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Date: Tue, 15 Feb 2005 14:04:49 -0500
From: Ernest Christley <echristl@cisco.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] For Ernest  Re: More on Header Tanks,  Venting &
 Pressure Reg Position
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Leon wrote:

First, I'd like to say thank you for the instruction, and  I look 
forward to buying you a suitable beverage at the earliest opportunity.

Second, I'm just trying to get educated here.  I won't fly anything 
until I get a consensus that it will work, from people who actually know 
something.  The wife and kids don't help much, so that leaves people 
like you.

Third, the difference between education and training.  A trained person 
knows what to do.  An educated person knows why to do it.  Neither gets 
far without the other.  I can follow the diagrams for multi-tank, 
quadruple pump systems (that's the training), but when the doesn't apply 
to my airplane the result will be an unmitigated mess unless I've been 
educated.  Training generally comes first, 'cause it's easier on the 
teacher, and then the best way to an education is to ASK, "What happens 
when I change this...?"

>So, ..."Good Luck"!!
>
>  
>
Luck is a harsh mistress.  You offer much better than that below.

>PRESSURE REGULATORS
>
>To wit,  with the EFI pressure reg.  Your assumption is wrong.  They do NOT
>maintain a SET pressure (at least in an EFI system). The fuel rail pressure
>is supposed to be dynamic,  and must be
>able to vary with the MAP (manifold absolute pressure).  At idle,  because
>the MAP is a pretty good vacuum,  the rail pressure is just under a Bar/1Atm
>LESS than at WOT
>where the MAP is essentially atmospheric,  so essentially,  from Idle to
>WOT,  the rail pressure varies just under 1 Atm/Bar or 14 PSI at Sea Level.
>
>  
>

So, I'm half correct.  The regulator maintains a set pressure, but that 
pressure is correctly referenced to the MAP.  If not connected to the 
manifold, you'll be referencing to atmospheric (or whatever other stray 
pressures you encounter), which can be a world of difference from what 
you'd like.

>If the pressure drop is NOT the same,  you are going to be forever chasing
>the correct A/F (Air Fuel) ratio
>as you climb and descend,  not to mention differences between one day and
>the next.  Which is fine if you want to do that,  but that's NOT the idea of
>a modern sophisticated EFI system.  It IS possible to simplify any system
>beyond the point of minimum functionality.
>
>  
>

First, chasing the A/F ratio is standard procedure in flight.  Part of 
the basic training.  Tracy even includes a knob on his controller to 
make it convenient.  But I will have to forward this question to those 
flying behind the EC2.  How much do you chase the A/F, and how much is 
handled by the computer? 

Second, and more importantly, will the A/F mixture be off enough for 
anyone to care?  I flew the first 30hrs of flight training full rich.  
Everywhere, all the time.  Wasn't until I went out with one of the 
younger instructors on a short cross country that anyone bother to 
explain how to use the mixture knob.  If I'm rich at idle, will it make 
a difference, and couldn't I just tuned the EC2 so that it know to 
deliver less fuel at those settings?

And third, I now see why the regulator is located so close to the 
injectors.  'Cause that is where the reference pressure is.  If is moved 
further away you kill its response.  Hydraulic damping of the pulses 
caused by the injectors is handled by the dampener.  (Correct?  I'm 
assuming someone chose that name for a reason.)  But if the manifold has 
to suck down the pressure in volume of a 6ft hose before the regulator 
can respond, you'll be over rich when the throttle is closed until the 
regulator can catch up.  When firewalled, you'll be lean for the same 
reason.  I think was Rusty that went through this recently to determine 
how much 'capacitance' to add to the MAP sensor on the EC2 to get smooth 
throttle response.  Would the use of a 'hypodermic' hose solve this 
problem by eliminating nearly all of the volume?

In any case, the third issue may be the deal breaker.  The beauty is the 
system I proposed was a single firewall penetration for the fuel 
system.  It is no harder to make a penetration for a return line, and 
then have the advantage of a constant flow of new fuel, than it is to 
make a penetration for a MAP line.