Question on launch rod size

[BobH48]

Hi,

I've just started building rockets again after 30+ years.

I have noticed that the advertising for anything with a 24 mm
motor states that you need to use a 3/16" launch rod.

My old Cherokee-D and Goblin have standard 1/8" launch lugs.

Is there a reason that you "MUST" use a 3/16" rod or is it just that the 1/8" rod is not all that rigid?

I guess I'm asking, should I go out and get a new launch pad that will hold a 3/16 rod and just put new launch lugs on my old rockets?

Would this also apply to clusters? I have my Astron Cobra that I built in 1968 but I never flew it .

 

[sandman]

Rod size is only related to rocket weight.

Motor size has nothing to do with it.

I flew a minimum diameter rocket (29mm) on a 29mm G25-15 motor and I used a 1/8" rod. It worked fine...right up until it disappeared at about 6,000 feet!

Some people just like to use larger rods to avoid rod whip.

sandman

 

[llickteig1]

What sandman wrote is all true. IMO, the part he mentioned about rod whip is the critical thing. Rod whip is due to too heavy a rocket on too flimsy a rod flexing as the rocket rises on the rod. When the rod flexes back the other way, if the rocket hasn't cleared the rod, the rocket could travel in an unpredictable direction, often other than straight up.

Positioning the rod at an angle other than directly vertical and/or wind can exacerbate rod whip.

Good luck and welcome back. This little world has changed a lot since the 70's.

--Lance.

 

[solrules]

Of course, if you have the estes mean machine, it is mighty hard to get up straight on a 1/8" rod. Mostly because its center of mass (quite a bit above the launch rod), not nessicarly its total mass. Of course, I had to figure this out the hard way.

 

[powderburner]

I agree with the comments already posted, and don't want to repeat. It's the combination of long/heavy rockets, wind, and minimal (1/8 diam) launch rods that gets bouncy and whippy. You should have no problems with rockets like the Cherokee-D or Goblin and still using the basic 1/8 rod.
Some other ideas:
You probably don't have to get a 'new' launch pad just to use a bigger rod; you can either enlarge (drill out) the 1/8 hole that is there or you can keep the 1/8 and add a second hole for a larger launch rod (there is often plenty of room in the launcher head to put a hole next to the first).
You can also get a stronger launch rod by sneaking up 1/32 to a 5/32 diam rod (you DO know about buying a 3 foot length of music wire at the hobby shop, don't you?). This will still fit inside most launch lugs, and may fit into the existing launcher. The bigger launch rod gives you a significantly straighter launch.
If you are going to go all the way to 3/16 or 1/4, go get a 6 foot length of 'round rod' at your local hardware store (Home Depot, Lowes, etc)----it's stocked with the allthread and angle iron.
Beyond that, you may as well get a rail setup. A bunch of these TRF guys can give you great advice on rail hardware and the matching buttons.

 

[moocrew]

i would say that this is more of a personnal opinion, but.... RAILS!
rails work great. they may not be exactly what you need...but there is hardly ever a problem with making a rocket launch off of one unless you build some kind of HPR that weighs about 200 lbs. And for the most part you can make your rail to be pretty "portable." But if all you plan to launch are Low-to-Mid power then a rod will be suitable 70% of the time.
Good Luck!
-moo

 

[BobH48]

Thank you everyone for all your feedback!

I expect that most of my activity will be low power - I seem to have the small field surrounded by tall trees problem.

My launch pad is the wooden tilt-a-pad from the 60's so it just has a hole drilled in it for the launch rod.

I guess I'll probably take a 40% off coupon over to Michaels and pick up a starter kit so I can get another launch pad and put a 3/16" music wire rod in it.

That way I can get another launch controller that doesn't need a 12 volt battery like my old one.

 

[Elapid]

welcome back!
we have MUCH bigger motors now...


regarding your old stuff...
that kind of thing can often bring huge prices on ebay, especially the goblin, even though it is already built...i saw Goblin kit go for 77 dollars recently.

I'd put it on the shelf and cherish it.
or sell em on ebay and finance your hobby!


buy new stuff, you'll be thankful to have equipment that's not 30 years old to work with. and you can fly big motors in a small field, you just need a really big rocket with a relatively small motor.


before buying anything on ebay, check the pricing at www.buyrockets.com

if you want to do clusters, you'll WANT a launch system that has big clips to hook to a 12v battery. that way you get a better chance at full ignition of the cluster.

 

[DynaSoar]

Originally posted by BobH48
Hi,

I've just started building rockets again after 30+ years.

I have noticed that the advertising for anything with a 24 mm
motor states that you need to use a 3/16" launch rod.

My old Cherokee-D and Goblin have standard 1/8" launch lugs.

Is there a reason that you "MUST" use a 3/16" rod or is it just that the 1/8" rod is not all that rigid?

I guess I'm asking, should I go out and get a new launch pad that will hold a 3/16 rod and just put new launch lugs on my old rockets?

Would this also apply to clusters? I have my Astron Cobra that I built in 1968 but I never flew it .

If it came with the kit, it's the right lug for the bird. You can up the size on those if you wish, but don't need to.

You sure your pad won't handle a 3/16" rod? The Estes porta-pad would, since at least around 1975 or so.

 

[BobH48]

Elapid,

I didn't realize that my old stuff would be worth anything. My sister sells stuff on Ebay but I don't want to be bothered.

I still have one Goblin kit but it's been opened. Estes used to give them away if you spent $10.00 on an order from their catalog.

I know I'll want a 12 volt launch system to ignite clusters, but my back yard is big enough to launch 1/2A and A rockets and I don't want to have to get my lawn tractor out just to launch a few.

DynaSoar,

The Tilt-a-pad had a wooden disc with an 1/8" hole in the middle where the rod is just pressed in. There is no way to clamp it. If I make the hole bigger for a 3/16" rod then the 1/8" rod will just drop through.

I still want to use the smaller rod for the small stuff so I thought I would just get another launch pad for when I'm ready for something bigger.