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pvalovich

Well Known Member
I'm finishing my -8A. I have an Aerosport IO-360 180hp engine with one Lightspeed and one mag. Electrical power is a B&C 40 amp alternator.

I am pondering component cooling requirements. The B&C guys say not to worry about separately cooling the alternator. The Lightspeed controller is aft of the firewall/ But what about the mag? Does it require a separate scat tube?

My original idea was to just leave a small gap on the aft baffle where it contacts the engine near the mag.

Whadda you guys think?
 
me too

I am finishing my -7 with the exact same setup (B&C, lightspeed, one mag) and I am struggling with the same question.

I haven't installed any blast tubes yet... I am thinking about flying with those temperature stickers on the mag/aternator to see how hot it really gets around there.

But then the next question is how hot can a mag get before it starts affecting its lifespan?

Marco
RV-7 TMX-IO360
N-Texas
 
pvalovich said:
I'm finishing my -8A. I have an Aerosport IO-360 180hp engine with one Lightspeed and one mag. Electrical power is a B&C 40 amp alternator.

I am pondering component cooling requirements. The B&C guys say not to worry about separately cooling the alternator. The Lightspeed controller is aft of the firewall/ But what about the mag? Does it require a separate scat tube?

My original idea was to just leave a small gap on the aft baffle where it contacts the engine near the mag.

Whadda you guys think?
Click to expand...

Lycoming data sheet to the rescue! The spec for the O-320 B, 2213-C, says: "Maximum permissible magneto temperature measured at a coil hold-down screw shall not exceed 180F." This is for a Scintilla S4LN-20 or -21. The spec for the O-320-D, 2283-G, says "Maximum permissible magneto temperature, measured is(sic) the pole laminations, shall not exceed 225F." This is for a Slick 4370, 4371.
If you're going to consider blast tubes, you may want to put a pair onto the fuel pump and gascolator to prevent vapor lock at high, hot, fields. If you've ever had it, it will surely get your attention. I'd say this is even more appropriate if you use auto fuel.
 
I decided to install some blast tubes on the back of the engine baffles on my -6A w/ O-360. There was not a lot of room between the baffles and the motor mount, but here is what I came up with:

Used the 1" diameter aluminum "SCAT" hose flange. Instead of using the SCAT tubing, I went to the auto parts store and found some pre-molded radiator hose that could be pressed / shoved inside the 1" flange. I used two different geometry hoses to snake from the baffle, under the motor mount top tube, and angle towards the top of the magneto; one setup for the left mag, one setup for the right mag.

Once the radiator hoses were cut to the needed length and positioned as required, I drilled a small hole through the top of the flange, through the radiator hose, and out through the bottom of the flange. I then inserted a length of safety wire through all of the holes and secured the wire to itself and the outside of the flange.

Seems to work fine.
 
I have the same set up on my 7A. I ran a blast tube to the back of the B&C alternator, 1 to the Mag and another to the fuel pump. I used the blast tubes that Vans sells.
 
Rick_A said:
I have the same set up on my 7A. I ran a blast tube to the back of the B&C alternator, 1 to the Mag and another to the fuel pump. I used the blast tubes that Vans sells.
Click to expand...

How about that, this is exactly the way I did it :D
 
Blast tubes

On a 0-320 powered RV6 I put blast tubes on both mags, Fuel pump, the bridge rectifier on the alternator and the avionics stack. Tubes were made from Van's black nylon corrigated tubing normally used for conduit. The avionics cooling air source was taken off the fresh air vents for cockpit air. All the others came off the rear engine baffle except the alternator comes off the front baffle. There are no flanges used on the baffles, just a hole (5/8" most likely but you better experiment since I am 1700 miles from my shop) in which the corrigation of the tube is forced into for a snap fit. At the alternator and fuel pump I made a sheet metal bracket to hold the opposite end of the blast tube. The mags have two tubes aimed at the top of each case. All of these tubes also have a piece of 1/8" (+ or -) diameter aluminum wire running through the inside of the blast tube full length to provide stability to the tube to prevent the cowl air from whipping them about. This wire was scrap from satellite dish ground wire & was fairly stiff...probably #10 or #8. Light welding rod, brazing rods even coat hanger wire would work but whatever you use, bent the baffle end of the wire into an eyelet for a #8 screw and bolt it down to the baffle adjacent to the conduit. You can then form the wire running it through the conduit into whatever shape you want and the conduit blast tube will take the same shape holding the blast tube at the targeted area. This idea was in a very early issue of the Rvator & was reprinted in "17 Years of the Rvator" and also "22 Years" after which I lost track. It has served me well for 400 hours except I added a simple shroud & blast tube to the firewall mounted voltage regulator after having two fail. I also have a heat shield over the exhaust stack where the fuel line passes closely over the top.

Dick DeCramer
RV6 N500DD 400 hours
RV8 Fuselage
Northfield, MN
 
I think a blast tube to your mag is a good idea also. My idea for routing the blast tube to the right spot and making it stay there is similar to Dick's. I used a piece of #12 insulated electrical wire. It's stiff enough to stay where you bend it. I tie-wrapped it to the outside of the black corrugated tubing from Vans with a tie-wrap about every inch or so. The wire is black like the tubing so it's not noticeable, if you care about how it looks. I put a short U-shaped bend at each end of the wire so it can't slip out of the tie-wraps. It works well, stays where you put it, and I have one going to my mag, fuel pump, and alternator (diode area).
 
It doesn't take a lot of air to carry off the heat. Did you ever consider using the soft aluminium tubing that you get at a hardware store in place of the corrugated tubing? It is smoother inside, easy to bend, and its ID can be smaller than the corrugated tubing with its higher pressure drop and still deliver the same amount of air.
 
I saw these at Oshkosh 2009.


magnetocooling.jpg
 
pvalovich said:
The B&C guys say not to worry about separately cooling the alternator.

Whadda you guys think?
Click to expand...

That's not what B&C told me. More specifically they said that while they do not stipulate a mandatory requirement for additional cooling for their alternators they are non-the-less of the opinion that providing such cooling should extend service life.

That is logical and is what you would expect. Electrical devices hate prolonged high temperatures.

I ran 3/4" scat from machined spiggots fastened to the baffles. I ran the scat to my two alternators and to my one magneto.

 
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