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Contra rotating propellers

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Dave Hodges

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henryk

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Thanks. I'm planning to use belts instead of gears. The test data on coaxial propellers was good information. I appreciate your time.
-multi V-belt gear is a good dampfer...

http://www.promex.rybnik.pl/jawa-250cc

=we want to change 2-stroke G-25 motor to the speedway engine JAWA 250 (24 kg, >40 HP...),
of course,with CR differential gear !
 

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henryk

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Has anyone actually flown a series electric HBA?
-great problem=battery weight and costs...

-but=

=motor (diesel)/ synchonous generator(EMRAX) +two synchronous
electromotors (f.e. EMRAX) +ONE controller (for rear motor),
may be today solution as hybrid power system
(only little kWh from battery !)
 

Geraldc

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I have been doing a bit of design work for a compound bevel contra rotating system.
The difference from other systems I am aware of is that I am using a vertical shaft motor.The reduction is in the ratio of the gears2 cylinder back.jpg
 

Geraldc

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I saw that video Henryk and I decided that I would not use the belt and instead
use auto crown and pinions and guibo for damping.
 

RonL

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=not CONTER, not ROTATING,
but OSCILLATING,very effective !

IFF to made proper size to air flying ???
Careful Henrik, I used the same link and believe it clinched my crackpot award just a little tighter. I agree with you that there is a very possible link to energy used and energy recovered that can apply to air travel, it involves timing of Nano or Micro-seconds of energy generated and reused.
:pilot:I believe you are thinking accurately about the motion taking place.
 

henryk

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I used the same link and believe it clinched my crackpot award just a little tighter
=moore simple (for my homemade english ...)?

-very short overloud pulses (< 1 ms) are not danger to us...
=many >500 "G" with puls bumper on my futh !
 

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Swampyankee

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If you're driving coaxial propellers with separate engines, making a center-line thrust twin, the mechanical complication may be worth it. Of course, to make the two systems independent, the engines will need to be as isolated as possible, with independent ignition, induction, exhaust, and cooling systems, and fuel systems that can be isolated.
 

Vigilant1

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If you're driving coaxial propellers with separate engines, making a center-line thrust twin, the mechanical complication may be worth it. Of course, to make the two systems independent, the engines will need to be as isolated as possible, with independent ignition, induction, exhaust, and cooling systems, and fuel systems that can be isolated.
Hooking the two engines to a single (prototype, experimental) transmission seems like a step backward if we are carrying 2 engines because we can safely fly on one, and we'd like to be able to do that. Why deliberately create a single point of failure? This is the biggest issue . And, unless the props have controllable pitch, a single remaining engine won't be able to develop best thrust when driving 2 props that have a pitch optimized for twice the HP input. Also, if two engines are in one engine bay/nacelle, what do we need to do if we see smoke, fire there? Shut down fuel to both engines.
I don't think anything about it is attractive when we consider the operational factors. If we're running two engines through a gearbox like this, I'd much rather just have 1 engine: lighter, cheaper, less likely to end up in the trees. And, FWIW, I'm firmly on record as a fan of appropriately designed centerline twins ( see the Beetlemaster thread and the Micromaster thread)
 
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Vigilant1

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=Tchech experiment was NEGATIVE result...

Thanks. So, their two-engine coaxial drive met some of their requirements (cancellation of torque reaction, etc), but was abandoned because:
"Thrust of two engines and propellers was not the sum, but only about. 70% of the expected value and was not sufficient for our intention."
 

henryk

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two engines and propellers was not the sum, but only about. 70% of the expected
=yes,it is !

-similar problem is with inverters (conter rotating with the same RPM s)

=rear propeller should be far away the first one...
f.e=


>15 kg...

BTW=auer differential < 3 kg !
 

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Riggerrob

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Fairy Gannet ASW carrier plane served long and hard with Double Mamba turbo-prop engines. The two propellers shared a common thrust-line, but only shared a few bearings. Every thing else (starters, oil coolers, etc.) were completely separate for each engine.
This separation is illustrated by engine start-ups with one engine turning and burning, while the second propeller remained stationary. I suspect that they shut down one engine during long patrols.

Thousands of multi-engined helicopters have been built with combining main gear-boxes. Sprague clutches allow under-performing engines to automatically dis-connect.
 
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