Cunning Reg reader cracks LOHAN hot coupling condundrum

We invite fans of our Low Orbit Helium Assisted Navigator (LOHAN) project to raise a glass or two today to the Reg reader who finally cracked the problem of just how to hook up our Vulture 2 spaceplanes's rocket motor heater. To summarise, we've got a space-grade Polyimide Thermofoil flexible heater wrapped round our aircraft' …

[Mark 85]

Truly a KISS moment

Simple and efficient it is. Have one and celebrate. ------------->

[Anonymous Coward]

Icing on the cake...

...would be if this idea came to him while he was contemplating the meaning of life in his shed.

[Anonymous Coward]

Weight

Isn't this plane looking a little heavy?

Will there be some test flights of the actual spaceplane before the big launch?

Not really related to this specific item, which is probably as lightweight as you'll get.

[Gordon 10]

Re: Weight

I asked that in a previous comments section. How heavy is the plane these days? Whats the lift calculation?

[Lester Haines]

Re: Re: Weight

We're just wrapping the final attachment of the canards and putting in the last few avionics bits, then we'll have a figure.

[hammarbtyp]

Testring?

I am assuming that it will be tested at operational high altitude temperatures to ensure that the release friction will be consistent?

[Lester Haines]

Re: Testring?

Yes, we can give the system a freeze test. Some of our ultra-low temp grease might be of use, but we'd have to check its conductivity.

[Vladimir Plouzhnikov]

Re: Testring?

Maybe graphite-based lube like ROCOL 210 would be suitable or CW7100 silver-filled grease...

There is also an issue of different heat expansion coefficients if the wires and the tube are made of different metals.

[Martin Budden]

Re: Testring?

Did you test the word "testring" with a spell-checker?

[chizz]

Why not use...

... pogo pins, as per any test fixture.

first thing that popped in my head

[Arachnoid]

Just a further suggestion

Could you not use thin strips of sticky metallic tape for the break point, it would provide good continuity between the tubes and the cabling but still have the ability to shear off cleanly on launch?

Alternately a reverse cloths peg style of clip that provided the connection onto the inside of the tube by sprung assisted friction alone and the thrust would again draw the clips out of the tube.

[Anonymous Coward]

Re. pogo pins

Sounds good.

I wondered about simply using a piece of 70C alloy, similar to Chipquik (tm) but with slightly less indium so it doesen't go brittle at low temperatures.

Only thing I'd do is add triple redundant contacts so if any two things break the failsafe still operates.

ie physically separate contacts encased in heatshrink to avoid shorting.

[b166er]

Re: Re. pogo pins

Magnets?

[Anonymous Coward]

Re: Re. pogo pins

> Magnets?

How do they work?

[Arachnoid]

> Magnets? How do they work?

https://www.youtube.com/watch?v=OvmvxAcT_Yc

[4ecks]

What is the voltage + current

expected to go through these connectors? You don't want hot-spots welding them together, low temperature conductive grease sounds like a good idea.

[Lester Haines]

Re: What is the voltage + current

12V, 2.24W. Yes, some grease is in order, and will be on order when I find a suitable product.

[Dave 32]

Conductive Grease

The conductive grease sounds like a good idea. Note that Copper oxidizes, producing Copper Oxide (I or II), which is either non-conductive, or a semiconductor. The conductive grease should prevent the oxidation. One could also get fancy and Silver plate the interior of the Copper tubes (Silver Oxide is a conductor); consider some of the electroless Silver plating solutions, which will deposit a few Angstroms of Silver (Cool-Amp is one maker (I have no connection, etc.).).

You might also consider ensuring that the end of the Copper tube has a slight flare to it, or, at least, is deburred. Cutting Copper tubing tends to produce a burr, or slight squeezing of the tube at the cut point, and, if you're counting on a dependable release, you don't want anything binding at the end of the Copper tube.

You could also consider some type of spring contact that would be inserted in the Copper tube. I'm thinking of something along the lines of a piece of Beryllium Copper that is folded and soldered to the wire.

http://en.wikipedia.org/wiki/Beryllium_copper

Good luck with it!

Dave

P.S. Remember that any landing you can walk away from it a success.

[Lester Haines]

Re: Conductive Grease

Well, we've got to have some of this, if only for the name: http://www.cool-amp.com/conducto_lube.html

The open end of the tube has indeed been deburred, with a very fine drill bit which created the desired slight flare.

I don't think we're going to get a spring contact inside, and it's an unnecessary refinement, to my mind.

[4ecks]

Re: Conductive Grease

Try these :- http://www.electrolube.com

Available from CPC and much cheaper than cool-amp by the looks of it.

[Lester Haines]

Re: Re: Conductive Grease

Thanks.

[John Smith 19]

Historically smoth breaking connectors have *always* been a problem

I think it was the Blue Steel cruise missile that had a monster 100+ connector for it's INS and other functions that had to break on separation.

I think they used something like a crumpled meter press stud on each connection.

[Zmodem]

whats a rocket assisted launch system that uses a balloon

[Ron 10]

Treating tubing

This may be quite unnecessary, but:

Improved connection contact behavior, if necessary. Clean the inside of the copper with a mild acid or cleaner of choice. Maybe a bit of abrasion.

Coat wires to be inserted and the inside of the copper tubing with a material called Stabilant 22. This improves the contact between the materials and protects from oxidation/corrosion. Plain copper generates an oxide film fairly quickly. This insures max current flow for the circuit. The Stabilant actually conducts under pressure.

This may change retention force to a bit lower.

I use this stuff on any electrical connections. PC connections to power connectors. It is similar to magic.

[Zmodem]

Re: Treating tubing

it would be easier to look at internal designs of hobby rockets then buy some brackets from model then look at a better eay

[Zmodem]

Re: Treating tubing

some of the 8 foot custom rockets can go 1.5km high, you can buy kits and parts easy with a google search and download simulators http://www.thrustcurve.org/simulators.shtml

and make orbital rockets http://www.instructables.com/id/Homemade-orbital-rocket/

[PKM]

Magnets

At the risk of making a brilliantly simple thing a bit less so, would a small magnet on the outside of the copper tube help keep the inserted steel wire pressed against the inside of the tube until the point of release? Seems like it would provide a little friction to help stop the wire from being vibrated out of the tube during ascent but not really impede disconnection.

[Lester Haines]

Re: Magnets

Hmmm. Interesting...