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

[Mike Griffin]

I wanted to compare and have often wondered about wing design.  For example, does a wing with a leading edge that sweeps back perform better than a wing with a straight leading edge and a constant chord?  Does a wing design that uses a constant chord and has flaps perform as well as a wing that has a swept back leading edge and tapers?  I am not positive but I think Tom N's HOBO might be an example of this type of wing.  One of my favorite planes was a Humongous.  It has a constant chord wing and no flaps and it flew very well.

Thank you in advance

Mike

[Steve Helmick]

The tapered wing (same A/R & span) should be better in wind turbulence, with less area at the tips for leverage by the wind. This also encourages tapered structure (opportunity not often taken), which lightens the wing tips and makes the wing right itself quicker (aka "barbell effect"). So, yes, it should be better in wind and turbulence off trees, buildings, ditches, etc.

A smaller tip chord  will create a smaller tip vortex, especially with a good tip shape (see Randy Smith's and Ted's designs...also the Flite Streak or Spitfire).  That'll reduce wake turbulence, which most of us have learned  to be a very nasty thing. Key word be "reduce", not same as "eliminate". Heavy planes also make more wake turbulence.

I also had a Humongus, and liked it (.46LA!). The OTS pattern is not so bad for wake turbulence, with only one square loop and all the corners and maneuvers much larger than the modern pattern.  Might explain why the constant chord is not a problem for that design? Also for combat models, where you'd better not be flying through the same spot very many times, or you'll get cut or killed!    Steve

[Howard Rush]

The tapered wing (same A/R & span) should be better in wind turbulence, with less area at the tips for leverage by the wind. This also encourages tapered structure (opportunity not often taken), which lightens the wing tips and makes the wing right itself quicker (aka "barbell effect"). So, yes, it should be better in wind and turbulence off trees, buildings, ditches, etc

Well stated. Also important is rolling moment due to sideslip, which can be explained without math. It's a disadvantage of sweep.

A smaller tip chord  will create a smaller tip vortex, especially with a good tip shape (see Randy Smith's and Ted's designs...also the Flite Streak or Spitfire).  That'll reduce wake turbulence, which most of us have learned  to be a very nasty thing.

Only a little bit.  There is a popular misconception about what makes vortices.

[Mike Griffin]

Steve and Howard

Thank you for the explanations.  If I am not mistaken (which is entirely possible) the Oriental that Dee Rice designed is a constant chord wing and I have seen a few of these in competition that did well.  I talk with Tom Morris quite often and he told me that he was cutting quite a few Humongi (plural of Humongous) for different folks now. My main interest before I had two back operations and a total knee replacement was to fly OLD TIME Stunt because I just seemed to enjoy that genre better than the others.  I quit producing kits because of back pain and I certainly cannot stand in a circle for 6 minutes going around as it hurts just walk.  But if I ever get this back fixed I would like to fly in Old Time.   In any case, thanks again for your help.

Mike

[Tim Wescott]

Any consideration of the wings should include the shape of the wings with the flaps.  As best as I can tell from looking at pictures, the Oriental wing is a constant-chord built-up structure, with tapered flaps stuck on.  Aerodynamically, those flaps make the wing tapered (and, incidentally, slightly forward-swept).

Stuff like that matters.  Only a little in terms of the taper, but a lot in terms of the wing area and how you'd go about calculating stability.

[Chuck_Smith]

Another thing to consider is that a tapered wing has a much closer lift distribution to the perfect eliptical wing than a straight wing. This increases the efficiencey of said wing and allows a smaller and thus lighter wing to generate lift with less drag than a straight wing.

[RandySmith]

Well stated. Also important is rolling moment due to sideslip, which can be explained without math. It's a disadvantage of sweep.

Only a little bit.  There is a popular misconception about what makes vortices.

I will say this for what is is worth,  I have personally seen wings with tips similar to a Nobler, and a Chipmonk, and a  SV-11 in the wind tunnel.
 The Nobler shaped tip had huge vorticies, the Chipmonk shape one did also, The SV shape tip had very small string looking vorticies, they all got bigger as the were rotated, the SV swept looking one was by far the smallest.
I also saw a tip very much like my Katana tips on my wing, it has very small vorticies also, There was a full scale glider tip put into the tunnel too it was a long skinny elliptical type except it had a tip that was reversed and looked like my Katana tips, this had a very small vorticies coming from it.

I have seen tips that were identical to the POND Racer, they were tiny, the OLD tips from the Piper Cruiser was very large and draggy.. The Hoerner Tips from many decades ago cleaned up Cessna's but really would not work well on our models

Randy

[Howard Rush]

I will say this for what is is worth,  I have personally seen wings with tips similar to a Nobler, and a Chipmonk, and a  SV-11 in the wind tunnel.
 The Nobler shaped tip had huge vorticies, the Chipmonk shape one did also, The SV shape tip had very small string looking vorticies, they all got bigger as the were rotated, the SV swept looking one was by far the smallest.
I also saw a tip very much like my Katana tips on my wing, it has very small vorticies also, There was a full scale glider tip put into the tunnel too it was a long skinny elliptical type except it had a tip that was reversed and looked like my Katana tips, this had a very small vorticies coming from it.

I have seen tips that were identical to the POND Racer, they were tiny, the OLD tips from the Piper Cruiser was very large and draggy.. The Hoerner Tips from many decades ago cleaned up Cessna's but really would not work well on our models

There is a popular misconception about what makes vortices.

[Randy Powell]

And what about elliptical wings?

[RandySmith]

And what about elliptical wings?

The only elliptical shape I have seen in those test was a new style elliptical wing that has swept back tips , these are on new design gliders, the wing is very similar to the one on the POND racer, or Nemesis Racer, but just much longer span and higher AR.  The Classic elliptical shape like a Spitfire was not included.
The vorticies I am speaking of are tip vorticies ,  The tip vorticies get very large on some type of tips when the AoA is changed rapidly, other tips are much smaller when the same is applied.

Randy

[Tim Wescott]

I think that when Prandle (sp?) came up with his "elliptical wings are best" rule not much was known about the whole "vortices make drag" thing.

I've tried to sketch out stunt wings with that flat-back elliptical wing.  Without flaps the drawback is that the leadout comes out of the leading edge at a point where it's sloped 45 degrees or more off of fore-and-aft.  With flaps, and trying to retain that pointing-back wing tip, you either need an elliptical hinge line or you need a really ugly swoop in the wing trailing edge.

[Trostle]

I've tried to sketch out stunt wings with that flat-back elliptical wing.  Without flaps the drawback is that the leadout comes out of the leading edge at a point where it's sloped 45 degrees or more off of fore-and-aft.  With flaps, and trying to retain that pointing-back wing tip, you either need an elliptical hinge line or you need a really ugly swoop in the wing trailing edge.

Regarding the flaps, maybe there is something to be learned from what the French were flying at several World Championships in the last decade.  They used flaps less than 50% of the span and what appears to be less than 8% of total wing area.  They turned with the best.  The French team placed 2nd in 2002 and 2004 at the World Championships, with most of their team members flying planes with this kind of flap arrangement. Something to think about.  Just goes to show there is no set formula for these CL Stunt Things.

Keith

[Tim Wescott]

Regarding the flaps, maybe there is something to be learned from what the French were flying at several World Championships in the last decade.  They used flaps less than 50% of the span and what appears to be less than 8% of total wing area.  They turned with the best.  The French team placed 2nd in 2002 and 2004 at the World Championships, with most of their team members flying planes with this kind of flap arrangement. Something to think about.  Just goes to show there is no set formual for these CL Stunt Things.

Hmm.  I recall someone (Howard?) saying something about reduced-span flaps, and there being a sort of anti-optimum at around 60 or 70% span.  If true, the 50% figure would make sense.

If you're using a super-zoot planform to reduce induced drag, and you have short-span flaps, wouldn't you get vorteces from the flap tips worse than the ones you're saving yourself from at the wing tips?

[Trostle]

Hmm.  I recall someone (Howard?) saying something about reduced-span flaps, and there being a sort of anti-optimum at around 60 or 70% span.  If true, the 50% figure would make sense.

If you're using a super-zoot planform to reduce induced drag, and you have short-span flaps, wouldn't you get vorteces from the flap tips worse than the ones you're saving yourself from at the wing tips?

On those French airplane, there was more than a moderate amount of TE sweep.  The tip chord on those short span flaps, set close to the fuselage, was extremely small, like less than 1/2" or at least in that ball park.  I do not have a good picture to show these, but when you see them, you have to wonder why even bother with flaps.  Again, those airplanes turned with the best of them.  They used 4-stroke engines also.

By the way Tim, I think you were making reference to some work by Ludwig Prandtl who was a pioneer in the early part of the last century who was fundmental in the establishment of systematic mathematical analyis to study the science of aeronautics which then became basis for aeronautical engineering.

Keith

[Brett Buck]

Hmm.  I recall someone (Howard?) saying something about reduced-span flaps, and there being a sort of anti-optimum at around 60 or 70% span.  If true, the 50% figure would make sense.

   There are other good reasons not to have partial-span flaps. And I know that Howard will be driven into another tizzy, but the argument in the Imitation article has proven to be compelling from my experience - you are probably better off from many aspects (heh) with narrow full-span flaps than wide partial-span flaps. Certainly, matching the areas but shortening the span does not appear to be a winner. If simply turning tightly with favorable control forces and a substantial wing loading was your only concern, the relatively small 18% chord, nearly full-span flaps on the Imitation airfoil definitely cuts the mustard. "Imitation" being a very appropriate name for the airplane, since it has been sincerely flattered by many people since. Myself included, of course.

     The Beringer airplanes with the teeny flaps had a lot of other interesting/tricky aspects besides the mere small area. They were also set up with extreme and intentional flexibility in both the flap horn and the prop. I can only speculate what they were trying to do. Remi's airplane flew very much differently from most others, it flew a whole lot like a typical flapless airplane without as much tendency to hop out of corners. It also slowed dramatically in the corners. My guess was that this was intentional, and the idea was to build what was essentially a flapless stunt plane by allowing the horn to flex and minimize the flap deflection at entry, and then count on it deflecting more as the speed bled off, making it less necessary to feather the controls at exit to control the hop that it would otherwise be prone to. The prop also flexed, presumably gaining pitch at the tips as the speed dropped, also making the end of the corner more tidy than it would otherwise have been. The severe static washout in the prop certainly enhanced the tendency to slow at corner entry, and maybe they needed the tip pitch to jump up as the speed washed out because of the "dead fish" response of the engine. How all this was adjusted to happen at the right time and by the right amount in a variety of conditions is anyone's guess.

I do know that I have been trying to make my airplanes do *exactly the opposite* for decades - minimizing the flexible aspects at the cost of weight, setting the engine/prop to minimize the speed loss (and gain) in the corners, and intentionally enlarging the flaps from the Imitation baseline to get a little more feedback at the handle. Precisely because I don't think I can (or at least don't want to have to) adjust it to make all the flexing and variation happen the same way at 50 degrees and Napa, 105 degrees in Woodland, and 90 degrees. 1000 feet, and very humid at Muncie.

   Brett

[Serge_Krauss]

As usual, several posts have appeared since I started typing tonight. This is not about flaps, but the french wings with those flaps would have had closer to a bell-shaped lift distribution, like the Horten flying wing theory, when deflected. 'might have been advantageous in being closer to elliptical in some respects and had other advantages from location...? Now Tim's has come up - haven't read that yet, but I gotta press "post" sometime!

The early Prandtl theory that is still useful was not concerned with wing shape but rather with spanwise lift distribution. Elliptical lift distribution, if I recall correctly, gives the greatest efficiency, because it produces a uniform span-wise downwash. An actual elliptical wing may not have a perfectly elliptical lift distribution. The first diagram below indicates that elliptical spanwise chord distributions have different efficiencies (based on amount of induced drag for a given lift) depending on the tip's chordwise position with "swept" tips having advantages, as mentioned above. The efficiency value of 100% assigned to the spitfire wing (tip at .25-chord) may be just a normalizing figure for comparison, since that wing is the most often used elliptical shape. The one with highest efficiency should be the one with closest to an actual elliptical lift distribution.

Many stunt designers see raked tips on rectangular wings as advantageous, and the second illustration backs them up. These report pages were reduced in size on old software to fit the SSWF 50-Kb limit and are thus really bad. 'sorry!

As posted elsewhere on these threads and earlier (often), The elliptical wing has its MAC, and therefore its aero center, very far inboard along the halfspan (at 42.4% of the half-span), which should make it less susceptable to gust upsets. As also posted here, a tapered wing can approximate an elliptical lift distribution because of tip losses. No wing without tip plates and/or multiple tips comes close to a rectangular lift distribution; lift always tapers off faster toward the tip. To get a "theoretical" (ideal in this case) aero center as far inboard on a tapered wing as on an elliptical wing, the taper ratio would have to be about .376 as in the white outline in the third picture. The Reynolds numbers for these wings can compromise the promised efficiency on too small a model. On triangular wings with zero tip chord, the a.c. falls at 33% of the half-span.

If the most efficient wing for a given structure (root bending moment) is desired, the fourth illustration says something interesting. Since it came from Dr. R.T. Jones in Soaring Magazine, it is a higher aspect ratio than we'd use, but the analysis holds for any elliptical wing.

Reminder, I've used the term "elliptical wing" loosely; the analyses hold for wings having the idealized elliptical lift distributions. We approximate this with elliptically shaped wings and adjust.

[Howard Rush]

The only elliptical shape I have seen in those test was a new style elliptical wing that has swept back tips , these are on new design gliders, the wing is very similar to the one on the POND racer, or Nemesis Racer, but just much longer span and higher AR.  The Classic elliptical shape like a Spitfire was not included.

The new ones work better than the Spitfire's, despite not looking as cool.  See Serge's piece above.

The vorticies I am speaking of are tip vorticies ,  The tip vorticies get very large on some type of tips when the AoA is changed rapidly, other tips are much smaller when the same is applied.

No, they're a little smaller.  There is a popular misconception about what makes vortices.

[Howard Rush]

I think that when Prandle (sp?) came up with his "elliptical wings are best" rule not much was known about the whole "vortices make drag" thing.

There is a popular misconception about what makes vortices. Prandtl knew.

[Howard Rush]

Hmm.  I recall someone (Howard?) saying something about reduced-span flaps, and there being a sort of anti-optimum at around 60 or 70% span.

That was my speculation about the most evil place to have a trim tab beyond the flap.

If you're using a super-zoot planform to reduce induced drag, and you have short-span flaps, wouldn't you get vorteces from the flap tips worse than the ones you're saving yourself from at the wing tips?

Yes.  There is a popular misconception about what makes vortices. Here again is a reference: http://www.smartcockpit.com/data/pdfs/flightops/aerodynamics/Wingtip_Devices.pdf

Once again, guys are obsessing over reducing vortices, which come from induced drag, when their stunt planes have about the right amount of induced drag.  The easiest way to reduce induced drag, hence vortices, is by reducing span loading, which we don't do, because the airplanes would go nuts in the wind.  I'd pick my wingtips based on their dihedral effect, whether they are easy to cover, and whether they look cool.  

[Chuck_Smith]

Interestingly, the "Induced" term in induced drag is very commonly misunderstood.

It comes from Biot-Savart and the laws of electrical induction.

Lot's of people make the mistake of thinking it's some mysterious drag force when it's really talking about the reduction in effective angle of attack due to ... wingtip vortices. Wingtip vortices were greatly understood in Prandtl's day as was the fact that Bernoulli has nothing to do with creating lift.

As for the straight trailing edge, swept LE and bends in the LE....meh. Yeah, looks great on a Discus or an ASW28 but on the AR's and L/Ds we tend to see these things it probably doesn't matter.

[RandySmith]

That was my speculation about the most evil place to have a trim tab beyond the flap.

Yes.  There is a popular misconception about what makes vortices. Here again is a reference: http://www.smartcockpit.com/data/pdfs/flightops/aerodynamics/Wingtip_Devices.pdf

Once again, guys are obsessing over reducing vortices, which come from induced drag, when their stunt planes have about the right amount of induced drag.  The easiest way to reduce induced drag, hence vortices, is by reducing span loading, which we don't do, because the airplanes would go nuts in the wind.  I'd pick my wingtips based on their dihedral effect, whether they are easy to cover, and whether they look cool.  

Not Found

The requested URL /data/pdfs/flightops/aerodynamics/Wingtip_Devices.pdf was not found on this server.

I get a dead link for it, Howard do you have a link that works? or does it show for you?

Randy

[Howard Rush]

Sorry.  It used to work.  I fetched the pdf and put it below.

[Tim Wescott]

The only elliptical shape I have seen in those test was a new style elliptical wing that has swept back tips , these are on new design gliders, the wing is very similar to the one on the POND racer, or Nemesis Racer, but just much longer span and higher AR.  The Classic elliptical shape like a Spitfire was not included.
The vorticies I am speaking of are tip vorticies ,  The tip vorticies get very large on some type of tips when the AoA is changed rapidly, other tips are much smaller when the same is applied.

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.

[Howard Rush]

It would make a nice hand launched glider.

[Tim Wescott]

It would make a nice hand launched glider.

I think it'd look great with a higher aspect ratio wing.  It does look great with a higher aspect ratio wing.  But the way that the elliptical shape packs the area in while needing a huge root chord makes the 5:1 aspect ratio wing look tubby in my mind.  Kind of like a 250 pound guy with a beer belly wearing a shiny set of bicycle racing togs.

[Serge_Krauss]

Of course that one will be harder to build and make rigid, but I'd like to see one built. I drew up something similar, but had the same reaction - didn't want to spend the time on it. But it would still be interesting, maybe even worthwhile to learn what it would do compared to a stock SkyRay!

SK

[Howard Rush]

You are on track to making a poor stunt plane.  If you are trading complexity and ability to fly stunt well for aesthetics, that's one thing, but if you are trading them for some perceived aerodynamic advantage, you might reconsider the total design.

[Howard Rush]

   There are other good reasons not to have partial-span flaps. And I know that Howard will be driven into another tizzy, but the argument in the Imitation article has proven to be compelling from my experience - you are probably better off from many aspects (heh) with narrow full-span flaps than wide partial-span flaps. Certainly, matching the areas but shortening the span does not appear to be a winner.

A tizzy of agreement.  That's what my ciphering shows.

[Howard Rush]

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

Feeding their misunderstanding. 

[RandySmith]

The new ones work better than the Spitfire's, despite not looking as cool.  See Serge's piece above.
 

Yes you are correct, and Yes I know that, hence the reason I went to many of the wing designs I use, this was started several decades ago, The Astra , Typhoon, KATANA and others use similar tips, these go back on my designs to the late 80s.
I have used other tips with the same plane and wing, They do not work as well and do not carry near as much weight, at least the planes with the tips going the opposite way, like a Chipmonk or Nobler tip, always seem to act like the plane is much heavier, they don't go thru corners as clean, and seem to require more power to do the tricks.
Randy

[John Miller]

I thought I might share the wing shapes I'm using on my most recent designs.

It's my understanding, using what information I can find, that they are a form rendering a near approximation of an ellyptical planform.

They come from two designs, of four airplanes in the same family. The 2 bits, and the 2 bits bipe.  I've also posted an experimental Spitfire styl ellyptical with egg crate style wing ribs 

[Howard Rush]

...the planes with the tips going the opposite way, like a Chipmonk or Nobler tip, always seem to act like the plane is much heavier...

If you are referring to mine, it's because it is much heavier.

[Howard Rush]

That third one is purty, John.

[Tim Wescott]

You are on track to making a poor stunt plane.  If you are trading complexity and ability to fly stunt well for aesthetics, that's one thing, but if you are trading them for some perceived aerodynamic advantage, you might reconsider the total design.

Yet a still agree with Serge that it might be worthwhile to build the airplane for the knowledge gained.

Of course, if I build it and fly it the verdict will be "it flies crappy".  Which would be the same verdict regardless of what plane it is, the problem being the pilot...

[Howard Rush]

Be sure to fly it in a stiff breeze when I'm there.

[Brett Buck]

Of course that one will be harder to build and make rigid, but I'd like to see one built. I drew up something similar, but had the same reaction - didn't want to spend the time on it. But it would still be interesting, maybe even worthwhile to learn what it would do compared to a stock SkyRay!

   Maybe. How does it address the observed issues with the stock design?

     Brett

[Tim Wescott]

   Maybe. How does it address the observed issues with the stock design?

What are the observed issues with the stock design?

I don't see it as a candidate for a better plane, but rather a tool to answer a "what if?" question.

[Brett Buck]

What are the observed issues with the stock design?

   Straight out of the box, the overwhelming problem is that it will self-destruct on the first minor crash, that's a fatal flaw (hence my recommendation...). Presuming that you rebuild it out of balsa to avoid that, the performance issues are (in no particular order):

1 Rate-limited corner
2 difficult tracking in level flight and straight-line segments
3 poor response to turbulence
4 hops out of corners

   With no other changes I would expect nothing you can do to the wing will fix #1. 2, 3, and 4, will likely alter it but you have to separate out the effects of your changes from other items that will likely affect them far more. I can't entirely follow what you are proposing as a change aside from the swoopy wingtips but if involved raising the aspect ratio AND introducing taper or the equivalent, those will tend to offset each other for 3 and 4.

    I would make 3 changes starting from my all-balsa model as a baseline:

   First  shorten the tail moment (arm, there you go Howard, I do talk good English) by around an inch, and enlarge the area to keep the same TVC. Intent is to solve #1. I would make that change without any other changes to aid in evaluation.

   Second would be to keep the same aspect ratio, but add taper, maybe 3/4" more root and 3/4" less tip chord. I would also make that change by itself. The goal is to reduce the tendency to bounce around in roll/yaw in turbulence.

    Third, providing that I got the tail moment right in step one, I would be tempted to reduce the aspect ratio to soften up the response to elevator motion.

    That would take a long time to get through. Note that I am certainly not going to do any of these changes. If I was going to pursue this line of reasoning, I would be far more inclined to start with a Medic or Doctor instead of a Skyray since I like the airfoil better and it's a lot closer to the end goal already. The Doctor, in particular, has only one and a half of the above-mentioned issues and I could be competitive in any contest in the world with it, as long as the air was perfect.

I don't see it as a candidate for a better plane, but rather a tool to answer a "what if?" question.

   The problem with doing this is that, for sure, the airplanes will fly differently. Whether it flies differently as a result of the changes you intended, or differently as a result of some other difference (like alignment, etc) is another issue.  I would suggest 5 of them, compared to 5 Skyrays.  Trim them all the different ways you can think of. Have them and have them evaluated by multiple experienced pilots. Compare notes,  find the common attributes and limitations, then you will have some idea what the effects of the change you made are and how much they changed. One example will be extremely prone to unit to unit variation, and with any but the most experienced pilots, you will also tend to blur variations in the airplane performance with difficulties you might have with the piloting.

  Not to mention that the characteristics you are intending to experiment (like the shape of the lift distribution and induced drag) are such tiny effect at the best of the time, and also utterly swamped by tiny moment-to-moment changes in the way the engine runs.

    It boils down to this - there have probably been 100,000 Green Box Noblers built since 1957. No two of them fly the same, and it takes a while and multiple examples to figure out what the design characteristics are, and how to adjust them VS someone putting one extra coat of Ambroid on the rib/spar joints.

    Brett

[Tim Wescott]

The problem with doing this is that, for sure, the airplanes will fly differently. Whether it flies differently as a result of the changes you intended, or differently as a result of some other difference (like alignment, etc) is another issue.  I would suggest 5 of them, compared to 5 Skyrays.

Yup.  40 years ago we could have just convinced the East Germans that their national prestige depended on winning CLPA events with flapless stunters and stood back to watch.  Can't do that now, though.

[Brett Buck]

Yup.  40 years ago we could have just convinced the East Germans that their national prestige depended on winning CLPA events with flapless stunters and stood back to watch.  Can't do that now, though.

   I am certainly not discouraging you from trying, but a one-shot experiment can lead you astray. More experience can shorten the process, of course.

    Brett

[Serge_Krauss]

Feeding their misunderstanding. 

'not sure where this is going. The raked tips seem to be slightly better, although I have never subscribed to the tips on our stunt models having anything near the effect of tip variation on large planes. What's the misunderstanding?

SK

[RandySmith]

If you are referring to mine, it's because it is much heavier.

Hi Howard

No I am not referring to yours, I am referring to mine with differant tips

Randy

[Howard Rush]

What's the misunderstanding?

That from that one parameter you can conclude an advantage to making stunt wings like that.  There is a bit more to the design process.  At work when we saw some promising airplane technology, we would formulate a trade between it and some baseline: LED wingtip lights vs. incandescent wingtip lights, for a wingtip example. Then, holding light output constant for all the design alternatives, we'd consider effects of weight, drag, electrical power, flight interruption, maintenance, spares, nonrecurring cost, and recurring cost.  These got put into a common figure of merit: in our case life-cycle cost over a fleet of airplanes each of which operates for 20 years.  

Assuming you aren't picking a shape for aesthetics and you don't believe some Internet poppycock about tip vortices, you could pick a wing with those tips and trade it against a straight-taper wing that has: 1) the same effective span loading, hence the same induced drag, hence the same vortex power for the same maneuvers, and that has 2) sufficient torsional stiffness to give the same flap hinge line curvature in the same maneuvers.  Then make a list of the relative benefits.  Include lateral-directional characteristics for sure and maybe fuel tank room.  Pick the better one. I guess the figure of merit would be stunt score over a range of contest conditions.  

It wouldn't surprise me if Randy is right about carrying more weight.  A wing with Flite Streak wingtips may have a higher max Cl, but that's not what that chart shows as its virtue.

Furthermore, I'll have you know that at the last contest, flying a common Impact with the wrong shape wingtips, I was able to beat out by 0.5 point an airplane with the aforementioned Flite Streak wingtips.

[Trostle]

Furthermore, I'll have you know that at the last contest, flying a common Impact with the wrong shape wingtips, I was able to beat out by 0.5 point an airplane with the aforementioned Flite Streak wingtips.

WOW!!!

That establishes a real trend setter if there ever was one.  CLPA technology has just advanced probably at least 5 years.

Howard, I am sure you appreciate my taking note of this to make sure your quantum leap forward gets recorded for infamy.

Keith

[RandySmith]

"It wouldn't surprise me if Randy is right about carrying more weight.  A wing with Flite Streak wingtips may have a higher max Cl, but that's not what that chart shows as its virtue."

This is fact for my airfoils and wings, the tip shape I use means the wing area can be reduced to 667 sq in,(early SVs were 750, 725, 700 sq in) and will carry the same weight as one with Chipmonk style tips at about 710 sq in.  For my Elliptical shaped planes Like the Dreadnought, StarFire etc, they need to be at 700 sq in or over to carry the same weights as the other ones do at around 667.

Also the wing vortices, coming off the tips, ARE much smaller and cleaner, coming from my wings with the shape used on many of my planes, they are also smaller when the AoA is changed, This I have seen with my own eyes and have tried various shapes, for my wings and airplane designs, this shape works better. This may or may not apply to other airfoils and other airplanes.

Bill Rich for example had a SV-11 in the TOP 5 that weighed 74 ounces, it did not stall or drop in hard corners, if you just cut off and change the tips on the plane to a Chipmonk shape it will not perform that well.

And Howard, you can quit being offended, the info I have written about is about my experience with my airfoils designs wings and tip/wing shapes, this is NOT an attack on you or your airplane design.

AS far as flaps go, The one I have migrated toward, are different than some, and the  DO NOT suffer from the evils of not being full span, as many other NATs and Worlds winning ones don't either.

The partial flaps also are easier to keep stiff than full span ones, and ones that the chord is larger in the center and taper smaller toward the tips are easier to keep stiffer, I didn't like the performance of the constant chord flaps all the way across the wing because I had trouble with the flexing too much, the constant chord ones were hard to make stiff and did not perform as well as the ones I typically use now. I know the fix to that is to use a non conventional flap horn and some sort of torque tube to keep the flexing out of the flaps.
Maybe If I had been as smart as Howard, just maybe I could have figured out a way to do this that I was both satisfied with the weight and stiffness of. The sets I made, I was never happy with. I think Howard may have  solved that problem with his carbon tube flaps. Another experiment to do for a new airplane.

Randy

[Serge_Krauss]

That from that one parameter you can conclude an advantage to making stunt wings like that.  There is a bit more to the design process.  

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...

[Howard Rush]

WOW!!!

That establishes a real trend setter if there ever was one.  CLPA technology has just advanced probably at least 5 years.

Howard, I am sure you appreciate my taking note of this to make sure your quantum leap forward gets recorded for infamy.

You were one of the first two people to document this achievement, and within seconds of its happening. 

[Howard Rush]

"It wouldn't surprise me if Randy is right about carrying more weight.  A wing with Flite Streak wingtips may have a higher max Cl, but that's not what that chart shows as its virtue."

This is fact for my airfoils and wings, the tip shape I use means the wing area can be reduced to 667 sq in,(early SVs were 750, 725, 700 sq in) and will carry the same weight as one with Chipmonk style tips at about 710 sq in.  For my Elliptical shaped planes Like the Dreadnought, StarFire etc, they need to be at 700 sq in or over to carry the same weights as the other ones do at around 667.

6% more lift.  That's a lot.  

And Howard, you can quit being offended, the info I have written about is about my experience with my airfoils designs wings and tip/wing shapes, this is NOT an attack on you or your airplane design.

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.  

[Howard Rush]

No I am not referring to yours, I am referring to mine with differant tips

That was a joke.  I don't use smilies.

[Howard Rush]

Hmmmm. Sure, but this seems kinda straight forward.

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.