Scratch Designed/Built Sailplane Fuselage

[Nodd]

This is a continuation of a couple of build threads I've been working on...

• Scratch Designed/Built Sailplane
• Sailplane Wing Design Round II

My original design flew beautifully but suffered from a design flaw in the wing (consequently it folded in half mid-flight). Since that fun learning experience I've redesigned & rebuilt a better wing. In fact the new wing turned out so nice that I'm reluctant to fly her with the original fuselage. So I'm going to redesign/build that also. This thread will document that process. Subscribe if you're interested.

[Nodd]

A new look
While I liked the profile of my old pod-n-boom design, seeing as I'm rebuilding this from scratch I have the opportunity to change the design if I wish. Here's a few "out there" ideas for the new pod. I'd love to hear your thoughts on which if any you like...



Let me know which you like & why.

[riverrat]

Nodd

"B" If the interior is roomy enough!
If not "A"

I know in my Guppy's it was really a squeeze;
even with Berg Micro Stamps, & 15003S

Regards!
Jimmy

[Nodd]

Thank you for the feedback. I'm not anticipating any issues with interior room although that is a consideration. Nice Guppy. My original fuselage was influenced somewhat by the Guppy. Beautiful airplane.

I've pooled the opinions from this & my mirror threads on other forums & as expected, the more modern sailplane profiles (A, B, F) were the most popular. I could certainly go with one of those & end up with a very nice sailplane. However after thinking about it some, I've realized I'm not necessarily looking for the most efficient, most sleek design. I'm now leaning towards doing something a little out of the ordinary. Something that'll stand out in the crowd. The gull wing achieves that goal to a point but I'd like a "quasi-vintage" fuselage to go with it.

So here's another batch of doodles...



A2
Modern sailplane profile, while sleek, lacks uniqueness.

B2, C2
Has a subtle avian feel (looks a little like a bird's head). I think these tie in wonderfully with the gull wing. Flying a giant bird might be fun.

D2, E2
An under-slung pod design. Inspired from some vintage sailplane designs I've seen. Again these work with the gull wing & would be a little different.

Once again I welcome comments & thoughts.

[Nodd]

Under-slung pod
I'm leaning towards an under-slung pod design, pretty sure that's where this sailplane is headed. Its fun, different & I can't see any major reasons why it shouldn't workout. So here's a new set of doodles...

[hayofstacks]

I like a3 and d3 for no specific reason.

L3 would make it stand out.

[Nodd]

Yeah A3 is pretty out there, I like that one too. D3 is probably the most slippery but I think its a tad too much like a modern sailplane. I leaning more towards something a little different.

Enough doodling
I could go on for weeks playing around with exotic pod shapes but I'd like to move on. Taking into account everyone's input (thank you) I've settled on this design that's a mixture of E3 & F3...



Artistic babble
While I like some of my more excentric designs, I think this one with its modern canopy merged with a retro pod works well. It has a few curves to keep things interesting without coming across as over-the-top.

Well I'm off to the LHS to pick up some wood. Time to start the build.

[riverrat]

NODD

I dont why- but I like it!!!

Regards
Jimmy

[Nodd]

Its a mystery to me also Jimmy *grin*

Fleshed out
I did a little more work in CAD, here's how the pod looks fleshed out in 3D...

[Nodd]

Bounce Bounce Bounce
A guy over at RC Groups pointed out that my pod fuselage may cause ground handling issues. Specifically he felt the design would be prone to skipping during landing. Once the pod contacts the ground the tail will hit next raising the nose alarmingly & back up she goes, hop hop hop. So to fix the issue I'm thinking a small tail-skid should keep the AOA from getting out of hand during landing. It looks kinda cool too...

[Nodd]

Construction begins!
Enough design work, time to start building this thing. I printed a set of templates from my CAD software...



Used the templates to cutout the various parts then started putting things together...



She's starting to look like something...



Filled in the rear of the pod with scrap balsa...



A little pre-shaping of the hardwood nose blocks. Once installed I'll finish carving these until the motor fits...



I'm using 1/4" plywood for the pod support (the piece that connects the pod to the wing)...



Test fitting the support. I won't glue this in until the pod has been shaped & sanded as it'll just get in the way...



That'll do for today. I'm headed to the NEAT Fair so will get back to this when I return next week. Cya there.

[Nodd]

Well I'm back from the NEAT Fair, four amazing days of flying. So now its back to working on the glider. Not a lot to show today, started sheeting the top & bottom of the pod...



Will have more soon.

[Nodd]

One month later...
Okay I'm done building my silly Piper Cub Sailplane, time to get back to working on a "real" sailplane. So where were we? Building a pod-n-boom fuselage that's right.

I taped up the top profile template...



Then using the belt sander (love that tool) sanded to my marks...



Set the sander's guide plate to 45° then began the rounding process...



I need to get the motor installed so I can shape the nose so it blends nicely with the spinner. I broke out the Dremal & started carving out the nose...



Major OOPS!
I got the motor in & then to my dismay discovered that some nit-whit (me) had installed the firewall way to far forwards. Look at the size of that gap! NOT GOOD!..



Move the firewall back? ...not happening. So the next best thing is to build up the nose so it matches the spinner's new position...



One nice thing about the belt sander is that it makes nice clean flat surfaces that I can easily glue scrap balsa too...



Glue scrap wood in place, trim with the sander...



...& glue more wood in place...



Now to take care of the gap. Added a piece of hard-wood to the nose...



Some more sanding & we're looking good...



That looks better!..



I still have lots more shaping to do but I'm happy with today's progress...



That was a bit of a PITA but on the up side I now have a nicely reinforced nose. Its good to be back working on this, fingers crossed there'll be no more distractions or hick-ups.

[k8zfj]

Very neat project and thanks for sharing your build techniques
Randy

[Nodd]

Thanks.

Thinking Ahead - Wing-Saddle
I should probably start planning how I'm going to mount the wing to the fuselage. Here's roughly how she'll look...



The challenge here is to securely but temporally mount this huge wing to a dinky piece of 1/4" plywood...



Whatever I use to mate these two together needs to be bullet-proof strong but lightweight at the same time...



Traditionally this sorta thing is done with a wing-saddle...



Making a wing-saddle from fiberglass & thin plywood shouldn't be a problem. What I need to figure out is how to attach that to the 1/4" plywood pylon so its strong. Any ideas would be appreciated.

[Nodd]

No one has any suggestions huh? Oh well. I got some good advice from the other forums thankfully.

Shaping
I spent a couple of hours today rounding off the pod...



You'll notice I deliberately didn't round off the line running along the lower edge. I kinda like the ways it looks, helps accent the pod's curves...



Looks a little like a flying boat hull in some ways. Remind me not to try landing on the water though...



Canopy
Those that have seen my other build threads will be familiar with my canopy making process. First I start by outlining the canopy...



Then on goes the two liter soda-bottle...



Starting along the bottom the bottle is heat-shrunk around the fuselage...



Draw some dots with a permanent marker before removing then cut her out...



Rough cut the fuselage...



Sand to the template & test fit...



Now she's starting to look more like a sailplane, getting excited.

[Frogchief]

Very cool stuff. Definitely NOT run of the mill sailplane design.

I didn't see the previous post until now, but would have simply built up the saddle junction with very light balsa triangle stock and fiberglassed the whole thing. Perhaps vertically inlaid with some carbon tow...

Sean
Bigtime glider-guider
LSF#8046

[Yakfishingfool]

Thrilled to be in on another of your projoects nod. The saddle sits squarely on the quarter inch hardwood...wouldn't a compo of epoxy and fg secure that connection? Another thought...it may sound a bit whack....Through wire it. When I build saltwater plugs I run SS welding wire through the length of the plug to attache hooks to. Very very strong. what about a Staple shaped SS wire, nearly length of saddle chord, placed from the top down, into the saddle and running a good 2 inches into the wood, fill holes with epoxy and clamp. got to believe it would never come out, no external view of the attachement keeps the joint between saddle and support clean. Could even open the vertical support with a couple of small , 2/8th inch holes, run wire into there, curl it, fill with epoxy and then sheath the vertical support. Definitely never come undone!

[k8zfj]

Re. Wing saddle mount- Make a "V" shaped mount to accept wing saddle

[Nodd]

I'm liking the advice, great stuff. I hear what you're saying about embedding wires here & there. I still have yards of Kevlar tow laying around from my spar wrapping adventures. I may run some of that through the structure, same concept as running wires I suppose.

A V shaped pylon would help by increasing the joint area, yeah. I may thicken the entire pylon some, same result.


[ ( { brackets } ) ]
So I took a leisurely stroll around the Home Depot today & stumbled upon these nifty little steal brackets...



I really like these as they have a bump that should add significant strength...



These are a little longer, no bump but they still feel really strong...



I'm liking the look of that. Simple, relatively lightweight & should be very strong...



These look like they'd work nicely too...



So not sure which of the two I'll use but I figure if I glue the brackets to a plywood wing-saddle then embed the whole thing in fiberglass I should be good to go...



The brackets are fairly lightweight but I can see maybe drilling some lightening holes here & there. That'll save some weight & give the fiberglass/epoxy more to grab a hold of. Simple, strong, sounds like a plan to me. Talk me out of it if you like.

[Yakfishingfool]

OK, I'll take a whack at it. Don't do it. Too ugly and certainly not within your style. Now if you want to make it out of ply and maybe reinforce with CF. Go for it. but everyone here, including yourself, would know those hideous metal brackets are holding that wing on.

[riverrat]

Originally Posted by Yakfishingfool

OK, I'll take a whack at it. Don't do it. Too ugly and certainly not within your style. Now if you want to make it out of ply and maybe reinforce with CF. Go for it. but everyone here, including yourself, would know those hideous metal brackets are holding that wing on.

Nodd!

CONCUR!!

Sorry
Jimmy

[Nodd]

Well I did ask for folks to talk me out of it but truth is I'm quite happy with the brackets. I think they'll work great & should add some well needed strength. It doesn't matter what they look like as they'll be completely buried in the pylon by the time I'm done (I'm planning to add shaped fairings on either side of the pylon).

I also plan to use ply, fiberglass, carbon fiber & whatnot but these brackets will be the meat of the joint. With 2½ meters of wing levering on that spot, I want something bullet-proof in there as a foundation. Stay tuned, I think you'll like what I come up with.

[kyleservicetech]

Originally Posted by Nodd

Well I did ask for folks to talk me out of it but truth is I'm quite happy with the brackets. I think they'll work great & should add some well needed strength. It doesn't matter what they look like as they'll be completely buried in the pylon by the time I'm done (I'm planning to add shaped fairings on either side of the pylon).

I also plan to use ply, fiberglass, carbon fiber & whatnot but these brackets will be the meat of the joint. With 2½ meters of wing levering on that spot, I want something bullet-proof in there as a foundation. Stay tuned, I think you'll like what I come up with.

Probably to late to use this, but take a look at one of the online metal supply houses like this one:
http://www.speedymetals.com/c-8342-aluminum.aspx
http://www.speedymetals.com/pc-2186-...-extruded.aspx

Not only do they have a very wide variety of metal works, they also provide typical uses for each of the metals they sell. Prices are fairly reasonable. I picked up two pieces of aluminum 3/8 by 6 by 12 inches last spring for a gas engine, alternator setup. If memory is correct, price was under $25.00.

Methinks 1/8 inch thick aluminum would be a little stronger than the sheet metal steel parts you show. And weight might be similar. Or, 3/16 ???

The shipping charge would likely be more than the cost of the materials. I've looked at the typical aluminum stuff in places like Home Depot, for the most part their stuff is very soft aluminum. About the same quality as a piece of lead sheet.

[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 than 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.