Dude's Ultralight Design

This is an attempt to offer the most minimalistic UL airship possible. So here is the idea.

The airship is based on a hang/para glider. The pilot will be slung beneath the envelope and will steer the craft with a weight shift bar. This will eliminate the need for wheels, seating, breaks, active control surfaces, windscreen, ect. The airship with be launched by foot. If the pilot is incapable of running up to stall steed, free spinning wheels can be added to the control bar. I have been calculating the minimum stall speed and it should be very low, around 10 mph. At this speed and lift coefficient, induced drag would be 98% of total drag. Take-off should be very short too, less than 100 ft if my numbers are accurate. The power plant is a single generator with about 2.5 kw output. Propulsion will be provided by an electric R/C brushless motor with reduction to a relatively large prop (around 2 m diameter). 

Flight duration would be very long and cheap with hours of flight per gallon of fuel.

Edit: I now favor a paraglider style harness and a gasoline engine.

Impressive and creative!
This is super minimalistic and a keeper design. Whether or not we build a sit-down skyboat, which this senior citizen airshipper prefers, we should also make one of these "hang blimps" because it will become popular due to its low TCO, Total Cost of Operation.

It'll really move with 2.5 kw of propulsion.  [That size gen weighs about 50 pounds]
 But it looks to me as if it'd fly nicely with the little Yammy EF1000 which puts out a cruising 900 watts, 1.2 hp. 

I think the way to go for this would be a deltoid shape, triangle like the older hang glider style.

Using the inflatable (pressurized tubing) wing type structure (inflataplane from previous link).

I think the body motion should control the engine though for manuevering.

Thanks for the input. 

I think the deltoid shape in a hang glider is for stability. With the pendulum effect, I don't think it would be necessary. But there may be other reasons to think about a deltoid shape.

Also after you land, you could just walk the blimp to a tie down location without unstrapping. That could make for really easy ground operations.

Might want to look into this company and find out if its adaptable.  He has made UL airplanes and probably already has an ultralight blimp that he flies around in....

http://www.ratsinc.net/

http://www.ratsinc.net/Gondola2.htm

That looks cool, but it seems a little complicated (and expensive) for our purposes. I think we could get away with something much simpler. 

What about a bicycle based Ship?

 If you could sit up you would lessen the fatigue factor from holding your hear up for long periods of flight.

Additionally, hanging a prop off either side with a power unit strapped to either side of the bike frame would allow differential steering and at altitude engine re-starts.

The bike would give you a number of attach points for the envelope for force distribution.

The handle bars would be a great GPS/Laptop attachment point.

The average "Grandma" bike weighs about 35 -40 lbs.

A recumbent would be heaver but would have advantages.

Using some of the numbers suggested here, I still had trouble hitting the 254 limit.

(This is a simplified- easy to build model)

Not "hear"  ... head

Also with reference to post # 0

How do you crank in yaw?

I assume you are not counting the pilot's weight as part of the 254? Also, your electric motors look heavy. I think there is room for improvement if we choose specialized motors. Standard motors are probably heavy compared to those built for R/C aircraft. 

I'm not sure how hang gliders deal with yaw control. We might need a rudder, if yaw control is a necessity. 

I'm amiable to the bike based gondola, I just though this would make hitting our weight limit easier. 

I assume you are not counting the pilot's weight as part of the 254?

-dude6935

You don't count the pilot as part of the 254. But you do add the pilot's weight to size the envelope volume and thus the area of the envelope and thus the weight of the envelope which is part of the 254.

Also, your electric motors look heavy.

-dude6935

COTS- any 1 horse motor is going to be heavy.

I think there is room for improvement if we choose specialized motors. Standard motors are probably heavy compared to those built for R/C aircraft.

-dude6935

If you back off to R/C's , you have to add battery and control weights. ( and $$$$$) If you stay with Nav's generator, you'll have to add a power inverter to get from the 110 to r/c voltages.

I'm not sure how hang gliders deal with yaw control. We might need a rudder, if yaw control is a necessity. 
I'm amiable to the bike based gondola, I just though this would make hitting our weight limit easier.

-dude6935

If you lean to the side, the ultralite will roll which gets your yaw on yaw/roll coupling. With a round airship with no wings for yaw/roll coupling, I'm not sure how you were going to turn it.

Well you have the total weight listed at 450. If you subtract the pilot weight, then that is 250 lbs. So even your heaviest version meets the requirement. 

We would have a "wing" if aerodynamic lift is being generated. So yaw/roll coupling may still exist. But, we can put a rudder behind the prop to get yaw, if we need it. 

As far as R/C motors, this one runs at about 1.7kw and it only weighs 18oz. Surly accommodating two of these parts would weigh less than 28 lbs.

http://www.rctoys.com/rc-toys-and-parts/HA-A50-16L/RC-PARTS-BRUSHLESS-MOTORS.html

We could probably find a bigger model so we would only need one motor. 

Here is better size. Power 2.6 Kw, weight 31.9 oz.

http://www.aero-model.com/Hacker-Brushless-A60-18L.aspx

I looked on a R/C site for a thrust calculation. This is what I got.

Do these motors get this performance because they know that they will only run for 20 sec? If you look at the thrust: How many of these motor/prop combination's will it take to get enough thrust to yank a 450 lb ship through the air?

If you take the total drag on the ship at velocity V, and multiply it times V, after a units change you get the drag horsepower. Divide that by the prop efficiency and the motor efficiency and you get the minimum size motor required to get to and stay at velocity V. ( This could be one big motor or several small motors.) So your ship size and shape sizes your propulsion. You also have to match the motor speed to the best prop efficiency speed to size the gearbox between them.

Having fun yet? 

That duration may be limited more by the battery pack than the motor. But even so, we won't need max thrust for long. After take-off we can power back and cruise. The generator has similar limitations, it won't be able to operate at max power forever either. It will have to reduce to about 80-90% after a while. 

Your calculation above delivers 17.5 lbs of thrust. I don't know off the top of my head if that is sufficient, but that is in the ballpark. 

Having fun yet?
-swampie777

Yah, I try to let excel do the fun stuff.

I guess I should have asked this question first. What speed do you expect to travel at?

  But even so, we won't need max thrust for long. After take-off we can power back and cruise.

-dude6935

You're right about that... I forgot to include that in the list of efficiencies you correct for. Most airplanes have a max power rating. Usually cruise is about 75% of that so you can't use the max to calculate the cruise velocity expected.

I would say 30 mph or more for cruise, if possible. 

So get your drag in lbs force, change 30 MPH to 44 FPS and multiply times the drag. Divide by 550 to get drag horsepower. Go through the efficiency list of corrections to size your engine. See if you're over 254 lbs weight.

I have integrated that into my excel spreadsheet, although it is all metric. I works it the other way to find the maximum cruise speed for a given power through an iterative process.  

The advantage of the way you're doing it is you can pick an off the shelf part (motor / engine) and see how well it does. If it is not good enough then you are free to buy two of them or pick the next larger standard size.

Usually if stuff off the shelf has a "high demand / sales volume" you'll usually get a good price / performance deal. This is where COTS makes the most sense.  One has to stay open to a specialty solution because if COTS was always the answer, everyone would have already done what we're trying to do.