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Launch Lug Position
#1
While I've been finishing up the rockets I started 2-1/2 years ago, I'm now at the point of starting new kits and some new designs.
My memory isn't as good as it use to be.
Where is the best place to put a launch lug?
By reviewing my old designs in RocSim it appears it put them centered on the COP or just above Center of Pressure.
Any comments welcome.
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#2
It varies among builders. Traditionally folks will have one or two.
if two, one is usually at/near the base, the other near the CG. (not CP).
It's less of an issue with LP.
For my new LP builds, that aren't repros I am going to start using mini, and micro rail buttons instead of lugs.
They are small, relatively low drag, and offer the ability to launch on the small rails, without the whip rods experience.
For repros I will continue to use the lugs...
Greg Young - L3
TRA 00234
NAR 42065
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#3
Does it make any difference if the launch lug is overly large?
That is, obviously if it's too small, it will be snug.
But is there such a thing as too loose?

I have had several low power rockets "bind" or loose thrust as they attempt to fly off a corroded launch rod with a "snug" launch lug.
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#4
Cleaning a launch rod is necessary, not matter the material it's made of.
I typically use a 3M Scotch Brite Red Pad (Item 7447) from most automotive parts stores.
It's 400 grit. If it's steel, use WD-40 with the pad until the rust is gone. Aluminum and SS use a dry pad.
Wipe down with soapy sponge and clean with a wet rag. Let dry.
Coat the rod with graphite powder, found at most hardware stores.
Also apply some to the inside of the launch lug at each launch, just a touch.
You should have no more problems with hanging lugs.
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#5
One size up is usually okay. Obviously if the lug is too big, then the rocket doesn't go straight up (it leans slightly). Also, you can get vibration that slows the velocity. So I would keep to no more than one size up (e.g., 1/8 to 3/16, 3/16 to 1/4, etc).

Also, nothing wrong with putting a little WD-40 on the rod.
John S.
NAR #96911
TRA #15253
MDRA
Level 1, 2014-Mar-15 -- Aerotech Sumo, H133BS
Level 2, 2014-Jun-21 -- Giant Leap Vertical Assault, J240RL
Level 3, 2016-03-12 -- MAC Performance Radial Flyer, M1101WH, 13,028 feet
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#6
Just my personal preference, but I prefer WD-40 on launch rods.  Graphite is slick, but what a mess it can be!  I just put graphite on a door lock, got some on my hands, and it gets down into pores and can take a day or more to clean out.  (Just looked -- still not completely gone. )  I do not want that all over my hands, and rockets, at a launch.

There may be graphite in more of a liquid or paste form (?), but the graphite I used was powder, and got everywhere after I applied it to the lock mechanism.

On a similar note, I used cornstarch of some chutes the other day, since I could not find my container of baby powder.  That was a huge mistake.  That stuff gets everywhere and clings like crazy.
Lee
NAR 55948, L2
In Build: Mars Snooper
Next: upscale Sky Hook (Panavia kitbash)
In Finishing:  Estes Honest John, Red Nova, Super Cobra
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#7
I personally find it is as much a function of aesthetics as it is launch rod performance, particularly on smaller models. Often, I will use one near the base, because it's easier to conceal there. If two, The upper will be a little bit higher, and that's as specific as I get with them. Then again, I do no competition flying and have no mission-critical parameters that must be met, so if I get a bit of lean or knock a few feet off of apogee, it's not that big of a deal to me. If I was engaging in TARC or something, I might give placement a bit more thought.


Later!

--Coop
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#8
I've used all kinds of things for lugs and have never been terribly picky about their placement on lpr or mpr. If I use one, I like it longish and around the CP/CG. I like two better. Many have been oversized. The only problem I've ever had is that a single oversized but short lug can also bind on a rod. After the second time, I added the second lug that I knew it should have had from the start. Don't remember the details of placement or composition.
Member of MDRA, NAR and NARHAMS;
Level-2 certified but mostly fly G and under;
Volunteer compiler of manufacturer's news for ROCKETS Magazine.
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#9
Thank you all for the tips.
Unfortunately, the gear master for our club flies ONLY high power, and as a result, though he sets up LPR rods and launch controller, he never gives  thought to cleaning the rods...so they continue to be coated/corroded since last month's launch while in storage!

I will pick up a scrub pad and some WD40 for tomorrow's launch.
I won't get 'burned' again.... Angry
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#10
(08-14-2015, 12:14 PM)Trident Wrote: Just my personal preference, but I prefer WD-40 on launch rods.  Graphite is slick, but what a mess it can be!  I just put graphite on a door lock, got some on my hands, and it gets down into pores and can take a day or more to clean out.  (Just looked -- still not completely gone. )  I do not want that all over my hands, and rockets, at a launch.

I wonder if they use graphite on the rods at NEFAR? After setting up, my rocket and hands were FILTHY. It took me a day to get my hands clean too. Not cool.

I use automotive spray silicone on my rods. Some of the Estes 3/16" rods are chrome plated, and silicone helps keep them from corroding.

As for the OP's question. I prefer four lugs: a pair of 1/8" and a pair of 3/16" so I have a better chance of finding an open rod at a launch. The lower set are placed either at the bottom of the body tube or between the fins. The upper set are usually an inch or two below the nose cone. The only downside is the potential of binding on a curved or bent rod.
Living life dangerously...launching C's on a B field.
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