Dude, Where’s My Rocket?

16 responses to “Dude, Where’s My Rocket?”

1. 

   jurvetson

   Sep 20, 2011 at 10:30 pm

   Here’s the HCX flight computer log. The red spike up to 28 G near t=0 is the thrust spike from this cool Cesaroni L640 Dual Thrust motor. It gives a kick to get going off the pad, and then goes into a nice long burn (thrustcurve).
   
   

   The on-board GPS recorded the apogee event at 14,410 ft. AGL, which is probably the most accurate.

   I got one decent launch photo; she went so fast. Pad cam in the foreground, Black Rock in the background:
   

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2. 

   Dr DAD (Daniel A D’Auria MD)

   Sep 20, 2011 at 10:43 pm

   You just have too much fun with this!

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3. 

   Jim Rees

   Sep 20, 2011 at 11:01 pm

   I wouldn’t complain about a 1% disagreement between barometer and GPS.

   Why does the acceleration go to -5 G after burnout? What’s the terminal velocity before the chute opens, and why does it reach terminal velocity so soon?

   Wish I’d had telemetry like this when I was launching Estes rockets in junior high. I couldn’t even afford the camroc.

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4. 

   Astrocatou

   Sep 20, 2011 at 11:14 pm

   interesting for sure…and once again drag was the huge issue.
   Presume that was the deceleration seen at burnout.
   (Suppose you could somehow calculate the drag at that point based on the deceleration…)
   🙂

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5. 

   Jim Rees

   Sep 20, 2011 at 11:45 pm

   It wouldn’t be hard. It’s just acceleration times the weight, right? I guess that makes sense, I’m just surprised it’s so much.

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6. 

   Astrocatou

   Sep 20, 2011 at 11:51 pm

   I am thinking that with such excellent telemetry you could (?) parse a lot of info.
   Once you have no fuel,no weight changes,no thrust,then the mathematics of the deceleration rate (at any given air speed) would tell you about the amount of drag present at any given air speed…
   (drag was the reason I sort of gave up on this hobby…at an earlier stage than this, mind you…)

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7. 

   solerena

   Sep 21, 2011 at 3:42 am

   Fun shots and video, love this shade of blue.."GPS data streaming down, a RF directional beacon, and an experienced rocketeer using his eyes. Two of the three worked just fine"
   sounds like two of the three eyes:D love the video at the end – how fast it goes…frame by frame.

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8. 

   jurvetson

   Sep 21, 2011 at 3:36 pm

   [http://www.flickr.com/photos/83025347@N00] – when you say terminal velocity, do you mean peak velocity? That will be at motor burnout, the apex of the green curve above, and on the table you can see that was Mach 1.14 or… 0 to 856 MPH in 3.64 seconds!

   For a sense of that acceleration, the 9V Duracell battery in the avionics bay "weighs" 2.8 lbs. A common failure mode for beginner rocketeers is the loss of power as the battery rips away from whatever was holding it in place. I use a metal L-bracket for support from bottom and side and a plastic strap to keep it aligned. I also try to mount it low enough that if it all ripped apart, it would not fall far enough before hitting a bulkhead to detach the connector. That happened last time I flew this bird, but I did not lose power. Whew!

   And Dave is right – drag is a huge factor in supersonic rockets. That’s why the minimum diameter airframes always win the altitude records (versus some marginal shaving of weight) and this is a 3" airframe which has more drag than a 54mm min diameter.

   This is less noticeable with Estes hobby rockets because drag grows with velocity squared.

   

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9. 

   Astrocatou

   Sep 21, 2011 at 4:27 pm

   Do you have a non HD video…(link) of the flight ?

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10. 

    jurvetson

    Sep 21, 2011 at 5:41 pm

    You can pull the "?hd=1" off the end of the URL and it will be back to vanilla YouTube

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11. 

    Jim Rees

    Sep 21, 2011 at 7:44 pm

    You can also click on the little "720p" below the frame towards the right and you’ll get a menu of various resolutions.

    By "terminal velocity" I mean the speed a body reaches when you drop it, it stops accelerating (downward), and the pull of gravity is exactly balanced by the drag. I think I picked up this term from the skydiving crowd. I guess I expected the rocket to fall a long time before reaching terminal velocity, but some back-of-the-envelope calculations suggest it doesn’t take long.

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12. 

    Astrocatou

    Sep 21, 2011 at 9:02 pm

    From the video,it sounds like Vt for this was100 fps…60mph

    That would be t=100(f/s)divided by 32(fps)…?
    High school physics…but I have I forgotten it all…

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13. 

    Jim Rees

    Sep 21, 2011 at 10:48 pm

    100 feet per second would be about 30 meters, and at 10m/s/s that would take three seconds. Of course it’s a bit longer because the acceleration drops as the drag increases, but it’s still going to be very short.

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14. 

    Astrocatou

    Sep 22, 2011 at 8:50 pm

    [http://www.flickr.com/photos/83025347@N00]
    That "720"icon trick is nifty…thanks
    Got any links to a good remedial (online) Calculus class…?

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15. 

    Jim Rees

    Sep 22, 2011 at 9:21 pm

    You don’t need calculus to divide speed by acceleration to get time. But I do remember ½at² being about the first thing we derived in beginning calculus.

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16. 

    jurvetson

    Sep 24, 2011 at 1:35 am

    and some photos by Donna:

    Hooking up igniter (all other people clear away):
    

    As found. GPS transmitter and RF beacon in green bubble wrap
    

    He’s adding this location to our GPS log of landing sites
    

    Reply