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Subject: Re: [FlyRotary] Re: Why Apha N??  : [FlyRotary] Re: With great power comes...the ability to muck things up
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From: dmlobner@gmail.com
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Date: Wed, 16 May 2012 14:39:16 -0500
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Ernest,

What version of mega squirt are you running?

Dustin

On May 16, 2012, at 2:19 PM, Ernest Christley <echristley@att.net> wrote:

> Ed Anderson wrote:
>> Good to hear you are back in  business, Ernest
>>=20
>> I do have one question - why did you switch from Speed Density to Alpha
>> N. For sea level applications high power operations I can sort of see
>> using Alpha N - but for aircraft application I would have assumed Speed
>> Density would be a better choice.  Would be interested in why you went
>> with Alpha N
>>=20
>=20
> I don't have a mixture control.  The throttle plate is fully opened at 50%=
 of the throttle lever's movement.  The design
> is to run the engine as close to lean cutoff as it will smoothly run up to=
 point where the plate is fully open.  Then I
> start making it richer, quickly skipping the peak EGT with a retarded spar=
k, until I'm at 12.5 AFR or whatever makes max
> power when I have the throttle full forward.
>=20
> To accomplish all this, I will actually have to use a mixture of Alpha-N (=
AN) and Speed-Density (SD).  The MegaSquirt
> lets you combine a primary and a secondary tune table with various percent=
ages of each.  Backing up one more step, you
> have to have a basic tune on each method before you can sanely combine the=
m.
>=20
> So here is the game plan.
>=20
> 1)  I make AN work as described.  Lean up to 50% throttle travel, then go r=
ich.  I misspoke in the previous email.  AN
> is what I have working now.  As long as I stay at sea-level pressure, this=
 will work reasonably well.
>=20
> 2) I create a separate tune using SD.  This tune will run at best power ac=
ross the throttle control range.  Once the
> throttle control hits 50% and the plate is completely open, the throttle w=
ill add no more power; the computer will be
> injecting the same amount of fuel from 50% to 100% of the throttle travel,=
 because it will be ingesting the same amount
> of air.
>=20
> 3) Now I combine the two.  Conceptually, the SD tune will modify the AN tu=
ne to compensate for density altitude.  *When
> I'm strafing Myrtle Beach at 75% throttle to impress all the bikini clad b=
eauties, the SD tune sees sea-level pressure
> and tells the computer to give 100% VE.  The AN tune sees the throttle at 7=
5% and tells the computer to give 75% VE.
> The result is the computer give 75% VE.  Hot and flustered from the bikini=
 clad beauties, and having been slapped on the
> back of the head from my wife not appreciating them, I climb to the cooler=
 air at 12,000.  SD sees half the pressure
> 50%, so it tells the computer to give 50% VE.  I still have the throttle a=
t 75%, so AN says 75%.  The result will be the
> computer sets the VE at 37.5, and turns the injectors on just long enough t=
o give me 75% of the power available at that
> altitude.
>=20
> TBD are what the SD tune looks like (I can pull numbers from the AN tune t=
o get started), and what the combination looks
> like.
>=20
>=20
> *All numbers represented are fictional.  Any resemblance to actual numbers=
 is purely coincidental.
>=20
> --
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