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Model Airplane News "Build to Win" Contest, Build Thread

Joker 53150

Mmmmmmm, balsa.
Mentor
#1
Most of you probably don't know, but Model Airplane News is running a build contest right now. The contest revolves around a "core" plane design that the builder finishes off in his own style. The core takes you about 75% of the way to a finished plane and from that point on it is up to the builder to decide how to finish it. It isn't a project for a first-time builder, but it isn't necessarily a difficult build depending on what you want the finished plane to look like.

Here are a couple of examples built by the plan designer. Both share the same fuselage and wing, but the tail, nose, and top of the fuselage are obviously very different.

(no, this isn't me)
RU Planes.jpg


I like building balsa models, although I've only done a few of them so far and I'm far from a seasoned builder. I don't have any expectations in winning anything in this contest, but am joining it for the fun and to build some skills along with the plane. As with my other balsa builds I've got a more detailed build thread on RC Groups HERE, but hope that creating the thread on FliteTest's forum might get people interested in really building a plane instead of simply assembling the parts. It is very rewarding watching something you built from pieces take to the sky!
 
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Joker 53150

Mmmmmmm, balsa.
Mentor
#2
So I knew I wanted to build for this contest, and found out my dad wanted to get into it as well, so I ordered two of the laser-cut kits from Hobby Hanger in Florida. The plans are available for free and include all the drawings so that you can scratch-build without having to buy a kit, but I prefer the laser cut kits when available. Their kit isn't as cheap as I think it should be considering it is a "short kit" (a number of stock pieces of balsa need to be purchased from your local hobby shop or online), but it still is worth the price to me.

With the kit on the way I had to come up with a design idea. I didn't want to change the overall design too much as I'm worried it wouldn't fly properly. I know people will make it a high-wing or even bi-wing, but I'm sticking with the standard low-wing. Searching for ideas I ran across a set of control-line plans for the Ryan Navion my dad purchased decades ago. It's almost the same size as the contest plane so I figure it would work out perfectly!

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Lining up both sets of plans I confirmed that the Navion plans will work well with little modification. The Navion's fuselage is more rounded, the tail surfaces are different, the canopy needs to be made, a cowl is required, etc. But I think I can pull it off.

The laser cut kits arrive in a few days and were nicely packed. I received two of the contest planes plus an L-19 I bought for my dad since he's wanted to build one of those for years.

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All balsa and plywood parts are cut very well, although there are a few spots of harder wood where I had to finish the cut with the hobby knife.

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I'm guessing they were rushing to have this kit ready for the publication date on the magazine because it isn't perfect. The vertical stabilizer doesn't line up exactly with the plans. I'm not using this tail anyway, so that didn't bother me much.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#3
The fuselage build is pretty straight forward. Add some stringers to the sides and mount the formers between the sides. However, once the stringers were glued to the sides the sides became much stronger than before and they didn't want to bend too easily. The nose is narrower than at the wing so I had to get creative to avoid breaking wood from bending it. I had read somewhere that spraying the balsa with Windex or another ammonia based window cleaner would make the wood flexible, but when it dried it was back to full strength. I tried it and found it works great! More on that later...

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So the basic fuselage structure is about done as far as the plans go. No changes from the plans this far. As I was building it the design reminds me a lot of a couple other balsa planes I've built, so I'm hoping to use what I learned there to make this one go together well.

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The Navion has a curved fuselage top that I wanted to copy for my build, so I grabbed some card stock and made a template. The template was transferred to 1/16" balsa sheet, but the balsa really doesn't want to curve into this shape without snapping. Out comes the Windex again and I soaked the sheet for a few minutes. It then curved very easily into shape on top of the fuselage. This pic is just a series of clamps to hold it in shape while it dries. Once dry it holds about 80% of the curve, plenty for me to work with in creating some structure inside it for strength. I'll need to do the same for the front of the fuselage, and will then need to trim the pieces down to work with a canopy.

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The battery location in the stock plans is in the nose between formers #1 and #2. The battery goes in through a hatch in the bottom, right in front of the wing. I'm planning on using electric retracts for this plane, assuming they ever arrive from China and actually fit, so the battery will have to go in another way. My plan right now is to make the canopy removable so the battery can go in from the top. But that may change depending on the retracts. Either way I'm going with trike-style gear on this plane instead of making it a tail-dragger.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#4
The wings are pretty straight forward and offered no surprises (yet), although I haven't finished them as I still need to see if the retracts will fit.

The wings are also where you need some of the extra balsa pieces not included with the kit. The tapered trailing edge and the leading edge are both from my LHS. The two gussets in the corners are from scrap in this kit. Ailerons will be cut out of the trailing edge once I get further along in the build.

I did find that the notches in the spar for the ribs were cut too wide. I'm guessing that the original design called for a thicker rib, or maybe it was just an error programming the laser and nobody noticed it. A small T-Square helps make sure all the ribs and false ribs are nice and straight. I use a combination of CA glue and TiteBond II for most of my building work. CA to get a quick bond when needed, but in this case I mostly used the TiteBond II.

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This is as far as I've gotten on the build. I really want to make sure the landing gear works before I do anything major with the wings. The fuselage is also on hold pending gear placement. The tail feathers are coming along, but I'm a slacker and haven't taken any pictures of 'em yet. :)
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#5
Oh, and here is the plan page for the control line Navion, as published by Mechanix Illustrates many many years ago. This picture shows the "repaired" plan. The pages were so old and weak that many of the folds were falling apart. I had to cut out little bits here and there that couldn't be saved. Once this was done I took the page to the Estimating Department at my office (I work in a field that deals with construction documents) and they were able to scan the full size page and print me new clean copies that don't show any of the old damage. Basically I've now got brand new 50 year old plans!

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Joker 53150

Mmmmmmm, balsa.
Mentor
#9
The tail surfaces will deviate from the original plans to better match the Navion inspiration for my build. Shown here are the plans from the original plan (above) and the plan from the Navion (below). The Navion stabilizer is wider, but shorter. The elevator is quite a bit larger as well so I'll have to be careful with the rates until I get a chance to dial it in. For the width/length issue the two versions are pretty close in overall square inches so I'm not going to try and scale or change it from the Navion plans.

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The pieces are all scratch-built from various stock I have on-hand. I'm going with 3/16" thick instead of the 1/8" called for on the plans. No particular reason other than I like the look of a slightly thicker surface. In this picture the horizontal stabilizer has been trimmed and sanded. Hinges have also been cut, but the finish work won't be done until I finish the elevator which obviously needs a lot of clean-up. I'm not sure yet what I'll have to do for the connection between the left and right elevator halves. It might work as-is or I might have to cut out the center where they are joined and use a small hardwood dowel to connect them. I'm waiting until I can test-fit the pieces with the vertical stab/rudder on the fuselage.

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earthsciteach

Moderator
Moderator
#10
Very cool build idea. Thanks for sharing the contest. If I hadn't sworn off new projects due to my backlog, I'd be in for this one.

The Navion is a really cool plane to base your build upon. They are beautiful aircraft! I've been a fan for a long time. Very cool that your dad owned/owns one. If I may make a suggestion... how about including wing tip tanks on the plane? They add a lot to the appearance of the plane, in my opinion.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#11
My dad actually only owns the plans from the Mechanix Illustrated, not the actual plane unfortunately. Although he co-owned an Aeronca Champ with another guy when he was in college. He recently got into RC after watching me and purchased a 60" span Champ that he hopes to fly some day. He is still getting up to speed with his new Apprentice S and a few other "expendable" planes before he takes on the Champ.

Wing tip tanks were on the list of modifications and I like them, but the stock wing design doesn't lend itself well to adding them. The stock wing doesn't taper towards the tip at all, so the tanks would have to be pretty large. The added weight might be an issue as well, as I'm trying to keep it light because of the weight the retracts will add. I'm hoping to get flight with a 1000mAh battery instead of the 1300 recommended, but we'll see what happens.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#12
A long weekend off should give me some time to both fly and build. A couple hours of flying this morning was followed by some more work on the contest plane. Hinge slots were cut, the elevator was planed and sanded, and the ends were trimmed up so everything lines up properly. It's not finished and ready for covering, but the basic structure is done.

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The vertical surfaces on the contest plane are very close in overall size to the Navion plan, so I'm using the Navion design directly for the contest plane.

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With most of the vertical pieces cut out I'm holding off on the little piece that extends forward of the vertical stabilizer. I don't know what angles I'll have to work with on the contest plane so no sense in cutting this piece yet. I'm also leaving the bottom of the vertical stabilizer a little long for now so it can be cut to fit on the plane when I get that far.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#13
I've been sort of avoiding work on the turtle shell for a while. The fuselage is done as far as the kit/plans go so I'm on my own for a while. The Windex trick worked great to get the thin balsa to curve properly, but it is so thin (1/16") it really needed support on the inside so I don't accidently crush it.

Below I'll show what I did. Best or worst way to do it I don't know, but so far it looks good. But first, a shot of the contest airframe on top of the Navion plans. The wing and firewall locations are almost a perfect match! Only the height and roundness of the fuselage are missing from the contest plane.

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I used my balsa stripper to rip a series of approx. 1/16" square strips which were glued to the inside of the turtle deck. I used TiteBond II glue and liberally applied it all over the thin sheet to coat things well. My hope was that it would also lend a hand in strengthening the sheet. Once those were installed I cut four thin strips to go across all of those strips and glued those in place. Finally I cut out two thin rounded pieces to fit inside the top at the widest areas. Sorry, I don't know the technical terms, but I'm avoiding terms like "do-hickey" and "thingie" so I consider that a plus. Once it all dried overnight the turtle back is nice and strong. In this picture the front part of the deck (the area that the canopy will cover) was left long. I didn't know how long I would need it so like the vertical stabilizer I just left some extra meat on it for now.

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Once I got a chance to think about it for a while I decided how much of the deck I could remove. I plan on making a removable canopy section for battery installation, very similar to my Mountain Models Switchback. The canopy will overlap the turtle deck which should (hopefully) hide the cut-line I just made in removing 3" of my decking.

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I mentioned my MM Switchback, and here it is. I'm using a few ideas I got from that build in the contest plane, such as the removable canopy for battery access. I'll probably also install a battery tray like the Switchback has, but we'll see what happens as I move along with this build. In this picture you can see the bottoms of the rudder and elevator servos. Installation and access is from the bottom with the wing removed. I like this idea and will probably go this route with the contest plane. The turtle deck on the contest Navion comes farther forward than the deck on the Switchback meaning access from above would be difficult. Accessing it from the bottom should mean I have plenty of room for adjustment, installation, etc.

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Last is a cross section of the turtle deck. Not perfect by any means, but it should work and feels plenty strong and light. I had thought about curving my cut on the turtle deck to more closely match the canopy which will eventually go on, but that would limit my access inside a bit. I'll end up with more visible seams on the finished plane but in the name of easy access I can live with that. Besides, this isn't a contest or anything. Oh, wait... Nevermind.

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#14
The technical terms to use are "widget" and "dingus", not "do-hickey" and "thingie". You find do-hickeys and thingies on farm equipment, not planes. :)

This is all very interesting, I can't wait to see how the rest of the build goes together.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#15
A little more time today to work before my wife starts to get irritated with me, so I got started with the mounting method for the rudder and elevator servos. There are no provisions included with the kit or plans for doing this, it's something each builder needs to figure out on his own. My method was lifted from the Mountain Models Switchback and it appears it'll work out great for this model. Two rails were added across the width of the fuselage, just far enough apart for the 9 gram servos to fit. I'll be able to mount them with the arms towards the center or with the servos centered and the arms pointing out. I'm leaning towards the pictured configuration figuring that the stresses on the cross pieces will be better handled this way. This is the view from the bottom. The wing mounts right above these servos so you can see how easy the access to them will be.

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Viewed from above you can see that there isn't as much access, and this will diminish more once the canopy is created. These servos were salvaged from a wing which met the earth at a high rate of speed. I just use them now for test-fitting like this.

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I'm not sure what motor I'll use yet, but I need to start considering where the motor shaft and prop will sit so I can work on the cowling and the rest of the front end. I have various nylon bolts and spacers on-hand so I did a quick mock-up. I'll need to get parts strong enough to handle the torque of the motor, but for now this will work and gives me the measurements I need.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#16
This may (or may not) be my last update of the day on this project. I don't want to jump ahead too quickly since I'm making things up as I go now and want to think through the options. The tail surfaces are now all fabricated, but not "finished" yet so I decided to see how it all fits together.

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So far so good, although there is a lot of detail work ahead, including fitting the retracts once they eventually arrive. But in the meantime it's seeing it in a state that vaguely resembles an airplane that gives me the inspiration to sally forth. If I squint my eyes and rub them really hard I can start to see a Navion!

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The tail appears to fit pretty well, and I'm glad I left a little meat at the bottom of the vertical stabilizer. I'll do the final fit for the horizontal stab soon and will then trim the base of the vertical to fit. I've got a few millimeters to spare before I have to re-cut the pieces. Once that is done I can finish the section between the back of the turtle deck and the vertical stab, plus the extension of the stab that runs a few inches up the deck. I've been trying to figure out the best placement for the horizontal and vertical stabs to go, and depending on what year Navion I look at it appears that the horizontal stab placement changes. Since that is the case and I'm not going for any specific year I'll go with it about where it is in this picture. That gives the rudder enough clearance without removing much material from the elevator.

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xuzme720

Dedicated foam bender
Mentor
#17
Lookie there! It's almost an airplane!

Nice work! Making me want to get started on the new kits, if only they were here...
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#18
The electric retracts from Hobby King FINALLY arrived! I went with servoless for the wings HERE and a servoless steerable for the nose HERE. The item of concern on the wing retracts is that in the picture the wires are orientated in a manner that would have the wheel 90 degrees off, which would work fine if the wheels retracted inline with the wing ribs, but I want them to go the traditional way and fold up towards the fuselage. At least one person commented that he couldn't get them turned properly, but knowing that the average comment on the Hobby King website is posted by .... well, insert your own comment about people who don't know jack here.

So I rolled the dice and figured I'd find a way to make 'em work. I took them out of the bags, grabbed a 1.5mm allen wrench and unscrewed two set screws. Out comes the retract wire, nice and easy! The wire has two flat spots for the grub screws, but it'd be easy enough to file new flats as needed. In the first picture are the three pieces. The left gear is the stock configuration, which wouldn't work for my application. On the right is the wire turned 90 degrees. The nose gear only has a stub of a wire, so time for more creativity!

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To figure out how I'm going to make the nosewheel work I took the assembly apart and found it was extremely similar to the larger servoless retracts I've got in my Dynam Grand Cruiser (Cessna 310). The second picture is the steerable nosegear stub with steering arm. The shaft is free to rotate in this piece.

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Movement is crisp and reasonably quick. I didn't find any slop which is a nice surprise. In fact, they seem better in quality than the stock pieces in my Dynam plane.

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When you compare the axle length for the stock retract against the Dynam Grand Cruiser gear you can see the GC's gear is about 1-1/4" longer. This is important for two reasons. First, the stock wire will have the Contesta sitting pretty low compared to what the plans are calling for. This would limit my prop size and would make the plane look kind of squatty when sitting on the ground. An easy solution - the shaft size from the Grand Cruiser is the same 3mm size as the stock wire so I just ordered a replacement gear set for the Cruiser for $4.50 (damn shipping was an extra $15.00.....).

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Here's the Grand Cuiser wire on the new retract. Possibly a little too long but that'll be easy to change by simply cutting it to length and filing a couple flats on it. These servoless retracts aren't as big/beefy as what is on the Grand Cruiser, but that plane is substantially larger/heavier so that size is needed. My only concern is making sure the nosewheel fits properly. There is a slight difference in how the pieces work, but I think it'll still work out well. I'm tempted to swipe all of the gear wire from the Cruiser now so I can keep working on the Contesta, but that plane is in the current heavy rotation and I don't want to do without it! Plus I don't think I'm getting much work done this weekend so we'll see what happens.

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Joker 53150

Mmmmmmm, balsa.
Mentor
#19
With new gear on order for the Dynam Grand Cruiser I decided to take the ones currently in use on that plane instead of waiting for the replacements. That keeps me from using the GC until the replacements are here, but I don't want to slow down on the Contesta too much.

I spent a lot of time looking at the parts trying to figure out how to best make it all work. I want to keep the gear back behind the spar and am hoping it's far enough back to keep the CoG reasonable. I figure I can fine tune it quite a bit with the battery once I get that far. Unfortunately I'm going to have to cut the spar, but it'll be hidden by the sheeting on the top/bottom of the wing near the center, so no big deal with the extra bracing I'll need to add.

To mount the gear in the wings I used some light plywood and cut it to size. The piece to the right overlaps the ribs at each end. It will also get some additional bracing on the inside of the wing. The ply to the left overlaps the spar and is butted up against the rib and half-rib. This too will get some additional bracing on the inside. I had thought about trying to close in the wing a bit around the wire leg, but think I'll leave it open for access to remove the gear easily if needed. Obviously I still have some cutting to do around the wheel.

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From the inside you can see where the spar will need "modification". There are doublers that give the wing it's dihedral that mate to the spar, so again I'll need to get a little creative to make sure it's strong and has the proper angles. There is a lot of room to add some bracing to the plywood pieces so it'll be strong enough to handle my landing attempts.

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Unfortunately, the gear assembly was taller than expected so I couldn't recess the entire thing as planned. If I did, the top side would have an ugly bulge from the top side of the retract housing. So I'll have to deal with the mounting plate being surface mounted instead. Other size retracts might have fit without a problem, but I can't wait 3 weeks on the roll of a dice again so I'll live with an exposed mounting plate. The top will look good, and that to me is more important.

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