P

prkaye

Well Known Member
I have a question about the fuel tank attach brackets. There is a bracket on the fuel tank that gets bolted to a bracket on the fuselage (DWG 38). The fuselage bracket gets a slot extending out from the bolt hole to the edge of the bracket... I believe this is so that in the event of an impact the fuel tank can tear away backwards away from the fuselage.
What I don't understand is why the corresponding hole on the fuel-tank bracket is specified to have a minimum 1/2" edge-distance. With the slot in the fuselage bracket, under a sufficient shear load the bolt would rip through the slot to the edge of the fuselage bracket long before it would rip through the (non-slotted) tank bracket. It seems strange that they would deliberately design a weakeness into one bracket but then insist on a very generous edge-distance on the second bracket that it gets bolted to.
Any ideas?
 
Vertical support...

The slotted bracket support the fuel tank in the vertical direction only. This is the only support point near the leading edge of the tank (fuselage side), as such, it could be submitted to quite high force during high G maneuvers.

Since this bracket play a role in maintaining the structural integrity of the assembly, that explain why it`s important to maintain the edge distance...


Michel R.
 
Phil: Also, if read the directions carefully, the bolt that is used in slot to hold the front edge in place must not be tighten normally. The idea is the bolt will hold the front load of the tank adequately. But in an impact allow, the wing the possibility to shear away without ripping open the inboard end of the tank and allowing all that expensive av gas to be wasted by splashing all over the fuselage. Dan
 
Differn't materials

Keep in mind the fuselage bracket is steel (chromoly?) while the tank bracket is Aluminum. To quote Van's they are unaware of edge any distance requirements for steel.
 
Also, IIRC, when the bracket system was originally designed on the earlier models there was no slot in the fuselage bracket. That was a modification that came later. So it may also be that the brackets weren't completely redesigned.
 
wingtime said:
Keep in mind the fuselage bracket is steel (chromoly?) while the tank bracket is Aluminum. To quote Van's they are unaware of edge any distance requirements for steel.
Click to expand...
On the -7, yes. On the -9, the fuselage bracket is aluminum angle.
 
The slotted bracket support the fuel tank in the vertical direction only.... Since this bracket play a role in maintaining the structural integrity of the assembly, that explain why it`s important to maintain the edge distance...
Click to expand...

But this edge distance is specifically shown in the horizontal direction (where the hole is closest to the edge because of the tapered shape of the bracket).
 
But this edge distance is specifically shown in the horizontal direction (where the hole is closest to the edge because of the tapered shape of the bracket).
Click to expand...

A vertical loading will be applied to the hole. If the hole is very close to the edge (horizontally, as you said), there won`t be enough material and you just create a high stress region were a crack/fracture can occur.

Michel R.
 
You must log in or register to reply here.