Launch Rod Measurement ????

[ckreef]

It is my understanding (I might be wrong) that you load your rocket on your launch rod. You then measure the distance from your top launch lug to the top of the rod and that is your actual rod length ???

So If I have a 72" rod w/ my rocket loaded on the rod --- If the distance from my top lug to the top of the rod is only 55" then my actual launch rod length is 55" NOT 72". I am try to get the most accurate simm data. Do I have this correct ???

 

[plano-doug]

If the distance from my top lug to the top of the rod is only 55" then my actual launch rod length is 55" NOT 72".

That's how I see it.

Doug

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[les]

How many lugs do you have?

Since you refer to multiple, I would assume 2.

After the top lug leaves the rod, the rocket should mostly be up to speed and the fins providing stability, but the lower lug is still on the rod providing additional stability/guidance. I'm not sure if "losing" the top lug off the rod would make a difference at this point.

So back to the original question, do you only use from the top lug or the bottom lug?

 

[bobkrech]

Top lug to top of rod/rail distance. Once your rocket is down to one lug, it can rotate.

Bob

 

[ckreef]

How many lugs do you have?

Since you refer to multiple, I would assume 2.

After the top lug leaves the rod, the rocket should mostly be up to speed and the fins providing stability, but the lower lug is still on the rod providing additional stability/guidance. I'm not sure if "losing" the top lug off the rod would make a difference at this point.

So back to the original question, do you only use from the top lug or the bottom lug?

I'm using 2 lugs. So the question is really --- Do you measure from the top lug or the bottom lug ????

Since this is a low, slow rocket the difference of 17" amounts to about 5 ft/s of velocity at the end of the rod --- and when your cutting it close for stability that might mean the difference between success and failure. Just trying to get the correct data into the simm.

 

[ckreef]

Top lug to top of rod/rail distance. Once your rocket is down to one lug, it can rotate.

Bob

That is what I had read in the past (especially with 1"L x 2 lugs.)

 

[SteveA]

In regards to this, if your launch rod is a standard steel rod and it's longer than 36 inches, how do you avoid whip when the rocket reaches the end of the rod? I had rods that started out at 40 inches and when I launched smaller and faster rockets off of them, I noticed the rods whipped after the rocket cleared. I cut them back to 36 inches and no whip. The longer rod seemed to cause the flight trajectory to arc a bit. (or maybe I just thought it did.) Mostly I found it unnerving.

 

[powderburner]

...... if your launch rod is a standard steel rod and it's longer than 36 inches, how do you avoid whip when the rocket reaches the end of the rod? ......

If you really need a launch rod that long, it's time to step up to a larger diameter. Low-power model rocket 1/8-inch-diam launch rods typically top out (as you noted) at 36 inches, or else rod whip gets bad. Low-power designs using D and E motors can run into rod whip problems even at that length and may require an early switch to 3/16 or 1/4 inch.

If you don't like the looks of monster launch lugs on your tiny low-power model rockets, you can try tower launcher designs....

 

[SteveA]

Low-power model rocket 1/8-inch-diam launch rods typically top out (as you noted) at 36 inches, or else rod whip gets bad. Low-power designs using D and E motors can run into rod whip problems even at that length and may require an early switch to 3/16 or 1/4 inch.

It was indeed, a 1/8 rod. I did cut it back to 36 inches and it stopped the whip. However, that's good to know about the 3/16th rods, I have one I designed and will build, that has a slow (in my opinion) take-off speed and will require a 3/16ths rod and I wanted to use a 40 inch launch rod to insure that it had plenty of length to reach stable fight speed before clearing the rod.

Thanks a bunch for the input! It was very helpful and I have a new wrinkle in the grey matter!