Forming aluminum for a cooling outlet fairing

[johnny stick]

Bob, thanks for presenting your results to date in a chart form, this is good stuff.

[Bob Axsom]

Originally Posted by Kevin Horton

Bob,

Have you ever tested the exact same configuration multiple times on different days to see how much scatter there is in the results?

I'm betting you would find a kt or two of scatter, which means that perhaps you need more than one test point on one flight to decide whether a change has given a small speed increase or not.

Why not fly a couple more tests on different days with your current configuration?

Any credible test program would need that. I want to try to see what I can get out of this strictly for the speed of this airplane so I am motivated a little differently. Test 14 in this series was a little disappointing - I am starting to visualize a combination of forces at play and I thought the relief of the cutouts in the cover would have a greater positive effect than I saw.



With the test rsults sorted by speed I think I have a better direction for the next step:



Here are some things I think are true from the test results so far:

The bump is better than no bump
Restriction in the outlet path can slow the plane down

There are a lot more things that I suspect but I do not know so I will just stew on those as I proceed. I am going to go back to test configuration #10 and re-fly that. I can rationalize that it is the best configuration tested so far just by direct observation but even with a test method error margin of 2kts it is still well within the top group tested.

Test configuration 7 and the related long cover configuration that was not tested but appeared to perform well but was shattered are also on my mind. I am not convinced that the long tail bump is better than the symetrical bump and I am not convinced that there is nothing to be gained from some form of cover - yet.

For now I'll re-fly test configuration #10 which I hope will not disappoint me. If test #10 results are validated I can focus on optimizing that configuration for a while.

Bob Axsom

[johnny stick]

the difference between runs 4 and 6 are significant and probably outside of the margin of error. I think here is a clue. By looking at the data, maybe the long rectangular fences and/or long cover is bringing the cowling air too far into the high pressure area from the wings. I am also wondering if the outside edges are seeing up flow from the wings or a slow down of the air on the underside due to influence of the wings. The air in the outlet area may not be going straight back along the fuse, but rather have an outward component; maybe the outside fences are catching this and that is why the rectangular are slower. maybe maybe maybe??

[johnny stick]

Why not try flow fences along the fuselage left and right sides just ahead of the leading edge maybe extending down the wing a little bit? Isn't this similar to the triangle fins but slightly more outboard?

[Bob Axsom]

I just got things cleaned up here at home and I heading to the airport to reconfigure to test #10 and see if that high number holds up in a re-fly.

Bob Axsom

[Bob Axsom]

I flew test case 10 again and the speed dropped off to 179.3 kts TAS. Then I reinstalled the vented cover and reflew test case #14 as suggested by Kevin Horton. It did not hold up either - 178.3 kts TAS. The hierachy is the same but the separation is reduced:





More thought required.

Bob Axsom

[Bob Axsom]

1 - Tests 15 and 16 show in the current form the uncovered version is still faster than the covered version even though there was a 2.8 kt drop in speed from the earlier uncovered test 10 and only a 1.5 kt drop from the repeated covered test 14.

2 - Tests 8 through 16 do not clearly demonstrate that the long tail bump is faster that the equal tail bump. A replacement for the operationally destroyed equal tail bump needs to be made and tested further.

3 - The results from test 13 are are very little different from those of test 15 (-0.2 kt) so the percieved ineffectiveness of the small triangular fins when compared with the results of test 10 may not be valid even though it is still slower.

4 - Tests 10 and 15 were flown with the aluminum angle and all the open platenuts for mounting the cover exposed to the open air. If new fins were made for this "no cover" version without cover mounting provisions would it be measurably faster?

5 - Test 13 seems to indicate that the outboard flow fences have to be taller than the bump by some amount for the bumps to be effective.

6 - Is the center fin necessary or does it add drag with no benefit?

7 - All tests have been with a 2" high bump, would a shorter bump be better?

First, I think I will answer the questions in thoughts 4 and 6. This could be done by making similar shaped fins from 0.032 aluminum, assemble, fly a test then mark and cut away the exposed portion of the center fin and fly another test. Gross differences in performance should be revealed. I may be able to do that today.

Bob Axsom

[kentb]

This most likely will not help you, but....
In looking at your speed sorted chart and dividing into good speeds and not so good speeds (I chose 180 as the break point). The only thing that can be eliminated is the "extended short cover". All other parts of the configuration appear both above and below the dividing line.
I believe that what you are seeing is the changes interact with each other and it will be hard to deduce the correct parts to use.
The only only hope will be to continue to try all the combination that you can think of and see which you like the best (fastest of course).

Good luck. I love you efforts and reports.

Kent

[RVbySDI]

Originally Posted by Bob Axsom

With the test rsults sorted by speed I think I have a better direction for the next step:

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

[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