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Engine cooling air exit tufting

bryanflood

bryanflood

Well Known Member
I keep thinking there should be a thread for builder modifications here, but maybe I am just missing it b/c I am not too familiar with the forums. Anyway, I have been working through several versions of modifications to my cooling air exit. I never believed van's solution, while simple and cost effective, was a total solution i.e. more optimization could be done for little cost with good gains in cruise speed. I would love to move to fuel injection a new exhaust and completely modified lower cowl, but I wanted a bolt on solution with a stock cowl, exhaust and carb b/c I am tight on $. I posted one of my earlier designs here and it was great in cruise (2 to 3 knots) but totally limited in climb cooling. This was not the solution I was looking for as I think reducing cooling air is a pretty obvious way to reduce drag and not practical in the real world w/o other mods.

I have posted a tufting video below of one of my later modification versions. I still have some work to do I think, but it meets many of my initial optimization goals in terms of speed and cooling. My disclaimer is that I am going to fly around with this design for a while before I suggest any numbers but I thought this might give good ideas to some others or perhaps others could suggest improvements to further optimize the design. Check out the video and let me know what you think (Still worried about that rear tuft, perhaps my angle is still too sharp).

Happy flying

Bryan

http://www.youtube.com/watch?v=QMINJXlwIV0

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Bryan,

That is a great idea. Keep us posted on what you find. With only 135 HP, I would be very interested in simple speed mods.
 
Alan Judy - you watching?

Bryan, great work. Some time ago, I posted some still pictures of tufts on the standard exit area. That, plus what I saw when I dotted the area with oil, convinced me that the area is ripe for improvement. Your video supports that very clearly.

I would really be interested to see tufting video on Alan Judy's exit on his 6. He has the most unique exit area I've seen.
 
fairing Version 3 video

I made another modification to my cooling exit area fairing. The mod from v2 to v3 was to make the rear a bit more full and remove what I thought was an angle that was too sharp by rounding the transition. Seems to be working a little better now, if I had to do it all over I would definitely make , the side walls straight for first 6 inches or so but now it's just too much trouble. So I am going to fly around for a while with it as is and evaluate it's speed and cooling performance which seems good at this point. Some people have asked for profile pictures, and I will try to get some this weekend.

Bryan

http://www.youtube.com/watch?v=CrvQeOGzJ7s

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Fantastic stuff

Hi Brian,

I saw your original video - but hadn't clicked / seen the fibreglass tray that was added as 'version 2' - now it makes more sense! The version 3 looks even better - but has generated a whole load of questions for me....

I'd like to try something similar, I feel our cowl is exit limited at the moment and clean up is a good win to help with coolling climb in particular. Can you provide a couple more bits of information - what model are you flying, NW / TW, horz/vert induction? What speed is the video shot at? How do you shoot the video - it is really stable. [ I'd like to try and do something similar and get more data points longer term ]

Then onto the modification - how is it made? A mould or just layup? Shape / design? Profile off fuse? Sizing? Does it wrap round the forward lip at all? What is the 'bump' for - Transponder aerial?

Keep the updates coming - great stuff.....

Carl
 
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Cool stuff

But I'm having trouble in visualising the fairing in V3 from the video...I am assuming the air from the firewall is going almost straight down and the bottom of the cooling scoop does not do a good job of turning the air parallel to the fuse bottom because it is too short...i.e does not extend behind the firewall.

If I remember AJ's cooling sccop is extended in such a manner (and it is narrow to make a kind of exhaust augmenter).

I wonder if it is better to extend the rear the scoop back as opposed to adding a fill-in fairing at the bottom of the fuse..Maybe tufting would show that having both measures would be an improvement?

Either way, great job and let see some pics of the fairing...If you have a nose gear (like I have) I wonder if fairing the round tubes nose gear tubes might be a benefit, assuming the fairings will fit.


Frank
 
Cooling exit area fairing mod

To answer some questions, RV-9A with a verticle induction carb on o-320, the fairing does go inside the cowling somewhat, but it's hard to do too much with the nosegear weldments in the way. The v2 part was made in a mold and then modified to v3 so I don't have a mold anymore. Then bump is for the trans antenna, which BTW is a bad place to put the antenna b/c I have trouble sometimes with reception when flying to a station at lower altitude. It seems successful so far in terms of no adverse effect on cooling, still need to verify speed with some runs. The idea is a bolt-on performance increase so I need to do some more testing to see if it's worthwhile. If I had to start over there are some definite changes I would make but I kind of got locked into a cetain foot print by the original mold.

Here is a picture of v1, which I didn't tuft. I do however believe there was at least a 1 knot performance gain if not more, possibly 2 knots. For various reasons it is really hard to verify speed increases so I try to be conservative. The problem however is that climb cooling was not good. Cruise cooling was fine. There was also a couple versions between v1 and v2, of which I did not take pictures. Possibly the speed increase of v1 came from reducing cooling airflow, so I want to be carefull about any speed promises I make on v3, although I am hopefull there willl be a gain.



Here is a picture of v3, guess I forgot to take a picture of v2. The main difference from v2 is in the angle and fullness of the rear section. v2 had a skinny rear section similar to v1.






Bryan
 
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Interesting Video

Bryan, how did you get that video
Is that actual in-flight or on the gournd.

Cool
 
exit air tufting

All the videos are in flight shot from the back of the nosegear, used a fiberglass mount that slips over the back of the wheel pant. The differences in the tuft patterns between climb and aprox. 160 knots true seem really minimal, I'm guessing b/c the area is so turbulent in general.

Bryan
 
Interesting

I think your fairing Bryan implies that the exit air is coming out at about 45 degrees to the bottom of the fuse.

I wonder if that angle will be reduced by extending the bottom edge backwards and maybe evn a curved fairing on the bottom edge of the firewall extending Northwards..Probably impossible to do with a nose gear.

An interesting data point for sure.

Frank
 
Great testing Bryan

Have you noticed heating effects on the fiberglass of your new fairing from the exhaust pipes?

Kent
 
Cooling exit area fairing

As you can see in version 1 the exhaust actually charred the fiberglass a little bit. In version 1.5 I modified the version 1 fairing to decrease angle of the exit and made both exits a bit wider. I also covered the exits in stainless to avoid the buring problem b/c the exhaust was so close. In version 2 the middle section from version 1.5 was removed completely making only 1 exit. At the time I didn't have any more stainless and the new exit angle moved the glass much futher away from the exhaust pipe so I just tried it w/o the stainless covers. Turns out the stainless seems not to be needed anymore. I have est. 4+ hours flight time on the new fairing and there are no signs of any charring of the glass. Of course once again, as I have said before, I need to fly around more before I make any promises, but I'm guessing it will not be an issue. The fairing glass is generally now further away from the exhaust pipe than the glass in the cowl and the exhaust gases themselves are not exiting the exhaust pipe and acting as directly on the glass as before. In fact I am defitinely tempted to cut my exhaust pipes parallel to the airflow but I haven't yet, mostly b/c I have mixed feelings about doing so.

Bryan
 
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exhaust pipes

I cut my exhaust pipes back a bit so the pipes wouldn't hang out in the wind and to get some "thrust" by having them exhaust back. I noticed about 1-2mph gain in speed. However, there was more vibration in the flooring and I had a lot more soot to clean off the belly than before. I like your fairing and will be curious to see if it gains you any speed. I would suspect that if the flow is not turbulant coming out of the cowling exit and the air stays attached, then cooling drag should be reduced and temps should come down. I am planning a mod on my RV-6 to cut out the 90 degree bend on the firewall and but something like the RV-8 has to smooth out the air coming out of the cowling. I will have to fab up something to go over the bottom engine mount tube. I take it if your fairing works out then you will make a mold and be selling fairings to the rest of us!:)
 
exit mod.

Found something on the Lancair site, regarding cutting off the exh. to make a more direct aft exit to the pipe. two pieces of stainless were welded to each side of the last 3in of pipe and joined by a cap between the two ---__--- invert this and put a circle in the center which is the pipe. This eliminated the exh. stain on the belly and the vibration in the floor. Worth a try.
Walt RV-6
IO-320 CS finishing up
 
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Bryan,

How's the testing coming?

Did this mod change your CHT's and oil temps any?

I was also wondering if you continued the fiber glass inside the cowling to help guide the exit air over the lip on the bottom of the firewall?
 
N941WR said:
Bryan,

How's the testing coming?

Did this mod change your CHT's and oil temps any?

I was also wondering if you continued the fiber glass inside the cowling to help guide the exit air over the lip on the bottom of the firewall?
Click to expand...

Bryan,

Any updates?
 
N941WR said:
Simpler speed mod... Dump the climb prop for a cruise prop.
Click to expand...

Not necesarily so. More rpms mean more hp for the same MP. If a prop is effiecient at higher rpms it wil go faster.
My climp prop is my race prop, Faster than my cruise prop @ compairable altitudes altho with higher rpms.
 
Good work.

Very interesting Brian. After an oil change, my RV-10 blew a little oil out the breather and onto my belly pod. The oil clearly showed that the boundary layer was a good couple inches thick along the belly... clearly a very draggy area. Examining the boundary layer downstream of your fairing might be useful in tweaking your design. Good luck!
 
Get ziggy with it

You might experiment with ziz-zag tape or small VGs just ahead of the separated area. With a little more energy, the flow might stay attached along that section.
 
Have you guys seen this by Larry Vetterman?

http://www.vansairforce.net/vetterman/subcowl_2.pdf

sdkhf.jpg
 
Robert would you know...

is the metal used around the exhaust pipes aluminum or stainless steel?

This look like a great mode.

Kent
 
Big Changes

rscott5559A said:
Have you guys seen this by Larry Vetterman?

http://www.vansairforce.net/vetterman/subcowl_2.pdf

sdkhf.jpg
Click to expand...

Did you notice the changes Larry made on this. He lost the louvers on the sides and ran the exhaust through the holes for that. Then he added
the center louver and closed the old exhaust holes. Putty time.
Looks faster and I hope Larry posts it with his oil and cht temps.

Maybe Larry will see this.
Boomer
 
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