Need clarification on RPM drop between Pri and SEC

[n502pd]

I would like to get some idea about the rpm drop between the primary and secondary ignition check. I have not flown yet, and my AeroVee has about 20 min ground run time total, so it isnt broken in. It runs fine, idles fine, WOT, briefly, shown just over 3000 with Prince p-tip prop. What do you guys routinely see as the drop between the two systems? Both mine show very close to 60/70 rpm, maybe a difference between Pri and sec of 10, if I see the tach correctly. The sound of the engine is the same for each test. Or, and this is my concern, should there be no drop at all on either, and no difference between the two systems? Sort of looking for data on this.

Thanks much!
Joe/ nearing DAR visit!

[wlarson861]

Sounds like your right on the money. Once you start flying you will need to check the ignition advance by flying a while on both ignitions and noting the CHT temps and then turning off the primary (magnatrons) and noting any increase in temps. That would indicate tweaking the electronic ignition advance is in order. But for static runs you are right where you want to be.

[mike.smith]

Yup. Right on. You're close enough on the ground. In the air is where you fine tune things.

[n502pd]

Thanks Bill and Mike! Now a more pointed question; what is the drop you see in rpm on each system? What initial rpm do you set for the test? I used 2000 for the initial rpm. I did not lean for any specific temp or anything, just not full rich. I did glance at one or two EGt and they were above 900 and climbing, so I might be pretty close for now. The exhaust outlets are a light to medium tan on 100LL.The engine pulls pretty hard and I am impressed when I do go to WOT.

[wlarson861]

It seems to me that mixture has an effect on the drop. If I am at just rich of peak lean I'll get 20 to 30 on the primary(electronic ignition switched off) and 60 to 100 with the primary off. As long as the difference is not to drastic it should be ok. Any more than 100 rpm difference might indicate fine tuning the advance, but do that based more on the in flight cht test. If your using an eifis the numbers jump around quite a bit so it can be hard to pinpoint a 20 to 75 rpm difference. More than 100 is noticeable though.

[n502pd]

Thanks Bill. That is more of what I need to know. I think I am , as said earlier, just where I need to be prior to actual flight testing. I am using analogue gauges, but very early electronic, 7 segment display tach. A very good forum..thanks to all!

Joe

[MichaelFarley56]

This is just my two cents, but I agree with Bill. I check my ignitions anywhere from 1800-2000 rpm and I'm happy as long as the drop in either system isn't more than 75-100 rpm. To me, even more important is that, when I switch of either system, the remaining system continues to run the engine and it runs smoothly. If you turn off one system and you get a rough running engine on the remaining system that could indicate a fouled plug, bad coil, etc.

As long as it runs well on either system and there's no excessive drop, you've checked all you can! Final secondary timing adjustments can't be done until you're in the air anyway.

Glad to hear she's running well Joe!

[n502pd]

Thanks Mike! That is exactly what I see here. I shall move on to the pants and farings for the gear. Then canopy finishing, W&B, CG and whatever else the DAR needs, then the DAR. It has been a long time getting here, and attempting to land tailwheel Kitfox is going well. Still need a bit more time thou!!

Thanks for all the responses.

Joe