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Date: Wed, 22 Jun 2005 22:10:28 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: PP debate  was  Re: Single PP HP?
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Lehanover@aol.com wrote:

> In a message dated 6/22/2005 7:23:37 AM Pacific Daylight Time, 
> 13brv3@bellsouth.net writes:
>
>     While Lynn seems to love PP for racing, I'm not sure I've seen him
>     state that he thinks it's the best way to go for aircraft.  How
>     about it Lynn, for, or against PP for aircraft use?  
>
>  
> Either side port (Bridgeport) or Pport will work just fine for 
> aircraft use.
>  
>  This is your lucky day. I have a tube frame with a first Gen body and 
> a factory Pport engine. It has a Weaver Brothers external pressure 
> pump, but the front iron is intact, so you could go back to the stock 
> pump if you like. It has a trans but no rear end. Needs a Speedway or 
> similar quickchange. A nice trailer is included.
>  
> The Pport has shorter intake timing than the "J" Bridgeport engine. It 
> idles much slower than the Bridgeport engine and has power a bit lower 
> in the RPM range than the Bridgeport.
> It is not difficult to drive around the paddock with a tall first 
> gear. The Bridgeport is a nasty mess to drive around, and has around 3 
> HP until it get wound up a bit.The Pport is also still making power 
> right through 10,000 RPM if that ever comes up. This is a 12-A Pport 
> with about 300 HP at 10,000.
>  
> The home built 13B Pport could be much better. It is just too easy to 
> build. As I pointed out with the 12A data at 7,500 212 HP and that 
> engine has the intake tuned to give best power at 9,400 RPM. Those are 
> real Ohio HP. Not those little California HP used to sell race engines.
>  
> A well done 13B Pport with very mild exhaust work should have 230 to 
> 250 continuous at 7,500 RPM. Plan fuel pickups for a 45 degree climb 
> angle.
>  
> If you only need 220 HP then the side port is quick and easy also.
>  
> Lynn E. Hanover

It's fun to bat around the incredible numbers a rotary is capable of, 
but for most of us 160-200 hp at cruise is about the most our airframes 
are designed for & can haul fuel for. Even big 4 seaters or very fast 
glass can't use more than around 225 continuous hp efficiently (75% of 
300 hp). The airframe drag going up means you just waste gas making more 
hp than the airframe design speed calls for.

The question I'd like answered is this: What configuration can be made 
the most fuel efficient while making hp in this range?

Should it be p-port & 2.1 redrive, p-port & 2.85, side-port & 2.85, etc 
etc?

My gut is betting on a small-diameter p-port & 2.85 drive, hoping for 
good takeoff performance with a big, fixed pitch prop & keeping fuel 
efficiency up turning whatever it takes to cruise at the above power 
range. My needs in an RV-7 would be in the 160-180hp (actual cruise 
power setting) & someone in an RV-10 would need 190-210 actual cruise hp.

Charlie