Warren girder
patented 1848
How retro can you get.
LOHAN flashes fantastical flying truss
It's taken us a while, and a not inconsiderable amount of head-scratching, but we've finally come up with a design for the Low Orbit Helium Assisted Navigator (LOHAN) launch platform. Click here for a bigger version of the LOHAN graphic Those of you who've been following LOHAN will recall the invitation to our beloved readers …
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Tuesday 21st February 2012 10:19 GMT James Micallef
Re: Horizontal
First thing I thought about when I saw the rig. The odds that the 2 balloons are filled exactly the same, have exactly the same leakage, exposure to gusts of air etc etc are virtually zero, so there needs to be some sort of harnessing structure between balloons and platform to keep the platform upright. Of course that might defeat the point of the design, which is to have some clear space directly above the platform to allow for the launch....
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Monday 20th February 2012 14:06 GMT Anonymous Coward
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.
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Monday 20th February 2012 14:57 GMT Anonymous Coward
Re: Keeping it Horizontal.
> I suggest a string from each end going to a single weight so it forms an inverted triangle.
Nice. This would also be easily adjustable; you could make the strings longer or shorter to provide different amounts of leverage as required.
Would the weight swing around appreciably in such a set-up though? Maybe a fixed pole instead?
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Monday 20th February 2012 15:59 GMT Anonymous Coward
Re: Keeping it Horizontal.
Would keeping the current layout but adding a string from each end to the other balloon work? I think that is stable from a "keeping the beam horizonal" point of view. Obviously it means the strings cross above the middle of the beam but from the pictures it looks like the launch is not vertical but slightly off to the side so should miss the strings. If the picture is misleading then, no, this method would just add something extra to crash into ...
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Monday 20th February 2012 23:09 GMT Vic
Re: Keeping it Horizontal.
> this will likely end up vertical
This might be massively over-complex, but here goes...
If your central weight (batteries etc.) can slide along the truss, you can then attach the cable from each balloon to that sliding mass.
Thus if one balloon supplies more lift than the other, the CoG of the truss will move towards it, reducing the turning moment. That will go some way towards stabilising the whole thing.
Of course, moving parts are always the weak point of any design, so the probability of terminal fuckup is quite high. But this is the best I can come up with on a single pint...
Vic.
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Tuesday 21st February 2012 12:40 GMT The First Dave
Re: both balloons bursting?
I think you actually meant _able_ but yes - if the weight of the rig is too great for a single balloon (and it would be a stupid waste of energy if it wasn't) then when one balloon bursts, the rig will descend substantially, and the second balloon will not burst, or at least not purely due to height.
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Monday 20th February 2012 14:29 GMT king_tut
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.
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Monday 20th February 2012 14:38 GMT Martin Gregorie
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.
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Monday 20th February 2012 14:53 GMT Pete 2
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.
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Monday 20th February 2012 15:17 GMT Graham Bartlett
Spinning
Take a child's swing. Horizontal surface, suspended by ropes at each end. Give it a bit of a rotational shove, and look at the results.
See, you have the problem that once the ropes have crossed, it takes very little extra spin to wrap the ropes up some more, and the result is highly unstable. So you're going to have a twisty mess of wound-up cable right in the middle, where LOHAN is launching through. And worse, when the cables have crossed then the balloons are going to be pulled together. So where LOHAN is launching through will also be occupied by two edges of balloon.
Not a good solution IMO.
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Monday 20th February 2012 16:05 GMT Amonynous
Re: Spinning
Spinning could be counteracted by means of a vertical stabilising fin at one end of the truss, so that it points in to the wind like a weather vane.
Clearly there is still the potential for the baloons to wind their tethers around each other. If the tethers are no more than half the length of the truss that would be impossible, and I suspect they could be somewhat longer than that with minimal risk of spinning.
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Tuesday 21st February 2012 12:44 GMT The First Dave
Re: Re: Spinning
"vertical stabilising fin" - Are you kidding? On a balloon? No aerodynamic device works on any floaty thing unless it is tethered like a kite (this isn't) or has power (like the engines of an airship)
That isn't even Aerodynamics 101 - it is more like the aptitude test to get into Aero class.
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Wednesday 22nd February 2012 13:22 GMT Amonynous
Re: Re: Re: Spinning
Incorrect. First let's be clear - the stabilising fin is attached to the truss, not the balloon.
a) As others have pointed out in the comments to the follow-up story, exactly this kind of arrangement has been used by other rockooniers to stabilise their platforms.
b) Whilst the balloon is not powering itself forwards through the air, the air (especially at high altitude) will be powering itself over the truss. It's a thing called "the wind".
c) Weather vanes are even less likely to move forwards through the air under their own power than a balloon (by vitrue of being attached to immovable objects such as churches), and yet they have succesfully managed to keep themselves oriented in to the wind for (at least) the past 2,000 years and probably a lot longer than that.
d) Even if I was suggesting stabilising the baloon, which I wasnt', that would also work. WWII barrage balloons had (inflatable) vertical and horizontal stabilisers to keep them pointed in to the wind, to avoid the balloon bobbling around like crazy and slicing off the heads of the operators with the winch cables as it did so. Again, they did not move through the air, the air did the moving.
A vertical stabilising fin of some sort (on a long extension pole from the truss as others have suggested, thus increasing the length of the lever) would certainly work very well on a single balloon arrangement as there is only one pivot point exactly like a weather vane.
What is more interesting to consider is whether it would work on a dual ballon set up with multiple tethers. I don't know the answer to that, might work or the combination might produce a spectacularly chaotic wobble of some sort. Miniature wind tunnel experiment might be called for here.
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Wednesday 22nd February 2012 15:26 GMT Vic
Re: Re: Re: Re: Spinning
> the air (especially at high altitude) will be powering itself over the truss.
> It's a thing called "the wind".
As anyone who's ever jumped an old-style parachute will tell you, you only feel the wind when it changes; in a steady wind, you're moving along at the same speed, so although you see the ground moving past you at more speed than you'd hoped for, you don't feel the wind rushing past you, because the relative speed is zero.
Newer parachutes have a forward velocity, so you feel the wind in your face - whichever direction you're pointing and whatever the wind speed. And you might well be travelling backwards.
Gusts of wind are what make the difference. I don't know how gusty it will be at altitude.
> they have succesfully managed to keep themselves oriented in to the wind
Weather vanes have a reaction base. A balloon does not.
Vic.
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Monday 20th February 2012 18:26 GMT Andus McCoatover
Re: Spinning
Well, when I first became a dad, when my kid swung on a seat, I'd be there behind it to hold the two cables apart.
As there's no way Lester's got the guts to go up with it, may I suggest a horizontal spur between the two, . If there's no bamboo left, maybe a row of playmobil folks holding hands?
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Wednesday 22nd February 2012 10:04 GMT Stoneshop
Re: Spinning
Take a sufficiently long bamboo or balsa rod, slightly longer than the truss, and stick it between the balloon tethers so that the remaining height between the rod and the balloons is less than about half the length of the rod.
This rod can also be used as the upper support for a launch guide rail, making it easier for LOHAN to be launched near-vertically.
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Monday 20th February 2012 15:50 GMT Anonymous Coward
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...
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