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Old Oct 30, 2009, 03:38 PM
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Ace12GA's Avatar
Canada, ON, Peterborough
Joined Oct 2009
425 Posts
Build Log
Twin boom pusher, MK2 underway, Video added.

So I have been lurking for a little while, gathering information, patterns, and wisdom. I have probably 3 hours of flight time on a Slo-V, 1 poor hour on an Aerobird extreme, and lets be generous and say 8 hours on a sim. I'm not going to count the 25 or 30 hours on coax helicopters. I'm not new to RC, but the 20 years of land based Rc just don't count when we add in the 3rd dimension. With that I thought it would be a good idea to build my own plane. Yeah, really.

So I ran out and bought some pink foam from Home Depot without really thinking about it. I looked at those 1" and 1/2" sheets for a week before doing some more research. I spent a week trying to build a hot wire foam cutter (unable to find a good enough transformer as of yet) after moving on from that, which is about the time I started to like profile foamies. Trip to the dollar store later, and I had several sheets to work with.

I built and wrecked an F22 I found on these boards, the little 18" guy. Had a blast building it, had a blast wrecking it. Motor was too heavy, battery was too heavy, it would struggle to stay level and crash terribly. Next I tried to build one of those 1 minute delta wings; I actually built 2. Actually got that one to fly around the yard a couple of times before I wrecked both airframes and 1 prop. I also bent the motor shaft a little. I learned a lot about working with the foam, and especially carbon fibre rods and tape hinges. And one interesting thing, the KFM airfoil; that would come in handy.

At this point I was a little frustrated. What I really wanted was a pusher that would just fly. Nothing fancy, nothing hard to make, just a simple pusher. I love the OV10 Bronco, but I didn't want a twin. The basic idea however, the layout, would still work. So that's what I went with, a twin boom layout, but still a pusher.

After trying a few things to shape the airfoil from the pink foam, I gave up and decided to build a KFM2 airfoil from the foam board. That proved to be very easy. Some staples premium packing tape and hot glue later, and I had a wing. The sheets of foam core board I get are 30" x 20", so the wingspan is 30", the biggest I can make it in one piece. That was just fine with me.

With the wing I started working out the rest of the plane, cutting, and gluing it all together. 2 hours of messing around turned into the plane you see in the pictures. I mounted a motor to it using a thin piece of pine and hot glue again. In fact, I used hot glue to assemble the whole thing. This is the motor:

http://www.hobbycity.com/hobbycity/s...00kv_Outrunner

I put a 10x4 prop on it, which gives loads of power on a 2s battery. I used the cheap HXT900 servos from hobby king as well, and they work great. 2 of them are survivors of the previous several attempts. One survived having the control horn tear loose and pull the wire into the prop, snapping the servo arm clean off its hub, and destroying the prop. I was impressed by that.

Its laid out with ailerons and an elevator. 3 servos are used in total. The servos are mounted by applying the premium packing tape to them, and then hot gluing in place on the wings. I used mixing in the radio on the ailerons. I did this to experiment with the effect of flaperons while landing. There is a huge empty field behind my home, but there is a 6' fence to cross coming back into my yard, meaning I have to come in steeper than I like; I thought I might be able to keep from stalling by simulating flaps on landing, to slow my approach while coming in steep. Still experimenting with that. The flaperons are done through mixing one of the rotary knobs on my radio to the servos that control the ailerons. The mix is turned on and off with one of the switches on my radio. The neat part is that it allows me adjust the flap angle easily by the rotary knob. If any of you guys have experience with this idea, let me know what your experience was like; success, failure, etc..

I powered it all with a 2s 1300mah lipo pack, which I mounted using a slot cut into the fuselage. The fuselage needed to be longer, because it was tail heavy. The CoG was more than half of the cord. I tried to fly it anyway and was rewarded with almost no control of roll. It was great. I almost crashed it into my wife. I taped a 9v to the nose to help balance it, and that did the trick. It flew. First flight was 100' across my yard. Awesome.

I spent some time cutting 1" square aluminum to use as weight in the nose, and was off to the races. The next flight was a full out flight. At the last minute I figured it could use the 9v battery for extra weight still, so I taped it on too.

I launched it by holding it forward of the wing and tossing it gently into the air at a 45 degree angle with the throttle at about half. It climbed comfortably and slowly. Little work on the trim and I started doing some circuits. It cruises well at half throttle, and in fact I didn't open the throttle up at all that first pack worth. I practiced landing and launching. I tried a roll, and nearly lost control when it dipped towards the ground quickly while half way through the loop. Of course I crashed it a couple of times. It survived, mostly. The final crash of the day took a little hot glue and tape to fix. It was too nose heavy, that 9v had to go.

The second flight was a little nicer, with a tendency to climb over half throttle. This time I got a little aggressive, doing a couple of loops, and some rolls. It rolled a lot nicer with the CoG dialed in. It looped well, tighter than I expected. In short, it flew great; hard to stall, easy to control, and docile, with the ability to do some fun stuff. Beyond 3/4 throttle it just gets noisier, not faster. I got 5 minutes or so flight time this flight; with a great nose snapping crash at the end. More tape and hot glue and it was back for more.

To prove it wasn't a fluke, I had another flight this morning, similar to the second, right down to the nose snapping landing at the end. I performed 5 great landings on grass, followed by one hard one when I lost orientation dodging a fence. My neighbour got a good laugh out of it though.

I'm already planing out my second version, which will hopefully be as successful as this one. That is really why I'm starting this thread, for the building of the second one.

EDIT: Video added, finally. It sort of sucks, shot from a tripod, but you get the idea. If I can ever get my wife to stand still and help film one, there will be better footage.

Home Built RC: Twin Boom Foam Pusher (1 min 24 sec)
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Last edited by Ace12GA; Nov 02, 2009 at 08:54 PM.
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Old Oct 30, 2009, 04:47 PM
Avro Arrow fan
Jaytee's Avatar
Canada, ON, Pembroke
Joined May 2006
34 Posts
Cool looking plane, congrats on the success. Plans??????????
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Old Oct 30, 2009, 05:09 PM
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Nebraska USA
Joined Mar 2008
1,450 Posts
Good job, Ace!

Regarding the flaperons, try reversing them into spoilerons, with the surfaces moving a few degrees up rather than down. I do this on a similar design (a modified Funder & Lightning) and it works much better than the flaperon method, mostly because of the outboard location of the ailerons. I also add a bit of up-elevator into the mix to hold the nose up. It really slows the plane and gives slow speed stability. Try it!

Keep up the good work, you're on a roll...!

~Roger
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Old Oct 30, 2009, 05:16 PM
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Surprise, AZ
Joined Jun 2009
121 Posts
Looks like fun man! I may have to try something similar soon. I have all I would need (besides motor and ESC) if I only used one servo for the ailerons, so all I would really be out is some foam. Now lets see a vid! HAHA!
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Old Oct 30, 2009, 06:51 PM
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Canada, ON, Peterborough
Joined Oct 2009
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I'm going to try to get some video of it on Sunday; winds are supposed to be about 5km/h, which is as close to dead calm as it gets around here. This mornings flight was in about 15km/h winds, and it handled them well enough. Sadly it rained the rest of today, and it is supposed to rain all of tomorrow to boot.

Zaurak3: I'm going to try that spoiler idea, just a simple turn of the knob on my radio to implement. I'll report back if its effective or not.

MusicManiac: You would need to set up aileron torque rods for one servo, which depending on my success with falperons/ spoilerons, I may do with the second version to save a servo. If I can build these with two servos total, that would be awesome.

Jaytee: No idea how to layout pdf plans like a lot of the guys do. I can do up a simple drawing however with the rough dimensions and CoG if you really want it.
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Old Oct 30, 2009, 07:20 PM
Goes in hot, comes out hotter.
Heathridge
Joined Oct 2009
182 Posts
Cool plane! Your wings are really short! I'd add a few inches more span - you'll get a lighter wing loading
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Old Oct 30, 2009, 07:31 PM
Avro Arrow fan
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Canada, ON, Pembroke
Joined May 2006
34 Posts
Ace, some rough dimensions would be fine. Enquiring minds want to know........
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Old Oct 30, 2009, 08:24 PM
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Nebraska USA
Joined Mar 2008
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Ace - I think you'll find the spoileron arrangement will work nicely with that design. It's very similar to my version of the F&L, and I can make steep, slow descents when I switch in the spoilerons. I originally thought to make mine a pusher as well, but I knew the CG would be too far aft without extending the fuselage forward, so stayed with the tractor config for now. I'm using a similar motor, a TP 2410-12 that provides plenty of power - cruises easily at 50% throttle. Will attach a photo.

Good luck on Sunday!

~Roger
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Old Oct 31, 2009, 12:15 AM
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Canada, ON, Peterborough
Joined Oct 2009
425 Posts
Wings

So I built the wings for the new one tonight. Trying something different, in that I changed the profile a little, increased the wingspan by 10", and am going with a KFM3 as opposed to a KFM2. I attached a few pics.

Basic process is this:

-Cut out the rough shape from 5mm foam board, and scored the fold point with a pen.
-I then used two strips of premium packing tape on the outside of the fold to support the foam.
-Before folding I used a .5" aluminum bar to partially compress the foam at the fold point. I then folded it.
-Next I cut 2" wide strips for the second step of the KFM3 design. I left the paper on these strips for rigidity. In the future I would probably use balsa instead.
-With hot glue (I know, I should use a spray adhesive, or something lighter), I glued the strips down.
-Once the strips are glued down, I completed the fold by gluing it down again with hot glue.
-Touch it up a little here and there, and use lots of even pressure while the glue sets.

Wings done! And so I am I for the night.

Start on the fuselage and tail booms tomorrow. I intend to use a balsa dowel or carbon fibre tube to reinforce the leading edge when I attach the wings together at the fuselage. I may try a fibreglass arrow shaft, which I think is lighter than balsa, and a lot cheaper than carbon fibre. See what's on sale at Walmart or Canadian Tire.
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Old Oct 31, 2009, 02:11 PM
Prop Buster Extraordinaire
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Seattle
Joined Aug 2009
1,201 Posts
Nice plane.

It will be interesting to see how your choice of step locations does. I went with 50% and 75% chord for mine.
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Old Nov 01, 2009, 10:19 PM
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Canada, ON, Peterborough
Joined Oct 2009
425 Posts
Made some progress over the weekend on the MK2. I built the fuselage and booms, and mated the two parts of the wing into one.

The fuselage is two 1" pieces of pink foam laminated together with spray adhesive, and then cut out on a band saw, and finally sanded lightly. I decided to mount the wing in an enclosed slot, as opposed to right on top. I cut the slot by drilling a series of holes and then using a hacksaw blade to cut it out. It turned out a lot better than I expected. I used two pieces for a little more weight and hopefully to be stronger. I also toyed with the idea of sanding it into a more rounded shape, but decided to save that for another build.

The booms are made from 1/2" pink foam just like the original. This time, like the fuselage, I cut a slot in them so they wrap fully around the wing. The horizontal stabilisers were cut separately and glued onto the booms.

Finally, the wing was glued together before being assembled into the fuselage. A 20" wooden dowel was glued into the wings to give support of the booms. The dowel extends 4" beyond the tail booms through the wing. The dowel is located at the first step in the wing.

I just need to cut the vertical stabilizer and the control surfaces before I start installing the electrics.

This will be powered by a similar motor to the first, but on a 3s pack with a 7x4 prop; that's the plan right now any way. I have some 8x4 props on the way, and I may use one of them instead.

I tried spoileron's on my first model, and it does slow it down nicely, but the reduced control makes me not want to use them. I shot some video from a tripod today, so I will try to get that up tomorrow. Need to edit out the boring parts first.
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Old Nov 02, 2009, 08:55 PM
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Canada, ON, Peterborough
Joined Oct 2009
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Video added in the first post. Its a little rough. MK2 is coming along well too. Just working on the hinges tonight, hopefully mount the electrics tomorrow night, and maiden it by this weekend.

If it flies well, I will post some plans, as best I can.
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Old Nov 02, 2009, 09:05 PM
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Nebraska USA
Joined Mar 2008
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The new one is looking good, Ace. I like the Bronco look. It'll be interesting to hear how that KFm3 wing performs for you.

With the spoilerons, you may have to use high-rates. I can fly almost 3D style with slow, tight turns on the wingtip with the spoilerons and a bit of up-elevator kicked in. Shut them off and the speed about doubles. Will watch for your video.

Yesterday was a great day here (finally!), took 4 models to the field and ran through 8 batteries for a nice afternoon's worth of flying.
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Old Nov 02, 2009, 09:13 PM
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Nebraska USA
Joined Mar 2008
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Just watched your video - nice! Seems quite agile with the short wing. How's the roll rate? I'd guess impressive. It'll be a good comparison with the larger wing area on your new one.
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Old Nov 03, 2009, 02:27 AM
just Some Useless Geek
Chicagoland
Joined Oct 2008
2,529 Posts
Hey, as I said on yer YT vid, you need to check out a Smart Dart XS for something soft and easy to fly as well as this high speed park jet. Gotta have this plane to fill your need for speed, but you gots to also have something relaxing to fly when you just want to put a plane in the air and watch it cruise around.
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