Improve the Bloody Wonder

As many have discovered the Bloody Wonder / FunBat is a marvelous plane. The thin wing combined with a huge wing area makes it possible to fly the plane both slowly and very, very fast. The large control surfaces make it possible to perform crazy quick turns with full control. The boxy body combined with the double vertical fins make it stable in turns. It is as agile as a flying wing, but has better side stability and is less pitchy.

The Bloody Wonder is also one of the simplest scratch builds available. This is due to the genius combination of the wing, tail and upper body into a single piece. You basically cut out the top of the plane, build a boxy fuselage that is attached below the wing and slap on two fins. That is it. It really can not get any simpler.

The original plane was constructed by Bloody Mick and called the FunBat. He used a motor for it that was sold under the name Blue Wonder. The motor is available from many sources and is quite capable for a 24 gram simple outrunner. The plane was made even more popular in a slightly modified version by FliteTest. They called their version the Bloody Wonder. The original FunBat uses a KF4 airfoil while the Bloody Wonder has a more conventional wing form. The Bloody Wonder is built to use the FliteTest standard power pod. I prefer the original FunBat version of the plane. It is easier to build and I have found the power pod construction to fragile for a stunt type plane.

By now I have built five versions of the Bloody Wonder/FunBat. For each version I have made modifications that improve the handling of the plane and makes it tougher and more crash resistant. At the same time I have made each version faster. This is plane number four in my series.

I know that a lot of people are building these planes and think that rather than going through the same refinement process, they might use my experiences directly to build a better version to start with.

Even if the plane is great there are a number of things that can be improved:

• The nose is simply to short. The snub nose makes it very hard to achieve a correct center of gravity and results in an overly pitchy plane.

• Bloody Mick drew his plans with an uncovered opening for the battery right behind the motor on the bottom of the fuselage. This was a terrible idea. Each time you land the opening is exposed to both direct force and dirt. Over time the landings will weaken the unprotected fuselage sides until they have no rigidity left. During that time your electronics will pick up dirt and dust.

• The original motor is under powered. It can not deliver enough pull to use the full potential of the airframe.

• The plane is a stunt plane. It is as made for flying fast. Really, really fast. This will inevetably result in crashes. The problem is that both the original and FliteTest versions are to fragile to stand much abuse. It is easy enough to rebuild it, but I prefer spending my time flying rather than repairing my planes

• I prefer the KF4 wing construction to FliteTest's wing. It is easier to build and I like the flying characteristics. But I do not like to weaken the foam wing by cutting in it to insert a spar.

Improve the power plant

My first improved power plant was an AXN FloaterJet motor. I bought this as a spare for a plane, but it has never been used since the original motor seems indestructible. This motor is cheap (9$), sturdy  and very powerful. It has a a high RPM of 2150 kv. Together with a small 6x4 prop, a 20 Amp ESC and a 1300 3s mAh battery you have a killer combination. The plane becomes much more fun to fly than with the original Blue Wonder type motor.

My second attempt to beef things up was to use the power setup from HobbyKing's funfighters. I had one left over from a RareBear that i crashed. The motor is  also available as a spare at a very good price.
The funfighters are a blast to fly. They are however extremely hard to handle at low speeds due to the minimal wing surfaces. Crashes at starts and landings are common. The power train is nearly as fast in a Bloody Wonder as in a funfighter. But it is a lot easier to handle the Bloody Wonder since the wing area is so much bigger. The motor is a 1950 kv unit, but it is intended for 4s batteries, so the RPM is higher than with the AXN motor. Together with the funfighter standard setup of a 40 Amp ESC a 5x5 prop and a 850 mAh battery you have a completely balistic setup.

I am happy with the resulting weight of both setups in comparison to their performance. The 4s variant is almost frightening fast with rocket like vertical capabilities. The 3s setup is less of a handful to control but quite fun anyways.

Modify the nose section

The nose section of the FunBat is less than ideal. The short nose makes for a very pitchy plane and the downward facing opening is fragile. Repeated damage to the nose of my first two FunBats were the reason for their demise. To fix the problem I modify my planes to have longer noses with the battery openings upwards rather than downwards. Another modification is that I give the fuselage undercarriage an angle from the wing tip forward. This means that my planes are able to handle rough landings much better than the original. They just slide on the ground, rather than crash, even at an acute landing angle.

In order to improve the strength of the nose I reinforce it with glass fiber reinforced tape (aka extreme packing tape). Duct tape would also work, but is heavier. The tape is wrapped from one side of the fuselage at just about the tip of the wing, around the front of the plane and to the other side of the fuselage. This prevents the motor mount plate from ripping off in a crash.

To further strengthen the construction I add a hatch made out of clear reinforced tape (rather like duct tape). The tape hatch is taped to one side of the fuselage and is fastened to the other side with a strip of Velcro. I make the openings just wide enough for my batteries of choice by adding foam inserts.

When the battery is in place and the hatch is closed, the nose is a solid piece of foam, tape and battery. The Velcro holds the hatch in place hard enough to provide a lot of rigidity in the nose.

Secure the wing to the body

Besides the weak nose, the thing that killed my first FunBats was that the glue joint between the wing and the fuselage got weaker by each hard landing and eventually broke apart. This resulted in catastrophic failures where the fuselage got crushed. The remedy is quite simple. I put one or two strips of reinforced packing tape over the top of the wing, down the side of the fuselage, around the bottom , up the other side of the fuselage and over the top of the wing.

The tape forms an X on top of the wing. The two parts of the plane will never separate after this.

Modify the servo placement

The original plans for both the FunBat and the Bloody Wonder suggest that two servos are installed on the top of the wing right on the center line of the plane. The front servo is connected to both ailerons while the rear one is connected to the elevator. This setup is very simple, but I do not really like it since the long control rods on the top of the plane are easily damaged. Another issue is that a single aileron servo might not be enough to cope with the speed from the more powerful motors. I prefer to embed a servo at each side of the wing and use a short control rod connected to each aileron. I have gotten away with using small 5 gram servos.

I place the elevator servo inside the fuselage so that the control rod is completely protected. You should use a 9 gram servo as elevator servo. I tried using 5 gram servos at first but the servo struggled to pull the plane out of steep dives at high speeds.

Gluing this servo to the inside of the body also provides a safer bond than gluing the servo in a hole cut through the top of the foam board.

In order to provide access to the servo I make a small service hatch in the vicinity. I also use this service hatch to install the receiver. I put clear packing tape over the hatch to maintain as much stability as possible in the fuselage.

Cover the plane with packing tape

Building planes out of foam paper clad boards is quick and easy. The downside is that the board surface is fragile and susceptible to water damage and scratches. The paper is also highly likely to peel of from the foam at the edges of the board. To fix these problems I cover the planes with packing tape. Besides adding a protective layer and making the planes tougher, the tape adds a lot of rigidity. I use colored packing tape for the aesthetics and to make it possible to differ between the top and the bottom of the planes.

On this particular plane I mixed clear and red packing tape to achieve a white and red pattern.

Another idea is to use colored pens or spray paint to color the planes and then cover them with clear packing tape. Covering your foam board planes with packing tape will cost you some time during construction, but the planes will last a lot longer and fly much better.

Wing reinforcement

The FT Bloody Wonder uses a foam board spar while the original FunBat has a wooden spar. I distrust the foam board spar and do not want to cut the board to insert a wood spar. I have experimented with a KF4 wing without any reinforcement at all. The KF4 wing has a lot of stability due to the fact that it is constructed by gluing two foam boards together. The wing worked well for a couple of flights, but the foam board lost its rigidity over time and soon the plane had to be scrapped to avoid a wing failure. I have also tried placing the spar between the boards at the very edge of the upper part, but I think that this adds to much height to the profile of the KF4 wing.

My own method is to use a type of L-shape spar made out of thin wood. I have access to 2mm thick wood intended for making window blinds. The wood is rather stiff. I think it is elm. Something like pine or birch would also do but balsa would clearly be to flexible. I cut two strips 5 mm wide and as long as the wing width. I glue one in between the foam boards and glue the other to the trailing edge of the upper wing segment. Together they form an L shape that provides a lot of strength but is quite light. Adding a second standing spar would add even more rigidity, but that has not been necessary for me. I use expanding PUR glue when I glue the wing halves together. When the glue expands the small gap behind the spar is filled and the whole wing becomes solid.

Flat carbon fiber strips would naturally be even lighter and stiffer, but the cost is higher.

Final Words

The result of all these modifications is a considerably quicker plane that will survive almost insane roll rates and pull-ups at very high speeds. The plane will also be more durable and can endure crashes better than the original. If you like adrenalin rushes you should go with the 4s setup. It will not disappoint.