Building and Flying the Semi-scale Nike-Asp

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By Michael J. Mangieri

I have always enjoyed building rockets of all kinds; kits, designs of my own imagination and scale replicas of real rockets. When I got my copy of "Rockets Of The World" by Peter Alway, back in 2002, I knew that I would be building a lot of scale models. Question was, which one would I build first?

After spending a few days cooped up inside during the winter of 2002, I came up with a list of around 30 rockets from both ROTW and a few of it’s supplements that I wanted to build. First off the assembly line was the 1:3.18 scale Terrapin, sporting a cluster of three 18mm motors, built in March 2003. She has flown 7 times since then and has always been a crowd pleaser at club launches with her majestic slow climb and huge black parachute. After that, I constructed a nice 1:5 semi-scale version of India's Rohini RH-200 sounding rocket, using standard BT60 and BT50 body tubes. Balsa Machining Service (BMS) provided the custom transition and nose cone. Then, wanting to try something a little more complex, the decision to build the Nike-Asp was made, and in April of 2003 design work on the Nike-Asp started.

I didn’t want to jump right in and build a large scale version which would have required mid-power RMS motors (in the E-G range), so part of my design plan was to keep the weight down so that standard Estes black powder motors could be used throughout. After spending a few weeks designing and re-designing various scale ratios, I decided that I needed a software tool to help me with determining the dimensions of the various parts automatically. Doing this longhand each time was getting tedious so I created ScaleData, an Excel spreadsheet for computing scale dimensions. This helped me quickly compare various scale ratios and I finally decided on 1:6.68 scale. This allowed BT-80 for the Nike booster and BT-50 for the Asp.

Since I was going to use an electronic timer for ignition of the second stage I knew that I would need sufficient power to lift this model, so I decided on a three motor cluster in the booster: a central 24mm and two 18mm. I also decided on rear ejection for the Nike’s recovery system (which would turn out to be bad design decision number one). The Asp’s 18mm motor would be lit by a PerfectFlite microTimer, and so I constructed a pull-pin mechanism to start the timer at liftoff (bad design decision number two). Built specifically to be flown from small fields, the total power is limited to about a small E motor in the D12-0, C6-3, C6-3 configuration. But even with this, a C6-5 sustainer will carry the upper stage to about 1000'. For those interested in more details of the design, you can check out the Nike-Asp (and other rockets) on my web page at http://takeoff.to/XCaliberRockets.

It wasn’t until April 16, 2004 (a year after initial design concepts were laid down) that the Nike-Asp had her first flight. Loaded with a D12-3 and 2 C6-3's in the booster and a 1/2A6-2 in the sustainer to keep peak altitude low, she was launched at about 7:00PM EDT. Boost was awesome! She lifted gracefully and slow, but neither rolled or pitched. The calm wind conditions obviously helped a lot here. At 2 seconds into the flight the PerfectFlite microTimer ignited the sustainer motor and the Asp separated as expected. The Asp continued on a perfectly straight trajectory until ejection when a streamer was deployed for recovery. The Nike continued up following the Asp until the delay charges ejected the two rear 14" mylar chutes at about 3.5 seconds into the flight. One small mishap was obvious, however, as only one of the chutes deployed; the other separated from the booster.

Now the Mangieri property is fairly large, 12 acres in all. But most of the acreage is covered with trees. The launch site is in my front yard where I have about 3 acres of somewhat open space. There are a few trees and of course the booster found one! Luckily, the Nike landed in a low branch and it only took a few minutes to coax her down.

The Asp decided to take a little trip to the east, heading right for the large, 40-50 foot tall trees at the back of my neighbor’s property. A fortuitous gust of wind at low altitude nudged her just enough to allow a nice landing in the green grass.

Upon examination on the ground it was determined that the failed chute deployment on the Nike was caused by heat from the motors burning through one of the Kevlar cords attaching the shroud lines to the rear of the Nike. Other than that, the flight was deemed a success and it was time to launch at the next NARHAMS club event after a few modifications to reinforce the rear chute attachment.

Since the Kevlar cord wasn’t string enough to withstand the heat of the motors I replaced them with small gauge picture frame wire. Although this fixed the burn through problem, the wire was stiff enough to make it fairly difficult to get the parachutes into the rear body tubes and to stay there without being pulled out by the weight of the wire. At this point I should have listened to that little voice in my head telling me: "you know, those chutes with all that wire and swivels are bound to get stuck in those small BT-5 tubes."

The second flight, on July 10, 2004, in front of 50+ spectators, did not proceed nearly as well. In one of the most embarrassing moments of my 40 years of amateur rocketry I did, what I understand from the RSO, isn’t all that uncommon – in my zeal to produce a really beautifully built semi-scale rocket I left off the launch lugs. Here I was, out at the launch pads, turning the model over and over looking for those lugs. Returning to my tent, I spend some time sanding off that wonderful paint job to make a good surface for the epoxy.

With the lugs now cemented on, and the spectators waiting for the launch, I was now prepping the Nike-Asp on the 48" rod. The pull-pin was inserted, the timer set, the clip-whip attached to each of the three motor igniters, I was set, ready for launch.

T-minus 5, 4, 3, 2, 1, launch. The boosters ignited and … smoke and flame but no motion?! In my haste to get her in the air I attached the timer’s pull-pin cord at an angle to the booster’s base. The wire was draped over the circular blast deflector plate and then attached to the base of the launch pad. At ignition, the pull-pin caught on the blast plate and the booster got hung up on the pad. With the three motors producing considerable smoke as the Nike-Asp remained on the pad, the crowd of kids laughed and yelled out, COOL. Then, adding insult to injury, while the 3 booster motors proceeded to destroy the whip-clip the pin gradually worked its way loose and activated the timer. The Asp launched at the end of the selected timer delay and actually had a very straight flight considering it wasn’t on a guide rod. The crowd cheered, and laughed, again!

Although the Asp had a very nice flight, it ended up in a tall tree and wasn’t recovered. Seems like I wasn’t going to win at anything that day.

The motor mount of the Nike was destroyed in the heat and flames of the booster motors, and with the Asp stuck up in that tree the only parts recovered intact were the Interstage Coupler, the Electronics Bay and the booster fins.

A redesign was in the works!

In January, 2004, the new design was completed. Remember those two "bad decisions". Both were addressed in this newer version of the Nike-Asp. First, the idea of rear deployment was abandoned (it was a silly idea anyway, trying to pack those 12" chutes into small sections of BT-20. What was I thinking? I should have listened to that voice!) In this new design the Interstage Coupler and Electronics Bay is ejected and the Nike is recovered with a large 24" nylon chute.

The Interstage Coupler and Electronics Bay was the only part of the original Nike-Asp to be recovered intact. It was used in the new design with a few modifications. The PerfectFlite microTimer was replaced by a PerfectFlite miniTimer. To accommodate the new timer’s voltage requirements, a SANYO N-6PT Rechargacell replaced the 4.5 v NiCd from the first rocket. This added additional weight to the booster and so the three motor cluster arrangement was replaced with a 4-24mm motor mount from FlisKits. I installed a 4" long piece of all-thread through the center of the motor mount with a washer and nut at the rear end for positive motor retention. Loaded with four D12s, the Nike-Asp would be lifted with the equivalent of an F-40.

Bad decision number two was corrected by installing a G-Switch on the miniTimer. No more pull pins getting stuck, the G-Switch would detect 2 g’s of acceleration and only then would the timer activate. Another plus with using the miniTimer is that I gained more flexibility in timer delay selection. With the microTimer, you have to cut circuit board traces to set the delay and the available times were 1-16 seconds in 1 second increments. The miniTimer is set programmatically at launch time via a push button on the unit. Delays are in 0.1 second increments making it easy to find an appropriate delay for various motor combinations.

On September 17, 2005, in front of 100+ spectators at MDRA, the newly designed Nike-Asp took to the skies with 4 D12-7s in the booster and an A8-5 in the sustainer. Lift-off was flawless, with all four D12s coming to life almost instantaneously. She gracefully lifted off the pad and headed into the blue sky. It was a really cool looking boost and the crowd loved it! With the miniTimer set for 2.7 seconds there was a noticeable period of quiet as the Nike-Asp climbed higher into the sky coasting for about a second as the timer counted down. The sustainer ignited on schedule and the Asp cleanly boosted off the Nike, streaking into the clear blue sky. The crowd cheered. The Nike, still with plenty of kinetic energy left, started a slow arc as gravity took it’s toll. At the time when the sustainer just about went out of sight, the booster motors ignited their ejection charges and that’s where the perfect flight went a little haywire. The main chute didn’t deploy all the way allowing the booster to fall at a rather large velocity. Upon impact the lower portion of the booster tube was slightly damaged, and two of the four surface mounted fins broke off. The sustainer returned safely on it’s long streamer.

Repairs are underway and the Nike-Asp will fly again. Because the fins were surface mounted, the tube was torn and that significantly weakened the integrity of the tube wall. I decided to glue an external patch over the rear end of the booster to strengthen it. I plan to fly the Nike-Asp a few more times and then move on to a larger version.

A larger scale version of the Nike-Asp is planned. The four cluster booster will be replaced with a standard 29mm motor mount to accommodate an RMS motor. Details are only sketchy at this time, but this up-scale of the Nike-Asp should be really nice.

What’s next? Not sure, but you can bet it will be another scale model of something from ROTW. This book, by Peter Alway, is a wonderful addition to the scale modeler’s collection and highly recommended.

(Note: Unfortunately, ROTW is now out of print. The supplements are still available).