Bill Freeman wrote:
Tracy beat me to it. I was going to say that this
was really
neat, but the ugly truth is that small turbines
have EXTREMELY
bad fuel specifics. I was going to guess 3X the
fuel flow of
an equivalent piston engine. Let's see -----
36 kg x 2.2 = about 80 lbs thrust
at 150 mph ===> (220 ft/sec) x 80 lbs = 17,600
ft-lb/sec
divided by 550 ft-lb/sec-hp = about 32 hp
thrust.
Assume a 82% efficient prop and you have total 39
hp at the
engines. With a 0.42 BSFC you should burn 16.4
lb/hr or
2.73 gal/hr. If the fuel specifics were ONLY 3X
as bad,
this would be 8.2 gal/hr.
>From Tracy's number of 18 gal/hr you are 6.23
times the
fuel flow. YIKES! Perhaps the thrust is 36 kg
PER ENGINE,
in which case the 3X is about right. Either way
pretty
catastrophically bad. Bet they cost an arm and a
leg to
buy, too.
When I was at Union Carbide in their machinery
technology
group at the tech center (about 100 yrs ago :-) ),
we were looking
at installing small turbines to recover some of
the energy in
some process flows (like recovering ~50,000 HP
from one
ethylene stream). We brought in DeLaval and did
some
prelim engineering work. The main thing I
remember these
many years later is that the efficiency of
turbines REALLY
STINKS as they get smaller. I believe one of the
main
problems is that the tip effects don't scale, so
short blades
are extremely inefficient. I forget the details
but we gave up
on the power recovery turbines, the there was some
REAL
money being expended 24/7, but it still wouldn't
pay.
There were other problems besides efficiency, like
polymerization
IN the turbine, but we won't go into that.
There are some improvements that have been made in
small
turbines in the last 10-15 yrs and I think that
the Williams
tiny turbine MIGHT have a chance, but it is far
from easy.
The key to the Williams will not be will it work,
but will the
fuel specifics and first cost "work"
(economically).
Does anybody know the fuel flows on some of the
small
Williams certified turbines like the FX44 (IIRC)?
How good
are the real A/C small turbofans that are in
production ?
Still pretty neat, tho. ;-)
Bill
I asked that question at the William's booth. In
fact the engineer recognized me when
I walked up. He said "Oh no! Not Paul Lamar!". He
then said you are going to ask me
the
specific fuel consumption aren't you. The answer is
the same as it was last year.
"I can't tell you". So much for our 100 million
dollars which is now nearly gone.
The price of the engine is now up to $100,000 which
is out of my price range.
Further funding is being sought which will raise the
final price even more.
What did we get for our 100 million dollars?
NOTHING!
Some small turbo prop engines are slightly below .65
BSFC.
Paul Lamar