F1A turbulation

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    posting this from a email message:

    Hi Jim and fellow FAI fliers

    I was wondering if you have any detailed info on the M&K extra long wing. Do they for instance do anything interesting re turbulation and invigorators?

    As an open series of questions:
    Should turbs and invigs alter as the wing chord narrows from 145 mm towards the tip 75 mm?

    I appreciate that I ought to buy several left wings, cover each one differently and then try each one out against the right hand one to see which one works better.

    I am generally interested in improving dead air performance, as it is a just a bit more of a challenge than the grunting and bunting with a thermal hooker that locks into lift and goes out of sight.

    Currently it is blowing 32 -45 mph over the Easter hols flying comp, so even my heavy weather Flying Anvil F1A is staying in its box.




    My rely to Nick:


    What I know / seen of M&K wings. Nothing special– standard turb at ~7%. On this last trip, they tried the medical “sponge” tape for the turbulator– when asked how it worked for the first time at MaxMex, the answer was OK but need more time. They have studied and spent time developing the tip airfoil on the flapper or VarCanber wing as Sclosberger calls it. On the standard long and extra long, they have gone to zero warp tips until approximately the the outboard 5-6 inches are washed out .2- .25. Also remember that back in 1991, the debute of thier classic long model, they flew winglets for a short time.

    My early mentor, Ken Phair did his turb experiment by trimming the model off a low hill to glide straight away. He then removed the turbulator from one wing to see the effect. I’m interested with what you do with left wings– ?

    Rene Limberger is flying a Stamov short (i think its a short) with no turbulators and says it’s better.

    Thermals, JIM


    Hello Guys

    Just reading some information on turbulation. This guy claims that multiple aft turbulators help also.

    Now who is it that I thought had aft turbulators on the wing at Maxmen this year?

    I will be doing some studying of this on flying models this summer.

    The other question was the England flyers recommended covering the top of the wing with Ikarex (rip stop nylon) and the lower with plastic. Has anyone got any numbers on this?

    How come the vultures, wood storks, and pelicans are better designed for more efficient low speed gliding? Is there something about the feather structure and wing tip treatment that outdoes our 2 dimensional thinking?

    I could not keep up with the climb of a wood stork in a thermal with my RC sailplane. I don’t think my best F1A would either!

    George Reinhart

    Q. Why can’t my glider keep up?
    A. Onboard autopilot coupled to the most accurate and sensitive variometer devised by mother nature and a multi-million year development history.
    Best advice I ever got when flying full size gliders was “Look for Mr. Boozard, he knows where the best thermals are”.



    Hello Pete

    Well the variometer had no affect, because we were flying in the same air in close proximity.

    My thinking is that the designer of these living models flys his right off the board in perfect trim and with superior materials.

    The feather structure is naturally turbulated, and the wing tips are fitted with low drag anti-vortex devices. Flying with lower aspect ratios, these wings are more efficient (less drag, more lift) than our best designs. The feather quills are flow straighteners and provide strength for a very thin airfoil. Adjustable dihedral is also a nice feature for varying the glide circle. Babenko and Verbitsky folders have nothing over these variable planforms for maximizing dive speed, and fitted with a geared engine would make for an amazing climb.

    Now how can we use some of these features with our primitive modeling materials?

    George Reinhart

    I beg to differ from personal experience, but I will leave it at that.
    I might mention also the infinitely variable, mission adaptive airframe which is also coupled to the vario/autopilot combination. Then too, there is the difference in reaction time, that is you on the ground reacting to what you think you see the bird do and the bird already having made the required adjustment. I suspect the bird has had more practice as well.


    The bird does it for a living. Learn or die might be a good mooto for him.


    Per Findle, current F1A WC likes the top Icarus, lower smooth covering- too bad it’s just the opposite needed for puncture resistance. JIM

    George Reinhart

    That too, Dan.
    It might even be the decicing factor.


    Hello Jim

    Sorry to make this thread confusing!

    Actually having plastic on the bottom may be easier to puncture, but it is much easier to repair. The Ikarex is a bugger to repair when it gets punctured.

    Having heard that Per Findahl agrees with the English, or vise versa, I have a set of uncovered wings that I will make up with Ikarex on top, and Ultracote light (Oracover) on bottom, and I can swap out wings or go half and half to see if there is a detectible difference. Luckily I already have a set of the same wings covered in Ikarex.

    From 170 feet, I have not been able to get more than 215 seconds in still air with a light weight towline glider. 170 feet is 164 feet of line with a 6 foot reach and a good launch/release at the top, no zoom or bunt. F1A models only do about 180 with a similar launch.

    So a 5% improvement in performance with turbulation or other enhancements means another 10 seconds. It makes for a difficult attempt to check for improvements.

    So going at the other end of the spectrum, one end being gliding efficiency, the other additional launch height from bunt or other types of launches, how much is glide hurt by going to lower drag high speed airfoils for gaining additional altitude. Or is a flapper going to give you the best of both worlds if properly done?


    Sorry to disagree with you Dan. The vultures do not do it for a living! They float around for hours on end just enjoying the sport of flying. They ride the thermals down wind, and then return upwind to start all over again. Kind of like us flying free flight models.

    Once in awhile they get hungry and attend to business, but the rest of the time is all PLAY! Now if we could get the same ratio of pleasure to business!


    “The other question was the England flyers recommended covering the top of the wing with Ikarex”

    Guys can I gently remind you that the UK is made up of other parts than just England. It would be like me saying that all Americans are Texans – geddit ?

    I don’t know who originated the Icarex upper, Profilm Lite lower but Per was the first I heard about. It then appeared in England and rapidly moved to Scotland via Hardian’s Wall; a few others have tried it as well. I’ll share my experiences where I have a bit of time to write it up as I found some interesting orientation effects.


    Sorry for the delay, been busy at work but this is the covering story so far.

    A Brit flyer appeared with a F1A covered with Icarex on the top and Profilm Lite (Orcafilm ?) on the bottom. In discussion he said it flew better and in particular glided better close to the ground. I parked the idea in my mind and came back to it early in 2007 when I needed to recover models prior to the Odessa Champs. I decided to try the Icarex/Profilmlite method but intended to put the Icarex on at an angle as the Danes had been doing. But on the first model I made a mistake and cut one lot of Icarex at 45 degree and the other at 0 degrees. I didn’t think it would make much difference so I covered it like that but when I flew the model again the trim had changed in a couple of ways; first it launched and glided better but second the glide turn had changed.

    I mulled it over and figured that a) the covering had improved thing and b) the orientation of the Icarex had made an effect. I needed to experiment so I kept the 0 degree covering (inboard, right panel) and modified the left by recovering with a 30 degree Icarex orientation. The glide was different again ! Now I played with some design of experiments software which came up with a set of covering options to pursue and its estimate of the optimum. All in all it took many weeks of effort with a total of 6 recovers of the left hand panel. I plugged the numbers back into the software and it reconfirmed the best solution; it also suggested a worse case for all the orientation options I looked at. Finally I recovered the model with the worst orientation and flew it in calm air to test performance. I then recovered it with the best solution and flew it in similar conditions. I compared the altimeter traces for both launch height and glide performance; the latter ensuring I hadn’t caught any lift.

    All set I then recovered another 4 models the same way all before Odessa ! Sadly the downdraught in round 3 of the W/Cs didn’t give me a chance to beat Per who had only used the 0 degree Icarex orientation.

    More is yet to come as I think the optimum angle is different as the airflow tends to ‘curve’ towards the tips of models. So I am now working on a ‘distorted’ pattern of fibres by covering with defined slack.

    This is really exciting stuff !


    I held off replying to CHE’s last post because I spotted the date he posted it (April Fool’s Day). Not that the findings seemed implausible, but the amount of decent testing weather he alluded to, in Scotland of all places, surely (I thought) it would have to be a joke.

    The whole topic of turbulation I have found fascinating as long as I can remember. My late father, Low Speed Aerodynamics guru Mike Gaster (1955 F1C World Champ), and I ran some experiments many years ago using F1C sheet covered wings as guinea pigs. To cut a very long story short, the different types of turbulators we see in f/f models have different effects. A turb. very close to the leading edge only has an effect at high lift coefficient, a turb. positioned just aft of the wing high point seemed generally beneficial at all points except high CL, both types seem to cause an energisation of the boundary layer before it encounters the adverse pressure gradient over the aft of the wing, thus changing (hopefully improving) the separation behaviour of the airflow. Invigorators effect the growth and formation of laminar separation bubbles within the region of adverse pressure gradient, again changing the separation behaviour. I guess there are many ways to skin a cat.

    To answer a question near the top of this thread, I see no reason to change the position of invigorators towards the tip of a f/f wing.

    Now then, wing tip spillage, which causes flow on the underside to migrate out, and the flow on the top to migrate inwards – how does the orientation of fibres in the covering relate to this? – hmmmmm, I have some notes somewhere on the behaviour of flow over sharks, which apparently have a ‘ribletted’ skin, which turns out to have a very beneficial effect on the growth/formation of Tolmien/Schlicting waves (precursors to separation). Yeah, I need to find those notes.



    I don’t think sharks are as applicable as raptors.

    The texture of a bird feather is probably superior to any man made material for low speed airfoil application. Then we have butterflys flying even slower with thin/flat plate technology.

    I have a bunch of wings to experiment with this summer, and I wonder if anything can achieve a 5% improvement over standard current F1A, F1B, F1C airfoils?

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