Alan Tolle wrote:
I need to clean up a few topics.
First to Niel Kruiswyk:
Yes, the weight and location of the four inch prop extension on the
prototype RV-6A were included in the calculations.
I agree that the placement of the water radiator(s) in the aircraft of
Tracy, Ed, and Jim as far forward as possible is a step in the right
direction weight and balance wise. But I suspect that these installations
are cooling limited. By that I mean that when these engines are producing
the 160 hp expected of them they will also be producing more heat than the
cooling systems can exchange.
I realize that for Tracy high performance was never an essential ingredient
in his formula. He clearly stated his objectives (modest performance at a
modest price) in his project and I think he met them admirably. (His
monograph has helped immensely in the guiding of others who desire to do
their own rotary engine conversions.) He may have gone to top speed for a
short time just to see what top speed was. But I don't think that on a
standard day at sea level he could hold that power for 30 minutes without
runaway water and oil temperatures. From the conversations Tracy and I
have had over the years I don't think that kind of performance is really his
concern. Other considerations, like fuel consumption, are more important.
Hence all the work on EFI. Correct me if I am wrong here, Tracy. It
doesn't sound like either Ed or Jim has had the opportunity to explore the
high performance end of flight testing as yet.
>From personal experience I know that a large enough water radiator installed
vertically behind the engine, coupled with an effective manually controlled
cowl flap, can exchange all the heat that a 210 - 215 hp peripheral port 13B
can produce at full tilt, and can do it all day. From what I read on these
pages some builders want that kind of performance. So that builder has to
plan for space behind the engine, which means a short gear box, which
improves the center of gravity situation as a bonus.
Neil, I noted earlier that your 235 Lancair was a special airplane which
required a special solution. It was designed around a lighter engine in the
first place (Everett Hatch built the engine for Lance for the prototype)
and the longer gear box may be just perfect with the water radiators in the
baggage compartment or in a belly scoop. It all depends on how your weight
and balance works out, and on the air ducting currently being discussed.
The Lancair project which Paul recently outlined sounds exciting and very
challenging technically. Go for it!
To Ed Anderson:
The Chris Ross data quoted from the Contact article gave the weight of their
suggested engine conversion, with accessories and ready to run. at 260
pounds. The Powersport 200, same configuration, was 265 pounds. Very
close. The main differences on the Powersport engine, besides the
peripheral porting, were stock oil pan and engine orientation, shorter gear
box (which moved the engine CG farther forward). Bendix style fuel injection
made by Airflow Performance, and home grown electronic ignition.
Ed, your center of gravity calculations look very much like mine. If
anything we are both slightly nose heavy which only means we can carry a
larger baggage load with impunity. You have already observed the presence
of adequate elevator authority to flare. Enough said. I look forward to
seeing your work someday.
Several have mentioned aluminum side housings. For the aircraft engine, I
doubt it, even though such side housings are available in the racing world.
Both the first and second prototype engines built by Everett Hatch had them,
home grown no less. Together the two engines accumulated about 400 hours of
flight time. Main problems were creep distortion and inadequacy of the wear
surface. Nothing much beats the nitrided surface of steel or nodular iron.
In the aircraft engine, durability has always come before light weight, and
it should probably stay that way. In the racing world engines are
expendable and if one breaks you put the car back in the trailer.
Jeff Spitzer noted that diesel in 100LL lowered the octane rating. And how!
Remember that in 1994 Chevron let a little diesel get mixed in with the
100LL at the Concord refinery.. The octane got a low as 89 at some pumps,
and the Company spent millions of dollars buying a lot of their customers
new engines. Literally, the customer had no choice --- he got a new engine
whether he wanted one or not. I know because one of my engines was
involved. I had purchased 21 gallons of the contaminated fuel at
Watsonville.
To utilize any kind of two cycle oil in the crankcase so that the stock
metering pump can lubricate the apex seals with something that will burn
cleanly leaves me wondering just how good of a job the two cycle oil is
doing inside the engine performing the tasks of lubricating the main and
rotor bearings, rotor timing gear teeth, and the various other things which
go around. The account from a car driver is interesting, but I think only
a petroleum chemical engineer can answer the lubrication versus clean burn
question. I am perhaps more concerned with the idea of crankcase oil
depletion in an airplane. When I see an RX-7 parked along side the
freeway I always wonder if it ran out of gas, or ran out of oil. They do
both.
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