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  #1  
Old 09-24-2018, 09:50 AM
Andy63 Andy63 is offline
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Default Black Brant II - FSI Version

Hi all.

I'm piecing a build together of FSI's Black Brant II. I downloaded the instructions from oldrocketplans.com/fsi/fsiMRK-14/FSI_Black_Brant_II.pdf. I printed the fin page and began to take some measurements. Compared with the scale drawing from G. Flynn (11/1/1971) the FSI fin seems to come up being on the small side. The tail cone also seems to want to be fatter at the nozzle end, too (1.75" vs 1.4" @ 1/8 scale). Has anyone else noticed this? I'm finding it rather difficut to find more than just a few sources of scale data on this bird.

Thanks all.
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  #2  
Old 09-24-2018, 10:00 AM
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Quote:
Originally Posted by Andy63
Hi all.

I'm piecing a build together of FSI's Black Brant II. I downloaded the instructions from oldrocketplans.com/fsi/fsiMRK-14/FSI_Black_Brant_II.pdf. I printed the fin page and began to take some measurements. Compared with the scale drawing from G. Flynn (11/1/1971) the FSI fin seems to come up being on the small side. The tail cone also seems to want to be fatter at the nozzle end, too (1.75" vs 1.4" @ 1/8 scale). Has anyone else noticed this? I'm finding it rather difficut to find more than just a few sources of scale data on this bird.

Thanks all.

IIRC, that was needed to fit in the motor tube and not be so thin that it ripped itself apart on the lathe. I did a lot of sanding due to a fairly rough finish on the boat tail, but I didn't try to make it perfectly scale. It's been a lot of years and I don't have mine in front of me or I'd measure it for you.

Don't forget that it took an FSI 27mm motor and you will need to go 29mm. You can go 24mm if you really want to scale the boat tail, since we have composite E's that are plenty strong for a safe flight and some low end 24mm F's.
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  #3  
Old 09-24-2018, 10:34 AM
astronwolf astronwolf is offline
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Sounds to me like you need to make a decision. Do you want to clone FSI's kit, or do you want a flying scale model of a Black Brant II? Both are scale models, but one approach will be a scale model of a scale model, and the other approach is just a scale model,

I recommend building your own scale model of a Black Brant II rocket using ST-20 tubing. It will be like the FSI kit, but better. Use the link below, if you haven't found it already. If you don't have Rockets of the World, buy it or find a local rocket club member who is willing to help you out with some data.

George Flynn's scale data appeared in the December 1971 issue of Model Rocketry Magazine:
http://www.ninfinger.org/rockets/Mo...04n03_12-71.pdf
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Old 09-24-2018, 11:03 AM
Andy63 Andy63 is offline
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Yep. Going with a 29mm mount (using an LT-115 series tube). The nearest ring off of erockets that matches the 1.4" diameter of the FSI is the SEM-CR-115-150P at 1.5". But when you do the math off the scale drawings, the narrowest part of the tail cone is 14" which works out to be 1.75" @ 1/8" scale. Its quite perplexing as to why the tail cones are/were made so narrow.

I've come to realize the FSI kit is only semi-scale. I just thought it may be a little closer in scale than it is (the nose cone is perfect). Just one of these things you find out when you nit-pick the details. End the end, I'll probably put it together knowing the fins are a bit undersized as well as the tail cone and appreciate it for what is it - still a **** good looking sounding rocket!
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Old 09-24-2018, 11:07 AM
Andy63 Andy63 is offline
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Quote:
Originally Posted by astronwolf
Sounds to me like you need to make a decision. Do you want to clone FSI's kit, or do you want a flying scale model of a Black Brant II? Both are scale models, but one approach will be a scale model of a scale model, and the other approach is just a scale model,

I recommend building your own scale model of a Black Brant II rocket using ST-20 tubing. It will be like the FSI kit, but better. Use the link below, if you haven't found it already. If you don't have Rockets of the World, buy it or find a local rocket club member who is willing to help you out with some data.

George Flynn's scale data appeared in the December 1971 issue of Model Rocketry Magazine:
http://www.ninfinger.org/rockets/Mo...04n03_12-71.pdf



Yes - I have Rockets of the World, I found the MRN article, too. I also found this: https://www.argoshpr.ch/j3/articles...ack%20Brant.pdf

And I have been asking myself all those questions (we like to torment ourselves, don't we?).
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Old 09-24-2018, 11:20 AM
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Quote:
Originally Posted by Andy63
Yep. Going with a 29mm mount (using an LT-115 series tube). The nearest ring off of erockets that matches the 1.4" diameter of the FSI is the SEM-CR-115-150P at 1.5". But when you do the math off the scale drawings, the narrowest part of the tail cone is 14" which works out to be 1.75" @ 1/8" scale. Its quite perplexing as to why the tail cones are/were made so narrow.

I've come to realize the FSI kit is only semi-scale. I just thought it may be a little closer in scale than it is (the nose cone is perfect). Just one of these things you find out when you nit-pick the details. End the end, I'll probably put it together knowing the fins are a bit undersized as well as the tail cone and appreciate it for what is it - still a **** good looking sounding rocket!

I was thinking backwards on your 1.75" vs 1.4" numbers and was thinking it was underscaled.

I'm guessing they had one or two reasons for it. They probably didn't want a big thick heavy hunk of wood back there so they may have cut the angle sharper to remove some mass. Possibly a better reason is that sometimes things don't look right to the eyeball when done to scale, so they exaggerate them. The Centuri Saturns (and more recent versions of the Estes models) are an example. Most people like them because you can see the corrugations better, but they are considerably exaggerated. Of course, there is another option. They could have just screwed up.
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  #7  
Old 09-24-2018, 01:14 PM
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Questor Questor is offline
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Default FSI pdf?

Was the fin template a pdf? Pdf's are small. You would need to enlarge abit to get the proper size.
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  #8  
Old 09-24-2018, 04:51 PM
Andy63 Andy63 is offline
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Quote:
Originally Posted by Questor
Was the fin template a pdf? Pdf's are small. You would need to enlarge abit to get the proper size.


Good tip. I did print the fin page from oldrocketplans, and it does have a ruler. I know it is printed correctly because the units on ruler next to the fin matches the units on a physical ruler.
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  #9  
Old 09-24-2018, 06:45 PM
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Comrades:

eRockets has all the Semroc parts including the fins to replicate an FSI Black Brant. I know this because I have them and have for several years. As I recall, he had the boat-tail for both 24mm and 29mm power. The plans are available on YORS (see the link at the bottom of the page).

Post some build pictures, I'd love to see it and I am certain I am not the only one.
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  #10  
Old 09-24-2018, 07:14 PM
BARGeezer BARGeezer is online now
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Quote:
Originally Posted by MarkB.
Comrades:

eRockets has all the Semroc parts including the fins to replicate an FSI Black Brant. I know this because I have them and have for several years. As I recall, he had the boat-tail for both 24mm and 29mm power. The plans are available on YORS (see the link at the bottom of the page).

Post some build pictures, I'd love to see it and I am certain I am not the only one.


Da, comrade:

http://www.erockets.biz/semroc-bals...sem-btc-20bb24/
http://www.erockets.biz/semroc-bals...st-20-3-0-29mm/
http://www.erockets.biz/semroc-bals...l-sem-bc-20107/
http://www.erockets.biz/semroc-lase...s-sem-ffs-1014/

The parts for my clone have been languishing in a box for months now. Too many projects ahead of it in the queue. The 29mm wasp waist tail cone is in stock at erockets, but the 24mm one is out. I would also love to see some build pictures as well.
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