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R-4360 Pratt & Whitneys Major Miracle Book

 
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rwahlgren



Joined: 15 Aug 2003
Posts: 139

PostPosted: Sat Nov 01, 2008 19:57    Post subject: R-4360 Pratt & Whitneys Major Miracle Book Reply with quote

I have a correction.

On page 90. LOW TENSION

"Each magneto fired the seven cylinders making up a row"

There are 4 magnetos on the low tension engines.
The upper magnetos are numbered R1, L1 and the lower magnetos respectively are numbered R2, L2. The R stands for Right, and the L for left and are physically situated on the engine like that.
Now on aircraft engines for safety reasons the manufacture keeps the ignition system redundant by having at least 2 magnetos and 2 independant spark plugs per cylinder. The statement on page 90 would make you think, eash magneto fires all spark plugs in the row, since the R-4360 does have 4 rows, and 4 magnetos. That is not the case.
Each of the 4 magnetos has a point breaker cam with 14 lobes on it similar to what an R-1830 has. So it is obvious that the magneto is meant to fire the spark plugs in 2 rows. So to keep the ignition system redundant, what happens is, Magneto R1 fires the RH plugs in rows B and D, Magneto L1 fires the LH plugs in rows B and D.
And respectively Magneto R2 fires RH plugs in rows A and C, Magneto
L2 fires LH plugs in rows A and C.
So to sum it up. Magnetos R1 and L1 are used to fire both sets of plugs in
Rows B and D, and Magnetos R2 and L2 are used to fire both sets of plugs in Row A and C.
You would not want one magneto firing a whole row by it self. If it failed it would cause alot of roughness because a 4th of the cylinders would be lost. With the system used you can loose 2 of the correct magnetos and not drop any cylinders.
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