Removing spent engine

[Pat Butler]

After a 20 year absence from rocketry, I finally built another two-stage rocket. I spent a lot of time on the finishing, using F&F to build up the fillets. Launched the darn thing today and it went just fine with no damage. But when I tried to remove the sustainer engine it was stuck really bad.

I couldn't use a dowel from the other end because there's an engine block in place. I got a good grip with some pliers but it just wouldn't budge. I've slowly been pulling the engine out from its innards but have been damaging the engine tube in the process- almost makes me want to cry.

Any ideas? thanks!

 

[Pat Butler]

Here's the damage

 

[brianc]

Originally posted by Pat Butler
I couldn't use a dowel from the other end because there's an engine block in place.

Try a dowel that's smaller than the thrust ring hole. Provided you haven't removed too much
of the clay nozzle, there should be something to push against.

You might try twisting the motor with your pliers while you pull. But be carefull! I once
twisted the entire MMT out this way.

GOOD LUCK!



BTW- great looking finish!

 

[Pat Butler]

I had already blew out the clay nozzle. It seemed pretty brittle to being with. Not only that, but I almost kinked my body tube when I was pulling with the pliers because my hand was holding it so tight. I only had one small piece of masking around the engine and I can't imagine what actually made it appear to glue itself into the mount.

 

[jflis]

Here's a thought.

Depending on how much damage your engine tube has sustained, this may or may not work, but is worth a try...

Clean up what remains of the INSIDE of the engine casing. Select a spot INSIDE the casing that is clean and does not expose itself to the engine tube...

Take the largest diameter wood dowel that will LOOSELY fit inside the casing (make sure this is a lot longer than the rocket body...

Pass it from the TOP of the rocket and into the casing from the inside. CAREFULLY glue this dowel to the INSIDE of the motor casing making SURE that you get NO glue on the engine tube or the engine block.

Let this dry overnight or, if using epoxy, let it set up the full time plus some...

Then you should be able to SHARPLY rap the other end of the wood dowel to dispense the casing.

NOTE: If possible, (an added thought) lower the temp of the casing/rocket. If it is being held in place by any adhesive (from the build, any tape, the casing itself), bitter cold will make this adhesive brittle and less likely to grab making it easier to knock out. If you try/choose to do this in your freezer, place the rocket in a sealed bag with as little air as possible to prevent moisture buildup...

Extreme measures for an extreme situation...

I will be most interested in how/if this works for you. keep us posted and good luck!

 

[jimn]

Once or twice back when I was a kid I got an engine really stuck. I ended up unspiralling the layers of cardboard from the inside, then cutting out the layers that had been unspiralled It took hours and hours and hours, but I finally got the engine out.

 

[shreadvector]

Most common causes for stuck motors:
* Use of a glue that melts at high temperature combined with drips of that glue inside the motor mounting area.
* Paint overspray inside the motor mount tube that melts at high temperature and then cools and cements the motor in place.
* Masking tape that melts and allows gooey adhesive to ooze out the ends which then glues the motor into the mouont tube.

You can try heating the entire model gently to at least 300 degrees (don't go for 451 F, that might be bad). If the heat soak makes the motor release, great. If not, then it's probably melted paint and will take some solvent to release.

I've peeled a few in my time and had to deal with damamged tubes....

Originally posted by Pat Butler
After a 20 year absence from rocketry, I finally built another two-stage rocket. I spent a lot of time on the finishing, using F&F to build up the fillets. Launched the darn thing today and it went just fine with no damage. But when I tried to remove the sustainer engine it was stuck really bad.

I couldn't use a dowel from the other end because there's an engine block in place. I got a good grip with some pliers but it just wouldn't budge. I've slowly been pulling the engine out from its innards but have been damaging the engine tube in the process- almost makes me want to cry.

Any ideas? thanks!

 

[BAR0051]

I have heard that alcohol will help if the problem is the stickem from tape used to retain the motor. Never tried it but it sounds like it might help.

 

[vjp]

I second the "unspiraling the motor from the inside" technique, a pair of needle-nose pliers might do the trick.

Gluing a smaller motor casing inside the spent one, with a dowel glued inside that, also sounds like a good plan. 5 minute epoxy should work well for this and won't swell the paper like water-based glues.

 

[Pat Butler]

Thanks for all of the suggestions. I think I'm going to try Jim's suggestion of gluing a dowel to the casing. If it doesn't work then I might have the only rocket with a dowel for a nose cone! I'm also going to try and subject it to some colder temperatures to see if there is any adhesive residue from the tape.

Is there any way to use an engine hook on the upper stage rather than friction fit? I used Estes method of taping the two engines together and I realize that poses a problem for the engine hook. But I understand that perhaps there are other methods besides the tape method that will still allow for upper stage ignition. Didn't Centuri have a different way of doing it?

I also noticed a little bit of scorching inside the tubes and was wondering if it was possible to vent some of the hot gasses in order to keep the temperature down. That might prevent any melting of the tape or paint or glue that might stick everything down.

 

[shreadvector]

I've never had a tape problem caused by multi-staging.

All tape oozing or melting problems are caused by either:
1) Cheap masking tape.
2) Use of cellophane tape when you should have used masking tape.

You never said what kind of tape you used.

Masking tape is to be used for friction fitting. Cellophane tape is to be used to connect booster to upper-stage motors.

AND, when you friction fit, DO NOT apply the masking tape in the middle of the motor! There are two reasons:
1) Middle of motor is swollen from propellant loading and after firing it will shrink, allowing the motor to eject.
2) It rolls up on itself and can gum up the works making the motor get stuck for eternity.

Always apply the masking tape with a small amount protruding beyond the forward edge of the upper stage (or single stage) motor casing. Then roll the edge all the way around. This forms a "Gentle Glide Applicator" edge which makes motor insertion much smoother - and it prevents the forward edge of the masking tape from rolling back on itself creating a jam.

Originally posted by Pat Butler
Thanks for all of the suggestions. I think I'm going to try Jim's suggestion of gluing a dowel to the casing. If it doesn't work then I might have the only rocket with a dowel for a nose cone! I'm also going to try and subject it to some colder temperatures to see if there is any adhesive residue from the tape.

Is there any way to use an engine hook on the upper stage rather than friction fit? I used Estes method of taping the two engines together and I realize that poses a problem for the engine hook. But I understand that perhaps there are other methods besides the tape method that will still allow for upper stage ignition. Didn't Centuri have a different way of doing it?

I also noticed a little bit of scorching inside the tubes and was wondering if it was possible to vent some of the hot gasses in order to keep the temperature down. That might prevent any melting of the tape or paint or glue that might stick everything down.

 

[zog43editor]

Originally posted by Pat Butler
Is there any way to use an engine hook on the upper stage rather than friction fit? I used Estes method of taping the two engines together and I realize that poses a problem for the engine hook. But I understand that perhaps there are other methods besides the tape method that will still allow for upper stage ignition. Didn't Centuri have a different way of doing it?

Yes you can use an engine hook and still use the tape together method. If you have the "new-fangled" hooks you need to make sure you have enough clearance to have it pushed over by the booster motor and still fit the stages together. Just tape them together and have the hook press against the lower motor. If you have the old style hooks (or cut off the extra bit of the new-fangled style with a dremel) then you can tape the motors together, and push the hook through the tape to engage the upper stage motor. I have done both of these plenty of times.

You must be thinking of the gap or pass-port staging that some Centuri kits used. I just re-read the chapter in the Handbook where Stine talks about it. Good stuff and very reliable as long as you vent the booster tube.

kj

 

[JRThro]

Originally posted by shreadvector
Then roll the edge all the way around.

Roll it inward. This may be obvious, but I had to read it twice before I realized that.