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  1. #876
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

















    And last but not least a picture from the EC in France together with the Dutch Team Manager:




  2. #877

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Great pictures!

    The narrow fuselage on my Wind S Pro also works well with the Contra.

    Based on my experience with my Wind S Pro, my thinking is that a narrow fuselage allows the rudder fin to be more effective, whereas a large profile fuselage masks the rudder fin. which reduces it's effectiveness, and using a Contra Drive shows this effect up because straightening the airflow over the fuselage makes the the fuselage more effective as a lifting surface, which compensates for reduced side area. The net result is more lift from the fuselage, more yaw stability from the rudder fin, and reduced parasitic drag, which is no longer needed for controlling speed on downlines because of the increased braking that you get from the Contra.

    Brenner ...

  3. #878

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes


    ORIGINAL: Spark09

    Nice Br@m
    My dad did a nice Job covering the plane in the Spark scheme.

    This plane called the Indira is actually based on the little Miss Wind 50 wich I liked a lot but it's to small for serious F3A flying.
    We can't afford the big Oxai Miss Wind so we scaled up the 50 size Miss Wind.
    And after a few version this is the latest one.
    It is completely wood built with foam wings and a carbon motor cowl.
    Sorry there are no plans available.

    This design flies very well with the contra drive, it seems that the small fuselage works very well with the contra drive.
    I flew mine at the 2012 EC at Chateroux France and finished 47 this was my first EC.
    I modified my wings with winglets like the Wind S Pro GFK version the bubble tips these seem to work better than the flat ones used on the Oxai Citrin. I also have them on the tips of the stabilizer for rock solid flight in windy conditions.
    I also widened the TE of the rudder by almost 2 cm.

    This was a very nice project and we had lots of fun !
    The project started in the winter of 2010 there where 7 planes buildt. 1 crashed by a Emcotec DPSI switch failure.
    Building and designing was done by Harry Wever, me and my dad. I've done the test flights and tweaking until it was at it's best.
    The contra drive was the last and best upgrade for this plane it is a match made in heaven

    Hope Br@m will enjoy the plane as much as I do.

    I will post some nice pictures from the EC plane I took to France.



    Hi Spark09,

    What's your ready to fly weight?

    Regards,
    Jason.

  4. #879
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hi Jason,

    It is 4950 grams weighted on the FAI scale at the EC.

    I use TP 4400 batteries wich are 1010 grams.
    Wolfgang Matt was flying the new TP 4700 packs and they where 150 gram lighter than the TP 5000 batteries as he told us.



  5. #880

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes


    ORIGINAL: Brenner

    Great pictures!

    The narrow fuselage on my Wind S Pro also works well with the Contra.

    Based on my experience with my Wind S Pro, my thinking is that a narrow fuselage allows the rudder fin to be more effective, whereas a large profile fuselage masks the rudder fin. which reduces it's effectiveness, and using a Contra Drive shows this effect up because straightening the airflow over the fuselage makes the the fuselage more effective as a lifting surface, which compensates for reduced side area. The net result is more lift from the fuselage, more yaw stability from the rudder fin, and reduced parasitic drag, which is no longer needed for controlling speed on downlines because of the increased braking that you get from the Contra.

    Brenner ...
    Hi Brenner,
    I agree completely with your narrow fuz,, observation.
    A new design could be even more narrow/less wide ?? -
    I think a bulbous LE on the fin may also be an issue, as it may be 'masking' the rest of the fin/rudder.
    I hope Bryan Hebert is tuned in to all the contributions here.

    Brian

  6. #881

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hi Spark09,
    You wrote ;
    Quote;
    ' I modified my wings with winglets like the Wind S Pro GFK version the bubble tips these seem to work better than the flat ones used on the Oxai Citrin. I also have them on the tips of the stabilizer for rock solid flight in windy conditions.
    I also widened the TE of the rudder by almost 2 cm. '

    I wonder is the 'bubble' actually giving a subtle 'toe in' effect ??
    It is the only reason that I can see for it being noticeably better.
    Interesting !!?

    Brian

  7. #882

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes


    ORIGINAL: serious power

    Hi Spark09,
    You wrote ;
    Quote;
    '....

    I wonder is the 'bubble' actually giving a subtle 'toe in' effect ??
    It is the only reason that I can see for it being noticeably better.
    Interesting !!?

    Brian
    I like your thought - it makes sense. Has anyone ever tried toe in? I recall Dave Snow trying a bunch of stuff.

    Jim O

  8. #883
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Yes the bubble version of the winglets give me a steadier flight.
    I personally think that it has something to do with the aerodynamics since the bubble version is smoother compared to the regular thin fins wich are noticable nervous during turbulent weather.

    I tried different styles with the thin fins, toe in and out and straight.
    Also experimented with height and dept.
    Because I fly a bipe it is more work and harder to notice the differences.

    The bubbles on the stabilizer give me a big difference in loops the tail of the plane tracks better.

    I would also like to try a bunch of small fins all over the wing.
    The Mitsubishi Evo 9 inspired me, they say the car is more stable at high speeds.

    Another experiment i would like to try is make a 2m F3A plane fly like a indoor F3P plane by creating more drag with brakes on the wings.

    Just some thoughts



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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hi Spark,
    I see a bigger rudder flair in the pic,, with the bubbles.
    Which did you do first.
    Did you try toe in on the tail with no flair.
    Do you have a record of the sequence of changes and the effects they had - or - maybe you made several changes at the same time.

    Brian

  10. #885
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    I made changes time by time, i started with the winglets the thin ones tries toe in, toe out and straight.
    After several flights i made the bubble version for better handling in windy conditions.
    When that was right i added the rudder flair for more drag and the plane heads better.
    It is always better to make a few flights with a new modification with different wind conditions.

    I'm currently trying the "zero gravity" flying method but that takes a few flights to get used to.
    The first flight where terrible !

  11. #886

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    What's "zero gravity" flying?

  12. #887

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Same amount of back stick pressure and forward stick pressure for upright and inverted flight straight flight I think.

  13. #888

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    hey !

    im also flying the contra drive and as i maybe use a different setup, brenner asked me to publish here. so here my setup :

    - im using a thunder power 8S lipo with 4350mAh
    - hacker C-50 competition 11winder with the hacker controler
    - gear ratio 10,33 x 1
    - front prop 22" x 20" rounded tips
    - rear prop 21" x 22" rounded tips and cutted of 1" from the 22" diameter

    right now im flying the drive, wich is running very smooth and silent, in my oxai beryll08. of course i needed some test flights to find my setup and im still playing with my center of gravity and the angle of incidence.
    first i had the 22" x 20" props front and rear, but this had been a lil bit too little power for strong wind conditions. instead of changing the gear ratio, brenner recommended to change the rear prop for 22" x 22", bcs mainly the rear prop gives more speed horizontal and power. so as i made the first flights with this new prop setup i just can confirm that this is true. now i have exactly the power i need for all conditions. i also must to say that we, here in germany, fly more slow (specialy me ;-) im flying slowmotion), so the setup is not made for full speed. of course i could change for another ratio and maybe fly a 22"x22" in front too, but is not my style.
    my fuel consumption is now between 3000 and 3500mAh max. before, with single prop, was always about 4000 and more! with the 22" x 20" rear prop was 2800 up to 3200mAh. so far i dont have any temp. problems even not with outside temp. of 37°C!
    the flight characteristics of my beryll changed so much with the contra drive that i can not believe. its a new airplane! everything is more easy now to controll, i have so much less work, the rudder is much sensible and effective so that the rolls gets amasing, like the turns as well. what realy surprised me is that the angle of attack of the fuselage during rolls is now nearly 0 !
    to controll the constant speed is very easy now, specialy bcs i can adjust the brake very sensitively. of course the effect of the brake is much more than with single prop before. about all im totaly happy with this change for the contra drive and just can recommend this for everybody! the support and service from brenner is amasing and professionel.
    bye, bye,

    dominik

  14. #889

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hey Domink,

    Thanks for sharing information about your unique setup. Your setup is the only one that I know of that uses an 8s pack, but Dave Snow tells me that you have inspired him to try this setup as well, so hopefully we will see another 8s setup here in the Chicago area in the near future.

    On another matter, Mike Gaishin has been doing some experimentation with his Contra powered Integer. (Mike's version of the Integral..) Mike originally designed this plane with significantly more fuselage side area than is typical, but he left the area of the rudder fin similar to existing designs, and with the Contra Drive, this resulted in significant yaw instability during high speed flight.

    Mike solved this stability problem by flairing his rudder. This was a very effective fix, but now he is planning for the next version that he will build this winter, and so he has done some experimentation to see how much area he needs to add to the rudder fin so that he can stop using the flared rudder. (which adds parasitic drag ..)

    What he has done was progressively increase the width of his original rudder until the plane was completely stable in yaw without having to use the flaired rudder. The attached pictures show how much he had to increase the rudder size. The flaired rudder is also show for comparision purposes.

    Mike now reports that the wider, unflaired rudder is actually more stable than the flaired rudder, so when redesigns his plane he will take the extra area and add it to the front of the rudder fin. He's going to add about 15 square inches to a rudder fin that has the same area now as the current integral rudder fin.

    Brenner ...
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  15. #890

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hi Brenner,

    I see you have a website now http://www.contradrive.com

    Looks like the model on the index page is on fire!

    Cheers,
    Jason.

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Well, sort of.

    It's kinda under construction right now. As soon as the contest season ends, I plan on getting it going properly...

    Brenner

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    And greatly reduced frontal/canopy side area!

    It looked very solid flying at the Nats.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Bob

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    hey!
    the weight difference to a 10S lipo setup is between 350 and 400 gramm !!! for f3a pattern class this is a lot and of course the aircraft handling changes a lil bit. also every aircraft have a different way to react on a contra prop system and this less weight. in the end must make a test bcs before you never know and is very dependent of the pilots flight style. but i can say that with me and my oxai beryll08 (4,6kg) works amasing. now i will build up a oxai axiome and see if works there in the same way or maybe even better. i can not imagine but as the base aircraft is better...............can be.
    in the winter i will also add the aerodynamik modifikation package of the asyuler eternal on my beryll, and im shure that than i will reach the highest level of flight performance i ever had on a single wing f3a plane! :-)
    nice flights, bye, bye,

    dominik

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hi Brenner,
    I think replacing the flare with more area amounts to the same thing both in terms of the effectiveness and the resulting drag.
    Relative placement of side area needs to be considered in this.
    eg; if one likes a 27% CG it should also be at 27% of the side area or as close as is possible. The fuz,, is the flying surface in knife=edge and during rolls etc.
    Also I think the blunt fin LE in the pic,, may be playing a negative role.
    I'm not saying it should be razor sharp - just a nice section in proportion to it's size.
    Look forward to the web-site.

    Brian

  20. #895

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hey Brian,

    Thanks for the advice. I'll pass it on to Mike.

    Brenner ...

  21. #896

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hi Brian I tried extending the rudder flare to about 3/4 of the rudder area and my nuance flew really well with it. The only negative change was in knife edge the plane pushed dramatically towards the bottom of the model. When I took it off on the next flight knife edge was quite straight. So it's not for me at the moment.
    Paul Houlihan

  22. #897
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    I'm guessing Paul but I think your extra flare moved the CG back a little and that is why your model pitched to the belly.

    Cheers,

    Malcolm

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hi Malcolm, I used 2 pieces of stiff cardboard to make the flair and after your post weighed them to discover they are heavier than I would have thought. 25 grams which would of course affect CG. I will balance model better for next trial. Isn't cardboard heavy!
    Paul Houlihan

  24. #899

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    The flare of the rudder actually enhances the effectiveness of the surface by helping to keep flow attached when deflected. It also creates a drag rise aft of the trailing edge of the rudder, creating a stabilizing force moment.
    Doug Cronkhite

  25. #900

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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Hi Doug,
    I have to say that I agree completely - based on observation (I'm not up on aerodynamics).
    I have just increased ,slightly, the flair on my Midrex. I removed a small area at the rear bottom of the rudder while doing so. I did this to get a more perpendicular TE as with a pronounced flair there is a pitch input if the rudder TE is is not square to the datum. Hinge line may also be an issue. A big flair will show these issues.
    Anyway the result of the bigger flair is all good.
    Great yaw stability and incredible rudder power.
    I am also playing with turbulator strips- just started to do so - we'll see.
    I'm sure that with enough area added to the rudder instead of flair a similar result can be attained for straight line flying.
    The other requirements of the fin/rudder need to be considered though.

    Brian


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