Estes advertised vs ThrustCurve.org projected atlitudes

Discussion in 'Low Power Rocketry (LPR)' started by Adam518, Dec 6, 2019.

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  1. Dec 6, 2019 #1

    Adam518

    Adam518

    Adam518

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    I have a few different mostly stock built Estes kits. When I plug the info into the thrustcurve website, the projected heights are much less than what Estes advertises. Many times the largest recommended motor by Estes shows to be a fail on thrustcuve because of inadequate speed leaving the launch pad.

    For example, I am just finishing the new ESAM-58 kit sold at Hobby Lobby. The package claims 800 ft with a C6. The package does not provide a finished weight & I could not find it anywhere online, but my finished rocket weighs 89 grams ready-to-fly less motor. The kit is supplied with 1/8" launch lugs. With the typical 30" long 1/8" rod on the basic Estes launch pad the thrustcurve fails the C6 motor because the rocket would leave the pad at only 38ft/sec. I installed 3/16" lugs and have a 3/16" launch pad with a 4 ft rod. The C6 still fails with a launch speed of 43 ft/sec. Hypothetically, it would take a 6 ft rod to allow the C6 to accelerate the rocket to their recommended 50 ft/sec minimum for safe lift-off.

    Secondly, even with the 6 ft hypothetical rod thrustcurve calculates an altitude of 466 ft with the C6. I guessed at the drag coefficient and plugged in .75. A difference of 800 ft vs 466 ft seems pretty big to me. Even if my build was slightly heavy and my guess at the drag is off I would think it would be closer than that.

    Swapping the motor mount to a 24mm in thrustcurve & leaving everything else the same a D12 would reach 758 ft.

    Does anyone have an opinion on which would be more accurate? I launch in a small-medium sized field & like to keep launches under 1000 ft. Too high and they are lost in thick woods that surround the pasture where I launch. Too slow lift-off speed & I end up with an unstable horizontal flight that also ends up in the woods.

    In the ESAM-58 example above, I'm ok with using a 24mm mount & a D12 if thrustcurve is reasonably accurate, however, if Estes is correct & a C6 will send it to 800 ft I am afraid that a D12 will send it out of sight.

    Thoughts??
     
    Last edited: Dec 6, 2019
  2. Dec 6, 2019 #2

    BEC

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    Estes' estimates are, in general, pretty optimistic. I fly LOTS of flights with altimeters and find that there are few models that reach the predicted altitudes (one glaring exception, amazingly, is the venerable Alpha III, which really does can to 1100 feet on a C6).

    The ESAM is a pretty big model - there's no way it would get to 800 feet on a C6. It might on a Q-Jet C12. In your situation, that's probably what I would do with that model.
     
  3. Dec 7, 2019 #3

    BABAR

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    My experience is that, except for very draggy rockets, the Estes engine chart for max lift off weight is pretty good
    https://estesrockets.com/wp-content/uploads/Educator/Estes_Engine_Chart.pdf

    Adding 13 grams motor weight to your 89 so far, puts you at 102 grams, you are still under the max lift off weight for. C of 113. My bet would be you would be good with a C6-3, a C6-5 may be pushing it.

    I would hope your winds are under 10 mph (than again, I ALWAYS hope the winds are less than 10 mph not matter what I fly, but I am strictly A Low Power Rocketry guy!)

    Not to start a firestorm (again) but the new RTF Saturn V is well OVER 113 grams, and from the forum posts MOST people felt it flew okay on a C as long as the motor was put in correctly. That rocket is clearly heavier and draggier than yours.

    Straight Trails!
     
  4. Dec 7, 2019 #4

    BEC

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    Yes....and that is one that about reaches the estimated altitude—of 200 feet—on a C6-3!

    The Q-Jet C12-4 takes it to almost 400.
     
  5. Dec 7, 2019 #5

    BABAR

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    Well, he SAID he had a small field! ;)
     
  6. Dec 7, 2019 #6

    BEC

    BEC

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    True, that he did.....
     
  7. Dec 7, 2019 #7

    John Taylor

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    I have found the Estes statements to be optimistic at best. And I've found the Thrust Curve statements to be conservative. IMHO I believe you are better off using Thrust Curve. They seem to be more accurate.
    Under ideal conditions you could get away with taking more of a chance using less impulse.
    Then there is the five to one recommendation for average thrust to model weight. Don't go below three to one for sure.
     
  8. Dec 7, 2019 #8

    John Taylor

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    I believe it's better to be safe than sorry, why push it? When do we ever have ideal conditions? I've had too many damaged rockets and embarrassing moments. I don't want more. Faster off the pad is always better.
     
  9. Dec 8, 2019 #9

    Tyler P

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    I have yet to have an Estes rocket not fly properly on a motor their packaging suggests, with the one exception of the Saturn V that came out before the 50th anniversary edition. There's no way a D12-3 would get that rocket off the pad with enough altitude to deploy recovery safely, haha. An E12-4 barely does it, lol.

    However, the rest of the 15 or 20 I've built have all flown just fine on the minimum recommended motors, and the maximum.
     
  10. Dec 9, 2019 #10

    BABAR

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    I think the ESAM should do fine on C6-3.

    Regarding some older Estes kits, Outlander, Venus Probe, and ExoSkell were marginal on available 18 mm motors.
     
  11. Dec 13, 2019 #11

    Adam518

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    I've had pretty good luck but did loose an Estes Majestic earlier this year on its 2nd launch. The 1st launch was with an E16 and it was perfect. It flew straight up and I had about a 50 yard walk to get it. The 2nd attempt was with an F15. It was a relatively calm day with very light gusts. It flew to about 60-70ft and made an almost 90 degree turn directly away from those of us watching. It was flying away perfectly horizontal. Almost immediately it made another 90 degree turn to the right from our point of view. Still flying horizontally it managed to find the only tree within 500ft of the launch pad. It planted itself about 70 feet up into a very large red oak tree. Much to the amusement of my friends and family the ejection charge went off about 1-2 seconds after landing in the tree. The shock cord wrapped itself nicely around a large branch and my Majestic is still in that same tree today. That was last January...and here it is December. I couldn't see it trough the summer but once the leaves came down this fall I can still see the pretty red chute and chrome nose cone.

    I used the suggested motors but Thrustcurve fails them both. They show the E16 left my pad at 37 fps and the F15 at 35 fps. I've tried to read a fair bit about minimum launch speed and both of these seem to be ok with zero wind but a tad slow with anything more than a dead calm day. Thrustcurve recommends 50 fps for a safe launch, which may not always be necessary, but I'd bet I'd still have my rocket if I used an AT F23.


    I'd say you're right but I ended up installing a 24mm mount in this one. I'd hate to loose the rocket either way, but I'd rather it fly out of site and drift off to glory than to have another failure due to inadequate launch speed.
     
  12. Dec 13, 2019 #12

    John Taylor

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    +1 for Thrust Curve
     

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