All,
After a review of the rocket I successfully used for L1 I was given great wisdom in the rule of thumb in the positioning of the launch lugs on the body of the rocket. This was great wisdom which I have failed to retain. So that I can make the necessary modifications, does anyone have great advice on the distances of the launch lugs along the body of the rockets?
Cheers.
Simon.
FWIW the only guidance I remember seeing was in a set of PML instructions and was for using rail buttons: the bottom button as low as possible (i.e. using the lowest centering ring to screw into) and the upper button at the center of gravity of the rocket without the motor installed. HTH
Tripoli #13468 L3
Tripoli Prefect #131
QRS President
Thanks for your post. From what I could recall US Rocketry luminary (Verne Knowles) once posted that a common rule of thumb for the positioning of launch lugs on the body of a model rocket is to place the first launch lug about one body tube diameter from the base of the rocket. This placement helps ensure that the rocket is stable on the launch rod during liftoff. The second launch lug, if used, should be positioned roughly halfway up the rocket or at a point that provides good stability while the rocket is on the launch rod, typically ensuring that the rod does not flex or bow under the weight of the rocket. This arrangement helps to guide the rocket straight during the initial, critical part of the ascent.
It's important to adjust these positions based on the specific design and size of the rocket, as well as the length of the launch rod. For larger rockets or those with longer rods, you might need to place the lugs further apart to prevent rod whip or to ensure the rocket remains guided until it has built up sufficient speed for the fins to stabilize its flight.
Interesting, thanks for the updated info... It would be good to see some guidelines for these positions based on rocket size / length, in particular what criteria should be used when weighing up a decision to move from a launch rod to a launch rail...
Tripoli #13468 L3
Tripoli Prefect #131
QRS President
Just to muddy the waters a bit more, Brendan pointed me at the following on the Apogee website:
Q:Where on the rocket should the rail buttons be positioned?
A:
First of all, radially, they should be placed equal-distant between any two fins. Remember, the rail is 1-inch wide, so you can't put them too close to any single fin or the fin itself will prevent the button from engaging the rail.
Forward-and-Aft Location: You would position them just like you would two small launch lugs. Ideally, you should put one button in front of the CG point, and one button behind. Most modelers place one at the very rear of the rocket so that it is easier to see it as it is being loaded onto the launch rail. Once you have the bottom button on the launch rail, it is easier to get the top button to slide on without scraping all the paint off the side of the vehicle.
The forward button's location is not too critical. As mentioned, ideally it should be positioned ahead of the CG point on the rocket. But if you have anything inside the rocket that needs to slide forward (like a parachute ejection-piston device), you'll have to put the button behind it so that the threaded screw on the inside of the tube doesn't prevent it from operating properly.
The nice thing about rail buttons is that they are more forgiving than traditional launch lugs. They can be slightly misaligned, and they will still slip easily along the rail (because they are circular).
Tripoli #13468 L3
Tripoli Prefect #131
QRS President