[NSRCA-discussion] Annhedral Stab

[Jack Keiser]

In the early 80's I was flying an EU-1A in competition. In those days, it 
was considered a large plane, I believe 965 sq in of wing and 9+ pounds. At 
any rate, it was a little different and had some unusual flight 
characteristics. Looping maneuvers weren't the greatest but it rolled like 
it was on a wire. Knife edges took some trimming; I don't remember which way 
it pulled but it was significant. That caused me, and others, to move the 
horizontal stab around; lower than the original, I believe, to solve that 
problem. And that introduced another problem - in vertical down lines with 
power off, the elevator would become totally ineffective. Blanked by the 
wing, I presume. Add some power and it was ok. Not a comforting way to fly.

So, I built another one, my third or fourth, and put anhedral in the 
horizontal stab , just like the Curare. Voila! Problem solved. I reasoned 
that some part of the elevator would be in clean air and it seemed to work. 
I suspect it had something to do with the low aspect ratio of the wing, as I 
haven't seen or heard of that problem since.

Since then, I've had occasion to talk with a designer who was involved with 
the F-4 Phantom, which has a significant amount of anhedral in the stab. His 
view was that the anhedral was a fix for some other problem and otherwise 
wouldn't be there. Don't remember any more of that conversation, but it 
seemed consistent with my modeling experience.

Jack
----- Original Message ----- 
From: "Nat Penton" <natpenton at centurytel.net>
To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
Sent: Sunday, April 20, 2008 10:38 PM
Subject: Re: [NSRCA-discussion] Annhedral Stab


> Jim
> I used anhedral, about 5 degrees, on my Express because the wing/stab
> separation is effectively zero. My fear was interference from the wing 
> shear
> line and the idea was to have the stab operate in a broader range of the
> wash.
>
> It is impossible to get the stab out of the downwash.
>
> I have experienced heart pounding rudder interference from forward fins 
> and
> wanted to avoid those puzzling instances of "was that me or was that the
> airplane".
>                                        Nat
> ----- Original Message ----- 
> From: "J N Hiller" <jnhiller at earthlink.net>
> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
> Sent: Sunday, April 20, 2008 1:01 PM
> Subject: [NSRCA-discussion] Annhedral Stab
>
>
>> Can I open a discussion on why some designs have an annhedral stab?
>> Was it to lower the effective flying height of the stab to reduce the 
>> wing
>> to stab vertical offset and knife edge belly pitch, or is there some 
>> other
>> reason?
>> Jim Hiller
>>
>> _______________________________________________
>> NSRCA-discussion mailing list
>> NSRCA-discussion at lists.nsrca.org
>> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>>
>
> _______________________________________________
> NSRCA-discussion mailing list
> NSRCA-discussion at lists.nsrca.org
> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion