Non-ejecting engines, that should

[tooth]

I’ve been experimenting with featherlights and lightweight rockets that are intended to eject the engine then streamer or just lightly fall on their own. I find more often than not the rocket comes back to earth with the engine still inserted.

I try to twist and turn the engine to be sure it can slide somewhat easily, but clearly my technique isn’t working very well (note Space Ranger who just had a rather fast trip down). Does anyone have a tip on how to make the engine slide out more consistently at the proper time? Thanks for your help..

 

[lakeroadster]

I had the opposite issue happen twice this year, motors that eject, that shouldn't. The Gods of recovery were with me however and no severe damage was done.

I guess to address your issue, a loose fit is better than a snug one. Are all your rockets' kits? This should have been addressed by the kit manufacturer.

 

[prfesser]

I’ve been experimenting with featherlights and lightweight rockets that are intended to eject the engine then streamer or just lightly fall on their own. I find more often than not the rocket comes back to earth with the engine still inserted.

I try to twist and turn the engine to be sure it can slide somewhat easily, but clearly my technique isn’t working very well (note Space Ranger who just had a rather fast trip down). Does anyone have a tip on how to make the engine slide out more consistently at the proper time? Thanks for your help..

View attachment 542513

Zooming in on the image it appears that there's a significant difference in diameter of the motor vs. the airframe. It looks as though the motor would drop free if the rocket was held upright. Are you friction-fitting the motor in place with masking tape? That's necessary when the motor is to stay with the rocket but shouldn't be necessary if the motor is to be ejected anyway.

At most, a little masking tape around the motor---just enough so that the motor doesn't fall out when attaching the micro-clips---is sufficient.

The forward end of the motor casing sometimes has a bit of a ridge, from the manufacturing process, and that makes the motor slightly harder to remove. Remove that ridge by pressing the edge of the motor against a hard surface, and rotating the motor as you press. Then see if the motor drops free.

 

[mh9162013]

a loose fit is better than a snug one.

But is that true for engines that should eject? If the fit is too loose, might some of the ejection gasses leak out from the top of the engine and down the sides of the engine case?

 

[tooth]

I'm really new at all this so lakeroadster I'm only building kits at this point. prfesser- the motor in the photo is a very snug fit to the body tube- it takes a fair amount of pressure to pull it out. I like your tip about checking the front end of the motor casing - will definitely try that before the next flight to see if I can get a little better slide out.

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[Oldschool77]

If reducing the ridge on the forward end the doesn't work, lightly sand the motor. If that doesn't work, try removing a thin wrap. U may end up adding cellophane back to get a good fit. Motor should slid in but not drop out w/o a lil pull for motor eject. Don't worry about ejection charge leakage. I have also seen very snug bt-20 & 50. If a chronic condition check motor tube for paint or glue.

 

[SolarYellow]

Revolvers have a cylinder gap and still manage to get the bullet to exit the barrel. If the motor is tight enough for friction to hold it in against gravity so it doesn't fall out on the launch pad, you'll be fine as far as maintaining ejection pressure.

 

[dr wogz]

The ejection charge should be enough to kick (eject) the motor when it fires. if not, then something is allowing the pressure to dissipate in another direction. Remember the ejection gasses will find the path of least resistance.

 

[lakeroadster]

But is that true for engines that should eject? If the fit is too loose, might some of the ejection gasses leak out from the top of the engine and down the sides of the engine case?

Loose... not sloppy.

 

[lakeroadster]

I'm really new at all this so lakeroadster I'm only building kits at this point.

Part of the issue may be your gluing techniques. What kind of glue are you using? If the glue is shrinking the motor tube, that may be causing the issues you are experiencing.

 

[dhbarr]

Check out that you don't have a dropped bead of glue in the motor area. If you do, probably you can wedge an exacto under one side and tear it free, then finely sand the resulting rough patch.

 

[tooth]

using Titebond as my standard glue. I try to keep it out of the motor tube but good idea to keep a close tab on that. Hopefully will get a launch day in soon to try some of these great ideas, thanks everyone.