Message-ID: <3F64A914.5000705@netdoor.com>
Date: Sun, 14 Sep 2003 12:44:52 -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: Good news, Bad news
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Russell Duffy wrote:

> With stock ports and
> pulling off power to limit boost. I think your only problem is the 
> waste gate
> size. Or flow, but that is the Idea.
>
> I certainly agree about the wastegate problem, and I'm skeptical that 
> porting it will help enough.  
>
> The cowl shape, or lack of a cowl is not
> going to make much difference in the climb at 100 KTS.
>
> Thanks for the confirmation of this, and to others who made it as 
> well.  It would seem that the cowl just can't be the whole problem.
>
> Taking out pitch, and then
> limiting RPM, limits excess HP required for climb. More typical would be
> enough pitch to stall the prop on a hot day and have to back off the 
> power slightly
> to unstall it until some ground speed has built up.
>
> I've been adjusting the throttle for 30 inches of MAP, rather than for 
> a particular RPM, so the RPM has in fact gone up with reducing 
> pitch.  Another reason to suspect that I'm not putting out the proper 
> amount of power is the pitch.  Warp estimated that I would need an 18 
> degree pitch setting, which is what I started out with.  Static RPM 
> wasn't constant at 18 or even as low as 15 degrees, and I found out 
> that the prop was indeed stalled to some extent at those pitch 
> settings.  My first climb RPM's were very low, 4700 with full 
> throttle, 15 degrees of pitch, and 36 inches MAP.  Reducing the pitch 
> to 12 degrees, gave me 6300 RPM at full throttle, 36 inches MAP.  This 
> is way below the pitch that Warp estimated, and I'm betting that they 
> wouldn't be off that much.  It would seem to indicate that I'm not 
> making the power I should be.
>
> Once you can lay into it at
> WOT all the way up to 6,500, you should see at least 160HP performance 
> or more.
>
> In my current configuration, I have to limit the throttle opening to 
> about half throttle, to maintain 30 inches MAP.  All along, I've been 
> assuming that this give me the same power as a NA engine using full 
> throttle.  I know there are some losses with the higher temp of the 
> intake, but I wouldn't expect them to add up to that much.
>
> Here's my question- Is my above assumption correct?  I've tried to 
> follow some intake flow discussions in the past on the RX-7 forum, 
> where they were stating that pressure isn't everything.  The idea (as 
> I think I understood it) was that having good pressure registering on 
> a gauge didn't guarantee anything, since the gauge isn't fast enough 
> to show you what's really happening.  They said that if the pipe was 
> restrictive, or there was some other obstacle to flow (throttle 
> butterflies half closed), you wouldn't get the power you should, 
> because the pressure would drop instantaneously when the ports 
> opened.  When that happens, I guess the engine doesn't get the charge 
> that it would appear to be getting from the gauge.  Is this more or 
> less what you're getting at when you say I need to be a WOT to get 
> good power?  
>
> Thanks for all the thoughts.
>  Rusty (still baffled)

Hi Rusty,

What's your fuel flow? (ultimate test) If you are tuned even half right, 
fuel flow will approximate hp.

Charlie