Van's Air Force
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Component Cooling
- Thread starter Jim P
- Start date
erich weaver
Well Known Member
B&C says blast tubes are not necessary for their alternators. Dont know about the Slick mags.
erich
erich
I've got 630+ hours on my Slick mags without cooling blast tubes, and when I opened them up at 600 hours for their 500 hour inspection, the points looked great - no way to tell if the coils or condenser have suffered anything until they fail....I'll tell you in another 600 hours or so..
My reason for NOT doing the tubes was basically that the FWF of the RV looks remarkably similar to the FWF on my old Grumman, and they didn't use blast tubes - in fact, the biggest problem there was keeping enough cooling air from leaking out of the baffles (so it would cool the cylinders), so I was pre-conditioned not to bleed off any plenum air. Not much engineering behind that rationale, I know...
Paul
My reason for NOT doing the tubes was basically that the FWF of the RV looks remarkably similar to the FWF on my old Grumman, and they didn't use blast tubes - in fact, the biggest problem there was keeping enough cooling air from leaking out of the baffles (so it would cool the cylinders), so I was pre-conditioned not to bleed off any plenum air. Not much engineering behind that rationale, I know...
Paul
gmcjetpilot
Well Known Member
Well my take on it
Factory planes for decades have had blast tubes on (in) the magneto, fuel pumps, gascolator alternator and even the battery. I suspect there is a operational LIMIT on temps and they found things where running hot during flight test. I would not unalatterly decide against any air blast tubes any where just because you don't want a small hole in the baffles.
Magneto - Cooling air will reduce wear & tear. Hard to put a number on it, but magneto parts, points and even springs often fail from heat related issues. Kent Paser even went so far as to route air into his magnetos. The coil & points of mags do get HOT all on their own! Kent Paser of "Speed w/ Economy" has some info on that.
Fuel Pump - Vapor lock happens even when running Av gas. There are good reasons to shroud and route air to our RV's mechanical fuel pump, especially if you might run Mogas in the future. Some even shield and blast the gascolater. Look at a piper the electric fuel pump & gascolator are in a shielded vented box. I'm just saying people know things. Don't be too fast to blow off the concept of cooling air to components all together.
Alternator - B&C says it does not need it. Cool for them. They don't have a voltage regulator on board, but than again their fan runs backwards from its intended direction for auto use.
If you're running an Internally Regulated Alternator I recommend a blast tube right on the back towards the voltage regulator fins. The idea is not force feeding air INSIDE the alternator but across the back, keeping convective hot air from impinging on or being sucked up by the alternator.
PART II of the hot alternator is "radiant heat". The #1 pipe stack has at least +1300F temp gas flowing through it, a handful of inches away. I recommend a heat shield regardless of brand of alternator. Nothing fancy just a piece of aluminum that keeps the pipe & alternator from having a direct line of sight of each other. Van sells heat shields but they are a little wimpy. May two together would give you coverage. A shield off the alternator would work as well or better. Clamp the shield off the alternator or exhaust pipe as you prefer. The sun gives earth radiant heat a 100 millions of miles away, it's pretty strong right. Radiation or radiant heat energy moves as waves in the infrared. Imagine if you where the size of an Ant, hanging on the back of the alternator, looking at that red hot (at least infrared red hot) exhaust pipe. Your little Ant body would be toast; it would be hot. A shield lowers the heat energy (and transfer), is cheap & light weight. You can utilize a shield independent of an air blast tube, but both shield & blast air would be best. Unlike the magneto, battery and to an extent the fuel pump the alternator is working right next to the exhaust. Remember automotive alternators where designed to be high and dry up front on top of a water cooled engine, away from exhaust. Some alternators on cars do have heat shields, typically turboed cars.
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The down side of punching holes in the baffle is more work & weight (although not much work or weight). The biggest negative is may be a tad more cooling drag. Bob or some one claimed they picked up a MPH or two by blocking all their air blast tubes? I don't know about that but I can see you are causing some cooling drag. Air being sucked in and routed around doing cooling is "work" and takes energy. Work is energy which is drag. Frankly your soft seals will probably be leaking more air than 12 air blast tubes. You just never are going to get it sealed perfectly. You don't know what the seals are sealing, in flight at 190 mph, its hidden from view. Also they get worn over time.
Pick your battles. I would go with the alternator cooling at minimum first, than fuel pump and mags second. Consider when you get it flying, do some temp surveys & see how hot the mags, pump and alternator are getting. The tighter your cowl (plenum) the more discrete cooling tubes are needed. I suspect soft seals allow air to spill over the baffle anyway and cool the mags. However if your workmanship is excellent and have minimum leaks at the back baffle seal, you might fry toast your magnetos with out cooling tubes? Who knows. If factory planes have them I wounder why. I would love to ask a magneto engineer. I suspect they are all retired.
Does not have the be a big hole, how about a small 1/4" or 3/8" or 1/2" hole.
Factory planes for decades have had blast tubes on (in) the magneto, fuel pumps, gascolator alternator and even the battery. I suspect there is a operational LIMIT on temps and they found things where running hot during flight test. I would not unalatterly decide against any air blast tubes any where just because you don't want a small hole in the baffles.
Magneto - Cooling air will reduce wear & tear. Hard to put a number on it, but magneto parts, points and even springs often fail from heat related issues. Kent Paser even went so far as to route air into his magnetos. The coil & points of mags do get HOT all on their own! Kent Paser of "Speed w/ Economy" has some info on that.
Fuel Pump - Vapor lock happens even when running Av gas. There are good reasons to shroud and route air to our RV's mechanical fuel pump, especially if you might run Mogas in the future. Some even shield and blast the gascolater. Look at a piper the electric fuel pump & gascolator are in a shielded vented box. I'm just saying people know things.
Don't be too fast to blow off the concept of cooling air to components all together. Alternator - B&C says it does not need it. Cool for them. They don't have a voltage regulator on board, but than again their fan runs backwards from its intended direction for auto use.
If you're running an Internally Regulated Alternator I recommend a blast tube right on the back towards the voltage regulator fins. The idea is not force feeding air INSIDE the alternator but across the back, keeping convective hot air from impinging on or being sucked up by the alternator.
PART II of the hot alternator is "radiant heat". The #1 pipe stack has at least +1300F temp gas flowing through it, a handful of inches away. I recommend a heat shield regardless of brand of alternator. Nothing fancy just a piece of aluminum that keeps the pipe & alternator from having a direct line of sight of each other. Van sells heat shields but they are a little wimpy. May two together would give you coverage. A shield off the alternator would work as well or better. Clamp the shield off the alternator or exhaust pipe as you prefer. The sun gives earth radiant heat a 100 millions of miles away, it's pretty strong right. Radiation or radiant heat energy moves as waves in the infrared. Imagine if you where the size of an Ant, hanging on the back of the alternator, looking at that red hot (at least infrared red hot) exhaust pipe. Your little Ant body would be toast; it would be hot. A shield lowers the heat energy (and transfer), is cheap & light weight. You can utilize a shield independent of an air blast tube, but both shield & blast air would be best. Unlike the magneto, battery and to an extent the fuel pump the alternator is working right next to the exhaust. Remember automotive alternators where designed to be high and dry up front on top of a water cooled engine, away from exhaust. Some alternators on cars do have heat shields, typically turboed cars.
********
The down side of punching holes in the baffle is more work & weight (although not much work or weight). The biggest negative is may be a tad more cooling drag. Bob or some one claimed they picked up a MPH or two by blocking all their air blast tubes? I don't know about that but I can see you are causing some cooling drag. Air being sucked in and routed around doing cooling is "work" and takes energy. Work is energy which is drag. Frankly your soft seals will probably be leaking more air than 12 air blast tubes. You just never are going to get it sealed perfectly. You don't know what the seals are sealing, in flight at 190 mph, its hidden from view. Also they get worn over time.
Pick your battles. I would go with the alternator cooling at minimum first, than fuel pump and mags second. Consider when you get it flying, do some temp surveys & see how hot the mags, pump and alternator are getting. The tighter your cowl (plenum) the more discrete cooling tubes are needed. I suspect soft seals allow air to spill over the baffle anyway and cool the mags. However if your workmanship is excellent and have minimum leaks at the back baffle seal, you might fry toast your magnetos with out cooling tubes? Who knows. If factory planes have them I wounder why. I would love to ask a magneto engineer. I suspect they are all retired.
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I have a 3/8" tube in my cowling just ahead of the alternator. Additionally, I have a 1"w X 1/2"h inlet at the top front center of the cowling. This goes through an expander duct on the bottom surface of the cowling top. Along the way I have four 1/4", 90 deg tubes that take some of this air and direct it to the four ignition coils on top of the crankcase. At the back of the duct near the firewall is a 2" square plenum. From this two 3/8" tubes go to the two LSE ignitions, one 3/8" tube goes to the gascolator, one 3/8" tube goes to the mechanical fuel pump, and one 1/4" tube goes into the oil separator to cool the vapors. In all of the flying I have done around the west with surface temps in the 90s and 100s, I have never experienced vapor lock. In my friend's Lancair 235/320, I had vapor lock several times at hot airports such as Las Vegas, NM and St.George, UT! The reason for the separate duct is that I don't have a cooling plenum across the top of the engine. I have separate cooling-air inlet expander ducts on each side that directly feed the tops of the cylinders.
Paul
I am going to make a two piece plenum for the engine and was thinking about seperate air intake for the pump and ect,. Looks like you already did the same.
Could you post a couple of photos? Would love to see what you describe.
gmcjetpilot
Well Known Member
I'm not paul but got some pics
Wade, I'm not Paul, but I'm running separate left/right plenums. Here are some pics of other projects I'm shamelessly copying.Paul, I am going to make a two piece plenum for the engine and was thinking about separate air intake for the pump and ect,. Looks like you already did the same.
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Acc. Cooling
To blast or not to blast? I'm going to cool my mags and alternators with blast tubes. I live in the PNW where we don't have a real hot climate even in the summer so I don't see it as robbing cooling air from my cylinders.
One of the ideas I saw was at a local aerobatic contest where several of the EDGE 540's had a small 3" x 8" or so door on top of the cowling right above the mags that the pilot would open via cable from the cockpit after exiting the runway and leave open until the next flight or the engine was cool. Both pilots commented that most of the heat affecting the accessories happened when the engine was shut down and there was no oil or cooling air flow through the cowling. Opening the door allowed the heat to escape and natural convection to draw cool air in the bottom and flow out through the door, made perfect sense to me and there was a good amount of hot air still flowing out through the opening 15 minutes after the engine had been s/d.
To blast or not to blast? I'm going to cool my mags and alternators with blast tubes. I live in the PNW where we don't have a real hot climate even in the summer so I don't see it as robbing cooling air from my cylinders.
One of the ideas I saw was at a local aerobatic contest where several of the EDGE 540's had a small 3" x 8" or so door on top of the cowling right above the mags that the pilot would open via cable from the cockpit after exiting the runway and leave open until the next flight or the engine was cool. Both pilots commented that most of the heat affecting the accessories happened when the engine was shut down and there was no oil or cooling air flow through the cowling. Opening the door allowed the heat to escape and natural convection to draw cool air in the bottom and flow out through the door, made perfect sense to me and there was a good amount of hot air still flowing out through the opening 15 minutes after the engine had been s/d.
no cooling here
Jim,
After talking with Tech support at Unison, I measured the mag temperature at the coil while doing a bunch of takeoffs. The mags didn't reach normal opertaing temperature until an hour of this. My mags were getting plenty of air without blast tubes. Blast tubes may be required if RV installations do not have sufficient air circulation behind the engine. I would suggest someone with the same model RV stick a thermocouple on the mag to see how well they cool. I also have 1,100 hours on a B&C alternator with no extra cooling (didn't measure the temperature on that one)
Chris
Jim,
After talking with Tech support at Unison, I measured the mag temperature at the coil while doing a bunch of takeoffs. The mags didn't reach normal opertaing temperature until an hour of this. My mags were getting plenty of air without blast tubes. Blast tubes may be required if RV installations do not have sufficient air circulation behind the engine. I would suggest someone with the same model RV stick a thermocouple on the mag to see how well they cool. I also have 1,100 hours on a B&C alternator with no extra cooling (didn't measure the temperature on that one)
Chris
