Wing and Stabilizer arrangement for aerobatics  
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All Forums >> RC Airplanes >> Aerodynamics >> Wing and Stabilizer arrangement for aerobatics
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Wing and Stabilizer arrangement for aerobatics - 1/21/2002 6:06:45 PM   
Mike James



Posts: 2431
Joined: 1/19/2002
From: Anchorage, AK, USA
Status: offline 		I've been doing a lot of research on both Pattern and IMAC designs, and in comparing notes, find 3 basic arrangements, on planes with typical Pattern dimensions...

The most popular one seems to be to have the wing about one inch below the thrust line, with the stab on the thrust line. The second most popular seems to be to have both the wing and stab on the same line, but slightly below the thrust line. The third most popular seems to be to have the wing and stab on the same line, right on the thrust line.

I'm hoping that someone here (Ollie or Paul?) may be able to shed some light on why this is so, and benefits/drawbacks of each.

THANKS!


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Mike James
RC Design and Building - www.nextcraft.com
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Wing and Stabilizer arrangement for aerobatics - 1/21/2002 9:11:00 PM   
Cactus.



Posts: 6138
Joined: 12/19/2001
From: CamborneCornwall, UNITED KINGDOM
Status: offline 		personaly i think it has more to do with looks, access, and engine/pipe arangement. i think the drag of the wing lower than the engine has sommit to do with 'on the thrust line' arangement to cancle that out. anymore than that i dont know

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Pattern Aircraft Alignment - 1/21/2002 9:43:36 PM   
Ollie


 

Posts: 958
Joined: 12/8/2001
From: Punta Gorda, FL
Status: offline 		I think the general idea is to have the thrust vector equal and opposite (aligned) to the total drag vector so that there is less pitch change when the throttle is advancing or retarding. The presence of a draggy landing gear would require that the wing be mounted a bit higher. A streamlined gear or retractable gear would allow the wing to be mounted a bit lower.

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Regards, Ollie

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Wing/Stab setup - 1/23/2002 1:49:01 PM   
Mike James



Posts: 2431
Joined: 1/19/2002
From: Anchorage, AK, USA
Status: offline 		Thanks Ollie! Any other opinions?


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Mike James
RC Design and Building - www.nextcraft.com

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Thrust line - 1/24/2002 8:56:46 AM   
uproar_15



Posts: 196
Joined: 12/28/2001
From: Daytona Beach, FL, USA
Status: offline 		i think it all depends on what performance you're looking for. i do know that having the wing and stabs on the thrust line you can get better rolls without coupling and hovering/TR's are alittle easier, because if the stab is slightly higher than the wing (CAP 232) you need to hover with the plane leaning toward the canopy rather than straight up so the stab and wing are in-line. Also have heard that moving the stab up away from the thrust line will increase sensitvity of the elevator.

rob o'

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Performance - 1/24/2002 10:11:19 AM   
Mike James



Posts: 2431
Joined: 1/19/2002
From: Anchorage, AK, USA
Status: offline 		I'm hoping to find out more from all of you. I suppose the "ultimate" performance would be "symmetrical in every axis with no coupling".

My first instinct would be to put both the wing and stab on the thrust line, since so many maneuvers are done inverted, and we want the same response. I would think that with most pattern-proportioned ships, the stab wouldn't be affected by the downwash from the wing. BUT... There are so many good designs (i.e. "Summit" series, vs. "PTX Vector" vs "Angel's Shadow", vs. ZN Line products) with different setups that all apparently work.

If any of you know the forces involved, (some aerodynamic, some related to mass forces, as Ollie stated) or have done your own research, please share some info with me!

Thanks again, everybody.


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Mike James
RC Design and Building - www.nextcraft.com

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Update: New place for Design discussion - 2/10/2002 6:31:42 AM   
Mike James



Posts: 2431
Joined: 1/19/2002
From: Anchorage, AK, USA
Status: offline 		As some of you are probably aware, the Administrator has kindly added "Design, CAD, and 3D" to the "Scratchbuilding" forum.

So, for questions and discussions of things like the "Aerobatics Setup" question above, as well as a variety of conceptual ideas, come on over and join us in "Scratchbuilding".

See you there!


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Mike James
RC Design and Building - www.nextcraft.com

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Wing and Stabilizer arrangement for aerobatics - 2/16/2002 3:17:48 AM   
Rotaryphile


 

Posts: 271
Joined: 2/15/2002
From: Fredericton, NB, CANADA
Status: offline 		I would avoid placing the stab directly in line with the chord line of a symmetrical section wing. This seemed to cause a peculiar pitch instability in level flight, which I think was caused by interaction of the vortex generated by the wing with the horizontal stab. I fixed the problem by giving the wing about 1/2 degree positive incidence, and never again placed the stab on the same line. Had the same problem many years ago with a control line speed model.

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Wing and Stabilizer arrangement for aerobatics - 2/19/2002 6:53:41 AM   
Diablo-RCU


 

Posts: 3208
Joined: 12/19/2001
From: Hammond, IN, USA
Status: offline 		Wing and stab in line? Dunno....works for the Edge. Not peculiar at all.

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Wing and Stabilizer arrangement for aerobatics - 2/19/2002 7:20:04 AM   
Rotaryphile


 

Posts: 271
Joined: 2/15/2002
From: Fredericton, NB, CANADA
Status: offline 		I built many U/C models with wing and stab in line, and only had problems with pitch stability in a couple of them, and in one R/C pattern model. I think the problem arises when the alignment just happens to be perfect, so the stagnation zone behind the wing hits the stab directly on its leading edge stagnation point, and may thus tend to be develop an unstable attachment to the stab, where random gust effects may attach the flow to either the underside or topside of the stab in a rather indeterminate manner, resulting in peculiar pitch excursions. I think the evidence for this is that a change of wing incidence as small as 1/2 degree corrected the problem completely for me. The fact that no full-scale Edge has reported any problem may be due to renolds number effects. In general, full scale designers tend to avoid having wind and stab directly in line, and I think the fact that such alignments usually work is due to small building errors that inadvertedly place the stab just a little above or below the wing chord line.

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Wing and Stabilizer arrangement for aerobatics - 2/19/2002 9:24:52 AM   
Rotaryphile


 

Posts: 271
Joined: 2/15/2002
From: Fredericton, NB, CANADA
Status: offline 		I just dug out the Edge 540 drawing from the factory brochure, and the horizontal stab appears to be about inches above the wing chordline. I would be surprised to see any full scale designer place the wing and stab directly in line.

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The original question - 2/19/2002 9:45:17 AM   
Mike James



Posts: 2431
Joined: 1/19/2002
From: Anchorage, AK, USA
Status: offline 		Hello everyody, and thanks for your input so far. Let me be a little more precise about my original question. I'm aware of the textbook "stab in the downwash" issues, but that doesn't seem to be a factor when we're talking about these long tail moment Pattern planes. What I am trying to determine is:

Suppose you had 3 identical models, with typical Pattern proportions. One has the wing and stab both on the thrust line. One has the wing and stab on the same line, but a bit below the thrust line. The third one has the stab on the thrust line, and the wing a bit below that. What would be the differences in performance? (All 3 of the above types have been championship winning setups, so what (besides "fashion" causes designers to selct one over the other?

I've asked this question on various forums, have written to the NSRCA, and have personally written to several "name" Pattern flyers, over the last year. So far I have not received even ONE definitive response. This leads me to believe that most designers don't really know, and are just experimenting until they get what they want. Any expert Pattern designers care to jump in here? I would sincerely appreciate it.

Thanks!


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Mike James
RC Design and Building - www.nextcraft.com

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Wing and Stabilizer arrangement for aerobatics - 2/19/2002 10:22:40 AM   
Rotaryphile


 

Posts: 271
Joined: 2/15/2002
From: Fredericton, NB, CANADA
Status: offline 		I don't think that there would be any significant differences, Mike, as long as the wing and stab are not directly in line, which can cause problems. Incidentally, I meant to say that the full scale Edge 540 appears to place the horizontal stab about 6" above the wing chord line, but finger trouble interfered. The trouble that I experienced with wing and stab directly in line reared its ugly head in the form of uncommanded pitch excursions from level flight, at random intervals, equivalent to sudden application of about 10% elevator deflection. Putting the horizontal stab as little as 1/4 inch above or below the wing chordline, I think, will probably prevent this from happening.

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Re: The original question - 2/20/2002 3:26:19 AM   
can773



Posts: 1642
Joined: 1/25/2002
From: Calgary, AB, CANADA
Status: offline 		[QUOTE]Originally posted by mikejames0
Hello everyody, and thanks for your input so far. Let me be a little more precise about my original question. I'm aware of the textbook "stab in the downwash" issues, but that doesn't seem to be a factor when we're talking about these long tail moment Pattern planes. What I am trying to determine is:

Suppose you had 3 identical models, with typical Pattern proportions. One has the wing and stab both on the thrust line. One has the wing and stab on the same line, but a bit below the thrust line. The third one has the stab on the thrust line, and the wing a bit below that. What would be the differences in performance? (All 3 of the above types have been championship winning setups, so what (besides "fashion" causes designers to selct one over the other?

I've asked this question on various forums, have written to the NSRCA, and have personally written to several "name" Pattern flyers, over the last year. So far I have not received even ONE definitive response. This leads me to believe that most designers don't really know, and are just experimenting until they get what they want. Any expert Pattern designers care to jump in here? I would sincerely appreciate it.

Thanks! [/QUOTE]


Mike

I spoke with Chip Hyde in Ireland at the worlds about some airplane design questions. Mainly what I got from him is that he feels that a lower wing design (unlike the Vector which is mid wing) will roll better than a mid wing design. As far as stab placement I think you need to look at the incidences that you want to carry. A 0-0 setup prefers a closer wing-stab arrangement and a + + setup requires the wing stab to be further apart, this is just what I have found from looking at different designs. I wouldnt get too concerned with the placement of the wing stab, go with something that is roughly conventional and looks good. From there the correct wing area, stab area, fuse side area and placement of the high point, airfoil, and WEIGHT are the most important design factors, with the weight being the greatest importance. With the new schedules you need a very light plane. In Ireland there were not a lot of planes over that 10.25 lb mark. Anyways I am not a designer, I just fly em and tell ya whats wrong with them!!


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Chad Northeast

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