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DIY Plenum

petehowell

Well Known Member
I really like the sticker on the back of the baggage compartment that says EXPERIMENTAL - it (ok, the certificate) gives us the ability to try new things (within reason) and see how they pan out. I have already done this to varying degrees with things like headsets, nav lights, landing lights, interior lights, canopies, O2 systems and trackers. For the most part, they have worked out well and saved me a few bux in the process.

My latest musings were around a plenum for engine cooling. My cooling has always been OK, but I have always thought it could be better. So I set out to copy some plenum designs I have seen here and on the web. My only criteria were to make it reversible in case I liked the baffle seals better, and it had to be pretty cheap to make. I only have about $60 into the design, so I think I have that one covered. The reversible design worked out OK, too, but I think it led to a less than optimal inlet design.

Here is the finished product:

Plenum%202_008.JPG


I started with a sheet of 2" stryo from Aviation Depot and started shaping with a surform and 40grit paper. The goal was to have the plenum fit inside the standard baffles and use the same holes for mounting.

Plenum_003.JPG


Progress

Plenum_023.JPG


Shape, fit, repeat. When I got close, I started fitting the upper cowl for clearance. Once it was shaped and I got a good fit, I blew off the dust and covered it in packing tape, and paste waxed it for good release.

Twins%20Bday%20015.jpg


I mixed up the EZ Poxy (good thermal properties) and applied 5 layers of 9 oz cheapo Fg cloth I found on sale at Av Depot.

Plenum%20top_001.JPG


I popped it off the mold, and trimmed the edges. Then, I fit it to the baffle sides and molded the ramps in place on the plane.

Plenum%20top_029.JPG


More to come in Part II.....................
 
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Part 2

Here is the plenum trimmed, fitted with nutplates and installed. It is sealed with speed tape for initial evaluation.

Plenum%20test_007.JPG


Another View

Plenum%20test_008.JPG


And a final view after painting - the Sky Pig 2 enhances the background view.

Plenum%202_004.JPG


I sealed the edges with black silicone and it looks pretty nice. How does it work? Well, it does seem to cool a bit better. On hot days, I can climb longer before I hit 400 CHT and back off. The cylinder temps are nicely evened out with the exception of #1 that needs a blocker(this is in work). Speed has increased 10 kts. Alex P and I have decided that you always claim 10kts on a drag reduction project. In reality I don't think it made a difference b/c the inlets were not resized. That may be the next project, so no real speed increase at this time.

Inlet as of now

Plenum%202_018.JPG


Temps balanced nicely

Plenum%20test_049.JPG


Was it worth it? Qualified yes- no great transformation occured, but it does run cooler and the there is room for inlet optimization and area reduction that should lead to better cooling and less drag. 10kts - Always claim 10 kts........ I did have fun and learned a few things, too. And for an aviation project, it was cheap.......

Watch for Part 3 when I rework the inlets
 
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Alright! I'm watching. Looks just like where I left mine, for now. Very interested in your exploration :). Great work, keep going.
 
Really nice work......

....Pete. Do a search on Alan Judy. He has really small inlets....removable ones for hotter days....and a pretty fast airplane too. There is an optimal inlet ramp and sides angle that I've read about somewhere. Someone on here should know and chime in.

Regards,
 
(these "how to" posts are always the best!)

BTW, Pete - I'm seriously considering stealing your paint scheme! :D
 
I love it Pete! I keep thinking I need a "do-able" project now and again....that looks pretty simple - and simple is elegant design.

Paul
 
NOT JUST A COVER

Pete....... Dave Anders got his plenum chamber right after much research. It is not just a motor cover. Yes, and done right, you will see 10 mph increase.

Dave has made a number of modifications to his RV-4 resulting in a substantial improvement in performance. He is able to achieve a top speed of 260+ MPH. Here is a link to his notes.

http://sacrvators.com/Aircraft Efficiency N230A.pdf

Please be sure to read page 3 and page 8 .......good luck....have fun.... :)
 
Thanks!

Hi Pete,

I have to agree with Fred. This "how to" and others that get posted here on VAF are invaluable!

Keep us posted!

/\/elson
 
Gasman - Thanks

The Dave Anders' notes are great! I've read the stories about him and it sounds like his dedication and work are top notch.
 
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Pete, some questions.

How does the top of the plenum mate/seal with the top cowl? Did you need to remove the ramps on the cowl?

Have you flown this yet, and are there any chaffing points?

Work looks good. I may have to copy your work on my plane.

Kent
 
Kent, some answers....

Hi Kent,

I did pop the cowl ramps off, I was able to get them off intact in case I needed to reinstall.

The plenum top does not mate to the top cowl, it rides below it, as no seal is needed. I did have one small area of chafing that I addressed.

I have about 60 hours on it now and am happy with the experiment. I am currently working to come up with an optimized inlet design.

Please let me know if you have questions - I'll help where I can.
 
The Dave Anders' notes are great! I've read the stories about him and it sounds like his dedication and work are top notch.

I met Dave Anders a few years ago at Van's tent at Oshkosh. When he found out I worked at NASA, I think he thought I was an aerodynamicist...not!!! But I did stay at a Holiday Inn last night!

When Dave Anders told me he studied Dr. Raspet's work and decided to use a parabolic cross-section on his air inlets, I KNEW he was into some serious research. I say he deserves every knot he's got! When you study what he's done, you soon realize there's a reason backed up by research for every change he's made on his RV.

Pete, I like your work. And thanks for sharing the photos and words with us.

Don
 
10 kts? sorry I don't believe it

John Huft keeps insisting I need to a plenum that does rely on the cowl but so far I am not convinced. All that I was able to achieve with inlet modification so far was increase the CHT. Good luck and I hope I'm wrong about you speed gain.

Bob Axsom
 
Read Closer

Hi Bob,

Read closer - The 10kts was tounge-in-cheek.

"How does it work? Well, it does seem to cool a bit better. On hot days, I can climb longer before I hit 400 CHT and back off. The cylinder temps are nicely evened out with the exception of #1 that needs a blocker(this is in work). Speed has increased 10 kts. Alex P and I have decided that you always claim 10kts on a drag reduction project. In reality I don't think it made a difference b/c the inlets were not resized. That may be the next project, so no real speed increase at this time"

I can tell you with just the plenum and no inlet re-design, my speed gain has been zilch and I did not expect any from just the plenum. I may experiment with optimized, smaller inlets to reduce cooling drag in the future. The only benefits I have realized are slightly better cooling and more even CHTs at cruise.

Sorry - I did not intend to mislead.
 
Don't tell that to Dave Anders...........

John Huft keeps insisting I need to a plenum that does rely on the cowl but so far I am not convinced. All that I was able to achieve with inlet modification so far was increase the CHT. Good luck and I hope I'm wrong about you speed gain.

Bob Axsom

Bob, Go back and read post 10 about Dave's notes.
 
On my plenum, I terminated the top cover straight across the front, just above the leading edge of the cylinder. From there forward, I made fiberglass inlets that matched the cowl opening and maximized smoothing of the airflow both on the bottom and top of the inlet.

The key is to get a smooth airflow transition into the plenum chamber to maximize flow and cooling. If it's turbulent, especially as it enters, it will REDUCE speed and REDUCE cooling significantly. At first, I used the RV-10 baffle kit as it came from Van's but was amazed at all the right angles in the inlets and cylinders. Just one ramp to push the air up over the #1 cylinder instead of smashing the air head on with a plate, improved cylinder and oil temperatures greatly.
 
Hi Bob,

Read closer - The 10kts was tounge-in-cheek.

"How does it work? Well, it does seem to cool a bit better. On hot days, I can climb longer before I hit 400 CHT and back off. The cylinder temps are nicely evened out with the exception of #1 that needs a blocker(this is in work). Speed has increased 10 kts. Alex P and I have decided that you always claim 10kts on a drag reduction project. In reality I don't think it made a difference b/c the inlets were not resized. That may be the next project, so no real speed increase at this time"

I can tell you with just the plenum and no inlet re-design, my speed gain has been zilch and I did not expect any from just the plenum. I may experiment with optimized, smaller inlets to reduce cooling drag in the future. The only benefits I have realized are slightly better cooling and more even CHTs at cruise.

Sorry - I did not intend to mislead.

Pete I did read the comments and realized that you presented no real indication of the 10 kt speed gain - it was just good humor. For the past four years I have methodically experimented with my RV-6A trying to increase the speed and I have been successful through many large and small changes to add 12 kts to the my original baseline maximum speed of 170.67 kts at 6000 ft density altitude. Cooling drag reduction made the largest contribution - 4+ kts. The problem is many people reading the information actually believe that if you put a separate top to the plenum instead of using the inside surface of the cowl for the top of the plenum the plane will increase its top speed by 10 kts. For my racing, the only change in the cooling air system before the cylinders that produced an increase in speed was cover plates for the plenum penetrations for the heater air port and three blast tube ports for the mags and vacuum pump. The major improvement in speed came from working with the flow of air after it passes the cylinders. I worked with this a lot! Many changes were made but the current configuration produced the best results. There is a baffle that is sealed to the back of the engine and plenum that curves to the bottom of the fuselage keeping all of the cooling air fwd of the engine mount, plumbing, wiring, equipment, and firewall. There are two angled rubber edged baffles that extend outward from this rear baffle at the width of the cooling air outlet to the lower cowl inside surfaces at the maximum non interference angle possible given the placement of cylinders 3 and 4. These baffles provide inclined planes to the air and direct it to the cooling air outlet from the sides as the rear baffle does it from the top. Two more rubber edged baffles extend from the rear and side baffles to the front of the cowl just below the top of the lower cowl. These last two narrow baffles were the key to my success. They seal the cowl interior into three chambers. Hi-temp RTV is used to seal these two baffles to the valve covers and outer wall of the plenum. The changes were made incrementally and until the last two little baffles were added the speed actually went down by 2 kts. Another fellow, Chris Zavatson, who has written an EAA article on the subject told me that the previous changes may have increased the air mass flow through the cooling system and resulted in the 2 kt slow down. You can imagine the feeling here when the chamber closure baffles were added and the speed jumped from down around 168 kts to well over 174 kts.

There is more to be gained in there but it requires a lot of work. I have talked a little bit to Larry Vetterman about an exaust system that would bring the pipes straight back rather than turning in to the current outlet area. then it might be possible to baffle the two sides of the lower cowl just outboard of the crankcase and keep all of the air out of the FAB, carbutetor and nose gear structure. There would be two cooling air outlets around the exhaust pipes and the center bottom cowl structur would be modified to bring it to a pointed closure, possibly with concave "Pressure recovery" lead in surface, aft of the nosegear. This would have to be seperable from the rest of the lower cowl for removal. Since I have the honey comb structure in the cowl walls and plenty of oil has touched the interior surface, this little after though is not a trivial modification.

Good luck with your pursuits I am with you in the quest of higher performance - especially speed in my case.

Bob Axsom
 
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a few questions

What an interesting thread...great stuff.

It seems inlets seem to be low...if they were higher they could flow over the top of the cyl heads more effectively. I was also wondering if two plenums would work better at keeping airflow where you want it? If you used a two into one exhaust on each side with exits inline with inlets would we have less cooling drag? It seems like there is a lot of drag when air enters on the outside ends of the cowl and exits in the center.

Just thinking...nothing factual
 
separate plenums

I believe the Jabiru engines have two separate plenums for the cylinders on each side.

Feasible/worthwhile for the Lycoming? Dunno.
 
What kind of fiberglass?

I considered making this change as well but found that most fiberglass is NOT for high temp areas. Expecially a engine plenum chamber. This is why is I bought the Sams James plenum (still not installed). It is curred differently and can stand high temp environments.

Keep an eye on it,
Steve
7A
 
EZ-Poxy

Hi Steve,

I corresponded with a Lancair builder that built his own(much nicer) plenum and after taking under the cowl temps, he concluded that a post cured plenum of Fiberglass and EZ-Poxy will work just fine. Fiberglass can handle the heat just fine - it is the resin that matters.

I have 60 hours on the plenum now including the hottest part of the midwest summer. I have seen no issues, but will watch it at every oil change.

More really good info here.

http://www.n91cz.com/cooling/Cowl_report_4-12-2005.pdf

I borrowed shamelessly, but have much work to do.
 
Cool

Good to hear. Hope it works out well.

Thanks for the attached article! Brought back some great memories for me. Christopher was the second homebuilder I ever meet at Arlington, WA around year 2000. I decided at that point I would build an airplane myself and use the same blue color Chris did. I still have multiple pics of his airplane as well as a hand written note of the color code!

Steve
7A
 
Are the stock cowl ramps needed with a plenum?

Hi Kent,

I did pop the cowl ramps off, I was able to get them off intact in case I needed to reinstall.
snipped

Please let me know if you have questions - I'll help where I can.

Pete,
I bought a cowl without the ramps from another builder. I am planning on using a plenum. Does your comment above mean that I should simply not worry about purchasing the cowl ramps from Vans?
Charlie Kuss
 
Two Piece cooling plenum

I believe the Jabiru engines have two separate plenums for the cylinders on each side.

Feasible/worthwhile for the Lycoming? Dunno.

Scott,
It's already been done. Mark Phillips did this on his RV6 several years ago. His ship won a workmanship award at Sun N' Fun that year (2006???) Mark has a lot of cool features on his RV. If you come to Sun N' Fun, look for his RV in the judging area. Mark's plenum was done in aluminum, rather than composite.
I've seen similar plenums on Canard aircraft.
Charlie Kuss

mark2pieceplenum1.jpg
 
Nope

Pete,
I bought a cowl without the ramps from another builder. I am planning on using a plenum. Does your comment above mean that I should simply not worry about purchasing the cowl ramps from Vans?
Charlie Kuss

Charlie,

If you build a plenum, you should not need the upper cowl ramps.
 
Used "Van's Elephant Ears" in inlet

After a disasterous first attempt at a plenum, I incorporated the inlet ramps from Van's into my inlets. My original inlets had no curvature on the top side. My conclusion was the air stalled at the inlet and prevented signifigant airflow, leading to a VERY hot engine on first flight. The second round went much better. There is a definite art and science to these inlets. I'm on my 4th generation inlets now and still have a lot to learn. I am getting a lot out of these threads, too.

Seb Trost
RV-7A
 
I used the upper cowl ramps as part of a female mold to make fibreglas diffusers that attach to the aft edge of the upper cowling. Three screws attach each diffuser to the upper cowling. A piece of ATV inner tube goes between the aft edge of the diffuser and the front edge of the plenum. This makes a flexible and apparently relatively airtight seal between the cowling and plenum. So far I've had way more cooling than I needed, but I haven't yet tested in worst case hot day conditions.

Pictures and description here.
 
Plenum

I installed a fiberglass plenum made by Russ Kamtz of KFNL. (Step up Aviation) The plenum sets in to the Vans baffle setup. You set the plenum into position, mark the inside edges and trim the baffles to fit. Reset the plenum, mark and drill holes for the nutplates thru the plenum and baffles. Install the nutplates on the plenum. Russ uses a pair of fiberglass ramps to feed and seal the inlets. The fit and install took about 4 hours. I am pleased with performance and fit ! If you are interested in an upgrade I can put you in touch with Russ :)

Les
 
Hey Les, got more...

I installed a fiberglass plenum made by Russ Kamtz of KFNL. (Step up Aviation) The plenum sets in to the Vans baffle setup. You set the plenum into position, mark the inside edges and trim the baffles to fit. Reset the plenum, mark and drill holes for the nutplates thru the plenum and baffles. Install the nutplates on the plenum. Russ uses a pair of fiberglass ramps to feed and seal the inlets. The fit and install took about 4 hours. I am pleased with performance and fit ! If you are interested in an upgrade I can put you in touch with Russ :)

Les

Les,
Do you have pix of your installation? Which engine?
thx,
Don
 
Plenum pictures

Don....email me at Les and Peggy at aol.com and I'll email you the pictures, I have'nt figured out how to post the pictures on this site.

Les
 
Here's mine

Just finished it yesterday. Overall really happy how it turned out. It could use some more block sanding but the matt finish really hides the lows. I may still sand when painting begins but then again I look forward to flying this year.
1268528652.jpg
 
Very Nice!

Just finished it yesterday. Overall really happy how it turned out. It could use some more block sanding but the matt finish really hides the lows. I may still sand when painting begins but then again I look forward to flying this year.
1268528652.jpg
 
here's mine

All metal, vans baffles with a lid. Works just perfect, nice even cylinder temps after baffle and inlet dam adjustments. Stabilizes the oil cooler mounting, and has way too many fasteners to deal with. No top cowl puffing in flight. 10 kts....

Regards, Chris

zu5bgn.jpg
 
Yeah, mine has about 45 fasteners. Using an electric driver will still only take about 3.5 or 4 minutes to remove. I think. Say 4 or 5 seconds per screw? Somewhere in that range. It could be done with fewer fasteners for sure.
 
Lots of beautiful work and proof once again that there are many ways to skin these cats. On most of the plenums shown in this thread the top of the plenum is even with the top of the baffles. I suspect it is there because the top of the baffle was a logical place to stay below and to fasten the top of the plenum. Is that the optimumn location for cooling and speed?

Baffles end up different heights due to differences on how we trim them, so every plenum would be at a slightly different height. Would it be best to have as much volume as possible above the cylinders or would it be best to cut the baffles down and bring the top of the plenum down closer to the cylinders?
 
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Definitely many different ways. I have read some "experts" say more volume and have read others say it is not important.

Paul Lipps, who seems to be pretty darn sharp, has no volume at all. Each cylinder on his Lancair is wrapped (its own plenum if you will). Intake air is ducted to the top of the cylinders, splits around each side and exits the bottom.

For me, 2 plenums, one for each side.
 
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