Optimum location for single launch lug?

Okey dokey, am probably going to get shot to ribbons for this but here goes

Is there an optimum location for a single launch lug on an LPR model? (Aside from adjacent a fin root, seems very far aft to me, but I know nothing)

The reason for the query is the statement in Harry's book that a single lug can account for 20%+ of the total drag of an air-frame

I've searched the forum, read Harry S cover to cover (I even resorted to examining the indexed references page by page) to no avail.

Centered between 2 fins, somewhere between the CG and CP, I guess depends on design, and length of lug you have. Mine range from just above the fins to several inches above the fins.

As per luke strawalker I've been burying the lug against the fin. There is already high turbulence there and the lug becomes just a part of that. Plus instead of two convex surfaces being glued together the lug fits in a "V"-ish area of fin root and body tube. I add a filet and the way it is wedged it's a much stronger position and there's the chance that turbulence from the two together is less than separated.

rcktnut said:

Centered between 2 fins, somewhere between the CG and CP.....

Click to expand...

I bias more toward the cg, but this gets down to picking nits. On small lowpower models the length of the LL might cover both cg and cp anyway.

Why limit yourself to a single LL? Are you worried about drag? If so, you should dispense with the LL completely and use a pop-lug, or go to a tower launcher (note: NOT a rail, a tower launcher---a set of guides spaced to surround the rocket's body---use the search button for more discussion).

For sport models, this really doesn't matter much. For scale models extra lugs might be either really really ugly, or might somehow fit better into existing scale features on the model. Either way, LLs on scale models aren't supposed to count against you, at least not for their presence, maybe if you have some poor craftsmanship getting them installed.

Two LL spaced apart a few inches do indeed add more drag (for the second LL) but this is less than 2x the drag of one LL. This is because the aft lug is in the turbulent airflow behind the fwd lug and does not generate as much drag. Two lugs also provide more stability on the launch rod and cause less binding and drag on the launch rod, allowing your rocket to separate from the launcher at a slightly higher speed.

For long rockets, I go for an added LL near the nose to hold the thing still on the launcher.

I tend to believe that a single lug for low power it probably doesn't matter that much.
For two lugs, one as far rear as possible and one near the CG. You don't want the top lug to far forward since as soon as it clears the rod it becomes useless.

How about NO lug and use something like this?

Your design works fine in concept, only thing I would be concerned with is whether it opens partially after it clears the tip of the launch rod, then possibly hangs up on a fin.....for part or all of the flight.

Pop lugs accomplish basically the same thing and have been proven to work pretty well.

Somewhere in the back of my design notes I have an idea for a retractable LL, but it isn't simple, light, or easy, and it does not fit on min-diam models. There is just no easy way to make a LL disappear. Thus, my recommendation for a tower launcher. They too have been proven over and over, and they work reeeeaaaallllll good.

I like powderburner tend to put single lugs over the Loaded CG location with about 2/3rds of the 1" lug behind the CG mark the remainder just ahead. This practice cuts down on the models ability to rotate during liftoff and binding on the rod.

All that said: I've gone almost completely over to using two smaller lugs with one buried in a fin/Body Joint. with the forward lug made as short as possible and 45° angle cut as well. Just to cut down on some of the Drag factors.

I've seen some boost gliders using two wire loop guides, sort of like two launch lugs. Basically two piece of wire, each bent into a loop, with the "ends" embedded in the rocket body. They were small, pretty light, wasn't sure how well they functioned compared to paper lugs.

Specifically not sure if they would have more drag (metal to metal) on the rod,
and not sure how they would behave aerodynamically.

Anybody have an inside scoop?

Thanks for the insights and advice.

I like to over the CG idea, but being a true Libran I like the dual lug (one buried, one short slash cut one) too. Ah, decisions, decisions

Why Sure!
Been using .020" Stainless "Antenna Loop" launch lugs on Scale models and PMC's for many years. They are slightly less draggy then dual small straw lugs but they are still an appendage from the body tube so are more an esthithic then drag reducing feature.

Couple of examples below.

Very nice!
Got any tips on attaching to balsa or paper body tubes?