LOHAN flashes fantastical flying truss

Horizontal

What's the likelihood of that beam actually being horizontal when attached to two ballons?

Good to see that pipe-smoking hasn't died out among the boffin fraternity.

LOHAN's truss is looking spectacular.

Keeping it Horizontal.

As others have pointed out, this will likely end up vertical if not stabilised. I suggest a string from each end going to a single weight so it forms an inverted triangle with the beam at the top, and the weight at the centre at the bottom. The weight could be useful stuff like batteries.

both balloons bursting?

That'll only happen if one balloon by itself is unable to continue to climb after the first balloon bursts.

Re: Horizontal

This was my concern as well.

In addition to the weight hanging in the middle (but suspended from the ends of the truss), how about rigging a pipe between the balloons? That way each balloon would have the same pressure inside, and in theory would be more likely to stay level (assuming each balloon is the same elasticity). The same pipe could also be used to fill both balloons at the same time.

I'd suggest some form of gyro, but the weight would be unacceptable.

Looks like a good design.

However, one or two suggestions:

- You'll have noticed that the JPL Aerospace airship required the pilot to destroy/release the second balloon when the first burst, so I trust you have a similar automatic mechanism in mind? If not, simply looping the end of each lift line round hooks on the ends of a V, which would be pivoted in the center, may do the trick. The first balloon to burst will let the second tilt the V towards it so its line slides off its hook. Launching would probably be easier if the V is fixed during launch and unlocked a few minutes later, when its above most of the turbulence. It may benefit from a spring that's to keep it centered in turbulence but weak enough to be overcome when the whole weight of the truss comes onto the remaining balloon.

- running the lift lines up inside tubes or along masts for, say, half the length of the truss sounds like a much better stabilizer that either equalizing the lift from the two balloons (tricky in a breeze) or using a suspended weight (which wastes lifting power).

- if you have a choice, go for larger diameter thin-walled tubes, such as fishing-rod sections, rather than kite rods for making the truss. The large, thin-walled tubes are lighter and more rigid that the rather small, thick-walled ones used to make kites. Rolled balsa tubes of around 30 mm diameter might be better yet, especially if covered with doped-on tissue paper or very light glass-cloth. However they'd take time to make.

A spot of wind

Aside from the question of balance, the design needs to be able to withstand high winds. ISTR that PARIS encountered some blowage at height and the extra stress of balloons wanting to go in different directions (a phenomenon some readers may be familiar with) could exceed the design loading of the truss.

Um, stupid question

Why not have a single baloon, put the plane at one end of the truss, a counterweight (batteries, camera etc) at the other and the string to the baloon in the middle. That would seem more balanced, and the plane's flight path is just as near the baloon as if it was flying between a pair of them. If you can make the counterweight heavier than the plane, you can move the string nearer the counterweight moving the plane away from the baloon.

I know there'll be a really obvious problem with this that everyone will now point out...

What happens when one balloon pops before the other. Will the lone leftover balloon have enough lift to keep the truss and kit rising to its burst altitude or will the weight of the truss be too much and have it start slowly descending until it hits the ground or just floating away and never popping.

Truss length!!??

How long would the truss have to be to ensure that there is actually a gap between the balloons when near their maximum altitude?

I read that weather balloons can reach 300ft diameter before bursting!!

horizontal solution

what is needed is to place a movable ballance weight within the trangle shape of the truss. quite what mechanicsm you would employ to move the ballance weight to keep things level i dont know. and then theres the issue of one balloon sheilding the other from wind which would also cause instability.

maybe a better solution would be one circular platform suspended from a ring. that ring would then have a single balloon dead centre above it. to secure the ballon, a string ring sits above the balloon which filled with helium would ensure it pushes up on the ring.

pit an extremely sharp pin on the tip of the rocket so when it launches, it goes up, pops the balloon and goes through the string ring that the balloon was seated in.

just dont look up when its on its way back down...

What about...

a triangular truss, with a balloon at each corner? You could sit the launch platform atop a pyramid, a bit like a d4.

you've got better engineers than me...

but isn't this a bifilar suspension (I remember that one coming up in my A-level Physics exam) - and it's a complex pendulum around the yaw axis.

Does the heading of Vulture 2's launch matter because it's going to become unpredictable. Worst cases are a) it gets rotated into a twisted up mess, as in the kid's swing posting above, or b) an imbalance generates a chaotic oscillation that spoils your in-flight videos with sideways motion blur and rolling shutter effects.

It wasn't the spinning that was a problem for PARIS, it was the cameras couldn't keep up with the movement. Controlled spinning is quite good for getting a good look around, but not being able to resolve the resulting images because the camera sensor can't keep up is a bummer.

If you asked RED very nicely, they might lend you a couple of their Epics to loft on board LOHAN and you'd have it all in lovely 120 frames per second at 5K definition - OK so they're over $50k each, plus lenses, but RED do so love a bit of publicity. You might have to beef up your girder a bit to carry them though.

spinning

just a thought

what causes the spinning for a single balloon ?

I seem to remember a video of a guy jumping out of a balloon very high, in a space suit,

he was under one very big balloon , and I can't remember that spinning, else he could not jump.

second thought, does spinning matter ?

launch down wards, drop,

let the gyro stabilise the plane and point the plane up !

I know nothing about balloons but a thought, and I wish you luck.

Horizontal

You need a single balloon with two quite long strings, one to to either end of the truss. It will look like a tall isosceles triangle with the balloon itself at the apex, and the truss at the base. This will keep the truss level (or whatever angle you like in fact).

This would also avoid the risk of two balloons getting entangled.

Long strings will help them stay out of the way of the rocket as it launches, and you can also launch the rocket at a bit of an angle to make sure it passes through the string triangle, missing both the strings and the balloon itself.

Bursting balloons.

Just to make sure... Det cord? That'd work.

Also can we tie the two balloons to one string (at differing heights) and inflate the lowest one the most, have the upper just inflated enough to lift for a staged burst? Removes the stability issue, adds extra coolness in the video, and cures AIDS (may be a lie).

I am replete

Coupla things.

First, Have you got the assembly right? It clearly consists of small-diameter wooden sticks, with flat ends which are joined to the circular the circular surface of similar sticks. So the actual contact area between the sticks is a line, there is no area contact. To try and increase the area by squeezing the sticks closer together will cause distortion in the sticks, and result in internal pressures. The super glue will have a contact line area, the rest is an illusion of strength. The benefits, if any, of the addition of woodglue to the assembly may be doubted. Certainly the woodglue will add weight.

Second, steel structures are usually tested to six-times calculated failure strength, do you have plans to do this?

The nearest parallel to what you are doing would appear to be the wooden fighter and bombers produced during WW2. Those little aircraft were subjected to enormous stresses, and the designers specified very precise construction and gluing (for they were glued!) techniques. Have you studied the work of those early aerial design geniuses?

Third, why bother about 2 balloons for lift. Why not use one, larger one to do the same job? You'd get the same lift for much less ballon material weight. It is not necessary, although prettier, to have two balloons, nor an horizontal lift-off configuration. The thing would probably work better, albeit less elegantly, if simply slung vertically from your bigger ballon (with 2 strings, in case one failed).

Come eject time the aircraft will shoot away safely from the carrier at whatever angle it lies at launch moment, think about Polaris-type missiles, launched under water, they straighten themselves up dramatically as they leave the sea.

Expansion Issue

You know that these balloons go to 6m+ diameter at altitude right?

I can't see how you are accommodating the Massive size these balloons will get to as the atmosphere thins.. Surely you need a 6M+ truss.

Or each balloon has a string to each end and one to a point say 2/5s along the truss. That way the launch area is kept clear and the beam has an autolevelling moment.

Assembly and size

Folks, you might like to notice that this is only a model of the real thing. RTFA and you'll see that they're talking about building the real thing out of carbon fibre.

Of course, how well a balsa wood model will represent the actual behaviour of a carbon-fibre thingy is open to debate.

In regards to horizontal stability

As you are already putting some electronics in there, would it be a big problem adding a tilt sensor connected to a small motor that could move a counterweight back and forward along underneath the length of the platform. I don't really know how much extra weight or power that would require, but it's couldn't be that much

There's a woman in the photo

And all everyone cares about is keeping the craft horizontal.

Today is a sad day.

Single balloon with shorter truss?

How about a single balloon with the truss suspended at a 45 or 60 degree angle, with the upper end of the truss extending beyond the upper securing string. The rocket could be launched from this sticky-out (technical term) section, with batteries, cameras, etc forming a counterweight at the other end of the truss. It would hopefully provide a launch platform without any obstructions (strings) and angled to miss the balloon above. You probably need a fin of sorts on the lower end of the truss to try and stop it spinning.

With this configuration, you could have a shorter (lighter) truss.

Clicking for bigger pictures of Katarina doesn't work.... :-(

That wooden contraption looks complicated - and unstable. Shouldn't you have some kind of a ballast weight on the underside of the launch vehicle to keep the business end of your V2, er, Vulture 2 rocket pointing out to spaaace? Not sure how that "wood" fly though.

On another note: Looking at that diagram of the phases and comparing it to the pictures, I don't think they meant balsa wood when they said "carbon fibre" on the plan. It's a matter of interpretation I guess. (Wood == natural carbon fibre?)

(Disclaimer: I'm not an engineer or a materials expert).

why a vertical launch?

What is the point of launching vertically upward? The thrust of the rocket motor is likely to be less than the weight of the aircraft, so why not launch horizontally or downward. Or ignite the rocket after the aircraft has been released and is in a stable glide? No chance of hitting the baloon then.

i do hope you try to beat the record for Unmanned gas balloon 53.0 km (173,900 ft) http://en.wikipedia.org/wiki/Flight_altitude_record#Unmanned_gas_balloon to launch the LOHAN) flight.

if so you really need to use (3)clustered slightly under inflated weather balloons to gain stability really and a 4th one on top to pop at or above the calibrated hight under tension so it can release a mechanical/electronic switch to start all the main action off.

your current outline of not using the full length of the support stricture seems like a waste not to take advantage of this longer 6 foot run to propel the craft (knicker elastic style along a track LOL) before it fires the main engine half way down the structure.