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Date: Sat, 19 Mar 2005 17:40:21 -0600
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Engine size
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Ed Anderson wrote:

>----- 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
>
duhhh....

Senior moment. Must have been the stress of working on my tax return. 
I'll think of a good excuse eventually.

I can say that going from a 62" dia climb prop to a 70" dia cruise prop 
shortened my takeoff roll by probably 20% & added about 5 kts to cruise 
at 100 lower rpm on a Lyc powered RV-4.

Charlie