Tony Bingelis vs. the Rest of the World (Bend Radius)

[rwanttaja]

Hmmmm.

According to just about every source I can find online, when one bends 4130N sheet steel, the bend radius should be at least three times the thickness of the metal (3T).

http://www.bjg-design.com/designbook/shbend.htm

However, on Tony Bingelis "Sportplane Construction Techniques," he specifies a 1T bend radius for "Aircraft steel".

Fly Babies use a bent 0.093" 4130 fitting to hold the landing gear on. Bowers doesn't specify a minimum radius, other than saying a "slight radius" in his generic instructions up front. Most Fly Babies I've seen seem to go for the 1T radius on this piece. Pete's cross-sectional diagram showing this piece also seems to show a tight radius.

So...3T or 1T? Anyone else want to throw an oar in?

Ron Wanttaja

[Frank Giger]

Well, Ron, since I've never heard of a Fly Baby having gear problems, I reckon Tony is onto something.

I tend to squint an eye on one-size-fits-all guidance, as it really matters on application. Not all pieces are under the same sorts of stresses, and that, more than anything, matters the most, IMHO.

[rwanttaja]

Well, Ron, since I've never heard of a Fly Baby having gear problems, I reckon Tony is onto something.

I tend to squint an eye on one-size-fits-all guidance, as it really matters on application. Not all pieces are under the same sorts of stresses, and that, more than anything, matters the most, IMHO.
Yeah, it's funny. I can find all sort of online data to justify the 3T bend radius.... but going against Tony Bingelis' recommendation is dangerously close to tugging on Superman's cape or spitting into the wind. On the Fly Baby, after making the bend, a piece of steel tubing is welded on the outside corner. Might be that any slight cracking gets taken care of during this process.

Been discussing this on FB^2 (Fly Baby Facebook page), and while most folks posted about the online references saying 3T, 1T was echoed by a tool and die maker. On page 44 of "Sportplane Construction Techniques" Bingelis shows the 1T as part of a table, and says the values were "....derived from reliable USAF and FAA references." Wonder our tool and die maker learned his trade at the same time as Tony. Tony also mentions the 1T guideline in an article in the January '72 issue of Sport Aviation.

Ron "Pulling the mask from that ol' Lone Ranger" Wanttaja

[Bill Berson]

I think Tony can bend tighter if the bend is correct for the sheet "grain"?

[ulpilot]

3T when bent parallel to the grain, 1T when bent 90 degrees to the grain. This is for normalized (N) 4130, annealed (A) 4130 can be bent to 1T regardless of grain direction. Annealed used to be readily available, but not so much nowadays.

[Frank Giger]

But annealing metal is fairly straight forward, as is normalizing the metal after a large bend.

I don't have Tony's books - do they discuss heat treating metals?

[ulpilot]

Annealing aluminum is easily accomplished in the home shop. Steel is more difficult to do correctly, temperature, duration at annealing temp, and rate of cool down need to be controlled. So a decent heat treating furnace is needed. I have done some in my shop using a torch, but results have varied greatly as I don't have the ability to control the process accurately.