T-905 Tank Attach Bracket

skelrad · #1 12-21-2021, 06:32 PM

The instructions basically say to fabricate the T-905 tank attach bracket out of the angle, then plop it into the nose of the tank and drill holes through the rib. There is no mention of how specific the alignment needs to be (I assume the angle that protrudes should be somewhat parallel to the tank baffle). I didn't really think about this until I had drilled my first hole and noticed the bracket had slipped. At that point it was obviously too late.

I looked at the plans, and my best guess at this point is the coinciding attach bracket on the fuselage gets drilled in assembly and can handle the tank bracket not being perfectly vertical (with the tank in final orientation). Is that correct? How much wiggle room do I have? If I need to get a new inboard rib and redo this so the bracket is actually parallel to the rear baffle, now is the time.

wirejock · #2 12-21-2021, 07:04 PM

Quote:

Originally Posted by skelrad

The instructions basically say to fabricate the T-905 tank attach bracket out of the angle, then plop it into the nose of the tank and drill holes through the rib. There is no mention of how specific the alignment needs to be (I assume the angle that protrudes should be somewhat parallel to the tank baffle). I didn't really think about this until I had drilled my first hole. At that point it was obviously too late.

I looked at the plans, and my best guess at this point is the coinciding attach bracket on the fuselage gets drilled in assembly and can handle the tank bracket not being perfectly vertical (with the tank in final orientation). Is that correct? How much wiggle room do I have? If I need to get a new inboard rib and redo this so the bracket is actually parallel to the rear baffle, now is the time.

Yes on the 7 and probably the same for the 9. Square it up to the baffle. The angle will have a hole and the steel angle on the fuse will have a slot. They overlap about an inch. The steel angle on the fuse can be tweaked a little but ideally you want to start with the tank angle oriented close to vertical.

alpinelakespilot2000 · #3 12-21-2021, 07:21 PM

Just try to get the vertex of the angle to be as parallel to the stiffening groove in the rib (or back baffle) as possible. Then, IIRC and as you presume, you’ll have a chance to adjust for any slight misalignment when you go to drill the companion angle to the fuselage.
Good luck.

PaulvS · #4 12-21-2021, 07:24 PM

Unfortunately the plans don't often give info on allowable tolerance. When I attached that angle to the tank I made it parallel to the baffle (measured using a straight edge clamped to the angle).

The sides of the fuselage (at the attachment point) taper in slightly toward the firewall and that is the only thing that might cause an issue if the angle is too far off from being parallel to the wing spar. I'd guess it would need to be out by more than at least 1/16" across the width of the angle to potentially be a problem. If yours is really really out and needs to be redone then it may be easier to replace and redrill the angle rather than the rib, or do some slight bending or shimming at final assembly.

skelrad · #5 12-21-2021, 08:02 PM

As much as I want to just move on, I think I'd better order a new inboard rib and take a mulligan. Thanks for the input.

ScottK · #6 12-22-2021, 07:51 PM

Quote:

Originally Posted by skelrad

As much as I want to just move on, I think I'd better order a new inboard rib and take a mulligan. Thanks for the input.

Well I hope not, I just drilled mine on by eyeballing the alignment. The handbook section 8 (8-14 in mine) talks about this, and refer to drawing 38 for the arrangement of mating bracket F-996A. It's drilled to the fuse in assembly, so any alignment roughly vertical to the floor ought to be fine.

skelrad · #7 12-22-2021, 08:14 PM

Quote:

Originally Posted by ScottK

Well I hope not, I just drilled mine on by eyeballing the alignment. The handbook section 8 (8-14 in mine) talks about this, and refer to drawing 38 for the arrangement of mating bracket F-996A. It's drilled to the fuse in assembly, so any alignment roughly vertical to the floor ought to be fine.

Eyeballing is probably fine. My mistake was I didn't consciously eyeball, and then during the drilling the bracket slipped a bit. I didn't realize it until it was too late, making it about 1/8" out of vertical from one side to the other. At $17 to replace the rib, it's worth it to me to not end up with a finished tank that then has a bracket that is impossible to use.