B

Bob Axsom

Well Known Member
I have used gaffer's tape to cover these hinge access holes in the rudder and elevators and the speed of the airplane was increased. There has to be a better way to do this (part of mine blew off in the last race). I have three possible designs to work on with 0.016" aluminum. I will have one of them installed and hopefully tested before the Palmeto 125 race in Ridgeland, SC on May 2. Has anyone else worked this problem?

Bob Axsom
 
On the older kits, we had to cut these holes ourselves. I didn't cut mine nearly as large as they come now.
 
Race to Ridgeland??

....Well, Bob, we'll finally meet! We placed 2nd last year, beaten by Ron Schreck (sp).

Where was the announcement?

Regards,
 
www.sportairrace.org

Pierre,

It is listed under "Calendar of Events" at the Sport Air Race League website www.sportairrace.org. Unfortunately there are two races scheduled on the same day. This is the first year that the Ridgeland event is holding a SARL sanctioned race called the Palmeto 125 in addition to the "Race to Ridgland" that they have held for at least three years. The other race sanctioned on the same date is the Big Country Air Fest race out of Dyess Air Force Base in Abilene, Texas. Last year they gave race entries the same perks as the show performers at the big event - free, motel, car, food and avgas - pretty hard to pass up. Things are cut back somewhat this year at BCAF I'm told but still very good. I was stationed at Shaw AFB, SC in 1957 so I have an attraction to the area and decided to go there anyway, weather permitting. You are going show me the back side of you RV-6A around the course I bet. I'm looking forward to the race.

Bob Axsom
 
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I don't think so...

...Bob. From the numbers you've posted, you'll be the one showing your tail to me!

We managed 203 MPH for the course last year WOT for 145 miles/45 minutes, more or less, two aboard.

Regards,
 
Fabric and Velcro?

My Bucker uses fabric to form a continuous gap seal. The rudder fabric and the VS fabric tie together with velcro. Of course, it is a fabric airplane but if gaffers tape works, perhaps velcro might be an option to secure some kind of fabric?
 
Gap seals

Bob,

Have you ever experimented with full-length mylar gap seals on the elevators and rudder? (rather than just blocking the bolt access cutouts)
 
Bob Axsom said:
I have used gaffer's tape to cover these hinge access holes in the rudder and elevators and the speed of the airplane was increased. There has to be a better way to do this (part of mine blew off in the last race). I have three possible designs to work on with 0.016" aluminum. I will have one of them installed and hopefully tested before the Palmeto 125 race in Ridgeland, SC on May 2. Has anyone else worked this problem?

Bob Axsom
Click to expand...

The sailplane guys use "gap seal tape". Its a slightly concave mylar that comes in a couple of different widths.
Problem is you've got to buy much more than you need as last I checked they sell it in 50' lengths. Uses a double stick tape to apply. A couple of us out on the left coast have used this for a while.
Tom
 
Covering holes

Bob Axsom said:
I have three possible designs to work on with 0.016" aluminum.
Bob Axsom
Click to expand...

Bob I don't know if this is what you are thinking but I haven't heard anyone mention using AL sheet with nut plates and cs screws at each end.

Here's my thinking - Fab a piece(s) of AL with a curve to match the opening that is a few inches wider (depth varies to your liking/safety) drill a hole each side, cs or dimple and attach nutplates. The piece(s) is removable to access the attach bolts and I don't think the wind will rip it off. Yeah I know, weight - weight - weight. Just an idea.
 
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No I haven't

Alan Carroll said:
Bob,

Have you ever experimented with full-length mylar gap seals on the elevators and rudder? (rather than just blocking the bolt access cutouts)
Click to expand...

I look at them on Larry Henny's Lancair and Tom Martin's EVO Rocket but I have never tried them yet. I like to keep the look I have if I can keep improving the speed but there may come a point where I just have to admit I'm a racer. Do you have them on your RV-8 - I have to study my photos of #12.

Bob Axsom
 
pazmanyflyer said:
Bob I don't know if this is what you are thinking but I haven't heard anyone mention using AL sheet with nut plates and cs screws at each end.

Here's my thinking - Fab a piece(s) of AL with a curve to match the opening that is a few inches wider (depth varies to your liking/safety) drill a hole each side, cs or dimple and attach nutplates. The piece(s) is removable to access the attach bolts and I don't think the wind will rip it off. Yeah I know, weight - weight - weight. Just an idea.
Click to expand...

That sounds similar to my plan - weight is not the speed problem that most people think it is - at least down at these levels. Here is my reply to a private message earlier:

I have also tested the effect of closing the holes. I found a very positive increase in speed last year when I worked very carefully to close the holes with gaffer's tape. I used the 6,000 ft density altitude triangular course test method, WOT, 2,720 rpm, leaned for best speed (~1300F EGT on cylinder #4) and entered the GPS ground speed and track angle for each leg into the NTPS spreadsheet.

After I removed the steps and before I taped the elevator and rudder attachment openings my KTAS on 6-24-08 was 181.2kts. After I taped the openings (very difficult to get it right) before the AirVenture Cup I flew the test on 7-22-08 and the speed increased to 182.6 kts. I flew with the same tape in place the rest of the season with no problem.

I had to take it off for the annual condition inspection in January and when I replaced it for the Taylor 100 air race on 3-15-09 I had no time to wash the plane and little time to restore the tape with the same care I had used last year. The result was part of the tape blew off. I want a more permanent solution anyway so I am starting to work on it tomorrow.

I will use 0.016 2024 T3 sheet aluminum and I will installed one closure plate in each surface opening (14 plates). I plan to have two small outboard tabs to hook the plate under the skin down toward the hinge line (leading edge) followed by a rectangular surface that overlaps the access opening on all three sides. There will be a rectangular cutout to clear the mounting flanges from the fixed surface during full deflection of the elevator/rudder in the worst interference direction. I plan to install a dimpled platenut under the skin at the rear of each cutout and secure the plate with a flathead #8 stainless steel screw (in combination with the tabs this will provide three point holding stability).

Bob Axsom
 
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full-length gap seals

Bob Axsom said:
Do you have them on your RV-8 - I have to study my photos of #12.
Click to expand...

I don't have them, I was hoping you could tell me if they work! John Ross said he tried gap seals before the AVC last year but that they came loose on the trip to SD.

I've got cheap vinyl tape covering the bolt access holes. The tape came from True Value and hasn't come loose since being applied last summer. Doesn't look particularly great though.
 
Concept trial

I had to spend most of my time at the airport today ramp checking my GS/LOC/VOR system today but I did end up with half an hour to work with som 0.016 2024T3 aluminum sheet today. with tracing paper, file folder material, ruler and pencil I layed out a crude shapeand cut it out of aluminum. It lays perfectly against the skin, fits closely around the mounting bracket, is solid with the two forward tabs, exposes no hole when the elevator is neutral and does not bind anywhere when the control surface is moved through the full range of motion. It looks very promising.

John Huft approachs the closure in a different manner but he also limits his concern to the holes themselves and not the whole length of the interface. That is about the best approach endorsement one is ever likely to get. I'm going to have these done by the next race on May second in Ridgeland, SC.

Bob Axsom
 
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Started making cover blanks

I spent a couple hours at the hangar today developing the shape of the hole cover plates. The one aluminum prototype was altered by riveting some more aluminum on to change the type and shape of the forward lock-in tabs. Those were progressively shapped and smoothed until the cover could be installed and removed easily. Once the shape was established it was used as a pattern to make a cover of the same shape but using only one piece of metal. It was trial fitted and tested for function. The trailing edge was thought to be too close the the location where I'm going to have to drill and dimple for the mounting screw at the rear of the cover plate so I used the new piece as a pattern for making another one but with approximately 1/4" extension on the trailing edge. This was trial fit and functionally tested and it was acceptable I made two copies of the eight I need for the elevator and everything looks fine. The trailing edge will be trimmed for each mounting location. More to come.

Bob Axsom

IMG_3524.jpg
 
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Basic configuration

I am going to trim metal off of the cover but ytou can see the basic concept in these photos. The covered hole is the outboard elevator attachment on the right side and the hole that is not covered is the same attachment on the left side. This will be faster based on my tape tests last year (maybe no faster than the tape but it will certainly be as fast.

Bob Axsom

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A couple of ways to skin a cat. I used gap seal tape (mylar) from the glider guys.
This also seals the full length of your control surfaces (not ailerons). Fabricated a small removable section should I ever need to get to the bolts. Mylar attaches with doublesided tape and then a very thin tape is used to cover the leading edge. The mylar is paintable if desired. This install has about 600 hours on it.
Tom
 
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Source of tape

RV3 Pilot said:
A couple of ways to skin a cat. I used gap seal tape (mylar) from the glider guys.
This also seals the full length of your control surfaces (not ailerons). Fabricated a small removable section should I ever need to get to the bolts. Mylar attaches with doublesided tape and then a very thin tape is used to cover the leading edge. The mylar is paintable if desired. This install has about 600 hours on it.
Tom
Click to expand...

Hi Tom,

I like the idea of the mylar solution, but all the local stuff I've seen is not wide enough to cover the gap. Who do you use as a source?

Did you do any before / after testing on the speed aspects?

Thanks,

Carl
 
zkvii said:
Hi Tom,

I like the idea of the mylar solution, but all the local stuff I've seen is not wide enough to cover the gap. Who do you use as a source?

Did you do any before / after testing on the speed aspects?

Thanks,

Carl
Click to expand...

Carl
I got the mylar from a glider supply house many years ago, as I recall if came in 2 or 3 different widths. I believe the stuff I have is 1 1/2" I see it everywhere on high peformance gliders so it must still be available. It is faster by a couple of miles an hour. At what point in your airframe cleanup you add it will make a difference in the speed increase.
Tom
 
Good stuff.
Wings and Wheels was my original source but Williams Soaring looks like a better deal for shorter lengths. 22mm might be a little small, 38mm might be a little large but you can trim it down. My stuff was 30mm. You will find all kinds of places for this stuff.
Tom
 
Final shape

I have all of the platenuts in the elevator and 6 of the 8 plates are complete and installed in unpainted final form. I still have the rudder to do so it will be a week or more before it is ready to test.

Bob Axsom

IMG_3533.jpg
 
The Cover plates are all installed

Shown below is the bottom rudder access hole coverplate. It is the only one that uses two mounting screws. One is the existing bottom rudder cap mounting screw and the other is added for this cover. the plate nuts are all dimpled platenuts and orientation is facilitated with outer to inner skin transition notches and the cutout for the mounting bracket. I still have to assure final alignment when I torque down the screw or screws. The elevator mounting bracket cutouts are final size but the rudder is not currently installed and the cutouts must be enlarged to final size on installation.

Bob Axsom

IMG_3542.jpg

IMG_3545.jpg
 
When You Actually Do it New Options Sometimes Appear

After a trip to Branson, Missouri for a couple of days I got back to the Rudder. I got it hung and started cutting the mounting bracket opening to size in the two lower cover plates to clear the bracket on the top and bottom and avoid hitting them before the rudder stops limit the rudder deflection. Working away with my nibbler, file and deburring tool I was almost done with the first one when I realized that the movement is so great that the opening will be exposed even when the rudder is in trail. At that point I focused on the file to remove metal only at the outer edges of the cutout to leave the "finger" extending forward to go between the the upper and lower mounting flanges and reduce the open area that would exist with a simple rectangular cutout. That worked fine but the damage was already done on the first plate. The second one was a little better but I began to consider ways to put material back in without scraping the cover plates. It occurred to me that I can add a bowed 0.016" aluminum strap between the upper and lower mounting brackets extending from the left cover plate to the right cover plate secured with flathead screws and dimpled platenuts on the left and right coverplates. This would effectively simulate a single coverplate with slots cutout for the rudder mounting brackets.

Bob Axsom
 
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Mod Complete - Flight Test Ready

All 14 coverplates are installed and the plane is ready to test. It could happen any day but the forecast for Monday is very good.

Bob Axsom
 
No test flying today because of the ceiling. I did spend a few hours refining the covers a little. This one is the left side middle cutout cover. This one and the bottom one are particularly bad as far as cutout size requirements are concerned. The vertical stabilizer and the rudder hanging brackets are extremely wide so a simple retangular cutout to accomodate full deflection was just not acceptable. In these to locations I added a center strap from side to side to block more of the hole. Should fly tomorrow.

Bob Axsom

IMG_3555.jpg
 
The results

IMG_3558.jpg


Started the engine at 0634 this morning and by 07:20 the testing was done. The results were disappointing as they often are. The test was flown at 6,000 ft density altitude the local altimeter setting before takeoff was 30.03 and after landing it was 30.05 so descending air negative effect on airspeed (ref. Mark Frederick). At 6,000 the temperature was 7C so the test was flown at 5,600 ft to get the 6,000 ft density altitude. The RPM = 2720; MP=24; OT and OP not recorded; CHT 1=296, 2=344, 3=343, 4=316; EGT 1=1227, 2=1357, 3=1338, 4=1307.

The GPS track speeds were:

360 = 146, 146, 146, 146, 145 = 145.8 avg
120 = 199, 200, 198, 199, 200 = 199.2 avg
240 = 194, 194, 194, 194, 194 = 194.0 avg

NTPS Spreadsheet
Wind = 35.7 kts
Wind direrction = 355.6
speed = 181.4 kts

My conclusion is the change provided no increase in racing speed over taping the same holes. The only advantage is the the covers will not blow off.

Bob Axsom
 
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Bob Axsom said:
IMG_3558.jpg


Started the engine at 0634 this morning and by 07:20 the testing was done. The results were disappointing as they often are. The test was flown at 6,000 ft density altitude the local altimeter setting before takeoff was 30.03 and after landing it was 30.05 so descending air negative effect on airspeed (ref. Mark Frederick). At 6,000 the temperature was 7C so the test was flown at 5,600 ft to get the 6,000 ft density altitude. The RPM = 2720; MP=24; OT and OP not recorded; CHT 1=296, 2=344, 3=343, 4=316; EGT 1=1227, 2=1357, 3=1338, 4=1307.

The GPS track speeds were:

360 = 146, 146, 146, 146, 145 = 145.8 avg
120 = 199, 200, 198, 199, 200 = 199.2 avg
240 = 194, 194, 194, 194, 194 = 194.0 avg

NTPS Spreadsheet
Wind = 35.7 kts
Wind direrction = 355.6
speed = 181.4 kts

My conclusion is the change provided no increase in racing speed over taping the same holes. The only advantage is the the covers will not blow off.

Bob Axsom
Click to expand...

Try the gap seal tape, especially on the tail feathers. Bet you a beer you'll see an increase in speed with good testing technique and................. added response to control inputs.
Tom
RV3 978TM
2000+ in a/c

just noticed your vor antenna, do you remove that for racing?
 
Yes I have but ...

For racing I have been removing the VOR antenna elements but some recent IMC/IFR approach issues have me rethinking that strategy. I also cover the tiedown ring holes. I know there is some error margin in any test method but my method is always the same and the results have been very consistent. I use the www.us-airrace.org handicap procedure, 3 directions, 6,000 ft density altitude and plug the results into the National Test Pilot School spreadsheet provided by Kevin Horton and John Huft. Neither of these fellows think my methods are rigorous enough but I'm happy with the data I get (the difference on two tests flown in the same configuration is usually a fraction of a knot). I have two objectives in my development, one is to keep the airplane looking good and the other is to make it go as fast as possible. Usually I can tell going in if the mod is going to reduce drag and in those cases I know the mod is going to be a permanent part of the racing configuration but sometimes as with cooling drag changes, intuitively obvious drag reductions result in speed reductions and I have to implement them in a manner that is compatible with post test removal. You may be right about the gap seal tape but so far the concept offends my sense of beauty - there now you know I have a flaw in my "anything for speed" makeup. I see Tom Moore taping everything on his fast RV-7A but I just can't bring myself to do it ... yet.

Bob Axsom
 
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