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Combat Wings XL EPP Flying Wing
Posted by Ken Nelson on Apr 2, 2003, 22:52


By Ken Nelson


After a 9-year hiatus from RC flying I got back into it in the fall of 2002. What really caught my interest was the new generation of electric airplanes available, particularly the foam flying wings called Zagis that everyone was talking about. I started flying electric Zagis and they were a ton of fun and almost totally indestructible. Another thing that I had always wanted to try was slope soaring. My first slope sailplane was a Zagi THL flying-wing that I built after buying the kit on Ebay dirt-cheap. Foam flying-wings are a great way to get into slope/sailplane flying because they are inexpensive, almost indestructible, easy to fly and they will fly well in light lift. I began to fool around at local sledding hills with mixed results. I stumbled on and made contact with Greg Smith and Mirko Bodul, soon I got my fist taste of real slope soaring on various Lake Michigan cliffs and I was hooked.


As much as I liked my Zagi THL and it's durability, it had some drawbacks: the plane was designed to be a hand launched model and it was very light (14 Oz.) and had very limited ability to penetrate winds much above about 15 MPH. Since I had built several flying wings and was comfortable with the building process I went shopping around for a higher performance flying wing. After watching the cool videos on their web site ( I ordered a CombatWings XL flying-wing combat slope sailplane. I ordered the kit but if you don't want to build one the good folks at CombatWings will professionally build one for you and ship it to you ready to fly complete with radio if you desire.  What attracted me to the XL was it's all EPP (Expanded Poly-Propylene) airframe, wide-chord design and the ability to use standard sized radio gear. 



I received my XL kit and started to build immediately. Like all of the flying wings I had previously built the "airframe" consisted of only 7 pieces: 2 EPP foam wing halves, 2 balsa wood elevons, 2 Coroplast (corrugated plastic) wing tips that tape on, and one carbon fiber spar.  The kit quality was very good.  Building these foam flying-wings is quick and easy so I won't get too deep into the assembly here; just follow the instructions. I will mention a few things that I did while building.  One thing I found was that the instructions mentioned, "inserting the spar into the wing" but failed to mention that there was a hole drilled down the center of the wing spanwise for this purpose. My kit had some EPP blocking the hole so I never saw it. I figured that they had forgotten to cut the spar channel so I just cut one myself like you do for most Zagis. I E-mailed the manufacturer (after I cut the channel and glued in the spar of course) about this and they explained that there was a pre-cut hole for the spar. If I had actually followed the link provided with the instructions (that I just found while writing this review) I would have known this from the nice, color assembly pictures provided. Radio installation is easy; just use a #11 X-acto knife (or a small router but be very careful not to hog out too big a cavity) to perform the required surgery. The kit is marked for radio gear location.  I used standard Hitec servos, a micro 555 receiver and a 700-mah flat pack at the marked locations and the CG was perfect with no weight required for balancing. Remember that you will need a transmitter with elevon or V-tail mixing OR a separate electronic mixer if your transmitter doesn't have one. I used an inexpensive Hitec Focus III, which has built in mixing. If you can afford it I would recommend a radio with dual rates for reasons I will mention later but the little Hitecs are inexpensive and work just fine. I cut the mounting lugs off my servos in order to make them fit tighter in a square cavity. Cut your radio gear mounting cavities a little undersized so the gear fits very tightly. If you do this you won't need to glue the gear in place as the instructions suggest, strapping tape over the top of the cavities will do the trick.  The directions suggest using various name-brand silicone adhesives but I used epoxy to join the wings and glue the spar in and it works fine.  The directions also recommend the use of 3-M 77 spray-adhesive over the foam to make the strapping tape and covering adhere better. I would follow the directions, however I will mention that I have built several foam flying-wings and have never used 3-M 77 due the sticky mess it makes. I keep everything clean and iron it down well and I have never had a problem with adhesion even in very cold weather. Many people cover foam planes with colored Mylar packing tape but I would highly recommend film coverings such as Ultracoat (Oracover) for a much stronger plane with less wing flex as well as much better looks.  About 325 degrees on the iron works well. Be sure to use bright colors with contrast between the top and bottom of the wing (light top and darker bottom seems to be best) because these wings can be hard to keep oriented due to the thin profile and lack of a tail. Have fun with it; wild swirls, checkers, flames, stripes and sunbursts are all cool. The gallery at should give you some ideas.


As I mentioned earlier, my XL balanced perfectly without ballast. The instructions tell you the CG location but they don't really tell you how to check it so here is what you do: tape a pencil to the bottom center of the wing 8 1/4 inches back from the very tip of the nose with the pencil parallel to the trailing edge of the wing. This pivot point is now the center of gravity (CG) where the plane must balance.  Put the plane down on a level table with the plane resting on the pencil. The plane is balanced when you can tilt the plane so it will rest on the nose end (nose and pencil touching the table) AND the tail end (wing trailing edge and pencil touching the table) without falling back in the other direction. Tape small amounts of lead weight or coins to the top of the wing (you will generally need nose weight if it doesn't balance) until it balances. Once you achieve balance cut a slit in the covering and foam (be sure you don't cut into your radio gear!) and shove the weight into the slit. Tape or cover over the slit and remove the pencil, you are balanced.


My first test flights with the XL were in a local park where I gave it some hand tosses to check flight characteristics and trim settings.  The XL, like all flying wings I have flown, will need the elevons set (reflexed) slightly "up" from flush with the top of the wing in order to achieve level flight. I was lucky this day because, although it was snowing and 25 degrees, there were easterly winds at 15 to 20 MPH which makes Milwaukee and it's Lake Michigan cliffs a sloper's paradise.  I drove to Sheridan Park in Cudahy Wisconsin for the maiden slope flight. I pushed the XL into the wind while holding it by the tail (the better technique in high winds is an overhand "baseball pitch" toss while holding the plane from the nose with your thumb on top) and it flew off into the snowstorm. I was immediately impressed with the plane. The XL weighs 22 oz. as opposed to my 14 oz. THL but with the added wing area due to the wide-chord planform, 593 sq/in compared to the THL's 408 sq/in, the wing loading is comparable. The XL flies in a very stable and solid manner and penetrates well. The THL tended to "float" with the air while the XL flies through the air. The XL accelerates quickly with the nose down and retains energy pretty well for a light foamy. The XL has a very good speed range and can fly much faster than the THL at comparable pitch angles while still being very stable and controllable at slower speeds. I had my control throws set up pretty high and the XL has a great roll rate, partly due to the generously sized elevons. It might be nice to have a radio with dual rates, because due to the mixing of channels 1 and 2 for the elevons it's not possible to get large aileron throws without having large elevator throws as well. The plane gets a little twitchy in the pitch axis with large elevator throws and it can be difficult to fly the plane smoothly this way. Dual rates would allow large aileron throws with smaller elevator throws as well as the option of turning down the aileron throws to make the plane "groove" well. The instruction manual doesn't provide any recommended control throws but the plane has big control surfaces so I would start with about 1/2 to 3/4 inch throws until you get used to the plane. If you have dual rates set the high aileron rate at about twice the elevator throw and you will get nice, fast rolls at higher speeds. The other nice feature of the XL is that it flies inverted very well without huge amounts of down elevator input.  After the maiden flight I flew the XL at Atwater Beach and Chapala Park that first day in the snow. Greg Smith got some great pictures of the XL with the lake in the background that day. I have flown the plane at Concordia, Bender Park and Crystal Ridge as well since then and have never been disappointed with it's flying characteristics. Greg and Russ also flew the XL at Bender Park and thought it was very nice for a light foamy. If you get the launch technique down the XL can be safely flown in strong winds. At some point I intend to add some ballast and see what it will do at higher weights in strong lift conditions. I also plan to add a tow hook for bungee launches so I can have fun with the XL anytime.



The verdict?  I like it; the XL is a high quality kit that is affordable, durable, easy to build and it flies really well.  It would be a great first slope plane for a beginner because it is easy to fly and will allow you many spectacular crashes without the need to go home and repair before the next "lesson." If you like slope flying (and you will, trust me) you will want to move on to higher performance planes at some point but the XL is still a nice plane to bring to the slope for combating (so far I've only flown combat with the ground….the ground always wins), testing the conditions, light wind flying and flying at locations where there is no suitable landing area for higher performance ships.


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