Scratch Designed/Built Sailplane Fuselage

[Yakfishingfool]

working in the dark? Guess it depends on the job

[kyleservicetech]

Originally Posted by Nodd

Yeah I noticed the HomeDepot aluminum is pretty flimsy stuff. Thanks for the links, I've bookmarked that site. I think these brackets will do for this application but I'll keep that site in mind for future projects.

Stubborn Bugger
I've not weighed the brackets but they're nothing I'm worried about, especially once I've "Swiss-cheesed" them. I'm getting lots of suggestions to just use fiberglass & I do intend to FG the heck out of the joint but I want something else in there too.

Fiberglass is good stuff no doubt but from experience I know it also has its limitations. For example look at what happened to my fiberglass four meter sailplane after a moderately bumpy landing...



Fiberglass is rigid & cracks, metal is substantially inflexible but when it does move it just bends. I think a combo of both will be perfect for this application.

I know you folks already know this stuff but I'd like to explain my thinking here:
This all comes down to leverage. Archimedes famously said, "If you give me a lever long enough and a place to stand, I can move the world." While I have no Earth moving aspirations, my understanding is because I have just 1/4" of pylon to work with here Vs a normal fuselage with its wide wing mounting area, there's going to be a lot more force on this joint that usual...



I did a little math & was astonished to learn...



So with that in mind, yeah I'm going to stick some steal in there along with some fiber-glassing.

So here's a rough diagram of what I'm building...



Anyway not sure exactly when I'll get to this. Situated directly in the path of hurricane Sandy I'm expecting some "interesting" weather over the next few days. At the very least I expect I'll lose power for a while, will have to see how I feel about working in the dark *grin*. Anyway see you all later this week I hope. Stay safe.

Yeah those bending forces get out of control very quickly. Also make certain that the portion of the wing that connects to your pylon is equally strong. Also need to be wary of that 1/4 inch thick plywood sheet bending or breaking.

Years ago, in a different club, a club member built up a 14 foot wingspan cross country sailplane. It was full of a lot of carbon fiber, fiberglass, if memory is correct, even some boron fibers. The wing joiner was a piece of 3/16 by 2 by 24 inch high grade steel. The plane got going to fast, went into flutter, and tore that steel wing joiner in half like a piece of toilet paper.

As for bending forces, I converted a Sherline lathe to a milling machine. Two pieces of oval shaped steel tubing from Speedy Metals were used. These pieces of tubing measure 4 by 6 inches by 24 inches, and 4 by 8 by 12 inches. They are welded together at right angles. By the way, that tubing has a 3/8 inch thick wall.

Amazing, I can put a dial indicator between the two pieces of 40 pounds worth of steel, push on the top 4X6 inch piece, and BEND it by 0.0015 inches!

[Nodd]

Hurricanes are zero fun!
Six days without power! Yeah that sucked but I can't complain. Lots of folks in my area don't even have houses anymore. Other than losing everything in the refrigerator there's no real damage at my place. The power finally came on a few days ago so I'm back in my workshop futzing with my airplane again.

Okay fine
I still feel these metal brackets would have been an elegant, effective, simple & strong solution for attaching the wing to the pylon but enough of you (mostly on the other forums) have grunted & grumbled about them that I've decided to go with a more traditional plywood/glass approach...



Before I can even start building the wing-saddle though, I need to figure out my wing-bolt system. I chose to install three hard-points on the wing, two right at the spar & one buried in the trailing-edge...



The carbon-bars are firmly attached to the structure using epoxy & Kevlar thread. This all looks a bit ugly right now but it'll get pretty again once its integrated into the wing-saddle...



Added the trailing edge & test fitted the rear wing-bolt. In this top view you can still see how the Kevlar is wrapped around the main-spar...



Wing Saddle
With my mounting system in place it was time to turn my attention towards the wing-saddle...



Testing fitting...



Before I can start adding fillets & glass, I need to get the tail-boom mounted. I'm using a double slot technique here which has worked nicely for me in the past...



Here's how she looks with a Bubble Dancer tail-boom attached...




Lets make this chunk of wood even more complicated...




Added some Kevlar wrapped carbon-fiber. The horizontal one to reinforce where the tail boom mounts, the vertical one to give the pylon some added support...




Here's how the wing-saddle is looking...




Gluing the pylon to the saddle...




The next step is to lay down some fiber-glass. Then I'll add some 1/2" balsa either side of the pylon & do some shaping. Will post more soon.

[JetPlaneFlyer]

Nodd,

There is very little bending moment going into the fuselage pylon because the fuselage is free to move, so very little bending moment can be generated. Your bending movement assumes that the fuselage is an immovable object which the wing is trying to pivot around, which is just not how it is in reality.
In reality almost all the bending moment goes through the dihedral brace in the wing centre section, which you built bomb proof if I recall. The pylon simply supports the fuselage.

I'm just concerned that you are massively over engineering the pylon and will end up with a heavy model because of it?

[CHELLIE]

Gee, How did I miss this Build Thread Very Nice Work Nodd I get to do the Maiden Flight LOL, Ok Just Kidding, Take care and Have Fun, Chellie

[Nodd]

You're more than welcome to come fly this contraption Chellie, assuming I ever get this project done :-)

Yeap JetPlaneFlyer you're totally correct. Its the fuselage that levers against the wing, not the wing levering against the fuselage. So the lever moment is actually more like 10 inches instead of 52. Still though I want this pylon to be strong. Like the rest of the build, yeah its possibly a tad over engineered but so far the pylon, tail-boom & wing-saddle weigh in at just 5oz. I'm pretty happy with that. Although I don't expect this sailplane to be a featherweight, she's on track weight-wise to be comparable to my previous design which flew very nicely. Even if she ends up a tad hefty, I'm actually fine with that. Some of my best flying machines have moderate wing loadings. Heck I even thermalled my silly Piper Cub Sailplane (flying brick) the other day, got a thirty minute flight out of her! I'll keep an eye on the weight all the same. Thanks for the caution.

[kyleservicetech]

Originally Posted by Nodd

You're more that welcome to come fly this contraption Chellie, assuming I ever get this project done :-)

Some of my best flying machines have moderate wing loadings. Heck I even thermalled my silly Piper Cub (flying brick) the other day, got a thirty minute flight out of her! I'll keep an eye on the weight all the same. Thanks for the caution.

Case in point was my pair of Craftaire Viking sailplanes in the mid 1980's. These were 10 foot wingspan models with very light wing loading. Both were converted to electric power launch. Added weight was perhaps a pound or two after removing the lead balance weight in the nose.

Both of these models flew better with the additional weight.

[Nodd]

That doesn't surprise me your EP conversions ended up flying better. In theory, more weight equals more speed, equals more air over the wing which equals more lift (well to a point that is).

Don't get me wrong though, lightness is important & I don't want to give the impression this plane is going to be a brick, its not. She's on track to be a nice floater.

Hairy sticky mess
Ahh how we love working with fiber-glass. Here's a second layer of 2oz glass ready for the epoxy. I'm using 3M contact spray to tack it in place, makes life a lot easier...



After a little more glassing & maybe some triangle stock, I'm planning to add balsa fairings either side of the pylon to hide all this ugliness. Before I can do that I need to attach the pylon to the pod...



Yeap that's one unusual looking fuselage, I'm liking it...



I also glued the tail-boom on there, no turning back now...



I used slow set epoxy for most of today's assembly so I'm going to let this setup good & solid. That's a wrap for today.

[Nodd]

Trimming some triangle stock...



On its own, the triangle balsa doesn't add much strength...



What it does do however is angle the fiberglass at 45° which should add a lot of strength...



I had some carbon-fiber thread I've been itching to use on something...



I placed three strips of it under the glass cloth. Man & I thought fiber-glass was difficult to work with, major pain in the butt trying to get the CF thread to lay down neatly. As you can see I wasn't too successful but it doesn't need to look pretty to do its job...



Time to hide all this structural stuff & make her pretty again...



I thought carving the turtle-deck on the first version of this sailplane was a challenge. I don't even what to think about how many hours I spent today whittling, sanding & test fitting these pieces...



The pylon balsa sidings are just roughly shaped at this point but she's starting to look like something, pretty pleased with how she's looking...



So just to recap here's how the new wing-saddle was put together...



Tomorrow I hope to finish shaping the pylon...

[CHELLIE]

Its Looking great

[Nodd]

Putty? That's cheating!
Filling the less than perfect areas with HobbyLite wood putty...



After sanding...



I'm probably going to paint the fuselage rather than cover it so these lightening holes need to go away...



The balsa plugs are lighter than the hardwood ply so I suppose they're still lightening holes...



Finished up the wing-bolt system, that's good to go...



Next step is to glass the entire thing with some lightweight cloth. Looks like I don't have enough so will head out tomorrow & get some more...

[earthsciteach]

This is truly beautiful. I wish I had your talent!

[JetPlaneFlyer]

She looks terrific Nodd, totally unique. 5oz actually isnt so bad for the weight of the pylon and boom, i'm sure you are right in that it will fly great. In this part of the world thermals are generally so weak that sailplanes need to built very light but it sounds like you have a bit more to play with.

Steve

[FlyWheel]

I'm not a pod and boom fan at all, but I am definitely finding this interesting. Great work. If I may add a tip after the fact, if (gods forbid) your current design should prove inadequate you may want to consider it for the re-kit. Your filleting is a great idea, but since you are using it for strength, not just aerodynamica I would remember the strength of balsa, or any other wood for that matter is along the grain. As such I would carve your fillets so the grain goes crosswise rather than lengthwise,along the hypotenuse of the triangle. This will strengthen the structure without adding any weight.

On a side note, could you start a separate thread detailing your heat forming technique, or send me a PM? I need a new nose cowl for my Miss Stik and none of the soda manufacturers seem to want to make an appropriately sized/shaped bottle

[Nodd]

Originally Posted by JetPlaneFlyer

...In this part of the world thermals are generally so weak that sailplanes need to built very light but it sounds like you have a bit more to play with...

Bummer about the thermals in Aberdeen. I'm guessing the highland slope soaring is pretty epic but if I recall my Scottish geography correctly, that's way West of you. Yes we're blessed with light to moderate lift here in Connecticut. I got caught in several boomers this Summer, the sorta lift where you need to fly inverted to get back down. We have it good here.

Originally Posted by FlyWheel

...Your filleting is a great idea, but since you are using it for strength, not just aerodynamica I would remember the strength of balsa, or any other wood for that matter is along the grain. As such I would carve your fillets so the grain goes crosswise rather than lengthwise,along the hypotenuse of the triangle. This will strengthen the structure without adding any weight...

You know I just noticed the grain direction last night. I wasn't really thinking these'd be structural when I put them in but you're right, I have the grain running in the worst possible direction LOL. I'm not too worried about it though as I'm about to fiberglass over the whole thing.

Originally Posted by FlyWheel

...On a side note, could you start a separate thread detailing your heat forming technique, or send me a PM? I need a new nose cowl for my Miss Stik and none of the soda manufacturers seem to want to make an appropriately sized/shaped bottle...

I've been meaning to feature the heat-shrink soda-bottle canopy/cowl technique in one of my Nodd RC YouTube episodes. Until I do here's where I first learned about it...

DIY Cowl mold
https://www.youtube.com/watch?v=iohEBgpAnfo

I'd figure a regular 2 liter soda-bottle should work for a Miss Stik. If that's too small I've seen 3 liter bottles on occasion. I usually carve my plugs from MDF wood as it has no grain & is easy to sand. There's a few photos of me doing that in my Spacewalker Nodd RC video. Anyway getting a little off topic here, PM me if you have questions.

[Nodd]

3/4oz glass
From experience I've learned, no matter how careful you are with fiber-glass, the epoxy just ends up getting everywhere. So first things first, I covered my spiffy Bubble Dancer tail-boom in plastic to protect it...



I sprayed the fuselage with 3M contact cement then laid down the glass...



I'd always thought fiber-glass was heavy stuff until I tried working with 3/4oz glass. This stuff is like silk, its virtually weightless...



Much of the weight however comes from the epoxy finishing resin but daub most of it off with paper towels & you're left with a nice lightweight fiber-glass covering...



This'll setup overnight then tomorrow I'll see about producing a nice paintable finish...

[Nodd]

Smells like wall
Well the fiber-glassing is cured & looking good. After a light sanding it was time to fill the weave so I can paint her. As I've mentioned before, I'm somewhat new to the glassing scene, so I did some reading up on the subject. Apparently there's no shortage of ways to produce a smooth finish, the one that grabbed me involved dry-wall spackling...



Right out of the tub this stuff is really thick. I mixed in some water until I had a creamy consistency somewhere between milk & yogurt. Then I slapped on a couple of coats...



I ended up with brush strokes in the finish but those should sand right out. I just need enough spackle on there to fill the glass' weave. Any more is just dead weight...



While I was at it I also did the glassed areas of the wing...



Well once again I need to let this dry. That's all for today.

[mclarkson]

This plane is looking beautiful, Sir!

[Nodd]

Thank you. Yeah I'm pretty excited about the way this project is going.

Both Wet & Dry?
This should look familiar if you've ever tried using fine sandpaper. It clogs quickly & then bad things happen to your finish...



Ordinarily I'd wet-sand but this spackling seems to be water soluble even after its dried. The wet sandpaper was producing a big white mess & seemed to be dissolving the spackling rather than sanding it. So I did some head-scratching & came up with a wet & dry system. I'd sand dry & then every few minutes I'd wash the paper with water & a sponge to unclog it. Then using an old hand-towel I dried the paper, then back to sanding. That seemed to work well...



The thin layer of spackling once sanded did exactly what I'd hoped. It filled the fiber-glass' weave beautifully without adding any real weight at all...



This may look rough but the surface is actually silky smooth. Spackling is my new best friend...



Paint Time
Next went on a dusting of primer...



Light sanding between coats & I'm blown away with how nice & smooth this is coming out, couldn't be happier...



Tomorrow I'll get back to construction, need to get the canopy mounted, maybe install the electronics. I also need to start thinking about the tail-feathers. Fun Fun.

[earthsciteach]

Hey! The spackling is a nice idea. I'll try that on my next glassed project, which is starting very soon. I am nearing the end of my first venture into glassing - 0.56 oz/yd over foam. I think the spacking will save me some work on the next one.

[Nodd]

Yeah I'm really impressed with the spackling. I can see me using this again for all sorts of stuff.


Look what RCAerotowing posted today...



This sure looks familiar...



Someone stole my design, went back in time & built a full-scale!
I swear I've never seen this airplane but it sure does look a lot like what I'm building here. I'm digging what they did with the tail, may have to copy that look. Especially like the way the v-stab protrudes down below the boom. As we figured out earlier in this build, some form of tail-skid maybe necessary to keep the fuselage level during landing. Its interesting they came up with more or less the same solution. I like it!

Anyway for those in the US, happy Turkey day! Lots of flying this weekend so not sure how much I'll get done, will post more soon.

[kyleservicetech]

Originally Posted by earthsciteach

Hey! The spackling is a nice idea. I'll try that on my next glassed project, which is starting very soon. I am nearing the end of my first venture into glassing - 0.56 oz/yd over foam. I think the spacking will save me some work on the next one.

Something about that spackling, I've used the super light weight stuff. This material has little strength, but hit it with a few drops of CA, and it turns to a solid piece of material.

This also makes it pretty much impossible to sand further though, try it on a piece of scrap material first!!!

[Nodd]

That's a good tip. While I'm not really looking for any strength out of the spackling (I just want it to smooth out the surface) that's good to know CA will toughen it up if need be. Thanks.

[kyleservicetech]

Originally Posted by Nodd

That's a good tip. While I'm not really looking for any strength out of the spackling (I just want it to smooth out the surface) that's good to know CA will toughen it up if need be. Thanks.

Also make certain your paint or covering material will work on a spackle/CA'd surface (just in case) Also check out the very old trick of baking soda plus very thin CA. Instant concrete, and about as easy to sand.

[karolenaz]

Awesome fuselage mate