Message-ID: <3F55475D.50709@netdoor.com>
Date: Tue, 02 Sep 2003 20:43:57 -0500
From: Charlie & Tupper England <cengland@netdoor.com>
Reply-To: cengland@netdoor.com
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: and another one fly's....
References: <list-2564693@logan.com>
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Russell Duffy wrote:

>     I'm experiencing similar disappointment as Rusty in my climb 
> speeds. However on the second flight we used the GPS to do a few runs 
> to check the airspeed we found that it reads 15-20 mph slow. This 
> meant we were climbing at too high of an airspeed. Even when we 
> adjusted for this is was still disappointing. I feel that a big part 
> over the problem may be that I'm over-propped.  
>  
>  
> Great news Todd.  Glad to hear all went reasonably well.  Very nice 
> temps too!  You didn't mention the climb speed that you were using.  I 
> can verify what Ed said about fixed pitch RV speeds.  My previous RV-8 
> had it's best climb rate between 90 and 105 kts, and just last night I 
> talked to a local RV-3 guy who said his RV-3 climbs best around 105 
> kts.  Why I've been using 78 kts (90 mph) is a mystery.  My buddy 
> confirmed that 78 kts would climb terribly on his plane as well, so 
> this is more good news.  For the record, he gets 2100 fpm on 160 hp, 
> so that's the initial number to beat, and I'm betting the next flight 
> will top that.  
>  
> Again, nice job.  
>  
> Rusty 

FWIW, Van 'hisself' talked about this in an RVator article several years 
ago. You've probably been using 78kts because all the books say to use 
1.x times the stall speed for best rate of climb, but it doesn't work 
that well on RV's due to the low aspect ratio wing. That combined with 
the large excess power to weight ratio  lets it climb fast at a 
relatively high airspeed. (If my rather flaky memory is working properly 
tonight...) He recommended something around 120 mph because the climb 
rate was the same but cooling is improved & you cover a lot more ground 
in the process.

On a slightly related topic, I tried out various approach speeds on the 
-4 I purchased recently. The sink rate on the VSI was the same at 90 mph 
& 70 mph.
 
Charlie