Kick your foam warbird up a notch by adding flaps! The techniques shown here upgrade a P-47 Thunderbolt that has optional functional flaps (an upgrade available on many small electrics). The flap outlines are already molded into the wing so it’s easy to figure out where the flaps belong. Here’s how to install them:
The first thing to do is to collect the required gear and materials.
- ▪ Two micro servos
- ▪ $5 worth of hardware to make the pushrod linkages, clevises and control horns
- ▪ Razor saw
- ▪ Sandpaper
- ▪ Foam-safe silver paint
- ▪ Foam doubled-sided tape (I use installation tape from the local hardware store)
- ▪ Y-harness (to connect your dual flap servos to the receiver)
AFTER Installing functional flaps are easier than you think and they’ll give you improved flight performance.
Below: You don’t need much to install working flaps—just basic hardware and tools!
1 Start by using a straightedge and lightly cut into the flap hinge line on top of the wing. Make a second cut along the hinge line under the wing. Don’t try to cut the flap in one pass. Two shallow cuts that meet in the middle produce a clearer job.
2 To cut the root end of the flap free of the wing, use a fine-tooth razor saw or hacksaw blade. Make the cut vertical and square to the end of the flap.
3 Use fine sandpaper and sand the cut edges and end of the flap so it is smooth and straight. Remove any “fuzz” left so when it is painted it will look clean and smooth.
4 Cut the base off a suitable control horn and then cut a slot into the bottom of the flap. Slide the horn in place and use foam-safe CA to glue it into place. I used Bob Smith Industries CA and glue accelerator. Use it sparingly—just a mist is enough.
5 Use a fine-tip pen and mark the locations of three hinges. To install the Robart Hinge Points, use a sharpened length of brass tubing to cut/drill the hinge pockets in the foam.
6 Twist and push gently with the tube about 45 degrees to the wing. Place your finger on the opposite side of the wing so you can feel the tube getting close to the outer surface. Try not to push all the way through or you’ll have to use some filler to fill the opening.
7 In this photo, the three Robart Hinge Point hinges have been glued into place. With the hingepins below the wing (offset hinging), the flap moves down and back from the wing. I used 15-minute epoxy so there is time to align the hinge pins. This allows the flap to move without binding.
8 The wing comes with clear tape that covers the aileron servo leads. Remove some of the tape so you can place the flap servo lead in the same channel.
9 To install the servo, clean the servo pocket in the wing with some rubbing alcohol and use a piece of doubled-sided foam tape. For the pushrod and clevis linkage, keep it simple and use a Z-bend to attach it to the servo arm. This photo shows the servo with flap in the up position.
10 Here is the flap in the down position. You’ll have to experiment a little to get the position of the servo arm and the hole/linkage placement right for the radio you are using. A programmable radio comes in handy here so you can precisely adjust the travel and endpoints for your flap servos.
11 After the installation is done, lightly spray silver foam-safe paint to cover the tape and the exposed foam edges of the flaps. A little paint on the servo won’t hurt anything and will help it blend in.
12 Here’s the finished wing with the flap in the down position. As you can see with the radio’s flap control knob, it is dialed in for full down. A twist of the knob brings the flap in the up position for normal flying. This modification takes just a couple hours and it is easy to do on any type of foam warbird you might have in your RC hangar. Give it a try—you’ll love how much better your airplane performs!
I had done this several times.
It works !
Just remember to put the servos in the same way, NOT mirrored, or you’ll have a problem… 🙂
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