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From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-811438@logan.com>
Subject: Re: [FlyRotary] Re: Engine size
Date: Sat, 19 Mar 2005 17:28:17 -0500
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----- Original Message -----
From: "Charlie England" <ceengland@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, March 19, 2005 12:22 PM
Subject: [FlyRotary] Re: Engine size


> randy echtinaw wrote:
>
> > Gentlemen,
> >     I am building an acro rated single seat biplane that the designer
> > has limited the max. engine size to IO-360. I am surmising that this
> > engine limitation is based on weight and airframe maximum speed. I
> > have decided to use rotary power and am slowly developing a plan as to
> > what I will use. I am looking for a little more help going "vertical."
> > The rotary weight (less) will be a bonus. I am not an engineer and am
> > not even related to one so my question:
> >     Can I go to a P-port 2 rotor in the 230-240 hp range if I do not
> > exceed the max. airframe speed.
> > Thank you,
> > Randy
>
>
> It's like real estate, except 'prop diameter, prop diameter, prop
> diameter'. I'm no aero engineer either but I do hear them talk about
> stuff like 'mass flow' increases with increases in prop diameter. Vance
> Jaqua, who contributed to the design of the KIS kit a/c, published a
> chart several years ago showing prop efficiency for various diameters at
> various speeds & it's pretty amazing what extra diameter can do,
> especially if you're stuck with fixed pitch.
>
> I don't know if Tracy or Ed flew their 68" props on the 2.85-1 gearboxes
> but if they did they could give you an idea on how much difference extra
> diameter makes on the same power. I believe that both are now running
> 74"-76" diameter with radical increases in climb performance.
>
> Relatively small increases in prop diameter result in large increases in
> climb ability. Consider that 160 hp in a 2seat helicopter will lift the
> a/c & 2 people straight up.
>
> Talk Tracy into making you a gearbox with the 3-1 ratio or talk to Ken
> Welter http://homepage.mac.com/rotarycoot/ about one of his belt drive
> reductions & build long gear legs for prop clearance.
>
> Charlie
>

Charlie, we could not compare the 68" prop on the 2.85 gear boxes because
the 2.85 rotates opposite to the 2.17. We might upset some of our canard
friends trying it.   However, I can tell you the combination of the increase
from 68-76 inch in prop diameter combined with the 2.85 gear ratio make a
considerable improvement in take off acceleration and climb - actually added
about 4-5 mph on the top end as well.  I have hit 6800 rpm in WOT level
flight.  I would think an areo type aircraft would have to use at least the
2.85.

Ed A
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com