Here is a little sketch I use (attached) - spark plug
holes at top, rotation CW. Note that the pulley with the 20BTDC mark is
about to reach the timing pointer. This means the lead spark plug is about
to be fired. Now if you also wanted to fire the trailing plug at the same
TIME as the leading plug then it (the trailing plug) would also
have to be fired at 20BTDC.
Now assuming you want to fire the trailing plug
later than the leading plug (as suggested by Lynn) then you would
set Trailing Plug Firing Point (TPFP) to = 20BTDC - (Desired lag
in Firing Trailing Plug). Say you want the trailing to fire 2 deg after
the leading plug, then TPFP = 20 - 2 = 18 BTDC, So in this
example the Lead plug would fire at 20 BTDC and the Trailing Plug would fire at
18 BTDC.
The key is the timing pointer reference relative to the
degrees on the pulley.
So I agree you have it correct, Ernest
Ed
From: "Ernest Christley" <echristley@att.net>
Sent:
Tuesday, May 10, 2011 10:28 AM
To: "Rotary motors in aircraft"
<flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: Stalled
again...ignition this time
> Lehanover@aol.com wrote:
>> Lets
us be sure that the trailing plugs fire at the same time or later
>>
than the leading plugs. Never before the leading plugs. Very bad
Mojo.
>>
>
>
> It is mental gymnastics for me every
time I look at this. This means that
> if I use 20*BTDC as my
firing point for the leading, the trailing should
> fire at a number less
than 20. Another way to look at it is the mark on
> the timing
wheel for the leading should pass the indicator BEFORE the mark
> for the
trailing.
>
> I'm positive I've got that right now. I'm also
positive that keeping this
> stuff straight give me a
headache.
>
>
>
>
>
>
0
10 20
>
TDC ->
|****|****|****|****|****
>
^
> leading plug set point
|
>
^
> trailing plug set point
|
>
> --
> Homepage: http://www.flyrotary.com/
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