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Plenum?

I have dealt with 2 different plenum son RV-10's. I my experience, you will get better cooling with the stock Van's cowl and baffles. Both planes had cooling problems. I think both have been able to get cooling under control, but in the 15 stock cowls and baffles, I have never had to worry about cooling. I would recommend you save the time and money and go stock unless you absolutely must have one of the aftermarket cowls for aesthetics.
 
400 hours on a James Cowl and plenum. It does require extra work and is not, in my opinion, for everyone. If you are not using the James Cowl there is little to be gained with a plenum.

The set up meets my design objective of fast, efficient cruise (as in better than a stock set up). I would do it again.

Carl
RV-8A (sold)
RV-10 (sold with regrets)
RV-8 in progress (will use stock cowl and homemade plenum)
 
You could do it again but I don't think the SJ cowl is available for the -10 any more...

Yep - I sent a few notes to Will James to reconsider the offering. They got burned early on by some bad internet press and decided they did not need the noise. Too bad - the system has proven out well for me.

Carl
 
Guys, let's not get confused. A plenum lid is just a sealing device. If it seals well, it has done its job, and it would be a very poor lid indeed that didn't seal better than conventional flap seals. Air which bypasses the hot engine fins is mass flow with no purpose, meaning it's just pure drag. In reality, a plenum lid is simply one component of a drag reduction system; good sealing allows a mass flow reduction, which is a function of exit area.

If you have poor cooling with some particular vendor package, don't blame the lid. Look to poor intake and duct design, the parts which connect the plenum volume with the outside world.
 
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Guys, let's not get confused. A plenum lid is just a sealing device. If it seals well, it has done its job, and it would be a very poor lid indeed that didn't seal better than conventional flap seals. Air which bypasses the hot engine fins is mass flow with no purpose, meaning it's just pure drag. In reality, a plenum lid is simply one component of a drag reduction system; good sealing allows a mass flow reduction, which is a function of exit area.

Exactly correct. If done well, a plenum will make the most of the pounds of cooling air coming into the engine such that you can reduce the total pounds of air and still have the same heat rejection as a standard cowl with baffles. This is the approach with the James Cowl.

There is no free lunch. Reduce the engine cooling drag and you have a faster airplane for the same power. Using a well designed plenum allows you do to this while maintaining adequate engine cooling. Note however this is for your design flight target. If your target is a fire breathing climb at 3000 fpm plane, a plenum is not for you. If you respect the engine, provide reasonable speed during a climb and want superior cruise efficiency, a plenum with an appropriate cowl is the path.

Carl
 
Exactly correct. If done well, a plenum will make the most of the pounds of cooling air coming into the engine such that you can reduce the total pounds of air and still have the same heat rejection as a standard cowl with baffles. This is the approach with the James Cowl.

There is no free lunch. Reduce the engine cooling drag and you have a faster airplane for the same power. Using a well designed plenum allows you do to this while maintaining adequate engine cooling. Note however this is for your design flight target. If your target is a fire breathing climb at 3000 fpm plane, a plenum is not for you. If you respect the engine, provide reasonable speed during a climb and want superior cruise efficiency, a plenum with an appropriate cowl is the path.

Carl

Why would that make any difference? The plenum just forces all the air through the cylinders. It doesn't control the ins & outs; that's a separate choice, right?
 
Why would that make any difference? The plenum just forces all the air through the cylinders. It doesn't control the ins & outs; that's a separate choice, right?

Correct. Design the cowl to take advantage of the plenum's better use of cooling air.

Carl
 
If your target is a fire breathing climb at 3000 fpm plane, a plenum is not for you.

With all due respect Carl, that's nonsense.

Again, a plenum lid is just a sealing device. There is no "design point" speed, and it does not control how much mass passes through the system. It only ensures none of the mass can bypass the engine and thus fail to pick up heat. As such, a plenum lid benefits every part of the performance envelope, but low velocity climb most of all, as that's when the least total pressure is available. When starting with very little, there is none to waste.
 
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With all due respect Carl, that's nonsense.

Again, a plenum lid is just a sealing device. There is no "design point" speed, and it does not control how much mass passes through the system. It only ensures none of the mass can bypass the engine and thus fail to pick up heat. As such, a plenum lid benefits every part of the performance envelope, but low velocity climb most of all, as that's when the least total pressure is available. When starting with very little, there is none to waste.

I should have been clearer. My design target was high efficiency cruise, not rate of climb competition. With that target, total engine cooling drag can be reduced (as compared to a stock cowl) while still providing adequate cooling. With a good plenum, you can do more engine cooling drag reduction and still retain adequate cooling at your target operational envelope as compared to leaky baffles.

If rate of climb is the target, open up to let as much air in and out as you can. The addition of a plenum would help at the margins.

Carl
 
I should have been clearer. My design target was high efficiency cruise, not rate of climb competition. With that target, total engine cooling drag can be reduced (as compared to a stock cowl) while still providing adequate cooling. With a good plenum, you can do more engine cooling drag reduction and still retain adequate cooling at your target operational envelope as compared to leaky baffles.

If rate of climb is the target, open up to let as much air in and out as you can. The addition of a plenum would help at the margins.Carl

There is no target speed or margins. Leakage reduction is a benefit across the entire operating range.

Clarify this one for us please:

If you are not using the James Cowl there is little to be gained with a plenum.

Seems be be at odds with your signature line:

RV-8 in progress (will use stock cowl and homemade plenum)
 
Yep - stock cowl for the new RV-8 project and a homebrew plenum. While I know there will be no big cruise gain with the stock cowl, I'm hopeful a few tweaks of the stock cowl will gain something for me.

If not for the required prop spacer for the James RV-8 cowl I would use it.

Carl
 
Hi John, you have asked about the rvbits plenum. I always say that if you can fabricate well fitting rubber seals, you do not need a plenum lid. But most battle a bit with this. With my plenum you build the cooling baffles as per the plans up to the point where you do the final trim and rubber seals. Then add the plenum lid. The guidelines can be found at rvbits.com
 
Thanks, Jan. I've pretty well figured it out. I finally figured out how the oil door is handled. The real reason I thought about it is the problems with putting the top cowling on without folding a rubber baffle the wrong way.
John
 
Thanks, Jan. I've pretty well figured it out. I finally figured out how the oil door is handled. The real reason I thought about it is the problems with putting the top cowling on without folding a rubber baffle the wrong way.
John

John,
I have the RVBits Plenum and have had no cooling issues to date. The oil door seal is accomplished by simply installing a seal from McMaster Carr around the perimeter of the plenum oil door cutout. I believe the instructions even list the part number.

I don't have it handy, but it is something along these lines: https://www.mcmaster.com/#catalog/122/3516/=15ru6jt

Shannon
 
One thing I didn't see mentioned is the additional engine service issues caused by a plenum. With a stock cowl sans plenum, you remove the top cowl and the engine is right there. With a plenum, at least on my airplane, you still have to remove a boat-load of small screws to get access to the top of the engine.

It's part of the "no free lunch" deal. Also, it's tough to seal the dip-stick tube so that it doesn't leak air. If I was building I wouldn't waste my time with a plenum.

-Marc
 
I'm not sure if my plenum leaks air around the dipstick tube cut out or not, but I don't have any cooling issues either. I am based out of Houston and have flown in temps over 100f with no issues what so ever. Isn't that the real goal?

I will admit that it does take a while to get direct access to the engine verse just taking off the cowl. The reality is that I haven't had to do it that often since phase 1 anyways. Oil changes, condition inspection etc. It takes an extra 5 minutes to remove the plenum.

Shannon
 
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