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Old Apr 10, 2012, 08:59 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
Build Log
Mountain Models Switchback Sport build

Well I swore years ago after building older kits for gas engines, I would start buying ARFs and support child slave labor in 3rd world countries and save me lots of time and suffering. I remembered it was a lot of work and most the time just Epoxy was used since CA wasn't really available to the RC world. I recently found two Mountain Model kits for sale, got a Switchback and a Dandy Sport for a combo price, making them about 40ish each, figured I will build the Switchback low wing and teach the son inlaw who is new to RC how to build a kit and let him build the high wing Dandy to learn all about ailerons. I could not find very many threads on the Switchback so I figured I would throw one in here, and hopefully a flight video at the end!

I was also pleasantly suprised that no longer would I need to shove pins through the balsa to hold it in place, just throw wax paper over the plan on a flat surface and hold, a little thin CA in the very tight and well fitted joints and BAM the tail feathers just flew together in minutes!
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Old Apr 10, 2012, 09:11 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
The fuselage also went together well, I was very impressed that these little laser cut parts were so clean on the edges and they fit very good together, a 3D jigsaw puzzle if you will. The wing halves also built fast and although they had no plywood in their main beams to save weight, I figured the entire wing would lose lots of its flex after the covering was added.

To my suprise, the stick mount was also a little 4 sided jig saw puzzle, I thought " was a little stick really that much more to put in the kit?" but I guess if you are laser cutting all the parts and spare material is available on one of the ply sheets, what the heck!

To power this beast I purchased the 32.00 Detrum combo pack from Hobbypartz, You get the motor, 8x4" prop, speed control, 3 servos and the motor does have a built in stick mount you can't see too good on the pic.
http://www.hobbypartz.com/60p-dy-1026.html I hope to try it out before I brag it up too much
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Old Apr 10, 2012, 09:17 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
The vertical Stab did not look like it would be supported enough with the thin balsa sheeting on the sides of it so I went for a little more beef and glued a little balsa extension that would sit on top of the Horizontal stab and a drop of epoxy on the bottom would let me move it back and forth a min or two until I got it perfectly square.
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Old Apr 10, 2012, 09:28 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
Another big reason I liked being able to frame up a Neked kit is the super ease of installing LED's inside the wing and using a clear colored Solite. I used the single LED's and put 10 inside the wing, placing a Red on the Right wingtip and Green on the Left wingtip. I placed white across the spar but to save weight and MAh's, I alternated front to back lighting like a checker board with White LED's, planning on using a Clear Blue over the wing. I plan to draw 5V from a spare receiver channel and ran them in parallel with the low voltage of course. Superbright LED's has been a great source for lights and the links to the LED diagram and calculator gives you the exact resistors you will need, these little buggers are very picky and resistors change if the voltage is off a few tenths of a volt! So I poked small holes through the balsa spar with a spare piece of my control rod, plugged in the LED's and then just bent them to the side opposite to keep them still during the soldering process.
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Old Apr 10, 2012, 09:43 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
The rear facing LED's I just poked another small hole on each side and fed the LED wires back through to the rear of the Spar, so all my connections and wires would be all in a row, easy to solder. First I soldered the resistors to the negative side of the LED and then used my favorite light weight Radio Shack 30 gauge insulated solid wrapping wire, I get a roll of Red for + and get a roll of White and use it for the - side of things. I used little plastic bezels for the wingtips to keep the look nice and clean, you do have to harden the balsa hole edge with CA or epoxy since there is a little pressure pushing them through and then holding onto the light from the inside.

I pull the wires from the center of the wing thru the factory rib holes to the outside tip, soldering it first. Whats nice about this tiny wire as most know, you just burn the insulation away with the soldering iron tip, so after soldering the tip, i just work back towards the center, burning away insulation, bending a J on LED and resistor ends, bend it over to loop around the wire before soldering. It went faster than I thought this way. I then bent a 90 deg bend on the LED wires to keep it a secure and give it a clean look. This also keeps everything apart so there is no trying to put tiny pieces of insulation or heat shrink on LED anodes or cathodes.

Entire framed wing with LEDs came in at 1.8 oz
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Old Apr 11, 2012, 07:02 PM
United States, CA, Santa Rosa
Joined Mar 2011
883 Posts
Nice build, I built a switchback sport last year and it's a great flier. One suggestion before you cover your wings, the green nav light should be on the right wing tip and the red on the left.
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Old Apr 11, 2012, 11:29 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
Crap, I did mix up the lights on the tip if I wanted to stick with FAA regulations Well its covered now dang it, and being a Broncos fan and the orange being half off at a local shop, I ordered the Blue from Mountain models and went to work. The Orange was slightly thicker than the Solite and much easier to manage, I did start to figure out the Solite only after discovering the great thread done by Brucea

http://www.rcgroups.com/forums/showthread.php?t=711624

I aint gonna lie to ya, I used some harsh language every time those edges curled up and stuck to itself while trying to get it tacked down. I also went with a fully removable canopy and modified the magnet to the rear and a ply tab on the front, works great so far! The original design would work great keeping a permanent hinge on one side, but hey what fun would it be if ya didnt have a chance to forget your canopy when you went flying?
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Old Apr 11, 2012, 11:39 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
I also made a small board inside to power the rear side lights and the Front landing light. It should put a nice spot of white light right at the front wheels when coming over the tarmac. I soldered the resistors, micro switch and some plugs on the board so I didnt have to put any resistors out by the lights. I also ended up cutting another small hole towards the rear of the plane below the lights for access, knowing the control rods would be low and I threw a 90Deg bend on them and threw a little insulation on the Anode side and shoved them in their bezels.

Also I decided to try some of those RGB LED's for the sides, they flash thru Red,Green,Blue colors and in a wild random pattern so figured they should generate some good UFO calls
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Old Apr 12, 2012, 11:25 AM
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Central Utah
Joined Feb 2005
480 Posts
Was not digging the idea of feeding the rubber bands under the aileron control rods or around the servo in the center, ya it will work but I cant leave well enough alone, I think we need a BOLT ON WING ! Now we had to do a little modification to the rud and elev servo mounting, as I soon realized a bolt on wing brace was right over the top of the rear servo screws Then I thot to myself " $#&^@(#^ ?" and decided to mount servos on the top side of the brace and run the screws thru the top instead of the bottom, one of the previous magnetic hatch pics shows the servos mounted this way, will get pics of wing mod soon. This way of mounting servos also made it to where you didnt have to grind out a larger opening on one end and squeeze the bottom half with wires down thru the tray.
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Old Apr 12, 2012, 08:46 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
Took two ply layers to make it strong, tried one and when I popped the 4-40 blind nuts with a small hammer onto them they cracked a little. I also made the bottom layer a little longer so it would reach under the balsa stringers. moving the servos also made them line up with the factory holes better with these particular servos since I was going to have to use new small holes for the control rods.
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Old Apr 12, 2012, 08:58 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
I didnt have my wing holes line up quite as nice with my blind nuts as I had planned, so I epoxied small left over dowel pieces in the holes and used a dremel to move the holes over a little, now my wing was square again! I just epoxied a small ply tongue on the front dowel of the wing, I know it is small and not very strong so I also epoxied a piece of balsa between it and the thin ply wing skin on the bottom, hoping this will make it strong enough for a few bumpy landings. Straight out from the dowel seemed to be the perfect placement for the ply tongue to catch on top of the rear bulklhead between it and the dowel. Also I am glad Mountain Models used super thin ply on the center of the wing since just balsa would not be strong enough for the bolt on challenge! I would have liked to see maybe one more piece of thin ply to finish covering the front top center portion of the wing, I think it would made it even stronger.
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Old Apr 13, 2012, 12:05 PM
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JimTMich's Avatar
United States, MI, Kalamazoo Township
Joined Aug 2006
2,374 Posts
Beautiful job!
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Old Apr 13, 2012, 03:56 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
Thanks Jim, I hope it flies as good as its turning out so far! Anyone else that has built and flow this model feel free to chime in, still not sure on the CG, sounds like its just behind the spar? I hope this Dubro Hinge tape I plan on using holds up as I have never used control surfaces beveled on just one edge and the tail wheel will have all rudder and downward pressure on it... hmmm
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Old Apr 13, 2012, 08:41 PM
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United States, MI, Kalamazoo Township
Joined Aug 2006
2,374 Posts
I usually fly with cg on the spar or back of the spar.
Still my favorite small area parkflyer.
Do a search for the switchback revival thread.
There are many of us enjoying this. Perfect parkflyer.
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Old Apr 15, 2012, 06:28 PM
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czechyour6's Avatar
Central Utah
Joined Feb 2005
480 Posts
Wow thanks, just found the thread you were talking about, will throw it here again also to save some guys a little trouble, and at 89 pages, WOW !

http://www.rcgroups.com/forums/showt...itchback+reviv

I also have another dilemma with the servos im using... The servos I had with the Hobbypartz combo pack did NOT come with any X arms, just straight ones. The kit is designed to use one with the ailerons, chopping the bottom off the X and halfing a V shapped 90 deg set up... Not sure if the angles will move the ailerons the exact same up as they do the opposite down, but If I could do it again I think I would maybe run 2 servos and fix the Horns more perpendicular with the hinge joint for nice straight connection! I did a photo shop example AND I just noticed that would also give ya NO servo in the way of rubber bands! I havent read thru the 89 pages of the above thread yet, anyone else think this may work better? oh I guess you would need a light weight mini Y also ..
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