Friction Fitting Motors

[Daddyisabar]

You mean freezing the engine before putting it in your rocket?

Oh No! Just to chill the whole rocket to get out used and friction fit cases. I have left rockets out in the winter, the freezer would be for those living in paradise climates.

Freezing an unused BP motor could lead to an Inquisition!

 

[Handeman]

I've never read or heard anyone saying that to use friction fit with your engines, you need to use pliers or other tools to get the engine in the rocket.

Except the OP said in his original post that he used a pliers to finalize the fit of his motor.

 

[Daddyisabar]

Pliers...sometimes the grip strength in the old dude's fingers ain't what it used to be.

 

[lakeroadster]

Except the OP said in his original post that he used a pliers to finalize the fit of his motor.

And it worked.... the issue is there's not much motor extension to grip onto.

Even using the pliers, it took some force to seat the motor that final 1/4", so that it seated against the thrust ring.

After the launch, while the motor and fin can were still warm, the motor pulled right out, by hand with very little effort.

Logic would tell us that the motor diameter increases during flight due to the high temperature and thermal expansion. This increase in diameter stretches the motor tube. That's why the motor comes out of the rocket easier after the launch.

 

[SolarYellow]

And it worked.... the issue is there's not much motor extension to grip onto.

Even using the pliers, it took some force to seat the motor that final 1/4", so that it seated against the thrust ring.

After the launch, while the motor and fin can were still warm, the motor pulled right out, by hand with very little effort.

Logic would tell us that the motor diameter increases during flight due to the high temperature and thermal expansion. This increase in diameter stretches the motor tube. That's why the motor comes out of the rocket easier after the launch.

Could also be the adhesive softening and flowing a little bit. Hopefully it's that. Would be better than stretching the motor tube.

 

[Handeman]

And it worked.... the issue is there's not much motor extension to grip onto.

Even using the pliers, it took some force to seat the motor that final 1/4", so that it seated against the thrust ring.

After the launch, while the motor and fin can were still warm, the motor pulled right out, by hand with very little effort.

Logic would tell us that the motor diameter increases during flight due to the high temperature and thermal expansion. This increase in diameter stretches the motor tube. That's why the motor comes out of the rocket easier after the launch.

I'm not sure I agree that the motor stretches the MMT. At least not enough to make that kind of difference. That would mean the motor has to permanently, or at least long term, increase the MMT ID against the centering rings and then the motor would have to cool and shrink more and faster than the MMT.

I can't say I have much experience with LPR/MPR and BP motors, but my experience with HPR would be counter to that happening. Usually if someone puts a motor in so tight that they need tools to get it in, it is even more difficult to get it to come back out.

 

[lakeroadster]

I'm not sure I agree that the motor stretches the MMT. At least not enough to make that kind of difference. That would mean the motor has to permanently, or at least long term, increase the MMT ID against the centering rings and then the motor would have to cool and shrink more and faster than the MMT.

I can't say I have much experience with LPR/MPR and BP motors, but my experience with HPR would be counter to that happening. Usually if someone puts a motor in so tight that they need tools to get it in, it is even more difficult to get it to come back out.

Different case materials, different thermal expansion rates, different results.