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Post by jetmex on Nov 5, 2004 10:12:49 GMT -7
Well, I went and did it. I've had the hots for the GP electric DC-3 ever since it came out, and after liquidating a few dead projects, was able to purchase one. Two main factors drove the decision--first, I was a crew chief on Gooneys for several years and I've always wanted to model one of the airplanes I worked on--N102BL. Second, I've always wanted to do a twin, but had been scared off by the cost and horror stories about engines out on takeoff. Now I might have the best of both worlds. The kit is an ARF with a fiberglass fuselage. She's powered by a pair of speed 400 motors, which, along with the BEC speed control, props and switch, are included with the kit. The quality is first rate in my opinion, and the fuselage glass work and paint are absolutely gorgeous. Everything was wrapped in plastic bags and partitioned off to keep the parts from banging around. Covering on wings appears to be monocote, and the supplied Eastern airlines decals are very good as well. I happened to luck into a Great Planes rebate on this model, which provides a $20 merchandise certificate redeemable at your local hobby shop. In addition, I had a Tower Hobbies $20 off special offer, so the price was definitely right. My other choice of airplanes for this project had been the Alfa Models Fw-190, but the Gooney provided more bang for my scarce hobby bucks. Naturally, the model arrived late afternoon on the day before I had to go back to work, so the anticipated building frenzy won't get started until next week! I did have time to start the transformation from Eastern Airlines livery to the scheme 102 wore while I was working on her. She was an ex-USAF C-47B, and was painted in postwar scheme--white upper fuselage with aluminum wings and lower fuselage. Aloha Airlines had flown this airplane before we got her, so the trim stripes will be their yellow and red. The left elevator will also be white, the result of a minor scuffle between the full scale airplane and my pickup truck one windy day in New Mexico! About halfway through the first mist coat, my spray can ran out of pressure, so it was off to wally world for a new one. I was little miffed until I realized that the old can didn't spit blobs of paint all over the place when it died. I also pulled some of the parts out to fondle and photograph them, and that was about as far as I got before my weekend was over. Here's a few pics. If anyone's interested, I'll make a build thread out of this and keep everyone posted on how it's going.
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Post by ctdahle on Nov 5, 2004 16:25:16 GMT -7
Hey Jaime,
I've been kind of drooling over the same airplane. Can't wait to see how yours turns out.
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Post by jetmex on Nov 7, 2004 21:15:31 GMT -7
I got some more work done on the Gooney today. The wings are now joined, no major problems there. The wood parts are all laser cut and the wing joiners were a good snug fit in the wings. A word of advice here--don't use a heat gun to tighten the covering. It's very low temp stuff (Econocote maybe?), use an iron with a sock on it.
The airplane is now wearing her color scheme as well. Stripes were applied with red and yellow monocote trim sheets (102 was an ex-Aloha Airlines airplane), the windshield and cockpit side windows were done in black. I had intended to use the kit decal windows until I found out they were clear and the stripes showed through underneath. They look solid on the decal sheet. The cabin windows will be done in black also to keep some continuity.
It was a little odd seeing a long gone flying machine resurrected, even if it was just a model. Some airplanes just get under your skin like that.....
I'll post some more pics as soon as I get some fresh batteries in the camera.
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Post by jetmex on Nov 8, 2004 16:58:44 GMT -7
The build continues: Installed the motors and their harness today. It was a pretty straightforward operation, two screws secure each motor to the mounts, which are preinstalled and set up with side and down thrust. There are strings installed in the wing center section to pull the wiring harness through. This proved a little tricky, as the precut holes in the wings are just barely large enough to fit the two-pin Deans connectors through. Use some care here, as the wing sheeting is pretty thin and if you yank on the strings too hard, something will break. I also started the nacelle/cowl installation. These are of light plastic, which looks a little flimsy at first. There isn't any vibration, glow gook or much else to contend with, and they don't have to support anything, so I guess they'll be ok for the job. The cut lines are very faint and hard to see. I left quite a bit of extra flange around each section, and will trim it down as I fit the pieces to the airplane. The instructions are a little vague as to how to attach these parts, suggesting either using CA or double sided tape. The tape idea doesn't appeal to me all that much (I have these visions of the tape coming loose in flight), so the plan for now is to CA the nacelle halves to the wings and to each other, then mount some thin plywood in a few spots around the inside to screw the cowling to. This leaves enough room at the forward end to unsolder and remove the motors if needed. If anyone has a better idea, I'm all ears! And finally, the lets-stick-it-together-and-see-what-it-looks-like shot:
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Post by ctdahle on Nov 12, 2004 12:37:03 GMT -7
What about using a couple of little dots of clear RTV silicone sealant to tack the nacelles to the wing?
Since you don't need to fuel proof, you could put the dots in strategic, concealed places and easily slice through it with a razor blade if you needed to remove the nacelles. The RTV left behind would be pretty easy to peel away from the monokote and the silicone would "give" a bit to vibration or an "incident"
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Post by Britbrat on Nov 12, 2004 16:47:21 GMT -7
I'm as envious as hell. What a yummy project. When you get tired of it as a C-47, you can upgrade to an R4D, or even one of the turboprop conversions -- or even more interestingly, back fit it to a DC-2. I hope it has a long & happy life.
Regards
Pat
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Post by jetmex on Nov 12, 2004 17:23:27 GMT -7
You know, Chris, I never thought of using RTV for the nacelles, though I think I will use it to secure the servo tray into the fuselage when I get to that point. The nacelles are now on the airplane, I decided to CA them onto the wings (old habits die hard!!). A good sharp knife blade would probably get them loose if needed, as the nacelles are stuck to the covering and not to bare wood. The problem of attaching the cowlings was solved by my friend Rick, who pointed out that since this was an electric, scotch tape would probably do just fine. And it does, and it's pretty much invisible! I'll post some more pics when I get done with my work week on Sunday.
Patrick, this one is going to stay as she is, because I was finally able to build a model of an airplane I worked on. But I would love to do one in a D-Day USAAF or RAF scheme, or as a Spooky gunship.
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Post by JohnC on Nov 12, 2004 18:56:13 GMT -7
CT's suggestion about the silicone is a good one. I use the darn stuff whenever I can... if I screw up, it's easy to correct it and it's amazing how many things you can find to use it on! JohnC
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Post by ctdahle on Nov 14, 2004 16:37:02 GMT -7
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Post by jetmex on Nov 15, 2004 6:11:11 GMT -7
The build continues: I reached another weekend, and it'll be time to get back to the Gooney after I get all the hunnydooz did! I got a little work done yesterday, and the first miss of the build showed up. A barbed shaft extension is provided to screw onto the motor shaft. The supplied 5x4 props have a rubber insert which goes into the prop hub and is then pressed onto the shaft. The problem is that it's not a really tight fit, and with the prop on the shaft, I can hold the motor shaft and turn the prop. Granted, there is a little resistance, but I don't have much confidence in their staying attached at full power. So I think I'm going to be purchasing some prop shaft adapters, to give me some method of actually securing the prop with a nut. Graupner p/n 6053-23 ought to work fine (Hobby Lobby has them), and they come with nice spinner nut to hold the prop on. The other miss was my fault--while moving the wing off the bench, I snagged the string for pulling the servo harness and managed to remove it completely from the right wing. DOH! Now I have to feed it back through, which might be a real pain, but that's what I get for not taping the loose end. There are reviews of this model in the July 2004 issue of RC report (I have a copy of the article saved, so if anyone would like to read it, email me and I'll send it to you), and on E-Zone here: www.rcgroups.com/links/index.php?id=4505And here a a couple of the best DC-3 sites on the web: www.douglasdc3.com/www.centercomp.com/dc3/
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Post by jetmex on Nov 21, 2004 13:07:05 GMT -7
Progress report: After a little fiddling, I got the servo wiring string back into the wing--with a little help from gravity and a small, but heavy, nut! The landing gear was tackled next. These came in a little bag all by themselves, and each gear consists of two struts, and axle, a couple of spacers, a threaded sleeve, a nice foam wheel and about a gazillion little setscrews. All of these are assembled to fashion the distinctive DC-3 twin strut landing gear. A little LocTite was used on all the setscrews, you sure don't want one of these coming out. Once the struts were assembled, it was time to install them on the airplane. One little problem--you can't do it with the struts put together!! The strut fits into a grooved gear block in the nacelle and wiring for the motor runs across the top of the part of the strut that goes into the block, and between the two strut halves. It's impossible to get it in without breaking something, so I had to take it all apart and install the strut halves in the airplane, and assemble the rest of the gear from there. The supplied wheels are about 2 inches in diameter, but I fly from grass, so these may be replaced with larger ones later on. The next step was to install the batteries and servo trays. These are laser cut and fit very well with a little sanding. Following a recommendation from a friend, I installed these using silicone a adehsive instead of epoxy. It made a good solid bond and was a lot easier to work with than the epoxy would have been. Then the pushrods were installed, from holes in the servo tray to the openings in the rear fuselage. A little tie wrap is provided to secure the tubes together mid run, but I think I'll be adding a balsa stick inside the fuse to support these. And, the stabilizer and all the moving parts of the tail were added. The elevators are joined with a bent wire joiner and hinged with CA type hinges, while the rudder is attached with hinge points. The only miss here was that the upper hinge hole for the rudder was misdrilled, and the top of the rudder doesn't quite fair with the fin. Relocating it would have opened up the hole enough to result in a loose fitting hinge, so I tweaked it as best I could. The model now looks like an airplane! There isn't too much more to be done, and maybe this weekend I'll get off my empennage and get a few more pics. Meantime, the assembly manual can be found here: www.electrifly.com/manuals/gpma1155-manual.pdf
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Post by Britbrat on Nov 21, 2004 16:22:06 GMT -7
Jaime -- why don't you plug the hole in the rudder with a balsa plug, & re-drill the hole --- or is it too late?
Can't wait to hear about the maiden flight.
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Post by jetmex on Dec 11, 2004 11:19:02 GMT -7
Well, I haven't much of a chance to work on the Gooney the last few weeks, but I did manage to get the aileron servos installed and tested. Pretty straightforward install there, no problems.
The elevators came out a little stiffer than I would like (hoping they'll loosen up as the hinges work in), so I'll be using a Futaba S-133 mini servo on that surface. It's got a little more torque, and there's a good chance I'll end up using one on the rudder also--we'll see how that goes.
I've also decided to use a standard size receiver in this model. The recommended micro receiver only has a range of about 900 feet. Our runway is 800 feet long, and I'm concerned about flying out of range to get over the oil tanks east of the runway, so I'll take the case off a standard unit and suffer with the small weight gain.
Patrick, I didn't notice the rudder until after I got it on, but it isn't too bad and I don't think it will affect anything.
I hope to get back to it this weekend, after I get the Christmas lights up!! ;D
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Post by jetmex on Jan 12, 2005 13:00:15 GMT -7
Santa was kind enough to bring me all the remaining pieces parts to finish the Gooney, so ff we go again....
Props and adapters are installed--per an RC Report article on this airplane, I'll be doing the first test flights with APC 7x4 slow flyer props. The adapters are Graupner items from Hobby Lobby which are setscrewed to the motor shaft and secure the prop with a nice spinner shaped nut. Aileron servos (Hitec HS-55s) were installed and wired--no big problems there. The kit supplied hardware was used to connect the servos to the ailerons.
The rudder (HS-55) and elevator (Futaba S-133) servos were installed. I had to cut the servo tray a little to fit the bigger Futaba servo. Pushrods come out right where they're supposed to, but here is another miss in the kit. The pushrods are the wire-in-tube type, and are glued into a bulkhead on the servo tray and into slots in the rear fuse. Apart from that, they are unsupported. I added one crossbrace aft of the servo mounts and they still flexed, so I added a second one farther down the fuse. That one was a bear to get in, but it took care of the flexing. Great Planes needs to do some major rethinking about that part of the installation!! Using the larger servo for the elevator turned out to be a good idea, as it's still a little stiff (hinges, I think).
Having done all of that, it was time to power the beast up for the first time. The 8 cell, 1800 mah NiMh battery was secured by the provided velcro straps into the nose and connected to the speed control with the supplied Deans connectors. The motors are also provided with these connectors, which fit very tightly together and could make removing and installing the wing a bit of a chore.
The speed control has a neat feature that prevents accidental startup of the motors if you bump the throttle. To arm the system, you have to move the throttle stick to full increase and then back to idle. Only then will the motors operate. All the servos worked just fine, though I did have to reverse a couple of them to get everything flapping in the right direction. When I throttled the motors up for the first time, I was a little disappointed that it doesn't really sound like a Gooney, but there's no mistaking it's a multi engine airplane!!
Next step will be securing all the remaining equipment and finishing off the cosmetic details. Does anyone out there have any good methods for doing panel lines that even I could understand? I want to at least reproduce the cargo door and cockpit escape door, which are pretty prominent. Also would like some ideas for the exhaust stacks, though I have some flexible soda straws lying around that look about right..... ;D
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Post by jetmex on Jan 27, 2005 10:05:54 GMT -7
I can't believe it, but the airplane is finished!! There are a few little tweaks to be made, and I'd still like to add some small scale details, but basically she's ready to fly.
Did some taxi tests in the driveway yesterday and confirmed ground handling is poor to nonexistent. That's my one big gripe with the kit--it would have been nice to have some tailwheel steering. After I fly her a little, I'll see if I can find a way to add that feature without butchering the airplane too badly. CG was bang on, and weight came out a little over the four pounds Great Planes says she should weigh, probably because I used a full size receiver and a mini servo on the elevator instead of a micro. I wasn't able to get a good full power motor run because I didn't have a fully charged battery and the esc hit the voltage cutoff. All the flight controls continued to work just fine after the motors cut out. This electric stuff takes a little getting used to, but at least I won't be having any single engine excitement on this model!!
Pictures are in the camera, as soon as I find the cable I'll post them here.
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Post by jetmex on Jan 30, 2005 16:14:44 GMT -7
As promised, here are the "finished" pics. There is still a little tweaking to do, and I'd like to add some panel lines and small scale details just to make her look a little better. I'm also looking for some decals to do the N-numbers with, so if anyone can help me out there, I'd appreciate it. I think they scale out to about 1/2 to 5/8 inch tall.....
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Post by ctdahle on Feb 4, 2005 17:18:05 GMT -7
She looks nice Jaime.
One thing I've been thinking about is that with an electric twin, you could mix two speed controls to the rudder so that at low speed, you could steer with throttle differential. Isn't that how the real Gooney worked? Was the tail wheel linked to the rudder or did it just caster? I'm guessing there were wheel brakes too.
I know it wouldn't work on this plane because you'd have to have two ESC's somehow working off of one BEC, but if someone was going to build a bigger one...
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Post by jetmex on Feb 5, 2005 11:52:11 GMT -7
Thanks, Chris! It brings back a lot of good memories also....
The real thing had a full castering tailwheel that could be locked fore and aft from a handle under the throttle quadrant. Normally, the rudder wasn't used for taxiing--steering was with differential power and brakes. Tailwheel would be locked for long straight runs and unlocked to turn. It was a bit of an art, one that is rapidly being lost.
This model has a single speed control for both motors, with the BEC incorporated into it. Still being a complete neophyte on this, I'm not sure how you could get differential throttle, but I have a set of plans for a big glow powered Lancaster that use the throttle trim for that. I don't think the lack of steering will be too big a deal, since I fly from grass and I'd just as soon save the battery for takeoffs.
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Post by Britbrat on Feb 21, 2005 7:51:49 GMT -7
That's a pretty bird. Put de-icing boots on it & go flying -- don't wait for spring. ;D
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Post by ctdahle on Feb 22, 2005 15:06:19 GMT -7
Just putting my thoughts into writing here-- Assuming, for sake of discussion that Rudder is channel 3 and throttle is channel 4, you'd need two esc's, each on a separate channel, put the left motor/esc on 4 and the right one on 5. You'd mix 4 to 5 and it would be a 1 to 1 mix so that advancing the throttle stick would wind up both motors.
Then you'd mix three inversely to four from the central rudder position to full left rudder so that as you added left rudder, the left motor would slow down, and then return to the set throttle position as the stick went to neutral. Same with the right motor, inversely mixing 3 to 6. You'd probably want to play with expo on all of the channels to make control manageable.
You could do the same with servos and IC engines too, with the added advantage that you could use the rudder trim tab to sync the motors, or for a neat scale effect, slightly "unsync" them....wwwwaa...wwwaaa...wwaaaa...waaaaa...aaaaaw...aaaaww...aaawww...aawwww!
If you had one of the new Multiplex Royal Evo radios, on that Lancaster, you could program trim changes to automatically come in as the gear came up, bomb bays opened and you dropped your scale bomb load...
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