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BBA/Winter Build 2017/18 - Top Flite Corsair


Skill Collector
Could always hack in a little Pololu voltage regulator to power the UMX servos with 3.2v from the 5v off the RMILEC.

I mean, if you're going way over the top anyway, why stop now? :p


Builder Extraordinare
Wrapping up the flaps we use steel rods inserted into the outer flaps that move freely in a out of the inner flap.

And deflected.

The push rod for the flaps is now internal. I drilled a pilot hole and then a 1/4" hole that took me right down to the wing skin. Two layers of 1/64" ply were CAed together to make the horn and the metal clevis can be adjusted inside the wing servo bay for each set of flaps.

Next I moved on to the tip blocks. They started as just that... blocks. I drew center lines all round and traced the wing profiled onto the block. I then planed down the top/bottom of the block to the rough shape. I glued using Titebond II and then planed more to give the taper. and then finally using a sanding bar for final shaping and blending into the leading edge. The leading edge was also shaped.

The other side. Sanding around the pitot tube was tricky but not impossible.

I cut the aileron stock to length. and traced the wing profile to the aileron LE and the side. I used the plans to define the curvature of the aileron at the tip. The bulk of the shaping was done with the planer again.

Very happy with the curve and verified that it is nearly perfectly scale.

An idea for size. The wing is on the floor and I'm 5'9" tall.

The main bulk of the build is nearly done now. Just a few things to wrap up this week. Many more fun things to come.


Builder Extraordinare
The Ailerons are done. Due to a busy life I forgot to snag pics of the aileron push rod setup so I'll snag some later and describe how it all gets done. For now, lets move on to how I did this scale setup.

The first thing to do is use a dremel and carve out a pocket where the aileron goes. As you get to the taper of the wing tip you need to use a #11 blade to cut away the balsa. Make sure to put your reference lines for the hinge locations on the bottom side so that you can transfer the line back to the pocket once it is carved out. Then mark a center line for where the hole for the hinge should be drilled. Drill the hole and you need to use your #11 again to widen the opening for the hinge.

Using the same reference marks on the wing, tape your aileron in place and mark the aileron where the hinges go. Drill holes for the hinges and then countersink the holes with 1/4" bit so that the knuckle of the hinge sits into the aileron by about 3/16". Don't forget to widen the hole to account for the taper of the hinge.

Once you have the hinges worked out you need to then do your fine adjustment of the fitment. Sanding shaping, planing... it all needs to be done so that you have proper deflection, 1/2" up and down. This is mostly done by shaping the aileron, not really the pocket, but you do want to try and make the top and bottom lips of the pocket as thin as you can. I went to about 1/64" using sandpaper and the tip of my finger. Here is how she looks with the ailerons hinged.

I got heavy-handed. Just showing that I do make mistakes.

And fixed.


Builder Extraordinare
I know I know. I need to update this more. Been an eventful couple of days.

Really quick. I wanted to cover the aileron control rod. Just Drilled a hole and made it bigger and then squared it off for the clevis. Piece of ply for the horn and that's really it. Pretty simple stuff but much more difficult to do on smaller aircraft.

Next we wrap up the bulk of the build by smearing epoxy all over the firewall and taping it into submission for a good long while.

Then you pop on the 4 blocks and the rear part of the cowl (ring) and the front part of the cowl and you are done the bulk of the project.

Just a few more angles so look overall.


This one you can see where I've started on the 3D printed dummy radial. Without the motor in-hand I'm not sure if it is sized right just yet but it fills out the cowl fairly well.


Builder Extraordinare
Ok so for the cowl flaps we start by cutting them into segments and then cut them off the cowl ring. I sanded in a bevel to the trailing edge so that bending on the hinges would be fairly simple. This picture is obviously after the fact but it illustrates the amount of cutting with the razor saw I had to do. The hinges are from old floppy disks. Cut them up after they have been roughed up with sandpaper and they make perfect lightweight hinges.

Then I put tiny segments of nylon push rod tubing on each segment of the flaps. I bent the nylon push rod to make a good circle and installed two servos to do the pushing. One has a reverser in it. I could do this with one servo but it works in sort of a ripple effect and using two servos really takes that out.

And here you can see there is actually a big difference in cooling for the motor with the flaps open. I'm pretty stoked about this. First time I've ever done this and nailed it the first time.


Builder Extraordinare
I'll include a clip of the cowl flaps working in my next video update. I posted one to FB but I do understand that not everyone on the forum is necessarily part of the FB group.

Worth mentioning is that I had intended to have the circular nylon push rod further away from the hinge line but due to the clearance between the flaps and the fuselage, I was unable to fit the nylon rod there. I could have gone to a Sullivan Goldnrod but I did not have one on-hand so I tried this first and it worked just fine. I figured if it did not work I could just take off the small guide tubes and re-do it after I got the thinner rod.

The motor mount is expected to be delivered tomorrow as well as the wheels. My 20A BEC arrived and I did some soldering to get connectors for the battery as well as power for the VTx.

Up next on the slate is to glass the main gear doors. I need to do this so that the curvature of the wood is retained through the glass and epoxy. Then I can cut them away, hinge them, and work on the closure. I think what I'll do is remove the wing and apply the glass to just the door area and work on hinges for the elevators and rudder. That way, when the wheels arrive, I can cut the gear doors free and make sure the doors clear the wheels and such.

Last week was a big milestone to wrap up the bulk of the build but I hope to have her on her legs this week, which is another big deal. I've got just over two months left until SEFF and I would like to fly the maiden before then. If I keep this good pace I should have time to do all the fun things I want to do for SEFF, including the animated cockpit.


Builder Extraordinare
As mentioned, I started the gear doors. First thing was to inspect my resin. This stuff was gifted to me years ago. The cool thing is that since it is in a metal can I can keep resurrecting it. Epoxy resin has a tendency to crystallize over time. Most people will throw it away assuming its bad but it really is not. I take the can and pop it open and throw it on the stove over medium heat. I am using an Oak dowel to break up the crystals and lumps as it heats but eventually it will mix back in.

Here you can clearly see how milky it looks inside. This should be a very transparent amber.

Not the greatest picture here but it does show the slight change in color, not really the transparency. Use a flashlight to see inside.

With the resin ready, I marked off where the gear doors should be with a fine tipped sharpie. Pencil will not show well through the glass. I mixed up 16cc and applied a coat directly to the wood. Then I added a layer of 6oz glass cloth and used the brush to apply a bit more resin. I use a stippling technique to push the epoxy into the cloth to make sure it is entirely wetted out. This cloth I purchased at the hardware store. It is generic stuff and heavy but will provide the stiffness needed to keep the compound curves. Then I applied a layer of 0.75oz glass to smooth things over and make less finish work for myself. THis cloth is found at a hobby shop or ebay. Added a touch more epoxy and again fully wetted the cloth. To further reduce my work, I applied a sheet of plastic wrap from the kitchen and stretched it smooth and worked out any air bubbles and squeezed some excess epoxy out to the sides. This helps reduce a bit of weight from excess epoxy but also further drives the epoxy into the layers of cloth. The smoothness of the plastic wrap makes a really good finish that will require minimal sanding. The other big advantage here is that It reduces the risk of the epoxy "flashing" as it cures. Flashing is when the moisture of the air gets into the epoxy and causes the resin and hardener to separate. This causes a huge sticky mess that ruins your layup. I live in a rather humid climate and I'm working in a basement... both things will contribute to this.

Once the epoxy is fully cured out I can trim the excess off at the tape lines. These will also be my cut lines for separating the doors from the wing. The tape provides a barrier where I can glass just these sections. Any seam in the layup can easily be blended through sanding.


Builder Extraordinare
Since I did a terrible job covering the hinge work on the ailerons I thought I would attempt to redeem myself as I did the tail control surfaces. Pictures are from one elevator.

With the control surface taped to the exact location you want, mark on the stab and control surface where the hinge will be located. Remove the control surface and on the center line drill the 1/8" hole for the hinges. You can see that I cut away a bit of the covering prior to drilling. More on that in the next picture.

I removed a portion of the covering film to countersink the hole for the hinge knuckle. The drill bit to counter sink will just chew into the film and make the hole a mess so take your #11 blade and be careful.

The hinge hole is countersunk into the control surface using a 1/4" drill bit.

Here you can see how the hinge fits into the hole. There is clearance on the sides of the knuckle for free movement but enough clearance vertically for proper movement. The hinge point is now offset from the leading edge of the control surface to pivot in a scale manner.

Mark vertical lines in your stab pockets and draw a center line to mark where to drill the holes for the hinges.

Drilled out, you now enlarge the holes slightly with your #11 blade for the hinges to seat properly. Trying to ram the hinges into just the round hole can cause the balsa to split so take this little extra step.

All of the tail control surfaces are now hinged. I also fitted the clevis for the elevator push rod to the servo. Something that I had not previously done.

Lastly, I started the install of the pneumatic system for the mains. The air tank is secured to the guide tube for the rudder using cable ties. It is a snug fit but works. The air valve and servo will be located to the other side of where the servos in the tray are. I'll use some luer fittings to make some quick connect/disconnect for the wing. They are made of UV-resistant and chemically resistant HDPE plastic that are rated up to 100psi. Plenty for the 80psi I intend to place on the system.
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Skill Collector
Thanks for the tip about epoxy flashing - I've experienced that before but thought it was my mix screwing up or the resin getting old. Will be keeping a tube of saran wrap in the shop now :)


Builder Extraordinare
@ rockyboy: Yeah man, I just steal a bit from the kitchen when I need it. As you can see, using epoxy is only as messy as YOU make it.

@ psyborg: Yes, once it cures out you can simply peel it off. I've never had an issue with it sticking profusely to the epoxy after curing. If it does, it is probably not fully cured or your mix was not thorough. Yes, you could probably just sand it off if you get a piece stuck here or there. It needs to be sanded anyway so it will likely come off for that.


Builder Extraordinare
We start work here by trimming away the excess cloth right at the perimeter of the blue tape. This should only take two, maybe three, light passes of a sharp razor blade. After that, trace where the gear doors will be cut. For the front door, I traced the outline of the door provided in the kit. This one is flat so the curved door will be better for overall aesthetic.

From there, Cut each door out individually with a SHARP blade. You are cutting through very dense epoxy AND very soft balsa. A really sharp blade helps here. Do not cut the entire perimeter out and then separate the doors. You will risk damaging them in that process. Pull the legs down and affix the wheels.

Putting the legs back down, you can see that the wheel is forcing the leg to sit a little high. The wheel is resting against a rib that is not quite shallow enough to accept the wheel.

The rib on the left here was the trouble spot. A few quick passes with the dremel and we are ready to test the fit again, and it was fine.

As the axles were protruding I used a dremel cutoff wheel to remove about 5mm. Nice and flush now with the oleo.


Builder Extraordinare
Moving along to the doors now. I had to cut a little bit from the outer rib to secure the door hinges. I used my #11 blade to do that. Apply some CA to the one side and you can put it in place.

I bevel the inside of the door along the hinge line to prevent the doors from binding with the bottom wing surface. Its a lot harder to do this once the doors are on so do it first.

The first door is affixed with CA and sits open in the perfect position.

And closed with the gear down you can see that the doors clear the wheel and oleo well. No further adjustments needed on that offending rib.

Rinse and repeat on the other side. There is less work since there is not a rib in the way. I ended up putting a piece of ply to the underside of the wing skin to make it more rigid. After removing the door, the skin was bowing more than the glassed door. The ply helped to correct that geometry.

And with the doors closed, no binding, no issues.