# Clusters and newton thrust

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#### nukemmcssret

##### Well-Known Member
Please tell me if I am correct. You add the Newtons of each engine/motor of the rocket to get its total thrust. So if you add three D engines with newtons that are say 20 newtons each, you would have 60 newtons of thrust. I would not need a level one certification. IS this correct. Thanks nukemmcssret

##### Well-Known Member
The summary graphic in the referenced PDF is fantastic, but I will attempt to clarify what may be mixed terminology in the original question.

"Newton" = force. It is used to tell you the thrust level at some particular time of the motor burn (like "15 Newtons of peak thrust followed by 5 Newtons of sustaining thrust".) or it is used to give the average thrust over the entire motor thrusting period (like "12 Newtons of average thrust".).

"Newton-seconds" = Total Impulse. This is the total 'power' contained in and released by the motor propellant. If you were to look at the thrust-time curve of the motor, it would simply be the area under the curve.

For a cluster, your Total-impulse is the total of the Total-impulse of all the motors added together.

For a cluster, the thrust level at any point in time is the total of the individual thrust level at that moment in time of each motor added together. For average thrust, it could be the average thrust of all motors added together if they all burn the same time. if some burn longer than others, then you will have a math problem to solve.

#### clreynolds

##### Well-Known Member
A quick example.

2 C6 motors clustered:
- Since both motors burned you add the total impulse of each, net D impulse.
- Since both motors were buring at the same time, you add the thrust, net 12 Newtons

So net is a D12.

or 2 C6 motors in a 2 stage:
- Since both motors burned you add the total impulse of each, net D impulse.
- Since only one motor was buring at a time, you don't add the thrust, net 6 Newtons

So net is a D6.

For your example of 3 D20's clustered, total impulse is in the F range (assuming they started at more that 33% of the D range) and the avg thrust is 3*20 Newtons, so an F60.

#### nukemmcssret

##### Well-Known Member
Thanks for all the information I now understand it. Thanks nukemmcssret