Hi Bill

 

I have the same concerns as you about fuels, hence my looking at alternatives.  If I had to get an engine now, though, I would probably just go with the IO 550 and have done with it but I'm not even close.  I did fly the SMA diesel a couple of years ago that had been STC'd on a Cessna 182.  It was butt ugly at the time because the inlet had to be enlarged but they have improved the air inlet and it isn't too heinous now.  But you will require more cooling with the diesels (I am told) and it would be a very difficult thing to butcher those gorgeous lines the cowling has now.  As to diesels in general, they have great low RPM torque, just the thing for direct drive to a prop.  The SMA got full rated HP at only 2100 RPM as I remember and they are ALL  turbo'd since with any compression ignition, at some altitude without a turbo, there just isn't enough air to compress. 

 

To offset that though, the limits of HP may be more one of contnuous duty rating.  Not all diesels are alike and some will allow more continuous HP than others. You also need to consider that if you loose the turbo, you loose the engine at high altitude.  DeltaHawk has a cool idea in that they have a supercharger that they use for starting but that drops off and a turbo charger kicks in afterwards for high altitude re-starts.  The other down side is that these are un-certificated engines and not designed for our planes and insurance can be an issue.  The plus being that they are less expensive.

 

So while the HP may be lower, due to higher torque, you can get the same or better performance with something like 75% of the horses.  The problem is the weight is still pretty high and there aren't many engines that are in the range of HP that we want to be looking at.  The DeltaHawk has plans for a 300 HP engine that could be very nice (at a weight penalty of course), but that has yet to be tested.  Theilert hasn't got anything either yet that I'm aware of.  And as someone pointed out, Jet A is about 1 lb/ga heavier than Avgas but it also has about 30% more energy density.  So you wouldn't necissarily require as much fuel anyway.  You should get by on about 70% of the fuel.  One German pilot I talked to last year said Avgas in his country was $8/ga.  I shudder to think what it is now!  So Jet fuel diesels have a lot to offer in Europe.  It isn't a big deal here yet but then again, we don't know what the future holds for 100 LL. 

 

So I am keeping my options open.  I don't have to worry about it yet but I can't help but think that in a few years, our lead loving engines are going to have problems.

Bill&Sue <5zq@cox.net> wrote: