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Author Topic: Tail aspect ratio and its effects  (Read 558 times)

Offline Mike Alimov

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Tail aspect ratio and its effects
« on: September 10, 2019, 01:17:34 PM »
I don't recall much discussion on the topic of the aspect ratio of (horizontal) tail surfaces.  [If there was - please provide citation or reference/link].  I've seen discussions of tail area as a % of wing area, tail moment, airfoil and leading edge radius. 

 I can think of pretty successful planes with pretty high (Stiletto) and pretty low (some Impacts) tail aspect ratios.  All seem to fly fine - I haven't flown them all, and I'm afraid I won't have time to experiment with this variable before winter sets in.

I would expect the higher aspect ratio tail to be more effective as a lifting surface, thus probably requiring less deflection - thus less drag in corners, not a bad thing, eh?


Offline phil c

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Re: Tail aspect ratio and its effects
« Reply #1 on: September 10, 2019, 03:13:01 PM »
from my  own experiments, a 25% of wing area stab with the elevator chord 30-60% of the chord.  A tail volume coefficient in the 25-30 range.  Lower aspect ratio on the tail seems to give a less abrupt control, say between 4 and 5.
A good pilot can learn how to make almost any plane fly well, so the effective design range is pretty large.

Read what Igor Burger has done with exponential flaps and fine tuning the stab incidence, airfoil, and position.
You could do a lot worse than his MAX II design.  With modern stunt power plants drag isn't much of a consideration.  Just put on a bigger engine or motor.
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Offline Brett Buck

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Re: Tail aspect ratio and its effects
« Reply #2 on: September 10, 2019, 10:28:07 PM »
I don't recall much discussion on the topic of the aspect ratio of (horizontal) tail surfaces.  [If there was - please provide citation or reference/link].  I've seen discussions of tail area as a % of wing area, tail moment, airfoil and leading edge radius. 

 I can think of pretty successful planes with pretty high (Stiletto) and pretty low (some Impacts) tail aspect ratios.  All seem to fly fine - I haven't flown them all, and I'm afraid I won't have time to experiment with this variable before winter sets in.

I would expect the higher aspect ratio tail to be more effective as a lifting surface, thus probably requiring less deflection - thus less drag in corners, not a bad thing, eh?

  Tail aspect ratio has been extensively discussed in the past. The Impact, Trivial Pursuit, ThunderGazer, and Infinity all have relatively low aspect ratios, which is I think is the correct solution. Mine is about 4.5:1. The split between the elevator and stabilizer should be somewhere between 66/33 to 60/40.

   The reason is that this seems to make it more likely to have the "lock-in" bottom and tracking with aft CGs, which all of us more-or-less copied from Gid Adkission's "Bud Light" Laser. Those that don't have it, and are otherwise excellent airplanes, always seem "vague" to me around neutral, the most notable being the Yatsenko Shark, which while it is a decently "honest" airplane and doesn't do anything unexpected when you control it, never seems to have any particular interest or tendency to fly in straight lines without constant attention. It will do it just fine - Orestes being noted for it - but it requires far, far more attention to be paid to make it that way.

   I don't know why, and since this dead horse has been beaten to a fine powder many times in the past, don't really want to start an argument on the topic, but that's what I think you should do.

     BTW, I am not sure how Phil is computing TVC, but a typical number for a modern stunt plane is on the order of .45 to .5.

     Brett

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Re: Tail aspect ratio and its effects
« Reply #3 on: September 11, 2019, 11:45:48 AM »
Not to be too pedantic, but I believe the stab/elev aspect ratio is around 3.5:1 on the impact, thunder gazer, infinity, ect.
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Offline Mike Alimov

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Re: Tail aspect ratio and its effects
« Reply #4 on: September 11, 2019, 02:52:18 PM »
Sorry if I missed the beating of this particular dead horse.  I have re-read Igor's Max Bee article, and did not find a discussion of the tail aspect ratio (I believe it is around 4.5).  I went back to the Imitation article, and found this:
"Again, it is important to remember that the force which causes pitch change comes from the lift produced by the entire tail, not solely by the amount of surface we are deflecting into the slipstream.  Therefore, what we are looking for is an efficient lift-producing surface. Probably the most efficient tail would have an elevator which comprised approximately 25% of the total tail surface - something like the FliteStreak, which everyone knows will outmaneuver the more conventional-tailed Ringmaster hands down.
There is, however, some compromise necessary in terms of drag and stability which makes larger than optimum elevators result in an aircraft which is more stable while maneuvering. Since moving the center of drag aft is stabilizing in its effect, and since a certain amount of drag comes hand in hand with the lift the tail produces to maneuver, it is apparent that at the sacrifice of a little more drag we can build an airplane which is more controllable while maneuvering, and which has less tendency to overshoot headings. For this same reason, the thicker tail was employed along with a lower aspect ratio.  Such a tail won't be the most efficient in terms of maximum rate of turn, but will come close, and the net effect will enhance the overall flyability of the airplane.  As a result of these compromises, the Imitation has a tail which totals 140 sq.in., of which 55% is stabilizer and 45% elevator.  The aspect ratio of the tail is 4.5 to 1."

Offline Tim Wescott

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Re: Tail aspect ratio and its effects
« Reply #5 on: September 11, 2019, 03:24:05 PM »
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online Brent Williams

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Re: Tail aspect ratio and its effects
« Reply #6 on: September 11, 2019, 07:22:06 PM »
The MaxBee uses an unconventionally large tail. 
From my measurements of Igor's plans, the tail is 30" wide, approximately 212 in.sq, with a 4.25:1 aspect ratio.  Big!  Roughly 32% of the wing area.

Works pretty well for Igor!



« Last Edit: September 11, 2019, 07:55:31 PM by Brent Williams »
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Offline Mike Alimov

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Re: Tail aspect ratio and its effects
« Reply #7 on: September 11, 2019, 08:27:52 PM »
https://stunthanger.com/smf/stunt-design/horizontal-tail-aspect-ratio/msg287284/#msg287284

Did you do a search on tail aspect ratio?

Search?  That's so late-20th century, Tim.  My kids are teaching me that the most reliable info is obtained simply by asking a question on social media, which is what StuntHangar is to me.
But seriously, thanks for the link.  No wonder I missed that thread - in 2012 I was too busy being a good parent.
 
So, the discussion went like this: Howard's tests with higher AR tails were, at best, inconclusive, or, in his words, underwhelming; Ted thinks that low AR tails are good because of the induced drag and resulting shift in CP, while Frank W. thinks its because more of the tail area ends up in the propwash; while Randy - who has flown a plane or two in his lifetime - has reported better results with higher AR tails.  Think about it: we have Imitation, long a design gold standard, with a 5.5 AR wing and 4.5 AR tail, and then there's the Yatsenko Classic (I'm too lazy to run math on the curvy Shark) with something like 4.6 AR wing and 5+ AR tail, just the opposite. Both reported to fly extremely well.  Clear as mud!

And Brent - yes, the Max Bee tail is rather large, but seems to work well (for the author, at least).  Here's what he writes in the Max Bee article about the tail size: "Enlarging up to that size [25% of wing area - M.A.] allows the CG to go further and
further back, while extending the tail size over 25% does not give
any further advantage. So I decided to make it a little over 25%,
just to be sure it is not too small."  So he throws some extra tail area in for a good measure and ends up with 32% (!)

And what about Remi Beringer's Gee Bee Sportster with its miniscule flaps, enormous tail arm, and airfoil seen only on vintage combat planes?  Wch Junior title, not too shabby.

If anybody will now tell me that the stunt community has enough knowledge to follow a rigorous, highly scientific process to start from scratch and arrive at an optimal design, I have evidence to the contrary. The designs seem as diverse as the people flying them. I think Phil may have hit the nail with his response, and it reminded me something I was told long, long time ago: stop complaining about your airplane and learn to fly what you have.

Online Howard Rush

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Re: Tail aspect ratio and its effects
« Reply #8 on: September 11, 2019, 10:20:01 PM »
Search?  That's so late-20th century, Tim.  ...

Much like facts and data. 

If anybody will now tell me that the stunt community has enough knowledge to follow a rigorous, highly scientific process to start from scratch and arrive at an optimal design, I have evidence to the contrary.

No, you have evidence that the stunt community wouldn't look at it. 
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Online Brent Williams

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Re: Tail aspect ratio and its effects
« Reply #9 on: September 11, 2019, 11:28:12 PM »
David Fitzgeralds De-Tails article was pretty thorough on the topic.  https://stunthanger.com/smf/open-forum/copy-of-the-david-fitzgerald-article-'de-tails'-from-the-marapr-98-stunt-news/msg511851/#msg511851

The record of contest wins from designs with the low aspect ratio tail makes for a compelling design argument. 
The names of the winners of the Walker Cup for the past 30 years would lead one to believe that there is something worthwhile to that design.  Look at what Paul Walker, David Fitzgerald, Ted Fancher, Brett Buck, ect have used.   Those champs don't use things arbitrarily.  If it helps them be consistent and win, they stick with it.  If it proves to be inconsistent and unsuccessful, they abandon it. 

Here is a drawing I put together showing the differences in aspect ratio.  All have the same area.  60/40 split. 
« Last Edit: September 12, 2019, 02:40:26 AM by Brent Williams »
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Online Ken Culbertson

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Re: Tail aspect ratio and its effects
« Reply #10 on: September 12, 2019, 12:52:01 PM »
David Fitzgeralds De-Tails article was pretty thorough on the topic.  https://stunthanger.com/smf/open-forum/copy-of-the-david-fitzgerald-article-'de-tails'-from-the-marapr-98-stunt-news/msg511851/#msg511851

The record of contest wins from designs with the low aspect ratio tail makes for a compelling design argument. 
The names of the winners of the Walker Cup for the past 30 years would lead one to believe that there is something worthwhile to that design.  Look at what Paul Walker, David Fitzgerald, Ted Fancher, Brett Buck, ect have used.   Those champs don't use things arbitrarily.  If it helps them be consistent and win, they stick with it.  If it proves to be inconsistent and unsuccessful, they abandon it. 

Here is a drawing I put together showing the differences in aspect ratio.  All have the same area.  60/40 split.
There are probably only three common element in the designs flown by the Top Fliers worthy of being called a standard - they are straight, trimmed and have a reliable power plant.  Everything else is tuning the plane to the pilot.  I think we spend far too much time time trying to make the plane fly perfect and far too little time making the pilot fly it perfect.  The only ultimate aspect ratio is the one that makes YOU fly better.  You can't totally rely on what the "Top Guys" are doing.  Those guys could probably beat most of us flying a burned out McCoy 35 bolted to a lawn chair.  But, if you have no clue what you want then copying what they do is a good starting point. 

Ken
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Offline Brett Buck

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Re: Tail aspect ratio and its effects
« Reply #11 on: September 14, 2019, 03:10:30 PM »
There are probably only three common element in the designs flown by the Top Fliers worthy of being called a standard - they are straight, trimmed and have a reliable power plant.  Everything else is tuning the plane to the pilot.  I think we spend far too much time time trying to make the plane fly perfect and far too little time making the pilot fly it perfect.

   On that one I could not disagree more. Under no circumstances should anyone at any level attempt to "practice away"  airplane problems, or at least not when there is any other alternative. Even slightly improving the airplane is usually a much more valuable way to spend your limited time than trying to burn in more flights.  The "get it close enough and then thrash out a hundred flights" plan is not going to work for most people.

     I have seen nearly no evidence that "pilot preference" matters, aside from very small variations. I have flown *many* nationally-competitive airplanes, from all over the place, and they all fly very very similarly, once the trim problems are corrected. There are a few small differences (tail aspect ratio being one of them, engine response being another) but this is far below the normal threshold of anyone but the best pilots. Most "pilot preference" examples turn out to be mistakes that someone accepted or didn't recognize, then they went out and thrashed for flight after flight. At which point, the bad habits formed are misinterpreted as "preference", when they are just mistakes that got compounded by additional mistakes/"work arounds" in piloting.

Of course, if you don't know that there is anything wrong, or don't know what to do about it, that's a problem that you need to overcome.

      I would add  - many or even most airplanes people are flying have multiple egregious problems, and if they were solved, they would improve their scores immensely in a few flights. I have seen people change their venturi by .005" and pick up an immediate 40-50 points. Even slight improvements are worth many, many practice flights.

     Brett

Online Ken Culbertson

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Re: Tail aspect ratio and its effects
« Reply #12 on: September 15, 2019, 09:07:45 AM »
   On that one I could not disagree more. Under no circumstances should anyone at any level attempt to "practice away"  airplane problems, or at least not when there is any other alternative. Even slightly improving the airplane is usually a much more valuable way to spend your limited time than trying to burn in more flights.  The "get it close enough and then thrash out a hundred flights" plan is not going to work for most people.

     I have seen nearly no evidence that "pilot preference" matters, aside from very small variations. I have flown *many* nationally-competitive airplanes, from all over the place, and they all fly very very similarly, once the trim problems are corrected. There are a few small differences (tail aspect ratio being one of them, engine response being another) but this is far below the normal threshold of anyone but the best pilots. Most "pilot preference" examples turn out to be mistakes that someone accepted or didn't recognize, then they went out and thrashed for flight after flight. At which point, the bad habits formed are misinterpreted as "preference", when they are just mistakes that got compounded by additional mistakes/"work arounds" in piloting.

Of course, if you don't know that there is anything wrong, or don't know what to do about it, that's a problem that you need to overcome.

      I would add  - many or even most airplanes people are flying have multiple egregious problems, and if they were solved, they would improve their scores immensely in a few flights. I have seen people change their venturi by .005" and pick up an immediate 40-50 points. Even slight improvements are worth many, many practice flights.

     Brett
Brett, there is nothing in your response that I would disagree with were I in the same flying environment you are in but I am not.  I have been flying competitive stunt since I was 14 years old and except for one period surrounding 1980 and a few fliers I know now, I have had no one to turn to that knew more about trimming than I did and I didn't know squat.  Another thing that we just don't do much of is flying other people's planes.  I am not sure why, we just don't. 

I was out of the sport from the end of the Fox 35 era till a couple of years ago. In my case that has means that I am flying .60 sized ship that I have built not having a clue what a properly trimmed ship of this size and power is supposed to feel like and I am not alone.

Lastly, I am lucky here to get in 8 flights a week and that is only if Mother Nature cooperates.  In those 8 flights you have to get wings level, lap time to your and the planes liking, c/g set and turn ratio's balanced, leadouts set and that is just so you can start the actual trimming and all of that is supposed to be done without violating the "one change at a time" "rule".  Before you know it's contest time and you are still trimming.

Let me end this by saying that you are ABSOLUTELY RIGHT in everything you said, it just won't work in the environment I fly in and I would venture a guess that a lot of us (most of which do not frequent this forum) are in the same boat.

Keep it up.  I learn a lot when you take me to the woodshed.

Ken
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