Elevator trim during Combat

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kk89,

When I made the remark that I should change my moniker to 'kopy kitty 89', I was making fun of myself, not accusing you of any wrongdoing. I was stumbling around half-awake when I read your post, and didn't really comprehend the part in reference to myself and the time of your post in the 'P-38 vs P-51' thread. In my semi-concious state (it was 5:30 am) I just thought you had beat me to it :rolleyes:

Hope this clears things up:)

JL
 
I have a question for you guys who are wizards in aerodynamics. I always thought that the horizontal stabiliser on an AC had a cross section like a wing, camber, so Bernoulli"s Principle made the HS produce lift. If I remember right a 172 I used to own part of had an air foil shaped HS. The Corsair had HSs that were interchangeable. The left could go on the right and vice versa. I read where it was not unusual to see sometimes one side of the HS with gravel marks on the top indicating that at one time that HS had been on the other side. How does that work aerodynamically?
 
renrich said:
I have a question for you guys who are wizards in aerodynamics. I always thought that the horizontal stabiliser on an AC had a cross section like a wing, camber, so Bernoulli"s Principle made the HS produce lift. If I remember right a 172 I used to own part of had an air foil shaped HS. The Corsair had HSs that were interchangeable. The left could go on the right and vice versa. I read where it was not unusual to see sometimes one side of the HS with gravel marks on the top indicating that at one time that HS had been on the other side. How does that work aerodynamically?
Click to expand...

Some HS airfoils are zero camber, others not.. sounds like the Corsair had a zero camber symmetrical airfoil... most fighter designs were that way.

Aircraft designed to fly most of their profile in steady criuse, subsonic, might have a cambered airfoil simply for that particular speed at the likely altitude range and for the design incidence of the HS - the slighly more cambered airfoil at zero elevator trim deflection might have less drag than trimming up the elevator.

Tail design is largely about Stability and control of the forces up at the center of gravity and the aerodynamic center of the wing. You look at dive pull out, cruise stability in the various Cg ranges, and rudder loads in turn (and roll if designed for that) profiles - so you size it first - then look for efficiencies second.
 
Thanks, Bill. I appreciate the info. Makes sense. An earlier question I had that never got answered perhaps you could do so. On Corsair the part of the wing which was the inverted gull would have a different lift vector than the main wing. Aerodynamically, what does that do? Seems to me it might the AC more positively stable in the roll axis which might not be a good thing for a fighter. However, the F4U was supposed to be excellent in roll so maybe not.
 
renrich said:
Thanks, Bill. I appreciate the info. Makes sense. An earlier question I had that never got answered perhaps you could do so. On Corsair the part of the wing which was the inverted gull would have a different lift vector than the main wing. Aerodynamically, what does that do? Seems to me it might the AC more positively stable in the roll axis which might not be a good thing for a fighter. However, the F4U was supposed to be excellent in roll so maybe not.
Click to expand...

I am curious about that also. I have never seen anything published on the Gull wing - ether high or low mount. My first reaction is that lift components result in slightly lower vertical components and 'equal but opposite' span wise lift vector... conceivably the aerodynamic center was moved slightly outboad on the F4U than from the the same wing but straight spar? Pure guess on my part


The primary consideration for roll rate is the rolling moment of intertia (think F-104, etc for awesome roll) but nothing about the Fw 190 just leaps out at me for example, about wing design... then the rolling forces caused by the aileron

Putting larger ailerons is another factor but you have to add some structure to anticipate twisting the wing and causing control reversal, and to take the additional loads of a larger aileron at high speeds. It is conceivable that adding the folding wing and carrier landing load considerations to the F4U forced the beef up on the wing enough to put a more powerful aileron on the wing - but I don't know.
 
FLYBOYJ said:
Just another comment on all this...

I knew Tony LeVier pretty well. He once told me that when the P-80 became transonic the ailerons would buzz and the nose would "tuck down." The same thing would happen with the F-94 except it wasn't as abrupt. Tony told me that he exceeded the speed of sound several times in the F-94 (without tip tanks) and even beat Chuck Yeager in a diving race, he flying the F-94, Yeager in an F-86.
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Short story about LeVier. I did not know him, just met him and his wife quite a few years ago at Oshkosh.. after he passed away another friend who had known Tony a long time asked me if I would prevail on his widow to release a manuscript that he had been working on and find a publisher for it.

I tried twice in 2002 and 2003, offering to put it together for nothing and find a couple of publishers for her to work with, but neither she nor her new husband would ever return the calls. If he in fact had put something together to follow up on his other book it is a shame to let something like that just disappear.
 
drgondog said:
Short story about LeVier. I did not know him, just met him and his wife quite a few years ago at Oshkosh.. after he passed away another friend who had known Tony a long time asked me if I would prevail on his widow to release a manuscript that he had been working on and find a publisher for it.

I tried twice in 2002 and 2003, offering to put it together for nothing and find a couple of publishers for her to work with, but neither she nor her new husband would ever return the calls. If he in fact had put something together to follow up on his other book it is a shame to let something like that just disappear.
Click to expand...

Interesting Bill...

My ex wife had an office right next door to him. Before they closed Burbank down, Lockheed allowed him to run his aviation consulting company (SAFE) out of the facility.

I interviewed him a few times for a small aviation magazine I worked for part time in the mid 1990s. He was a great guy to talk to and always had some great stories.
 
I have mentioned this before but Vought reportedly spent more than 700 flight test hours improving the ailerons on the Corsair. My point about roll rate being degraded by excess positive stability in the longitudinal axis(and I don't know enough about it to be very positive) is that if the AC is positively stable in that axis, when forced to roll, it wants to return to level flight so would be constantly resisting roll. Is that all wet?
 
renrich said:
I have mentioned this before but Vought reportedly spent more than 700 flight test hours improving the ailerons on the Corsair. My point about roll rate being degraded by excess positive stability in the longitudinal axis(and I don't know enough about it to be very positive) is that if the AC is positively stable in that axis, when forced to roll, it wants to return to level flight so would be constantly resisting roll. Is that all wet?
Click to expand...

Your question isn't a silly one Rich. I just don't know the answer about a.) whether the Gull gave it an additional roll intertia or not, or b.) whether it made a significant difference if it did.
 
Well the Corsair's wings being a gull shape were ofcourse heavier compared to span than conventional wings, and so there would be more intertia than normal. But I can't say how much this affected roll rate, however Vought seems to have been abit concerned about it, but AFAIK they solved it with the boosted ailerons.

There is also the difference in the lift vector caused by the gull shape ofcourse...
 
Yep some later models had, it was used on one in the Navy tests with the captured Fw190 A-5.
 
I've searched around on Google and can't find any mention of boosted ailerons on any model of the Corsair.

The only note is the change from wooden to metal ailerons.
 
Ok, not hydrolic power-boosted ailerons like the P-38, but a special "boost tab" installed on the inboard portion of the aileron. Attached to a joint on the wing the tab moves in the opposite direction as the aileron, lightening controll forces and increasing mechanical advantage. (a servo tab)


View: https://www.youtube.com/watch?v=G69yNblVO2k at 4:15
 
The later Corsairs were noted for light control forces with excellent control modulation. Reportedly better than F6F or F8F. On some WW2 AC, roll rate was hindered by the amount of muscle the pilot could exert on the aileron controls. Soren, thanks for your info on TA152 kills in the other thread. I can't post a comment on that thread now.
 
That video of the PoF Corsair was an F4U-1, and he noted it for having very light ailerons (said you could almost use your fingertips), and a light rudder as well. Though the elevator was heavy at high speeds.

They showed the "boost tab" as well.

It's such a simple mechinism, I wonder why other contemporary a/c didn't use it. (did any other fighters use somthing similar)
 
I had read about the boost tabs but did not know how they worked until seeing the video. What an elegant engineering solution. As you know, I am not unbiased, but I believe the Corsair when seen in those videos, more than lives up to it's reputation. It is a clean but powerful and agile looking AC, especially when one knows it's capabilities. It is unfortunate that it's early teething problems did not allow it to play a greater role in the war. I remember reading a description of how the Corsair flew by Frank Tallman(Tallmantz Aviation, Tallman and Mantz owned a bunch of warbirds and rented them and flew them for Hollywood.) He said the Corsair had moves like a leopard, it was so agile, while the P51 flew like it was on rails.
 
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