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Old Nov 14, 2012, 09:14 PM
RC FPVer
surf1punk's Avatar
United States, FL
Joined Nov 2011
486 Posts
Quote:
Originally Posted by Airplanekid333 View Post
could i get away using 3s? or does this airplane absolutely need power for FPV? what is the biggest prop i can put on this badboy? i will be ordering one for christmas.
I run a 5000mah 3s on a 1400kv motor on a 9x6, runs great. More than enough power, I hardly take it above 1/2 throttle, cruise closer to 1/4.
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Old Nov 14, 2012, 09:42 PM
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Mtrhd0024's Avatar
Joined Feb 2012
31 Posts
Skywalker banking issue...

Whats up guys!

I have a V5 Skywalker I built up slowly over the past year, taking my time to do it all right... I only say that to reinforce the fact that I've been patient with this thing, and didn't take any shortcuts with the build.

I have now made about 10 flights with this thing (no crashes so far, fingers crossed!) and it insists on wanting to bank to the left, to the point where i have to use full right aileron to get it to fly straight and level, and if I hold it full right for about 10 seconds, it will SLOWWWLYYYY start to bank to the right. Even with the trim set to full right aileron, it's only marginally better. It's so bad, that I finally caved, and added a bendable aluminum trim tab on the right wingtip to try and help drop it back down. I flew it with that for the first time today, and it kinda sorta helped.

I'm beginning to think this thing has roots in NASCAR or something; I pretty much only fly in wideee left hand circles around the field, because even flying straight is a challenge!!

What puzzles me is, there is nothing obviously wrong with the build that would cause it to do this. I've never had a plane bank so badly to one side that I couldn't trim it out, without something obviously wrong.

A few of the things I've checked so far:
a) All control surfaces are in a neutral position before takeoff. The rudder is centered, and ailerons are even with each wingtip.

b) The tail is not twisted. Sighting from the front or back of the airplane, the main wing, and the horizontal stab are parallel with each other.

c) Its not the thrust angle of the motor, or P factor, the plane still banks to the left in a power off glide. Makes approaches and landing interesting (not in a good way)

d) The main wing is balanced from side to side, within about 1cm from the very center.

e) The angle of incidence of each wing half is the same.

A few build details that might help:

Its a V5 Skywalker 168 with the single CF Spar, which I beefed up by machining down a dowel, and then sliding it inside the CF spar, and gorilla gluing in place. This was to prevent the possibility of the CF spar snapping, and the wings folding in the center. Sounds heavy I know, but the dowel actually weighed less than the CF spar after machining. The wingtips (past the main spar) are reinforced with CF ribbons, inserted into the wings edgewise, to prevent the wingtips from folding.

All control surfaces, including the flaps, were cut free from their respective wing, and reinstalled with Pinned hinges to reduce the stress on servo's. I tossed the standard skywalker "press in and glue" control horns in the trash, in favor of screw on Dubro control horns. Each control-surface push-rod was made from CF rod and nylon clevis ends.

The motor mount is custom made from 1/8" ply to accommodate the somewhat oversized (but common) NTM 35-36A 1400kv motor & 60amp plush ESC power combo. Prop is a nicely balanced 9x6 APC.

The wings are permanently joined at the center, and a single 6pin multiplex connector handles all 4 servos in the main wing. (2 aileron, 2 flap)

Payload consists of a dragonlink receiver and RVOSD5 & anti-vibration mount in the belly, a 3s 4,000 or 5,000mah lipo mounted in the nose, the Video TX and 1.3 cloverleaf antenna on the tail boom, and the video cam mounted on a pan and tilt on top of the fuselage, just in front of the wing. The dragonlink antenna is mounted vertically in the tail.

My only other observation is that I need to check my CG again, because I think its a bit tail heavy. It requires a bit of nose down trim to fly well, and I think either a GoPro, or another lipo up front would help that.

What gives!? I feel stupid even asking this, because it sounds like it would be something obvious, but I've been pretty thorough with this plane.

Since I don't get to fly often, I've been racking my head for the past 2 months (since I first flew it) trying to figure it out... I'm almost at the point of thinking its a manufacturers defect in my wings, (something about the wing geometry I can't easily see or measure) and I'm kinda tempted to order a 2nd set of wings from BEVRC, possibly the new 1900mm ones, to try them out.

Anyone else have this problem?

I can post pictures of everything later on tonight if that would help.
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Old Nov 14, 2012, 10:03 PM
If it's to be, it's up to me.
subsonic's Avatar
Sydney, Australia
Joined Jan 2007
3,120 Posts
I feel like I just wrote answered a similar question on this the other day. Wasn't you, was it?

Anyway, how much aileron differential do you have? High wing "trainer" config planes like this one need quite a lot or you get adverse yaw overpowering the roll command and a straight line results no matter how much you bend the aileron stick.
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Old Nov 14, 2012, 10:08 PM
"Every boy has a dream to fly"
Airplanekid333's Avatar
Fort Collins Colorado
Joined Sep 2009
510 Posts
Quote:
Originally Posted by Daemon View Post
Yes, many people run 3S with a 10 inch prop. Have to move the motor mount up a bit.
do you mean like angle it upwards? i look at pictures of the motor mount and it seems like there is not a whole lot of room to move around with.
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Old Nov 14, 2012, 10:22 PM
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Daemon's Avatar
Lakewood, Colorado
Joined Aug 2002
28,936 Posts
Quote:
Originally Posted by Airplanekid333 View Post
do you mean like angle it upwards? i look at pictures of the motor mount and it seems like there is not a whole lot of room to move around with.
No, like add a plate of plywood on top of the stock mount, and move it upwards
a half inch higher.

ian
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Old Nov 14, 2012, 10:34 PM
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Daemon's Avatar
Lakewood, Colorado
Joined Aug 2002
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Quote:
Originally Posted by Mtrhd0024 View Post
I have now made about 10 flights with this thing (no crashes so far, fingers crossed!) and it insists on wanting to bank to the left, to the point where i have to use full right aileron to get it to fly straight and level, and if I hold it full right for about 10 seconds, it will SLOWWWLYYYY start to bank to the right.
...
Anyone else have this problem?
No, never to that degree. Occasionally people will find that the plane leans a little this
way or that (usually due to some warpage during build or hangar abuse), and it
can usually be addressed by balancing a little aileron trim against a little opposite rudder trim.
For instance if my SW were banked a little to the right while flying straight, I'd
give it a little right rudder trim, and left aileron trim until it flew wings level. Or if
it only pulls to the right on-throttle, then give it some left rudder trim, and right aileron trim
to offset, as the rudder is most affected by prop wash.

The only thing I can think of that would require full aileron stick to fly level, would be a twisted
wing, perhaps having occurred when you glued the wing halves together, so one
whole wing half is at a slightly different angle of attack than the other. Tape some long
straight dowels or carbon rods to the flat bottom of the airfoil at the root and tips of both
wing halves, sticking out in front of the wing, and then sight along the length of the wing
to see if they're all aligned with each other.

As for the slooowww response. Have never seen that. My SW is very responsive
on roll axis. I don't use any rudder input for aggressive flying. I do use about 50% differential
(50% more up throw than down), to provide axial rolls with less drag.

Requiring down trim (elevator trailing edge below horizontal stab trailing edge) with an optimal
CG, is normal. There's a lot of decalage built into the horizontal stab (effectively up elevator trim)
so as the CG moves back you have to dial that out.

ian
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Old Nov 15, 2012, 12:53 AM
Foam Snow
South Africa, WC, Cape Town
Joined Aug 2011
1,334 Posts
Quote:
Originally Posted by Mtrhd0024 View Post
I have now made about 10 flights with this thing (no crashes so far, fingers crossed!) and it insists on wanting to bank to the left, to the point where i have to use full right aileron to get it to fly straight and level, and if I hold it full right for about 10 seconds, it will SLOWWWLYYYY start to bank to the right. Even with the trim set to full right aileron, it's only marginally better. It's so bad, that I finally caved, and added a bendable aluminum trim tab on the right wingtip to try and help drop it back down. I flew it with that for the first time today, and it kinda sorta helped.

...

Anyone else have this problem?
Check your tail boom - I had this problem, it turned out I didn't fix the tail boom properly after a crash, it was at a very slight angle and caused a rudder effect and had got so bad I could only turn left. Fixed the tail boom straight and all was well. Perhaps your boom was slightly bent during shipping?
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Old Nov 15, 2012, 04:24 AM
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Mtrhd0024's Avatar
Joined Feb 2012
31 Posts
Wow, thanks for all the quick replies! I'll start from the top here...

Quote:
Originally Posted by subsonic View Post
I feel like I just wrote answered a similar question on this the other day. Wasn't you, was it?

Anyway, how much aileron differential do you have? High wing "trainer" config planes like this one need quite a lot or you get adverse yaw overpowering the roll command and a straight line results no matter how much you bend the aileron stick.
Since you didn't quote, I'm assuming you're talking about me, but naw, wasn't me!

I should probably clarify that the roll rate is only slow to the right, due to the severe banking problem I describe... It rolls just fine to the left, since it already wants to bank that way anyway...

That said, I probably don't have as much aileron differential dialed in as you describe, so if I have any problems after I get it flying right, I'll be sure to do this!

Quote:
Originally Posted by Daemon View Post
No, never to that degree. Occasionally people will find that the plane leans a little this
way or that (usually due to some warpage during build or hangar abuse), and it
can usually be addressed by balancing a little aileron trim against a little opposite rudder trim.
For instance if my SW were banked a little to the right while flying straight, I'd
give it a little right rudder trim, and left aileron trim until it flew wings level. Or if
it only pulls to the right on-throttle, then give it some left rudder trim, and right aileron trim
to offset, as the rudder is most affected by prop wash.
Right, I would expect to have to put in a little trim here and there, but my problem is, its so bad I CAN'T trim it out!

Quote:
Originally Posted by Daemon View Post
The only thing I can think of that would require full aileron stick to fly level, would be a twisted
wing, perhaps having occurred when you glued the wing halves together, so one
whole wing half is at a slightly different angle of attack than the other. Tape some long
straight dowels or carbon rods to the flat bottom of the airfoil at the root and tips of both
wing halves, sticking out in front of the wing, and then sight along the length of the wing
to see if they're all aligned with each other.
Hmm, yea, VISUALLY anyway, the angle of incidence (cord line of the wings relative to the longitudinal axis of the fuselage) is equal on both wing halves, however I haven't thought to try taping dowels to the bottom of the wings... This should indeed visually amplify any difference, and make it easier to see. I will try this and report my results!

Quote:
Originally Posted by Daemon View Post
As for the slooowww response. Have never seen that. My SW is very responsive
on roll axis. I don't use any rudder input for aggressive flying. I do use about 50% differential
(50% more up throw than down), to provide axial rolls with less drag.
Yea, I think I failed to clarify. That is only when attempting to bank to the right; when banking to the left it rolls just fine! Its just that the ailerons have a hard time counteracting whatever issue it is that is currently causing the plane to bank left!

Quote:
Originally Posted by Daemon View Post
Requiring down trim (elevator trailing edge below horizontal stab trailing edge) with an optimal
CG, is normal. There's a lot of decalage built into the horizontal stab (effectively up elevator trim)
so as the CG moves back you have to dial that out.

ian
Good to know Daemon, thank you for your very in depth response!

Quote:
Originally Posted by heinduplessis View Post
Check your tail boom - I had this problem, it turned out I didn't fix the tail boom properly after a crash, it was at a very slight angle and caused a rudder effect and had got so bad I could only turn left. Fixed the tail boom straight and all was well. Perhaps your boom was slightly bent during shipping?
Thanks hein, I assume you mean the twist in the tail boom which causes the vertical stabilizer to lean left or right? (and being a "T Tail" configuration, that also affects the horizontal stab) If so, I have checked this, and my tail appears to be pretty straight...

Thanks again for all of the thoughtful responses, I'll check into these suggestions, and see what I can find!

It seems my thoughts were similar to Daemons, in that either the angle of incidence of the wing halves are off relative to one another, OR there is some warping in my wing somewhere, so I will pursue this further... hmm...
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Old Nov 15, 2012, 08:04 AM
Crash=start of next project
CN I Dawg's Avatar
United States, CA, Los Angeles
Joined Nov 2010
783 Posts
Quote:
Originally Posted by heinduplessis View Post
I've tried 2 different HXT900's a TowerPro 9g and some unbranded orange and blue digital servo from HK. Proximity of the RC TX makes no difference.

Maybe I should invest in more expensive servos.
Many have good results with this servo> http://www.pololu.com/catalog/product/522
Digital servos always "buzz" they also tend to like the higher voltage, 6V. You will also find that some servos are affected by RFI from the VTx. Hitec are pretty immune from this noise and are a good "safe bet" choice. Search the forum for susceptibility to RF noise and you should find some studies.
BR,
Steven
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Old Nov 15, 2012, 08:21 AM
Crash=start of next project
CN I Dawg's Avatar
United States, CA, Los Angeles
Joined Nov 2010
783 Posts
Quote:
Right, I would expect to have to put in a little trim here and there, but my problem is, its so bad I CAN'T trim it out!

Yea, I think I failed to clarify. That is only when attempting to bank to the right; when banking to the left it rolls just fine! Its just that the ailerons have a hard time counteracting whatever issue it is that is currently causing the plane to bank left!
This may seem obvious but many times I've over looked the obvious. With slow response in one direction there may be a servo problem or linkage binding. Check by simulating flight loads on ailerons while moving the stick. Pay particular attention to servo responsiveness, unusual servo noise or binding. Make sure you do this under load. Hope you work it out.
BR,
Steven
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Old Nov 16, 2012, 01:20 AM
Foam Snow
South Africa, WC, Cape Town
Joined Aug 2011
1,334 Posts
Quote:
Originally Posted by CN I Dawg View Post
Many have good results with this servo> http://www.pololu.com/catalog/product/522
Digital servos always "buzz" they also tend to like the higher voltage, 6V. You will also find that some servos are affected by RFI from the VTx. HiTech are pretty immune from this noise and are a good "safe bet" choice. Search the forum for susceptibility to RF noise and you should find some studies.
BR,
Steven
Thanks for the recommendation, Steven. I've disconnected all RF sources (and minimised my Radio TX output) and still I get jitter. Interesting site btw!
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Old Nov 17, 2012, 01:01 AM
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Mtrhd0024's Avatar
Joined Feb 2012
31 Posts
Quote:
Originally Posted by Mtrhd0024 View Post
Quote:
Originally Posted by Daemon View Post
The only thing I can think of that would require full aileron stick to fly level, would be a twisted
wing, perhaps having occurred when you glued the wing halves together, so one
whole wing half is at a slightly different angle of attack than the other. Tape some long
straight dowels or carbon rods to the flat bottom of the airfoil at the root and tips of both
wing halves, sticking out in front of the wing, and then sight along the length of the wing
to see if they're all aligned with each other.
Hmm, yea, VISUALLY anyway, the angle of incidence (cord line of the wings relative to the longitudinal axis of the fuselage) is equal on both wing halves, however I haven't thought to try taping dowels to the bottom of the wings... This should indeed visually amplify any difference, and make it easier to see. I will try this and report my results!
Alright, so here are the results of this test:

The easiest long, straight object I could come up with 4 of, were some welding rods I had in my garage. I cut two of them in half, to make 4 equal length straight pieces, and taped them to the bottom of my wing as shown: (please forgive the improvised workspace! )


The result showed that the angle of incidence of my two wing halves are pretty much dead on even with each other. Here are two pictures from slightly different angles showing how even they are:


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Old Nov 17, 2012, 01:19 AM
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Lakewood, Colorado
Joined Aug 2002
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Ya, that looks straight enough. That only leaves the tail then.
Regardless of what the rudder looks like, try just trimming it out
with rudder. If you're holding full right aileron to fly straight, give it a bunch of right rudder
trim in the air until you don't need any any aileron input to fly straight.

ian
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Old Nov 17, 2012, 01:33 AM
Registered User
Mtrhd0024's Avatar
Joined Feb 2012
31 Posts
Quote:
Originally Posted by Daemon View Post
Ya, that looks straight enough. That only leaves the tail then.
Regardless of what the rudder looks like, try just trimming it out
with rudder. If you're holding full right aileron to fly straight, give it a bunch of right rudder
trim in the air until you don't need any any aileron input to fly straight.

ian
Ok, I'm hoping to fly the thing tomorrow, so I'll report back then. I'm not seeing much twist in the tail either though... Here's a picture of the Horizontal stab. in relationship with the main wing:


(Those rubber bands aren't used for flight btw, I just used them to temporarily mount the wing for this pic!)

Its pretty much dead even with the main wing. It may take a bunch of rudder to get this thing trimmed out too... I'm not positive, but I'm pretty sure I tried using rudder in one of my first flights a couple months back, and I still don't think it really solved things.
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Old Nov 17, 2012, 01:51 AM
Foam Snow
South Africa, WC, Cape Town
Joined Aug 2011
1,334 Posts
Quote:
Originally Posted by Mtrhd0024 View Post
Ok, I'm hoping to fly the thing tomorrow, so I'll report back then. I'm not seeing much twist in the tail either though... Here's a picture of the Horizontal stab. in relationship with the main wing:
Can you give us a top view, and place something straight, like a carbon tube, or dropper, etc next to your plane, parallel to the boom?
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