Paul,

     the trigger pulse repetition maximum of about 250ms is a build in
     feature in the MSD unit. M&W does not have it, that is why it works.
     It certainly has nothing to do with battery voltage.

     Richard Sohn

     I don't understand what you mean about this. "pulse repetition
     maximum of about 250ms"

     Did you mean 2.50 ms??

     If you did I don't think that is right because the rotary racers are
     turning up to 11,500 before shifting with MSD. systems. Lynn Hanover
     raced his rotary for years at 9300 RPM


     133.3 revs per minute. 2.22 revs per second  at 8000 RPM. There are
     a thousand ms in each second. That is one rev in 2,222. ms. That is
     a long time in a micro computer.

     Check my arithmetic.

     This is with a 3:1 gear box. Most aircraft people won't turn the
     engine that fast.

     The MSD 6 is a real old design. Great improvements in switching
     transistors have been made in the last few years so it is now
     possible to build a system with better specs. Better even than the
     M&W. Check out the Mallory CD.

     Here is a 3 rotor on the RB dyno with six MSD's

     For years it was the standard ignition for rotaries.


     Paul Lamar



     What I am saying is if the second trigger is not coming at 250 ms
     after the first one there won't be a firing. The first trigger never
     does fire. Once the time between the first and subsequent trigger is
     less then 250 ms it will always fire. I can only say how it is, I
     have no idea what is behind that. I could never find anybody at MSD
     willing to talk.

     Richard Sohn

     The MSD is a very complicated circuit. The engineer that designed it
     may be dead.

     500 RPM is  8.33 rev per second. Or the period is 120 ms. 250 RPM is
     twice that period or 240 ms

     So what I think you are saying..... unless the starter can turn the
     engine over at least 250 RPM the engine won't start.

     Obviously hand propping is out of the question.

     Does that sound right?

     Paul Lamar

   Right Paul, that is it.  If you are using one unit per rotor, you have
   the same frequency as the single rotor and possibly the same problem.
   But there is the M&W to save it.

   No, I am not a M&W sales man. It just saved my day with the airplane.

   Richard Sohn

   You could fix that easy enough with a 555 oscillator. Then it could
   be hand prop-able.

   You should have contacted me :-) I could wip you up something
   'pretty quick :-)

   The MSD 6 is now well and truly obsolete.

   Paul Lamar

The MSD-6AL is for severe service as in dirt cars and off the road. It is (was) potted solid. It has a built in rev limiter controlled by plug in chips. Keep in mind that these fire once when turned on. And, once when turned off.
The car or prop may move without warning.

Lynn E. Hanover



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