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<< Lancair Builders' Mail List >>
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<<Many moons ago, the list discussed the phase-out of 100LL (any
lead-additive to AvGas). We also discussed reliability of piston v. turbine.>>
There is a serious question of whether small turbines are really viable
replacements for piston engines in light singles. One of the funniest things
I ever saw was an Allison turbine conversion on an A36 Bonanza at Osh'97.
They stretched the nose of the cowling to get the lighter turbine engine in
CG, added tip tanks because the turbine burned more fuel, added stall fences
because the tip tanks caused wing tip stall (anyone remember the T-33 "widow
maker"?), the added some 12" x 18" leading edge vortex generators to improve
aileron authority that was somehow lost in the process. The net result was
an aircraft with more empty weight than stock, less than 20 kt faster in
cruise at altitude, burned double the gas (in weight), and had turned into a
two place aircraft with full fuel. All this for ~$250k I believe and four
times the DOC including engine overhaul costs/hour. Such a deal.
Now, the Lancair has a lot of advantages that will help prevent some of these
problems. The whole wing is wet, so there's plenty of fuel volume. Payload
is a little limited though once we put 94 gal. of Jet A in there. That's 630
lb., which leaves ~370 lb. for two svelte pilots and no baggage. Fill the
extended tanks with 110 gal total and we get 737 lb. of fuel and ~263 lb. of
one pilot and a fair amount of baggage. We're not saying that's a bad deal,
it's the owner's decision. Just don't fool yourself about what this will
cost you in utility as well as cost. With all due respect, the "27% more
fuel by gallons" quoted by Lancair isn't really applicable for two BIG
reasons:
1. Jet A is heavier and we fly limited in useful load by weight, not gallons.
For the same power, the Walter burns 46% more POUNDS of fuel. No big deal
if you're by yourself; with the family along, the range goes to nothing.
Unless you're willing to fly well over gross.
2. No pilot that I have ever met is going to sit there with another 100 HP on
tap and not use it. Gimmeabreak! This translates to the 77% more fuel (in
pounds) vs. the 6% speed increase that I wrote earlier based on 700 HP @sea
level std day. A 720 HP turbine gets ~324 HP at 25,000 ft. std day
conditions, not 400.
The turbine would be a viable replacement for the Lycoming engine because of
their excessive SFC. The Continental SFC is actually pretty good and can be
made better with a few mods. Wait a couple of months for the
Finoglio/Patterson Lancair to demonstrate just what redundant FADEC and
ceramics can do for SFC (sorry, verboten word there!).
<<The only structural changes have been to the firewall, which now has an
inverted circular area designed to accommodate the longer/heavier turbine
engine.>>
So much for turbines being lighter. Why should we say anything about
turbines with real power at altitude being heavier when Lancair has done it
for us.
Victor Delta raises many good points, it is doubtful that these run outs will
be guaranteed. We can tell you from decades of turbine experience that NO
ONE is going to rebuild a hot section with new cans, blades and seals for
under $100k. For the price quoted it is most likely that they are throwing
some walnut shells through the intake (this clears out deposits), and
changing some external items. The auto start is nice, but there's still
nothing to prevent you from shoving the throttle up too far on a hot day
during go around and melting the hot section. In "the east" they use water
injection.
Turbines are not magic. And outside this country, you will find the quality
of Jet A falls off faster than gasoline. Also, we can filter even the worst
gasoline of the third world and poor in additives to make it better than
AvGas LOOOOONNNGG before we could ever turn third world diesel into anything
approximating US spec Jet A. True, avgas is very expensive in Europe; so is
auto gas, and by about the same factor. The real question is how many of us
are planning on flying across the Atlantic to Europe in single engine
aircraft?
To the demise of 100LL, we answer with FADEC and ceramics. Our company
spec's performance based on 91 octane (rated) autogas. It's actually much
lower than that. The new 82 UL will cause no big cruise power problems in
modern piston engines, or even Con/Lyc's modernized with high end EFI, FADEC
and ceramics. Takeoff power in some engines will be limited by octane, again
it's really a problem with the old type and not the modern engines. The old
ones? Upgrade the fuel and ignition systems, stick to cruise power and you
won't even notice the switch.
Except you'll get better SFC, since the technology does that and lower octane
fuel has more BTU/lb. and BTU/gallon. What's that? The dealer told you to
put 20c/gal more expensive premium in your "high performance" car? Unless it
knocks on regular, don't waste your money on 5 lousy octane points.
Reliability? It really comes down to what technology level your are talking
about. Old piston engines run gently can and do last to TBO. So can
anything. Run hard and hot, the older technology piston engine can burn jugs
like Christmas tree lights. Overtemp a turbine just once and you can paint
the fence with melted blades, I've watched it happen. Turbines aren't magic.
To me the best solution to the reliability conundrum is to get more engine
than you need. Since the instinct is to firewall the throttle anyway, get
more than the airplane can use. The cruiser's definition of "enough power"
is enough to pull up to Vc max / Mc max in level cruise at max continuous.
The racer's definition is enough to pull through Vne at sea level! I
advocate the former, it keeps us from ever needing to use everything the
engine can give. That's the best reliability insurance I've ever found.
We'll never know the service history of these east block "rebuilt" turbines.
Zero time PT6's are good for anywhere from 2,000 to 3,500 hours depending on
version. The 601E is equivalent to a very early PT6, so it's a 500 to 2,000
hour hot section; A lot less if anyone overtemp'd it anytime in its history.
The parts cost alone of a new hot section is well over $100k. At the cost
quoted for these rebuilt engines, they are not zero timing them. If anyone
believes that, I have a bridge to sell you <LOL> Granted, the old design
certificated piston engines are no prize either. We opt for the new
technology piston engine with superior reliability to a turbine and lower SFC
than the cert pistons.
We welcome the inevitable competition between a 601E Lancair IV and one with
a Zehrbach 650 and a Star Aerospace LLC firewall forward kit. If the factory
is on schedule, both should be running at Oshkosh. Then we can race.
Everyone has to take 4 people and some baggage and cannot go over gross.
We'll weigh the aircraft before takeoff and drop the flag. 1,500 miles
sounds like a good distance.
Eric Ahlstrom
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LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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