Adjusting from Estes Series III

I've casually looked through google for an answer to this one. Not much info that I could find. I've been working to build ancient Estes rockets. Many of them were designed for series III engines. What changes do I need in order to modify them for use with current engines? I've never done this type of calculation before. I've considered simply extending the BT by the same amount as the length difference from the series III to modern engines, but not sure that will adjust the CG/CP ratio enough. Any suggestions?

Better to just put a mount for a 13mm motor (the "T" motors Estes sells) in 'em. Also, when Semroc gets back up an running perhaps the short casings will be available. In that case you can press (or glue) an Estes 13mm motor into one and use it in an unmodified model designed for the old short Series III motors.

Take a spent 18mm motor, and cut it down to the same length as the series III, take 1 in off it, from the Nozzle end. Then you should be able to use this as an adapter for the 13mm engines. You can see an explanation here https://modelrocketbuilding.blogspot.com/2012/10/launch-prep-some-hurdles-part-4.html

Kruegon said:

... I've been working to build ancient Estes rockets ... Any suggestions?

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Bookmark the ninfinger site. All the ancient scrolls and papyrus and not just Estes. www.ninfinger.org/rockets/

From the 1971 Estes catalog:



+1 on adapting the motor mount to todays 13mm motors.

I like to do it Mikey's way, build the designs original, and make a "shorty" engine using a 13mm friction fit in a chopped 18 mm casing. This makes a fairly authentic series III motor, which had a thick casing with an inner diameter about the same as a mini.

Semroc makes shorty adapters too, which were simply a 1.75" long 18mm casing. Perhaps they'll be available when they reopen.

Couldn't I just use centering rings and a BT-5 mini engine mount like the mini fatboy or better yet the mini patriot?

Kruegon said:

Couldn't I just use centering rings and a BT-5 mini engine mount like the mini fatboy or better yet the mini patriot?

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Yes. Again, personal design decision. Some guys just make adapters out out whatever they have handy. Like spend 18mm engine casings.