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Old Feb 25, 2007, 03:38 PM
Professor of Wood
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Nampa. Idaho
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Small Gasoline engines

I thought the new Zenoah G20ei was going the right direction for smaller planes and power plants that use a standard 2 cycle gasoline mixture. But look what I just spotted.

Dan

http://www.bmeengine.com/html/point90.htm
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Old Feb 25, 2007, 05:26 PM
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Small gas engines

Well found Dan! Small gas engines are rarer than hen's teeth! (Good ones that is)
I was asked to evaluate some Italian engines a while back, 10 cc, ie .60 size. The carb was nearly as big as the engine! Very heavy, about as much power as a .40, and all kinds of problems for airplane use ; apparently originally intended for powering a small electric generator. Not recommended! Weston UK Ltd used to market a kit of Hall effect pick-up, little magnet you drilled a hole for and epoxied in place in the prop driver, and battery holder etc. Never heard of anyone trying it. Supposed to be applicable to anything with a big enough prop driver.
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Old Feb 25, 2007, 05:28 PM
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Further to above; just bought an O.S.90 for a project; would have got one of these S.T.s if I had known! That's life!
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Old Feb 25, 2007, 05:42 PM
Professor of Wood
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Nampa. Idaho
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Agreed. My brain hasnít stopped turning over a twin tail boom design UAV/AP platform to fit around this engine since I found it. It also retains some great RPM and horsepower numbers for its size. It would be a great candidate for the Sullivan Genesys In-Flight power system.

http://www2.towerhobbies.com/cgi-bin...?&I=LXFV20&P=7

Dan
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Old Feb 27, 2007, 07:22 AM
K4UAV
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...or possibly:


or similar )from Cyber-Flyer.com
-dave
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Old Feb 27, 2007, 03:03 PM
It just keeps getting better!
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Eureka, CA
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There are also string trimmer and chain saw conversions!
http://www.carrprecision.com/Pages/prod02.htm
Be careful! You are now leaving the realm of model RC aircraft and entering
the realm of experimental aircraft, at least if are planning on flying beyond visual
range.

-Dave
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Old Feb 27, 2007, 06:55 PM
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Quote:
Originally Posted by Blue Sky
There are also string trimmer and chain saw conversions!
http://www.carrprecision.com/Pages/prod02.htm
Be careful! You are now leaving the realm of model RC aircraft and entering
the realm of experimental aircraft, at least if are planning on flying beyond visual
range.

-Dave
The Super Tigre range of engines, designed specifically for model aircraft use, has been around a few years; strimmer or chain-saw engines they are not! Super Tigre themselves have done quite a bit of work on petrol-fuelled versions of their engines; with the normal carb, but with beefed up crank-pins etc.
As to the comment about "beyond visual range" can I be the first to point out that this section of forum is about UAVs. They are frequently operated beyond visual range.
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Old Feb 27, 2007, 07:43 PM
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I'm a little suspicious about the performance claims for this motor. On the BME web site it is claimed that the fuel consumption is approx 1pound/hour at max power (2.7HP). This gives a brake specific fuel consumption (sfc) of 0.37 lb/(hp-hr) which is better than any gas 4-stroke on the market! I think the HP number is highly exaggerated. Most 2 stroke gasoline engines get an sfc of 1.0 lb/(hp-hr). If you assumethe fuel consumption number is correct, this would put the peak HP at around 1HP which is much more believable. I dyno-tested a Zenoah G-26 at 1.5 HP at 8500 RPM and an sfc of approx 1.0 lb/(hp-hr). I haven't seen any gas 2 strokes perform much better than this. The Zenoah is very reliable, rugged, and can be run backwards for easy integration into a pusher airframe while still using conventional propellers. My engines are stripped down and use electronic ignition for reduced weight. It's still not as light as the Supertigre 0.90, but the reliability is great.

A few years ago I spent some time converting an OS 0.61 heli engine to gasoline with a Walbro carb (see attached photo). It ran well, but after approx. 20 hours the connecting rod failed (no needle bearings). I know the Supertigre is better designed, but I'm still nervous about using any model airplane engine on a UAV that will operate for 100's of hours. Does the Supertigre use a standard size spark plug? The glow plug sized ones (1/4"thread) are not very reliable. If you run this engine as a pusher, cooling may be an issue because of the small fin size. The industrial 2-strokes (Zenoah, etc.) have big fins and can easily run wide open with little airflow and not overheat. A motor using gasoline will run hotter than when fueled with glow fuel, so be prepared to watch the cylinder head temp.

Steve
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Old Feb 27, 2007, 10:19 PM
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Dear Steve,

How can I runs a zenoah backwards? Any internal modification I should do?

Thanks

-doni-
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Old Feb 27, 2007, 10:58 PM
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Quote:
Originally Posted by wadiprawita
Dear Steve,

How can I runs a zenoah backwards? Any internal modification I should do?

Thanks

-doni-
All you need to do is change the ignition timing, the intake is a piston port-type and does not need to be re-timed. If you install an electronic ignition you'll need to set the timing anyway, so you simply adjust for the proper spark advance in the reverse rotation direction. I have 100's of hours on one of my Zenoah's that's been used exclusively as a pusher, and there have been no problems. I use an APC16x8 (standard) propeller on my UAV.


Steve
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Old Feb 28, 2007, 01:34 AM
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KD7ost:

The BME 90 is an airplane engine, but about a year ago the heli guys began to outfit 90 sized heli's with them. They were a bit of a fad, but seemed like fine engines. They stayed in one piece, were comparable to a .70 nitro in power, and were reported to be smooth and efficient. if an airplane engine survives in a heli with limited cooling, I trust it would not be overheating in a plane. I did not have one but read a lot. I contacted BME asking for a 50 sized gasser, it never came to fruition.
Here's a discussion, 410 posts
http://www.runryder.com/helicopter/t...ghlight=bme+90
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Old Feb 28, 2007, 06:59 AM
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I have emailed BME , asking about fuel consumption and here is the answer : 'Sorry, we have not tested for specific fuel consumption. Most customers tell us that the engine is at least as strong as a .75 and runs about 30 minutes on ten ounces of fuel at mid to full throttle setting.'
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Old Mar 01, 2007, 12:12 AM
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Dear Steve,

My knowledge and experience is limited in engine, so is there any website about converting zenoah from puller to pusher engine? Thank's

I also have 3W, the 3W website told me that it can also be converted to pusher, but no further information about this.

Thank's

-doni-
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Old Mar 01, 2007, 10:17 AM
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Quote:
Originally Posted by wadiprawita
Dear Steve,

My knowledge and experience is limited in engine, so is there any website about converting zenoah from puller to pusher engine? Thank's

I also have 3W, the 3W website told me that it can also be converted to pusher, but no further information about this.

Thank's

-doni-
Doni,

It's beyond me to explain in detail how to set the engine timing. You should contact the engine manufacturer or dealer and they can tell you how to do it.


Steve
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Old Mar 01, 2007, 06:57 PM
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I can confirm tha Tigre engines don't seem to have a cooling problem; visited Cyprus quite a bit, many Tigre engines used there because no over-heating problems; frequently day temperatures top 100 degrees.Note that Tigre recommend not to use Nitro in fuel "Don't need it" they say; that would help temps of course. Mac
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