Saturday, September 13, 2014

Estes Black Brant III, Part 2, Fin Drawing

I found the instructions and fins at Old Rocket Plans HERE

Buzz McDermott submitted the plans and placed a ruler reference below the fins.
TIP: If you ever submit plans to a website, place a ruler in the picture for size reference.

The fin picture was copied and dropped into Corel Draw.
I drew a 1" square box and matched the ruler in the picture to the 1" span.
A fin outline was traced. 
To be sure I was tracing the fin outline and not just a shadow, the original tracing was set on the two other fins. Small adjustments were made, the final fin drawing is on the right.

I had assumed the kit fins were 3/32" thick but JeffyJeep went with 1/16" thick basswood.
Page 344 of Peter Alway's Rockets Of The World shows the Black Brant fins being thin so the 1/16" thickness was probably included in the Estes kit.
As shown in the upper right, the fins will get the scale taper so basswood will be used instead of balsa for strength.


  1. Fin thickness unfortunately is missing information on a lot of the OOP plans online. In most cases it's probably not a big deal but here's a case where I'd say it definitely matters. For old Estes plans with balsa sheets having BFS- part numbers there's a table of thicknesses at . That's how I learned recently the K-6 Ranger fins were not 3/32" or 1/8" but 3/16"... another case where the right thickness is important.

  2. Hi Rich,
    I've used that chart many times before.
    I never understood the reasoning behind the Estes numbering system whether it was tubes, nose cones of fin stock thickness.
    The Black Brant III information came from a combination of the Rockets Of The World book by Peter Alway and the Estes kit information.
    ROTW showed the fins to be very thin so I started with the 1/16" basswood.
    Thanks for the information on the Ranger - I never knew the fins were that thick!

  3. Er, they weren't, apparently! I just looked again and the instructions say BFS-30, which is 3/32". What got me confused was on the copy NARTREK sent out, 3/16" is written next to it.

    And I figured that made sense, for those long, swept back fins on a 3-motor cluster. Or at least 1/8", right? But no, apparently they were 3/32". Which surprises me.

  4. That surprises me too!
    The Ranger instructions at JimZ say BFS-30 and that's 3/32" thick.
    But - the Big Bertha fins are BFS-40 - 1/8" thick!
    I would think the three engine cluster would use the thicker fins.
    Who knows why . . .

    1. Especially since TR-6, published the same year the Ranger was introduced. says the best fin thickness for cluster rockets is 1/8". Later version (1967) of TR-6 says under 1/8" can be used but fins should be strengthened with paper lamination or balsa ribs. Yet in 1967 the Ranger was still on the market and as far as I know still had 3/32", un-strengthened (long, swept back!) fins...