RV-6 Longeron drilling

Happy new year to you all !

I am slowly making progress on my RV6 slow build ? With the fuselage still upside down in jig I am now ready to dimple / countersink all the holes to get the skins ready for priming - I have a few questions regarding the best way to prepare the holes in the longeron ? I find the drawing not to be very clear ....

From Bulkhead F605 all the way back I have drilled for 426-3 with a 1? spacing.

Is the general view that it is best to countersink the longeron all the way ? then dimple all the skins ? ? Then back drill when the fuselage is out of the jig to secure the two rear top skins ? and dimple them as well.

From Bulkhead F605 to the firewall ? I plan to drill for 426-4 with a 1 ? ? spacing ? Clearly the longeron has to be countersunk here to take account of the larger rivets.

On the part of the fuselage that is behind the wing root ? I plan to use mostly 470-4 rivets ? But on the F604 bulkhead at what point do you transition to the smaller 426-3 rivets ? Or do you use 426-4 up to the longeron, or just up to the part that is viable outside the wing root ? Then 426-3 all the way up to the longeron ?

On F605 at the top end I have the F605 E channel with the two spacer strips H & I (I am building a tip up canopy) ? With the spacers strips in place I can not see how I can dimple that part of F605 ? So countersinking looks appropriate ? then I can dimple the skin ? the part of F605 that does not have the E channel can of course easily be dimpled.

Does this all make sense ??

Jan

2012 ? paid up...

2013 ? Not yet ? on the to do list ...

JanRV6UK said:

From Bulkhead F605 all the way back I have drilled for 426-3 with a 1” spacing.

Is the general view that it is best to countersink the longeron all the way – then dimple all the skins ? – Then back drill when the fuselage is out of the jig to secure the two rear top skins – and dimple them as well.

..

Click to expand...

Hi Jan,

Page 8-25 of my old instructions (pre-word processor) talk about installing the aft side skins in a partial manner with 3 inch spacing rivets and then drilling to the final 1 inch spacing when the upper skin is installed.

It also says - "Also since the F-675 skin is only 0.025 thick it will need to be dimple countersunk, and the longeron/side skin build-up is to be machine countersunk to accept it."

So you only dimple the outer skin and c/s the longeron/"middle skin" combination.

This is easier, and a bit more accurate if you are back drilling the skins from inside the fuselage.

I used this method and it worked out well. The "temporary" 3 inch spaced rivets of the side skin/longeron can be laid out to not interfere with the final 1 inch rivets that will be visible after construction.

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On F605 at the top end I have the F605 E channel with the two spacer strips H & I (I am building a tip up canopy) – With the spacers strips in place I can not see how I can dimple that part of F605 – So countersinking looks appropriate – then I can dimple the skin – the part of F605 that does not have the E channel can of course easily be dimpled.

Yes - that works....

Hope this helps...

Hi Gil,

Thanks for the feedback ! I missed the part of the 3” spacing before installing the top skin - So ended up with drilling all the aft holes (behind F605) with a 1” spacing.

Sounds like the best way now is to dimple the side skin and countersink the longeron every 3” – rivet in place.

Then when I do the top skin I back drill using all the holes I already have made – Then I machine countersink the side skin and longeron (together) – and dimple the top skin.

What did you do in front of the F605 when you only have a single skin ? Did you countersink the side skin for the #4 rivets – or did you dimple and countersink the longeron ? - Or did you use the 1” spacing with the #3 rivets and countersink the .032 skin ) then no need to remove any material from the longeron ??

Longeron

I am building my RV-6 fuselage right now.
This is my second one.
I used 1" spacing on the main longeron and 1 1/4" spacing all the the stringer.
IF all of your lower skins are ready to go, you will COUNTERSINK the longeron and DIMPLE the lower side skins. I attached the side skins with a rivet between the 1" spacing every 4th hole. SO this mean you have to drill an extra hole it between the 4 and 5 hole. However, I did not countersink this hole. I just deburred it and then when I riveted the side skins on, I used the small headed rivetes and slightly countersunk this rivet into the .025 side skin. This arrangement holds the side skin in place while you get the top turtle deck skins on. The turtle deck skins are all dimpled. Make sure you put a slight bend on the edges of the turtle deck skin before you dimple the skin so your skin will not have puckers along the overlap of the top skin and side skins. I use the ones that are from Cleaveland that are on a pair of vise-grips.
Also, before you final rivet the top skins on over the side skins, take your deburing tool (the one with the funny shaped "s" handle) and give each dimple on the SIDE SKIN a little "shave". Just one turn in the dimpled hole with the deburring tool. This "shaves" the little bump out of the top of the dimple where the flat skin is presses into the cone of the dimple tool. Your top skin will lay down nice and flat over the side skins if you do this. A little extra work but when you look down the side of the fuselage, there will be no puckers or skin edges slightly lifted. DO NOT FORGET TO PRIME THE AREA OF THE SIDE SKIN THAT THE TOP SKIN WILL OVERLAP AND COVER. This is where corrosion really likes live on airplanes.

Also get some AN4263-5.5 rivets for the top skin riveting to the longerons. The -5 supplied with the kit are just not long enough.

Thanks for your feedback Aden - Just working on this today.