"Echo Lake Fishing Resort (Georges Boucher)" wrote:
Hi! I'm a new subscriber and have a couple of questions. I'm building a STOL Christavia Mk IV on floats (2200lbs gross) using a 1991 13b NA 6 port Mazda engine with RWS's 2.85:1 PSRU as well
as
there EC2 EFI/Ignition & EM2 Monitor. I'm considering a 2 blade 84" Ivopro Prop or a Warp Drive 72" 4 blade . Here are my questions, I want 200 to 220 hp ( I also want reliability, not a hand
grenade), what kind of porting should I do street port? P-ports? where can I get templates, I was told Mazdatrix but couldn't find templates on there site. Second I have 38 years experience as
a
mechanic but never had anything to do with rotaries, please critic the above combination any suggestions would be appreciated.
Regards.
Georges & Gail Boucher
Well for over 200 HP you will need a p-port or a turbo charger.
A p-port is cheaper, weighs less and is more reliable than a turbo.
A Christavia on floats is unlikely to cruise long distances at 14,000 feet
where a turbo charger would pay off big time.
The basic 2 rotor engine is structurally good for 800 HP.
A Warp drive would probably work but a wood prop might be slightly more
efficient. Large diameter is good for low speed thrust but 84 inch might limit the
RPM and therefore the HP. You want to shoot for about 7500 RPM for takeoff.
My guess for a first cut is keep the prop diameter down to about 76 inches.
Best to use a variable pitch prop with sea planes. An IVO prop is variable
twist which is not what you need. Also Ken Welter has extensively used NOS
in his 3000 pound Coot to get it off the water.
Paul Lamar
"Echo Lake Fishing Resort (Georges Boucher)" wrote:
Hi! Paul
Thank you for your reply to my questions. From what I read 200hp with street porting is attainable ( local racer claim 212hp, how true I don't know). I'm concerned about idle speed with P-ports
on
a float plane. I'm considering street porting with NOS for take-off on small high lakes. I have a McCauley FFA 7563 prop. (from a 180hp Grumman Tiger that I can use as measuring stick without
NOS.
I have little knowledge of NOS possible ill effects on a rotary and would appreciate any input. What is your opinion?
Regards.
Georges & Gail Boucher
Yes the idle might be a problem. Power Sport and others put butterflies close
to the rotor housing and claimed the idle was much better but I don't
have any numbers. On the other hand with a 2.85:1 PSRU the engine can idle
at 1750 RPM while the prop is turning only 600 RPM. About the same
as most direct drive AC engines can idle. I am almost certain a P-port with
the throttle close to the rotor housing will idle at 1700 RPM.
Here is a P-port slide throttle that is worth 10 or 15 HP over butterflies.
I am working on designing a sheet metal version that will be cheaper to
makes.
Paul Lamar
"Echo Lake Fishing Resort (Georges Boucher)" wrote:
Hi! Paul
Ivopro's site shows an electrical in flight adjustable prop & Warp drive doesn't show a controlable prop.
Did you have it mixed?
Thanks.
Georges & Gail Boucher
2126 Creighton Valley Road
Lumby, British Columbia
Canada V0E 2G1
(250) 547-6434
www.echolakefishingresort.com
www.echolakefishingresort.ca
Yes that is correct. IVO is not really a variable pitch prop however. The blade
is twisted rather than pivots like a true adjustable pitch prop.
The Warp Drive is ground adjustable. Also as Ken mentioned you can add
more blades for more blade area. Ken has years and years experience
with rotary powered Coots. Here are a couple of pictures of Ken's Coot.
Apparently blade area pays off in high static thrust for getting you
up on the step and off the water. Sensenich makes air boat props with
lots of blade area. Here is a shot of a Sensenich air boat prop.
This one is also ground adjustable.
There are other ways to go. You could use a Mistral gear box that has provisions
for a hydraulic constant speed prop. Cost is around 7,000 as I recall and another
500 to 1,000 for a governor used or new. Then there is the prop it self at 2,500
to 6,500 used or new.
Another way is to use the Tracy Crook gear box and a German Hoffman or MT electric
prop. About 3,000 for the gear box and 10,000 for the prop all US dollars.
Frankly with a Christavia sea plane on floats take off and cruise speed are pretty
close together due to the high drag so a ground adjustable prop like the Warp Drive
or Sensenich is the low cost way to go. You will see little advantage with
a true adjustable pitch prop.
Paul Lamar
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