Have to use a 1/8" launch rod on a new rocket, but a questions about it

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Bill S

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I've started construction on a rocket that is unusual, in that the rear is wider than the middle/front. I designed an internal launch lug that runs the length of the wider rear assembly and exits the front. Initially I had planned to use a 3/16" launch rod, but failed to note that there isn't enough clearance for a 3/16 rod, let alone the diameter of a 3/16" lug. So I downgraded the lug/rod to 1/8", which looks like it'll work.

The rocket will be just under 24" long, and launch weight should be around 6.5oz. I'm using a C11-3 and later a D12-5 to power the rocket. I want to avoid rod whip, so I wonder if I am likely to encounter any problems with such a configuration. Launch speed is around 44fps off a 36" rod, according to Rocksim.

In theory I can redesign the rocket to use a wider rear tube, but that will cause further delays and cost, which I would prefer to avoid if I can.

Thoughts?
 

kuririn

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Alternatively you can glue stand offs to the launch lugs and glue them to the main (smaller) body tube. That way you can use the stiffer 3/16" rod.
 

shreadvector

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I've started construction on a rocket that is unusual, in that the rear is wider than the middle/front. I designed an internal launch lug that runs the length of the wider rear assembly and exits the front. Initially I had planned to use a 3/16" launch rod, but failed to note that there isn't enough clearance for a 3/16 rod, let alone the diameter of a 3/16" lug. So I downgraded the lug/rod to 1/8", which looks like it'll work.

The rocket will be just under 24" long, and launch weight should be around 6.5oz. I'm using a C11-3 and later a D12-5 to power the rocket. I want to avoid rod whip, so I wonder if I am likely to encounter any problems with such a configuration. Launch speed is around 44fps off a 36" rod, according to Rocksim.

In theory I can redesign the rocket to use a wider rear tube, but that will cause further delays and cost, which I would prefer to avoid if I can.

Thoughts?
Steel rod should be fine. The motors have a decent intial thrust to get the rocket moving and a steel rod will not whip unless there is some strange side force/binding on the rod.

Home Depot and lowes sell 1/8" diameter by 4 foot long steel rods for about $5. Four foot long is good.
 

KennB

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The distance of the motor centerline to the rod will impact the amount of whip you create. The larger the rocket's diameter the more it will want to torque the rod.
At this point, the best you can do it complete it and give it a try.
 

Bill S

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The club and launch area I have access to use 36" rods for 1/8" as far as I know.
 

shreadvector

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The club and launch area I have access to use 36" rods for 1/8" as far as I know.
Ask them if you brought your own better rod, would they let you use it on their pad.

We have club pads and also allow indivuduals to use their own systems (after inspection for safety). If the rocket they check in is too heavy and slow for the standard Estes rod, we tell them they have to launch it from the club pad with the 4 foot long rods or buy a rod for their pad.

We also use 3/6" dia x 5' steel and 1/4" dia x 6 foot Stainless Steel (2 part screw together for transport and storage).

I use a plain steel 1/4" x 6 foot rod from Home Depot/Lowes for my personal large pad. ust sand it with fine sandpaper as needed and lube with WD-40.
 
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