contra rotating prop brushless - Page 27 - RC Groups
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Nov 04, 2005, 05:07 AM
Registered User
JJ1,

it dosn't matter if you add a little more distance. With this close prop setup the aft prop have to cross the turbulence of the front one.
What gives the best result is measuring rpm vs. current one each motor separate. You will find a setup where at a given amp load the props turn faster; with a bit luck even faster as alone. They help each other. But it is only a small step, and all is lost. Be careful with the aligning of the aft-prop pitch. Mine is about an half inch higher than at front, but this can change. It may depend on pitch-speed, overall power, torque, etc.
The 10A range may be okay; when all is fine, the current may go down a bit.

Hope this helps,
Kuni
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Nov 10, 2005, 05:46 PM
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Stefan.s's Avatar

GWS Contra rotating


Hi there

Just saw this thread, funny ! I have made a gws contra rotating system that works great,its easy to make and funny to fly with. Very easy to hover.
I am going to make one with Apache outrunner also, this was just an experiment .


Stefan
Nov 10, 2005, 09:15 PM
Fidler & twidler
empeabee's Avatar
Quote:
Originally Posted by Stefan.s
Hi there

Just saw this thread, funny ! I have made a gws contra rotating system that works great,its easy to make and funny to fly with. Very easy to hover.
I am going to make one with Apache outrunner also, this was just an experiment .


Stefan
Very neat and interesting.
Can you post props/rpm/current/thrust figures?
Mike
Nov 10, 2005, 10:08 PM
Registered User
for a given disk area, thrust goes with power^3/2, so comparisons to a single prop should be done at an equal total power or thrust (don't expect twice the thrust from two motors)

you might do a little better than the single by sharing the power between both motors equally using two ESC, where you should recover the swirl energy from the slipstream.

has anybody hovered with a contra-rotating setup? does canceling the gyro and swirl terms change the handling?
Nov 11, 2005, 02:50 AM
jj1
jj1
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jj1's Avatar
@stefan, nice work.
Btw where did u get those props?

-JJ
Nov 11, 2005, 03:41 AM
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Stefan.s's Avatar
Thanks , i have not checked the motors thrust, amps yet. I think it is really strong and im going to test with a gyro on one motor to se if it will stop rotation. It is very stable but i think the motors dont goes exactly the same, i try with one more ESC and test with a gyro today. The props comes from Todd`s modells and are quite cheep, i bought 15 sets for $ 3.99 each.
I am also going to build a 8 propeller heli,a sort of draganflyer but very big and perhaps with countra rotating props.Any one out there who have some advice how to program the radio, i have a Multiplex mc 4000.

/Stefan
Last edited by Stefan.s; Nov 11, 2005 at 07:28 AM.
Dec 22, 2005, 08:28 PM
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Airboatflyingshp's Avatar

Has anyone built a contra prop using a single motor?


I ask this because Ive thought up an idea very simple for a second stage bolt on gearbox for any pimary motor/gearbox combo brushed or brushless given size and wt. constraints ie its easier/suits Med to large sized models/motors better.

The beauty is you can swap around the primary set up given common input shaft sizes and with some engineering skill or luck possibly even build in a slight differential in propeller speeds sould you require that variable. Theres also no worry about two controllers as you only ever need one .............Im testing the water so can anyone see any problems with the basic concept of using one larger and hopefully efficient motor to drive two contra props ??
Dec 22, 2005, 08:58 PM
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gmitano's Avatar

Mimic Contra Heli Design?


Quote:
Originally Posted by Airboatflyingshp
Im testing the water so can anyone see any problems with the basic concept of using one larger and hopefully efficient motor to drive two contra props ??
Do you know if any of the contra helis that are becoming popular (Megatech, etc.) use one or two motors? If any use just one, they may yield some design ideas. - Gary
Dec 22, 2005, 11:18 PM
Suspended Account
In full scale the Griffon (Rollsroyce) motor does it with just a gearbox.
also there was a much smaller scale version used in a "target drone" aircraft
made by the company where Maryln Monroe worked... (and was subsequently discovered at)
jimbo
Dec 22, 2005, 11:31 PM
CD-ROM Junkie
Art Newland's Avatar
I had a Blade-runner coaxial heli and it used to motors very much like the pictures in Stefan's post.
Dec 23, 2005, 03:46 AM
Tech freak
Still no good source for left rotating prop right?
I want to se some different alternatives.

/Wheaz
Dec 23, 2005, 04:34 AM
Registered User
Stefan.s's Avatar
Quote:
Originally Posted by Wheazel
Still no good source for left rotating prop right?
I want to se some different alternatives.

/Wheaz
Todd´s modells sells them, 10 x 4,7.

Finns säkert fler sorter ,läs igenom hela tråden så kanske du finner.

/Stefan
Dec 23, 2005, 08:45 AM
Registered User
Airboatflyingshp's Avatar

third time lucky...jimbo knows something


Quote:
Originally Posted by Eljimb0
In full scale the Griffon (Rollsroyce) motor does it with just a gearbox.
also there was a much smaller scale version used in a "target drone" aircraft
made by the company where Maryln Monroe worked... (and was subsequently discovered at)
jimbo
Ive been asking jim questions because of that motor
I bought the Supermarine Seagull 381 plan from Traplet 60" span and powered by a motor Im not familliar with and it looks like its no longer made a MEC Tubo10plus mated to a 3:1 graupner off set gearbox driving a .10x6 Grish Tornado..
I did some reseach and from the bits I picked up it sounds quite powerfull any suggestions???? Jim would yours do it???...because of the layout and being scale Im limmited to 3 bladed prop diameters of 10 possibly 11inch........unless I grow it all by 10-20% -72" span at the latter.


Im told that Im going to need to generate 300 watts plus.....NiMhs 8-12 cells no lipos.....so Im looking for motors that can deliver and doesn't cost a an arm and a leg and will fit in that tapering cowl There's another complication the space for the motor has to be no more than 3 1/2" front to back at original scale unless I start modifying the center section.
Last edited by Airboatflyingshp; Dec 24, 2005 at 11:19 AM.
Dec 23, 2005, 01:49 PM
Suspended Account
Airboatflyingship,
My motor does 500 watts with no noticeable heat buildup, I am not sure if all 500 watts are going towards forward motion... at least 100 seem to be going towards making noise. I like the idea of a bigger diameter prop. The master airscrew props I am using are suited for what I did.. 60" wings I think would like an 11" diameter pair... That is just intuition not engineering. The "colorado" stator that Kuni used (see superdittos site) would be good.

It is tough to find enough of them.
jimbo
Dec 23, 2005, 06:55 PM
Registered User
Nobert's Avatar
Wheaz
Jeff at eflightline has them(www.e-flightline.com).
Neal


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