Check the 18mm yellow tube - there may be a slit already cut for the upper bend of the engine mount.
It might not be in the right location, usually it's too close to the top end of the tube.
TIP: Slit the tube as shown in the directions. Make sure that pre-cut slit is on the upper side where the thrust ring will be glued in. This will strengthen the the pre-cut area on the tube.
The red rings won't easily slide onto the yellow tube.
Notice the compression bulges on the inside of the ring.
I wrapped some 400 grit around my Sharpie to sand down the raised bumps.
On the left is the lower ring notch,
On the right is the upper notch which sets over the top bend of the engine hook.
Here's the finished 18mm mount.
No tape wrap is needed on this one.
The 18mm mount slides into the 24mm mount.
You'll have to do a friction fit to retain the smaller mount so it doesn't get blown out at ejection.
Here I tried a tape wrap around the two engine hooks. This probably isn't the best plan.
I'm thinking that a possible mod to eliminate friction fit could be to split instead of notch the second red centering ring and glue it even to the end of the motor tube and use vinyl tape for hook retention. Then the 24mm engine hook will have something more to grab onto instead of just the edge of the 18mm motor tube.
ReplyDeleteAlso forgot to mention if you also move the forward red centering ring even with the end of the tube you will have both CRs flush against the tabs of the 24 mm motor hook when the 18mm adapter is in place. No backward movement at ejection.
DeleteHi BAR,
DeleteThese models were being built for Quest, according to their provided instructions. I have already written up suggestions, very similar to what you've commented here.
Isn't the usual pattern for motor adaptor (one to fit a smaller-diameter motor into a model that uses larger diameter motor) is to construct the adaptor itself is sized the same as the larger motor casing? You'd use three thick centering rings -- with the fore and aft centering ring positioned at the fore and aft part of the adaptor, and the middle ring allows the motor to be properly centered (as the aft centering ring often ends up outside the motor mount tube). If the adaptor uses a motor hook, the aft ring would be split to allow the motor hook to be flexed. The smaller motor usually ends up aft of where the larger motor would be (typically around 1/4") -- but this shouldn't adversely affect the CG since the combined weight of the smaller motor and adaptor generally is less than that of a larger motor itself.
ReplyDeleteOn a side note.-- As I'd gotten into model rocketry back around 1976, it was several years after the short motor series had been discontinued (and the few models that used them had already been revised for 13mm motors). I do remember that I'd gotten several packs (in the "diamond box" package) of as a birthday present, and amongst the lot I'd ended up with packs of A5-2S, which had me puzzled briefly. I'd noticed that they were the same diameter as the "regular" 18mm motor, but shorter in length, and had an extra-thick casing. I did notice that they were the same length as the 13mm "mini" size motor, and the inner diameter of the casing was a similar match. At that point I'd surmised these might be an evolutionary middle step between the 18mm and 13mm motor (the then-current catalog I had seemed to indicate that the 13mm motors were relatively new). I ended up cutting off a piece of spent 18mm casing to use as a spacer that made up for the shorter length and used the motors in my models.
ReplyDeleteOf course, by now there will probably some collector types screaming "NOOOOOO!!" in response to having used up those motors. (shrug)
Hi Naoto,
DeleteI've cut up many used engine casings over the years to make spacers and engine blocks. I remember that transition from 18mm short engines to 13mm mini engines. I had quite a few adapters then.