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Thread: Starting build on 60" zephyr

  1. #11
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    dang radial that it a wobbler! if you share a video of your control surfaces moving so i can see how far they move etc. that could help. also some photos of the finished bird including the motor angle would be good. you have the cg set to 10.5 right!

    my elevator moves 1cm and ailerons are set at 1.5cm

    we will get this sorted for you bro.

  2. #12
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    I redid the measurements in more detail. I . The CG was actually 27.5cm/10.8" from the front, so it's a bit tail-heavy. It's supposed to be a bit tail-heavy too, since there's no gopro mounted. Assuming 10.5" is dead-on CG. Putting the gopro on might then give me something less than 10.5, which reportedly improves flight characteristics slightly. I don't think this CG placement should be causing the plane to pitch like this. It's still possible the pitch trim needs to be adjusted a bit more.

    Knowing whether the thrust angle is correct is more important. Looking at the picture, I measured a difference of 3mm between the front and the back. 8mm at the back, 11mm at the front. If there are better ways to express this then let me know. I don't think the bottom of the wing is supposed to be in the same plane as the horizon. What should be the difference between front and back? I can fill up with washers and they should make immense differences starting to do that. One washer is 0.5mm.

    Ok. I think my elevator movement may be a bit too heavy there. Sounds like I need to re-mix the radio settings for that. When you see the plane go up/down with the pitch, it's because I'm compensating for the nose going down the entire time. Every time it goes up, I'm pulling back on the elevator a bit.

    The launches do show a wobbly wing, but the rolling motions disappear when it gets up to speed. The first round was just for a rough trim. The second round I learned some more. Both flights were LOS. So if you look again, the roll is ok and there's very little sideways motion. The main issue is the pitching of the nose downwards.

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  3. #13
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    A tail heavy wing will be ultra pitch sensative and will need alot of down trim to get it to fly, thats why its going down so much.
    Just about any wing will be wobly till some airspeed is gained .
    Flipping the motor to the other side of the bracket just mite give you what you need for attaining CG.

  4. #14
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    add some expo too ... if you have too big throws the plane will react like that (all wobbly). it's probably a combination of these issues.

  5. #15
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    i cant see where the motor is pointing from that photo.

    you will know if it is pointing wrong because when you throttle up it will affect the pitch. once you fix your rates try slamming the throttle after a glide. if it pitches up the motor has down thrust and if it pitches down you have too much up thrust.

    you need to have the cg no further that 10.5 it will make it fly much better when you fix that man.

    expo is a good buffer when the adrenaline is pumping so your thumping heart doesn't transfer through to the plane

  6. #16
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    Thanks guys for the comments. I'm going to do the following:

    - Elevator+aileron already had -40% expo. Setting -80% on ailerons.
    - Set endpoints on ailerons and elevator. Elevator 1cm, ailerons 1.5cm movement.
    - Move CG forward to 10.5 or further up.

    - Insert a washer on both sides to get a better thrust angle.
    - Retrim everything.
    - Check again and add one more if needed, retrim, refly.

    If anyone still has their measurements how deep the motor mount plate is in reference to the bottom of the wing, I'd be able to use that to know how many washers I should need. The angle seems off by quite a bit, but don't know exactly how far.

  7. #17
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    Is there any reason that you mounted your servos at an angle like that? I know that it was to make the pushrod at a 90 degree angle to the control surface but from most Zeph builds I have seen they mount the servos straight and parallel to the center line.

    Just curious since I am going to cut the holes for my servos tonight.


    -80 expo sounds pretty insane as well, it would be better to drop down your dual rates and keep your expo around 20-40.
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  8. #18
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    Edit: Nevermind, figured the collet question out.
    Last edited by airbagit13; 12th September 2011 at 01:49 PM.
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  9. #19
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    Re: servo... the intention is to prevent any stresses that may occur either on the pushrod or the tape. Disadvantage is added drag due to servo arm+pushrod sticking out over a significant part. I don't think this should impact steering smoothness at all (due to turbulence induced by the pushrod drag), because the majority of the control surface is on the outer side of the wing and there's nothing blocking it there, except the antenna. Should be ok.

    From the master himself: http://fpvlab.com/forums/showthread....ll=1#post18200

    It makes sense to first set a sensible amount of maximum travel on the elevons, then adjust the expo accordingly. Dual rates may actually be a great option to choose between "docile" and "aggressive" mode, so in the end it comes down to what you prefer. I think I'll try the -80 first and choose from there.

  10. #20
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    I took the zephyr for another flight today... The intention was to verify the recent work I did on this and to hopefully make a flight that took me a bit further than last time. Sadly this resulted in a bit of a heavy crash, but damage is repairable and no electronics got killed.

    The good news is that the wing now handles much better as compared to last time. I did not have time to do trimming and I'm sure I could have improved this a bit further. This time, no heavy adjustments on the stick were necessary. I basically added two washers under each bolt on the back of the motor mount, added 40% expo on ailerons and got the CG a little bit forward (although it's still slightly tail-heavy). The camera had a white haze over it due to bias/level settings where PAL/NTSC settings are done. If you press "OK" there, you get to configure this bias/level stuff. That's now at minimum, but it's still somewhat hazy.

    The bad news is that the flight only lasted 20 seconds or so due to pilot error. Basically not being used to the aircraft at all, its extreme control surfaces and I probably oversteered, causing loss of velocity? Flight was LOS with a low, strong sun surrounded by cirrus. I took a left after launch because there was more room there and then ended up flying right against the sun. It then went sideways to the left and headed for the ground. I managed to recover when it came back in view, but I think the manoeuver was too extreme and it caused the wing to lose most of its velocity. It looks like it then stalled over the right wing and hit the ground. Here's the vid for your viewing pleasure:



    Overall, it looks like I'm still oversteering the control surfaces, where all it really needs is just a pinch in any direction to get it to do what you want. Just didn't have enough flying time with it yet to get used to the responsiveness.

    Anyway, the motor mount got ripped off, winglet broke in half and the camera catapulted off, but everything else is still in working order:
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    So it does look very bad, but I get the impression this is easily fixed. The rest of the body is still in one piece. Considering the force it came down with and how the motor mount was bent, it's impressive the wing didn't get torn in half...

    Question is:
    What's the best glue to use to put the motor mount back on? Suppose the wing has other little damages or gets split in the future, which glue do you use to put it back together? What I intend to do for the motor mount is:
    - Bend back the mount itself, make it straight again
    - File off excess epoxy and goo
    - Use epoxy over the entire break surface and reattach it to the wing (or is CA/PU glue better?)
    - Clamp it down with glue clamps for at least 5 mins.
    - Rest overnight

    The other question relates to whether you pay attention to how props are attached to the motor axle and which way they turn in relation to the axle threading. I noticed after the last flight that the nut on the axle was undone somewhat, enough to cause 'slip' of the prop in relation to the motor and I could just unscrew the nut by hand. So in my case, the motor turns clockwise as seen from the back, it has a reverse mount on it with clockwise threading as seen from the back. The prop turns clockwise along with the motor, but it is essentially resisting this movement. Wouldn't this potentially cause the nut to unscrew from the axle if either the nut is not tightened sufficiently, or over time? It sounds that this kind of mount requires a rotation of the motor contrary to the threading of the reverse mount, so that the resistance of the propeller fastens the nut rather than loosens it? Does anyone pay attention to that?

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