Inboard or outboard launch lugs?

[McKailas Dad]

Ok, say you're scratch-building a LPR rocket with a (plastic egg) NC much larger than the BT. Should the launch lugs (2) go 'inboard' (i.e., thru the NC) or 'outboard', as like with those ugly stand-offs?

Will a ~1/8" hole thru the NC make much aerodynamic difference? Will it cock to the side that the hole is in? I figure I would have to run a lug all the way thru the NC, to seal it for the ejection charge?

Also, can a lug be placed further out on a fin, as in not at the root/fillet? Like, halfway out? 3/4? End of fin? Maybe 1 lug-per-fin as for aero balance and more visual appeal.:confused2:

TIA

 

[Gillard]

Ok, say you're scratch-building a LPR rocket with a (plastic egg) NC much larger than the BT. Should the launch lugs (2) go 'inboard' (i.e., thru the NC) or 'outboard', as like with those ugly stand-offs?

Will a ~1/8" hole thru the NC make much aerodynamic difference? Will it cock to the side that the hole is in? I figure I would have to run a lug all the way thru the NC, to seal it for the ejection charge?

TIA

sorry to point out the obvious, but if your putting an egg in the nose cone, then you cannot put the vrod through it!
if the egg nosecone isn't for an egg, then i'd put a hole through the nose cone. should not need to put a lug in the nosecone, as usually that part of the nose cone is not open to ejection charge.
the estes death star is similiar to what you are describing. it does not cock to one side because of the whole (it cocked to the side because of the massive ball on top of the rocket!)

 

[JStarStar]

I have built a couple birds of this type; what I usually do in a case like this is mount one lug on a fin and another smaller lug on the perimeter of the nose cone (obviously making sure they line up).

IF you are launching an egg, putting the lug on the fin only is risky IMO because with the very heavy nose weight of the egg, the rocket is subject to wobble as you get ignition and liftoff, and any significant lateral wobble between the egg section and the launch lug mounted on a fin is very likely to result in the fin popping off as you lift off, with horrible results all around. :y:

Mounting a small "guide lug" on the nose cone, in line with the other lug on the fin, is likely to keep the nose and the tail both moving in the same direction hopefully resulting in all lugs and fins remaining on the rocket.

 

[jflis]

No, I don't think he is launching an egg. I think he is using that as a descriptor of the nose cone (eg: egg-lofter-like as in fatter than the body tube)

To answer your question, the hole in the nose cone *will* have an affect, but it will not be all that major. If your real concern is performance you should go with a different nose to be with anyway One problem with doing this is to make sure that you have the cone properly aligned to fit on the rod. I would also recommend that you either over-size the hole in the cone *or* install an actual launch lug inside the cone.

What I have done with similar designs in the past is to create some detail in the design (such as fin strakes) that give me a nice place for the lugs, out away from the body, that don't look that bad. Another idea is to make the lug look like a gun or antenna, or other such detail, adding other lugs to balance the look.

hope this helps!
jim

 

[Micromeister]

It all depends on what your planning on doing with the model.

If it's just a Sport flying model that well never need the space used for the LL it's OK to have it pass through the Nosecone or transition and nosecone or even through the entire length of the model if you like.

Over the years i've seen and build many models with Launch lugs that for one reason or another I didn't want to use stand-offs. Some are a little harder then others to construct but it's all up to what your trying to do

Like a 4" diameter ball Sputnik with a BT-20 core motor mount with the launch rod running up beside the BT-20
or some of these off placed LL locations

 

[JStarStar]

No, I don't think he is launching an egg. I think he is using that as a descriptor of the nose cone (eg: egg-lofter-like as in fatter than the body tube)

To answer your question, the hole in the nose cone *will* have an affect, but it will not be all that major. If your real concern is performance you should go with a different nose to be with anyway One problem with doing this is to make sure that you have the cone properly aligned to fit on the rod. I would also recommend that you either over-size the hole in the cone *or* install an actual launch lug inside the cone.

What I have done with similar designs in the past is to create some detail in the design (such as fin strakes) that give me a nice place for the lugs, out away from the body, that don't look that bad. Another idea is to make the lug look like a gun or antenna, or other such detail, adding other lugs to balance the look.

hope this helps!
jim

ah, OK, after making the post I realized I had probably mis-read the OP and he was probably not launching an EGG per se.

As you note there are plenty of ways to install a lug and make it look like a structural part of the rocket. And I don't think at any rate we're worried about marginal increases in drag here, it doesn't sound like this is any kind of altitude-competition model.

 

[shreadvector]

Lug on fin and small lug on small standoff at or just aft of the c.g.

 

[luke strawwalker]

Ok, say you're scratch-building a LPR rocket with a (plastic egg) NC much larger than the BT. Should the launch lugs (2) go 'inboard' (i.e., thru the NC) or 'outboard', as like with those ugly stand-offs?

Will a ~1/8" hole thru the NC make much aerodynamic difference? Will it cock to the side that the hole is in? I figure I would have to run a lug all the way thru the NC, to seal it for the ejection charge?

Also, can a lug be placed further out on a fin, as in not at the root/fillet? Like, halfway out? 3/4? End of fin? Maybe 1 lug-per-fin as for aero balance and more visual appeal.:confused2:

TIA

That's how I did my "Warp Drive" rocket (Big Bertha clone with an electric LED whirlygig toy nosecone) night flyer. I simply put the launch lug about halfway out one of the fins from the root, and used an 'ugly standoff' for the forward lug to clear the nosecone.

Internal lugs isn't really anything new. You just want to make sure they don't foul the chute/wadding packing in the process of getting it on the rod. There isn't any reason you should have to "seal" the hole in the nosecone-- a small hole will have no discernable effect on either aerodynamics or ejection.

Good luck! OL JR