[Balloon-makers] basket bottomes

[GlennADavis.net]

I have seen the recent discussion regarding the materials for a basket
bottom.

I am an experienced engineer but very new to balloon design but I had some
thoughts regarding the recent inquiry about choosing the right material for
a basket bottom.

If  I were going to build a basket, I’d either copy one that has been
popular or go through some design process in an attempt  to improve it.
Copying a basket doesn’t require much thought but I have some ideas
regarding a redesign.  Since I am new to ballooning you might consider my
ideas more an exercise in brainstorming.  Perhaps someone with more
experience could  give the floor some thought and try to improve it.  Here
are my thoughts.

The first approach in designing the floor is to delineate what you want to
accomplish.  That doesn’t seem so simple to me.  I’m sure there is criteria
in the back of the minds of experienced people, but I’ve never seen any
design criteria listed which would be a good basis for input from others in
a collaborated design approach.

Possible design requirements might include resistance to puncture, light
weight, high strength to weight ratio, energy absorbing,  abrasion
resistance,  easy to slide into a van or onto a lift, appearance, and ease
in transitioning to wicker sides (if a wicker basket).

Treated plywood is hard to beat.  Plywood with water resistant glue (what
used to be called marine plywood) makes the most sense.   If you have
sufficient armor on the bottom and crisscrossed cables underneath, the
chances are that half inch plywood would be adequate for dead load. Double
this for impact loads.  Instead of using ¾ inch  plywood, why not use two
layers of half inch. Then trim out the edges and add skids.  Skids should
probably be placed in the direction in which you are loading the basket onto
a lift , van or trailer floor. Skids should be armored with something
slippery like Teflon or high density polyethylene. They need not be large or
deep and any type of material might well be adequate provided it is
reasonably abrasion resistant or armored with something.   Two layers in the
floor would allow you to slip in a thin sheet of steel to provide some
puncture resistance. (I cringe at the thought of being impaled on a sharp
object that came through the bottom in an unfortunate landing.) Kevlar is
another possibility.   I would consider the extra 40 or 50 lbs that a 40-50
guage steel plate weighs, worth  the loss in load capacity for the benefit
it might provide..

The crisscrossing of ribs on the underside of the floor (which I have seen
often) seems to be a bad option except for the fact that you can hide
crisscrossed cables within them.  It is not appropriate for ribs to
reinforce the floor or for skids. Structurally it would make sense to run
any ribs in the long direction however from a loading up point of view it
might be better to run them in the short direction and if so, they would be
less strong but strong enough and much more efficient for loading up onto a
lift or trailer. From my experience with plywood, I would think that except
for very large baskets, skids are only needed for abrasion resistance, not
for strenght.

Could someone experienced list some design criteria, and let’s start getting
innovative together.  Its time to apply some of the technology we now have
to overhaul the design of the floor.

Glenn A. Davis, P.E.
gdavis at glennadavis.net