Tuesday, August 21, 2012

Launch Report 2012-11

Location: Mattie Stepanek Park
Weather: 75 degrees, wind 0++ mph, partly cloudy
Total flights: Today - (3); YTD - 80
Total motors: Today - 0; YTD - 95
Motors by class YTD: (Air -3); MicroHybrid -1; MMX - 6; A - 6; B - 5; C - 32; D - 7; E - 23; F - 6; G - 9

Today, I launched the AlaskaPaperModelworks Honest John using a PVC air launcher.  I went to a few potential launch sites only to find them populated with people enjoying the mild weather.  Although the 39" rocket is fairly light, it has no recovery mechanism and I wasn't sure if there was any slightly-upper level breezes.  My launcher is complicated by the fact it it either has to plug into the car or I have to lug the launcher, pump and 12v portable battery around.  I finally found a sufficiently open area, which unfortunately had more pavement than grass. Photos of the launch are at the bottom of this report and below the jump break. 

My old tire pump has a hard time getting over 30psi. I don't know if this is expected or it is fighting a small leak in the pressure chamber.  I had a hard time getting my pressure chamber sealed but it passed a soapy water test at 30psi.  The last leak was at the pressure vent on the air valve (made from a 1" Orbit sprinkler valve). The first photo shows the set up.

Flight #1 (40psi): Being under the flight and having no landmarks, it was hard to estimate the altitude. However, it was a pretty satisfying boost.  The rocket fell sideways for a while but ended up lawn darting onto the pavement.  Ouch. Two 'after' photos are attached.

Flight #2 (50psi): I straightened the nose, popped the broken body section in, and pulled the nose section off the body. The flight was noticeably higher but the profile was the same. BOINK! I only have a before shot of this flight.

Flight #3 (60psi): Thus time, the nose tip was beyond straightening and I couldn't get the two sections back apart. So, I launched it as-is.  The altitude seemed closer to that of the first flight and, yup, BOINK! The final photo shows the compacted stomp rocket next to the one that I converted for 24mm motors.





Launcher set up.
After the first flight.
After the first flight.
Before the second flight.
Videos of second and third flights:


The final aftermath.


5 comments:

  1. That's very cool Dick! :) I like your PVC launcher as well. You got some very nice flights out of it. Sorry to see it crash like that though. .... all you now need is a little bit of water .... and presto ... :)

    How much does the air version of the rocket weigh?

    Great flight report and photos too from the pyro version of this rocket.

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  2. Thanks George! The stomp version weighs a mere 3 oz.

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  3. Artemi, I looked at your site and have a question...how did you initiate recovery on your air models?

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  4. Hi Dick,

    Sorry, I have not noticed your question in comments here.

    Regarding recovery, it is indeed an issue in case of air rockets. Guys on the Water rocket forum (http://www.waterrocketforum.com/) invent all sorts of things as they face the same challenge. However, they have enough power to lift up all their contraptions. Most of them are too heavy for an air rocket.

    I fiddled a lot with free falling nose cones trying to get reliable deployment and did not have much luck. It worked sometimes, but in most cases the nose cone ether did not deploy (too tight) or was blown off during the lift off (too loose), or the parachute did not come off. A video on our site is a rare example of successful launch.

    You mentioned in the report that the rocket fell sideways for a bit. I think it can be seen in the videos as well. I think it indicates that the model has backsliding (or backgliding) tendencies. I have a detailed explanation of this effect here - https://sites.google.com/site/theskydartteam/openrocket#TOC-Designing-a-Back-Glider-Rocket-using-Open-Rocket.

    Our most successfully recovery system basically used this effect as well. I will refer to 22nd second of the video here - https://sites.google.com/site/theskydartteam/projects/air-rocketry/helicopter-recovery. An additional weight is mentioned in the caption. It can be seen attached to the body tube right below one of the fins - a small dark rectangle about 1x1 cm. Without it (in fact there are three such weights between all fins) the rocket very quickly would turn nose down at apogee. The weights move CG down to create situation favourable for back gliding. In our case full transition to a horizontal position was not needed as such. It was enough to get the model moving backwards at apogee.

    Returning to the 22nd seconds of our video, imagine the rocket going up. The air strim keeps the "rotor blades" pressed to the body tube. At apogee instead of turning nose down the rocket stops and begins moving backwards fins first the same way your model did I think. Now the air strim opens the blades and they drag the nosecone (as they attached to it) off the tube.

    The "blades" were not true blades. It was a tube cut into 120 degree segments without any profiling common for proper helicopter rockets. I never tested it, but I think it could be possible to use the same principle to deploy a parachute or a strimmer. Much shorter "blades" will not be sufficient to slow descent enough, but they should be enough to pull the nose cone and the main recovery off the rocket.

    The whole idea work only in relatively calm conditions. Wind can upset the transition phase to such degree that backgliding never happens. This is how I lost my Comanche-Backslider ( https://sites.google.com/site/theskydartteam/projects/model-rocketry/comanche-backslider )

    Does the above explanation answers your questions?


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  5. Yes, thanks for the extra info. I'm trying a rocket with a VERY loos top section and we'll see what happens. I suspect it won't work. Mike Bauer is working on a Tomy-timer based solution. More pressure with longer pressure tubes will help.

    I've has 2 long rockets that naturally were backsliders although they weren't built as such. One was a slightly shortened mean machine. I'm having a hard time rolling the tubes and haven't thought about trying a really long air rocket.

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