Babydoll 21" Scratchbuild (the hard way)

[speedbirdted]

My stubbornness knows no bounds it seems. What do you do when Kinko's is snowed in and you can't be bothered to build one of the millions of other plans in your stash? You make your own!

I have drawn quite a few plans in my life but this is the first one I'm actually going to try to build. I feel my design ability has progressed far enough to allow this. However don't be at all surprised if this build is a lot rockier than some of my others as this is mostly uncharted territory for me. The building part I can do, but can I design something actually buildable?

The design choices are kind of like a cross between a Gee Bee Dreamer and a SlowPoke. I wanted the cartoonish bathtub kinda look to it. The name I didn't pick. Up until two days ago this airplane had no name; I was showing it around some club members and someone suggested I put in a doll as the pilot and then someone said "babydoll" so I guess that's it's name now. Some will shout at me for not even bothering to add a vertical and just a rudder, but: the fuselage design is such that the fuselage itself acts as the vertical. I have a large area behind the CG so theoretically it should be directionally stable.

I figured with Balsa 250 fast approaching I would also design something in that weight range. The span here is 21" and I didn't bother calculating the wing area but it's not much. I wanted a high wing loading, that will let it go faster Being a small airplane means if I happen to have done everything wrong in terms of design and have created a conceptually unflyable airplane it won't be much of a waste of material if that's the case.

I have an unhealthy tendency to hoard Cox engines like you'd hoard water in a drought; so I might as well put one to use. I really wanted to use a TD 020 but sadly they're too expensive and I think an 010 wouldn't be enough power (and far too annoying!) so a Peewee 020 it is. My only concern with this is the integrated tanks on these things tend to give you about 30 seconds of engine runtime on a good day. Usually they run out of fuel before you can even get them tuned right. If it doesn't work well enough for my liking I might as well bypass it and add an external tank in the fuselage.

I started basic construction today too but I haven't got too much to show so far. The wing rib blanks (24 in total) are the three stacks of eight sheets of 1/16 balsa. The large 1/8x15/32 stick is the spar. I'm not sure why I weighed everything at this stage because so much crap is going to get shaved off. The wood is pretty much standard fare hardware store quality however they had a few nice 1/16 sheets in stock which I snapped up. I'm going to do a better job of materials selection here Unfortunately this is kind of all I could do in terms of construction for today. Later I will print off some more wing rib templates to cut the ribs out...

I put in an order to Willy Nillies for a bunch of servos and hardware and related stuff the other day so I might as well take it slow until it gets here, no need to rush building if all the parts aren't even here yet. More to come...

 

[jsknockoff]

Glad to hear I’m not the only one with a Cox engine addiction lol.

 

[TooJung2Die]

Cool looking design! Cox .020 was my favorite engine for the little free flight I built as a boy. I never ran one on a full tank. I was shooting for about 30 seconds of fuel. If I had RC I would have been grateful for only a 3 minute nerve wracking run. 🙂 I'm looking forward to seeing how this turns out.

 

[speedbirdted]

Progress! I decided to cheat slightly with the engine shim and cut it out on the laser. Getting something this precise with a scroll saw is impossible...

Also printed a big sheet of templates. This is why I dislike building primarily sheet-based airplanes; it requires lots of precise parts to be cut out. This is sheet one of three; sheets two and three are just an extra copy of the fuselage because I have to cut out the sides for it plus the rudder. You can see I tried to print the rudder here too; though for some reason even if you set the margins at 0 in LibreOffice it cuts some off the edges anyway.

Stuck all the templates down. I found that a 1/8 sheet would probably be too heavy for the horizontal and elevator so I changed it to a 3/32 sheet. The covering film will make it plenty stiff.

Wing ribs. I couldn't cut all 24 at once because my scroll saw doesn't have enough clearance and plus some of the ribs need to be shaped differently than others. Usually if I'm going to screw up it's when I'm making these but overall I think they came out pretty well.

Everything cut out. The formers still need to be glued together and some need to have notches added to them but that can wait until the fuselage construction starts. The elevator also needs to be cut in half but that can also wait because slight ambiguities in the finished fuselage shape means I may need to cut it to a different shape than I originally thought I'd have to.

Now onto wing construction. Very simple, nothing ground breaking here...

I built the semi-symmetrical airfoil shimmed up like so to get it straight. The trailing edge stick is intentionally too large, so it can lay against the table. After the glue is laid down and the wing comes off the building board, the excess can be planed away. This technique worked out quite nicely, and neither wing has any noticeable twist in it. You just have to do a good job to line up the tops of the ribs with the top of the trailing edge stick, since nothing is really holding it there before you glue other than simple friction. This picture shows one of the inner shorter ribs (they're like that to accommodate sheeting) which were a pain to get spaced right but eventually I managed to do it.

All I can get done for now, but the basic construction is complete. I will need to cut away some of the sheeting to put in the central servo but that comes later anyhow. The major missing piece here is the trailing edge. I don't have the right thickness to make the strip ailerons so I will have to go to the store again and get some. Not to mention I also don't have the aileron torque rods, that need to be installed before the trailing edge bit in the center can go on.

The landing gear legs which go into the first rib past the sheeting have also not been added yet but I think I'll wait on that until I figure out how big of wheels I want because the landing gear should be ideally as short as I can make it.

The resemblance to a Q-tee wing with more ribs is only sort of accidental...

 

[The Hangar]

Progress! I decided to cheat slightly with the engine shim and cut it out on the laser. Getting something this precise with a scroll saw is impossible...

View attachment 192937

Also printed a big sheet of templates. This is why I dislike building primarily sheet-based airplanes; it requires lots of precise parts to be cut out. This is sheet one of three; sheets two and three are just an extra copy of the fuselage because I have to cut out the sides for it plus the rudder. You can see I tried to print the rudder here too; though for some reason even if you set the margins at 0 in LibreOffice it cuts some off the edges anyway.

View attachment 192938

Stuck all the templates down. I found that a 1/8 sheet would probably be too heavy for the horizontal and elevator so I changed it to a 3/32 sheet. The covering film will make it plenty stiff.

View attachment 192939

Wing ribs. I couldn't cut all 24 at once because my scroll saw doesn't have enough clearance and plus some of the ribs need to be shaped differently than others. Usually if I'm going to screw up it's when I'm making these but overall I think they came out pretty well.

View attachment 192940

Everything cut out. The formers still need to be glued together and some need to have notches added to them but that can wait until the fuselage construction starts. The elevator also needs to be cut in half but that can also wait because slight ambiguities in the finished fuselage shape means I may need to cut it to a different shape than I originally thought I'd have to.

View attachment 192941

Now onto wing construction. Very simple, nothing ground breaking here...

View attachment 192942

I built the semi-symmetrical airfoil shimmed up like so to get it straight. The trailing edge stick is intentionally too large, so it can lay against the table. After the glue is laid down and the wing comes off the building board, the excess can be planed away. This technique worked out quite nicely, and neither wing has any noticeable twist in it. You just have to do a good job to line up the tops of the ribs with the top of the trailing edge stick, since nothing is really holding it there before you glue other than simple friction. This picture shows one of the inner shorter ribs (they're like that to accommodate sheeting) which were a pain to get spaced right but eventually I managed to do it.

View attachment 192943

All I can get done for now, but the basic construction is complete. I will need to cut away some of the sheeting to put in the central servo but that comes later anyhow. The major missing piece here is the trailing edge. I don't have the right thickness to make the strip ailerons so I will have to go to the store again and get some. Not to mention I also don't have the aileron torque rods, that need to be installed before the trailing edge bit in the center can go on.

The resemblance to a Q-tee wing with more ribs is only sort of accidental...

View attachment 192944

Looks good!

 

[danskis]

Looks like a kit....that's a compliment

 

[Jesse Dupreez]

Progress! I decided to cheat slightly with the engine shim and cut it out on the laser. Getting something this precise with a scroll saw is impossible...

View attachment 192937

Also printed a big sheet of templates. This is why I dislike building primarily sheet-based airplanes; it requires lots of precise parts to be cut out. This is sheet one of three; sheets two and three are just an extra copy of the fuselage because I have to cut out the sides for it plus the rudder. You can see I tried to print the rudder here too; though for some reason even if you set the margins at 0 in LibreOffice it cuts some off the edges anyway.

View attachment 192938

Stuck all the templates down. I found that a 1/8 sheet would probably be too heavy for the horizontal and elevator so I changed it to a 3/32 sheet. The covering film will make it plenty stiff.

View attachment 192939

Wing ribs. I couldn't cut all 24 at once because my scroll saw doesn't have enough clearance and plus some of the ribs need to be shaped differently than others. Usually if I'm going to screw up it's when I'm making these but overall I think they came out pretty well.

View attachment 192940

Everything cut out. The formers still need to be glued together and some need to have notches added to them but that can wait until the fuselage construction starts. The elevator also needs to be cut in half but that can also wait because slight ambiguities in the finished fuselage shape means I may need to cut it to a different shape than I originally thought I'd have to.

View attachment 192941

Now onto wing construction. Very simple, nothing ground breaking here...

View attachment 192942

I built the semi-symmetrical airfoil shimmed up like so to get it straight. The trailing edge stick is intentionally too large, so it can lay against the table. After the glue is laid down and the wing comes off the building board, the excess can be planed away. This technique worked out quite nicely, and neither wing has any noticeable twist in it. You just have to do a good job to line up the tops of the ribs with the top of the trailing edge stick, since nothing is really holding it there before you glue other than simple friction. This picture shows one of the inner shorter ribs (they're like that to accommodate sheeting) which were a pain to get spaced right but eventually I managed to do it.

View attachment 192943

All I can get done for now, but the basic construction is complete. I will need to cut away some of the sheeting to put in the central servo but that comes later anyhow. The major missing piece here is the trailing edge. I don't have the right thickness to make the strip ailerons so I will have to go to the store again and get some. Not to mention I also don't have the aileron torque rods, that need to be installed before the trailing edge bit in the center can go on.

The landing gear legs which go into the first rib past the sheeting have also not been added yet but I think I'll wait on that until I figure out how big of wheels I want because the landing gear should be ideally as short as I can make it.

The resemblance to a Q-tee wing with more ribs is only sort of accidental...

View attachment 192944

is that a nitro engine?

 

[speedbirdted]

is that a nitro engine?

Yeah. Cox 020, spinning an APC 4.2x2. Should be enough power for some serious ass haulage.

Unfortunately the store wasn't open (covid related) so I had to concentrate on other areas. Fuselage building started today with cutting out the sides and the rails to both accommodate the bottom of the top sheets and the cockpit floor. They're made of a 1/4x1/16 stick with a 1/8x1/16 stick sitting atop of it like so. I almost got caught out making two right handed sticks.

Dry fit in the rudimentary jig, everything seems to be lining up nicely.

Adding the rear sheeting (I guess you could call this the vertical?) I wetted the balsa by running it under warm water. It doesn't need to be terribly soaked. It bent into place perfectly; I thought I would need to fight it some or replace it with something thinner.

Just needed a touch of filler to clean up the seam with the fuselage sides, other than that it went decent. I test fit the rudder just to see how it would look. I like it. I may need to sand a bit off of it still even after I add the 1/16 bottom sheeting to match the fuselage contour but that's no difficult task.

The forward turtle deck sheeting is only installed on one side right now; the lack of a cockpit contour on the other side makes that obvious. I have left it off to permit access into the fuselage to install the blind nuts for the engine mounting bolts; same story for the forward bottom sheeting. The rear sheeting is also left off to allow the pushrods to be routed through the holes in the formers; as soon as those are on the fuselage will get sheeted up.

It's impossible to convey the profoundly weird feeling of building an airplane that literally has no vertical. I keep forgetting the fuselage itself is the vertical and it'll do the same job...

Does anyone have any ideas for pilot figures? I want to go with one on the larger side to make it look like the old Thompson Trophy racers where the only function of the airframe was to be a lift-producing aerodynamic sock wrapped as tightly as possible around the engine and pilot...

 

[rockyboy]

Love this project!

How about a 2 dimensional barnstormer pilot?

 

[speedbirdted]

Love this project!

How about a 2 dimensional barnstormer pilot?
View attachment 193049

I like that, but I wanted a character with a bit more depth.






ok ok i'm sorry please put the gun away

I knocked out the wheels and pants today. I ended up abandoning the shape on the plans, wasn't really thinking when I dreamed it up I guess. I went with something a little sleeker and reduced the wheel size a bit too. I started with building the pants; I actually used the wood cut away to make the wheels to ensure they would fit snugly. They're made of five laminations of 1/8 inch soft balsa sheet; the inner portion where the wheel well is is three sheets wide.

Putting them together and sanding them to shape, little by little. I find if you sand off only flat portions to begin with and effectively increase the number of flat portions gradually and evenly on both sides, the part turns out perfectly symmetrical every time. One of the side sheets on each pant is attached with Super 77 instead of CA - this is so I can peel it off later (you'll see why)

Nearly finished.

I wanted to build the wheels out of foam since it tends to be easier to lathe but this is an outside-only airplane and as such will be landing on terrain that will rapidly make foam unhappy so balsa it is. As you read earlier I used the material cut away from the pants when cutting them out, except just two layers thick. This is to make sure the wheels will fit in the pants without binding.

Here are the blanks I started with...

... and turned to shape and prettied up. The center portion of the wheel is ugly but that's no issue as it will never be seen by the eyes of ever-critical fellow modellers, hiding under the pant at all times. The tires have some minimal tread too but I generally suck at making treads so don't look at it please.

The wheels will be painted black (I'm going to leave the rim portion unpainted, the wood looks nice) and then coat them in a layer of lacquer or resin for extra protection.

So... onto the pant mounting. People who have looked at my previous builds will know my only other attempt to do this was a horrible failure and that was due to lack of forethought; I will make sure that is not the case here.

Remember how one side of the pants was separable? Well, that was so I could sand the pant to shape and then remove the side to determine the gear leg angle in order to cut a notch into the inside the pant side. I will then thread and CA the landing gear leg into the pant and then glue the side on permanently with CA (the little dots are where the thread will pass through the pant) I'll also add a 90 degree bend into the gear wire at the point that the notch ends, and the wheel will be held in place by the length of its brass tube bearing being determined precisely. Hopefully that will prevent it from going on any unintended field trips. However all this will be done after I complete the wing covering as getting to it with the pant in the way will be a major pain.

Test fitting it all....

I also stuck the tail on and test fitted everything. I'm torn between it being just weird or almost kinda cute in a way. Either way with the engine test mounted it seems like CG problems will not be the case as right now it feels good and everything that isn't the covering or pushrods will go in front of it. Everything in this picture plus the engine is a slice under 80 grams. 250 will be smooth sailing, if I even get close to that I'll be having problems...

How should I cover it? I'm thinking white on the wing and horizontal with a checkerboard underside, and I honestly want to do clear on the fuselage or at least part of it. I think the wood grain just looks real nice.

 

[rockyboy]

Those pants are looking great! Nicely done!

Checkers on the bottom sounds like a good idea and with such a tall fuselage side there, it seems like it's calling for some arrows / angles / decoration of some sort.

 

[speedbirdted]

Upon further review I decided I wanted a scalloped type color transition (like you'd put on a lazy bee ) and a checkerboard pattern would clash with it. So I think I'll just do the bottom of the wing in black, which if I do the top in white should contrast nicely. I think for the fuselage I'll do the scalloped pattern with white transitioning to clear, with a black pinstripe. Now the dilemma is what color do I make the wheel pants? White would clash with the bottom of the wing and black would clash with everything else...

In other news, mail day!

I worked on the servo installations in the fuselage and wing some. I had an elaborate method for the wing all figured out where I'd build a nice basswood box for the servo to sit on top of the wing, but then I noticed that it'd probably be just as strong if I went with a couple of thicker basswood beams just glued to the sheeting. It's 1/16 but that's comparatively very large here so it's plenty strong.

I also covered half the wing in white willykote (technically a quarter since I only did the top) just to see if there would be any hiccups with the covering anywhere. I think it looks okay but judgement from others is welcome I think just solid white will look fine so long as the area on the fuselage where the wing joins it is also white. I'll add some registration numbers to it or something to jazz it up a bit...

Another side note is the Dubro 2-56 mounting bolts that you can buy through willy nillies have heads that are too large in diameter to work with the Cox engine radial mounts. If you don't grind them down like so (left is ground bolt, right is stock) they will bind against the fuel tank and scratch it up.

My phone camera hasn't got a macro feature so this is all I can really do in terms of photographic documentation...

I also needed to make some control horns. Building the Sprat taught me just how much I detest doing this task manually so I had the laser do it for me. They're made of 1/32 basswood. I cut a bunch because I knew I'd break some trying to get them installed...

As it sits right now, the only tasks left to do are slotting for the control surfaces and covering the fuselage and the rest of the wing. I've also got to figure out where the electrics will go inside but that's easy. Maybe I'll add a little bit of cockpit detail too. I was really hoping this would take longer as I don't have any ideas lined up for what to build next!

 

[TooJung2Die]

Wheel pants are exactly what this airplane needs to complete the golden age look. Hope it flies as good as it looks. 😎👍

 

[speedbirdted]

Been a bit pushed for time lately but today I got the electronics all sorted out. If there is one thing this airplane hides it's that it has a surprising amount of interior real estate. I didn't realize the fuselage would be so narrow but I got everything shoved in there somehow anyway. I'm using a 300mA 2s lipo for power, with a 3A BEC to step it down to 5v. It's kinda overkill for 3 tiny servos but I figured better safe than sorry (and I didn't have anything smaller) With the battery in the position it's in the CG feels fine, but that's both without the tail control surfaces and tailskid installed. There's another sheet of velcro farther forward and the battery will go there if CG gremlins crop up.

Fun fact: The switch on this bird is at least 50 years old! (The box it was in had a price tag marked 1969 so that's what I'm going with) It was the smallest one I had. No hope of getting one with the integral charging jack to fit...

Now that the pushrods are installed (they went in arrow straight through the holes I put on the plan and don't bind even in the slightest - a testament to good planning) and all the electronics are where I want them to be I can stick the bottom sheeting on. Getting closer every day now...

 

[speedbirdted]

No time to work during the past few days but I got a bit to work on it today. The cockpit got painted, I used three coats of acrylic, with one more clear. I masked it off with tape as the black paint will show through the white covering pretty badly, so smudging is to be kept to a minimum. I'll add some gauges or something, not sure if I'll just use printed paper ones or give them some actual dimension. As for pilot figures I might go to Goodwill and go get some kind of stuffed animal or something to go along for the ride...

I also came up with an idea to make a faux leather cockpit coaming using clunk tubing that had a slit cut in one side of it. I'll paint it brown to look like leather and maybe add some stitching to it too...

I finished screwing around with the aileron setup too; now it works perfect. I wouldn't wish it upon anyone to set up torque rod ailerons on this tiny of a model; it's just far too finnicky to be any fun, especially since the trailing edge pieces you usually end up working with are just so thin and small.

I also got around to covering the clear coated sections of the fuselage with 1.5 mil doculam. I also coated the rudder in this; it hardly shrinks, which I really like because it didn't bend it all out of shape.

I thought long and hard about how to determine how to do the white scalloping on the forward fuselage. I thought about maybe adhering the covering at low temperature and then cutting it while it was on the fuselage but then I might accidentally cut through both layers of covering and damage the wood underneath. Eventually I decided to make some paper templates that could be taped to the fuselage after being cut to shape; I made a bunch of them and cut them all sorts of different ways trying to find one I liked. It took probably 25 attempts but I finally got one that looked semi decent, and decided that was the one I was going to cut out. I forgot to take a picture of it but the one in the shown picture is the other one I also wanted to do....

From there all that was left to do was to take the template off the fuselage and then trace it out onto some white monokote. I tried my damnest to take a good picture of the process but it's completely white-on-white and my shop lighting is not great to begin with so the pictures ended up being pretty useless.

Covering on, at least on one side. This will be either the good or the bad side; I don't know yet Right now it's the bad side because the filler which was advertised as being balsa colored is clearly not so. I'll figure out some method to do black pinstriping tomorrow. I'm tempted to try doing it with paint because I can never get it consistently to be the same width with a covering film, but I'm not sure what kinds of paint stick to both monokote and doculam nicely....

Save for that this is pretty much how it will look complete. I'll add N numbers (something NX - the racers and homebuilts all had those) and some cockpit detail and I think that'll be all. Oh yeah and also the elevators. I stupidly broke the one that had the horn slot in it so I need to fix it but that's easy. I like how this is looking so far...

AUW will be about 170 grams. Considering a Peewee 020 will put out about 4-5 oz of thrust this should go pretty good....

 

[TooJung2Die]

It's looking great. Only 170 grams AUW? I would've guessed more. Well done.

 

[Tench745]

Lovely little plane. For my dollar, I would switch to built-up tail surfaces instead of the solid sheet ones.
Personal preferences aside, I strongly recommend adding a piece of balsa to the tips of the h-stab and trailing edge of the rudder. Make it so the the grain of the new pieces run 90degrees to the grain on the surface. This will help prevent the surface from cupping over time. Something like this: The 90º piece doesn't have to be so large.

 

[speedbirdted]

Lovely little plane. For my dollar, I would switch to built-up tail surfaces instead of the solid sheet ones.
Personal preferences aside, I strongly recommend adding a piece of balsa to the tips of the h-stab and trailing edge of the rudder. Make it so the the grain of the new pieces run 90degrees to the grain on the surface. This will help prevent the surface from cupping over time. Something like this: The 90º piece doesn't have to be so large.

Dang! That's a good idea. The tail group is all covered up by now and luckily it doesn't seem to be warping yet but only time will tell. If it gets too bad I'll do just that.

It's looking great. Only 170 grams AUW? I would've guessed more. Well done.

I'm a liar. A big fat stinkin' liar...

Pinstripe job commenced today. I put a lot of forethought into it but it's still far from perfect; but at least here both sides are about equal in terms of imperfection so it's not Q-tee level bad. I made the curved sections by taping tracing paper to the fuselage and then tracing the outline of the curve to be made onto that then just kinda eyeing it for how wide the pinstripe should be around the corner. On the shallower curves it looks just fine but the real sharp one I really started suffering.

Now that we're talking about suffering... I did a lot more of that trying to cut this out. I did it by hand (don't do that) because the library's cricut machine is unavailable because the library is closed. I went through like 3 or 4 before I got to one I liked. If you look at the actual logo used by the Fighting 31 it's only an approximate representation but I think I did pretty well.

I did it to honor a recently passed club member who served in VFA-31 in Vietnam in the 60s. Personally he was a great mentor to me, I learned a hell of a lot from the guy (for instance basically everything I know about covering film) and he more than deserves the representation...

Wheel pants were also put on. Here's the nitty gritty of it; basic thread reinforcement was all I needed to do, they're stuck on there plenty good. I then put the wheel on and glued the other half of the pant on and covered the seam. Came out a lot slicker looking than I thought it would and the exposed thread on the outside of the pant doesn't actually look bad at all.

Getting mighty close now. All I really need to do now is figure out the cockpit and find a willing pilot.

As for the N-number I picked.... it's the birthday of a special someone Now let's see how long it takes her to notice it...

I wonder why this thread hasn't rolled over into a second page yet? Finishing a build in one page, whoever did such a thing....

 

[rockyboy]

The covering looks sharp! Nicely done sir!

 

[hsquier]

If you look at the actual logo used by the Fighting 31 it's only an approximate representation but I think I did pretty well.

Hats off, I'm truly impressed (and in general a big fan of own design you brilliantly achieved).

May I ask for some more on how you did the logo ? In particular very impressed by the finesse of the line between the eyes.
Is it out cut from black sticker? covering film ?
Once out cut how did you apply it on the wing ? Did you use a secondary "apply-tape" ??
And How, and how and how ...

You see, for me what you achieved is still a mystery.