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back to article LOHAN's fantastical flying truss sprouts tail

The Low Orbit Helium Assisted Navigator (LOHAN) team has been bogged down over the last few weeks in hypobaric rocket motor tests, but we've also been busy firming up the design for the Vulture 2 launch platform - our fantastical flying truss. Click here for a bigger version of the LOHAN graphic It's been a while since we last …

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truss construction

what excites me most about LOHAN is the 3D printing. why not use this extremely cool tech to print the truss and other bits as a single object?

i know LOHAN has weight issues and you can't print carbon fibre, but it might allow a clever design that uses less material and could not be produced using conventional fabrication methods.

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Re: truss construction

3D printing the truss connectors could be an excellent idea.

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(Written by Reg staff) Bronze badge

Re: truss construction

In a word: money. 3D printing is expensive, and there's also the constraint of the build chamber, which is of finite size (ie, less than 2m long). I do like the other suggestion of using the Vulture 2 printing to knock out some other parts, though. Watch this space...

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wings?

I was looking at your diagram, I was wondering at the height you're hoping this will rise to will the wings do anything?

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Silver badge

Re: wings?

I suspect they do rather less on the way up, but there are still fifteen miles to come *down*...

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Vane in vain?

Will the 'weather vane effect' work when the balloons are travelling at the same speed as the wind?

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Anonymous Coward

Re: Vane in vain?

As above...

Vanes only have an effect with a differential flow.

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Bronze badge
Go

Re: Vane in vain?

If the wind is gusty, then there will be periods of differential flow, ie when the balloon + is moving at x m/s, but the wind gusts to x+y m/s.

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(Written by Reg staff) Bronze badge

Re: Vane in vain?

It should do. If anything, we've got less of a problem with spinning when the truss is suspended from the balloon, rather than a fixed object, because it will be travelling with the wind.

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Anonymous Coward

Re: Vane in vain?

Lester, a bit tired? try again.

More of a problem suspended from the balloon because everything is moving at the same wind speed, so no wind flow past the vane!

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(Written by Reg staff) Bronze badge

Re: Re: Vane in vain?

The truss is at the end of a 40m tether, so the wind acting on it is still an issue.

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Anonymous Coward

Re: Vane in vain?

It is possible that the wind would be different 40m away from the balloon but surely that's quiet an assumption to make?

If the balloon truss and vane are moving at the same speed as the wind, then it'll behave like a kite with no string. no aerodynamic differential = no effect.

You are only going to gain benefit of a vane during gusts and wind speed changes where the balloon, truss and vane is slower to adjust to the new speed and a diminishing differential exists temporarily.

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Gimp

Re: Vane in vain?

Assuming you need only a slight differential in wind speeds to provide the weather vane effect, why not put a small drogue 'chute on the end of the truss to act as a wind anchor rather than a vane

The tether for this should be long enough so that the amount of movement in the drogue is less apparent at the attachment point.

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Anonymous Coward

Re: Vane in vain?

again relies on differential.. drogue chute would likely just hang.. imaging a mini drogue on a floating bubble.. So as useless as a fin.

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Launching into the wind.

There's a small risk the rocket will be pushed back into the balloon.

Maybe launch downwind?

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Silver badge

Re: Launching into the wind.

Not that this is exactly the same thing, but I've found that launching smallish rockets at a slight angle into the wind causes the rocket to act like a weather vane too. Rather than getting blown back, the nose seems to tilt into the wind and fight against it. Of course, this could also be a good reason to put any kind of primitive guidance onto the thing during the rocket burn, if only to stop a directional wind from causing LOHAN to blast more sideways than upward. Once the rocket is going fast enough (which won't take long), I'm pretty sure whatever is on the tailplane, in conjunction with the onboard autopilot, will be enough to keep the nose pointing toward the sky.

Just my tuppence worth.

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Re: Launching into the wind.

The phenomenon you describe is called “weathercocking”. It’s not that the nose rotates into the wind; it’s that the fins are deflected by the wind gust, which in turn directs the rocket windward.

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Re: Launching into the wind.

We've tried the weathervane approach in an effort to mitigate spin rate and consequent mal de mer when viewing live video. It doesn't work very well, and here's why:

The dominant airflow vector is vertical, since the balloon envelope has far greater drag area than any reasonable vane. However, even minor wind shear will cause the payload line to "swing and sway with Sammy Kaye", and the tail fin (weathervane) will respond nicely to that with a series of snappy 180-degree turns.

What DOES work quite well, however, is increasing the rotational inertia around the payload's vertical axis. On our GoPro DVR, we installed a pair of 1m long 1mm x 3mm carbon fibre flats rigidly cantilevered horizontally from the payload structure in opposing directions with 10 g of Pb weight added to each extreme end. This resulted in a rather profesional-looking slow and smooth pan rate looking at the horizon.

Since there's negligible horizontal airflow velocity, there doesn't seem to be any point in your endeavor to launch LOHAN into the wind, but keeping the spin rate down might make for a more manageable launch trajectory.

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Bronze badge

Ice

I know that this has not been hammered out yet, but I was looking at the titanium launch rod and I remembered that with PARIS some ice formed on the wing binding it to the control box. Is there going to be a similar issue here, where ice could form between the loops on Vulture 2 and the titanium rod?

If that were to happen, would the proposed rocket motor break them easily so as not to significantly affect its performance?

Will the low temperature grease you used on the release mechanism last time work its magic in these circumstances?

If this has been discussed already, just ignore me. Or, if I am just being an idiot ignore me too.

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Re: Ice

That has already been thought of which it what the teflon inserts are for in the diagram.

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(Written by Reg staff) Bronze badge

Re: Ice

We're on the case with this one. We're using a teflon insert wider than the tube diameter, and we have the added back-up of low-temp grease, if required.

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Re: Ice

I can't remember if it's been mentioned before (probably, I'm just back in the office after 3 weeks on Olympic duty so I'm having difficulty remembering anything at the moment!) but what about passing an electrical current through the guide rod as an anti-icing mechanism?

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(Written by Reg staff) Bronze badge

Re: Re: Ice

Yup, it's been mentioned. I'm not too keen on more battery-powered stuff, if we can avoid it.

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i wonder

who or what the truss will eventually fall on, i could imagine, since it is totally random depending on wind, that there maybe some insurance required, at least it could make for a snappy headline on the reg.

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Silver badge

Re: i wonder

Bit of a long shot for the telly ad -- "Have you had LOHAN landing on your face?"

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Bronze badge

Re: i wonder

The truss will have it's own parachute, to come down safely after the balloon bursts. (And it's own tracking device to retrieve it probably :)

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Paris Hilton

Re: i wonder

Should be "Have you had LOHAN's weighty rear end landing on your face?"

Paris because there's no Lohan icon...

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Pint

Sail wind indicators

When sailing boats use wind indicators they use cloth supported at the top and side, allowing the tail end to feather.

this is apparently to stop the juddering of small amounts of airflow twitching the direction.

I wonder if a similar thing would be useful in this case??

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Megaphone

What goes up generaly comes down...

Will the flying truss pose a danger to any unwary sole that happens to be passing by as it falls to earth?

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Silver badge
Headmaster

Re: What goes up generaly comes down...

Soles are salt water fishes, and a quick shufti with a map and a ruler suggests that the nearest sole, unwary or not, might be found some 1807 brontosauruses (250km) west from PARIS' launch site, on the Portuguese coast, although I can't tell if one could actually find soles (unwary or not, as noted already) at this location. Note that I have discounted soles on display at a fishmonger, as those are a) generally quite stationary in a batch of ice and therefore not happening to be passing by, and b) by and large protected from falling aerial debris by shops' roofs or market stall awnings.

If you meant the type of sole generally found at the contact point between a standing or walking being and the surface it's in contact with: it's their very location that makes them unlikely to be susceptible from being hit by Lohan's truss; the upper parts of that being's anatomy would be hit first, unless it was doing a handstand or had a habit of walking around with a shoe on its head.

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Re: What goes up generaly comes down...

Better not launch it over Australia then.

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Bronze badge
Happy

Re: What goes up generaly comes down...

@Stoneshop, treat yourself to a pint for that one! I needed a good laugh today.

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Happy

Re: What goes up generaly comes down...

Stoneshop - go to the top of the class!

I'm still laughing (and checking this for typo's).

Andy

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Headmaster

@ Andy E

Did you check for unnecessary apostrophes?

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Anonymous Coward

Re: @ Andy E

Technicality: Contraction of typographical errors

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Anonymous Coward

Have you verified you won't hit CoCom limits on your GPS?

This may have already been sorted out a long time ago but just in case...

You need to ensure that any GPS you use for guidance has a altitude & velocity implementation of the CoCom limits rather than an either/or implementation.

http://en.wikipedia.org/wiki/CoCom#Legacy

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Anonymous Coward

Re: Have you verified you won't hit CoCom limits on your GPS?

These problems have been discussed before. The LOHAN team is aware of the problem and looking for a "tried and tested" GPS module that is know to work at high altitude.

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dpb
Paris Hilton

Kite style tail?

Seems to be a lot of comments against a vane/fixed tail. Just wondered if a kite (string based) tail might work better for stability? I've no idea - it is genuinely a question.

I guess it would slow the ascent slightly and could make LOHAN travel more distance away from the launch site as the wind carries it.

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Linux

Avoiding a possible faraday cage in Vulture 2...

Slightly off topic.

I noticed that Vulture 1 was lovingly painted in metallic paint.

Later it was discovered that the onboard location signal was surprisingly weak.

Is there a connection between these two things, could the metallic paint have been acting as a Faraday cage?

Just a thought, probably hardly worth thinking about...

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effect of wings

I suspect that the wings of the aircraft will affect the truss more than a tail.

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Coat

I keep reading

Lohan's fantastical flying brussels sprouts

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