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ENGINE COOLING

N942R

Member
MOST RV's do not cool properly.. There Iv'e said it... Depending on where you live most RV's do not cool adequately.. Ya we douse them with 100LL or climb at high speeds or reduced power and deal with it... The problem is that the Van's baffles do not allow the lower aft one fourth of the rear cylinders to get any or enough air... Also to a lesser extent the front lower one fourth of the front cylinders are not doing much better... Some have tried to add exit air which will
help a little just because the rest of the cylinder gets a little more air but does not
solve the problem...
Take the time and go look at the baffles on an old 60's Cherokee and you will see that they addressed those areas way back then... An instructor and student can beat up on one of those all day long without getting hot.... Ya they have a larger
opening but also going much slower so not much pressure..
The RV's need a duct down the back side of the right baffle and forward under the lower fin area of at least 1.5 square inches and the existing wrap removed from just below midpoint of the cylinder... Also the it needs a duct down the inboard side of the oil cooler and then forward under the fin area. Also 1.5 square inches and the wrap removed... Then holes cut in the baffles above to admit air into the
ducts of at least 2 square inches..
The front cylinders need almost 1 square inch down to below the midpoint of the cylinder and into the wrap..
For your information, I have built 7 RV's of different models, have around
1000 hrs in them, and have been around big bore Lycomings almost since they were first introduced.:: without divulging my age!!!!
It is a lot of work but these engines are expensive and we are kind of relying on them to stay healthy... I have seen 25 to 30 degrees F. decrease in head temps
 
Sketches and photos are priceless and appreciated

Some sketches or photos of your detailed solutions would be appreciated beyond words.

And if that is too much work, just mail them to Dan Horton and he will post them give you credit.
 
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As I said in the original post, it takes 1.5 square inches to feed those 1 1/4 deep fins below. Ya cant do it with a 1/16 or 1/8 space into the "wrap" or adding a washer to leave a little space... If you want your engine to be cooled properly you just need to bite the bullet and spend a day or three making some ducts to feed air down there... You will think you are flying a different airplane..... Re read my original post. It works.... The RV cowls have plenty of inlet and outlet area without luevers or cowl flaps or lips added on to them... Ya spent a year building an airplane, what is another day or two making the engine happy.....
High oil temps are usually the airplanes with oil squirts on the cams or pistons.
On those I have mounted the oil coolers on a NACA duct on the "Right side" of the cowl which will solve that problem.. Nothing wrong with the coolers... But that is a separate issue........
Please go look at an old Cherokee and it will be plain what to do... They are lots of them setting around and the old ones with the metal cowl can be opened up easily so you can see... They left the front baffles below midpoint of the cylinder
so they can get air down there..
 
High oil temps are usually the airplanes with oil squirts on the cams or pistons. On those I have mounted the oil coolers on a NACA duct on the "Right side" of the cowl which will solve that problem.. Nothing wrong with the coolers

Would like to see pictures if available. Are there Naca ducts readily available that are large enough for this? Wouldn?t such a set up mean that the duct has to be disconnected every time the lower cowl is pulled?

Thanks

Erich
 
Engine cooling

Oil cooler is mounted to the engine mount at an angle to the airplane ...
NACA on the cowl just butts up to it without being fastened to it...
 
Any photos / drawings of cylinder 1 & 2

Have know about the problem on rear #3 cylinder and addressing that now as I install my baffling for the first time but a little foggy on the front cylinders.
Just what modifications do you propose to improve airflow in that area. This thread is so timely. Want to do it right or at least close to right the first time if possible. Not understanding where to remove or achieve the 1.5 sq. in addition.:confused:
 
Have know about the problem on rear #3 cylinder and addressing that now as I install my baffling for the first time but a little foggy on the front cylinders.
Just what modifications do you propose to improve airflow in that area. This thread is so timely. Want to do it right or at least close to right the first time if possible. Not understanding where to remove or achieve the 1.5 sq. in addition.:confused:

Click on the link on post #6 , then go to page #2, and see post #12 by alpinelakespilot2000. That shows you most of what you are asking about.

it is only Cyl #2 on the front side that has the shallow fin issue.
 
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So looking at link in post #6 page 2 to create a plenum to channel air past the area with little or no cooling fins on #2 cylinder. My question is do you drill a hole in the inlet ramp for air flow into this plenum? There is little or no gap behind the Al angle and vertical plate on this cylinder.
I have done the mod to #3 cylinder and was markedly cooler during a ground run. I have yet to fly with it. Have to thank all the people that take the time to help, it is very much appreciated.
 
So looking at link in post #6 page 2 to create a plenum to channel air past the area with little or no cooling fins on #2 cylinder. My question is do you drill a hole in the inlet ramp for air flow into this plenum? There is little or no gap behind the Al angle and vertical plate on this cylinder.
I have done the mod to #3 cylinder and was markedly cooler during a ground run. I have yet to fly with it. Have to thank all the people that take the time to help, it is very much appreciated.

In short, yes.
To see the drilled holes, see post number 10 on page 1 of the link.
Michael Robinson (toobuilder) shows an angle valve cylinder #2 with the drilled holes visible in the first photo before the plenum is in place.

I suspect the plenum in post #12, is deeper front to back and would allow holes to be drilled( or an oval /rectangular port) in the ramp ahead of the angle bracket.
 
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The simpler duct shown in post #16 of my other thread is now my default bypass duct. I have one on cylinder #5 on the Rocket's new baffles as well as an identical example on #2. The one on #2 includes the full wrap around the top fins, so it has the appearance of the fins being completely "blocked" to the incoming rush of air. This is an experiment for me and my hope is the total plenum volume is large enough that the local airflow velocity will be low enough to "turn the corner" and flow down through the fins as in the rear. This may not work on a standard Vans cowl, and it may not work on mine. That said, it will be easy to trim off the top half of this duct flush with the inlet ramp floor and allow air entry through the funnel of the bypass duct. If you dont have the physical space because the air filter is there, then a short but wide duct is the answer. A series of half inch holes serving as the inlet is not ideal but keeps some of the structural integrity of the angle intact.
 
Click on the link on post #6 , then go to page #2, and see post #12 by alpinelakespilot2000. That shows you most of what you are asking about.

it is only Cyl #2 on the front side that has the shallow fin issue.

Yes, now I see. Would you do that on Cylinder 1 also? And how about #4. I have never seen any thoughts on widening the gap at the left rear of the baffling near the oil cooler. Excuse my moronic questions. Trying to fulling understand and eliminate any cooling problems that might occur. And could there be any downside to fabricating and adding these extra cooling ducts.
 
Here you can see the slot and flange removed for the inlet side of #2 cylinder.

wb7oQmPUOr9P6QY-IfrCdKbIxDepgBn0mhJmhDmUx6WpImCP8WeUdGgLKl_rKffN2VYgOnDJrXFb7wugkqtvGULMXv_JSaeevZlIvbswIrJzvgYqtk60-zzZ786NIk1ZE4Hl2TTFjIikLslYVjeE3FU61zLUD94EGV1s8w0ieo8_Ycrkt_URlaB9QtRmJMttBy2tMW62CJ_AHa_IYNZd3zWbyXGQpEEAG7nThQOLLb82FqeYjtcDJ16SY_cwpNzF67wjc2fpp-F9vdeZDPzMyyfCmWPS8V0uJ_SEBSBHPIbbCtRht58e3azulsC3zUoUUqi6U0MkTgwHPuQWuaEzcIz7c1mlkeYj45k_p6OkNiwrQ9D_JnD8MMBx49U4qYDjs3mx1ng81mg64ldwkeyLgVA57nq5cP73sMvNRFFNBxjxuOnYacszySI7GIF7ZKyghvOkLvg-R2wNTNLfo1aNnrEL2j6C8fbpFV9vW5k2nNOzg7rvfhgfS7uc7YPBaq5Twg7bG-9QpPmTZwCoeqh91IoJUx7e7XSO9HO3iDkdSzwnO-jO4b47ll_2qs550ve0Dsj4SDXIfJ4abdXpqemFLuXhICo32ly-amfLTXPzNESRGekkAtjvFCO_D1BXjzpjSd8Q7uwJBwIssRVER9Q8FppczRuKA3n3L6naj2kjErCmR_e2XHK3VZGe=w538-h717-no
 
Yes, now I see. Would you do that on Cylinder 1 also? And how about #4. I have never seen any thoughts on widening the gap at the left rear of the baffling near the oil cooler. Excuse my moronic questions. Trying to fulling understand and eliminate any cooling problems that might occur. And could there be any downside to fabricating and adding these extra cooling ducts.

1 & 4 do not have that issue. If you look at those cylinders the fins are deeper where they come up against the baffles in the #1 #4 position and there is plenty of airflow.

It will become very clear if you just look at some cylinders. All 4 cylinders are the same, but the shallow fin section of 1 and 4 merge with a deep fin section of 2 and 3, so they have plenty of airflow as a result.
Therefore 1 and 4 do not need the bypass in the baffle face.

It is only #2 and #3 that have the shallow to virtually no depth of fins where they run up against the baffle wrap. That is what the Dan, Michael and Bill are trying to illustrate and the OP was trying to make people aware of. There are a lot of RV's and other home builts with Lycomings that people have not seen the solution for, nor do they understood there is a cooling issue that can be easily cured.



Wow, but that is nice work Bill.
 
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A photo IS worth a thousand words

Here you can see the slot and flange removed for the inlet side of #2 cylinder.

wb7oQmPUOr9P6QY-IfrCdKbIxDepgBn0mhJmhDmUx6WpImCP8WeUdGgLKl_rKffN2VYgOnDJrXFb7wugkqtvGULMXv_JSaeevZlIvbswIrJzvgYqtk60-zzZ786NIk1ZE4Hl2TTFjIikLslYVjeE3FU61zLUD94EGV1s8w0ieo8_Ycrkt_URlaB9QtRmJMttBy2tMW62CJ_AHa_IYNZd3zWbyXGQpEEAG7nThQOLLb82FqeYjtcDJ16SY_cwpNzF67wjc2fpp-F9vdeZDPzMyyfCmWPS8V0uJ_SEBSBHPIbbCtRht58e3azulsC3zUoUUqi6U0MkTgwHPuQWuaEzcIz7c1mlkeYj45k_p6OkNiwrQ9D_JnD8MMBx49U4qYDjs3mx1ng81mg64ldwkeyLgVA57nq5cP73sMvNRFFNBxjxuOnYacszySI7GIF7ZKyghvOkLvg-R2wNTNLfo1aNnrEL2j6C8fbpFV9vW5k2nNOzg7rvfhgfS7uc7YPBaq5Twg7bG-9QpPmTZwCoeqh91IoJUx7e7XSO9HO3iDkdSzwnO-jO4b47ll_2qs550ve0Dsj4SDXIfJ4abdXpqemFLuXhICo32ly-amfLTXPzNESRGekkAtjvFCO_D1BXjzpjSd8Q7uwJBwIssRVER9Q8FppczRuKA3n3L6naj2kjErCmR_e2XHK3VZGe=w538-h717-no
Ok, now I got it. Sure doesn?t take much does it. I?m going to use these photos as guides. Thanks in advance for hopefully a cool running motor.
Hope mine look half as nice as yours. :)
 
Great thread, and timely for me as I'm going to do some baffle modifications at the next oil change to lower CHTs

I think this would make an excellent sticky....great photos and links to threads that Dan H. has compiled.
 
I used the RV-14 Baffles on my RV-8A powered by an XP400 and the fit is very good.
Bottom right of this photo shows the updated #3 aft baffle (upside down). Note the deep channel and the standoff.

IMG_1286.jpg
 
My cylinder head temps are fine no matter how hot it is in my 7. The issue I have is with the Sam James plenum and minimum space for the oil cooler inlet duct. I increased the opening , added a larger oil cooler and a 4 inch Scat tube. I have to watch it as it will get to 230 degrees if not at cruise altitude. It settles down to around 215 in cruise. Still working on a fix but its better now than when I purchased it. I am 195 HP with 10 to 1 and oil squirters. Also e mag p mag ignition. I guess this is what you have to deal with on experimental airplanes. My Husky stays cool no matter what temp it is so this is new to me
 
I guess this is what you have to deal with on experimental airplanes.

No, you don't. Quite the opposite. With an experimental we are free to make whatever changes we wish to improve cooling performance. Of course, the two-edged sword rule applies; we're equally free to make bad choices.
 
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I finished the baffle modifications for cylinders 2 & 3 (quite similar to the pic that BillL posted) and am extremely happy with the results. No. 2 (the hottest) dropped about 25 degrees and is now the coolest! No. 3 is down about 10 degrees. Shoulda done this sooner.
 
Just finished the #2 cylinder mod as presented by Bill and also having completed the widely accepted modification duct on #4. Glad to hear your results were acceptable Doug. Confident I have avoided a potential overheating problem. Would never have know about these proven solutions if not for the ?VAF? Thank you gentelmen.:)
 
Does anyone have any pictures of successful baffling improvements for cylinder #4? I've seen lot's of great ideas for #2 and #3. Thanks!

IO-360 parallel valve, Van's baffling with stock oil cooler.
 
I know this thread has been extensively discussed last fall, but I have a different question. Our RV14A IO390 runs cold. Typically front cylinders 1and 2 low 200’s CHT’s, rear’s 3 and 4 mid to upper 200’s. This is at cruise. Almost never see 300 CHT’s. The CHT input curves were switched in our G3X from K to J or vice versa (can’t remember) then the CHT’s look normal. The ones with the cold numbers were the correct for our installation.
Any input appreciated.
 
I know this thread has been extensively discussed last fall, but I have a different question. Our RV14A IO390 runs cold. Typically front cylinders 1and 2 low 200’s CHT’s, rear’s 3 and 4 mid to upper 200’s. This is at cruise. Almost never see 300 CHT’s. The CHT input curves were switched in our G3X from K to J or vice versa (can’t remember) then the CHT’s look normal. The ones with the cold numbers were the correct for our installation.
Any input appreciated.

Highly suspect in my opinion. Type K thermocouple wire must not be mixed with Type J. The correct wire must be used with the correct probe, then configured properly in the G3X. Wire color is the easy way to tell which you have. Read this builders note from SteinAir:

http://www.steinair.com/wp-content/uploads/2016/03/Builders-Note-Thermocouple-cable.pdf

Wire:
https://www.steinair.com/product-category/wire-coax/thermocouple/

Also, I recently learned there are some grounded and ungrounded CHT probes. If I remember correctly, Advanced Flight Systems used ungrounded Type J CHT probes. Those WILL NOT work with a G3X. I had to change out 4 probes on a recent build to Grounded Type J (so I could use all my existing wiring behind the panel) and that corrected the false indication.

Low 200's at any power setting other than idle, in the winter, doesn't seem possible.
 
BA

On those I have mounted the oil coolers on a NACA duct on the "Right side" of the cowl which will solve that problem.. Nothing wrong with the coolers... But that is a separate issue.
Submerged NACA ducts are problematic for an oil cooler, many test, experience, articles has shown this success is not automatic with a NACA scoop. Love to see your whole NACA oil cooler set up.

1) NACA - you can also cause overheating by pressurizing the lower cowl with your NACA scoop if the oil cooler is dumping air back inside the lower cowl.

2) NACA can flow volume when there is little to no resistance and lower pressure at discharge. Dave Anders wrote an article in Kit plane (Oct 2018 Optimizing Induction Air Fine-tuning intake system runners for increased performance and economy. Speed with Economy, Kent Paser wrote about NACA scoops more enthusiastically in his classic book. However they are not magic and often implemented, located and used incorrectly. They always look "cool" but they are no free lunch. They do add drag and may produce very little airflow unless you do everything correctly. You might be better off with an external scoop and take the drag and get real RAM Pressure, with a discharge separate from lower cowl plenum. Many planes like the DC-3 has the oil cowl completely outside the cowl. The cooler needs high delta P to flow air and NACA scoops don't create pressure but flow air, at lower pressure head. Add back pressure on the exit side of the cooler inside cowl you may end up with no flow or reverse flow.

http://www.vansairforce.com/community/showthread.php?t=5551

http://www.vansairforce.com/community/showthread.php?t=97016


Car guys also debate the Scoop vs (submerged) NACA
apr_naca_duct.jpg
 
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Do I have Recovery? Pressure Recovery.....

After a lot of hours, I'm taking a new look at my cowl and engine cooling. I had stock baffles for the first few years, then I made a bad plenum that has worked fine for many hours, but I never knew if it worked well. I know the seal at the inlets was not great and the FAB to cowl seal was not great either, but I know both can be improved...... My only real complaint is full power ROP climbs get the back two cylinders to 425 quickly before I pull back(on the rare occasion that I do it)

Following the teachings of Professor Horton, I made piccolo tubes and found a cheap used digital manometer - then I got some data tonight, allowing me to ask the question:

"Do I have recovery" What say you cowl doctors? The cowl needs some rework after 2600 hours, so maybe this winter I cut some fiberglass.....

Here is the cockpit setup running in diff pressure mode. I took some data comparing the upper and lower to ambient cockpit pressure, and the diff was same as the diff pressure on the screen.

AL9nZEXMxMTXTFvhFhfCvtmytjR6ffOPocsA-41NCWgs_ThlVYZ5vYAEpaM8RMZhjfdiu3IOxX4VJI0PZGOCHM5-wc2mMzPmfkMuDdULB_Ot6HK3L8mdirHIl6VEoRRSpf5unzrYU75Ikc7Nd3iyLL8s-6g5IA=w600-h938


Here is the data and a graph (all data @ 3000ft)
HbGjk4NW3bWHREy2jr9QR5nbj9EgIsAWr5yMZNvE9cV9IWwGLLUs3mMJ72BqRVKij_yYKcvTBFv4J66Wg246kDIgV9Hci7k_XIeHdm2MEyLlAYWfVEd6Tm1v6lh2ayU_uNARqO9Ew5rTy7SG8FYAWMs9zHcz77hsfNBWrCWmqDh1rzO8uzfT66KtcL-BwUsVzGUk2dTBqCaEW-jXHocUFdwCdZhRwDliPXOOtKBklH4xCqemmEdvT-BVslZUnsaRhETLmIX_LbfeRsdO7DblJRXgXDKWiMZW-6ztY_KUKpjHanx7A7WYdMT60X3PTstomkGGMLScCg_2EKy_nLp4_X9OvzqbuJhIdAsZf-TUQWGdXojiUU5zqdx47g6Vt6zbhVtqc-q1cieoSEyt6W_Npzflnnu-uZFEF4AkhRhaRxyZG7VSpGkiKqKucQm3TBd28pjBW6RzkaZZUFVI1a9NTdbKx2VpUlCy_lUyAY1BBUZNGok9-u_R0KpoEJxlkWHwQgk9nMCSqLRIAx-QL5CEOR8yA0PglzG-HE9GQEaXtSXa_rq6AE32TmA6A2mInfJlqx2-HH7fWXQOqC-Jnbp_i0_NynOpiNYgHHTd2auu6N78j_B2eM5edp8pk1w2pY7Sr70PfwF-oS1pYjzgPVK3RXZZc8AcAFX20cDBAfRyN7hAFwtqkVw7o7bpiNTFe9GLWx07V0s07dCuwJqW7aBqgLldfzpNv12LK0EKBOBQjPpyhV1axBtlcVivRMJpu8c=w600-h237


AL9nZEXq3IjiZBRHXGsTA1UHCK1wS-m5CG6d9sXsgDN4yxCQ4g92zpdcYKd4Jw4ihIrqA8_eAjOOsWcd6Fq2DsUSFYT9VrM-dJa2rMu7RMWLgs6tbI6KC2v4r7qwE4QE9f1nfGMEqEMDsXdBnS9oAgIU4fUd9g=w600
 
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"Do I have recovery" Here is the cockpit setup running in diff pressure mode. I took some data comparing the upper and lower to ambient cockpit pressure, and the diff was same as the diff pressure on the screen.

Hi Pete. Yes, you have recovery. The question is how much, specifically the percentage of available dynamic pressure converted to upper plenum static pressure. DeltaP across the baffles doesn't help us; we need upper plenum deltaP vs freestream static. I tap the aircraft static system for freestream static.

So, easy as 1-2-3...

1. List upper plenum static vs freestream static deltaP for each airspeed.

2. Compute available freestream dynamic pressure for each airspeed and convert it to inches of water.

(There is an excellent online calculator here: http://www.aerospaceweb.org/design/scripts/atmosphere/ Don't neglect the temperature correction, plus or minus standard day temperature for that altitude. 25C would be a +14 above standard for 3000 ft.)

3. Divide upper plenum static by freestream dynamic. Good systems are generally above 0.8.

It's very hard to fly a specific true airspeed, for example, exactly 150 KTAS. It's a lot easier and more accurate to fly a NTPS 3-leg while collecting the pressure information. That way you have an exact airspeed for each data point, thus a precise dynamic pressure.

Illustration below from NASA CR3405.
.
 

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More data

**** - I have to fly again..... Thanks for the input, I'll tap the static and get the data!

Hi Pete. Yes, you have recovery. The question is how much, specifically the percentage of available dynamic pressure converted to upper plenum static pressure. DeltaP across the baffles doesn't help us; we need upper plenum deltaP vs freestream static. I tap the aircraft static system for freestream static.

So, easy as 1-2-3...

1. List upper plenum static vs freestream static deltaP for each airspeed.

2. Compute available freestream dynamic pressure for each airspeed and convert it to inches of water.

(There is an excellent online calculator here: http://www.aerospaceweb.org/design/scripts/atmosphere/ Don't neglect the temperature correction, plus or minus standard day temperature for that altitude. 25C would be a +14 above standard for 3000 ft.)

3. Divide upper plenum static by freestream dynamic. Good systems are generally above 0.8.

It's very hard to fly a specific true airspeed, for example, exactly 150 KTAS. It's a lot easier and more accurate to fly a NTPS 3-leg while collecting the pressure information. That way you have an exact airspeed for each data point, thus a precise dynamic pressure.

Illustration below from NASA CR3405.
.
 
Great start with data!

Pete, please do plot the upper plenum pressure vs airspeed to assess the recovery. Just shooting from the hip(looking at your data), and your comment about leakage, it seems that the by pass leakage may be at the root of the issue.

Let's say the baffles are all sealed pretty well, it appears you have some wraps on the inside of the barrels to about midway. Then the restrictions are inlets, fins/leakages, then exit. With stock inlets and exit, that leaves looking at where the flow goes from the inlets. If a lot of air bypasses the fins (upper plenum) it does two things, chokes the exit with excess mass flow, and lowers the upper pressure as there is no resistance against which to build that dynamic pressure.

While it is also possible that you could have such poor diffusion (recovery of dynamic pressure) in the inlet-to-plenum transition, the fact that your lower cowl pressures rise that much indicates (to me) that it is leakage/by-pass air that is currently dominant factor. More precise information on the expected dynamic pressure is a good step to solidify the situation.

Now - there is another seldom discussed restriction between the upper chamber/cowl/plenum and lower cowl. That is the opening(s) at the bottom of the heads and barrels. If everything else (bypass wise) is perfect, this can result in lower mass flows. Vans baffles/instructions/drawings/ don't address this as it is typically a design feature and the opening is controlled by proper installation and fitting so they are snug. If one made baffles from scratch, this might be a variable to be controlled, and in Sam James baffle instructions for making baffles it is specified. Typically it would manifest itself in a cylinder to cylinder temperature imbalance but is usually overridden by other issues, like front dams, and blockage of #3 and#2 casting limitations. OK now I am down in the weeds, but important to know the effect exists.
 
Take 2!

Now that I is more smart, I gots more datas. Tapped the static system. Flew big squares, used Ottopilot. Used the Manometer function that averages readings over time to get a better result. Used Test Pilot Sheet to verify speeds flown. Despite what Andi says, i can be trained.

This is what I had time to get tonight. Let me know if this looks correct.

(Upper cowl press - aircraft static press) / calculated freestream dynamic press = Cp

Over 0.8 is good. I fall short........more work to do. Thanks Dan, Bill and others.

AL9nZEWn5u6MIufqc-oc5WTlz2blMa4g9ezMjCv72H4meAsBw9yJ2LISp2aXBLbSyBtvK189lYWF8qKBJoco48BjjXynITXWWsTIczu70OpdqmSU1wj6ljUjiSwC3g01w5buhK95N0nFM1ah5lF_ZJzBadXmoA=w1152-h592
 
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Andi is right, as usual. Nice work!

Quick review says it's valid. Are you using the common piccolo setup from the white paper?

What Bill said. Pressure recovery is only one part of the puzzle, and changes to other parts can affect pressure recovery. Put another way, good pressure recovery doesn't guarantee good cooling, but it's hard to get good cooling without it.
 
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Std Setup

Yes sir! - piccolos from your diagrams in the same locations - made them in the kitchen - got some side eye when she got home......

I'll make some plans for a winter project to improve things.

Andi is right, as usual. Nice work!

Quick review says it's valid. Are you using the common piccolo setup from the white paper?

What Bill said. Pressure recovery is only one part of the puzzle, and changes to other parts can affect pressure recovery. Put another way, good pressure recovery doesn't guarantee good cooling, but it's hard to get good cooling without it.
 
Sorry a little confused.

I am missing something, Pete. The chart says pressure differential - is that upper to lower or upper to static?

Maybe a terminology thing. I would call upper pressure referencing static port "Upper pressure" and differential upper-lower.

I typically reference static on one side of the manometer, attache upper tube, then lower tube then lower to static side for differential. All while stacking pennies, watching the traffic monitor, and recording URL time. Then go back and do my get my detailed airspeed averages from recorded garmin data.

The cockpit is full of stuff (as is my head at the time) so I use a board with velcro and tape to attach the digital manometer and secure the tubes from writhing around like snakes looking for a place to hide. This way the labeled tubes are swapped so as to prevent vertigo.
 
Hi Bill,

Upper vs static in the chart (in the red cells) is the diff b/t the upper cowl pressure and the line I tapped into the static system. I just compared them across the manometer using the average reading over time function. Lower cowl pressure was not used for this set of data.

I agree the cockpit was busy!


I am missing something, Pete. The chart says pressure differential - is that upper to lower or upper to static?

Maybe a terminology thing. I would call upper pressure referencing static port "Upper pressure" and differential upper-lower.

I typically reference static on one side of the manometer, attache upper tube, then lower tube then lower to static side for differential. All while stacking pennies, watching the traffic monitor, and recording URL time. Then go back and do my get my detailed airspeed averages from recorded garmin data.

The cockpit is full of stuff (as is my head at the time) so I use a board with velcro and tape to attach the digital manometer and secure the tubes from writhing around like snakes looking for a place to hide. This way the labeled tubes are swapped so as to prevent vertigo.
 
Bad Bill . . . . :eek:

Hi Bill,

Upper vs static in the chart (in the red cells) is the diff b/t the upper cowl pressure and the line I tapped into the static system. I just compared them across the manometer using the average reading over time function. Lower cowl pressure was not used for this set of data.

I agree the cockpit was busy!

Excellent, I fixated on the differential and missed the big red label "upper vs static" :eek:

Looks pretty stable over the speed range.
 
Dynamic pressure available due to aircraft velocity.

Should have asked a better question(s). How/where measured? Does the EFIS data strip out the value or derived from manually referencing Ps?

Probably most importantly, what purpose does it serve in the troubleshooting?
 
Should have asked a better question(s). How/where measured?

Here it is calculated. The classic equation is...

0.5 * density in slugs per cubic ft * velocity^2 in ft per second = q in lbs per sq ft

...but to make life easy there are spreadsheets or good online calculators which allow entries as pressure altitude, KTAS, choice of temperature unit, etc.

Probably most importantly, what purpose does it serve in the troubleshooting?

It's a baseline, the pressure available to push mass through the system. The point of interest is how much of it is captured as increased upper plenum static pressure.
 
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Edit - I realize I really just said the same thing Dan did above.......

No sure this is all correct, but I think of freestream dynamic as the the static pressure plus the pressure available due to the velocity we are moving thru the air. If we had a perfectly efficient cowl setup, the pressure we measure inside the top cowl would equal the freestream dynamic pressure.

Really tough to get it perfect, but Dan, Bill and others have done really well capturing 80+%, proving it is possible. As Bill said in an earlier post, this is the first step to good cooling, capturing as much of that pressure as possible - next is using that captured energy(pressure) to make the air mass carry the heat away from your engine. Make all that energy work for you - plug leaks, and channel air to where it can be used most effectively.

Finally, if you can get really efficient, you can use less air to do the same cooling - less air requires less power. Trade that power not used for cooling to go faster, use less gas...... or both.




Here it is calculated. The classic equation is...

0.5 * density in slugs per cubic ft * velocity^2 = q in lbs per sq ft

...but to make life easy there are spreadsheets or good online calculators.



It's a baseline, the pressure available to push mass through the system. The point of interest is how much of it is captured as increased upper plenum static pressure.
 
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Boy, how willing I would be to make a good Persian dish and have you guys over to explain this in a way that I the light bulb would be on brighter. Nevertheless, I thank you guys for explaining here, though I admit the light bulb is still very dim regarding freestream dynamic pressure and how it relates to the cooling in the cowl.

My simple mind looks at this in the following process;
There is air pressure in the upper cowl and lower cowl. These pressures are some what driven based on the air entering the top cowl and exiting the lower cowl minus the friction that is caused by going thru the engine block. The more pressure in the lower cowl, the less air can travel thru the engine block for cooling. At the same time, the more air exit the lower cowl, the more drag. So, the goal would be to limit the exit air just to the point that there is enough cooling. Do I have this remotely correct?

As a RV14 driver, my limitation on cooling has always been on oil temp rather CHT. I would like to improve the oil temp or to trade some of that temp if possible, so far not with much luck. The baffling is very tight and unlike swiss cheese and the 5" scat tobing to the oil cooler has done very little, I presume since the exit air out of the oil cooler is the bottleneck.
 
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No sure this is all correct, but I think of freestream dynamic as the the static pressure plus the pressure available due to the velocity we are moving thru the air.

Close! Dynamic pressure can be thought of as kinetic energy due to mass and motion. Static pressure + dynamic pressure = total pressure. Static and dynamic can trade back and forth. In the cowl application we trade dynamic to get static.

If we had a perfectly efficient cowl setup, the pressure we measure inside the top cowl would equal the freestream dynamic pressure.

For the static rise to equal freestream dynamic, we would need to fully halt the flow, i.e zero velocity. We call that a pitot tube, a closed end system. Can't cool with a closed end system.

As Bill said in an earlier post, this is the first step to good cooling, capturing as much of that pressure as possible - next is using that captured energy(pressure) to make the air mass carry the heat away from your engine.

Yep, maximize heat transfer...use less air and heat it more.

Try this: https://vansairforce.net/community/showpost.php?p=1169174&postcount=26
 
Boy, how willing I would be to make a good Persian dish and have you guys over to explain this in a way that I the light bulb would be on brighter...(snip)...Do I have this remotely correct?

No. Clearly this will require the Persian dish to explain it properly. There are typically 8 to 10 in our dinner group under the HBC gazebo, and next year your night is Wednesday ;)

As a RV14 driver, my limitation on cooling has always been on oil temp rather CHT.

Such is life with a 390. Which cooler are you using?
 
Good cooling is important but ideally we'd like to recover as much momentum as possible, exiting that cooling air at as close to free stream velocity as possible. An excellent system will exit the air at above the free stream velocity, offsetting cooling drag or even creating slight thrust.

Next step is to instrument your exit with a pitot tube and temp sensor to see what you have for exit velocity.
 
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