Engine cooling air exit tufting

bryanflood · #1 06-22-2008, 03:52 PM

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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N941WR · #2 06-22-2008, 05:46 PM

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.

AlexPeterson · #3 06-22-2008, 08:23 PM

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.

bryanflood · #4 07-04-2008, 10:49 AM

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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zkvii · #5 07-04-2008, 02:36 PM

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

frankh · #6 07-04-2008, 04:45 PM

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

bryanflood · #7 07-05-2008, 10:15 AM

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

TGRV7 · #8 07-05-2008, 11:01 AM

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

Cool

bryanflood · #9 07-06-2008, 08:32 AM

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

frankh · #10 07-06-2008, 11:31 AM

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