Mag Cooling Blast Tubes

The various threads on cooling and my personal quest to root out leaks in my baffles leads me to wondering if closing off the 2 cooling blast tubes for my mags would be a worthwhile solution. I can easily block them off to test to see if doing so results in a CHT drop. However I'm concerned whether the mags would suffer as a result, particularly long term. To be honest, I don't even know whether those blast tubes are actually doing the mags any good to begin with. Thoughts?

Auburntsts said:

The various threads on cooling and my personal quest to root out leaks in my baffles leads me to wondering if closing off the 2 cooling blast tubes for my mags would be a worthwhile solution. I can easily block them off to test to see if doing so results in a CHT drop. However I'm concerned whether the mags would suffer as a result, particularly long term. To be honest, I don't even know whether those blast tubes are actually doing the mags any good to begin with. Thoughts?

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Easy enough to validate. Just duct tape them closed and see what happens.

As far as the mags go, that's a good question that I don't have the answer. I am aware of many RV-10s that don't have the blast tubes.

bob

Put a thermocouple or temperature dots on the housing by the mag coil and see what the temp is with, then without the blast tubes. Then you know for sure. Champion Aero says 185F is their limit. You might want to make an allowance for a "hot" day to ensure it is always below 185F.

I removed my cabin heat and blocked off the opening behind #3cylinder. I did not notice any change in cooling. But I didnt do anything empirical either.

BillL said:

Put a thermocouple or temperature dots on the housing by the mag coil and see what the temp is with, then without the blast tubes. Then you know for sure. Champion Aero says 185F is their limit. You might want to make an allowance for a "hot" day to ensure it is always below 185F.

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Bill and I very often think alike. I had phoned the same engineer at Champion and he called back yesterday. 185F is the official line, but he cheerfully agreed that mags see more, often much more, in service.

I have routinely measured breather gas exit temperature at more than 200F in flight. Oil temperature is measured post-cooler, so sump (and accessory case) temperature is higher than indicated. Cowl air exit temperatures are coming in at 125 to 200 plus; air in the accessory case area is also pretty warm. And we've seen P-mags measuring 200+ after shutdown, when blast tubes do nothing.

I don't know how much a set of blast tubes would affect cooling pressures, simply because I've never been inclined to install and remove a set just to make the measurement. Now if somebody already had a set installed, it would be relatively easy to get pressures, land, tape the tubes closed, and immediately fly again.

Bill is 100% right. If you really want answers, measure it yourself. One good measurement is worth 1000 opinions.

Information about rigging temperature probes and pressure piccolos here:

http://www.vansairforce.com/community/showthread.php?p=977603

I reduced the inlet size of my blast tubes with RTV while chasing down cooling leaks shortly after flying my hours off. A few weeks later I had a mag fail at 70 hours while giving rides on a 90 degree day. Coincidence? Maybe. Regardless, I returned the blast tubes to stock configuration, and fly happier knowing both ignitions and alternator have a healthy blast of cooling air. Engine temperature control is challenging during summer climbs, but I can keep all cylinders below 380 by managing airspeed and mixture at full throttle.
Jay

1100 hrs on my 8. No blast tubes whatsoever. Just did the first 500 hr inspection at 1025 hrs. 1 mag needed a new gear, other one was still like new inside. Plane power Alt still running great.

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Soak back heat may be the highest temps for accessories. Heat damage to electrical components is usually dictated by the highest temp and not prolonged temp in the operating range. I open the oil service door after landing if I'm at home to let the hot air out. I don't know how much it helps but I don't think it hurts. and don't charge your battery when it's hot, I didn't get much life from it, my lesson learned.