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Old Feb 15, 2016, 07:16 PM
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Electric Duelist Mk II

I've wanted a Duelist for at least 15 years. Got the plans last spring, but let myself get intimidated. Finally decided to just go ahead and give it a shot.

Electric power, with the pack in the fuse, unlike all the other conversions I've seen. It's the only way to get decent performance and flight time, as two batteries in the nacelles, if big enough, result in a lot of extra weight. Two motors on one pack gives the best combination of speed, thrust, and flight time.

Scorpion SII 4025-520s. Zippy compact 5800 8S 25/35C. Ice 50 ESCs. 10x8 APC sport counter rotating props. Should be good for about 90mph, a 33mph vertical speed, and around 9 minutes mixed throttle flight time. Maximum amperage is around 55 for both motors.

There are some bugs in the drawings (from Air Age Store) but they're not too terrible.

I'm using Hobbico mechanical 40/60 size retracts with separate servos for the nose and mains. I made a 1/4 inch birch ply nose gear deck that plugs into the 3/8 x 1/8 crutch pieces called for on the plans. My crutches are spruce instead of balsa. The nose gear, retract servo, and nose wheel steering servo are all mounted on the deck.

The elevator and rudder servos had to be moved to aft of the wing opening bulkhead F6, to make room for the pack. All the formers from the wing TE forward are birch ply, with the TE and LE formers being 1/4 inch. All the formers aft of the wing are 1/8 lite ply. The upper and lower pack decks (upper is installed in the pics) are of 3/16 balsa. A removable canopy hatch will allow the battery to be R&Rd and connected. The fuse as designed could not have handled the weight of the pack.

I'll be using separate channels for the ESCs, so that I can program differential throttle action on the ground. (A switch to enable) This also allows the 5 amps from each ESC's BEC to be used to power the servos. I'm using the Futaba 8J S Bus system, so this approach works out very nicely.

I'm going to modify the wing to allow some very large split flaps. Hoping to use Tru Turn turbo cool spinners.
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Last edited by Bob Hunt; Feb 17, 2016 at 10:37 PM.
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Old Feb 16, 2016, 08:16 AM
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I thought about doing one of these as well. I had a kit and was surprised at how big the model actually was, and also just how involved a build it would be. I ultimately decided I didn't want to put that much work in it, and sold it. But no doubt it will be a sharp looking model when done.

Any particular reason you are not going with electric retracts? Given how common they are now, and the ease of installation compared to mechanical retracts, I would think that would be the way to go...Pete M
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Old Feb 16, 2016, 10:22 AM
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Pete: on the retracts, I went for cost and reliability. The Hobbico retracts are 25 bucks, servos 28 apiece. Under a hundred bucks. The Horizon 60-120 size are way over $200, and have been getting a reputation for the trunions speading. (The aluminum's not hardened, I guess.)

I've used the Hobbicos on a couple models, and they've always been reliable.
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Old Feb 17, 2016, 10:35 PM
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The plans say to sheet the fuse with one huge piece of 1/8 balsa per side. Yeah, right. Sorry, Dave. I used a 2" piece that basically followed the crutch, then a one inch above that, and half inch pieces above those. That's about as high as I can go until I make the tail feathers, glue them on, and hook up the elevator and rudder pushrods. (The servos will be buried after all the sheeting is on.) The joys of electric conversions. The pack is where those servos would normally live.

I've built so many models from plans (maybe 30?) that I've managed to learn a few tricks along the way. Ed Westwood taught me to centerline EVERYTHING, both sides. Then, I don't trust anymore that anything will come out straight or even on both sides. I always check for verticals getting out of whack due to gluing stress. Most importantly, I always measure out from the centerline to the edge of each former, both sides, top and bottom to see if they truly are symmetrical. Had to do some shaving and filling on this one, but it truly has turned out straighter and more symmetrical than anything I've ever built.

Got the rudder halves epoxying together as this is written.
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Old Feb 18, 2016, 09:09 AM
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Onward and upward.
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Wow, nice build, Bob. I'll be watching this one. I've always liked the lines of this ship. It looks like you're building it like one as well.
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Old Feb 18, 2016, 12:09 PM
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Retract's

Pete: I do the same as Bob. Lot's of very robust mechanical retracts available cheap. Use a servo on each leg and you basically have electric retracts that are less expensive and more durable than electric retracts. Also with the migration to electric retracts there are lot's of larger air retracts being dumped by guy's pretty cheaply. Air retracts are pretty easy to convert to servo operated mechanicals. Larger retracts with high torque metal gear servos are still much less than a large set of electrics.

Give it a try.

John
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Old Feb 18, 2016, 02:24 PM
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Oh, I have done both mechanical and air retracts in my day, but now prefer the electric. Can get some pretty inexpensive sets from Hobby King now...Pete M
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Old Feb 19, 2016, 03:21 PM
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Stab and elevator completed and hinged, stab epoxied on. I've had really good luck with the dubro heavy duty nylon, two piece hinges. I use a single piece of .047 piano wire. Makes removing and refitting the control surfaces really easy. Gluing them in place is also easy: I assemble the fixed and movable surfaces with a single piece of wire, and then use a T pin to punch a hole through the top, and just through the hole in the hinge. Then flood the holes with thin CA. Important to put a couple drops of oil on each hinge joint before gluing, so the CA won't get in there and make them bind.

Playing around with ecalc today, and realized the Power 52 will do a better job than the Scorpions. More than a hundred bucks difference. Ordered a pair from Horizon today.
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Old Feb 23, 2016, 03:49 PM
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Giving me a flash back on my second kit build ever. Mine runs power 32 on 4s batts in the nacelles. I added flaps and electric retracts. 10 lbs. give or take. Good luck with her. Looking great. ps- mine runs standard rotation 3 blade props. Tracks straight as a arrow. No issues at all. 160 watts per lb. there are more than one way to achieve your goals.
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Old Feb 23, 2016, 05:26 PM
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Thanks, Walter. I really love your VVS rendition. What's the pitch and diameter on the three blades, and what size pack? So you evidently had the Pica kit?
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Old Feb 24, 2016, 06:39 AM
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I guess it is because I am a kit builder but I have never seen this technique with the formers glued to the board to build a fuse before! It looks like just an excellent way to go to me though. I wonder why it is not more 'standard'?
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Old Feb 24, 2016, 07:04 AM
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im using a 4000 4s pack in each nacelle. i am not sure of the pitch. i would guess around 8.
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Old Feb 24, 2016, 07:21 AM
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I used the "tabbed formers" once before, on a Pavel Bosak F-4. He didn't draw it that way, but I couldn't figure out any other way to do it. I was surprised to see it used on the Duelist. Makes construction much easier, IMHO.

Walter: I ran the numbers on yours across ecalc. Looks pretty peppy with that combination.
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Old Feb 24, 2016, 07:28 AM
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After testing with watt meter I came up with 160 watts per lb. give or take. She flys well. She is a pica kit.
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Old Feb 27, 2016, 02:13 PM
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I saw the Pica duelist kits offered when I first got into RC at the end of 2001. Still kicking myself in the butt for not getting 2 or 3 of them.

After much labor, the upper fuse and battery/canopy hatch are complete. Hatch held on by dowels front and 5 rare earth magnet sets aft. Works great. Turned out much better than I had any reason to expect. Having the assembly firmly held to the bench on the tabs really helped, with sanding, gluing, measuring, shaping, etc. I might use this method on future builds, depending.

Next step is to cut it off the tabs and finish the bottom of the fuse.
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