Estes Executioner MMT Failure on an E20-4W

[asheriff]

So I took my 6 year old son's advice and launched my beloved Estes Executioner on a SU Aerotech E20-4W. Nice flight, but the ejection charge blew the motor mount out of the back of the rocket. The Tightbond2 glue joints failed where the centering rings were attached to the inside of the body tube and where the TTW fins were attached to the motor mount.

The build was stock, except I added a Centuri-style ejection baffle about 4 inches from the top of the body tube. I don't think the nosecone was overly tight, and the chute did deploy. The rocket had been successfully lauched on Estes D and E motors six times.

Anyone have an experience like this? I'm fairly new to rocketry and I was under the impression that the E20s can be used in place of the Estes E9s. Are ejection charges on the Aerotech SU motors that much more energetic than the Estes BP motors?

 

[shreadvector]

Ejection charge is stronger and the baffle caused a big backpressure that blew out the motor tube.

You need bigger holes if useing an Aerotech motor with a baffle.


Using the Aerotech motor in the stock kit would have been fine, as long as you did not have a very tight nose cone.

 

[SacEsq]

Could using epoxy in the construction and installation of the mm prevent this?

 

[shreadvector]

If there is too much pressure to pass through the baffle holes, then something has to "give" or "fail". Either the motor mount tube will fail, or the baffle will be blown forward or the motor will be ejected (ripping out the motor hook) or the side of the rocket body tube will blow out (like an "alien" popping out of your abdomen).

Epoxy may hold the mount tube in so one of the other areas will have to fail to release the massive overpressure caused by the use of a baffle with holes that are too small to allow the proper amount of ejection gas to pass.

 

[paul.nortness]

or the baffle will be blown forward

I had this happen on my Executioner's first flight. It makes a wonderful impression of a fence post when this happens

 

[[POW]Eagle159]

I launched my Saturn V on an AT E20-4w and the ejection charge was so strong, It blew out the bottom cardboard plate of the nosecone section!
I say the Aerotech charges are twice as powerful as estes.

 

[asheriff]

The holes on the baffle were on the smallish side, at least by me eyeballing it in comparison to pics online.

FWIW, the the part I was worried about -- masking tape retention system -- worked like a champ! The casing was still in the MMT.

 

[BEC]

I haven't flown Aerotech Es in anything but BT-80 birds (Maxi Alpha 3) but I have had a number of models flown on Aerotech/valuerockests D10s and D21s suffer damage from energetic ejection charges - usually failed shock cords. I also have had heat damage - for example the paint immediately ahead of the motor mount in my Nova Payloader bubbled up after its first flight on a D10. They definitely pack a punch.

Even so, I persist in using them.

 

[o1d_dude]

I fly this one on E30's.

View attachment 88047

It's very quick off the pad.

 

[Handeman]

I'm not sure about the SU, but the 29mm Hobbyline motors come with 0.7 g of BP for the ejection charge. My guess is the 29mm SU are about the same.

 

[Stymye]

I've had rockets overpressure baffles a few times , either too small diameter rocket , clusters ,and too much ejection in the motors.... not a big fan of baffles
they do have their limits sometimes when using fully loaded ejection charges