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fuel efficient engines?

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Im hoping to fly as far as I can so I'm researching the most fuel efficient engine technology there is. I've basically ruled out electrics since the battery weight for extended flight becomes cumbersome, even for the better 3 phase design.(correct me if im wrong). So that leaves fueled engines. The most efficient fuel design in RC is (supposedly) the four stroke. The most efficient fuel is diesel. But appearently they don't make four stroke diesels because of the complexity of valves and variable compression in such a small package. I'd like to stick with four strokes (I think) but do I use nitro, or deal with an ignition system and go gas? Or would a two stroke diesel be more efficient than any four stroke? What are your thoughts/expierences?

Thanks guys.

Sean

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http://www.rcgroups.com/forums/showthread....ight=long+range

Here's a thread where some of that was discussed. There are some people chiming in that work in the UAV community. "Long Range" is a pretty subjective term. Generally speaking, a low RPM big prop will be more efficient than a small prop turning fast.

4 stroke glow engines are much more efficient than 2 stroke counterparts. It comes complete with glow fuel residue though. (Think pusher) They're more expensive than the two strokes too.

You can convert quite a few variations of 2 stroke glow engines to diesel using a converter from http://www.davisdieseldevelopment.com/ These run as economically as the 4 strokes with less residue but you have to order the special fuel or mix your own though. It's not DF2 from the local gas station. It costs as much or more than glow fuel.

2 stroke gasoline engines with smaller than stock carbs seem to be getting some really good range. These engines are about 1.5 to 2 cid though. You're not going to run that on a Telemaster 40. But you could on a Rascal 110. The fuel is very affordable too. Standard 2 stroke mix. I run gasoline engines like this in planes and get 1 hour of run time on a Zenoah G26 or Fuji BT32 with only 1 quart of fuel. This is running full throttle so is a worst case scenario. The spark plug cost less than an expensive glow plug and will last for hundreds of hours.

There are a few 4 stroke gasoline engines out now. They cost a bit more though. Check http://www2.towerhobbies.com/cgi-bin/wti00...p?&I=LXJDJ5&P=7 and http://www2.towerhobbies.com/cgi-bin/wti00...p?&I=LXJDJ6&P=7

Personally I have grief with both these only because they gave it an electronic ignition. I wish they had a version with a reliable old flywheel. I hate to have to run a battery pack to generate spark when a flywheel and coil could have done it making the engine a true stand alone pleasure.

Dan

Edited by kd7ost

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Thank you very much kd7ost, that was an excellent link and post. You have given me quite a bit of information to work with. It turns out also, that electrics aren't as improbable as I thought. I think my next step from here is to try and assemble a side by side comparison of propulsion types and their specifications. Although, I hear a lot that engine manufacturers don't post relvent data on their engines on websites. it looks like it might take some digging.

Thanks.

Sean

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Enya model engines have now bought out a Diesel four-stroke. Note that kerosene/paraffin has , like "real" diesel fuel, more B.T.Us than eptrol or methanol, hence more urge per c.c.

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