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  1. #51
    The_Mongrel's Avatar
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    RE: Twin motor aircraft and Counter rotating props

    OK... Let me clear a few things up!!

    Firstly... both props on my plane are standard 10x8 slow fly props and they spin in the same direction.

    SWIFT - You can not be serious when you suggest turning one prop around and reverse the motor surely? Have you even tried this? Do you know what happens? Well I can assure you that I have!! I did this before I even posted this thread. In fact - I did quite some time ago when I was not educated on this hobby. If you have not done this, let me give you a step by step.

    Reversing the motor will make the prop spin in the opposite direction
    This will cause it to push air in a FORWARD direction.
    Reversing the prop will see it continue to PUSH AIR FORWARD - although not as powerful as before.

    If you get a conventional prop and on a conventional motor and reverse it, your plane will still fly!! Just not as well as the performance of the prop will reduce the performance of your aircraft. I have since discovered that my problem is not the fact that I have motors that are rotating in the same direction. My problem is there is no water rudder.

    My suggestion is that you go and get one of your aircraft and reverse the prop and see the affect first hand, before making further comment on this thread.

    EDIT - I would also like to add that SWIFT, you obviously have not even taken the time to read my posts correctly - You refer to photo of my plane, but as I posted, that is NOT a picture of MY PLANE!!!

    Regards
    -J
    Crashing is such sweet sorrow!

  2. #52
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: Tall Paul

    Swift, you really oughta look AT the hardware you talk so much about but obviously have never used.
    A pusher prop mounted on a tractor motor which is rotating CW when viewed from the front is no different than a normal prop on a tractor motor rotating CCW, viewed from the front.
    Also, the problem the OP has isn't "torque", it's lack of steering authority in the water.
    That needs either a water rudder.. simplest.. or differential steering with the motors.
    Changing to a pusher prop and reversing the motor rotation won't have any effect on the water steering problem.
    With glow motors the direction of rotation can't be changed, so pusher props are needed in pusher installations.
    You are quit right. I did some more experimenting on the weekend. I have NO problem in flight. She does require a bit of trim to the right to keep her straight, but I have a feeling it is caused by a misaligned vertical stabaliser. I glued a piece of Depron onto the rudder that extends down and makes contact with the water when I apply some power. It is probably not long enough, but it did solve my problem.

    I would love to setup differential steering using the motors, but I am not sure if my DX7 will support it... need to do a bit more research.

    Thanks for the input.
    -J
    Crashing is such sweet sorrow!

  3. #53

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    RE: Twin motor aircraft and Counter rotating props

    I've done differential steering with twins using a Futaba 6EXA transmitter, which has a knob useable for mixing the two motors.
    Cumbersome and not really good for ground handling, I used it to see how rudder authority was altered with one motor off.
    On the DX-7, you may be able to get a mix with the throttle channels and the rudder stick, for water manuvering.
    Sparky Paul
    http://www.angelfire.com/indie/aerostuff

  4. #54
    The_Mongrel's Avatar
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: Tall Paul

    I've done differential steering with twins using a Futaba 6EXA transmitter, which has a knob useable for mixing the two motors.
    Cumbersome and not really good for ground handling, I used it to see how rudder authority was altered with one motor off.
    On the DX-7, you may be able to get a mix with the throttle channels and the rudder stick, for water manuvering.
    Hmmm.. I am just not sure how to run two motors on two channels. I gather I would need to ESC? Would that be right?

    Might try and stick with the idea of a better water rudder as her flying characteristics are fine.

    Cheers mate
    -J
    Crashing is such sweet sorrow!

  5. #55
    Moderator Matt Kirsch's Avatar
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    RE: Twin motor aircraft and Counter rotating props

    You'd need a separate ESC for each motor, but if you've got brushless motors, you must have two ESCs already to have reliable operation. This is how I think it should work, as I've never set one up.

    To start off, you'd connect each ESC to a separate channel on the receiver, left to the normal throttle, and right to another channel, like channel 7.

    Next, you'd program a mix into the transmitter so that channel 7 is a slave to the throttle channel to make both motors operate in unison. [ I have done this on a twin, and it works well ]

    Then, you'd program a second mix into the transmitter so that the throttle channel is mixed to rudder. Left rudder will reduce the throttle, right rudder increases the throttle.

    Finally, a third mix for channel 7 to rudder. Right rudder will reduce the channel 7 and left rudder will increase it.

    You'll need to play with the numbers to get it working.

  6. #56
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    RE: Twin motor aircraft and Counter rotating props

    Matt,

    I can see how this would work, and in fact, after doing a bit of reading, I think the DX7 can handle it. I am about to upgrade the bird to brushless anyway, and I the RX I am using has an AUX channel that I can mix the crap out of.

    Hmmm... even if it is not the ideal solution, would sure be a great learning experience to set it up and get it working.

    Thanks a bunch... I just might give that a whirl - just for the hell of it!

    Cheers
    -J
    Crashing is such sweet sorrow!

  7. #57
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    RE: Twin motor aircraft and Counter rotating props

    The TwinSync from RC Showcase makes this very easy to program. Not cheap but an outstanding piece of technology.
    ...and then the unthinkable happened!

  8. #58
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    RE: Twin motor aircraft and Counter rotating props

    I ran Tall Paul's comment past a pilot with over 20 years of experience with both gas and electric. He said you've got to be kidding when I told him Tall Paul thinks a Zagi Maxx 5x5 prop is a conventional prop and not a pusher prop. He said maybe he's a kid with AirHogs or just a troublemaker and best to leave him alone.

    Bye, bye
    Never Give Up, Never Slow Down, Never Grow Old, and Never Ever Die Young

  9. #59
    The_Mongrel's Avatar
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    RE: Twin motor aircraft and Counter rotating props

    Swift - Mate - You have got to be kidding!! If you are not able to come here and post constructively, then we kindly request that you not post at all.

    Thank you
    -J
    Crashing is such sweet sorrow!

  10. #60

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    RE: Twin motor aircraft and Counter rotating props

    Conventional prop and pusher prop are both the same. Just depends whether it's on the front of the wing or the back.
    Gord
    Dreamed I was a muffler. Woke up exhausted.

  11. #61
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: Flypaper 2

    Conventional prop and pusher prop are both the same. Just depends whether it's on the front of the wing or the back.
    Correct in the fact that they will move the aircraft in the same direction. However the props themselves are very different... Opposite in fact. The images posted above by Tall Paul highlight this perfectly.

    But yes - the outcome will be different depending on where you mount them.

    Cheers
    -J
    Crashing is such sweet sorrow!

  12. #62

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    RE: Twin motor aircraft and Counter rotating props

    I think the big mixup is conventional pitch and reverse pitch prop. You can take a Zagi,Gunther prop and use it on the back as a pusher, then take the motor off, reverse the motor direction by reversing the wires on the brush motor, then mount the motor on the front with the same prop as a tractor.
    Gord
    Dreamed I was a muffler. Woke up exhausted.

  13. #63
    The_Mongrel's Avatar
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: Flypaper 2

    I think the big mixup is conventional pitch and reverse pitch prop. You can take a Zagi,Gunther prop and use it on the back as a pusher, then take the motor off, reverse the motor direction by reversing the wires on the brush motor, then mount the motor on the front with the same prop as a tractor.
    A reverse pitch prop and a pusher prop, are the same thing to my knowledge... but maybe someone else will chime in.

    Like any prop, if you spin the motor in the other direction, it will push air in the other direction. So if you put a pusher prop on the front, and you spin the motor in the opposite direction the prop will "pull". The same as you can mount a conventional prop on the rear (as I have done with my EZ Star) - As long as the prop still faces the right direction, it will work like a pusher.

    however, there were comments made hear earlier that by turning a prop around and reversing the motor, you can get a conventional prop to work in a counter rotating fashion, and that is just not right.

    If you put a conventional prop on a motor spinning in the opposite direction, you are still going to get air pushing forward - not pulling back.

    Cheers
    -J
    Crashing is such sweet sorrow!

  14. #64
    GaGeeBees's Avatar
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: Swift427

    maybe he's a kid with AirHogs or just a troublemaker and best to leave him alone.
    It's funny, I was thinking the very same thing... about Swift427.
    ...and then the unthinkable happened!

  15. #65
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: GaGeeBees

    It's funny, I was thinking the very same thing... about Swift427.
    Hehe Yep! I just don't know what his problem is!

    Anyways... Thanks to all that offered their help. I now have a few options to try and will hopefully post back the results, but it may be some time.

    Cheers
    -J
    Crashing is such sweet sorrow!

  16. #66

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    RE: Twin motor aircraft and Counter rotating props

    Best of flying to You. Here is another possible source for 10x4.5 props
    http://www.rctoys.com/rc-toys-and-pa...ROPELLERS.html



    Counter-rotating props are almost always arranged so that the propeller blades move inboard at the top of their arc, and outboard at the bottom. So as you stand in front of the airplane the left engine rotates clockwise and the right rotates counter-clockwise. When the airplane is at a steep angle of attack the descending blade takes a slightly larger "bite" of air than the rising blade, producing slightly greater thrust on that side of the prop arc. Having the props both swing inboard at the tops of their arcs puts the descending blade closest to the airplane centerline. The advantage there is that when one engine fails on takeoff or climb (when the airplane is at a high angle of attack), the center of thrust of the remaining engine is slightly closer to the centerline of the airplane than it would have otherwise been. The effect is not huge, but at critical phases it can make the difference between staying in control and less pleasant alternatives.

    The most notable exception to the inwards-at-the-top guideline for counter-rotating props is the P-38 which had the props rotating outward-at-the-top. Kelly Johnson and the rest of what became the Skunk Works gang originally developed the P-38 with conventional in-at-the-top counter-rotating props to make single-engine handling as benign as practical. The resulting propwash caused adverse buffeting of the tail, so they reversed both engines to unconventional out-at-the-top rotation, which fixed the buffeting at the expense of engine-out handling. That involved tradeoffs that made pilots' lives more dangerous when an engine failed, but they were carefully evaluated tradeoffs.

    Hope these excerpts by Don Stackhouse are of interest.
    http://www.djaerotech.com/

  17. #67
    The_Mongrel's Avatar
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    RE: Twin motor aircraft and Counter rotating props

    Hmmm Call me a cynic but have a look at this....

    AIR SCREW
    Posts: 1
    Joined: 3/31/2008
    From: Hudson, WI, USA
    Status: offline

    So this is his first post - and no introduction. Surely your first post is in a thread where you are either asking a question or have been invited by a friend!!

    Nice try Swift.
    Crashing is such sweet sorrow!

  18. #68

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    RE: Twin motor aircraft and Counter rotating props

    As Randy Jackson says, β€œHey Dog, Check it out.”

    Matt – 7th reply, page 1 – 3/25/08,
    What do you mean by "torque roll problems?"

    Nearly all full-scale, multi-engine prop planes have all their props spinning in the same direction, for simplicity in manufacturing and maintenance.

    Handling issues can be overcome with adequate vertical fin area, and adjusting the down/right thrust on each individual motor. A degree or two of down thrust on the starboard (right) engine will take a huge bite out of the plane's tendency to pitch up and/or roll to the left under power.

    A conventional engine will tend to roll a plane left and lift the nose when mounted square to the airframe due to these factors. Down and right thrust counteract these factors.
    Hughes Spruce Goose had four powerful engines on each wing with all 8 props spinning in the same direction. The Spruce Goose had a very large vertical fin to counteract the yaw from all 8 engines spinning in the same direction.

    β€œThe vertical tail on typical twins vs. typical single-engine aircraft tend to have two or three times more vertical tail than singles. The need for enough rudder authority to counteract the yawing problems with critical engine dead is what usually determines the vertical size for a multi-engined aircraft.” - Don Stackhouse

    β€œThe bottomline is that for a typical electric model, especially backyard type, counter-rotating props are usually not worth the trouble. If single-motor planes don’t need contra-rotating props on the same axis spinning in opposite directions to counteract P-factor and torque, a twin model of the same size and power will need counter-rotating props even less!” – Don Stackhouse


    Matt – 16th reply, page 1 – 3/26/08,

    That starboard motor appears to have some up and left thrust in it from the picture. It may be the cowling is on crooked, or an optical illusion. Up thrust and left thrust would explain the problems you are having.

    BTW, the Catalina's engines both rotate in the same direction on the full scale version.
    Can any one name even one twin engine civilian aircraft with counter-rotating props?

    If counter-rotating props aren’t necessary on a civilian aircraft why are they needed on a Catalina electric model. The Catalina is no WWII Lockheed P-38 fighter.

    The comments by my flying buddy Swift427 made about as much sense as your need to use a right-handed tractor prop on one motor and a reverse pitch, left-handed pusher prop on the other motor for counter-rotating twin motors on your electric model Catalina.

  19. #69
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: Air Screw


    The comments by my flying buddy Swift427 made about as much sense as your need to use a right-handed tractor prop on one motor and a reverse pitch, left-handed pusher prop on the other motor for counter-rotating twin motors on your electric model Catalina.

    AHAHAH That's funny! Really...do you think we are that stupid! ahahah at least I got a giggle!!

    Nice try!
    Crashing is such sweet sorrow!

  20. #70
    Moderator Matt Kirsch's Avatar
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    RE: Twin motor aircraft and Counter rotating props

    Okay fellas, I'm going to have to put my moderator hat on here and kindly ask that we just put the controversy behind us.

    No opinions will be swayed by further discussion of the tractor vs. pusher subject, and I'd really hate to have to lock this thread.

    Mongrel, you have several good suggestions as to how to handle your water handling issue, and you pretty much know which ones will work and which ones won't. Mine are the best, I must say

  21. #71
    The_Mongrel's Avatar
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: Matt Kirsch

    Okay fellas, I'm going to have to put my moderator hat on here and kindly ask that we just put the controversy behind us.

    No opinions will be swayed by further discussion of the tractor vs. pusher subject, and I'd really hate to have to lock this thread.

    Mongrel, you have several good suggestions as to how to handle your water handling issue, and you pretty much know which ones will work and which ones won't. Mine are the best, I must say

    hehehh I agree in part - That is I have to try a few things

    I have been trying to get her on the water for a few days, but the weather gods have been up to no good. Hopefully I will get a chance soon - but the forecast is for more wind. I will post back the results when I get a break in the weather.

    Cheers
    -J
    Crashing is such sweet sorrow!

  22. #72
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    RE: Twin motor aircraft and Counter rotating props

    "hey Mate - This photo is not my bird. It is the photo from the importer's web site."

    Yeh, and I'm Nicole Mary Kidman and my father Dr. Antony Kidman has his office in Sydney.
    Never Give Up, Never Slow Down, Never Grow Old, and Never Ever Die Young

  23. #73

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    RE: Twin motor aircraft and Counter rotating props

    Talking to a user of the Eflite PBY, it has a small but not quite adequate water rudder.
    The ones I've seen do behave properly in moderate weather conditions when taxiing.
    Sparky Paul
    http://www.angelfire.com/indie/aerostuff

  24. #74
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: Swift427

    "hey Mate - This photo is not my bird. It is the photo from the importer's web site."

    Yeh, and I'm Nicole Mary Kidman and my father Dr. Antony Kidman has his office in Sydney.

    here ya go Swifty - and fyi for any Aussies interested in purchasing this baby...

    http://www.aussieflight.com.au/shop/...roducts_id=187

    The truth is always easier
    Crashing is such sweet sorrow!

  25. #75
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    RE: Twin motor aircraft and Counter rotating props


    ORIGINAL: Tall Paul

    Talking to a user of the Eflite PBY, it has a small but not quite adequate water rudder.
    The ones I've seen do behave properly in moderate weather conditions when taxiing.
    Yeah I just had a look at the E-Flight PBY. Nice bird too. The rudder seems to be in a better position to be able to contact the water. If mine does not work I will look at moving it the base of the rudder and see if that helps.

    It just might end up being 'one of those things' that is not really fixable, and I will have to learn to live with it!

    Cheers
    -J
    Crashing is such sweet sorrow!


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