How to interpret the "max liftoff wgt*" on packaging?

[rgather1]

I recently purchased a G80-7T and noticed on the packaging that it recommends a max liftoff wgt* of 52 oz/1474 gms. My question is, does this weight include the weight of the motor, or is it the weight of the model rocket without the motor installed?

I am looking to calculate a 4:1 thrust to weight ratio.

Thanks in advance for the help.

 

[jnmiller]

It includes the weight of the motor

 

[waltr]

Yes, lift off weight is the TOTAL weight with motor as it will be on the pad.

Maker's recommended weights also calculate for the Delay Time. This is a rough estimate of time from burn-out to apogee.

Typical TTW ratios are based on the Average Thrust (80N for a G80).
Divide the average thrust by 9.81 (Earths gravity acceleration) to get thrust in kg (kilo-grams).
Then divide by the TTW ratio you desire (4 in your case).

Math: 80/9.81 = 8.15kg thrust. /4 = 2.04kg total mass for a 4:1 TTW ratio.

Reverse calc for the recommended weight of 1.474kg:
8.15/1.474 = 5.5:1 TTW.
And this is for a 7 second delay.

With a 2kg rocket you may want a 5 or 6 second delay.
Check all this in a simulator such as Open Rocket.

 

[mikec]

In the specific case of the G80-7T, AT didn't want to make a shorter delay, but the max weight they list is honestly a little high for the 7-second delay. I flew a rocket at max weight and while it was OK, it would have been happier with a 4 or 5-second delay.