Squirrel Works Freebird / Imp

Freebird / Imp
2-stage variation of Squirrel Works kit

Inspired by my childhood Alpha, complete with upside down fins - an apparently common mistake - Don at Squirrel Works was prompted to offer this kit. At first, it was called the Freebird, and given out as a promotional item. Later, it was renamed the Imp and became a standard catalog item.

Right: Don's Freebird circa February 2005.

When I began building mine, it was still called the Freebird, but during the months in my build queue, it became the Imp complete with a new paint scheme and decal.

Don had given me an extra set of fins, so I was planning all along to do a 2-stage variation, but when the new paint scheme came out, I opted to paint the booster in the Freebird colors and the sustainer in the Imp colors.

I also tweaked the design to use a shorter nosecone. It's still an ogive, but I made it shorter to keep it more in scale with the Alpha.

Over time, the rocket has had several good flights...and one bad one. At right is a liftoff shot of the time the sustainer didn't light. After a good liftoff, the booster burned out and separated without the sustainer lighting.

It lawndarted, and the outcome wasn't pretty.

So the rocket was repaired by adding a new section of tubing to replace the broken part. The paint scheme was kept simple with the intent of later painting one fin red. Another Imp decal was applied, and the rocket looked pretty good.

Here's a blurry liftoff shot of the repaired rocket in action.

On the way up, I heard the thrust sound change, and then saw it stage a moment later. So I knew the sound didn't come from the staging event. The sustainer put in a good flight and was recovered in good condition.

Upon recovering the booster, it became clear what caused the change in the sound of the motor burning. A common problem with stagers is the booster motor coming out at staging while the booster stage remains attached to the sustainer motor and gets fried by its exhaust.. But that's not what happened here. Almost all my boosters have an aft ring or a hook to ensure that the booster separates with the motor.

Thus, with positive motor retention, the booster stage need only have enough grip on the motor to hold it on during boost. A bit of tape wrapped around the motor is usually all that's required. In hundreds of flights, I've never had this happen, but on this day, as the rocket accelerated and the drag increased, the booster section slid aft on the booster motor until it was about half off the motor, which was still burning.

The result was that the booster was fried.

I cut off the fins and threw away the rest of the debris. Someday I may build another booster for the Imp, but in the mean time, I'll fly it single stage.

In the pic below, the hook can be seen sticking up between the blue fins. A couple wraps of tape around the hook and the motor would have held it firmly in place and prevented the destruction.

1-11-2009