Turbo Diesel 722 engine for... a large UAV?

Diesel Plane

New member

Equipment
Kubota 722
Mar 12, 2025
1
0
1
Oakland, CA
Hello folks,

I am new to this forum, but have already benefited greatly from the contents. Thank you everyone.

I'm working on an unusual project with some friends. We want to use a Kubota turbo diesel engine for a very long range UAV. Likely the 722 given our power requirements. The UAV needs to run on JP-8, thus the unusual concept of a turbo diesel. The heavy fuel engine options for UAVs on the market in this size category are over $50k with a terrible TBOs, believe it or not. They aren't actual compression diesel engines.

I've seen a number of people successfully add turbos to the 722 engine, typically the RHB31 turbo. It looks like folks are able to get around 8PSI of boost out of it, which would be perfect for our application. Our target is something around 18-20kW of continuous power at sea level, ideally closer to 20kW.

I've got a few questions that folks here might be able to help with:

1) Does getting this kind of continuous power out of the engine seem... crazy?
2) Does anyone have experience operating the 722 with ~8PSI of boost at fairly high RPMs (north of 3,000) continuously? I'd imagine some folks who run heavy grass cutting equipment and the like who've turbocharged their engines might be operating in a similar way to what we'd be looking to do. Any issues you ran into?
3) We're trying to figure out how much weight we could cut out of the engine. We'll be adding our own starter/generator to the thing, and it won't actually be spinning a propellor (the UAV will be a hybrid aircraft believe it or not). We haven't purchased one yet. Does anyone know how much any of the non-engine-core parts weigh like the fly wheel, starter, other tidbits? Any ideas for were we could cut weight? We are perfectly happy to machine new parts for the engine.

Thank you, and apologies in advance that this is totally off topic. I hope it's a sufficiently interesting thought experiment to not get shut down :p

-Michael
 

North Idaho Wolfman

Moderator
Staff member
Lifetime Member

Equipment
L3450DT-GST, Woods FEL, B7100 HSD, FEL, 60" SB, 743 Bobcat with V2203, and more
Jun 9, 2013
32,039
7,766
113
Sandpoint, ID
Your not going to get a D722 to put out that much power especially on JP-8!
Your probably realistically only looking at around 16kw at max RPM 3600 at sea level.
Maybe look at a D902 or D905, that will get you much closer, and there really is no weight difference.
But that's a stretch too.
The main reason you don't see many of any Diesel compression engines flying is there is huge loss in performance with altitude.
I don't think it will be able to put out half its ground HP at normal flight altitude.
It's not going to be a super light motor, no matter what you do.

Good luck to you!