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Quick help on new Thor

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firemanup

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Any suggestions here from anyone would be appreciated.

I've started construction, and found a small error in the measurement in the directions. The directions say the rear fin root is 6 3/4" long, it's actually 6.5" long.

I doubt it makes any difference, but should i move the rear fins up the 1/4 inch to keep the gap between front and rear fin the same distance the directions list. (1 5/8")

Or should i move them back and lengthen the gap between front and rear fins by a 1/4".

I imagine it doesn't matter but am not sure. If it doesn't make any difference which would give a better "whistle" the front and rear fins closer together or farther apart by a 1/4"?

Thanks
 

lalligood

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firemanup,

I can definitely relate to your confusion with the Thor. I went through the exact same thing when I built & finished mine back in October. It seems that the design of the kit has changed slightly over the past year or so but the instructions appear to have not been modified to compensate for changes in the kit. (Another example is the mentioning of two 17" payload sections when they are now in fact, 10" & 24"...) Take look at the review on EMRR & you'll see what I mean by the differences in design...

I built mine so that the aft fin(s) are mounted against the aft centering ring & the forward fin(s) are sandwiched between (read: touching) both the forward & mid centering rings. Forgive me for not being able to give you an exact measurement right now! (If you want an exact measurement, PM me & I'll take a look when I get home tonight.) Measure the distance of the gap of the fins from there. Obey the old addage: "Measure twice; cut once". If nothing else, cut the gap too big & trim it to fit.

Lastly, I have great confidence that you'll be pleased with the whistle that the fins create during flight. I launched my Thor for the first time just this past Saturday (12/13) on a Pro38 I285. As the roar of the motor began to trail off, there was a distinctly clear whistle for several seconds as it continued skyward! :D :D

Keep us up to date with your progress!
 

firemanup

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Thanks for the info lalli,

I ended up just splittin the difference....

Motor tube is built, fin slots cut, fins beveled, nuttin to do now but wait on epoxy to dry during the oncoming stages.....
 

bsexton

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Your Thor looks like it just came off the showroom floor as usual - great job!
 

bsdrocketry

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Okay guys,

First, the lower fins should rest on the rear centering ring. With good fillets, the fins will not rip off regardless where you mount it. Now my 4" Thor with a 75mm mmt is a different story. Can you say all-thread?

Second, the design of the Thor has changed a little since the origianl design. More room in the main payload section was requested from our customers. We took 7 inches from the avionics section and put in on the main payload section.

Third, the fin root on the lower Thor fin is indeed 6.5" long not 6.75". We are reviewing the assembly instructions for the 4" Thor to make corrections for this error.

It is a beautiful piece of work.

Mark Saunders, KJ7BS
BSD High Power Rocketry
Glendale, AZ
info@bsdrocketry.com
http://www.bsdrocketry.com
 

firemanup

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Thanks Mark,

I did place the lower fins on the rear centering ring, after internal fillets. So we should be in good shape.......

Forward fins are sandwiched between the two upper centering rings...

And she came out looking sweet......
 
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