Estes Mercury Atlas - Cluster of Three 24mm Motors
Contributed by Robert A. Morstadt
This is a modification of the Estes Atlas Mercury kit to use a cluster of three 24mm D12-3 motors.
This is how I modified the Estes Atlas-Mercury kit to use a cluster of three black powder 24 mm motors.
The original Estes kit uses one central motor with two outer booster simulated engines being the location for extension tubes that have fins to stabilize the model for flight. The basic idea here is to use the outer tubes for motors as in the real Atlas and to put clear fins in slots that are next to the central motor.
The first step is to mark where the four fins will go on the aft cardboard bulkhead as shown in Fig. 1. I made a backup pattern in case something went wrong.
Fig. 1. Centerline for 4 fin slots marked on aft bulkhead.
The fins are cut from 3/32” thick polycarbonate using a scroll saw after first making a few practice cuts. It is helpful to cut the fins ahead of time in order to set the slot guides at the proper locations. I first cut one slot in the cardboard for the clear fin all the way across and a small notch next to the central tube to accommodate the 1/8” x 3/8” aircraft birch strut that protrudes beyond the cardboard bulkhead as shown in Fig. 2.
Fig. 2. Constructing the first clear fin slot tacking the struts in place.
As shown in Fig. 2 wood glue holds the strut and fin in place together. Note that a small hole is drilled into the protruding struts to accommodate a small machine screw that will prevent the clear plastic fins from sliding out during flight. Eventually the rear bulkhead will need to be cut into quadrants as shown in Fig. 3 in order to hold all 4 fins.
Fig. 3. Shown are the four fins and the inner struts that help form the slots.
To complete all four slots, two more outer struts per slot need to be glued in place as shown in Fig. 4. Note that engine hooks have been placed in all three motor tubes.
Fig. 4. Shown are the wood struts that are needed to complete the fins slots.
This completes the most time consuming part of the modification and the rest of the construction follows the Estes instructions except for a few more details. I permanently glued in the simulated outer (booster) nozzles, but I found that I needed to leave inner (sustainer) nozzle removable in order to get the fins in and out as shown in Fig. 5. In addition I had to cut notches into the sides of the fins so that they would fit around the sustainer nozzle.
Fig. 5. Shown is the removable sustainer nozzle along with notches cut into the fins.
I would recommend not using the Estes parachutes, but rather buy the thermal blanket material shown in Fig. 6 for a few dollars at your local sporting goods store and make one large parachute. I made a parachute that is 44” in diameter.
Fig. 6. Shown is thermal blanket material that can be used to make parachutes.
These modifications in the aft-end require quite a bit of nose weight in the forward end as shown in Fig. 7. I put a large screw eye in the forward plastic transition section and wrapped about 2 ounces of flexible lead weight that I bought a fishing tackle store.
Fig. 7. Shown is the nose weight needed to make a stable flying model.
I tried Estes solar igniters for the clustered motors, but I did not have good luck with them. I then went with Quest Q2G2 igniters and had no problems. With all these modifications I had a good flight with a cluster of three D12-3’s to about 900 feet as shown in Fig. 8 and Fig. 9.
Fig. 8. Shown is lift-off with a three D12-3 cluster.
Fig. 9. Shown is a recovery with a 44” diameter parachute.
What You Can Do