Flitzebogen 2 – Build Report – Wing

Last Update: 23.06.2019

[⇐ Concepts] | [⇑ Overview] | [Tailplane ⇒]

Servo Pockets

The location of the servo pockets is indicated by respective recesses in the lower wing surface. The cut is marked with plastic tape leaving a rim of 3 mm for the cover.

Cut, scrape and pick out the foam using X-acto knives with different blades, the Dremel and tweezers. A vacuum cleaner will come in handy as well. Be sure not to hurt the upper wing skin.

With all surplus Rohacell foam removed, some very helpful features come to light. There is a servo wire channel going from each pocket to the center of the wing’s leading edge (white plastic rod on picture below). And the slot for the steering linkage to the ailerons is precut as well (steel wire on picture below). This saves the time and trouble of measuring and double-checking locations, symmetry and perpendicularity for the pushrod exits.

Aileron Control Horns

I’m going to use the 8 mm horns which came with the kit. 8 mm is the distance measured between the aileron’s rotation axis and the pushrod’s pivot in the horn. The size of the slot to be cut in the aileron is determined by the dimensions of the horn. In this case: 20 x 1.5 mm.

There is a lateral offset of about 2 mm between the steering linkage channel in the wing and the control horn seat in the aileron. This will allow for the push rod to exit the wing and, bent by 90°, hook into the horn. Again, remove all the foam from the slot but don’t hurt the skin.

Aileron Servos

It’s about time now to decide between the servo installation variants. It’s one out of KST’s X08 family, no question, but will it be the lugless glued-in X08N or the X08H with RC-Solution’s wooden frame? With Flying Tom’s bulding standards in mind, I choose to go for X08H. This will add 2 grams to the flight weight, but I believe it’s worth the investment. Installation, adjustments and subsequent maintenance will be much easier.

However, there is a downside: Compared to the variant with the servos wedged directly into the wing, this setup is might end up with a weak spot in the area of the servo pockets. I’ll try to make up for that with some generous dabs of epoxy around the frame, sealing the carbon skin and the foam in the servo pocket. This will include the servo frame in the bearing structure of the wing, especially once the servo is mounted.

The servo pockets need to be enlarged a little bit to make room for the frame.

This is going to be tight. With a lever of 4.5 mm and the rest of the servo arm cut and sanded down to minimum, total height of the servo unit is 9.8 mm. Pocket depth is 10 mm. Forfeiting even a fraction of a millimetre in height, we simply cannot afford.

Wing Wiring Harness

Wiring the wing is not too complex a topic. Basically, it boils down to two questions:

  1. How do I get the servo leads through the narrow ex factory cable ducts?
  2. How do I connect the wing wiring to the rest of the plane, if the wing is to remain removable for transport?

To cut a long story short, this I my solution. The servo leads, as they came from box, original length, original connectors, go all the way through wing and fuselage and will connect directly to the receiver.

But how do the camels pass through the eye of the needle? I don’t not want to enlarge to cable duct to the size of the servo connector. This would be another weak spot. Instead I remove the plug housing temporarily. This is quite a fiddly task. The delicate plastic tongues of the housing need to be lifted a little bit, in this case with the blade of an X-Acto knife, in order to let the metal plug slip out. The three plugs are then shrunk into one end of a 100 mm piece of 3 mm diameter shrinking tube. The shrink tube will easily pass through the cable duct from the servo pocket side and pull the servo wires and plugs along.

Steering Linkage

The servo needs to be upside down to allow for threading the pushrod in the servo arm.

Then the servo is flipped over and carefully pressed into the servo frame.

Although the servos fit tightly in the frames and will hardly fall out with the covers pocket cover in place, do not forget to screw them on.

Lauch Peg


The wing is completed. With everything in place, servos and frames, wiring, steering linkage, pocket covers and launch peg, the tally stops at 121 grams.

[⇐ Concepts] | [⇑ Overview] | [Tailplane ⇒]

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