Robert M

Robert M

Well Known Member
I'll bet this is the first time this question has been asked! :D

The bottom of the VS rear spar has a doubler. The plans hanging on my wall show, (SECTION A-A), dimpling the rear spar and CS the doubler.

Has anyone countersunk the rear spar?

I believe the head on the AN4 rivets are a tad thicker than the spar itself (spar .080 +- & rivet head .095 +-).

If countersinking is an option a slight amount of countersinking goes into the doubler - should I do both of them clecoed together?
 
Dimple

If you countersink through the spar into the doubler the joint will be too weak. Look at chapter 5 of your builder plans and you will see where countersinking too deep is a no no. I dimpled mine and never even thought about countersinking. JMHO.
 
dimpling

Thanks Gregg. I was confused about that part. Section 5 really didn't say a lot about #4 1/8" rivets. It kinda focused on the #3 3/32" rivets. But it doesn't matter, if it can be countersunk with no problems - I'll geeter done.

Thanks again,
 
In my section 5 it shows that .050 is the thinnest material you can countersink for a 426-4 rivet, unless the countersunk piece is sandwiched between two other pieces. In general, dimpling creates a stronger joint because of the nesting of the pieces. Unless it is too thick to dimple (or Van's suggests otherwise, as on the tanks) I always prefer that to countersinking. Good luck.
 
I went ahead and dimpled the rear spar - that was easy enough. :D I had to give a few of the holes an extra whack to get the rivet head flush.

I read the same thing in section 5. The material thickness for the HS rear spar is between around .085". The rear spar is outside of the minimum of .050 that Van's recommends for countersinking. That's the reason I was asking, I was just curious if anyone had countersunk with good results.

Thanks agian for the input.
 
Robert--

Not sure if I follow your previous post, but material that is .085 is definitely countersink-able. It's anything LESS than .050 for 426-4 rivets that you should stay away from.

When you get to the HS spars (if you haven't done so already), Van's specifically instructs us to countersink, so watch out for that. The reason is that if you try to dimple a piece of material that is too thick, you'll tend to get some distortion and/or the piece will tend to bow a little because a dimple can have sort of the same effect as fluting. I forget what the rule of thumb is, but I generally dimple anything less than .050 and countersink anything greater, unless Van's recommends otherwise.

Also, if you do countersink for a flush rivet where the skin above is dimpled, don't try to measure the size of the countersink or rivet head. Van's general recommendation is countersink until the rivet is flush and then add a couple clicks on your microstop cage to allow the skin to nest completely. In most cases I've found that 5-6 extra clicks works best.

Hope all this helps.
 
Sorry Steve. I meant to say the thickness of the "VS" (vertical stabilizer) rear spar is .085" and yes that is countersinkable - is that a word? :D . Sometimes I confuse even me - not hard to do.

I did countersink my "HS" stab spars. That process went quite well.

Thanks for the "heads up" on the 5-6 extra clicks. I'm just gonna have to make sure the doubler sits flush against the spar.

One day it will fly - right now it's just aluminum.
 
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