In a message dated 1/5/2005 8:24:43 AM Central Standard Time, 13brv3@bellsouth.net writes:

<<  If we
shoot for making top power in the "low" 7000-7500 rpm range, will we gain
anything from the PP configuration?  In other words, if you compare a street
port, to a tamed PP at 7500 rpm, will there be significantly more power with
the PP?  >>


I see the advantage as a simplified induction system and a big weight reduction. Even a poorly done Pport will out perform a big street port. You can do the street port on an Iron set in one day. The Pport would take 2 days. You can buy or may own the manifold, for the big street port. You have to manufacture the most of the manifold for the Pport. You could start with the RB Pport manifold and add the extension runners. But that makes the mating face on the home made Pport more complex. Just a tube sticking out of the housing is adequate. Best power from a big street port is about 229-230 HP at 9,000+ RPM. Power Sport Pport is about 215 at 6,500 RPM.

My bridge ported 12A has 173 HP at 6,500 RPM and 196 HP at 7,000 and 218 HP at 7,500 RPM. and 244.9 at 9,400 RPM. With the higher ratio reduction unit, the idle performance is less of a factor. So more exotic porting could be used with little effect on the aircraft. You could have a high engine idle speed and a low prop rpm, so ground handling would be normal.

If you do a big street port, and keep the ends of the side seal supported, you can build the Pport engine later, and use the same irons. Or build a whole second engine with irons that are unpopular in other applications. So long as they are flat and rust free before assembly. The runners and port openings will be filled with epoxy anyway.

Look up the HP numbers for popular piston airplane engines. Note that some are rated at 2,700 or 2,750 RPM. That RPM is not attainable for continuos output, or not at all with an approved prop in place. Some are in fact limited to lower RPM with approved props. So the rated (advertised) HP of these engines is never available unless the nose pointed straight down, and in most of those cases, additional HP is not on your mind.

Now a propeller doesn't know about RATED HP and what RPM the crank breaks, and so on. The prop knows RPM and torque. So to compare a non aviation engine to an aviation engine we need the flat out full throttle RPM the aviation engine will be turning in cruise at say 6,000 feet, or wherever you like to run. So you need dyno sheets that show the power at that RPM and that figure needs to be corrected (SAE) from sea level to 6,000 feet to get a figure to bandy about.

Now suppose that the rotary engine/reduction drive were not two things bolted together, but just another airplane engine. So as long as it is inside the cowl we can only measure the propeller RPM and torque at the prop flange.

So with a max prop RPM of 3000 a 2.17 drive will get you engine 6,510 RPM.
At 6,500 the little 12A has 139.6 foot pounds of torque or (x 2.17) 302.9 foot pounds at the prop flange. With a 2.85 reduction and 3000 prop RPM, the engine could turn 8,550. Not all of the time of course). and at that RPM prop flange torque would be 147.7 (X 2.85) 420 foot pounds. So now you look up what (real) airplane engine has 420 foot pounds of torque. (if we are to believe the advertising). So if you can find some airplane engine dyno sheets, and using the cruise RPM typical for that engine, and the max RPM with a typical prop, What is the Torque at that HP number? Compare that number to the rotary with reduction box. And that is how Tracy goes faster than the 360s. Lynn E. Hanover