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Old Jul 04, 2012, 01:22 AM
Midnight Express is offline
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Joined Jun 2012
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So its been a bit more slow going then I anticipated. I hand cut out the ribs and the main wing spars with the dihedral and started to put it together and ran into problems. I am using basswood for the wingspar and tried cutting it with a composite disk via dremel and a hobby saw, both of which left crooked wing ribs. The initial design had a half cut out in the rib and half in the spar leaving the two flush top and bottom. So, I've been redesigning the ribs in profili to slide on the wingspar helping to correct some of the warping and hopefully making it easier to construct. Though now I am seeing the benefit of taking the time to use CAD and have the pieces cut for you. I just wish I could get DevProf to open up so I could export the cad files. I dont know if its Comodo keeping it from opening or what, as I've already added it to the safe programs list.

I've also been working on the "retardant" dropping system. Thanks again for the info Charlie! After doing some wing loading calculations(Im still totally guessing here) if I could come in at 16 LBS with 1 gallon of water on board that would bring the wing loading to about 31cu oz which will be heavy but flyable, if Im understanding the system right. The only way to do that and keep the tank under the plane to scale is to have a tank inside the fuselage and have a hose with a valve to the tank under the plane. I did some flow rate calculations and found water will flow between 5-18 MPH. At 5MPH through a 5/8 inch hose it should dump the gallon in about 13 seconds. With that and the wingloading at 31, the stall speed via this calculator was about 30 MPH. So 30 MPH is about 44 feet per second leaving about 542 feet of "fire line". The tank on the bottom is always open and basically will become the nozzle. The plan now is to have a quarter turn valve on a 1 inch line from the internal tank to the external scale tank. That way the flow rate can be controlled via the radio by like the throw rates. Giving more control on the visibility of the drops and making it closer to scale by having the ability to control that in the air period. I was also contemplating make the opening in the scale bottom tank adjustable by channel 8 so the coverage rate or width could be controlled. I hope to have a mock up of the scale tank constructed sometime soon as well so I can test some of these theorys. Taking your suggestion of the slurry mix, I looked at the real slurries that are currently in use by the USFS. Of course the exact make ups are closely guarded trade secrets, but I found that Phoscheck has a binding agent of Guar Gum, which is readily available at your local grocer. So my first attempt at slurry will be with that.

I have yet to locate a quarter turn valve or ball valve that is both light enough, with smooth enough operation that a small servo would easily be able to open and close it within a second.

I'll try and get some pictures up of the new and old designs of the wing ribs soon, as well as the test rigs for the slurry system. If I can get the devprof protion of Profili to run I may just send the designs off to national balsa and have them laser cut. But thats cheating right??

Thanks for all of the help already. This community is really great! My name is Michael, but most of my friends call me Mick.
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