... for Aerobatics and VTPR* !
(* Voltige Très Près du Relief)
Since the EPP exists and is very popular and widely used by large manufacturers, there is an area where almost nobody went, excepted some very seldom small specialised manufacturers: Aerobatic slope flying, and more particularly the VTPR (Voltige très près du relief), invented in France, which consists in flying aerobatics very close to the ground, without inertia, and with an extreme agility. These flying style becomes less and less confidential all over the world, and even our american friends really start to like VTPR after discovering it on various forum and thanks to video sequences shared by french pilots. Therefore this is an excellent news that Telink (www.telink.cz), one of the precursor of the EPP in Europe introduces on the market this Multifun, an small painted EPP glider, which should interrest most of you.
An interesting concept
The Multifun is in fact a 3 in 1 glider since you can build it in its aerobatics version, in its " sport " version by adding two winglets, or in its beginner version by using the 2 axis wings you can buy in option. Wings are removable thanks to a piano wire joiner.
What is missing is the radio equipment and the glue to build the Multifun: I used cyanoacrylate and a " Goop " equivalent called "résiste à tout".
The recommended radio equipment is to use 9mm servos for the wings and for the fuselage. Since I didn't have such servos in stock, I finally found old but still good 13 mm Futaba servos that fit, but this is clearly the maximum thickness that can be used. The receiver is a thin but 6 channels Corona receiver, and the battery is composed of 4 AAA size cells, that I bought in a big supermarket. They have 800 mAh of capacity.
An innovating fuselage
The EPP, this wonderful material, has however the drawback to not allow to obtain easily complex shapes, when hot wired cutted, without shaping and sanding. Telink fixed this drawback in a very interesting manner by splitting the fuselage in pieces: First of all the main part is a about 3 cm large silhouette fuselage, on which come half round section EPP parts which bring the final touch without any shaping nor sanding. Additionally, it allows to have a simili canopy that gives access to the radio equipment, fully integrated in the fuselage.
The stiffness of this fuselage is obtained thanks to 2 carbon rods that are inserted and glued on each side of the fuselage. This is very discreet especially if you disimulate them with the decoration (using the border line between the black and the yellow).
The tailplane, before to be installed and glued in place, receives 2 thin carbon spars (1mm) on the underside and upperside after doing a cutter line on the surface of the tailplane. A small piece of plywood is glued as stiffener at the function of the elevator control surfaces.
Then we can installed the fin+rudder in place while paying attention to the alignment with the tailplane and the fuselage. My tail and rudder servos being 13 mm large, I had to enlarge a little bit the space reserved for them. They are then fixed in place using goop like glue.The receiver takes place behind, and must be easily removable in order to plug the ailerons when mounting the plane before to fly.
To finalise the fuselage there several holes to do:
The first operation is to prepare the spars. They consists in fiberglass tubes, pretty heavy, that receive on one end the piano wire joiner. In order to avoid the tube to explode during a hard landing, the extremity of the tube is reinforced with a string all around the tube, and glued with cyanoacrylate. The tube are then glued in place and the remaining space is filled in with small parts of EPP supplied. I found this step a little bit laborious and I personnaly think that it would have been better to CNC cut the exact round space for the spar tube.
The next operation is to install the servos in the space reserved for it. Once again, because I used 13 mm servos, I had to enlarge the hole, and also dig it without fragilizing it. The servos wire is inserted in the foam, and the connector exits on the root rib. Try to have around 8 to 10 cm in order to reach the receiver.
The control horn is glued in place with cyanoacrylate and accelerator before to connect the piano wire control pushrod. The last operation is to install a small fiber glass pin (3 mm diameter) to block the wing in rotation at the right incidence. The parts provided are not very convenient since they are difficult to ajust and because they desintegrate slowly in small fibers on the surface of the rod. Therefore, I replaced them by the equivalent in carbon wich works perfectly.
Very good agility in flight
First of all, the Multifun is not in its advantage when flying is very small conditions, even if it is able to spirale, it is penalize by its lack of finesse. What prefers the Multifun is a small and sharp slope with a light breeze giving a constant lift. In that conditions, the Multifun will express all its potential and will give you lots of satisfactions.
The plane is agile on all axis: The ailerons are nervous and provide a very good roll precision thanks also to the thin and high fuselage which brings a great stability in trajectory. The elevator is more conventional, but the rudder is an example of what should always be a rudder: amazing efficiency bur certainly not violent. In any position of the plane or during rolls, the rudder is a pure joy to use without any secondary effects. Therefore you can easily imagine that the Multifun cannot fly " normally " but instead invites you immediately to fly aerobatics.
The only small shadow is that because of the light weight and the small wing ratio, the Multifun has a lack of inertia and consequently, vertical manoeuvres are not wide enough. The addition of ballast should however improve this. For the rest, all manoeuvres are possible, and even more. Knife edge flying is very simple thanks to the lateral area of the fuselage. Rolls and steps rolls are a joy, the upside down flight, whithout being exceptional, can stay for a very long time as soon as the lift is sufficient. After few minutes, you will surprise you flying lower and lower, closer and closer, doing lots of crazy things without any fear because of the low inertia and the EPP material. The upside down launch and catching is a simple exercice...
Without being at the "state of the art" in term of aerodynamic design, the Multifun remains certainly very interesting in its concept and in the pleasure it gives you in flight, especially when flying aerobatics and VTPR. The kit is complete and the assembly quick. The painted decoration brings the esthetic touch which is, from my point of view a big plus. If you are looking for a kit of a small aerobatic glider, then you should consider the Multifun because it is definitively designed for that type of flying.
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