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Old Dec 19, 2013, 08:15 PM
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Originally Posted by Bernd Brunner View Post
John,

can you give me some hints on how you have installed the tubes and fitting for the TEK probe in the fin?
I have an X4 on the bench as well, which should be modified for GPS flying...

Bernd
Hi Bernd

I am using the RC Electronics vario with the Sky Melody TEK probe. The probe mount is nothing more than a short piece of brass tubing. I soldered this short piece of brass tube to longer piece of brass tubing. The plastic pneumatic tubing was attached to the rear of this brass tube assembly. The X2 vertical fin has two shear webs running vertically in the fin, one near the leading edge and one closer to the hinge line. (See the photo below of the vertical fin, the two dark vertical lines in the fin are the shear webs) I drilled a hole thru the leading edge of the vertical fin and the front shear web closest to the leading edge. I then fed the plastic tubing thru the hole in the leading edge of the fin and thru the hole in the first shear web. As the plastic tubing was pushed into the fin it runs into the aft shear web and then is forced downward towards the bottom of the fuse. At that point, after much manipulation I was able to force the plastic tubing to run along the tailboom towards the front of the fuselage. The brass tubing assembly(with the plasting tubing attached to the rear of the assembly) is then fed into the hole in the leading edge of the vertical fin and into the hole in the first shear web and glued in place. This way the brass tubing assembly is supported in two places, the leading edge of the fin and the shear web.

The only difficult part is trying to fed the plastic tubing thru the fuse and getting it to the front of the fuse.

I have also practiced GPS Triangle racing with my X2xc. I am hoping that some day there will be GPS competitions for non-scale gliders. I think this is would be much more like fullzise soaring than the typical Thermal duration or F3J type competition.

John
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Old Apr 08, 2014, 10:25 PM
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Joined Jan 2005
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X2 wins at Davis

This last weekend Rick Shelby and I competed in the Davis Cross Country event with the X2xc. The weather was windy both days which definitely gave the advantage to the highly loaded X2. The conditions proved to be very difficult with only 2 teams completing the task of Saturday. Rick Shelby and I were one of the teams completing the task coming first. Sunday only two teams were able to even get off the field and no team completed the 18 mile task. Again Rick and I with the X2 came in first managing to complete 13.4 miles of the 18 mile task. All four days of competition the X2 has been flown with full ballast at approximately 174 oz. Having flown the X2 for total of four contests days, I think I have enough time on it to make some observations and comparisons:

There is little doubt in my mind it has a better L/D than my MXC, especially at higher speeds. The faster the airspeed the bigger the advantage for the X2.

The X2 climbs reasonably well in thermals. The few times we were able to thermal with other gliders, the X2 did not seem to get out-climbed.
Max altitude for me with the X2 is probably around 3000’ to 3200’ agl. I have gotten as high as 2800’ and still felt quite comfortable. This is probably a good 600’ below my limit with the MXC.

The X2 handling is good but not quite as docile as the MXC. I have managed to tip stall the X2 at least 3 times during the 4 days of competing, always at high altitude while thermaling. The tip stall results in a ½ turn spin with quick recovery. With the MXC I don’t think I have ever seen it spin at all.

I noticed in Davis when landing the X2 there were some hard to control yawing oscillations. The X2 looked like a dog wagging its tail back and forth. In my landing mode I have 100% rudder mixed with the aileron stick. I also noticed this a couple of times at altitude but to a much lesser extent. It could be that the oscillations were the result of excessive stick movement on my part, trying to control the glider in the strong wind and turbulence. However, it could also be due to the mass of the ballast in the wings creating a good deal of inertia when the glider yaws. These oscillations no doubt create drag. I was hoping the longer tail moment would be enough to resist the inertia created by the ballast. In hindsight I wish I had installed permanent ballast in the fuse at the CG under the batteries when I had the fuse cut in two. I could not have fit anywhere near the 5 pounds of ballast, but even a pound or so in the fuse at the CG would helped reduce the inertia. I do not want to cut into the fuse now to add lead, so I am looking into installing a larger rudder.

The X2 has now flown in 4 contest days with 3 first place finishes and one 2nd place finish. It has definitely proven itself in windy conditions, where the lift has topped out relatively low. Now we just need to see how it performs in strong, non-windy conditions, where the lift goes to unlimited altitude. I am planning on using it as my primary ship at the up-coming 4 day Montague event.

John
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Old Apr 09, 2014, 09:11 AM
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John,
Congratulations on your fine performance at Davis and Cal Valley.. Your XC is definitely a game changer.. Very much like Dick Schreders HP-8 fullsize from the late 50's, a higher wing loading and higher cruising speeds is a hard combination for the competition to cope with.. I was able to observe your model on approach during a relaunch.
I would suggest that your rudder -aileron mix needs some tuning. If it were me I would tone the mix down say 40% and try inputting the rudder as needed. This may also be the source of your spinning at high altitude. I believe the higher inertia in the wings does show the poor yaw damping of this set-up, however it is just a symptom not the source. You might also want to try some experiments with aileron differential.
I also wanted to comment on the excellent conversations at dinner Saturday night.. It was a very nice event I shall remember for a long time. I look forward to seeing you at Montague.. Larry
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Old Apr 09, 2014, 11:20 PM
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Originally Posted by Larry Jolly View Post
John,

I would suggest that your rudder -aileron mix needs some tuning. If it were me I would tone the mix down say 40% and try inputting the rudder as needed. This may also be the source of your spinning at high altitude. I believe the higher inertia in the wings does show the poor yaw damping of this set-up, however it is just a symptom not the source. You might also want to try some experiments with aileron differential.
Hi Larry, thank you. I'm glad you were able to see the problem I was having. I also received an email from my good friend Dieter down in Columbia advising me of the same thing you are. I think you guys might be right. I will try reducing my rudder-aileron mix. Besides, that will be much easier than installing a larger rudder.

If you liked Davis, you are going to love Montague!

John
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