Thrust Plate

This page refers to the means of transferring thrust from the motor to the rocket. For information on mounting and constraining the motor, see the Motor Mount and Retention page.

The thrust plate is the part of the rocket that transfers the force of the engine to the body of the rocket. It is usually situated near the base of the motor. Despite the name, a thrust plate does not always have to be a plate. It can be the motor tube itself, a boat tail, or just a lip on another part. It is not necessary for it to be a solid plate of material at the base of your rocket.

Most motors transfer their force through the motor lip, which can be found at the base of the motor casing. The lip provides very little contact area, so you need to make sure that the material selection can stand up to the peak motor force, as well as a factor of safety. 

For smaller rockets, like L1s and L2s, thrust plates are commonly just the motor mount tube (cardboard or blue tube), or a 3D-printed adapter.

For larger rockets, like L3s and larger L2s, the thrust plate is usually a machined component. If the rocket has a metal boat tail, it is common to machine the lip to the inside of the boat tail. If not, usually an aluminum plate or a fiberglass tube does the trick. 

An FEA package like Fusion 360 can be used to determine if the thrust plate is sufficient.

Continuing Force Transfer

Once the force is transferred from the motor to the thrust plate, you still need to be cognizant of how the force will be transferred to the rest of the rocket. If you are using the motor mount tube as a thrust plate, for instance, you will most likely need more, larger centering rings with more epoxy than you would normally, to transfer that force from the motor mount tube to the airframe. If you are using a plate or boat tail, it is common for these to have a lip that has them sit underneath the main body tube, so they can press upwards.