How Much is Too Much? G Forces and MPH

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1 year 2 months ago #199 by mcfrye2014
I have a LOC Sand Hawk 2.2.  The fins are attached with Epoxy but are not Fiber-glassed.

Per Rocksim:  an I280DM-14 will have it fly to 5,169 feet at 781 MPH with a Max of 26 Gs.

Granted, the deployment is too fast - but would my Rocket Shred?

Per Rocksim:  an I140W-10 will have it fly to 4,031 feet at 542 MPH with a Max of 17 Gs.

I am not worried about the Gs, what about the speed?  Would my rocket shred?

Thanks in advance for the commentary!

 

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1 year 2 months ago #200 by achoward
Well, the rocket could exceed Mach on the DM motor. All construction aspects are important. For example, the rail buttons, if not attached well could get ripped off on liftoff (saw a few of those failures at Thunderstruck resulting in bad results along with failed cert attempts.) At Mach speeds, there's a problem with fin flutter which this rocket could experience, possibly ripping them off. Shear pins and vent holes would be needed so the pressure change wouldn't pop things apart at the wrong times. Also, being a really light rocket, at over 5K if could drift a long ways and possibly end up near the wires depending on flight path and wind. We have a 6K waiver, but I'm not sure the field can really handle flights that high especially with the wire constraints. A tracker would be needed as spotting that size rocket from a mile away would be challenging. My thoughts would be to go with something less than the I280.

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1 year 2 months ago #201 by mcfrye2014
Thank you Alan - I appreciate the feedback and help!

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1 year 2 months ago #202 by akakitsune
Even getting up near Mach (trans-sonic) makes everything wonky. Fiberglassing your fins end-to-end would help with fin flutter by stiffening them and changing their period- as well as help keep them on, a layer of full and a layer of 3/4 from tip to tip would be enough, just scuff the existing epoxy with 120 grit. A better solution might just be adding weight higher up. Overdo the quicklink and swivel. Toss some clay in where 25G won't kill anything. Put in way too much wadding (but still loose).

And I'd really suggest dual deploy since it'll go so high but that's kind of difficult. I'd err on the smaller side of chute or even a 7x70 streamer or 2 smaller streamers - as long as you're under 22 ft/s in Openrocket/rocksim.
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1 year 2 months ago #204 by mcfrye2014
Thank You for your tips - I appreciate it!

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