, but reading about the test flights and crashes reminded me once again that test pilots have a lot of guts!  Back in the day, before aircraft were designed with computers, it seems like half the planes (or even most planes) were seriously flawed when they first flew.   The designers, builders and pilots really had no idea how the plane would behave when they first pulled the stick and lifted off the ground, whereas I think today's computer aided design and simulators that help mimic that behavior before the plane is actually built can minimize the 'unknowns'.   It's still dangerous but back pre-70s or so it was borderline crazy to climb into a new design for the first flight (or the first of any maneuver).   Plus, they didn't have Aces 2 ejection seats back then, so a pilot would have to physically climb out and jump for his life if a failure occurred.  






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