Aerotech 24/40 F motor cato

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Terry Lee

New Member
Mar 15, 2004
Reaction score
I have recently started flying mid power rockets (Aerotech Tomahawk and Initiator) and have had relative success. However, on a couple of launches using the 24/40 housing and an F load, the grain did not fire but the ejection charge did. The last result of this was a housing blown into the motor tube and an hour search for the rear bulkhead. My current theory is that the ignitor (Copperhead) was in contact with the delay and lit the delay and not the grain. Has anyone had this problem and have a solution?
Never had a problem like that but for what it's worth I place a strip of masking tape across the delay end of my fuel grain before it slides into the liner tube. This prevents the ignitor from advancing too far into the assembly. The only difficulty I have had with the 24/40 is the liner to casing fit seems to be much tighter than my 29/40-120. The amount of grease needed to install one usually makes me cringe till I see the chute open!
Welcome to the forum Terry Lee!

If the rear closure blew off... the motor catoed. Was there any delay left. The propellant did ignite... but when the bulhead blew off, the motor lost its presure, and the propellant goes out from the sudden decompression.

Contact Aerotech. They should replace the damaged case, and give you a new pack of F reloads :).
I have used Aerotech hobby line reload cases for around one hundred flights.

First, as mentioned earlier, you must have a peace of tape at the delay end of the fuel grain before the fuel grain spacer to keep the copper head from coming in contact with the delay grain.

If you followed the above instructions then I once seen that a reload set had the wrong delay grains in them for that type of fuel grain such as Blue Thunder delays in Black Jack fuel grains. The delay grain burned through which allowed the fuel to blow through the end of the motor case and destoryed the rocket and the end of the motor.

One other time this same thing took place when someone drilled away some of the delay grain to shorten it's time.

Hope this helps,
Trying to hit a bunch of things at once.....

1) Placing tape across the slot in the fuel grain is only useful if the motor grain requires a spacer. None of the 24/40 F reloads (F12, F24, F39) requires a spacer.

2) The chances of lighting the delay only without igniting the propellant are slim and none. I am not saying that it couldn't possibly happen but I have never seen it.

3) What was the delay from the ignitor firing and the CATO? A delay grain burning all by itself burns at about 1/32" per second. With the motor burning, that jumps to about 3/32" per second. So if it was just the delay, it would burn for a long time before the ejection charge went off.

4) Blowing the aft closure out the back end and the motor case into the rocket is not something that happens when the ejection charge goes off. This is what happens when the aft closure comes off. Probably due to over pressure.

I have had only one CATO of a 24/40 motor (F39) and it was my fault. In hindsight, I installed an ignitor that had wires that were too large. They plugged the nozzle and it didn't like it at all.

It is possible that after the first CATO, the motor case will be more likely to spit the aft closure. The threads on the closure might have been worn slightly or the case might have expanded past its elastic limit and is now slightly larger than it used to be. Careful examination will show if this is a problem.

To help prevent this sort of CATO, do not use large ignitors in motors with small nozzle throats. Also, make sure that the nozzle is not resting on the blast deflector. Particularly if you have a red nozzle cap in place.
Originally posted by BigT
The only difficulty I have had with the 24/40 is the liner to casing fit seems to be much tighter than my 29/40-120. The amount of grease needed to install one usually makes me cringe till I see the chute open!

You could always take a wrap of paper off the outside. I had to do this on an F40 once. Spacer wouldn't fit, so I had to take a wrap off the outside of the spacer.

The 24mm motors are notorious for that. Peeling the layer of paper is the only solution. I usually coat the liner with plenty of grease... if you don't, it may become difficult to remove.
I'm embarassed to admit it but I never thought of peeling a layer off the liner. Thanks!:D