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  1. #1

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    Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    It's a stock Integral with a counter rotating drive swinging a pair of 22 X 18 handmade (by Mike Gaishin ...) carbon fiber props. The motor is a stock Hacker C50-14XL.

    I started working on the design back in November of last year, and with the help of Mike and Andy Gaishin of Gaishin Manufacturing doing all of the fabrication, I've finally got it in the air.

    I first flew it last Thursday for three quick flights, and I got another three quick flights in on Saturday afternoon after the Jimmy Hubbard Memorial Contest in Chicago. All during those six flights I was trying to get the right mixes in for knife edge, and downlines, but I was still struggling with my vertical uplines. They seemed okay, but the plane wasn't locked in like I'm used to with my Integral.

    So last night I added 0.5 degrees of down thrust and flew it again this evening, and it was like throwing a switch. All of a sudden it was absolutely perfect! The uplines are now locked in like the plane is climbing a ladder and the downlines are plumb line straight.

    I am absolutely over the moon. Right now it's flying exactly like I hoped it would fly but better because it seems there are additional benefits that I didn't anticipate.

    A point by point summary of flight performance is as follows:

    1/.. The double prop setup generates a huge braking effect when the throttle is at idle, so the plane flies at the same speed regardless of whether it's climbing vertically up, dropping vertically down, doing an eight point roll, or flying over the top of an avalanche.

    2/.. This constant speed characteristic makes snap rolls much easier to do, because the plane always snaps in exactly the same way, with exactly the same roll rate.

    3/.. For some reason, I had to cut my rudder travel by more than 30% because it was way too sensitive. I haven't figured this one out yet.

    4/.. The rolling performance is considerably improved over my other Integral, (even though that rolling performance was pretty good to begin with ...) and requires almost no rudder to maintain altitude. This is going to significantly improve my half reverse cuban with 2 of 2, my eight point roll, and my 2 of 2 reversed.

    5/.. Stall turns are much easier and more predictable because now it's possible to let the plane slow down until it just hangs on the prop and then pinwheel it around with rudder without having the wings twist out of plane. This makes it much easier to do a perfect figure M.

    6/.. The motor braking effect lets me do a perfect spin entry even without any headwind.

    7/.. The motor braking effect also means that I need to fly it in under power when I'm landing, even with no headwind. Fortunately deadsticks are rare with electric.

    8/.. Takeoffs are much easier, because there are no motor torque effects that need correcting. Now I can take off at full power and fly out perfectly straight.

    9/.. Loop tracking is the same right side up as inverted. Now all I use the rudder for is to gently nudge the plane either to the left or right. At no time do I have to hold any constant stick pressure.

    I checked the noise at 9 ft, and I measured 92db. On the ground it doesn't sound much different from my hacker C50-14XL with a 21X14 APC prop, but as soon as it leaves the ground you can hear a syncopating rhythm as the prop blades pass each other. It doesn't sound loud, just different.

    Right now I am using about 3000 mah for the current AMA Masters pattern. If this holds up for windy days, I might consider switching from the 5350 mah packs that I use now to 4350 mah packs.
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  2. #2
    DaveL322's Avatar
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Brenner,

    Can't wait to see this at the NATs.

    I'd say #s 3, 4, 5, 8, and 9 are improved due minimal (if any) gyroscopics and minimal (if any) spiral airflow over the tail surfaces.

    Amps and RPM? 3000 mah is definitely low for Masters. Are you still flying the same style as you did in 2009? Which was quite large and fast, at least the round I judged on Site 1

    Regards,
    Regards,

    Dave Lockhart
    Team JR Americas, Thunder Power, Castle Creations, F3A Unlimited, NeuMotors, Team Contra, Central Hobbies, Tech Aero

  3. #3

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

    Hey Dave,

    Rpm is little hard to measure because of the double props, but if I divide the readings I get by a factor of two, then I'm measuring 3750 rpm, which is pretty much what I predicted.

    With a fresh pack I'm drawing 69 amps, and 2450 Watts.

    3000 mah is for a day without a lot of wind. I'm reserving judgment until I fly it on a really windy day. My calculations are telling me that it should draw exactly the same mah from the pack as my C50-14XL does. If it's drawing any less, then it can only be due to an interaction between the front and rear props because I didn't include any of these effects in my calculations.

    And yes, I'm still flying the same style as last year, but only with my old Integral. With this new Integral I'm able to fly much closer in, due in part to the constant speed characteristics, and a slower flight speed. It's much more relaxing to fly this way. I have a much better view of what the plane is doing, and much more time to react to it.

    Also, I've set the motor up with zero degrees right thrust, and only 0.5 degrees of down thrust. The stab is set at zero degrees, and the wing is set at 0.5 degrees.

  4. #4

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

    Really neat!
    I've always liked the idea, but wasn't sure that the AXI? 2-motor setup was light enough.
    You must have it geared down to swing 2 much bigger props - gear ratio and rpm? What drove you to choose those props?
    How much does the extra drive/gearing weigh?
    Nice job!

    Dan

  5. #5

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

    Great work! I am very interested in the contra-rotating prop system for pattern but i don't quite understand how it works. Can you please post some images of the prop gearing system or a schematic drawing to explain how it works?
    Thanks.

  6. #6

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

    Brenner,

    That really looks great, my dad said it was very cool to see fly in Chicago. I wish I could have been out there to see it. Looks like mike did a really nice job on the carbon props and overall system. For those that havnt seen the machining and design of this gearbox is very amazing!

    Andrew

  7. #7

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

    The rpm of the props are 3750 rpm. The gear ratio is 9.8:1. I chose the 22 inch diameter prop because I wanted to swing as large a diameter prop as I could to maximize propeller efficiency, and I chose 18 inches of pitch because I was trading off reduced propeller efficiency at low speeds versus straight line flight speed.

    Based on my initial flight tests it looks like the 22X18 prop is working well, but there are fewer problems at low speeds than I anticipated, which is probably due to the fact that the front prop speeds the air up before it enters the blades of the second prop, so even if the front prop blades are stalled, the rear prop blades aren't. Based on this I think I could increase pitch up to 20 inches and beyond, and still not have problems at low speed.

    Comparing system weights isn't straight forward because I'm removing the stock Hacker gearcase, and the stock spinner, and replacing them with a new spinner/gearcase that's integrated into a single assembly, and then I'm adding a second prop.

    However, what I can say is that the Integral with the complete contra rotating system and the same flight pack, came out two ounces heavier than my old Integral with the stock Hacker C50-14XL, and a single 21X14 APC prop.
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  8. #8

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

    Hey Andrew,

    Mike was really inspired when he saw the quality of your carbon fiber props in Kentucky. Based on that he changed his whole approach to making the props, and now he's able to make props that have exactly the arfoil I wanted, and with the same sharp trailing edges that you get with APC props.

    I'm very impressed with what he's accomplished. It took a lot of work on his part, and I know because he had me polishing molds before he layed the first props up. (my arms are still tired ...) My job was to design everything, and then do exactly what Mike tells me to do in order to help him build everything.

  9. #9

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

    Very nice!

    Any pics of the gearbox? The ring gear housing / integrated rear spinner section is really neat. Would love to see how you attached the unit to the motor.

    Do you plan to market the unit?
    Earl

  10. #10

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

    Here are some pictures from the Pro-Engineer solid model that I used to design the unit with.

    We are to prepared to market the unit if there is enough interest, but the pricing is highly dependent on the level of interest, because for small quantities most of the cost is due to CNC setup time. If the interest is high then we can consider making some tooling and fixtures that would have the potential to bring the price down considerably.
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  11. #11
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    I want One of this device!
    Keep us tuned please I very interested because no way to buy an efactor system
    Best regards.
    Philippe
    P-47 Thunderbolt Brotherhood #122

  12. #12

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

    Hi Brenner,

    What is your indicative pricing at the moment?

    Cheers
    Jason.

  13. #13

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

    Brenner it has the potential to bea game changer like I told you.
    The combination of your engineering prowess and Mike Gaishin's tool and die expertiseandmanufacturing capabilities is what will make this work.
    Now I have to scheme even harder to beat you at the contests. Your tough man!
    All the best with this unit and I really look forward to seeing it in competition. Mike Mueller
    Mike Mueller
    F3AUnlimited.com and Gator-RC Products
    1800 591 2875
    mikemueller@F3AUnlimited.com
    Team JR America

  14. #14

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

    Any chance it could be made to fit on a Neu F3A?
    Team JR

  15. #15

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

    Hey Jason,

    I'm really loathe to mention a specific number right now because we haven't worked out any formal pricing since we have no idea of what the demand for something like this would be. I personally would like to get the price as low as possible to get the technology within reach of the average flyer, but Mike is concerned (and rightly so ...) that the potential market is too small for it make sense for us to spend any money on tooling or fixtures that would bring the price down.

    So right now we are going to focus on exploring and proving out the theoretical benefits through flight testing, etc. We figure this should be easy to prove one way or another, because everyone knows how well I fly and how well I do against competition, and if I can't improve my scores then the Contra is not much more than an interesting toy, but if my scores do improve, we'll have to move forward with plans to make the technology available to everyone.

    As far as fitting on to a Neu motor is concerned, I'm not familiar with design of the Neu, but I can't imagine why it couldn't be fitted with a Contra drive.

  16. #16
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    I wonder if the Contra driver can work with any f3a outrunner motors. Thanks.
    Where facts are few, experts are many.
    Perfection is God\'\'\'\'s business.

  17. #17

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

    The problem with fitting a Contra Drive to an outrunner motor is that it would be much heavier than a similar system that uses an inrunner motor. This is because inrunners already use a planetary reduction gearbox, and this gearbox can just be swapped out which minimizes the weight increase.

    If weight is not a consideration then it could be done. Also, if an outrunner was spefically designed for the application, then maybe then it would be more practical.

  18. #18
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes


    ORIGINAL: nonstoprc

    I wonder if the Contra driver can work with any f3a outrunner motors. Thanks.
    Certainly wouldn't work with the current 9.8:1 gearing. The direct drive outrunners are designed to run 5500 - 7000 RPM, while the C50-14XL being used by Brenner is designed to run through a gearbox.

    Regards,
    Regards,

    Dave Lockhart
    Team JR Americas, Thunder Power, Castle Creations, F3A Unlimited, NeuMotors, Team Contra, Central Hobbies, Tech Aero

  19. #19

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

    Dave is right. The fundamental problem with outrunners is that they spin too slowly. You would have to design a special type of outrunner that spun faster, but if you go to all that trouble it's a lot easier to just use an existing inrunner.

  20. #20

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

    Hi
    I certainly would be interested in getting one. but if you are concerned that there is not a big enough market to justify tooling up to manufacture it then perhaps you could offer the plans and the parts you already have moulding for, leaving it up to the individual to get the machined parts done etc.. This approach seems to work well for the home build turbine guys and should work here also.

    Mike

  21. #21

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

    I would certainly be very happy for getting one of those niece thing between my fingers

  22. #22

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

    Hey Mike,

    Interesting idea, but with this approach I'd be concerned that the individual cost would turn out to be very expensive if people have to go out and pay for setup, and CNC machine time for single parts. People who already have access to CNC equipment would benefit, but I don't think most people have this kind of access.

    The problem is that there are a lot of parts involved, and most of them are not straight forward to program. Mike and Andy spent a lot time trying to figure out how to make these parts. Wherever possible they tried to minimize changing setups for each part because if you have to unchuck, or unclamp a part in order to turn it around you lose accuracy between the machining you do on one side, and the machining you do on the other side. Also, there are already quite a few fixtures made already because they were necessary in order to be able to make the parts.

    The kind of tooling we are talking about that would lower the cost is stuff like making dies that will let us make the ring gear, the planet gears, and the pinion gear out of powder metal instead of having to machine each gear tooth individually.

  23. #23
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    Brenner, that is quite a marvel to behold. I hope it pans out, in theory it should make for a quite neutral airframe.

    Pete
    Team YS, Team Airtronics
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  24. #24
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    RE: Contra Rotating Propeller Drive for f3a 2m Pattern Planes

    <meta charset="utf-8">Hello Brenner,

    I certainly would be interested in getting two of these for both my Hacker C50s..


    Regards,

    Roy

  25. #25

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

    Brenner,
    CONGRATULATIONS on the successful test flights. I am absolutely beside myself that I went back to the hotel early and missed the test flights. You know how very interested I was to see that baby in action.

    Having seen it in person and gotten the disassembled tour by the designer himself, I have to say it is one amazing piece of artwork! Very well designed and well thought out with easy maintenance and high performance in mind. And it is beautiful to boot.

    Great job Brenner

    And oh yeah, I am still on the list for at least one of those

    Anthony


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