I'm probably going to clone an Estes K-6 Ranger sometime over winter for NARTREK Silver.

Looking at the Ranger instructions (as posted on the JimZ site; also a copy is included in the Silver packet) I'm surprised to see the fins are cut from BFS-30 balsa sheet. BFS-30 indicates the thickness is 3/32".

Surprised because in the first version of TR-6: Cluster Techniques, which was issued the same year as the Ranger (1963), it says 1/8" is the best thickness for cluster rocket fins; and in the 1967 revision it says less than 1/8" thickness can be used but should be reinforced with paper lamination or with balsa ribs parallel to the root edge.

Yet from the same time and same company here's this cluster rocket with long, swept back fins hitting the ground first, and they're 3/32"!

Even more peculiar, in 1965 the Big Bertha comes out, essentially a single motor Ranger, and uses BFS-40 (1/8") for its fins! (Although the Big Bertha plans published in 1963 in Model Rocket News called for BFS-30.)

So what's the story? I presume it really is true the Ranger had 3/32" fins originally. Were they ever thickened to 1/8" before the kit's discontinuation in 1971? Or strengthened? Or was Estes really continuing to sell a design that their own TR advised against?

(Me, I'm considering 1/8" basswood. Maybe papered.)

__________________
Rich Holmes
Camillus, NY
Secretary / newsletter editor
Syracuse Rocket Club

http://richsrockets.wordpress.com

I have only seen one Ranger kit before; one I picked up about a year ago. It is probably from the end of the kit run in the very early 70s (early Damon era). It has 3/32 fin stock. I recall being a 'bit' surprised at that choice, but probably is fine for most cluster flights with A and B engines. A cluster of C6s might seem to be pushing things.

Seems like I recall my vintage Scrambler kit has 1/8 fin stock. If the Big Bertha also had 1/8th fin stock, one would think the logical choice for the Ranger would have been the same.

Earl

__________________
Earl L. Cagle, Jr.
NAR# 29523
TRA# 962
SAM# 73
Owner/Producer
Point 39 Productions

Rocket-Brained Since 1970

My original that I built a LONG time ago has 3/32 fins, as do my Astron Cobra and Astron Scrambler.
The Scrambler lists the B14-5 in a cluster with 3/32 fins as an acceptable motor, which has almost 3 times the kick of a C6 cluster.
I have NEVER had a problem with 3 C6-5's clustered with 3/32" fins.
Glue them on correctly with good fillets and you will have no problems.

1/8" fins on a BT-60 look too 'thick' anyway.

__________________
When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, and HAVOC !

It probably also depends on if it Is C grain balsa.

__________________
BAR in his second tour of duty.
Nar# 32629

Yes, the Scrambler (and Cobra) instructions specify BFS-40, or 1/8".

__________________
Rich Holmes
Camillus, NY
Secretary / newsletter editor
Syracuse Rocket Club

http://richsrockets.wordpress.com

My Ranger clone has 1/8" thick fins. I don't recall which version of the plans I used, but I think it was one of the older ones.

It would be tricky to mount the Ranger's fins TTY, because of the irregular depth available. If it weren't for that, TTW would be an ideal way of stiffening the fins and keeping them on under high-thrust boost.

__________________
NAR #27085 - Oregon Rocketry - SAM

Rich,

The differences in thickness were likely trade-offs in both refinement of the design over time, and in the set-up of kit making. Here's something else to look for: The shape of the Ranger fin is slightly different from the Bertha. Not eye-popping different, but not quite the same either. You might also notice that the BB fin shape from the original MRN plan to the kit version changed over time.

The best way to think about the Ranger and the BB is as a family of designs, which includes the Apogee and Apogee II, the Mini Bertha, and even the modern Baby Bertha. Since the BB was a derivative of the Ranger, you might use the early MRN fin pattern as the starting point.

It's been a while since I looked at those fins, but I know there were differences between all of them.

__________________
Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
BARCLONE Blogsite -- http://barclone.wordpress.com
BARCLONE Forum -- BARCLONE Forum

BARs helping BARs

SAM 0044
AMA 352635

Yeah, I've looked at comparisons of the size and shape of the Ranger, Big Bertha, and Baby Bertha... all similar but all different.*

That doesn't surprise me, but the 3/32" thickness for the Ranger at a time when (and up to 8 years after) the Estes Technical Reports were recommending 1/8" does. Unless there was a change to a thicker fin early on, but I'm not aware there was.

* The MRN (EIRP) and kit BB fins actually were just about the same, according to the information I've found, except for the thickness. Though I think the kit BB fin has changed some over the years, so it would depend on which kit you're comparing.

Attached Thumbnails

 

__________________
Rich Holmes
Camillus, NY
Secretary / newsletter editor
Syracuse Rocket Club

http://richsrockets.wordpress.com

Let's not forget that the nose cone has changed shape over the years also. If you just want a sport Ranger, use a Big Bertha kit with its 1/8" fins and plastic cone and just swap the mount. If you want it to be retro with the 3/32" fins, you also need to locate or turn the proper shape nose cone for that period.

__________________
I love sanding.

I'm actually thinking BNC-60L nose (got one already from BMS) but probably 1/8" basswood fins. If that's inconsistent, well, I'm inconsistent. But to me the look of the nose cone matters, whereas the look of the fins is subordinate to wanting them stronger.

__________________
Rich Holmes
Camillus, NY
Secretary / newsletter editor
Syracuse Rocket Club

http://richsrockets.wordpress.com