Thermal Airship Prototype (RC)

This is the prototype for an electric powered thermal blimp I'm eventually going to build.  It's a fully functional RC model that is 40 ft long.  I'll post pictures of my progress here since you guys seem to be interested in this sort of thing.

Here's the pictures for the construction of the gondola frame, made from welded aluminum tubing.  The full size one will be made from welded stainless steel tubing, but the basic structure will look much the same.

Here's a few more pictuers with the completed burner unit attached

The art work and the metal work are outstanding!

What software is the model built in?

Really top notch work all around, congratulations on a job well done. The kid is looking longingly at the gondola, thinking, gee, I can just fit in there........

LOL, not another balloon boy!

I agree, looks great. You gonna run a fan to keep the envelope pressurized? I thought I saw little ducted fans on the gondola, but wasn't sure. Keep us posted.

The modeling is done in Rhino 3D, which is a full featured 3D modeling program without the big price tag of the  ones like SolidWorks or 3D Studio.  My wife is taking a few college courses so I used her student ID to get a "student edition" of Rhino, which doesn't have any restrictions or missing features but only costs $150 instead of the normal $800!  There is a free trial version of Rhino where the only limitation is you can only save your work 25 times.  I used the free version to design several blimp envelopes before finally buying it.

Rhino can calculate the volume of curved solids, so getting an accurate volume of your envelope is easy.  Then you can model the gores and flatten them out onto a plane to get templates for actually cutting them out.  I've come up with a fast method of producing the templates where I burn a scale image of each panel onto a CD slide show, then use a video projector to project them onto the wall at the proper scale where I can then trace the images onto a large sheet of paper.  This is a LOT easier than the tedious process of having to graph out the data manually and connect the dots.

LOL, not another balloon boy!
You gonna run a fan to keep the envelope pressurized? I thought I saw little ducted fans on the gondola, but wasn't sure. Keep us posted.

-dude6935

Yes, there are two ducted fans which serve three purposes: 1) pressurize the envelope so it holds it's shape (pressure from  hot air is not enough), 2) feed fresh oxygen to the burners and 3) force out the carbon dioxide byproduct of combustion which collects in the bottom of the envelope and would normally smother the burner within 10 minutes if not vented out.  This could be done with one single larger ducted fan, but I had two of them laying around from another project so I put them to use.  Larger size ducted fans also do not seem to be common on the market, whereas these little ones are everywhere and pretty cheap.  A deflection shield above each fan directs part of the airflow into the burner.

If the carbon dioxide is a hot burner product, why would it collect in the bottom?

If the carbon dioxide is a hot burner product, why would it collect in the bottom?

-swampie777

Because CO2 is heavier than air.  All gases in the bag are heated equally, so the temp doesn't play a role.  The heaviest molecules sink to the bottom, which is actually a good thing it does because it makes it easy to vent with minimal heat loss when letting it escape from a flap in the bottom.

I got the propulsion system done over the weekend.  The final gondola weighs in at 23 pounds fully fueled!

Well, that was the hard part.  Now for the sewing :)

Nice work  Pyro !    What  do  you  expect  your  max hot air lift  will be ?  As  far as I know ,  this  will be  the first  vectored  thrust  HAAS  in  the  world !   
   Also  How  long  do  you  expect the  propane  to last ?   Again  very  nice  craftsmanship .
 IM

I think it is indeed the first vectored thrust themral airship ever built actually.  Probably because the vectored thrust is not completely necessary on a thermal airship the way it is on a gas airship which can't dynamicaly change its lift, but I think it has two primary benefits on a thermal: 1) if you underestimate the response time of a burn and can't get lift in time to avoid an undesireable situation, you have an additional method of adding instant lift to avoid the problem and 2) being able to point the thrust downward allows you to land heavy without a bounce, which in turn allows you to "stick" the landing better without having to vent hot air.  The way I look at it, there's not much more cost in terms of weight or complexity to add the vectored thrust feature, so might as well have it available to play with.

My first blimp with the 15 pound gondola and 2900 cf volume could go 15 to 20 minutes on two tanks of fuel (including inflation).  This 23 pound gondola is going to require more volume to lift it, but I would imagine the numbers won't change all that much just like they don't change much on real hot air balloons when going from one size up to the next such as from a 90K to 105K volume.  I'm making the new envelope big enough to lift a third or even fourth fuel tank for longer flight times between change-outs.  So say 25 lbs gondola (three tanks), 10 lbs envelope, 2 lbs for fins and tail thruster and throw in 1 lb for good measure and arrive at 38lb total system weight.  I use a lift factor of 13 pounds per 1000 cubic feet, which is for an envelope temperature of 200 deg. F and an outside temp of 80 deg. F.  By designing for a low operating temp on a hot day, you give yourself more wiggle room for overshooting your weight estmiates and other factors like air density.  So if I want 40 lbs of lift I only need a 3076 cf envelope.    The envelope in the drawings above is actually 3230 cu ft, which is the envelope I'm actually going to make.  So my total lift on an 80deg day at 200deg envelope temp will be 42 pounds.