Brief:
This is a 2.9x semi-scale replication of the MPC Delta Katt. I got the original plans from JimZ's website. The finished bird consists of a 45 3/8" long BT-60 booster with 24mm motor mount and a 31 7/8" long canard glider with a rear delta wing having wingspan 16 1/2" from tip to tip. The booster and the glider each weigh 3 5/8oz, for a total launch weight of 7.25oz plus motor.

Construction:
Most of the parts were obtained from FlisKits. Fast service, good quality parts. Here is a parts list:

• 2 4" x 48" x 1/16" balsa sheets
• 1 4" x 48" x 3/32" basswood sheet
• 42" of BT-60 tubing
• NCB60L nose cone
• 2 BT-60 couplers
• 1 24mm engine mount kit for BT-60
• Booster recovery equipment (screw eye, Kevlar®, elastic, parachute)
• glider trimming weight (various washers)

The glider is exactly 2.9x scale except for thickness, which I kept minimal to save weight. The wings were made from two sections of 4" wide by 1/16" thick balsa. (Coincidentally, the 2.9 scale factor was chosen so I could just squeeze each wing onto two adjacent 4" wide balsa sheets.) The remainder of the glider was also 1/16" balsa, except for the fuselage which was 3/32" basswood for strength. Like Nardei, I gave the delta wing a dihedral for added stability. Nardei's review states that only the top stabilizer fins get an outboard slant, but Jim Z's instructions give both top and bottom fins an outboard slant. I followed Jim Z's version with equal, scale slants.

I deviated from 2.9x scale on the booster, because my scribbled calculations suggested I needed about 42" of body tube (much longer than scale) to counterbalance the large glider. The glider mount was built to scale, with several exceptions. First, the central basswood portion with mounting pin was not recessed to scale depth. Rather, it was recessed only 7/16" to ensure easy glider release. Second, this portion was trimmed to remove a strip about 1cm wide from nearest the body tube to save weight. Third, this portion was wallpapered with construction paper and white glue on both sides to give a tiny additional width, again preventing the glider from being too snug. Finally, I added thin braces along the leading edge of the balsa mount sheathing to reinforce the balsa. This last addition was only needed because I had partially cracked the balsa sheathing during the balancing experiments described below.

There are two critical elements to the Delta Katt design. First, the glider is aligned in a way that its fuselage is not parallel with the booster. This is ensured by the shape of the glider nose, which I replicated to scale. The result is that the delta wing has zero angle of attack, but the canard has a nonzero attack angle. This necessitates the second critical feature: the CG of the fully assembled unit must be right at the center of the canard so that the canard's influence on the rocket during boost is minimized. To ensure this, I strapped the whole thing together with rubber bands and moved the mounting assembly up the tube until the CG was correct. The pin is 6" up from the aft end of the rocket. This glider mount position is more forward than scale (and hence I had overestimated the required body tube length).

Finishing:
I did no balsa sealing and minimized finishing to keep weight down. The underside of the delta and canard got one coat of black paint for visibility and the rest of the glider was decorated with Sharpie pens. Having already decorated the glider, I decided to retain the same style with the booster. The bubble pattern took an especially long time...never again! The resulting 60's-70's look motivated the name: Groovy Katt.

Flight:
During the build, the canard leaned a bit as the glue dried, leaving it tilted a bit with respect to the delta wing, although both had the same dihedral angle. The result was a strong right turn. I trimmed this away with 6 grams of weight added to the left tip of the canard. With another 7 grams added to the nose, I achieved a fantastic glide, skimming the grass gently for a beautiful landing. Unfortunately, I forgot to do this trimming until after I had glued the glider mount, so the additional nose weight I added to the glider messed up the rocket CG slightly. The importance of the CG here is only to minimize the canard effect during boost: the CP is much further back so stability is not a serious concern.

With a total assembled length of over 67" and 28" of that length hanging below the lower launch lug, a special launch assembly was needed. I drilled a hole lengthwise in the end of a dowel and wedged the rod in it. I then mounted the dowel on a platform and stabilized with guy wires and rocks.

I built my motor mount for both Estes D and E engines but opted for a D12-3 for the first flight. There was premature separation at about 60 feet. As best I could determine from other people's descriptions and a post-mortem investigation, it appeared that the top portion of the notch on the glider fuselage splintered off, causing glider to fall away and booster to buzz around unstable. Nobody could tell me if the premature separation was the cause or the effect of the problem.

I repaired the notch with bombproof epoxy and touched up a few other dings. I believed that the glider probably fluttered too much during ascent and this wobble basically tore the craft off the booster. Because of the enormous size and small attachment, I assumed it was a hopeless case and I put the rocket away indefinitely.

On a calm sunny day in April, I decided to try again. I stuck in another D12-3 fully expecting a shred. Amazingly, it boosted smoothly and perfectly straight to about 400 feet, where it hung at apogee seemingly forever before detaching the glider. The booster landed 20 feet from the pad. The glider circled lazily overhead, sliding to a gentle landing after about a 1 minute and 20 second glide. We all jumped and screamed with excitement...it actually worked!

A third flight was attempted immediately afterwards on another D12-3. We got another perfect boost--higher--to 500 feet and another perfect separation. The glide lasted about 1:30.

More jubilation! We reach quickly for a E9-4. Alas, the motor had burned away the Kevlar® pull-strings attached to the motor adapter, and I couldn't get the adapter out to fit in the E motor. This will have to wait for another day.

Recovery:
The glider is very light for its size and is trimmed absolutely perfectly.

Summary:
In retrospect, I decided that the first failed flight was simply breakage at the fuselage notch, in the direction of the grain. It was not from excessive flutter. The basic design is absolutely flightworthy, even at 2.9x upscale, and with the right touch you will have a real winner. I highly recommend this project for anyone looking for a challenge that will reignite your passion for rocketry.