Our First Post! by Helios Airships

Hello Fellow Airship Fanatics! My name is Brady and I am the Marketing Director for Helios Airships. We are manufacturers of cargo-carrying airships for the logistics industry. I was honored by your generous invitation to join your forum. I will not be able to post too often as we are terribly busy getting ready to launch our newest prototype, the X2. Catch us online at: www.heliosairships.com and of course, twitter. I hope that Helios and I will be able to help you with tips and advice in the coming months. Airships are truly the wave of the future, and you and I are all riding it, together.

Cheers!

Hey Brady, thanks for introducing yourself and welcome to the forum. I look forward to hearing any input you guys have. I also hope you keep us posted on your development. 

Hi Brady, your website is encouraging.   I see you are eagerly awaiting investments so you can build your first ship and you have the website to help generate income, that's great, I wish we could all do that.  Maybe after a proof of concept prototype is built....or a few of them.
   We are scaled down smaller than your concepts for budget reasons mostly.  But we have come to the same realization that we need to start small before we make any large ships.   I have about four models of different sizes to flesh out and the fellows here critique ,  analyze and make suggestions to help avoid pitfalls and mistakes that would knock us out of the air, take the wind out of our sails, so to speak.
.   First of all I want to commend you for thinking big and useful.   Solar is the way to go and I think it will be possible in the next ten years to run just about everything off of solar power.   You mention you will have to hire some engineers to build this and there are many such private and amateur engineers here devoted to making an air ship work.  

.    I would very much like to see you get your egg shaped ship to speeds over 30 miles per hour, but for the small one I believe you will need over 200 pounds of thrust for the huge cross section you have to deal with.  With a 10 pound of thrust for  one horsepower  ratio you can expect to need at least 20 hp to get over 30 miles per hour.   Turnigy makes 10 and 20 hp brushless motors available at Hobbyking.com  They are very affordable.   What brand motor did you have in mind?  Or had you gotten a supplier yet?
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.     I was doing the math on the 578 square feet of solar panel/film you will be using for the small ship.    I think that will be good if you can get over 20 percent efficiency out of it.  That's 64 square yards.  A yard of sunlight produces almost 1000 watts of power..   If your film is about 10 % efficient you could expect to get a little over 6400 watts of power.  That is over 8.5 horsepower at 10 percent efficiency.  Which after going through a power controller and motors of 90 percent, you will be doing well to get 7 hp or 70 pounds of thrust.   But, if you can get solar film up to 20% efficient then that would double everything and give you the 140 lbs of thrust you need to cruse over 20 mph.   Battery power obviously will aid you a great deal, for you will not be cruising all day long in most instances and a good battery could double your power output.   Two 20 hp motors could give you up to 400 lbs of thrust.
You know, you would not have to fill a ship that size with helium to fly it unloaded, you could test it with hot air.
But not at high altitude.  You will need huge ballonettes to allow for the expansion of helium to get that ship over 20,000 feet.   I have proposed the idea of starting out with hot air in the ballonettes to increase the initial lift of that volume of air to almost 0.02 lbs per cubic foot or 20 lbs per 1,000 cubic feet.  If you have a 20,000 cubic foot ballonette volume to allow for expansion at high altitude, you could gain an extra 400 lbs of lift from heating it.   I don't know how hot your would have to heat it, some of the others are better versed at hot air than I am.    
What kind of material were you planing on using?  Do you have a supplier yet?
Good luck with your projects and the X2 especially and get back with us as soon as you can.

I don't think they need significantly more power than they have listed (2Kw). Their numbers are pretty inline with the calculations I did for my modified lenticular concept. The "egg" shape they are using is also strikingly similar to the profile I had envisioned. That is one reason why I like it. 

Sorry about the font size, I cold not fix it to save my life.

Reposted for inventive47.""

2 kilowatts is less than three horsepower, which is less than thirty pounds of force.   I don't have exact numbers but am good with illustrations.  Those kites they fly on the beaches in 30 mile winds will sometimes lift the person off the ground.   160 lbs of force from a little kite the size of a bed sheet.  Impressive.   It takes the weight of a parachutist to pull a parachute down through the air at 5 or 10 miles an hour.  How big is the parachute?   The small air ship mentioned above is 44 x 28 on the leading face.  That's over 900 square feet of cross section from a blunt end the shape of a sphere.   What is the square area of a parachute? 300 ?   If your aerodynamics translates 900 square feet down to a practical 300 it will take the weight of a person, say 180 lbs to pull that cross section down at a speed of 10 miles per hour.  18 hp.   = 15 kilowatts.   And I would shoot for a little more.   I don't know how much assist the ship will get from battery power.   But I would like to see some tests on thrust against different cross sections and shapes like spheres verses torpedoes of the same cross section.  I think that would give us some valuable calculating evidence to how much hp we might need.

According to the Goodyear website, the three active GZ-20 blimps are 192 feet (58 meters) long, 59.5 feet (18 meters) tall, and 50 feet (15 meters) wide.

The GZ-20 uses two fuel injected Continental I0-360's, producing 210 horsepower each.  That's over 400 horsepower and the Typical cruising speed is 35 mph in zero wind. Top speed is 53 mph on the GZ20.   This ship is only slightly larger than the Navy's L-4  which compares to the P-500 mentioned at the Helios Airships website.

Specifications (L-4)

General characteristics

Crew: Two

Length: 147 ft 6 in (44.97 m)

Diameter: 39 ft 10 in (12.14 m)

Height: 34 ft 0 in (16.46 m)

Volume: 123,000 ft³ (3,482 m³)

Useful lift: 2,540 lb (1,152 kg)

Powerplant: 2 × Warner R-500-2 radials,, 145 hp (108 kW) each

Performance

Maximum speed: 61 mph (96 km/h)

Cruise speed: 46 mph (74 km/h)

Range: 2,205 miles (3,537 km)

Endurance: 11 hours  54 minutes                                                                                                

   In conclusion a medium sized air ship like the above L-4 takes almost 300 hp or 216 kilowatts to do 61 miles per hour assuming it is producing about 2,000 pounds of thrust, we should be able to get a ball park figure  for doing half that speed with a cross section of half.   My guestimate from this is around 50 hp for Brady's small ship.   The Good Year blimp cruises at 35 mph with a top speed of about 53 mph and it takes about 4,000 lbs of thrust to do it.   If anyone can minimize these figures please do so.   I would love to be wrong in this instance, for my own ships' power requirements  is around 300 hp and I would love to bring that down.  Good luck to us all.

Volume is usually a better indicator of drag than cross sectional area for airships.

Drag = Volume^(2/3)*1.22*Velocity^2*Cd*0.5
           m^3                           m/sec
Try that calculation with cd = .03. That will tell you about how much drag there will be (in newtons). Then divide that by 4.9 and you should have it in lbs. 

Volume does not take into account the shape.  And I don't know if your formula is calculating friction on the surface, which involves surface area, not volume, or if it is more about displacing huge amounts of air as it passes through it.   I cannot do your formula as written for it is unfamiliar to me.  I am not metric minded.  If the ship is more torpedo shape it will have less drag for the same amount of volume and a smaller cross section.   So that leaves two more numbers to add into the equation, surface friction, and shape or cross section, unless those are accounted for and I don't realize it.  But what did you come up with that is compatible with the current streamlined and powered blimps? 
     I believe your  elipse saucer idea will have a low drag coefficient.  Especially with a thin edge.  I think that if you can get your fans behind the center of gravity you will have a shot at stable steering above 20 mph, other wise it may catch the wind like a parachute and flip up and come to a stop.  I think that by applying power, strong, weak, strong and weak you will overcome this pendulum effect that I have seen with parachutists who catch a little wind.

That is embedded in the drag coefficient (Cd). Cd is found through experimentation. I just picked a Cd to get a ballpark estimate.  

I ran the calculation with all the needed info (except I guessed at Cd). 

Vol = 1205.6 m^3
V= 13.4 m/s
Cd= .03

I got 83.4 lbs of thrust needed. Keep in mind they need this thrust at 30 mph, not at 0. So you may be right. I expected the volume to be lower. 

For the L-4 I got a drag coefficient of 0.00169

BTW I-47 if you take the volume and raise it to the 2/3 power you're getting an averaged cross-sectional area.

Thanks, I hope you are right about the thrust.  Though 30 miles an hour doesn't sound fast, there is a lot more to see at 500 feet than at ground level.
      I made the hoop for the model today at about 12 feet long by 9 feet wide with a 4 foot flat end and I will experiment with radial bracing before I cut a sheet of plastic for it.   I have come up with a way to include the radial spoke bracing into the frame and then cover it.  100% silicone is a very good adhesive and there are better ones according to Mike.  May not need a hot iron after all.
     The best part is it can glue over the strings or straps that will be attached to the hoop.  Make about a one inch glue seam around the perimeter with the spoke strings and plastic collapsed flat.   Leave a flap all the way around to  wrap around your hoop pipe,  say five inches on the top gore and then wrap it around and glue it a second time to the original seam.   No skill involved.  This will do fine and you won't need a slotted pipe.   The good thing about the slotted pipe idea is that you can change out gores as they become damaged, stretched, or aged.   The glue method means replacing the whole thing at once.

 A trick   that may  work   , if  the  glue  seams  are  strong  enough   ,  is  to  wrap  your  tubing  with  painters tape    before  gluing the envelope  to   them .    this  allows you to  cut  the envelope off ,  then  unwrap  the  tubing  from  the  residue  left, saving your tubing  .
  I  would be  real happy  with  30 MPH .  This is  comparable to  Paragliders  and hang gliders  speeds .     

Yes, I-man, tape along the inside edge is a good precaution, though I don't intent to get any glue on the pipe it is difficult not to when dealing with silicone and having to roll it out flat and squeeze the glue out to the edge.   If I have some I will try testing silicone today.

Urethane Glues  may be  the better  option here. The  5200 mentioned  is   holy crap  strong .   Silicone  leaches oils ,  and may  actually  cause  the  seam  to  fail over time  .  Thats  why  you cant paint over silicon  and  make it stick .   Urethane  glues   are  much  better . Typically   the  material  being  joined   will  tear up  before  the  glue  pulls off ,  or separates   from itself .  Thats  the stuff  we want. .   

Good info, but lets try to stay on Helios in this thread. It might be a good idea to start a thread dedicated to glues. Thanks guys. 

Hello, this is Mark from Helios. Sorry for the delay, I've been really busy with the electrical systems of the X2 prototype. But now I'm waiting for a power unit to ship from China, so I figured I'd take a moment to catch up with you guys.

Let's see... so many questions. As far as engines, the prototypes and the P500 all use common brushless electric engines. I have 2 I'm eyeballing for the P500, one is more expensive and peaks at about 11kW, and the other is really cheap and peaks at 6kW. Both are 90+% efficient including the propeller. Which one I get will probably depend on whether we ever end up getting funding assistance, or if I'm paying for this myself...

20% would be very optimistic for the solar panels, sadly. At STP (Standard Temperature and Pressure) the panels I used on the first prototype were only about 8% efficient. However, at 25,000 feet the super cold air increases energy production by about 30%. So that helps. As you say, if you aren't planning on 24/7 flight you can use more power than the panels actually provide. The real limiting factor is the power system. More on the math behind the speeds will be below. It gets pretty dry and I don't want to put you to sleep before I answer all your questions :)

You mentioned using hot air or heating the lifting gas, which is a pretty cool idea and I could definitely see that working in a combustion engine design. I know the Graff and Hindenburg both had ventilation systems coming off their engines that worked well. However, in an electrical world heating isn't a luxury we can afford. It takes too much power, and the engines are so efficient they don't product much excess heat. I have been toying with the idea of putting the engine controllers in a position where air could blow across them into the pilot area, to heat the hands of the pilot. The controllers get fairly warm during constant use. But it definitely wouldn't be enough to heat the envelope.

You asked about materials. The X1 envelope was made with laminated nylon, because its light and easy to work with. However the X2 is meant to be a high fidelity prototype, so I'm using alot of the same materials I will use on the P500. It has a seperate outer envelope and inner envelope. The outer is made with Dacron, the same material used in aircraft and sailboat sails. Its not quite as strong as nylon, however it has better endurance in weather and sunlight. The inner envelope of the X2 was made with laminated nylon, and the P500 will be a thicker ripstop nylon/PU mix. I got some sample materials from Lamcotec, and they had a strong and lightweight nylon/PU that I liked. In the X1, X2, and P500 the gondola is made with fiberglass composites, mixed with sheet styrene and even some styrofoam in the X1.

Ok, now the math part. Got your caffeine ready? So, the formula for the velocity of a basic aerodynamic shape is:

Power = 0.5 * AirDensity * Velocity^3 * CrossSection * DragCoefficient

Where Power is the power required in watts, AirDensity is the kg/m3, Velocity^3 is the velocity in meters per second cubed (that cubed is a real kicker). CrossSection is the cross section against the flow of air in square meters, and DragCoefficient is a number that basically represents how aerodynamic the shape is. In my tests with the X1, the DragCoefficient was between 0.03 and 0.05. I went with the conservative number of 0.05.

AirDensity is 0.56 kg/m3 at 25,000 feet, and the cross section of the P500 is 90 m2. (All the units have to be metric for the equation to work)

The maximum power output of the P500 depends on how many power units are installed. For this example I'll assume they put in 50 power units, which can deliver about 6kW sustained.

6000=0.5*0.56*V^3*90*0.05

Simplified, that gives
4761.9 = V^3
So then V must be about 17. Now, thats in meters per second. To get MPH, we can multiply 2.24. So, it can go a maximum sustained speed of 38 MPH. It can keep going for about an hour and a half before the batteries are exhausted.

For a 24/7 sustained speed, we look at the power of the panels, which is 2700W at 25,000 feet. Averaged over a 24 hour period we can assume you will get about 1/3 of that because of the changing angle of the sun throughout the day (remember, no clouds at 25,000 feet). So our power we are working with is 877 watts. The battery chargers are about 91% efficient and the engines+propellers are about 90% efficient. So we really have about 718W around the clock. Plug that back into the equation above and we get about 18 MPH. Not very fast, to be sure. But then you fly into the jet stream for another 95 MPH added to your speed, and you can coast along at 113 MPH. Only flying east, of course. That's something that would be more beneficial to a cargo ship flying to China and back perhaps. Because you just keep flying east the whole time.

Still, I could see this being popular with the general aviation crowd. Basically you fly to the local lake or whatever, float around on the water while the solar panels charge back up, then fly home.

Please keep us up to date on how your solar panels work. There is progress every year in improved performance, I would like to see five horsepower for a ship the size of your prototype. Weight is critical, too, a flexible film panel would be best.

Thanks for the update Mark. I really like the use of the jet-stream to carry cargo at a decent speed. That is brilliant.