back to article Boffins unimpressed by LOHAN's sizzling thruster

The Low Orbit Helium Assisted Navigator (LOHAN) team has just about shaken off the effects of excessive Yule cheer, and is back at the workbench further pondering a potential powerplant for the Vulture 2 spaceplane. Click here for a bigger version of the LOHAN graphic Our first instinct was to go for an off-the-shelf unit, and …

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Windows

Multiple engines sounds good - see NASA inc.

But, OK to get the drag down and make it slippy, have you checked out the freezing tempareture of KY Jelly?

I've a couple of drag-artists friends, I could always ask....

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Paris Hilton

Pop Lohan's ?

I think a Combustion Heightening & Enhancing Reaction Restriction Yoke is just what LOHAN needs!

Paris never had one I bet.

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Hybrid

In 2 minds about this one, my main concern would be oxidiser staying in the tank on the accent.

The other issue as listed, is complexity, more to go wrong.

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Go

Go NO2 monopropellant, or use an NO2/petrofuel blend...

El' Wiki has a pretty concise write-up on such boffinry:

-- -- Wikipedia: Nitrous oxide (Section "Rocket motors"):

-- -- -- -- http://en.wikipedia.org/wiki/Nitrous_oxide#Rocket_motors

My thoughts would be to lean toward the NO2/petrofuel blend idea. If you increase the dimensions of the glider, you could probably carry quite a bit of fuel. Add a small Arduino-based microcontroller and a solenoid-controlled throttle valve, and the University chaps should be able to bodge together a fairly practical liquid-fuel engine...

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Thumb Up

I always thought the idea of a Lofstrom Loop was cool. El Reg would be doing a major service to humanity if it could work out how to build one of them :)

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Pirate

Remind me again

why LOHAN is going to have engines? I mean, if it rides a balloon(s) up to 98,000 feet, what difference is the extra 200m from the engines going to make? Or are the engines a "just to say we did it" kind of thing?

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Bronze badge

Also puzzled

I'm with you - not sure what adding rather less than 1% to the altitude gets for them other than just proving it can be done.

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Boffin

Me too - since the decision appears to have been made to launch the rocket before the balloon bursts, you will have to sacrifice way more than 100 - 200m altitude, making the whole thing rather pointless.

Still waiting to hear anything definitive on steering by the way - similar issue of course: thin air at altitude reduces the effect of aerodynamic surfaces just as much as it reduces 'plain' drag.

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Boffin

Where is the Drag issue coming from?

Please help me understand why everyone is so concerned about "Drag"? Since the rocket will be balloon assisted up to 98,000 feet, drag should be next to negligible as the air density is very low.

The complicated controls required for a liquid fuel rocket will just reduce probability of success.

Staged, solid fuel rockets are MUCH more reliable and safer and the profile should not need to change drastically.

Lots of weather and lightning research rockets make 100,000 foot on staged solid fuel engines WITHOUT a balloon.

I think the real reason is that the Lohan crew just wants a license for unlimited supplies of Nitrous. Party Hearty boys!

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Happy

I'm also assuming the use of nitrous isn't solely for propulsion...

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"Lots of weather and lightning research rockets make 100,000 foot on staged solid fuel engines WITHOUT a balloon."

Simples... get one of those, add Playmonaut, and balloon launch it from 100,000 ft. It might take a few extra balloons but hey... the photos from 200,000 ft would be worth it

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says:

So, is Vulture 2 going to be 3D printed? The first 3D-printed rocket-plane in SPAAAAACE?

The big problem is no matter how streamlined you make it those wings are, by their inherent nature, going to create loads of drag when under power. Either that or they'll need to fold up under acceleration, and then you have to hope they unfold again.

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Boffin

3D Printed

I think you've just come up with an idea for Vulture 3.

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multi stage with multiple engines in stage 1 is als an option...I always planned making a micro with a B8-0 1st stage (3 clustered engines) and a d12-3 second stage. The burst from the 1st stage will bring the rocket up to speed, the long burn duration of the D-engine will gain you massive altitude....

btw your altitude seems poor, we've done 150-200m with single stage D rockets and 300+ with triple stage C's

Feel free to add me to your rocket team :) (Vlaamse Raket Organisatie represent!)

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Agree about the altitude

I've seen the S8E guys flying and I'm certain they get a lot more than 80m. Besides, 500g is damn heavy: if I built a 2.2m span F1A glider that weighed more than 450g I'd want to pull my head off with blunt pliers. F1A gliders are strong. They routinely take 30+G launch loads for every launch and still last for years. So, if LOHAN weighs more than 200-250g its probably overweight.

S8E is an international competition class for radio controlled rocket boost gliders. They use a single 20-40 newton-second motor, must weigh less than 300g and have a minimum wingspan of 1100mm. The aim of the event is to make a flight of precisely 360 secs, landing so the model stops with its nose as close as possible to a designated point. One point is deducted for every second of deviation from the target flight time and 10 points are deducted for every meter between the nose of the model and the target point.

"These models can reach approximately 1000 feet in 10 seconds and then glide in dead air for about 7 minutes using an E6 (20-40 n/s) motor. Typical models weigh 200 grams or less after motor burnout and are 200 square inches wing area plus or minus about 25 square inches. The smaller the model is, the higher it will boost and longer it will stay up in dead air. However, the smaller it is and the higher it boosts, the harder it is to see and control. So, eyesight is the ultimate limiting factor. A clean 200g model will boost to about 1100 feet on an AeroTech E6 motor." - from an American S8 page.

UK-centric details are here: http://www.fairocketry.org.uk/S8_glider.html

You guys should put your design team in touch with the British S8E flyers: Mike Francies, the UK S8E champion, is currently the chairman of FAI Rocketry. Contact details are on the Contacts page linked from the URL given above.

HTH

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Extra Rocket weight?

The extra rockets will add weight, but what if you release them as they finish their burn? They would probably have to fire in pairs so that the rocket doesn't turn into a space catherine wheel.

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@Ioannis

" ...what if you release them as they finish their burn?" I thought the same, and then worked it through, and saw that it would add a great deal of complexity to the design. This has to be a KISS project, or it isn't likely to work.

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Mushroom

Simplicity is possible...

As the rockets are the source of thrust, they could be held in place by that thrust, and allowed to fall away when the thrust from the next rocket pair kicks in.

The only difficulty would be in holding the rockets in before they thrust, but I would imagine that would be possible with something along the lines of thick cellophane; as soon as the rocket fires, the cellophane would burn away. I don't think this would add much complexity.

(Nuclear blast as an example of how the cellophane would burn when the rocket fires, of course.)

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Silver badge

Thing about hobbyist rocket engines...

...is that many (but not all) of them tend to have an ejection charge. This would normally blow the top off the rocket and get the parachute out at the end of the ride, but there's nowt saying it can't blow the expended rocket engine out backwards instead.

Of course if we're going for very-much-not-off-the-shelf hybrid motor fun, this could change things. I'd suggest either my idea from a while ago, where the aircraft sits in a fairing atop the rocket like a satellite would, or riding piggy back for a slightly easier but very much less swanky option.

Would it be breaking any laws to fill a Soda Stream bottle with liquid oxygen?

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Pint

Hybrid Rocket

Of course this would allow for the amusing possibility of having LOHAN with a large sausage inside.

http://youtu.be/i0zon3xOaI4

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Anonymous Coward

Top Gear Reliant Robin

What about talking to those guys? They seemed to be able to punt a small car a thousand feet or so.. a few kilo payload should be no problem... :)

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moved on....

The main guy behind the Robin has moved on to hangliding these days. Others are aware of this but I am not sure that they are likely to be interested. The Reliant Robin Shuttle used 9 O class hybrid motors and a pile of L class solid motors in the two SRBs I believe. A tad bigger than a small hybrid or G class boost glider motor ;)

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Coat

Someone remind me what the rocket's for?

Removing the extra mass of the cartridge + launch system would probably get more altitude than is gained by the burn.

Taking a sounding rocket to altitude and then firing it would be amusing but might violate a few international treaties.

Mine's the one with the Skylark 7 in the pocket (https://en.wikipedia.org/wiki/Skylark_%28rocket%29)

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Boffin

Surprised it's so bad

These figures are about a factor of 10 lower than I calculated in a comment to http://forums.theregister.co.uk/forum/1/2011/09/12/lohan_motor/ on Sep 12 @ 16:21. It's true I ignored drag, but that shouldn't have that drastic effect. I've just re-done the calculation using your figures for mass, density, etc, and using the thrust profile in the graph. Mass and thrust are functions of time and drag is a function of velocity, so integrating dV/dt using Simpson's rule and then integrating velocity to get height, I get the following:

LOHAN initially falls until 0.39 sec, falling through 25.4cm. It then begins to accelerate upwards, reaching a maximum velocity of 79.8m/s at 5.13 sec and a maximum altitude of 650.6 metres at 13.91 sec.

E-mail me if you want a copy of the Python program I used to calculate it.

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Anonymous Coward

The real problem here is surely that the proportions are all wrong - your propellant mass is less than 10% of the total which guarantees that you can't get much delta-v out of the system overall.

As per Dan Paul's comment the drag is clearly negligible (at least while the rocket is firing - just look at the numbers!) although I think that the area you have used looks quite large.

I don't get why the thrust profile in both sets of graphs is the same though, and the back of my envelope suggests you should still get 70-odd m/s out of a single unit. So I'd double check the complicated calculations, but you still need to send the glider on a diet......

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Facepalm

Thrust for 3 engines...

Doesn't look right. Why would the thrust curve for 3 engines look identical to that for the single engine case? Plotting fubar is my guess (the times 3 is taken account of in the other curves?).

Also, while weight goes up, drag seems overly pessimistic (50% increase?) since that is controlled by the design around the engine fairings.

I dunno, though - I'm a simple software engineer, not a rocket surgeon.

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Mushroom

H is for...

How about using hydrogen instead of helium, and use that as fuel?

Icon as a reminder about which isotope to use.

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try talking to MARRS...

I Think they did the top gear reliant robin 'shuttle' ?

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MARRS?

I think they're more used to pumping up the volume than inflating LOHAN's assets.

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Constant g?

Is g still around 9.81 at 100,000+ feet or should a smaller average value be used?

As I recall, gravity reduces by the inverse square of distance from the Earth's center once you leave the ground.

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Flame

Only a little less

About 1% less at 100,000 feet

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Anonymous Coward

You have to go above 250km before gravity drops to 9 ms^-2, and at 40km it is less than 1% reduction, so no, it's no biggie.

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If that plane in the current design for LOHAN...

then massive thumbs up for elliptical Spitfire-type wings!

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Mushroom

Multiple Engines Bad

Good thing that engines burning in parallel has been ruled out. Simultaneous ignition at amateur rocket scale is iffy at best. also with the weight and forces involved, even if one engine lights a few 10's or 100's of milliseconds later it can cause the trajectory of the rocket to veer wildly. then you have the slight differences in thrust from each motor.

Definitely go the hybrid!

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Paris Hilton

Baby hybrids not so cute

It'd be a fun final year project to come up with a decent, low mass-fraction hybrid system of that diminutive size, let alone one that'll reliably ignite remotely after it's ascent. Good luck to them if they want the challenge but I can't see hybrids being a magic solution - they could mass-optimise the solid for a lot less research time/budget if it's that critical, but a hybrid intrinsically requires more parts and infrastructure and they only scale down to a point. See, for instance, the smallest Contrail motors - 38x400mm for a G100/123/130/300, Skyripper motors - 29x300mm for a G63 or 38x400mm for a G125, the MicroHybrid project - 24x140mm for a D with a truly terrible mass fraction. At 32x150mm the G12 is just metal tubing, nozzle and bulkheads, everything else is fuel; the hybrids are all this, plus injector assembly, ignition system, fill mechanism, with the tubing being twice as long/heavy - that's a heavy penalty to overcome.

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Headmaster

A bit sloppy

g is not 9.81ms-2. As I calculated in http://forums.theregister.co.uk/forum/1/2010/11/01/paris_climax/ it is only 99.15% of that, or 9.73 ms-2. Due to irregularities in the Earth's composition, the final digit is only approximate but the effects of altitude are greater than that uncertainty.

It is sloppy to use figures that you know to be wrong and that you can easily calculate, even if the added accuracy makes little difference to your result. A figure of 9.8 or 9.7 I would have accepted. but to quote the extra figure when it is wrong shows a lack of attention to detail and implies inadequate understanding.

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Coat

What if

What if you used a "medium sized" Big Johnson (nitrous) for the initial in order to keep the mass down, followed up by the Three-Way (solids)?

Since the straight three-way just won't do it for her anymore. It makes sense that the solid propellant is denser and that means more mass to overcome at relatively lower speeds.

And of course anthing to make the whole package as slippery as possible. Although sometimes its useful to have just the right amount of drag in just the right places.

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Go

You could be more ambitious

How about a scaled down version of this:

http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41563/1/05-3857.pdf

or save that for Lohan's sucessor?

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Too advanced to be of interest?

I agree with a few posts here that the project is getting away from the "Men in Sheds" appeal of the PARIS project. Powder laser sintering is expensive and beyond most to replicate. Has anyone considered using a RepRap machine as this is within most peoples reach and would bring back the appeal.

Also this is a British project, where is the Union Flag? Come on guys RJ Mitchell and Barnes Wallace will be turing in their graves.

Currently it seems to be dressed in Italian livery, which is almost certainly more chic, but may make the aircraft less reliable!

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