Received-SPF: softfail
 receiver=logan.com; client-ip=64.102.122.148; envelope-from=echristley@nc.rr.com
Message-ID: <46448F51.4060906@nc.rr.com>
Date: Fri, 11 May 2007 11:44:17 -0400
From: Ernest Christley <echristley@nc.rr.com>
Reply-To: echristley@nc.rr.com
User-Agent: Thunderbird 1.5.0.10 (X11/20070403)
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: EC2 question
References: <list-2037910@logan.com>
In-Reply-To: <list-2037910@logan.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Finn Lassen wrote:
> I'm not Tracy but the way I understand it is you don't want this.
> Why did Powersport get such poor fuel efficiency against the Lycoming 
> fly-offs in the RV-8's.
> Because there was no option for leaning past max power setting.
>
> I guess you could have a max-power/best-fuel-efficiency switch, but 
> then again you don't have a single lever. And there would probably be 
> times when you want something in-between and you're back to the 
> variable mixture control.
>
Could we discuss single power lever controls for just a moment, because 
I've been thinking about this for a while.  I'm eliminating leaded 
gasoline, and I'm willing to accept the inconveniences that will 
entail.  A 50gal tank mixed with a roadable airplane makes that somewhat 
easier to accept.  This makes a closed loop system with a wide-band 
oxygen sensor possible, ie the computer always knows the fuel-air ratio.

As I see it, there are two regimes to consider.  Max power and max 
efficiency.  Max power occurs at a ratio of about 11 or 12, and max 
efficiency at a ratio of 16.5 to 17.  We don't have to worry about 
burning exhaust valves so running a peak EGT is a non-issue (assuming 
the exhaust is designed to handle peak EGT).  One less thing to worry over.

The way I think the single lever should work is that the TPS should be 
located on the throttle lever (instead of on the throttle).  The 
throttle plate should operate normally, except that the last 10 to 15% 
of travel is spring loaded.  That is, the lever will have some motion 
left, but the throttle is max open.

How this works.  For the first 85% of throttle travel, operation would 
be exactly as normal.  The computer senses throttle opening and operates 
the injectors to feed an appropriate amount of fuel to maintain the most 
efficient operation.  It would be easy to tune to the most efficient 
point by searching for the lean surge at each TPS set point.  If you're 
running at half throttle, is there ever a need to try to flood fuel to 
the engine for more power that couldn't be done by opening the throttle 
a little more?  I seriously can't think of a reason to provide more fuel 
than needed for smooth operation when the throttle isn't fully open, but 
I'm willing to being disavowed of any misconceptions I have.

Now, once the throttle hits the full open, the lever still moves, but is 
compressing a spring instead of moving a throttle plate.  The computer 
sees the throttle position indicator still moving, and begins adding 
more fuel to enrich the mixture.  85 to 90% would move the mixture to 
15, 90 to 95% gives you 14, 95 to 98 give you 13, and 98 to 100% gives 
whatever is the exact best power ratio.  The last 15% of throttle 
movement would progressively enrich the mixture, and in effect becomes a 
mixture control, the computer interpolating between set points.  A 
detent at the 85% switchover point will give the pilot positive 
indication that they've crossed over from enriched to max efficiency.

In operation, the mixture is automatically enriched for start and 
warm-up.  The pilot taxis at highly reduced power, always at max 
efficiency.  The runnup won't require a cross into the heavy fuel 
regime, so he's still at max efficiency, power controlled by adding more 
air.    He gets clearance, lines up and goes full throttle.  The 
computer senses 100% throttle and pours fuel in to get that 12 ratio.  
Pilot clears the trees, and pull back to a cruise climb with the 
throttle at 90%.  Happens to be a little shy of lean of peak, the 
throttle is full open, but the pilot doesn't care as he's getting the 
climb rate he wants.  Pilot reaches altitude and rolls the throttle back 
to 75%.  The throttle plate is cocked sideways a bit, and the computer 
is delivering just enough fuel to maintain the max efficiency.  If more 
power is necessary, move the lever.  When the engine can't give more 
power by opening up the throttle plate, it will start giving more power 
by adding fuel...to the point where it can't give any more power.

The system would be exactly the same for ground vs altitude, or if you 
added a turbo or supercharger.  Give max efficiency until the throttle 
is completely open, and then start working toward max power.

Comments?