Gap staging vent hole size

User avatar
Commander
Space Commander
Space Commander
Posts: 723
Joined: Wed, 30 Mar 16, 01:49 am
Location: On the Starport

#1 Gap staging vent hole size

Post by Commander » Sun, 12 Jun 16, 21:58 pm

Much like TMacklin, I am also retrofitting my Renegade to a 24 mm engine booster. Mine was the recent Renegade D 2410 that I had built to the 2109 multi-stage version. Needless to say, I now see the error of my ways in trying to launch this rocket using a C engine making it woefully under-powered (at least with a C6, We'll see what a 24 mm C11 can do). Video of the first flight two years ago can be seen here https://www.youtube.com/watch?v=XSeQ2FDClKM, I don't have a video of the second flight, but it was much the same thing, only in the other direction (meaning south) and so stuck in the grass and dirt.

Well, now the question is, since I am using gap staging, even if it is a very small gap, (okay not really, the engines will be butted together, just not taped) is there information out there relating to the size of the vent hole compared to the total impulse of the engine in the booster? The only thing I have found is in Tim Van Mulligan's Model Rocket Design and Construction which just states that the vent hole should be 6.35mm in dia. or smaller if more than one vent. There is no mention of the total impulse of the engine for this size hole or even if it should be adjusted for larger engines.

Also, would it be more prudent to create two vent holes on either side of the body tube to prevent any unwanted pitching of the upper stage?

Thanks for your input.
Commander
Starport Sagitta
NAR No.97971

User avatar
luke strawwalker
Space Vice Admiral
Space Vice Admiral
Posts: 1468
Joined: Thu, 07 Apr 16, 04:45 am

#2 Re: Gap staging vent hole size

Post by luke strawwalker » Mon, 13 Jun 16, 14:35 pm

I'd do two holes, probably about hole-punch size. I'd rather have the holes a bit too large than too small, myself. 6.35mm... that specific?? Wonder if that's the size hole left by a hole punch?? LOL:)

On the Dr. Zooch Vanguard Eagle kit (which was designed and built as an actual functional two-stager like the prototype, unlike the Estes X-prize Vanguard Eagle), the first stage was designed to vent through the four outboard paper "nozzles" glued to the aft centering ring of the motor mount. You cut holes in the motor mounts to allow the gases to pass through the centering rings and out the back "faux nozzles" which, IMHO, should add at least a tiny amount of impulse from the engine blow-through, even if it's only relieving base pressure of the model. Better than venting it out the sides IMHO, if it's possible to do with the particular design you're working on. Here's the build thread on YORF to show how it works. The Zooch Vanguard Eagle uses a long motor tube in the large diameter lower stage like a "stuffer tube" to ensure ignition of the upper stage, but the same idea of venting through the aft centering ring can be used on a smaller (not minimum motor-diameter) rocket by simply cutting vents in the centering rings-- I'd cut large openings in the upper centering ring with a drill bit or hobby knife to minimize any pressure-drop across the opening and ensure easy and full flow of the gases through the upper ring, and then the "actual size" ports in the lower ring, however many you want. Remember at staging, it's not just the motor blow-through gases you're trying to vent, it's the air trapped in the stage body itself that those gases displace (and heat up as the extremely hot combustion gases cool off by giving up heat to the trapped air inside the stage). Here's the thread with lots of pics showing how it works on the Zooch Vanguard Eagle...

http://www.oldrocketforum.com/showthread.php?t=7444

Later! OL J R :)
My MUNIFICENCE is BOUNDLESS, Mr. Bond...


User avatar
Ghrocketman
Space Petty Officer
Space Petty Officer
Posts: 96
Joined: Thu, 28 Apr 16, 15:16 pm
Location: Michigan

#4 Re: Gap staging vent hole size

Post by Ghrocketman » Tue, 14 Jun 16, 00:51 am

+1 to Verna's post. Two 1/4" holes opposite of each other are plenty.
President, MAYHEM AGITATORS, Inc.
Always MAYHEM, always !

User avatar
Commander
Space Commander
Space Commander
Posts: 723
Joined: Wed, 30 Mar 16, 01:49 am
Location: On the Starport

#5 Re: Gap staging vent hole size

Post by Commander » Fri, 17 Jun 16, 01:46 am

The sustainer has been repaired. In this second repair operation, the sustainer's damages were similar to the first time . In a way it made it simpler to repair as all I did for the split body tube suffered when the nose cone was jammed in, was to peel the original 2" of replacement tube off the coupler, sand the coupler, and glue on a new 2" section of BT-60.

Since it went the other direction and thus into the grass and not the gravel of the dog walk park, there was much less damage to the nose cone.
E-013-001-01_repairs1.JPG
E-013-001-01_repairs1.JPG (66.48 KiB) Viewed 5255 times
E-013-001-01_repairs2.JPG
E-013-001-01_repairs2.JPG (61.14 KiB) Viewed 5255 times

Those astute enough, besides seeing the two new 6mm holes may notice something else strange. When I originally decided to build this as a two stager, I had seen that one of the problems was that the booster would come in ballistic. To keep that from happening, :idea: I built in a section of a half BT-5 into the motor mount and attached a streamer to the booster which was rolled up and fitted in the BT-5 section of the motor mount for launch. It worked, if it wasn't for the fact the whole rocket was now overweight for a C6-0 launch and tended to weathercock badly. :shock:
Commander
Starport Sagitta
NAR No.97971

User avatar
Commander
Space Commander
Space Commander
Posts: 723
Joined: Wed, 30 Mar 16, 01:49 am
Location: On the Starport

#6 Re: Gap staging vent hole size

Post by Commander » Sat, 22 Oct 16, 00:07 am

I have been doing a bit more work on the Renegade. I have the booster motor mount rebuilt in 24mm and ready to be glued in. Originally I threaded the streamer anchor cord through the centering ring and tied it around the engine tube then glued in place as is the current custom. As I was visiting some other sites, I came across a thread for a "replaceable shock cord" mounting technique. This is what is shown in the picture of my mount below.
Renegade new motor mount.JPG
Renegade new motor mount.JPG (97.19 KiB) Viewed 5159 times
Since finishing that mount, I have come across a similar technique that differs only in placing a section of launch lug tubing between the centering rings to make it easier to thread the string when it needs replacement. At this point I figure I can thread it easily with a wire passed through the two holes (much like a needle) and would therefore not be adding any additional weight to this monster, especially in the rear.
Commander
Starport Sagitta
NAR No.97971

User avatar
bernomatic
Site Admin
Site Admin
Posts: 1014
Joined: Tue, 29 Mar 16, 03:55 am
Location: Cleveland, Ohio
Contact:

#7 Re: Gap staging vent hole size

Post by bernomatic » Wed, 30 Nov 16, 05:17 am

Quick update...

I glued the new 24mm motor mount into the booster and the repairs are almost complete. I have some spots that are going to require filling and sanding, then comes the priming and painting. Before I do the painting however, I want to launch her once (or twice) to make sure everything is flight worthy. I tried doing a swing test, but it was inconclusive as I couldn't get it spinning fast enough. Hmmm, maybe I'll have to build a wind tunnel. I am off next week and am hoping for at least one good day to get this baby in the air.
Chief Cook -n- bottle washer

User avatar
Rocket Babe
Space Babe
Space Babe
Posts: 383
Joined: Wed, 30 Mar 16, 23:34 pm
Location: Alabama
Contact:

#8 Re: Gap staging vent hole size

Post by Rocket Babe » Thu, 02 Feb 17, 19:26 pm

Did you ever get this one back in the air?

User avatar
Commander
Space Commander
Space Commander
Posts: 723
Joined: Wed, 30 Mar 16, 01:49 am
Location: On the Starport

#9 Re: Gap staging vent hole size

Post by Commander » Thu, 02 Feb 17, 19:40 pm

To be honest, it has been sitting there ready to fly (except for some cosmetic touches which I'll take care of after a successful flight). I've been following Ted's escapades to gain some feeling for how to continue. It looks to me that with the field I generally fly from that I will go with a C11-0 to a B6-4 combination.

Ted didn't seem to have a problem with his booster till he started going to the D's. I'm thinking that may give too much altitude for the booster to tumble from without damaging it, especially with all the froo froo on the booster. I do have the streamer attached to the booster, but it is not a long one.

Of course right now in Cleveland we're standing in about 2' of accumulated snow, so even if work, the wife, the..... were right, I might not try it.
Commander
Starport Sagitta
NAR No.97971

User avatar
Commander
Space Commander
Space Commander
Posts: 723
Joined: Wed, 30 Mar 16, 01:49 am
Location: On the Starport

#10 Re: Gap staging vent hole size

Post by Commander » Tue, 20 Jun 17, 03:29 am

The time is coming closer to put this puppy to the test. I ordered the C11-0'S and they are on there way. Hopefully before the end of the month, I'll have an answer on whether this one becomes a shelf queen or goes back to active duty.

She's not completely finished. there are still some cosmetic damages to fix, but those can wait till after she has proven herself in flight.
Last edited by bernomatic on Tue, 20 Jun 17, 12:35 pm, edited 1 time in total.
Reason: Sp
Commander
Starport Sagitta
NAR No.97971

Post Reply