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Old 11-03-2014, 10:38 PM   #1
mclarkson
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Default What? Another build? SC-7 Skyvan

After a couple of less-than-successful builds, I'm back at it again.

My inspiration this time? The SC-7 Skyvan.


Planned wingspan around 36". This will be my first KFm-3 airfoil.

I'm going to be using two 24gram 1300kV on Plush 10A ESCs.

I'll be using Dollar Tree Foam or blue Dow FFF. I still haven't decided.

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Old 11-04-2014, 12:30 AM   #2
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Nice subject and also a good one for Depron foam. I thought a good bit about building one of those when I started the Aerovan project. Was almost a coin toss between the two subjects. The Aerovan did fine with two 17gm motors and 9A ESCs. You don't need much motor when you have two of them. You'll probably be pleasantly surprised with the efficiency of the high aspect ratio wing also. My 30 some inch DC3 is not light compared with other models its size, but floats off easy with a light hand toss. It was far better than I anticipated.
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Old 11-04-2014, 12:35 AM   #3
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Try using cellfoam 88, its great stuff, its like depron foam. its much much better than dollar tree foam or Blue Dow FF

http://www.hobbypeople.net/index.php...-1-2-2-sh.html

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 11-04-2014, 02:01 AM   #4
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Make sure the back drops open so you can send out the paratroopers. Flitetest has free plans for something that looks like this. Funny what people are dropping out the back end. Like a radio control tank that gets dropped at low I mean low altitude then drives off.
Be following along looks like a fun one.
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Old 11-04-2014, 03:01 AM   #5
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Thanks, guys. I'm building it with what I have on-hand and won't be too bothered if it strays a bit for 'scale.' For example, the nacelles are set so close the the fuse that they'd need 4.5" props to provide clearance. I expect I'll slide them outboard a bit, etc.

gramps, I'm definitely planning some kind of drop capability.

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Old 11-04-2014, 03:24 AM   #6
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Gotta have the drop capacity. A guy I fly with built a few of these with the blue foam boards from Lowes/Depot. One is the mother ship to launch a scratch built space shuttle. Another one has tilting wings (the whole wing structure goes up and down) for STOl, and the other has twin 64MM EDF units on it. All are really fun to fly. Good luck with your build.
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Old 11-04-2014, 04:05 AM   #7
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This is the only dropping I've done so far, but it worked out great.

YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.

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Old 11-04-2014, 05:44 AM   #8
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Mark,

Cool stuff. I was thinking of making a release mech to add to my 1700mm VQ Beaver. I have several small plane candidates this will work well with such as the little JPowers jobs( jets and small props)

Was thinking of attaching directly to the plane or a tow and release scheme with string. Not quite sure how to make it work with a 9g servo.
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Old 11-05-2014, 10:24 AM   #9
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Here we go. I've decided on the Dow FFF for my primary material.

I started with the wing, which sports a Kline Fogelman KFm3 airfoil. (Steps at 50% and 75%.) Wingspan is 36" and the chord is 4" - a tad fatter than the real plane, but I'm a bit worried about wing loading.


An arrowshaft will serve as a spar.


I've enlarged the ailerons a bit over the scale plane.


The fuselage is basically a box.




Getting a feel for the size and shape of the final plane.

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Old 11-05-2014, 11:11 AM   #10
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Dang it. I've just realized I'm gonna have to put counter-rotating props on this and that means buying a whole different kind of propellers.

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Old 11-05-2014, 11:08 PM   #11
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Moving on. I worked on the tail a bit today. The Skyvan's vertical and horizontal stabilizers are interlocked so I cut some slots and slid them together.







Another quick test assembly.

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Old 11-06-2014, 12:27 AM   #12
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That looks very nice.
It looks like you are intending to mount the servo vertically sticking out into the air stream. Is there a reason for this?
I always mount mine on their sides so they are buried within the wing with just the tip of the horn sticking out. Not only does it have less drag but more importantly the axis of the servo arm is then the same as the aileron hinge so the linkage geometry is better.
Just my "twopennyo'th"!
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Old 11-06-2014, 12:40 AM   #13
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Here's a few vids from Demon Driver. Chris makes a lot of airliners. Here's a couple of Shorts 360 Skyvans he whipped together.

http://youtu.be/HQAqblcXptc

http://youtu.be/SlQXco3g0-I
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Old 11-06-2014, 02:33 AM   #14
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quorneng, I hadn't thought about it but you're probably right. I'll take a look at laying them down in another orientation. As usual, I have no real plan.

dahawk, mine will never be a sweet looking as those, I'm afraid.

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Old 11-06-2014, 11:53 AM   #15
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I've re-located my aileron servos. Not perfect, but probably less wind interference and minimal holes to patch in the wing.



I eventually managed to snake the extra-long servo leads thru the hollow part of the wing, alongside the spar. They exit in the bottom center of the wing.



Rear tail assembly nearing completion.


I've cut out the top, back of the fuselage but I'm going to try and hold off attaching it until I figure out what/how/if I'm gonna rig the cargo door and etc.

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Old 11-06-2014, 03:46 PM   #16
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Can't wait for the Kit, ARF, and PNP version to be released!

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Old 11-07-2014, 03:24 AM   #17
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Argh! Decided on the GWS 7035x3 3-bladed propeller and ... they're out of stock everywhere on the planet. It's always something. :/

Wait. Hold the phone! I found a set of them at Grayson Hobby.

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Old 11-07-2014, 02:41 PM   #18
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Originally Posted by mclarkson View Post
Argh! Decided on the GWS 7035x3 3-bladed propeller and ... they're out of stock everywhere on the planet. It's always something. :/

Wait. Hold the phone! I found a set of them at Grayson Hobby.
Here is my go to spot for GWS props....and they are in-stock too! ULTRA cheap shipping... Normal and CR too!

http://gwsprops.com/3_blade_props.htm

Mike
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Old 11-07-2014, 10:30 PM   #19
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Thanks. Too late for me this time, but I'll remember them for next time.

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Old 11-07-2014, 11:52 PM   #20
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Nice twin build cant wait to see it with paint on it. joe
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Old 11-08-2014, 03:37 AM   #21
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Pinned together the cockpit. I'm not going to attempt a realistic curved nose. Still came out a little wonky. I may have to re-do it.


Added a little 'shelf' inside the fuselage to seat the servos in. I argued with myself endlessly about whether to put it lower - and block the cargo deck - or higher and poke out through the fuselage.


Here are the tail control surfaces hooked up and ready to go.

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Old 11-08-2014, 03:41 AM   #22
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This will be my first ever twin build. I'm using twin 0.9oz 1300kV KEDA motors from StrongRC. The are definitely going to be overkill.


After what seemed like a -ton of soldering, I've got everything wired up. I decided to make a 'y' adapter for the battery rather than wire the ESCs directly together. Like all of my other ad-hoc decisions, I'm now doubting this one. Nonetheless, everything works just fine.

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Old 11-08-2014, 03:46 AM   #23
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Which brings me to a question. When using 2 ESCs, I seemed to recall that you were supposed to pull the power lead on one of them for some reason. Re-researching this question last night, I found lots of apparently contradictory information. There was some implication that it varied from ESC to ESC. (I'm using Turnigy Plush 12A ESCs)

I forgot this question altogether when it came time to test my wiring. I plugged in the ESCs and the plane fired right up. All control surfaces and both motors responded normally. If there's a problem, I don't know what to look for.

Any wisdom on the subject?

Thanks.

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Old 11-08-2014, 01:25 PM   #24
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Yes cut the red wire on one. In fact I cut both and use a separate BEC.



Trust me. The vast majority of built in BEC's simply don't play well together, one winds up overloading and you have issues. My small twins all get separate BEC's, my big ones get LiFe packs. I have done tons-o-twins.

Also, on twins I know almost exclusively use differential thrust instead of rudders. Saves lots of weight, complexity and works astonishingly well. Highly recommended.

Mike
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Old 11-08-2014, 02:14 PM   #25
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Hmmm
If the BECs are linear it is quite safe to keep both (or all four in one of mine!) red wires connected. They do not interact it is just that unless their output voltages are truly identical (unlikely) the one with the higher output voltage will do virtually all the work so the safe maximum current is still limited by one BEC but should it fail the other will take over.
All my 'multies' are done this way but then I am using very cheap ESCs that definitely have linear BECs.
Switch mode BECs on the other hand must not be connected together so if you are not sure which you have - leave one red feed out or as rcers says use a separate UBEC.
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