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back to article LOHAN to straddle meaty titanium rod

After much head-scratching, and a good number of beermat sketches, we're finally ready to unveil our concept for the Low Orbit Helium Assisted Navigator (LOHAN) Vulture 2 launch platform. Click here for a bigger version of the LOHAN graphic To recap, we've been pondering just how to attach our spaceplane to the carbon-fibre …

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Anonymous Coward

The Vulture 2 will simply slide off the rod

Yes because two objects in free fall always repel each other.. its that well known scientific principle of illogicum.

(PS parachutes and drogues have negligible effect until the atmosphere thickens up)

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Re: The Vulture 2 will simply slide off the rod

Agreed. I see no need to counter-balance the electronics package. Love the design though! seems solid enough

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I am not an engineer...

Will there be any effect on the position of the launch platform from the force of the exhaust hitting the plate behind it? Will it not make the support spin/tilt?

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Re: I am not an engineer...

I was wondering that, and was considering the use of ducting to capture and direct some of the exhaust gas to act as stabilizing thrusters for the truss when I realised the idea was probably unnecessarily complex plus it's a Friday afternoon and I just couldn't be bothered with that thinking malarkey that is reserved the less fun parts of the week

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(Written by Reg staff) Bronze badge

Re: Re: I am not an engineer...

Agreed. Get back to me on your plan when you're feeling less fun-filled.

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Re: I am not an engineer...

My worry about that isn't the force of the exhaust, it's the heat. For a short time, there's going to be a lot of flame coming out of the back of the rocket, bouncing off that plate and coming back at LOHAN. Drilling a hole in the plate for the flames to go through, or better yet just resting LOHAN on the back of the fuselage instead of covering the rocket exhaust, would seem like a good idea.

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Re: I am not an engineer...

It seems there is only one way to resolve that question: a low altitude test launch/flight. It won't really matter until we know what mass the Vulture 2 will actually have in its final form. I would think some back pressure from the plate is a good idea to help push the whole rig out of the way.

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Happy

Looks like a solid design to me.

Good luck with your skirt lifting thruster.

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TRT
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I doubt that LOHAN would slide free of the truss by gravity, as the greater air resistance of the glider would cause it to be snatched free of the truss by the wind.

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Premature ejection

> The Vulture 2 will simply slide off the rod, its weight breaking the rocket ignitor wires (not shown in pic), and it can then fly back to base.

Presumably if the igniter wires are broken in the situation described, that would boot up the electronics in Vulture 2, to that it's glide could be documented and its radio beacon used to find where it ends up.

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(Written by Reg staff) Bronze badge

Re: Premature ejection

Yes - the idea is that Vulture 2's guidance and tracking are active whether motor fires or not. That way, the mission's not a complete write-off if the balloon pops too soon.

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Re: Premature ejection

If the weight of the craft is enough to break the ignitor wires then a good gust of wind would also be capable of the same and lifting it off the rod. I liked the idea of securing it with fishing line behind the motor which should melt on ignition but then again may crack at low temperature. Also I think you're putting too much faith in the truss remaining at the same attitude for the ascent, at times it might be tipped down.

Whatever, I think relying on the ignitor wires is dodgy and the tethering needs more thought. It may be better to have a properly secured craft and a parachute descent so the craft lives to fly another day than half a flight.

I'd also put some padded struts almost touching the wings to minimise roll during the ascent so if a violent gust catches a wing it doesn't slam into the truss causing a snapped wing.

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Looks spot-on to me. Perhaps provide a hole in the back plate for the motor to thrust through so the truss isn't affected by the takeoff?

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Anonymous Coward

Two comments

1) Why not keep the launch rail short and combine with a tethering system that is released on ignition; my own suggestion is based on pinholes at opposite sides of the exhaust tube and a loop of fishing line through these to tether the rocket. The line will be destroyed when the engine ignites, releasing the rocket to slide along the rail.

2) Use a tension sensor (probably a DIY job) on the line holding the balloon to detect when the line goes slack; combine with a timer so that when the line goes slack for a suitable period (5 seconds?) the launch is triggered.

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(Written by Reg staff) Bronze badge

Re: Two comments

Interesting, but we're just trying to keep the thing as simple as possible, and without any sort of release mechanism at all.

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Re: Two comments

Why would you need to monitor the tension on the balloon anchor line? Surely it would be enough to detect that upward motion has translated into downward motion?

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Anonymous Coward

Re: Two comments

Detecting the difference between upward and downward motion isn't always easy (look at what happened to Air France 447).

Detecting when a line has tension or not is much simpler.

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Anonymous Coward

Re: Two comments

OK, but my point 1) still stands. I think that a positive retention system will be better than relying on things always being the right way up.

I'm also not sure whether, in free fall, the glider will slide free of the truss. To ensure this you need to retard the descent of the truss and ensure the correct attitude; with a drogue 'chute maybe (but I note earlier concerns about air density on this).

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Icing on the cake

> Air France 447

Now that brings up the very real question of how to deal with ice forming on the launch rod, to the extent where it blocks the free running of V2. (Or weighs-down the whole kaboodle and makes it un-aerodynamic)

I guess the pragmatic answer is to launch on a clear day, so the ascent is not through cloud: no matter how high/thin it may seem to be

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@AC 14:44 Re: Two comments

Drogue chute: it does not really matter if LOHAN slides off the rod immediately after the rubber bursting, only that she does so that they don't hit the ground together. So at what height the chute really comes into play is of little concern.

Alternatively, simply firing the motor on loss of lift, no matter at what altitude, will ensure that LOHAN is at maximum height anyway, while alsosolving the separation problem.

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Let it swing

When it comes to launch, the truss assembly will be swaying, and potentially rotating. Will this have an impact on the angle of attack when the rocket fires?

It appears that Lohan will be resting against the sacrificial rubber pad during ascent. Is there any danger she will freeze to the rubber?

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dpb
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titanium rod mount

The mount between the titanium rod and the aluminium plate will have to be pretty impressive to maintain the parallel line - you'll probably need a second point a bit back behind that plate.

Other than that looks good to me.

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Re: titanium rod mount

Also, have you considered the relative thermal contraction rates of aluminium and titanium? Depending on how you attach the two this could have some effect on the integrity of the joint.

Also, making the Teflon inserts of a considerably larger diameter than the titanium rod will reduce the resistance between the two (smaller surface area in contact).

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(Written by Reg staff) Bronze badge

Re: Re: titanium rod mount

Yup, we'll do some tests to make sure low temps don't cause a problem. Agreed about the Teflon diameter.

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Re: titanium rod mount

It won't be parallel, the rod will be at 90 degrees to the plate.

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gyro?

Would a gyroscope on the truss stop it from spinning, or at least control it a bit?

It would be good to take some video of the departure of LOHAN from the truss - maybe a prism mounted to see above the rail?

You _could_ mount LOHAN like a PIAT round, ie with a great big spring. That way even if the rocket doesn't fire you can get a launch.

ttfn

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Swingers Delight

Is there any chance that the swinging motion will be violent at any point in the ascent? If freezing is deemed not to be a problem with materials used, would a two rod option provide mitigation against any unwanted swinger related damage?

The deisgn is very elegant, top work. Although I do have zero experience in this field, apart from the fact I always wanted to build a rocket.

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(Written by Reg staff) Bronze badge

Re: Swingers Delight

I don't think the swinging will be violent - the whole thing goes with the wind, however fast that is.

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Re: Swingers Delight

>the whole thing goes with the wind, however fast that is.

Respectfully I disagree. The large surface area of the wing and the open truss will most likely not move together. You need a wind tunnel to see what might happen.

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(Written by Reg staff) Bronze badge

Re: Re: Swingers Delight

Fair enough. We'll do a wind tunnel test.

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Re: Swingers Delight

Kitchen utensil aside, I've no experience with Teflon. Will water ice adhere to Teflon? If not, a rail should be superior to a rod, eliminating potential wing-truss contact.

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Re: Swingers Delight

Frost will form on teflon, but fall off at the slightest touch. A rocket should have no problem without serious icing. I don't see how you could prevent the same icing from forming on a rail.

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@Chris W: Re: Swingers Delight

I suggest you watch the video in this article: http://www.theregister.co.uk/2012/03/06/lego_shuttle/

The launch day weather doesn't appear to be very clement, and still the swaying and turning doesn't show a level that would upset the LOHAN/truss combo.

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Why titanium rod?

Ok, it's sexy and allows for a few cheap puns.

But wouldn't a tube serve the same purpose, at perhaps a quarter of the weight? And if it becomes a tube, are there any reasons against using a carbon fiber tube? Since you already have your low temperature test facility, dropping a piece of CF tube in there (in similar proximity to the exhaust as in the final launch setup) probably wouldn't be too much of a problem.

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Re: Why titanium rod?

If you used a tube could you fill it with whatever is in those chemical hand-warmer thingies, just before launching, & at that altitude would it do enough/anything to stop freezing?

Ignore me if I'm talking shit, it's already beer 'o' clock round these here parts & I know nothing.

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Anonymous Coward

Rod vs Rail

Have you considered a C shaped teflon thing with the gap at the top instead of a ring shape?

Then use a strip attached all the way along to a rod inside the C as the rail. This allows more attachment points to the truss to keep the rail straight. So, in pictures... C with a o-| rail inside it, all rotated left by 90 degrees.

Now lets hope that doesn't get translated into some kind of smiley when I hit post.

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Re: Rod vs Rail

You mean ... like a lot of curtain tracks ?

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Re: Rod vs Rail

Unneccessarily complex. Since the whole enchilada, truss and all, is hanging from a tether, you can't guarantee a specific direction and angle anyway, and the main function of the guide rod/tube/rail is to give LOHAN some sense of direction: more or less parallel to the truss, and especially not slamming into the underside of same. There is a minor thrust component forcing LOHAN nose-up, and to counter that a sufficiently stiff tube/rod looks to me to be quite adequate already. This allows simple attachment/guidance rings, and simple means the highest probability that there's separation at the right moment.

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Alert

That and don't bang the tail off

I share the concerns regarding the "simple" dropping of LOHAN in the event of premature balloon rupture. I seriously doubt that the spaceplane would simply slide off the rail. I'll grant that it /might/, but more likely in my mind it will fall at about the same rate as everything else regardless of the orientation, only separating when it falls into thicker atmosphere and the truss assembly is slowed by the recovery system. What damage might the spaceplane suffer in the interim, and what affect would that have on the "flight altitude" record?

The problem of motor exhaust changing the relative orientation of the truss is all but certain. The questions are how much and how important. The issue that I see is that it will cause the launch rail angle to decrease relative to the horizon and so you will lose some ultimate altitude. How much is the question. This can and should be tested for on the ground. Understanding how the platform will behave at the time of launch is important since it will determine the orientation of the spaceplane when it leaves the launch rod.

Finally, I'm concerned that if sufficient winds and/or turbulence are incountered during the ascent, the spaceplane could be damaged by impact with the truss as it swings back and forth on the rail. This may or may not be easy to prevent depending on how far below the truss you can reliably mount the rod (insert appropriate LOHAN joke here). If the rod can be placed slightly more than 1/2 wingspan below the truss, LOHAN can swing any way she wants and not hit anything (potential future application in NAOMI project?). A slightly more complex alternative would be to build a cradle that the space plane would rest in and then slip out of during launch. The cradle would prevent LOHAN from swaying until the motor ignites.

Great work lads, have a beer.

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(Written by Reg staff) Bronze badge

Re: That and don't bang the tail off

I need to clarify here - the truss comes down by parachute, so when that deploys the Vulture 2 should drop off the rod. That's the idea, anyway.

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alu plate/sacrificial pad?

Isn't there a risk of that diverting rocket blast/debris to places you don't want? Why not just put a clamp on the titanium rod, so that the rearmost sliding mount rests on it? Then the nozzle has a clear line of fire.

I am disappointed that there are no exploding bolts in this. I always wanted to build something with them.

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Re: alu plate/sacrificial pad?

Agree with the lack of need of the allu plate - that way you don't risk melting the structure of Vulture 2 with the any exhaust reflecting off the plate as well as not risking melting a plate? Plus you then remove mass from the end you want to be lighter in case of a downward slide launch...

Is there some possibility that the v-tail could become entangled in the truss, if it rotates about the the rod? A possible way round this would be to have a predator drone style v-tail (upside down)...

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Boffin

Backronym?

You are obviously going to need one for this device. May I suggest:

Titanium

Assisted

Direction-

Guiding

Exoatmospheric

Release

I therefore hope we can look forward seeing LOHAN riding into space astride a well lubed-up TADGER.

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TRT
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Just call it what is is...

A rigid shaft.

If it's backronyms you want. It's a LOHAN Titanium Aerial Release Device.

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Tail.

"For obvious reasons, the Vulture 2 must have a "V" tail elevon configuration."

Nothing obvious there and no need for the dihedral tail. I'd have thought a conventional horizontal stabiliser / elevator configuration with a fin / rudder at each end would be simpler and more practical. Have a look at an Avro Lancaster for a practical implementation. You still have to tie the two rudders together (assuming rudder control to be a requirement at all), but you don't have to get into the horror of managing the synchronisation of the two "rudderators" independantly to produce the desired turn / pitch movements.

Pedantry bit: An "elevon" is something found on a "tailless" aircraft (usually delta wing designs), being a combination of the elevator, for pitch control and the aileron, for roll control. Your design combines the rudder, for yaw control and elevator as mentioned. I've used "rudderator", there's probably a proper word for this..........

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Elevons are not such a problem...

We RC modelers operate V-tail configurations routinely. There are simple mechanical and simpler electronic methods for making this work well, so it's not really an issue. Most mid-range RC transmitters do elevon mixing, and an on-board controller could certainly do that as well.

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GBE

Re: Tail.

No need for either a V tail or a double fin. Just put a standard single-fin on the bottom.

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Re: Tail.

That's exactly what I came here to say. The only reason planes have their tails on the top is so the tail doesn't bump the runway. In this case there is no runway, so the tail can go underneath. K.I.S.S.

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Boffin

Re: Tail.

The proper word is "Ruddervator", with a "v". It rolls of the tongue a bit more easily than rudderator.

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Secondary balloon line?

Could some sort of second line be used, linked to the balloon and a tension-sensor (but not linked to the truss)? My thinking would be that if the balloon prematurely pops, that second line going slack would be sensed and that could be used as an "emergency" trigger for the rocket motor?

Similar to the idea above, but by using a second line it can be thinner/lighter and not get in the way of the main line that the balloon is using to hold everything up.

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