Is the fin pattern for the original Estes Astron Ranger the same as the one for the Big Bertha? I'm restoring an old Ranger and have a fin pattern for the Bertha. I have a sneaking hunch that the Ranger was just a 3-engine Bertha with a payload section.

Joe

It's the other way around. The Ranger came first, then Vern stuck a single mount in a solid 18" tube (no payload section) to make the Bertha.

I think the fins were the same, at least for the early ones that you had to cut from patterns yourself. I have no idea if they are the same now as they were back then. The Alpha's fins have mutated a little over the decades so the Bertha's could have also. Print the pattern out and compare it to your current Bertha fins.

http://www.spacemodeling.org/JimZ/estes/k-06.pdf

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There is actually a slight difference in the shapes. Not really noticeable at first glance, but it is when you measure them, or place one from the Ranger up against one from the Big Bertha. IIRC, the Ranger fin is just a bit smaller.

I'm inclined to think the difference was more accidental than intentional.

Look at the files from JimZ, especially between the K-6 and the DOM/EIRP plan for the Bertha, then compare them to later Berthas. It's a small difference, but it's there.

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Is the DOM/EIRP plan larger, or the modern Bertha, or both? If the DOM plan is larger, could it be attributed to error in early mass photocopying/mimeographing and later scanning, or is there a difference in angles?

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The Ranger and Big Bertha were intended to have the SAME fins.
As explained directly by Vern, the BB is a single 18mm powered (instead of 3x18 cluster) Ranger minus the payload section.
The Ranger was designed for 3 engine power as the designers did not think available single engines were powerful enough to launch a rocket the size of the Ranger. They obviously were wrong. A Ranger with nothing in the payload gets quite high in a hurry on just a 3xA8-3 cluster as this amounts to a 3/4 C24-3

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The Bertha fins may have changed several times along the way; I think we had a discussion of that here before.

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Looking at the fin patterns, there is a difference in the outlines between the EIRP 13 plan and the K-23 plan. This follows the original thought about the BB being a "single-engine Ranger".

The later outline for both the K-23 and 1223 versions are longer along the "tip" edge.

Attached is a composite image of three fin outlines, for the EIRP, K-23, and K-6.

Attached Thumbnails

 

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I am not really concerned about the evolution of the fin design of the Bertha, or the Ranger , for that matter................all I really need to know is this: was the fin pattern for the original K-6 Ranger identical to that of the original K-23 Bertha? I think GHRocketman is stating that they were identical. Any dissenting views??

Joe

If you compare the fins in CP's drawing, you will see that they are very close but not identical, just like he said. They are close enough that the difference could easily be explained by someone making a slight error when drawing patterns in the sets of instructions for the new kits, or someone literally outlining a Ranger fin that had been sanded a little unevenly for the early Bertha plans.

They are close enough that if you sand the edges round on fins from all three patterns and mount them on a rocket, a person would not notice unless asked to compare them. Even then they would expect it was just slight differences in the way the pattern was cut and the edges were sanded.

Of course, you could have just looked at CP's drawing like I did and seen for yourself.
Now you have to decide whether to use the Ranger pattern for authenticity, or just use a Bertha kit cause they are already cut for you.

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The variation is a bit more than that. The Ranger K-6 fin is a bit too short; put all three on one rocket and it wouldn't stand right.


Yes, I've aligned the upper ends of the fins, but even with the lower end of the root edges aligned, the Ranger fin is still short.

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