What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Blast Tubes

CharlieWaffles

CharlieWaffles

Well Known Member
I'm curious what blast tubes if any the typical RV10 builder is installing. I am using stock slick magnetos and stock plane power alternator. Are people installing blast tubes for the slicks? How about for the alternator?
 
I did not install them on anything. My slicks or fuel pump temp labels never exceeded 200F. My alternator temp label reached 225F surface temp on the side exposed to exhaust pipe radiant heat. No problems yet, but that does not mean their life will not be shortened. Occasionally had rough running after hot start, but cured with boost pump and 1200-1500 rpm for 30 sec. No mech fuel pump shroud. I would recommend a small heat shield to protect alternator, which I will install soon.
 
I installed a shroud on my mechanical fuel pump and used a 1" aluminum flange on the rear baffle and 1" scat as I want to run auto fuel. I also ran a blast tube on my alternator but I am using the Nippondenso auto alternator and want to keep the VR and diodes cool. I attached a 1" aluminum flange on the alternator's rear shroud and also put one on the air baffle intake ramp and used 1" scat. I am not bothering with blast tubes on the mags yet.
 
I've seen reference that Plane Power says the blast tube isn't necessary and is left over from when Vans was using Auto alternators. But it wouldn't be experimental aviation without conflicting information. The Plane Power install manual from their website says to use a blast tube - http://www.plane-power.com/images/Installation_Packages/AL12-EI60_B.pdf

I just called PP and they said if you are below the max current of the alternator you don't NEED a blast tube. They said it can't hurt and the cooler it is the more efficient it is. For the stock 60Am, they said if your standard load is below 50A, there is no need for the blast tube, but above 50A you should have a blast tube.
 
Last edited:
Yes on the mag (I have one) but not on the Plane Power alternator. Plane Power will tell you that the blast tube is not necessary. My CHTs are plenty cool, so I'm not worried about the loss due to the blast tube.

-Rob
 
One on the mag, one on the fuel pump and one on the PP alternator.
It works without it for most people but cooler is definitely better when it comes to electrical stuff.
As for the fuel pump, I run mogas most of the time and keeping things cool is what I want.

IMG_2750.JPG


IMG_2751.JPG


IMG_2023.JPG
 
Alternator cooling

Ernst, I think the blast tube on your alternator is in the wrong place to be of any use. According to Plane Power, the alternator is cooled via a centrifugal fan that draws air in from the rear and blows it out sides. To aid in cooling, you want to have your blast tube dump cold air on the rear of the alternator, where the air is drawn in (on the rear shroud where the diodes are located). Where your blast tube is currently positioned, it is attempting to dump cold air exactly where the alternator is blowing out hot air.



N427EF said:
One on the mag, one on the fuel pump and one on the PP alternator.
It works without it for most people but cooler is definitely better when it comes to electrical stuff.

IMG_2023.JPG
Click to expand...
 
Hmmm, not sure I understand what you mean.
The blast tube is directed towards the diode pack to the rear of the alternator,
The cap on the back has no baffles and as I understand it the PP alternator does draw air from the rear but that is as far as the rear goes. In other words, from what I understand that opening between the diode pack and the alternator housing is where air is pulled in for cooling.
I could be wrong and the fix would be simple.
 
My understanding is the air is drawn in from the rear. Not between the rear shroud and the main housing as you have it, but through the openings in the rear face of the rear shroud. In other words, the blast tube should terminate truly behind the alternator, pointed at the rear shroud from behind. Not on the side. This was confirmed by a conversation with Plane Power tech support.

The installation document for another one of their alternators, the 70A one, shows this more clearly. That alternator actually comes with a part bolted to the rear that accepts a scat tube. Look there as an example, and it should become more clear:

http://www.plane-power.com/images/Installation_Packages/AL12-EI70_B.pdf
 
I can't speak about the Plane Power units, but empirical and anecdotal results show that pointing the blast tube at the regulator on the ND alternators (as Ernst has done) significantly increases lifetime. On the ND's, it is rare for a failure in the big chunks of the alternator - it's the reg that usually fails first, and keeping it cool makes thing a lot better.
 
Roee is correct, here is how I did mine, there is a slot in the tube that directs the air into the rear of the alternator, the bottom of the tube is plugged.

IMG_4369b.jpg
 
Walt said:
Roee is correct, here is how I did mine, there is a slot in the tube that directs the air into the rear of the alternator, the bottom of the tube is plugged.

IMG_4369b.jpg
Click to expand...

I agree with ROEE and Walt. I suffered a Plane a Plane Power failure returning from OSH in 2011. I had my blast tube aimed just like Ernst has his. PP made it clear that it was incorrect, because that is the rear fan exit air you are fighting against. They also told me blast tube installation was optional but if you use one. it needed to be directed directly at the center back of the shround where the diode pack is.

I reinstalled mine similar to Walt's but with the open end of the tube curved around in a 180 to point directly at the center of the rear shround. I like Walt's better because mine had to have stand offs to hold it in place. I think there are many RV's flying like Ernst's picture and I wonder if it is doing more harm than good and contributing to the PP failures like I had.
 
Caveman said:
I think there are many RV's flying like Ernst's picture and I wonder if it is doing more harm than good and contributing to the PP failures like I had.
Click to expand...

I would say almost everyone does it wrong, I have redone quite a few that have come thru my shop for a condition inspection.
 
I hate to pile on, but I'm gonna do it anyway. Pumping unfiltered air into the magnetos is just begging for trouble. Especially if you fly through rain. I wouldn't pass that on an inspection. I know someone is gonna squawk that they've been doing it for 3 hunnerd hours, but I don't care. It ain't right.
 
Beware of absolutes....

Walt said:
I would say almost everyone does it wrong, I have redone quite a few that have come thru my shop for a condition inspection.
Click to expand...

Now Walt "WRONG" is a pretty absolute term. There are a lot of different alternators out there, and a lot of different results. Yours of course are absolutely correct for your installation - I have had an ND alternator that purred along just great at 1,000 hours with the cooling from the front (of the reg housing). It depends on the design of the alternator, and this thread seems to say that there is an ABSOLUTE answer for EVERY alternator. Do you really want to leave that impression with the inexperienced folks that are looking for answers?

I encourage everyone to figure out how their particular installation works and apply the appropriate documentation and lessons from others for their gear. That is the "RIGHT" answer.

Paul
 
N427EF said:
One on the mag, one on the fuel pump and one on the PP alternator.
It works without it for most people but cooler is definitely better when it comes to electrical stuff.
IMG_2750.JPG
Click to expand...

I agree with aerhed, there is nothing in the mag that is "electronic" that requires cooling air, as long as it's filtered and not subject to water injestion it probably would be benefiical.
 
Last edited:
Ironflight said:
Now Walt "WRONG" is a pretty absolute term. There are a lot of different alternators out there, and a lot of different results. Yours of course are absolutely correct for your installation - I have had an ND alternator that purred along just great at 1,000 hours with the cooling from the front (of the reg housing). It depends on the design of the alternator, and this thread seems to say that there is an ABSOLUTE answer for EVERY alternator. Do you really want to leave that impression with the inexperienced folks that are looking for answers?

I encourage everyone to figure out how their particular installation works and apply the appropriate documentation and lessons from others for their gear. That is the "RIGHT" answer.

Paul
Click to expand...

Paul is correct, my cooling configuration is what I would recommend for the PP and B&C units. However, the diode packs on every alternator are mounted to the rear frame. Cooling air is "usually" drawn in from the rear to keep the diodes and regulator (for IR units) cool, these are the primary components you are trying to cool so consider this when evaluating your installation.
 
Last edited:
Educational

Sometimes I post pictures in hopes that someone will notice a mistake.
I will redirect the blast tube to the PP alternator.
The mag cooling air has a filter of course and is done the same way in some certified birds. Generally one could expect 5 to 600 hours from a mag before something goes.
You are right, I am looking at my friends tightly cowled glasair II and 1500 hours
On the same magneto and the same set up.
 
Water was one of my reasons for not installing them. I have 97 hours now and will let everyone know if the 200*F ambient temps cause any problems. I routinely charge two batteries(680/925L) pulling 55-57A initially after startup.
 
You must log in or register to reply here.
Back
Top