Light Sport Category ~ 660 Lbs

The below article gives a brief description of the FAA Light Sport Category guidelines with a 660lbs maximum takeoff weight for airships under this classification.

http://www.iflyamerica.org/sportpilot.asp

Maybe this is the classification that the small blimp should try for?  This would need to include the envelope, control surfaces, motor(s), fuel, seats/cabin structure, and I believe helium as well.

I did a little research, the White Dwarf  http://home.teleport.com/~reedg/whitedwarf.html
came in at 140lbs empty, adding in the helium at 6200 cubic feet at about .011 lbs http://www.howeverythingworks.org/page1.php?QNum=1492  so about another 68.2 lbs.

So is it possible to create a two person ship under this category?

-Paul

Yah, I think that might be a good target for a two person blimp. For a one person blimp you could shoot for being ultralite which I believe is around 250 pounds empty. Both light sport and ultralite classifications make it easier and cheaper to fly and far as licensing go. 

And I believe that it shouldn't be difficult to come in under 660 lbs. for a two seater blimp. I assume that weight does not include the occupants right?

I think the weight includes the passengers, with that in mind 660lb maximum takeoff doesn't leave much room for error, don't think I'm biased against anorexia but I'm a good 200-210lbs and having two of me flying would be 400lbs leaving only 260 for everything else.

Just my thoughts, but I could be wrong.

The 660 lb limit is the "max take-off weight" for a "lighter than air aircraft". So I guess it does include the weight of the occupants...

That might be tough. 

The weight limit for regular aircraft is 1320 lbs. 

 Not saying its a bad thing , but  now  you need  Sport rating to fly  it with  an Airship indorsement ,  and  FAA  inspections. It  would be  under the   ELSA  provisions ,  And  the  water gets murky  from here.  

Still designing for 660 is a LOT easier than 254 !

6200 cubic feet of helium is only 400 pounds of lift.  Your outer skin will be about 20% of that, maybe a little less, that's 80 pounds. 20 pounds for batteries and brush-less motors, 10 percent for inner bags, 40 lbs,  some kind of frame, weather it is internal or external is going to be 40 to 100 lbs, say 70 and 20 lbs for hardware and landing gear.  That's 240 right there, if you weigh in at around 160 you can bring a soda and a sandwich.  But for two people?   I believe a more ridged frame is needed and much more volume.   Consider proposing a weight budget for everything you can think of, assign it a percentage and then find materials that you can use to come in under budget.  I have done this for ships that are not practical, such as the Enterprise and Reliant and the Millennium Falcon until I came up with a size ship that would work.   If you are given a restriction, then everything must be scaled down to that, creating a small budget for everything.   For instance, if you had 20,000 cubic feet of helium, a ridged frame for a nearly round cross section might be 40 percent, the skin has to be thick and strong to retain helium, at about 20% or an ounce per square foot or less.   I can give you weight statistics for various grades of PVC pipe that is light enough to build an air ship.  Aluminum and Magnesium are far too heavy and expensive.  A four foot by 16 foot cabin can be built inside the ship with about 100 lbs of materials, air tight.   That is less than 8 percent of the 1300 pounds of lift.   Frame @ 40% is 520 lbs, skin @ 20% is 260, inner bags at 5% 65lbs, a cabin is 100 lbs,  motors and batteries at 2% 26 lbs, say 30 lbs that's about 75 % so far, and one quarter of 1300 is 325 lbs, that is two light people.   That is a ship in cylinder form about 20 feet in diameter and 66 feet long.   If you make a blimp with no frame, then you have to have an external carriage or gondola that is supported with ropes attached to multiple points all around the outside of the ship.  Am I right.  Can you build a box inside a blimp and support it well?  It might deform the shape and steering ability.   can you give me some more info on this project?

I would design to the maximum weight limit, since that weight limit is not very high and airships become more efficient with size. That would mean starting with an envelope that produces 660 lbs of gross lift. Now you have more lift to play with for occupants and everything else. For helium, that would be about 300 m^3 or nearly 10600 ft^3. Now if you find that you have lift to spare after accounting for everything, you can reduce the volume a little.

How about a lift assisted aircraft?  Since the limit for sport aircraft is 1320 lbs you could design a lifting body that was not quite bouyant at its empty weight and depend on dynamic lift for the payload weight.  That would also make landing easier.  There have been many such designs proposed and I think that a few built, at least in reduced scale.  When flown with only one person the takeoff performance would be spectacular.

If the envelope is a lenticular (M&M) airfoil shape the lift coefficient required would be very low because of the large surface area.  The extra weight allowed would also make it easier to make a rigid airship which would make the airfoil shape more efficient and lower drag.  I suspect exceeding the upper 130 mph would not be anyting to worry about.

Also, you would have to limit the propulsion to one engine and one fixed pitch prop to meet the lght sport aircraft requirements.  A qood question to pose to the FAA would be the use of one engine/generator or hydraulic pump and multiple remote motor/prop units that were not individually controllable.  The argument could be made that they constituted one propulsion unit.  The regs don't say anythng about a swiveling propeller so you could develop enough thrust for near vertical takeoff that way provided the thrust line was at the C.G.

Vince Homer

See my recent comment on this as it may give you a new path for your project.

Also, PVC pipe may be cheaper, but I think you will find that from a strength standpoint, aluminum would be much lighter to get the same rigidity.  About 30 years ago there was a couple guys building a dirigible using electrical conduit.  The got to the one-man stage and I lost contact with the project.  It was featured in the Lighter-than-air society newsletter several times if anyone has copies rom the 70's.  I'm currently in Saudi arabia and don't have access to my back issue collection.

Vince Homer

Never heard of people using electrical conduit. That is a cool idea, not that I am a fan of rigidity in general. 

And yes a hybrid airship would be much easier to get two people into, while being under the weight limit. I don't want to be at the mercy of the FAA on whether a hybrid qualifies for the higher weight limit. We might have to send them a letter to verify that we would qualify. 

Fill it with hot air on a sunny day,....it will qualify. :)

Are you referring back to your #6 post? The size of an envelope for two people is going to be too draggy on hot air. Maximum affordable lift with good drag performance will come from using Hydrogen.