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Author Topic: ice cream cone airfoils?  (Read 54742 times)

Online Howard Rush

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Re: ice cream cone airfoils?
« Reply #50 on: February 08, 2015, 09:40:46 AM »
The Imitation has an airfoil similar to those (very blunt and with a high point at about 21%...yes, including the flaps) and, under power, pretty much couldn't be stalled.

Send me (preferably electronically) a drawing of it, and put it into a formula that can be input into CAD.
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Offline Ted Fancher

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Re: ice cream cone airfoils?
« Reply #51 on: February 10, 2015, 01:32:09 PM »
Send me (preferably electronically) a drawing of it, and put it into a formula that can be input into CAD.

Howard,

Would a scan of the airfoil from the magazine plane be adequate?

Ted

Online Howard Rush

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Re: ice cream cone airfoils?
« Reply #52 on: February 10, 2015, 02:08:34 PM »
Maybe not if it's blown up from the magazine itself.   The best might be from running a pencil around the rib template you used (or shoe sole, if you still have those shoes). 
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Offline Ted Fancher

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Re: ice cream cone airfoils?
« Reply #53 on: February 11, 2015, 06:27:53 PM »
Maybe not if it's blown up from the magazine itself.   The best might be from running a pencil around the rib template you used (or shoe sole, if you still have those shoes). 

C'mon, Howie.  I've got small feet.  I had to use a scientific method at least 10% superior to even my Tux shoes. 

I used two different french curves, one curve eerily  identical to Bridgette Bardot's fanny and the other replicating a particularly appealing curve of her bosom.  The fanny one provided the curve aft of the 22% MAC high point of the airfoil back to the hinge line and the other the enchanting curve from the high point to the Leading Edge radius (which was  pretty much a boring arc whose dimension I don't recall but I would call moderately blunt).  The root was ~18.2% thick and the tip about 18.4 (probably because the pencil was sharper when I drew the root).  The only hard part about drawing the ribs along the french curves was that Bridgette would wiggle because it tickled her.  Other than the boring arc part, an airfoil doesn't get any sexier than that. 

My Imitation wing was cut by Bob Hunt who also made the templates from which he cut the cores.  I know he still had them a few years ago because I ordered a wing of slightly modified structure (and, perhaps, a slightly longer span although I can't recall exactly) which I wanted to use in a twin four stroke (just to hear the two engines running at the same time) for a fun beater.  Never have done anything with it and it's in a pile of stuff in the attic.

Maybe Bob can scan the template and post it.

Ted

Online Howard Rush

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Re: ice cream cone airfoils?
« Reply #54 on: February 11, 2015, 08:54:11 PM »
Or draw around it and mail it.
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Offline Brett Buck

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Re: ice cream cone airfoils?
« Reply #55 on: February 11, 2015, 09:17:02 PM »
I used two different french curves, one curve eerily  identical to Bridgette Bardot's fanny and the other replicating a particularly appealing curve of her bosom.

    I am quite curious how you determined this. And whether it resulted in any legal action. Although, at this point, she might be glad you still cared.

     Brett
« Last Edit: February 11, 2015, 10:55:48 PM by Brett Buck »

Online Howard Rush

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Re: ice cream cone airfoils?
« Reply #56 on: February 11, 2015, 09:43:16 PM »
At this point, the airfoil has changed.  I think there's been some laminar flow.
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Offline Ted Fancher

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Re: ice cream cone airfoils?
« Reply #57 on: February 14, 2015, 07:58:14 PM »
   I am quite curious how you determined this. And whether it resulted in any legal action. Although, at this point, she might be glad you still cared.

     Brett

At the time I drew up the Imitation plans Ms. Bardot's singularly memorable anatomy was still regularly animating multiple parts of the world's  male anatomies...including my drawing fingers.  As I recall I drew the airfoil freehand from memory with my eyes closed.  I've never asked if it was good for her, too...although in today's PC world I probably would have.

Ted

Offline Ted Fancher

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Re: ice cream cone airfoils?
« Reply #58 on: February 17, 2015, 01:12:54 PM »
Might be worth taking a close look at the picture of Bob Whitley's Derringer at the '77 Nats thread in the "Open Forum" section to see the first "ice cream cone" airfoil that caught my attention.  Same airplane (or maybe another version of it) won, I believe, the '78 Nats.  What caught my eye was that the very heavy (well over 70 oz on an ST .46) flew dead flat both ways in level flight and stopped precisely that way every time it pulled out of a corner...sort of like it was landing on a pillow at five feet AGL.  That characteristic was more or less replicated in the Imitation although seldom as consistently as Bob flew the Derringer.  There is merit to the concept IMHO.


Ted

Online Howard Rush

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Re: ice cream cone airfoils?
« Reply #59 on: February 17, 2015, 01:20:17 PM »
Same airplane (or maybe another version of it) won, I believe, the '78 Nats. 

While over on the grass, Mr. P. T. Granderson of the Jive Combat Team won combat with such an airfoil.
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Offline Ted Fancher

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Re: ice cream cone airfoils?
« Reply #60 on: February 18, 2015, 12:58:41 PM »
While over on the grass, Mr. P. T. Granderson of the Jive Combat Team won combat with such an airfoil.

What more proof does one need!  Make mine a banana split.

Ted

Offline Keith Renecle

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Re: ice cream cone airfoils?
« Reply #61 on: March 04, 2015, 10:36:42 AM »
Dave, you can't go wrong with that kind of airfoil for combat.  It works remarkably well on a unflapped stunter too.  Typical version has the high point at 18%+/- and a thickness that is convenient,  ~15% at the root and 18% at the tip.  Use a fair amount of taper.  The tip should be no more than 50% of the root chord.  Another newer trick is to leave the trailing edge squared off 2-3% of chord.  The another is to match the weight and speed so the plane has lots of line tension at all times.  Keeps it from getting blown in by a gust.  Various designers are doing things like engine offset and building offset in aerodynamically to keep the plane pulling out hard.
Hi Phil,
This is most interesting! I am very curious to know why you say that the tip should be no more than 50% of the root chord?? I'll tell you why I ask. Some years ago I tried to make some simple low cost stunt trainers and I used the Russian style combat wing because it is indeed easy to make, and is quite tough as well. I made the first one for a .25 to .30 engine and it flew really well. I then made a bunch of .15 size versions and they too flew very well, so I tried a .40 size one. It never really performed well unless it flew really fast. It did serve to test a few engines and then my initial electric stuff was all tested on it as well. After a few mods and prangs it became tatty, so I decided to fix it up to make it look better. At the same time I thought that maybe it could use some more wing area, so I widened the tips to increase the wing area. Guess what?? It flew even worse, hence my question on the 50% wingtip thing. It would be very interesting if you could explain that a bit more please. Thanks.

Keith R
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Offline Keith Renecle

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Re: ice cream cone airfoils?
« Reply #62 on: March 04, 2015, 10:40:26 AM »
Oops! Sorry about the double post. My internet stopped as I was trying to post this, so I did it over, and it did a double take!

Keith R
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Offline phil c

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Re: ice cream cone airfoils?
« Reply #63 on: March 13, 2015, 12:27:15 PM »
Hi Phil,
This is most interesting! I am very curious to know why you say that the tip should be no more than 50% of the root chord?? I'll tell you why I ask. Some years ago I tried to make some simple low cost stunt trainers and I used the Russian style combat wing because it is indeed easy to make, and is quite tough as well. I made the first one for a .25 to .30 engine and it flew really well. I then made a bunch of .15 size versions and they too flew very well, so I tried a .40 size one. It never really performed well unless it flew really fast. It did serve to test a few engines and then my initial electric stuff was all tested on it as well. After a few mods and prangs it became tatty, so I decided to fix it up to make it look better. At the same time I thought that maybe it could use some more wing area, so I widened the tips to increase the wing area. Guess what?? It flew even worse, hence my question on the 50% wingtip thing. It would be very interesting if you could explain that a bit more please. Thanks.

Keith R

The 50% comes from an old NACA chart.  based on their measurements and calculations they showed that the induced drag of the wing was minimized when the tip was approximately 30% of the root.  Below that the drag went up quickly.  Longer than that the drag increased less quickly, so 50% seemed like a reasonable compromise- in terms of building and especially cutting foam wings.  We also can run into Reynolds number problems if tips are very narrow.
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Offline Keith Renecle

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Re: ice cream cone airfoils?
« Reply #64 on: March 14, 2015, 12:12:20 AM »
Thanks Phil, that is most interesting.

Keith R
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Offline John Sunderland

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Re: ice cream cone airfoils?
« Reply #65 on: March 14, 2015, 12:56:56 AM »
Speed makes them work well. We dont fly fast. Repeatable accuracy counts where we are concerned. We dont flick fast forward CG planes in stunt.....we fly through our corners. Blunt works for lift of heavy airplanes, better induced and parasitic drag in average conditions, and negates stall... but it accelerates even faster and tighter in real windy conditions. Rotation does not stop easily when the wind is up.

Online Igor Burger

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Re: ice cream cone airfoils?
« Reply #66 on: March 27, 2015, 07:16:38 AM »
I would say that those 50% of "optimal" tip chord comes from tapered planform with minimized induced drag. It should be closest to elliptical planform, however we know that the elliptical planform does not give us visible benefits, I would even say that it is sometimes suboptimal  because of tip stalls, so I would (and I also do) use longer tip chords then 50%. Even tip flap chord should be proportionally shorther to root ... in meaning tip flap chord : tip chord should be less then root flap chord : root wing chord because of the same reason. It will allow harder corners with less risk of unexpected roll caused by tip stall.   

Offline Tim Wescott

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Re: ice cream cone airfoils?
« Reply #67 on: March 27, 2015, 10:45:15 AM »
... however we know that the elliptical planform does not give us visible benefits ...

Oh, it gives visible benefits -- it looks better!  Just maybe not palpable benefits.

I have a book on designing full-scale aircraft.  It's written for pilots, so the math is very much dumbed-down, but it has a section on wing planform and where the stall will start.  It points out that the reason you see so many light aviation aircraft with no wing taper isn't just because the wing's easy to build -- it's also because such a wing will stall in the center first.

I've spent a little bit of time with full-scale aircraft, and something you often see on small and medium-sized general aviation planes with tapered wings is a section of angle-aluminum, six to twelve inches long, riveted onto the leading edge of the wing at the root.  That is there specifically to induce stall at the wing root before the tips stall.  A determined pilot can still stall a tip, but not before the airplane has stalled at the root and given him lots of warning about what's going on.

If the various experts, you and Howard included, are to be believed, then designing a stunt wing specifically to minimize induced drag (or overall drag, for that matter) means giving up on other facets of performance that may be more important.
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Offline Brett Buck

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Re: ice cream cone airfoils?
« Reply #68 on: March 27, 2015, 01:16:54 PM »

If the various experts, you and Howard included, are to be believed, then designing a stunt wing specifically to minimize induced drag (or overall drag, for that matter) means giving up on other facets of performance that may be more important.

   I don't think we are running anywhere close to stalling a reasonable conventional wing anyway, at least in competition. So I don't think I care about where it stills first.

    Brett

Online Howard Rush

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Re: ice cream cone airfoils?
« Reply #69 on: March 27, 2015, 05:03:21 PM »
   I don't think we are running anywhere close to stalling a reasonable conventional wing anyway, at least in competition.

Then you don't have enough paint.
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Offline John Sunderland

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Re: ice cream cone airfoils?
« Reply #70 on: March 28, 2015, 03:24:43 AM »
C'mon, Howie.  I've got small feet.  I had to use a scientific method at least 10% superior to even my Tux shoes. 

I used two different french curves, one curve eerily  identical to Bridgette Bardot's fanny and the other replicating a particularly appealing curve of her bosom.  The fanny one provided the curve aft of the 22% MAC high point of the airfoil back to the hinge line and the other the enchanting curve from the high point to the Leading Edge radius (which was  pretty much a boring arc whose dimension I don't recall but I would call moderately blunt).  The root was ~18.2% thick and the tip about 18.4 (probably because the pencil was sharper when I drew the root).  The only hard part about drawing the ribs along the french curves was that Bridgette would wiggle because it tickled her.  Other than the boring arc part, an airfoil doesn't get any sexier than that. 

My Imitation wing was cut by Bob Hunt who also made the templates from which he cut the cores.  I know he still had them a few years ago because I ordered a wing of slightly modified structure (and, perhaps, a slightly longer span although I can't recall exactly) which I wanted to use in a twin four stroke (just to hear the two engines running at the same time) for a fun beater.  Never have done anything with it and it's in a pile of stuff in the attic.

Maybe Bob can scan the template and post it.

Ted

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Offline phil c

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Re: ice cream cone airfoils?
« Reply #71 on: March 29, 2015, 07:49:04 PM »
I would say that those 50% of "optimal" tip chord comes from tapered planform with minimized induced drag. It should be closest to elliptical planform, however we know that the elliptical planform does not give us visible benefits, I would even say that it is sometimes suboptimal  because of tip stalls, so I would (and I also do) use longer tip chords then 50%. Even tip flap chord should be proportionally shorther to root ... in meaning tip flap chord : tip chord should be less then root flap chord : root wing chord because of the same reason. It will allow harder corners with less risk of unexpected roll caused by tip stall.   

Igor, none of the planes we fly ever come anywhere near stalling.  I have seen overweight stunters appear to stall, but I think that was more falling out of the sky due to overcontrol and the flaps stalling and slowing the plane way down.

The narrow tip chord does settle a plane down a lot in gusty weather.  The French champs plane and Brian Eather's Firecracker are good examples of this philosophy.  I was flying a quite light, quite large(740sq.in, 64in span) with no flaps, so I hoped reducing drag in turns would help.
phil Cartier

Online Igor Burger

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Re: ice cream cone airfoils?
« Reply #72 on: March 30, 2015, 02:05:40 AM »
none of the planes we fly ever come anywhere near stalling

Phil and Brett ... may be you can try harder corners :- ))))))))

... sorry kidding, but it is not completely so, yes I can agree in romal circumstances, but it can easily happen in thin air, I remember when Claus Maikis asked me what is that strange noise from my model in hard corners ... well it was from air separtion, the contest was during nice and sunny day (warm air) on field high in Alps and I simply flew the same corners as I do low on our airfiled. Our modern planes (including my Max which is designed to be so) with long and large tails are self controlling the way that wing stalls earlier and tail is large enough to ponit nose down (in direction of lift) and it simply opens the radius a prevents stall (I mean forced stall, nost classic stall when airplanes falls down from sky). However you can still exceed the elevator deflection to the extent when separation starts and that effect of stabilizing tail can start to do its task (it cannot if stall does not start).

But that what I wrote is not about that. The roll induced angle of attack of wing tip can easily exceed critical angle of attack in case that model is close to its maximal lift (but still not stalled) and model is disturbed the way that one of tips falls down, in that case tip needs some reserve between actual AoA and critical AoA to damp that movement (lift can still grow up during that movement) instead of magnify it (lift will fall down due to LE flow separation). And yes that French approach with flap only to 1/2 of span does exactly that - that model was able quicly turn on high AoA and it was still stable and controllable in mean that pitching rate was high, but radius was also large - it was visible on Keith R. analysis of one of such flight, most visible was triangle which looked sharp from outside, but CG movement was terribly round - means model was at very large AoA, certainly over its linear lift curve segment. 

Offline phil c

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Re: ice cream cone airfoils?
« Reply #73 on: March 30, 2015, 04:01:54 PM »
Well, if you ever do get an actual stall the plane will snap roll in or drop the outboard tip and slow down or simply fall out of the sky if it happens above 45 deg.  I suspect the noise you heard was flow separation over the flap hinge.  With an electric powered plane it's possible to hear that sort of thing, at least on some flights.

I looked at one of Remi Beringer's flights and agree, the "sharp" corners were extremely soft, compared to other planes the same year, and the WC flights last year.  Many of flights look pretty good in the reverse wingover, but none of them appear to keep that quick corner in the squares, triangles, square eights or hourglass.  It is hard to find a videographer who can get a good view of a PA flight and keeping the same distances and alignment for different flights is even harder  to find.
phil Cartier

Offline Keith Renecle

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Re: ice cream cone airfoils?
« Reply #74 on: April 03, 2015, 12:49:30 AM »
As Igor said, the Beringer Sportster must be flying the loops at a high AoA because when I traced the flight path it looked quite weird with the tail angled quite far out of the path of the actual loop. Something like a comet with it's tail pointing away from the sun! Serge Delabarde's model at the 2004 world champs in Muncie flew the same, as it was based on the Beringer designs. The models with these very good pilots, flew a neat pattern so that could be(?) why they scored so high, but the turn radius was HUGE. I would like to think that these days, the judging at world champs will not score these soft corners high.

Keith R
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Online Howard Rush

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Re: ice cream cone airfoils?
« Reply #75 on: April 03, 2015, 01:34:26 AM »
With an electric powered plane it's possible to hear that sort of thing, at least on some flights.

I can hear it on mine, especially the heavy one.  One can even hear it on combat planes over the sound of the unmuffled engine if the airfoil is bad enough. 
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