RCU Review: Graupner BO 209 Monsun

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    Contributed by: Grant MacDonald | Published: March 2003 | Views: 27052 | email icon Email this Article | PDFpdf icon


    By Grant MacDonald
    RCU Member: Cadet



    Wing Area:

    Power System:


    225 sq. in.
    23 oz.
    Speed 400 motor geared 2.33:1
    APC 9x6 and CAM 9x6 (recommended)
    Hobby Lobby

    Radio Used:
    Speed Control:

    8 Cell 600 AE
    Hitec 555
    Hitec HS-55
    JR 421EX
    Jeti 110

    I N T R O D U C T I O N

    The Monsun is an all wood ARF produced by Graupner in Germany and imported by Hobby Lobby for the North American market. The first thing I noticed when I received the model was how well it was packaged. There was an outer box, then a layer of packing foam and finally the model itself. Needless to say it arrived in perfect condition. The box contained all of the major components - a nice complete set of decals and some very light plastic moldings.


    First Impressions:

    Quality, that old word pretty much sums up the level of workmanship on both the aircraft and the instructions. All of the covering was tight and reasonably well trimmed, the wings were very nice and light, and all of the pushrod housings were pre-installed. The manufacturers of this model obviously have a much higher skill level with a covering iron than I do, and it shows. At this point I was anticipating a nice fast build. The only thing that caught my attention was the listed weight of the model relative to its power and wing area. It seemed that the lighter I could build it the better it would perform. So with that in mind I set out to minimize my use of adhesives and anything else that would add extra weight.

    Getting Started:

    The First step is to read the English instructions and separate them out of the booklet. This way you can look at the pictures in the German section and read along instead of flipping back and forth. I found that this made assembly much faster.

    A Note on Adhesives:

    In the instructions they talk about "UHU" and "UHU plus Acrylit". I had never heard of these products in North America so I assumed they were available in Europe where the kit is produced. My general rule of thumb to you is this: For joints between two or more pieces of wood use CA. For all other joints use 5 minute epoxy. I will also note which I used throughout this review.

    C O N S T R U C T I O N


    Wing Assembly:

    This is the first step covered in the manual and I found it to be quite well explained. One thing to note is that I used epoxy for both the control horns and the main gear attachment. The friction fit between the landing gear and its slot was superb, a testament to the quality of the build. I also chose to screw the aileron servo into the bottom of the wing as opposed to the way it was laid out in the booklet, which looked like it would leave the pointy end of the screws pointed outward. Probably the most challenging part of the entire process was adjusting the pushrods using the method described in the manual.

    Servo Installation and Tail Panels:

    This step was also very easy provided you follow the instructions. Be careful you do not build yourself into a corner here. First you hinge the elevator and rudder much like the ailerons. Then install the servos. I found the holes for them to be a little too short, so I used a hobby knife to shave down one edge until they fit snuggly; they are then placed in and screwed down. I found it very difficult to get a screw driver into the back part of the compartment to tighten the rear screws because of where the wing saddle is located. Next, trim the control rod outers that stick into the radio compartment. Do this now so you don't forget. Once the control rods are in, this becomes much more difficult to do neatly. The rest of this step goes very smoothly provided you have the control rods hooked into the control horns and installed before making the final glue joints between the tail pieces and fuselage. I checked alignment first by eye and then with a piece of marked string before cementing tailpieces in with CA.


    Power System:

    Here is truly a good example of why aircraft that are designed for certain power systems and vice versa go together so easily. This is by far the easiest way I have ever seen to mount a drive system of this size. This step is so well covered and simple that I won't go into detail except to say that it is very close to how internal combustion motors are often on models. The most challenging part was soldering the motor leads on with the right polarity, which can be avoided by buying a ready-to-install drive system or getting someone with soldering experience to do for you. The only recommendation I have is to increase the right thrust as much as possible: see flight-testing. The nose-gear also gets installed exactly like the main gear at this point. The cowling is then attached. I would recommend using tape rather than the supplied screws. Mine stripped out in the soft balsa wood of the fuselage.


    Canopy Installation:

    Cutting out the two canopy pieces was probably the most time consuming and difficult step in the whole building process. I highly recommend you borrow or purchase a pair of canopy scissors, they will make this step significantly easier and will come in very handy for future projects. I would also recommend using some form of canopy glue that dries perfectly clear in order to keep the plastic looking good. Once the pieces are assembled they are then fixed in place with some double-sided tape. I also chose to route my antenna out through a hole in the canopy and then to the top of the vertical stab.


    Radio Installation:

    This is where your individual installation has to vary depending on what size gear you choose. I used a system very similar to the manual to mount everything except the speed controller and receiver. The speed controller on my installation is attached with the provided sticky backed Velcro and stuck to where the instructions place the receiver. The receiver is then given the same treatment and stuck to the roof of the compartment just ahead of the servos. I then mounted the battery as shown, but I supplemented the adhesive on the Velcro with some CA around the edges; this has held up well to in-flight stress and battery removal. This is the point at which I set up my radio and get the control throws dialed in, I went with the manuals recommended set up.

    Finishing Up:

    We?re now we're getting close! There were only two steps to complete (or three if you are going to use the decals). The first is to check the center of gravity (CG) and adjust it by repositioning the battery. Mine was "spot-on" the first try! The next step is to charge the battery and, go flying! If you do decide to use the decals, there are quite a few good methods to getting them on nicely. I recommend that you a.) spray the surface with window cleaner, b.) lay the decal down, and c.) squeegee all the cleaner away, rubbing with a damp paper towel to remove all bubbles from under the decal, or, they will become permanent!

    F L I G H T R E P O R T


    First flight:

    I chose the first calm day to try to get the Monsun in the air. I also chose to use my trusty, unbreakable APC 9x6 e-prop rather than the fragile-looking Graupner prop that came with the kit. I did a quick control check, placed the aircraft down on a nice long piece of cement, gave it full throttle, and immediately noticed a strong pull to the left while taxiing. I corrected with right rudder, and the model was off, climbing slowly. One thing I noticed was that it wanted to be flown fast, "on the wing", indicating that it didn't have a lot of power in reserve. I also noticed that the ailerons and rudder were quite effective, but that the elevator was rather dampened. Turns were nice, and the Monsun really looked scale just flying circuits. My timer beeped 4 minutes and I brought it in scale, just flying circuits, and I brought it in for a quick go-around, since I had flown it too fast the first time. I went home and changed to the APC 9x6 from the Graupner 9x6, adding some right thrust to correct the taxi problem.


    Second flight:

    This was the flight where I decided to see what the ship could really do. On takeoff, I noticed an immediate increase in thrust with the new prop, along with less tendency to pull left. Once in the air, it climbed better and seemed to be a bit faster too. I could attribute this to a.) the gearbox being a bit more broken in, b.) to the battery being charged closer to the beginning of the flight and, and, of course, c.) to the new prop! The first thing that I wanted to test was its stall. For a plane that I thought was a little heavy, she had a very nice, easy stall. Next I tried a loop --- no go! It just pitched up then back down. I tried with more airspeed, --- less elevator, --- EVERYTHING!, but still, .......NO LOOP! I shrugged it off, "No problem --- time for a roll! --- Oops! ---Grrrr!" The end result was what looked like a corkscrew slowing bending towards the earth; "Not really great!" The timer went off and I made another easy landing on the grass. By now I was thinking that if I moved the CG back a little bit, everything would be fine.


    Third flight:

    By this time, I had moved the CG as far back as moving the battery would allow and gave it full up-elevator. Takeoff and climbout were both very good. Next I tried a loop --- (same deal!); went for some rolls --- (a little better!); tried a spin --- (nice!); got some more altitude; tried another ---(very nice!) --- (finally, a maneuver she does well!) I did a few more, then decided to just cruise around, shooting approaches. This made me realize that the Monsun was at its best just flying around looking nice and scale. Subsequent flights have revealed that this is true and she has become my favorite plane to just fly around the park to appreciate for how it looks in the air.

    S U M M A R Y






    Basic Aerobatics


    Low Speed Flight:

    Instruction Manual:

    High Speed Flight:

    Ease of Assembly:

    Stall Characteristics:

    Kit Completeness:



    • Motor mounting.

    • Good looks.

    • Strength.

    • Excellent build quality.

    • Nice Decals.

    • Overweight.

    • Won't take off from grass.

    • Instructions were written for experienced modelers.


    The Monsun is a plane that can be flown by almost anyone with some aileron flying experience and will delight modelers with the opportunity to have a plane that looks quite scale right out of the box. If you're looking for something to fly aerobatics with, this is NOT the plane for you. The good news is that there are plenty of excellent models to fit your needs available from Hobby Lobby. I'm sure that the Monsun will respond very well to adding more power in the form of a brushless or cobalt motor, long as the overall weight isn't increased too much. I enjoyed building and flying this plane, and it will remain in my hanger for as many years as it can survive my piloting technique.

    February 2003

    Manufacturer & Distributor Information

    Hobby Lobby
    5614 Franklin Pike Circle
    Brentwood, TN 37027 USA
    Phone: 615-373-1444 Fax: 615-377-6948


    Hitec RCD USA, Inc.
    12115 Paine St.
    Poway CA, 92064
    Phone: 858-748-6948 Fax: 858-748-1767
    Website: www.hitecrcd.com

    Landing Products (APC Propellers)
    1222 Harter

    Woodland, CA 95776
    Phone: 530-661-0399 Fax: 530-666-6661

    Comments on RCU Review: Graupner BO 209 Monsun

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    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

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