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  1. #1
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    Estes 18mm and 24mm length

    Are the Estes 24mm motors the same length as the 18mm ones? If not, what is the length difference.
    Thanks,
    Reed

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  2. #2
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    Re: Estes 18mm and 24mm length

    Originally posted by Reed Goodwin
    Are the Estes 24mm motors the same length as the 18mm ones? If not, what is the length difference.
    Thanks,
    Reed
    The 18mm and c11 and d12 engines are all 2,75 inches long. The e9s are 3.75 inches long.

    BTW, why are motors measured using two different measurment systems?


  3. #3
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    Estes C11's, D11's, and D12's are the same length as their 18mm motors (2.75"). The E9's are 3.75" long.

  4. #4
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    Re: Re: Estes 18mm and 24mm length

    Originally posted by Jimn
    The 18mm and c11 and d12 engines are all 2,75 inches long. The e9s are 3.75 inches long.

    BTW, why are motors measured using two different measurment systems?
    My guess: modelers don't have any control over tube diameters, so they've always been oddball values. I'm not even sure whether or not the diameters are rounded to the nearest mm. Hobbyists DO have control over tube lengths, and since the U.S. never switched to metric, most modelers still use inches when measuring and cutting their tubes.

  5. #5
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    Not sure

    Originally posted by Jimn
    BTW, why are motors measured using two different measurment systems?
    Having never seen the 'official' specs on how Estes (or anyone else) dimensions their product, I don't really know, but I suspect that they use one system.

    My guess: the metric part slipped into use after U.S. rocketeers made contact with the Europeans. Back in the old days I believe Estes used to describe their motor diameters in both fraction and decimal inches. IIRC, motor lengths have always been described in inches.

    There is a lot of common-use-type verbage that eventually gets ascribed to some official source, but is really still just plain common-use-type verbage (and sometimes just plain wrong). In your own post you use both "engine" and "motor"...... which is it?
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  6. #6
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    Has anyone else noticed that motors are slightly wider at the nozzle end? It seems like whenever I put a motor in backwards (accidentally, of course) it is much tighter.

    Why can't we just use metric? I lived in Canada and Europe for a few years and metric is so much easier (once you know it). I especially don't like sequential fractions like 3/16, 13/64, 7/32, 15/64, 1/4.

  7. #7
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    Re: Not sure

    Originally posted by powderburner
    Having never seen the 'official' specs on how Estes (or anyone else) dimensions their product, I don't really know, but I suspect that they use one system.
    I don't ever recall Estes calling their motors 18mm and 24mm - I believe AVI was the first and maybe only company to do so. If you get a really old Estes catalog it lists the diameter as 11/16", currently it lists it as .690" which works out to about 17.5mm more or less. The D&E motors are 15/16" or .945" if you allow for a little swelling. By the way 29mm, 38mm 54mm and all other standard motor sizes are just 'rounded off' values of SAE fractional standards

    My guess: the metric part slipped into use after U.S. rocketeers made contact with the Europeans.

    When I went to school in the '60s and early'70s we were all taught to "think metric" because if the United States didn't convert to the metric system like the rest of the industrial world, by the magical year 2000 we would be a third world country!
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  8. #8
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    Thanks, guys, I knew I could count on you. Cool, onward I go.
    Reed
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  9. #9
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    Re: Re: Not sure

    Originally posted by bazookadale
    When I went to school in the '60s and early'70s we were all taught to "think metric" because if the United States didn't convert to the metric system like the rest of the industrial world, by the magical year 2000 we would be a third world country!
    They still tell the kids in school that.

    Although, in some cases it is easier to use metric than English.

  10. #10
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    Re: Re: Estes 18mm and 24mm length

    Originally posted by Jimn
    The 18mm and c11 and d12 engines are all 2,75 inches long. The e9s are 3.75 inches long.

    BTW, why are motors measured using two different measurment systems?
    On this page (http://nar.org/SandT/NARenglist.shtml) at the NAR website, motor dimensions are given in mm.

    Estes motors are listed as:
    13 x 45 mm for the 13 mm by 1.75" motors
    18 x 70 mm for the 18 mm by 2.75" motors
    24 x 70 mm for the 24 mm by 2.75" motors
    24 x 95 mm for the 24 mm by 3.75" motors
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  11. #11
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    Re: Re: Re: Not sure

    Originally posted by Nuke Rocketeer
    They still tell the kids in school that.

    Although, in some cases it is easier to use metric than English.
    IMO, metric is easier in basically ALL cases. Still, that's a debate for another thread...
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  12. #12
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    Estes motor size picture

    I don't recall where I originally lifted this image (I would guess Estes) & a quick
    search doesn't reveal the source. Anyway here's Estes motor dimensions in
    both metric and English.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	motordimensions.jpg 
Views:	40 
Size:	42.2 KB 
ID:	213928  
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  13. #13
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    fat rear end

    Originally posted by m85476585
    Has anyone else noticed that motors are slightly wider at the nozzle end? It seems like whenever I put a motor in backwards (accidentally, of course) it is much tighter.
    I think the motors *are* larger in diameter at the nozzle.
    This is because the nozzle clay is stamped into place at extremely high pressure, to form it into a strong solid. It must contain the pressure of the combustion chamber without disintegrating, it must (reasonably) withstand the erosive flow at the nozzle throat, and it must stay in place without sliding out the back end of the motor case. Looks to me like the nozzle-stamping process bulges the motor case by a couple hundredths of an inch.
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  14. #14
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    Re: Re: Re: Re: Not sure

    Originally posted by cjl
    IMO, metric is easier in basically ALL cases. Still, that's a debate for another thread...
    Except for thermodynamics you are right.


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