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  #1  
Old 02-01-2009, 09:42 AM
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aeromoe aeromoe is offline
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Default Pop Lugs

Hey all - Any of you have any diagrams or tips on constructing pop lugs you care to share?

I have the general idea for two methods (spring loaded wrap-around, and the music wire top/bottom method using a stand off)

Any information would be most welcome.

Thanks,

Moe
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  #2  
Old 02-01-2009, 11:14 AM
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My buddy and I used the wire method on a Stiletto when we were kids. IIRC, we did it based on a diagram in a Model Rocketeer NAR mag back in the mid to late 70's. We used copper wire.

It was fairly simple. A pinhole was poked into the rocket to receive the wire which was bent upwards. on a length of balsa strip. We used a couple of pieces of wire at the bottom to hook underneath the lip of the body tube. On the opposite side of the wires, we had a couple of short pieces of launch lug. This assembly was put on the launch rod with a few wraps of tape at the top to stop the lug assembly from leaving the pad.

I'll have to dig around to find the issue with the diagrams and better description.
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Old 02-01-2009, 01:18 PM
shockwaveriderz shockwaveriderz is offline
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moe:

pop lugs were popularized by Howard Kuhn of CMR back in the late 60's and early 70's.

I don't know if Howard actually invented them and there use, but this is who I first saw them from.

G.Harry Stine developed a clip on launch lug in the earlier 60's.

Here's a CMR plan that describes the use and construction of a standoff pop lug:


http://www.oldrocketplans.com/cmr/cmrC9/C9.pdf

Jflis currently sells pop lugs :


http://www.fliskits.com/products/01prod_fs.htm

http://www.oldrocketplans.com/pubs/CMR/pop_lug.pdf

"9.4.d Pop Lugs - A CMR pop lug described

From Fred Schecter:

A long lug (2 inches at least) or two smaller pieces of lug glued to along standoff (the standoff is long in length, but does not stand off from the rocket very far).

The standoff has bent/formed music wire epoxied to the top and bottom. The bottom piece forms a little "U" shape that captures the lower lip of the rocket body tube. The top piece is a flattened "V" (almost a point) and it is angled slightly toward the rocket. This top piece is inserted through a tiny hole in the body tube.

The entire rocket can sit on the lug while on the rod (that's why you have the lower "U"). You apply a few wraps of masking tape to the top of the launch rod and when the rocket takes off, it slides up the rod until the lug hits the tape, The lug stops ("POPS OFF") but the rocket keeps going straight since it has built up enough speed to fly stably.

The top pin MUST FIT SNUG!!!!! Otherwise it will pop off at ignition. That would be bad. "

In addition to pop lugs there are "fly-away" type launch lugs.

hth

terry dean
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Old 02-01-2009, 01:28 PM
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Guys - I appreciate all the info. I'd like to experiment with both types (fly away and standoff) and you guys have helped quite a bit.

Moe
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Old 02-01-2009, 01:34 PM
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The CMR pop lug is almost identical to the way we did ours. Instead of a folded piece of wire at the top, we used a single strand of wire, letting us poke a smaller hole in the rocket. We also used some small copper wire instead of music wire. It worked, so we were happy.

We did everything we could to make it as light as possible, thinking that a heavy pop pod would waste enough energy at liftoff to nullify any drag advantages. Considering we were about 12 and had no real science background, I'm actually amazed today that we thought through it that much back then.
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Old 02-01-2009, 02:49 PM
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The fly away pop lug always confused me. It seemed thay used the launch rod to hold the lug together and when the rod was cleared the lugs "flew away". But, it seems to me, that this would add friction between the rod and lug and thus induce binding. Am I missing something?
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Old 02-01-2009, 03:28 PM
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Quote:
Originally Posted by barone
The fly away pop lug always confused me. It seemed thay used the launch rod to hold the lug together and when the rod was cleared the lugs "flew away". But, it seems to me, that this would add friction between the rod and lug and thus induce binding. Am I missing something?


That's exactly the way I see it to. Evidently there's a happy medium somewhere...tight enough to keep it on the rocket, loose enough to slide up the rod.
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Old 02-01-2009, 04:40 PM
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I use to use the pop-lugs a lot back in my early days of NAR competition, but nowadays most
of our contestants here in the Houston area contests bring their easily adjustable launch
towers, which are even better. And some of us still use the CMR style piston launchers, which normally don't require the use of a launch rod.
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Old 02-02-2009, 09:18 PM
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Quote:
Originally Posted by barone
The fly away pop lug always confused me. It seemed thay used the launch rod to hold the lug together and when the rod was cleared the lugs "flew away". But, it seems to me, that this would add friction between the rod and lug and thus induce binding. Am I missing something?


I've used these (I call 'em wrap-around lugs) on a few scale models, most recent probably the Roachwerks LJ-II at NARAM 47. There is a fine line between too tight and too loose, but that can usually be overcome with thrust. In fact, I find that more thrust, like a bigger hammer, is usually a good solution to most of life's problems.

Long and short of it--I've used plenty of different pop lug options, and much prefer the version with small hole in the body tube and a pair of wire legs that wrap around the fins (buy a Fliskits Cougar which includes a great pop lug kit) to the wrap around, but I'd use a wrap-around for higher end competition where even a tiny hole in that's not scale can cost a couple points. I do, actually, try to model around things like hatch covers or rivets so that the hole can be more scale-like.
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Old 02-02-2009, 10:07 PM
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You can buy our Pop Lug kit separately (P/N: PL001 for $3.65) under Misc in the Components section of our products page
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