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Message-ID: <4C67EE2F.3040904@canardaviation.com>
Date: Sun, 15 Aug 2010 09:39:59 -0400
From: John Slade <jslade@canardaviation.com>
Reply-To: jslade@canardaviation.com
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Turbo Questions
References: <list-4431440@logan.com>
In-Reply-To: <list-4431440@logan.com>
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  On 8/15/2010 9:03 AM, Ed Anderson wrote:
> The engine doesn't know or care how this increase in pressure comes 
> about - well, actually it does. If you use a turbo or supercharger you 
> are also heating the air through their compression process (which is 
> why you need an intercooler in many cases) thereby moving closer to 
> detonation. 
Ed, this sentence summarizes the advice I received from the Aussie 
rotary expert, Leon Promet (anyone know what became of him?) and others. 
The way he put it, using the non-turbo (9.7:1) rotors in a turbo 
installation gets you an extra 30 HP "for free" because this part of the 
increased pressure doesn't involve heating the air via the turbo. You 
still have to deal with the potential detonation either way if mixture 
and timing are wrong.

My experience with detonation (or pre-detonation) was much less severe 
than yours. I heard 'popping' at high rpm during run-up at around 44MAP. 
Reduce the throttle a hair and the popping ceased. This was with a big 
fixed pitch prop that I could only turn at around 4900 rpm. I had the 
feeling that it was rather like flooring a car in top gear on a hill. 
(remember in the old days before ECUs and knock sensors when that would 
get you a popping sound?). I was able to fly my first 40 hours with no 
issues from detonation by keeping the throttle away from the area that 
caused it during runup. I never experienced (or at least heard) any 
popping once airborne, even during a high-speed run at 44 MAP and 6300 
rpm. I once tried hooking up a knock sensor to the intercom without 
success. I never had any damage to the plugs.

When I installed the adjustable IVO prop my static rpm when from 4900 to 
5600rpm and the popping sound disappeared (analogous to changing gear on 
the hill?). I haven't experienced any popping since. I think Tracy's ECU 
does a good job of providing a rich mixture at high rpm to keep you away 
from detonation.

Regards,
John Slade
Cozy IV, N96PM