Cowling Mods! Speed Increase! Cooling issues! Many Pictures.

A few of the pilots and builders on the James / Holy Cowl RV Forum ask me to post Pics and things that I've done to my -6 on VAF,,,, so now I'm finally getting around to doing this. BTW I've never attended a Forum of any sort until I joined the yahoo/james/holy/cowl/ forum and then finally a little over a month +++ ago joined this awesome VAF Forum because I just never got around to it and because of issues with my job or an ex wife over a year ago and her not understanding???? enough said about her... I'm single now and I have the time to do what I love to do now and that is experiment, fabricate, share things with friends and RV builder / pilots. So I'm on the computer now sharing what I've built and modified on my RV-6. I made these mods before I ever knew about what Bob Axsom did with his lower cowl mods BTW. I finally found a thread awhile back about what Bob Axsom had done and he had already done it but with aluminum. I visited with Bob on the phone a few weeks ago and he is a very open and honest and I like that. He's as good as GOLD. We have the same interests just like many of us and that's what makes great friends, sharing ideas and getting our RV's more effiecient or better MPG. I wished that I had been on this forum a long time ago to follow up with Bob and other builder mods but I was off doing my own things and never looked around on the computer. Most of my lower cowl mods were done at the early part of this year and I've seen many improvements over the past few months. To date: at 4,125ft MSL, 27.1" MAP, turning 2,680 rpm. GPS ground runs of N:248mph, E:222mph, S:195mph, W:220mph. Average of 221.25mph. I know these numbers do not give a TAS but you get the idea. Barometric Pressure today was low btw.... Running at these settings were with outside air temps around 70F air temps Indicating 205-208 mph, rough windy air today in Oklahoma,, ,,, CHT's temps were #1-282F, #2-283F, #3-283F, #4-278F. These temps were with 2 3/4" round diffuser cowl inlets. I posted another thread yesterday with higher CHT's ,,, but the CHT's are around 350-360F temp range with 2 1/8"" cowl inlets. I've made a few changes sinces then so some of the numbers do not apply with the recent mods to the cooling system. For numbers!!! Here they are,,, Cowl inlet area for the engine cooling needs and not the oilcooler included is 7.09 Inches total inlet area with the 2 1/8" inlets. Oil is fed by a 4" NACA DUCT mounted at a very sweet spot on the right side of the lower cowl catching much prop blast on climb out and is a very good location for climbout and cruise. This location required much tuft work to find the right spot and keeping it at the correct angle for a NACA duct to work efficient was very critical! Total area on the oil cooler inlet is 12.56 square inches at the full open range if needed. It's a Big Stewart Warner Oil Cooler, Dual Bypass 11 Row and is an excellent oil cooler. YES they cost $$$$ The Oil cooler has a 4" NACA Duct feeding to it that I can control Via an inlet door to control temps. I can control the temps at any setting I want. I can keep the oil temps at 190F in a climb on 100F++ days mostly because of prop wash because the oil cooler inlet is placed much further out from the centerline of the crank radius / prop hub. OK,,,Numbers: Cowl outlet is 25.14 square inches. Detonation is another concern of mine because I'm running a TRUE 10:5;1 comp and the cooler CHT temps will help in this area along with keeping EGT's on the rich side---100-125F ++++ range rich of peak over 75% or more. Sorry it took so long to post this from everyone asking questions from along time back. Anyone have any questions feel free to ask. AJ

Pictures

Pictures

Beautiful Cowl Work

I copied the official results of the 2006 AirVenture Cup Race from the EAA web site for the RV Blue (360 cu. in.) and Red Classes (320 cu.in.) and included them below. At 1000 ft AGL there was a headwind component of 5 to 7 kts for the better part of the first 300 nautical miles of the 407 nautical mile race. The speeds below are listed in statute miles per hour. As you can see you would have done very well in the Blue class. Fuel consumption is something to manage. The fellow that finished last in the red class had to stop and refuel - I heard his disappointed radio call on the race frequency as we were nearing the end of the race. As we flew the short distance to Fond Du Lac for recovery I had my hand on the main fuel valve ready to switch tanks at the first sign of fuel pressure drop.

RV Blue
27 RV-8 N207RV Jon Ross 210.26
18 RV-8 N184JH John and Teresa Huft 210.12
19 RV-8 N630RL Robert Saltsman, Jr. 201.47
16 RV-7 N441K James Klusmier and Paul Laherty 200.76
43 RV-8 N128RV William Hess 200.07
84 RV-8 N184CM Craig Moen & Elaine Kash 194.37
71 RV-6A N710BJ Robert Axsom & Jeanine Axsom 193.42
76 RV-6 N709BW Benjamin Witmer Jr & Warren Daugherty Jr 179.55

RV Red
63 RV-3 N13BV Bob Vasey 200.31
48 RV-6 N7219D Dave Weisgerber 193.37
17 RV-6A N17LD Larry Klusmier & Lori Ulichney 193
34 RV-4 N117CM Chris Murphy 192.21
72 RV-4 N2QT Bobbi Boucher 190.76
53 RV-6A N506RV Scott Gesele & Wendy Gesele 187.11
51 RV-6A N51PW Mark Phillips 139.45

Bob Axsom

Stock Cowl inlet versus smaller inlet. The Green Tape work is for testing OK.

More Pictures

More Pictures

Pictures

Turtle back Mod to Slider.

4 into 1 exhaust.

Cowl outlet and exhaust.

Oooops

Forgot to mention::::: The engine BTW is an IO-360-A1B6 that I built in house and is far from OEM with many thermal barrier coatings applied along with heat dispersing coatings in other areas. The Plenum, custom baffling on top of the engine and below, the 321 stainless 4 into 1 exhaust and all of the cowl mods I designed and built myself. The mods that I have done are not for everyone and I suggest to anyone reading this to test or make changes at their own risk.

Wow!

That (the whole installation) is just jaw-dropping gorgeous!!!

A Saint

Alan,
You're a saint.......well, sort of.

All you other guys just don't realize the value of all this tried and tested information that is so hard to come by. Here you have speed results, CHT's and engine mod info.......WOW. Additionally is some beautiful carbon fiber work and aero mods for your picking!!

Thanks a ton, Alan for being so unselfish and such a great contributor to this forum!!WOW! You'd have Opec on your butt if they knew all this gas-saving stuff!
Regards,

Absolutely excellent, Alan. You are an inspiration.
I've got much work to do to get a Subaru H6 to perform better.....thank you for posting the write up and pictures.

David Domeier
Troy, Missouri

BTW

Hi again, Alan,
Are the intake tubes wrapped to keep a denser charge? Or just to keep exhaust heat from warming them up. or both? Does the air flowing down from the cylinders not cool them enough?
Regards,

Cowl Mods

Alan:

Please describe your induction/filter setup from the cowl to your fuel servo. What air filter are you using? Do you have alternate air?

My homebrew setup looks very similar.

Mannan Thomason
RV-8 N161RL

NICE

Looks good, you have done a lot of exploring new ground that the rest of us can benifit from.

Thanks.

A couple of comments, and a question.

Did you fly with a "stock" exhaust prior to the 4>1 setup, and if so, what changes did that make.

Sure is easier to make the exit air baffeling without the training wheel in the way.

Your NACAish oil cooler duct-------I think you may have missed the boat on that one. A true NACA duct works by using the boundry layer, which is why they are so low in drag. With the addition of your door/scoop, I think you just lost most if not all of the benifit of a true NACA duct-----probably even caused additional drag in the open position. Maybe some of the engineer types out there can comment on this one.

The inner profile of the aluminum inlet ring was there for a purpose, when you closed down the inlets, green tape photos, it looks like you didn't keep the profile. You probably reduced your cooling flow (more than just the smaller opening) due to this. Steve designed the inlets to cool 200 HP, and feed the oil cooler, so by picking up oil cooler air elsewhere, I think you are correct in reducing the inlet diameter.

Very Nice.

Mike

Is your oil cooler model # SW 10611R ????

-Ron

rv969wf said:

GPS ground runs of N:248mph, E:222mph, S:195mph, W:220mph. Average of 221.25mph.

Click to expand...

Thank you very much for the pictures and description. You have done a beautiful job.

One very small point: the average of GPS ground speeds in several directions is equal to the TAS only if the wind is zero. The error is small if the wind speed is low, but the error will be several mph if the wind is strong.

If you are trying to measure speed changes due to small mods, you should consider a more accurate method of assessing performance. I recommend you record GPS ground speed and GPS track on four runs in a box pattern, then use the NTPS spreadsheet. More info at this thread, and this one

INstrumentation for cowling mods

Awesome thread!!! Thanks to Bob and Alan for all their work and openness. I've pasted a link here to Chris Zavatson's site. Chris has taken the speed gain game one step further and out-lines how to instrument pressure recovery and loss in a paper here: http://www.n91cz.com/Pressure/PlenumPressure.pdf

Art in Asheville

I have done quite a bit of speed testing with my rockets using the three leg gps formulae that Keven Horton advocates. It is a quick test and easily repeatable. High winds tend to lead to errors as the high winds, in my testing, do not seem to be that consistent. Also,other factors that are not mentioned are outside air temperature and manifold pressure. These can have a large impact on engine HP so you really should try to take that into consideration if your testing occurs on different days. Pressure altititude should always be used so that you are consistent in that regard.

Tom Martin

How ya do that?

Alan How does the canopy fast back work. The track is covered and the track bump on the canopy is gone?? Cool how did you do that. Looks great. G

NACA Duct

I believe that Mike S is correct about the naca duct. The low drag benefits occur from it's flush profile when open. When closed, it really wouldn't matter what the shape was. To get the proper benefit, you'd want to hinge the door at the front, and have it drop down flush with the bottom of the ramp when open. The internal geometry is quite specific (7 degree ramp if memory serves correctly), as is the exact shape of the outer curves, but that should be quite Googleable. You've got a ton of beautiful work in your plane - most impressive.

Bill, thanks.

The EAA magazine had a nice tech writeup recently on NACA ducts. You are correct about the ramp slope being critical, so is the edge of the ramp lip, and the radius of the "top" of the opening hole.

A drop down door as suggested, or possably a butterfly like in a carb should be a better way to control the air flow, and not diminsh the ducts benifits.

Mike

Answering questions

I'm going to try and answer most of the questions that everyone has ask about. I first started flying the -6 in 2001, 5 yrs ago and 208mph was it. Oil temps were out of the green range and not controllable. I tried several different oil coolers mounted on the left rear baffle, right rear baffle, even two of them one on each side of the rear plenum, nothing worked great in the summer or in a hard climb. Another problem was when I did get the Big Stewart Warner oil cooler Part #10631S at $615 I found out the added weight, vibration and harmonics was cracking out the plenum and also ruined one oil cooler, not the new one though. I had a terrible time with controlling the oil temps between winter and summer. I did have a door on the cooler but still had cracking issues with the plenum and oil cooler mounts. That's when I decided to relocate the cooler and on a -6 there is not much room to put one even with scat tubing coming off the rear plenum. What you see in the pictures is where I finally made it permanent. The NACA duct was installed without a door at first and I was quite shocked to see the changes. Testing was done 4 yrs ago in July on 100F+ days and without any door installed I could not get the oil temps past 170F even when climbing to 10,000 ft. indicating 120mph at full power and running 100ROP. Later the door was made and I agree that it is not designed correctly and it should have the door hinged at the front and not the rear. Things were so tight in the cowl and trying to make a front pivot point was going to be very complex so I scratched that idea and settled with what I've got. Another problem was the 3D curve of the cowl and trying to make a good looking operable door or floor that hinged at the front that looked good and worked. I wanted the door to fit flush and not stick out like a sore thumb. If hinged at the front, the curve of the cowl door was going to block off half of the inlet area and a gapping hole would be in the cowl inside to make it work. Something interesting that I found out is that the door floats at half open, meaning the door is not trying to be ripped off the cowl and it is very sensitive. 1/8" movement in door gap makes a huge difference. Something else that shocked me was the fact that the oil temp is colder with the door installed and open than not even having it installed. Speed I did not see any losses, after I installed the controlable door, I thought it would slow the plane but for some reason it didn't make any differences. I was more concerned about keeping the oil cool. I did have smaller air inlets but they were crude and not designed right either. I accumulated over 200 hours of trying this and that and each time I flew, notes were taken with each change I made, CHT's EGT', fuel flow, oil temps, fuel pressure, outside temps, Barrometric pressures, IAS, ground speeds, wind conditions, etc. etc. No speed was gained by locating the oil cooler where it is to date except in the winter time when the door is shut / flush. The exit end of the cooler is poor in my opinion but I'm stuck with how it dumbs the air into the lower cowl. My biggest gain with the oil cooler location is the fact that I can control the oil temp and maintain it at 190F all the times.

Someone ask about the intake runners wrapped. First they were powder coated along with a heat barrier coating applied then wrapped with 1/4" fire retardent insulation and then 2,000F aluminum tape. I did this to keep the intake air more dense and cool. Free horsepower, but not good for fuel economy.

Question about the air box. The air filter system is "Barnard design" and it has a K&N air filter inside.

Exhaust questions: I started out with a vetterman crossover and ran that for several years. Later built the custom 4 into 1. Any gain??? No dyno don't know. But after flying with the 4 into 1 and taking many notes, I'm seeing more fuel burn on take off and at full throttle. Any faster? At low altitude a little, but at high altitude nothing because the engine is not making much power.

Inlet Diffuser shapes. Testing with foam inserts and green tape is crude and not aerodynamic at all. I'm very aware that the shape and profile is very critical the first few inches. I mostly just kept shinking things down to get a general idea of a size. Final cowl inlet inserts will be profiled and shaped out of glass. One thing I did note was that with the stock 4 1/4" round inlets was that the engine started running cooler when they were downsized to around the 3-3 1/2" diam range. Im assuming the stock 4 1/4" inlets were creating a plume of air or were not shaped correctly.

Question about canopy mod? The hump or bump is not seen because the front section is raised. There is another post that I have on here with quite a few pictures of the canopy if anyone wants to look at it. I hope this answers some of the questions asked. Thanks for all the comments. AJ

Thanks

AJ, thanks for the reply.

I was impressed by all you have done, and only mentioned stuff as a bit of "constructive critism".

Your efforts deserve to be acknowledged.

Mike

Slider canopy mod

gmcjetpilot said:

Alan How does the canopy fast back work. The track is covered and the track bump on the canopy is gone?? Cool how did you do that. Looks great. G

Click to expand...

George I have a post with probably 6-8 pictures of the slider canopy mod. Do a search for "slider canopy back half mod" or something like that. I attached more pictures yesterday on that link. AJ

More Pics



Early stages of the work. Kinda gives you an idea.

Wow. Awesome work AJ, This is very much like some work one of my friend did on a skybolt. I'm amazed how much brillant minds think alike! I'm working on some mods for my dads cardinal to help cooling. It's nice to see that I'm doing some of the right things.

Something to think about.

Not sure how to post this but after looking over my notes on CHT's and Oil temps I wanted to share a few other things. From what I found out by seperating the cooling needs for the engine cylinders/heads and bringing in an alternate air supply for the oil cooler, I found that the oil cooler on my Lycoming needed at least the same / more volume or Square inches of air mass as than the engine itself . Example: I can keep CHT's at an average of 355F degrees with a total of only 7 square inches of inlet area cruising around at say 200mph on a tested 79F day. My oil cooler duct has a total of 12.56 Square inches of area if needed on hot days. I can't say what the actual square inch area of inlet needs are for the oil cooler at all times because of the door on the forward side of the NACA duct varys with how much the door is open or shut. I guess what I'm trying to say, think or have learned is that the oil cooler on my angle valved 200HP engine needs maybe an equal amount of cooling air to the oil cooler than the actual engine itself. From what I've seen or learned,,,,,,, and someone tell me different if I'm wrong or not, but on my application the oil cooler exit / outlet air into the lower cowl is probably just as important as the the cylinder / head exit air. Does this make since? If the oil cooler exit point could be placed at a more precise place down at the cowl outlet it should help on cooling drag and not let the oil cooler outlet air go all over the place and get turbulent in the cowl. I've got a few ideas but have not done them yet. One needs to remember that an angle valve Lyc. has piston oil cooling nozzles that spray oil on the bottoms of the piston crown, so oil cooling needs are higher on this engine. I did not ever get these low CHT or Oil temp numbers until I made many mods to the plenum, baffles and a few other things that can't be seen in any of the pictures. The plenum is 100% air tight on the top and the baffling that wraps around the cylinders is not OEM or Spam Cam Lycoming specs. What I mean by this is the clearances and shape around the fin areas on each cylinder is slighty different. Gaps on the lower baffles are all at 1" on the cylinder fins, lower baffle gaps on the cylinder head fins are 2 1/4". Please do not change these gaps on the lower baffles to try and lower a CHT problem, if these gaps are not correct, hot spots on the cylinders can be created and what that does is make the cylinder out of round and you make less HP. The air flow around the cylinders and heads need to be uniform and attached with NO leaks around the sides or anywhere, then exit the air out at equal amounts. Most of the changes I've made are on the top inside the plenum and around the sides of the baffling, not on the bottom gaps. To get an air cooled engine to run cool you need to use the air where it is needed and not let it spill / leak or go some other place. Main thing is no leaks. A well sealed plenum will pick up speed and the faster you go the smaller you can make your cowl inlets or air needs. One example is I can say fly at 185mph IAS and I can have an average CHT of say 350F. If I run wide open and increase my speed to 205mph IAS, I'm seeing 15F degrees reduction in CHT's with the same mixture setting BTW. 20 mph gained in speed gave me a 15F reduction in CHT's and that is at max power and making more heat in the engine by making more horsepower. Anyone with cooling issues can fix them if you know what to look for. I've gained 12 mph trying new things and I must admit that some of that is engine HP and not all cooling drag. My notes show a gain of 4-5 mph with my newest engine and the cooling drag reduction at this moment is about 7 mph. Before I started making any changes to anything, I did have a Steve Barnard sealed plenum with a lower compression IO-360 200HP engine several years ago. Other issues I have not touched on are rigging problems that I have on one gear leg fare and wheel pant that are not correct. Presently my -6 is flying half a bubble off and one wing low because of this. One more thing to fix. Anyone with any quesitons feel free. Later, gotta go to bed, AJ

Slicker'n snot...

Very nice glass work! We know how fast it can go, now can you visit me at my 950' grass strip... How sloooow can you go?

RR

Intlet cooling

AJ,

I have the standard SJ cowl/plenum on my RV-9A with a firewall mounted oil cooler fed with a 3" scat off the back of #3. This time of year I have to block 95% of the output going to the oil cooler to get the oil up to temp, so it works really well. I need to design some sort of dampner system though so I can control it in the cockpit.

Question... with the temps being in the 30's this time of year in KS, I have to tape over the front of #1 and #2 cylinders so they don't freeze to death. I'm curious if you did anything in the way of 'ramps' in front of the front two cylinders. The pictures you have posted don't show anything in this area.

PS - Saw your plane at Fairview last weekend. I flew in the unpainted RV-9A parked on the front row.

Front two cyl head fins blocked.

N523RV said:

AJ,

Question... with the temps being in the 30's this time of year in KS, I have to tape over the front of #1 and #2 cylinders so they don't freeze to death. I'm curious if you did anything in the way of 'ramps' in front of the front two cylinders. The pictures you have posted don't show anything in this area.

PS - Saw your plane at Fairview last weekend. I flew in the unpainted RV-9A parked on the front row.

Click to expand...

Click to expand...

Hi Mathew, Sorry the pictures don't show anything, but yes I have the front of #1 & #2 Cyl head fins blocked all the time between winter and summer. They are profiled out of carbon fiber and contour the shape of the cyl fins and do have a slight curve to them. I'm leaving 1/4" of fin area exposed. The rear cyl fins on #3 & #4 also are wraped at the rear area with a radius towards the top. When I have the plenum off I plan on making triangle shaped / 3D style diffuser in front of these two cylinders to direct the air more smoothly around the sides and top of these cyl heads. Sorry I don't have any pictures or I would post them. I tried to balanced the CHT's the best I could with the clearances between the side baffling. #3 is the most critical at the rear of the cyl fin area and then #2 at the front cyl fin area where the air is allowed to wrap and flow to the bottom outlet. Between summer and winter all of the CHT's stay close to each other but they're not perfect. Hope this helps, sorry I missed you at the Fairview Flyin, did you enjoy the fly-by if you were still around when I left? AJ

Forward sloping windshield

Wanted to add this if anyone has thought of it. Forward sloping windshield on RV-6. I tested and tested !!!!! It made no improvement, no speed gain, nothing. This was a temporary .125" lexan taped in front of the OEM windshield. Waste of time if anyone is thinking about it. Only positive was a 2 db noise reduction and maybe a less chance of a bird comming thru if made 1/4" -3/8" +++

Plenum

Alan: Have you posted any information on how you designed and built your plenum in the first place? I'm looking to build one for my F1 and could use some helpful hints!

Regards,

Lee...

rv969wf said:

Wanted to add this if anyone has thought of it. Forward sloping windshield on RV-6. I tested and tested !!!!! It made no improvement, no speed gain, nothing.

Click to expand...

Sorry to let this go so long....Alan, thanks very much for this post. It is hard for us to be as proud of our failures as we are of our successes, but they are just as important...You get the big "Attaboy" for posting this.

Plenum

logansc said:

Alan: Have you posted any information on how you designed and built your plenum in the first place? I'm looking to build one for my F1 and could use some helpful hints!

Regards,

Lee...

Click to expand...

Hi Lee. I started out with a Steve Barnard Plenum which is now Sam James in Florida. Barnards design was a little different than what SJ has btw. I didn't like the Barnard Plenum so I started over but having it on hand helped. What I use to make patterns for shapes is Acetate Plastic, various thickness .032"- .040" thick range, McMaster Carr Supply carries the Acetate. The nice thing about Acetate plastic is the fact that it is clear in color and you can see through it, so when your making different shapes you can see through it and see how much clearance you have in certain areas. Poster board I found out is not stiff enough and you can't see through it. I do used poster board for patterns then transfer them to the hard flexable Acetate plastic sheets. I also use Aluminum tape that is used for heating units as it will hold the plastic sheets or patterns to shape and it sticks very well. Another note on the plastic Acetate, I use a heat gun to shape it then cool it with a cold rag to hold its shape. When I built the lower glass piece below the engine that are in the pictures I used this same technique. The Aluminum tape helps to hold everything together and makes the mold more rigid. When I have the piece, part, pattern shaped I wax up the acetate plastic and aluminum tape, apply release agent to the mold and lay up the glass. Pop the glass off the mold the next day and start trimming. I have a dummy engine on a stand that I use for mockup and did all the glass work on the dummy engine. I have only used modeling clay in a few areas but a large piece like the plenum I don't use any. Not everyone will agree with me on how I make parts but everyone has there own techniques and this seems to work good for me and it's simple. Hope this helps a little.

rv969wf said:

Not sure how to post this but after looking over my notes on CHT's and Oil temps I wanted to share a few other things. From what I found out by seperating the cooling needs for the engine cylinders/heads and bringing in an alternate air supply for the oil cooler, I found that the oil cooler on my Lycoming needed at least the same / more volume or Square inches of air mass as than the engine itself . Example: I can keep CHT's at an average of 355F degrees with a total of only 7 square inches of inlet area cruising around at say 200mph on a tested 79F day. My oil cooler duct has a total of 12.56 Square inches of area if needed on hot days. I can't say what the actual square inch area of inlet needs are for the oil cooler at all times because of the door on the forward side of the NACA duct varys with how much the door is open or shut. I guess what I'm trying to say, think or have learned is that the oil cooler on my angle valved 200HP engine needs maybe an equal amount of cooling air to the oil cooler than the actual engine itself. From what I've seen or learned,,,,,,, and someone tell me different if I'm wrong or not, but on my application the oil cooler exit / outlet air into the lower cowl is probably just as important as the the cylinder / head exit air. Does this make since? If the oil cooler exit point could be placed at a more precise place down at the cowl outlet it should help on cooling drag and not let the oil cooler outlet air go all over the place and get turbulent in the cowl. I've got a few ideas but have not done them yet. One needs to remember that an angle valve Lyc. has piston oil cooling nozzles that spray oil on the bottoms of the piston crown, so oil cooling needs are higher on this engine. I did not ever get these low CHT or Oil temp numbers until I made many mods to the plenum, baffles and a few other things that can't be seen in any of the pictures. The plenum is 100% air tight on the top and the baffling that wraps around the cylinders is not OEM or Spam Cam Lycoming specs. What I mean by this is the clearances and shape around the fin areas on each cylinder is slighty different. Gaps on the lower baffles are all at 1" on the cylinder fins, lower baffle gaps on the cylinder head fins are 2 1/4". Please do not change these gaps on the lower baffles to try and lower a CHT problem, if these gaps are not correct, hot spots on the cylinders can be created and what that does is make the cylinder out of round and you make less HP. The air flow around the cylinders and heads need to be uniform and attached with NO leaks around the sides or anywhere, then exit the air out at equal amounts. Most of the changes I've made are on the top inside the plenum and around the sides of the baffling, not on the bottom gaps. To get an air cooled engine to run cool you need to use the air where it is needed and not let it spill / leak or go some other place. Main thing is no leaks. A well sealed plenum will pick up speed and the faster you go the smaller you can make your cowl inlets or air needs. One example is I can say fly at 185mph IAS and I can have an average CHT of say 350F. If I run wide open and increase my speed to 205mph IAS, I'm seeing 15F degrees reduction in CHT's with the same mixture setting BTW. 20 mph gained in speed gave me a 15F reduction in CHT's and that is at max power and making more heat in the engine by making more horsepower. Anyone with cooling issues can fix them if you know what to look for. I've gained 12 mph trying new things and I must admit that some of that is engine HP and not all cooling drag. My notes show a gain of 4-5 mph with my newest engine and the cooling drag reduction at this moment is about 7 mph. Before I started making any changes to anything, I did have a Steve Barnard sealed plenum with a lower compression IO-360 200HP engine several years ago. Other issues I have not touched on are rigging problems that I have on one gear leg fare and wheel pant that are not correct. Presently my -6 is flying half a bubble off and one wing low because of this. One more thing to fix. Anyone with any quesitons feel free. Later, gotta go to bed, AJ

Click to expand...

AJ, I cant thank you enough for your posts. We have just finished a RV7A four months ago. We now have 30 hrs on it, but have had high oil temp issues. I purchased and used the large oil cooler that Vans recomends for 540's and 200hp engines. We came off of the back baffling with a two inch scatt tube on each side. I dont think we have enough air flow over the oil cooler. Do you think it would help if I change the scatt tubing from the two 2" scatt tubes to the oil cooler plenium to one 4" scatt tube coming off the baffling behind the #4 cylinder. We dont have any problem with high cylinder head temps, just high oil temps. Any advice would be very appreciated.

It's red... and got checkers too.

That's got to be good for at least 5 extra knots!

I like it!

I always wanted to see Alan at a race

It would have been one of those special experiences I'm sure but it never happened. Every so often I think about this dynamo and wonder what ever happened to him. I know life happens and we cannot do what we want.

Bob Axsom

Augmenter tubes

Bob, I have read lots of your thread regarding exhaust modifications to clean up airflow while dealing with cooling issues and now this thread with lots of similar ideas and so I have to ask a question. Has anybody ever tried augmenter tubes in an RV? As I understand the design, if you set them up correctly the augmenter tube will scavenge air from the lower cowling hopefully improving cooling. The piston powered T-34s I have flow all had large and somewhat tightly cowled engines. What they did not have were cowl flaps or over heating problems whereas the Bonanzas I have flown (same engine and cowling essentially) all had cowl flaps and yet still had cooling issues. Just wondered if anybody had done it yet.

rv969wf said:

Wanted to add this if anyone has thought of it. Forward sloping windshield on RV-6. I tested and tested !!!!! It made no improvement, no speed gain, nothing. This was a temporary .125" lexan taped in front of the OEM windshield. Waste of time if anyone is thinking about it. Only positive was a 2 db noise reduction and maybe a less chance of a bird comming thru if made 1/4" -3/8" +++

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Interesting! Good on you for doing this testing. It looks like you approached it very resourcefully.

This test supports my general thesis that simple-curved windshields are too often subject to forming high-pressure zones, and that the drag that results offsets any drag reduction you might expect from the shallower slope. This is one of the reasons that I'm not a big fan of the long windshields popular on the Rocket airplanes. Yeah, it looks all cool and F-15-like, but it has no overall drag benefits and sometimes results in a tangency mismatch where it meets the canopy. The stock windshield, on the other hand, is virtually guaranteed to match the profile of the canopy.

I think that another good test would be a shallow-sloped windshield that has been blown a bit so that it is somewhat convex on the outside. I think that that would have a better pressure gradient and lower pressure, and consequently lower drag, overall.

Thanks, Bob K.

fkyser said:

...Do you think it would help if I change the scatt tubing from the two 2" scatt tubes to the oil cooler plenium to one 4" scatt tube coming off the baffling behind the #4 cylinder...

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The formula for the area of a circle is pi*radius^2. So the area of a 2" diameter circle is 3.14*1^2=3.14 in^2. Two of those would have a combined area of 6.28 in^2.

However, a 4" diameter circle has an area of 3.14*2^2 = 3.14*4 = 12.56 in^2. So the one 4" tube will have the twice the cross-sectional area and will flow about twice as much.

So, yeah, I think that a single 4" or even 3.5" tube will beat the heck out of a pair of 2" tubes. The 3.5" tube works great on the RV-8 that I helped build, which also has the larger RV-10-sized oil cooler.

Thanks, Bob K.

Not that I know of

xblueh2o said:

Bob, I have read lots of your thread regarding exhaust modifications to clean up airflow while dealing with cooling issues and now this thread with lots of similar ideas and so I have to ask a question. Has anybody ever tried augmenter tubes in an RV? As I understand the design, if you set them up correctly the augmenter tube will scavenge air from the lower cowling hopefully improving cooling. The piston powered T-34s I have flow all had large and somewhat tightly cowled engines. What they did not have were cowl flaps or over heating problems whereas the Bonanzas I have flown (same engine and cowling essentially) all had cowl flaps and yet still had cooling issues. Just wondered if anybody had done it yet.

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After a lot of experimenting and testing I picked up ~1.7 kts on our RV-6A with that outlet work but I know of no one with an RV attempting the traditional augmenter tubes. Bob and Sarah Bean built them into their Glasair III but I never heard of any verified speed gain from them. As I recall from reading Jack Cox's article on them and the plane several years ago they were in the original build and I assume there was no "with and without" comparison testing done. They raced the plane so they were looking for speed but they were lost in a crash in 2010 during normal a trip.

Bob Axsom

Interesting post, because while I have made significant progress on in flight cooling with my F1 in the last year, I'm still fighting ground cooling issues on a high DA day here in the Rockies. In reviewing the NACA literature, it is clear that the geometries required for linear flow through augmentation would require major rework on an RV or Rocket. And with suboptimal geometries the cooling effects tend to drop off quickly.

Having said that I believe Paul Lipps was running his own unique exhaust augmentation, and I believe he was trying to patent his idea. I've often wondered how he was able to run his tightly cowled, small inlet, O-320 on the ground on a hot summers day. I think Rocket Bob and Tom Martin were familiar with his work--any inputs, guys?

Paul's augmenters started right at the cylinders. I seem to recall drawings in a Contact article.....

I'm alive Bob.

Bob Axsom said:

It would have been one of those special experiences I'm sure but it never happened. Every so often I think about this dynamo and wonder what ever happened to him. I know life happens and we cannot do what we want.

Bob Axsom

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I'm still around Bob, I don't get on VAF very much. I've got 660 hours on the Red bird without any issues. I always wanted to attend a race but it just never worked out for me and my work schedule. I haven't made any changes over the last few years and happy to just be able to fly when I can.

Paul Lipps

There was a special issue of Contact entirely about Pauls Lancair and his Props.

How about the Grove Oklahoma November 3, 2012

rv969wf said:

I'm still around Bob, I don't get on VAF very much. I've got 660 hours on the Red bird without any issues. I always wanted to attend a race but it just never worked out for me and my work schedule. I haven't made any changes over the last few years and happy to just be able to fly when I can.

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There is a SARL race planned at Grove Oklahoma on 11-3-12. Details at www.sportairrace.org under Calendar of events.

Bob Axsom

Alan, you might as well give in and race! Bob is never going to give up trying to get you to a SARL race at least once and pretty much EVERYONE wants to see your RV!

Best wishes and congratulations again on such a sterling effort on your airplane.

Lee...

Links Broken

It looks like all the links to Alan's pictures in this thread are broken. Alan, if you're still on VAF, would you repost the pictures or give us a link to them if they are still on line somewhere?

Can't view photos

I'm having the same issue.......can't view photos.