Question on Aerotech 29mm motors:

[1bad442]

Hello,

New to the forum and I'm building a Quest Big Dog rocket with my son. Motor mount is in place and I've noticed that there is no clip to hold the F42-8T Aerotech motor in to the mount. There is a an adapter kit (with clip) if you want to downsize to a D motor, etc., but not with the original mount intended for the 29mm. The instructions also do not show any clip. There appears to be a lip on the motor where one could glue the motor in, but that just makes no sense to me.

Any thoughts?

Thanks,
Steve

 

[eggplant]

Tape!

 

[Aksrockets]

Tape!

I second that. Come on, havnt you seen MacGyver!

 

[o1d_dude]

Step away from the glue! You want to be able to remove the spent casing so glue is not answer.

Masking tape may well work as the above members noted. There's a relatively simple technique involved called frction fitting. I 'm no expert on it so I'll let someone who is familiar with it and your rocket explain.

Welcome to TRF.

 

[Agent Titan]

Yes, tape is the easiest option.

First, as o1d dude said, do not glue it in. Bad choice.

What you should do is this: Take an inch or so of masking tape, and wrap it around the motor case below the lip, or thrust ring, however you want to call it.

Then, test it in the motor mount. If it fits tight, and it takes a little work to pull it out, good! Leave it like that.

If it still is too loose, then put another 3/4" or so on it. If it fits good, once again, leave it. But, if it is too tight, to where you can't push it in, then take enough off to where you can put it in easily and take it out rightly. If loose, repeat.

Hope this helps!

 

[o1d_dude]

Thanks, AT. Hard work for me to type all the directions in on my phone.

Good description of the process.

 

[Agent Titan]

Thank you!

 

[MarkII]

The lip on the motor is the thrust block or thrust ring. There is no need to glue a thrust block inside the motor tube at the forward end because this lip prevents the motor from flying up through the rocket at ignition. As others have mentioned, putting a few wraps of tape around the motor so that it fits tightly in the motor tube is the classic (in fact, the oldest) form of motor retention (friction fitting, it is called). Put enough on that it takes a firm push to get the motor in, but not so much that you'll need to pound it back out afterward with a dowel and a mallet. (That will cause serious damage to your rocket!) One suggested method is to wrap the tape in a loose (spaced out) spiral (twisting) pattern from end to end. You then twist the motor into the mount when you install it and twist again in the opposite direction to get it back out. Another thing to do to augment the retention is to wrap tape tightly a few times around the end of the motor tube where the motor protrudes from it. (Half of the tape's width on the end of the tube, and half on the end of the motor.) It is called "taping the motor in" and, despite how simple it sounds, this technique is quite effective at preventing the motor from being kicked out of the mount when the ejection charge fires. While either one of these techniques will work by itself, a good, prudent practice is to use both of them together.

 

[Rocketjunkie]

Another method, if you have some of the motor tube sticking out beyond the rear centering ring and can get to it. Insert the motor and wrap a couple layers of masking tape over the motor tube - motor thrust ring joint.
The first picture is a CTI 24 mm case. The thrust ring is the black part.
The second picture is the case inserted into the motor tube.
The third picture is 2 wraps of tape over the joint.

 

[MarkII]

Another method, if you have some of the motor tube sticking out beyond the rear centering ring and can get to it. Insert the motor and wrap a couple layers of masking tape over the motor tube - motor thrust ring joint.
The first picture is a CTI 24 mm case. The thrust ring is the black part.
The second picture is the case inserted into the motor tube.
The third picture is 2 wraps of tape over the joint.

Exactly! That's the second technique that I was talking about in my previous post, but your photos make it much clearer.

 

[Initiator001]

Hello,

New to the forum and I'm building a Quest Big Dog rocket with my son. Motor mount is in place and I've noticed that there is no clip to hold the F42-8T Aerotech motor in to the mount.

Thanks,
Steve

Steve,

I've built and flown a Quest Big Dog kit several times on Quest D8-3 and Estes D12-5 motors.

I have flown many AeroTech F42 motors.

Based on my experience with both of these products, a Big Dog with an F42 motor may be too much for the rocket.

An -8 second delay is too short for a stock built Big Dog. My slightly modified Big Dog weighs in at 7.1 oz sans motor. I fly F42-8Ts in my AeroTech Arreaux which weighs in around 14 oz less motor. The Arreaux really 'scoots' on the F42.

An AeroTech E15-7 or E20-7 motor using the 24mm motor adapter supplied in the Big Dog kit may be a better choice.

Whatever you decide, the Big Dog is a fun model. Enjoy!