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back to article LOHAN's flying truss: One orb or two?

The roll-out yesterday of our Low Orbit Helium Assisted Navigator (LOHAN) fantastical flying truss prompted a flurry of comments from readers unimpressed with our twin-globe proposal. Click here for a bigger version of the LOHAN graphic To recap, our cunning plan for the Vulture 2 spaceplane launch platform involves a …

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  1. Vladimir Plouzhnikov

    How about

    Weighted canards on the vehicle?

    Launch horizontally, the canards will droop due to the weights, pitching the vehicle up.

    Once the trajectory becomes vertical, the weights will no longer deflect the canards and the rocket will go straight up.

    Will need some experimenting with the weights and limiters on the canards to give the turn radius large enough to clear the balloon but tight enough to make the turn while the motor is still going. Launch downwind, to make things easier.

    Here is what I mean: http://www.ukimagehost.com/view/d92ea6d9cd0b9aba.jpg

    Aerofoils at 60,000ft will generate less lift than at sea level density, so the canards will need to be scaled up accordingly.

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    1. M Gale
      Reply Icon

      Re: How about

      Unfortunately, in a tight loop, you will feel the right way up even when you're upside down. Nothing that relies on weights, balances, or anything that will stop working properly if gravity doesn't act like it should, will work on an aeroplane. This is why autopilot systems are a little more complex than attaching a pendulum to the ailerons.

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      1. Vladimir Plouzhnikov
        Reply Icon

        Re: Re: How about

        Provided the vehicle is stable in roll, there is no reason for it not to work if the counterweight is calibrated properly. There is thrust, gravity, turning G-force. With horn-balanced canard the drag force's turning moment can be neutralised. Problem is that it may be too complicated to tune the system by trial and error for it to be practical.

        Also, after I posted the first message I remembered that LOHAN needs to fly back to a landing, which will be difficult with a system that wants to pitch up the craft into vertical all the time. It will just constantly stall and fall :-(

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        1. M Gale
          Reply Icon

          Re: Re: Re: How about

          See here's the problem: You have a system that is relying on gravity to tell it where "down" is. WHile LOHAN is resting nicely on the launch platform, this system will be fairly, if not entirely accurate. As soon as the rockets kick in however, the aircraft will get a massive kick in the pants which will make any gravity-based system think that "down" is toward the rear of the aircraft, no matter what orientation the aircraft is in.

          Try it yourself with a bucket half full of water on a string. Swing it around your head. The water is being pressed into the bucket through centrifugal force, basically an accelerative force trying to push the water out of the bottom of the bucket. The bucket thinks "down" is straight up when it's above your head, so long as you keep that acceleration going.

          More than one pilot has died in a crash due to instrument failure in bad weather, because a human's built-in, gravity-derived senses cannot accurately tell where "down" is, and the pilot might well flop an aircraft upside down into a lake, believing themselves to be in level flight right up until the last moment.

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          1. Vladimir Plouzhnikov
            Reply Icon

            Re: Re: Re: Re: How about

            Well, I know the basics of Newtonian physics. If you draw vectors of forces acting on the counterweight for different points in the trajectory you will see that it might just work, provided the thrust/weight ratio is high enough and the machine is not pulling more than, say, 2 Gs while turning. It will overshoot the vertical, the canard deflection will reduce, which will reduce the turning Gs, which will let the canards deflect into pitch-down and the whole thing will oscillate in this way around the vertical and, I believe, the oscillations will decay.

            P.S. All aircraft have slip ball indicators which are purely gravity (acceleration) based. :-)

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            1. Vic
              Reply Icon

              Re: Re: Re: Re: Re: How about

              > P.S. All aircraft have slip ball indicators which are purely gravity (acceleration) based. :-)

              They're acceleration-based, not gravity-based except during level flight.

              In a turn, the ball doesn't point down...

              Vic.

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              1. Vladimir Plouzhnikov
                Reply Icon

                @Vic

                Isn't that what I said?

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                1. Vic
                  Reply Icon

                  Re: @Vic

                  > Isn't that what I said?

                  I don't think so. You said they were "purely gravity (acceleration) based.". But they're not gravity-based...

                  Vic.

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                  1. Vladimir Plouzhnikov
                    Reply Icon

                    Re: Re: @Vic

                    Let's not split the hairs here we both know we are talking about the same thing.

                    The ball senses total acceleration which includes free-fall acceleration due to gravity and which consists solely of free-fall acceleration in a straight and level flight. That's what I meant.

                    I also meant it to stress that the ball is an instrument which relies only on gravity (and acceleration) and not on any gyroscopic or magnetic forces, pressures or external references (radio or optical).

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                    1. M Gale
                      Reply Icon

                      Re: Re: Re: @Vic

                      That slip ball is there to measure acceleration forces, so therefore uses acceleration. It still doesn't know where "down" is, which is what anything connected to a control surface, robot or human, needs to know if it doesn't want to become a lawn dart.

                      That's why aircraft have artificial horizons kept in place with gyroscopes and other funkiness. If you don't know your orientation, you can't fly.

                      Besides which, LOHAN will have some kind of readily available autopilot on board anyway. That's if Lester doesn't just want to use a really long string and a slight angle from the vertical, which seems to be the KISS option.

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  2. TRT Silver badge

    Couldn't you get payload higher still by carrying a second stage, under-inflated balloon? By the time the main lifting balloon bursts due to its size, the second stage balloon will have inflated. Sure, it'll be able to carry less mass, but with a bit of careful design, it might work. Any views anyone?

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  3. Chris Glen-smith

    Why have verticle launch?

    Other than for the beautifull symboligy of thrusting between the magnificent orbs of course.

    Launch enough above horizontal to avoid losing height then have the autopilot convert to verticle.

    The idea of using the truss as a launch rail sounds good to me.

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    1. Stoneshop
      Reply Icon
      Boffin

      Re: Why have verticle launch?

      Because there's very little air for control surfaces to be even a little bit effective (so an attitude change should be achieved with a gimbaled exhaust), and the burn time of the rocket motor is not that long (so there's little time to achieve the change of direction, and you're wasting propulsion in a direction you don't want it)

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  4. Reg J Mitchell
    Happy

    Bent truss

    Similar to the T shaped truss idea, how about a V shaped truss. With all the weight at the bottom of the V it should be adequately stable with two similarly inflated balloons.

    More elegant would be a curved truss. A half circle or parabola would add a smile to the contraption (see icon!).

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  5. Kieran Marsh
    Go

    Dihedral

    Why not put a dihedral angle on the girder?

    http://en.wikipedia.org/wiki/Dihedral_(aircraft)

    Put your launch pad in the centre and the balloons a either end, the dihedral will tend to stabilise it, some damping would likely be necessary to prevent oscillation.

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  6. pwibble
    Pint

    Neat Triangular Truss

    Tricky problem - the essence of it boils down to the following:

    How do you get the launch platform to stay in the required geometry relative to the balloon(s) with 100mph winds blowing it all about?

    I like the idea of just using a very long cord between the balloon and the platform. Simple, effective. Low chance that the Vulture2 will hit the balloon, so this must be part of the solution. My guess is that 50m will be enough, but you guys can do the maths on this.

    Another aspect is that some kind of control electronics will be needed to assess the launch angle and only fire when the Vulture really is vertical - or exactly 10 degrees off vertical to avoid hitting the balloon. Tricky, but sounds possible to solve. I think if you don't do this then it could go off at almost any angle due to winds.

    The single straight truss doesn't look good to me. I like the construction concept, but I would go for a triangle with the three corners connected to a single balloon. Again, it gives more chance of clearance on launch because the Vulture will not be exacly underneath the balloon(s). Should be fairly easy to get the triangle in balance by positioning the cameras and Vulture 2 itself.

    So - the solution(!).... triangular launch platform (similar to current design, but three trusses linked together). Connect the corners of the triangle to a balloon (or balloons) on a long cable. Launch when Vulture2 is just off vertical. Should work :-)

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  7. drben

    Single balloon, vertical beam?

    Didn't spot this mentioned anywhere above...

    Single balloon seems to me to be unavoidable, so put this with a long cable, as suggested, and suspend the beam vertically - i.e. from one end only.

    The rocket could have a nice long launch rail (to give you some confidence that it'll go where it's pointed), starting from the bottom and just missing the cameras at the top, at whatever angle you see fit.

    (PS @Equalise pressure?: Glad someone is awake!)

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  8. S 11
    Angel

    Can I buy your Magic Truss

    Every day I get in the queue (Too much, the Magic Truss)

    To get on the Truss that takes me to you (Too much, the Magic Truss)

    I'm so nervous, I just sit and smile (Too much, the Magic Truss)

    Your house is only another mile (Too much, the Magic Truss)

    Thank you, driver, for gettin' me here (Too much, the Magic Truss)

    You'll be an inspector, have no fear (Too much, the Magic Truss)

    I don't want to cause a fuss (Too much, the Magic Truss)

    Can I buy your Magic Truss? (Too much, the Magic Truss)

    Rock on Vulture.

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  9. pwibble
    Pint

    drben is Spot On

    Dr Ben,

    Sounds like a plan. Simple, efficient, beautiful. Like you say...just suspend the truss down from the balloon(s) and the truss inherently becomes the launch rails. Like it. Forget all that messing about with triangles I was ranting about.

    Slight challenge in terms of how to miss the balloon, but on the other hand as long as the cable between the truss and the balloon is long, should not be a problem. I mean, it will be difficult / impossible to get Vulture2 to really go exacly vertical anyway. And the launch rails can just have a slight incline at the end to push the rocket slightly to the side.

    Simple, less is more - this is the way to go. And you don't even need to change the parts you already built really. Brilliant.

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  10. Schultz

    "... the Vulture 2 launch trajectory, which needs to be as vertical as possible without any risk of the aircraft hitting the balloon."

    Don't worry about hitting the balloon, just make sure the launch has the necessary punch to pop the balloon. I want to see the video of that! Maybe add some explosive charge (type 'potato cannon') to get some rapid velocity .

    More seriously, you should bend the truss (inverted U), so it'll be in a stable position during launch.

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  11. Acadene
    Black Helicopters

    Lohan's thrust may snap the member

    Just thinking thay you guys should test the bending moment and shear force of Lohan on the carbon fibre truss as she fires up. Even though carbon fibre rods are extremely flexible and strong, they don't react kindly to sudden shear forces - causing the truss to fail.

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    1. M Gale
      Reply Icon

      Re: Lohan's thrust may snap the member

      So long as LOHAN has left the platform, who cares what happens? If the whole thing comes down on parachute looking like it just picked a fight with a polar bear, that's just awesome footage!

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  12. Magnus_Pym

    Spinning control

    It seems to me that in order to control the spin there must be air moving over a control surface. In order for that to happen the device must be moving relative to the air around it. In other words some sort of motive power is required. Would it add too much weight to have a solar panel/electric motor/propeller combo on one end of the truss and a large rudder on the other? The motor could kick in at the upper altitudes to stabilize the rig before launch.

    I also add my vote to the design where a single string hangs down from the lifting force to a single central swivel. From the swivel two strings support the truss , one at each end. One of these string s is shorter than the other in order to set the whole truss at the required angle for launch. The rocket can be slung underneath on a short launch rail parallel to the truss. i.e. pointing upwards at the required launch angle.

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