On "Open Rocket" the CG moves around with different motors. Do I use the heaviest motor or the lighest motor as the reference for CG?Old rule of thumb. 1 caliber below CG.
What is the actual technical justification for this rule? I can't intuit the reason.Old rule of thumb. 1 caliber below CG.
On "Open Rocket" the CG moves around with different motors. Do I use the heaviest motor or the lighest motor as the reference for CG?
Is "1 caliber" equal to the width of the body tube?
Well this gives me lots of flexibility. I like having options. The wall on the body tube of the Estes Super Big Bertha is pretty thin. If I could place the upper button on the coupler joint (halfway up) that would provide a better/more secure grip for the rail button screw. The tube is twice as thick at this location.The center of pressure isn't really relevant on the rail, it only applies once the rocket is in free flight. What you want is to make sure the rocket is under the control of the rail buttons until stable velocity is achieved and the fins can take over ensuring straight flight. A very important part of rail button placement is making sure the rocket does not bind due to wind, CG issues, or under thrust. They need to be far enough apart to avoid a short moment arm that could lead to binding but no so far that you loose rail length. Of course you can always use a longer rail if needed.
Tony
You can also go with Giant Leap's Acme Conformal[emoji2400] Rail Guides, Some people don't like the metal on metal aspect of them but I've used them for years and never! had any issues.
That is lot of rocket.CP does not matter at all for locating an upper lug....
An extreme example in this image of our team's 14.75 foot long G Superroc....
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