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Old Dec 11, 2005, 04:14 AM
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New Zealand
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High fuel efficiency for long endurance flights

I am looking for information about highly efficient engines for long endurance flights, for a UAV.

I would like information about things like fuel injection, heavy fuels, spark ignition (for converted glow engines), and so on. Any links, information, or advice would be appreciated.

Best of-the-shelf engine I can find seems to be the Honda GX25 at:
http://www.carrprecision.com/Pages/prod02.htm
but I would like something smaller/lighter, and would like to experiment with things like a home made fuel injection system (perhaps using inkjet printer jets as injectors...)

Has anyone made a small DIY dynamometer?

This thread includes discussion of efficient engines used on commercial UAVs:
http://www.rcgroups.com/forums/showthread.php?t=360145
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Old Dec 11, 2005, 10:47 AM
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San Antonio, TX
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I haven't been involved in flying for many years, but I did pick up a mag at hobby shop a couple of years ago that featured an article about Maynard Hill, Dave Brown, and several other guys who worked for a number of years preparing engines/planes for trans-atlantic flight. They were successful. Great article if you can find it. He converted a glow engine to ignition and he also added a small electric motor to back of crank. He had converted electric motor to a generator to keep batteries and ignition working well. He and his crew also designed electronics to work on GPS.

Here is their website: http://tam.plannet21.com/
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Old Dec 11, 2005, 10:55 AM
3 cylinders or more...
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Reggio Emilia, Italy
Joined Jul 2005
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Maybe this is the article you are talking about, JDP530

Maynard Hill's transatlantic flight

Radial.
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Old Dec 11, 2005, 11:11 AM
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San Antonio, TX
Joined Oct 2005
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Hi Rad, thanks for help locating articles. BTW, do you follow 1/8th scale on-road racing there in Italy? My son has been an rc racer for many years, running 10th and 8th scale on-road, and off-road, and we always run the Nova Rossi engines. Great engines, but quite expensive compared to rc airplane engines.
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Old Dec 11, 2005, 06:52 PM
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I think I read the engine was an OS61SF with a OS10 carb for fuel economy.
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Old Dec 12, 2005, 12:58 AM
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New Zealand
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Thanks JDP530, Radial, Speedster,

I was already aware of Maynard Hill et. al. and their amazing feat, but the article is very interesting!

Anyone have any useful information about fuel injection (esp. DIY)?

DIY electronic ignition?

Thanks, Hugo.
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Old Dec 12, 2005, 06:58 AM
3 cylinders or more...
Radial power's Avatar
Reggio Emilia, Italy
Joined Jul 2005
202 Posts
Quote:
Originally Posted by JDP530
Hi Rad, thanks for help locating articles. BTW, do you follow 1/8th scale on-road racing there in Italy? My son has been an rc racer for many years, running 10th and 8th scale on-road, and off-road, and we always run the Nova Rossi engines. Great engines, but quite expensive compared to rc airplane engines.
JDP530, unfortunately I don't follow RC car racing (and, to be honest, I'm fairly new to airplanes too ).

Radial.
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Old Dec 12, 2005, 10:32 AM
3 cylinders or more...
Radial power's Avatar
Reggio Emilia, Italy
Joined Jul 2005
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Some ideas

Hugo, there are many ways to create a highly fuel efficient powerplant.

First of all you have to start with a four stroke engine, since these have fuel economy as one of their natural advantages. Then it all depends on how much you want/can modify the base engine: spark ignition sure helps, as well as electronic controlled fuel injection .
I'm not an engine expert at all, but it seems to me that glow engines generate more power for a given displacement than gas engines: this makes me think that methanol has more power than gasoline, so for an endurance flight you'd better use methanol, as it provides the same power using less fuel (again, I'm not sure of this, so if I'm wrong please correct me).

Finally an independent lubrication system with a separate oil tank, an oil filter and an oil pump would allow you to use fuel without oil, thus getting even more power out of the same amount of fuel (particularly when the transition is from 16%/20% oil to 0%, that is to say standard glow fuel). As a side effect of his, you could set the engine with an intentionally lean mixture, knowing that you will still have proper lubrication and that you will be saving fuel .

Hope this helps,

Radial.
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Old Dec 12, 2005, 10:50 AM
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A glow engine on glow fuel but with spark ignition uses less glow fuel. Convert a 4-stroke to spark ignition and you'll be close to the fuel efficiency of a 2-stroke gasoline engine (I guess). Unfortunately the spark ignition adds weight.
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Old Dec 12, 2005, 01:16 PM
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I was at a talk by Maynard Hill a while ago where he explained for his endurance records, he used a Mk1 OS 61 4 stroke with altered timing and swinging a large prop at low speed to get a fuel consumption of 2 Oz per hour. I heard recently that the Atlantic crossing was done with a diesel conversion on a 4 stroke (not sure which type) to get 1 Oz consumption per hour. Diesel is after all more efficient than Gasoline.

Andy.
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Old Dec 12, 2005, 01:42 PM
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You're right on the money, Andy! I keep forgetting about the engines I started with in the hobby.

That 4-stroke conversion to diesel should be very interesting! I wonder how they figured out the valves and the compression adjusting piston.
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Old Dec 12, 2005, 03:56 PM
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Hmm, this should be interesting
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Old Dec 13, 2005, 12:22 PM
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There was a Laser 4 stroke Diesel a while ago...

http://www.rcgroups.com/forums/showt...t=laser+diesel

Andy.
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Old Dec 14, 2005, 01:46 PM
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Hi,
What you need is a small displacement gasoline engine. Magnito ignotion would be best because it has no batteries to go dead. A 25cc conversion, such as a Toro would work well. 3.5lbs ready to run and swinging a 18x6 prop. With the right carb and prop it should ony usae about 1/2 oz. per min. They can be found on RCU classifieds for around $150 new. Radio and transmitter batteries may be a concern, but not ignition.

Dave

Quote:
Originally Posted by hugo_vincent
I am looking for information about highly efficient engines for long endurance flights, for a UAV.

I would like information about things like fuel injection, heavy fuels, spark ignition (for converted glow engines), and so on. Any links, information, or advice would be appreciated.

Best of-the-shelf engine I can find seems to be the Honda GX25 at:
http://www.carrprecision.com/Pages/prod02.htm
but I would like something smaller/lighter, and would like to experiment with things like a home made fuel injection system (perhaps using inkjet printer jets as injectors...)

Has anyone made a small DIY dynamometer?

This thread includes discussion of efficient engines used on commercial UAVs:
http://www.rcgroups.com/forums/showthread.php?t=360145
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Old Dec 14, 2005, 06:26 PM
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New Zealand
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Thanks DaveWallace,

I agree that a small displacement gas engine is probably best. Magneto ignition is nice in that it doesn't need batteries, but it does weigh a lot... and we will need a generator/alternator anyway (a little brushless DC motor off the back of the crankshaft).

BTW, Maynard Hill's trans-atlantic flight used about 2oz of fuel per hour!!
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