Spinning saucer stability and speed off the rod

Discussion in 'Oddrocs' started by Charles_McG, Jun 3, 2018.

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  1. Jun 3, 2018 #1

    Charles_McG

    Charles_McG

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    Does a design like the Estes Blender have different thrust to weight or speed off the rod requirements from traditional (n)FNC rockets?

    I love me a long burn blender flight, and I have some of these Apogee F10s floating around, along with a 29mm Blender upscale. But the Blender-29 weighs 150g dry. Loaded, it’s over the listed max liftoff weight.

    But would it be okay anyway, between spin and base drag?
     
  2. Jun 3, 2018 #2

    djs

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    Speed of off the rod requirements are to ensure enough air is flowing past the fins to keep the rocket stable. Since an oddroc doesn't have usable fins (and is stabilized by base drag), you can go a bit lower on thrust/weight. This is assuming, of course, that it's a fairly low wind day.

    I calculate a loaded weight of around 207g. The initial thrust of an F10 is 2267 grams. This means you're still looking at an initial thrust/weight of 10:1 (If my math doesn't suck).

    Remember that max liftoff weight is often calculated conservatively and also based on the delay time. Since these are odd rocs, this should matter less.


    Personally, I think you should petition Aerotech to get a few of the G8 motors.. you know, in the interest of science and data :)
     
  3. Jun 3, 2018 #3

    Charles_McG

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    I worked out the same conclusion, Glen, with slightly different numbers.

    I’d be ok with a G10 or a G12.
     
  4. Jun 3, 2018 #4

    neil_w

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    I’ve wondered about this as well. Spinning shouldn’t help off the rod because it can’t spin on the rod (right?) The question is at what speed base drag kicks in enough to stabilize the rocket. There should be some math that could answer that, but I don’t know what it is.
     
  5. Jun 3, 2018 #5

    Charles_McG

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    Oh, I think they spin on the rod. Even the Quinstar. The big Quinstar gives quite a bit of rod whip from the spin. The blenders hold their center of mass closer.
     
  6. Jun 3, 2018 #6

    Charles_McG

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    Either way, it’s likely not the normal relationships we are used to. A blender starts with an angle of attack above 15 degrees :)
     
  7. Jun 3, 2018 #7

    neil_w

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    Hmm, I guess it’s possible. Next time I fly mine I’ll take some high speed video on the rod and see.
     
  8. Jun 3, 2018 #8

    kuririn

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    It can definitely spin around the rod,with the launch lug as the axis. That is why Rocketarium recommends launching off a shorter rod for their Turbo Vortico: 1/4" 16 - 18" rod. If you have a two piece rod, use only the lower piece. Nice straight flight on a G-64, by the way. I guess once it spin stabilizes, a guide rod is unnecessary, even a hindrance.
     
  9. Sep 9, 2019 #9

    neil_w

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    @Charles_McG, did you ever end up flying your Blender on the F10? I'm trying to ascertain whether I could fly my upscale Quinstar on one...
     
  10. Sep 9, 2019 #10

    Charles_McG

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    @neil_w , yes I did. I just looked, and i don't appear to have a video of the flight.

    It lifted off the pad/rod just fine. Climbed to ~100-200' in a few seconds. I'm a terrible judge of distance. Then it just hung there, eventually tipping to one side and scooting a fair bit cross range. I don't think I'd do it again.

    I love the long burns - but 8 sec of low thrust gets scary. The 4 second CTI mellows are more comfortable.
     
  11. Sep 9, 2019 #11

    neil_w

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    Thanks. I need to go weigh my Quinstar and see how it compares to your Blender. I feel like I weighed it at some point and posted the weight (or messaged you, or something) but I can't for the life of me find it.
     
  12. Sep 9, 2019 #12

    neil_w

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    Just took another look at the F10 thrust curve... after the initial peak, it levels off around 8.5N. That should be enough to keep a 150g rocket moving upward, shouldn't it?

    I'm just thinking, there's no way my Quinstar weighs less than 150g.
     
  13. Sep 9, 2019 #13

    Charles_McG

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    Recall that there is also drag, and change in angular momentum that are stealing from any energy going ‘up’.
     
  14. Sep 9, 2019 #14

    mbeels

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    Untitled.png

    Naively, I would have guessed that 8N of thrust would have a 5:1 thrust ratio with a 160 g rocket, and still be "ok". But (as Charles mentioned), a saucer is a different beast. Interesting.
     
  15. Sep 9, 2019 #15

    Charles_McG

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    Motor is 83g, so loaded weight would be about 230g. 8N makes about 3.5:1.

    It flew up just fine. But it loitered/hovered in a way that was visually awesome - until it slid off to one side. Which makes recovery scary.

    The two stage I flew with an F10 in the sustainer was somewhat similar. Burn goes on -forever-. Awesome. Way into the gravity turn. Not so much.

    The eggtimer Proton on board showed that the sustainer decelerated nearly continuously during the burn. Not as much as a coast, but the F10 couldn't hold the speed given by the G115 in the booster.
     

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