SoarNeck
Mar 27, 2003, 01:00 AM
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<td align="center" width="100%" colSpan=2><BR><A href="/articles/liftzone/2003/mar/combat/Finished_Wing_Top.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Wing_Top_t.jpg" width=200></A> <BR><BR></TD></TR>
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<TD align=left width="30%"><STRONG>Wingspan</STRONG></TD>
<TD align=left width="70%">48"</TD>
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<TD align=left width="30%"><STRONG>Wing area</STRONG></TD>
<TD align=left width="70%">515 sq. in</TD></TR>
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<TD align=left width="30%"><STRONG>Weight</STRONG></TD>
<TD align=left width="70%">19.3 oz (as reviewed)</TD></TR>
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<TD align=left width="30%"><STRONG>Wing Loading</STRONG></TD>
<TD align=left width="70%">5.4 oz/sq.ft</TD></TR>
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<TD align=left width="30%"><STRONG>Radio Battery</STRONG></TD>
<TD align=left width="70%">5-cell Sanyo 500mAH (1/2 sub-C)</TD></TR>
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<TD align=left width="30%"><STRONG>Servos</STRONG></TD>
<TD align=left width="70%">2 x Hitec HS-85MG (Elevons)</TD></TR>
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<TD align=left width="30%"><STRONG>Available from</STRONG></TD>
<TD align=left width="70%"><A href="http://www.combatwings.com/">Combat Wings</A></TD></TR></TBODY></TABLE></DIV>
<P><b><big>Introduction</big></b></P>
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<P>Whether you're a fan of EPP or not, whether you like flying wings or prefer other models, nobody can deny that flying wing designs are probably the most popular slope models flown today. And why not? They work well for combat sessions, they're simple to build, and most are nearly indestructible when formed in EPP.</P>
<P>The XR, produced by Combat Wings out of Fountain Valley, California, is one of the newer models on the market. Since Trick R/C's Zagi series of kits seem to be the universal benchmark for flying wings, I was interested to see how the XR would compare to the numerous Zagi's that frequent my local slopes.</P>
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<P><b><big>Overview</big></b></P>
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<P>Upon receiving the kit, I was happy to see that that all the components had arrived in perfect shape. Not that there were many components to the XR, mind you, but the box was well packaged nonetheless. The wing itself looks to be hot-wire cut, and arrives with suggested locations for gear placement outlined in black felt marker.</P>
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<P align=center><A href="/articles/liftzone/2003/mar/combat/Box_Contents.jpg"><IMG height=150 alt="" hspace=0 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Box_Contents_t.jpg" width=200 border=2></A> </P></TD></TR>
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<P align=center><b>This is the view that greets you when you first open the neatly packaged box.</b></P></TD></TR></TBODY></TABLE></P>
<P>The XR kit includes all hardware necessary to complete the model, but happily it doesn't include covering tape. Since I've never cared for tape-covered models, I actually appreciated not having received a roll of covering that I never intended to use.</P>
<P>With only three days left before the weekend, I was curious to see whether I could complete the model in time. The fact that good sloping weather was forecast was a nice incentive...</P>
<P><b>Equipment Selection</b></P>
<P>While some people prefer models that come with pre-cut equipment pockets, I liked the fact that Combat Wings only penned suggested location in felt marker. I like the ability to move my gear around to achieve proper balance, and usually use odd gear for foamies anyway.</P>
<P>As an example of this, I had 5 older (but unused) red Sanyo 500mah 1/2 Sub-C cells that are perfect for a project like this. Had I been forced to conform to a precut bay, using these cells would have been made more difficult. </P>
<P>I also had 2 HS-85MG servos that needed a home, and chose a Hitec Superslim 7-channel receiver to handle the signal processing chores. The metal gear servos are a nice choice for any model that might see combat or training duty.</P>
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<P><b><big>Construction</big></b></P>
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<P>After removing the wing cores from their beds, I spent about twenty minutes removing the melted foam slag that accompanies a hot-wire cut core. This can either be accomplished by hand or by using a spare piece of foam as a brush.</P>
<P>The first construction step that is required with the XR is to join the two wing halves. I was pleasantly surprised to see that this is achieved by using a carbon arrow shaft spar that is mounted in a pre-cut channel inside the wing cores. Many EPP models use spar slots cut into the surface of the wing core, which inevitably leaves a visible ridge in the surface of the model, and can lead to alignment problems if care is not taken. With the XR, the core halves are simply slipped over the tube, and alignment is automatic.</P>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Spar_Alignment.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Spar_Alignment_t.jpg" width=200></A></TD></TR>
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<td align="center" width="50%"><b>The pre-cut slot for the spar makes alignment of the wing halves a breeze.</b></TD></TR></TBODY></TABLE></DIV>
<P>After applying a thin coating of Household Goop to both the spar and the core root faces, I completed the assembly and left it to dry in the original core beds. While the instructions recommend this as a two-step process, I had no problems completing the construction in a single step.</P>
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<P><A href="/articles/liftzone/2003/mar/combat/Gluing_Halves.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Gluing_Halves_t.jpg" width=200></A></P></TD></TR>
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<P><b>Old sealed batteries and boxes of e-flight cells make great building weights.</b></P></TD></TR></TBODY></TABLE></P>
<p>When the Goop had dried overnight, the next step to be completed was installation of the radio components. While the penned locations that are suggested by Combat Wings will be fine for most installations, I would recommend that care be taken to mount these components as far forward as possible to avoid the use of any nose weight.</P>
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<P align=center><A href="/articles/liftzone/2003/mar/combat/Gear_Placement.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Gear_Placement_t.jpg" width=200></A></P></TD></TR>
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<P><b>Try to locate your radio equipment as far forward as possible.</b></P></TD></TR></TBODY></TABLE></P>
<P>To give maximum protection to the radio gear, I try to leave a thin skin of EPP on all sides of the components. Make sure to preserve the top surface of the section that you remove as a cutout, and you can restore the skin to almost prefect shape before you cover the model. The thin patch can be glued back in place after the radio component is installed, and your covering job will benefit from the smooth surface.</P>
<P>I installed my servos deep into the wing, so that only a small part of the horn was exposed. While this necessitates using a slight bend in the pushrod, it prevents the servo horns being damaged in slope furballs.<BR></P>
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<P align=center><A href="/articles/liftzone/2003/mar/combat/Closeup_of_Clevis_and_Switch.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Closeup_of_Clevis_and_Switch_t.jpg" width=200></A></P></TD></TR>
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<P><b>You'll have to bend the pushrod slightly if you recess your servos.</b></P></TD></TR></TBODY></TABLE></P>
<P dir=ltr align=left>While the wing may seem flexible at this point, is really stiffens up after the strapping tape is applied. I lightly sketched the locations of the tape reinforcements, and applied a light coat of 3M 77 spray adhesive. Try to apply the tape with a minimal number of wrinkles, but this isn't hard since the model has few difficult curves. </P>
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<P align=center><A href="/articles/liftzone/2003/mar/combat/Taping_Wing.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Taping_Wing_t.jpg" width=200></A></P></TD>
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<P align=center><A href="/articles/liftzone/2003/mar/combat/Nose_Taping.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Nose_Taping_t.jpg" width=200></A></P></TD></TR>
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<p align=center><b>The recommended taping pattern from the instructions.</b></P></TD>
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<P align=center><b>A closer view of the taping pattern around the nose area.</b></P></TD></TR></TBODY></TABLE></P>
<P>I chose to cover my model in fluorescent Ultracote, which is a pleasant material to work with. Make sure to dust the entire surface of the wing with spray adhesive to allow the covering to adhere properly, and allow for generous overlaps in the covering since the model will then take a bounce or two without having the seams come apart. Make sure to have some way to locate your switch, charge lead and servo horns under the surface, or you'll be forced to poke around with a pin until you locate them. </P>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Guidelines_for_Square_Pattern.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Guidelines_for_Square_Pattern_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Finished_Checkerboard.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Checkerboard_t.jpg" width=200></A> </TD></TR>
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<td align="center" width="50%"><b>The secret to getting a good checkerboard is alignment.</b></TD>
<td align="center" width="50%"><b>Tack the squares down with low heat, and finish with a hotter iron.</b></TD></TR></TBODY></TABLE></P>
<p>The elevons are also covered in Ultracote, though no spray adhesive is needed here as the surfaces are sheet balsa. Make sure to bevel the leading edge of the control surface, but leave the trailing edge square. If you're feeling particularly diligent you can try to sand the elevon in a taper towards the trailing edge, but I only like to do this if I will be fibreglassing the elevons as the balsa can get a little thin. I hinged the surfaces with Ultracote as well, since there aren't many tapes that will hold up to the Canadian winter without cracking or delaminating.</P>
<p>The control rods are a relatively simple affair, consisting of a straight 2-56 threaded rod, a z-bend, and a Dubro metal clevis. I'm personally not a big fan of z-bends, but they get the job done. As I said earlier, my rods required a slight bend to clear the wing surface, but control remained slop-free and very positive. Make sure to install your control horns parallel to the control rod (not to the hinge line) in order to prevent the servo from binding. You can install the horns parallel to the hinge line if you choose to use ball links instead, just remember that these can be knocked off fairly easily in combat.</P>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Control_Horn_and_Z_Bend.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Control_Horn_and_Z_Bend_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Finished_Control_Rods_and_Logo.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Control_Rods_and_Logo_t.jpg" width=200></A> </TD></TR>
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<td align="center" width="50%"><b>A Z-bend terminates the outboard end of the pushrod.</b></TD>
<td align="center" width="50%"><b>Try to keep your pushrods parallel to the line of action for the servo arms.</b></TD></TR></TBODY></TABLE></P>
<p>Finally, the Coroplast winglets are attached with small pieces of strapping tape. You may use Goop to adhere them as well if you would like a more permanent installation, but the strapping tape method works well.</P>
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<td align="center" width="100%"><A href="/articles/liftzone/2003/mar/combat/Marking_Tip_Slits.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Marking_Tip_Slits_t.jpg" width=200></A> <A href="/articles/liftzone/2003/mar/combat/image28.jpg"></A></TD></TR>
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<td align="center" width="100%"><b>A couple of quick guidelines makes it much easier to keep the winglets in proper alignment.</b></TD></TR></TBODY></TABLE>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Finished_Wing_Top.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Wing_Top_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Finished_Wing_Bottom.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Wing_Bottom_t.jpg" width=200></A> </TD></TR>
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<td align="center" width="50%"><b>I finished the top of the wing with neon purple, silver, and fluorescent pink Ultracote...</b></TD>
<td align="center" width="50%"><b>...and yellow and black Ultracote to finish the bottom surface. The bit of tape reminds me where the recommended center of gravity lies.</b></TD></TR></TBODY></TABLE></P>
<p><b>Balancing</b></P>
<p>My model required very little weight to balance to the recommended rear point (thermal setting). I ended up adding 0.1 oz to the nose for longitudinal balance, and 0.1 oz to the right tip for lateral balance.<BR></P>
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<p><b><big>Flying</big></b></P>
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<p>The weekend forecast turned into a day that was all that was promised and more. Over the course of the day on Saturday, I encountered a wide range of wind conditions, and was really able to wring the model out.</P>
<p>The maiden flights of the XR took place on a large hill overlooking the town of Longview, Alberta. The slope is one of my favorites for flying all sorts of models, since the lift-band is broad and tall. It also has a nice grassy landing zone that is perfect for landing big scale models, though that's certainly not a requirement when flying a foam model. The fact that the Longview slope has a perfect view of the snowcapped Rocky Mountains nicely completes the package.</P>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Longview_Alberta2.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Longview_Alberta2_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Longview_Alberta3.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Longview_Alberta3_t.jpg" width=200></A> </TD></TR>
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<td align="center" width="50%"><b>Looking north at Longview.</b></TD>
<td align="center" width="50%"><b>Looking south...</b></TD></TR></TBODY></TABLE></P>
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<td align="center" width="100%"><A href="/articles/liftzone/2003/mar/combat/Longview_Alberta.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Longview_Alberta_t.jpg" width=200></A> </TD></TR>
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<td align="center" width="100%"><b>...and straight west. I can't think of better scenery than this!</b></TD></TR></TBODY></TABLE></P>
<p>The day started out with a brisk 15-20kph breeze blowing straight onto the slope face, which was perfect for a first toss. After checking the control linkages and throws for a final time, I tossed the model off into the lift. It was immediately on step and climbing nicely, and I was suitably impressed by its responsiveness to the controls with the recommended control throws and c/g (thermal mode).</P>
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<td align="center" width="100%"><A href="/articles/liftzone/2003/mar/combat/Nose_Toss.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Nose_Toss_t.jpg" width=200></A> <A href="/articles/liftzone/2003/mar/combat/image28.jpg"></A></TD></TR>
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<td align="center" width="100%"><b>I find it easiest to toss flying wings from the nose in brisk conditions.</b></TD></TR></TBODY></TABLE></DIV>
<P>Rolls weren't exactly axial, but then they rarely are with a swept flying wing. Playing with aileron differential didn't seem to make much of a difference to the rolling behavior of the model, and I eventually just accepted the little bit of pitch coupling that seems built into the airplane. I ultimately left the differential at 0% (equal throw each direction).</P>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Wing_at_Rest.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Wing_at_Rest_t.jpg" width=200></A> </TD></TR>
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<P><b>XR with the rest of the crew. The scale model is Ryan van Beurden's Icare 3.2m DG-600, and the racer is his molded Ray.</b></P></TD></TR></TBODY></TABLE></DIV>
<P>I was pleasantly surprised to see that the XR doesn't have any tendency to fall into a spin. Zagi pilots seem to just accept the "Zagi stall" that often puts these models into the ground after spinning at low altitude, but I've always thought of it as a design flaw. At the thermal c/g setting, the XR will not spin even with ridiculous provocation, which is a desirable characteristic for a model that will likely see some twisting slope dogfights!</P>
<P> Full control-deflection loops showed no tendency to snap at the top, and were easy to complete given enough energy.</P>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/XR_Clouds2.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/XR_Clouds2_t.jpg" width=200></A> </TD></TR>
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<td align="center" width="50%"><b>The XR shows good energy retention for a foamie wing.</b></TD></TR></TBODY></TABLE></DIV>
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<P>The XR also excels at inverted flight, with only a hair of down elevon needed to maintain altitude in decent lift. The model had no bad habits in inverted flight, and I found myself flying inverted as much as upright for much of the day.</P>
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<P>One of the guys flying with me had a Zagi 3C with him, and it didn't take long before we started trying to knock each other out of the sky. The XR seemed to be able to out climb the 3C in the moderate conditions, and was markedly faster in level and diving flight. We made sure to keep out of the way of the scale models that were sharing the slope at the same time, but combat furballs rarely get very fall from the slope face anyway, so there were no conflicts. Unfortunately, I wasn't able to test how the XR recovers from combat hits, since neither of us could hit the broad side of a barn with our models, let alone each other!<P>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Wing_Combat_Mountains.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Wing_Combat_Mountains_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Zagi_and_XR.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Zagi_and_XR_t.jpg" width=200></A> </TD></TR>
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<td align="center" width="50%"><b>A Zagi 3C tries to sneak up on the XR from below!</b></TD>
<td align="center" width="50%"><b>Matt Bielecki and I mix it up in a one-on-one dogfight!</b></TD></TR></TBODY></TABLE></DIV>
<P>As the day progressed, the wind began to pick up to the point where flying unballasted was uncomfortable (~35-40 kph). I had a sheet of 1/8" plate lead along for just this situation, and not having a pair of scissors with me, I decided to try the whole plate (19 oz, or about the same as the dry weight of the model!). These are the kinds of things that one will only try with a foamie!</P>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Wing_and_Ballast.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Wing_and_Ballast_t.jpg" width=200></A> </TD></TR>
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<p><b>Please be very careful with tape-on ballast, since it can easily come loose in flight. Ballast always goes over the c/g.</b></P>
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<p>After firmly securing the ballast, I heaved the model into the gathering winds. It was definitely having difficulty climbing as aggressively as before, but energy retention and glide speed were much enhanced (not a big surprise, as the wing loading was now 10.7 oz/sqft. Since the weight was concentrated on the centerline (same roll and pitch inertia), the models handling characteristics seemed largely unaffected. I can happily say that the model responds well to ballast, but 5-10 oz would have been plenty in these winds.</P>
<p>Finally, as the day drew to a close, the winds diminished to about half of what they had been in the morning (5-10kph). It was a nice opportunity to see how the model would pinch in light conditions, and I was happy to see the XR handle these light winds well. Rolls and loops now required a fair dive to gather kinetic energy, but that was to be expected.</P>
<p>The XR isn't as aerobatic as my full-house racers, but it will do anything that you can think of for an aileron/elevator model. </P>
<p>All in all, I went home happy. <BR></P>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Wing_and_Big_Brother.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Wing_and_Big_Brother_t.jpg" width=200></A> </TD></TR>
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<p><b>Suddenly it's so small! Here's the XR with Simon van Leuween's 6m DG-600.</b></P></TD></TR></TBODY></TABLE></P>
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<P><b><big>Conclusion</big></b></P>
<blockquote>
<p>I've had the opportunity to build four EPP models so far, and this kit provided no unusual challenges.</P>
<p>I was very impressed by the instructions included with the XR, and the kit went together quickly thanks to the pre-routed spar slot.</P>
<p>The XR kit builds into a nice flying model, which displays none of the adverse stalling tendencies that I dislike from the Zagi lineup. It flies almost as well inverted as upright, and handles ballast well.</P>
<p>Basically, the XR kit builds easily and flies well - who could ask for more?</P>
<p>Final Control Settings ((based on subsequent flying sessions):</P>
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<TD align=left width="30%">Final Balance</TD>
<TD align=left width="70%">7 5/8" from LE </TD></TR>
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<TD align=left width="30%">Elevon Throw (Aileron Function)</TD>
<TD align=left width="70%">5/16" up & down (0% differential), measured at the inboard tip of the elevon.<BR></TD></TR>
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<TD align=left width="30%">Elevon Throw (Elevator Function)</TD>
<TD align=left width="70%">3/16" up & down, measured at the inboard tip of the elevon</TD></TR>
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<TD align=left width="30%">Exponential (Aileron Function)</TD>
<TD align=left width="70%">35% (soft center)<A href="http://www.combatwings.com/"></A></TD></TR>
<TR>
<TD>Exponential (Elevator Function)</TD>
<TD>40% (soft center)</TD></TR></TBODY></TABLE></P>
</blockquote>
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<TBODY>
<TR>
<td align="center" width="100%" colSpan=2><BR><A href="/articles/liftzone/2003/mar/combat/Finished_Wing_Top.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Wing_Top_t.jpg" width=200></A> <BR><BR></TD></TR>
<TR>
<TD align=left width="30%"><STRONG>Wingspan</STRONG></TD>
<TD align=left width="70%">48"</TD>
<TR>
<TD align=left width="30%"><STRONG>Wing area</STRONG></TD>
<TD align=left width="70%">515 sq. in</TD></TR>
<TR>
<TD align=left width="30%"><STRONG>Weight</STRONG></TD>
<TD align=left width="70%">19.3 oz (as reviewed)</TD></TR>
<TR>
<TD align=left width="30%"><STRONG>Wing Loading</STRONG></TD>
<TD align=left width="70%">5.4 oz/sq.ft</TD></TR>
<TR>
<TD align=left width="30%"><STRONG>Radio Battery</STRONG></TD>
<TD align=left width="70%">5-cell Sanyo 500mAH (1/2 sub-C)</TD></TR>
<TR>
<TD align=left width="30%"><STRONG>Servos</STRONG></TD>
<TD align=left width="70%">2 x Hitec HS-85MG (Elevons)</TD></TR>
<TR>
<TD align=left width="30%"><STRONG>Available from</STRONG></TD>
<TD align=left width="70%"><A href="http://www.combatwings.com/">Combat Wings</A></TD></TR></TBODY></TABLE></DIV>
<P><b><big>Introduction</big></b></P>
<blockquote>
<P>Whether you're a fan of EPP or not, whether you like flying wings or prefer other models, nobody can deny that flying wing designs are probably the most popular slope models flown today. And why not? They work well for combat sessions, they're simple to build, and most are nearly indestructible when formed in EPP.</P>
<P>The XR, produced by Combat Wings out of Fountain Valley, California, is one of the newer models on the market. Since Trick R/C's Zagi series of kits seem to be the universal benchmark for flying wings, I was interested to see how the XR would compare to the numerous Zagi's that frequent my local slopes.</P>
</blockquote>
<P><b><big>Overview</big></b></P>
<blockquote>
<P>Upon receiving the kit, I was happy to see that that all the components had arrived in perfect shape. Not that there were many components to the XR, mind you, but the box was well packaged nonetheless. The wing itself looks to be hot-wire cut, and arrives with suggested locations for gear placement outlined in black felt marker.</P>
<P align=center>
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<td align="center" width="50%">
<P align=center><A href="/articles/liftzone/2003/mar/combat/Box_Contents.jpg"><IMG height=150 alt="" hspace=0 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Box_Contents_t.jpg" width=200 border=2></A> </P></TD></TR>
<TR>
<td align="center" width="50%">
<P align=center><b>This is the view that greets you when you first open the neatly packaged box.</b></P></TD></TR></TBODY></TABLE></P>
<P>The XR kit includes all hardware necessary to complete the model, but happily it doesn't include covering tape. Since I've never cared for tape-covered models, I actually appreciated not having received a roll of covering that I never intended to use.</P>
<P>With only three days left before the weekend, I was curious to see whether I could complete the model in time. The fact that good sloping weather was forecast was a nice incentive...</P>
<P><b>Equipment Selection</b></P>
<P>While some people prefer models that come with pre-cut equipment pockets, I liked the fact that Combat Wings only penned suggested location in felt marker. I like the ability to move my gear around to achieve proper balance, and usually use odd gear for foamies anyway.</P>
<P>As an example of this, I had 5 older (but unused) red Sanyo 500mah 1/2 Sub-C cells that are perfect for a project like this. Had I been forced to conform to a precut bay, using these cells would have been made more difficult. </P>
<P>I also had 2 HS-85MG servos that needed a home, and chose a Hitec Superslim 7-channel receiver to handle the signal processing chores. The metal gear servos are a nice choice for any model that might see combat or training duty.</P>
</blockquote>
<P><b><big>Construction</big></b></P>
<blockquote>
<P>After removing the wing cores from their beds, I spent about twenty minutes removing the melted foam slag that accompanies a hot-wire cut core. This can either be accomplished by hand or by using a spare piece of foam as a brush.</P>
<P>The first construction step that is required with the XR is to join the two wing halves. I was pleasantly surprised to see that this is achieved by using a carbon arrow shaft spar that is mounted in a pre-cut channel inside the wing cores. Many EPP models use spar slots cut into the surface of the wing core, which inevitably leaves a visible ridge in the surface of the model, and can lead to alignment problems if care is not taken. With the XR, the core halves are simply slipped over the tube, and alignment is automatic.</P>
<DIV align=center>
<TABLE cellSpacing=10 cellPadding=4 width="350" bgColor=#e6e6e6 border=0 align="center">
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Spar_Alignment.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Spar_Alignment_t.jpg" width=200></A></TD></TR>
<TR>
<td align="center" width="50%"><b>The pre-cut slot for the spar makes alignment of the wing halves a breeze.</b></TD></TR></TBODY></TABLE></DIV>
<P>After applying a thin coating of Household Goop to both the spar and the core root faces, I completed the assembly and left it to dry in the original core beds. While the instructions recommend this as a two-step process, I had no problems completing the construction in a single step.</P>
<P align=center>
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<td align="center" width="50%">
<P><A href="/articles/liftzone/2003/mar/combat/Gluing_Halves.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Gluing_Halves_t.jpg" width=200></A></P></TD></TR>
<TR>
<td align="center" width="50%">
<P><b>Old sealed batteries and boxes of e-flight cells make great building weights.</b></P></TD></TR></TBODY></TABLE></P>
<p>When the Goop had dried overnight, the next step to be completed was installation of the radio components. While the penned locations that are suggested by Combat Wings will be fine for most installations, I would recommend that care be taken to mount these components as far forward as possible to avoid the use of any nose weight.</P>
<P dir=ltr align=center>
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<td align="center" width="50%">
<P align=center><A href="/articles/liftzone/2003/mar/combat/Gear_Placement.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Gear_Placement_t.jpg" width=200></A></P></TD></TR>
<TR>
<td align="center" width="50%">
<P><b>Try to locate your radio equipment as far forward as possible.</b></P></TD></TR></TBODY></TABLE></P>
<P>To give maximum protection to the radio gear, I try to leave a thin skin of EPP on all sides of the components. Make sure to preserve the top surface of the section that you remove as a cutout, and you can restore the skin to almost prefect shape before you cover the model. The thin patch can be glued back in place after the radio component is installed, and your covering job will benefit from the smooth surface.</P>
<P>I installed my servos deep into the wing, so that only a small part of the horn was exposed. While this necessitates using a slight bend in the pushrod, it prevents the servo horns being damaged in slope furballs.<BR></P>
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<td align="center" width="50%">
<P align=center><A href="/articles/liftzone/2003/mar/combat/Closeup_of_Clevis_and_Switch.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Closeup_of_Clevis_and_Switch_t.jpg" width=200></A></P></TD></TR>
<TR>
<td align="center" width="50%">
<P><b>You'll have to bend the pushrod slightly if you recess your servos.</b></P></TD></TR></TBODY></TABLE></P>
<P dir=ltr align=left>While the wing may seem flexible at this point, is really stiffens up after the strapping tape is applied. I lightly sketched the locations of the tape reinforcements, and applied a light coat of 3M 77 spray adhesive. Try to apply the tape with a minimal number of wrinkles, but this isn't hard since the model has few difficult curves. </P>
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<td align="center" width="50%">
<P align=center><A href="/articles/liftzone/2003/mar/combat/Taping_Wing.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Taping_Wing_t.jpg" width=200></A></P></TD>
<TD>
<P align=center><A href="/articles/liftzone/2003/mar/combat/Nose_Taping.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Nose_Taping_t.jpg" width=200></A></P></TD></TR>
<TR>
<td align="center" width="50%">
<p align=center><b>The recommended taping pattern from the instructions.</b></P></TD>
<TD>
<P align=center><b>A closer view of the taping pattern around the nose area.</b></P></TD></TR></TBODY></TABLE></P>
<P>I chose to cover my model in fluorescent Ultracote, which is a pleasant material to work with. Make sure to dust the entire surface of the wing with spray adhesive to allow the covering to adhere properly, and allow for generous overlaps in the covering since the model will then take a bounce or two without having the seams come apart. Make sure to have some way to locate your switch, charge lead and servo horns under the surface, or you'll be forced to poke around with a pin until you locate them. </P>
<P align=center>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Guidelines_for_Square_Pattern.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Guidelines_for_Square_Pattern_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Finished_Checkerboard.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Checkerboard_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="50%"><b>The secret to getting a good checkerboard is alignment.</b></TD>
<td align="center" width="50%"><b>Tack the squares down with low heat, and finish with a hotter iron.</b></TD></TR></TBODY></TABLE></P>
<p>The elevons are also covered in Ultracote, though no spray adhesive is needed here as the surfaces are sheet balsa. Make sure to bevel the leading edge of the control surface, but leave the trailing edge square. If you're feeling particularly diligent you can try to sand the elevon in a taper towards the trailing edge, but I only like to do this if I will be fibreglassing the elevons as the balsa can get a little thin. I hinged the surfaces with Ultracote as well, since there aren't many tapes that will hold up to the Canadian winter without cracking or delaminating.</P>
<p>The control rods are a relatively simple affair, consisting of a straight 2-56 threaded rod, a z-bend, and a Dubro metal clevis. I'm personally not a big fan of z-bends, but they get the job done. As I said earlier, my rods required a slight bend to clear the wing surface, but control remained slop-free and very positive. Make sure to install your control horns parallel to the control rod (not to the hinge line) in order to prevent the servo from binding. You can install the horns parallel to the hinge line if you choose to use ball links instead, just remember that these can be knocked off fairly easily in combat.</P>
<P align=center>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Control_Horn_and_Z_Bend.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Control_Horn_and_Z_Bend_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Finished_Control_Rods_and_Logo.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Control_Rods_and_Logo_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="50%"><b>A Z-bend terminates the outboard end of the pushrod.</b></TD>
<td align="center" width="50%"><b>Try to keep your pushrods parallel to the line of action for the servo arms.</b></TD></TR></TBODY></TABLE></P>
<p>Finally, the Coroplast winglets are attached with small pieces of strapping tape. You may use Goop to adhere them as well if you would like a more permanent installation, but the strapping tape method works well.</P>
<P align=center>
<TABLE cellSpacing=10 cellPadding=4 width="350" bgColor=#e6e6e6 border=0 align="center">
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<td align="center" width="100%"><A href="/articles/liftzone/2003/mar/combat/Marking_Tip_Slits.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Marking_Tip_Slits_t.jpg" width=200></A> <A href="/articles/liftzone/2003/mar/combat/image28.jpg"></A></TD></TR>
<TR>
<td align="center" width="100%"><b>A couple of quick guidelines makes it much easier to keep the winglets in proper alignment.</b></TD></TR></TBODY></TABLE>
<br>
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<TR>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Finished_Wing_Top.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Wing_Top_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Finished_Wing_Bottom.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Finished_Wing_Bottom_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="50%"><b>I finished the top of the wing with neon purple, silver, and fluorescent pink Ultracote...</b></TD>
<td align="center" width="50%"><b>...and yellow and black Ultracote to finish the bottom surface. The bit of tape reminds me where the recommended center of gravity lies.</b></TD></TR></TBODY></TABLE></P>
<p><b>Balancing</b></P>
<p>My model required very little weight to balance to the recommended rear point (thermal setting). I ended up adding 0.1 oz to the nose for longitudinal balance, and 0.1 oz to the right tip for lateral balance.<BR></P>
</blockquote>
<p><b><big>Flying</big></b></P>
<blockquote>
<p>The weekend forecast turned into a day that was all that was promised and more. Over the course of the day on Saturday, I encountered a wide range of wind conditions, and was really able to wring the model out.</P>
<p>The maiden flights of the XR took place on a large hill overlooking the town of Longview, Alberta. The slope is one of my favorites for flying all sorts of models, since the lift-band is broad and tall. It also has a nice grassy landing zone that is perfect for landing big scale models, though that's certainly not a requirement when flying a foam model. The fact that the Longview slope has a perfect view of the snowcapped Rocky Mountains nicely completes the package.</P>
<P align=center>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Longview_Alberta2.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Longview_Alberta2_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Longview_Alberta3.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Longview_Alberta3_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="50%"><b>Looking north at Longview.</b></TD>
<td align="center" width="50%"><b>Looking south...</b></TD></TR></TBODY></TABLE></P>
<P align=center>
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<td align="center" width="100%"><A href="/articles/liftzone/2003/mar/combat/Longview_Alberta.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Longview_Alberta_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="100%"><b>...and straight west. I can't think of better scenery than this!</b></TD></TR></TBODY></TABLE></P>
<p>The day started out with a brisk 15-20kph breeze blowing straight onto the slope face, which was perfect for a first toss. After checking the control linkages and throws for a final time, I tossed the model off into the lift. It was immediately on step and climbing nicely, and I was suitably impressed by its responsiveness to the controls with the recommended control throws and c/g (thermal mode).</P>
<DIV align=center>
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<td align="center" width="100%"><A href="/articles/liftzone/2003/mar/combat/Nose_Toss.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Nose_Toss_t.jpg" width=200></A> <A href="/articles/liftzone/2003/mar/combat/image28.jpg"></A></TD></TR>
<TR>
<td align="center" width="100%"><b>I find it easiest to toss flying wings from the nose in brisk conditions.</b></TD></TR></TBODY></TABLE></DIV>
<P>Rolls weren't exactly axial, but then they rarely are with a swept flying wing. Playing with aileron differential didn't seem to make much of a difference to the rolling behavior of the model, and I eventually just accepted the little bit of pitch coupling that seems built into the airplane. I ultimately left the differential at 0% (equal throw each direction).</P>
<DIV align=center>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Wing_at_Rest.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Wing_at_Rest_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="50%">
<P><b>XR with the rest of the crew. The scale model is Ryan van Beurden's Icare 3.2m DG-600, and the racer is his molded Ray.</b></P></TD></TR></TBODY></TABLE></DIV>
<P>I was pleasantly surprised to see that the XR doesn't have any tendency to fall into a spin. Zagi pilots seem to just accept the "Zagi stall" that often puts these models into the ground after spinning at low altitude, but I've always thought of it as a design flaw. At the thermal c/g setting, the XR will not spin even with ridiculous provocation, which is a desirable characteristic for a model that will likely see some twisting slope dogfights!</P>
<P> Full control-deflection loops showed no tendency to snap at the top, and were easy to complete given enough energy.</P>
<DIV align=center>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/XR_Clouds2.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/XR_Clouds2_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="50%"><b>The XR shows good energy retention for a foamie wing.</b></TD></TR></TBODY></TABLE></DIV>
<DIV align=center> </DIV>
<P>The XR also excels at inverted flight, with only a hair of down elevon needed to maintain altitude in decent lift. The model had no bad habits in inverted flight, and I found myself flying inverted as much as upright for much of the day.</P>
<DIV align=left> </DIV>
<P>One of the guys flying with me had a Zagi 3C with him, and it didn't take long before we started trying to knock each other out of the sky. The XR seemed to be able to out climb the 3C in the moderate conditions, and was markedly faster in level and diving flight. We made sure to keep out of the way of the scale models that were sharing the slope at the same time, but combat furballs rarely get very fall from the slope face anyway, so there were no conflicts. Unfortunately, I wasn't able to test how the XR recovers from combat hits, since neither of us could hit the broad side of a barn with our models, let alone each other!<P>
<DIV align=left> </DIV>
<DIV dir=ltr align=center>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Wing_Combat_Mountains.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Wing_Combat_Mountains_t.jpg" width=200></A> </TD>
<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Zagi_and_XR.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Zagi_and_XR_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="50%"><b>A Zagi 3C tries to sneak up on the XR from below!</b></TD>
<td align="center" width="50%"><b>Matt Bielecki and I mix it up in a one-on-one dogfight!</b></TD></TR></TBODY></TABLE></DIV>
<P>As the day progressed, the wind began to pick up to the point where flying unballasted was uncomfortable (~35-40 kph). I had a sheet of 1/8" plate lead along for just this situation, and not having a pair of scissors with me, I decided to try the whole plate (19 oz, or about the same as the dry weight of the model!). These are the kinds of things that one will only try with a foamie!</P>
<DIV align=center>
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Wing_and_Ballast.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Wing_and_Ballast_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="50%">
<p><b>Please be very careful with tape-on ballast, since it can easily come loose in flight. Ballast always goes over the c/g.</b></P>
</TD></TR></TBODY></TABLE></DIV>
<DIV align=left><BR></DIV>
<p>After firmly securing the ballast, I heaved the model into the gathering winds. It was definitely having difficulty climbing as aggressively as before, but energy retention and glide speed were much enhanced (not a big surprise, as the wing loading was now 10.7 oz/sqft. Since the weight was concentrated on the centerline (same roll and pitch inertia), the models handling characteristics seemed largely unaffected. I can happily say that the model responds well to ballast, but 5-10 oz would have been plenty in these winds.</P>
<p>Finally, as the day drew to a close, the winds diminished to about half of what they had been in the morning (5-10kph). It was a nice opportunity to see how the model would pinch in light conditions, and I was happy to see the XR handle these light winds well. Rolls and loops now required a fair dive to gather kinetic energy, but that was to be expected.</P>
<p>The XR isn't as aerobatic as my full-house racers, but it will do anything that you can think of for an aileron/elevator model. </P>
<p>All in all, I went home happy. <BR></P>
<P align=center>
<TABLE cellSpacing=10 cellPadding=4 width="350" bgColor=#e6e6e6 border=0 align="center">
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<td align="center" width="50%"><A href="/articles/liftzone/2003/mar/combat/Wing_and_Big_Brother.jpg"><IMG height=150 src="http://static.rcgroups.com/articles/liftzone/2003/mar/combat/Wing_and_Big_Brother_t.jpg" width=200></A> </TD></TR>
<TR>
<td align="center" width="50%">
<p><b>Suddenly it's so small! Here's the XR with Simon van Leuween's 6m DG-600.</b></P></TD></TR></TBODY></TABLE></P>
</blockquote>
<P><b><big>Conclusion</big></b></P>
<blockquote>
<p>I've had the opportunity to build four EPP models so far, and this kit provided no unusual challenges.</P>
<p>I was very impressed by the instructions included with the XR, and the kit went together quickly thanks to the pre-routed spar slot.</P>
<p>The XR kit builds into a nice flying model, which displays none of the adverse stalling tendencies that I dislike from the Zagi lineup. It flies almost as well inverted as upright, and handles ballast well.</P>
<p>Basically, the XR kit builds easily and flies well - who could ask for more?</P>
<p>Final Control Settings ((based on subsequent flying sessions):</P>
<P align=center>
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<TD align=left width="30%">Final Balance</TD>
<TD align=left width="70%">7 5/8" from LE </TD></TR>
<TR>
<TD align=left width="30%">Elevon Throw (Aileron Function)</TD>
<TD align=left width="70%">5/16" up & down (0% differential), measured at the inboard tip of the elevon.<BR></TD></TR>
<TR>
<TD align=left width="30%">Elevon Throw (Elevator Function)</TD>
<TD align=left width="70%">3/16" up & down, measured at the inboard tip of the elevon</TD></TR>
<TR>
<TD align=left width="30%">Exponential (Aileron Function)</TD>
<TD align=left width="70%">35% (soft center)<A href="http://www.combatwings.com/"></A></TD></TR>
<TR>
<TD>Exponential (Elevator Function)</TD>
<TD>40% (soft center)</TD></TR></TBODY></TABLE></P>
</blockquote>