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Old May 12, 2013, 08:49 PM
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United States, CT
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Build Log
EF-111A twin 64mm

I'm fairly new to RC flying, but I've dabbled in RC and other modeling off and on my entire adult life (and most of my childhood.) I've built a number of planes over the years -- usually balsa and ply covered with tissue or Monokote -- but I had never succeeded in flying any of these more than once or twice before premature contact with the ground resulted in splintered wood and torn coverings. Some never even made it that far -- I recall spending weeks building a gorgeous tissue covered free-flight scale Spitfire only to have my grandfather inadvertently sit on it.

I recently reentered the hobby and discovered a metamorphosis has been brought about by the combination of outrunner electric motors and Lipo batteries. I bought myself an MX2 airfoil kit from FancyFoam (EPS, not Depron) and have succeeded in learning to fly it. Flying an RC plane more than once is a new experience for me, and I am quite enjoying it. Aside from the occasional encounter with the magnetic trees that seem to grow around here, I am able to fly my MX2 around fairly capably. No 3D yet, but it goes where I want it to and I can roll it, inside/ outside loop it, and land it. That it is still in one piece after 20+ flights is a testament not only to lightweight foam construction, but also to the decent RC simulator (Phoenix) that I practiced on during the winter.

Although I consider myself a rank novice where it comes to flying RC planes, I do have actual aviation experience. I spent the 1980s flying EF-111s at Mt Home AFB and RAF Upper Heyford as an EWO. It seems only natural that I build an EDF F-111 or -- better yet -- an EF-111A. My RC flying skills are not currently up to flying such a model, but they will improve and in the meantime, I can start building it.

There do not seem to be any EDF F-111 kits around, however. I searched fairly extensively, and all I found were some rumors of a twin 70mm one due out a couple of years ago that never materialized (http://www.rcgroups.com/forums/showthread.php?t=1509300). I have therefore decided I will scratch build an EF-111A. My build will be based on the plans by Momotaro at http://www.rcgroups.com/forums/showthread.php?t=827177 . Momotaro has a build log of this at http://momo-machine-works.seesaa.net.../557895-3.html but it does not appear that he ever finished it. There is also a build thread of these plans by Frenche at http://www.rcgroups.com/forums/showthread.php?t=1369105 but it does not appear that he ever finished his build either.

I believe a reason for the scarcity of F-111 RC models is due in part to the high wing loading of the plane. Momo's plans are for a 1/20 scale twin 50mm model, and looking at various 50mm EDF options it didn't seem like there was anything that would have enough umph without an extremely light build and then structural rigidity (or lack thereof) is an issue. Building it light and then putting a pusher prop on the back of it is an option, but I want to build a scale model of what I used to fly, and what I flew definitely didn't have propellers on the back.

I've decided to scale Momo's plans up by 125% and build a 1/16 scale twin 64 mm EF-111A. There are 64mm EDFs with decent thrust (e.g..http://www.hobbyking.com/hobbyking/s...it_2s_4s_.html ) and I can build a stiffer plane if it is a bit larger and I include CF and balsa or ply. I'd like to keep the wing loading to 25 oz/ ft^2 -- at 1/16 scale this equates to a 4 lb flying weight. I am figuring on 2 to 2.5 lbs for the hardware (EDFs, batteries, servos, etc.) which means I will need to try to keep the empty plane to 1.5 to 2 lbs. I will use a combination of balsa, CF, and foam and cover it with 1/2 oz fiberglass. Even if I end up a bit heavier than I intend, the Hobbyking Mercury Alloy 64mm EDF units should still be able to provide better than 1:1 thrust to weight. I am not planning on any landing gear so I may have to launch it with a catapult/ bungee. If I can figure out how to get retractable gear into the fuselage without much added weight, I might try, but a no-gear plane with a PVC-rail bungee launcher seems simplest (and certainly lightest) and the EF-111A's bottom 'canoe' (jamming pod) and tail strakes should make nice reinforcements for belly landings. Needless to say, the wings will sweep. Both pitch and roll will be controlled by the horizontal stabs (elevons). No ailerons or flaps, and w/o landing gear, I see no need for rudder control either.

Specs will be:
wingspan: 3' 11" (unswept); 2' 0" (swept)
length: 4' 9"
EDFs: HK Mercury Alloy 64mm 4700KV X 2
AUW: 4 lb 0 oz
Wing Loading: 25 oz / sq ft

I've started the build already -- I'll post some pics of what I've done so far next.
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Old May 12, 2013, 09:48 PM
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United States, CT
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Since the 'heart' of the plane is the swing wing, I decided to start by building the wing box. Everything attaches to this: the wings and also the front and back fuselage halves. I used a combination of 1/8" light-ply and 1/8" and 1/16" hardwood ply for the box. 1/8" light-ply isn't really quite 1/8" and by doubling this with the 1/16" aircraft ply, I was able to get the correct scaled thickness and also save a little weight. Instead of drilling out holes in the box as the plans showed, I cut out the entire inside of the box. It's the hinges themselves that will take the stress -- the center portion of the box even with the cutout isn't going anywhere.
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Old May 12, 2013, 10:00 PM
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United States, CT
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Since the wings attach to the wingbox, I built these next. I added a secondary CF spar and some 1/16" ply reinforcement at the wingtip and 1/64" ply along the trailing edge. I used a few playing cards as shims to create a couple mm (about 2-3 degrees) of washout at the wingtips.

I attached both wings to the spar box to get an idea of scale and make sure things fit correctly. My cat oversaw the operation. He is also a very helpful building companion and has a chair next to mine from which he supervises my building efforts.
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Old May 12, 2013, 10:08 PM
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The whole point of a two layer construction is that the top and bottom skins need to communicate with each other, so I added balsa ribs and secondary spars that will support the upper skin.

To get the airfoil section for the ribs, I measured the heights at the spar locations and then subdivided each span in half and added half the differences in heights at this location -- I eyeballed it after that.
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Old May 12, 2013, 10:23 PM
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United States, CT
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I saw the thread here about a $10 vacuum bagging system ( http://www.rcgroups.com/forums/showthread.php?t=966524 ) and thought I'd try it. The air pump I used was from Walmart and didn't even cost $10, but $7.95. I suppose the coffee can cost another $2 with the coffee in it, but I drink that anyway, so it was scarcely an expense.

To try this out, I cut out and shaped the two horizontal stabilizers from 6mm Depron and vacuum-bag glassed them with 1/2 oz fiberglass cloth inside a 2 gallon freezer bag using my home made pump. I reinforced both foam pieces with 1/8" light-ply along the inboard edges before I bagged them. My homemade pump worked well, but the pieces of plastic I used for the mylars (laminating plastic from Walmart) were too thin, or my paper towel was too firm, because I ended up with the paper towel pattern embossed into the stabs. I can fill this with primer or I might try again with a stiffer plastic for the vacuum bagging 'sandwich.'
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Old May 12, 2013, 10:47 PM
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I precurved the upper wing panels by pulling them across a table top and also applying mild heat (hair dryer, not heat gun.) To glue these, I first epoxied the training edges to the 1/64" ply that I had used to reinforce the TE's. The 3mm Depron is thin enough that after this cured, I could easily flex the pieces upwards enough to apply epoxy to the ribs and spanwise spars to attach everything else. Since the TE was already firmly glued at this point, I didn't need to worry about futzing with the alignment and could make sure everything was evenly weighted and in proper contact.

After the top panels had cured, I cut the leading edges out of 1/4" sheet balsa and epoxied these to the wings before sanding them into their final shape.

This post catches up to where I am at now in the build, so from now on things will be at the slower pace of real life, meaning there probably won't be much more progress until next weekend.
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Old May 12, 2013, 10:57 PM
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Hampton, VA
Joined Mar 2009
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Was wondering when someone else would pick up on Momotaro's plans. I was kinda green around the gills, when I first cut foam. The twist, I scaled down for a twin 30mm setup. At the time, I think I may have been reaching a bit. But now, I think it's doable. Still have all the parts I cut. Subscribed!!!

Ksqm
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Old May 13, 2013, 12:16 AM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
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cool project ,i love working with depron its fun to heat form it ck out my Draken Thread i did a few years ago.i just glassed my parts with out vacuum bag.depron is too soft to bag ,unless you use it for a core material in a mold so you get a glass smooth suface.
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Old May 13, 2013, 04:11 AM
ooooh yeah
Frenche's Avatar
Ballarat, Victoria, Australia
Joined May 2004
1,599 Posts
Yeah I still have mine, somewhere. Build stalled when I was trying to figure out what power system to go for, either lightweight 3s setup or a heavier more powerful 4s setup (those wings are damn tiny!). Then I decided to switch jobs and buy a house so it kinda got shuffled down the pile. I keep meaning to design my own around about twin 70mm size for hand launch (figuring a nice light setup) but just need to find the time.

If you want anything drawn in 3d let my know, I'm a design draftsman by trade so am pretty handy with solidworks.
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Old May 13, 2013, 07:43 AM
Buildings what I enjoy.
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Looking good so far. Can't wait for the rest of the build log.
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Old May 13, 2013, 07:50 AM
Aus
ʎןɟ inverted ɹǝpunuʍop
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Did I hear a pig squeal? Subscribed.
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Old May 18, 2013, 01:15 AM
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Thanks for all the kind replies. Air Sally, that Draken of yours is gorgeous. ksqm, I had seen your posts about your smaller build previously -- you should see if it flies. (Then you can tell me where to put my CG.) Frenche, thanks for the CAD offer but I tend to just sketch things out in pencil on the foamboard I'm cutting on. Aus, I love your avatar. When I saw it, I realized that I neglected to mention that Momo's plans were using the extended wings that the Aussie F-111Cs and the SAC FB-111s had. The EF-111A did NOT have these, and I had shortened the wings on Momo's plans accordingly before I started building them.

I still haven't started on the fuselage, but have been futzing around with how to finish the model. I figured my semi-successful vacuum bagged glassed stabs would be a good test-bed for finishes since they weren't that hard to make, and if I had to do them over again (using a heavier Mylar), I wouldn't mind. Trying to find the correct colors in rattle cans has been trying, but has given me something to do on the way home from work during the week. (Home Depot, Lowes, Advance Auto, Walmart, and two LHS's.) I was beginning to think I might actually need to learn to use the airbrush I have that has been sitting in its box for 15 years so I could mix the colors I needed, but I have decided that Testors Model Master 'Camouflage Gray' is a good match for the underside and that Valspar 'Silver Fox' (a Lowe's item) is good for the cooler darker topside gray. MM 'Dark Ghost Gray' would also work for the top, but it is not available in rattle cans. MM 'Gull Gray' will work for the warmer gray that is on the radome and a few other spots.

After I trimmed the excess fiberglass off the two stabs, I became concerned that the 1/8" lightweight ply I had used for the inboard edges might not be stiff enough. A floating stab worries me since if the front of it flexes, this will be an unstable situation leading to increased AOA with flexion. (Think about why we don't put ailerons on the leading edges of wings.) I don't know if this would really be a problem, but to be safe, I drilled into the two leading edges near the front and ran 1/8" CF tubes into the front halves of the stabs. This messed up the LE a bit, so I fixed this with epoxy and micro filler. If I were doing this again, I would use proper 1/8" hardwood ply instead of the light-weight stuff for the inboard edges.

I started priming the stabs using some DupliColor primer I got at Advance Auto Parts. As you can see in the attached photo, the paper towel texture is pretty evident, but another coat or two should fill it. Of course, this totally defeats the purpose of the vacuum bagging which was to save some weight, but the stabs aren't that big, so the weight of the extra primer shouldn't be too much. (And I may end up redoing them anyway if I screw up when experimenting with the finish.)
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Old May 19, 2013, 04:50 PM
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After I added the second coat of primer to the vacuum-bagged horizontal stabs, some pinholes appeared, so I rubbed lightweight spackle into the surface before I added another primer coat. It seems to have worked. Although the surfaces are nowhere near perfect, I stopped after the third 'spray on / sand off' of primer. I added some detail in the form of lightning dissipaters (0.025" piano wire) and the small nubbins at the apex of the TE that I'm guessing are anti-flutter weights. (You'd think I should know what these are, but I don't.)

I painted the tops and bottom with the rattle cans last night. Both paints (the MM and the Valspar) are enamels and are not nearly dry enough to clear coat yet. I took some pictures anyway. The Testors MM 'camouflage gray' is very slightly too khaki. The underside grey on the real planes was a warmer grey than the top, but not quite as warm as this. The Lowes Valspar 'silver fox' still looks like a good match for the topside color.

The stabs weigh about 3/4 oz. each now whereas before the priming (but after the vacuum bagging) they were about 1/2 oz., so I'm going to need to improve my priming technique. The stabs are very thin, flat, and strong, though, and I am pleased with the results.
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Old May 19, 2013, 05:16 PM
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As you can see, I am dallying with starting the fuselage. I'm thinking I may start with the top rear first. I've been perusing Momo's plans (which are in Japanese) and his blog (which is also in Japanese) and have come to the conclusion that the part at the bottom of page 7 and shown in the illustration on this same page is only a template for feathering the foam to support the top panel correctly or is a leftover from a less detailed plan. If this part were glued in place, I do not see how the top panel or the rudder could be attached.

@Frenche and ksqm (or Momotaro if you are around): can you confirm that the part on the bottom of page 7 of the plans (circled in red in the attached image) is just a template?
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Old May 19, 2013, 09:43 PM
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Hampton, VA
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Grant58,

That d@#m part drove me crazy.LOL Yes, I think it's just a template to get the ramp right. I must of studied Momotaro's web site for a month, before it hit me.

Ksqm
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