----- 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