To add to Greg's advice, that fancy extra bit at the end of the hook makes it much more prone to snagging on something at that pad such as the clothespin/standoff or the ignitor clips. I've seen more than one bird light and sit on the pad, held in place by the hook. So by all means, cut off the excess.

Some things are over-engineered. As a frequenter of such behavior, I'm imminently qualified to recognize it

Doug

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YORF member #11

I've only ever had one stuck motor result in a damaged rocket. I had one of the notoriously fat A10-0T's get stuck in the BT-5 of a Midget booster, and ended up breaking fins trying to get it out. Needless to say, I was more than a little PO'd. Ever since, I've had a better method.

The trick I was taught is to use a wooden dowel, as fat as possible. The fatter, the stiffer, and hence the less lateral deflection at impact. I slide the rocket over the dowel and slide it all the way down to the nozzle if possible. Or have the dowel large enough to solidly engage the forward end of the motor.

Either way, once solid contact is made, I hold the dowel and rocket together and bang the end of the dowel against a hard object such as concrete floor. Sometimes at the field, I can't find anything hard enough and must wait until home.

Sometimes I get a motor stuck half way in during prep. I use the same method. I don't like banging against the ejection end of an unburnt motor out of fear of damaging it, so I will form a pad of folded paper towel affixed to the dowel to soften the blow on the motor.

In fact, I find myself using this more often during prep than post flight.

After flying, I can often pull burnt motors - hot or cold - out easily with my fingers. My take is that the motors will shrink a bit after use and thus aren't so tight in the rocket then.

A couple of times, I've had to do some pretty hard banging, but got the motor out eventually without bringing the MMT with it I've had one or two really difficult ones, but as I said, it's usually easier for me after flying, with the difficult post-burn ones pretty rare.

Doug

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YORF member #11

Bob - your invention was brilliant - no question about that. I use versions of the Klips in almost all of my AP motor mounts.

The threaded rods in that 7x18mm mount do not extend very far below the ends of the rocket engines. I have the rods sized to be just long enough to allow me to add the washers and to secure the hex nuts. By the way, I have since replaced the hex nuts with nylon-insert locknuts. I did think about replacing them with acorn nuts, but the locknuts work fine and are blunt enough. There is no rod extending past the top of the nut when it is fully screwed down. The mount I showed is one of a set of interchangeable motor mounts that I constructed for one of my LT-225-based upscales. On that particular rocket, the fins have some sweep. When it touches back down during recovery, it will be the fins that make contact, not the motor mount.

I do have another rocket that I equipped with a 3x24mm mount. The engines in that mount are all retained with typical engine clips. I did not design that one; it is a commercially-made mount, and that's what it came with.

Mark \\.

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SAM # 0011

Well, by a freak coincidence, Jim, the competition model that I had to "carve" the motor out of was my FlisKits Cougar 660. I tried almost all of the techniques you listed for freeing a stuck engine (I didn't think to try putting it into the freezer), commencing at the launch field immediately upon recovering the rocket and getting the flight recorded. Nothing worked. The only thing left to do was to knock (actually, in my case, it was drill) out the nozzle and peel the casing from the inside, which is what I meant when I said that I had to carve it out.

Look, I agree with what everyone said about situations in which friction-fitting is the most appropriate method of retention, and I agree that it is a method that everyone should know how to do. All I mean to say is that, for my own builds, when I have another option available that is feasible for the design, I choose the other option practically every time.

I do have some rockets that I cannot stand on their ends because of the presence of an engine hook. In my experience, rockets with such designs do not stand upright on their own very well even when there are no hooks in the way; they tend to topple over all too easily. Adding the hook isn't really taking anything away in that case - these rockets always need some sort of support or stand anyway.

Mark \\.

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SAM # 0011

There seems to be a lot of friction in this thread.

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I love sanding.

If you're doing a group launch, such as a scout pack or YMCA group, it's good to pick a rocket that includes a motor hook. These are best for newb fliers.


Born again rocketeer is correct. 3FNC is three fins and a nosecone. It refers to a basic, simple flier. No cluster, no staging, no complex prep effort.

The standard motors are 18mm dia x 70mm len. This includes A-C impulse and also one 1/2A motor. The mini motors are 13mm dia x 45mm len. These consist of 1/4A, 1/2A and A impulse motors including the A10-3T (T for mini) and A3-4T.

These latter two are full A motors, just in a smaller form factor, which lures many inexperienced fliers into losing one or two rockets to the rocket gods because their subconscious tells them that they can't possibly be full power motors Many Quarks and Mosquitos have gone to rocket heaven this way

Most newbs, and BARs too, learn this lesson. http://www.doug79.com/quark-c

Doug

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YORF member #11

No, it's debate! Friendly debate and discussion. The best kind, in fact; one that focuses on ideas, approaches and techniques. And, amazingly, it is all rocketry-specific, too!

I would like to add something else to what I said in my previous post. I really liked my FlisKits Cougar 660. It was my first competition rocket, and it has been my favorite. That's why I was unhappy that I messed it up when I had to free that motor from it. I really enjoyed building it; that is not something that I can say about very many comp. models that I have built. It flew great, too. There will certainly be more FlisKits Cougar 660's and 440's in my fleet - you can be sure of that!

Mark \\.

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SAM # 0011

John,

You're an engineer. A little web research (ie, reading this thread) and a conversation at the range with a couple of experienced fliers combined your own instincts will get you up the learning curve with no problems. Having someone demonstrate is always beneficial, but I encourage you to work your thru some stuff solo. It adds to the excitement when the LCO pushes the button

As for the actual cost, the 17 hours of sanding and painting I have invested dwarf the 12 dollars I paid for the rocket

Doug

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YORF member #11

That's a bummer about your rocket, Mark. I have one in my round'tuit pile I got from Jim years ago, at a NARCON or NSL or NARAM, can't recall which, but I'm pretty sure it was in Texas. The NIB Cougar sits in one of my rocket cabinets next to a NIB Semroc Skyhook I also got at a NAR event. One of these days....

Doug

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YORF member #11

Doug is right, John. You think I have any second thoughts about launching some of my favorite scale models using friction fitting? Here's a few pics showing my GT-3 and Gauchito
using friction fitting:

Attached Thumbnails

           

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Dave, NAR # 21853 SR.