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PostPosted: Wed May 21, 2008 11:55 pm
by ozzie
google this

DI Pietro air motor.

15 hp model looks like the go.

i don't know about cost or availability but a guy north of me is involved somehow and is putting one on an early rag and bone u/l to see how it goes.


PostPosted: Thu May 22, 2008 11:22 pm
by Chappy
Hi Ozzie,

I don't know, but I wouldn't expect too much from that motor. First off, from what I've read, compressed air engines have suffered from very poor efficiency, so just having 100% better efficiency really isn't saying too much. But the real problem is "fuel". Gasoline is a very dense fuel - it contains a lot of energy per weight and volume. I just don't see compressed air as a practical fuel for an airplane, plus the tank will be either very heavy and/or very expensive. I imagine getting similar energy densities to gasoline would require astronomical pressures. And then you've got to get the very high pressure air, not something that is a trivial matter. The whole thing is more analogous to designing and building an electric plane.

Gasoline contains 12,722 W-hr/kg energy, while lithium-ion batteries only contain about 150 (and lead-acid batteries trail at only 50!). I have no idea what the compressed air required for this engine is, so we can't come up with any meaningful comparison. But this shows you what a tall order it is indeed to try and replace a typical gasoline powered engine with something else, even taking into account gasoline engine's very poor efficiency. Diesel fuel contains more energy than gasoline, so is generally more efficient in ground transportation vehicles, but since it also weighs more than gasoline, for aircraft use the advantages are mostly negated.

BTW, I see that Randall Fishman, who converted a Trike to electric propulsion some time ago, has converted a Moni-motorglider to battery/electric and has it flying - beating Monnet's team in their quest to do it. ... a7a4bdcd4f


PostPosted: Sat May 24, 2008 7:54 pm
by ozzie
Hi Chappy,
we will have to wait and see how good this motor is. as for powering things like small cars, carts and boats it seems to be proving itself as a efficent alternative to petrol and electric. A home builder here has somehow got his hands on one of these and is searching for a suitable light airframe to try it out. I've asked him to keep in touch.
I noticed how the EAA is asking the FAA to have the op regs changed to remove 'recipricating' from the ruling. making some enquiries over here i found that we may not have to follow suit as the RAAus regs basically state. one engine, one propellor, no turbines.(lazair is exempt from engine number rule). so there will be no need for anyone to apply for exemption. one major headache not to have to deal with.