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Alternator blast tube

Condor

Condor

Member
I’ve built my RV14 as per the plans firewall forward which means that I have the vent fitted on the right hand forward inlet ramp to direct air to the heater muffs on the exhaust. This is standard for the non EXP119 IO-390.

I haven’t fitted a cooling blast tube for the Plane Power alternator and wondering if I should modify the inlet ramp to accept a second takeoff point for a blast tube.

What have others done? I’ve only 20 hours on the aircraft at this stage and hoping for a reasonable lifespan for the alternator.

Thanks in anticipation for any replies.

Ian
RV14A EI-XIV.
 
I did exactly that on my RV-10. I forget if it was in the plans or not, but keeping the alternator cool seemed logical to me.
 
Blast tube +

Besides adding a blast tube, I added a heat shield so the red hot exhaust pipe is not "seen" by the alternator. In my mind, this may be more critical for long life.
 
I know this subject was covered several times including a year ago when James Hartline asked the same question but I’m looking for the latest info and thoughts on whether or not a blast tube is actually needed. Also is there any relevant temperature information available on the RV14 installation.
Thanks
Ian.
 
I have had a 3/4" blast tube to the alternator on all three planes and consider this standard for me. I have never had any issues with the alternator on any of the three planes.
 
Condor said:
I know this subject was covered several times including a year ago when James Hartline asked the same question but I’m looking for the latest info and thoughts on whether or not a blast tube is actually needed. Also is there any relevant temperature information available on the RV14 installation.
Thanks
Ian.
Click to expand...

Hi Ian, just this weekend several people commented that I don't have an alternator cooling blast tube on my RV-8. I didn't give it a lot of thought, but recall seeing some saying it was required, and some saying it was not needed. I guess I took the easy path. My normal alternator load is about 9-12 amps, so perhaps I'm not working it very hard. So far about 250 hours on my Hartzell/PP alternator. I hope I didn't jinx it!
 
Hi Ian, just this weekend several people commented that I don't have an alternator cooling blast tube on my RV-8. I didn't give it a lot of thought, but recall seeing some saying it was required, and some saying it was not needed. I guess I took the easy path. My normal alternator load is about 9-12 amps, so perhaps I'm not working it very hard. So far about 250 hours on my Hartzell/PP alternator. I hope I didn't jinx it!
__________________
Mickey Coggins

My alternator load is about the same and I’ve made sure the drive belt is not too tight. I did see a post referring to a better spec on the later PP alternator since Hartzell took over but this could be an urban myth!
Ian.
 
No blast tubes on either of my planes. 900 hours on the $35 ND alt and keeps on chugging along. Key to longevity is buying the right alt. Pp alt is not on that list for me anyway. I also prefer externally regulated to keep temps low on the electronics

Larry
 
lr172 said:
No blast tubes on either of my planes. 900 hours on the $35 ND alt and keeps on chugging along. Key to longevity is buying the right alt. Pp alt is not on that list for me anyway. I also prefer externally regulated to keep temps low on the electronics

Larry
Click to expand...

Sorry for the thread hijack, but do you buy ND alternators that already support external VR or do you do surgery on it yourself?
 
lr172 said:
No blast tubes on either of my planes. 900 hours on the $35 ND alt and keeps on chugging along. Key to longevity is buying the right alt. Pp alt is not on that list for me anyway. I also prefer externally regulated to keep temps low on the electronics

Larry
Click to expand...

Same here. ND from NAPA auto parts and modified for the B&C external regulator. With EFI, I cruise at 25+ amps. No external cooling.

Flew into Vegas last night and OAT on downwind was 102 degrees at 1945 hrs

No issues in 400 hours on this alternator system
 
Condor said:
I know this subject was covered several times including a year ago when James Hartline asked the same question but I’m looking for the latest info and thoughts on whether or not a blast tube is actually needed. Also is there any relevant temperature information available on the RV14 installation.
Thanks
Ian.
Click to expand...

I’m the one that wrote about in my -14 (that I did not build) where I had the Plane Power rebuilt then I bought a new one when the second time it failed. There was no blast tube when I bought it. The second time I looked through the “blueprints” and saw where a blast tube IS REQUIRED!

My first failure was at about 300 hours the second one about 600 hours. I have a blast tube AND a heat shield (along with the exhaust muff assembly for the cabin heat which I had removed somewhere along the way to stop a constant heat source behind the right rudder pedals).

So I suggest air (like the plans show) and any protection provided by heat muffs and/or heat shields
 
3/4 Blast tube

Condor said:
I’ve built my RV14 as per the plans firewall forward which means that I have the vent fitted on the right hand forward inlet ramp to direct air to the heater muffs on the exhaust. This is standard for the non EXP119 IO-390.

I haven’t fitted a cooling blast tube for the Plane Power alternator and wondering if I should modify the inlet ramp to accept a second takeoff point for a blast tube.

What have others done? I’ve only 20 hours on the aircraft at this stage and hoping for a reasonable lifespan for the alternator.

Thanks in anticipation for any replies.

Ian
RV14A EI-XIV.
Click to expand...

There should be 2 - 3/4" knock outs on the back of the plenum to attach blast tubes for E or P mags. Use these or a Y adapter to add a blast tube as needed.
 
Where do you place the end of the blast tube?

What is the measured temperature drop of what component, tube vs no tube?
 
jimkwalton said:
I’m the one that wrote about in my -14 (that I did not build) where I had the Plane Power rebuilt then I bought a new one when the second time it failed. There was no blast tube when I bought it. The second time I looked through the “blueprints” and saw where a blast tube IS REQUIRED!

My first failure was at about 300 hours the second one about 600 hours. I have a blast tube AND a heat shield (along with the exhaust muff assembly for the cabin heat which I had removed somewhere along the way to stop a constant heat source behind the right rudder pedals).

So I suggest air (like the plans show) and any protection provided by heat muffs and/or heat shields
Click to expand...

Jim,

Can you reference where you see the call out for a blast tube on the alternator on the RV-14? Perhaps I am misunderstanding what you are referring to in the "blueprints"
 
rv8ch said:
Sorry for the thread hijack, but do you buy ND alternators that already support external VR or do you do surgery on it yourself?
Click to expand...

I buy the ND versions that are already set up for ext regulation. I converted an internally regulated alt to support a special battery charging regulator on a sailboat. It is not that hard, but does require some research before you do it as there are two different field polarity arrangements out there.

I should add that I buy the versions that are setup for the old hondas that run in the opposite direction from normal. I believe the proper fan blade arrangement provides better cooling, but seems that others have similar longevity as well, so likely not that important.

Larry
 
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Jetmart said:
Jim,

Can you reference where you see the call out for a blast tube on the alternator on the RV-14? Perhaps I am misunderstanding what you are referring to in the "blueprints"
Click to expand...

I have an electronic copy of the build instructions and "leafed" through it until I found the alternator installation instructions and there on the diagram was the air blast tube from the right air inlet to the alternator. I also added back the heat muff that I had removed earlier and added another heat shield to help protect the blast tube. The first blast tube MELTED!
 
Condor said:
I’ve built my RV14 as per the plans firewall forward which means that I have the vent fitted on the right hand forward inlet ramp to direct air to the heater muffs on the exhaust. This is standard for the non EXP119 IO-390.

I haven’t fitted a cooling blast tube for the Plane Power alternator and wondering if I should modify the inlet ramp to accept a second takeoff point for a blast tube.

What have others done? I’ve only 20 hours on the aircraft at this stage and hoping for a reasonable lifespan for the alternator.

Thanks in anticipation for any replies.

Ian
RV14A EI-XIV.
Click to expand...
I bought my -14 built, only 160 hours. I went through 2 alternators (failed inflight) before I saw in the plans that a cooling tube was SUPPOSED to be installed, but was not. I put a small flexible tube in from the right air inlet and pointed at the Plane Power alternator. Have not had an issue since. Yes, in the plans, it shows a vent tube installed.
 
jimkwalton said:
I bought my -14 built, only 160 hours. I went through 2 alternators (failed inflight) before I saw in the plans that a cooling tube was SUPPOSED to be installed, but was not. I put a small flexible tube in from the right air inlet and pointed at the Plane Power alternator. Have not had an issue since. Yes, in the plans, it shows a vent tube installed.
Click to expand...
Can you reference the section in the plans where it calls for a blast tube on the alternator for a RV - 14?
 
jimkwalton said:
I bought my -14 built, only 160 hours. I went through 2 alternators (failed inflight) before I saw in the plans that a cooling tube was SUPPOSED to be installed, but was not. I put a small flexible tube in from the right air inlet and pointed at the Plane Power alternator. Have not had an issue since. Yes, in the plans, it shows a vent tube installed.
Click to expand...

Would also be interested in the section no. that calls this out. Did see the strap from the alternator to the starter the plans recommend (I did not use this) but not a blast rube. B&C alternators (Main and pad mount) and Skytec NL now 525 hrs. no issues.
 
Condor said:
What have others done? I’ve only 20 hours on the aircraft at this stage and hoping for a reasonable lifespan for the alternator.
Click to expand...
RV-10 with Plane Power alternator, 10 years and 800 hours, no blast tube and no problems.
 
My RV7 has a PP 60AMP with a blast tube from the right inlet to the back side of the alternator and is just past 1000 hours in use, still going strong.
 
On the PP, it would be likely best to keep the aft bearing cooler. So, how ever the air can be directed there could be helpful. 3/8 tube might be enough, or 1" might not be enough. The 60 Amp has a marginal bearing clearance and heat makes it worse. If yours has black aluminum dust on it, time to take it off and check in a vice like DanH has suggested. Wiggle to see if rear bearing is orbiting/loose.
 
If you are using a lithium battery vs lead-acid, it may be a factor as to whether to run an alternator blast tube. Lithium batteries can absorb current at a higher rate and today's alternators can deliver it at low RPM. The problem is that at low RPM some alternator cooling fans don't deliver enough air for the high load. Boat and recreational vehicle guys learned this the hard way when many switched to lithium and started cooking alternators. As a result, controllers have been developed to modify the field current based on alternator temperature. Google 'alternators and lithium batteries'.
 
Installation instructions for my B&C 40 amp alternator (externally regulated) says no blast tube required. Typical in flight load is less than 10 amps.
 
Halleffect said:
If you are using a lithium battery vs lead-acid, it may be a factor as to whether to run an alternator blast tube. Lithium batteries can absorb current at a higher rate and today's alternators can deliver it at low RPM. The problem is that at low RPM some alternator cooling fans don't deliver enough air for the high load. Boat and recreational vehicle guys learned this the hard way when many switched to lithium and started cooking alternators. As a result, controllers have been developed to modify the field current based on alternator temperature. Google 'alternators and lithium batteries'.
Click to expand...
I cooked an expensive gear driven alternator on an IO550N not so long after switching to lithium.
When I installed the new alternator, I glued a thermocouple to the stator with thermally conductive, non electrical conductive epoxy.

I went for a quick hop and temps shot way high. I modified the cooling (custom carbon baffles and plenum) and temps are now well behaved (plastic plane).

See graphs for before and after. I second the vote on making sure you have adequate cooling with lithium.
 

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