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Posted for Newlan2dl@aol.com:
From: "Dan Newland" <Dan.Newland@orcon.com>
I tried the SMA diesel last year in their C182 at OSH and think it really has some potential but also some limitations. Keep in mind I'm
not an engine guru but here's what I've gleaned from talking to the SMA,
Theilert and DeltaHawk people.
Like many, I'm pretty excited about the possibility of the diesels but they have their limitations. What was great was the potential fuel
savings since kerosene has about 30 % more energy potential than
gasoline. Also a turbo that will give 100% power up to around 12,000'
(they say it's based on well proven auto technology and extremely
reliable and not nearly as twitchy as existing aircraft blowers...well,
maybe). Note that since the diesels are compression ignition, they all
require turbo's or super chargers to be able to work at higher
altitudes. Doing some simple calculations, at higher altitude cruise,
say 10,000-12,000', you should see about 35% more power than the
normally aspirated engines so that would net out about 10% more speed.
On the ES, that could make the plane cruise at close to 210 kts. Not
too bad! And at full power, they should have only about the same fuel
burn as their conventional counterparts at 65%. So you should see
either more range at the same speed or more speed at the same range.
Also they are simpler since their is no ignition system and they should have a longer TBO. Related to this, they are all (apparently)
essentially FADEC equipped. Well, they don't need the same controls but
from what I heard, it's a single lever operation. And of course the BIG
ONE is that depending on what happens with leaded AVGAS, you may make a
complete end run about the replacement fuel/regulatory issues problem we
are facing.
And last on the positive side is that diesels like to run at low RPM and give high torque which is more of a problem for the gas engines. In
fact, the rated HP is for 2200 RPM which should give less external noise
since the prop is farther away from critical Mach than the gasoline
counterparts.
As to the down side, the SMA (I don't know about the others) required an additional air inlet that was HUGE and BUTT UGLY. They doubled (as a
guess) the air coming in. They say they will be reducing the size by
about 15% but it is still REALLY BAD. If it could be reduced to be a
tiny sliver of additional inlet area or just enlarging the existing
inlets a bit, OK but not the way they did the 182. Lets face it, we got
the Lancairs because they look like little rocket ships, not Pietenpol
Aircampers. I don't know if this is a characteristic of the other
engines, anyone have a guess?
Also, as they currently are designed, they can't restart above 12,000' if there is an engine failure since without the turbo, they can't get
enough air to compress for ingnition. I heard one manufacturer is
looking at a super charger that drops out and goes to turbo charger but
that's just a rumor. You engine guys can figure out the details.
And another down side is the weight. The SMA comes close to the equivilent gasoline engine but they aren't quite there and I've been
told that the Super ES's are already at the forward limits of the CG so
they and probably others would require ballasting aft.
Another issue is fit under the hood. The SMA is designed to be a sort of "drop-in" replacement, air inlet issues aside but it looks like (I
don't know for sure) the prop hub is lower on the Theilert than the
Continental or Lycoming engines. And the DeltaHawk is a "V"
configuration requiring cowl mods, too. Can't say I'm wild about either
of those mods to make 'em fit.
So for now, I'm undecided. There is a lot more development that has to be done before I plop down the money to get a diesel.
Dan Newland
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