Flink

OVERVIEW:

The Flink is an aerobatic scratch built foam board airplane. The Flink is roughly influenced by the Wattage Mad Max kit. The Flink is quite capable at aerobatics but can also be pretty tame with the control rates dialed down. 

The Flink uses classic Flitetest build techniques but I would consider it an intermediate build at minimum. The short moment arm of the nose section makes achieving a satisfactory center of gravity (CG) a bit of a challenge. Build the tail light and place all of the electronics as far forward as possible. The nose could also be extended slightly to place the motor farther forward.

The wing design is based on the FT3D wing. Other than the planform, the biggest change was the spar. Instead of sandwitching the spar (a paint stir stick) between the two foam spars, I replaced the center section of the lower foam spar with the paint stir stick. Although not very scientific, my testing involved performing full speed dives and then pulling up with full elevator. So far so good!

Oh, and the name. Flink means "nimble" in German... or so I am told (by Google translate).

SPECS
Wingspan: 36"
Length: 26.5"
Weight (as build, ready to fly): 19oz

SUGGESTED PARTS:
Motor: 2212 1000kv
ESC: 30A
Servos: 9 gram (or possible 5 gram)
Prop: 9x5
Battery: 1600mah 3S 

For the motor and ESC, I used this set from Banggood:
http://www.banggood.com/XXD-2212-MotorZTW-AL30A-Brushless-Motor1045-Propeller-p-85721.html

For the servos, I just used some extras that were laying around. That meant 9 gram servos for the rudder and elevator and a pair of old 6.2 gram servos for the ailerons. It may be possible to use 5 gram servos all around but I have not tested with that size.

The plane uses two sheets of Dollar Tree foam board. Also, you will need a piece of wood for the wing spar. I used paint stir stick about 10 inches in length.

PLANS:
Flink Plan Part 1
Flink Plan Part 2

Tiled plans
Flink Plan Part 1 (Tiled)
Flink Plan Part 2 (Tiled) 

BUILD VIDEO:

FLIGHT VIDEO:

This is the video of the maiden flight. The wind was blowing at approximately 10 mph but the Flink handles it just fine. Not a single click of trim needed.

BUILD PICTURES:

Fuselage cut out:

The angle of the upper sides of the fuselage are set by the triangle guages (included on the plans). The point of the triangle should be lined up with the fold.

Picture of the fuselage profile:

Extra supports added to the fuselage to strengthen the wing and landing gear skewer holes:

Rudder and elevator linkage configuration. The servos could also be mounted from the inside to provide a smaller profile.

The Wattage Mad Max. This is the inspiration for the Flink.

FINAL THOUGHTS

The design presented here is version two of the Flink. In the first version, I tried to design a wing with a curved upper and lower camber rather than the folded design you see here. After attempting several flight tests, it was very apparent I needed a new wing (in other words, deep stalls resulting in slamming straight into the ground). While this proved the durability of the airplane, I decided that I should go with a proven wing design and therefore based it on the FT3D. The only other change to the plane was to make the rudder larger so the Flink can maintain knife edge. 

The Flink has proven to be a fun flying airplane. Although I am not a great aerobatic pilot by any means, it has handled all the manuevers that I have thrown at it. The motor and prop combination that I am using allow it to climb out very well. It is quick in flight, although I wouldn't say it is fast. It slows down nicely for landing, too. Since the Flink has no diahedral, I would not recommend it for the beginner. Someone with a little more experience should have no problems flying it at all.

Leave a comment if you decide to try building the Flink or have any questions. Thanks!