"Back on the Flaps and Dive Brakes!"

Glassing & Sealing the Flaps & Brakes

OK, back to the flaps and dive brakes. With them already built up, I proceeded to the glassing and sealing stage. I hit them with a couple coats of Deft Lacquer Sanding Sealer to seal and harden them first, and sanded them smooth.
Next I used 3/4 ounce glass and Minwax waterbased poly to glass the "outside surfaces" only. When the glassing was cured, I cut the holes back out of the glass cloth with an X-acto knife, and sanded everything down well for priming. Glassing the flat outside surfaces will add a lot of strength to the thin 1/16" aircraft ply flaps and brakes.

Control Horns and Hinges

With the glassing cured, primed and sanded, I proceeded to add hinges and control horns. This proved to be quite interesting, since I was going for the most scale appearance I could get, balancing the difficulty and dependability factors into play. I wanted to get a good scale hing look from the outside, and hide as much of the control linkage internally as possible.

My choice was to go with metal piano hinges from Nelson Hobby. They come in various widths and lengths so I got four 5/8" by 24" hinges and one 5/8" by 36" hinge. I also used standard heavy duty nylon control horns that were mounted in one of two different configurations.

I cut the piano hinges to length for each surface and notched them out where the control horns/linkages would go. I then scuffed them up well with 320 sandpaper and epoxied them into place on each surface. I also pinned the hinges into the surfaces using about 4 servo screws on each hinge. Next I cut down 5 control horns to provide "short horns" with only one hole left, and positioned them into place on each surface. Since the 3 flaps are on the bottom of the plane, and the 2 brakes are on the top, I mounted their respective horns a little differently...

Flap horns...

For the flaps, I mounted the horns on the inside, sandwiching the ply flap between the horn and the nylon backplate that mounted on the outside. I used standard 2-56 screws to secure them in place. Since the screw heads and backplates were on the bottom of the plane (less visible), I didn't mind the fact that they were external. Also, they're low profile and white, and the bottom of the plane is white... not too intrusive.

Dive Brake horns...

As for the brakes, that's a different story. I didn't want the backplate and screws sticking out externally on the topside of the wing so I used a different mounting technique. I cut a 1/16 ply plate about 1/4 inch larger than the base of the control horn and epoxied it to the inside of the brake. This allowed me to countersink sheet metal screws into the outside of the brake and still have something for the threads to "bit into" before threading into the "inverted" horns themselves. This provided me with a solid mounted horn, but gave me 3 flush screw heads on the topside of the brakes. I can putty and paint right over them and you'll never see them.

Painting the inside surfaces

After priming and sanding again, I painted the inside surfaces with Tamiya "bright red" enamel. I'll paint the outside surfaces when I paint the rest of the plane, but the red inside surfaces will be much easier to paint now before mounting.
Next I went ahead and started tweaking the color by adding weathering, distressing and natural airflow streaks by using waterbased hobby acrylics and an Iwata airbrush. I sealed all this work in by hitting it next with a few coats of Nelson Hobby clear. I mix gloss and flat at 50/50 to get a satin finish.

Getting the"perfect red" for these flaps proved to be a little harder than I thought. There is some debate as to just "which red" the SBD Dauntless actually used on these surfaces. Some say it's "Bright Red" (FS-31136) and some say it's "Insignia Red" (FS-30109). Checking my Frank Tiano color chip book, I found the Bright Red to be what I would call "stop sign" or "fire engine" red. However the Insignia Red looks more like "rust" or even "cedar red" (more brownish).
Of all the photos, models and restorations I've seen, it appears that they used the Bright Red. Also, with age, grime, dirt, seawater salt, airflow streaking, and other types of weathering, I'm sure they varied somewhat in hue, saturation and lightness from plane to plane, flap to flap and even different areas on any one surface. I'll probably continue to "tweak" this red on the plane later until I'm completely satisfied that it looks authentic, scale and realistic.

Finished flaps and brakes weighing in at 15 ounces total with hinges, horns, glassing and paint!

Redesigned "5-Servo" Configuration/Mod

As I mentioned earlier in the site, this Bates design called for one servo for flaps and one for brakes, and used an elaborate array of pushrods and bellcranks to each surface. I tried this out, didn't like it, pulled it and started over. My choice was to redesign it for 5 servos, with one HS-475 dedicated to each surface. That will give me about 70 ounces of torque on each of the 5 surfaces, which translates to about 140 oz on the brakes and 210 on the flaps.
I cut a servo bay in the center section with a removable servo mounting plate for the center flap servo, the made a removable ply hatch on each of the wings to hold the flap and brake servos. The center section servo mounted "upright" in the wing and the 4 servos in the wing mounted "inverted" in the wing.

All servo linkages remain completely internal with only a small portion of the conrol clevice sticking out through holes in the trailing edge to connect with the internal horns. The 256 rods used Z-bends on the servo arms and metal clevices on the nylon horns. The rods were all about 2 to 3 inches long.

Temporary "Mounting & Operation" Test

I temporarily mounted the surfaces to the trailing edges of the wing by using a few button-head sheat metal screws. These would be used again later to align and pin the hinges into the wing when final epoxying is done.
I decided not to complicate the electronics and expense ($$) by adding servo reversers, a Matchbox, digital servos, etc... so getting the 5 surfaces to deflect perfectly took a little patience. Without servo reversers, the servos/hatches had to be offset a little differently on each wing to line up with the horns. Unfortunatley this gave me a slightly different deflection and throw on each surface. I was able to work most of it out.

Temporary "Mounting & Operation" Test

Ultimately I ended up with "slightly" more throw on the center section flap, but not so much that it looks bad. I was able to get equal throws and default positons on the four flap and brake surfaces after a good bit of work.
Unfortunately, I'll have to do it all again later since I've got to remove these surfaces for glassing, priming and detailing the wing. This photo shows the surfaces being operated in the three main flying configurations (closed for cruising speed, full flaps for landing, and full flaps and brakes for dive bombing).

Conclusions...

My biggest issue/complaint with the flaps and brakes are the "droop 'n' warp" factor. Since they are built out of very large pieces of only 1/16" light aircraft ply, they tend to bow, droop and sag a little differently on each surface. This means that they really don't "seal" together perfectly across the full length of the trailing edges of the brakes. The flaps and brakes pinch together tightly at the trailing edges in some areas, the droop to a 1/8 inch or so gap in other areas. Also, they don't always seem to "settle" to the exact same position every time, especially depending on whether the wing is upright or inverted.

I'm probably being a little "anal" on this, since the photos I've seen of other RC scale Dauntlesses seem to have the same issue. I'm sure it would be less of a problem for those who have elected to have "fixed/non-operational" dive brakes, since that's one less surface to deal with. Maybe digital servos & servo programmer, or a Matchbox might have helped a little too, but it's not worth the expense. Ultimately, the light ply would probably still droop and bow a little any way.

Every piece of 1/16 aircraft ply I've ever seen over 12" long has always had some bow or warp to it, I don't know how you could ever get it to lay perfectly level and true within 1/16 inch tolerance when you're anchoring it on only one side. The very small ribs and the 1/4" balsa spar don't really provide enough support or rigidity to this design to effectively hold it flat. The weight and warp of the ply itself tends to overpower the ribs and spar in my opinion.

My final take on this setup however is very positive. I like the 5 servo setup much better than the 2 servo/bellcrank system. It's much stronger, more precise and just a cleaner setup. It weighs a little more, but not enough to hurt. Bottom line is this... standing behind that wing and flippin the "Dive Brake Switch" on my radio, watching all 5 of them big ol' red surfaces jump into position is just WAAAAAAY COOL!!!!!!!!

UPDATE: The most recent version of the Bates plans still has the bellcrank system, but has been redesigned. It uses 4 servos now, 2 for flaps and 2 for brakes, and has moved forward to a position between the front and rear dihedral braces. I like my 5 servo system better (so far) but it would be nice to not have the access hatches I have to use.