[Balloon-makers] Racer Shape

[Donnelly, Shanon]

Dave,

Just the kind of experience I was hoping to hear about.  I would 
certainly agree that there are some questions about safety and going 
too far.  People seem to be getting close to the limits with this 
generation of racers and rates of climb and decent in the 2000 fpm ball 
park.  Any balloon can be pushed too far and it is our job to not do 
that.  I would love to hear Phil's talk on the history of racers.

I guess my general answer is that I hope to minimize the unkowns by 
following in the footsteps of tested products.  Even if I don't 
reproduce them exactly.  Part of the fun of homebuilding, to me, is the 
freedom to screw up and the responsibility to not screw up too badly. 
But in no way am I advocating people to build one thing or another.

Given the choice, I bet most folks would choose a racer over a Semco 
and lots of folks survived those :)

Thanks and good to see some action on the list,

Shanon

Kent, OH

Quoting Dave Steven <daveandjanis at gmail.com>:

> 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¢ 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
>