Wings and wings airfoil for the full size stunt plane

[PJ Rowland]

Well brett in all fairness to VGs, but we had a fairly good understanding of what works and what didnt 21 years ago.. thats thousands of flights over 2 decades with a system that essentially hasnt changed since its inception.


Summer of 1996 I first put them on, by the summer of 2000 I placed 3rd at the Nats and had built 4 aircraft in thaose development years. The system by 2000 was set and standardisation was also made with respect to size, location, configuration.

I debuted the system at the World champs in 2004 and then the US nats after that, where a few questions were answered.

Fast forward to the Perth World champs 10 years later.. 2 out of 3 of the US team members ran the system !
( thats 2 from 3 world champions )


Put them where I recommended, the size I recommended and your set to have improvement. This has been replicated on many different airframes and many different Nats winners.

The issue is trying to find MORE improvements by adding more in different spots. This almost never works as my initial 500 odd test flights where I varied them in countless configurations.

What your wanting is a aero analysis of the specifics of height, size, and energy transferred from laminar to turbulent..

. Sure I cannot quantify any of those details, but I have seen my wing with Vgs running in some great test environments, that utilise both wind tunnel and CFD and the circular flow provided by just 1 pair of VGs if you widen the opening up to 3" will provide more than enough boundary layer "grip" to stabalise the airflow across the wing when flaps are deflected.

Thats the same as what I expect to see; a stability to the airstream under deflection, net yeild improvement is consistency under deflection.

The problem with running more pairs is you effectively slow down the overall airflow over the entire wing, and the real issue is the washout effect and our wings arent designed with linear washout. You want the tips to " roll " to mitigate any roll tendency. Putting VGs further out causes more issues than it solves for that reason.. the wing itself..

If you look at the thickness of most wings the % is higher toward the fuse centreline. You only need to add 5% improvement to this section to get improvements over the entire wing. 

Its seems pretty clear to Howard and myself.
Not everything CAN be quantified with math, hence we descibe things as " feel "

A plane feels like it has more turn and lock. With just a minor addition. Like Als rudder, people over do it without understanding it..

Just my opinion..

But we are are 21 years past "cut and try" ive moved on to NOT thinking about VGs
. I treat them like taping the hingelimes,  its done before flight one and I dont add or subtract,  I simply practice.

[Brett Buck]

Well brett in all fairness to VGs, but we had a fairly good understanding of what works and what didnt 21 years ago.. thats thousands of flights over 2 decades with a system that essentially hasnt changed since its inception.

....


Its seems pretty clear to Howard and myself.
Not everything CAN be quantified with math, hence we descibe things as " feel "

    Oh, really, Howard can explain the mechanism of action? Last time this came up, I said I couldn't tell the difference with and without VGs, and your explanation was, more or less, that you were surprised to find that I *couldn't fly well enough to tell the difference*.

     I have since tried it again, and it still doesn't make any difference - I guess I am still not up to standard.

    Moving my elevator horn slider by about .020", however, had a remarkable effect, and putting tape over my wheel hubs also had a remarkable effect - so much even *I* could tell that changed something...

    BTW, I am just pulling your chain.

    There are a lot of things that seem to make *vastly* more difference than VGs, tripper strips on the tail in particular, and only in some cases. Until we can explain why it works sometimes and not others, we don't really understand it.

    Brett

[Howard Rush]

Its seems pretty clear to Howard and myself.

Not to me, but if you put them where PJ says, you won't go wrong.

[Howard Rush]

Oh, really, Howard can explain the mechanism of action?

Yes, but not well enough to tell you where to put them.

[Brett Buck]

Yes, but not well enough to tell you where to put them.

    PJ said I was hopeless anyway, so doesn't really matter...

   An alternate explanation was that my airfoil was right in the first place, so it didn't need fixing. But saying that in public would be quite impolitic.

    Brett

[Howard Rush]

Last time this came up, I said I couldn't tell the difference with and without VGs, and your explanation was, more or less, that you were surprised to find that I *couldn't fly well enough to tell the difference*.

 I have since tried it again, and it still doesn't make any difference - I guess I am still not up to standard.

My guess is that your wing doesn't need them.  I suspect that some wings benefit from them more than others. 

[Howard Rush]

 
   An alternate explanation was that my airfoil was right in the first place, so it didn't need fixing. But saying that in public would be quite impolitic.

Ha! Our posts crossed in the mail.  I can delete mine above if it embarrasses you.

[PJ Rowland]

Brett.

Please, Im not slinging any arrows your direction.

And I NEVER said you weren't good enough to tell the difference I said I was Surprised a pilot of your skill couldnt tell a difference when people who consistently best you at Nats CAN tell a difference.

If you wish to interpret that as " I think your not good enough " then thats your problem, not mine. Im just stating facts.

The mechanism of action is well understood. Any 2nd year aerodynamics student can tell you how a VG works, and its understood well enough to be on commercial aircraft.

Dont be bitter about it..

I would agree with Howard your infitnity wing MUST work so well you dont feel the difference. Its a ompliment not a critism.

Its very simply.. if you dont feel they work for YOU then do t use them.. Its not a difficult problem. 

The game has moved on since the old days of Bar Stock motors and a vague understanding of sprial strip stream effects.

I spent 1000s of flights developing the correct place to put them, I find it a little offensive you dismiss these results, when ive been able to advise others on the EXACT placmemt and tell them EXACTLY what to experience.

Last year : 4 out of 5 of Top 5 were using the technology !!!

And ive got NO problem in saying your airfoil is excellent. The infinity design is excellent and your understanding of stunt theory just as intimidating.

Noone is knocking you Brett, least of all me. Ive said publicily your one of the top guys.

[Brett Buck]

And I NEVER said you weren't good enough to tell the difference I said I was Surprised a pilot of your skill couldnt tell a difference when people who consistently best you at Nats CAN tell a difference.

    Exactly!  I prefer to believe that I (unlike David) am so darn talented that I don't need any extra assistance. 

    The alternative explanation is that they really didn't do anything significant on my airplane - but that can't be it, surely.

       Brett

[RandySmith]

    Oh, really, Howard can explain the mechanism of action? Last time this came up, I said I couldn't tell the difference with and without VGs, and your explanation was, more or less, that you were surprised to find that I *couldn't fly well enough to tell the difference*.

     I have since tried it again, and it still doesn't make any difference - I guess I am still not up to standard.

    Moving my elevator horn slider by about .020", however, had a remarkable effect, and putting tape over my wheel hubs also had a remarkable effect - so much even *I* could tell that changed something...

    BTW, I am just pulling your chain.

    There are a lot of things that seem to make *vastly* more difference than VGs, tripper strips on the tail in particular, and only in some cases. Until we can explain why it works sometimes and not others, we don't really understand it.

    Brett

I can relate  to  Brett's statements, The VGs  nor the trips  made any difference in the flight performance of my planes, and I tried them many times on 2 ships, however, having said that, I think it maybe more  the  weight of the plane vs the  design, maybe 70-30 in favor of  weight.  I may have used  the wrong test plane.
I say this  because  I have seen them work very well on other planes,  and  I have seen them improve the exact  same  SV that I fly, but   that belong to others. all of them  a little heavier.
I would like to do the  Ted Fancher  trick, of  adding  weight  to a plane, then  repeating  the  test with VGs  on one of my planes.  Maybe I will  get to do that this spring.  I also have a friend i am going to try to talk into this  too.
About the  trips, I have seen first hand 2 pilots  who are  world class performers, and  had  their planes  performance  go down in bad weather, and were greatly improved with adding them to the stab.
So in my mind, there is  worthwhile things  to test to  try to improve the understanding of  both  VGs  trips..zigzag tape  etc.
Kudos  for  PJ for his  work  testing these and  telling  everyone what his knowledge of them are 

[PJ Rowland]

Brett,

I have no doubt your infinity IS trimmed to ideal conditions, and Im not going to get into a debate over the viability or effectiveness of VGs.

The sport is FULL of people who think what they are doing is correct and other approaches are not as effective.

I respect EVERYONE who adds some value to the unique sport we call C/L Stunt.

Please understand,  I didnt have anyone to give me help when I was younger, I didnt have the calibre of a Ted Fancher, Brett Buck, Dave Fitzgerald or a Randy Smith to talk to and regularly see at Nats to get assistance.

In fact here are a few examples of what I DID face as a young junior pilot..

I once asked a fellow Australian top pilot " How do you get such a nice finish" response ; " Ohh its too difficult for you "

Or how about this one  :

Dad asks a fellow Top pilot to test fly one of my planes to see if they could help me with a trim problem.

Reply : I dont fly other peoples planes.

Or another ;

 I send 2 x ST60s to get rebuilt by a Top engine guy I get a reply back that the 2 engines in question were beyond repair and not fit even for parts.
Come the Nats some 6 month later someone was flying a very nice plane with an ST60 and he said " yeah I got these motors from some *@% "

Or the YEARS upon YEARS of attenting Nats being laughed at for using VGs in comp.. being told my planes were too heavy and I needed it, or Im just kidding myself that they do anything..

Or the best one I ever heard " If you built straight you would fly better and you wouldnt need bird @#$% on your wing"

So when I figured out back in 1997 that the only person who was going to help ME was ME. I set out to read and learn everything that I could get my hands on.
 
I realised I could test things on field "cut and paste" method is very effective in learning what works and what doesnt in real time.

If I had a motor problem, I had to figure it out.
If I had a trim problem, I had to fix it.
If I needed help with the pattern,  I got a camera.

If I wanted to compete at the highest level ; I had to do it.

Sure I havent made it to Top 5, but I have been able to make it to a reasonable standard and I openly share my findings to my colleagues who ARE at the top of the tree.

[PJ Rowland]

Brett,

I can offer a reasonable explantion as to why your infinity design "feels no different" with VGs.

I did a series of tests that looked at the effect of landing gear location. The test was designed to show that moving the gear forward to fuse mounted vs wing was better for CG placement.

What I found was that having wheel fairings located on the wing acted in the same way as a pair of VGs.

See the plane seldom sees airflow "directly straight" because we fly in an arc. Those wheel fairings see airflow at that angle and this does induce a vortex wake that will energize the boundary layer for the bottom of the wing.

Any negative manouver is "enhanced " whereas positive manouvers see only a small amount of this underside energy.

Its no "coincidence" that your infinity wheel fairings are located in almost the EXACT location for a pair of VGs.

Note that Igors Max Bee has fuse mounted gear. I also personally have run fuse mounted gear since 1996!
Howard also has fuse mounted gear.

[M Spencer]

What I found was that having wheel fairings located on the wing acted in the same way as a pair of VGs.

The Bigger the Better ! . 



Must be why these fly so well .  About resurected , for counter clockwise , Still rubbing out .Set up for the Irvine 40, but on a test run fuels hoseing out at the front bearing . 
Intrestingly , the other ( MC 72 ) was twitcy laterally to gusts . With narrow flat sided floats . ( V Low aspect ratio lower wings !!!! ) WHEREAS replacement larger more bouyant ROUNDED ones
it is not steering about or displacing laterally ( YAW ) in wind . However itt threw the C G out so leads out aft . May get rebuilt to for counter clock & theres replacement ' original ' floats underway
for C. G. weight reasons . Was deadly accurate & relaxed with unsilenced K&B 40 series 70 on a 11 x 5  . Unless the needle was a turn in so it was at 90 mph at dusk surrounded by pine tree hedges.

Which was a little destabilising. for the Pilot .

AERODYNAMICALLY they act like runners. or rails .

Square turns , they swing it round . the extra aerodynamic ' support ' is most discernable on outsides at higher 'G's . Bottoms - in a breeze . ( Where the ' steering from crosswinds also discernable  )

Rounds , Theres a sort of ' sticking ' before the turn , so a ' twitch ' to initiate has a higher initial feedback load at the handle . But the tracking is ' locked it ' in the circular paths - no detriment  .

Semi Beringer in that the flaps are more ' trim tabs ' than lift/ drag devices . Incidently the Airfoils only 16 %. Definately not stall prone in original configuration.
On smooth water , needs spped and full up to rotae if alowed to sit flat till at speed .

 

Intend to set em up to Comp. readyness shortly .

Need 5/32 wire front legs for ridgidity

[Howard Rush]

That is wonderful.  I'd put pontoons like that on my Tucker Special, but then it wouldn't be an authentic Tucker Special.  Besides, most of our Classic contests are on paved surfaces. 

[M Spencer]

Thats why Ive put al omum skids under the keels . 

Incidently its acctually 16.9 % Airfoil , on paper . But Built , with the silk & paper , 17 % might pass ,.
Has full span flaps now, about 2 1/4 wide . Tho the MC 72s keeping the Beringer , of actually 50s Aeromodellor Stunt Artical derived
small add on flaps, but let into the trailing edge. 

Did a Morley T-Bolt , with Floats . With a Fox 19 , back 76 .
Which sat into wind and waves quitely ( ? ) workinging along toward me as I quitely backed up along the shore .
Thus , at the time , I figured If the Lines were on the other wing , Itd walk quitely AWAY from me. And thus the line tension would be remarkable .

Full UP , to get out of the grass , a wheeled device , flown clockwise , is remarkable. As it jumps out away from you. Rather than at you , whom requires ( usually , to back up, or leap backward. As required . 

SO, Floats .
For Water , the prop tourgue / wash , has it away from you , flown  clockwise , on a right hand ( conventional ) prop .Or V c V . i.e. L H Prop flown conventional counter clockwise .
HOWEVER ,
on grass , the away bit gets it chewing / skewing in the grass . Thus going nowhere . Unless the pilot walks  parralel to plane . Unless the pit man lierally lets it go - drops it . from 2 inches over the grass .
Depending on when the grass was cut, its length, stickyness, and dryness . It can be quite slippery . Sometimes even people have been seen to slip on slippery grass .

I Figure for Tarmac or Concrette , W T H . Either small dia ( 40 thou.) wire runners , or alloy skids , or just replace the keels as they wear .
Concrette and ashpelt are often faily slippery , but vary also .

Obviously , a pair or two pir , of team race streamline wheels , or even a pair of ballon wheels , could be let into the float undersides. 3/16 or 1/4 protrusion .
But consider wheel housings shoulda be waterproof. With a receptical ( tubes ) for a replaceable axle . For waterproofing & maintanance . 

[Matt Piatkowski]

Hello Everybody.
The discussion is interesting.
Please continue.

Frank Williams's reply (#38), dated Jan. 4, 2021, had the formulas attached.
I am aware of these relationships, but I cannot find the reason for "2 Pi" to be present in the equation for Cp (power coefficient).
Any comments?

These formulas have one practical effect - they allow estimating the diameter of the equivalent propeller.
For example: going from two-blade (diameter=D2)  to three-blade propeller (diameter=D3), the formula is D3=D2 x (2/3)^0.25.
This equation, taken from one of the websites, may have a mistake or not - the exponent coefficient maybe 0.20.
I will create the spreadsheet with the formulas built-in, and then we will know or sure.
Any comments?

Regards, stay safe,
M

[Igor Burger]

May be late, but better late than never ... 

I will try answer all in one post.

1/ I do not keep any secrets Matt, you certainly saw my article about airfoil, there is all answered about Max airfoil. It is not laminar airfoil, it is cloned from NACA 0018 with modified hinge line to remove kink which appears at high flap angles, so certainly not extremely thin, not extremely thick, but LE radius is constant from root to tip (blunter at tip than 0018). Difference is visible from distance of circle - Jiri V. (you know him) told once that he can tell while looking to flying model if there is that airfoil or other after first corner figure. It goes thru the corner like knife in butter without loosing speed, so pilot without experience with that model wakes up when the corner is already done. It does not mean it is better, it is simple different - someone likes it, someone not. It needs to do more flights to live with it, some pilots simply need to feel some "resistance".

2/ Brett - I did not see what Al did before. We did not have access to literature from "west". We had only east sources and what Al does wasn't published there. We saw only few WCh winners like Stiletto and Juno. First access to sources from west I had when I went work to Germany and I had access to Compuserve. So it was not "copy" of his work, may be that was reason why I did not try to improve his airfoil, I took NACA 0018 instead. However I saw attempts to do that before, so it was not from "my" head. I saw such solutions on another local models (for example also some models from Ukraine had round flap hinge line and they use it until now) and also opposite unsuccessful attempts and I had also Juno which had airfoiled flaps also matching upper surface angle when deflected. I knew what is the point here and I had chance to test it on simulator, so I did it. Al need test it real, I had chance to do it digitally.

3/ PJ - so you say you have such pure education? No one told you how it really works? And you are going to tell us with such pure education how to make VGs???    ... just kidding of course, but PJ likes it as he mistakenly told me ... but yes, there are several thing VGs and tabulators do. There is obvious and well documented improving of drag and lift as Chuck wrote. But that is not that most important in this case. I do not use VGs, I use turbulators and reason for them is they control and stabilize transition point what has impact to controllability. My Max Bee warped on outer wing little bit in rain and it did some ill effects after that. So I tried turbulators on several points and it helped, so I used them. But that was only on one model, since then I use composite wings and I did not have such problem anymore I do not see or feel any significant improvement. I always try them during trimming but usually I put them down. So while it works on one model, it does not on another (and I am speaking about the same type of model). So it can well answer why Brett not needs to feel anything. (just to make it clear - I am speaking about wing, not stab, that is different story)

4/ Matt and Frank - there is difference between recalculation coefficient for multiblade props. You can use either 5th or 4th power both will work well ... BUT you must know if you keep constant P/D or you keep constant RPM (means only P) . If you scale whole prop, means also pitch to keep constant P/D then you must use D^5 if you scale with constant P then D^4 ... it can continue - if you keep P and also blade width then you have to use D^3 ... etc. However you must count that it is only approximate recalculation, there are many changing variables like RE number, airfoil (A0) etc.

and btw, thanks for kind words Matt and Milton :- ))

[Brett Buck]

2/ Brett - I did not see what Al did before. We did not have access to literature from "west". We had only east sources and what Al does wasn't published there. We saw only few WCh winners like Stiletto and Juno. First access to sources from west I had when I went work to Germany and I had access to Compuserve. So it was not "copy" of his work, may be that was reason why I did not try to improve his airfoil, I took NACA 0018 instead. However I saw attempts to do that before, so it was not from "my" head. I saw such solutions on another local models (for example also some models from Ukraine had round flap hinge line and they use it until now) and also opposite unsuccessful attempts and I had also Juno which had airfoiled flaps also matching upper surface angle when deflected. I knew what is the point here and I had chance to test it on simulator, so I did it. Al need test it real, I had chance to do it digitally.

  I figured there was a good chance you hadn't seen it before, therefore you invented the same thing for the same reason. That happens a lot - I may have "invented" several model rocket (spacemodeling) designs that others also invented, because the same problem leads to the same solution.  I know that Larry Renger and several others all invented particular things in model rocketry at nearly the same time.  So no slight was intended or implied.

   Have you actually seen his article now?  It was remarkably advanced for the time, when a lot of "airplane design" was taking the wing and tail parts out of a Green Box Nobler and putting a "2x4 with a rocket fin" fuselage on it. It was well-executed, but involved making a *large number* of full built-up stunt wings, I think all built up and fully-sheeted!

   Al actually had another (self-imposed) limitation - he wanted to keep the LE radius down for appearance reasons on his semi-scale airplanes. He may have got it in his head because his is Mr. F-51 in real life,  which of course famously uses a laminar-flow airfoil. Be aware also that he used his own personal definition of percent thickness that didn't include the flaps.

    I never even thought about too much that until I flew a few airplanes that were, essentially, the opposite, a dead straight line from the TE forward to near the high point. They all had astronomical control forces, and even a little bit of surface curvature seemed to be make that go away completely - even when it was not nearly enough to fair into the flaps when deflected. Part of it is that we don't deflect the flaps nearly as far as Al thought he was, and couldn't, because there's nowhere near enough line tension to crank it over that far.

     Brett

   

   

   

   

[Igor Burger]

Yes, sure, when I saw there is something like Pampa and SN, I ordered many back years of SN and I saw what you are doin on you side of work ...  not necessary to reinvent everything 

[PJ Rowland]

Its all relative at the end of the day.

Igor pretty much described the same effect " stability around deflection" Ive always advocated that the effect is felt during manouvers.
Igor and I had a LONG conversation about the effectivness of VGs vs Zigzag strips he uses. I would guess that having 80 + deviations into the airflow would have some effect on stabalisation of the flow to be more linear when flap deflects. I just found you could be really specific with the placement and height and having just 1 pair made a signifigant improvement.

Its personal choice. But talking specifically about airfoils I found that it wasnt until I physically had the Max
Bee plans that I was able to superimpose the 2 airfoils over eachother and other than length they were virtually identical.

It never made sense to me why anyone would have a straight line airfoil nobler style.. not to mention large flaps...
Control load deflection is catastrophic at best..

[Matt Piatkowski]

Hello,
Thank you everyone for your input.
Please see the attached summary of this thread.
Your suggestions, opinions, and friendly critique are, as always, welcome.
Regards, Stay Safe,
M