How retro can you get.
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 …
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....
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.
> 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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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 ...
> 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...
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.
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.
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.
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.
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.
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.
"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.
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.
> 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.
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?
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.
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.
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...
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.
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.
Check the history books for what worked then. A single balloon launches the rocket at an angle to miss the balloon. See http://en.wikipedia.org/wiki/Rockoon, for starters.
You could hang the rocket on a rail running along the lowest apex of the truss, with the instrument deck looking down at it. You could also nest the rocket inside the truss -- that's been done before, too.
Also, hang a streamer from the bottom end of the truss. It might keep the truss from spinning madly, and keep the rocket pointed into the wind during launch. The solid instrument deck could act as a sail to catch the wind and start things spinning. I don't know how much wind acts on the truss. Wind should push the balloon downwind almost as fast as it is blowing, but all the camera footage I've seen from prior launches seemed to feature an incredible amount of wind noise on the soundtrack.
Manufacturers of triangular truss actually recommend this way around.
Also see these for examples of how to wrap the string holding the truss to the balloons - you want the string to go around all the chords, not just the top two.
The reason is quite simple - many materials are stronger in tension than compression, so you want two bars in compression and one bar in tension.
With wood it's more complicated.
Along the grain sapwood is stronger in tension than compression, and heartwood vice-versa. Across the grain wood is weak in tension and ok in compression. So you want the grain to run along the beams - which it will as balsa rods would barely survive otherwise.
I doubt you're getting balsa heartwood - not sure it even really has any!
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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.
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).
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.
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.
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
Yeah, I already suggested that. I think that such a mechanism, though, would be useless given the buffeting that the launcher will have to endure.
Wind speed at high altitudes can vary between 5mph and 125mph, and temperatures can get as low as -60°C. This is going to be one tough nut to crack.
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.
I should probably clarify: the rocket would be launched along the truss, not perpendicularly to it, using some sort of guide rail or pole. This would hopefully allow it to get up to speed, and therefore be aerodynamically stable, before separation from the launch platform.
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).
You seem to be somewhat unaware of the expansion these balloons undergo (and need to) as they climb. Keeping the volume restricted (as with the tube part inside the truss) would limit the volume of displaced air, and hence the lift, quickly reaching equilibrium with gravity as the air thins. You also don't want those balloons actually touching something rigid, like you seem to be suggesting with those "blobs". And finally, this does not only not solve any of the potential unbalance problems, it would cause even more of them.
Like the project. Why have the added complexity of two balloons? Current design will no doubt end up more vertical than horizontal! There are better ways of making the truss stick out to clear a single balloon, so there's no valid reason to have two. Keep it simple, stupid. Also, as mentioned, probably one balloon will burst, then the contraption will drop either to the ground or to an altitude where there's an equilibrium between lift of remaining balloon and weight of the thing, then just float around.
Here's my 2 cents:
Keep your truss design. Attach with a bit of string a single, larger balloon to one end. To that end attach a 2nd, fairly long, rigid strut or truss in-line with said 1st truss but about 70 deg. below horizontal. To the end of this mount your battery and, if needed, attach a frame to which you can add and remove weights, or a container which you can fill with water.
The centre of mass of this set-up should mean that truss stays level. It would have a tendency to see-saw which could be reduced by increasing counterweight or maybe by increasing length of 2nd strut / truss.
You could mount your rocket at the end of the main truss and cameras in the middle. Rocket has clearance from balloon, truss stays fairly level, job (hopefully) done.
I think there's less chance from debris from a single balloon bursting at altitude to foul up LOHAN's launch, than constructions like these actually working as designed.
Just suspend a guide rod from the (single) balloon with a long rope. The guide rod is to be dimensioned so that it has maximal rotational inertia within its weight restrictions. Trigger LOHAN's motor from the balloon bursting (loss of pull on the suspension rope); you are then also at maximum altitude.
The simpler the construction is, the less chance there is of something fouling, clapping out or simply not working as expected.
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.
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