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RepmikeBrown

Well Known Member
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What is the reason for countersinking the upper mounting platenuts and dimple counter sinking the lower platenuts? I got on a roll and installed all drilled countersunk platenuts for the bottomside of tank and was wondering if I've got to drill them all out now? I haven't done anything to the tank skin yet so it's just a matter of drilling out several platenuts.

I'll try to insert a pic of the plans of the tank, the area I'm referring to is at the bottom, two rows of holes locations. The platenuts go on the spar flange. Thanks Mike
repmikebrown
 
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Photo

Hi

Although I have built several tanks I am not sure of where you are talking about, a photo would help.
 
Hi

There are several reasons why the upper tank attach flange is not dimpled. Quite apart from the fact any dimple would be almost on the radius of the 90 degree bend in it, For it to work it would require the tank skin and the rear baffle to be dimpled and there is not enough material on the rear baffle to do this.

Also if the skin and baffle were dimpled they would require stretching over the spar attach plate so the tank dimples could sit in the upper attach flange dimples. This would probably break any seal on the rear baffle and cause the tank to leak, and would be impossible to get on without scratching the upper attach flange.

You will see in the plans that the tank skin and rear baffle are countersunk to accept the mounting screws. I really hope you have not dimpled the upper attach flange, if you have not it is relatively easy to remove and replace the platenuts. If you have dimpled the flange....then life is considerably more difficult as squeezing the dimple flat would leave the area significantly weakened especially if you have anodized parts. I really would not want to do this as this is the main attach point for the tank.

We all make mistakes especially when we think we are on a roll...... it is best when doing things like this where one type of platenut is used close to a different type to mark each type called out for in a different colour sharpie on the plans and part being worked on........then to triple check you have marked them correctly.

Hope this helps...
 
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Steve,
Thanks for the reply, I haven't dimpled anything yet. Just installed the drilled platenuts on the bottom where dimpled platenuts were to be installed. Since the materials are the same would the machined countersunk work instead. This is only the bottom 8 or so.
 
Go with the plans

Hi,

I think what your asking is, 'is it Ok to countersink the spar web where the lower row of tank screws will fit rather than dimpling them."

Again I would not go there..... reason,firstly the spar web is too thin to accept a countersink that deep, secondly it takes away material quite close to where the rivets attach the platenuts and you probably would not have enough meat there to prevent cracking...... not desirable on a high stressed part!!

I have to say Van did a good job when he though the tank attach out and basically it has to be done as per plans to make it work...... in fact that can be said of almost all the airframe.

The answer her is to carefully drill out the incorrect platenuts and build is as per plans..... the spar and tank attach are not really areas you can improvise too much on. It really wont take long to drill out and replace the platenuts and you will have the peace of mind knowing its built correctly.
 
Thanks Steve,
After talking with Vans this morning I'm doing what you said.
The tank skin isn't thick enough for the machine counter sunk either.
Lesson learned. At least the other tank will go quicker
 
Helpfull.

Hi,

Well is one thing to read the plans, another to follow and build to them, and yet another to understand why things have been designed that way!!

The best way to build an RV is as per plans....the basic construction that is.... there are things that can be improved....... for example if I were to build again I would go fastback. The basic construction though is well thought out and has stood the test of time.

Feel free to ask if you hit any more snags...... best to learn from others mistakes rather than make your own.
 
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