We at the Special Projects Bureau have been mulling just how our Low Orbit Helium Assisted Navigator (LOHAN) project is going to work and, having looked at your suggestions and ideas, have put together our initial thoughts. Click here for a bigger version of the LOHAN graphic To recap, we're going to launch a rocket-powered …
I've got a Spitfire in the loft constructed from balsa wood covered with tissue paper which I made years ago at school if you want a prettier aircraft design (and a rocket powered spitfire in space would be cool)
On a slightly more serious note, the instructions (it was a very old kit) mentioned the use of a Jetex rocket motor. These don't produce a lot of power but burn at lower temperatures which might be useful if building the model out of burnable materials. http://en.wikipedia.org/wiki/Jetex_engine
just a little hydrogen?
Would not a Helium/hydrogen mix be safe? If the hydrogen is dilute enough would it not reduce the risk of a firestorm...but give more lift? Are there other lighter than air gasses that could act as retardants to be added if SOME hydrogen was in the balloon.....
Don't call it a space plane! The last attempt reached 17 miles, whereas the widely recognized edge of space is about 62 miles (100 km), so El Reg whilst they should be applauded for trying, are still 237,600 ft short of reaching space!!!
Vulture Evolution; or how we went from 2D to 3D printer .. ehm .. output material?
""Structure formed from composite material (eg, carbon-fibre-reinforced polymer), or selective laser sintered nylon.""
I don't understand how this is still a question?
Vulture 1 (PARIS) was created from high quality (but 2D) printer paper, providing it with the necessary IT angle. It's only a natural step in the evolution of the Vulture project that #2 (LOHAN) is created by a 3D printer.
Objections? No? Then it's agreed :D
So the angle of the dangle is key
// and a very happy Sysadmin Day to all the BOFHs out there.
And are you absolutely certain that nose-mounted rockets aren't the old http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy in a new form?
This is a pendulum fallacy in the making. It simply won't work. Not even a new form - Arca in Romania were about to launch a very similar rocket when they seemed to read up on the Pendulum fallacy and changed their minds....
That is actually a new one for me. However, there are important differences in my LOHAN design; I think this will compensate. It would also not be impossibly difficult to have the top of the tower be a universal joint with servos that can alter the net thrust angle and guide the rocket-plane on its desired path.
The long nose tower holding the rockets a safe distance from the plane will shift the CG forward a fair bit — probably 20–30 centimetres, I’d estimate — which will convert the gliding configuration into a stable boost configuration. After engine burnout, wing deployment and tower separation, the glider will naturally adjust itself (eventually, given the extreme altitude) into gliding mode.
Absolutely not right
LOHAN will be equipped with functional stabilisers, unlike the rockets described in the Wikipedia article. Of course, the trick is to get them to keep the craft at roughly 45 degrees nose-up during engine burn (I can't readily find burn time numbers, but it appears to be just a couple of seconds max for most sizes). As long as your sideways momentum is small relative to the total length of the craft, nothing much is going to happen in that time, and even if it did pitch down immediately, it's at some 25km altitude, still quite some time and distance away from becoming a lawn dart.
What about this bit from the Wiki page
"Even a Goddard-type rocket, with the engine at the front, will fly correctly if fitted with fins or another means of control. "
As the icon says: proceed with this nonsense at flank speed!
Your design is definitely not as unstable as the classic pendulum rockets - the wings, and consequently having the centre of mass ahead of the centre of aerodynamic pressure (I doubt you could avoid that with this design even if you wanted to!) will make this stable once it gets going - so it might well be OK. The start is the tricky bit, combining low speed with thin air... I'm not sure I'm qualified to predict what would happen there but it sounds like a job for very conservative design if ever I heard one.
Steering the whole engine unit, though, sounds problematic to me - will moving the entire engine mass relative to the entire fuselage mass be able to respond fast enough? Isn't this why big rockets usually rotate small subsidiary thrusters rather than the main engine?
I'm really looking forward to this... whatever happens I'm sure it will be fun to watch!
With the configuration I have suggested — 2 stages of 6, Aerotech E15 composite engines each — the burn time will only be about 5 seconds total. But that should be enough to get a 3 kilogram plane up to hundreds of kilometres per hour.... if it doesn’t completely tumble.
A nose gyroscope may be a good idea for initial stability.
Thanks for the vote of confidence!
We may be able to get quite effective attitude control if we combine slight directional rocket-pod adjustments with a super-fast gyroscope in the pod..... This may take servos capable of delivering a lot of force, so using longish lever-arms is advisable. The lever arm could, for example, extend 50cm down the rocket tower to the servos, which would be able to make small directional changes and control the craft.
— Murray Pearson
GPS at altitude
Apparently all GPS units that can work over 18km (which is pretty feasible) are classified as munitions. Have you got access to unrestricted GPS? (of course you know all of this I'm sure)
http://www.armscontrol.org/documents/mtcr (item 11)
If you want to get around the traditional speed & height limitations of GPS, you should speak to the chaps that helped you with your hypobaric experiments on project PARIS.
And or Or?
Isn't it only if you're going over 1,000 knots, too? The statement in that document is "AND".
Wouldn't be surprised if many chipsets use an "OR" limitation though, and the altitude information on civilian GPS does not work too well up there.
Time to start packing gyros, accelerometers, barometers, and compasses?
"Time to start packing gyros, accelerometers, barometers, and compasses?"
Sounds a lot like you need a smartphone for guidance. Recently I've had the urge to build an inertial navigation system which uses GPS for the initial reference and is then supplemented by data from the accelerometer and gyroscope to work out it's position in 3D space.
Plus it could double as a downlink once it's in GPRS range
AND it could be used to film the Playmonaut's adventure.
Single-engined tractor config would be more reliable.
Trying to ignite two or more engines simultaneously is asking for trouble - if one engine fails to ignite, ignites later or burns out earlier than the other then the craft is forced into a pretty disastrous spin.
A single-engined tractor means that the craft needs to be a slightly odd shape, however that didn't trouble the X-Prize winners.
Aside from that, two 'cockpits' looks pretty cool - one for the Playmonaut and batteries (ballast), the other for the camera and electronics.
Incidentally, don't go with SLS nylon. It's really quite heavy and fragile compared to carbon fibre matting.
You work with carbon fibre matting much the same way as fibreglass, it's really easy to form and extremely strong. Obviously you need to use the right resin, but that's a simple detail.
Alternative to angle-of-dangle
What's wrong with a long horizontal pole? Plane at one end, counterbalance at other end, balloon in the middle. The plane can then launch straight up without any extra faffing about. If you know what altitude you're going to release at, Boyle's Law will even tell you how big the balloon's going to be, and hence how long the pole needs to be.
Of course you need to keep the pole horizontal, but simply having two support cables running from the balloon to each end of the pole will sort that.
Problem with a long pole:
Weight. To hold the craft steady far enough away to ensure clear passage past the enormous balloon (at altitude), the beam would have to be very long indeed — especially if the counterweight was substantially less than the aircraft weight, which I am estimating at about 2 kilograms (the wing by itself, without ballast, is 900 grams). Hoisting that much dead weight will surely limit altitude. Furthermore, with my aforementioned aimable thrust-pod, it will be a far smaller penalty to launch at 45° slope and use thrust-vectoring to attain a near-vertical trajectory after, say, 50 metres of flight.
— Murray Pearson
or a donut-shaped balloon
for a really weird-looking solution. The rocket could fire straight through the centre hole. You might even be able to get sponsored by any well-known maker of donuts..
I know such a balloon will not be available off-the-shelf, but it would look cool.
A few thoughts:
Could the aircraft be suspended directly from the balloon with the suspension arranged to give the 45 deg launch angle? This would avoid the additional mass of a separate module attached to the balloon.
I wonder if the release method could be by running the attachment cable through the rocket exhaust so that when the rocket is fired the cable is burnt through and the craft is released.
The suggested multi rocket design seems to be vulnerable to problems if the rockets don't all start at the same time.
Are folding wings neccessary? It's additional complexity and there aren't any narrow spaces it has to fit through.
Doughnut - Shaped Balloon allows vertical take-off - Thunderbird 3 is go!
If you had a large doughnut-with-a-hole shaped balloon, then the rocket could be mounted vertically and take off through the middle - like Thunderbird 3 does when it launches :-) Means you wouldn't need to bother with all the 45 degree stuff. You could wait until the balloon burst for max height, then a small drogue parachute at the top of the rocket could keep it's attitude vertical until the engines could ignite.
You don't need a doughnut
Three balloons will form a hole at the centre as they firm up at altitude, a small hole granted but possibly big enough to shoot LOHAN through.
Those folding wings look like they are designed to keep the wings out of the way of the rocket exhausts. surely an easier way is to just have the rockets above and below, not left and right.
That's exactly what is going on...
The thrustlines are 2D projections of diagonal thrust, which was my initial idea and is, frankly, probably not the optimal configuration. But, say, if we have a 6-engine cluster per stage, then we can have four engines firing above the wings at a shallow angle, and two engines pointing over the folded wings at a greater angle, such that the horizontal thrusts balance out.
One detail that Lester did not mention is the toughening of the wings from covering the foam with 1/64" (0.4mm) aircraft-grade plywood and heatproofing with a layer of aluminum foil, shiny side out.
My concept was using two, 6-engine cluster stages with Aerotech E15 engines (http://www.jetboyrockets.com/motor/detail/23/) which have a relatively steady and long burn (2.6 sec, average thrust 15N, max 28N per engine) along with the specific impulse oomph of ammonium perchlorate composite propellant, and the advantage of having reloadable cartridges.
— Murray Pearson
IIRC, it wasn't the hydrogen so much as the flammable skin and other materials which made the aircraft crispy. Hydrogen burns and goes upwards rapidly
Incidentally the biggest airship disaster wasn't the Hindenburg; it was the Akron, a helium filled vessel....
I have one major objection to this. It removes the need to shove a rocket up LOHAN's arse.
Round here, that should be a showstopper.
Alternative to underslung rocket?
It sounds like the plane itself will be light compared to the payload module, so would it be possible, instead of mounting it under the balloon, to mount it directly above it? The payload module would act as ballast to keep the whole structure stable during the assent, and LOHAN could then blast vertically.
The balloon is not a rigid platform. Furthermore, it's quite fragile, so putting anything on top of it *) will, providing it stays put in the first place, induce stresses that will cause the balloon to stop being one prematurely.
*) this advice provided free of charge by a card-carrying member of the Society for Putting Things on top of Other Things.
Hydrogen vs Helium
Just wondering, its much easier to make your own hydrogen than buy helium. Would this give extra lift, does anyone know?
It's been stated before
that due to the incompatibilities between hydrogen and several of SPB's members lifestyle, it's a no-go.
Re: It's been stated before
They need the helium for their funny voices?
Slightly better than Helium. H2 molecular weight = 2 (plus a smidgeon for the Deuterium). He molecular / atomic weight 4 (less a smidgeon for the Helium-3). Air average molecular weight about 29. So 2/29 extra lift.
I still think that a smallish rubber or polymer balloon filled with hydrogen in an open outdoors location is safe. Extreme incompetence or a lightning strike would result in a fire burning upwards, ie away from the people. Just put a small exclusion zone around the balloon during the initial fill (until it's bouyant enough to be tethered a fair number of feet above any human heads). Or get it to no-load bouyancy with Helium, float it upwards, switch the fill to Hydrogen.
Helium is dead easy to buy and transport.
Hydrogen less so - if nothing else, the insurance people don't appear to like it when you carry significant quantities of compressed flammable gases around.
It's generally considered a bad thing if your hire car catches fire or explodes.
Use acidified water, and a battery
You can make Hydrogen as needed, by electrolysis of water (and throw the Oxygen away into the atmosphere). Don't store the stuff (apart from in the balloon).
Outdoors, with any breeze, this is safe. There's nowhere for any leaking hydrogen to accumulate and mix with air to an explosive concentration. Indoors, this is a recipe for an explosion.
Can the solid fuel rocket motor be detachable, like the Shuttle boosters? Then you can have LOHAN sitting on (or hanging under) the motor which drops away when spent, leaving LOHAN lighter and better able to glide?
Possibly also avoids the issues of bits of LOHAN exposed to the rocket exhaust too.
The rocket tower does jettison.
See the diagram? The top plan view shows the glide configuration, the other plan views show the tower in place with unfolded and folded wings.
With one balloon providing the main lifting force, and a cluster of three partially-inflated smaller balloons you could trigger on the main balloon bursting (IMO the best and simplest way to signal that maximum altitude has been reached) while still keeping the tether taut after bursting and thus the launch platform at the predetermined attitude.
Plus a long cardboard (?) launch tube that goes up the middle gap between the three balloons, Vertical launch, avoid the balloons, and you have three for more lift.
As to GPS and the like, check out the arocket archives - lots of stuff on rocket suitable GPS there. Generally you lose tracking at over 1000knt, but recover it pretty quick once speed decreases. Also lots of posts on rockoons etc.
Problem with a launch tube....
Where would the wings go? If there are slots wide enough to pass the glider wings, how would the tube be held together?
The rocket could just go straight up a rail betwen the 3 balloons.
I was going to point out the weight of a rigid launch rail, but in fact that might be a really good idea — provided the rail is made from extremely light materials, such as a basswood/thin plywood truss.
A metal rail of sufficient thickness would be ludicrously heavy, but a carefully-made wooden launch rail / balloon-separating apparatus could be just what the doctor ordered.
Hi-ho, I am gonna fire up my crappy CAD software tonight, and send Lester another file.
— Murray Pearson
Conical rocket motor assembly
Would an alternative (to get around the need for synchronous, reliable ignition of multiple motors) be a single large motor with a titanium cone sitting behind the exhaust?
...because the drag of the thrust on the titanium cone would essentially equal the motor’s thrust. It would be spectacularly inefficient.
Besides, it’s really not too hard to get simultaneous ignition. In my test rig over the weekend — which was my first ever attempt at a cluster rocket — I achieved ignition of three engines with nothing more than a 6V lantern battery and parallel-wired Estes ignitors. Of course, for weight reasons you don’t want to use that for LOHAN, but a stack of supercapacitors kept charged up with lightweight high-tech batteries can source a spectacular jolt of current for a brief time, enough to get 6 engines going with no problem, and not weighing too much either.
— Murray Pearson
may be a Right Thing given the launch platform may be unstable. Possibly, the configuration can be designed in such a way that it slowly turns upwards in the flight, then the initial launch angle will be unimportant. Maybe the launch even can be triggered by the burst of the balloon.
How do you plan to overcome the problem of asymmetric thrust? Single chamber, multiple nozzles?
If the GPS does not work at high altitude, you might just keep the right direction (via magnetic or solar sensor) until the GPS locks in.
Thrust asymmetry can mostly be solved with trigonometry: as mentined above, four engine4s firing away from the folded wingtips at a shallow angle providing the upward oomph, with two engines firing at a larger angle from the centreline in order to clear the folded wings and balance the thrust. A single combustion chamber with multiple nozzles would need custom manufacturing and would be extremely difficult to make, especially given weight constraints.
The tricky part will be ensuring simultaneous ignition; this can be addressed by having highly charged supercapacitors for the igniters. They will provide a REALLY high-current pulse which should be enough to fire all 6 igniters within a millisecond or so of each other, especially if the igniters are all wired in parallel (the first igniters burning out will result in even more current through the laggards, triggering near-instantaneous completion of ignition).
One problem I forsee is frozen control surfaces. That means the rocket will go in circles and the plane stage will not operate until lower altitudes de-ice it - assuming it has not already broken by then pushing against a non-moving surface.
I think you will have to do one of these:
1) provide heating, perhaps using wire through the hinge points
2) use "wing warping" for steering instead, though it would take more power
3) some other novel method of steering such as weight shift (as used by hang gliders) in a heated container. But I don't think it as ever been done in a model and is probably impractical.
You can make R/C control surfaces that are immune from binding by avoiding discrete hinges entirely. Instead, stitch the control surface to its mounting point using monofilament line in a figure-8 pattern, viewed in cross section. This should work well even at extremely low temperatures, as monofilament is really tough stuff — but of course, a trial is required.
Launch near-horizontally. Have your guidance system point the nose up at 45 degrees as of say, 0.5 to 1 seconds after ignition and hold it there for the duration of the rocket burn. Then you can use as many balloons as you like!
The tractor design seems a bit iffy. Nothing wrong with a little bizarreness, but this is going to mean that you have burning hot exhaust gasses flowing over your aircraft. Not to mention the Wikipedia link on pendulum rocketry that RayG posted! Don't forget that the tractor escape system on various NASA rocketry has never been put to use, and they probably have a much bigger budget to make sure it would work properly! If you're worried about getting up to a speed where control surfaces will work, then can't you put, say, a "sacrificial" flap or two in the rocket stream? Doesn't matter too much if they burn up, so long as they last long enough to get you going in the right direction. That or make the rocket nozzles directable.
I still think balloon clusters would be an idea. You don't just have one cluster with all the balloons touching. The idea is that if an entire cluster does go bang, you still have redundant clusters. Have a heavily inflated lower set, a normally-inflated middle set and an upper set only just inflated enough that they will lift the rig on their own. You get the ballocket through all that turbulent weather nice and nippy-quick, plus footage from an upward-pointing camera of the staged balloon bursts would be pretty awesome. Plus the rig will most likely go higher, as the upper set only needs to just-about-barely carry the weight of everything. I would also think it pretty obvious that a cluster of three balloons needs to be inflated vastly less than a single balloon, and therefore will go much higher before burst.
Off the shelf rocket motors also tend to have an ejection charge in the tip, and I don't know what that would mean with them mounted in a tractor config like that. It seems like you'd need your own extra method of removing the tractor scaffold after the burn completes. Mounted to the side or underneath in a more normal fashion, you could use the ejection charges to blow your rocket modules clear in a Shuttle SRB style.
The folding wing idea is something. Perhaps have a design where the force of the air sweeps the wings back like a fighter? You're going to need something to keep wing surface area to a minimum during the rocket burn, as otherwise you will more than likely rip both wings off (or at least, limit your potential maximum speed) even up at that rarified altitude. Don't worry too much about fitting ailerons to a moving wing. Elevons work extremely well for controlling both pitch and roll, and you reduce your servo count by two. A simple V Mixer (available from most model shops for about a tenner) can turn your aileron/elevator signals into elevon signals easily enough. Just like this, and yes, that is me: http://www.youtube.com/watch?v=0x2mbEVqJW4
Finally, and I've already said this but it bears repeating: Cameras. Cameras and more cameras. On the launch rig. On the Vulture 2. Hell, on the rocket boosters too. Cameras everywhere!