To Plenum, Or Not........

[PaulR]

Randy
Would you expand upon your experience with the cooling ramps, particularly on the right side? I've always felt like that was a problem if installed as Van's directs. I believe the instructions were "where they fit best". There is a significant difference between #1 and #2 in the room between the ramps and the cylinders and I have always wondered if that made a difference.

I'm about to go to paint and am seriously thinking about a redo on the right side.

[RV8RIVETER]

Originally Posted by RV10inOz

It is just my opinion......but based on the evidence so far the plenum is not working and while some folk with the will argue....I say show me the data.

You bring up a good point, though I completely disagree with your conclusion. The data is out there.

The point is there is nothing magic about a plenum, so just because you choose to use one does not mean it will work. Just as with a stock set-up you must carefully consider how you are controlling the air flow, from the inlet all the way to the exit. It must be sealed well so that the air only goes where you want it to. Simplified.

The only difference between a plenum and stock baffle set-up is the ability to form a completely pressurized seal of the incoming air.

[jdeas]

Originally Posted by RV8RIVETER

The point is there is nothing magic about a plenum, so just because you choose to use one does not mean it will work. Just as with a stock set-up you must carefully consider how you are controlling the air flow, from the inlet all the way to the exit. It must be sealed well so that the air only goes where you want it to. Simplified.

The only difference between a plenum and stock baffle set-up is the ability to form a completely pressurized seal of the incoming air.

A plenum is also easier to inspect for leaks as you can disregard the distortion of the cowl in flight.

[Ironflight]

I think there are some very neat plenums out there, and they can work very well if you put the time into them (which is, of course, experimenting, and the point for many in "experimental aviation").

On the other hand, with very few exceptions, if a person has cooling problems with their new RV, the first thing an experienced troubleshooter will ask is what did you do differently from the Van's design?" And almost invariably, the builder has done something original (maybe a plenum, maybe something else).

Let me state with emphasis - there is nothing wrong with experimenting and working to find something better! However, recognize that tinkering may be required to perfect your new ideas, and accept that.

BTW, I think enclosed plenums are kinda' cool....

[f1rocket]

Originally Posted by PaulR

Randy
Would you expand upon your experience with the cooling ramps, particularly on the right side? I've always felt like that was a problem if installed as Van's directs. I believe the instructions were "where they fit best". There is a significant difference between #1 and #2 in the room between the ramps and the cylinders and I have always wondered if that made a difference.

I'm about to go to paint and am seriously thinking about a redo on the right side.

The right side is where cylinder one is. On this side, the cylinders are offset towards the front and the ramp on this side tends to get too close to the cylinder to allow enough cooling air into the pressure side. Cut the edge of the ramp back so that it makes the transition up to the top of the cowl more quickly. The ramps are too long in this area and need to be trimmed back prior to installation. Again, the test is if you can get your fist in between the ramp and the number one cylinder. If not, re-install the ramp.

[Mike S]

Originally Posted by f1rocket

The right side is where cylinder one is. On this side, the cylinders are offset towards the front and the ramp on this side tends to get too close to the cylinder to allow enough cooling air into the pressure side. Cut the edge of the ramp back so that it makes the transition up to the top of the cowl more quickly. The ramps are too long in this area and need to be trimmed back prior to installation. Again, the test is if you can get your fist in between the ramp and the number one cylinder. If not, re-install the ramp.

Good info, this may be one of the problems I am fighting.

I need to go investigate ................

[MarkW]

Great topic. I have long considered a plenum to be more effective than baffles. I would not go to the trouble of a Sam's Cowl and plenum but I did see another build where the builder made his own plenum.
I have seen certified LSA with very good looking dual plenums. I also remember seeing were someone made the comment that the plenum help with vibration and noise since there would no longer be the baffling rubbing on the bottom of the cowl. I would assume the toughest part of a homemade plenum would be the transition from the inlets. One advantage of the Sam's cowl, round inlets. I don't really want to add more time to the build but some aspect of a plenum seem nice.

[danP]

I have a 7A and I experienced some cooling issues early on. The chts were not extremely high but I would like them to run around 325-350 I installed cooling fins on the bottom of the cowl and replaced the vans black baffling with the thicker orange. That did the trick ! I have a Vettermans 4 pipe exhaust and I think that the opening was not quite large enough. Also I have learned how to run lean of peak and that really drops your chts.

[tcone1]

Originally Posted by RV10inOz

In 100% of cases with plenums on RV7's that I know of, they all have chronic CHT issues.
Just remember that no amount of science and data can overcome the warm fuzzy feeling of a closely held superstition.

Your last line applies to you as well...

My -8 has a Sam James Plenum and rings grafted to a stock Van's cowl and I have zero cooling issues. I have tested in 40 deg C temps and have never seen a cylinder above 400F despite 80 knot climbs to 10,000 feet.

[Jamie Aust]

Originally Posted by RV10inOz

In 100% of cases with plenums on RV7's that I know of, they all have chronic CHT issues.

Here is a picture of my chronic CHT.



I still have a problem with #3 in the climb, it will hit 400F, if I climb slower than 100kts, once I level off I can see 350 - 360 F on all CHTs.
I love my DIY ( experimental ) plenum, however I would be just as happy if I had made a baffle system.