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

mike newall

Well Known Member
Sponsor
Installed a plenum on our 7.

We still have issues with high CHT's and am not sure if they are related.

Cracking on with the 8 and wondering.....

Do we plenum or baffle.

Let me have some thoughts please.

Mike & Mark
 
Hello
I have a Plenum on my RV6A with a NEW Lycoming 0360 A1A and although I only have 6hrs on her the CHT are 350 -360 degrees runniing the engine at 2400rpm and full mixture because I'm running it in.
If you send me your email I will send you pic. The guy who made the Plenum is Wayne miller at HWO 305 298-2603 does a nice job.
Hope this helps.
[email protected]
 
Hi Mike how about both. I installed a Sam James cowling on my RV6A and it is built with a baffling system and a plenum.

Bill
 
I've done both and what I have realized is that they both work but you must seal every air leak, regardless if you have a plenum or not.
 
I have two plenums, one for each side and it works very well so far. I made composite cylinder wraps that keep the air inside the fins until it exits the bottom of the cylinders. My inlet area is just about 50% of the stock cowl and the highest CHT on the first few flights was 390, Texas, September, 2 hours on a rebuilt engine. They were all within 20-30 degree of each other.











 
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Plenum

I have the James plenum and 90hrs on my 9:1 0-320. Its winter here with temps ranging 20-40*F. I am only getting 325* max in cruise, reducing to 250* when I throttle back for the circuit. I think the plenum cools too efficiently. Time to make a cooling air exit restriction.
 
NO PLENUMS

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

In 100% of cases of standard baffles (not the black rubber though the orange stuff) that I know of the CHT's are good, i.e. around 300 +/-10 when LOP and 330-360 ROP.

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.

It is ironic you are asking the question when I think you know the answer already, but just are not sure you want to accept it.

Just remember that no amount of science and data can overcome the warm fuzzy feeling of a closely held superstition.
 
I say show me the data.

Here are my RV8's with the plenum.

IMG_0734_zps045ad0b3.jpg


I can't say anything on the RV7 but at least on (my) RV8 it works pretty well. Not too hot/cold and CHTs are really close.
Never had any issues for the moment from 90F to 10F OAT.

I am sure baffles work well if you pay attention to the leaks (as you would also do with a plenum)

Note: Mike do you have the ECI cylinders with the tapered fins? If you have them and did not do any mod on the cylinder baffle, it could be an issue resulting in high CHTs.
 
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The biggest and most often cooling issue I see is restricted airflow into the plenum/baffle caused by the air ramps in the upper cowling. Often, these are glassed into the upper cowling without trimming them back to open up the airflow. I've solved several CHT/Oil temp issues by cutting this back.

Stick your fist into your cowl opening on the right side. If your fist won't fit, your opening is too small. Fix that first and you may be surprised by the results.
 
Here are my RV8's with the plenum.

I can't say anything on the RV7 but at least on (my) RV8 it works pretty well. Not to hot/cold and CHTs are really close.
Never had any issues for the moment from 90F to 10F OAT.

I am sure baffles work well if you pay attention to the leaks (as you would also do with a plenum)

Note: Mike do you have the ECI cylinders with the tapered fins? If you have them and did not do any mod on the cylinder baffle, it could be an issue resulting in high CHTs.

Exactly my point. I would class that as a Plenum FAIL.

Sorry if you feel upset by that harsh comment but lets be real here folks, the OAT is -8 deg C and at 61% power and running LOP !!!!

That should be CHT of around 290 d F.

You have proven my point exactly. ;)

You are confirming exactly what I see here. Try that in Australia or the southern USA.

Here is +8degC OAT, and 67% power LOP
m_IMG_1227.jpg


or how about +2deg C at 63% LOP
photo3-1.jpg


How about -2dC at 61% power and before I fixed a few things
IMG_0473.jpg


and last one for tonight, +13dC, 68% power and check out the CHT
IMG_0466.jpg


I understand my post above and this one will hurt some feelings, but you can have 100 opinions and beliefs, all it takes is one shot of real data to shoot them down.

All the properly baffled -7 and -10 installations I have seen have had good results.
 
Air inlets

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.
 
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.
 
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.
1685z83.jpg
 
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.... :)
 
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.
 
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 ................
 
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.
 
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.
 
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.
 
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. ;)

cam0603custom.jpg


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.
 
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I contemplated the Sam James plenum but in the end ended up going with the standard Van's baffle. I am running the standard Vans baffles with the Oil cooler mounted on the baffle behind the #4 Cylinder. Here are three different flight pics I have taken over the years flying LOP. Most of the time my CHT temps range anywhere in the 275 F to the 320 F range while flying LOP. The 4 cylinders usually are within 10 deg F of each other when doing so.

The numbers may be hard to see but this pic shows flight at 9500ft, OAT 29F, CHT's 261-273F:
LOP%2520%2540%252029F.jpg


And another flight at 11500ft, OAT 37F, CHT's 292-297F:
LOP%2520%2540%252037F.jpg


And one down low at 3000ft, OAT 42F, CHT's 268-275F:
LOP%2520%2540%252042F.jpg
 
Sam James plenum, IO-320 ...

My Sam James plenum has cooled wonderfully from Day 1. I spent a reasonable (i.e. not excessive) amount of time sealing up the front edges where it abuts the engine case, and have a soft gasket across the aft edge at the rear baffle(s). My oil cooler is behind Cyl#4, and despite my pre-flying concerns about high oil temps given that location, my problem is too much cooling when air temps are under 40 to 45F. In these winter months I have 80% of the oil cooler blocked off to get oil temps of 175 to 180; my CHTs running LOP are very close to 300 depending on OAT. Quite honestly, I couldn't be happier with the plenum arrangement.
 
Build the cowling the way Van asks you to and it will always work just fine, in my opinion a separte plenum is a total waste of money and building time and weight.
 
Waste of time and money is in the eye of the beholder....also in the eye of the fuel receipt holder.

I took off last of 4 RV's heading to OSH last year, but landed 15 minutes in front of everyone at the first fuel stop. I also took less fuel then anyone else(even the 320).

YMMV, but I like cruising fast. 8.5gph is 178kts TAS at 9500' CHTs 340-350.
 
Here is a picture of my chronic CHT. ;)

cam0603custom.jpg


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.

Jamie, you should be saying if you climb slower than 120+ knots, you are only using 100 on initial climb out.

And at 29LPH, despite the Dynon being confused there about ROP, the CHT's should be down around 295-310, exactly as others report. I have had a few PM's on this thread, all agreeing but not having taken the time to photograph it. I hope they do.

Experiment for sure, but don't settle for something less than optimal is what I am saying.
 
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.

Tim sure thing, but where was I holding the superstition? Please point it out if I have. We as humans are all guilty of it at times. We will justify the indefensible for hours despite the data, just because we have a pride issue with the purchasing decission we made. I am just as capable of this as anyone.

Now how about you define the "zero cooling issues" a little bit. You may well have a Sam James plenum that is set up well and works as effectively as the standard baffles. I would like to see the evidence, and I would be really pleased if you did achieve it. I would like to see others with plenums have success. But so far I have not.

Why go to all that trouble and expense and have higher CHT's? Unless you gained 10+ knots in cooling drag reduction I would argue it was not worth it.

They also make it harder to get to the top of the engine, plugs etc. Despite looking cool! ;)
 
Down here in OZ its pretty warm a lot of the time.
As David says, almost all of the RVs here with plenums that I know of, run significantly higher CHTs than those with stock setups. This seems counter-intuitive, I agree, but thats the data set we have.
I have a standard baffle setup and never see higher than 380 in climb on very hot (40c+) days Cruise ROP around 330-350 dependent on ambient, and 310 or thereabouts LOP.

One theory we have kicked around here is that the plenum removes a lot of the Al baffle material which undoubtedly acts as additional heat sink for cylinder heads in a stock setup. Im not sure how one would quantify that though.

Its also hard to make apples/apples comparisons of how much air is flowing throught the different setups. All things being equal, hotter = less air which should equal less drag - which is the selling point of aftermarket cowls and plenums in the first place. So one would expect a plenum to be hotter and quicker. Or if you talk to someone with a plenum cooler and quicker! ;)

my 2c

Cheers
 
Richard,

Funny your data set or experience is like mine.

The unfortunate part is I wonder if some plenums are not just hotter, but hotter and slower.

DanH is probably the VAF guru on this topic and I would suggest he has helped many folk succeed in getting cooling right.

So far I have never seen anyone with better cooling results and a faster plane than one with standard baffles using the better seal material.

Heck, mine have leaks in the corners and around the front near the crankshaft.

Tufting an engine and lots of camera's is the answer! I know folk who did this to STC Beech baffles, and they learned a whole heap of stuff that defied commonly held beliefs that even they had. The data changed their minds, even if it was hard to swallow at the time.

This is external testing http://www.youtube.com/watch?v=QbMQWPTzS3M
 
I looked for some pics, but can't locate many with enough info.

This was taken about a year ago during race testing. I was running about as hard as possible. 2600rpm, 150ROP, 24.7"mp. OAT 2C. CHTs under 350. 190KTAS
aviation2012013.jpg


Then in April I ran the Hill Country 150 at similar power settings but OAT was about 21C. CHTs were under 395. I was making max power for the conditions and still below 400. :)

Coming back from OSH'12, we were at gross weight and ramp temp in South Dakota was 33*C. It was still 27C at 8500', I kept climbing looking for some relief of the bumps and heat. CHTs never got above 390. I like my plenum.

To be fair, I did have a cooling issue the first summer after phase 1(jan-feb11). When summer rolled around I had to step climb several times to keep oil temp and CHTs in check. I found many "leaks" in plenum and plugging them was the fix.
 
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Not bad, but not as good as or better than the standard baffle results, but to be fair, you are operating at a different MO than the normal cruise. It would be interesting to see what you get operating at a DA of say 8-9K and WOT and 10-20LOP.
By the way your % power is wrong, some engine settings are not entered right. It should be showing about 79% power.

Just to thro the can among the pidgeons a bit, here is 29.6" MP (yes high QNH) and 2450RPM, about 80dF LOP and a genuine 79% power This was S&L in the cruise at 1000'AMSL. It is true that the denser air helps.

photo2-3.jpg
 
Going from memory here...but 8500' for me is 23"mp, WOT, 2450rpm and 8.5gph will give me 178Ktas and CHTs are about 330-340.

I know my %power is wrong, but can't seem to correct it. I always assumed it was off about 8%, thinking it something to do with running ROP fuel flow.

When you say "good but not as good as standard" I don't understand. What is the goal you are trying to achieve. As cool as possible? Fast? Even spread?

I could make mine run cooler but am balancing running fast (racing) and yet still climb during the summer at gross. So we all have parameters we are trying to achieve. I probably can't hit your benchmark...but show me a RV-7 with a parallel valve 360 that can run 190kts flat out for an hour, cruise 178-180kts on 8.5-9.0 gph AND meet your 310*CHTs.
 
Ok, flame suit on: :eek:
So what if my CHT are 50 - 60 F over what everyone else has. I can still run LOP, what damage can I do to my 0-360 its still within the lycoming CHT range for normal OPs.
Ahhhh I can remember the good old days when the C172 only had one EGT !
:D
 
To your point Jamie, if your engine is "within limits" why worry? I think it boils down to "What am I getting for this extra temperature?" That is the basis for Hydroguys posts about intentional higher temps being traded for higher speed at lower fuel consumption.

I'm verry happy with my "normal" baffles because I spent more than average time fabricating good nose seals. I don't have performance pic to share yet. Might get some tomorrow in a flight to see first grandson (kids at hospital today).

I would like to pose the following position with upfront apologies to some. My supposition is that well done engine cooling systems will perform similarly no matter whether they are std baffled or plenumed. With enough data (temp, weight, maint PITA), I could be convinced that a plenum could do better than std baffles. I have yet to see enough hard data to swing my internal "value meter" towards plenums.

**EDIT** Here are pics from a flight today. 70% power (both from RPM/MP Lyc chart and LOP 14.9 calc)
Sorry for the fuzzy pics. Poor field of focus on camera setting. Images were taken a few seconds apart.

11940409145105d9d0148e1.jpg


16460479955105d9d00ae9c.jpg
 
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LOP & Percet power

I think what may be missing in this discussion is what is true % power these CHT's are recorded at?
I believe % power calculations are based on ROP, at least on GRT equipment.
Try using Fuel flow / 14.9 (assuming 8.5 CR), you probably will find you get a much lower % power than your engine monitor, hence the lower CHTs
Tim
 
My RV-7 with a parallel valve IO-360, standard pink cowl and stock baffles is decidedly not the best-cooled example of its type. I can easily get CHTs above (well above) 400 degrees on a hot day slow climbout at full throttle. Or at least I can based on the numbers displayed on my EFIS. Cruising at, say, 5500 feet on a hot Sacramento Valley day where OAT might still be above 80 degrees, I struggle to get CHTs below 350 even running LOP.

Which makes me wonder: there is an implicit assumption in this discussion that indicated CHT values are accurate. Even assuming that every EFIS is dead-on, how much accuracy degradation can one expect to see due to differences in individual probes, installation (in the cylinder head), wiring? In the context of this discussion, 20 degrees fahrenheit difference is a lot, but it's only a 5% delta at 400 degrees.
 
Jamie, you should be saying if you climb slower than 120+ knots, you are only using 100 on initial climb out.

And at 29LPH, despite the Dynon being confused there about ROP, the CHT's should be down around 295-310, exactly as others report. I have had a few PM's on this thread, all agreeing but not having taken the time to photograph it. I hope they do.

Experiment for sure, but don't settle for something less than optimal is what I am saying.

Post #25

Hello

I hope I'm not hijacking this thread. I noticed in Jamie's picture one of his EGT's was higher in comparision to the others. His CHT's are nice and balanced. I also have this situation on my RV6A with ECI IO360. It has a plenum. Total hours on the engine are approximately 75 hours. My number 2cylinder is the coolest CHT of the 4, CHT's are within 10-15 degrees of each other (middle 350's in cruise). My number 2 EGT runs about 60-80 degrees above the others in cruise. EGT's run 1350's, while the number 2 will show 1430.
Looking for some advice.
Tony
 
When I was trying to increase cooling, I spoke with a very experienced A&P about all my numbers. I was concerned about oil temp going above 215 and chts above 400(during hot summer days w/extended climbs), after his review of the situation he said "it appears your problem is...too much information, Go fly your airplane!"
 
The original question was whether to use a plenum or not.

As with every other choice on aircraft it boils down to what you, as the builder want to do and what goals are to be achieved.
Do you want the engine to run the coldest that is possible?
Do you want the aircraft to be as fast as possible?
Do you want the most efficiency, highest speed but OK temps all year round?

Your choices will choose the route you will be happy with. There is no one answer that is a cure all. The cooling system like any other must be taken as a whole, it is the sum of all of it's parts, starting at the inlet and going all of the way to the exit. To optimize cooling you need to optimize each stage of the system.

---

As for those wanting data, it is out there. As has been posted many times Chris Zavatson's Lancair article is a very good source. Different airplane , same cooling system choices.
http://www.n91cz.net/cooling/webCowlrep.htm

The Miss St. study. Dave Anders RV-4 work. Reno Racing articles. If you want more efficiency a plenum is the best choice.

It is simple physics, the more air you take in, the more mass momentum you absorb and the slower you will go.

To say some plenum installations had issues, therefore they are a worse choice is an error in logic. A plenum install done badly is the same as a stock cooling system done badly.

I read many posts on here about a 200 hp motor in an RV-8 and how they had to put in louvers to get adequate cooling. I guess I should have thought that the stock set-up was a failure? I cut my inlet area in half, which I was told was crazy and would not work, but alas my CHTs are fine.
 
Brian, I am very impressed with your speed results, and if you have actually achieved far less cooling drag, and gained some speed, and you can verify that, all at the same time as having reasonable and manageable CHT's you have hit a sweet spot.

Despite what your A&P said about too much info, data confirms that CHT's should be kept under 380, and that over 400 you really want to avoid this as much as possible. Remember the limits in the manual are certification limits, not where you should be running to if you want a long healthy engine life.

For the average punter, and I would say you are not, but the average guy is going to struggle. What we see is higher CHT's (less margin on hot and or heavy weight days) and we see no speed gain. In fact it could be said speed loss.

Guys like Dan Horton and yourself and a small group have probably cracked the sweet spot, but the vast majority are going to struggle.

When you say "good but not as good as standard" I don't understand. What is the goal you are trying to achieve. As cool as possible? Fast? Even spread?

What I am saying is that assuming most folk will not get a speed gain, or not significant, they should be focussed on making the cooling system deliver lower temps, ROP running around 350-360 max in the cruise is a good goal. Remember in a climb the aim is to keep them under 380F. When running LOP depending on altitude etc you would expect something like 300-330dF.

The standard baffles done properly achieve this. Anything less effective is obviously sub optimal. Is it going to kill your engine? No, but over the life of it it may make a difference to repairs or total life.

So summing up, unless you make significant gains over the standard baffles you are going backwards. For most people that is what needs careful thought. And the reason I think you should aim for the kinds of cruise numbers I am talking about is margin above left over for hot climbs and MTOW and not going over 380.


Jamie, you are a stirrer boy! Wait until you drop in later this morning, I'll set Dudley onto you:D:D

Tony, Ignore what the difference in EGT is, that is not critical, probe placement can do that alone. Your CHT's being within 20dF of each other is pretty good and typical. 350dF in the cruise is good, but only if that is ROP, a 10-20dF LOP cruise should yield a bit less. To make a value judgement more info is required.

% POWER on your EMS
To my knowledge, so far the only EMS that are on the market in the TSO world is the Auracle. I know why too, a former VAF contributor spent a lot of time helping them get their overall EMS package correct. In the experimental world the Dynon does it right, for a 8.5CR engine. I am not sure about the others like AFS and GRT but I suspect they may have either ROP or LOP calcs correct but not both. I would like to know if anyone has proof of it.

In simple mental maths terms to do a % power calculation in flight take USGPH x 15 (14.9 for most engines CR) but 15 is near enough. If you are ROP, then Mass Air Flow is the governing factor so a simple (and its rough but close enough) %age of MP x %age of RPM will do it. For example 25"/29.9 is 83.6% and 2430RPM is 2430/2700 or 90%. Answer is roughly 75% power.

In flight you could say .85 x .9 and you get 76.5%.....so who cares. Near enough:)

Brian, for your Dynon % power, go to your manual and find this section
E
ngine Type Configuration
W
ithin the GLOBAL menu, press DOWN▼ until you have selected ENGINE TYPE. Press SEL► to toggle between LY/CON, ROTAX, and OTHER.
ENGINE TYPE: LY/CON
Setting ENGINE TYPE to LY/CON enables a percent power display for normally aspirated/non-turbocharged Lycoming or Continental engines. Press DOWN▼ to select HP RATING and use the INC+ and DEC- buttons to set the value to the actual horsepower rating for your engine. Given the horsepower rating, an OAT, fuel flow, and altitude (from a connected EFIS-based product or GPS), the EMS-D120 will calculate percent power and lean-of-peak/rich-of-peak status, displaying both next to the Manifold Pressure gauge.
For percent power status to be calculated as accurately as possible, TACHOMETER (RPM) HI RED/YEL should be set to the RPM value specified by the Engine Manufacturer. (This is commonly referred to as ?Redline?).
I
f you do not have a fuel flow sender, the EMS-D120 will still display a percent power reading based on rich-of-peak calculations only. During lean-of-peak operation, percent power is displayed but is incorrect. While you are in LEAN mode, percent power is not displayed.

I hope that is helpful :)
 
Thanks David. Following the Sport Air Racing League and folks like Bob Axsom, Dan Horton, and a few others pushed me to where I am. I knew many planes were leaving something on the table. Great all around performance but little things make a difference. I think there is another 3-5kts waiting for me to unleash. So, I have a few more things I want to implement, but my aviation budget is depleted these days.

Concerning the Dynon settings...I've entered the data things you mention, but must have an error somewhere. My engine was originally an O-360 180hp, but we rebuilt it with 9:1 pistons, AFP F.I. and Pmags, so figure it is closer to 190hp. What should I use for HP rating? Also not sure where I set the Tach red/yellow...I run a WW200 prop which is limited to 2600 continuous so may have set some parameters wrong based on that. I'll look tomorrow if I go to the hangar.
 
Efficiencies aside, the problem with full plenums is that they do not allow for easy inspection of the top of the engine when the top cowling is removed. There's potentially a number of items on top of the engine that are best monitored regularly including the fuel flow divider and associated injection lines, ignition coils, and plug leads. My guess is that with most plenum systems the top of the engine is inspected only at annuals.

Ease of access for inspection of an aircraft is in itself a safety factor.
 
The Dynon is going to be a little confused on the LOP side of the curve, as it uses the fuel flow x 14.9 to calculate the actual HP and then as a percentage of what you enter as the full rated HP.

You are getting 15.47HP per USG.

For the ROP side of the curve, if you set your redline (RED/YEL) at 2700 and just set your Yellow/Green at the 2600 limit that will fix up the % power. On the ROP side the HP number you enter in the setup menu makes not difference. It is basically MP and RPM that dictate the numbers.

Now to get the LOP side somewhere near correct, I guess by basic numbers you are probably making 186 HP, and rough enough is good enough here, but to compensate for the higher HP/USG due to the higher CR, you need to fudge the system so set in 180 HP and see how it goes.

Get in flight, set a genuine LOP setting, and see what % it says, compare that to the USG x 15.47 (actual HP) compared to our guessed 186HP.

May not be perfect, but it should be damned close.
 
A lot of this conversation is confusing inlet performance issues (the conversion of dynamic pressure to static pressure) with leakage issues (allowing some percentage of cooling mass to bypass the hot parts). The confusion is natural as the two are linked; the method of connecting and sealing a plenum lid to the cowl inlets tends to affect inlet performance via choices of shape and size.

To the original question...a really well crafted set of silicone flap seals can seal as well as a so-so plenum. It may have better inlet performance; measurement suggests the Vans inlet performance is very good.

A really well crafted plenum will seal better than the best flap seals. Given equal inlet performance the effect will be to allow lower mass flows (allow a reduction in exit area) with the same total heat transfer....the exit air will be hotter.

Side note....if your CHT values are very low, even on warm days at slow speeds, you are to be congratulated. However, you're going a lot slower than you could go. Overcooling is, literally, a drag.....
 
Side note....if your CHT values are very low, even on warm days at slow speeds, you are to be congratulated. However, you're going a lot slower than you could go. Overcooling is, literally, a drag.....

Absolutely! The question then becomes what basis determines the margin of "overcooling" needed to provide an educated, purposefully engineered reduction in exit flow required to minimize cooling drag? The answer, in my view, is the design, certified engine operating limits. While some would have you believe these limits are not valid I invite them to review 14 CFR Part 33.49
http://www.flightsimaviation.com/data/FARS/part_33-49.html

Which specifies reciprocating engine endurance testing requirements. The most significant of which requires the engine to be operated at max rated power for a minimum of 35 hours with 1 cyl no lower than its max operating limit with the others no lower than 50 degrees below the limit. That is 1 cyl at or above 500 deg and the others at or above 450 deg for 35 hours at max rated power. The total endurance test is 150 hour upon which a tear down inspection must occur. See 14 CFR 33.57

http://www.flightsimaviation.com/data/FARS/part_33-55.html

Upon conclusion of the test all parts must meet the design type specification - Which in FAA parlance means every part must conform to the approved drawings. This is the test for wear and conformity. Each part is measured and compared to the spec with data being tracked to determine wear rates which goes into the formula for determining TBO. In reality the major engine manufacturers conduct far more than the minimum 150 hrs during their development and have far more data than needed to substantiate their limits. The 150 hr test is conducted on what the manufacturer submits as their final conforming engine design at which point the specs are frozen and the test conducted. They KNOW what their engines are capable of with thousands upon thousands of controlled and well documented test hours.

This oft repeated notion CHT MUST remain below 380 value in climb, and 360 value in cruise for your engine to remain healthy is based upon anecdotal information and a bunch of clever marketing. However, if it makes you feel good it can't hurt :)

However, no matter what your belief about CHT limits, physics doesn't lie and the cooler you can operate your engine the more margin you have (against whatever limits make you happy) to reduce the exit and recover some of the lost momentum thereby increasing your speed.

Dan and I have both measured our Upper Plenum pressures using standardized techniques and equipment. He has a covered plenum with round inlets and I the standard Van's seals and inlets. Our upper plenum pressures are virtually identical through our entire speed range. Our lower plenum pressures vary based upon our exit sizes (at the time his was fixed and mine variable). Based upon our data it is my view when done well both offer nearly identical pressure recovery. The covered plenum has some advantages: Should be easier to do well, relieves stress upon the upper cowl hinge line, and probably requires less care and maintenance over time.

We plan to publish our full results in the future, but probably have more testing to conduct. We were hoping to get a few more folks with stock installations to participate, specifically parallel valve 0-360 with stock inlets and baffles. Any takers? Between Dan and I we can supply you with probes, test equipment, our test methodology and data analysis - FREE :)
 
...Side note....if your CHT values are very low, even on warm days at slow speeds, you are to be congratulated. However, you're going a lot slower than you could go. Overcooling is, literally, a drag.....

This is the boat I'm now in. With 20 or so hours since my cooling mods, I'm @300 or less in cruise on all cylinders. Climb is still pretty warm, but as soon as I pushover and go LOP, the temps just plummet. Still have some summer flying to verify, but I think this is pretty compelling evidence that I need variable geometry on the outlet.

It's time to trade in some of that cooling margin for more speed!
 
Dan and I have both measured our Upper Plenum pressures using standardized techniques and equipment. He has a covered plenum with round inlets and I the standard Van's seals and inlets. Our upper plenum pressures are virtually identical through our entire speed range.

Again, lets not confuse inlet performance with what kind of lid closes the upper deck plenum. Ken is telling you the stock Vans inlet does a good job of converting Q to static, at least as good as the low Vi/Vo round inlet on my cowl.

However, equal upper plenum pressures does not necessarily mean equal leakage rates. Despite equal pressures we're recording significant differences in cooling efficiency, a measure of how much heat is being transferred to the cooling mass on its pass through the cowl. At this time we don't know how much of that difference is due to leakage (bypassing the hot parts), how much is due to the difference in fin area between Ken's parallel valve motor and my angle valve (less area of hot parts), and how much is due to differences in baffling (how closely and how long the cooling mas is kept in contact with the hot parts).

A really good plenum lid affects only leakage. That said, I remain convinced that a good plenum lid seals better than the best flap seals....and way, way better than average flap seals. That much is found in NASA CR3405.

Always something more to learn.
 
Why go to all that trouble and expense and have higher CHT's? Unless you gained 10+ knots in cooling drag reduction I would argue it was not worth it.
I claim no personal genius on my setup...I adapted Sam James stuff onto a stock cowl. Maybe I'm the luckiest guy in the world because it just worked right out of the gate. I didn't even bother sealing stuff too well until I decided to run at the Reno Air Races.

I don't know about 10 knots faster, but my poor little ole stock, carb'd 8.5:1 o-360 was able to pull my -8 around the pylons at Reno at 218+ mph on a 8000' DA day. Back in phase 1 flight testing, about 900 hours ago, she'd do 193 KNOTs at Sea level using the NTPS 3 way gps test method.

The plenum did add about a week of build time and does add about 10 minutes to the time required to remove the top plugs. Remove 14 screws and viola, it's off.

Zero cooling issues means...it's never gotten hot despite living in a very warm climate. I saw 410 degrees once while taxing out for the third flight of the afternoon on a 108 degree afternoon. By 1,000 feet agl in the climb, the cht was back down below 360.

My oil cooler is on the baffle behind #4 cylinder...oil temp has never been above 210 and must be blocked in the winter to get temps above 180.

My experience with this plenum has been a net positive. I enjoyed adding it to the airplane, and it has more than paid me back in terms of increased cruise speed and hassle free operations.
 
That said, I remain convinced that a good plenum lid seals better than the best flap seals....and way, way better than average flap seals. That much is found in NASA CR3405.

Always something more to learn.

With regards to inlet performance...lets not forget the upper plenum is also part of the inlet system from a thermodynamics point of view. Factor affecting pressure recovery efficiency includes the shape, size, radius of the inlet opening as well as the transition to and upper plenum volumes.

Concur wholeheartedly... In the standard baffling the upper cowl is required to absorb the load developed in converting dynamic pressure to static. Our cowls are flexible and only supported around the perimeter thereby allowing deformation when pressurized. Evidence is found in scalloping along the upper cowl perimeter during high speed flight - Dan has accurately described this as akin to blowing up a balloon. At 165ktas we measured about 14.25 inH2O which is about .51 psi. The upper plenum area is about (very rough mental measurement here) 360 square inches. This results in a force of about 186lbs exerted upward on the upper cowling. As the cowl deforms the standard baffles will not be as effective. Additionally, by their nature they rely upon pressure for a good seal which really means during those high power relatively low speed climbs they are at their worst condition for a good seal. The enclosed upper plenum, when designed appropriately, carries all the load developed in the pressure recovery process leaving the cowl to carry loads created by the lower plenum pressure which are much reduced.

As Dan mentions, the difference in engine cyl fin area between the angled (his) and parallel (mine) makes data difficult to compare for overall efficiency from a plenum vs baffle perspective. The angle valve has a significantly larger total fin area than the parallel valve which given the exact same baffle or plenum setup should result in better cooling with potential for even better drag reduction.
 
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