Tape retention and reloadable motors - knurled aft closure?

[SolarYellow]

Lots of discussion of building masking tape thrust rings on Estes motors. Some do friction fit, with the thrust ring, and some build the thrust ring to the same diameter as the BT, then wrap the thrust ring and BT with a layer of tape to prevent ejection.

I'm wanting to use tape retention on a MD rocket with a CTI or AT motor, but was thinking I'd like to stay away from friction fit. Like tape around the BT and also the OD of the aft closure. Problem is, the rings appear to be somewhat larger diameter than a MD BT. The CTI, in particular for a 24 or 29mm motor, is knurled, so there's virtually no surface for the tape to adhere to. The AT ring is narrow, so not a lot of surface for the tape to adhere to. I guess it might work better with aluminum tape wrapped over the edge.

One idea I had was throw the CTI closure in the lathe and turn down the tips of the knurling until it is the same OD as the BT. This would increase adhesion area and couldn't possibly reduce the strength of the part, as the bottom of each knurling groove is the weakest part and the points are not loaded. Would it get me in trouble with the "no modification of the motor" rule?

Are people who use tape for these just going with friction fit? Any advice or pics of things that work?

 

[mikec]

Some people like aluminum tape for this. My limited experience on MD rockets is that it doesn't work very well and leaves gunk all over. If you don't want to use friction fit, then use a form of retention that picks up the forward closure, like the Aeropack or something you can make yourself with a coupler and bulkhead.

I don't think machining the knurling off a CTI closure will really help that much relative to the level of effort.

 

[SolarYellow]

The Aero Pack threaded retainers are only compatible with 38mm and larger motors. I'm looking at 24 and 29mm motors. There don't appear to be any alternative options to replace the CTI delay/ejection module on 24 and 29mm motors with a closed/threaded plug.

 

[user 35280]

Would these work for you?
https://www.mach1rocketry.com/product-page/bandit-screw-cap-retainers

 

[SolarYellow]

Not on MD rockets. It's like a little air brake right at the back of the airframe.

29mm and up with a larger tube, I like the Giant Leap stuff. Might go with the Estes if it fit inside the outer tube diameter; the weight and cost are both favorable. But for now, the focus is on MD airframes.

 

[Rocketjunkie]

I've used the tape in method on reloads. I do use enough tape on the body of the reload for a friction fit. Not so tight that it's hard to to remove but enough it doesn't fall out. Then I tape over the motor tube/motor rear closure joint. Haven't had one fall out. In small rockets you have to watch the ejection strength carefully as the forces are large. You might want to do some ground testing.

 

[rharshberger]

Some people like aluminum tape for this. My limited experience on MD rockets is that it doesn't work very well and leaves gunk all over. If you don't want to use friction fit, then use a form of retention that picks up the forward closure, like the Aeropack or something you can make yourself with a coupler and bulkhead.

I don't think machining the knurling off a CTI closure will really help that much relative to the level of effort.

+1 aluminum tape for this, trim it a bit long and wrap it around the airframe and the rear closure, as well as under the closure. I disagree it leaves gunk all over, I do it frequently, just make sure a cardboard airframe is epoxy or CA toughened so when you remove the tape it doesn't peel away the cardboard.

 

[prfesser]

Possible solution, if the rocket will be stable when doing this: Wrap a masking tape ring around the aft end of the casing (not the closure) to match the o.d. of the airframe, then tape around airframe and the tape ring. The motor will extend out the rocket by the width of the masking tape, so run sims.

 

[bjphoenix]

Possible solution, if the rocket will be stable when doing this: Wrap a masking tape ring around the aft end of the casing (not the closure) to match the o.d. of the airframe, then tape around airframe and the tape ring. The motor will extend out the rocket by the width of the masking tape, so run sims.

What do you think- maybe 1/4" ?

 

[prfesser]

Someone who regularly uses masking tape for retention should probably answer this. Absent any additional information I'd probably go with 1/2". Possibly wider. Depends on whether the rocket will be stable with the motor extending 1/2" or 3/4" out the MMT.

 

[SolarYellow]

1/4 inch wide rolls of masking tape are available, and probably worth it.

Best option I've found is the 3M 401+ at McMaster if you're already placing an order there (high-adhesion, high temp and reasonably priced/roll), but there are other choices on Amazon and fleabay.

 

[user 35280]

https://www.asp-rocketry.com/ecommerce/1-4-Masking-Tape.cfm?item_id=29&parent=73&navPanel=

 

[Rocketjunkie]

error. deleted

 

[Rocketjunkie]

1/4 inch wide rolls of masking tape are available, and probably worth it.

Best option I've found is the 3M 401+ at McMaster if you're already placing an order there (high-adhesion, high temp and reasonably priced/roll), but there are other choices on Amazon and fleabay.

You can usually get narrow masking tape at auto supply stores in the paint section as 'pin-striping tape'.

 

[Titan II]

1/4 inch wide rolls of masking tape are available, and probably worth it.

Another option.....you can also use a set screw and be flush with the body OD.

 

[LithosphereRocketry]

View attachment 535256

Another option.....you can also use a set screw and be flush with the body OD.

View attachment 535262

wait - did you just drill a hole in your case? That's a no from me.

 

[boatgeek]

I've used a bunch of different tape options for MD, and electrical tape stretched tight has been the most reliable for 24mm and 29mm motors. The stretch in the tape handles the difference in diameter. I do make sure that the edge of the tape goes past the aft end of the closure, so there's extra retention there. Other people don't like electrical tape, but it's been great for me on smaller motors.

If you use aluminum duct tape, make sure it's the kind with the thick layer of adhesive. I tried using the aluminum tape that's glorified packing tape and it didn't stick well at all.

 

[MidOH]

I still love friction fit. But, I set it so tight, I need Robogrip pliers to get the motor out.

 

[BABAR]

Does the tail end of your rocket have a circumferential ”fin free” segment, ideally at least 1/2” long?

if so, a ”pre-wrap” of tape around this section can protect the paint an body tube from tape REMOVAL of your wrapping tape post flight.

if you have a nice paint job and don’t want to change the color, cellophane tape is fine. Otherwise I like colored Mylar tapes. Trim it off beyond the tail edge of your tube.

Ideally wrap it the OPPOSITE DIRECTION (think the un-natural direction) from your tape wrap, so when you UNWRAP the tape post flight, it doesn’t accidentally pick up and unwrap your flight retention tape.

I overlap the flight tape (masking tape works fine for black powder motors, I don’t know if reloads get significantly hotter) 50/50, 1/2 over the body tube tape, the rest over the motor, and extra beyond the rear margin of the motor I wrap around the base of the motor so long as doesn’t cover nozzle.

haven’t had any problems with tape gunking up, if so could CAREFULLY remove the base tape layer (to avoid peeling off paint or delaminating tube) and replace it.

interestingly I have had motor hooks fail, where external tape wraps haven’t.

best of luck.