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Forming aluminum for a cooling outlet fairing

Getting better focused

Today went well. The hardest part of some of these mods is the implementation details while preserving the quality of the airplane. It is so frustrating to do rough work to test a concept with things that are crude and it is a double edged sword ... Ah well. I've been fighting some infection with 300 Mg Clindamycin for the last week and today is the first one that I feel like I am good. Consequently I am better organized and patient with this one and it is going to look good and be a good installation even if it doesn't work and that makes me feel good.

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Bob Axsom
 
Just got home from the airport - good 12 hr day

It is amazing how little I got done but I'm using platenuts and screws To put this version together. I only had 8 single ear platenuts in my stash so ordered the total requirement (12) in regular, miniature and floating for 36 to cover any complications with next day air delivery. The next race is Saturday and this is Wednesday (well technically it's Thursday). Parts $24 shipping $35 There is no way everything is going to come together before the race. I'm still carrying the bug gut load from Texoma but washing is going to have to wait again. What I have together so far looks great.

Bob Axsom
 
It will not be on the plane at Terrell, TX tomorrow

The support structure is done to a first cut stage but it needs more time to finish than I have before the race in Terrell, TX tomorrow. Going to have to put the plane back together, fly there, run the race to stay in the point hunt and come home to finish it before the race at Carbondale on 6-9-12.

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Bob Axsom
 
Spent 5 hours on it today 5-28-12

The right panel (bump?) skin is fitted and trial installed except for the trailing edge. I should work that out tomorrow.

Bob Axsom
 
5-30-12 The Big Muddy is only 10 days from now!

Obviously I did the right thing not trying to cram this in before the race at Terrell, TX last Saturday. I will have it done before the Big Muddy race at Carbondale, Illinois a week from Saturday. As far as the bumps are concerned they are essentially done except for securing the tail end. I will have to use some RTV which I did not want to do but I have some side gaps so I got to plug'm. I was successful in making the panels and support beams removable with a screw driver - it's more experimenter friendly that way - and no additional holes were added to the airframe.

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The little stainless steel part is one of two that I will finish tomorrow to secure the trailing edge of the panels.

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They are unique for each panel to match the interface. The relief cutout in the trailing edges provides a path for the outlet air from cowl zone 3 - oil cooler, blast tubes (when not blocked for racing), etc.

I plan to fly the first test using the cover with the exhaust cutouts. I haven't decided yet but I am thinking of enlarging the cutouts to match the exhaust pattern deposited on the inside during previous tests.

I hope for a knot out of this but expect nothing.

Bob Axsom
 
6-1-12 ready to fly but ceiling limited

When I used to drive up the 405 to LAX this was a common visual treat:

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So why on this day was it in Fayetteville, Arkansas? Walmart shareholder's meeting perhaps ...

Anyway, as you can see 6,000 ft density altitude VFR for speed testing wasn't possible. Maybe tomorrow. I did enlarge the cutouts in the cover.

IMG_5983.jpg

IMG_5984.jpg


Bob Axsom
 
6-2-12 Flew two speed test same configuration

After flight photo (no shattered panels)

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Results in test order:

T1to23.jpg


Sorted by speed and ranked:

rankedT1to23.jpg


These are encouraging. I will probably fly this configuration at Carbondale, IL in the Big Muddy Air Race since it is fairly fast and I have so much cleanup to do to get ready. But all the fence and cover configurations need to be tested with these bumps. The two test results were only 0.6 kts apart even though it was bumpy and I could not meet the USAR Handicap procedure requirement of no deviation of more than 1 kt in a series of five samples 20 seconds apart. At 180.6 and 180.0 kts They rank 6th and 9th in the series of 23 tests. My gut feel is this configuration of bump is worth more study.

Bob Axsom

P.S. The Goodyear blimp is still at Drake Field - they must be giving VIP Walmart shareholders rides. I asked if the Goodyear blimp is the one I used to drive by on the 405 on my way to LAX and the pilot responded "No that one is still there, this one is based at Akron, Ohio."

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BA
 
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Comparison To Old Cessna 180

Just to compare the exit areas to what my 1955 Cessna 180 has, here are some photos. The 180 has cowl flaps which are VERY effective both for cooling and for speed.

Here's the inlet area. Pretty large, eh? Also notice the diverging duct to the large air filter. Somewhat spoiled by the edge of the lower lip, though.

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Here's the cowl flaps open:

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And again from the side:

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Here's the cowl flaps closed. Note the relatively small exit area and the position and length of the exhaust pipe:

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Here's what they look like inside the cowl. Note that the sides are effective even when the flaps are closed, to channel the air into the exit:

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As you can see from the cracks and doublers, there's a lot of vibration down there. For reference, this airplane has about 3,600 hours TT.

Dave
 
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I can see drifting that way

I have thought of cowl flaps of course and have discussed them with the likes of Tom Martin but I don't want to go there yet. The NLG structure and FAB requirements have to be considered. One option that might work is to retain the side view profile for ground operation and climb the pull the trailing edge up toward the fuselage to reduce the opening to limit the cooling air mass flow. I have approached that configuration with the long unvented cover and the two inch bump. The temperatures went up as I would expect but also under cylinder #2 the aluminized cover for the heat barrier was destroyed by heat from the exhaust I just patched that last night with a new piece of heat barrier - this is all that expensive $79 a package stuff from Aircraft Spruce. It is really good stuff but even it has its limits and I have to be careful. I don't know exactly what outlet configuration I need to optimize this for speed and safety - I am trying not to be too conservative but at the same time paying attention to what the airplane is telling me. The exhaust pipes are very close to the new forward shifted bumps that may cause me some problems as well - I may have to re-rig that whole tail pipe suspension system and that requires a lot of intricate work with my lower cowl baffling going right through it. I sound defensive I'm sure but I really appreciate your input and the real world example of what works for you on that airplane.

Bob Axsom
 
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6-5-12 Test Without Cover

I removed the cover and reran the test twice with the new bump which is a continuation of the baffle between the engine and the bottom of the firewall.

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The speeds of the two tests were 181.8 and 181.7 kts respectively and both are faster than the two tests of the same bump with a cover with large exhaust cutouts.

All tests in the order conducted:
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All tests sorted by speed and ranked fastest to slowest:
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Bob Axsom
 
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You got it

Bob,
It looks like you have acheived success. Good job and great perserverance. A few more tweaks and you could be well over the 185 mark.
 
I have a good feeling about it as well

When I flew the test yesterday three normal race prep items were not done so the results could have been a fraction of a knot higher. The other parameters I noted: RPM 2720, CHT 1=362, 2=373, 3=366, 4=inop, EGT 4=1299.

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At least superficially it appears that the new bump is the best so far and that covers are worse than no covers. The flow fence info is not as clear. The best speeds so far are the thick flow fences with the vertically tapered aft end with all the cover mount hardware attached.

Bob Axsom
 
Bad Luck Day

Pulling the plane out for the test flight I heard a strange noise from the Right MLG. Looking closely the inboard side of the rear half of the subfairing was rubbing the tire and a large chunk was missing.

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I removed the subfairings from both main landing gear and flew the test but even though I previously stated I couldn't measure any benefit from them, it is not a directly comparable test. The speeds were slower at 180.8 and 179.9 respectively. I am going to have to go back to the modeling clay stage to get this rebuilt for the race in Washington on the 16th. I'm going to have to go without them in Carbondale, IL this Saturday (6-9-12). It will be a while before this test is ready to repeat.
 
6-10-12 status

The speed was good in the Big Muddy Air Race at Carbondale on 6-9-12 at just under 211 mph without the subfairings on the MLG, not tape, tiedown rings left in by oversight and not quite perfect flying so I think this outlet configuration is going to be a winner. I just got back from the hangar where I applied the first layer of fiberglass on the fairing, clay and tire. I use 24 hour cure EZ Poxy resin so this will take three or four days to complete through paint. and I have to fly to Ephrata, Washington for the Great Northwest Air Race III on Saturday so there is a good chance the test will be after I get home - we will see.

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Round mold tire in route from Aircraft Spruce.

Bob Axsom
 
6-21-12 Status

The new mod has still not been tested. I flew from northwest Arkansas to Ephrata, Washington, then flew in the Great Northwest Air Race III and returned home. It needs the oil changed and a modification to the panel on the left side. The race speed at Ephrata was 216+ mph which is my best so far this year but that is with my best effort to work the wind and doesn't necessarily mean anything with respect to the top speed of the airplane.

Texoma 208.14
Taylor 208.84
Hill Country 212.86
BCAF 212.18
Terrell 206.28
Big Muddy 210.98
GNAR III 216.05

Yesterday the oil and filter arrived from Aircraft Spruce and I removed the cowl to start the oil change and mod examination. The left panel made of 0.016" 2024-T3 has been cut by the trailing edge of the exhaust pipe. The possibility of failure of the panel at this point was not unexpected because of the closeness of the exhaust pipe and the thinness of the aluminum panel. The cut is a very straight line conforming to the edge of the exhaust pipe approximately 3/4" long and 1/32" wide. The operating time was a little over 20 hours. Closer examination revealed cracks in the panel starting at the cut and progressing forward toward the front of the plane in an irregular pattern. The nature of the cracks appears to me to be exactly the same as the failed panels observed after the completion of the Hill Country race but they are isolated to the area directly aligned with the side of the exhaust pipe. No cracks extend from the rear of the cut in the panel. I may replace the panel with one made of stainless steel or I may put in a bump strip of stainless steel or I may re-rig the exhaust pipe suspension (not an easy job with all the baffling I have in the lower cowl).

Bob Axsom
 
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Damaged panel removed and cleaned up

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There are cracks on on both sides of the exhaust pipe cut. I plan to replace the easily replaceable panel with one made of 0.016 stainless steel and currently I'm thinking an extension link in the exhaust suspension.

Interesting critter on my rear window (it is about 6" long):

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Bob Axsom
 
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Little interuption in the experiment work

Observed a crack in the FAB mounting plate when I removed the cowl for the oil change.
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When I took that off I noticed a cracked rivet head by one of the platenut installations on the FAB mounting flange. When I tried to drill the rivet the whole installation fell off in my hand.

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As I worked that salvage with a ring doubler I noticed a tiny crack about 1/4" long at each end of the FAB metal top at each end of the slight bend about 4" back from the front.

My fix for all of this was to drill out all of the rivets holding the fiberglass bowl to the top plate install a ring doubler on the inside with a spacer plate where the piece had broken out. Stop drill the cracks, debur the holes and add doublers across the end of the bend area.

IMG_6082.jpg


I also have to replace a vacuum hose (ordered Saturday) so the long awaited test of the new "bump" with the triangular fins probably will not happen before Thursday

Bob Axsom
 
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All in a days work. good catch to find it before complete failure.

I wish I had found my loose exhaust hanger BEFORE failure. I'm waiting for the return parts to be here...maybe tomorrow. But I did fix some other stuff the popped up.
 
Fabricated the stainless steel replacement panel today

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This panel is made of 0.016" stainless steel to replace the 0.016 aluminum panel that was damaged by the exhaust pipe. The final fitting and trimming has been completed.

Bob Axsom
 
Mornin' Bob,

Good to see another senior citizen at work all hours of the day and night. :)

It's gettin' so hot around here, sure its the same story where you live, the only time to get anything done is early in the day. We're expecting 108F this afternoon.

I enjoy following this thread.

Exhaust systems need attention. Long time ago, I had a failure with a pusher that took out the prop, that was an interesting day.
 
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I got everything together today in time to fly a test

I actually flew two tests in this configuration earlier but without the MLG subfairings on June 7, 2012 the speeds were 180.8 kts and 179.9 kts. Today I had the sub fairings on the MLG and the speed for the one test I was able to get in before dark was 181.2. The surface winds were calm and according to the NTPS spread sheet they were only 7.4 kts at 6,000 dalt. I made the three leg run just before dark and I had to get back fast to be legal with no lights but I think the results are good. The first two legs met the USAR handicap procedure requirements of no variation of more than one kt in 5 consecutive 20 sec. interval readings but the last leg did not:

000 - 188, 189, 189, 188, 189
120 - 177, 177, 178, 177, 177
240 - 177, 179, 178, 176, 178

NTPS KTAS = 181.2, Wind = 178.2 deg. 7.4 kts

Normally I would fly until it stabilized with nice calm conditions like I experienced tonight but I was out of daylight and I need some numbers so I took what I got.

This doesn't seem like a bad configuration but there are some things to look at and think about before trying something different.

I'm down to a can of corn, sauerkraut and crescent rolls so I have to take a break and go to my neighborhood Walmart Super Center and get some groceries while I think about this. If I go in there after midnight there is some subtle hostility from the shelf restocking crews so I try to avoid doing that. More later.

Bob Axsom

P.S. It was around 100F here today and the highest CHT (#2) was 384.
 
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Configurations tested

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I am working on a summary of the testing so far and in the process I made up these combination tables. There are 144 configurations of the three main variables in my testing so far. The tables show the combinations, the ones that have been tested and the number of times they have been tested. Just interim information.

Bob Axsom
 
Relative Speed in Tests

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The numbers in the cells are the relative speeds in the 28 tests. The current firewall baffle continuation bump matrix represents 7 tests. 5 are in the "No cover" column and all would be in the top 10 test speeds if the MLG sub fairings had been installed in 2 of the tests where they were removed for repair.

The number 1 speed in the 2" long tail bump test I consider invalid because a repeat test of the same configuration yielded the #18 speed.

I think the matrices for no bump and 2" long tail bump show they are inferior.

That leaves the 2" equal tail bump that had the #3 test speed and performed well in the race at Llano, TX but was found shattered after the race.

All of this leads me to believe that the firewall baffle continuation bump is the right way to go but it needs to be higher - perhaps 2". Tests of similar configurations show an increase of CHT which I relate to reduced cooling air mass flow.

More work to do.

Bob Axsom
 
4 days until I leave for the race at Three Forks, MT

The upcoming race demands preparation that supersedes development so I have to pick a race configuration and hold off of the bump change for now. The experience I have with the thin triangular fences/fins is that they are slower that the thicker ones that taper on the aft portion only and this is true even with all of the open platenuts hanging in the breeze. So I am going to switch to those. I have the 0.090 material at the hangar and I could duplicate the thick fins without the platenuts if all goes well. I have not tested this bump with the long cover - perhaps I could squeeze that in before I go. I don't expect it to be faster but for completeness I would like to do it. I added a layer of fiberglass (4th) to the repaired RMLG subfairing yesterday and tonight I put on a coat of epoxy resin and microballoon fill. I still need to sand that and paint it so whatever the testing I do will not happen until Monday or Tuesday.

Bob Axsom
 
when is your planned arrival at Three Forks? I'll come meet you.

I got my exhaust back and installed yesterday, finishing up my intake boot rework and making some injection adjustments tomorrow. I hope to test everything monday night or tuesday morning. then finish race prep thursday.
 
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No flight plan yet

Thanks Brian. I would guess 2 to 3 pm local on Thursday but I haven't planned the flight yet - just a guess based on the flight to Ephrata earlier.

Bob Axsom
 
I'm pretty sure you'll be the first one here is you come in on Thursday. I'll let Cody know and make sure the courtesy car is available for you.

BTW, got Aurora put back together tonight, made some AFP injection adjustments and the new intake boot is much better. Probably won't see any speed change, but I'll do a test tomorrow, maybe prerun the course, too.

oh and then this view from our porch a few minutes ago. Fire started an hour ago in the fooothills west of turn 7, burning towards turn 8 pushed by 40mph winds. rain may be coming behind it though
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BATMAN

After a few days to apply another layer of fiberglass the the right MLG subfairing, fill it and paint it I finally got back to the outlet fairing work. As an elementary school student one of my comic book heros was Batman. In the mid 60s a popular song that Jeanine and I danced to was the Batman theme (listen to the Ventures version to get an idea). So, when I made this latest cover mod I had a feeling that destiny was being played out before my eyes.

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The thought was, at the angle of attack of the airplane in flight any squared off surface perpendicular to the flight path is going to have a broad turbulent flow coming off of it and if these kinds of surfaces were brought to points like a "V" there would be less drag.

At 19:53 CDT I was ready to test the batman cover. Both runs were near identical:

180.5 kts
180.8 kts

Good but no cigar. The no cover tests with the thick fins with the platenuts hanging in the breeze are still the fastest followed closely by the thin fins and no cover which in turn is followed closely by the Batman cover. Tomorrow is the last day before going to Montana for the Big Sky Air Race on Saturday. I guess I have no choice but to remove the Batman cover and go to Montana with the thick fins and no cover. I would like to make up a set of thick fins without the platenuts hanging in the breeze and test that but I'm out of time.

Bob Axsom
 
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Changed the cover cutout from Batman

I enlarged the batman cutouts by cutting a triangular section out of the two inboard edges and rounding the fwd end of the cutout.

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I made two trips around the area in normal three leg 6,000 ft dalt test fashion. The speeds were 182.6 kts and 181.5 kts respectively for an average of 182.05 kts. These rank as the fastest and the 7th fastest of the 32 test flights in this series. The average of the two test flights today is 1/2 of a tenth of a kt slower than the previous high speed in this test series.

Bon Axsom
 
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I have to think about that

It's a thought. I suspect the improvement in speed has to do with the exhaust plume impinging on the cover based on experimental observations. If that is true the focus of each cutout should be centered on the exhaust pipe outlets (which is what I have been instinctively moving toward without considering a parabolic shape). The interaction of the cooling air flow and the exhaust flow has always been a question.

Good observation thanks. I think I will make a pattern of the current cutouts using file folder stock the recut the development cover following a more parabolic line and give it a test flight.

Bob Axsom
 
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Also, what about adding exhaust extensions? I'm thinking that they could extend the current tube another eight inches or a foot, then make a gentle bend so that they end up parallel to the airflow. That would give you some exhaust separation from the skin.

You'd no doubt need some bracing for that, both to keep the extension under control and to keep from putting too high loads on the upper parts of the pipes. And it could well be that the trade-off between the drag of all that might not be made up by the added thrust and cleaned-up exhaust.

It would separate the effects of the exhaust from the cooling air exit to some degree, but it might be to the detriment of both. As you can tell, I'm not at all sure whether this would offer an advantage or not.

This is sort of the opposite of a jet-augmented exhaust, which might be preferable if it could practically be done.

Dave
 
Thanks Again but this time I'll have to pass

Also, what about adding exhaust extensions? I'm thinking that they could extend the current tube another eight inches or a foot, then make a gentle bend so that they end up parallel to the airflow. That would give you some exhaust separation from the skin.

You'd no doubt need some bracing for that, both to keep the extension under control and to keep from putting too high loads on the upper parts of the pipes. And it could well be that the trade-off between the drag of all that might not be made up by the added thrust and cleaned-up exhaust.

It would separate the effects of the exhaust from the cooling air exit to some degree, but it might be to the detriment of both. As you can tell, I'm not at all sure whether this would offer an advantage or not.

This is sort of the opposite of a jet-augmented exhaust, which might be preferable if it could practically be done.

Dave

I sawed off the exhaust to get the direction I have now and got a speed gain I see no reason to go back I think I'm guiding it in the right direction as far as these pipes are concerned. On the positive side I recut the cover outlet - not technically a parabola but in that vicinity as opposed to a blunted triangle.

IMG_6130.jpg


I spent so much time trying to coordinate things on the computer today that I will have to wait until tomorrow to test fly the change but it is ready to go:

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Bob Axsom
 
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Dang! After a career in aerospace development, that's the quickest I've seen one of my suggestions implemented in hardware. Usually it takes a couple days or more. Usually more.

I'm impressed. Fly safe!

Dave
 
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Success!

I flew the test this morning when every thing was calm and the results were good. The first test was 184 kts and the second was 182 kts for an average of 183 kts. Now that I know what I'm looking at, it seems to me that the right side cutout of the cover at the forward outboard edge could be relieved a little more and I might pick up another fraction of a knot. Unfortunately I am starting to run into AVC launch schedule pressure. I am thinking about tracing the current cutout outline then cutting it once again and making one more test flight but first, breakfast!

Bob Axsom
 
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The magic 185kts

Bob,
Seems you have almost hit the magic 185kts.Wow what a great accomplishment. What's the next mod series, wing root fairings?
 
Here are the table and chart

Next I have to convert this development patch work cover and outboard fins into a single piece and retain the center fin as is - hopefully in the next few days.

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Bob Axsom
 
Rough cut and fit

The development cover and outboard fences unrolled to pattern flatness.

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I had some 0.040" 6061 O bare so that is the first (hopefully the last) single piece copy:

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I fit well:
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Bob Axsom
 
Have you ever thought about getting rid of those draggy com antennas?
as Bert once said, (anything hanging out is drag)
Hold a old antenna or a welding rod at arms length out your car window at 75mph and notice the pull on your hand, DUA !! now imagine that at 180k.
 
Pitot/COM antenna

Have you ever thought about getting rid of those draggy com antennas?
as Bert once said, (anything hanging out is drag)
Hold a old antenna or a welding rod at arms length out your car window at 75mph and notice the pull on your hand, DUA !! now imagine that at 180k.

I am currently working on eliminating the COM antenna. I don't want to put an Archer antenna in a wingtip. My idea is to create a COM antenna/Pitot tube combination. Every time I look at my simple 1/4" pipe pitot tube I think "why can't that also be my antenna"? I have searched on the internet about this idea for a GA airplane and have not come up with anything. Someone else must have thought of this idea before.

I have been reading about handheld tranciever antenna design from HAM radio sources since they are a shorter 1/4 wave antenna than a standard whip. The VSWR/field strength meter I ordered will show up next week and I will start experimenting. I expect the performance will be less than the bent whip currently on the belly of my RV8 and not sure what the result will be but looking forward to the learning process.
 
Yes I have thought about it but ...

Have you ever thought about getting rid of those draggy com antennas?
as Bert once said, (anything hanging out is drag)
Hold a old antenna or a welding rod at arms length out your car window at 75mph and notice the pull on your hand, DUA !! now imagine that at 180k.

I think about EVERYTHING that touches the air - inside and out - I can't imagine a racer that doesn't. A long time ago I was a guy that worked on com equipment in the Air Force and I draw the line at compromising my com system for anything. During a race I have to make turn calls, finish calls and that's all - pretty trivial stuff - but the plane is my transportation, it's not just a racer.

I live in Arkansas but last Saturday I was in a race in Three Forks, Montana. When I was coming home I was very tired. I had only slept for about three hours because I had to prepare for the race, then I flew the race, waited for the disappointing results and finally it was time to head for home. Storms were over Colorado in the Denver area and I knew from talking to a briefer in Sheridan, Wyoming that they were moving north. Coming south from Muddy Mountain VOR I could see it and I'm flying VFR but on Victor airways. I left the airway to the east, flying to light and lowering terrain, looking for an out. I know it's on me to find the way out and I am too tired to play super pilot, drag out my IFR charts and try to work my way into the system while flying the plane avoiding the storm, etc. Regardless of what CFIs and other perfect pilots do, I Fly the plane and work my way through the options that I personally have control over first. At one point I saw the path to Cheyenne was VFR but a low ceiling. It was not night time but under the clouds it was pretty dark. I was in the 20-30 mile range from the airport and according to the ATIS it was still VFR there. I committed to flying there and I called the tower on the way in. I gave my location and all the usual stuff but I also emphasized that I was not familiar with the area. He said do you see the large tank painted red and white ? I confirmed that I did and he said the airport is not far behind that. As I got in closer at about 500 ft AGL getting squeezed between the land and the clouds I saw the airport and reported it. He cleared me to land on runway 31 and I told him that I had a runway insight to my right but I could not confirm that it was 31. He said no that is a different runway, whatever number it was. So I continued on until another one showed up on the right and we confirmed that it was 31 and I landed and taxied off. I had no Idea where the FBO was because I had not planned to land there but it was a port in a storm and I really didn't care if it was a little awkward. I called ground told the operator I need to taxi to the FBO, I would be staying the night and I was unfamiliar with the airport. He gave me taxi instructions and it was all over but tucking the Blue Bird away and getting a room for the night. Drag could not have been further from my mind. I do unscrew the nav antenna elements during a race but my previous testing of drag effect was not measurable - still if they are off it is less drag. I am sure the bent whips are even less draggy. It's a personal choice but so far I don't mess with my optimized VHF com antennas.

Bob Axsom
 
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Bob: For what it's worth, the SL-40 you sold me works better (has more range and is clearer) on my Rocket transmitting and receiving through a cheap(er) Bob Archer antenna in my right wingtip than does my Garmin 530W transceiver operating through a more expensive exterior Comant whip antenna located on the belly of my airplane.

Based on that (admittedly only a single data point), I would say that you don't necessarily have to give up any communications performance to gain an improvement in drag by dropping your external antenna.

Just a thought...


Lee...
 
internal antenna

Has anyone thought about mounting an antenna under the canopy, above the passenger's seat? You'd have to build a support structure of some sort and perhaps a ground plane. It would also have to be easily removable to return the airplane to non-racing configuration.

I agree about the drag being pretty low; I remove one of my two com antennas for racing but can't measure a difference in speed.
 
Bob, I've been following the whole thread. Glad you are finally beginning to see some good results.

The current configuration is looking a lot like the one I fashioned basically on intuition. I have always though that getting the outlet curves smooth is a benefit by minimizing sharp discontinuities that "trip" the airflow into something more turbulent than it needs to be.

Gettin' smooth now!

Have you seen any consistent effect on CHT's.

Continued good results!!
 
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The CHTs have increased a little

The CHTs range from around 350 for #1 to 373 for #2 now and before they were 320 to 350. It indicates to me that the air mass flowing through the system has been reduced some.

Bob Axsom
 
Has anyone thought about mounting an antenna under the canopy, above the passenger's seat? You'd have to build a support structure of some sort and perhaps a ground plane. It would also have to be easily removable to return the airplane to non-racing configuration.

I agree about the drag being pretty low; I remove one of my two com antennas for racing but can't measure a difference in speed.

We mounted an ELT antenna inside of the tipup rollbar on the passenger side as COM2. Fine for short range stuff, ground or formation communication. Not useable for inflight/ATC, too limited in range / field of view.

Sounds like the Bob Archer used for COM as well would be a better way to go.... Still possible issues with field of view however.
 
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