Sharp LE (is it a myth?)
 

Well done awards in trying a new thing. Applause. Being able to throw away over 1/4 of the wing weight is a good step in the right direction.

Now make an exact duplicate and keep the wing the same except for a fully filled in flat bottom and compare them to each other. I would be interested in the results.

I tend to cringe when I see one of your type of machines. Not from an aero standpoint (they are interesting) but from an equipment environment. Couldn't you wrap your receiver in a plastic baggy or something? I am from the old times when you had to clean the servo wipers every 10 flights, be extra special in servo mounting and had to suspend the receiver in the softest foam known to man.

Sharp LE (is it a myth?)
 

Actually, I don't have to do a comparison, because this airplane actually grew out of 5 years of just such experiments, and well over 300 wings, and until this airplane, using 4mm for a .25 sized airplane was too heavy. To close the wing would bump the weight up another 3-5 (or maybe even a little more in sandwiched ailerons and glue) ounces and destroy the airplanes wingloading...yes it would fly, because we've done it, but with nowhere near the performance.

I'll have to agree, on the equipment, and it's taken me years to get over the phobia...but let me put it into perspective...in the last 5 years I've built and flown over 300 airplanes, and currently own 20 flight packs. In the last 5 years, I've lost only ONE Rx and it was due to a mid-air, and have lost only two standard servos. In other words, the equipment has never failed because of it's envoronment, and believe me, I put it through hell. In comparison, years ago I had a Falcon 56...I was learning how to tear up the sky and flew it hard...and the spar broke. The lawn dart landed in the parking lot, and NOTHING inside the airplane survived...including the engine...all reduced to garbage. The ONLY thing left from that crash was an aileron servo with no lead. I guess it's all relative...because that one crash ruined more equipment...than the rest of my R/C carreer put together.:)

Sharp LE (is it a myth?)
 

The only part of this that makes me cringe is the addition of the phrase "strategically shishkabobed " being added to the science and lore of aerodynamics. It just lacks a certain.... uh,.... well.... I guess a bit of "je ne sais quoi"..... :D

Way to go with the new plane. This has been an interesting thread.

For the record I did a control line combat model many years ago that used a diamond airfoil with a leading edge radius much like the corroplast bend in size. The max thickness was at the usual 1/3 spot and had 1/2 inch wide flats. The rest of the shape was straight lines all around. It flew well but did have a bit of a stalling mushiness to it after two or three successive loops. But then most of the 15 size combats we flew did that.

Sharp LE (is it a myth?)
 

Tatoo, I have broken enough equipment to keep a small manufacturer in business:-) A friend at the local field landied a profile machine and as were were talking he turned it over. The exhaust was directly on the throttle servo, it was coated in oil and working fine. I am certianly impressed with modern equipment, I wish it had been so years ago. Sigh........

I trust your data point, you can't fly that much without having a great feel for your airplanes. Again I am impressed.

I am going to try the airfoil on a yard flier just for the heck of it. I make them out of 2mm white foam and can build one almost as fast as the plastic you use. I have used 2mm foam cambered and flat airfoils to date. I have 7 waiting to fly if it ever gets warm so might as well add to the fleet. A damaged heart has stopped flying in the winter. Thank goodness for Realflight to cut some of the edge off the "gotta fly" shakes.

Again, very good work on your project and excellent reporting, very enjoyable to read and look at. Have you posted it on the SPAD site.

Sharp LE (is it a myth?)
 

I forgot to mention, it is actually cute!

Sharp LE (is it a myth?)
 

Thanks for the compliments and encouragement!:):):D Everything I've ever touched since I can remember has turned into an airplane. It's always been build it, fly it...if it doesn't work trash it, if it works tweek it. I usually don't measure stuff or anylize why something works until someone asks:)...

Hopefully Mr. Clean will get the plane posted on the Spad site sometime this week!

Looking forward to a report on this airfoil on the yard flyers...there are a growing number of Spadders getting into electrics and 1/2A stuff, and this might be a great direction for them to go in!

Sharp LE (is it a myth?)
 

Tatoo,

Just found this thread. Most inserting discussions on airfoils, stab placement etc. Many thanks for this, learned a lot.

I'd bet that if you built a true, flat bottom wing with detachable leading edges and experimented, you'd find that sharp leading edges work best within a narrow speed range and angle of attack. You see a lot of them on free flights. Contrast this with some of the full size, extreme aerobatic, planes. They take the blunt leading edge concept to the extreme and it works well, for the pupose intended.

The airfoil on the Big Ugly, apparently contains an element not present on other airfoils that compensates for the well established notion that sharp leading edges are, generally, detrimental. That difference is the long, thin, trailing edge downward reflex. A negative angle of attack, renders this portion of the wing ineffective. At positive angles of attack, this reflex "grabs" a lot of air and compensates for any excess up-pitch. It's like having automatic down elevator every time the wing pitches up due to the sharp leading edge. It's this downwash part of the wing that prevents the oscillations around neutral.

Kudos on the innovative hollow airfoil. That it works well is most intriguing. How about anyone with access to a wind tunnel doing some tests and getting back to us?

Sharp LE (is it a myth?)
 

1705493,

I think it's simpler than that. My bet is that sharp leading edges simply don't have a strong tendency toward pitch instability, so there isn't anything for a reflexed trailing edge to compensate for. A sharp leading edge probably causes stall to occur at a lower angle of attack than a blunt leading edge, and could well cause a separation bubble near the leading edge at fairly low angles of attack. I don't think either of these things usually causes significant pitch instability. I think that concerns about some evil sharp leading edge voodoo are generally without basis.

banktoturn

Sharp LE (is it a myth?)
 

Thanks!

In the last couple days, several other guys have built and flown this latest design, and the reports are coming in...the overwhelming observation is stability. The plane won't stall or fall off at all. When it reaches nose high stall speed, all it does is begin a slow harrier decent. One guy even said it was stable enough to use as a trainer, and on slow flight, had self righting charicteristics of a dihedral wing. There may be more going on with this airfoil than I understand. I've also been told that although respectable, the ailerons are not as fast as one would think on a wing span of this size. Is it possible that some kind of stabilizing airflow is being generated under or at the tips of this wing giving it the stability and resisting roll input? In my experience, a wing this size would normally roll 5 or 6 time a second with a normal airfoil...this design with the same aileron travel gives me about 2 rolls a second.

Sharp LE (is it a myth?)
 

I just had to come back here and thank you guys for inspiring a design that has turned into the most fun I've had in R/C in a long long time! The simple airframe is inspiring all kinds of directions, and I wouldn't even be able to guess how many are flying now!

http://members.cox.net/spad/pics/pdqhor2.jpg
http://members.cox.net/spad/pics/pdqhor1.jpg
http://members.cox.net/spad/pics/geebeespad.jpg

Sharp LE (is it a myth?)
 

There appears to be commercial potential there....
.
Actually your airfoil resembles a mating between a Klein-Fogelman, and an undercambered shape.
.
All that chord is typical of a plane that can loop til the cows come home.
.
Way back when Riley Wooten had a diamond-airfoiled combat plane along the lines of his Voodoo in Flying Models or MAN.. NACA had just released the use of diamond shapes on full-scales about that time, so the more adventurous model designers tried it.
I believe that's the one Ben mentions. Mine flew well, but not remarkably.

Sharp LE (is it a myth?)
 

After examining my BUHOR wing while it sits on the dining room table, drinking lots of coffee and playing/ bending things, I think that what happens to this wing shape at high angles of attack is that the ailerons "washout" at the tips somewhat. They are stiffest near the root of the wing, and are actually quite flimsy near the tip. At high angles of attack, then ends of the ailerons would flex to align themselves more to the direction of the airflow at the tips of the wings than at the root. Am I just blowing smoke here? Am I wrong?

Sharp LE (is it a myth?)
 

The washout probably happens as you desribe. The surface will seek a position where it sees no load, and will twist towards that position.

Sharp LE (is it a myth?)
 

I also think this is what happens to the QHOR, except that the entire trailing edge tips of the "wing" flex upward considerably when the nose is pulled up sharply. I can SEE the tips flexing up quite a bit. This would have the tendency to stabilize the manuver, as the only part of the wing that would stall would be the center.

Sharp LE (is it a myth?)
 

Thought you'all might be interested in some videos of the aircraft that have been inspired by and created because of this thread.

http://www.hsrcm.com/awe-hor_movies.htm

http://www.riversedgerc.com/communit...p=getit&lid=37

http://rcfunflyers.com/DANNY%20SPAD%20QHOR.WMV

Sharp LE (is it a myth?)
 

Looked at your movies, I must say it does fly well. What happened though - the ones you showed us in this forum look nice but the ones in the first site I looked at looked positively homely.

Sharp LE (is it a myth?)
 

It's all about cheap fun, not necessarily asthetics. These planes cost less than $10 to build, and usually less than 2 hours to do it. Amazing when you consider they outfly airplanes many many times their cost. BTW, the videos are not my planes, they were found in various topics here on RCU...the designs and ideas are really getting popular.

Sharp LE (is it a myth?)
 

Just thought I'd revisit the thread that inspired the most fun plane I've ever flown. It's still evolving. The latest has an almost flat wing with a much rounder leading edge (Imagine that Cajun!:)) and the flight charicteristics keep getting better! Like I've mentioned previously, I know little about aerodynamics...I just build em and try em. This airfoil would be an interesting one to anylize. High alpha crawls, hover, and inverted pitch response in incredable, the wing refuses to stall, and yet full throttle stability is solid as a rock. Flat spins, especially inverted beat anything I've ever flown, and if done just right, can actually gain altitude in the spin.

One page plans
http://members.cox.net/spad/pics/spa3d02.jpg

Building instructions (Text)
http://members.cox.net/spad/pics/spa...tructions.html

Reference Photos
http://members.cox.net/spad/pics/spa3d01.jpg
http://members.cox.net/spad/pics/spa3d03.jpg
http://members.cox.net/spad/pics/spa3d04.jpg
http://members.cox.net/spad/pics/spa3d05.jpg
http://members.cox.net/spad/pics/spa3d06.jpg
http://members.cox.net/spad/pics/spa3d07.jpg


http://members.cox.net/spad/pics/pqhor40.jpg

http://members.cox.net/spad/pics/spa3dharrier.JPG

Sharp LE (is it a myth?)
 

I'm one of those guys who love the smell of balsa on a warm afternoon. This Spad stuff, though, has me intrigued. One question. I see a lot of servos zip strapped to the airframe. Vibration not a problem? Or, do you just use cheap servos and toss them from time to time?

Sharp LE (is it a myth?)
 

Stuffing the servo in the rail with no "insulation" hasn't been an issue. The throttle servo is mounted right next to the engine, and I've got servos that have been in 50+ SPAD's over the last five years - and I have yet to lose one to vibration.

BTW - I use run-of-the-mil Hitec HS-81MG's, HS-300's and HS-422's for all my planes.

Sharp LE (is it a myth?)
 

Thanks Kraut,

That's encouraging. Will give this thing a try. :D

Sharp LE (is it a myth?)
 

Had a look at some of the videos. Thanks Tattoo. thanks also for the plans. OK. What's the best engine/fuel/prop combo for to maximize this thing?

It appears that excellent throttling is a large factor.

Sharp LE (is it a myth?)
 

Good strong .46 or .47, 10 ounce tank, built to Spa3d plans, 12 x 4

Here's a pic of Kraut's in flight

Sharp LE (is it a myth?)
 

Define "good strong .46 or .47" Also, what brand of prop? Wood or plastic? What fuel? Want to get it right the first time.

Sharp LE (is it a myth?)
 

GMS .47's are strong, some prefer the TT Engines.