What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Removable Rudder Bottom Fairing

Daniel S.

Well Known Member
Okay guys.
An opinion question here. I've come to the realization that I am going to make my bottom rudder fairing removable for several preferential reasons... Should I go with #6 or #8 screws. I bought some #8 tinnerman CS washers that I was going to use for this task but the diameter of the washers is too big and overlaps the aluminum skin. This morning, I went ahead and ordered some "normal" #6 & #8 CS washers... We'll see what fits best in this area. Are there any concerns with using #6 screws?
 
For the rudder bottom, I went with #6 screws and no washers. If it needs washers, they will be added later.

Watch out for the trailing two screws, they should be staggered so they don't interfere with each other.
 
Lot's of builders use #6, including me. No down side that I'm aware of. Why would you use tinnerman washers in that application? The fairing isn't going to come off very often so wear isn't an issue, and you don't need them for strength.
If you go without the washers then #8 should also work just fine. Slightly more weight at the tail end which is a consideration for some.
 
Here's what I did:

IMG_9873.JPG


IMG_9872.JPG


Not flying yet but have seen it done elsewhere.
 
Thanks guys... # 6 it is :D.

Mark. I actually do have that adaptor ring. The reason I personally want access is wiring. I am running an extra wire back there just "incase" I get noise with the local ground or if I ever want a different light. etc.
 
I never use anything smaller than #8 - no problem

If the outer surface on a lap joint is aluminum I typically dimple the aluminum.

If it is some development work and I am using soft aluminum (6061-O) as the outer surface of a joint I drill the holes in the outer surface (like my outlet fairing) to 3/8" and use dimpled washers. This allows the dimpled portion of the washer to go down in the hole and the flat portion of the washer to clamp the joint together.

Anytime I am working with soft material like fiberglass of plexiglass as the outer surface I do the same as above with soft aluminum - 3/8" hole in the outer piece of material in the joint to allow the wide distribution of pressure clamping as well as centering function.

Mating hole alignment perfection is difficult no matter how hard you try. I have a procedure that works pretty well but It takes longer to explain than most peoples attention span on such things. It involves such things as 1/8" holes and clecoes for the initial mating hole pattern with holes enlarged later to suit the application (in this type of situation - #8 flathead screw - I enlarge the screw hole to 3/16"). Even with all of my best precision effort I still have screws that bind somewhere in the pattern occasionally as I try to install them. Sometimes this can be fixed by enlarging a hole slightly and in worst cases I replace the one piece platenut at a binding location with a floating platenut.

I mounted the lower rudder cap only with screws and I did it because of the light installation. Many people don't - it's a personal choice. Some people add holes and access panels as they look ahead to service issues while they are still building their airplanes because of prior experience with servicing airplanes. I did not add any of those.

In 8 years of flying our airplane I have had to remove the lower rudder cap approximately three times for modification, and repair.

Bob Axsom
 
Last edited:
Bob,

I totally agree with the washers. I just don't like the looks of them. You'll notice from the two photos I posted that the front hole/screw does have the washer. This is for security in a critical area. The rest will be watched and if they start to wear, then they too will get the washer treatement.

You are correct in that it is a real bear to get the alignment perfect. Someone on here once said 'perfection is the enemy of completion' or somthing like that. How true!
 
Follow up on how I did my fairing

Hey all-
My removable fairing came out perfect & wanted to share with my process with ya'll if it's ever usefull for someone down the road wanting a removable rudder fairing.

1. I elected to go with #6 SS screws and CS SS washers on a 2.5 inch spacing. a total of 14 screws. # 8 scews / washers in this application simply don't leave a decent edge distance. Plus the washers overlap the aluminum. As a former - out of practice old-school A&P, I did NOT drill the most forward area which would entail drilling through the side of the main rudder spar and/or the control horn bracing. Thats a "no-no" in my book, as the forces on that area are insane during spin recovery ect. I only used the intended attach strips & used a heat gun to form the frontal to a nice tight fit.

2. After final triming / filing / sanding / fitting of the fairing to my liking, then used packing tape to keep the fairing in place while I laid out a center line for the rivet line / screw line (8/32nds)from the aluminum skin. Finally, I used a fan spacer to lay out the 2.5 inch spacing.

3. Then used a center punch to mark the exact location of each hole to drill. dilled these hole to a #40 size hole & clecoed.

4. After ensuring the alignment of the fairing after drilling, I came back through with a #30 bit and replace the corresponding clecos.

5. With the fairing clecoed in place, I counter-sunk the fairing to except the CS tinnerman type washers. Counter sinking while the fairing was in place allowed me to used the "harder" aluminum holes at a templet for my counter sinks. Then followed up inlarging the hole finally to a #27 bit.

6. Then I removed the fairing and used a #6 nut plate jig to drill for the nut plates. This tool is worth it's weight in gold!!! I have them for #6, #8 & #10 nut plates. It took about a minute to drill for all of the nut plates.

7. Finally, deburred, dimpled and riveted the nut plates in place. When I re-mounted the fairing with the final attach hardware, the alignment was ABSOLUTELY PERFECT. No need for floating nutplates etc.

it sounds like a lot of work but the whole process took about an hour or less.

I hope someone can use this method in the future as I am extremely happy how it all turned out. I'll post pictures in my log later today.

Again guys, Thank you for your input, Without it, I wouldn't have come up with this basterdized method that kind of solved issues others had :D
 
To Each His Own but ... another method

Edge Distance - I don't like the tiny little screws. Maybe there is some compelling reason your edge distance is short but on ours it is a function of the size of the underlapping sub-flange and where I chose to locate the attachment hole line for the platenuts. There is no short edge distance in our installation with #8 hardware.

Platenut tools:

- When I locate a line of holes for #8 platenuts I drill the initial hole with a #30 drill and clecoe it with a bronze (1/8" clecoe) and repeat as I go through the entire pattern.

- When I am done with that set of undesize hole locations I take a fixed (not floating) platenut and clecoe it to the accessible side of the structural member it is to be attached to with a bronze clecoe.

- I use a #40 drill and drill the first mounting hole through one of the mounting holes in the platenut using it as a drill guide then I clecoe it with a silver (3/32") clecoe to stabilize the orientation of the platenut.

- I use the other platenut mounting hole as a drill guide and drill the other mounting hole.

- Then remove the clecoes and platenut and drill out the screw hole in the structure to 3/16".

It is so stone simple I can't imagine what a special platenut tool gives you - certainly not accuracy. If you go with miniature platenuts the mounting locations are different of course but I guess the tool compensates for that - the actual miniature platenut certainly does.

Bob Axsom

P.S. The Mil-specs identify them as platenuts, nutplates and anchor nuts so there is DOD published precedent for all three names but very early in my career (1958 to be exact) it was firmly established in my young mind that they are types of nuts not types of plates and a nut plate is a flat structural member containing nuts.

BA
 
Last edited:
Me too

My experience is that the method Bob just described works well for me.
Better than the specialized tool.
Bill
 
Cleveland Tool Tail Light Adapter Ring

Anyone know if the tailbeacon from Uavionix will fit through the Cleveland Tool adapter ring?
 
Flush Washer

I have found that flush washers (also known as finishing washers) are a good alternative to tinnerman washers. I painted my wing tanks separately and mounted them with #8 screws with flush washers. Now the tanks can be removed with no damage to the paint job and the task is 100% easier. (Anyone who thinks that they will never have to remove their fuel tanks is a cockeyed optimist, IMHO.) I use these washers on my wheel pants as well and believe they would look great on a removable rudder fairing.

Flush Washer



 
Edge Distance - I don't like the tiny little screws. Maybe there is some compelling reason your edge distance is short but on ours it is a function of the size of the underlapping sub-flange and where I chose to locate the attachment hole line for the platenuts. There is no short edge distance in our installation with #8 hardware.
BA
I used #4 screws to attach my bottom fairing.
 
I have found that flush washers (also known as finishing washers) are a good alternative to tinnerman washers.

My flush choice too. Tinnermans? Yuk.

The tank screw idea is pretty slick.

I'm sure it costs me a milliknot or two, but on glass I generally use stainless AN526 screws and a nylon washer. No countersinking, full thickness edge to the hole.

https://www.aircraftspruce.com/pages/ha/screws/an526.php

https://www.aircraftspruce.com/catalog/hapages/hanylonwashers.php?clickkey=3010106
 
removable

Was planning on removable, but then with the hole at each end, it's pretty easy to get full access. I couldn't quite recall the motivation for making it removable so I used blind rivets.
 
I have found that flush washers (also known as finishing washers) are a good alternative to tinnerman washers. I painted my wing tanks separately and mounted them with #8 screws with flush washers. Now the tanks can be removed with no damage to the paint job and the task is 100% easier. (Anyone who thinks that they will never have to remove their fuel tanks is a cockeyed optimist, IMHO.) I use these washers on my wheel pants as well and believe they would look great on a removable rudder fairing.

Flush Washer


Very easy to make your own SS finishing washers. Source a thin stainless washer and use the proper dimple die. Comes out great.
 
Last edited:
Reviving an old thread. I'm planning to make my bottom rudder fairing removable as well (#6 screws), to give more convenient access to the tail light wiring. I found the fit of the fiberglass part against the rudder skin is not very precise. In particular:

1. The fiberglass is thicker than the rudder skin, leaving a pronounced edge along the surface. If I were permanently attaching, I might choose to fill that edge with some epoxy and file it smooth. Any good approaches for making this edge nice while keeping the bottom removable?

2. The fit is particularly bad against the forward R-710 "horn brace" where there are no fasteners called out. There is at least a 1/16" gap between the metal and the fiberglass part. Suggestions on how to solve?
 
Rudder cap

Reviving an old thread. I'm planning to make my bottom rudder fairing removable as well (#6 screws), to give more convenient access to the tail light wiring. I found the fit of the fiberglass part against the rudder skin is not very precise. In particular:

1. The fiberglass is thicker than the rudder skin, leaving a pronounced edge along the surface. If I were permanently attaching, I might choose to fill that edge with some epoxy and file it smooth. Any good approaches for making this edge nice while keeping the bottom removable?

2. The fit is particularly bad against the forward R-710 "horn brace" where there are no fasteners called out. There is at least a 1/16" gap between the metal and the fiberglass part. Suggestions on how to solve?

Check my blog. Mine fits after surgery. I pop riveted it but easy to build removeable.
Look about 5/11/20 on this page
https://wirejockrv7a.blogspot.com/p/finishing-page-01012020.html?m=1
 
Thanks, Larry, that is very helpful. I like how you cut it to install aft-to-forward rather than by pushing up. Wish I discovered that idea but sadly I already cut mine.

Looks like you also filled the VS and HS tips, using the foam backing. Having a bear of a time doing that, too. Fiberglass layups don't seem to want to bend 90 degrees around the edge of the cap. Not sure what I'm doing wrong.
 
Thanks, Larry, that is very helpful. I like how you cut it to install aft-to-forward rather than by pushing up. Wish I discovered that idea but sadly I already cut mine.

Looks like you also filled the VS and HS tips, using the foam backing. Having a bear of a time doing that, too. Fiberglass layups don't seem to want to bend 90 degrees around the edge of the cap. Not sure what I'm doing wrong.

I put down a fillet of epoxy & micro to alleviate that problem. The 7725 I used just wasn't going to make the full 90 bend without leaving bubbles. I also used a 1/4" thick piece of structural foam bonded in with a micro slurry (w/ fillets and filled in the surface) and just left it in there. I recessed it about 1/16", applied two layers of 7725 on the outside, one on the inside, and then finished flush with a thin coat of micro.
 
Back
Top