Major or Minor Change?

[DanH]

What would concern me is that this mount isn't backed up with the stock belt... This belt is the backup for the stock belt...

Nope. These are the mounts for the ratchet belt. In aerobatic flight they are primary, as they will be a heck of a lot tighter than anyone can pull the stock belt. If they fail, then the poor fellow is hanging on the stock belt, which in theory is good for the -3 limit load. He will probably bump his head on the canopy, and he may crap his pants...but he won't leave the airplane.

 

[Snowflake]

Nope. These are the mounts for the ratchet belt. In aerobatic flight they are primary, as they will be a heck of a lot tighter than anyone can pull the stock belt. If they fail, then the poor fellow is hanging on the stock belt, which in theory is good for the -3 limit load. He will probably bump his head on the canopy, and he may crap his pants...but he won't leave the airplane.

Ah! Okay, that makes sense. My discomfort with loading the fasteners all in tension and directly to the flange remains, however.

 

[DanH]

Ah! Okay, that makes sense. My discomfort with loading the fasteners all in tension and directly to the flange remains, however.

Understand. As noted previously, I too had concerns, thus the basic redneck stress calculations. Best would be as Jack suggested, FEA followed by a test model or two. Or just build stout to the point where no one has discomfort. Given the very small weight gain, I sure ain't knockin' it.

 

[skylor]

Y&

Ah! Okay, that makes sense. My discomfort with loading the fasteners all in tension and directly to the flange remains, however.

Why? Fasteners can be loaded in tension if sized for it and we do have some critical fasteners in our aircraft that are. These include the forward HS stab bolts (in some loading scenarios), engine mount bolts, nearly every critical engine fastener, RV-8 landing gear bolts, and control pushrod rod-ends. The main thing to ensure longevity of tension loaded fasteners is that they have sufficient preload (torque) to prevent fastener exposure to cyclic stress loading under the max design loads.

Skylor

 

[Snowflake]

Why? Fasteners can be loaded in tension if sized for it and we do have some critical fasteners in our aircraft that are. These include the forward HS stab bolts (in some loading scenarios), engine mount bolts, nearly every critical engine fastener, RV-8 landing gear bolts, and control pushrod rod-ends. The main thing to ensure longevity of tension loaded fasteners is that they have sufficient preload (torque) to prevent fastener exposure to cyclic stress loading under the max design loads.

Sorry, I should have said that there's nothing inherently wrong with loading a bolt in tension, just that i'd prefer to load one in shear instead. Mostly for the reasons you give... Preload is key, and easy to f-up. A bolt in shear doesn't need any torque, just a pin through the nut so the bolt can't fall out.

 

[Mikeyb]

There is some advantage to moving the attach points forward a few more inches. The belts tend to bunch up as is. Maybe tying the crossmember into the angle brackets .