3' or 6' launch rod.

[Senior Space Cadet]

I'm just finishing a BT-50 (24mm) build that I designed with the intension of it going pretty high. I'm going to put a Quest C12-8 motor in it.
It has the smallest fins I've ever put on a rocket this size. Theoretically, they are enough, but I'm wondering about the length of the launch rod I should use.
In 3/16, I have both 3' and a 6' launch rods. There will be friction between the lugs and rod for less distance with the 3', but the rocket will leave the 6' rod at a higher speed, so might fly straighter.
Just wondering what some of you more experienced rocketeers think?

 

[Nytrunner]

How fast is it exiting the rod for the 3'?

(you can change the rail/rod length in OpenRocket, go to edit simulation)
((Also remember you only have guidance from the lug to the rod end, so subtract any rod length that's below the lug))

 

[rharshberger]

One problem with small diameter long rods is rod whip is worse with longer rods. 3/16 kind of have a sweet spot between 3' and 4' any longer and the get "whippy". Use a 5' 10mm Makerbeam rail and Micro rail buttons instead ( www.rail-buttons.com ).

 

[Senior Space Cadet]

One problem with small diameter long rods is rod whip is worse with longer rods. 3/16 kind of have a sweet spot between 3' and 4' any longer and the get "whippy". Use a 5' 10mm Makerbeam rail and Micro rail buttons instead ( www.rail-buttons.com ).

Too late for that now. Rocket is built.
I've been putting off making a rail launcher because of the cost and difficulty, but I'll have to do it eventually..
I have a 6ft. 1/4" rod too. Could of gone with that, but it's a pretty small rocket.

 

[XrayLizard]

No lugs. Tower launcher. Lol

 

[CalebJ]

Cut your longer 3/16" rod to 4 feet.

 

[XrayLizard]

https://www.apogeerockets.com/downloads/PDFs/naram99.pdf

 

[dpower]

Agree with others, a 4' long 3/16" rod is about right. If more length is needed for stable flight, I go with 1/4" lugs, and a 5' long 1/4" rod. If 5' isn't enough for stable flight, a rail is needed in my opinion.

This is my rule-of-thumb, for rod/rail size vs distance needed for stability:

3' - 1/8" rod
4' - 3/16" rod
5' - 1/4" rod
6' - 1010 rail

Of course, this doesn't always work, for example flying a small rocket on an E30 may only need 2', but the initial impulse can flex a 1/8" rod significantly.

I also use a mini rail sometimes, but in retrospect, I should have purchased a 5' one, the 4' one isn't always long enough.

 

[Handeman]

This is my rule-of-thumb, for rod/rail size vs distance needed for stability:

3' - 1/8" rod
4' - 3/16" rod
5' - 1/4" rod
6' - 1010 rail

I agree with those sizes and that is pretty much the way our club does it with our pads. The only other rule we have is, NO rockets with G motors or large can be launched from rods. We also supply 1010 rails at our LPR pads because most TARC teams are buttons only now even with E & F motors.

We used to allow large rods on the HPR pads for the rare folks that had old rockets with 3/8", 1/2", or 3/4" launch lugs. No longer, it is rails only for HPR.

 

[JohnCoker]

We used to allow large rods on the HPR pads for the rare folks that had old rockets with 3/8", 1/2", or 3/4" launch lugs. No longer, it is rails only for HPR.

Talk of big launch lugs reminds me of a bad idea of my own: trying to launch a 110lb rocket with a 1in rod: Big Kahuna fail. (Had to come back the following year with a rail.)

 

[dpower]

Talk of big launch lugs reminds me of a bad idea of my own: trying to launch a 110lb rocket with a 1in rod: Big Kahuna fail. (Had to come back the following year with a rail.)

So it was the pad size, not the rod size that was the problem?

 

[JohnCoker]

So it was the pad size, not the rod size that was the problem?

Well, both I think, but certainly the pad.