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First off, I want to say that I fully believe that there is a better engine
for the Lancair IVP than the stock TSIO-550. I don't think that we have seen
it yet though.
<< The prototype EPI PSRU was in the aircraft which won the
Kittyhawk-to-Oshkosh race in 2000 (and which nearly won in 2001). >>
Well, the aircraft has broken the time as well as the credulity barrier then.
<LOL> Last time I checked, the 2001 Oshkosh race was still a few months
away. If we offset by one year, we get last year's results as the "nearly
won".
Let's be totally clear about last year's Dayton to Oshkosh race. The Kitty
Hawk leg was canceled due to bad weather so the second day everyone could run
flat out from Dayton to Oshkosh, burn all the fuel they wanted, and cook the
engines. It still didn't matter. On the remaining leg a factory stock
Lancair IVP finished first overall at 319 mph average equipped with a full
interior and powered by a TSIO-550; all stock. Less than one minute back at
315 mph and ahead of the Engineair was Lee Behel's Venture WITH A STOCK
IO-550! No turbos, no high compression, no ceramics. The only mods on the
aircraft were wing root fairings and cowl outlets done by our company and
Lee's A&P. At the ~4,000 ft. cruising altitude, this engine was good for
~290 HP. A far cry from the competition!
Engineair finished behind the factory stock aircraft and a normally aspirated
Venture. Period.
When a well tuned, stock TSIO-550 Lancair IVP has been up against the
Engineair in previous years, the difference has been marginal at best.
On another note, Livio Bognuda has consistently finished first in the annual
get together at the factory in his stock Lancair IVP. The last time out, the
factory pushed the Tigress out front with the engine temps in the red and
only managed to stay ~1 mph in front. So much for the Orenda option. That's
supposed to be a 600 HP engine...
Bottom line, it's going to take more than Orenda and Engineair have been able
to do to beat the factory Continental. The new entrants to the field are
worth watching, but these two have had years to prove the claimed vast
superiority and haven't.
As for helical gears being inferior to straight cut, every turboprop engine
on the market uses a reduction unit. Almost all use helical gears. They are
nothing new and helical has proven it's superiority in load carrying on
everything from turboprops to the prop reduction units on aircraft carriers
(yes, the 100 rpm, hundreds of thousand ft-lb. props pushing the ship). Yes,
torsional impulses are worse with a piston engine and must be dealt with and
designed for, but they're not as bad as the torsional impulses coming back
from the props of a ship. And they use helicals. I congratulate the
Engineair team on their attention in the area of PSRU theory and their long
articles on the list. However, they have ignored the vast database of both
piston and turbine aviation engine reduction unit design that goes back
nearly to WWI. All of the big radials used reduction units, none were
designed the way that the Engineair PSRU is. Ditto for the turbines which
haul millions of passengers on commuter airliners and business aircraft every
day.
It is fascinating to hear all the argument over PSRU's and hear the same
people who don't like them speak highly of turboprops. All turboprops use
PSRU's.
Perhaps the difference is that the turboprop PSRU's have decades of service
and half a century of development. This is an advantage. I would hesitate
to ignore this fountain of design information if I were to ever sit down and
design a reduction unit. In fact, I would copy as much as I could from
proven designs and only make changes that were needed for the unique
requirements of the reduction ratio, prop and torque impulses of the system I
was using. As an engineer, it is not my job to invent everything myself,
especially when there is a large database of applicable hardware already
available. For an offset reduction unit on a piston engine, I would look to
the V-12 engines used in WWII and just after. Many of them dealt with far
more severe conditions than we would need on a Lancair IVP sized powerplant.
Some had short lives at excessive power levels, but that's really a function
of loading and that's what engineering is for when the solution already
exists.
Eric Ahlstrom
Star Aerospace LLC
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