Confusion over engine sizes, can someone enlighten me?

Im working on a UAV hybrid, and i have 2 engines with differing and confusing specs.

My aim is to gear down the output to around 5000 RPM to match the alternator.

The first engine, is a Kyosho GT 0.15Ci (2.5cc) rated at just under 0.5 Hp at 29,000 RPM so reduced to 5000 RPM should give me a theoretical 3 Hp or approx 2.2Kw..ish

The other is an elderly MAX OS 40, ive not found out much data on this engine, but even though from what i can find out, its 0.4Ci (about 6.2cc) but only rated at just under 0.7Hp at 12,000 RPM, geared down will give me less power.

Have i researched the wrong data, and are the facts ive found, wrong?

So from the above, which is the better engine to use?...I get the feeling it might be the Kyosho, can you please advise.


Views: 4426

Reply to This

Replies to This Discussion

Yes, there are such parameters around a parachute.  Low altitude, low speed flight is just risky, no matter the platform.  Yet that is precisely where the helicopter is most useful.

I have no idea how good other 2-stroke engines might work, but for those so inclined, they worth looking into.  It's interesting to note that McCulloch tried to market a gyrocopter in the late 60's.

No, I dare say you're not missing anything.  :-)

   There's no reason to be embarrassed Brad.  Your analysis was enlightening and reasonable, even if it wasn't well grounded in actual real world numbers.

   As far as the APU is concerned... I called Honeywell and they wanted a specific part number.  I told them I was just looking off of their brochure.  The lady said there are a number of different units under that same model number, but that they range from $700k-1M.  That seems kind of steep to me too, but that's what I was told.  I can PM you her name and extension if you want to negotiate with them.  It did take a bit of phone system navigating to even reach someone who could give me a price range.

   Long story short... nobody has yet been able to even propose a viable gas-electric hybrid flying machine.  So the next time someone says it can be done... Just tell them "Well nobody's done it yet, so prove it!"

Yeah, sheesh, you'd think I was trying to sell carbon credits in the Fox News forums!


            We are not aiming for efficiency either, its the endurance. The target of whatever we get off the ground, is 45 mins minimum flight time. If we add efficiency later, hopefully the flight time will increase with what we have.

There isn't a lot of data available at all in this field, what there is, is contradictory and confusing to say the least!

This topic, and its contributors, have given me more information and idea's then Google has in this area.

To date, assimilating all this information, given by members, has just reinforced the belief, that brute force and gut feeling is the way to go, but adding the help and info given here, it now has a finer and more positive direction.

Originally when i posted this, i found confusing information on a Kyosho engine, even the website contradicted what i had read,  HP between 0.5 and 2.5 at 29,000RPM and unsure of what power was required to lift a lump into the air. Subsequent postings have enlightened me enormously. 

For what it's worth, I wish you the best of luck.  And I hope that you will share your progress and findings here with us.

There are sure to be some applications that will make a hybrid design worthwhile.


The OS will run forever and the Kyosho won't. Kyosho makes good stuff but the smaller engine is really stressed at that high of rpm.

Also, the hp of the engine doesn't change but the torque would be multiplied roughly equivalent to the ratio.


Reply to Discussion


© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service