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Tuesday, June 26, 2012

Estes Thor Agena B Build Part 23 Removable Fin Unit

The Estes kit had clear fins "glued" to a clear coupler wrapped around the body tube.
After my experience with the 260 Booster's clear fins breaking off on landing, I wanted to try something else.

On the right is the OOP Dr. Zooch Discoverer Thor, with it's small Delta shaped fins.
(The first two pictures are from John Lee's review on rocketreviews.com)
You can see the resemblance between the Thor Agena B and the Discoverer Thor.

Trying to stay away from clear fins, I thought I'd compromise a bit and make a removable fin unit with the Delta shaped fins. Not scale, but still in the same Thor family.

Looking at the second picture, I could get a rough idea of the fin size from the 1" square grid on John Lee's cutting board.

The original Thor Agena B kit fins have a 1 1/2" root edge.
I'll draw my Delta fins with that 1 1/2" root.
The leading edge is a 45 degree angle to the outside of the trailing edge.
The four fins were cut from 3/32" balsa.

An outside wrap was cut from some scrap BT-60 tubing I had in my spare parts box.
Cutting the sleeve down it's length leaves a gap. The open gap will allow the sleeve to be taped tight around the body tube.

The original kit had three clear fins. This model will have four smaller fins.

An email from Dr. Zooch let me know that his Discover Thor kit had 1/2 oz. of weight in the top of the adapter. The smaller fins in the Zooch kit made nose weight necessary.
I'll have to figure out a way to put clay weight near the nose cone. 

The sleeve was cut to 2 3/8" long. It'll cover and protect the nozzle, turbine exhaust and vernier assemblies on a rough recovery.
This will set the fins a little lower and help with stability.

Here's how the fins will look on the removable fin unit. Note the nozzle is covered.

While it's not scale, I think it still captures the feel of the Thor rockets.
I don't display my Dr. Zooch rockets with the flame fins installed. I'll display this one with the slip on fin unit removed.

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