Graupner BO 209 Monsun ARF - RC Groups
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Graupner BO 209 Monsun ARF

The Graupner Monsun is an almost ready to fly kit that is a semi-scale low wing plane equipped with ailerons, rudder, and elevator that looks very sweet and promises to be a fun plane to fly.

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  • Wingspan: approximately 920 mm / 36 3/8 inches
  • Wing area: 14.5 dm2 / 227.5 sq. in.
  • Length: approximately 750 mm / 30 inches
  • Weight: 650 grams / 21.75 ounces
  • Wing Loading: 10.4 oz/sq. ft.
  • Radio: Hitec 555 receiver
  • Servos: 3 Hitec Sub-micro 55 servos
  • Controls: aileron, rudder, elevator and throttle
  • Motor: Graupner speed 400 6 volt with gearbox 2.33:1
  • Speed Controller: Jeti Jes 110
  • Battery: 9.6 volt 500 AR side by side
  • Propeller: Graupner Cam slim prop 9 x 6
  • Spinner: Graupner 4 mm (Mine was custom drilled to fit.)
  • Manufacturer: Graupner
  • Available From: Hobby Lobby International Inc.

What Is A Monsun?

The Graupner Monsun is an almost ready to fly kit that is a semi-scale low wing plane equipped with ailerons, rudder, and elevator that looks very sweet in its pictures and promises to be a fun plane to fly. It is copied from the real plane built in Germany starting in the early seventies. The real BO 209 is a sport plane that can hold two people and a small amount of luggage. Although officially it is a semi-scale kit, you can see that it has an excellent likeness of the very pretty plane it is modeled after. The recommended Graupner speed 400, 6-volt geared motor powers my model with a 2.33:1 gear drive and a 9x6 propeller.
The kit that arrived was indeed "sweet". The main components all arrived constructed and the quality looked very good. After reading through the English version of the instructions and looking at the assembly photos, most of my questions were answered. It appeared that anyone who had put together several planes previously should have little trouble putting together the Monsun. The challenge for me with this kit was to make it as aesthetically pleasing looking as the one pictured on the box. That would involve painting the white wheel skirts and cowl red in the places shown on the picture and cutting out the white canopy "supports" with nice smooth edges. I decided I would start with those aspects of the project while I was fresh and hopfully do the job right. However, I made a big mistake in painting the cowling when I did, as I will discuss below.

Painting And Trimming

I carefully cut out the canopy, the exterior cuts on the white canopy support, the wheel skirts, and the cowling. I did these cuts with short sharp scissors and was off to a good start. I decided to work on the wheel skirts first. I used a 3/32 drill bit and hand drilled the holes for the landing gear wire at the inside base of the slots molded into the wheel skirts. (I just spun the drill bit between my fingers.) I used an Exacto knife to trim away the plastic remains from the drilled hole. Using masking tape, I wrapped the wheel skirts to leave the bottom area exposed for spray-painting the bottom of the skirts red. I used Krylon, "Banner Red Gloss" spray paint #2108, and sprayed the wheel skirts. There was some slight bleeding of the paint in a couple of spots under the tape. Some I left as is, but I cleaned up the worst two areas with a razor blade. I next applied the stripe decals to the wheel skirts, and they were ready to install. I strongly recommend anyone who is going to paint their wheel skirts to do it before they are installed on the plane, as it is much easier. Second, get the proper masking material from a craft store and avoid the bleeding of paint that I had under the plain masking tape.
Next, I practice mounted the cowling squarely to the fuselage for the white stripe on the cowling. I needed it to line up with the white/red trim on the fuselage. I started the masking tape process while the cowling was squarely on the fuselage. With the areas to remain white masked, I sprayed the canopy with the same paint I used on the wheel skirts. Once again, I had some minor paint bleeding to clean up off the "white stripe" area. This was again done very carefully with a razor blade. As you can see in the pictures, my work was not perfect, but for me, I was at least satisfied that I could show the plane in public with the painting I had done! I didn't learn about my big cowling alignment error until I went to mount the cowling permanently to the fuselage with the geared motor installed. The cowling doesn't mount squarely to the fuselage, but rather mounts at an angle with an upward forward thrust. Thus, my original white stripe was not level with the stripe decals on the plane as you can see in some of the pictures. I recommend painting the wheel skirts in advance of assembly, but paint the cowling at the end.
Finally, I had to cut out the parts that needed to be removed from the inside of the white canopy support. Since I cannot cut a straight line without a straight edge, I took the "coward's" way out. I didn't cut at the marked lines, but rather inside them using a new blade on my Exacto knife and a sharp pair of scissors. Next, I used my Dremel power tool with a sanding wheel to get to the line, and then used a small sanding block to finish the process. The majority of you will probably have no trouble just scoring the lines and removing the pieces that need removing, but I felt safer doing it my way. With the "pretty" pieces ready to go, I started to assemble the kit.

Assembling The Monsun

The assembly starts with the ailerons being attached with tape that is supplied in the kit. I cut a piece of tape to the correct length, and then carefully attached it to the top of the wing so that half of the width was on the wing and half was over the area for the aileron. I put the aileron into position from below the wing, with the aileron in the down position, and maneuvered it so that it was up against the trailing edge of the wing and under the tape. I then pushed the tape down onto the aileron and smoothed it out over the entire area the tape covered. Next, I taped the underside of the aileron. To do this I cut a piece of tape to the correct length, folded the aileron so that it was resting on the top of the wing, and applied the tape to the aileron's 45 degree edge and the wings trailing edge at the same time. There was a little extra width of the tape, and I folded that over to the bottom rear edge of the wing. The process is repeated on the other side of the wing for the second aileron. I drilled the holes for the control horns using a 7/64-inch drill bit and cut off excess post from the control horns. I removed some covering that would be under the control horns and then epoxied the control horns into place as shown in the pictures per the instructions. (The rudder and elevator were later taped, drilled, and glued in exactly the same manner.)
Next, I mounted the Hitec 55 servo that controls both ailerons. This required cutting the covering in both the top and bottom of the wing to reveal the holes made for the servo. These spaces can be found by looking at the pictures in the instructions and then feeling with your finger. You remove the control arm from the servo and install the servo upside down, going in from the top on the wing with just a portion of the top of the servo popping out through the bottom of the wing. I used a 1/16th drill bit and drilled holes through the bottom wing, using the holes on the servo mounting horns as guides. With the holes drilled, I pulled the servo partially out of the wing and placed the mounting screws that came with the servo into the holes on the mounting horns. I then repositioned it back to where it was to be installed, partially screwed in each screw, and then tightened both of them to install the servo.
The next process includes taking two pieces of wire from the long piece of music wire included with the kit to form two linkages to connect the servo arm with the two ailerons. Although they show pictures of these wires, I think it would have been better to have a picture to scale of the wire on the plans with the proper bends on the plans for people to compare with directly. Bending these wires can be a little tricky if you haven't done it before, but look at the pictures and copy as best you can. The really critical bend is the next to last one to line up with the proper aileron servo armhole so that the ailerons line up where they should with the wing. If you are slightly off with this bend, it can be corrected by playing with the other bends you made in the control wire until the ailerons are properly positioned. Once you make the critical alignment bend and are happy with it, you make a final 90-degree (finishing the Z-bend) that will hold the wire in place in the servo arm. You can make these bends using needle nose pliers to hold the wire where you want the bend and merely bend the wire by pushing it with your hand. (I didn't cut the wire until a complete control linkage was formed.) This works well when the wire is still a long piece and you have leverage. An alternative is to use a Z-bender tool to make both of these final bends in one motion. (The Z-Bender is a specialty tool available in many hobby shops and with one squeeze it puts a Z-bend in the wire that will fit into a servo arm or control horn and stay in place.)
Later, the wing will be mounted to the fuselage per the instructions using a dowel in the front of the wing and a plastic bolt in the back that goes into a metal base you install in the fuselage. The holes for these are predrilled, and you only have to find them to mount the wing per the instructions. Although the written instructions are a little skimpy, the pictures of each step made the rest of the construction a simple operation. I used five-minute epoxy for most of my gluing needs. I later went back and reattached the front wheel skirt using Household Goo. I found I barely had enough music wire to make the four control rods so don't be wasteful in cutting those to length. I also had trouble with the elevator control rod, as it moved in a snake like fashion rather than pushing the elevator up when I tested the radio controls. This was corrected by using epoxy to secure the tube holding the wire at the point where it went into and out of the fuselage, and I added a small wooden block to the horizontal stabilizer in the back of the fuselage and glued the elevator control rod tubing to the wooden block. With the tubing thus stiffened, the control rod worked the elevator both up and down. As I was doing this gluing, I also better secured the tube for the rudder control as well. I had no further problems with either of these controls.
The motor used is the recommended Graupner speed 400 6-volt attached to a 2.33:1 gearbox and mounts with four self-tapping screws, but is first practice mounted with just one screw to confirm the proper location. The motor mount had the proper angles built in to compensate for motor torque, but there was no mention of this fact in the instructions. Then, as mentioned above, I went to install the cowling over the motor and front of the fuselage. That is when I learned that the cowling mounts at an angle with it going up in the front. It was then I learned my white strip on the cowling was misdirected. I corrected this mistake by repainting the cowling all red and adding a white stripe with tape in the proper location and reinstalled the decals. I decided this would be a more honest review if I also shared with you how I initially messed up. Therefore, I took pictures of my mistake as well. If it helps one person avoid the mistake, I'll live with my shame!
Having mounted the motor and cowl with the self-taping screws, I recommend that you remove the screws and put a small drop of thin CA glue through the now empty screw holes to harden the wood. This greatly strengthens the mount for general use. When the CA is dry, reinstall the motor and the cowling using these now hardened screw holes. The canopy and white canopy "support" are mounted together and to the fuselage using double-sided tape. I used 3M permanent tape for this and cut the pieces of tape to fit.
The plane assembles very quickly and can be done in two to three evenings by the experienced builder with a couple planes under his/her belt. Cutting and bending the control rods into the proper positions may challenge the novice builder, but this is a skill that needs to be learned sometime. Pick up an extra piece of .8mm music wire in case you need it. Be sure to secure the control rod tubes with glue where they enter and exit the fuselage for proper control of the rudder and elevator. I programmed my transmitter for the plane, and I thought I was ready to go flying. During a final check of everything, the motor wouldn't turn on although it had tested fine before installing on the plane. I tracked down the problem to a loose wire inside the plug and play connectors connecting the motor to the speed controller. I corrected this by cutting off the plug and play connectors and soldering the wires together and everything then worked fine. The kit and parts arrived on Tuesday. The painting and canopy cutting were done on Wednesday night. The assembly and radio/motor mounting were done on Thursday and Friday nights. The canopy was repainted and the plug and play problem was diagnosed and corrected on Saturday.

Test Flights

Although I planned to perform the first test flight after my clubs monthly glider thermal duration contest, I decided to postpone the tests as it got to windy to risk a new plane. I did get to show the plane off to club members and all seemed to be impressed with its good looks. I took some pictures of the plane on the ground and then latter decided to trim the bottom edge of the canopy some more. You may detect a difference in the canopy fit in the different pictures.

On the first flight, I got in about a 45-second test flight, but landed to adjust the ailerons. I had no one to take pictures and it was a small park, so I thought I should save the plane for a bigger field. I called my good friend Jeff Hunter to go flying with me, and we went out to one of our club's flying sites. Jeff is a tremendous pilot, so I had him fly while I took pictures. The plane flew very well. After take-off, Jeff did a couple of close passes, climbed, and did a couple axial roles. He flew for about four minutes and brought it in for a very nice landing. The in-flight photos were taken during that flight. Unfortunately, the epoxy gave way on one of the wheel skirts during the landing, and although the wheel skirt stayed on, it was a bit scuffed up. The plane had no bad habits, and Jeff had a good time flying it while I took the pictures. I decided to repair the wheel skirt by securing it with Household Goo. I used Goo on both of the wheel skirts under the wing, and now all three are held in place with the flexible Goo rather then epoxy.
The next day, I got in two full flights of my own in the calm early morning hours, and I love the plane. I only did a couple loops and rolls each flight, as I was simply enjoying the scale like appearance of the plane flying through the sky. It required only a little down trim to fly level while inverted. The landings were with power off and coasting in at the time of touchdown, and I was surprised on how smoothly it landed on the tricycle landing gear. Once on the ground, it rolled smoothly to a stop, but seemed to pull a little to the left and right rudder didn't help much at that point. When on pavement or hard ground, it tends to point itself into the wind if given a chance, so I will bear that in mind for the future if I have to do a more serious crosswind landing. I found power to be very adequate with the recommended motor, prop, and battery combination. The first three flights were all with the 8-cell 500AR battery pack that was recommended. The fourth flight was with a 10-cell 500AR pack and the plane was noticeably quicker with that pack. Most of my flying will be with the 8-cell pack, as I was very happy with that performance. If you like to fly fast get the Graupner Speed 400 7.2 volt with the same gear drive and use ten cells all the time or upgrade to a geared brushless like the AstroFlight 020.


The standard construction requires you to remove the wing to access the battery. Michael in Toronto, an EZone member, has modified his Monsun to have an access hatch in the front bottom of the plane to access the battery compartment. He has shared a picture of his modification; he has also switched to a brushless AstroFlight 020 motor.


While this plane can be flown in a large baseball field, it is really a lot better if you have at least twice that much space or more. I would recommend against normal grass landings with the wheel skirts attached, as that will tear them up. The Goo worked fine on the wheel skirts, as I took off and landed from a dirt field on Wednesday without any problems. I would recommend using Goo or other flexible adhesive with the wheel skirts from the beginning. Having built it and flown it, I still consider it a plane for an intermediate or experienced pilot. It showed no bad tendencies, but it is my conservative opinion that non-foam aileron controlled planes are not for beginner pilots. This beautiful built up wooden plane handles very nicely and flies reasonably on the recommended power set-up. If you like its looks, you will love the Monsun in flight.
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