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  #81  
Old 11-23-2011, 11:35 PM
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blackshire blackshire is offline
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I think the BT-40 was an "adopted" tube size, from leftover MMI (Model Missiles, Inc.) body tubes for their Aerobee-Hi and Arcon kits that Estes acquired when MMI went bust. Estes also sold the vinyl MMI Aerobee-Hi/Arcon nose cones at that time.
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  #82  
Old 11-24-2011, 12:01 AM
vulcanitebill vulcanitebill is offline
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Quote:
Originally Posted by blackshire
I think the BT-40 was an "adopted" tube size, from leftover MMI (Model Missiles, Inc.) body tubes for their Aerobee-Hi and Arcon kits that Estes acquired when MMI went bust. Estes also sold the vinyl MMI Aerobee-Hi/Arcon nose cones at that time.


I have one of those long vinyl nose cones, and the one that I have fits a BT30.
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  #83  
Old 11-24-2011, 12:27 AM
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Quote:
Originally Posted by vulcanitebill
I have one of those long vinyl nose cones, and the one that I have fits a BT30.
Here is a 1965 Estes Free Plan for an Aerobee-Hi that used BT-40 (see: http://www.spacemodeling.org/JimZ/eirp_32.htm ). It used a vinyl nose cone whose designation was PNC-40G. I wonder if your nose cone might be one of the leftover firework missile parts that Estes Industries sold in the early days (Vern Estes was in the fireworks business before he founded Estes Industries)?
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Last edited by blackshire : 11-24-2011 at 12:29 AM. Reason: This ol' hoss done had to correct a typo.
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  #84  
Old 11-24-2011, 01:17 AM
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Quote:
Originally Posted by foamy
Thanks for the answer. It's interesting. I'll have to get around to building one some day—kinda like I did with the 'Bertha.


Though I've heard from good sources that over the past few years the Hi-Flyer is the big seller.
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  #85  
Old 11-24-2011, 01:31 AM
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Note that prior to 1968 and the metric conversion, the NAR Total Impulse chart was a bit different.

It didn't nicely double over the whole range.

1/4A 0 - .175 lb-sec
1/2A .176 - .350 lb-sec
A .351 - .700 lb-sec
B .701 - 1.200 lb-sec Whoops!
C 1.201 - 2.00 lb-sec Whoops! again!
D 2.01 - 4.00 lb -sec ah, back to doubling
E 4.01 - 8.00 lb-sec
F 8.01 - 16.00 lb-sec
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  #86  
Old 11-24-2011, 02:02 AM
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Quote:
Originally Posted by Royatl
Though I've heard from good sources that over the past few years the Hi-Flyer is the big seller.
Due to its large fin area and Center of Pressure/Center of Gravity relationship, the Hi-Flyer can be (like the Estes Phoenix missile scale kit) one of Estes' more...exciting rockets to fly, especially on the heavier "C" motors that move the CG more rearward--"No two flights the same!" :-)
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  #87  
Old 11-24-2011, 07:57 AM
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Quote:
Originally Posted by Royatl
Though I've heard from good sources that over the past few years the Hi-Flyer is the big seller.


I will say that I have purchased a large number of Hi-Flyers myself. I've only built one as a Hi-Flyer, and that one was built with a 13mm motor mount. Why did I buy so many of them (and continue to do so)? Two reasons - it is cheaper than any other BT-20 based rocket ($6-7 as opposed to $8-9 for a Wizard or Viking) and the body tube is a bit longer than that in the Wizard or Viking. Thus, the Hi-Flyer is really good for kit bashing into various types of contest models (18mm boost glider pods, egg-on-a-stick boosters, quick and dirty streamer duration models, etc.). Because of the price, that sucker's just a kitbasher's dream!

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  #88  
Old 11-24-2011, 10:33 AM
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Quote:
Originally Posted by vulcanitebill
So obviously my FSI engine mount doesn't use a BT40.
Could it have instead been an Estes motor shipping tube? These were usually light blue, and should have been about the right size for the FSI motor.

Doug

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  #89  
Old 11-24-2011, 10:58 PM
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Quote:
Originally Posted by vulcanitebill
I was trying to reconcile bits of my memory and I think I jumped to incorrect conclusions. I just took some measurements and that changes my conclusions.

I thought I remembered hand rolling a paper tube to use as a motor mount. The motor tube in the rocket is thinner than normal Estes tubes, but smoother on the inside than I would have expected myself to make at age 14 or so. The ID of this tube is 0.945" and as I recall it fits the FSI engine about like an Estes BT20 fits their 18mm engines, or maybe a bit larger. That should be a good gauge of what the FSI engines required.

I knew that the other rocket that I still have used a tube somewhere in between BT20 and BT50, and I had forgotten about BT40 until I read this thread. This rocket has centering rings at the back end and a balsa adapter glued into the front end so I can't measure the ID. The OD measures about 0.905".

So obviously my FSI engine mount doesn't use a BT40.
The Quest D5 motors are 20mm in diameter (0.787"), FSI's A4, B3, C4, D4 and E5 motors were 21mm in diameter (0.827"). Their E60, F7 and F100 motors were 27mm in diameter (1.063") and their A6, B6 and C6 motors were 18mm (0.709") in diameter. When I was thinking about the possibility of using BT-40 for motor tube, I was extrapolating from the fact that I use it for the 20mm Quest D5 motors. But I was incorrect because the FSI motors wouldn't have fit. The best fit in existing tubing would have been in Centuri ST-8, which had an ID of 0.865" and an OD of 0.908". This was a commonly-available tube and is probably what you used. I never had any FSI motors so I have no experience with adapting them to fit into a motor mount.

FSI themselves used RT-8 as a motor tube for their 21mm motors. This had an ID of 0.885" and an OD of 0.921". Throughout most of their catalogs, the company incorrectly labeled RT-8 as "0.903" tubing." I have no idea how they derived that number, but it doesn't match any dimension of RT-8.

Did you mean to say that 0.945" was the outside diameter of your old tube? If so, it matches the OD of Semroc Series 085 tubing. It would have been a perfect fit inside 24mm motor mount tubing, such as Estes BT-50.
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  #90  
Old 11-24-2011, 11:02 PM
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Quote:
Originally Posted by Doug Sams
Could it have instead been an Estes motor shipping tube? These were usually light blue, and should have been about the right size for the FSI motor.

Doug

.
From what I have read, Estes motor shipping tubes were just a smidgen larger on the inside than the diameter of the 18mm motors. I would think that it would have been too small to accommodate a 21mm FSI motor.
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