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Old Jun 09, 2011, 03:42 PM
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Originally Posted by omegamanuk View Post
Targetlocman thanks for the quick reply, the motors a 2814/09 not 1814/09 as I typed, will see if I can get a 4 blade prop locally, as I understand it 9 id the diameter and 6 is the pitch, so a 9x 8 say would give more thrust?
9x8 would theoretically, but as you get to higher pitch angles you run the risk of a prop stall.

If you want to stay with a two blade, consider moving the motor mount higher to use a larger diameter such as 10 or 11.
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Old Jun 09, 2011, 03:48 PM
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Skywalker v2 maiden flight remarks

I just flew my Skywalker v2 for the first time today in a non-FPV configuration. To my surprise it flew quite well without any need for trimming.

I noticed 2 problems though that need fixing:
  • The ailerons cause a strong adverse yaw effect as I expected due to the ridiculously wide bevelled gaps. When an aileron goes down, then the huge bevel comes down as a panel that's at almost 90 degrees to the airflow. I'll probably fill the bevelled area with balsa so that only the necessary amount of bevelling is present and tape some white tape over it all. Has anyone done this already?
  • When I throttle up, the nose pitches down immediately, and when I cut the throttle the nose pitches up immediately. I've seen posts here where people have had the opposite effect which seems strange to me. I assume the effect I'm having is because the motor is pointing up slightly and causing the relative airflow at high throttle settings over the stabiliser to give it a higher angle of attack which results in a pitch down. The effect isn't big, but enough to be annoying. Hopefully some washers to make the motor point up less will fix this. The CoG is on the servo wire gaps which from the dive tests seems correct as it has only a slight tendency to pull up which is what I want to happen if I loose radio control.

Then the less important things I noticed:
  • Inverted flying is easy and only a little bit of down stick is required.
  • Rolls are very slow even with moderate amounts of aileron throw.
  • It doesn't want to tip stall which is a good thing.
  • I can slow it down and hold full stick up and put it in a deep stall keeping direction using rudder. This is thanks to it's high wing and very low centre of gravity/mass.
  • I can't get it to spin yet even though I'm using moderate amounts of control throws. In order to spin the rudder must be much more effective and I doubt it will be enough even if it moves out at 45 degrees.
  • I've reinforced the wings with 3 extra carbon strips each (2 below and 1 on top) and the wings still flex in turbulence and when pulling G's so I've been gentle on the controls at high speeds.
  • Flaps aren't really necessary to fly slower, however they may be useful to make it brake and sink faster. They are just so small though, that I have doubts about their effectiveness should I decide to build them in.
  • It is actually possible to perform touch and goes on grass with it.
  • It's possible to fly around using rudder only instead of ailerons. It actually turns much neater this way without the unsightly adverse yaw effect.
  • My Turnigy 60amp ESC gets quite warm under the wing. It's too large to mount outside below the motor, so I guess I'll order a smaller 40 amp ESC and mount it outside.

My setup is:
  • Turnigy 35-36B 1300kv motor and a 9x6 APC-E prop drawing almost 40 amps.
  • 2 * 3S 2200mah 20C Zippy LiPo batteries in parallel so that I can stuff more battery mass up front (effectively a 3S2P pack which is stouter than a 1P 5000mah pack)
  • A chunk of lead substituting the GoPro that still needs to be mounted up front.

I'm still doing research on possible UHF antenna combinations I can use and their placements with my Scherrer UHF receiver which comes with 2 short dipole antennae which I'm afraid are too close to the other noisy electronics (ESC, motor, and cameras). Turnstile looks promising for one. The other will probably be a vertical dipole.

For testing today I just used a 2.4ghz receiver with my 500mw 2.4ghz video transmitter is already mounted (but disconnected) right out on one wingtip and lead in the other.

-Craig
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Old Jun 09, 2011, 03:54 PM
Gravity is patient............
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Quote:
Originally Posted by omegamanuk View Post
Targetlocman thanks for the quick reply, the motors a 2814/09 not 1814/09 as I typed, will see if I can get a 4 blade prop locally, as I understand it 9 id the diameter and 6 is the pitch, so a 9x 8 say would give more thrust?
I assumed that was the case. The results I gave you earlier are correct.
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Old Jun 09, 2011, 03:55 PM
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cmanley_nl did you try using differential in the ailerons??
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Old Jun 09, 2011, 04:01 PM
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Originally Posted by Targetlocman View Post
cmanley_nl did you try using differential in the ailerons??
Yes, I've got that mechanically built in (with horn placement), but that's not near enough to compensate for the drag induced by those huge bevels.
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Old Jun 09, 2011, 04:01 PM
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Any/every plane with a lot of camber will produce adverse yaw if you don't either set
up some differential in the aileron throws (more up throw than down), or
an aileron to rudder mix. The lifting wing always produces more drag
than the dropping one. It has almost nothing to do with the bevel on the hingeline.
Mine doesn't do it.

Any plane with a high mounted pusher will push the nose down the moment
you mash the throttle. It's an inertia thing (pushing forward above the center of
mass of the plane causes a forward pitching moment), not an aerodynamic one. The
cure for that, is don't mash the throttle. Ease into it. What's important is
whether it pitches up or down at higher airspeeds. If you find you have to push
more and more down elevator as the plane flies faster, you're nose heavy. If it
continues to pitch down by itself as it goes faster, it's tail heavy. Generally you
want something close to neutral that can cruise level hands off.

ian
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Old Jun 09, 2011, 04:14 PM
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Quote:
Originally Posted by Daemon View Post
Any/every plane with a lot of camber will produce adverse yaw if you don't either set
up some differential in the aileron throws (more up throw than down), or
an aileron to rudder mix. The lifting wing always produces more drag
than the dropping one. It has almost nothing to do with the bevel on the hingeline.
Mine doesn't do it.

Any plane with a high mounted pusher will push the nose down the moment
you mash the throttle. It's an inertia thing (pushing forward above the center of
mass of the plane causes a forward pitching moment), not an aerodynamic one. The
cure for that, is don't mash the throttle. Ease into it. What's important is
whether it pitches up or down at higher airspeeds. If you find you have to push
more and more down elevator as the plane flies faster, you're nose heavy. If it
continues to pitch down by itself as it goes faster, it's tail heavy. Generally you
want something close to neutral that can cruise level hands off.

ian
That's true, but even when I eased the throttle in and waited for airspeed to pick up, I had to pull slightly up continuously to fly horizontally, which was not the case at low throttle settings.

I mainly fly RC gliders and even they have less adverse yaw than my Skywalker. I built the differential in already, mechanically, because I want the ailerons to be ready for use on a Y-cable and not be reliant on 2 channels with software mixing.

I'm pretty sure I can move the CoG back and solve the problem that way but then I'll create another problem and that is that the Skywalker will no longer automatically pull itself out of a dive. Based on the dive tests I did I like the CoG where it is. I think lowering the angle of the motor will be the solution.
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Last edited by cmanley_nl; Jun 09, 2011 at 04:18 PM. Reason: add last paragraph
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Old Jun 09, 2011, 04:38 PM
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United States, CA, Fountain Valley
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Quote:
Originally Posted by omegamanuk View Post
On the subject of power, I'm on my third outing now with my SW, it feels really under powered im using :-

KMS quantum 2814/09 motor 830 KV and supposed to run 20a continuous
Ripmax dragon 45A ESC
9 x 6 APC Thin Electric Prop
3s 5000 lipo

One cause of the under power may be the motor timing, motor says 20-30 deg but the esc default is 1 deg and the beeps for programming don't relate to the manual , even had my wife see if she could work them out, but to no avail.

Most I'm seeing on the osd is 12amps wot. Could the timing make such a difference, or do I need a different esc , motor, prop??
With a 830 kV value and a 9x6 prop you could almost run this motor on 5S (18.5V).
In my opinion the minimum to use is a 4S and then thrust may still be wanting.
With a 4 bladed prop on 3S my guess would be that you will still want more. Staying with a 2 blade prop you may need to swing 12 or 13" diameter to get respectable thrust on 3S.
So either change to a higher kV motor or change to 4S or 5S power.
Make sure not to over-amp the motor though.
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Old Jun 09, 2011, 06:34 PM
Gravity is patient............
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Originally Posted by henkvdw View Post
With a 830 kV value and a 9x6 prop you could almost run this motor on 5S (18.5V).
In my opinion the minimum to use is a 4S and then thrust may still be wanting.
With a 4 bladed prop on 3S my guess would be that you will still want more. Staying with a 2 blade prop you may need to swing 12 or 13" diameter to get respectable thrust on 3S.
So either change to a higher kV motor or change to 4S or 5S power.
Make sure not to over-amp the motor though.
That's a good point. I run 920kv with 4s so 830kv on 3s is really low rpms.
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Old Jun 09, 2011, 07:08 PM
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Quote:
Originally Posted by cmanley_nl View Post
I'm pretty sure I can move the CoG back and solve the problem that way but then I'll create another problem and that is that the Skywalker will no longer automatically pull itself out of a dive. Based on the dive tests I did I like the CoG where it is. I think lowering the angle of the motor will be the solution.
Lowering the angle of the motor will make the problem worse, not better, as you're
putting the thrust line even further from both the center of mass, and the
largest producer of drag, the main wing. The thrust line on a high mounted pusher is tipped up,
specifically to reduce that effect.

I have my CG a little behind 30mm behind the servo wire slot, and my SW is almost
dead neutral on and off the throttle, at any speed. The only time it pitches over
a little is if I'm low and slow, and try to go to full throttle really quickly.

If you don't have a throttle->down elevator mix (not an uncommon mix) then
your symptoms, as described, are indicating a tail heavy plane (CG too far back).

ian
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Old Jun 09, 2011, 07:14 PM
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Quote:
Originally Posted by cmanley_nl View Post
Yes, I've got that mechanically built in (with horn placement), but that's not near enough to compensate for the drag induced by those huge bevels.
How exactly did you do this? Could you show a pic?
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Old Jun 09, 2011, 07:27 PM
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Originally Posted by Ecibob View Post
How exactly did you do this? Could you show a pic?
I don't have a photo, but it's just simple (it's not like I made some mechanical contraption). There are 2 ways (that may be combined) to do it:
  • Position the servo horn so that the horn is tilted forward when the servo is in the neutral position.
  • Move the aileron horn rearward so that the holes are behind the hinge line.
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Old Jun 09, 2011, 10:06 PM
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Originally Posted by venquessa View Post
This isn't a good idea. Brushless motors/ESCs don't work like that.

A brushless motor will draw as much current as it can to achieve it's rated Kv RPM with the particular prop.

If at 100% throttle it needs 60amps to achieve close to it's Kv, then at 50% throttle it will draw 60amps (or more!) for 50% of the time. (Delivering 50% the overall 'workdone', by consuming half the current load, half the time.) The drop in prop rpm is because the motor can't reach full Kv cause it's powers being cut away by the ESC.

This means there will still be 60amps running through the motor coils... rated for 35A.

It will heat up a lot and fail very early in life.

Down prop it or down cell it, end of. You want a prop, where the motor draws 35-40A at WOT.
I appreciate the feedback but your comment about the amp draw at 50% throttle doesn't seem "logical". Could you please point me toward some literature that might explain your statement so I can understand it. THANKS !
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Old Jun 09, 2011, 10:47 PM
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Quote:
Originally Posted by cmanley_nl View Post
I don't have a photo, but it's just simple (it's not like I made some mechanical contraption). There are 2 ways (that may be combined) to do it:
  • Position the servo horn so that the horn is tilted forward when the servo is in the neutral position.
This is with the servo positioned at bottom of wing. For top mounted servo, the horn should be tilted rearwards when the servo is at the neutral position, correct?
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Old Jun 09, 2011, 10:59 PM
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Originally Posted by thekubiaks View Post
I appreciate the feedback but your comment about the amp draw at 50% throttle doesn't seem "logical". Could you please point me toward some literature that might explain your statement so I can understand it. THANKS !
http://en.wikipedia.org/wiki/Electronic_speed_control

venquessa is correct. 50% throttle will still deliver the same amps as 100% throttle but it only delivers the current for 50% of the time.
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