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The Shrinking Exit

DanH

Legacy Member
Mentor
Recall I've been experimenting with a different approach to cooling....large, low velocity inlets with a throttled exit (and a bunch of details). The cowl was modified so I could swap exit panels and thus vary the exit area.

Started with the one on the left, changed to the middle one at 15 hours or so, and just started flying the one on the right. All are smaller than stock by a good margin. I'll fly the latest into warmer weather, then consider the next step. I want to do some temperature and pressure measurements when it gets really hot this summer. Plus, from a standpoint of break-in, I'm only at 70 hours or so. his Sunday, with the smallest exit, a WOT/2700 climb at 105 knots from 200MSL to 5500 MSL at 50F OAT netted a highest CHT of 366F. CHT spread is 20F. 60% cruise is 300F or less. No cylinder has ever seen 400F. Engine is an angle valve IO-390.

Exits%201,%202,%20and%203.jpg


Stock cowl:

Stock%20Exit%20Area.jpg


It was modified right after the above photo. Pipe was also modified to raise it all vertically:

Cut%20Cowl.JPG


Reduced%20Exit%20Area%20(Panel%201).jpg


Small%20Exit%20Area%20(Panel%202).jpg


Exit%20%233%20Installed.jpg
 
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Shape

Hi Dan

I have come to the conclusion that your cooling strategy (exterior pressure recovery) is the best compromise ideal for the kind of flying RVs do and and the limited space we have to work with under the cowl.

I could probably find pictures somewhere but I will just ask. What shape and how large of inlets?

I presume the desired effect of reducing the tunnel bump are less frontal area and better aerodynamics. It will also produce higher pressures in the lower cowl to help kick the cooling air out at a higher velocity (less drag). Sealing the lower cowl then takes on a more critical role.

I am interested in your sealing measures around the prop and cowl seams. I think I recall a thread where you described what you did around the prop. I have wondered at what point the lower cowl starts to distort as it does not have the the best shape to hold a lot of pressure. Have you played with a manometer as you put the various subcowls sheets on?
 
Hi Dan

I have come to the conclusion that your cooling strategy (exterior pressure recovery) is the best compromise ideal for the kind of flying RVs do and and the limited space we have to work with under the cowl.

Me too, which is why I went from theory to experiment.

What shape and how large of inlets?

6" diameter. No claim of optimum size; my math could be wrong.

Inlet%20Prelim2.jpg


I presume the desired effect of reducing the tunnel bump are less frontal area and better aerodynamics. It will also produce higher pressures in the lower cowl to help kick the cooling air out at a higher velocity (less drag). Sealing the lower cowl then takes on a more critical role.

Didn't consider frontal area reduction; goal is to increase exit velocity. Cowl sealing is tricky and hardly perfect. I have a few tweaks in mind for the future.

I am interested in your sealing measures around the prop and cowl seams. I think I recall a thread where you described what you did around the prop. I have wondered at what point the lower cowl starts to distort as it does not have the the best shape to hold a lot of pressure. Have you played with a manometer as you put the various subcowls sheets on?

Propshaft%20Seal1.JPG


Propshaft%20Seal2.JPG


The flap seal shown above is doing fine. More or less as expected it has glazed a nice smooth strip on the ring gear casting after wearing itself to a feather edge. Not perfect, but it's what I did. Tom Martin took a different approach with some foam rubber, but I don't have a prop extension.

Cowl%20Sealing%20Surface.jpg


I too am wondering about rising internal pressure, which is one reason I'm not going smaller than exit #3 until I install pressure and temperature transducers. Real data will tell the tale.
 
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Truly nice work Dan!

Do you have an estimate as to what your exit area is now?

My first pass at my nozzle exit area is approx (6.1 inch dia) 29 sq inches. I will be making different size and configuration exit nozzles to test.
 
what kind of airflow control have you done on the firewall corner where it comes down to that reflective ramp?
 
Experimental!

Dan, I know the work you do is its own reward, and you hardly need any praise from the likes of me to motivate your efforts, but I want you to know how much I am inspired by not only your experiments, but also by your willingness to share your progress with all of us.

There are so many disparate reasons each of us are doing this, but for so many of us, the claim to "Experimental" is just an FAA label, not a badge of honor. We build to fly, standing on the shoulders of all those who came before us, learning ourselves, but not adding very much to the body of knowledge in our community. Sure, I'm still proud of my participation in homebuilt aviation, but it's people like you who earn the right to put "Experimental" on your airplane as an actual, bona-fide reward.

Thanks for helping us all expand our knowledge of the black magic that improves our craft.

--Stephen
 
You're in the ballpark Wade....I didn't build the latest exit to any precise dimension, but it should be between 25 to 30 sq in. Intake area is 56.5.

So much for those much-discussed intake-exit area ratios eh? ;)

what kind of airflow control have you done on the firewall corner where it comes down to that reflective ramp?

A stock -8 has a rolled sheet aluminum radius on the firewall corner, 2", maybe 3" diameter, leading into an inset ramp in the belly. I elected to build a converging duct to feed the inset ramp. Here you're looking upward with the exit panel removed from the cowl:

Exit%20Bell1.JPG


Early concept sketch:

Interior%20partial%20duct.jpg


You've seen the reverse flow in the exit tuft video from an RV-6 (-7?). Pretty sure it's the result of very slow exit velocity.
 
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Thank you Dan, that photo helps me visualize much better. I would not expect a 90* corner on your airplane.

I also would like to say thank you for your explanations, photos and considerate attitude. I appreciate it.

it would be very interesting to have a camera and some smoke to see airflow inside the cowl..
 
Exit area ratio

To Dan's point on rules of thumb for exit area ratio, there are so many factors to consider that there is simply no way a single ratio could be considered ideal.

Dan has chosen external pressure recover so he has much bigger inlets than would be required for internal recovery. I will bet he will see nearly 100 percent velocity pressure in the plenum. The plenum will maintain more of that pressure. His lower cowl is sealed, so little pressure will be lost there. Finally, he has the cleanest discharge tunnel I can remember seeing so that pressure will be efficiently converted back to velocity and associated volume through a relatively small opening.

My bet is that all of those factors will add up to a record (low) outlet area/inlet area for RVs. And, low drag.

Dan, you probably could have save all of that streamlining on your pitot and just put a port in the plenum! Kidding but it will interesting to see your pressure data!
 
Converging Duct

Dan,
As always, great workmanship!

Do you have any photos of the converging duct with the cowl off?

Is the duct aluminum or stainless? I'm guessing you attached it to the engine mount at the leading edge?

Thanks,
Mike
 
Nice work, Dan! It's good to see that there are still experimenters around in Experimental aviation!
 
You're in the ballpark Wade....I didn't build the latest exit to any precise dimension, but it should be between 25 to 30 sq in. Intake area is 56.5.

So much for those much-discussed intake-exit area ratios eh? ;)

Dan. Thank you very much for sharing. It is the posters like you, Paul, and others that make experimenting rewarding. I don't think much of those "ideal" ratios, just too many variables in individual installs.

In the interest of sharing, my inlet area is approx 12 sq inches per inlet, each one feeding a separate plenum. Plus 1.7" Dia oil cooler inlet.
 
Do you have any photos of the converging duct with the cowl off? Is the duct aluminum or stainless? I'm guessing you attached it to the engine mount at the leading edge?

This from early in fabrication:

Exit%20Bell2.JPG


Exit%20Bell3.JPG


....and another from below:

Exit%20Bell%204.jpg


2024T3.....in a former life, stock turtledeck skin. Finished duct has a 3/4" diameter transverse tube at the upper edge, attached to the motor mount tubes with adels.
 
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intake lip shaping

Dan,

As you close down the exit, you get more spillage on the inlets. As long as the inlet lips are designed right, this spillage will cause negligible drag, and the reduced frontal area and increased exit velocity will pay off.

The key is that the inlet lips need to be nicely radiused. The fairly sharp lip on Sam James inlets and LoPresti inlets are fine as long as they are sized to match the exit and there is very little spillage, but lips that sharp will cause flow separation on the exterior of the lip when the exit area is closed down. The separated flow around a sharp inlet lip is about like a leading-edge stall on a sharp leading edge airfoil. The flow will reattach, but you pay a price in lost lip suction.

To get an idea of what good intake lips should look like, look at the intake on a commercial transport nacelle. They are sized for take-off mass flow, and at cruise, the spillage is often 30% or so. You are probably spilling almost that much with your smallest exit.
 
steve

The key is that the inlet lips need to be nicely radiused.

Would you say then the stock Van's intake lips are more forgiving of a mismatch between intake volume and exit size?? ie. less draggy when spillage occurs??

This answer may help me formulate a plan as I begin to squeeze down my exit area using a vetterman type fairing. I have stock Van's openings, mated to a Sam James plenum going to a stock cowl outlet (with a firewall exit ramp fairing). I have great cooling and my speeds indicate fairly low drag. I plan some tuft tests to determine exit flow velocity/smoothness.

This may all fall into line with Dan's theory of slow, spill tolerant inlets matched to a correctly sized outlet to match outlet flow velocity.

Hmm, getting interesting!
 
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That is the finest exit ever! I need to build a TD just to swipe your ideas! The large transition makes complete fluid flow sense. A masterpiece Dan.

I will bet you will do very well in an efficiency comparison (fly side by side with someone and see who uses less gas). In my book, that is the comparison that ultimately matters.
 
To get an idea of what good intake lips should look like, look at the intake on a commercial transport nacelle. They are sized for take-off mass flow, and at cruise, the spillage is often 30% or so. You are probably spilling almost that much with your smallest exit.

I think the only way I could get closer would be to install some very tiny Norwegian folks:

Intake%20Shape.JPG

Norwegians.jpg


(Thanks Alf!)
 
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Dan,

As you close down the exit, you get more spillage on the inlets. As long as the inlet lips are designed right, this spillage will cause negligible drag, and the reduced frontal area and increased exit velocity will pay off.

The key is that the inlet lips need to be nicely radiused. The fairly sharp lip on Sam James inlets and LoPresti inlets are fine as long as they are sized to match the exit and there is very little spillage, but lips that sharp will cause flow separation on the exterior of the lip when the exit area is closed down. The separated flow around a sharp inlet lip is about like a leading-edge stall on a sharp leading edge airfoil. The flow will reattach, but you pay a price in lost lip suction.

To get an idea of what good intake lips should look like, look at the intake on a commercial transport nacelle. They are sized for take-off mass flow, and at cruise, the spillage is often 30% or so. You are probably spilling almost that much with your smallest exit.

Keep in mind, too, that the airflow from the propeller, if the prop root has an airfoil shape and is producing some thrust will be flowing up into the left, pilot-side inlet and down into the right inlet, so it is very important to have these nice, rounded lips, sorta like Angelina Jolie!
 
Dan,

Very nice work, good experimenting.

Have you considered shortening your 4-into-1 exhaust pipe to provide some exhaust driven velocity augmentation for your exiting cooling air?
 
Have you considered shortening your 4-into-1 exhaust pipe to provide some exhaust driven velocity augmentation for your exiting cooling air?

Nope. That's a whole different experiment.

What's your cruise CHT's at 75%? At 60% at similar OATs I'm in the low 300's. This is with a stock RV-6 cowl.

So far only about 5 minutes at 75% with exit #3, and didn't pay much attention to CHT. I tend to focus on the critical case with a fixed exit; high AOA, low airspeed, full power.
 
So far only about 5 minutes at 75% with exit #3, and didn't pay much attention to CHT. I tend to focus on the critical case with a fixed exit; high AOA, low airspeed, full power.

Sure, makes sense, but the real test will be 100 deg. OAT, with a passenger, on a long extended climb. That's the critical case. What's cool about your setup (no pun intended) is you can switch exits for the cooler times of the year, or for a race.
 
Beautiful work Dan. I really appreciate the experimenting you are doing here. Bob Axsom is probably starting work on his new cowling as we speak :)

What are you seeing for cruise TAS and fuel flow ROP or LOP?
 
Sure, makes sense, but the real test will be 100 deg. OAT, with a passenger, on a long extended climb. That's the critical case.

Absolutely. So far the highest test OAT at 08A has been about 80F, as I didn't start flying until October. Those flights suggest a worst case of using exit #2 for general fun flying in Alabama's hot months; WOT/85 knot field departures and 100 knot climbs to 10K.

Remember, this is an effort to reduce cooling drag, which is related to but not quite the same thing as reducing temperatures. I mention specific temperatures and conditions only to communicate that nothing here has created a temperature problem. In the end, the very lowest drag system will indicate rather high temps. I'll probably get to that in due course, but for now I'm looking for balanced performance.....the Vans mantra.

Dan, have you recorded any performance increase in speed with this modification?

Well, obviously I didn't built an identical airplane with a stock cowl for comparison purposes, so here's the plan. With break-in done and these three exits in hand I'll instrument the cowl for pressure and temperature, then swap 'em out for three quick back to back NTPS-method speed cal runs. I figure I'll need to do it twice, the first morning running exits 1-2-3 and the second morning 3-2-1, so as to minimize the effect of OAT rise into the day.

For now, no specific speed claims. The few early cal runs I did with exit#2 say it is not slow.

What are you seeing for cruise TAS and fuel flow ROP or LOP?

Kevin, no valid data right now. Only balanced the restrictors a few weeks ago, and lately I've been shaving the static ports...need new airspeed calibration.
 
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Non scientific reply...

ALCON,

Guilt him into flying to Oshkosh this year, then go see it for yourselves. The airplane is beautiful, goes like ****, and is a hoot upside-down...

I think Dan's powered by beer, and I don't know if he's had New Glarus Spotted Cow Ale in a while.

Maybe he'll bring the small Norwegians with him.

Loko
 
Yes, absolutely!

Would you say then the stock Van's intake lips are more forgiving of a mismatch between intake volume and exit size?? ie. less draggy when spillage occurs??

This answer may help me formulate a plan as I begin to squeeze down my exit area using a vetterman type fairing. I have stock Van's openings, mated to a Sam James plenum going to a stock cowl outlet (with a firewall exit ramp fairing). I have great cooling and my speeds indicate fairly low drag. I plan some tuft tests to determine exit flow velocity/smoothness.

This may all fall into line with Dan's theory of slow, spill tolerant inlets matched to a correctly sized outlet to match outlet flow velocity.

Hmm, getting interesting!

Yes - the stock cowl inlets are extremely tolerant of spillage. You could darn-near close the exit off entirely and the spillage drag on a stock cowl would be small.

I am planning a cowl flap similar to what you would see on a C-182 or a Bonanza, mounted between my two exhaust pipes. When open, it will match the stock cowl exit shape. When closed, it will form a surface in line with the basic fuselage shape, not counting the RV-8 exit ramp.
 
Steve, can you post some sketches or illustrations of spillage and flow separation?

Here's a fun paper...postwar research to rework the B-29 engine cowl.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093587_1993093587.pdf

Interesting subject.

In the following illustration, which of the three lip profiles resulted in a cruise drag reduction of 60 hp, and 108 hp saved at 250 mph?

B-29%20Inlet.jpg


Scroll down






Surprise....it was the 43" opening with the smaller lip radius, in a Vi/Vo range of 0.256 to 0.144....indeed, a very large, very slow inlet.
 
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Dan

Facinating and needless to say, the profile of the 43" inlet should look pretty familiar to anyone that has banged around a Van's stock inlet.

Thanks for finding me some serious sleeping pill reading!

oh yea, and thanks Steve for the confirmation. Gives me the confidence to think my swag approach might prove effective.
 
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notional picture of spillage drag on sharp-lipped inlets

Here's a notional picture for you:

inlet_spillage.pdf


its a .pdf - maybe they don't post like a picture. Well, try the link:
http://www.hpaircraft.com/rv8/inlet_spillage.pdf

The B-29 cowl is interesting. It looks to me like the problem with the smaller inlets is the interior flow separation and incomplete pressure recovery. It doesn't take much - the flow is trying to stop and the pressure is rising, but it will waste pressure on recirculation on the back side of an abrupt lip like that. I think our cowls are "good enough" inside.

Looking forward to some speed data, Dan.
 
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That bad inlet is indeed sharp-edged.

The B-29 cowl is interesting. It looks to me like the problem with the smaller inlets is the interior flow separation and incomplete pressure recovery. It doesn't take much - the flow is trying to stop and the pressure is rising, but it will waste pressure on recirculation on the back side of an abrupt lip like that.

The old radial engine NACA papers are excellent for this stuff. Radial cowls are the ultimate large inlet, throttled exit systems.

Interior flow separation is not much of a concern given the interior velocity. Remember, in this case the Vi/Vo range (note for the non-engineers: Vi/Vo = inlet velocity divided by freestream velocity, a measure of how much you slowed the air before it actually entered the inlet) is 0.256 to 0.144, thus the entire range of V behind the lip, inside the inlet, is something like 64 mph in the high speed case (250 mph with cowl flaps open) and as low as 15 mph (100 mph, cowl flaps closed).

Inlets with very low Vi/Vo values require little or no flow control behind the inlet lip. Here's a late model example, the inlet on a Mooney Acclaim:

Acclaim%20Intake%20600W.jpg


Acclaim%20Engine%20Install%20Small.jpg


There's nothing inside the inlet....zip. It just dumps into the plenum.

I think our cowls are "good enough" inside.

I think the the stock inlet is a bit better than the GA average, but hardly optimum for either internal or external recovery.

Looking forward to some speed data, Dan.

Ok, but do remember the goal.....top speed AND good cooling at low speed/high power. That was the challenge with those ultimate piston powered bombers, yes? ;)
 
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Nice day here, so I went out and did some speed runs. Needed them to recalibrate the IAS anyway, as I've been shaving down the aluminum button static ports (BTW, the method works and my thanks to whomever suggested it).

Exit #3, 2500 density altitude, 3-leg NTPS method, no taping, waxing, or prep, CG near forward limit:

All handles forward, 203.2 knots. About 6 minutes at WOT, highest CHT 317F, lowest CHT 298F, oil 187F.

Previous speed with exit #2 was 197.8 knots.

Kevin, you asked for some efficiency numbers. How would these compare with your benchmark -8?

22/2200, 50 LOP, 162.2 knots @ 7.5 GPH fuel flow (FF not fully calibrated but believed close), highest CHT 294F, lowest CHT 267F.
 
22/2200, 50 LOP, 162.2 knots @ 7.5 GPH fuel flow (FF not fully calibrated but believed close), highest CHT 294F, lowest CHT 267F.

Great work as usual, Dan. I've been dreaming of reworking my cowl for awhile now. Maybe I'll copy your stuff. Not sure if I have the skills and/or energy, though.

At what altitude did you get those numbers?

Thx.
 
All handles forward, 203.2 knots. About 6 minutes at WOT, highest CHT 317F, lowest CHT 298F, oil 187F.
Very impressive speed - congratulations.

Previous speed with exit #2 was 197.8 knots.
Nice increase, so the experiment is worthwhile.

Kevin, you asked for some efficiency numbers. How would these compare with your benchmark -8?

22/2200, 50 LOP, 162.2 knots @ 7.5 GPH fuel flow (FF not fully calibrated but believed close), highest CHT 294F, lowest CHT 267F.
My aircraft, with stock Van's cowling and a cooling plenum and a three-bladed MT prop would be burning around 8.2 gph at that speed at 50 deg LOP at 8000 ft. My original old Hartzell (not the new blended airfoil Hartzell) was roughly five kt faster at the same power setting.
 
Dan,

Is there a thread or website where you have listed your "mods" to achieve 200kts?

I'd sure like to get the kind of mileage out of my 8...
 
what was the FF at WOT? :eek:

Don't know....electric fuel pump is on for WOT runs, which skews the FF numbers.

At what altitude did you get those numbers?

2500 ft density altitude for both data sets.

My aircraft, with stock Van's cowling and a cooling plenum and a three-bladed MT prop would be burning around 8.2 gph at that speed at 50 deg LOP at 8000 ft.

Thanks Kevin. If I get out to the airport today I'll pop up to 8000 DA and record another run. Obviously a 22/2200 run at 2500 DA was throttled.

Is there a thread or website where you have listed your "mods" to achieve 200kts?

Exclusive to VAF......scattered, but all here somewhere.
 
OK, took a few minutes and searched for some past posts.

The cowl inlets and the exit mods are obvious. Note the inlets are relocated upward and outward...diameter is 6".

The upper plenum is common practice, with the only significant difference being the rubber duct inlet experiment.

Less obvious is the detailed tweaks of baffle fit and sealing. Every molecule of air passes between cylinder fins or oil cooler fins.

The cowl is sealed, imperfectly but far better than average. Can't generate exit velocity if the pressure leaks away through 20 different "exits" all over the cowl.

It's a system. Capture lots of pressure. Maximize heat transfer. Maintain pressure to a clean exit.

http://www.vansairforce.com/community/showpost.php?p=326745&postcount=20

http://www.vansairforce.com/community/showpost.php?p=330315&postcount=33

http://www.vansairforce.com/community/showpost.php?p=438389&postcount=15

http://www.vansairforce.com/community/showpost.php?p=276028&postcount=1

http://www.vansairforce.com/community/showpost.php?p=325749&postcount=1
 
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I bow before you ,O Great Dan. You have taken workmanship to a whole new level. Ive been told Im a perfectionist, clearly "they" havent seen your work.
You have brought advanced technology to our RV species.
Absolutely fascinating .
 
Interesting work Dan, and your engine temperature results echo what I was finding with my rocket. My goal with the rocket is to get exit air moving as smoothly as possible as straight back as possible. My converging duct is very similar to what you have come up with. I have a cowl flap but have found that I have never had to open the flap in any flight condition.
As I continued in my cooling experiments CHTs continued to drop and oil temperature became my limiting factor, which is what I am seeing with your data as well. I have a personal maximum operating oil temp of 200F and that is where I ran into a wall with the exit air size. The rocket cowling/firewall step, does not allow a nice way to duct the oil cooler air to the bottom of the cowling and so I am experimenting with ducting the oil cooler through the side of the cowling. I followed some of the early NACA experiments in shaping a bluff body for that exit air and it seems to be working well. I can now independently work on the oil cooler exit air separate from the CHT exit air. This has allowed me to close the exit duct a bit more and I finally have the cooling system that I was looking for. Ideally it would be nice to have a completely separate inlet and outlet for the oil cooler but that will have to wait for my next project.
In my case the only quantitative speed gains came with work to the inlets rather then exit air but as you have stated earlier it is a system and no one change will guarantee success in improved cooling or drag reduction. Improved cooling has often resulted in reduced speed. It makes sense as more airflow will often result in increased drag.
 
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The rocket cowling/firewall step, does not allow a nice way to duct the oil cooler air to the bottom of the cowling and so I am experimenting with ducting the oil cooler through the side of the cowling. I followed some of the early NACA experiments in shaping a bluff body for that exit air and it seems to be working well. I can now independently work on the oil cooler exit air separate from the CHT exit air. This has allowed me to close the exit duct a bit more and I finally have the cooling system that I was looking for. Ideally it would be nice to have a completely separate inlet and outlet for the oil cooler but that will have to wait for my next project.

How dare you, sir! I thought that I was the only Experimenter to go boldly where no one had gone before, and have a separate oil-cooler inlet and outlet, and here are you trying to steal my thunder. If this is kept up it will lead to others doing the same thing and seeing their increased performance which should have been mine and mine alone! Please keep your results to yourself or I shall put a pox on you and your household! Pshaw!
 
As I continued in my cooling experiments CHTs continued to drop and oil temperature became my limiting factor, which is what I am seeing with your data as well.

Yes Tom, I agree. Oil high, cylinders good. A separate oil cooler inlet would change one bit of CHT data. Cyl #3 runs warmer than the others with all exit sizes and all conditions. I pull oil cooler air with a 4"D duct from the baffle wall behind #3. It's probably a local pressure loss at that cylinder. Don't consider it a problem at these CHT levels, but....

Here's another stressful condition, high power at what may be the highest altitude at which I can get 75% (have to check that detail). Anyway, 125-150 ROP for power, indicated true 183 knots. I could drop CHTs and oil temperature by going richer or leaner, just like the theory says, but also went slower.

2nh24w0.jpg


Paul, who you kidding? Clearly you stole the separate oil cooler inlet idea from that B-29 paper I referenced earlier ;)
 
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Lots of WWII fighters had oil coolers installed under the wings with inlets and outlets; Hoerner covers a lot of them in Fluid Dynamic Drag. Here's something to consider. It seems to me the flat side of the cowling toward the rear on the right or the left would make an ideal place to install an oil cooler, with a 6"W X 3/4" high inlet feeding it, and a 6"W X 1" outlet at the back. Kevin Eldredge had the oil cooler on Relentless NXT mounted on the bottom of the cowling, with a separate inlet at the front and the regular engine outlet at the back. He used quick-disconnect hoses so that it was not a problem removing the cowl. The same Q-D set-up could be used with the cowling side mount. BTW; my OC IO was on my plane when I got my airworthiness in 2001, so that trumps the one in 2006! :p
 
Kevin Eldredge had the oil cooler on Relentless NXT mounted on the bottom of the cowling, with a separate inlet at the front and the regular engine outlet at the back. He used quick-disconnect hoses so that it was not a problem removing the cowl.

Saw pictures of that somewhere, trick indeed.

I need several pressure measurements in the outlet area, then I'll make plans. Right now the oil cooler duct outlet is in the roof of the exit bell a few inches forward of the actual cowl outlet, which may not be the location with the lowest pressure. See previous photos.
 
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About 8 months ago Paul Lipps posted a recommendation for pressure and temperature sensors (thanks Paul):

http://www.vansairforce.com/community/showpost.php?p=439444&postcount=31

Rainy weekend here, so I built a little board to go under the cowl:

21kywdj.jpg


The temperature probes are under the black heat shrink at the ends of the 3-wire shielded cables. No particular reason for the shields; I just had the cable in the spare wire box and the sensor needs at least two leads. The third lead allows a calibration adjustment but I doubt I'll use it.

The two small differential pressure sensors have a range suitable for measurements like pressure drop across the cylinders or the oil cooler. The large sensor (Freescale MPX5010DP) is suitable for dynamic pressure in our speed range. I'll hook one side of it to the aircraft static system and use it for velocity, in particular inlet and exit.

Primary goal is gathering data on this low velocity inlet/throttled exit system, but it would then be interesting to do the same with a standard RV-8 cowl and perhaps another with poor cooling performance.

POSTSCRIPT 2018 Eventually switched to a basic electronic manometer for pressure. The above sensors were a bit too fragile.
 
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