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Whirlwind and PMags

JDA_BTR

Well Known Member
I have the literature on the whirlwind 300 and 330s. In the limitations it states that “pmags must use jumper wire”. I asked the rep at whirlwind why and didn’t get a good reason just that I should look in the Pmag manual about how to do it. Does anyone here know why that would be? On my RV14 I don’t run with the jumpers in but it isn’t very aggressive about the timing change anyway.

I’m interested because I want a 15” spinner to go with my showplanes cowl rv8. But every time I look into another option like this another gremlin pops up.
 
I have a Whirlwind 74HRT and dual P-mags on an IO-360-A series engine without counterweights.
This engine has a large rpm avoid band from 2050 to 2350 rpm when paired with the Hartzell I used to have for torsional vibration reasons. Whirlwind suggest this restriction continues to be observed. Adding ignition advance is unlikely to do anything to reduce the torsional vibration.
Without any data my guess would be there are torsional vibration "concerns" that using the jumper will reduce and provide better long term longevity for the prop.
There are always compromises to be made in selecting the parts for your airplane. Perhaps running with the jumper is factor to consider is you really must have a 15" spinner. What real world difference does running with the jumper make?
 
I’m interested because I want a 15” spinner to go with my showplanes cowl rv8. But every time I look into another option like this another gremlin pops up.

What gremlin? Buy the prop and spinner, observe the Whirlwind restriction.
 
I have the literature on the whirlwind 300 and 330s. In the limitations it states that “pmags must use jumper wire”. I asked the rep at whirlwind why and didn’t get a good reason just that I should look in the Pmag manual about how to do it. Does anyone here know why that would be? On my RV14 I don’t run with the jumpers in but it isn’t very aggressive about the timing change anyway.

I suggest you should run with the jumper in. Jumper in limits advance to ~9 degrees (so 29 degrees BTDC for the high altitude cruise for angle head Lycomings, 34 degrees BTDC for PV engines). This is about the limit of high altitude cruise engine efficiently gain for typical RV engines. I’m sure there are examples where more advance is ok, but most of us do not fly at such fringes.

I’ve tested an IO-390 RV-14A with dual pMags, jumper in and jumper out. The jumper in is far preferred for CHT temps and engine vibration (this engine had a composite prop) and shows no downside. I did the same test, with the same CHT results on an IO-360 (PV with Hartzell prop). After these tests I stopped installing a “jumper in, jumper out” switch on the panels.

But - run your own tests and let us know the results.

Carl
 
On my RV14 I don’t run with the jumpers in but it isn’t very aggressive about the timing change anyway.

That's a pretty aggressive timing curve for the 390 which is generally not recommended.
Not sure on spinner options but no restrictions that I'm aware of with MTV9
 
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