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  #11  
Old 05-22-2017, 09:53 AM
Tango Juliet Tango Juliet is offline
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When using a "Pop Lug", how snug is snug? Obviously, too snug and it could adversely affect the flight path at separation at the top of the rod; too loose and the rocket leaves the "Pop Lug" too soon, also adversely affecting the flight path. Can anyone put into words how snug is snug?
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  #12  
Old 05-22-2017, 10:32 AM
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chanstevens chanstevens is offline
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I assume you're worried about wrap-around style pop lugs in terms of a friction problem. In general, it's better to err on the side of too loose rather than too snug. This is because even if a wimpy "too loose" elastic doesn't fully open the lug, the drag hitting the model as it is clearing the rod is often enough to nudge them apart.

Besides, applying the principle of maximizing worst case outcomes, too much friction/too tight can mean insufficient velocity when clearing the rod and unstable flight. Too loose means the lug stays with the model the whole flight (really unlikely) or partially, costing a bit of altitude (at most maybe 5-10% depending on whether it partially opens and pieces flap around). Which of those two problems would you REALLY not want to experience?
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  #13  
Old 05-22-2017, 10:55 AM
Tango Juliet Tango Juliet is offline
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Actually I was referring to the fit of the old CMR type of Pop Lug to the rocket using the wire pins/loops.
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  #14  
Old 05-22-2017, 11:33 AM
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Chas Russell Chas Russell is offline
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I have used the CMR-type pop-off launch lugs for egglofters and scale models. My experience is that you should be able to give the model a gentle shake and not have the pop lug come off. I usually would tap the top of the lug firmly to ensure that it does release. Not hit it hard, but more than a touch.

One technique I used for certain egglofters and a BT-50 Sandhawk is to make the bottom attachment a centering ring that the motor fits into instead of using hooks. You may have to use more of a standoff from the launch lug to get the ring in the proper position. For the Sandhawk I used a long spruce strip as the backbone of the pop lug. Launch lugs at top and bottom. Wires at top engaged the Sandhawk's scale forward lug and a centering ring at the bottom engaged the motor.

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  #15  
Old 05-22-2017, 11:48 AM
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chanstevens chanstevens is offline
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Quote:
Originally Posted by Tango Juliet
Actually I was referring to the fit of the old CMR type of Pop Lug to the rocket using the wire pins/loops.


In that case, then "snugness" is not really supposed to be an issue. The angle of the forward bend in the pop lug that holds it in place determines how sloppy or loose the fit is and how easily it separates when it hits the tape at the end of the rod. At the extreme, for example, if it were a 90-degree bend and its length exactly equaled the tube thickness, it would be a very tight fit but never come off. If it were more like 30 degrees and spanned more than the tube thickness it would be loose and sloppy, but come off very easily.

I believe the right balance and middle ground is for the angle to be about 45 degrees, but most critically the span should be very close to the wall thickness, maybe no more than 1/16" greater. The key is for there to be two parallel legs on the lug that are basically just a hair more than the wall thickness apart, separated by the angled bend. The angled bend is just supposed to "nudge" the lug away from the body when the lug it's attached to strikes the tape and starts to slide back along the body.
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  #16  
Old 05-22-2017, 11:54 AM
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Joe Wooten Joe Wooten is offline
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I still have a bunch of CMR pop lugs in the packages and a bunch of built ones in my range box.
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  #17  
Old 05-22-2017, 02:58 PM
Tango Juliet Tango Juliet is offline
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Chan, have you got any images of what you're describing? I've got a drawing/image of the old CMR type, but it's not "exactly" as you're describing it.
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