An RMR Descon X entry
by David Fergus
(Place your mouse over photos to view the captions.(IE5))
This rocket is a kit bash of the Estes Gemini DC. It flies on an 18mm motor, and recovers on dual 12" parachutes ejected from the nose. When ejection delays are longer than apogee, the rocket has a tail first recovery profile before chute deployment. It is 14" long, has a span of 6", and weighs 2.8 oz. without engine. The front section of the fuselage is a unique oval shape rather than the traditional round shape.
The X-File is a single pilot fighter-interceptor. A squadron of 10 X-Files are typically carried on board Excaliber class star cruisers. They are typically used as scouts or escorts for shuttles. Their primary purpose is coordinated defense of the mother ship at extended ranges. Vessels that are designed to operate in space do not need aerodynamic features, but the X-File was originally envisioned to extend operation into planetary atmospheres. The X-File, therefore, has aerodynamic fins and body. No provision was made for landing gear however, but emergency chutes will deploy if the rocket is forced to make a tail first landing on a planet. Ten years of operational deployments have only led to three instances when the planetary emergency landing system was necessary, and it performed flawlessly in each case with safe recovery of the pilot. The name X-File is really a nickname based on the official Space Command designation of X-FIL with a hull number. The X signifies the x-wing configuration. The FI signifies the fighter/interceptor role. The L signifies the primary weapon, which was originally a directed energy laser, but has since expanded to include photon torpedoes and grenades. Thus, most X-Files are really X-FIP's, but the original nickname has stuck, and most Space Command personnel unofficially call these vessels the X-File. The hull number of the rocket modeled is X-FIL-31; which is one of the few remaining rockets not configured to carry photon torpedoes.
They have a maximum endurance of six hours at optimal acceleration speed, and a maximum speed of 0.9 warp for two ten minute bursts if needed. Weapons loads typically include 2 photon torpedoes, a single directed energy "gun" (mounted underbody and aimed by steering the entire vessel), and a self-defense photon grenade launcher, which ejects small photon grenades into the wake of the X-File. The impulse engine is located in the aft main body, and the four anti-matter engine nacelles are used for the near warp speed bursts only. The impulse engine is an advanced design that provides power for propulsion as well as life support, weapons, and the anti-matter control & containment fields. A small anti-matter containment field is maintained in the forward portion of the engine section, and anti-matter is ported to the nacelles via small diameter pipes when "afterburner" (to borrow a term from ancient earthbound days) is needed. Since anti-matter is contained and controlled with magnetic fields, rather than physical boundaries, the boost nacelles appear to be nothing more than hollow tubes. In actuality, there are powerful magnetic fields in each nacelle controlling and porting the anti-matter/matter reaction to provide the near-warp burst capability for the X-file. Maneuver/steering is accomplished with small chemical impulse jets in the bow and stern. Navigation is not complex, as the X-File cannot stray further than 3 hours cruise distance from the mother ship. Communication is strictly line-of-sight in the GHF frequency range. Pilot ingress/egress is accomplished via a small hatch on the side of the fuselage with airlock latches mated to the mother ship.
One (1) Estes Gemini DC kit
1/8" x 12" wooden dowel
1/8 inch braided Kevlar (6 inch length)
Carpenters wood glue
Krylon gray sandable primer, gloss pewter gray, & clear sealer
Testor's gloss black enamel, gold enamel, silver enamel, gloss red enamel
Fine point black Sharpie
Deviation Notes: RMR Descon X allows 18 inches of BT-20, but the Gemini kit comes with two pieces of BT-20 that are only 6 inches long. I used the kit body tubes rather than the longer stock. In addition, the Estes kit includes a small cardboard tube to vent ejection gases from the main engine tube to the two side tubes. This tube was not included in the Descon X list of parts, but was used in this kitbash.
1. From the Gemini kit, find the small one inch long cardboard tube. Cut off a small portion about 0.25" long. The shorter piece will be used to equalize pressure between the two BT-20 body tubes (and fill in the holes on the sides of these body tubes that are used by the Gemini DC kit to port ejection gases from the main tube to the side tubes) on the front section of the rocket body. The longer portion will be attached later to simulate the laser weapon.
2. Glue the two sections of BT-20 tubes together using the small section of vent tube from Step 1 to mate the two pieces and fill in the portholes in the side of the body tubes. Place the assembly on a flat table to ensure the two tubes are parallel while the glue sets and dries. After the glue is dry, draw four parallel lines on the top and bottom of each tube where the tube would touch the table when lying down. These lines will be used as general reference and to guide placement of cardstock in later steps.
3. Build the engine mount per instructions for the Gemini DC. Set aside to dry.
4. Mark and cut the BT-50 tube as follows:
*One piece 6" long (the portion including the pre-cut fin slots and gas port holes)
*Four pieces 3" long (these will be the anti-matter boost nacelles)
5. Mark and cut the front end of the 6" engine section (BT-50) as shown in the picture. In the front end of the engine section (the one with the port holes) cut out sections 1.25" deep and approx. 0.75" high. Use the front section of the two glued-together BT-20 tubes as a guide as to where to start the cuts. Also, cut four small slots 0.25" deep into the back of the front section (the small vent tube installed in step 2 is towards the back) where it mates with the engine section. This will add strength to this important joint when glued together.
6. Take the two pieces cut out in step 5 and glue them inside the engine section to cover the two ejection gas port holes (which are unused in this kit bash).
7. Carefully separate the 4 pre-cut fins from the sheet of balsa. Sand them to taste.
8. Using the waste balsa from the sheet of fin stock, fabricate four quasi-heart-shaped balsa support tabs that will center the front section inside the engine section. The two pieces in the rear will also direct ejection gases and particles from the engine section into the two tubes of the front section. Therefore, they need to be reinforced on both sides with a good layer of wood glue. Fabricate 2 moon-shaped pieces of balsa tabs that will close the rear ends of the front section that hang outside the BT-50 engine section. These pieces will also see ejection gas pressure and will thus need to be strongly reinforced from the inside with wood glue.
9. Glue the four quasi-heart-shaped tabs to the appropriate location on the front section. Place them in locations that allow good glue fillets on all joints and surfaces. Test fit and sand to a good fit. Glue the two moon-shaped tabs to the engine section just aft of the cutouts. Again, sand to fit the front section to the engine section. Reinforce with liberal amounts of glue all surfaces and joints that will be inaccessible when the engine section is joined to the front section.
10. Glue the engine mount into the engine section so that the heavy duty centering rings are not located under fin slots. Center the engine hook between the two "bottom" fins.
11. Glue the front section to the engine section. Ensure the combined unit dries straight. Use healthy dollops of wood glue so that the balsa tabs are protected from hot ejection gas and particles. Add healthy glue fillets on all joints.
12. Mark several 0.75" strips down the long length of the back of the card stock that comes in the Gemini DC package. Cut them out with scissors. Measure and cut two pieces to cover the two exposed tubes of the front section. Lightly glue the strips to each side of the front section. Note that too much wood glue could cause the card stock to wrinkle as the glue dries and shrinks. Cut out two more pieces of card stock and lightly glue them on top of the first two flat pieces. Construction of the nose section will be done in following steps.
13. Install the two PNC-20 nose cones into the two tubes of the front section. Carefully glue the two nose cones together by putting a dab of CA in the joint where the two nose cones touch each other. (Do not let any CA run back to the joint of the nose cones with the front section, or you will have to figure out another method of recovery other than parachute since both ends of the rocket will be glued shut!) If you have to pull them out slightly to avoid getting CA on the cardboard tubes of the front section, be careful not to change the parallel orientation of the cones to each other along their centerlines. After the CA cures, reinforce this joint with epoxy.
14. Measure and cut two more 0.75 inch wide strips of card stock that will fit over the curved portion of the nose cones. When finished, the front section of the rocket when viewed from the front will look like an oval rather than the more typical round body tube. Use small amounts of CA to glue these strips of card stock to the nose assembly. Measure and cut two more pieces and glue them on top of the first two strips. Trim the front tip of the nose assembly to be straight, then measure, cut and glue a small piece of cardstock to the front end of the nose assembly to cover the small gap between the tips of the two nose cones.
15. Remove the nose assembly from the rocket. Epoxy a 6 inch length of 1/8" braided Kevlar (available from Pratt Hobbies) into the inside of one of the two nose cones. Tie a small loop in the loose end and epoxy the knot. Glue the two Estes shock cord mounts and elastic shock cords into the front ends of the front section body tubes. Leave enough room for the shoulders of the nose cones. Use longer lengths of elastic than provided in the kit if needed (Actually, the elastic that came with the chutes was longer than I am used to, and was long enough this time). If you go overboard with long elastic, you won't have room in the tubes for wadding, chutes and shock cords. After all glues are completely dry, tie one length of elastic to the loop of braided Kevlar. Attach both 12" orange chutes to the ends of the two elastic shock cords. Note that the nose assembly will only be attached to one of the two elastic shock cords and corresponding parachute.
16. Measure and mark a line on each fin parallel to the fin root 2 cm. from the root. Cut each fin into two pieces along these lines. Glue the four base fins into the engine section through the pre-cut slots. Put healthy glue fillets on all joints.
17. Mark straight lines 180 degrees apart on each of the four short pieces (3 inches long) of BT-50. Glue the tubes to the ends of the base fins with the front of the tube towards the front of the fin, leaving a short piece of fin to overhang at the back of the nacelle. Glue the other half of the fins to the top of each tube/nacelle. Put healthy glue fillets on all joints.
18. Glue the longer length of 0.25 inch cardboard tube centered on the underbody (corresponding to the engine hook) near the nose of the front section. This tube simulates the laser weapon. Cut out a couple of triangular pieces of balsa and glue them behind this tube side by side. This simulates the wave guide to the back of the "gun". Glue the 1/8 inch launch lug near the rear of the engine section on the same "bottom" as the engine hook. Place it in the angle of one of the two bottom fins so it will clear the "anti-matter porting tube" installed in the next step. This launch lug simulates the photon grenade launcher. Make sure it is located where it can also serve as a real launch lug.
19. Two options on a pilot canopy: a) Fabricate a pilot canopy using paper from the Gemini DC instruction sheet using a known pattern or design one of your own scale. Glue it in an appropriate location on the "top" of the front section. b) (heavier but still acceptable of two options) The PNC-50 nose cone could also be used for this purpose if cut down in size somewhat on a jigsaw or small band saw. Place the two halves end to end on the "top" of the front section, and glue in place. This is the option exercised on this model.
20. Fabricate the "anti-matter pipes" from the 1/8 inch dowel. Measure and cut 4 pieces each 3 inches long. Place 2 of them on the top of the front part of the engine section to the four boost nacelles so that the end of the pipe is centered in the middle of the boost nacelle hollow tube. Use healthy dollops of wood glue to secure them. When dry, repeat the process for the bottom two anti-matter pipes.
1. Spray a coat of grey sandable primer over the whole rocket.
2. Because the body tubes for this kit are the white Estes tubes, the spiral grooves are particularly deep and wide. Sand and fill cracks, crevices, body tubes and fins with Elmer's F&F as appropriate.
3. Spray several coats of Krylon gloss pewter grey over the whole rocket.
4. Brush paint black enamel on the pilot canopy and the intakes of the four boost nacelles.
5. To stick to the theme of kitbash, all of the detail added is hand lettered and hand sketched; rather than use decals from other kits. Using a black fine point Sharpie, print the hull number (X-FIL-31) on all four fins. Trace out a square egress hatch below the pilot canopy. Trace out forward and aft side thrusters (for steering). Add other detail as the whimsy takes you, such as no-step warnings, weapons system warnings, etc. Note: kitbash could use stuff from other kits, but I chose not to for the contest. After the contest, I will add battle damage decals from my son's Star Wars X-wing (which will make that thing worth something other than a hood ornament...).
6. Brush paint silver, gold and red highlights to taste on the rocket.
7. Spray a couple of coats of clear Krylon to protect the paint and other details.
While waiting for the weather to warm up and the snow to melt up here in Minnesota, which did not occur this March, our club (Minnesota Amateur SpaceModeler Association; MASA) had a winter launch at the small site in White Bear Lake, MN. X-File had her first two flights in 21 degree weather with a 2 inch crust of frozen snow, and light breezes out of the northwest. See the club flight report here. MASA March Flight Report
Flight Prep Notes: Both body tubes get about an inch of dog barf (bio-degradable wadding) pushed down to where the small side tube intersects the two tubes. One body tube has an orange Estes chute attached to an elastic shockcord and not attached to the nose section. The other elastic shock cord is attached to the 2nd chute and the loop in the nose cone attachment cord. Due to the cold, generous amounts of baby powder was used on the chutes.
Flight 1: A8-3. RSO asked "Are you sure this isn't too heavy for an A engine?" I said "It's OK barely, but I need to explore the flight envelope" and the button was pushed. X-File rose slowly to about 80 feet, began to fall back down tail first, and popped both chutes at about 40 feet for a safe recovery.
Flight 2: B6-4. X-FIL-31 flew quicker this time to about 200 feet, again with a slightly long delay, allowing the chutes to pop as the rocket begins to fall tail first. This time, one of the two chutes didn't fully deploy, but one chute is adequate for a safe recovery. Inspection after the flight reveals that the stock parachutes provided in the kit by Estes (with the cotton rather than dacron shrouds) are weak. Four of the six shroud lines had parted. The third test flight on a C engine will be delayed until a better parachute shroud material can be obtained and installed.
Flight 3: C6-3. MASA May launch; Good straight boost to about 400 ft, good tail first recovery on both chutes to a soft landing on the sod.
Test Flight Analysis:
Test flights prove that the actual CG with an expended engine is aft of the center of the rocket resulting in a tail-first flight profile after apogee before chute deployment. The CP is still aft of the CG by a safe distance indicated by the straight, stable flights under boost. The four tubular boost nacelles draw the CP further aft than would be normal for a typical 4FNC rocket, thus creating a stable rocket that does not need nose weight. It is flyable on an A8-3, but just barely. A B6-4 is good, and a C6-3 or C6-5 are better yet.