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HomeAircraftHelicopterMain Discussion › why do people not use 4 strokes on helis?
03-07-2008 10:57 PM  10 years agoPost 61
bigdad390

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East. Liverpool, Ohio

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I think that the RCV CD series of fourstrokes might work . No pushrods , no valves to bounce etc , should allow them to rev harder than your usual aero fourstrokes .
The thing you have to think about is, even if you have a 4 stroke cycle engine that will rev, it still only produces a power stroke half as often as a 2 stroke cycle engine.

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03-07-2008 11:07 PM  10 years agoPost 62
ChopperEddie

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Pennsylvania, USA!

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Does anyone have a video of a Wankel in a model aircraft? I've never heard one run in a model before.

-- Runway? We don't need no stinking runway! --

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03-08-2008 12:00 AM  10 years agoPost 63
nivlek

rrProfessor

Norfolk England

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A quick trek to the OS site shows:

OS .50 Hyper 1.9 HP
OSFSH .52 0.9 HP
The main reason that fourstrokes to do well in fixed wing and not helis is that the quoted powers produced by two strokes are generally not realised in fixed wing machines due to the rpm at which they are used.
In a heli , we do run them at 17,000 or thereabouts , where as in a fixed wing application we usually don't go above maybe 14000 .

With four strokes , where their maximum rated power is at a much lower rpm figure , we do get much closer in fixed wing applications .

So , a 36 running at say 12,000 rpm flat out , will produce similar power to a a 56 ish four stroke running at around 10,000 rpm flat out , but unload the 36 and let it rev at 17,000 and the fourstroke can't compete .
If you load the OS50 to 12,000 it will probably produce no more than 1.3 bhp a lot less than the 1.9bhp at 17000 .

If none of that makes any sense , please be aware that I've just got back from the pub , my other hobby . Hic

At the end of the day , it gets dark .

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03-08-2008 01:06 AM  10 years agoPost 64
GimbalFan (RIP)

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Big Coppitt Key, FL

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Searching <os graupner wankel> brings up some interesting reading, at the top of which is this.

It seems the only distinct advantage to wankels in RC is the balanced, vibration-free operation and the cool sound. They guzzle fuel and they leak.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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03-08-2008 01:46 AM  10 years agoPost 65
Seablade

rrKey Veteran

earth

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How loud is that "cool sound" from a Wankel?
I was in the pits at the 1984 Le Mans and the car was wankel powered,
coming down the straights it was so loud it was painful. (fast too!)

"Vini, Vidi, Velcro"

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03-08-2008 01:48 AM  10 years agoPost 66
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

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According to the article in that link and others, the gear noise between the rotor and the crankshaft can be quite noisy if the mesh isn't just right.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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03-08-2008 03:35 AM  10 years agoPost 67
Wingman77

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Pulaski Tennessee

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wow I left for a few hours and this thread went crazy. lots of good input, I do like my saito 4s in my plank and thought it would be good in helis to, so it seems it wont but it is good it does not bug me anymore. ........I do like the way my 4s sounds though.....

thanks for all the great input guys

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03-08-2008 07:14 AM  10 years agoPost 68
rc-whirlybird

rrApprentice

Shelby Twp, Michigan,USA

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I just done convertion the Raven50 with YS63s 4 stroke in it.
All ready to fly, just don't have time to test fly and the weather is still bad. I've started and run a few time in garage and sound ok, can't wait to test fly it.

More picture in my gallery

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03-08-2008 08:07 AM  10 years agoPost 69
nivlek

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Norfolk England

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How loud is that "cool sound" from a Wankel?
It's quieter than a two stroke , sounds like an air tool , and has instantaneous throttle response .

In fact on my first Wankel , I had problems with the muffler coming loose and decided to run it open exhaust . The noise was still not loud , so I decided to fly .
Anyway the noise remained OK , until I dived the model , even just a 20 degree dive resulted in the noise level going wild ! I assume that the rpm was rising , but why the hell it made so much more noise has always puzzled me .

At the end of the day , it gets dark .

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HomeAircraftHelicopterMain Discussion › why do people not use 4 strokes on helis?
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