Gap staging questions

[STRMan]

I've been searching through previous threads and I can't find an answer to these specific questions.

I am gap staging a couple of 24 mm engines. They will be a gap of about 1 inch from the end of one motor to the beginning of the next. I plan on drilling three vent holes 120 degrees apart around the tube, one dead center between each pair of fins.

What diameter should I drill these vent holes?

Should they upper edge of each hole be right at the lower edge of the upper engine, or set back some distance?

[JRThro]

I've been searching through previous threads and I can't find an answer to these specific questions.

I am gap staging a couple of 24 mm engines. They will be a gap of about 1 inch from the end of one motor to the beginning of the next. I plan on drilling three vent holes 120 degrees apart around the tube, one dead center between each pair of fins.

What diameter should I drill these vent holes?

Should they upper edge of each hole be right at the lower edge of the upper engine, or set back some distance?
Since you want things to flow up to the sustainer engine as much as possible, having the vent holes up high makes sense. This is theoretical; someone with gap staging experience should chime in here with actual practical advice.

[ghrocketman]

With a 1" gap between the engines, I would drill three 1/4" diameter holes equidistantly spaced (120 degrees apart) at the midpoint (1/2" above the booster engine) between the two engines.
If the distance was a long one, I would place them 1" below the sustainer (top) engine.

[tbzep]

That's what I would do also, but the holes aren't always necessary. The Estes Omega is gap staged and doesn't have vent holes. I've staged successfully with it and it seems to be pretty reliable from what I've read over the years. It's still better to add the holes, especially with a minimum diameter airframe and/or longer gap.

BTW, a lot of people use a paper hole punch in order to get an easy clean circle. That's probably why we see so many of them at 1/4" or slightly larger.

[Doug Sams]

I've been searching through previous threads and I can't find an answer to these specific questions.

I am gap staging a couple of 24 mm engines. They will be a gap of about 1 inch from the end of one motor to the beginning of the next. I plan on drilling three vent holes 120 degrees apart around the tube, one dead center between each pair of fins.

What diameter should I drill these vent holes?

Should they upper edge of each hole be right at the lower edge of the upper engine, or set back some distance?Here's my 2 cents.

I try to place the holes midway in the gap. That said, I don't think it's crtical. As long as there are holes to relieve the pressure, they can be just about anywhere in the voids around the motors. Some people have even placed them in the booster centering rings so that the pressure is vented aft.

Like others, I prefer 1/4" holes, but have used 1/8" holes on smaller rockets. I like two holes placed opposite each other.

I typically drill them. The paper tends to tear thus enlarging the hole, so I run the drill at low speed, start out with a smaller bit and work my way up. After getting the first, smaller hole drilled, I clean off any excess paper fuzz, then soak some CA in and around the hole, and let it harden. That way, when the next larger drill bit is used, there is much less tendency for the paper to tear and I get a much cleaner looking hole. Finally, I use some 150 or 220 grit and clean up around the holes. Also, I roll a bit of sandpaper up and use it as a round file to smooth the holes.

I pretty much use this same procedure for adding alitmeter vent holes.

Doug


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[barone]

...........Some people have even placed them in the booster centering rings so that the pressure is vented aft............Oh yeah. I like that idea. Two reasons....

1. Doesn't mess with the airstream at the surface of the rocket thus less drag.
2. Get a little more boost with the pressure venting aft.... ;)

[Eagle3]

Placement of the holes is irrelevant. I've put the vent holes in the centering rings, basically venting the pressure aft and staged fine. I've done this with gaps up to 8". The beauty of venting through the centering rings is you don't see the holes. You still want to run a stuffer tube up as close to the sustainer motor as possible. If you socket the stuffer onto the sustainer motor then you'll need a couple of holes in the stuffer tube. Again, as long as you're not going minimum diameter you can hide all of the venting internally.

[foose4string]

Oh yeah. I like that idea. Two reasons....

1. Doesn't mess with the airstream at the surface of the rocket thus less drag.
2. Get a little more boost with the pressure venting aft.... ;)

This is the way the Semroc Texas Firefly is done. This method is very clean looking and very reliable.

[STRMan]

Thanks for all the great advice. In my application, I am in fact using a minimum diameter body tube, so aft venting is not an option.

I'll report back and let everyone know what I finally do and how it works.

[ghrocketman]

I like that "centering ring" vent idea and will try it on my next gap-stager....most certainly will result in a "cleaner" looking rocket too.