Just before Thanksgiving I was discussing motor retention in minimum diameter rockets with Ed Shihadeh at Giant Leap. He was pretty excited about a new product that he was going to introduce after the first of the year. Ed said that this product would cause rocketeers to rethink the way they retain their motors because of two factors.

First, it provides a solid, aerodynamically clean solution to minimum diameter rocket motor retention, and secondly, he claimed that this product's design would rival the elegantly designed Aero Pack retention system and do it for significantly less money.

I admit I was a bit skeptical. I'm a big fan of Aero Pack's retention system and had even reluctantly used a 54mm Aero Pack retainer on my PML Sudden Rush equipped with a boattail.

I say "reluctantly" because Aero Pack 's retention design includes an externally mounted screw-on retainer that causes extra drag on a minimum diameter rocket or one with a boattail.

This is due to its abrupt enlargement of the airframe profile. High performance of a minimum diameter rocket means paying close attention to maintaining an aerodynamically clean profile.

Since I was in the middle of building another minimum diameter rocket, a PML Nimbus, I agreed to hold off on motor retention until Ed's new system, SLIMLINE, was available.

I received my SLIMLINE at the end of January. My first impressions were that the SLIMLINE and the Aero Pack appear to be a lot alike.

The are both expertly machined, both are black anodized aluminum, both come in two parts, and both install with JB Weld onto the last 1/4 inch or so of the motor tube.

Upon a little closer inspection, it was clear there are two very significant differences.

The first difference is that instead of the externally screwed on retainer, the SLIMLINE employs a retainer that is installed into a machined groove on the inside of the retainer sleeve.

What this means is that the retention system's aerodynamic profile is significantly improved in the SLIMLINE.

The second difference is the price: $19.95 for the 54mm retainer.

Ed was right again. That's a considerable saving over a similarly sized Aero Pack retainer (about $32).

That hand-installed split internal ring had me wondering, though. How hard will it be to install and remove it?

My first attempt made me feel as fumble-fingered as a new boyscout tying his first sheetbend knot.

I soon learned the secret is to anchor the tapered end of the ring in the machined internal groove with a finger and then progressively work the rest of the ring into the groove with your other hand.

Removing the ring was simple. Lift the tapered end of ring out of the groove using a screwdriver or penknife. Then pull the ring out.

With five minutes of practice, I was installing and removing the ring in seconds.

I installed the SLIMLINE on my minimum diameter Nimbus. Not only was the retainer's low profile an improvement over the Aero Pack retainer, but I was able to reduce drag further by using red body glazing to create a smooth transition from airframe to retainer sleeve.

Boattail equipped rockets will be even nicer. Because the SLIMLINE relies on an internal fit, the SLIMLINE can be mounted inside the boattail, flush with the end of the airframe.

Giant Leap will be the exclusive distributor of SLIMLINE. Ed shared with me that an engineer designed the SLIMLINE and has it manufactured to NASA-type specs by a NASA contractor. It's machined out of 6061-T6 aircraft-grade aluminum and is currently available in 29 through 54mm sizes.

Like the Aero Pack, it requires approximately 1/4 inch of exposed motor mount for mounting. SLIMLINE retainers for 75 and 98mm airframes are also planned for later this year. The SLIMLINE is sized for an optimal fit in phenolic airframes, but can also be used in LOC-sized airframes with some minimal hand-fitting techniques. All SLIMLINES have a spacer ring to accommodate Kosdon, Ellis Mountain and hybrid motors, too.

Giant Leap will be the exclusive distributor of the new SLIMLINE system. Coming soon will be a line of SLIMLINE adapters that will allow you to downsize a 54mm SLIMLINE-equipped rocket to fly SLIMLINE retained 38mm motors. A similar adapter will be available to fly 29mm motors in a rocket fitted with a 38mm SLIMLINE.

The Aero Pack will remain a good choice for rocketeers who like the handy screw-on retainer and who are willing to pay the extra money for that feature.

But bottom line, I really like the SLIMLINE. It fills a large market niche of flyers who want and need a clean, effective and inexpensive motor retention system for their everyday rockets, and who can't or won't pay the higher price of an Aero Pack. And, it provides an aerodynamically cleaner retention system for minimum diameter rockets.