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Author Topic: Wing Thickness %  (Read 2443 times)

Online Ken Culbertson

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Wing Thickness %
« on: May 12, 2018, 05:07:06 PM »
What is the average thickness of wings now days?  I am thinking 17% t 20% including flaps.  I don't get much on a search.  Anybody have a link to some recent discussions?

Thanks
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Offline Brett Buck

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Re: Wing Thickness %
« Reply #1 on: May 13, 2018, 08:33:14 PM »
What is the average thickness of wings now days?  I am thinking 17% t 20% including flaps.  I don't get much on a search.  Anybody have a link to some recent discussions?

    More-or-less, if everything else is right, it doesn't make much difference. Mine is 26% (including flaps), and the Trivial Pursuit is slightly thinner. But I have seen very good results with as little as about 14-15% (Diva, etc). The key takeaway from the entire situation is that the lift is not the limiting factor if you have the rest of the shape right, and that the lift coefficient is only weakly related to the thickness.

     You have to have the LE bunt enough, and you do not need large flap percentages, and probably want as narrow a flap chord as you can get away with. You want the high point relatively far forward, but you also need at least some curvature in the aft section, DO NOT make it a straight line. Round off all the corners near the hinge line, and seal the hinge line,

    Beyond that, choose it for your desired other properties of parasitic drag and structural qualities (thicker stiffer for a given mass). I would use a relatively thick wing for very powerful IC engines, and it's particularly important to get the right amount of parasitic drag VS horsepower available for 4-2 break IC engines and 4-strokes.


It's much less important with tuned pipe engines, assuming you know what you are doing, because the lack of parasitic drag from a thin wing, which would cause large speed variations in the wind on a 4-2 break engine, you can instead control with the engine response.  That presumes, of course, that you know how to make the engine do what you want -  for which there is abundant information, although no one pays any attention to most of it, preferring their barnyard bullshit theories on the topic to both analysis and extraordinarily successful contest record by those who developed and propagated the information.

     For electric, I am far from an expert, but while you have infinite control over the power delivery with Igor's feedback system, or similar, you still have to consider drag because you have to carry a big enough battery to make it through the flight with margin to keep them from self-destructing. Given that the lift is more-or-less  a non-issue, I have opted to have a relatively thing wing compared to my current airplane, around 20%.

    As in the "best  airfoil" thread, the answer is something close to the Imitation airfoil (which was considered thick at the time, but not so much any more) is a good compromise.

     Brett

   

Online Ken Culbertson

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Re: Wing Thickness %
« Reply #2 on: May 14, 2018, 10:50:31 AM »


    As in the "best  airfoil" thread, the answer is something close to the Imitation airfoil (which was considered thick at the time, but not so much any more) is a good compromise.

     Brett

 

Thank you for your thoughtful response.  I checked out the Imitation and it is really close.  Two quick questions and I am off to the drawing board.  #1 Why should you not have a flat on the back of the wing and #2 do flaps recessed into the wing act as a seal.  I have always had the last 2" of my wings flat.  No reason other than ease of construction.  I recess the flaps and elevator simply because it looks cool and may offer a slight advantage but that is one of those things that everybody at the top would be doing if it actually offered an advantage so I suspect my only justification is the "looks cool" one.  Again - Thanks
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Offline phil c

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Re: Wing Thickness %
« Reply #3 on: May 14, 2018, 11:35:15 AM »
Look at other posts on airfoils following this particular thread.

Al Rabe and Igor Burger have pretty well shown that fairing the airfoil behind the high point back into the flap at about 30 degrees deflection gives the best results.  At our low speeds and Reynolds number the airflow can detach from the wing and give less lift and/or other strange effects such as a sudden drop in lift when the flaps reach a certain angle or a gust of wind hits the plane.  Whether or not you need to tape the hinge line depends entirely on how well the rounded front of the flap is fitted into the wing.  Taping the hinge ensures no air leaks through, making the flap less effective and maybe depending on how much it is deflected which could give inconsistent results.
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Online Ken Culbertson

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Re: Wing Thickness %
« Reply #4 on: May 14, 2018, 01:33:30 PM »
Look at other posts on airfoils following this particular thread.

Al Rabe and Igor Burger have pretty well shown that fairing the airfoil behind the high point back into the flap at about 30 degrees deflection gives the best results.  At our low speeds and Reynolds number the airflow can detach from the wing and give less lift and/or other strange effects such as a sudden drop in lift when the flaps reach a certain angle or a gust of wind hits the plane.  Whether or not you need to tape the hinge line depends entirely on how well the rounded front of the flap is fitted into the wing.  Taping the hinge ensures no air leaks through, making the flap less effective and maybe depending on how much it is deflected which could give inconsistent results.

I recess the flap/elevator so that the hinge axis is at the center of the flap LE radius so that it rotates like a wheel.  The flap is recessed into the wing to where the axis is just inside the wing TE.  This causes the hinge to completely close at about 30 degrees with no hump on the side opposite the deflection.  I first started using this type of hinge after seeing how well Al Rabe's plane flew using them and being impressed with how good they looked.  I know he stopped but I never heard exactly why.   It could have been that the plane was flying so well because it was Al flying it and had nothing to do with the flaps!  As for the gap, I use two sheets of typing paper to create the spacing when I pull the flaps int to the carve-out (pocket) in the wing and glue the hinge-points in place.  I just want to know that I am not making things worse.  If this was truly superior, everybody would be doing it.
I don't know if it is even possible to seal that kind gap
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Offline Brett Buck

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Re: Wing Thickness %
« Reply #5 on: May 14, 2018, 03:53:56 PM »
I know he stopped but I never heard exactly why. 

    Because when he tested it with his car hood test, despite his expectations of being superior, it was actually worse than a conventional arrangement. Keith has some opinions on why it turned out that way and that maybe it wasn't done correctly, but it definitely did not work as well as everyone expected. When diagnosing it, he hit upon the issue with discontinuity at the hinge line.

     He seems to have missed the issue of sealing the gap and now would argue vociferously that the gap works like a slot on a slotted flap, which it almost certainly does not, but is irrelevant even if it was true, since "getting more lift" is not an issue with stunt planes with modern power systems - which he also does not agree with.

Quote
I just want to know that I am not making things worse.  If this was truly superior, everybody would be doing it.
I don't know if it is even possible to seal that kind gap

    You are *probably* making it worse and it is probably not possible to seal that gap. Use a conventional airfoil with a tapered or even flat sheet flap, hinged with a square TE and a "wedge" LE on the flap, and knock all the corners the air is going to flow across with about a 1/8" or more radius.
 
     The reason you do not want a significant straight section on the aft part of the airfoil (like a straight line from just behind the high point to the TE) is that it seems to cause disproportionate hinge moments. It also violates Al's rule about blending the top surface of the airfoil with the deflected flap, but just about any amount of curvature seems to be acceptable, even very slight, and certainly not the degree of curvature on Al's or Igor's.

    Brett

Online Ken Culbertson

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Re: Wing Thickness %
« Reply #6 on: May 14, 2018, 05:12:15 PM »
    Because when he tested it with his car hood test, despite his expectations of being superior, it was actually worse than a conventional arrangement. Keith has some opinions on why it turned out that way and that maybe it wasn't done correctly, but it definitely did not work as well as everyone expected. When diagnosing it, he hit upon the issue with discontinuity at the hinge line.

     He seems to have missed the issue of sealing the gap and now would argue vociferously that the gap works like a slot on a slotted flap, which it almost certainly does not, but is irrelevant even if it was true, since "getting more lift" is not an issue with stunt planes with modern power systems - which he also does not agree with.

    You are *probably* making it worse and it is probably not possible to seal that gap. Use a conventional airfoil with a tapered or even flat sheet flap, hinged with a square TE and a "wedge" LE on the flap, and knock all the corners the air is going to flow across with about a 1/8" or more radius.
 
     The reason you do not want a significant straight section on the aft part of the airfoil (like a straight line from just behind the high point to the TE) is that it seems to cause disproportionate hinge moments. It also violates Al's rule about blending the top surface of the airfoil with the deflected flap, but just about any amount of curvature seems to be acceptable, even very slight, and certainly not the degree of curvature on Al's or Igor's.

    Brett

Thanks.  I am going to miss the 2-3 days of micro-sanding to get the fit.  I still think it looks cool though and I agree about Al's experiments.

Ken
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Offline Howard Rush

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Re: Wing Thickness %
« Reply #7 on: May 14, 2018, 09:33:47 PM »
... but you also need at least some curvature in the aft section, DO NOT make it a straight line.   

Other reasons not to make it a straight line are that it's harder to sand and some airplanes with flat-in-the-back airfoils have structural problems.

However, Gordan Delaney's Pathfinder Two has an airfoil that's a straight line for much of the chord, and the Impact airfoil is almost a straight line near the TE. 
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Offline Howard Rush

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Re: Wing Thickness %
« Reply #8 on: May 14, 2018, 09:40:31 PM »
The reason you do not want a significant straight section on the aft part of the airfoil (like a straight line from just behind the high point to the TE) is that it seems to cause disproportionate hinge moments.

What's the evidence of that?
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Online Trostle

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Re: Wing Thickness %
« Reply #9 on: May 14, 2018, 10:26:33 PM »
    Because when he tested it with his car hood test, despite his expectations of being superior, it was actually worse than a conventional arrangement. Keith has some opinions on why it turned out that way and that maybe it wasn't done correctly, but it definitely did not work as well as everyone expected. When diagnosing it, he hit upon the issue with discontinuity at the hinge line.

(Clip)
     
    Brett

If you go back to the article where Al described his tests on developing his airfoil, he tried the airfoil/flap arrangement that I have on my 1968-1970 Focke Wulf that won the Nats in 1970.  He used something that was close to the airfoil that I used (and still do on all of my open ships) where the flap is part of the airfoil and not just a sheet at the back of the wing TE.  The hinge line is basically at the radius of the flap LE.  He discarded this and most of the others in favor of the one he adopted for his Sea Fury and later Mustangs and later Bearcats.  To my knowledge, Al did not incorporate this "integrated airfoil/flap" arrangement in any of his models.

Al performed those tests with wing/flap sections on an apparatus mounted to the hood of his car where he could test various angles of attack and various flap deflections at our stunt model speeds and measure the lift being generated.

On the test section that he used similar to my integrated airfoil/flap section but he incorporated one factor of change, not used by me, which I think is significant.  His article shows that he placed the hinge line slightly behind the radius center of the flap LE.  He did this so that as the flap rotated, the leading edge of the flap would start to close the gap between the wing TE and the flap LE.  In so doing, the flap LE would actually start to protrude above the wing TE surface (for down flap deflection - the opposite for up flap deflection).  Based on a long experience with these things, I am convinced that portion of the flap that protrudes above the wing TE causes additional turbulence and separation aft of the wing TE, eliminating much of any lift being created by the deflected flap and negating the effectiveness of the flap.  On my models, I place the pivot point slightly ahead (like 1/32" or less) of the radius center of the moving flap.  That way, there is no way for the flap LE to raise above the wing TE to disturb the airflow there more than it already is.

I can explain how I am certain this is a fact, but it will take a long explanation here.  It has to do with what I have found in the various ways that I tape/seal the gap between the wing or stab trailing edges and the flap/elevator leading edges, even with these thick moving surfaces.  If anyone is really interested in my conclusions on this, I will explain.

Later models of my design using this kind of wing/flap arrangement have been successful, placing in the top 20 three times at the Nats in the mid '70's.  One of those designs was a later version of my Focke Wulf where the flap is almost 1" thick at the root and tapers to about 5/8" near the tip.

(For the record, career requirements sort of stopped any serious competition from about 1980 till after 2000.)

Keith


Offline Brett Buck

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Re: Wing Thickness %
« Reply #10 on: May 14, 2018, 11:00:14 PM »
What's the evidence of that?

   Having flown about a dozen airplanes with "straight-line" sections, all of which had otherwise inexplicably high control loading.

     Brett

Offline Brent Williams

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Re: Wing Thickness %
« Reply #11 on: May 15, 2018, 02:45:21 AM »

However, Gordan Delaney's Pathfinder Two has an airfoil that's a straight line for much of the chord, and the Impact airfoil is almost a straight line near the TE.

Hi Brett, I am not trying to contradict, speak out of turn or pretend to have your level of training and understanding of engineering and flight dynamics.  To comment on that would be totally out of my depth.  My experience is narrow, but I thought I might comment on this topic for whatever it's worth. 

Of interest, attached, is Gordan Delaney's actual airfoil outline that he uses on his own profile planes.  (This is the airfoil shape with the 1/16" sheeting/capstrips included.)  It is different from what John Miller drew for the plans in the Brodak Pathfinder kit.  Gordy's airfoil features a much more blunt, elliptical leading edge and a nice gentle curve from the high point back into the straight aft section.  It does allow for building flat on the bench, which is nice. 

You have spoken openly regarding your experiences and misgivings about the straight aft section airfoils.  You have observed higher than normal stick pressures of the several planes you have flown with this design, including a mention of Gordan's big maroon ST.51 plane from back the mid 90's.  As Gordan has described regarding that plane, it was his trim mistake and was quickly remedied by moving the CG and changing the flap setting after those flights.  It was said to be very easy to fly after that.   

Regarding the Pathfinder Two (twin):  From the many glowingly positive descriptions from Bob Hunt, Bob Whitely, Howard Rush(who now owns the plane), ect, regarding Gordan's twin FP15 Pathfinder Two, it is often described as very gentle on the handle and is a point and shoot airplane.   Built on the same basic PF airfoil.  Bob Hunt referred to that PF twin as one of the finest stunt planes he had ever flown and the inspiration for his own twin designs.   

In my own limited experience, having flown Gordy's yellow LA46 Pathfinder profile, I found it to be have a fantastic corner yet be extremely gentle, predictable, maneuverable and very light regarding handle pressure.  Very crisp maneuvers especially when watching Gordan, Norm Whittle and Bart Klapinsky fly it.  Even up here in our rarefied air 4500ft elevation (6000ft + DA).  I also found his larger PA51 Pathfinder L.E. very gentle to fly.  It has a more traditional, curved aft section airfoil.  Pat Johnston uses a basically identical, flat aft section style airfoil (+P) in his many designs with good success.

Gordan has often commented that your Infinity planes were absolutely magnificent to fly and a great experience (flights on Dave's ThunderGazer's as well.)  Nats/World winning designs should be great to fly, though!   
« Last Edit: May 15, 2018, 05:46:05 AM by Brent Williams »
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Offline Ted Fancher

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Re: Wing Thickness %
« Reply #12 on: May 15, 2018, 11:54:27 AM »

snip

(For the record, career requirements sort of stopped any serious competition from about 1980 till after 2000.)

Keith

Lengthy post "snipped" to add only the following:

That's one "great" picture that represents a significant amount of devotion to the success and history of CLPA and F2B around the world.  Les, Claus and the Colonel!  The stunt fraternity owes a lot to these three!

Salut!

Ted

Online Ken Culbertson

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Re: Wing Thickness %
« Reply #13 on: May 15, 2018, 02:25:06 PM »
In my own limited experience, having flown Gordy's yellow LA46 Pathfinder profile, I found it to be have a fantastic corner yet be extremely gentle, predictable, maneuverable and very light regarding handle pressure.

I think I am going to use a flat aft section on one wing and rounded on the other.  This is what happens when people who's opinion you value differ!

I am leaning towards the flat from about 1" behind the high-point and here is why (please feel free to call me an idiot).  It may really be an issue of style.  I learned to fly stunt back in the early 60's when not much was known about all of this technical stuff that can make a plane almost fly by itself.  It was definitely seat of the pants.  My mentors, and I can't remember their names any longer were touched by the number of times I was having to rebuild my Flight Streak trying to learn to stay inverted and still be at the field every Saturday morning.  They asked me what I was thinking when I got it upside down and I said "Up is Down, Down is Up".  One of them told me to stop thinking that and start thinking that there is no up or down, only which way do you want to make the airplane go.  He said "pick one - canopy or wheels.  I picked the canopy.  Now all you have to remember is that if you want to make the plane go towards the canopy you pull up and away from the canopy you push down and that one piece of advice saved the life of my Flight Streak and within a month I was flying the entire pattern (on the Nobler I was scared to fly before).  To me the ability of a plane to follow where your eyes tell it to go and re-track when it gets there is it's most important characteristic and once you have mastered this it is like "riding a bicycle", you don't know why you don't fall down, you just don't and you never forget.

I have seen several Brodak Pathfinders fly and they all seem to have that characteristic.    However, on the flaps issue, calmer minds prevail. I still think embedded really looks cool but I am convinced that it is not worth the effort and I will invest instead in a roll of Scotch tape.

Ken
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Offline Brett Buck

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Re: Wing Thickness %
« Reply #14 on: May 15, 2018, 05:45:40 PM »
OK, everyone is free to do as they please.

    Brett


p.s. And, for goodness sake, do you think I would make such a blanket statement after flying *one* flight on *one airplane*? I have flown at least a dozen that had that same type of airfoil, including two of my own, and that's why I came to such a conclusion. This is a not a referendum on the Pathfinder.

  I should have known better than to say anything.
« Last Edit: May 15, 2018, 08:19:38 PM by Brett Buck »

Offline curtis williams

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Re: Wing Thickness %
« Reply #15 on: May 15, 2018, 07:51:58 PM »
Holy @#$%, just build and fly something.   This endless debate about  ice cream shaped airfoils is getting old.  I haven't watched any profile fly better than Gordon pathfinders.  None!!!

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Re: Wing Thickness %
« Reply #16 on: May 15, 2018, 08:42:33 PM »
I guess that was a little much. Sorry.  Go Ringmasters! !!!

Online Ken Culbertson

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Re: Wing Thickness %
« Reply #17 on: May 15, 2018, 11:04:25 PM »
Holy @#$%, just build and fly something.   This endless debate about  ice cream shaped airfoils is getting old.  I haven't watched any profile fly better than Gordon pathfinders.  None!!!
I got my questions answered (and that doesn't always happen) so thanks to all. 
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Offline Howard Rush

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Re: Wing Thickness %
« Reply #18 on: May 15, 2018, 11:26:26 PM »
And, for goodness sake, do you think I would make such a blanket statement after flying *one* flight on *one airplane*? I have flown at least a dozen that had that same type of airfoil, including two of my own, and that's why I came to such a conclusion.

I figured you had solid evidence.  I just wondered whether it was from flying or from something like NACA data.  I've seen the latter for hinge moment effect of control surface shape, but not for hinge moment effect of wing shape.
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Offline Brent Williams

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Re: Wing Thickness %
« Reply #19 on: May 16, 2018, 01:03:16 AM »
I wasn't trying to provoke anger or start an argument.  The goal of the post was to promote discussion, not instill a chilling effect on the topic.
I just wanted to share an alternate viewpoint/experience.  Sorry if it was interpreted as anything that might have made it come across any other way.
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Offline Brett Buck

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Re: Wing Thickness %
« Reply #20 on: May 16, 2018, 10:56:44 AM »
I figured you had solid evidence.  I just wondered whether it was from flying or from something like NACA data.  I've seen the latter for hinge moment effect of control surface shape, but not for hinge moment effect of wing shape.

      I note that as soon as they started using these sorts of airfoils in full-scale aerobatics (chosen not for any characteristic we care about, but for abrupt stall performance), they also invented aileron "spades".

      Brett

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Re: Wing Thickness %
« Reply #21 on: May 16, 2018, 11:13:41 AM »
I wasn't trying to provoke anger or start an argument.  The goal of the post was to promote discussion, not instill a chilling effect on the topic.
I just wanted to share an alternate viewpoint/experience.  Sorry if it was interpreted as anything that might have made it come across any other way.

  It's fine, but come on, do you think this is the result of one flight on one airplane? This is a classic case of thinking that I was goring someone's ox, and rushing to the defense by reflex. I consider Gordan Delany to be a good friend and a fine competitor, this is not me trying to badmouth him indirectly.

     This is why it is completely impossible to have a reasonable engineering discussion, you have to tiptoe around everyones precious feelings, even when they aren't being insulted in any way.

   I don't think this (the "ice cream cone" airfoil) is a good idea for stunt, but if you think otherwise, by all means, follow your own path, it doesn't matter to me. But it's not necessary to divide yourself in to warring camps over the matter or assuming that I am taking potshots at individuals. We have contests, somewhere, every single weekend, that will tell you what you need to know.

     Brett

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Re: Wing Thickness %
« Reply #22 on: May 16, 2018, 02:36:37 PM »
The whole idea for the Pathfinder was Pete Peterson needed a better plane to learn the pattern.  That airplane did what it was designed to do.  I am glad everyone has a opinion.  Built straight and light and have fun with it.



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Re: Wing Thickness %
« Reply #23 on: May 16, 2018, 04:11:20 PM »
Ken's original question was hopefully covered adequately.   

Brett is an Walker Cup Champion and an engineer of the highest order.  I am neither of those things.  Thus, I pay very close attention to what info he and his peers share.  I detoured the thrust of the original conversation.  I wasn't trying to ruffle feathers or antagonize Brett or anyone else in any way.  Nor am I trying to sound like a defensive toady, bootlicker or brown noser to anyone or to their pet design.  I'm trying to gracefully back out of this thread.  Let's move on now please. 

(And no worries, my feelings are covered in a very thick skin.  No filter on comments or education directed at me is needed or wanted.  I need no safe space!  LOL!  If we were having this conversation in person or on the phone it would be with a hearty laugh, I am sure.  Keyboards don't always convey intent/content)
 
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Online Ken Culbertson

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Re: Wing Thickness %
« Reply #24 on: May 16, 2018, 05:22:45 PM »
Ken's original question was hopefully covered adequately.   

Brett is an Walker Cup Champion and an engineer of the highest order.  I am neither of those things.  Thus, I pay very close attention to what info he and his peers share.  I detoured the thrust of the original conversation.  I wasn't trying to ruffle feathers or antagonize Brett or anyone else in any way.  Nor am I trying to sound like a defensive toady, bootlicker or brown noser to anyone or to their pet design.  I'm trying to gracefully back out of this thread.  Let's move on now please. 

(And no worries, my feelings are covered in a very thick skin.  No filter on comments or education directed at me is needed or wanted.  I need no safe space!  LOL!  If we were having this conversation in person or on the phone it would be with a hearty laugh, I am sure.  Keyboards don't always convey intent/content)
 

It was and I would not have asked if I did not respect the opinions of those likely to respond.   This is what I came up with taking everybody's comments into consideration.  No need to comment, I just thought you would like to see what making "sausage" ended up producing.   

Ken
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Re: Wing Thickness %
« Reply #25 on: May 21, 2018, 09:11:52 PM »
Ken here is my two cents.
Since it looks like you are going electric, maintain the wing area but go thin on the airfoil. You still create plenty of lift without the drag penalty. On my new bird I have 16% at root 14% at tip maybe even a 15% root 13% tip. Pay attention to spar stiffness, as you don't want the wing flexing up and down.
A thinner airfoil will keep the flow laminar better than a fat one. Thinner airfoil will create less drag too that means smaller battery and smaller motor too. But I would go with a bigger motor anyway. Rob Peter to Pay Paul.

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Re: Wing Thickness %
« Reply #26 on: May 22, 2018, 12:08:40 AM »
Ken here is my two cents.
Since it looks like you are going electric, maintain the wing area but go thin on the airfoil. You still create plenty of lift without the drag penalty. On my new bird I have 16% at root 14% at tip maybe even a 15% root 13% tip. Pay attention to spar stiffness, as you don't want the wing flexing up and down.
A thinner airfoil will keep the flow laminar better than a fat one. Thinner airfoil will create less drag too that means smaller battery and smaller motor too. But I would go with a bigger motor anyway. Rob Peter to Pay Paul.

I am conflicted on this one myself.  All of the advice I am receiving is coming from people that know what they are talking about yet when I go to the field on a typical day in Texas the wind will be blowing a choppy 10 - 15.    I just got back in after a long absence so I don't have a whole shop full of planes to choose from.  I have a 38oz OS35s powered Nobler and a 52oz OS46LA powered blunt thick wing design with an airfoil similar to the Cardinal.  In winds under 10 the Cardinal wing totally outperforms the Nobler.  In the 10-15 range they fly about the same if the wind is steady but when it gets choppy/gusty the Nobler cuts through it with minimal bouncing around and the Cardinal wing is all over the place.  Another problem I have with the thick wing is takeoff and landing in wind.  It is hard to keep it on the ground long enough and climb smoothly as it has too much lift at low speeds and it is difficult to get a long enough glide to get a decent landing.  I suspect that this it what a thick airfoil does and I just need to learn how to control it.  It may also be a bit tail heavy but it doesn't turn like it is.

I build light.  Both planes have wing loading of about 11oz.  I am starting to wonder if the thicker wings really need more weight.  I am going to have to live with whatever I build on this next one for a long time so I am researching it to death.  The lure of having a more forward C/G at the end of the pattern and for landing is probably not enough reason to go electric but your comments really apply to both.  I think you just shaved 2-3% off my airfoil.  The best flying wind plane I ever had was 15% with a 40% high point and elliptical LE.  Today they call that one Heresy.

Ken
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Offline Howard Rush

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Re: Wing Thickness %
« Reply #27 on: May 23, 2018, 01:51:04 PM »
A thinner airfoil will keep the flow laminar better than a fat one.

This enabled me to win a lot of combat matches. 

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Re: Wing Thickness %
« Reply #28 on: June 21, 2018, 01:43:31 PM »
Ken you should favor a wing in the 15% root 13% at tip with the typical Nobler-ish platform. This will give you decent lift distribution with nice flying characteristics in the wind. Use the motor wide band of throttle to keep speed under control. A rear CG to help with compression when you fly in windy conditions and help with the turn.
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Re: Wing Thickness %
« Reply #29 on: June 21, 2018, 05:36:33 PM »
If you go back to the article where Al described his tests on developing his airfoil, he tried the airfoil/flap arrangement that I have on my 1968-1970 Focke Wulf that won the Nats in 1970.  He used something that was close to the airfoil that I used (and still do on all of my open ships) where the flap is part of the airfoil and not just a sheet at the back of the wing TE.  The hinge line is basically at the radius of the flap LE.  He discarded this and most of the others in favor of the one he adopted for his Sea Fury and later Mustangs and later Bearcats.  To my knowledge, Al did not incorporate this "integrated airfoil/flap" arrangement in any of his models.

Al performed those tests with wing/flap sections on an apparatus mounted to the hood of his car where he could test various angles of attack and various flap deflections at our stunt model speeds and measure the lift being generated.

On the test section that he used similar to my integrated airfoil/flap section but he incorporated one factor of change, not used by me, which I think is significant.  His article shows that he placed the hinge line slightly behind the radius center of the flap LE.  He did this so that as the flap rotated, the leading edge of the flap would start to close the gap between the wing TE and the flap LE.  In so doing, the flap LE would actually start to protrude above the wing TE surface (for down flap deflection - the opposite for up flap deflection).  Based on a long experience with these things, I am convinced that portion of the flap that protrudes above the wing TE causes additional turbulence and separation aft of the wing TE, eliminating much of any lift being created by the deflected flap and negating the effectiveness of the flap.  On my models, I place the pivot point slightly ahead (like 1/32" or less) of the radius center of the moving flap.  That way, there is no way for the flap LE to raise above the wing TE to disturb the airflow there more than it already is.

I can explain how I am certain this is a fact, but it will take a long explanation here.  It has to do with what I have found in the various ways that I tape/seal the gap between the wing or stab trailing edges and the flap/elevator leading edges, even with these thick moving surfaces.  If anyone is really interested in my conclusions on this, I will explain.

Later models of my design using this kind of wing/flap arrangement have been successful, placing in the top 20 three times at the Nats in the mid '70's.  One of those designs was a later version of my Focke Wulf where the flap is almost 1" thick at the root and tapers to about 5/8" near the tip.

(For the record, career requirements sort of stopped any serious competition from about 1980 till after 2000.)

Keith

Keith, I'm curious!  Please elaborate!
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Re: Wing Thickness %
« Reply #30 on: June 21, 2018, 07:51:03 PM »
Keith, I'm curious!  Please elaborate!

I am curious too.  I have had very good luck with embedded flaps and elevators.  I hinge mine as close to dead center on the radius of the flap as I can and embed them just over the hinge point.  They seal at about 20 degrees on the flaps and 30 on the elevator.  I use a lot of Monokote which makes for a flexible seal so I get 30 and 45 movement.  More than enough. .  Consensus among those who have looked at them is that they don't need to be sealed.  If they do, how would you do it?  I still don't know it there is any performance benefit but they sure do look cool.

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Re: Wing Thickness %
« Reply #31 on: June 21, 2018, 10:45:10 PM »
A rear CG to help with compression when you fly in windy conditions and help with the turn.

Compression?
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Re: Wing Thickness %
« Reply #32 on: June 21, 2018, 11:22:52 PM »
Compression?

If you have enough you can hold the prop and flip the plane.
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Re: Wing Thickness %
« Reply #33 on: June 22, 2018, 08:57:11 AM »
Howard when we do maneuvers in the wind it feels like there is constant pressure that want to push the model down any time you are above level flight. That pressure wants to slow you down every time you go up and sling shots you in to the ground when the nose goes down. I call that compression. Might have the wrong term but whatever you want to call it.
Ken I was not referring to IC motors at all.
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Re: Wing Thickness %
« Reply #34 on: July 02, 2018, 11:24:45 PM »
Howard when we do maneuvers in the wind it feels like there is constant pressure that want to push the model down any time you are above level flight. That pressure wants to slow you down every time you go up and sling shots you in to the ground when the nose goes down. I call that compression. Might have the wrong term but whatever you want to call it.
Ken I was not referring to IC motors at all.
Your post got me thinking and I think what you call "compression" exists but is not unique to electric.  I needed to make a test flight in a 20mph wind Sunday so I looked out for the phenomenon and to my surprise it was there.  It was most noticeable at the tops of the square maneuvers both inside and out and explains why I usually fly them a bit larger or "pop" the corners in excessive wind to allow for the intense acceleration.  An aft CG helps this but makes everything else worse, especially the overhead stuff.  How does this differ from "winding up" except that it happens sooner and how would a thinner airfoil make any difference?  I am pretty sure that this is a function of exposing the surface of the wing to the wind and actually has the opposite effect on the upwind side where we are just flying level most of the pattern.  I would think the extra lift and drag of the thicker airfoil would be better.  Where am I wrong?

KEn
« Last Edit: July 03, 2018, 06:03:20 AM by Ken Culbertson »
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Re: Wing Thickness %
« Reply #35 on: July 03, 2018, 12:09:12 AM »
Howard when we do maneuvers in the wind it feels like there is constant pressure that want to push the model down any time you are above level flight. That pressure wants to slow you down every time you go up and sling shots you in to the ground when the nose goes down. I call that compression. Might have the wrong term but whatever you want to call it.

  Whip-up.

   Brett

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Re: Wing Thickness %
« Reply #36 on: July 03, 2018, 12:27:45 PM »
I would think the extra lift and drag of the thicker airfoil would be better. 

Better than one that's too thin, anyhow.  I'd err on the thick side.  An Impact wing works well.
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Re: Wing Thickness %
« Reply #37 on: July 04, 2018, 11:18:23 PM »
Keith, I'm curious!  Please elaborate!

Greg,

You  and Ken Culbertson asked for more of an explanation on my findings regarding the thicker flaps and elevators that I use on my models.  (Reference my May 14 post above.)  I intentionally place the hinge line 1/32" forward of the center of the flap leading edge radius and same with the elevator leading edge radius.  (Ken mentioned that he places his hinge line on those radius points which is probably OK, it is just that I do not do that any more.)  With this forward position of the hinge lines, when the flaps and the elevators start to deflect, the leading edge of those surfaces start pull away from the surfaces ahead of the flaps (in other words the wing and tail trailing edges just ahead of the flaps and elevators.  When Al Rabe did his tests on various airfoils, he included the airfoil that I used on the 1970 Nats winning Focke Wulf that used the thick flaps (like 3/4" thick at the root).  He intentionally placed the hinge line BEHIND the radius of the flaps so that when the flaps start to deflect, the leading edge of the flap starts to close the gap between the wing and flaps until at a certain deflection, that gap is not only closed, BUT the leading edge of the flap is slightly above the wing trailing edge surface that results in a "bump" across the span of the wing at the wing/flap hinge line.  I am convinced this "bump" represents a discontinuity in the airflow over this part of the wing, creating separation of the airflow over the flap.  In my opinion, the airflow at this point is no longer laminar, but is turbulent and at least somewhat attached to the surfaces it is passing over but it takes very little to cause separation of the airflow that is already turbulent and that bump does that, significantly reducing the effectiveness of the deflected flap.  This is what I discussed in my May 14 post above that you both asked for further explanation.

I will try to explain without resorting to drawings.  I seal these hinge lines with the recessed hinge lines on surfaces from 1/4" thick to elevators that are 1/2" thick to flaps that are nearly 1" thick.  I use Moore Crystal Clear tape that can be found in art supply stores.  It is thinner (more flexible) than many of the other clear tapes that some use.  In order to seal these hinge lines, the tape must adhere to the flap LE as it rotates inward when the flap is deflected.  The tape is applied to the wing TE and the flap LE portion when the flap is fully deflected, then, as the flap approaches neutral and moves to its opposite deflection, the tape is pulled into the gap between the flap and the wing TE.  This works for me and seems to have negligible effect on the movement freedom of the flap because there is enough gap between the wing/tail trailing edges and the flap/elevator leading edges.  I do the same on my elevators, even on my OTS ship with 1/4" thick stab, and the Rabe Bearcat that I had some success with for several years.  Now, this is where it gets interesting, because I first noticed this on the Bearcat with its 3/8" thick flat stab. Most people who watched that Bearcat fly would comment on how well it performed square maneuvers.  Because of the way the tape was between the stab TE and the elevators LE, the tape had to flex.  The tape is applied to the bottom side of the flap/elevators.   After a number of flights, oil from the exhaust would get inside those hinge lines and eventually would cause the tape to lift away from being attached to the very edge of the stab TE.  It would lift the tape slightly (like 1/16") above the stab TE just ahead of the hinge line gap.  With the tape on the bottom side of the horizontal tail, up elevator would cause that bump to appear at the hinge line on the bottom of the tail because the oil had allowed the tape to to raise.  This bump on the bottom of the up deflected elevators might only be 2" or 3" in length, but as soon as that bump appeared, the inside turning ability of the Bearcat was being definitely affected, even with the relatively short length of that bump across the span of the horizontal tail.  (This bump essentially represented what Rabe was intentionally doing with his airfoil tests.)  When this occurred, I simply removed the tape, thoroughly cleaned the hing line surfaces of oil, put on fresh tape where the tape would remain adhered to the stab TE and the turning ability of the Bearcat was instantly restored.  I have experienced this on the several models where the hinge line is behind the surface LE.  I am convinced that "Bump" definitely affects the turning ability (as in the squares), so I make sure the hinge line is always slightly ahead of the LE radius.

I hope this explanation makes sense.

Keith


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Re: Wing Thickness %
« Reply #38 on: July 05, 2018, 05:00:50 PM »
Keith, so something like this?

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Re: Wing Thickness %
« Reply #39 on: July 05, 2018, 05:43:43 PM »
Keith, so something like this?

Exactly.  Neat drawings.  I am glad that I was able to explain it in a way that could be understood.

I am convinced that that protrusion is not a good thing.  Maybe the "clearance" as you show is not the best, but it is certainly better than the protrusion and should not be any worse, if not better than the gaps that appear with the more "conventional" methods of flap and elevator hinges on our stunt ships.

Keith

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Re: Wing Thickness %
« Reply #40 on: July 05, 2018, 08:45:48 PM »
....but it is certainly better than the protrusion and should not be any worse, if not better than the gaps that appear with the more "conventional" methods of flap and elevator hinges on our stunt ships.

Keith
I will try moving the pivot point on the next set.  Thanks for the explanation, it really helped convince me that I am not wasting time.  I have had several expert fliers observe my plane in flight and on the ground and the consensus is that I do not need to seal them but after reading what you just wrote I may give it a shot and see what affect it has.
Thanks Again - Ken
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Re: Wing Thickness %
« Reply #41 on: July 05, 2018, 10:09:36 PM »
I will try moving the pivot point on the next set.  Thanks for the explanation, it really helped convince me that I am not wasting time.  I have had several expert fliers observe my plane in flight and on the ground and the consensus is that I do not need to seal them but after reading what you just wrote I may give it a shot and see what affect it has.
Thanks Again - Ken

I should explain that on my Rabe Bearcat, I tried taping the flap hinge line only, the elevator hinge line only and both hinge lines.  I found little or no improvement with tape on the flap hinge line, but significant turning ability with the elevators being taped.

On the several Chizlers I have had, definite improvement with tape on the elevators, and enough improvement with the flaps to put up with the maintenance required to replace the tape after every 20 to 30 flights. 

Keith

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Re: Wing Thickness %
« Reply #42 on: July 05, 2018, 10:52:26 PM »
I should explain that on my Rabe Bearcat, I tried taping the flap hinge line only, the elevator hinge line only and both hinge lines.  I found little or no improvement with tape on the flap hinge line, but significant turning ability with the elevators being taped.

On the several Chizlers I have had, definite improvement with tape on the elevators, and enough improvement with the flaps to put up with the maintenance required to replace the tape after every 20 to 30 flights. 

Keith
I will try the elevator first.  I keep waiting for the TV add for "Flap Gap Seal" with a second can free, just pay an extra fee.  I can do a set of normal flaps and the elevator in about a 1/2 hour.   Somehow I think this is going to be a bit more tricky.  I am not sure I have enough gap in the flaps to fit a double thickness of tape but thanks to some 30 min epoxy that set up in 20 min I do have enough room in the elevator.
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Re: Wing Thickness %
« Reply #43 on: July 06, 2018, 10:08:08 PM »
I should explain that on my Rabe Bearcat, I tried taping the flap hinge line only, the elevator hinge line only and both hinge lines.  I found little or no improvement with tape on the flap hinge line, but significant turning ability with the elevators being taped.

On the several Chizlers I have had, definite improvement with tape on the elevators, and enough improvement with the flaps to put up with the maintenance required to replace the tape after every 20 to 30 flights. 

Keith
Keith:

Thanks for the tips.  I had no idea you could seal recessed flaps/elevator but you were right, you can.  Using your method I was able to seal both and to my surprise there was almost no tightening of the controls.   Best part is that you can't see it at all like you can on std. flaps.   I will know tomorrow AM if it was worth it!

Ken
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Re: Wing Thickness %
« Reply #44 on: July 10, 2018, 10:56:55 AM »
Keith:

Thanks for the tips.  I had no idea you could seal recessed flaps/elevator but you were right, you can.  Using your method I was able to seal both and to my surprise there was almost no tightening of the controls.   Best part is that you can't see it at all like you can on std. flaps.   I will know tomorrow AM if it was worth it!

Ken

Keith:

It was worth it.  Corners are much smoother and I am using less control to get the same radius.  Soon as I retrim the pilot things will be fine.

THANKS - Ken
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