Big Rocket Rail Button spacing

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droopy

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Planning on launching my Level 3 rocket on Saturday. It's about 16 feet long, 47 pounds. I have the rail buttons located in the centering rings at the top and bottom of the motor mount approximately 30 inches apart. I'm using buttons for the 1010 rails.

The more I look at it, I'm wondering if I shouldn't have a third button up higher. It's to late to hard mount one, but I could fairly easily glue one on with the screw epoxied into the body tube.

What's the thoughts here on whether the two buttons 2.5ft apart (and very securely mounted) are adequate for this tall of a stack?

John
TRA Level 2 (hopefully 3 this weekend)
 
The 2 you have should do fine as long as they are secure..Adding a 3rd will just cause an alignment headach to make sure it is EXACTLY in line with the other 2..If not you will get a lot of resistance coming off the rail..

Personally I would just go with the existing 2..
 
Planning on launching my Level 3 rocket on Saturday. It's about 16 feet long, 47 pounds. I have the rail buttons located in the centering rings at the top and bottom of the motor mount approximately 30 inches apart. I'm using buttons for the 1010 rails.

The more I look at it, I'm wondering if I shouldn't have a third button up higher. It's to late to hard mount one, but I could fairly easily glue one on with the screw epoxied into the body tube.

What's the thoughts here on whether the two buttons 2.5ft apart (and very securely mounted) are adequate for this tall of a stack?

John
TRA Level 2 (hopefully 3 this weekend)


Where are you launching?
 
The general rule of thumb is....one button near or in the bottom centering ring and the upper, close to the center of gravity, or slightly below , if you are trying to hit an upper centering ring. Having one high up on you rocket doesn't do that much.

You want the buttons in contact with the rail as long as possible, to increase your attaining stabiilty. As Jon said a third one just makes it harder to maintain alignment.
 
If the third button is located on a part of the airframe that can be rotated into an alignment with the other two buttons, there's no extra resistance or sticking issue, and indeed it can be beneficial if you are in a windy launch site. With only two buttons located at the aft of the rocket, I have seen rotational torque loading due to wind gusts to break off surface-mounted rail buttons. Having a third button near the NC eliminates this torque loading.

Bob
 
Sounds like the buttons you have will be fine. The theoretical best position for lugs or buttons is to have them equidistant from the CG, but depending on the range of motors you plan to use, choosing the mean distance and sound anchor points is best. In my humble opinion that is... :D Good luck on your cert!
 
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