What are the ranges of what you would call a thin airfoil?  A thick airfoil?  What kind of LE?  High point location?  Are you going to consider flap in chord width to do your comparisons?  In short, what is your real question?  And I am not trying to be trite.

And this should be in the design section.

  I am in quest of your observations & findings as the title subject goes. I seem to always have so much line tension & feel the need to reduce it.  Also the need of more power to pull a thicker airfoil ,Is there truely a down side of a thinner airfoil? Also what are some of the thinner airfoils?  Dave Fitzgerald's plane ? Phil Granderson's? Junar? I'd like to hear something on the subject.
  John

It's not a trivial issue, and you'll get a lot of misinformation in a place like this.  You can get Profili or Javafoil free or cheap and get a clue.  Also, Igor wrote an article for Stunt News that has some interesting information.  Alas, the NACA (as far as I know) didn't do tests on airfoils with flaps like we use.  I can't see how airfoil thickness can affect line tension except for wing weight or some perverse aeroelastic effect from a flexible structure.  Here are some points:

You can have an airfoil of any thickness that sucks (both figuratively and literally).

The thinner the airfoil, the heavier the structure it will take to keep it from blowing off.

Drag (or power required) is not proportional to thickness.  It's not even necessarily bad.  Read what Igor has posted in Stunth Anger or Google "drag bucket".

You can get Profili or Javafoil free or cheap and get a clue.

Do you really feel that the airfoil simulation tools are really up to snuff as far as telling it like it is?  Or did you mean get just a clue, and then still have to build some planes to try out?

Do you really feel that the airfoil simulation tools are really up to snuff as far as telling it like it is?  Or did you mean get just a clue, and then still have to build some planes to try out?

  You have to build some airplanes to find out. One thing you will find out is that airfoil polars, while interesting and educational, will not tell you much of what you need to know about it from a practical standpoint.  I do know one thing - that you can't figure it out independent of the engine/propulsion characteristics.

    Brett

John,
In regards to your question regarding those programs, the answer is yes and no. Meaning, for some aspects of model aviation yes. For our needs definitely not. Specifically, those programs were designed for, and will do an okay job on simple freeflights and RC glider planes. They were never designed, and in no way, are they capable of handling the maneuver aerodynamics we do.

While I can tell you what would be required, that would be beyond the scope of this discussion.

Go for it.

Howard Rush,Serge Krauss etc. would enjoy it. But, the poor cat who started this thread, with his simple question, would wonder what the hell is up with us.  

It is analogous to a guy who asks what glow plug to use, and next thing you know, we are knee deep into blow down, by pass ports, BHP, etc.

Howard Rush,Serge Krauss etc. would enjoy it. But, the poor cat who started this thread, with his simple question, would wonder what the hell is up with us. 

It is analogous to a guy who asks what glow plug to use, and next thing you know, we are knee deep into blow down, by pass ports, BHP, etc.

So start a new thread.  You'll get plenty of attention.  I know there's unsteady aerodynamics and stuff in a stunt corner, but I can't figure out what's going on.

I think Phil Granderson has.  He's built Divas with different thickness wings.  Rich Walbridge built one, too.  The thin one is called the Skinny Diva.  I was going to build one with an extra-thick wing and call it Big Leg Diva, but that's a lot of work for a joke. 

.....  I can't see how airfoil thickness can affect line tension except for wing weight or some perverse aeroelastic effect from a flexible structure. 

....... Drag (or power required) is not proportional to thickness. 

But its logical to assume that drag (or power required) is 'related' to thickness and the greater frontal area of a 'thick' section will effect wind penetration and therefore speed, and therefore line tension.

I know that 'flat plate' types of sections penetrate windy conditions better on combat wings than a properly shaped airfoil.

I flew very thick blunt airfoils and found that they worked well for the power plant I originally built it around, but I didnt like how it performed with some real ponies under the hood when I went to the pipe. My airfoil created to much lift for the new ponies IMO. It was easy to over control. What I found was, the more usable controlled power you have, the less airplane weight is a factor and the new found power renders the once necessary fat airfoil obsolete unless you get into extremes of gross over building and paint. The static thrust you feel on high RPM low pitch set-ups or in a nut shell "modern power plants" makes a helluva difference! As does all the nice control systems we enjoy and construction techniques that equate to stiffer flying surfaces and so on.

IMHO, After test flying two of PTG's masterpeices, and buiding a Diva of my own, I have to say from just raw, gut feeling, I feel that the performance package (engine, pipe, surface areas, airfoil, and moments) have really opened my eyes! I don't think I'll ever build a thick airfoiled plane again.

    This is where the engine setup makes such a big difference. It's been clear for a couple of decades that with unlimited power on tap and low-pitch props, a plane of any reasonable weight and a sufficiently blunt LE (to minimize separation at the LE) could generate sufficient lift almost regardless of the thickness. Once you get past that, it's a matter of how you run the engine and how much speed stability you need. Thicker = more speed stability, thinner = less speed stability.

    Note that perfect speed stability is not necessarily what you want. It's swell if it's nice conditions, in heavy conditions I would rather have a little less than perfect to ensure that the groundspeed/line tension doesn't vary so much.

    With a very soft-running engine (like we have been striving for for many years) it's easy to get too much speed stability. The Trivial Pursuit and Infinity were designed before we fully grasped the implications of piped engine performance. While they have an enviable record, with the relative flat-running engine setups the wing thickness was probably overdone. First time I flew David's first Thunder Gazer, in a pretty decent wind, I was astonished that when I turned back in to the wind on the overhead, it didn't float, it just went through. This despite the PA75 being set up to run very softly like a RO-Jett. The same engine in a Trivial Pursuit got a little floaty in the same spot. Part of the difference was the higher wing loading, and part of it was the airfoil thickness - the wing is very close in all relevant dimensions to the Imitation, an ST46 airplane from 78, which was on the thick side at the time for the available power but is nothing compared to a TP or Infinity-type airfoil.

     Note also Howard's comments that the drag and the lift aren't remotely proportional to the thickness, in fact it's a pretty weak function of thickness - twice as thick doesn't mean twice the lift in any thickness we could actually use.

    Brett

If you examine video of the Stargazer, and the Thundergazer, the Stargazer seems to have more of a cracking corner, and the Thundergazer seems to have significantly better penetration. No doubt, the very different wing sections are at play hear. Suffice to say, the only person that can substantiate this is Mr. Fitzgerald.

  I *have* flown both airplanes and do have some idea the thinking that went into them, particularly the TP/Star Gazer since that and the Infinity were designed at essentially the same time and the same underlying ideas, based on a lengthy conversation between Ted, Keith and I in around 1990.

      One thing is certain and that is that neither of them is running out of lift anywhere at any competitive corner radius. The Thundergazer wing is hardly any different from the airplane I flew successfully in 1987 with an ST46 and a lowly *35FP*. The difference is that with the tremendously improved ability to keep the speed up in the corners, his corners better at 15 oz/sq ft than mine did at 11.2!

    This is not 1985 any more and we aren't using ST46/60 any more. You don't have to design the airplane exactly the right size and with exactly the airfoil thickness to get good performance. Unless you completely screw up (like the ARF Strega where they don't bother to shape the LE correctly), they all turn more tightly than you need them to.

   If you do want to use 4-2 break motors, then, maybe you need to follow the same design concepts we used to. People had fiddled with that for 40 years, they had found the right answer for that particular problem - just build a Temptation with an ST46, it's not going get a lot better than that.

    Otherwise, there's a huge range of combinations that will work, and within that range, you can design to get the types of speed characteristics  and feel you want and around the type of engine run you want to use.

   Brett

This issue of pumping 60 class power into 46 size goes back aways. Jimmy Casales argued vehemently for this. He went on to back it up with 4 Nats wins. All with 60 muscle in 46 size ships. 4 Nats wins is good.

  When that was the only option, yes. The 4 viable options we have now - Retro 60 or similar, piped whatever, 4-stroke, or electric - all provide more performance without the problems you get when you put an  ST60 in an ST46 airplane.

   
   Brett

(Clip)

By the way, Gene flew the most consistently correct shapes to maneuvers of anybody I've watched over the years, and when coupled with his oft acclaimed tight corners it was a deadly combination.  That he didn't win the big ones consistently was a head scratcher.

Ted

At least one year, Gene was high point at the Team Trials, I think it was in Dayton.

Keith

I should add something from the other side of the pond too. Russian designs have pretty much settled on 18% airfoils several decades ago and their airplanes are pretty competitive too.   

Igor Patchenko flies one of those ships in Classic.

At least one year, Gene was high point at the Team Trials, I think it was in Dayton.

Keith

You're right, Keith.  I probably should have said "more" consistently. 

Although I may have been more easily impressed in those days, what I recall was a very rule book sized pattern with consistently excellent shapes and  great corners all performed apparently effortlessly.  A similar effort I found particularly impressive (that belied the "then and now" preference for bigger, muscled up powerwise ships), was Billy's Perroquet (sp?) which was  Ares sized with something like an HP 40 running in much the same manner as Gene's ST powered ship.  Seems like he flew that ship for a couple of years at the same time Gene was flying the same approach.  They both flew with sewing machine precision with no "bellowing" in the nose.  Great stuff.

Ted

  Hey Rich,
  Glad to hear from you. I saw your plane but didnt watch very many flights last May . I talked to Phil & the Zelot is my next plane nothing else seems close .OPS .40 for power, I'm  really anxious.
  John

A thicker wing also allows better structure and stiffness, and stiffness is actually pretty critical on how an aircraft responds.

Amen

What is often missed in CLPA aerodynamics is apparent mass effects.

Amen again.  Heck, all of dynamics is often missed.  I would like to include apparent mass in my ciphering, but I don't know how.  Can you point me to a source?

I actually have Bode plots of the Wright Flyer if anyone else is that deep into the nerd forest and would like to see them.)

You betcha.

Back to "thick and thin".  I've tried all sorts of stunt airfoils.  Still the best seems to be the lowly NACA 0018.  With or without flaps, it gives the best all around good results.

Floyd