motor retainer advice?

PML makes a nice retainer for 15-20 bucks. I have one and like it because it can be fitted and used on all the HPR rockets in my fleet.

I have a rocket with an Aeropack retainer as well. Those are nice, but pricey, and you have to buy extra bases at 15-20 bucks a pop to use it on other rockets.

On the LOC Weasel-29 that I have, the motor mount is 29 mm and the airframe is (I think) 38 mm. This does not allow the t nut method (of which I am a fan). Unless someone can drill into 4.5 mm of plywood on each side without ruining the integrity of the aft centering ring.

Masking tape should work fine. Leave a little bit (1/2 inch or so) of motor tubing sticking out past the rear of the aft centering ring. Wrap tape around the nozzle end of the motor (if using single-use) to build up a "thrust ring" that will bear against the aft end of the motor tube; insert motor; and wrap some tape over the joint to secure the motor in the tube.

-dave w

Yeah, I'd seen that one, but it doesn't work on "almost minimum diameter" rockets where the centering ring is not large enough for the threaded inserts - same problem that Kaplow Klips have.

For minimum, and almost minimum diameter rockets, I feel the Slimline retainers work best, but are pricey. Tape should work fine for you in this instance, since your not working with an especially large motor.

One solution that worked quite well on my son's PML Bull Puppy 2.1 was to insert t-nuts into the SIDE of the body tube, just above the end of the rocket. We then fabricated retention straps by grabbing some metal strips from the hobby store, drilling a hole in them, and bending them around the bottom of the rocket. They create a small amount of drag, but unless your going for altitude records, that doesn't really matter.

sure of the pros/cons of various engine retaining systems (beyond just masking tape, which has me leary).

Tape is adaquate if you pay attention to detail. I've used it for up to my biggest motors flown to date (38mm I's). Of course I make sure there's enough tape that it's in so tight I have to usually pound the casings back out. Single use motors can need the tape retaining rings but once you get into reloads the casings have that integral to them (least mine do) My newer rockets are getting retention systems, such as T-nuts, homemade Kaplow clips, washers, etc. At those times, such as with the LOC centering rings, I've bought extras to doubled them up so there's extra thickness and strength. I've also retrofitted my EZI-65 for similar by epoxying 4 small oak blocks onto the centering ring with above retentions attached to them. My 54-38mm motor adapter is the next retrofit, as is my 54-29mm adapter. Minimum diameter birds, and my

38-29mm adapter, are still using tape since there's just no room. And think nothing of the off-list advice I'd sent you, that's what we're supposed to be here for. Right folks?

Chuck

Hi,

I have a LOC Vulcanite with a 29mm adapter. I have had no problems using masking tape as motor retention using Aerotechs 29mm single-use motors.

First, I made a thrust ring by wrapping the tape about 1/4" above the end of the casing. Keep wrapping until the ring is thick enough, maybe as thick as the MMT. Since it was 1" tape, this left a ring hanging off the end of the case which I trimmed off with a razor knife.

Then a strip of tape spiraled down the case provided enough friction to prevent the motor from slipping out during ejection.

I am working on another rocket that has a 29mm MMT inside of a 54mm airframe. There is not enough width to the centering ring to accommodate a #8 T-nut so I /very carefully/ epoxied a washer and nut to the backside of the centering ring. This will accept a machine screw and another washer to hold the motor. I only have one motor retention point because I didn't want to weaken the centering ring any more than I had to.

HTH,

--dennis

Drill a small hole in the bottom of a couple of fins, then use safety wire.

Sorry, I'm not clear on what you mean. How does one "use safety wire"?

"Safety wire" is .030" soft stainless steel wire, which can be had at motorcycle shops and aircraft supply dealers. Its usual use is to be strung through holes in the heads of bolts and twisted tight to make sure the bolt doesn't go anywhere if it wants to try to vibrate loose. (This is a common precaution for things like the crankcase drain plug on a racing motorcycle, or the bolts attaching an airplane propeller to the engine shaft hub...)

In this case, the wire would be looped through the hole in the bottom of a fin and led across the aft end of the rocket, around the motor nozzle, and through the hole in another fin. (The ends can be then twisted together and trimmed off short. Simply cut the wires to remove the motor after flight.)

I used this method on my PML Cirrus Dart (which has a min. dia. airframe with no aft-extending motor tube): it works well.

-dave w

Haven't built a Weasel yet but I have done several Legacy's though. What I did was use the AT engine hook with the forward bend cut off and used fiberglass tape for reinforcement to the MMT. Works great. Think of it like Estes engine hook on steroids.

Ted Novak TRA#5512 IEAS#75

bit eimer wrote:

Forgot to mention that for this to work properly you do need use a masking tape thrust ring on SU motors.

Ted Novak TRA#5512 IEAS#75

nedtovak wrote:

Ahh, that's for the explanation

Never seen an AT engine hook and it doesn't look like they're are available other than in an AT kit.

Think its frabricable?

Totally. Hardware store should have suitable metal band/strip.

I know my local Hub Hobby in MN has the hooks. If needed maybe something could arranged shipping wise.

Ted Novak TRA#5512 IEAS#75

Yes, thanks David. Me good ol' Winders box crashed again, so I have been in "recovery".

;-)

Could you/someone provide metal type and approximate dimensions? Length, width, thickness.

TIA,

I think I might have a few in the workshop. Where in the workshop I don't know but tonight I'll do a looksie.

Ted Novak TRA#5512 IEAS#75