Bad idea for kaplow clips?

Hi- I brain-farted and realized on my way home from work tonight that, while I had planned and built to accommodate kaplow clips for my L2 cert attempt, I had this far neglected to source the parts. I stopped at ace and found one mirror hanger that would work really well, but only one, I need three. Bought it anyway. Also found some smaller ones like those I used on my 38mm L1, so I bought some of those too. Then I found these other things in screen door hardware that looked promising.
The screen door things fit very well, with one concern: the tail rests against the outer edge of the airframe.

I've fiberglassed the tube, so it's not just cardboard, but I'm worried that the rearward force of the casing at ejection will turn those three tabs into levers (fulcrum is the retaining screw) and mash the tube in, releasing the casing.

I could throw a bunch of washers on there so the brunt of the force isn't taken by the tube, but don't know if I'm being paranoid. Any advice in the next few hours is appreciated!! If none comes I'll washer 2 and use the third as a test.

I see 2 good options here.

1- add a bit of tape to the motor tube and make it a combo of friction fit with back up clips.

2- make your own clips that fit perfectly.

Maybe cut/file the out edge of the clip off so that it fits inside the BT? Epoxy a small piece of dowel inside the BT so the clip rests on the dowel instead of the BT?

You are only trying to keep the motor from sliding backward at ejection. Especially using 3 of them, that will impart a minimum amount of force on each one. I say use them as is for your flight (tomorrow morning?) and see what damage they cause if any and go from there.

T-Rex said:

Maybe cut/file the out edge of the clip off so that it fits inside the BT? Epoxy a small piece of dowel inside the BT so the clip rests on the dowel instead of the BT?

You are only trying to keep the motor from sliding backward at ejection. Especially using 3 of them, that will impart a minimum amount of force on each one. I say use them as is for your flight (tomorrow morning?) and see what damage they cause if any and go from there.

Click to expand...

Ditto...

JP

Stacked washers. Cheap, easy, no airframe damage possible.

Thanks all! I'm trying a bit of everything suggested- stacked washers on two of them, third left alone to see what happens! Looking forward to a successful launch, sorry for my East coast friends, but today's shaping up to be 78 degrees in the desert!

I hate to say it, but you may have a bigger problem. Those clips are made of aluminum and depending on how hot the exhaust is and how long for the burn, you stand a fair chance of them eroding during boost. I found that out the hard way.Though if the nozzle for the CTI case protrudes far enough, you may be OK. My experience was with a snap ring motor.

You can file a matching curve in the ends. It looks like there is enough material there so that you won't have to worry about weakling the end near the slot too much. You will need to get the clip parallel to the motor mount centering ring . I have seen ejection events kick just enough with slanted clips of this type to cause them to either shift or open just enough to allow the casing to kick out and be come its own special recovery problem. The easiest way to "level" the clips is with some brass tubing whose ID is wider than the clip slot. Just cut it to length and you'll be fine and won't have a bizzillon washers to deal with.

Take care,

Duane

H_Rocket said:

I hate to say it, but you may have a bigger problem. Those clips are made of aluminum and depending on how hot the exhaust is and how long for the burn, you stand a fair chance of them eroding during boost. I found that out the hard way.Though if the nozzle for the CTI case protrudes far enough, you may be OK. My experience was with a snap ring motor.

Click to expand...

Hi Al- thanks for the advice- I was concerned about the material choice due to its ductility, but had not thought about the chemical/thermal changes that may occur. Thankfully they lasted for my cert flight, but I do plan on finding something that fits better- in a pinch they did work though!