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- Jan 18, 2009
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Long story:
About 5 years ago, I built a "park flyer" for our local, small-field launch.
It's a Mini-Mag with a 54mm hole.
I loaded it with a motor (motor-eject) and took it to the field to launch RTF.
When I got there, I found the launch queue way too deep for my allotted attendance time so I bailed.
The rocket sat in my garage, RTF, for the approximate 5 years.
We had a pickup launch this weekend and while packing I pulled it out and figured it was time to get this thing flown.
Over the years, I had forgotten what motor was installed.
It was 54mm and had a medusa nozzle with the center plus 3 outer holes open.
I grabbed the rocket and a First-Fire and went to launch it.
When it became time to install the igniter, I couldn't using any holes. It wouldn't go in.
I had to take it off the pad and back to camp so I could undo the retention and get the motor out and see what was going on.
It was then that I discovered I was using a J180T C-Slot motor and none of the nozzles were exposing the slot.
So I rotated the nozzle a bit to line up an outer hole with the slot and re-assembled.
I then could feed the First-Fire down the OUTER HOLE into the slot.
At the pad, I tied the wire to the pad so it would help pull it out if it wasn't already spit out.
But I did worry about using the outer hole instead of the middle.
I didn't have the instructions so I went with my gut figuring a nozzle obstruction is the same everywhere as far as "plugged area" and the impact on Kn is concerned.
But what did give me slight concern was that the plugging was none-uniform across the nozzle and was primarily under the flow of the slot.
Until the wire cleared, this would cause the flow to "zig" sideways across the [non-existent] convergence-cone of the medusa before escaping out the center.
Of course, I didn't think of all this until I was walking to the pad.
I convinced myself that it would be OK - probably aided by the fact that it was 100 degrees out and I wanted to be up-and-back ASAP and going back to camp a second time to get the igniter out and fished into the slot from the center hole was going to take more time in the heat.
The flight was fine - it was OK.
The POINT of this all: What is the proper insertion for slot motor with a medusa nozzle? Is it OK to routinely use the outer holes, or did I get lucky?
About 5 years ago, I built a "park flyer" for our local, small-field launch.
It's a Mini-Mag with a 54mm hole.
I loaded it with a motor (motor-eject) and took it to the field to launch RTF.
When I got there, I found the launch queue way too deep for my allotted attendance time so I bailed.
The rocket sat in my garage, RTF, for the approximate 5 years.
We had a pickup launch this weekend and while packing I pulled it out and figured it was time to get this thing flown.
Over the years, I had forgotten what motor was installed.
It was 54mm and had a medusa nozzle with the center plus 3 outer holes open.
I grabbed the rocket and a First-Fire and went to launch it.
When it became time to install the igniter, I couldn't using any holes. It wouldn't go in.
I had to take it off the pad and back to camp so I could undo the retention and get the motor out and see what was going on.
It was then that I discovered I was using a J180T C-Slot motor and none of the nozzles were exposing the slot.
So I rotated the nozzle a bit to line up an outer hole with the slot and re-assembled.
I then could feed the First-Fire down the OUTER HOLE into the slot.
At the pad, I tied the wire to the pad so it would help pull it out if it wasn't already spit out.
But I did worry about using the outer hole instead of the middle.
I didn't have the instructions so I went with my gut figuring a nozzle obstruction is the same everywhere as far as "plugged area" and the impact on Kn is concerned.
But what did give me slight concern was that the plugging was none-uniform across the nozzle and was primarily under the flow of the slot.
Until the wire cleared, this would cause the flow to "zig" sideways across the [non-existent] convergence-cone of the medusa before escaping out the center.
Of course, I didn't think of all this until I was walking to the pad.
I convinced myself that it would be OK - probably aided by the fact that it was 100 degrees out and I wanted to be up-and-back ASAP and going back to camp a second time to get the igniter out and fished into the slot from the center hole was going to take more time in the heat.
The flight was fine - it was OK.
The POINT of this all: What is the proper insertion for slot motor with a medusa nozzle? Is it OK to routinely use the outer holes, or did I get lucky?
