Wing Shapes (and I promise I will not delete this thread :)

[RandySmith]

Hmmmm. Sure, but this seems kinda straight forward. The wing with the raked tip has about the same lift for any given drag as the rectangular one until a drag coefficient of .013 is reached, after which the raked-tip wing has more lift. I personally don't think these tip-related induced-drag savings alone make significant differences on tapered model wings, but if one just shoots for an ideal in a total sum of parts - and we're always aware of weight, flex, and complexity - then he might well choose that raked tip - cleaned up some.

FWIW, same area, but larger span...

Serge

Just to be clear without confusing what I have wrote, I am NOT talking about a square tipped wing, I was very clear in saying what tip shapes I have tested/ used, I also have used square but see no advantage over the ones I have, and I believe the ones I have still will carry the same weight as square being slightly smaller, as well as cleaner in a wind tunnel.

Regards
Randy

[RandySmith]

"I didn't take it as such.  It's maybe an attack on fact.   Based on what I have gleaned on how wings work, I don't think that wingtip shape is an aerodynamic free lunch for wake vortices, nor are those vortices divorced from the induced drag that folks count on to hold down airplane mach number on a windy day.  I think theory doesn't support your claim, nor the equivalent claims of hundreds of others on the Internet. "

I have never seen the 100s of people to whom you are referring to, and I do not know of but a very few who have actually built and done test on this.
I also think the people who built and design high performance Gliders, Racers, and High efficient wings would disagree with you. I don't see very draggy Tips like a Chipmonk on new design planes . I don't think theory supports your claims that the Chipmonk. draggy tips are as clean or cleaner than mine either.

And I also think you do not want to go there, about beating planes with my tip shape, I think the record on my design are pretty clearly very positve. So for one to insinuate that the SV planes are not good because you beat one is just plain silly...   I could make some of those claims TOO Howard.... IF  I cared to

Randy

[Serge_Krauss]

I have difficulty communicating clearly.  You picked one parameter, oblivious to all the others, and said that changing wing shape to change this one parameter makes for a better stunt plane.  The example was particularly notable, because it's so easy to see another wing change that would change that one parameter by the same amount, hence providing an alternative for comparison of all the other consequences of a different wing shape.

Things seem to be going downhill some. I seem to be the one failing to communicate - or perhaps to remember!

I just can't quite remember saying either of those things. I think over the years I've mentioned a lot of options, if not so many in the rates of change categories. The raked tip was mentioned in reference to another common wing form. Well,...

I personally don't think these tip-related induced-drag savings alone make significant differences on tapered model wings, but if one just shoots for an ideal in a total sum of parts - and we're always aware of weight, flex, and complexity - then he might well choose that raked tip - cleaned up some.

But now that you mention it, I might say in my current dementia that I think that kind of wing may often enough be better - in the combination with other compatable configurational qualities. I've used similar tips Hey, I get to do that.

Just to be clear without confusing what I have wrote, I am NOT talking about a square tipped wing, I was very clear in saying what tip shapes I have tested/ used, I also have used square but see no advantage over the ones I have, and I believe the ones I have still will carry the same weight as square being slightly smaller, as well as cleaner in a wind tunnel. Regards
Randy

Also in my elderly dementia, I don't remember attributing any particular wing tip other than raked to Randy's comparison. I think the data I displayed supports him (more lift for same drag). I just don't think that with modern engines and such relatively small chords compared to "full-sized" planes that our tips are as important to models as they are to the larger planes, because of unscaled molecular spacing in the air for each.

Finally, answering Brett among others, when I draw up my own planes on anything but aesthetic grounds, it's just to satisfy curiosity as often as to aim at some perceived ideal. I've used similar tips and looked at some pretty weird stuff too. So I wasn't suggesting ignoring one's best option - nor have I addressed any SkyRay issues.

'probably still not clear. Ya git's whatcha pays fer.

SK

[Howard Rush]

... I do not know of but a very few who have actually built and done test on this.

I believe that.   However, my homies do these test(s) all the time.  There's big money in it.

I also think the people who built and design high performance Gliders, Racers, and High efficient wings would disagree with you.

I'm actually one of those people-- well, not directly, but I used to eat lunch with them.  

And I also think you do not want to go there, about beating planes with my tip shape, I think the record on my design are pretty clearly very positve. So for one to insinuate that the SV planes are not good because you beat one is just plain silly...   I could make some of those claims TOO Howard.... IF  I cared to
[/quote]

Look, I am not going to start using smilies.  You are going to have to sort out the humor for yourself.  Here's a hint: if it rhymes, it's probably serious.

You may feel better to know that that particular incident did not involve one of your designs.  Furthermore, it wasn't a fair contest. I had an electric plane.

I don't think theory supports your claims that the Chipmonk. draggy tips are as clean or cleaner than mine either.

Correct.  Neither theory nor I said that.  I said that based on what I have gleaned on how wings work, I don't think that wingtip shape is an aerodynamic free lunch for wake vortices, nor are those vortices divorced from the induced drag that folks count on to hold down airplane mach number on a windy day.  You said, as I remember, that your tip shape cuts way down on vortices, relative to some other shape.  That's what I meant by an aerodynamic free lunch.  

[Howard Rush]

Serge, here's what you said:

Many stunt designers see raked tips on rectangular wings as advantageous, and the second illustration backs them up.

I just don't think that with modern engines and such relatively small chords compared to "full-sized" planes that our tips are as important to models as they are to the larger planes, because of unscaled molecular spacing in the air for each.

Model gliders probably would see the benefit.  Full-size stunt planes may or may not.  No, not because of "unscaled molecular spacing."

I'll admit I've been picking on you.  If I were to claim expertise at music and say wrong things or things wrong about it, you might start picking on me after awhile.  Well, probably not, because you are a nicer person than I.

[Serge_Krauss]

Ok, I'm going to be even more aggravating.

Serge, here's what you said:

Many stunt designers see raked tips on rectangular wings as advantageous, and the second illustration backs them up.

Model gliders probably would see the benefit.  Full-size stunt planes may or may not.  No, not because of "unscaled molecular spacing."

I'll admit I've been picking on you.  If I were to claim expertise at music and say wrong things or things wrong about it, you might start picking on me after awhile.  Well, probably not, because you are a nicer person than I.

1) They do and it does, so far as I can see from that data. I could also have put that into my previous post, with the same comment.

2) Model gliders don't seem very comparable, launching fast and then gliding at RN's significantly lower than stunt stabilizers (which usually get different treatment from wings). BUT...I'll think more on and look further into the CL's vs. RN's and tip actions. You have me going back to basics on this.

It might be nice to know where a "tip" really begins, based on span-wise lift distributions. I'd hate to think that CL stunt is the only aero endeavor where some of these forms make no difference. Since air does not move purely streamwise near the tips, it would seem that no tip shape is neutral (or 'square one') here. Each is a choice and each has its consequences. So I'm not going to say make no choice, if you don't know the answer. If something is not necessarily a "good" choice, I'd want to know what one would be. That means that if an NACA quoted report indicates that a straight wing with a "triangular" tip has more lift in the linear zone than a rectangular wing for a given induced drag, I'd want to know why not to believe that or, why I should interpret that comparison of two common wing shapes as invalid for our purposes. SO...

3) Maybe, maybe not. What I'd probably do is explain.

SK

[Howard Rush]

2) Model gliders don't seem very comparable, launching fast and then gliding at RN's significantly lower than stunt stabilizers (which usually get different treatment from wings). BUT...I'll think more on and look further into the CL's vs. RN's and tip actions. You have me going back to basics on this.

I was just thinking of the gliding part, but, depending on the glider event, yes, you'd need to optimize over the whole flight.  I thought that Lee Hines's Sweepette had a peculiar planform until Gary James showed me why that swept ellipse works.  I wouldn't think the aerodynamically optimal wingtip shape would vary much with Reynolds number, nor would I think that lateral-directional stability derivatives would either, considering the mechanisms that affect them, but holler if you find data.  I don't think looking for it would be too fruitful.  What would be is the variation of lateral-directional stability derivatives with different wingtip shapes.  All I've seen old NACA data for is taper and sweep.
 

I'd hate to think that CL stunt is the only aero endeavor where some of these forms make no difference.

Randy Powell has convinced himself that stunt wings with lots more aspect ratio than usual are not the bees' knees.  Stunt planes have settled on some moderate aspect ratio.  Were I to do a trade study -- an important concept for anybody "designing" an airplane or part thereof-- on wingtip shape, I would probably hold effective aspect ratio constant and try to figure out the consequences of the differences between candidate configurations.  Below is a picture of an Impact wing compared to a wing with the same effective aspect ratio, but with Flite Streak wingtips.  It's approximate, but gives the notion.  The red wing is supposed to have the same area, but with less span.  Differences that stick out to me are sweep affecting rolling moment due to sideslip, leadout restoring moment for gust upsets, aerodynamic center, and propensity to twist in maneuvers.  

3) Maybe, maybe not. What I'd probably do is explain.

I've tried.  Do a search here on "rolling moment due to sideslip".  

This looks kinda obvious to me, but stuff that one spends a lot of time on seems obvious after awhile, and it becomes hard to see why others don't get it immediately.  I have flown combat for 50 years.  about 40 years ago I started wondering if there was something I could do to avoid "hinging", as stunt fliers call it, in downwind maneuvers and having the airplane blow in at me in upwind maneuvers.  I discovered tapered foam wings and NACA Report 1098.  Aha.  Then Gary James gave me a swept-forward wing that fixed the problem.  Everybody else figured it out independently, and current combat planes can maneuver anywhere on the circle.  The stunt flight envelope is different, but the effect is still there, and if I were to accept any more sweep in my wing, I'd want there to be a significant benefit to the trade.  

The second thing that seems obvious is the notion of a trade study.  I spent my last ten working years building and showing folks how to use a computer model to do airplane trade studies, so it's sorta in the front of my mind.  

Wing configuration comes up on these fora every few weeks, especially wingtip shape.  I spout out the same stuff.  There have been so many repetitions lately that I've gotten even lazier about responding.  Even without doing any calculation, looking up references to explain stuff gets kinda time-consuming.    Nevertheless, I've taken three (I think) stabs at an explanation here.  

[Serge_Krauss]

Jive combat leader -

I want to build today; so general unstructured response...

I certainly agree about aspect ratio. That's part of my design sequence suggestion to Mike, although we haven't gotten into the tradeoffs and how one chooses. Certainly we've discussed that enough on the forums. So, of course I think of tradeoffs. I consider rolling moment due to sideslip too, but have not quantified it. Like you, I have assumed that others would expect that. The one difference is that, less skilled flyer that I am, I have apparently underestimated its relative importance, believing that roll has resulted mostly from my ham-handed input at intersections. The planes I've drawn up have usually had quarter-chords lined up. My interest in elliptical wings with aft tips does not indicate a preference - as my posts over the years should have clarified. When I point out something like that it is for information and for others to consider in context. BUT I'd still really like to see someone else substitute such a wing into a familiar design and report their results.

I suppose this boarders on something else that has always been a "pet peeve" with me. So often when I find something interesting or significant, someone else will immediately assume some strong advocacy. As a curious guy too, haven't you often in your life been annoyed when friends or acquaintences have said about your enthusiasm, "Who cares? Why are you so worried about that?" when you're just being entertained or curious? Anyway, when I find something I consider interesting and/or important, I just expect knowledgeable people to accept the offering and themselves put it into context.

I noted recently that the top five and ten at the Nats had good representations of all three main categories of tips. That should say something. Aesthetically, I prefer the classic "Cavalier" style of tip. 'doesn't mean I think it most efficient - or best compromise. It works fine.

BUT I really thought you'd expect me to think of tips, for instance, in a broader context without my having to say it. That said, I haven't thus far expected the small area of tip rake normally employed to affect roll from sideslip significantly. Apparently that's wrong.

AND I have appreciated everything you've posted.

SK

[Russell Shaffer]

Does the tip shape effect also apply to vertical and horizontal stabilizers?

[Tim Wescott]

Does the tip shape effect also apply to vertical and horizontal stabilizers?

To my knowledge, as airfoils, yes it does.  But I rather suspect that it doesn't matter nearly as much as does tip shape on wings -- the total lift generated by the stab/elevator is much less than the wing, and the total lift generated by the vertical stab is much much less.

Howard had a thread here recently on high vs. low aspect ratio tails.  To the extent that matching the aspect ratio of the tail up to the aspect ratio of the wing really matters, changing the effective aspect ratio of the tail by changing the tip shape is going to affect the way the plane flies.

I think it's going to be a long time before that matters to me...

[Serge_Krauss]

'was just noticing this morning the varience in "Impact" stab/elevator aspect ratios. For instance Howard's and Paul's in the nationals pictures. As was said in the other thread(s), there've been some changes from plane to plane.

SK

[Tim Wescott]

So, after flogging this subject this long, it occurs to me that no one has turned the question around and asked the practical one:

If I have a plane that I like, but I change the tip shape, what all am I going to do to the aircraft performance?

For example, if I start with an Impact but I build it with nice pretty-looking round wingtips, what will that do?

What if I keep the area the same by making the span a bit more?

What if I keep the area and span the same by increasing the wing chord oh-so-slightly?

[Howard Rush]

So, after flogging this subject this long, it occurs to me that no one has turned the question around and asked the practical one:
If I have a plane that I like, but I change the tip shape, what all am I going to do to the aircraft performance?

That's how an engineer would look at it.  There would be several consequences, probably all puny, but you could get a clue analytically as to what they are.  If you take an optimized design and change something, you'd probably want to take some measures to mitigate risk.  If I were to put Flite Streak wingtips on an Impact, I'd stiffen the left wing in torsion and maybe add a hole or two to the aft leadout guide.  After a plane or two, one would settle into an optimum for the new tip shape.  That's a difference between tweaking an existing design and designing an airplane from scratch, a distinction that took me awhile to get across at work.   

For example, if I start with an Impact but I build it with nice pretty-looking round wingtips, what will that do?

What if I keep the area the same by making the span a bit more?

What if I keep the area and span the same by increasing the wing chord oh-so-slightly?

I'm not sure if these examples were to clarify the first question or are actual what-to-expect questions.  If the latter, gimme some more detail about the shape to which you propose to change.

[Tim Wescott]

I'm not sure if these examples were to clarify the first question or are actual what-to-expect questions.  If the latter, gimme some more detail about the shape to which you propose to change.

Well, it was really meant to clarify the first question, but what the heck:

Let's say I take an Impact, and I say to myself "Hmm.  That doesn't look enough like a P-40.  But I like how it flies".  So I find the circle that can be drawn tangent to both the wing leading edge and the trailing edge of the flap, and that, when you let the outboard sorta-half of the circle define the new wing outline, maintains the same wing area as before (mostly because I'm lazy and I don't want to redraw all those ribs, but if anyone asks I'll feed them a song and dance about how it buys back the efficiency lost to rounded tips).

Assume also that there is no net gain or loss of either weight or structural rigidity -- I'm using Magic Foam to make the modification.

Somehow I think you're going to tell me that the change in induced drag will be insignificant, but the extra span will make it not happy in the wind, and that you couldn't find Magic Foam on either the Tower or the Sig websites -- but I'm a-listening!

[Howard Rush]

Like this?  I'm pretty sure I couldn't tell any difference, other than it being ugly.  The neutral point might move back an RCH. Calculate X of the quarter MAC for both and let us know.  

Keeping the span and area by adding a tad of chord to the LE should make any difference microscopic. 

[phil c]

I decided to try out Randy's elliptic-swept wing on for size.  This is a plan view of a 5:1 aspect ratio airplane with areas and moment arms (MAC to MAC) roughly equal to a Sig Skyray.  Pretty, ain't it?  It ain't pretty!  I think the swept-elliptical shape works better with much higher aspect ratios.

When I build an elliptical wing plane it will look like the Spitfire because the Spit looks sexy.  Just like the rudder on the Oriental.  A sexy looking plane gets more points than a square box every time.

[RandySmith]

When I build an elliptical wing plane it will look like the Spitfire because the Spit looks sexy.  Just like the rudder on the Oriental.  A sexy looking plane gets more points than a square box every time.

NOt from a Judge who knows what he is doing...

Randy

[Tim Wescott]

NOt from a Judge who knows what he is doing...

So, a sexy looking airplane gets the same scores from the really sharp judges, and better scores from the guys who got recruited to round out the numbers.  And they look better sitting in your workshop.

What's to lose?

[Brett Buck]

NOt from a Judge who knows what he is doing...

   It's amazing how people routinely flying at the highest levels fail to see all these "rules" and things "everybody knows" about the judging, while casual observers and sport fliers know all about them.

    Brett

[RandySmith]

So, a sexy looking airplane gets the same scores from the really sharp judges, and better scores from the guys who got recruited to round out the numbers.  And they look better sitting in your workshop.

What's to lose?

Ya don't know , what ya don't know...   Tim it doesn't have to do with sexy, or type, or style ,or color, or shape,of the plane, it has to do with how it performs!     
You will get rewarded for doing the tricks accurate (quoting Howard) and you will get lower scores for ones...not as good... doesn't matter if your plane is sexy or a flying billboard...( I think I am quoting Ted there)
If a judge is giving points because he thinks the airplane is sexy, pretty, or he likes the static apperance, then he really needs more training, and another closer look at the rule book and guide.

Regards
Randy

[Randy Powell]

If you think that having a cool looking plane makes no difference, then you know zero about human psychology. Good judges have every intention to just judge geometry. But subconsciously, they are much more likely to be lenient if they like the design. It's not at all intentional but they really can't really help it. It's basic psychology. All other things being equal, a pretty plane will score better than a plain one.

Now if I'm flying the prettiest, coolest plane on the planet and Paul Walker is flying something that looks like an ugly brick, he will still win. Both because he's a lot better pilot than I am and because he's Paul Walker.

[Brett Buck]

If you think that having a cool looking plane makes no difference, then you know zero about human psychology. Good judges have every intention to just judge geometry. But subconsciously, they are much more likely to be lenient if they like the design. It's not at all intentional but they really can't really help it. It's basic psychology. All other things being equal, a pretty plane will score better than a plain one.

   There's certainly a psychological principle at work here. It's not the one you think, however. The problem at work here is that as long as you concern yourself with how the judges score pretty airplanes, "what they are buying", "judging who not what", presentation, whatever that means,   you will not be worried about what actually matters, that is, flying more accurate patterns. It's a formula for getting "stuck" in your progress.

   Even if you are right, it still wouldn't matter, the solution is still to *fly more accurate patterns*.

  EVERYBODY who has ever flown a stunt pattern in any venue has made a fair number of significant mistakes. That leaves plenty of opportunity to fly fewer mistakes and win.

    Brett

     

[Tim Wescott]

If you think that having a cool looking plane makes no difference, then you know zero about human psychology. Good judges have every intention to just judge geometry. But subconsciously, they are much more likely to be lenient if they like the design. It's not at all intentional but they really can't really help it. It's basic psychology. All other things being equal, a pretty plane will score better than a plain one.

In "How to fly U-Control", Dick Mathis mentions that he did a sociological study on stunt judging at the 1967 Nats, and he found that judges really are human and react to things outside of the written rules.  He does talk about aircraft appearance, but more in the vein of how to make the airplane look impressive and how to shape it to give an illusion of smoothness to the flight (think Chizler).  But then, he says that a loud airplane flying close to the judges helps, too: this doesn't explain why an Impact whispering through the air can get such high scores so consistently.

[Derek Barry]

   There's certainly a psychological principle at work here. It's not the one you think, however. The problem at work here is that as long as you concern yourself with how the judges score pretty airplanes, "what they are buying", "judging who not what", presentation, whatever that means,   you will not be worried about what actually matters, that is, flying more accurate patterns. It's a formula for getting "stuck" in your progress.

   Even if you are right, it still wouldn't matter, the solution is still to *fly more accurate patterns*.

  EVERYBODY who has ever flown a stunt pattern in any venue has made a fair number of significant mistakes. That leaves plenty of opportunity to fly fewer mistakes and win.

    Brett

     

Brett is absolutely correct. It is hard to do sometimes, but if you look at yourself rather than blame others you will see that there were things that you could have done to better your score.

Derek

[Brett Buck]

It is hard to do sometimes, but if you look at yourself rather than blame others you will see that there were things that you could have done to better your score.

  One of the many valuable things I have learned from Ted over the years is that *you can't concern yourself with what other people are going to do*. Go out, build and fly the best you can, and that's the end of the story, it comes out how it comes out. If anyone thinks that they are close to perfecting the flying part, and that these perceived psychological issues are all that is keeping them out of the trophies - well, that's what I mean by "stuck", because you really aren't close to perfecting the flying part.  There are numerous famous examples.

  Of course appearance is part of the score, and certainly your job is to make it *look* more accurate whether it is or not, but the solution is still entirely in your own grasp.

    I find it unfathomable that this is such a hard thing for people to believe, but apparently it is quite difficult. I guess it's like everything else, you can tell people exactly what you do, and why, and they still argue about it, tell you why you are wrong, and in many cases go off and do the exact opposite.

   Brett

[RandySmith]

If you think that having a cool looking plane makes no difference, then you know zero about human psychology. Good judges have every intention to just judge geometry. But subconsciously, they are much more likely to be lenient if they like the design. It's not at all intentional but they really can't really help it. It's basic psychology. All other things being equal, a pretty plane will score better than a plain one.

Now if I'm flying the prettiest, coolest plane on the planet and Paul Walker is flying something that looks like an ugly brick, he will still win. Both because he's a lot better pilot than I am and because he's Paul Walker.

Well I will state this:  if you think that a plane that you think, is sexy, and better looking than anything out there, and you wear white pants, white shoes, or a TUX, or a clown suit, that any of that will help you get better points from TTs or NATs caliber judges.... you may have a rude awaking at the Major contest! You may get something extra from one who does not know how to properly assign points, but not from those who do, you certainly are not going to win the NATs with airplane looks alone, the AP points are a tiny part of your score, yes they are important, but only on AP day at processing.
What will pay off many many many times better is to practice both your building, and flying skills, bring a well trimmed model that you have practiced with (preferably in front  of a good coach) YOu will get way more point this way.
That may or may not have been true back many decades ago...it is certainly not now.

Regards
Randy

[phil c]

Every stunt flight I've seen has been filled with minor to major errors, according to the rule book.  If the judges are folks who notice things like the apppearance of the planne, the pilot's dressage, or other extraneous stuff all you can do is hope and pray.  If they are good judges and go by the book, ignoring the extraneous stuff they will see tons of errors during the contest, most of them very similar.

So the best way to stand out is to not present them with any unusual errors that might not be huge but are different from what everybody else is making.  Then try to develop two or three manuevers that are really good, particularly on tracking.  Good judges will notice a few really good maneuvers and reward them well because they stand out from all the errors they are used to seeing all day long.  Because of all the noise in scoring it is much harder to get half a point extra on each maneuver than it is to get 2-3 points more on a few really good ones.