Dave Arbogast wrote:
Can we safely turbocharge / port a Renesis to achieve 310 hp? Or is it
safer
to
do so with the 20b?
How much would a new Renesis cost from Mazda? The one on ebay is over 5k
and
has
not reached the reserve yet.
--
-dave
http://arb.net
Hello Dave,
How many psi of boost would you have to give to achieve the 310 hp? at sea
level? Assume you are thinking about the 247 hp. 6 side port RENESIS?
Doug fir
The problem with that Doug is as of right now there are no low compression
rotors out
there for the RENESIS RX8 engine. My guess is 10 psi would make 310 HP for
you on the current engine. IMHO if you try 10 psi with the current high
compression
RX8 rotors you risk detonation.
Paul Lamar
BTW I think a bit more explanation is needed on the RX8 engine. Yes it is
rated
at 8500 RPM. That implies that you find a 3:1 psru and run the prop at 2830
RPM
for takeoff. That is possible for a 65 inch or so prop but that is not
the prop you need for a heavy aircraft let alone an amphibian. This is because
the
tips of the prop run into a drag brick wall drastically increasing the
HP consumption without transferring the engine HP to thrust.
The situation is worse with a 2.85:1 gear box. In that case prop RPM would
be 2980. In any event for a heavy airplane you are going to need a large
diameter prop around 72 to 74 inches. Max prop RPM and I am guessing here is
down
around 2400 to 2500 hundred so you will not achieve the max HP of the RX8
engine. My guess is 7300 engine RPM or about 220 HP is all you are going to
get with a 72" to 74" PROP and an RX8 high power engine. Not the automatic
RX8 engine. A turbo charger can make up for this of course.
For good MPG at cruise you will need to slow the airplane and the engine RPM
for best BSFC. That will require a variable pitch prop. Best BSFC never occurs
at high engine RPM due to engine friction. Another factor is the tip velocity
of the prop at a given RPM increases with forward speed. The tip velocity is
the vector sum of the forward velocity and the circumference velocity of the
tip. See the chart below.
Right at the moment and well into the future I will not be able to predict
what that power and engine RPM setting is because Mazda does not release a
BSFC map for any of the engine they have made. It is going to be best
done by experiment on a specific airplane.
Here is an old summary of the problem from a pre WW II book.
Paul Lamar
Douglas Fir wrote:
Hi Paul,
Thanks for the insight and detailed explantion. SeaWinds typically use 76"
constant speed props. Even with the MX constant speed and Beta able prop
four blade 74" dia. it looks like I may be trying to get more out the RX8
engine than possible at this point. Perhaps I am chasing the holy grail
here. Light weight, high good cruise performance, and high horsepower
occasionally. A turbo normalized 20B will work without a doubt and I may
have to look at weighs:) to lighted it up significantly. I will go to
Racing Beat Monday the 17th. I'll probably head towards SLO on the morning
of the 18th.
Still thinking
Doug
For an amphibian probably a fair solution would be to get one of Francois
gear boxes and use a relatively low cost, used, constant speed hydraulic prop.
May be lower in overall cost than paying the Germans for a Hoffman or MT
electric prop at $10,000. Another alternative that might work is a 3 blade IVO
(shudder) with root cuffs. Not exactly variable pitch more like variable
twist but it might be better than a fixed pitch prop.
Paul Lamar
Paul,
In this discourse, you mentioned "heavy aircraft"-- can you give me your definition of "heavy" in this context? I'm looking at a GW of 1850 lbs in the final form. I want to make sure I can get what I need from a 13B without extensive modification.
Bob
1850 is no problem. Heavy is 3000 pounds gross. Then the 13B becomes marginal.
BTW Jerry Bass blew a water hose and crashed. This was similar to what happened
to Ian and Ken. He is OK. Pay close attention to the plumbing guys. Use SS
braided AN hose wherever possible and the right kind of hose clamps,
hose barbs and silicone coolant hose when AN is not possible. Car type plumbing
is an accident waiting to happen.
Paul Lamar
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