It takes a lot of extreme cycling to get BP to cato.

Back on the 1980s in my High School chemistry class, I did a little experiment of my own:

I took 3 D12-5's and heat cycled them in the lab oven (only 200 degrees as not to start a fire... paper ignites at 451 Deg F, so I cut that in half).

1 D12 was heated for 1 hour (the time of a class period) 1 D12 was heated for 3 hours (three class sessions) and the final D12 was heated for 5 hours (5 class periods).

I then took each motor and froze them in my home freezer for 1 hour, 3 one hour periods for the 2nd, and finally 5, 1 hour periods for the thrid.

So I heated, then cooled, heated, then cooled, expansion ... contraction, expansion... contraction ... I wanted to see what it would take to get the propellant to separate from the casing and to get cracks in the grain.

The first 2 D12s operated just fine in my Astron Renegade. The final D12 that was heated at 200 degrees F 5 times, then frozen at one hour intervals frozen 5 times, did cato at ignition and destroyed the entire lower half of the rocket.

The above coupled with my own stash of 60's 70's motors that I use work fine. And I know they have been heat/cold cycled HUNDREDS of times since their creation! Well not at 200+/-32 Deg F, but they are stored in the garage, transported in mail and freight trucks where the inside temps get into the mid 100s, and in mailboxes were the temps are similar.

It is my opinion that BP motors that cato are the result of problems with their manufacture and not dependent if they sat in your car trunk all day long. For if that were case, all motors should be catoing as they are transported in containers that easily reach higher temps than your car trunk on a hot summer afternoon.

My opinion and comment ... take it at what ever value you chose.

Jonathan

Did you let them come to room temperature before firing?

Did you fire at the low temp (i.e. since you're in Colorado, this would be easier in the dead of winter)? I've found, somewhat anecdotally, that most black powder catos happen in cold weather.

__________________
Roy
nar12605

No, I took them outside and they warmed at the ambient tempature of the afternoon. Dragnet impersination:

It was sunny in Los Angles, with a little mid-afternoon wind...

For a COLD situation:

I would fly motors at HUVARS (Michigan) winter launches. I remember one day in the early 1990's, I used 4 Estes E15s *GULP* and converted a Pro-Series Maxiforce into a 4 cluster rocket (1 center motor and 3 E15s mounted in pods on the fin-tips). Eagle3 was there along with the rest of the HUVAR gang.

All motors lit without a problem except they lit at different times. The bird cart-wheeled and hit someone's car and did a litle damage to the paint. I remember Peter Alway got a big laugh out of it so I reasoned my work there was done

I am not lying when I say, I have yet to have an Estes motor cato on me. Maybe I have been EXTREMELY lucky, but it has never happened.

Now I did have an early Aerotech J125 with Medusa Nozzle suffer a cato at a Michigan TRA launch I bought from Red Arrow hobbies ... it was the early filiment casing that should never have been sold to me so Gary at Aerotech replaced it. The motor should have been returned by Dave, but it made for a spectacular flight:

I built a LOC Magnum with center 54mm and 6 29mm mount. The flight profile was 6 G80 (ejection charge removed) and the J125 airstarted.

All G80s lit and the Magnum lifted majestically from the Earth. Then at about 300' up, the J125 lit ... the crowd loved it ... about half a second later the forward closure on the J125 failed, the motor's contrail stopped, and the rocket started tumbling ... the propellant burned through the entire lower section of the Magnum, then burned out of the side of the airframe. The chute went one way, the rocket was coming down in parts, with propellant grains buring and streaking downward.

One of the spectators shouted, 'Shades of the Challenger!', compairing the flight to the Challenger after the explosion. I was both sad with the loss, but excited with the out come ... kinda wierd huh?


Jonathan