Hi,

I am student in Ireland who is carrying out a final year project in the design and building of a light weight generator. In the project I will have to incorporate an engine to power the unit.

I decided to use model aircraft engines as I know this is quite a well developed field which will suit my needs, i.e. weight as well as a good power to weight ratio.

At the moment I am trying to decide what kind of an engine to use - according to my professor it must be a 2 stroke engine. Therefore I have investigated a number of engines produced by companies such as O.S. , Super Tigre, YS, Irvine Engines etc.

However I am just not sure of what engine to use. At the moment the O.S. engine ".25 LA" sounds the most promising. The reason for this is that I want a power output of roughly 200W and the .6hp output would comfortably achieve this objective. Yet I have also come to realise that the ".25 LA-S" engine could maybe better suit my requirements.
http://www.osengines.com/engines/osmg1440.html
This is because it replaces the carburettor with a venturi that keeps the engine running at a constant speed.

Basically I am asking what are the experts thoughts on these engines! Are there better, more suitable engines for my needs out there?

Also my professor wants detailed data sheets on these engines, e.g. power-rpm curves etc. Do such data sheets exist on these or any other engines??

I know this may be a somewhat unusual application of the engine so thanks for any help,
UCC

BTW Please excuse any glaring inaccuracies in my post - i am new to this game....

Is there a displacement limit? I only asked this to make sure you leave an "operational confort zone". In other words, you don't want to have to run it at max RPM to achieve your goal if you don't have to per the assignment.

If you are limited to the .25 size range, I would go an FX series os over the LA series, user friendly and more power. O.S. is not the most powerful for a given size on the market, but they are user friendly.

Sorry, but I forgot to convert to hp in all cases!!

I roughly want .3hp so i was thinking, to be on the safe side, to have an engine that outputted .6hp. This should cover me as regards the operating comfort zone. Anything above this would just be a waste, I think!

The reason I went for OS is that I read reviews of their engines and most were positive. Also I read the results of the recent thread on the best engine manufacturer and OS seemed to lead the way. Is this assumption a good one or should I look into it more thoroughly? I really need to make up my mind on an engine in the next day or 2 in order to keep with the project schedule.

You're certainly doing your homework. For user-friendliness, the OS engine can't be beat, and the LA series is fine for your project. You won't need to run this generator for hundreds of hours, right?

Don't be too dependent on the manufacturer's specifications. Maximum horsepower is often calculated, based on tests at much lower RPMs. They find the peak torque, then calculate the horsepower based on the theoretical maximum RPM the engine can turn. That .6HP figure is not obtainable. Realistically, that engine is only capable of about half to 2/3 of that.

Glow fuel makes for awful expensive electricity

Keep in mind that the HP figures given by the MFG are at the max RPM, typically 15000 to 17000.

Here is something that may help with your generator. Sullivan makes an on board power system for aircraft.

http://www.sullivanproducts.com/Gene...mMainFrame.htm

Here's a new thought;

Get yourself somthing in the .46 displacement or larger range. Then, after getting top marks on your project, celebrate by buying the engine a new plane to live in!!!

Anyway, you are probably leaning in the correct direction with what you stated so far. Also, some good advice by everyone else!

Another option would be a .21 (or bigger) buggy engine with a pullstart. They also have heads with a lot of surface area for cooling because there is no prop blast. Be prepared to run the engine pretty fast to get the power you want. You can also pipe it if you want and increase your power. You can get a lot of power out of those little engines.

For the buggy engines, expect up to 35,000 + RPM...

UCC...your choice of engine will depend a lot on what revs you need the generator to turn. If the generator can handle 10,000+ revs then the small LA 25 should be suitable. Remember though that it's going to have to drive a small propellor as well just for cooling which will absorb some of the power output. If the generator needs less revs then it would be possible to use a belt drive to gear it down but in that case the LA wouldn't be suitable because it's a plain bearing engine. As a first guess on a more suitable engine I'd suggest maybe an OS 32 Heli which has a ball raced crankshaft, and a larger heat sink head.
http://www.osengines.com/engines/osmg1940.html

Alternatively, if the generator needs to be run at lower revs, then you can use a bigger engine and direct drive but throttle the engine down to the revs desired. At these lower revs the bigger engine will still develop the power needed to drive the cooling prop (or fan) and have enough excess to run the generator. This excess has to include what's necessary to overcome the friction of the generator plus whatever the efficiency is of the generator.

Your biggest problem will be that as the load on the generator varies then so will the load on the engine. That means you'll need some sort of feedback to the throttle on the engine so that it's excess output matches what you want to draw from the generator. This of course means that you can't use a fixed venturi (control line) version of any engine.

There aren't any data sheets for HP curves although it's fairly simple to draw a reasonably accurate curve using a tacho and a range of propellors (mainly APC) that have a known power absorbtion.

I was also going to recommend a Helicopter, or buggy engine due to the cooling factor. Unless you're spinning a prop in front of the engine, it will overheat QUICKLY!!

Hey Guys,
Thanks for all the help - am a bit wiser now!! Although maybe a bit more confused as well!!
Will have to look into the engine choice in more detail and discuss all of the above with my professor asap. Although must admit I think I am closer to a decision.

Will prob have to get back to ye for more help....

Thanks,
UCC