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Date: Wed, 21 Jul 2004 17:23:58 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Tracy Report
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Russell Duffy wrote:

>  Since Tracy and I had the same static rpm with the previous props 
> (which were the same made by Performance Prop), I expect I would have 
> the same static he is getting if I had the 74" which I believe he 
> indicated was around 6200 rpm or about 1000 rpm higher than with the 
> old 2.14 and 68x72" prop.  That 1000 rpm increase will translate into 
> approx 30HP more for take off and move the torque from 345 lb-ft to 
> 455 lb-ft or a gain of approx 110 lb-ft torque for take off.  
> According to my spreadsheet that would move the take off HP from 
> around 155 up to 185 for a standard day - in the cooler weather of 
> all, it will be even more impressive.
>  
>  
> Talking to Tracy about the difference between his B and C setups got 
> me all excited again.  Sounds like he was REALLY happy with the 
> performance difference. 
>  
> There's a fairly simple formula I saw once that converts excess HP to 
> climb rate, given the weight of the plane.  Do you have that?  It 
> would be interesting to see what 30 extra HP would do. 
>  
> Cheers,
> Rusty (I need a runway)

1hp=33,000 lb raised 1 foot per minute

A rough number should be 33000/gross weight * excess hp.

@ 1500 lb, 22 fpm per hp, minus small compensation for drag due to 
increased angle of attack.

Does that pass a sanity check?
Charlie