CONSTRUCTION

The five and a half inch tubes are forty eight inches long. I use two of them in the rocket. The sustainer section has three centering rings, two of which will “lock” the fins in place, and the third holds the motor mount centered in the body tube.

The top body tube is cut in half. The lower section is attached to the sustainer tube by ¼ inch t-nuts. The coupler is attached with t-nuts to the sustainer. T-nuts also restrain the payload bay in the top body tube.

The nose cone is the four ogive LOC 5.5” cone, which is an exact scale nose cone. Fins are cut from 3/16 inch Baltic Birch. All the centering rings and bulkplates are cut from ½ inch Baltic Birch.

This rocket must be reinforced to handle the thrust of an M motor. But first I had to learn how to do it. To accomplish this, I decided to build and fly a scale model. The body diameter of the Excel, Jr. is 2.6 inches, which is 50% scale.

I began my Level 3 project by constructing a working scale model of the final design. The purpose of the scale model is to test all the necessary construction technique.

The design calls for t-nuts to hold different sections of body tube together, and to hold the coupler tube which will join the sustainer to the second body tube. It is a modular design which allows for easy repairs to body tubes if necessary.

Here all the screws and the rail buttons are installed. In this illustration the screw for the upper rail button penetrates the body tube and the coupler tube.

Figure 6

The rocket is ready to assemble. The electronics sled is long enough to fit a Missile Works RRC2. Power is switched on or off using a Radio Shack POPO switch. Note that the fins are not reinforced. The fins were taken from a stock Binder Design Excel, Jr. kit.

The Loki Research EX motor is the 38mm 880 Ns case and just fits in the sustainer with the coupler installed. The opening in an AeroPack motor retainer was filed to a slightly larger diameter to allow the motor retainer to fit over the EX motors. It works. An Aerotech 1080Ns motor will also fit in the sustainer, and is the largest motor which does fit.

First flight of the scale model of the Level 3 project. This flight used an Aerotech I-284 and dual deployment. The rocket lifted to 4400 feet and worked as intended.

I named this rocket Soliton, which is the technical name for a traveling wave. It has flown eighteen times to date.

The list below details the motors used to fly Soliton.

Certified Motors

That's 18 successful dual deployment flights. These results prove the concept of modular construction.

I replaced the Missile Works RRC2 with an ARTS altimeter for the two most recent flights. The last flight with a certified motor used a Cesaroni J330. The ARTS indicated 907 fps and apogee at 6629 feet AGL. The most recent flight is shown below, at the MDRA launch ESL 89. Here an EX I-199 motor burning a formula called Orange Sunset lifts Soliton to 3945 feet AGL.

The utility of this Excel’s design is that the relatively small fins, light weight, and fast liftoff speeds appear to reduce weathercocking.

It can easily travel out of sight, as it did on this flight.

The only certified motor left to fly in Soliton is the Aerotech J570. This motor may push the rocket through Mach 1. As the stock Excel, Jr. fins are not reinforced, and are only one-eighth inch in thickness, they may not survive the transition through the sound barrier. Before I fly this motor I intend to laminate the fins with a tip-to-tip layer of four ounce fiberglass. That may be the most important lesson from this rocket. With the right motor it should be capable of supersonic flight, but I think it unlikely that the stock plywood fins will hold up.

The lessons to apply to the Level 3 version are 1) Modular construction works, 2) reinforce the fins with fiberglass laminations and, 3) this rocket flies where you point it. If you point it straight up, it flies straight up and comes straight back down. Point it at an angle and you have a long walk to collect it, even with dual deployment.

I began by collecting up the necessary components: two body tubes, a 75mm motor mount, two coupler tubes, coupler and bulkhead plates, the nosecone. I cut the fins from 3/16 inch Baltic Birch. I decided to try to use the three inch Aero Pack motor retainer as I have had good experience with the 38mm version with Soliton.

The first job is to cut the fin slots. Then peel the glassine layer off the paper tubes so one gets a strong bond between the epoxy, fiberglass and body tube. Figure 9 below shows me working on the rocket.

Figure 11

Finished Sustainer Tube

The fins slots have been recut and the tube is fully cured. It is quite strong.The next step is to build the motor mount. The first issue is to attach the AeroPack motor retainer in the right place. Following the directions, I eventually got it on, using a Loki Research L motor casing to keep the motor mount, centering rings, and motor casing adequately centered. Next I decided to strengthen then centering rings by incorporating three ¼ inch threaded rods the full length of the motor mount. Once the motor retainer was in place, I drilled through all the centering rings at once, and installed the threaded rods. See Figure 13 below.

Figure 13.

Motor Retainer and Threaded Rod Installation. 

Satisfactory placement of the 12 screws for the motor retainer required that I drill the holes larger than the directions indicated. I used epoxy to secure the threaded inserts in the centering ring, which was allowed to “float” until the epoxy set. This ring will have a generous coating of epoxy over the retainer screws and the nuts securing the threaded rods. In addition, 6-48 machine screws will secure the centering rings to the body tubes. The motor mount is not removable.

Once the centering rings, threaded rods and motor retention were installed, I could turn to attaching the fins. The motor tube was rough sanded and the centering ring above the fins was moved up the tube about six inches. This allows clearance for the initial fin attachment.

The fins were laminated with a layer of nine ounce fiberglass cloth. A vacuum was pulled on the fins and glass, and they were allowed to cure over night. Then the excess epoxy was sanded off and an airfoil shape was sanded onto the fin edges. The fin root was sanded flat and a series of small holes drilled into the fin root to allow JB Weld to penetrate.

The motor mount was dry fit into the body tube to the correct location so that each fin would butt against the front edge of the aft centering ring. A small batch of JB Weld was mixed and spread on the root edge of the fin, which was placed through a fin slot and held in place while it set. This was repeated for the remaining fins.

The result is a heat resistant bond on the body tube. The next step is to remove this from the body tube and strengthen the joint between the fins and the motor tube. I marked the outer edge of the body tube on all fins. Then I cut a thin slice from the end of the fin slot to the aft end of the body tube on one side of the fin slot. I marked one fin and the body tube so I can return the fins to the correct slots. Figure 14 shows the removal of the fin can from the body tube.

When all the epoxy was fully cured, the centering rings bonded to the motor tube, and the fin assembly ready to be reinstalled in the body tube, I took a final picture. See Figure 16 below.

Figure 16.

Completed fin assembly.

In the photo above, the details of the coupler tube to be inserted at the top of the sustainer are shown. This unit is built from two couplers. One is a standard LOC 5.5” coupler tube, internally reinforced with two layers of 6 oz fiberglass tape and epoxy. A second coupler tube, a LOC “stiffy” coupler was also internally reinforced with 6 ounce fiberglass tape. A coupler bulkplate was sanded to fit inside the reinforced outer coupler tune and a two inch U-bolt was installed. The stiffy coupler was cut in two at a point eight inches from the bottom. The long end was epoxied into the outer coupler tube. The bulkplate was installed from the front end and the remaining section of the stiffy coupler installed and epoxied into the front end.

This makes for a very strong attachment point for the recovery system. It has redundant security. The bulkplate is held in place by the internal stiffy coupler. The T-nuts, which will hold the coupler to the body tubes will penetrate both coupler tubes above and below the bulkplate.

The electronics sled is also hardened. The typical manner of construction is to epoxy some copper or phenolic tubes to a thin slab of plywood and mount the electronics to it. My experience with my first Level 2 Excel showed what happens when a forward closure slams into the electronics bay bulkhead at high speed. Everything gets wrecked.

To try to avoid this, I used a thin slab of plywood and epoxied to it two 11 inch sections of 3/8 inch (i.d.) copper tubing. Then I laminated both sides of the electronics sled with 9 ounce fiberglass tape, and vacuum bagged the entire assembly. See Figure 18.

Figure 18.

Reinforced Electronics Sled.

This unit has holes for two altimeters, two batteries, and two on-off switches.

The reason to vacuum bag the reinforcement is that epoxy does not bond to copper. There is nothing for the epoxide molecule to bond to on the surface of the metal, so I wanted to ensure that the fiberglass cloth will not delaminate under thrust or impact.

Project Performance

This unit will rocket into the sky. I do not have actual weights yet, as it is not yet completely assembled. Assuming 30 lbs at liftoff, RockSim version 6 generates a simulated altitude of 11,110 feet and a maximum velocity of 1123 fps. This uses the Aerotech M1297 motor.

It does meet the design goal of staying under the waiver at Whitakers.