I see! Where are you ordering you Skywalker X8 frames from? We ordered two frames from different vendors on Aliexpress, but both of them arrived with bad damages from the transportation
I’m in Australia and I usually get them from porcupinerc.com. They ship by EMS which is a reasonable cost and fast. They are out of stock so this time around I ordered mine from Banggood again with shipping via EMS. I once ordered one from AliExpress and it never showed up. Their dispute process is done with an automated system that was no help whatsoever. So I was out the entire cost.
Hi Darrell. We are building an X8 VTOL for research at our university. Your posts have helped so much in getting things together. We had our first hover test today, and ran into a bit of a rigidity issue. The lifting spars can be forced to twist a little bit forward and back. This causes an intense oscillation when rotating or moving diagonally (that is when the twist is greatest).
byuX8-1 You can see the flex on the lifting spars in the beginning of this one.
byuX8-2 We experimented with crossing some carbon spars on the landing gear for rigidity.
What did you do on your frame to give it enough rigidity? We did not use aluminum inserts, but rather a larger square tube with aluminum supports epoxied to the outside around the spar holes. Do you know what might be an effective way of making our frame more rigid?
Also I have a .dxf of the wing extension that we used as a template that I will share here.
We created our own CAD files for the wing extension. Here is the .dxf of our stencil.
X8 Aerofoil V4.dxf (36.6 KB)
We manufactured ours by laser cutting the stencil out on two 1/8" (3mm) wood and used finishing nails to fasten it to either end of a foam block (blue insulation foam) after which it was cut on a hot wire by hand. The holes in various points are the locations of our nail holes, feel free to remove them.
Here is a .dxf of our wing extensions which might be more usable for others. We had two channels going through in order to run wiring and dots for nail holes to assist in our manufacturing.
X8 Aerofoil V4.dxf (36.6 KB)
When using wing extensions flex is a real problem. I’ve noticed quad planes mounting the motor bars under the wings without an extension seem to not be effected by this.
Having said this, I have managed to make several Skywalkers with wing extensions that worked. They weren’t perfect but they did work. I do stiffen the wings quite a bit with wing tape covered with vinyl wrap. The vinyl wrap really makes a difference as when heated up it shrinks and tightens up the wing.
If you are getting oscillation that’s a sign that your gains are too high. I’ve had to drop the gains on roll quite a bit and there’s a very fine range that you need to find. You can also check if there’s any specific vibration that would respond to being filtered out with notch filters.
Hi Darrel, great job!
One question on the CG, I know 4400mm from the nose is the standard setup, but I heard 4200mm is better using the extended wing. Which value is better according to your experience?..thank you in advance.
Definitely move the COG forward. Adding length to the wings does move the COG forward.
Thank you for your answer. One question more…you tune, or autotune, without wings?. I always mount the wings, thinking that this detail affects the result.
About your build, I think you will resolve part of the temperature issue mounting the ESC embedded in the extension wing…this is my mount:
Very nice build. I’ve only tried autotuning once. I’m no expert but I do believe that the wings need to be attached as the COG and weight are much different without them. I ended up manually tuning mine. I haven’t had much time to work with autotuning but I think part of the issue is that you may need to turn it down from the default as the roll axis gets quite aggressive with the standard setting. Let us know how you go.
Hi Darel ,
Hope you are fine, I still remember our discussion long time ago about your X8 previously built. I am also will start build my X8 soon with my own wing extension 2x30 cm…What is your AUW on your last built? If I remember correctly your AUW was 6500 -7000 gr correct? At that time I think you use 13x8 prop.correct? What is KV number of your motor?
What is average current drawn during cruise speed?
I think mine will end up to be 7000 gr .
Tks.
@sofamio
Nice build. What is your AUW?
Tks
My builds come out around 6.5kg which is quite heavy for a Skywalker but they do fly ok. I got an hour flight out of one of the builds not long ago. Do whatever you can do to keep the weight down and make sure you strengthen the wings. I’m sorry but I don’t recall the current draw.
Hello Tony
The weight is 4.73kg with 1x multistar Lipo 16000mAh 4S. I am thinking to make a double circuit, but for now only will use a single one. .