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THUNDERBIRD SAM DESIGN
CHANGES FROM PROTOTYPE
Once I was able to inspect some actual photographs of the Thunderbird, I was surprised to find that my Basset prototype was not terribly inaccurate. The length of the sustainer and boosters was very close relative to the width of the 54mm tube used in the boosters. There was a tapered boat tail that was not at all apparent in the photo I saw back in 1975 (the photo was from a rear angle) - so not only did I not include the boat tail, I also miscalculated the diameter of the sustainer. I learned from the web site of my British colleague, Adrian Hurt, that the Thunderbird had more than one forward fin configuration for the sustainer, and some photos show that I made those fins fairly well. The same was true with the booster fins. I was not real close with the shape of the aft sustainer fins. The picture at the right shows why they are difficult to discern.
These are the main changes required to make the second Thunderbird a more accurate scale representation:
- Increase sustainer diameter from 3" to 4"
- Increase booster lengths slightly
- Increase sustainer length slightly
- Add boat tail
- Add asymmetrical booster nose cones
- Add vectored booster exhaust shrouds
- Add miscellaneous cosmetic changes
This photo shows the Thunderbird sustainer prior to gluing compared to the sustainer from the RAF Basset prototype.
COMPUTER SIMULATIONS
I used RockSim 5.0 to model the design to help determine Center of Pressure. The new functionality that allows special cluster configurations was extremely helpful in creating the parallel boosters. (Click to download to RockSim 5.0 Thunderbird File)
There was no way to attach the booster fins to the boosters - they are attached to the sustainer in the simulation - so you'll notice that the above drawing shows the sustainer fins bisecting the boosters rather than passing between them.
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I had to create some really thick 'fins' to emulate the asymmetrical nose cones, but that was really just for the 3D rendering. (It throws the Coefficient of Drag calculation off severely; so input a static value of 0.75 to 0.8 when you do a flight simulation).
The color variation on the boosters in these drawings is just to highlight the different parts.
(Note - I really like the RockSim 5.0 software! I've built a lot of rockets on my computer that I'm glad I never built on the workbench! It's a great tool, and the 3D rendering in version 5.0 is a lot of fun.)
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