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Bill,
Bob has responded better than I could have.
There may be a problem with the word "staged". I've see it used where
staged means using only the primary injectors and also sometimes the
opposite where it means using all of the injectors. I've tried to use
the terminology of MAP above or below the staging threshold to avoid
confusion but may not have been successful at this.
Steve Boese
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Bob White
Sent: Monday, July 13, 2009 7:37 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: cold switch and injector backup mode
Hi Bill,
What you've posted below shown behind '>' :
> Below staging manifold pressure, cold start doubles fuel flow by
> turning on both sets of injectors, effectively canceling staging.
True, but I think this the right way to look at it is that the staging
bit cuts the pulse width in half at the same time the cold start switch
doubles it, so the net effect is that both sets of injectors are being
triggered with the same pulse width you started with (below staging).
> The injector disable does not work above the staging point. If you
> kill one set above the staging manifold pressure, you will just be
> running on one set at the normal pulse width. This will result in
> only half power or less available anywhere above the staging point
> manifold pressure.
Not true, mostly. If you've disabled one set of injectors below
staging, then the engine is receiving the correct amount of fuel and
it's effectively running as though it only has two injectors. As power
is increased, the pulse width increases until the injectors are flowing
the maximum amount of fuel possible. The total power will be limited to
that level, but not half. If two injectors will flow enough gas to run
at full power, then you will be able to produce full power.
You aren't running with the "normal" pulse width above the original
staging point. The staging point would have cut the pulse width in
half, but since the staging has effectively already taken place, the
pulse width is correct for above the old staging point also.
So, your assumption will be true only if you require both sets of
injectors to produce full power and they will only do so if running at
full capacity. Two 50# injectors will flow 100 lb/hr and at a bsfc of
.5 that will allow 200 hp, or at .6 bsfc, 166 hp.
In thinking about it this way, it seems to me to be a bad idea to use
the small RX-8 injectors for the primaries, because disabling the
secondaries would limit you to less than half power. Mazda does it for
better idle in the car, but not a big problem in aircraft use. Better
to use the same size injectors for primary and secondary and size them
to maintain enough power for level flight as a absolute minimum. There's
a problem even then as it's easy to push the engine too lean with the
throttle when the injectors max out. Same size Pri and Sec also
eliminates one adjustment in the EC2, and it has more than enough
adjustments as it is. :)
Bob W.
On Mon, 13 Jul 2009 19:50:12 -0400
"Bill Bradburry" <bbradburry@bellsouth.net> wrote:
> Steve,
>
>
>
> If I understand your observations.embedded below.
>
>
>
> Bill B
>
> _____
>
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
> On Behalf Of sboese
> Sent: Monday, July 13, 2009 6:24 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] cold switch and injector backup mode
>
> This weekend I had a chance to make some observations concerning the
> previous discussion on the use of the cold switch and the injector
> backup mode on my EC2 used with a 13B.
>
>
>
> When idling, turning on the cold switch results in all four injectors
> delivering fuel at the pulse width that was used by the primary
> injectors before the cold switch was turned on.
>
> Below staging manifold pressure, cold start doubles fuel flow by
> turning on both sets of injectors, effectively canceling staging.
>
>
>
> When idling, turning on the cold switch results in the staging data
> bit changing from indicating operation at MAP below the staging
> threshold to operation above the staging threshold even though the MAP
> is very low.
>
> When staging is canceled by the cold start switch, it is indicated on
> the EM-2
>
>
>
> With the cold switch on, gradually increasing MAP results in a
> gradually increasing injector pulse width from idle to full throttle
> with no discontinuity when the staging threshold is crossed.
>
> Cold start has no effect on the fuel delivery after the normal staging
> point has been reached.
>
>
>
> Turning off the power to either the primary or secondary injectors has
> no effect on the pulse width applied to the injectors or the status of
> the staging data bit.
>
> The injector disable does not work above the staging point. If you
> kill one set above the staging manifold pressure, you will just be
> running on one set at the normal pulse width. This will result in
> only half power or less available anywhere above the staging point
> manifold pressure.
>
> This does not sound like the way I had previously understood the
> injector disable to work. Are you sure you have it wired correctly?
>
>
>
> Based on the above observations, it appears that the EC2 does not need
> to know whether or not power is being sent to the injectors.
> Regardless of the MAP at the time, turning on the cold switch results
> in the EC2 operating with all four injectors as if the MAP was above
> the staging threshold but with a pulse width appropriate for only two
> injectors being used.
>
>
>
> My statements below concerning the cold switch position appear to be
> in error. The position of the Cold Switch is not one of the things
> contained in the data log captured from the EC2 so that piece of data
> was from my memory which is poor at best. Sorry Bob.
>
>
>
> I probably should have maintained the "Avoid reading.." subject line.
>
>
>
> Steve Boese
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