The Xplorer F3J model, produced by NAN Models in Bulgaria, is said to be the most popular molded F3J/Thermal Duration model in the world since its introduction to the US market in mid-2008. The Xplorer had success in 2007 in the hands of European pilots, including Benedikt Feigl, who won the F3J World Championship in 2008 with a v-tail version.
The model has evolved because the original D-box iterations were slightly fragile under the heavy winch foot of some US pilots.
NAN redesigned the wing structure with a full carbon version in 2009, and in 2010 a new, lighter Spread Tow version was introduced with an average flying weight of 70 ounces. This ST version has seen major success in its three span variants of 3.5 meters, 3.8 meters, and 4.0 meters. It has proven to be reliable and robust. With a wing loading between 7.2 and 8.5 ounces per square foot, this model’s dead-air performance is not easily matched by similar F3J models.
The Xplorer’s floating characteristics make it docile and easy to fly, while providing many pilots with a solid platform to outlast opponents in light lift. The exaggerated “in section” undercamber of the NAN F3J airfoil contributes greatly to its excellent floating and low-speed performance. This is also its Achilles heel, as it makes the Xplorer more difficult to get moving into the wind for the all-important run home from a long downwind jaunt.
Many pilots have misjudged their returns and landed their Xplorers out. Often the “higher drag” section at moderate and higher air speeds was to blame. Nevertheless, the Xplorer has certainly seen a lot of airtime in the US and won many contests while the popularity of other legendary models such as the Sharon and the Pike have waned.
It seemed apparent that any new version of the Xplorer would need to sport a more slippery airfoil if it were to be an improvement. In April 2012, Bob Breaux of SoaringUSA announced the arrival of a batch of the new X2s and they indeed featured a new airfoil which promised better legs than the original.
Bob promised the new X2 would be significantly lighter while maintaining full strength. I placed an order for a 3.5-meter X2, because I had flown four different Xplorers during the last two years and am fond of the lighter, more nimble 3.5-meter span as opposed to the larger Xplorer variants.
The model arrived from SoaringUSA nicely packaged in a timber-reinforced box. I weighed each of the components and, including all of the supplied hardware, the entire airframe weighed slightly more than 50.5 ounces.
This bodes well for a potential build to finish in the low 60-ounce range using quality electronics. This would be a 7-ounce improvement over my previous Xplorer, which flew off the bench at 67.5 ounces. At 1,176 square inches, this should build out with a wing loading of less than 7.5 ounces per square foot, which would be similar to the lightest of the renowned 4.0 ST Xplorers.
I chose my electronics based on reliability, precision, and light weight, using MKS Ds6125 Minis in the ailerons, MKS Ds6125s for flap, the MKS Ds6125H for elevator, and the lighter MKS Ds6188 for rudder. I selected the MKS wooden wing trays and the standard SoaringUSA wiring harness.
With a four-cell 2/3A battery, the Spektrum Carbon AR9310 receiver, and using “trick” clear servo covers from Merril Brady, the total weight of all components was 61.43 ounces.
After the build (which is detailed in the online version of this column), I was pleased to discover that on the scales I had added only slightly more than 1/2 ounce in adhesives, shrink wrap, antenna tubes, and tape. With the model initially balanced at 120mm from the LE, it only needed 3/4 ounce taped to the four-cell battery pack, making the final ready-to-fly weight slightly less than 63 ounces.
While flying this model, it was immediately apparent that the new foil has made what was already a contest-winning sailplane even better. It is so lightweight that it’s easily hand-thrown into lift and returns from downwind unballasted with greater predictability than before.
The model provides excellent feedback to an attentive pilot in all conditions; it responds significantly to the slightest active air, yet remains gentle and very predictable to fly while turning in thermals.
A significant improvement has also been made in the way this Xplorer launches. The lighter weight contributes to much faster acceleration in the zoom. The more streamlined section appears to help the vertical climb after the zoom to go on seemingly forever (compared with the X1.)
I like the X2’s forgiving nature. You don’t need special skills to extract great performance from this lightweight glider. It has no bad habits and does everything a Thermal Duration pilot needs it to do with style. No doubt about it, this model is a big step forward from what was already a sound design—and at a very affordable price point. I love mine.
Fly downwind and soar.[dingo]
SOURCES:
SoaringUSA
(626) 967-6660
www.soaringusa.com
Horizon Hobby
(800) 338-4639
www.horizonhobby.com
NAN Models
www.nanmodels.com
MM Glider Tech
[email protected]
www.mmglidertech.com
West System
(866) 937-8797
www.westsystem.com
League of Silent Flight
www.silentflight.org
“Radio Control Soaring” full online column
www.ModelAviation.com
It’s finally time for a maiden flight. Dillon Graves prepares to throw the X2 into orbit on its first day out at an Indian River Kontrol Society Soaring contest in Cocoa FL.
This tracing of the old and new airfoils shows a sharper LE on the X2 combined with a thicker airfoil at the hinge line while retaining the same thickness at the spar.
The model was delivered from SoaringUSA in a nice, wood-reinforced box to make sure that no crushing occurred.
The parts for the model included a bag of hardware with everything required to assemble the model except the adhesives, wiring harness, and electronics.
Benedikt Feigl won the 2012 F3J World Championships with a v-tail, 3.8-meter X2 specially made by NAN Models at an even lighter weight of approximately 54 ounces.
