2 stage ignition

Technically, you want 2nd stage ignition on velocity regardless of the actual coast time interval. But I prefer KISS.

Alan

Reply to
Alan Jones
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It's a timing fuse. The original, "real" Thermalite is the kind you need. It burns at a specific rate in the open, but when it is sheathed in heat-shrink or teflon tubing, the sheathed section burns almost instantly. This is necessary for APCP motors because they generally have a long core, and must be ignited from the top of the core only. So you sheath the part that fits into the motor (leaving 1-2" unsheathed and bent over at the top), and then measure out enough of the unsheathed portion at the bottom end to give you the correct delay time.

Slow Thermalite is wrapped in reddish fibers and burns at about 1" per second. "Fast" Thermalite has a yellowish wrapper and burns at 5" per second.

You can see some pics and drawings of how I use it on this site:

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Unfortunately genuine Thermalite can be hard to obtain these days as it is no longer made and may require a LEUP to purchase.

There is another type of timing fuse marketed as "Thermolite" (notice the "o" in the middle), which has a gray plastic coating and burns at about 1" per second. However, it does NOT burn noticeably faster when confined, so usually the time to ignition would be much too long when used in large APCP motors. It still may be useful for smaller motors, and also makes an excellent, simple ejection delay for use with plugged motors in lieu of electronics.

You can get it from

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Reply to
RayDunakin

Shock wrote:

Reply to
RayDunakin

I agree with you there, Larry. The J350 I used in my BSD Intrepid destroyed my interstage coupler and while it was separating it ruined the inside airframe of my sustainer. I'm not sure how I'm going to fix that. A small BP works very well (prior launch).

Eric F.

"I learned this the hard way - a J350 igniting before stage separation really makes a mess of an epoxy-coated (for protection, I thought) interstage coupler."

Reply to
Eric F.

I strongly recommend a GWiz to do the job. It's worked fine every time I have flown my scratch built 2 stage rocket. I used a timer the first flight and the effect I was after wasn't there. I had the timer set to ignite too soon and the burns just ran together.

What I think looks awesome is when the booster burns out and it drag separates THEN the second stage lights and away it goes! :)) hmmmmm Can't wait to fly it again!

Reply to
Jason Andersen

This should be in the FAQ.

Reply to
Jerry Irvine

For someone with little to no experience with staging, yes, I would agree to stick with the easy to light propellants.

Reply to
Kurt Kesler

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