Forming aluminum for a cooling outlet fairing

[kentb]

Originally Posted by Bob Axsom

It has been apparent to me over the last few days that I am not dealing with a single variable even when I change only one variable. I agree with your observations and conclusion.

All I got done yesterday was pull the parts off to replace the three vertical elements. Will try to do more today. I am trying to force myself to exercise properly for my health. I have been working until 3 am many nights until I was too tired to exercise so yesterday I switched priorities and you can imagine the result.

I also deleted some of the obsolete tables from photobucket and learned not to do that again. It effects the thread here in a couple of ways. The images are linked and not really resident here so when they are deleted from there they are deleted from here also. There is usually a notice posted here so there is some awareness. However, I found one image that was not in this thread before so at least under some conditions the link can be associated with the wrong image. In the case I saw it was a different subject all together (a magazine cover) but some different image re-links could go undetected and provide incorrect information. I will not do that again. Well it's afternoon and I haven't exercised so I had better get at it or I will not get the change for retest done today either.

Bob Axsom

And I don't be the flight testing. We all need to take care of our bodies, which means our minds too. A rested and health test pilot will always collect the best information.
Rest, exercise and have a good meal. Than go back to doing flight testing.

Kent

[Bob Axsom]

Originally Posted by RVbySDI

Bob,
I am getting an error message on your images stating they have been moved. Any thing you can look into?

I have all of the images and can supply them to you. I guess I owe it to everyone to go through the thread and put the images back in or insert the updated table. I have the excel files but in order to get them presented here properly I have to print then, scan them, move them to the desk top, import them to iphoto, edit them by cropping to the proper size (the size of the table), upload to to photobucket, copy and paste as an image here. Maybe I will just do that for each table configuration that was in the thread - it is kind of important to the continuity of it all. That will be tonight's task. Jeanine always said I have OCD.

Bob Axsom

[LarryT]

Bob,

I truly applaud all the work you are doing. We will all benefit.

While I know part of the enjoyment of this excercise is getting to fly the plane, you've burned a lot of AvGas flying straight and level very carefully.

Do you think it would help to tuft the airframe and video it in flight? There are enough interactive variables that a person more skilled than I (i.e., you) might spot trends.

During testing your speed differentials have been on the order of 1 - 2%, which are pretty difficult to attribute solely to airframe modifications since variations in temperature, pressure and humidity are wider than that.

Larry Tompkins
544WB -6A
W52 Battle Ground WA

[Bob Axsom]

We all have our ways and many work. My way is to go for the objective directly. When the outlet configuration allows the plane to go faster the plane will be faster regardless of the way it came to be. I just can't use the camera and yarn approach to in hopes that when the tufts align with the flight path that is proof that all of the physical variables of the outlet are optimized. It just can't be true that there is only one configuration that will yield straight after outlet flow and that configuration is also the fastest configuration. The speed is ALL I care about.

I guess I am committed to go back and try to fix my problem with the posted images now - that pains me.

Bob Axsom

[Bob Axsom]

I went through all 31 pages and could only find post 299 on page 30 and post 302 on page 31 in this obvious category.

Bob Axsom

[rvmills]

Bob,

Been watching this each night as I toil away at the other end of my cowling. Haven't posted in this thread in a bit, but lots of interesting things going on.

I'm glad you are re-testing various configurations and doing multiple comparative tests. With the numbers so close, its hard to tell whether results are in the scatter and noise, or if you are seeing real delta v. That's the hardest thing to determine in our speed mod testing, eh!

I queried a while back on how committed you are to the long fences, because I have the forms for Gary Reed's original outlet mod design (this one):


The feeling I got from the last time we corresponded on it was that the large fences are a bit too permanent to swap out for something like Gary's design. However, if you can make the swap more easily than I understood it before, with Gary's permission, I can send you his templates to work with and send back. (I won't have the time to work exit shape this season (well, if I want to fly this year!). I also want to test the new Ram Air set-up first, which (as you know) I've been working to blend into my current cowl exit shape. Putting glass on the form tomorrow...here's the current look:


Between the ram-to-cowl blend and the spinner gap fill I've got a pretty complex layup ahead of me (old spinner was 12" and had a 1.5" wide backplate...new Van's spinner is 13" and has the narrow backplate...result, BIG gap to fill).

To keep this on topic, after I test and fly this configuration for this season, I want to go back and mod the exit. As you can see, my tunnel diverges laterally...my guess is that is not a good thing. Looks cool, but probably not conducive to acceleration and alignment of the exit air. I'd like to change the shape to make the tunnel sides parallel to the longitudinal axis, and decrease the cavernous volume it currently has. With the new ram air having a round shape, it's started me thinking about a 6 into 1 exhaust, and keeping that round shape moving aft to the exit, much like Dan's smallest exit. Different to a degree because I have no exit ramp like the 8, but along those lines. If I stay with 6 into 2, I'd have to figure out how to decrease the cross section and deal with the two pipes. Channeling flow aft of the firewall would be step 2 for me (my thinking at this point anyhoo.)

That last part is the other suggestion I thought I'd make to you, though its a departure from your current path. Ken and Dan have had success by reducing the volume of the exit tunnel (Dan with a variable insert, Ken with a smaller cross-section exit and a cowl flap). But both those guys seem to have pinched the flow forward of the firewall (at least to a degree).

Have you given any thought to reducing the size of the cowl tunnel? I know the NG leg slot makes it harder, but that might be where some more acceleration potential of exit air is hiding.

Just some thoughts...really admire your rigor in all of this, and the multiple tests will be interesting to watch for data. I feel like I should throw some Avgas $$ your way, since you are testing a bunch of stuff for all of us!

Good luck on the testing ahead!

Cheers,
Bob

[Bob Axsom]

Yes I have thought of pinching the flow forward of the firewall and made several mods and tested only to find they slowed the plane down. the only thing that worked was the curved surface extending from the bottom rear of the engine to the bottom of the fuselage, side wedge planes that reduce the width of the outlet flow from full cowl to the ~14" wide outlet opening, and the horizontal plates closing off the the lower cowl outboard of the baffle and valve covers just below the cowl split line. This combination yielded the largest single speed gain of any mod I have made to the airplane - 4kts. Nothing else including something that looked like a rectangular venturi was anything but negative (many aluminum and rubber assemblies offered to the god of speed to no avail). I am completely against any further work inside the cowl. I think I have very close to the best possible combination in there.

I do not feel the same way about the exit itself and I am a long way from exhausting the possibilities. The problem is I cannot conceive an idea with supporting rational and immediately test it. Each variation has to be fabricated, materials have to be purchased and shipped, implementation details like mounting have to be worked out, the work has to be done, the test flown using exactly the same test method as previous tests, the raw data post processed, the results studied, compared with other test results and recorded for the evolving effort. Judgement, aversion to wasted effort and laziness do effect my progress - imagination is not a problem. If I merely copy mindlessly there would be little motivation for me to do the work - think of a prospector and a ditch digger. This little paragraph describes some realities I have to deal with in my mental, physical, time and life process.

Reducing the exit cross section in the outlet flow path - This has been accomplished by the two 2" bumps between the flow fences on the bottom of the fuselage and the cover. The evidence is provided by the increased cylinder head temperatures. Is the 2" height too much? I suspect it is. This was an arbitrary size triggered as a starting point by Mark Frederick's comment about cutting the size in half earlier in this thread. The installation of these bumps is quite complex and that is a hinderance to finding the right size. Since this may be turning into a long term effort I may have to stop and come up with a different installation method. The RTV is also a significant problem. It has been pointed out that it is not structural but you wouldn't think so if you had to clean it off. I have some ideas.

Turning the outlet flow with the shape of the bump - This may be the most important part of the whole experiment. Most of the testing has been with the one 2" high long tail shape and the most successful configuration is without a cover. I suspect that the long tail eliminates the turning force too early in the flow and the tested and raced once equal tailed bump may be better. I need to test it more.

The sun is coming up and I need to get work done today and I need more sleep so I will stop this post.

Bob Axsom

[rvmills]

Hi back atcha Bob! All that you said with respect to experimenting and testing makes sense. I've considered how to work with my current exit shape to see if I can find improvements, and still may do some of the followng:

1. Because my exit bottom is large and raked forward (the aft edge of the cowl tunnel is not vertical...the lower edge is forward of the firewall, giving me about 85 sq in of exit...cavernous), Tom Martin told me to first extend the skin (with sheet AL) back to the pipes and see what the result was. Easy first step.

2. Then I could start filling in the cavern from the bottom up to see if acceleraton of the air and more speed results (foam or whatever...gotta think on that, as I don't want to create a fire hazard).

3. Then I could add fences and/or a Vetterman-like after-body to check the results.

All that sounds good, but my lower cowl tunnel is so low, that the more I think about it, the more I think I need to just bite the bullet and reduce the area by cutting the aft cowl and re-shaping it. Dan's switch-able set-up is attractive, because it allows one to go bigger if you find cooling inadequate.

Recently a smart aero guy whispered in my ear that reducing the stock -6 exit to about 1/2 the normal area, and adding a cowl flap for climb may be as effective as all the fence/afterbody work.

Not sure how one would accomplish this is a -6A (with the nose strut and slot), but what I was getting at above and am referring to here is that you might find more benefit from taking the plunge and reducing the outer cowl tunnel dimensions, instead of just filling the inside. Inside shape will remain important, but reducing the outer shape will give you convergence and reduced frontal area all at once. Its a large commitment though...and one I'm wrestling with hard right now!

Just more thoughts...looking forward to your continued work Bob! Having fun following along, and scheming with you!

Cheers,
Bob

[F1Boss]

If the nose strut is in the way for proper outlet placement, or function, why not move the outlet?

Statement overheard at Reno:
"I've never seen an idea so good that I couldn't copy it!"

Look where Lancair put the outlets on the go-fast Legacy. There is science behind that placement (on the bottom, near the outer corner) - might as well give it a shot! Might take some exh system re-configuring? Won't work on the skinny tandem airframes...

Using Dan's idea of a replaceable outlet section, it would be easy to experiment. Are ya listenin', Super Bob?

Carry on!
Mark

[gereed75]

Bob, I see now how your non-standard exit changes from the standard.

By all means, forward my prototype to where ever it might do the most good (or harm!?!?). I remain convinced that just streamlining the exit air has significant benefit, both for cooling efficiency and drag reduction.

Right now I am kinda freezing my design. I have some ideas about where to go, but I am wondering about the benefit at this point. It seems that I am stuck on a plateau.

Multiple 3 leg NTPS speed runs without configuration changes on different days with the same method yield results +/- 1.5 knots.

I recently closed my elevator ends with no apparent speed increase (maybe a decrease). I kind of wonder if 180 - 181 KTAS at 6000 DA corrected for temps is as fast as my stock IO 360 can make my particular -6 go?????

Waiting for my first SARL opportunity (Indy) to see what happens.