We will divert from the kit design just slightly here. The Estes design makes use of one adapter ring (part# AR-2050) at the nose end and a much thinner card stock adapter ring at the rear.
This may have been to save weight or more likely cost (punched card stock is much cheaper than the heavy paper tube the AR-2050 adapter rings are cut from).
If I decide to fly this model, stronger is better so we will make use of two AR-2050s to center the engine mount in the body tube, but we will save the cardstock version for a cosmetic cover in the next step. Notice that the cardstock rear adapter ring has a notch cut out of it for the engine hook. This is to allow the engine hook to move slightly to insert a motor. We will have to cut a similar notch in the AR-2050.
ADDITIONAL NOTE: Notice that Estes part numbers (e.g. AR-2050) tell you quite a bit about the part. The “AR” tells you what kind of part it is (Adapter Ring in this case) and the 2050 tells you that it is sized to adapt between a BT-20 body tube and a BT-50 body tube.
The second modification (improvement) we will make is the addition of an engine block above the retention hook inside the motor tube. This is just an added precaution and gives the head end of the motor a little more surface area to “push” against during the boost phase. This is another inexpensive piece of insurance and I will add these to any kit that relies solely on the hook to retain the motor in position during flight.
After glueing the thrust block and second adapter ring in place, we now we have our completed engine mount:
This completes steps 1 and 2 in the kit instructions and our engine mount is now ready to be installed in the main body tube. This is actually step 5 in the instructions as steps 3 and 4 deal with ataching the shock cord and shock cord mount in the main body tube. However, as described in an earlier post we will not be using the kit supplied shock cord. So we will come back to steps 3 and 4 in a later post. It is often easier to delay shock cord atachment until later in construction with smaller models where the shock cord is to be mounted to the inside of the main body tube.
ADDITIONAL NOTE: When I first built this kit back in 1977, I used good old Elmer’s glue for most of the construction. While that’s fine for smaller rockets that won’t have to endure massive boost forces, I think that there are better options out there. Some people like to use cyanacrylates (super glues) for just about everything but I find them unforgiving and prone to getting finger prints on the exterior parts of the model (maybe I’m just sloppy). So for construction of this kit, I have chosen to use two-part epoxy as my primary adhesive. It is slightly more cumbersome to use than other adhesives due to having to mix each batch as you go, but the fact that it cures in 5 minutes, is strong and ages well (not a lot of shrinkage or brittleness) makes it worth the extra effort in my opinion.
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