Blast tubes to P-Mags

For those of you who have P-Mags in your plane, how did you route the blast tubes for cooling? I have an RV-9A with an O-320. Mostly I'm interested in how you fixed the position of the tube right at the P-Mag. there's not much around there to hook it to. Pictures would be great. Thanks!

I just put a hole in the rear of the baffle, one each side directly above each P-Mag for the blast tubes. And then zip tied the tubes to the engine mount, directing the blast onto the base of the P-Mags. I was a little concerned that the movement of the engine might dislodge the tubes from the baffle. but the tubes must have enough flex, as in 200 hrs they are still good and doing their job.

I routed the blast tube (I used 5/8" SCAT ducting) under the engine mount tube, i.e. between the engine mount tube and the accessory case. And it makes contact with neither the engine accessory case nor the engine mount tube. It has about 1/4" clearance to each. See first two photos.

Then, to position the blast tube at the P-Mag end, I made a little fixture that attaches to the engine via the upper magneto clamp stud. This way, both ends of the blast tube are attached to the engine, never to the engine mount, so there is no relative motion to worry about.

The attachment fixture has a handful of parts, but it's quite simple. A little tab of 0.032" sheet aluminum attaches to the upper magneto clamp stud on the engine. Then a short length of 5/8" aluminum tubing is attached to the tab via an aluminum tubing clamp. And finally the SCAT duct is attached to the aluminum tube using a hose clamp. Makes for an installation that's neat, robust, and easily adjustable. See the third photo.

Here's how I did mine... The rod is 1/8 brazing rod with the flux knocked off. One end threaded, 6-32 if I remember right, and bent to hold the shape you want the blast tube to take. Not flying yet so longevity unknown.

I ran a piece of safety wire down thru the tube and wrapped it around the Pmag and back up the tube, tied it off and it has worked great.

Not tested yet but this is what I did. In the last photo, the mag has been removed to install the SD-20 but the end of the tube is visable as it is wired into place. Just one idea!

Is it a good idea to cool the standard Bendix mags like you are doing to these Emags??

Brantel said:

I ran a piece of safety wire down thru the tube and wrapped it around the Pmag and back up the tube, tied it off and it has worked great.

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Oh boy, am I going to steal THAT idea!!! Nice, easy and effective.

Great ideas

This post has some great ideas - and timely for me. I have been thinking about how I am going to mount those blast tubes for my dual PMags.

I opened up the holes on an adel clamp to fit over the Mag studs.



Only downside is the orientation is off to one side. I blew compressed air down the tubing and it seems to spread out over the mag just fine. Time will tell if it works.

An ignorant question?

Ron RV8 said:

Here's how I did mine... The rod is 1/8 brazing rod with the flux knocked off. One end threaded, 6-32 if I remember right, and bent to hold the shape you want the blast tube to take. Not flying yet so longevity unknown.

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Will that plastic conduit tolerate the heat in the engine compartment?

RV7AJeremy said:

Will that plastic conduit tolerate the heat in the engine compartment?

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No problem in my 7

The tubing does just fine on my 7. I have the same tube for blast tubes on the P-mag, Gascolator, and mechanical fuel pump. No sign of melting.

I would not run it near an exhaust pipe however....

I used the black corrugated tubing Van's supplies for wiring conduit as blast tubes for my two magnetos and my alternator on the RV-8. I attached it with Permatex gasket maker so it does not rotate in the hole through the baffling and shaped it into position to direct the airflow where I wanted it with a heat gun. It seems to hold position just fine and the heat of the engine compartment does not affect it, probably because there is cool air blowing through it. I think I recall this was a recommended usage by Van's.

my 9A was done like this as well (slick mags). 400+ hours. no issues so far.

RV7AJeremy said:

Will that plastic conduit tolerate the heat in the engine compartment?

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The builder on my -7A wrapped safety wire around the tube end and then affixed it to the PMAG mount stud. Doesn't seem to move at all. 400+ hours.

Great ideas everybody, thanks for your suggestions, I appreciate it!