How to retain my motor?

[nickrulercreator]

First, for clarification, I do know how to retain motors. You can use the friction method (tape), end cap, and thrust plate that screws over the motor nozzle. My problem is that my rocket can't do the latter 2, and I don't want to risk a flight on a High-powered motor with only the friction method.

Here's photos of the rocket's motor end:

Edit: Forgot, 38mm motor

As you can see there's no place for a thrust plate and no room for an end cap. What else can I do? I've been thinking of sanding down some of the end of the fins to be able to fit an end cap, but I don't know if this is possible, or how it'd affect the rocket's flying.

Is the friction method the only way?

 

[blackjack2564]

What size is your motor mount? [diam.]

I know a very simple way for reloadable motors if they are longer than the motor mount.

 

[dr wogz]

Friction fit does work for a lot of motors.. But does get dicey when you get to 38mm and above..

From what I see, you can get away with the fin slicing & sanding to add a proper screw type retainer. I won't affect the flight, but may shave off a few feet of altitude (added weight).

 

[nickrulercreator]

What size is your motor mount? [diam.]

I know a very simple way for reloadable motors if they are longer than the motor mount.

Wow I forgot that! 38mm

 

[Dave A]

I have done this with my V-2, notch enough of the fins that meets the tube so the retainer body will slid in with a snug fit. Just take a dremel or hacksaw blade, only have to cut away about 1/4" to 1/2".
The slimline will have less in the air stream. Scuff the area, I even drill a few small hole for the epoxy to grab.
Epoxy it on and go!

 

[T-Rex]

It isn't pretty, but it is simple and cheap. Get 1 or 2 long wood or drywall screws and a couple washers. Drill a hole smaller than the screw in the lower centering ring. Carefully screw the screw in, then remove it. Harden the hole with thin CA. When you fly, slip a washer over the screw to retain the motor. I would also us a zip-tie or piece of wire wrapped around both screws to hold them against the motor tube. Size the washers as necessary so the retain the motor but do not interfere with the nozzle.

I have friction fitted 38mm motors. Scary considering the cost, but it does work.

 

[Dave A]

It doesn't get any easier than this.

 

[Dave A]

Slimline or Aeropak will work

 

[blackjack2564]

Finally a bit of thinking outside the box for motor retention.
Measure MM tube, 6.5 inches long. Mark that on motor. Wrap several layers of tape around case at that point.
Load reload into case. [no rear closure YET]
slide motor in from front of airframe, drop into position, THEN screw rear closure on.
Motor now captured between MM tube and can't go anywhere.....with no need for fancy retention or friction fit.
Safe ...bulletproof.. simple motor retention. This one is 29mm. I use on 38 & 54mm. No need for store bought...LOL



Just stick tape measure up MM to get length the tab on end of tape will catch on inside end.

PS: I still friction fit motors ...even 75mm on minimum diameter birds, have not lost a motor yet. Yes..there is an art to it. Once shown, never forgotten.

 

[CORZERO]

Finally a bit of thinking outside the box for motor retention.
Measure MM tube, 6.5 inches long. Mark that on motor. Wrap several layers of tape around case at that point.
Load reload into case. [no rear closure YET]
slide motor in from front of airframe, drop into position, THEN screw rear closure on.
Motor now captured between MM tube and can't go anywhere.....with no need for fancy retention or friction fit.
Safe ...bulletproof.. simple motor retention. This one is 29mm. I use on 38 & 54mm. No need for store bought...LOL

View attachment 316157

Just stick tape measure up MM to get length the tab on end of tape will catch on inside end.

PS: I still friction fit motors ...even 75mm on minimum diameter birds, have not lost a motor yet. Yes..there is an art to it. Once shown, never forgotten.

Brilliant!

 

[Nathan]

If the centering rings are plywood then you can just stick a couple of wood screws in the aft centering ring and then use thin baling wire to retain the motor. Kind of like safety wiring a bolt.

 

[jimzcatz]

First, for clarification, I do know how to retain motors. You can use the friction method (tape), end cap, and thrust plate that screws over the motor nozzle. My problem is that my rocket can't do the latter 2, and I don't want to risk a flight on a High-powered motor with only the friction method.

Here's photos of the rocket's motor end: View attachment 316112 View attachment 316113

Edit: Forgot, 38mm motor

As you can see there's no place for a thrust plate and no room for an end cap. What else can I do? I've been thinking of sanding down some of the end of the fins to be able to fit an end cap, but I don't know if this is possible, or how it'd affect the rocket's flying.

Is the friction method the only way?

There is no risk with friction fit if done right. That's all we had in the early days. If you don't trust yourself don't do it, but saying it's unreliable is just plain wrong. Whatever you decide, good luck.