[Balloon-makers] Racer Shape

[Dave Steven]

On 8/9/07, Donnelly, Shanon <sdonnell at indiana.edu> wrote:Greetings all,

I am coming to the end of building a racer shape and am curious to hear
folks thoughts on some of the questions posed in the previous couple of
emails.

This all may be moot since your balloon is "coming to an end" but I'll throw
my 3=A2 in here.

When I built my first balloon in 1977 I used a "natural shape" program that
was developed by Litton Industries via some declassified US Government
project and available thru one of their publishing outlets. (Springfield, VA
comes to mind)

The local FAA office wanted me to do a Terminal Velocity Descent in my
homebuilt before giving me my Airworthiness Certificate. I borrowed a seat
type parachute, put on my motorcycle helmet and did just that.

Fast forward a dozen years and I'm in Chateau d'OEx Switzerland watching the
J&B Scotch bottle special shape balloon. The pilot (Tom Donnelly?) hated to
fly it as it had a tendency to "drop out of the sky" if you didn't stay on
the burner. Even tethering was a PITA as the neck of the bottle would flop
over and not re-inflate.

My point is this question: Is your "racer shape" balloon recoverable from a
TVD? The J&B bottle was not. Mine was. With an engine out in an airplane and
you have some glide path. Will a burner out in your racer shape cause it to
eventually streamer to the ground?  I don't know; is there a design "tipping
point".

How do you want to find out?

Dave Steven


1st logbook entry: Semco 1975
1st used balloon: Piccard
1st new balloon: Barnes
1st used airship: Cameron D38
1st new airship: Colt AS42
Last logbook entry: Sky 320 1999



On 8/9/07, Donnelly, Shanon <sdonnell at indiana.edu> wrote:
>
> Greetings all,
>
> I am coming to the end of building a racer shape and am curious to hear
> folks thoughts on some of the questions posed in the previous couple of
> emails.  I took the path of basing my pattern off of one of the
> commercial builder's shapes and so the volume should come out similar
> to that (60k).  It would not take too much CAD knowledge to scale the
> pattern to another volume.  Obviously, in terms of surface area to
> volume, a racer does not use fabric efficiently.  The fact that the
> panels are closer to rectangles might save a bit on wastage, but not
> much.  I have been told by the manufacturers (that are trying to sell
> their balloons) that the tall/skinny racer shape has a higher lift to
> volume efficiency due to something about less thermal stratification
> and therefore more of the volume can be heated to a higher temp.
>
> A year and half ago when I started, I just wanted to build something
> different...now these things are everywhere.  c'est la vie.
>
> Happy to share the pattern I used if anyone cares to look at it.
>
> best,
>
> Shanon
>
> Kent, OH
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