Cooling drag question

[chuck]

In another RV, I think his name is Jeff Nielsen has cowl inlet flaps. They are butterfly valves that are laptop computer controlled! They inlets look massive. Active variable cooling geometry? An area to consider may be. The question to ask, is it practical. With microprocessors and robotics why not.

I have been thinking along the lines of active control though I'm not quite sure what the actuator looks like. What scares me about these pictures is that there is a position that is completely or mostly closed. Assuming that the reliability of a software system is 0 (standard practice in medical devices...) it seems to me that a single point software problem will ruin your day.

It also seems that this installation has higher drag when the inlet is closed (atleast from the stand point of air spilling back out the inlet). Perhaps the net drag is reduced?

Are there any numbers or race results from this configuration? (I checked the website on this an the inlet flaps are not to reduce drag but prevent shock cooling (according to gmc's link).)

 

[rv6ejguy]

I've followed your 360 efforts along and of course am in the middle of my own Legacy. I think I'm headed down the path of a Plenum as well and the other mods that Andy Chiavetta does at Aerochia.com. I'm a NA bird, so I'll stay with the stock cowling, but it looks like Andy has the plenum, and other parts figured out for a Legacy...

These are smart boys and they build nice stuff for Reno racers. Flight and race proven to go fast and work.

Through flow bench studies and calculation that I've done, just about all typical inlet ducts with typical radaii and lengths are in fact well into the turbulent flow range. Laminar flow is highly unlikely and possibly not very important when it comes to cooling air intakes on aircraft. Speculation without lab or instrumented, videotaped flight testing is just that. If the engine cools better and you go faster- you are on the right track. If not, try something else.

Many people would be very surprised on how air is actually flowing backwards or not at all inside some ducts, inlets and cowlings.

The Aerochia boys have got it going on IMHO. DG coming close to 400mph on the front straight last year validates their concepts.

 

[gmcjetpilot]

Req info all I got

Are there any numbers or race results from this configuration?

Chuck here is the site, http://www3.telus.net/haywire/RV-9/C-FSTB.htm click on link towards bottom, left side: Jeff Nielsen. Interesting.

 

[RV8RIVETER]

OK, George, thanks for clearing that up. I understood and noticed very small amounts of narrowing at the throat in duct designs. But that picture you posted got me doubting if I ain't as smart as I thought I wuz.

 

[gmcjetpilot]

Great Q

OK, George, thanks for clearing that up. I understood and noticed very small amounts of narrowing at the throat in duct designs. But that picture you posted got me doubting if I ain't as smart as I thought I wuz.

Not at all very smart question. You got me thinking and your gut or intuitive observation is right. That first picture (which I shot at some airshow in the last 5 years was odd looking. Not sure it was the angle of the picture or what.

I guess instead of the too long post, I could after thinking about it boil it down to the inlet ring does narrow in the first inch but is really just a continuation of a very large radii as good practice in making any inlet.

Here is a pic of Dick Martin's RV-8 with a SJ cowl, which I meant to post;

This inlet ring looks like it has much less "camber" or narrowing than mine. My inlet is a cross between this SJ cowl supplied ring and the one I originally showed that had a pronounced bell mouth. Like I said my inlet it 4.6" dia at the mouth and 4" dia at the exit over 1.75", where most of the change is in the first inch of the curved internal surface. The back 1/3rd is almost flat.

 

[Walter Atkinson]

Chris:

Your comments are accurate--exceptany assumption that we are not working on more than the baffles! There is work being done on inlet vs. outlet design to address exactly what you are discussing. Slow-going... but going. <g>

Science carries no watch.

Walter

 

[rv969wf]

Cowling plenum mods

Hi Bob and others interested in experimenting with cooling drag reduction, I'm new to this site as of today and I wanted to share a few pictures of some mods I have done to my RV-6. I built a fiberglass lower cowl piece kinda like what you made out of aluminum. I ran across your name from James Aircraft Holy Cowl Forum the other day. I have 52 pics of some of the things that I have changed and modified with my plenum, lower cowl, oil cooler, cowl outlet and yes I'm very pleased with the end results. The link is http://groups.yahoo.com/group/JamesAircraft/
When you go to the site go to photos: find Alan Judy RV-6 cowling mods. Also you can do a search on this site under cooling problems or high cylinder head temps and read about some of the things I did with some of the results. Anyway just wanted to say I had some of the same ideas as you had. Happy flying Alan

The information about the reduction of volume in the lower cowl and devising a way to get the air directed to the outlet cleanly is very interesting and consistent with what I saw in my experiment. My first modification addressed the idea of getting the air to the outlet cleanly. Basically three surfaces: (1) a surface that starts straight down then curves back to overlap the outlet area of the lower fuselage skin (2) a verticle plane extending at and angle determined by the location of cylinder #3 from the right side of the outlet to the right side of the cowl (3) a verticle plane extending at and angle determined by the location of cylinder #4 from the left side of the outlet to the left side of the cowl. I saw a 2 kt loss in speed in a flight test.

In a subsequent experiment I further modified the system by running a baffle a little below the edge of the lower cowl from the angled baffles added in the first modification. This reduced the volume in the post cylinder area and it reduced the flow options of the air leaving the cylinder fins. The speed increased 6 kts over the first mod and 4 kts over the stock configuration. Photos and test results were added to the builder mod area of this website. These results are exactly in line with some of the information in George's post.

Today I will finish a mod to the air box that converts the top to a flat plate. No test yet of course but the results could go either way. I seems that as the flow gets cleaner the volume of air (mass) increases for greater cooling but it also produces an increase in cooling drag. Because the cooling efficiency is greater you can cut down the air mass required to flow through the system for appropriate cooling. This can be done at the inlet or outlet (I'm just at the thinking stage on this but when I have more time I plan on restricting the outlet and testing it now that I have CHT probes in all cylinders).

Bob Axsom

 

[videobobk]

Cooling mod pics

I couldn't access your photos (guess you have to be a member of the Yahoo group.) There are a bunch of us who would like to check them out since cooling mods can be so important, speed wise. Anyway you could post them here, or is there another way to access them?

Bob Kelly

 

[rv969wf]

Hi Bob, I not sure how to post the pics and everything here but if you go to

http://groups.yahoo.com/group/JamesAircraft/

Join the group and it's FREE and then you can see all the pictures and questions and responses that I wrote. Quite a bit of good information on the James Aircraft site. Alan

 

[rv969wf]

Low Cylinder Head Temps

It's been a while since this thread was looked at but someone on here was hoping to see their CHT's in the low 300F degree range. If you see this then send me an email and I'll help you with what I've done on my RV-6, it is far from stock firewall forward BTW. Here are some numbers / temps if anyone is interested.....

#1 CHT 280F / EGT 1390F
#2 CHT 278F / EGT 1374F
#3 CHT 289F / EGT 1392F
#4 CHT 278F / EGT 1394F

NOTE: These temps were colder than normal because I had the larger 4 1/4" round inlet diffuser rings and not the smaller ones installed on this flight.

Oil Temp is controlled VIA inlet door / NACA Duct / I keep Oil temps at all times 185-190F

YES these TEMPS are correct. I calibrated and tested the Mircovision Probes and guages with a $5,000+ Jofra calibrater that is certified.

The day I took these numbers were at an Ambient outside temp of 64F degrees. 5,500 Ft, 23" MAP, 2,450 RPM, indicating 186mph / true airspeed ???210 / 212 mph ????. Fuel mixture at 100F lean of peek. 4 1/4" ID diffuser inlet rings. The engine I built is an IO-360A1B6 with 10:50 comp pistons custom made, Slick mags with 22degree timing top, 20degree bottom timing / split timing, no electronic Yet.... I applied Thermal barrier coatings to many internal parts such as piston tops, cylinder combustion chambers, intake / exhaust valves, rod / main brgs, exhaust and intake ports, internal barrier coating inside the oil pan, valve covers, valve springs, external Heat dispersent coatings applied to dissipate heat on cyl / head cooling fins, insulated intake runners. Camshaft timing change, 'Techline' coating to 4into1 exhaust that I custom built. Heat is a killer!!!! What happens inside the combustion chambers needs to be kept there and spent / swept out the exhaust system. If the combustion chamber temps disperse outside through the cyl/heads then the cooling system / air flow over the cooling fins has to cool things more without the thermal barriers... That means you need more cooling air/mass etc.

Engine in my RV WAS stock then I tore it down to make changes.

I did a before and after test with the coatings and the temp changes were very impressive. Tests were done before cowling mods OK.. Later saw more temp reductions with modifying other cooling items...... Cowling is a Highly modified Barnard design, high pressure plenum is modified, cylinder tin mods, cowl outlet design change, coke bottle design / venturi and extended past firewall 6", reduction on diffuser ring inlets, lower plenum mod below cylinders. You can look at over 50+ pics on this site: http://groups.yahoo.com/group/JamesAircraft/ Join the group as its free. The group is mostly about the "HOLY COWL" / Sam James cowling / plenums. Attention to detail is the key. I normally run my CHT's in the 300F range but others might disagree, If I want to go faster I reduce my diffuser inlets down very very small and get the CHT's up in the 375-380F range and yes I pick up speed. I'm a firm believer in CHT's on the minimum with the oil temp in the green and at times but I will run the oil temp up to 220F to boil off condensate via oil air inlet door on NACA duct. Leakdown tests are always 78,79/80. Oil samples are below normal PPM. If anyone has questions feel free to ask and I'll share anything with you.

 

[gmcjetpilot]

Oh yes, I am interested

The engine I built is an IO-360A1B6 with 10:50 comp pistons custom made, Slick mags with 22degree timing top, 20degree bottom timing / split timing, no electronic Yet.... I applied Thermal barrier coatings to many internal parts such as piston tops, cylinder combustion chambers, intake / exhaust valves, rod / main brgs, exhaust and intake ports, internal barrier coating inside the oil pan, valve covers, valve springs, external Heat dispersant coatings applied to dissipate heat on cyl / head cooling fins, insulated intake runners. Camshaft timing change, 'Techline' coating to 4into1 exhaust that I custom built. Heat is a killer!!!! What happens inside the combustion chambers needs to be kept there and spent / swept out the exhaust system. If the combustion chamber temps disperse outside through the cyl/heads then the cooling system / air flow over the cooling fins has to cool things more without the thermal barriers... That means you need more cooling air/mass etc.

Alan tell me more about the coatings. Where did you have them done?

It sounds like you have two ot three types of coatings,

"Thermal barrier coatings to many internal parts such as piston tops, cylinder combustion chambers, intake / exhaust valves, rod / main brgs, exhaust and intake ports, internal barrier coating inside the oil pan, valve covers, valve springs,"

"external Heat dispersant coatings applied to dissipate heat on cyl / head cooling fins, insulated intake runners."

"'Techline' coating to 4into1 exhaust that I custom built."

Internal heat barrier? I know ECI makes some coating on rings and pistons, but not sure they are doing the same thing. Can you tell me cost and who does this coating. Is there any danger of the coating coming off? What does it do? Does it make more power or reduce wear?

The external heat dispersant? I know some people do different things like paint the jugs black an leave the heads bare. I guess gray Lyc paint is not idea for dispersing heat. Can you tell me more about this, the who, what, where and why plus cost?

I understand the idea of the exhaust coating, I assume ceramic, to keep the heat in the pipe, not spread heat under the cowl, which can affect performance, such as heat the intake air and lower the air density. I would like my 4 into 1 coated. Techline is in Texas and have heard they are the place to go. What did it cost? What coating did you choose (temp, thickness, color, inside and out I assume)?

Thanks George

 

[rv969wf]

Coatings

Hey George, give me a phone call sometime and I'll tell you the details about the coatings because I'd have to write a book here to explain everything. You asked who did the coatings?? (Your talking to him). Me.... I do all of my own coatings / work in house and for whoever is interested. AJ

 

[RV8RIVETER]

Coatings

George

I am coating my exhaust and engine as well. I am lucky enough to have a local connection.

www.cradin.com alot of info here.

He is an ex Pratt&Whittney engineer as well as "old school" A&P. Great guy to talk to as well.

 

[gmcjetpilot]

Thanks Gents

Thaks Alan and Wade,

 

[RV8RIVETER]

COOOL!

George

You are welcome. By the way, a new airpark neighbor who just moved in had is -320 coated inside and out. He said when Lycon dyno'd it it came in at 185hp (+10.5 - 1 pistons and race cam) and ran over 100deg cooler than any -320 they have ever ran.

Alan

Great pictures! And great job! You have done what I am planning, except I am thinking two piece upper plenum and will extend the lower outlet to include exhaust pumping. Did you modify the stock cowl with rings (way I am going), or did you buy the James cowl?

Thanks,

 

[rv969wf]

George

You are welcome. By the way, a new airpark neighbor who just moved in had is -320 coated inside and out. He said when Lycon dyno'd it it came in at 185hp (+10.5 - 1 pistons and race cam) and ran over 100deg cooler than any -320 they have ever ran.

Alan

Great pictures! And great job! You have done what I am planning, except I am thinking two piece upper plenum and will extend the lower outlet to include exhaust pumping. Did you modify the stock cowl with rings (way I am going), or did you buy the James cowl?

Thanks,

Hi Wade, my cowling is an earlier 1998 "Steve Barnard" Design with 3.5" prop extension and round inlets. It is far from original as I wacked and cut it up quite a lot to get the results I did. From the pictures that you saw on the "James Site" you'll see that the bottom cowl is what was changed mostly. Thanks AJ