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Author Topic: The best stunt airfoil  (Read 1694 times)

Offline Vitalis Pilkionis

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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.


Offline Igor Burger

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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.

Online Brett Buck

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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

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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

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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

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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

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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 »

Online Brett Buck

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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

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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 »

Online Brent Williams

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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.

Online Brett Buck

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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

Offline Lauri Malila

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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

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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

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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^^

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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 »

Online Brett Buck

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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

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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

Online Brett Buck

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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

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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

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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

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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.

Offline Igor Burger

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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.

Offline Lauri Malila

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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

Offline Igor Burger

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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 :- ))

Online Brett Buck

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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

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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

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Re: The best stunt airfoil
« Reply #75 on: Today at 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


Offline Avaiojet

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Re: The best stunt airfoil
« Reply #76 on: Today at 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
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Offline Vitalis Pilkionis

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Re: The best stunt airfoil
« Reply #77 on: Today at 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

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Re: The best stunt airfoil
« Reply #78 on: Today at 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


Tags: f2b stunt Airfoil