AIM-9 Sidewinder short kit from KN Aeronautics

Bob in Phoenix

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I am building my AIM-9 short kit from KN. But I have - posers....
I installed a 29 mm motor tube in the fin unit. Glued fin unit to body tube using Bob Smith epoxy.
Now I need to find the center of gravity. Instructions say it should be the midpoint of the 22 inch body tube.
So I loaded a CTI H133 into a 3 grain case and installed it. Put on the nose cone. And I used a 4 inch wide 1/8 inch thick piece of basswood as my "knife edge".
It is really tail heavy. I added Daisy steel bbs to the nose cone. (Yeah, I know - lead shot would be better.) And the CG moves forward. But not enough.
So I wind up with 333 grams of bbs in an almost full nose cone, and it is still short of the mark.
Have I missed something? Have I made a mistake?
If you have built one of these how much weight did you put in the nose. And what did you use? Lead shot? Tungsten? Depleted uranium?
Thanks to all.

Bob in Phoenix
NAR 112473
Level 1 THOY Falcon CTI H163 21 Nov 21
 

NateB

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Don't the kits normally list CG/CP without a motor? Did you build a sim file and check it with different motor options?
 

Bob in Phoenix

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Don't the kits normally list CG/CP without a motor? Did you build a sim file and check it with different motor options?
NateB: The kit instructions do not give a center of pressure. The correct center of gravity is described as a point midway along the 22 inch body tube, +/- 1.5 inches.
I have a working copy of Rocksim 9, but alas, I don't know how to use it. I do have some reloads and cases on hand, so I can try to make the determination by experiment.
I have two sources of information: the notes which appeared in the Ebay ad, and the instructions which came with the kit. On Ebay, it says the kit is designed to fly on F and G motors. In the instructions, it says to balance the rocket with the heaviest engine you plan to use. That is why I picked the H engine. I will try a G engine.
In the words of Valery Legasov, "Maybe I've just spent too much time in my lab. Maybe I'm just stupid."
I hope not.

Bob in Phoenix
 

Sandy H.

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NateB: The kit instructions do not give a center of pressure. The correct center of gravity is described as a point midway along the 22 inch body tube, +/- 1.5 inches.
I have a working copy of Rocksim 9, but alas, I don't know how to use it. I do have some reloads and cases on hand, so I can try to make the determination by experiment.
I have two sources of information: the notes which appeared in the Ebay ad, and the instructions which came with the kit. On Ebay, it says the kit is designed to fly on F and G motors. In the instructions, it says to balance the rocket with the heaviest engine you plan to use. That is why I picked the H engine. I will try a G engine.
In the words of Valery Legasov, "Maybe I've just spent too much time in my lab. Maybe I'm just stupid."
I hope not.

Bob in Phoenix
I did a quick google search and didn't find anything related to 'KN short kit'. Do you have a link to what you have?

Sandy.
 

Bob in Phoenix

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I did a quick google search and didn't find anything related to 'KN short kit'. Do you have a link to what you have?

Sandy.
Sandy H: I bought my kit on Ebay under KN Aeronautics, aka Kyle Newman. In my latest visits there his rocket stuff is gone. Search the Forum under KN Aeronautics; others here are building the same kit.
Bob in Phoenix
 

NateB

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I wish I had found that kit. I build the Estes one in 8th grade and have no idea what happened to it. I'd love to build a larger one.

Sidewinders have huge tail fins, so I could see them being tail heavy. I would be shocked to see a need for a nosecone full of BBs. If I were building the kit, I would skim the instructions for any advise specific to the kitted parts and proceed building as normal. For me, I use Open Rocket and create a sim file from all the unassembled parts and update the weights to account for epoxy and paint as I go, including any electronics and recovery materials used. Then, I note the CP that Open Rocket calculates and also mark a minimum CG. Last, I use the sim to help pick a suitable motor and make any needed adjustments to nose weight. I'd rather have trial and error on the computer than in the air whenever I can.
 

BDB

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I didn't know anything about these kits. Is there a website?
 

BDB

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I just checked it out on Ebay. Great stuff!
 
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