[WANTED] Estes ARCAS (K-26) Info
 

Working on a sim of the ARCAS, and I've got a conundrum... JimZ's scan of the instructions clearly states that the kit uses a JC-55C. The Estes 1971 catalog gives it as 1.3". OR's default gives it as 1.25", and Semroc says that a JC-55C is 1".

When it comes to this kit (the K-26) which spec is correct?

Also need to know more about the fins... Those shapes are pretty complex, and if I can get the length of the fin support pattern, I should be able to scale both fin shapes based on that.

Thanks!
Jim

Comrade,

Note that the K-26 was a little short scale wise. The "correct" BT-55 length should be 20.24 inches as per Rockets of the World. The JT-55C I have is 1.25 inches, I have a later blue card version but it still has the balsa nose.

Thanks for the reply!

You wouldn't happen to have the instructions for your version would you?

Let me look.

The Estes ARCAS kit was used to produce the original Cherokee-D -- I found these discussions about the nose:

http://modelrocketbuilding.blogspot...art-5-nose.html

http://www.rocketryforum.com/showth...okee-X-nosecone

I always thought is was a secant ogive but according to Carl in the TRF thread it wasn't quite that either...

D'oh! I just realized something...

To scale a .pdf file when you are unsure of something's scale is to find out something about it that is a constant. In the file from JimZ's site the fin pattern is on the same document as the fin spacing guide. The ARCAS has 4 fins, and uses a BT-55. So, if that's the case... A BT-55 is 1.325" in diameter... Multiplied by Pi, gives us the circumference , divide that result by 4... and you get a result of how far the fins should be spaced (1.04065").

Downloading the image from the .pdf has them at 113 pixels apart

(104x100)/113 = 92.035

The image needs to be reduced by 92%...

And

I've got my fin pattern's dimensions. Sure there's a small margin of error due to rounding, but it's the best I can do.

You know . . . .

You could ask Randy to make a sheet of K-26 fins and mounts. Carl had the pattern on the machine. I know because I have one. Although its not presently on the eRockets site, it wouldn't hurt to ask. . . .

Talked to Randy about the ARCAS today, and he told me that they have a BT-60 based one, and another. I'm just simming this up, and not really interested in a build... yet.

Randy might be a little confused.

The Estes K-26 ARCAS is BT-55 as you've sim'ed.

Semroc had/has two ARCAS', the KS-8 built on Series 15 tubing for 18mm power and the KS-5 SLS for mid to Level 1 power on heavy-walled BT-70.

If you can find one, BMS made a Peter Alway-designed ARCAS on BT-50 that's fun to fly on 13mm power .

There are others, but these are the ones, I've built.

You know, I should have responded to this earlier... I'll chalk up the delay to being sick (food poisoning), and fatigue following a really bad weekend (I work weekends).

I honestly didn't know that the BNC/PNC-55AC was based on this design.

Thanks for the info!