In article ,
Ernest Christley wrote:

Richard Lamb wrote:
Smitty Two wrote:

In article . net,
Richard Lamb wrote:


Ernest Christley wrote:

I can't figure this one out.

I want to add a retractable step that will stick out of the fuselage
at a 40 degree from vertical angle. It sticks out 10" and is made
of 3/4" square, .065 thick, 4130 tube. Assuming no weakness in the
support, will this support a 300lb man (me with all my luggage on my
back), and how can you tell?


I think it's the "assuming no weakness in the support" part that has
everybody tongue tied.

The square tube sees healthy enough.

It's the "rest of the story" that will make a difference.



Well, if I'm tongue-tied, it's mostly because I don't know why he
wants a step that sticks out from vertical at some angle other than 90
degrees.


yep!


It's retractable. It has to have someplace to retract to. It is
attached to the outboard end of a delta wing, not a conventional
fuselage. The odd angle is so that I can attach it to structural
members and have it stick out past the leading edge. The height is such
that it has to be lower than the leading edge to be useful.

The plans call for a step welded to the leading edge that does not
retract. This leaves an ugly step dangling in the wind, where it's
turbulanc can do maximum damage. It is also so high that it is barely
useful. You almost need a step ladder to reach the step. It works, and
is simple, but I think I can do better.

The 3/4" tube has a sleeve welded around the top. It slides in a
1"x.065 square tube that has a sleeve welded around the inside at the
bottom. The 1" tube is to be welded to structural members. The sleeves
positively capture the inside tube, and there is 1.5" of overlap in the
two tubes. Both sleeves have several inches of weld.

My biggest concern is the inside tube not being strong enough and taking
a slight bend over time. Then it will no longer slide. Hence my
question. If it were a straight beam, I think I could run the
calculations, but how do you analyze it when the cantilevered beam isn't
straight?

OK, now that's a little more clear, but we're still talking about a
support member. It's good to say what we mean, I think. A step support
bar isn't a step anymore than a spar is a wing.

Engineers spend too much time thinking. Clamp the piece of steel to
something solid and jump up and down on it. You'll have your answer in
the time it would take you to find the back of an envelope and dust off
your slide rule.