"Last week, the Low Orbit Helium* Assisted Navigator (LOHAN) team"
*Hydrogen. Tra la la la-laa....
Last week, the Low Orbit Helium Assisted Navigator (LOHAN) team welcomed rocketeer Paul Shackleton aboard our audacious spaceplane mission. Click here for a bigger version of the LOHAN graphic Accordingly, it's an opportune moment to report on progress on the Vulture 2 motor heater, which will hopefully prevent the aircraft's …
A couple of steel contact patches on Lohan's skin and a pair of wires from the external power pack ending in small magnets should do the trick. The slight drag on detachment should not be an issue if you ensure that the wires are short enough that this will occur while the spaceplane's still travelling along the launch rod so the trajectory cannot be affected.
Or braided brushes, a la Scalextric cars/track?
Or don't use wires, use foil strip and pass that behind the exhaust. It should melt rapidly. In fact, foil with a small notch cut each side should just tear apart as LOHAN's powerful drive thrusts its slim body along the supporting member to penetrate the unknown void...
Sorry, getting carried away there, as you were.
popped bubble wrap and ruptured polystyrene STILL has structure that hold things apart and the air that has gone is replaced by vacuum... a far better insulator with the only mode of heat transfer from one side to the other being conduction through the plastic and radiation across the vacuum... bubble wrap and expanded polystyrene have the additional mode of convection inside the cells...
all in all, popped bubble-wrap and ruptured expanded polystyrene will still have a very good insulation figure...
I'm not sure aerogel will deconstruct as it is an open celled structure in the first place so the air will be replaced by vacuum...
in fact, aerogel was exposed to open space in the Stardust spacecraft as a trap for particles from comet Wild 2
Perhaps it's time to rethink the whole setup, what with all these appuratances anticipated to be wrapping around her, hanging off of her, sticking up her rear end, and such, potentially hindering her free deployment.
How about an insulated box / hangar, where she can be protected and warm, with some cunning exit portal that she can easily pass through on her way out. Maybe one of those millions-of-bristls type.
of course, the hangar must have a name: The commentards can be find a good backcronym for JAIL. Oh, and the portal might be called COURT?
Have you space for multiple layers of space blanket and heatshrink?
Can you crumple up the space blanket(s) so it's more likely to have small airspaces too? Assuming the heatshrink is strong enough to contain the overpressure air if it's completely trapped - it certainly looks strong enough...
Or some other variety of voltage-stepping jiggery pokery to allow more current to penetrate the resistance of the circuit and get that heater up to more of a toasty temperature. Maybe just two battery packs in series if you want to KISS.
If you're using a thermocouple and an onboard computer anyway, you could possibly make a slightly more intelligent thermostat than just "on, off". Call one of the computer's analogue IO pins "heater out", feed it into a couple of MOSFETS (maybe via a cheapo signal transistor), and you're laughing.
It would only require a few components to make something like an isolating power supply, running at 40 kHz or so, with each of the two transformer coils in separate halves of a ferrite-cored transformer. The two halves could be held together by Vulture 2's weight if they were to be mounted on the rubber pad at the end of the titanium rod.
Lets get your understanding of heat radiation up to speed:
Heat radiation takes place even in a vacuum (obviously, otherwise we couldn't see/feel the Sun).
Heat **convection** is what drops as the ambient density goes down, because the currents of air wafting past your heat source can carry away less heat because of their lower density. I remember 1 of my lecturers commenting that heat loss is dominated by radiation for a small temperature difference like 4 deg. C. Hence the results of your REHAB experiment are what I would have expected: Now, if you had put a more powerful heater in your hyperbaric chamber (bigger delta-T) maybe the result would have been different...
Just as an FYI, the project's namesake escaped prison with an enforced home-based 90 day rehab. However, later that same evening Lindsay was photographed with friends by paparazzi outside a Los Angeles nightclub. When she realized she had been spotted in the back of her friends car, Ms. Lohan ducked down in the back seat and threw a blanket over herself.
Just thought you should know!!
How feasible to make a low-pressure wind tunnel for testing this? Doesn't need to be quite on the scale of the full hypobaric chamber.
Something like a tube of metal with a glass or polycarbonate window in it, in a circuit with a fan somewhere in it? Have a bulge in the viewing section large enough to put LOHAN. I hear RVK do some pretty neat inline ventilation fans with a quite formidable throughput. The 5" one I've played with creates a veritable hurricane at normal atmospheric pressures. Failing that, see if any model flyers have ducted fans you can borrow?
Add a variac (or if you're cheap, a dimmer switch) for adjustability in the case of the RVK. Standard speed controller if it's the model aeroplane ducted fan. Use stress sensors on the model mounts to see if there's any lift/control when the surfaces are moved? Perhaps use a smaller section made to be shaped like a part of LOHAN, if you can't fit it all in the tube at once.
But mostly, use a variac for the steampunk factor.
Wrap the wires in Thermate-TH3 or another incendiary, kind of like using thermite but a much lower ignition temperature. Rig up a fuse that can be triggered electrically shortly before your rocket release. You don't want to rely on the rocket plume to trigger the break in the wires, because it might not hang around long enough to provide heat to do the job - and you'll end up with wires still connected. Triggering electronically gives you far more control on timing, and a good incendiary means you can have decent sized insulated wires that aren't going to break easily, but still cut through them in short order when you need to.
No need to muck about with anything incendiary - just use a short length of fuse-wire in the right place, and a circuit that is capable of providing the required overload. Even if your burn-out circuit fails to fire, fuse-wire is so soft that it should break anyway once the rocket motor fires.
This post has been deleted by its author
A neat little trick is to solder a flat metal tab onto the ends of two pieces of wire, and then hold together the tabs by sandwiching them between two rare-earth magnets, the size of the magnets determining the force to pull the tabs apart. K&J Magnetics is a great place for magnet shopping.
If you are worried about shorting against something, paint the tabs with liquid electrical tape to insulate them.
Likely too late in the design cycle but as I cannot find details of the Vulture 2 design I am left wondering if the cavity for the rocket motor could be enlarged slightly in diameter to accommodate a cylinder of insulation material and perhaps a mm or two in additional depth for an insulation hat for the non-functional end of the motor.
This is a back-yard shed project, right? Hold the stripped ends of two wires together with a clothes peg: enough squeeze to hold the wires in contact with each other, loose enough that the wires will pull out easily when LOHAN launches, and exactly the right amount of shed-bodge-ness.
The easiest ways I can think of for an easy break power connector are:
1. A slip ring on the pole and a small spring contact (think electric racing car) in the outer tube, allows for rotation an some movement with almost zero breaking force.
2. Ball up some wire in your typical wall wort connector, sits pretty securely until you pull on it.
3. Small audio connector, 2.5mm. A well used one comes apart very easy.
4. Paint connections. Attach thin wires to the body of the rocket with electrically conductive paint, the same stuff you use to repair windows demisters.
A space blanket wont help when pressed against the engine. Space blankets work by reflecting thermal emission not by insulating them. The silvery surface both reflects more and emits less energy then say a matte black surface would. While the material of a space blanket its self is probably a good conductor of heat. As suggested by "paulc" you want to use an aerogel or foam of some type to insulate it all.
"Space blankets work by reflecting thermal emission..."
You mean like reflecting the thermal emissions of the heater layer back in toward the motor where they're wanted rather than letting them warm up the shrinkwrap? That may be why it produces the improvement seen in testing.
I think that in the test, the space blanket might have reduced the heat transfer to the heatshrink somewhat due to trapped air pockets. But I think it would be far better deployed on the outside (ideally with as little contact as possible between the heatshrink and the space blanket) so that the silvery non-radiative surface is presented to the sky, rather than the efficient black radiator made of heatshrink.
If you still want the sandwich, at least put another layer of space blanket on the outside so that the external surface won't radiate so much. At altitude, radiation will be the main factor causing cooling.
With thanks and apologies to Brian Wragg, might I suggest a substitution for the shrink-wrap, one that might also be useful for your quick power disconnection requirement? If the 57 mm Al tube is close to the size of your heater-and-space-blanket-wrapped rocket motor, then a condom could be unrolled over the assembly to hold it all together. Folding the bottom back over itself and then down again would give you a rubber insulated elasticized pocket to hold loosely twisted power supply wires for the heater. Especially with a lubricated condom, the wires should pull apart readily when the time, erm, comes. This admittedly possibly poppycock  idea would certainly be consistent with the spirit of this noble endeavor: clever, effective, cheap, and (when possible) lewd.
1. The word "poppycock" is all the justification I need for the Paris icon.
Biting the hand that feeds IT © 1998–2021