Lessons Learned:

Aerotech 38mm RMS Assembly Error

If you are making the leap from mid to high power rocketry, chances are pretty good that you'll be moving up from a 29mm enclosure to a 38mm enclosure. One of the downfalls of the Aerotech line of motors is that the assembly instructions vary from motor to motor.

One of the more painful and embarrassing lessons I learned about the difference between the 29mm RMS and the 38mm RMS is as follows: The 38mm systems includes an additional fiber spacer called the 'aft insulator' (it looks like a fiber washer) that fits between the propellant and the nozzle.

The aft insulator rests against the inner sleeve that holds the propellant grains. Because the inner sleeve is slightly longer (in most motors) than the stack of propellant grains, the washer holds the nozzle tight against the aft enclosure. The propellant grains can actually slide around loose inside the fully assembled casing.

Here's what I learned - without this washer, the nozzle will cant at an angle and send your rocket in every direction but up. And as a testament to my inability to learn any lesson the first time, I have two sets of photos from the same day documenting the exact same mistake. (These awesome photos were taken by - and purchased from - Nadine Kinney of Photos by Nadine. You may contact her at photos.by.nadine@pcisys.net.)

CLICK FOR LARGER IMAGE

Motor ignition. Note that exhaust jet is canted at an angle.	The rocket leaves the launch rod and the vectored thrust flips the rocket.	Light colored smoke from the air-started boosters is visible after one full revolution. All four boosters lit.
Motor ignition. Once again, exhaust jet is canted at an angle.	The rocket leaves the launch rod and the vectored thrust flips the rocket.	After several revolutions the pumpkin nose cone detaches due to centrifugal force.

Click Here for Downloadable video of the Basset sequences above (this one is better footage)
Click Here for Downloadable video of the Halloweener sequences above

1. Have an orderly work surface. - On the day of these launches I inadvertently left my table at home, so I prepped my rockets on an overturned box. I later found the unused fiber washers laying in the dust on the ground.
   
   
2. When possible, have a colleague oversee your prep. - I've been extremely grateful when an onlooker reminded me that I left out something important. Oversight is required on certification attempts, and a real good idea for everything else.
   
   
3. Don't try to do too much - Stress is bad. I've learned to limit that number of flights and the amount of prep time I try to cram in a single launch day. It becomes too easy to make a mistake if you are rushing your work.
   
   
4. If you need a prep team, work out assignments ahead of time and make sure everyone understands their role. - On this particular day, my brothers flew in from out of town for the launch. The reason we first started talking about the get-together was because I was going to fly some fairly complicated designs (multi-staging, parallel staging, air starts, electronics). Somewhere along the line we forgot about that and each of us was completely absorbed in doing our own thing. None of us really helped each other prep to any extent, and if we had we probably would have gotten just as many flights in (but with fewer mishaps).

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