News:




  • August 19, 2018, 01:30:42 AM

Login with username, password and session length

Author Topic: The best stunt airfoil  (Read 7583 times)

Offline Vitalis Pilkionis

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 73
Re: The best stunt airfoil
« Reply #50 on: February 11, 2018, 10:30:09 AM »
22 is too little deflection for corners, go over, to 30 or so and you will see forming those bumps on lift curve and abrupt changes of momoment.

Dear Igor, of course your airfoil is perfect in terms it doesn't have any bumps on ascending part of Cl curve, even with flap at 55 degrees (and I'm not kidding here). And Cl with flaps at 30 is phenomenal.
But hey, all those numbers are just numbers, although you really made me doubt  ~^
As we all know even on your own model flaps are restricted to 27 degrees. At this setup Cl of your airfoil can theoretically reach almost 2.35 at 8 degrees of AoA.
Now.. if another (clearly not so noble) airfoil can smoothly reach Cl=2.1 at the same 8 degrees AoA and stay there up until 20, does that really matters to what angle flaps are deflected 27 or 22 ???
Yes it starts to form a bump with flaps deflected over 22 degrees and probably a model with this airfoil will not be able to perform extremely sharp corners, but I believe it's going to be at least a competitive one.


Online Igor Burger

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1934
Re: The best stunt airfoil
« Reply #51 on: February 11, 2018, 11:20:45 AM »

Now.. if another (clearly not so noble) airfoil can smoothly reach Cl=2.1 at the same 8 degrees AoA and stay there up until 20, does that really matters to what angle flaps are deflected 27 or 22 ???

Yes, it is mechanically limited, but I explained in my article the air flow hits the wing so, that the real deflection is higher, it can be 30 degrees.

And yes, you can make it travel less and ger lift say 10% less, it will need wing those 10% larger. ... plus you must tune flap to elevator ratio.

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #52 on: February 11, 2018, 01:10:52 PM »
Does anybody know why Brett is so sensitive about Strega, Patternmaster and all the derivatives of Big Jim's legacy? Cmon, Brett, lay down your pain finally   b1

   The most important observation is above - at least the ARF Strega version has a pretty serious defect. It is NOT a "patternmaster" and the differences are significant and make a huge difference. Just looking at the results, I would suggest Phil Granderson knows a lot more about stunt airfoils than whoever drew the ARF Strega plans (which is not that surprising, frankly). In fact, the Brodak website contains this gem:

http://www.brodak.com/files/file/Strega_Building_Wing_Instructions.pdf

   telling you to round of the LE, which probably originated from an SSW post by Gerry Arana from a conversation with Ted and I in 2007.

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=280959&mesg_id=280959&listing_type=search

     This fixes it, good on everyone involved, there was an issue, and it was addressed.

   But once you realize that the LE is the problem, you can see how they came up with the other "features" - gigantically thick section and gigantic flaps. The Strega is far from the worst case, the MIG and others from the era had 40% flaps (which is derived from Abbott and von Denhoff, Figure 115). This in attempt to "get more lift" since it didn't work otherwise.

    Of course, fix the LE, and you can run much smaller flaps and a much thinner airfoil, which then permits you to trim the airplane conventionally, instead of trying to manufacture tremendous amounts of line tension and run the CG forward to "get more flap deflection". That was the fatal flaw with Windy's system, and NO ONE competitive ever watched one of those airplanes fly, and then ran off saying "boy I better get the plans for that because I am going to lose otherwise".

    People tell me the Strega plans actually show the LE shaped the same way, which I cannot confirm, since I have never seen the Strega plans. I do know that the Red/Silver Strega that Kent Tysor was flying didn't have that shape to it, and in fact, could not be achieved using the construction of the ARF. It seems to fly just fine and has none of these problems.  I don't know about the original Patternmaster or BJ plans from Big Jim, himself, because I never did more than glance at them over someone else's shoulder one time.

The annoying part is that it has been repeatedly claimed that my buddies copied it or our airplanes are "based on it",  in particular, that the Infinity, Trivial Pursuit, and even the Impact were "patternmaster derivatives". This is absurd from any perspective, but the most annoying is that it seems like we would *bother* copying something that already wasn't competitive. Why rip off Windy when I can rip off Paul/Ted/Billy (whose designs are astronomically more successful)? And in any case, I make absolutely no claims otherwise, freely admitting where I ripped off things and from whom, and where I came up with it myself.  I did rip off Big Jim when it came to solid fuselage construction, which I also freely admit. I probably stole more stuff from Paul than anyone, and anything I might have gotten from Ted and David is kind of hard to pin down, since it was a free collaboration. I would never admit I stole anything from David, just on principle, of course.

     But I also get all sorts of ideas and useful information from these threads, even the ones from beginners and neophytes.

   For a long time, perhaps still, Windy was claiming that the Vector 40 was "based on the proven Profile Cardinal aerodynamics", which I am sure Randy greatly appreciated and is one of the most absurdly and demonstrably false bits of ad copy I have seen in this business.

   It's that kind of stuff that drove everybody crazy about Windy. It was insulting and false, and served to take credit for other people's success. No one gave a flying tinker's damn about what he did on the field and I never had any issue with what he did as a competitor  (although he was a fascinating case study).  He was/probably still is an exceptional stunt competitor, with a record beyond 99.999% of everyone who has ever flown this event. Most people would be absolutely thrilled to be in even *one* Top 5 flyoff, much less dozens.

    The off-field stuff, we "resolved" in private and we each know where each other stands.

     Big Jim, I talked to him for a few minutes one time 34 years ago, seemed like a good guy, and he had some very good observations that advanced the state of the art, in engine operation at least. His design experiments were moderately successful, maybe it didn't lead too far -  but no one knew that when they started and ultimately there's only one way to find out for sure.  I have seen several pretty good-flying Patternmasters - but an ARF Strega is not a Patternmaster and only vaguely related, as far as I can tell.

  I have said the same thing to people in public and private for years. Guys like you come around trying to spin up a controversy every so often, I don't know what you get out of it, but it is something I have come to expect. And besides, I am not the one trying to build a stunt wing with a conformally-mapped Ringmaster airfoil.  We could all be wrong about that, too - but I doubt it.

     Brett

Offline Matt Spencer

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3045
Re: The best stunt airfoil
« Reply #53 on: February 11, 2018, 04:18:55 PM »
Gosh .

Fair Enough Too .

This thing is Prety Much the P M 60 ,





As you can see , it cant be totally hopeless .
' The Story ' is its supposed to voek in da vind , But WHAT KIND of WIND . The Blowy Bumpy rough stuff , We Presume . As In it Dosnt get Blown into the Ground .

But Did That CHIPMUNK with the Thick wing Predeceed it ? . ( Yes ! ) Wot appens if you blow up the Chipmunk rib to the 9 & 11 in Chord ? How Thick . ?

This is the SIG Super Chipmonk that Rib Sets were availiable For , more than one plan in F M useing that rib set . RIGHT .
Sarpoulous , Sheeks , . . . .



Effective Incidance ,
------------------------
If we allow theres a ' seperation point ' at the L. E. , and the Departure is at the Aft Flap Edge , wot we have as a Line Through . Effective Incidance . ( Flap Deflected ) .
plus allowing for the tangental radius bit , as per Igor .

SO . . . . . . . . . . . . IF the FLAP is TWICE the Chord , Half the Deflection gets the Same Effective Incidance ( Thereabouts - leaving out a bit of algebra etc )

or a extreme example would be , Flap 3/4 of Total Chord . . . almost a variable incidace Wing ! .
if we put the wing at 5 or 10 5 O. A. Chord and the FLAP at 95 or 90 % , you can see where we're getting .

Less Extreme but no less , the Wide Chord L J Flap - Assume Rear Edge Deflection - Comparable to Std. deflection of common narrow chord flap -
and you start to see the picture .
But IS the moment / force AGAINST the Turn Comparable ??

Presumably with the flap deflected the C/L moves aft , approx % of O A Chord - as % of Wing Only Chord , Non Integral airfoil ( FLAT ) Flap . :-\ Thereabouts .

Thus The Dungers Shown below , Dont Approach the 1:1 Flap / elevator deflection ratio .



( Just Laminated Doublers for a Std ish Narrow Flap Blunt LE thing , simultaeneously ready to go on a wide flap sharp clean airfoiled ' wind ship ' ,
Both Fly Completely Differantly - but horses for courses . First bucks & Buffets in wind but good in calm  , second WORKS Well with air moving, dull in calm air .)
( But do I build the BIG layout of the wind ship with ST 76 , or the STD one with the HP 40 , found Id done the mid sized trundler  when I checked .  :P Just as Well )

« Last Edit: February 11, 2018, 05:30:39 PM by Matt Spencer »

Offline Vitalis Pilkionis

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 73
Re: The best stunt airfoil
« Reply #54 on: February 11, 2018, 05:29:34 PM »
   ...and in fact, could not be achieved using the construction of the ARF.

Thank you for your honesty, Brett - it's a very interesting story.

But actually it's not so difficult to modify a wing of the ARF, one just needs a long metal ruler and a sharp snap-off blade.

Offline Frank Wadle

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 55
Re: The best stunt airfoil
« Reply #55 on: February 14, 2018, 04:25:06 AM »
Igor,
I understand your explanations, your formulas and thoughts. It all makes sense to me and I agree with most if not all of it.

What I don’t understand is how a Yatsenko airfoil ties in with this.
-   They have a blunt leading edge but with a slight sharp edge. Almost like the STREGA ARF but not as extreme.
-   They have almost no curvature behind the thickest point.
-   They have an almost fully integrated flap, so at around 5° Flap deflection the “hingeline-kink” occurs that seems to be so fatal.

It seems they did everything wrong. Yet these airplanes fly very well, very predictable, very maneuverable, and very stable. Overall they are a very good package both with IC and electric powerplant.
Can you explain why?
Could it be that they make use of the “saw tooth” in the Cl diagram? Assuming that there is one at Flap deflections higher than 5°.
Could it be that this saw tooth comes so early that the entire pattern happens beyond that point?

I have not seen an airfoil diagram of a Yatsenko airfoil so I’m just guessing here.


Offline Istvan Travnik

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 79
Re: The best stunt airfoil
« Reply #56 on: February 14, 2018, 06:31:48 AM »
Dear friends, dear colleagues,
I would like to have a little request of you, as follows:
I would like to make some statistics of experiments. Please, fly one half inside loop, as tight as you can, and a half outside loop, similarly.
Please, write me/us the achieved minimal heights. It can be estimated very precisely,  and shows far more than analyzing any videos on square /triangle loops' corners' radii.
Will you help me? (and all of us...)
Thanks: Istvan

PS: explanations of the reason later...
« Last Edit: February 14, 2018, 01:16:07 PM by Istvan Travnik »

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #57 on: February 14, 2018, 11:25:24 AM »
Igor,
I understand your explanations, your formulas and thoughts. It all makes sense to me and I agree with most if not all of it.

What I don’t understand is how a Yatsenko airfoil ties in with this.
-   They have a blunt leading edge but with a slight sharp edge. Almost like the STREGA ARF but not as extreme.
-   They have almost no curvature behind the thickest point.
   
   ??? The few Yatsenko planes I have looked at closely have nearly a perfect ellipse as the LE shape, with even more curvature than the Infinity in the area about 1/2" behind the LE. There was nothing like the 45 degree pointy wedge.  Take a try-square and put it on the LE of the ARF Strega, it fits perfectly and from the LE to about 1" along the surface, it's a DEAD STRAIGHT LINE at 45 degrees to the chord line.

    Again, I would note that this IS NOT the same as the Patternmasters or the (not-ARF) Strega like Kent Tysors, at least those I have seen.   You cannot make the ARF LE look like Kent's airplane with a wood rasp, if you tried you would wind up with 3/4" less chord and no structure to speak of. You would have to completely remove the ARF LE wood and make a new LE "plate". But you don't need to, the modification shown on the Brodak website seems to be sufficient, at least to resolve the worst of the problems.

      Similarly, the Yatsenko airfoils I have seen are nearly flat around the high point, and have decent curvature which is required to make it down to the hinge line. The first 2.5-3" from the high point have a noticable hump. It's not like Igor's or Al Rabe's, with a lot of curve towards the TE, but it's certainly not like the Frankenstunt or other examples I have seen that are drawn with a ruler from right behind the high point to the TE. There's no problem with the ARF Strega or Patternmaster, or any other common airfoil, in this regard. That's why you can fix the ARF by rounding off the LE, even with the skinny 1/4" LE wood.

    Note that the flat aft section TE is intentional, it's made that way so you can build the wing with the TE on the building board and lay the straight aft section flat on the building board.  But every airplane I have flown with that airfoil has had ASTRONOMICAL control loading, almost no matter what you did with the rest of the airplane.

       So, I don't see what you are getting at all, the Yatsenko Shark airfoils (and other similar Iron Curtain airplanes from others) I have see seem perfectly fine to me and I actually like the LE shape, it's very similar to the examples I came up with by plotting ellipses and then tacking a reasonable-looking aft section (using my shoe or any available curved smooth edge). Say what you want about the Yatsenko planes ruining stunt, but they *do* fly pretty well even by current standards, and at least the wing seems fine to me.

     Brett

Offline Vitalis Pilkionis

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 73
Re: The best stunt airfoil
« Reply #58 on: February 14, 2018, 03:53:19 PM »
What I don’t understand is how a Yatsenko airfoil ties in with this.

Here is a quick analysis of Yatsenko Shark Ellipse airfoil with flaps at 30 degrees. The airfoil can be found in drawings here:
http://discovery-aeromodels.com/en/andrey-yatsenko-shark-ellipse-2-control-line-f2b-model.html

Note: this is NOT an official analysis and I have not been provided with airfoil data from the manufacturer. It is very sketchy, as it is based on a low resolution drawings. You should not make any evaluation or conclusion from these images about true performance of real Yatsenko Shark stunt models.

« Last Edit: February 14, 2018, 04:35:58 PM by Vitalis Pilkionis »

Offline Brent Williams

  • 2018 Supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 596
  • Making America Fly Stunt Again!
    • Fancher Handles - Presented by Brent Williams
Re: The best stunt airfoil
« Reply #59 on: February 14, 2018, 05:13:26 PM »
Here are some drawings and pictures of the Yatsenko Shark airfoil for study.
The drawing was supplied directly by Yatsenko, according to PipeMakerMike.  PDF and JPG are attached.
http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=311411&mesg_id=311411&page=9&topic_page=2



Laser-cut, "Ted Fancher Precision-Pro" Hard Point Handle Kits are available again.  PM for info.
https://stunthanger.com/smf/brent-williams'-fancher-handles-and-cl-parts/ted-fancher's-precision-pro-handle-kit-by-brent-williams-information/

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #60 on: February 14, 2018, 05:17:46 PM »
Here are some drawings and pictures of the Yatsenko Shark airfoil for study.
The drawing was supplied directly by Yatsenko, according to PipeMakerMike.  PDF and JPG are attached.
http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=311411&mesg_id=311411&page=9&topic_page=2

   Right, there's nothing like a point on that, and the aft section has a good curve to it. And it's negligibly different from a NACA 0020. The small differences shown here make NO difference in the results.

     Brett

Online Lauri Malila

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1100
Re: The best stunt airfoil
« Reply #61 on: February 14, 2018, 06:51:31 PM »
Andrey’s airfoil (Shark) has the rear surface more flat than Yuriy’s. Andrey told that he took the airfoil from some real aerobatic plane, I forgot which one, propably Sukhoi.
I know this because we had some issues with Shark wing skin resonating and breaking the wing ribs, a non-existent problem in Yuriy’s designs.
Also, Yuriy went back to a little sharper l.e. because some issues in landing glide (FAI 1 lap from 1,5m altitude), a blunter foil did not penetrate well enough. L

Offline Matt Spencer

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3045
Re: The best stunt airfoil
« Reply #62 on: February 14, 2018, 09:12:27 PM »
Quote
Andrey told that he took the airfoil from some real aerobatic plane, I forgot which one, propably Sukhoi.

Im not sure that a good rate of roll is neccesary for F2B Ship . Hence a less blunt Airfoil may be a better proposition .

Offline Matt Spencer

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3045
Re: The best stunt airfoil
« Reply #63 on: February 14, 2018, 09:30:32 PM »
not a clear one of Berringer Airfoil . ( used a Sharper Derivative on My Yak 1 / 11 , light , lively, responsive , bigger ( 200% ) Flaps . Light W/L ) .





The Flat Flank Airfoils ( Flaps inboard 50% Span only, seem to ' air brake ', 'G' Wise - and hold in turn , under pressure / variable winds )

Igors Airfoil seems Very Similar to me to Al Rabes , ( 3rd & 5th down .)



Id used his Mustang 5 Airfoil on a 17.5 / Sq Ft. Martin Baker MB3 . The Clean Corner - no bobble - apparently the no L?D Bump curve .
Good Penetration ( at that weight  VD~ with G 51 Going Hard. In V Wind & V Rough Air , latter was going to down pitch to 4 in ,
which helped smooth the bumps- Torpedo 40 8011 with perry pump - still got the on/off 2-4 bit , but the fuel kept up , not ' out 'G'd .

Was a hair stand on end , razors edge job at that loading - but accurate & almost flew itself exact . Pilot just hung on and hit the handle
at the appropriate moments .  ;D LL~

Not Exactly Relaxing - equivilant of Dodge 440 precision driving test on wet skidpan with the throttle stuck . But very Rewarding .

The Windships underway , with the bearers & doublers in . Laminate up a good spar worthy of a Windjammer round the Horn , Next .

 S?P S?P H^^

P.S. ,

The ' BUMP ' in the Lift Drag Curve , would be what gave the olde ' Nailed & Turned ' Squares , aka Hunt etc , with the 4-2 run .
In FACT I BELIEVE THAT WAS WHY THE 4-2 was so popular - overcome the sudden increse in drag , IN the TIGHt Corners .  :-X

Do the Hunt / Werwage Airfoils have the sudden bump in the L/D curve ?? H^^

*
Al's 25/22 AIRFOIL IS AT THE root only , Progresses to 22/22 at the deheadral break/ gear leg position , with simetrical out from there .

« Last Edit: February 14, 2018, 09:50:55 PM by Matt Spencer »

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #64 on: February 14, 2018, 09:32:47 PM »
Andrey’s airfoil (Shark) has the rear surface more flat than Yuriy’s. Andrey told that he took the airfoil from some real aerobatic plane, I forgot which one, propably Sukhoi.

    That is a common thing on full-scale aerobatic airplanes, but it seem to cause extreme control pressure on CL planes - probably for the same reason it improves the aileron effectiveness. Note that the full-scale airplanes also usually have spades or other control-pressure-reducing counterbalances.  Just a little curvature seems to change it completely. I would add that the cambered version (i,e, slice the same thing in about half so it is flat-bottomed) seems to work great for propellors, and for HLG wings.

     The airfoils that I am talking about (exhibiting all the bad characteristics) look like diamond-shaped flat plates with the edges slightly knocked off. A 5th bad characteristic is lots of curvature near the high point. That is necessary if you start with a diamond and knock off the corner formed at the high point. That is literally how I used to modify props, flat facets, then round off the sharp edges, and how you carve/sand HLG wings.

    The ARF Strega only has the diamond shape in the front 1.5" or so (the rear half seems to be fine), presumably explaining why knocking the point off to a still-pretty-sharp 3/6 or 1/4" radius seems to fix it/  The Frankenstunt and many full-scale aerobatic airfoils have all of them. For those we have usually ended up using turbulators taped near the high point to get the air to go "around the corner" that the high point represents. It turned Frankenstunt (which is an Uncle Jimby airplane) from a disaster to merely extremely difficult to fly.

    Bobby Hunt watched Jim fly the Frankenstunt at the NATs, and told him "you have a 200 mph airplane and 100 mph skills".

     Brett

Offline Matt Spencer

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3045
Re: The best stunt airfoil
« Reply #65 on: February 14, 2018, 09:44:54 PM »
DIAMONDS ? yea, airfoilss are mathmatical ?? ( :-X) derivatives or ellipses & teardops / raindrops . I Should Think .  :o



A bit of pushing & pulling , and youve got most of them .  %^@ S?P

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #66 on: February 14, 2018, 10:33:09 PM »



As you can see , it cant be totally hopeless .
' The Story ' is its supposed to voek in da vind , But WHAT KIND of WIND . The Blowy Bumpy rough stuff , We Presume . As In it Dosnt get Blown into the Ground .

    Matt, be advised that I was present for that entire week, and watched every single official flight Bob did very closely. I was also one of the few people still willing to talk to him - briefly.

     I saw him do a practice flight on Monday and it was immediately obvious that he was the favorite - just like the 81 Team Trials, if he was really "on", he was nearly untouchable. He wasn't always "on", and unfortunately for him (and the rest of us) he was unable to tell the difference or accept that other people could tell the difference.

    As it happened, he just blew through the week as expected, and through the first flyoff flight. Then, it got a bit windy, and he started having problems. But so did Ted, with first his engine just fading for reasons we never figured out, then the infamous "bubble gum" flight. Then things got very close, and clearly Ted was flying better. But at the time, the scoring range in the flyoff was very narrow, and once Bob had posted his first flight score (560), it would have taken a big shift of something to catch him. It ended up pretty close but he still won.

 Interestingly he was calling Mike Rogers between flights to try to get some coaching and suggestions over the phone. Mike's Patternmaster was far and away the best example I have seen.

    BTW, I also note that you can see, even in the picture, that the LE is rounded off to the same degree or more than we suggested for the ARF Strega. And to give credit where credit is due, Al Rabe made the same point about pointy LEs in his American Aircraft Modeler column in about 1974, and when we did it more-or-less like Al recommended, it solved the problem.

   As a completely unrelated aside, of all the really great fliers I have been around, including those who are much better in general, I probably try to emulate the way Bob Baron flew at his best (81 TT and 96 NATs) more than anyone  - "clean" and "simple".

     Brett

 
« Last Edit: February 15, 2018, 10:55:32 PM by Brett Buck »

Offline Frank Wadle

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 55
Re: The best stunt airfoil
« Reply #67 on: February 15, 2018, 01:41:34 AM »
Vitalis,
If I interpret your diagrams correctly, then this Yatsenko airfoil has a nice Cl diagram without bumps up to 8° or 9° AoA.
It seems that the kink in the profile created by the deflected flap has no influence??
Very interesting!
Maybe it has to do with the hinge construction? I mean the leading edge of the flap itself is a perfect circle. Therefore when deflected there is no sharp corner.

I once talked to Yuriy Yatsenko about the logarithmic device like Igor is using it. He mentioned that his airplanes have something similar…. The hinge gap of the flap. He explained that the hinge gap on his design will change with increasing deflection. I checked this on my planes and indeed, the gap changes a little when you deflect the flap.

That reminds me of an airplane I saw last year. It belongs to a Ukrainian pilot and was designed by Sergey Belko. The hinges were made in such a way that there was almost no gap around 0° deflection. At around 20° deflection the hinge gap opens up to several millimeters. This was made intentionally, not by accident.

PS:
I doubt that a Yatsenk plane will have as much as 30° flap deflection in a corner. They usually have a ratio of 1/1.2 to 1/1.3 flap to elevator. 30° Flap would make 36° to 39° elevator. At least it is like that on my planes.


Here is a quick analysis of Yatsenko Shark Ellipse airfoil with flaps at 30 degrees. The airfoil can be found in drawings here:
http://discovery-aeromodels.com/en/andrey-yatsenko-shark-ellipse-2-control-line-f2b-model.html

Note: this is NOT an official analysis and I have not been provided with airfoil data from the manufacturer. It is very sketchy, as it is based on a low resolution drawings. You should not make any evaluation or conclusion from these images about true performance of real Yatsenko Shark stunt models.

Offline Vitalis Pilkionis

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 73
Re: The best stunt airfoil
« Reply #68 on: February 15, 2018, 04:04:24 AM »
Vitalis,
If I interpret your diagrams correctly, then this Yatsenko airfoil has a nice Cl diagram without bumps up to 8° or 9° AoA.

Indeed. An ascending part of Cl curve is as good as on Igors airfoil and the airfoil can produce a fair amout of lift.

Quote
It seems that the kink in the profile created by the deflected flap has no influence??

I think it has. What's so different about Igors airfoil is a top part of Cl curve. It has a very smooth transition from ascending to descending part over high point. That makes Igors airfoil act predictable at AoA higher than optimal.

Quote
Maybe it has to do with the hinge construction? I mean the leading edge of the flap itself is a perfect circle. Therefore when deflected there is no sharp corner.

I think you're right. The big radius on LE of the flaps certainly helps to avoid a sharp bump on Cl curve. Is that enough for any possible flight conditions, well I don't know.

Quote
I once talked to Yuriy Yatsenko about the logarithmic device like Igor is using it. He mentioned that his airplanes have something similar…. The hinge gap of the flap. He explained that the hinge gap on his design will change with increasing deflection. I checked this on my planes and indeed, the gap changes a little when you deflect the flap.

I think the statement has a sense. There is no doubt that a varying gap does affect flap's performance, the question - exactly how. Unfortunately I have not found a way to reproduce influence of a hinge gap in Javafoil software (still need to learn it)  :(

Quote
I doubt that a Yatsenk plane will have as much as 30° flap deflection in a corner. They usually have a ratio of 1/1.2 to 1/1.3 flap to elevator. 30° Flap would make 36° to 39° elevator. At least it is like that on my planes.

I have a saved message by Peter Germann about Shark where he claims that "... the flap / elevator deflection ratio is approx. 30° flaps at 45° elevator"
Moreover, derivatives of a Shark made by Leonidov that I'v seen had no restriction in deflection at all.


Regards,
Vitalis

Offline Frank Wadle

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 55
Re: The best stunt airfoil
« Reply #69 on: February 15, 2018, 07:12:33 AM »

I have a saved message by Peter Germann about Shark where he claims that "... the flap / elevator deflection ratio is approx. 30° flaps at 45° elevator"
Moreover, derivatives of a Shark made by Leonidov that I'v seen had no restriction in deflection at all.


I just checked the trimm on my Yuriy Yatsenko planes.
They vary between 1/1,3  to  1/1,4
That would be 39° to 42° elevator for 30° flap.

Online Igor Burger

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1934
Re: The best stunt airfoil
« Reply #70 on: February 15, 2018, 08:02:53 AM »
What I don’t understand is how a Yatsenko airfoil ties in with this.

Actually ... perfectly :- ))

Take closer look to pictures posted by Vitalis, if you really look what is happenening at 8 deg AoA, you will clearly see hysteresy problem which I methioned in that article. Step on lift curve making tracking problem and the same on moment curve making positive pitching feedback at that angle.
Means wing load must be lower than with airfoil having it at 10 deg AoA (or not having at all) so they will not need to go close or even exceed that point. And also 8 instead of 10 deg AoA making time for corner transition 20% shorter. 

Real life influence is clear and known from real experience, those models fly Ok when light, it means also 20% less resistant in wind and turbulence. They need some extra flight to accomodate for different air density to avoid exceeding those steps, and they lead to oveshooting corners in case of stressy turns.

But I understand you, your model use it, so simply fly it as its is, I happy for that :- )))))

And regarding that gap - well, I am not going to comment its function because I did not analyze, and I will not, because it is making problems with trimming. But what is for sure different, is feedback from hinge moment. My unit limits feedback from hinge moment in corners what allows much easier flying especially in wind. That is second essential property of that unit and I would say most important. That gap cannot do it.

Online Lauri Malila

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1100
Re: The best stunt airfoil
« Reply #71 on: February 15, 2018, 10:56:26 AM »
They need some extra flight to accomodate for different air density to avoid exceeding those steps, and they lead to oveshooting corners in case of stressy turns.
[

In some models I did seal the gap with some sort of a lip seal and result was exactly that, especially in turbulent wind.
Anoher bad thing is increased friction, especially in landing glide. Kind of a stick’n slip. L

Online Igor Burger

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1934
Re: The best stunt airfoil
« Reply #72 on: February 15, 2018, 11:29:53 AM »
They need some extra flight to accomodate for different air density to avoid exceeding those steps, and they lead to oveshooting corners in case of stressy turns.
[

In some models I did seal the gap with some sort of a lip seal and result was exactly that, especially in turbulent wind.
Anoher bad thing is increased friction, especially in landing glide. Kind of a stick’n slip. L

For sure, because sealed flaps make higher lift coeffient and that makes even lower AoA at low weight ... so it perfectly matchs theory and proofs what I wrote :- ))

Friction is clear if you do it on Yatsenko model, because it has pivot point aft of flap LE, means LE is moving up and down. That is actually nice trick to lower hinge moment. But it is very difficult to do sealing on such hinge construction. If you try it on classic hinges where is no moving on sealing tape, only deflecting, you will not see any friction. .. 10000 times tried :- ))

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #73 on: February 15, 2018, 11:50:02 AM »
For sure, because sealed flaps make higher lift coeffient and that makes even lower AoA at low weight ... so it perfectly matchs theory and proofs what I wrote :- ))

Friction is clear if you do it on Yatsenko model, because it has pivot point aft of flap LE, means LE is moving up and down. That is actually nice trick to lower hinge moment. But it is very difficult to do sealing on such hinge construction.

   Once I had the opportunity to look at one of the airplanes closely, I think the attempted construction was to not have the LE moving up or down, but to have it "roll" where the pivot is exactly at the center of the round flap LE. That doesn't really counterbalance anything, it just doesn't increase it as much as it might otherwise. That's more-or-less what Keith Trostle did on his Focke-Wulfs, and Al tested on his car hood (with arguable results). The Yatsenko hinge line construction is effectively identical to Keith's aside from the materials.

    Done perfectly, that *at least* solves the "giant discontinuous hinge line" problem you would have with "blended" flaps,  and if you make it fit tightly enough, would tend to have a significant effect of reducing the flow through the "gap". Unfortunately, on both the airplanes I saw, the pivot wasn't centered in the flap, so the rounded LE of the flap rose up above the surface when travelling in one direction, and was recessed below the surface in the other direction. This also required the hinge be installed with a much larger gap than would be hypothetically possible to prevent binding, so it was pretty wide open. It was also a much different gap in one direction than the other, once it got towards the end of travel.
 
    Unlike most of the other strange and overblown analysis we sometimes do (and I engage it in too, that is not an accusation...) this sort of thing definitely DOES make a big difference. I have come to mostly the same conclusion of most others back to Al's car hood, you probably do better making the flap and stationary part of the wing thin at the hinge line, and doing everything possible to smooth the flow over the hinge line - putting a bit of curve in the aft portion to better fair in the surface when deflected, preventing flow through the gap, and rounding off all the corners it has to flow over.   

      In order, the people I ripped off for these tremendous personal insights, in order, Al, Denny Adamisin, and Paul Walker. If you are going to steal, steal from the best, I say.

     Brett
« Last Edit: February 15, 2018, 03:55:31 PM by Brett Buck »

Offline Serge_Krauss

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1134
Re: The best stunt airfoil
« Reply #74 on: February 15, 2018, 12:31:56 PM »
Just a FWIW comparison, if this old image is clear enough (low res for SSW Forum years ago). I drew up a couple rather "fat" sections: a 23% section with an elliptical l.e. shape to the 30%-chord point and modified NACA aft drawn over an NACA 0023 section (as computed). They are pretty close. The black one is elliptical.

Offline Matt Spencer

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3045
Re: The best stunt airfoil
« Reply #75 on: February 17, 2018, 06:32:57 AM »
Vauge relevance , does have flaps , even if the airfoils ' inappropriate ' .




of couse , all you need is a desert road & a sun roof , preferably in a van , a driver would save steering via string or your toes , while you do the tests .  S?P


addn ; Measured from gen u wine PM 60 Patternmaster plan ( the Stilletto look use one ) Airfoil Depth O / A .

2 - 13 / 16 root , 2 - 3 / 32 Tip . L E Dia. , 13 mm root , 12 mm tip . ( checked with circle template ) These Exact measurements .
« Last Edit: February 19, 2018, 04:31:06 PM by Matt Spencer »

Offline Avaiojet

  • 2018 Supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 6495
Re: The best stunt airfoil
« Reply #76 on: February 17, 2018, 07:10:04 AM »
I'm saving this just in case I build a model with wheel pants.

I'll use it for the outline.

CB
Trump Derangement Syndrome. TDS

Avaiojet Derangement Syndrome. ADS

Please visit my updated Website! www.cfcgraphics.com

If you're Trolled, you know you're doing something right.

Alpha Mike Foxtrot.

Owner of CFC Graphics. "Model Airplane Graphics from a Model Airplane Builder."

"No one has ever made a difference by being like everyone else."

Marcus Cordeiro, The "Mark of Excellence," you will not be forgotten.

I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King.

"Ya gotta love it when a plane comes together."

Proverb 11.9  "With his mouth the Godless destroys his neighbor..."

"Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane." David McCellan, 1980.

Offline Vitalis Pilkionis

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 73
Re: The best stunt airfoil
« Reply #77 on: February 17, 2018, 08:39:33 AM »
I'm saving this just in case I build a model with wheel pants.
I'll use it for the outline.
CB

I'm very glad you like it. Actually this photo is distorted by fish-eye effect of a lenses.

Vitalis

Offline Vitalis Pilkionis

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 73
Re: The best stunt airfoil
« Reply #78 on: February 17, 2018, 08:42:57 AM »
Now I would like to share with you a Javafoil analysis of another one airfoil. Actually I'v been highly interested in it, since I built an electric version of a Brodak T-Rex last year. So here it is with a flaps at 30 degrees.
As you can see, Cl curve is linear only at negative AoA and does an abrupt dive at AoA 8 degrees. At the very same time Cd curve jumps up, indicating a strong positive pitching feedback.
Another thing is that the airfoil has the same tendency even with flaps at 15 degrees. Obviously this airfoil is good only for flapless designs, in a case with flaps it is necessary to avoid flight conditions where wing AoA can exceed 8 degrees.

Vitalis

Offline Matt Spencer

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3045
Re: The best stunt airfoil
« Reply #79 on: February 21, 2018, 10:17:08 PM »
Saved for ' when they thought its all over '

Id Thought the ' Drag Spike ' combined with the 4-2 run , Gave the ' Nailed & Turned ' Square Corners ;

With the engine break evening the delay & accelerating from the turn . The " CLASSIC " Stunt Run .

Thus horses for courses , the types requireing diferant answers from differing parameters .  S?P S?P

Online Howard Rush

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 6267
Re: The best stunt airfoil
« Reply #80 on: February 22, 2018, 01:11:19 AM »
Now I would like to share with you a Javafoil analysis of another one airfoil. Actually I'v been highly interested in it, since I built an electric version of a Brodak T-Rex last year. So here it is with a flaps at 30 degrees.
As you can see, Cl curve is linear only at negative AoA and does an abrupt dive at AoA 8 degrees. At the very same time Cd curve jumps up, indicating a strong positive pitching feedback.
Another thing is that the airfoil has the same tendency even with flaps at 15 degrees. Obviously this airfoil is good only for flapless designs, in a case with flaps it is necessary to avoid flight conditions where wing AoA can exceed 8 degrees.

Vitalis

Just keep AoA less than 8 degrees.  It has plenty of Cl, although not as much as the sealed-flap Shark.

Edited to add some background, although not necessarily applicable to stunt.  In bygone years I flew combat planes with an airfoil with an abrupt stall.  It was a really good airfoil otherwise.  The wings had to be straight, and the controls had to have stops to keep the AoA below stall, but the airplanes worked great.
« Last Edit: February 22, 2018, 03:38:19 PM by Howard Rush »
The Jive Combat Team
Making combat and stunt great again

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 10285
Re: The best stunt airfoil
« Reply #81 on: February 22, 2018, 01:43:22 PM »
Just keep AoA less than 8 degrees.  It has plenty of Cl, although not as much as the sealed-flap Shark.

Actually, if you watch our planes fly in competition, the AoA is kept pretty low, if not negative.  When you go through the part of Paul Walker's trim chart where you adjust the plane's elevator-to-flap ratio and bias so that it's level both upright and inverted, you're coming pretty close to adjusting it so that the fuselage flies tangent to a loop, instead of having to point inward as a flapless design would.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Brent Williams

  • 2018 Supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 596
  • Making America Fly Stunt Again!
    • Fancher Handles - Presented by Brent Williams
Re: The best stunt airfoil
« Reply #82 on: February 23, 2018, 12:45:46 AM »
Now I would like to share with you a Javafoil analysis of another one airfoil. Actually I'v been highly interested in it, since I built an electric version of a Brodak T-Rex last year. So here it is with a flaps at 30 degrees.
As you can see, Cl curve is linear only at negative AoA and does an abrupt dive at AoA 8 degrees. At the very same time Cd curve jumps up, indicating a strong positive pitching feedback.
Another thing is that the airfoil has the same tendency even with flaps at 15 degrees. Obviously this airfoil is good only for flapless designs, in a case with flaps it is necessary to avoid flight conditions where wing AoA can exceed 8 degrees.

Vitalis

Bradley Walker used Bob Hunt's Saturn airfoil when he designed the T-Rex.  https://stunthanger.com/smf/stunt-design/wing-thickness/msg135532/#msg135532
Not trying to be contrary, but it's doubtful that anyone heard of Bob Hunt's Saturn having any big troubles turning or falling out of the sky due to AoA. 

The Bradleymobile uses the Saturn airfoil.  Which is what I call my "thin standard" airfoil.  I believe it is the perfect compromise in the slightly lower aspect ratio T-Rex (I mean Bradleymobile).  I was particularly adamant with the factory that the front of the airfoil must perfect match the plans.  They did not disappoint.

Viewed in CAD all of these airfoils start looking alike, at least from the Hunt and SV series.  Randy's SV airfoils are about 3/32" thicker top and bottom than the Saturn airfoil (if blown up the same chord).  The Saturn airfoil was supposedly derived from Billy Werwage.  The Saturn airfoil looks suspiciously like a Genesi/Legacy/Buccaneer airfoil.  As Brett said, these are all not way off the Imitation airfoil (which is a favorite of mine also).

I would not go thicker than Randy's airfoil.  There is no need.  Just adds weight, drag, etc.

I would suspect the Saturn airfoil is similar to PT airfoil also.
Laser-cut, "Ted Fancher Precision-Pro" Hard Point Handle Kits are available again.  PM for info.
https://stunthanger.com/smf/brent-williams'-fancher-handles-and-cl-parts/ted-fancher's-precision-pro-handle-kit-by-brent-williams-information/

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #83 on: February 23, 2018, 01:09:49 AM »
Another thing is that the airfoil has the same tendency even with flaps at 15 degrees. Obviously this airfoil is good only for flapless designs, in a case with flaps it is necessary to avoid flight conditions where wing AoA can exceed 8 degrees.


   OK, not to be offensive, but the above suggests you have spent a bit too much time looking at javafoil, and not enough flying model airplanes.

   Of course, with flaps, you are far less likely to get to the "critical" 8 degrees than you would without flaps - which suggests (if you believe the simulation, which in this case I don't, or at least not to the degree you are believing it), you would do even less well on a flapless design. The fact that the Saturn, which is known to be one of the better modern stunt designs, uses this airfoil  - *very* similar in the important characteristics to others like the Thunderbolt  and many other highly successful designs - gives you some important "ground truth" by which you can judge the plausibility of your CFD.

   Additionally, a flaw I see with these simulations, particularly with flaps included, is that there seems to be no realistic modeling of the flow around the hinge line, which is known to be absolutely critical. That's not unique to your model, all of those I have seen have the same problem. Meaning it might well be right, or pretty close, with the flaps at neutral, and wildly incorrect (like I suspect) with the flaps deflected.

    Brett

Offline frank williams

  • AMA Member
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 442
Re: The best stunt airfoil
« Reply #84 on: February 23, 2018, 08:31:36 AM »
Javafoil and cfd is useful.... but be careful .... it may lead you to sniffing a brick wall

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #85 on: February 23, 2018, 10:36:32 AM »
Javafoil and cfd is useful.... but be careful .... it may lead you to sniffing a brick wall

     Any simulation has more-or-less the same problem, CFD, space shuttle, satellite, etc. What is relatively new is that people seem to want to believe them with a lot less skepticism than we used to.

    It's a variant on the Powerpoint effect. When you had to hand-generate vue-foils, they usually looked crude to one degree or another, even the "production quality" types. With Powerpoint, you can make something that looks so slick and clean, that people tend for forget that the content may be questionable. This is particularly true with management types who have and never will *actually understand* what you are talking about, and judge the plausibility of your arguments based on how well presented it is, how confident/arrogant you seem, and how many hoops you are willing to jump through to prove your point. "Gee he's willing to call the corporate Chief Engineer in Baltimore, this must be really important..."

   Same trap is even easier to fall into with simulation data. You can run 10,000 simulations a week, but if you  didn't bother to set a particular single bit (out of megabits or gigabits) in any of them - which only one person in the world might grasp the relevance of - you might never find a really fundamental problem that will nonethless completely screw the pooch when you encounter the right conditions.

     ANY time you do any simulation, you have to somehow validate the results somehow with reality somehow. The aerospace industry it littered with people who thought that they could dispense with sim results validation and just dot it all on a computer, and usually coming to grief later at some point.

     Brett

Online Lauri Malila

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1100
Re: The best stunt airfoil
« Reply #86 on: February 23, 2018, 10:57:44 AM »
Brett,

Could you please quit your job and US, and move in Switzerland to work for high end/luxury watch industry? L

Offline Vitalis Pilkionis

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 73
Re: The best stunt airfoil
« Reply #87 on: February 23, 2018, 11:46:02 AM »

   OK, not to be offensive, but the above suggests you have spent a bit too much time looking at javafoil, and not enough flying model airplanes.


I'v had an electric T-Rex for more than a year now, and spent all last year tinkering with it. The weight is 1830g (64,5 oz) RTF. Аll in all I'v flown approx 150 flights. That's not a lot, but still enough to come with some thoughts.
So here I going to speak from my own little experiece.
It is not a bad design, but certainly has its flaws. One of those being a wing. I did not succeed to get a crisp corner out of it, and that was most obvious on triangles - way too big radius. I tried to play with elevator/flap travel, but it did not become any better whatever I did. Just a force on a handle increased tremendously to a level, that a few times I hurt my wrist and literraly I was unable to continue any stunt for the rest of a flight. So I set elevators back anf forgot that.
Another flaw - the plane doesn't have enought stability, at least to my requirements. I'v made a new stab from a scratch with a larger area and sharp LE, also moved it back for a half of an inch. That fixed stability issue quite a lot, but still not to the level of my old stunt plane. But that's not the case here.
Now Javafoil opened my I eyes a little bit, at least I can see thats going on with the airfoil. So I think that was not a bad idea to invest my time in learning it. I am also going to fly my T-Rex this spring (it's my first electric ship also), I will try to make some more adjustments, since I'v had more knowledges through the winter time.

Peace,
Vitalis
« Last Edit: February 23, 2018, 12:21:54 PM by Vitalis Pilkionis »

Online curtis williams

  • Trade Count: (0)
  • New Pilot
  • *
  • Posts: 14
Re: The best stunt airfoil
« Reply #88 on: February 23, 2018, 03:25:01 PM »
I really enjoy when Brett Buck adds to conversations.  He really gets people wound up.  Remember it's for fun! 

Online Howard Rush

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 6267
Re: The best stunt airfoil
« Reply #89 on: February 23, 2018, 07:22:34 PM »
Brett,

Could you please quit your job and US, and move in Switzerland to work for high end/luxury watch industry? L

Brett’s ancestors left Switzerland because the cheese had holes in it, and as Baptists, they refused to guard the Pope.
The Jive Combat Team
Making combat and stunt great again

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #90 on: February 25, 2018, 03:38:10 PM »
I'v had an electric T-Rex for more than a year now, and spent all last year tinkering with it. The weight is 1830g (64,5 oz) RTF. Аll in all I'v flown approx 150 flights. That's not a lot, but still enough to come with some thoughts.
So here I going to speak from my own little experiece.
It is not a bad design, but certainly has its flaws. One of those being a wing. I did not succeed to get a crisp corner out of it, and that was most obvious on triangles - way too big radius. I tried to play with elevator/flap travel, but it did not become any better whatever I did. Just a force on a handle increased tremendously to a level, that a few times I hurt my wrist and literraly I was unable to continue any stunt for the rest of a flight. So I set elevators back anf forgot that.
Another flaw - the plane doesn't have enought stability, at least to my requirements. I'v made a new stab from a scratch with a larger area and sharp LE, also moved it back for a half of an inch. That fixed stability issue quite a lot, but still not to the level of my old stunt plane. But that's not the case here.
Now Javafoil opened my I eyes a little bit, at least I can see thats going on with the airfoil. So I think that was not a bad idea to invest my time in learning it. I am also going to fly my T-Rex this spring (it's my first electric ship also), I will try to make some more adjustments, since I'v had more knowledges through the winter time.

  Don't get me wrong, I am not trying to start anything, but there are about 1000 reasons that your airplane doesn't fly the way you want that I would look into before some obscure hypothetical property of the airfoil. In any case, the airfoil you modeled in Javafoil is not the one you actually have, and it's neither two-dimensional, nor the same when you look at it in 3 dimensions. For instance, you will get potentially relevant change depending on how tight the covering is shrunk, and it is definitely different between ribs compared to where it has ribs. In fact, guessing at what causes your unexpected separation in the math model, billowing or sunk-in covering would tend to DRASTICALLY alter the separation point. Have a few wrinkles in the right place, congratulations, you have turbulators.   As far as I can tell, you are not modeling the hinge line flow at all, that, too would potentially have dramatic effects on exactly the sort of hypothetical problems you are having, and how they manifest themselves in real life. That's the problem with CFD modeling without the approrpriate controls or validation, and in this case there are very obvious potential flaws with it that you could easily predict.

   I seem to recall the largest airplane manufacturer in the world designing a wing entirely using CFD, then finding the wing had a higher CL with the wing LE slats stowed than with them deployed when they actually flew the airplane. I also seem to recall people trying to do CFD models on stunt planes to prove that turbulators were worthless - even though we managed to get Ted's airplane through a NATs in the rain by taping 0.018 flying lines to the surface. Now, some of the same people have found no theoretical value for vortex generators that nonetheless were last seen with airplanes festooned with them, the bigger the better.

     It's entirely within the realm of possibility that you have indeed found something that causes a problem. It's entirely possible that I will get hit by a meteorite on my way to pick up my Powerball winnings with my new girlfriend Cindy Crawford. But after reading back through the thread, I am even more inclined to suspect Frank's dog drawing is in fact on point. I would add that Frank was, among other things, a simulation expert for the Space Shuttle and I ran about 1500 simulations of a highly non-linear and moderately complex system 2 weeks ago, and spent most of the last week validating it with flight data. Mine had no air involved, but the more experience you have, the less you are willing to take simulations as unvarnished truth without validation.

     The T-Rex is a decent and reasonably conservative design, if it doesn't fly well, we can probably help you get it to work.

    Brett

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #91 on: February 25, 2018, 04:05:06 PM »
Thank you for your honesty, Brett - it's a very interesting story.

But actually it's not so difficult to modify a wing of the ARF, one just needs a long metal ruler and a sharp snap-off blade.

   A method I also suggested here:

https://stunthanger.com/smf/open-forum/strega-arf-trim-video-and-strega-arf-'control-line-world'-written-by-windy/msg456421/#msg456421

   Do that, and there's no problem - but one you solve that problem, you also don't need it to be 3" thick any more, nor the large flaps, and by corollary, the nose-heavy trim or to manufacture lots and lots of line tension to deflect all this stuff into the relative wind.  Which suggests that you might do better when designing your airplane starting with something that doesn't need to be "fixed".

    Brett

Offline Frank Wadle

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 55
Re: The best stunt airfoil
« Reply #92 on: February 26, 2018, 08:35:59 AM »
Brett, I completely agree with you... No simulation should be trusted until it got validated in real life. And I agree that the means of simulation we have (javafoil) can't simulate all aspects of a F2B ship.

Writing this right now I feel rather stupid for starting this thread in the first place. Or maybe not?
Wouldn't a airfoil that is superior to another in theore be superior in real life as well? What I mean is, we make the same "mistakes" when calculating an airfoil for both, the superior and the other airfoil.

I think it is fascinating where this thread went so far.
It is also very fascinating to read the different theories. So many different concepts and they all seem to work. Beringer, Yatsenko, Burger, Windy..... All rather different but all seem to work.

So maybe there is a chance that the Wortmann airfoil in question will work as well!
The designer claims to have built a test plane last year and that seems to work just fine for him.

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #93 on: February 26, 2018, 10:55:22 AM »
Writing this right now I feel rather stupid for starting this thread in the first place. Or maybe not?
Wouldn't a airfoil that is superior to another in theore be superior in real life as well? What I mean is, we make the same "mistakes" when calculating an airfoil for both, the superior and the other airfoil.

I think it is fascinating where this thread went so far.
It is also very fascinating to read the different theories. So many different concepts and they all seem to work. Beringer, Yatsenko, Burger, Windy..... All rather different but all seem to work.

   It wasn't stupid at all, it's a very obvious question that happens to have no definitive answer.

  After 70ish years of people cutting and trying, now somewhat enhanced by CFD (with the positives and negatives/pitfalls it brings), we think we have learned at least what NOT to do. And we are still learning, or at least confirming, previous understanding every time someone comes up with something new. In the last few years we have seen what happens when you get the shape, particularly around the LE, correct, you might be able to run 1/3 the thickness we used to use without any lack of lift performance.

    Also, your list contains two that I would consider questionable - but nonetheless won a WC and lot of high NATs finishes. I think it might have been in spite of rather than because of the airfoil, but that just shows that if you are willing to thrash long enough and you are in the ballpark of OK, and get other things right, it doesn't make that much difference. It also shows that you can easily get led astray trying to fix an issue by misdiagnosing the problem.

    The thing Frank and I were cautioning about was over-interpreting your data. Maybe someone comes up with a theory, tests it with a great-looking CFD run, builds it, and finds that the airplane flies great. That still might prove nearly nothing about the underlying theory because there are a million other things that are varying that *wouldn't* show up in a CFD run. Maybe you still have a crap airfoil or crap theory, but you happened to get everything else righter than you ever had before.

      When you can do something (Vortex generators) that could do nothing but degrade the traditional airfoil qualities, and have the airplane fly better, or in some cases, MUCH better, that tells you beyond any doubt that these traditional airfoil qualities are not the determining factor in performance. Same thing with altering the first 1/4" of a 14" chord (rounding off the point at the Strega LE).

   The other issue is that people get their egos wrapped up in these "theories" and then defend them to the death, regardless of the objective results. That's hardly unique to airfoil design.

   Finally - the best stunt airfoil is the airfoil from the Imitation.

    Brett

Offline frank williams

  • AMA Member
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 442
Re: The best stunt airfoil
« Reply #94 on: February 26, 2018, 02:44:16 PM »
Mr. Wadle, not a bad question at all …. We are all still looking for the best airfoil shape, everyone thinks there might be something better out there.  We have learned some things that are good and some things not to do, like building to a ¼ inch square le spar.
One of the biggest PA regrets through the years that I have, is not following up on the wind tunnel tests that were performed in the low speed tunnel at the University of Illinois at Urbana (UIUC) by graduate students of Dr. Michael Selig.  Selig was/is a sailplane flyer and was involved in low speed wind tunnel testing during his education.  He put out a request for models to test in the tunnel.  All you had to do was build a model to the tunnel specs and it would be tested. 
I wanted to test a Fancher type airfoil with flaps, a Rabe type airfoil with flaps, a Nobler, etc.  , but I never got around to getting my project off the ground.  The Selig project resulted in several volumes of data through the years.
http://m-selig.ae.illinois.edu/uiuc_lsat.html
 Many sailplane airfoils were tested.  The nearest airfoils to a stuntship wing were in some of the later tests of several RC trainer wings.  Two of these tests were for the Ultra-Sport 1000 and the Trainer 60 airfoils.
The results of these tests, once again real wind tunnel measurements at Reynolds numbers appropriate to PA aerodynamics, turned out to be fruitful for us.  Similar thickness airfoils (UltraSport and Trainer)with different leading edge radius, the two airfoil tests do clearly show an earlier stall of the sharper leading edge section.  Although I haven’t done it, it might be interesting to load these two sections into JavaFoil as a comparison of numerical analysis to windtunnel results.  Attached are the Selig results for these two airfoils at a Re = 500,000. 

Offline Frank Wadle

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 55
Re: The best stunt airfoil
« Reply #95 on: February 26, 2018, 04:38:12 PM »
Please don't call me Mister :-)

Offline Wolfgang Nieuwkamp

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 73
Re: The best stunt airfoil
« Reply #96 on: February 27, 2018, 01:08:35 PM »
Frank Wadle,
as Frank Williams suggested, open http://m-selig.ae.illinois.edu/uiuc_lsat.html
On that website, you can download the thesis of  Williamson, G.A. Experimental Wind Tunnel Study of Airfoils with Large Flap Deflections at Low Reynolds Numbers.

There you could look at the data of airfoil W1015, with flap deviation up to 45°, at Re=400 000. CL up to 1,9!

Regards,
Wolfgang

Offline phil c

  • 2015
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1844
Re: The best stunt airfoil
« Reply #97 on: March 14, 2018, 08:14:39 PM »
I built a flapless plane with the Wortmann FX 71-L-150/25 airfoil.  It flew just fine.  No different than a typical NACA airfoil of the the same thickness.  The thin trailing edge does make it heavier to build.  I cut it out of foam with a slot for a 1/64in. ply trailing edge.   That added enough extra weight to negate any possible performance benefits.

It would be really nice if one of the X-Foil junkies would run the airfoils needed to get a true picture of what actually happens on a stunt plane.- 0 flap at 0 AOA, taking into account that the airfoil with a deflected flap has an angle of attack from the leading edge to the trailing edge of the flap.  A sequence of, say, 0 AOA 0 flap, 5 deg airfoil angle 10 deg deflection, 10 deg airfoil angle 20 deg flap, 15 deg airfoil angle 30 deg flap, maybe 20 deg airfoil 40deg flap.  Plot the results against the combined airfoil/flap AOA at each deflection.  I believe that would give a better idea of what is actually going on.

Igor's idea of contouring the airfoil('ala Al Rabe) to prevent the flap stall is still a good one.  It worked for Al, and Igor has refined it quite a bit in other aspects of the plane design.
phil Cartier

Online Howard Rush

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 6267
Re: The best stunt airfoil
« Reply #98 on: March 14, 2018, 09:34:01 PM »
It would be really nice if one of the X-Foil junkies would run the airfoils needed to get a true picture of what actually happens on a stunt plane.- 0 flap at 0 AOA, taking into account that the airfoil with a deflected flap has an angle of attack from the leading edge to the trailing edge of the flap.  A sequence of, say, 0 AOA 0 flap, 5 deg airfoil angle 10 deg deflection, 10 deg airfoil angle 20 deg flap, 15 deg airfoil angle 30 deg flap, maybe 20 deg airfoil 40deg flap.  Plot the results against the combined airfoil/flap AOA at each deflection.  I believe that would give a better idea of what is actually going on.

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=371054&sub_topic_id=371056&mesg_id=&page=#371073  Start with post 42.  Defining the angle of attack as being from the LE of the wing to the TE of the flap is not very useful and not done by folks who use such data.  I did it for Ted's amusement in post 78.
The Jive Combat Team
Making combat and stunt great again

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 8860
Re: The best stunt airfoil
« Reply #99 on: March 14, 2018, 11:08:43 PM »
It would be really nice if one of the X-Foil junkies would run the airfoils needed to get a true picture of what actually happens on a stunt plane.- 0 flap at 0 AOA, taking into account that the airfoil with a deflected flap has an angle of attack from the leading edge to the trailing edge of the flap.  A sequence of, say, 0 AOA 0 flap, 5 deg airfoil angle 10 deg deflection, 10 deg airfoil angle 20 deg flap, 15 deg airfoil angle 30 deg flap, maybe 20 deg airfoil 40deg flap.  Plot the results against the combined airfoil/flap AOA at each deflection.  I believe that would give a better idea of what is actually going on.

    You still have the problem of validation of the results, and the known limitations (like section characteristics VS finite span effects) of the CFD program. What you actually get in flight could be wildly different from the simulation.

Quote

Igor's idea of contouring the airfoil('ala Al Rabe) to prevent the flap stall is still a good one.  It worked for Al, and Igor has refined it quite a bit in other aspects of the plane design.

   That certainly seems to help, and in Al's case, is a good example of "guided cut-and-try" with real-life results. Whether he was trying to solve the right problem is certainly open to debate.

    Brett


Tags: f2b stunt Airfoil