Launch Lug Placement

[rocketgroupmike]

I think I remember that the lug goes at the CG, when fully loaded. Is that true?

 

[Elapid]

if you only use one launch lug, make it a bit long and make sure it crosses the CG.

i typically use two lugs, one at the CG, and the other near the aft end of the body tube.

good luck!

 

[Karl]

Ive only been placing the launch lug in the center of the rocket , or one about 1" from the top and bottom.

 

[eugenefl]

Originally posted by Karl
Ive only been placing the launch lug in the center of the rocket , or one about 1" from the top and bottom.

I wouldn't worry all that much if it's just LPR rockets. Placing the LL at the CG is for optimal "guidance" performance off the rod. If the lug is too far at the top or bottom, the LL runs the risk of being "twisted" off from the initial thrust from ignition.

 

[Karl]

Yeh It's only LPR stuff I've done that with . Any HPR stuff I use a rail .
Karl

 

[powderburner]

I don't like to use just one LL, whether on the vehicle c.g. or not. I figure that a LL placed perfectly on the nominal c.g. will be out of position anyway if I later have to add nose ballast, or do a tail repair, or use a heavier motor, or . . . you get the idea. I usually use at least two LLs, spread apart a few inches on either side of where I think the c.g. will be. When you examine the dynamics of a rocket launch (even a low-power one) you will see that the elapsed time between these two spaced LLs is just about nil. For practical purposes, there is no chance for any transients to tilt the rocket as the fwd lug clears the tip of the launch rod.

If it is a really long rocket I will also add a short piece of LL near the front, to help hold the rocket steady on the launch rod on a windy day.

Note: the above comments apply only to sport rocket designs. I do not use lugs on competition rockets.

 

[astronboy]

I usually use a single 3" LL at the CG for most of my model rockets. For mid power, I go up to 3/16", and two lugs: 1 at CG and one near the bottom of the airframe.

Although I used to be famous for forgetting to add launch lug while building a model, I have never had one wrench off during boost.

Phred

 

[rbeckey]

No matter where I put lauch lugs, I mount them on a thin scrap of wood, usually a flat coffee stir stick. That keeps the rod off the paint.