Douglas E. Dempsey
Bellvue, CO 80512
970-221-0261
shearbond@aol.com
Questions & Comments to those interested in Rotary Power!
Questions:
1. Could someone please tell me how attempting to cool an engine that runs
at BSFC of 0.6 instead of 0.45 ......and utilizes a temperature differential
of (200-100) vs. (400-100) can result in less cooling drag? Surely it takes
so much mass of air heated so many degrees to cool so many BTU's of reject
heat?? Doesn't that lead to more sq. in. of air inlet in the airstream?
Very good point Doug. I don't think it will. The point is; air cooled aircraft
engines don't run at .45 during max power. They too run closer to .6 BSFC
when full rich and WOT. The turbo versions run .65 according to Flying magazine.
I have some data to prove this but my scanner is down. Page 21 Aircraft
Powerplants fifth edition by Bent/McKinley McGraw Hill PL
How can water do more with less?? More options for the shape of the devices
for
utilizing the ultimate cooling medium: AIR, yes! More options for placement
of devices, yes! But.......less lbm. of air??? Obviously, I am missing
something!
I agree it cannot. Bill Freeman is fond of saying that a water cooled aircraft
engines makes about as much sense as an air cooled submarines. This is
the cross we need to bear with a liquid cooled Mazda rotary engine.
2. Does anyone know where I can get waterpump technical information? Yes, I
read the PowerSports information, but it is very incomplete.
I don't and the Power Sport data is all we have so far in two and a half years.
PL
Does anyone know how to get technical information of this kind from Mazda??
I can imagine that most of it is generally uncirculated due to lack of
general interest, but I would think getting to the right persons at Mazda
Engineering would find this information is not confidential. Perhaps in
Japanese and metric for certain, but still providing valuable information
with just a little translation (my adopted niece is Japanese)!
I have read my collection of Mazda SAE papers over and over again
and I have yet to see flow data for any Mazda coolant pumps. Jim Mederer
at Racing Beat might be able to help us out on that as he has good contacts
with the Mazda factory engineers.
3. With an RPM limit of 7,000-7500 (whatever??), it is difficult to believe
that Mazda would put on a waterpump that cavitates at 6,200 RPM? Not
likely......!
I don't think 6200 pump RPM is the correct number. I also think Mazda
made improvements in the pump over the years. Bulent's 13B Cosmo engine
pump is significantly different than even the 1988 turbo engine pump.
The 1993 and later pump is entirely different and made by Kabuto
as I recall. PL
Stewart Engineering says NEVER underdrive the waterpump.
Their recommendation is 1.0-1.3 C/S RPM for the waterpump. I can imagine
10,000 RPM will cavitate the waterpumps and underdrive is perhaps the way to
go. But why does everyone think they need to underdrive the waterpump at
6,200 RPM?? Obviously, I am again missing something.
4. How can Mazda exhausts run 'hotter'? than other IC engines?? In 'Thermo
of IC Engine', we were taught that burning temperatures of various fuels
were characteristic of the properties of the fuel and the air:fuel mixtures
being burned........not what kind of vessel within which they were being
burned?? It is apparent that the BSFC of Mazda...at least at high power
outputs is higher than most other C/S/Piston IC engines and more of the fuel
energy taken in is rejected out the exhaust. My question....how does it get
'hotter' ie..higher temperatures, than any other spark IC engine at the same
air:fuel mixture ratio?
I think one answer to that (there may be others) is there is no exhaust valve
to cool the exhaust on it's way out. Less of the exhaust heat is transferred
to the block and then to the coolant through the exhaust valve stem and seat.
The price we pay for no exhaust valve. I am more than willing to pay that
price :-) PL
Comments:
The reason I am installing an auto conversion is because when I was a product
engineer at FoMoCo in the late 60's, engines were run at maximum advertised
HP for days, not hours! One has to see yellow orange headers all the way to
the head and hear the noise to truly appreciate the 'event'. I suspect
(SWAG) there is more dyno testing in a week at FoMoCo than Lycoming has ever
conducted on any engine variant in 70 years.
The issue is NOT do they (auto majors) know what to do to make their engines
last under extreme conditions......the issue is: what are the consequences of
producing 100,000's of engines which will not perform at the advertised
specifications (perhaps Firestone's current dilemma is instructive).
If you want HOT!!, try trailer towing at WOT up long grades as speeds of less
than 50 mph at near sea level elevations, as major auto mfgrs. do in testing.
Would you want, or do you believe your auto should, fail catastrophically
under these conditions?? And, of course, do you believe that many consumers
read and conform to towing limits....and keep their radiators full of clean
and fresh coolant...and tire pressures on the dot???? The major auto mfgrs.
know they don't and attempt to create testing conditions which reflect these
occurrences and compensate for them by making their tests even more difficult
than expected (unless Marketing knows better of such things!!). Of course,
there is a limit and that is where most mfgrs. differ. It is also where most
of the foreign mfgrs. went sadly astray 30 years ago, when they came into the
USA to compete. It took probably 10 years of some dismal failures before
they became convinced of the variety of conditions under which American
consumers used their vehicles and what they expected. Most of them
learned their lessons well, but for some the R&D required and the changes
which would have to be made, caused the profit to be nil. Certainly some of
you have owned one of these OK, but not suited to the task vehicles.
Of course......then again, Mazda only rated the N.A. 13B at 140 HP or
thereabouts!!
Perhaps they know something we don't Then again, 285 HP @ 10,000 is
impressive and will certainly move 3,000 lbs around on the ground...and
should kill lots of bugs the slow way on an RV-6!!
>From my experience, high HP engines are able to do one thing.....handle lots
of heat effectively. Perhaps not efficiently, but effectively. It is partly
engineering, but more likely the design fundamentals of the engine and the
compromises that were made for cost, manufacturing or intended usage
reasons..and a fair amount of fortuitous happenings (joss). In my opinion,
the Mazda developed rotary is one which flows the fuel and cools the parts up
to at least 1.3 HP per equivalent cu.in. That would mean approximately 203
HP for the 13B and 304 for the 20B. Beyond that.....one had better do lots
of sophisticated testing.
Doug Dempsey
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