First attempt at balsa - Corben Super Ace

[JUSS10]

First attempt at balsa - Corben Super Ace | 2017/2018 Balsa Build Along!

Lately I've been getting the itch to try building a balsa plane. I've built a few things from balsa and ply over the years but never a plane.

A while back I was able to acquire some CAD plans for a 44" Corben Super Ace. I've always loved this plane and thought it would be fun to try. I was looking for CAD plans as I run a laser cutter at work and wanted to cut the parts out.

As stated I have never built a plane, so this will be a bit of an experiment and should be fun whether it works out or now.

the plan was originally for a 3 channel plane with quite a bit of dihedral. I modified the wing to be a flat wing and added ailerons based on some other plans I looked up.

The wing plans also called for a balsa spar and 1/16" ribs. I had some birch ply laying around and decided to cut the spar from ply for strength. I also changed the ribs to 3/32 (once again, based on some other plans i found of similar sized planes) Hoping those two choices don't screw this up.

With those choices made I cut out all the balsa for the wing last night and did a test fit of the ribs. Everything seems fine. I have some ceiling tile pieces from a basement remodel a few years back that I plan to use as a building mat. Also printed out the plans to build on top of.

I have watched the one video that FT did on balsa building and plan to use some of those tips. Anything else I should really know before I start gluing this wing up?

I think I'll just start with the wing and see how it goes. I'm not always the most patient person so we'll see how this goes. Hopefully I don't loose interest.

Here are some photos of the real plane, the plans I have and the parts I have cut so far.

Justin

 

[rockyboy]

Welcome to the balsa building side of the hobby! This is really where we keep the most fun and satisfaction, but we try not to rub anyone's nose in that

Doing your own kit from scratch as a first build is ambitious, but based on the work I see on the table I think you're off to a great start! Since you're able to work upside down to assemble that wing, you'll have no problems with the rest of it

Switching the balsa spar to a birch one will add a pretty good amount of weight, and it's really surprising how much strength the whole assembly will have when completed with a good hard grade balsa as the spar. Or you could try and convert the plans to a box or D spar design like the Mountain Models EVA Sport, but that might get a little complicated. I do think the 1/16 to 3/32 move on the ribs is a good idea with how wide the spacing is here.

There are some great threads here in the Balsa section of the forum that do some detailed step by step builds that might give you some ideas on technique. The biggest recommendation I'd have is try to think ahead all the way to the end product with each part of the build before you add glue.

Things like how are the servos going to mount up, running wires and control rods, the impact of servo placement on balance, etc. are all much easier dealt with early in the build vs. at the end. For example, looking at what you have so far, to make a solid aileron servo mount you might want to add an extra rib in the wing - check out my EVA Sport Build Thread around post #50 for some ideas of one way to lay it out.

Also, some of those threads (I know in most of mine) there are the moments of 'oh crap, I really should have done this differently several nights ago, and here's what I have to do to recover now' - these could help you make all new mistakes of your own, instead of repeating all of ours. :black_eyed:

 

[JUSS10]

Thanks for the input.

for starters, I'm not using good balsa, I just ran to hobby lobby and bought a sheet of balsa with a 40% off coupon so I currently only have a few bucks in to the wing. This was sort of a "lets have fun and see what happens"

To that point, where do you all get "good" balsa from. the balsa I have here is really soft. I know balsa is light but this doesn't seem the best (and I'm sure its not).

Maybe I'll start over with a balsa spar and good balsa. I don't have a ton of hobby shop options that have balsa. Everyone just sells the horizon foam planes now and spare parts for those.

As for the ribs where the aileron go, should I just ditch the two riblets and do full ribs there to support that part where the aileron mounts?

I guess as stated, I am just playing around. Maybe its a waste and I should just start with a kit that I know has good materials. If I get this built with the material I have, maybe I'll just hang it and not cover it if the balsa isn't good enough. Would hate to go through the effort of building the frame, covering it, and just having it fall apart in the air.

If I were wanting to look in to a kit, are there any affordable kits (say sub $60) that make a good plane to get started with? Really wish my hobby shop sold kits like those radical RC kits that FT started that one episode. Those look simple and affordable to start with and get the hang of things.

Justin

 

[TexMechsRobot]

Hobby Lobby balsa is very inconsistent. You can find good wood there but it's unlikely. You best bet for local purchases is to find a hobby store dedicated to this type of hobby (RC stuff, scale models, trains, etc.). To get the best consistent wood, you'll need to go online to a place like Specialized Balsa Wood, LLC. There, you can pick the sizes you want in the densities you want.

The art of picking good balsa takes time and experience. I'm not yet good at it. Knowing the differences between A, B, and C grain is a start. Density is another key item. Hard balsa is more dense (heavier and stronger) and soft balsa is less dense (softer and weaker).

As far as picking a good kit to start on, most kits have decent wood but not great wood. That said, they're plenty good for someone (like me) who's learning to build and fly. Mountain Models makes good kits that are easy to follow. Sig also makes decent kits. There are plenty of others. For your price range, Dumas kits may fit the bill but they'll require modifications for RC flight. They are built for rubber power.

 

[rockyboy]

This is not a wasted effort at all man! You're ripping into this, and even if you decide to grab a kit for a first build to get a feel for what good balsa should be like, I have full confidence you can do this project! :applause:

For the aileron servo mounting I'd recommend doing two full length ribs - one on either side of the servo - with a healthy amount of room around the servo for the installation plate. Check the link I put to the EVA build thread in my other post for an idea of the proportions I like, but there are other ways to go about this too.

For online balsa, I've had great luck with http://shop.balsausa.com/Default.asp - they seem to have every size you can think of available. I don't think you'll end up with it falling apart in mid-air from soft balsa, but the first landing might also be the last :black_eyed:

As for some good kits to get started with if you want to get one of those under your belt before this build (which I'd sorta recommend so you can follow a full set of instructions before doing one without training wheels) I'd first recommend something from either of these two manufacturers.

http://www.mountainmodels.com/
https://www.stevensaero.com/

In my opinion (and shared by quite a few others who frequent these Balsa Builders forum) these are two of the best modern kit manufacturers with very good instructions and both provide excellent customer service as well. Avoid HobbyKing kits until you consider yourself an expert builder! Yes they can be cheap, but they are frequently missing parts, missing instruction steps, or have just plain incorrect instructions. The Spacewalker that Wilsonman is finishing up right now is one of the best kits HK has ever produced, and he is still documenting multiple issues with the kit and instructions that make it not appropriate for a novice builder.

So depending on your flight skilz and interest I'd say try one of these kits:

MM Dandy Sport: High wing easy flier $59
http://www.mountainmodels.com/product_info.php?products_id=230

MM Switchback Sport: Low wing easy flier with sport potential $60
http://www.mountainmodels.com/product_info.php?products_id=225

SA Playmite: High wing classic styling indoor or backyard flyer uses UMX electronics on sale for $55
https://www.stevensaero.com/StevensAero-Playmite-Toon-Playboy-RC.html

SA Toon Rocketeer: High wing classic styling indoor or backyard flyer uses UMX electronics on sale for $55

The larger StevensAero models are a little more expensive than the $60 target, but his kits are very well designed and worth every penny still.

As a third manufacturer option, I've had great success with a Mini Drake from Zeke's Park Scale Models and think his LOLO and LOLA kits look like they could be a good fit for you too. They also run on very inexpensive electronics compared to the UMX stuff (unless you have a busted UMX plane to harvest from). But while I had excellent service and experience with his kit, I know at least one person here on the forums that had a very long shipping delay to get a kit from him. I hope that problem is well behind him, but I haven't ordered anything from Zeke's in about two years to find out.

No matter what you decide to build, join in with the 2017/2018 Balsa Build Along here in the forums!

 

[JUSS10]

No matter what you decide to build, join in with the 2017/2018 Balsa Build Along here in the forums!

Should I start a new thread? I got one wing half glued up tonight already. wen't pretty good. Just need to build the other, join and skin the middle.

 

[rockyboy]

Should I start a new thread? I got one wing half glued up tonight already. wen't pretty good. Just need to build the other, join and skin the middle.

I am a firm believer in keeping project threads whole, no matter what restarts might be needed or mistakes have occurred. I think it's more valuable for new folks to see the honest progress of a project, and growth of skills, and to be able to learn from the missteps of others so they don't get too discouraged when they make missteps of their own.

That said, I'm also a fan of 'new project, new thread'


And glad to hear the gluing is proceeding - now where are the pictures!

 

[JUSS10]

Well then I guess I'll just keep this one going.

Ok so since my photos when imported from my iphone to my PC go upside down, I'll post them from an image hosting site instead.

first parts off the laser



dry fitting



pinning in place and gluing first wing half (I shifted one of the ribs by the aileron for better servo mounting)



first half glued up! just need to add the end plate (not sure of term) to the wing and then build up and glue the other half then sheet.




A few things. Pretty sure this balsa is too weak/brittle. Its very very soft (spongy almost) maybe it will hold together fine but I'm not certain.

Also need to figure out how I plan to mount the wing. This plane is sort of like a parasol but not really. essentially there is just not a lot of surface area in the middle for it to mount. Need to figure that out. Also will need to get the flush mount servo plates in once i figure how I want to do that. Oh, and will also need some input on making the ailerons as I have an idea, but once again, first timer with balsa here and only own foam planes currently... though there is a swap meet this weekend that I hope to walk away with something balsa....

Justin

 

[Joker 53150]

Dang, if I had access to a laser cutter my family would never see me again!

 

[JUSS10]

well crap, not sure what to do now.

I had to go in and work this morning (I'm a model maker of sorts by trade and have some prototypes to finish). Took all the pars for the other half of the wing to work with me. I start dry fitting the other half and should have just stopped when I saw that my laser cut plywood spar was warped a bit. I just figured I'd pin it straight and after assembling the whole thing, It'll square up. Well I pinned everything in place and glued it up. It went together about as good as the other half, but not as good. Anyway, went to a large setup table and put the wings side to side. not perfect where they meet up but not bad either. Seemed ok. Ran a long piece of tape on the table and took a straight edge to it and drew a line. put the wing halves down, aligned the spars, added some weight so it wouldn't move and glued the center brace that holds the wings together in place once it was all straight (or as straight as could be). That seemed to go ok so I started skinning the center of the wing. took the weight off the wing half and the side I built today just popped up, a lot. Crap, its warped and I should have stopped before I even began today. The left wing half has a pretty solid twist and lifts about 3/16". Is there anything I can do?

I think a mix of my lack of balsa building knowledge as well as use of crap balsa from hobby lobby, this may just be chalked up as a $10-15 learning experience. I really think if I want this to work right, I need to switch to all balsa in the wing and good quality balsa that is made for model planes, not art stores.

Kind of defeating as it looks so cool but I can't seem to find a way to get the warp out. Also some of the ribs are so soft, they pretty much break if you breath on them.

Justin







picture showing just how much twist it has



best I can think to do is cut all the ribs on that side and cut new ones with a but more slop that will allow the spar to have some twist but the ribs will be flat.

 

[JUSS10]

Well I licked my wounds and got some balsa from the local hobby shop. It's from Midwest and seems much nicer. I'll recut it all next week. Wondering if building the whole wing as one piece would be better as well.

 

[Joker 53150]

If the wing has any dihedral I'd just build it as 2 separate pieces, then join them together when each is done.

When it comes to balsa selection, there are a lot of options, and you really should look at the pieces available to try and match them up for the application. Example - I avoid lightweight wood for spars, leading or trailing edges, or ribs, as they tend to be weaker. If you hobby shop has a good selection you can dig through it and find the best wood for the job. Look up details on balsa grades, it's pretty interesting and will certainly help you build a plane.

 

[JUSS10]

The wing did have dihedral but I flattened it when i added the ailerons as I prefer flat winged planes.

I did go through the stack of balsa. It was sold in two packs that was shrink wrapped but this balsa feels much harder and less spongy than the stuff I last used.

I think I may try and build the wing as one pieces and see how that goes. Feels like i could make it stronger and more square that way.

I'm also going to a rather large swap meet tomorrow that will have tons of older balsa planes. Hoping to either get a cheap one that needs so work to learn on or maybe find a nice kit for cheap thats in the box and try and build that. Was looking for kits at the hobby shop but they just didn't have much. Little disappointed as its one of the older hobby shops in the area but they seemed to have transitioned to the foam planes and mainly RC cars and trucks.

Justin

 

[Joker 53150]

Doing a flat wing will certainly let the ailerons do their job. I've found on a few planes I did that with that keeping a small amount of dihedral keeps the wings from looking "droopy". A foamie I did that with actually looks like there is anhedral even though it's a flat wing.

 

[JUSS10]

Ok, so I'm still wanting to work on this guy this winter. I got better balsa and plan to give it another go.

I've been going over the plans I have, as well as other more complete plans. Thinking of cutting out the fuselage parts and giving it a go. a few questions. The elevator and rudder show they are 1/8" thick. can I cut them out of 1/16 and glue them together to make a "laminated" surface for strength? Also, the side skins are solid, should I add square holes between the formers to lighten the air frame?

 

[Joker 53150]

I wouldn't laminate the sheets together, as it's very likely you end up with some warping in the parts. If they're clamped tightly and evenly together while the glue dries this could be minimized. Any reason to not just use the 1/8" sheet?

Adding the holes to lighten the structure isn't a bad idea, I've done it a few times in the past. Obviously the structure will be weaker when you start removing material, so don't go crazy with it. Many older designs that were intended for glow or gas are over-engineered compared to what is needed for electric since there is far less vibration.

 

[JUSS10]

hmm I would think laminating would actually make it less likely to warp, thats why plywood is so strong and stable, multiple layers of glue... Main reason is I just have a lot of 1/16" balsa so I thought laminating them would be a good way to use the balsa I had on hand and make it stronger hypothetically.

 

[Joker 53150]

The idea is good, running grain in different directions with the extra strength of glue would be stronger, but unlike ply or hardwood the balsa will warp easily unless it's firmly clamped with flat surfaces on both sides. Plus, if you're doing hinges set into the balsa you'll have to cut slots through the glue which can be a pain. Basically, 1/8" sheet is typically fine for the application and it'll be less work. Just my $0.02.

 

[JUSS10]

Ok so this morning I took a few minute to tack together the fuselage. I think it went together pretty well. Here are some pictures.

my next main question is in regards to the stringers for the back of the fuselage. There are A LOT for this plane. it has a sort of double hump to the back of it that requires quite a lot of stringers to get the form correct. Which ones do I do first? the two front frames clearly have room for them all but by the time you get to the rear of the fuselage, there is only one notch for the stringers for the center one. should I do corner stringers first then fill in the rest?

Thanks!

Justin

 

[Joker 53150]

I think the usual method is to do all the full-length stringers first, then the next longest, etc. Sometimes a stringer will stop at a former and other times it dies in the structure of the plane past the former. Take into account where the covering needs to go and what kind of support it needs and go from there.