Half a Lug

[DynaSoar]

While bashing spare parts together into a streamer bird, I figured out I don't need a whole launch lug. I can cut it almost in half lengthwise, glue it between the body and the fin, and it works fine. Saves weight in lug, and in glue since it doesn't require so much filling.

 

[Micromeister]

Dyna:
Have you ever heard of a "Pop Lug"? Any lug carried aloft adds an awful amount of drag, two or three different types of drag. This is the reason most BTC's used a launch tower, or a pop-lug to eliminate the lags completely. Pop Lugs are fairly easy to make and once you get used to them are a pleasure to use. Heres a copy of the Old insturctions sheet. I've used long 1/8" straws or 6mm tubes in place of the specified launch lugs in recent years with .020 music wire. Give em a try, you will be amazed at the NOTICABLE altitude difference by getting rid of that little straw

 

[scadaman29325]

Originally posted by DynaSoar
... I don't need a whole launch lug. I can cut it almost in half ...

I did the same thing when I lost a lug during a build and stole half of one from another kit. Seemed to work OK, no problems yet.

 

[Micromeister]

Don't get me wrong..Dyna was talking about a competition model..
I haven't used a whole 2" launch lug on any sport model in years. If LL are used they (a pair) are no more the 1/2" long. and tapered. Location is very important, a single lug will have a tendency to hang up on the launch rod. 2 are better then one! One in the fin fillet and one near the CG usually works best. By the time the models forward lug leaves the rod the air speed is high enough to keep the model moving in that direction.
I don't really have a good photo of lug placement, we usually want to hide the ugly things in pictures In the pic below you'll just be able to see the forward lug about 2/3rds of the way up the body, while the other is tucked out of sight in the fin body joint at the forward edge of a fin.
Hope this helps

 

[jflis]

Originally posted by Micromister
Dyna:
Have you ever heard of a "Pop Lug"? Any lug carried aloft adds an awful amount of drag, two or three different types of drag.

The drag added by a launch lug is typically accepted as about 15%. A *lot* higher than most people would think!

FlisKits has a nice pop lug kit (PL001) for $2.25.

Here's a sketch of it:

 

[Silverleaf]

Jim,

I cleaned up that image for you..made it easier to read as well.

Thanks for posting it, great idea !

 

[Silverleaf]

Wrong attachment..*slaps forehead*

 

[DynaSoar]

Originally posted by Micromister
Dyna:
Have you ever heard of a "Pop Lug"? Any lug carried aloft adds an awful amount of drag, two or three different types of drag. This is the reason most BTC's used a launch tower, or a pop-lug to eliminate the lags completely.

Thanks for the memories. I do remember pop lugs when they first got popular. If I recall correctly, the drawing you provided was one of the original instructions to come out.

I know pop lugs, or better, no lug, is the best design. That's why I'm planning on building a tower. The bird I tried this on was a test bird, using composite fins (styrene sheet folder over a balsa root) so I wasn't being to picky about design. If this design works out I'll replicate it without a lug and start working on the tower.

To be honest, this only occured to me because the local shop didn't have lugs for sale, so I bought a package of styrene tube for R/C aircraft cables. Very thick walls, and so obviously heavy. In the process of shaving it down, my brand new X-acto blade slipped and went way under my thumbnail. I said Golly Gee Whiz. Did you know you can't put stitches through a thumb nail?

Yes indeed, time to start on that tower.

Thanks to everyone for the tips.

 

[Micromeister]

Ouch! Dyna! sorry to hear about your thumbnail slice..NOW that's gotta hurt!!
if your looking for thin wall styrene tubing try Evergreen or Plastistruct. most hobby shops have at least some the the tubes, many of the evergreen brand have a .030" wall.
Hope this helps.

Wow Jim:
I didn't know you had a Pop lug in stock. guess I have to really go over your site better

 

[scadaman29325]

Were there any problems associated with the pop lug?

It really sounds like a good idea, but I would think the hole would show a lot of wear after a while.

Could you use a two hole (one at the top and bottom) or three hole ( one at the top and two at the bottom) method instead of hooks at the bottom?

 

[Micromeister]

Originally posted by scadaman29325
Were there any problems associated with the pop lug?

It really sounds like a good idea, but I would think the hole would show a lot of wear after a while.

Could you use a two hole (one at the top and bottom) or three hole ( one at the top and two at the bottom) method instead of hooks at the bottom?

Ya only need the one at the top and a tiny dab of CA at the hole wll out last the model. the hole isn't a problem at all.

 

[jflis]

You only want the one hole and John's recommendation about the CA is the best solution to keep the area around the hole in tack. The hooks at the bottom of the pop lug are the best way to go as putting more holes in the airframe will simply add drag.

the 3point hook up (front pin and 2 rear hooks) is the best and most elegant. It also has many advantages over a tower including ease of use, cost and in some cases even a competative edge.

jim

 

[mike_bar]

What size music wire is used for a scratch-built pop lug?

Sorry Jim, I am in a scratch building frame of mind...

 

[powderburner]

If you are using music wire, it is pretty tough stuff to begin with, so you don't need a very large size. You are probably using this with a competition PD, or SD, or altitude rocket, and they just aren't very big or heavy.
Something like 1/16 or 3/32 would be huge.
I usually use about 3/64 or 1/32 and it stands up quite well.

 

[Micromeister]

The music wire I've always used for pop lugs is .022" very thin and light weight. You want to be able to adjust the fin hooks to the model being flown. Sometimes we don't get those fins at exactly 120 degree spaceing now do we Very thin wire make it easy to adjust the lug at the pad if necessary.
Hope this helps.

 

[Micromeister]

It occured to me we haven't mentioned making nearly invisible music wire or stainless wire lugs. I've used these for a long time on Scale models and PMCs. I wind a turn or two around an old launch rod with a pair of pliers and a small vise-grip. Make the lead in and out configuration for the model by either connecting both eyes with about an inch of wire between the two or leave about 1/2" of straight wire on each size of the eye bent perpendicular to the eye and facing the line of travel. If applied to a scale model a small channel can be needle filed into the body tube CA or expoied in place and sanded flush with the body. if for a Plastic Model conversion lead in & outs can be left straight, heated with a propane torch or soldering iron and pressed into the model styrene body self sealing and pernanent. Wire lugs does have a short leaning curve and a couple will not bend in the way wanted but with a little practice can dress up those nasty looking but necessary launch lugs.

Unfortunately these wire lugs blend in so well it's hard to pick them up in most model photos, If you look closely at the lower pic, just behind the forward wheel on this1 65th F100-C you may just be able to see one of the two .022" wire wound lugs for a 1/8" launch rod, painted white.
Hope this helps a little

 

[richalex2010]

That model plane/rocket looks very good. Could I use any wire that is stiff enough to hold it's shape, that is easy to find around my house (I do have some metal guitar-like string though, for my Zither that I don't use anmore)?

 

[powderburner]

Yes, in theory, you can use wire as small as you like.
You may run into some practical limits on minimum wire gauge, like durability of the wire or your ability to fashion it into the desired shape. But there is no rule against using thin wire for this.

 

[Micromeister]

Pretty much what Powder said,
I've used copper 20 gauge wire a time or two. While easier to form a more precise eye and anchor points these soft metal lugs soon deform under flight conditions chipping off most of the paint. They still work fine but are now that dingy copper color I've found its worth the trip to the hobby shop to find the smallest diameter music wire they have usually .022" diameter. .022" wire forms well, keep their shape under flight stress and hold primer and paint through many flights.
I use this diameter wire for several other items, flew-wing springs, Helicopter and glider rubberband hooks, pins etc. so I purchased a tube of 100 12" pieces from (Who else) McMaster-Carr. I found they not only have stamdard steel music wire but 302-304 stainless steel wire as well (#8908k22). I went with the stainless. Works just like the standard music wire but doesn't rust when wound or formed into springs, hooks, clips and hinges. Holds paint OK and even if chipped off here and there don't show up as badly.
Hope this helps