[Balloon-makers] Oxygen Starved Burner?

[Kyle Kepley]

Hi Noah,

I've attached some pictures of my project.  The blimp pictures are actually 
a smaller one that was my first attempt, which was 1300 cubic feet.  This 
one was under powered for propulsion because I didn't bother to actually 
calculate the thrust required based on the internal mass of the air to be 
moved.  The new one has much bigger motors, which can be seen in the 
gondola pictures.  There was also a problem in this first model that the 
air would rush to one end and cause the blimp to stand on its nose or tail. 
 I tried usnig a half-wall bulkhead to stop that, but with only a single 
burner I couldn't heat the air on either side of it so that didn't work 
either.  Thus the new gondola has two burners angled at 45 degrees and the 
bulkhead is sewn in directly above them.  This now works quite well.  I had 
to rebuild the blimp to a size of 2900 cubic feet to lift the additional 
weight, but it still looks the same as the first one pictured here.

The blimp in the picture has a very yellow flame because I'm mostly flying 
these at night and I liked how the yellow flame lights the whole thing up.  
I can adjust this though, and in the new blimp I have it set so the flame 
is blue from where it comes out of the burner to about 50% of the flame 
length, then it is yellow at the tip.  This doesn't light up the blimp 
nearly as well, but I guess it's a trade-off.

I cold inflate the blimp to about 75% full and then hot inflate it the rest 
of the way.  There's a zipper access panel at the bottom which I open up 
during hot inflation to bleed of excess air so the envelope doesn't pop.

The pressurization fan blows straight up directly between the burners.  It 
sucks air up from the outside of course.  The envelope mounts to the 
gondola frame right under the angled "roof" that the burners are mounted 
to.  There are no open holes other than the ducted pressurization fan.  
Since the burners need to throw two flames in a wide V pattern, I don't 
think there is any way they could ever be mounted externally.  The large 
hole this would require would make it impossible to keep the envelop 
pressurized.  The envelope must be tight to support the weight of the frame 
members that keep the fins rigid, otherwise the tail will sag.

I designed the envelope to be very air tight, since my thinking was that 
I'm burning all this fuel to reduce the air density and letting more dense 
air in from the outside only wastes fuel.  But now it looks like there is 
no alternative due to the oxygen starvation problem, adding more evidence 
that thermal airships are probably the most energy inefficient flying 
machines ever devised!  I only hope that the burners are not consuming 2900 
cubic feet worth of air per 15 minutes, because there is no way I can 
replace it at that rate.  I'm hoping that the air in the top half of the 
blimp still has oxygen but just doesn't get to the burners since it stays 
at the top.  If this is the case, then I would only be depleting oxygen out 
of the cooler air sitting at the bottom of the blimp and might have a 
chance at pumping enough fresh air to keep up with the rate of consumption. 
 Perhaps I could redirect the air-flow from the pressurization fan so that 
it blows right up under the burner.

This initially started as a practice project to learn how to sew balloons, 
then thurned into an addicting series of challanges that seem to never end! 
 It looks like I'm down to just this one problem now.  Of course once I fix 
this there will probably just be another problem to replace it .

-Kyle

 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.taleos.com/balloon-makers/attachments/20090411/f536cd42/attachment-0001.htm 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: flying_1.jpg
Type: application/octet-stream
Size: 191222 bytes
Desc: not available
Url : http://lists.taleos.com/balloon-makers/attachments/20090411/f536cd42/attachment-0004.obj 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: fins2.jpg
Type: application/octet-stream
Size: 368598 bytes
Desc: not available
Url : http://lists.taleos.com/balloon-makers/attachments/20090411/f536cd42/attachment-0005.obj 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: blimp2_burner1.jpg
Type: application/octet-stream
Size: 83524 bytes
Desc: not available
Url : http://lists.taleos.com/balloon-makers/attachments/20090411/f536cd42/attachment-0006.obj 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: blimp2_burner2.jpg
Type: application/octet-stream
Size: 96105 bytes
Desc: not available
Url : http://lists.taleos.com/balloon-makers/attachments/20090411/f536cd42/attachment-0007.obj