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Author Topic: What's to know about T_Tails and stunt?  (Read 1188 times)

Offline John Miller

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What's to know about T_Tails and stunt?
« on: July 19, 2007, 10:21:14 AM »
I posted much the same thing yesterday overr on SSW forum, but not too many answers yet. So figuring that someone who might know, is on this forum exclusivly, I'm asking here too.

I'm considerring a T-Tail version of a design Gordan and I are working on, but, I've heard that real T-Tails require more positive incidence than we would believe.

Are there any guide lines, or formulas I can use to figure a solution rather than cut and try? If I can't get good information, I'm considering a stab using an adjustable feature for incidence.  A bit worried about the stregnth of the mounting system though.

John Miller
Getting a line on life. AMA 1601

Offline Don Hutchinson AMA5402

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Re: What's to know about T_Tails and stunt?
« Reply #1 on: July 19, 2007, 10:43:54 AM »
Hi John- Don't see any reason that a T tail would need more incidence, it is considerably further out of the wing downwash that a standard configuration. Ask John Wright, he flew a T tailed model for a while and can give you some insight about how it worked.

Offline John Miller

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Re: What's to know about T_Tails and stunt?
« Reply #2 on: July 19, 2007, 10:52:00 AM »
Thanks Don, I'll check with John. I understand that Tom Mclain has also had a successful T-Tail stunter.
Getting a line on life. AMA 1601

Offline Mark Scarborough

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Re: What's to know about T_Tails and stunt?
« Reply #3 on: July 19, 2007, 11:50:49 AM »
My limited knowledge would indicate that some incidence would be helpfull in order to counter the drag moment increase. However as to quantifying the amount, , I think an adjustable setup would be a good start. However, by building it zero zero, you can get a feel by how much down elevator you trim in to get balanced flight, then reflect that on further prototypes,, (you like to build man, so its ok to hve to build a couple)
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Offline Peter Nevai

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Re: What's to know about T_Tails and stunt?
« Reply #4 on: July 19, 2007, 06:29:44 PM »
IMHO a T tails drawbacks are primarily 1. Rigidity (Being perched atop of the relatively thin vertical stab.
2. Additional complexity in controls configuration.
Words Spoken by the first human to set foot on Mars... "Now What?"

Offline Jim Pollock

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Re: What's to know about T_Tails and stunt?
« Reply #5 on: July 19, 2007, 08:12:21 PM »
John,

One of the things that Tom learned about a T-Tail is not to make the horizontal surface a stabalator.  It just didn't work as needed.  Tom changed it to a conventional stab/elevator layout and was much more satisfied with the results.

Jim Pollock    H^^ 

Offline Air Ministry .

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Re: What's to know about T_Tails and stunt?
« Reply #6 on: July 20, 2007, 07:41:43 PM »

  You need good torsional ridgidity in the fin ( spelt - use aryldite )
 Sometimes full size stuff gets ' buffeting ' wich is airflow istability .
 which they solve by fitting a ' bullet - fairing ' , teardrop shaped ,
 at - through the intersection of the fin - stab , to guide and
 smooth the air flow . It also helps the ridgidity .

 If the stabs shuddering and trying to jump ship , thats 'buffeting '

 Only needs an iota of incedance if adjacent to the wing airlow.
 ( pressure differential ) If its ' way up ' in its own clean  air ,
 you can feel that  it flying along up there !

 DRAG - tecnically a flat sheet stab is the most efficent -
 In more ways than one .
 IF you use a big thick blunt L.E.  ' thing ' up there,
 you would have a bit of drag , up high and back .

 IF you had a detachable stab fitted with a couple of machine screws,
 you could shim the incidance.

 The other bit's a hollow fin, a guide at the base for the push rod,
 and a vertical 1/4 ply 'upstand' epoxied to it,with the wire end fitted to the top ,to fit to the Elevator horn .

  My profile Westland Whirlwind ( Oriental wing ), just has the push rod from the flap horn to the elevator horn,
 with a guide half way along ( up ? ) And flys well enough to scare most people, but is a bit stable for combat,
 so it makes a very good stunt ship .

Offline Shultzie

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Re: What's to know about T_Tails and stunt?
« Reply #7 on: August 09, 2007, 06:59:30 PM »
Also perhaps one might give some thought about the possibility that the WING NOT BLANKET THE STAB AND ELEVATORS IN HARD INSIDE CORNERS....and remember that one could always add thin but stiff pulltruded graphite wire braces from the fuselage to the high T tail....
HOWEVER....AERODYNAMICALLY it has always boggled my mind when I found out just how much tubulence and drag...simple wire struts add to any flying machine...be it a large 747 or a teenie little stunt model...

Hey Gary Letsinger...and you  engineering aerodynamoooooos??? Any thoughts???? S?P na#
Don Shultz

steven yampolsky

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Re: What's to know about T_Tails and stunt?
« Reply #8 on: August 09, 2007, 08:57:47 PM »
A bit worried about the stregnth of the mounting system though.
That would be my primary concern too. What are you thoughts on making it rigid?

Offline Shultzie

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  • Don Shultz "1969 Nats Sting Ray"
Re: What's to know about T_Tails and stunt?
« Reply #9 on: August 10, 2007, 04:19:38 PM »
That would be my primary concern too. What are you thoughts on making it rigid?

Uhhh? VIAGRA? LL~ :-X oops...sorry. Looks like my mind is "stickin out" again?
Don Shultz

Offline John Miller

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Re: What's to know about T_Tails and stunt?
« Reply #10 on: August 11, 2007, 05:33:31 PM »
Thanks guys for the helpful advice. Several golden nuggets will be used when I get to the project. (M. Spencer, thanks for your insights).

As for the supporting structure, I'm considering a relativly thicker verticle stab. It should be at least as good as a profile fuse.

The design I'm considering, is the last Pathfinder, but only after the prototype is finished as per plans.

Again thanks for your help.
Getting a line on life. AMA 1601

Offline Ted Fancher

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Re: What's to know about T_Tails and stunt?
« Reply #11 on: August 11, 2007, 09:29:21 PM »
Hi John,

It might be worth noting that, although in steady state flight a high stab wouldn't have much effect on the vertical location of the center of drag (especially if thin and flat as suggested), when maneuvering (like we tend to do with stunt ships) that situation will be fairly dramatically altered.  When maneuvering the stab/elevator produces a lot of lift and, with lift, comes induced drag.  The drag that comes with this (necessary for maneuvering) lift will be "above" where the same drag would be with a conventional "inline to modestly above" the thrustline layout of the "standard" stunt ship.  I would expect the drag to cause a vertical pitching moment about the CG, thus tightening inside pitches and fighting against outside ones. 

This "likely reality" might make a designer consider using a stab configuration that minimizes drag while still  producing the lift necessary.  Possible means would include a higher aspect ratio surface or even a stabilator (flying tail).  Stabilators have a "sketchy" history in stunt ships but a properly configured one -- really rigid, with a comparatively high AR, and a pivot forward of 25% of the average chord  -- might mitigate the drag issues.  Also, locating the tail no higher than necessary to achieve the "look" you're after would be a good safety valve as well. 

Finally, I like the idea previously mentioned about adjustable stabilizer incidence if you used a fixed stab/elevator combination.  It might well be that a little more than the "norm" in positive incidence might prove beneficial. I'd not, however, suggest "wag"ging a certain amount and gluing it in place the first time around!

Ted

p.s. If you do want to experiment with the flying tail approach be sure to make the flap/elevator ratio seriously adjustable.  Expect to use quite a bit less stabilator movement than flaps and anticipate the liklihood that slower stabilator response will be preferable.  Most likely a conventional relationship between bellcrank and flap horns will be fine and the slower stab response will be taken care of by the lessened flap/stabilator ratio.

Offline John Miller

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Re: What's to know about T_Tails and stunt?
« Reply #12 on: August 13, 2007, 04:32:56 PM »
Ted and all,

Thanks for taking the time to help me out with this question. I know that there are inherent problems with using a T-Tail in an aerobatic design.

I'm beginning to think that an additional structure, like a similated radome/anti missle structure, at the juncture of the stab and vert. stab, as described by Matt would help with rigidity and strength issues.

The possibility of the higher drag from the high tail affecting the turn as Ted describes makes me understand better why incidence, and that should be positive, is likely to be needed.

Here's where the incidence adjustable stab would be really great.

I've tended, lately, to design towards more stationary stab to elevator ratios. The idea of a stabilator, esp. one with a high AR, has me wandering around trying to make a decision. I looked at Gordy's combat ships over the weekend. He has always told me that they grooved well. They have a smaller high AR stabilator, but the hinge point is at the leading edge. They don't need a lot of throw to really manuever the ship around either. I'm thinking that such a stabilator, used as a T-Tail for a stunt ship might be workable. Adjusting the incidence is simply a matter of shortening the pushrod.

I think I'll be laying out some throws and ratios on the computer. I agree that this might be a time when I'd have more flap than elevator. Scary thought.

Getting a line on life. AMA 1601

Offline Leo Mehl

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Re: What's to know about T_Tails and stunt?
« Reply #13 on: September 28, 2007, 08:16:51 PM »
Also perhaps one might give some thought about the possibility that the WING NOT BLANKET THE STAB AND ELEVATORS IN HARD INSIDE CORNERS....and remember that one could always add thin but stiff pulltruded graphite wire braces from the fuselage to the high T tail....
HOWEVER....AERODYNAMICALLY it has always boggled my mind when I found out just how much tubulence and drag...simple wire struts add to any flying machine...be it a large 747 or a teenie little stunt model...

Hey Gary Letsinger...and you  engineering aerodynamoooooos??? Any thoughts???? S?P na#
Shultzie, My Grinder has wire struts to help support the stabilizer. Couldn't tell the difference!


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