1/4 Scale Bud Nosen Designed Citabria

[Joker 53150]

Here's a little tip/trick on mounting a horizontal stabilizer or wing perpendicular to the fuselage. In this case I'm lining up the horizontal stab.

First, I picked a spot that would allow me to easily move a string from one side of the fuselage to the other without obstruction. In this case, it was the hardwood at the front of the wing saddle. I found the exact center side-to-side and put the pin in. A small loop was tied in the string, and then placed over the pin. I picked a spot on the horizontal stab (not the elevator) and used the string to measure from the pin to the spot.

While keeping my spot on the string marked I simply move the string to the other side and line up with the same spot on the horizontal stab. If the marked spot is the same then the stabilizer is perpendicular to the fuselage. If one side measures longer than the other you simply re-position the stab and measure again until the measurements are the same.

Note that this will really only work is you measure to the same point on each side, and if your center-point for the pin is actually on the center line of the plane. Oh, and the stab needs to have a mirror image left to right as well. In my case, it was darn near perfect right from the start. I still need to level the mounting base for the stab and will then re-check the measurements before gluing the stab in place permanently.

 

[TooJung2Die]

Big improvements. Looking good. Sometimes you have to wonder why so much weight is added to make things stronger. The better idea is the lighter you build it the less strength it needs. If you build it too heavy you end up with needing landing gear that's half the weight of the airplane. Light is might.

 

[Joker 53150]

Yes, but the over building may be why it survived a few aggressive landings. Or it may be why I had the bad landings.

 

[rockyboy]

Love the string trick - will have to remember that for future builds. Gives a little more confidence than the TLAR method, but a lot easier than trying to measure perpendicularly back from the wing trailing edge.

It's a vicious cycle of build heavy to survive crash leads to poor flights and crashes, so build to survive crashes. I think the best answer is somewhere between Pat Trittle and built to handle an out of balance nitro engine.

 

[Joker 53150]

Back at it after a week traveling for work! Before I left I glued the horizontal and vertical stabilizers in place so I could make sure the pull-pull wires and pushrods would be installed properly and nothing would interfere. With those surfaces installed the next step is making the stabilization wires that connect both stabilizers to the fuselage. There are plenty of ways to do it, including braided or solid wire. Both work, and in this case I am going with braided wire with a black coating. This is another item I picked up at an estate sale, along with some non-coated wire. Also in the picture you can see the original pieces which were removed from the plane. They are a bit too long for how I'm re-building the plane, and I also wanted to use fewer hardware bits for simplicity.

The right side is pretty much done and I'm happy with how it's turning out. I've got a lot of adjustment to tighten the wires if needed. I'm guessing the plane could be made without these pieces if strong enough balsa is used for construction, but having these braces gives the plane an additional level of detail and they certainly help make the surfaces sturdy!

 

[Joker 53150]

With all of the stabilizer wires in place I did a quick test to see how much strength they add.

Before installing them I tried lifting the tail of the plane by lifting at the outside end of the stabilizer. The stab flexed a lot and had a considerable amount of curve to the structure.

With the wires installed there was no flex and the tail lifted easily. The wires do a great job transmitting the force down to the hardwood mounting point on the bottom of the fuselage.

They aren’t easy to adjust, but are well worth the effort on bigger planes like this.

 

[TooJung2Die]

No doubt the guy wires add a tremendous amount of strength. That's how all the early wood and cloth airplanes were held together. A triangle is the strongest geometric shape. Wires look good too. It's not a detail you see too often. Tested it without the covering on? You're going to see even more strength after it's covered. Covering film adds a lot of strength.

 

[Joker 53150]

No doubt the guy wires add a tremendous amount of strength. That's how all the early wood and cloth airplanes were held together. A triangle is the strongest geometric shape. Wires look good too. It's not a detail you see too often. Tested it without the covering on? You're going to see even more strength after it's covered. Covering film adds a lot of strength.

Yeah, I'm looking forward to seeing how much it improves with the covering, which will be similar to Solar Tex, so nice and strong!

More progress - the control surfaces are all hinged and installed temporarily. Guy wires are working their magic, and I've installed the fuselage longerons that the original builder omitted for some reason. In the second picture you can see I also gave the big piece of sheet material run down the top of the fuselage a trim, removing about 25% of it. The more work I do on this plane the more I love the lines. This work will give it back some of the "sharp" edges the design is known for.

 

[Joker 53150]

I may be jumping way too far into this build, but I've got my reasons. The rudder hinges are epoxied into place and have been pinned with short sections of 1/8" hardwood dowels. I also covered the rudder with SolarTex, which unfortunately isn't in production anymore. I've got a white roll and a red roll, but I want the plane to be blue and white when complete, so it'll be paint over white. If/when I run out of SolarTex I'll switch to the new covering Balsa USA has which is very similar. I should have plenty of white to finish the entire fuselage.

With the rudder hinged and covered I did another check of the gap between the top of the vertical stab and the rudder, and found the gap at the leading edge (by the blue piece of tape) is a little tighter than back by the guy wire. The solution will be easy - sand it slightly to increase the gap.

Another reason to cover the rudder this early in the build is to try out some 1/4 scale pinking tape I ordered. It's supposed to simply iron on and then it's ready for paint, and I want to test it out well before the entire plane is getting covered. The full scale Citabria has far less internal structure than this model, and I'm hoping that the pinking can be applied and finished like the original and NOT show the internal structure hidden underneath.

Here's a full scale 1999 ACA 7ECA Citabria being re-covered as an example. The main body of the fuselage will match pretty well with the model, but the tail differs greatly.

 

[Joker 53150]

Switching gears while waiting for parts to arrive, work begins on one of the wings. The wing itself appears ok (although built too heavily), but the aileron and hinges are too rough to save.

The aileron construction is marginal, and fixing it would require more work than simply building a new one. Like the fuselage there is an excess amount of glue, including some applied after covering somehow, which resulted in covering glued permanently to the aileron.

So to keep my sanity I’ll cut the hinges from the wing aileron pocket and install new ones, along with building the new aileron from plans.

I also realized that the plane wasn’t built with jury struts for the wing struts. Since I’m going through a lot of work already I may as well fix the struts as well. I’ll probably do something similar to what I did on my 1/4 scale Cub’s struts, which gives a lot of great detail.

 

[Joker 53150]

Aileron work in progress. It took a little effort, but I was able to pull the hinge pins out and remove the aileron. I also cut the aileron in half to better see how it was constructed and found some discrepancies when compared to the plans. I can't blame the builder too much as the plans really aren't that clear. One additional thing that will be changed is how the aileron servo is installed. You can see the servo pocket here, and the servo is simply dropped down into the pocket and screwed in place. I'm pretty sure there is enough room to recess the servo completely along with a hatch to cover it, which will give a much cleaner look. I'm also thinking about adding flaps, which are shown as optional on the plans. They're exactly the same design as the ailerons, just shorter.

Here's an issue from the original aileron that I'm fixing on mine - notice how small the plywood piece is for the control horn to mount to. Heck, two screws are only in balsa and the third is barely touching the ply! It would have been very easy for the aileron to pull loose from the horn, resulting in a crash. My version uses ply to tie the leading edge and sheet together much more securely. You can't see it in the picture, but the ply on mine extends all the way into the leading edge of the aileron.

I've got to do a little more measuring, but it appears the original aileron was built about 1/3" too short. I'm strongly considering adding flaps which will make that problem go away. If I don't add flaps I either have to shorten the new aileron (easy) or make the aileron pocket wider (hard). Good times!

 

[Joker 53150]

Arrrgh, there is more work ahead of me on the wings than expected. I’m pulling out the old servo rails, which damages two ribs enough that they too need to be replaced.

Since those ribs are coming out I’ve got easier access to also remove a couple 1/4” thick plywood blocks which were epoxied (heavily) into place. I’m not sure why these blocks were installed, but they’re coming out.

Back to the aileron construction, I noticed that the original ailerons are about 1/8” thinner than plans show. I’m not sure why, and it appears (so far?) that the aileron pocket on the wing was made to the right size. Strange....

 

[Joker 53150]

Happy-time-band-saw-chopping time! I ended up removing 3 ribs instead of two as there was "collateral damage" trying to remove the excess 1/4" ply and gobs of epoxy. The plan was to surgically remove the ribs with the X-acto knife, saw, Dremel, etc., but there was just so darn much epoxy and ply I had to go medieval on it with the bandsaw. Unfortunately that meant I also had to cut through both rear spars, but I can repair those easily enough. The bandsaw made the job pretty quick, it's a luxury tool that's worth it's weight in gold at times. With the excess removed I tried test-fitting the new aileron, but it's just a hair too long to fit into the aileron pocket (or what's left of it...).

Here's why it's too long - the pocket was made slightly too short. Not a big deal, I could easily just shorten the aileron by about 1/8" and it'd be fine. In fact, I'll probably do that after re-building the aileron pocket and cleaning up the original work a bit more. I'm also removing about 2mm of each rib to make the pocket a little deeper, so it matches the plan. Otherwise the new ailerons will hang out at the TE of the wing.

Aaaaaaand, while I'm at it with the bandsaw I may as well remove more material to prep the wing for a flap. The flaps are the same cross section as the ailerons, just shorter. The upcoming work shouldn't be too bad, and it probably looks worse than it really is. If I didn't have a set of original plans it'd certainly be more "interesting". The hardest part will probably be making it all line up smoothly so it doesn't look like a major repair.

 

[Joker 53150]

After careful measurements and double-checking how the aileron will fit in the pocket, I came to the conclusion that the parts I'm rebuilding need slight modifications so everything will fit. Basically, the pocket needs to be about 1/8" deeper than drawn to make room for the aileron and the hinges. Not a huge issue, but without this change the aileron and flap would be hanging out the TE of the wing. The piece will sit for the next few days while I'm away for work, but upon my return I should be able to get the wing buttoned up fairly easily. Some cosmetic work will follow as there are areas that need to be planed down and others that need wood added to make it all straight.

 

[Joker 53150]

I've run the pull-pull cables for the rudder, and with that out of the way I could focus on the dual pushrods for the elevators. This plane has one servo for each elevator half, which means two pushrods fighting for space. Lucky for me, the elevator pushrods want to sit above the pull-pull cables so they won't touch. To be safe I'll run a couple spacers in the fuselage to make sure they aren't going to rub against each other which could cause wear.

The pull-pull setup is very light, which is great. However, the current mock-up for the elevators uses 4-40 threaded rod lengths (about 10" long) which transition to a lighter fiberglass shaft. The elevator pushrod runs are nice and straight, but the weight of that 4-40 rod and the heavy-duty control horns are concerning. Over the weekend I'm going to try and change it to a Gold-n-Rod style flexible pushrod to shave some weight. Even if that works, the final 3-5" or so will have to be the stiffer 4-40 rod as it'll be unsupported after it leaves the fuselage and it can't have any flex. I'd love to have re-used the original pushrods and control horns that were on the plane when I got it, but with the horns installed properly (mounted to the plywood in the elevator and not the balsa) the pushrods are too short.

 

[Joker 53150]

Back to the wings! Reconstruction of the first one is heavily underway, with three new ribs and top rib caps installed. Before capping the bottoms of the ribs I need to make servo hatches and servo mounts to better hide the aileron and flap servos. Before starting the flaps I'll probably have to do a run to a hobby shop to pick up some more balsa sheet as I'm out of longer pieces needed to do this work without tons of splices.

Something new also arrived today, pinking tape! This isn't the generic stuff you can pick up at craft stores, this is laser cut from SolarTex-type covering specifically to be 1/4 (ish) scale. They also make 1/3 scale, 1/5th, etc. I've got 1/2" wide for ribs and fuselage sides and 1" wide for edges and the perimeter of the wing. This material is supposed to simply iron on and will then be ready for paint. Hopefully. I don't think I'm going to try adding the fake rib-stitching to go with it.

 

[Joker 53150]

I'm kicking myself for not checking the rib heights before capping the ribs... Once I capped the ribs I put a straightedge on the wing and found that all of the caps I just installed along with two original caps sit well below the rest of the wing. I haven't sanded mine down at all, so that wasn't the problem. My ribs were made to match the plans which could be the issue, but I only replaced 3 ribs and 7 are too low. I think the original ribs were all hand-cut, and MAYBE some were cut taller than others? For giggles I checked the other wing and found the same problem - the ribs in the center sit lower than the inner and outer ribs, so I'm just going to chalk it up to questionable building.

To fix the problem I could try to remove my new caps (and the two original caps I didn't touch) without damaging the ribs, but the easier method will be to cap the caps. When the glue dries I'll come back with a long sanding block and get them flush with the remaining original rib caps. When I do the other wing I'll plan on making the ribs taller to avoid doing this nonsense again.

 

[Ryan O.]

dang, i wish i had the dough to do that type of stuff=(

A ton of older guys are leaving glow and gas so they are selling it for dirt cheap. For getting cheap glow fuel the key is bulk purchases with other members at the field. If you want to get into giant scale then I would recommend going electric unless you can find an old glow or gas system for cheap. An old beat up Balsa plane can be found for cheap or nothing if you can find the right swap meet. There are also probably some kits on Ebay for cheap if you want to start Balsa. Another way to save money, buy servos in packs of 10, you have spares, and for me it cut the cost of one build by a third. One thing to never cheap out on is the covering, if it is easier to put on then the time saved is worth it. Hope this helped

 

[Ryan O.]

I'm kicking myself for not checking the rib heights before capping the ribs... Once I capped the ribs I put a straightedge on the wing and found that all of the caps I just installed along with two original caps sit well below the rest of the wing. I haven't sanded mine down at all, so that wasn't the problem. My ribs were made to match the plans which could be the issue, but I only replaced 3 ribs and 7 are too low. I think the original ribs were all hand-cut, and MAYBE some were cut taller than others? For giggles I checked the other wing and found the same problem - the ribs in the center sit lower than the inner and outer ribs, so I'm just going to chalk it up to questionable building.

To fix the problem I could try to remove my new caps (and the two original caps I didn't touch) without damaging the ribs, but the easier method will be to cap the caps. When the glue dries I'll come back with a long sanding block and get them flush with the remaining original rib caps. When I do the other wing I'll plan on making the ribs taller to avoid doing this nonsense again.

View attachment 148214

Mistakes happen to everyone, I have forgotten to put servos in a plane several times.

 

[Joker 53150]

Mistakes happen to everyone, I have forgotten to put servos in a plane several times.

Agreed, I make plenty of them, and this one is kind of a pain in the butt to fix. At least I'm ready for the other wing...!