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Old Oct 04, 2012, 04:24 AM
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Zurich
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L/R trim trick w/o alu wts. [for V2.0 and V1]

I have successfully now done this on both the V1 and V2.0 [if you have doubts and have a removed broken wing, you can try this technique first on that one] >


IFF* the "weak" wing (with less thrust) also has its trailing edge in the outer third of the wing curled UP, simply:

1. Find a cylinder w/ about 1"/2.5cm diameter,

2. cover it with soft tissue paper,

3. rest the up-curled trailing edge (outer third of wing) on it and

4. carefully curl that segment of trailing edge down using using a hairdrier, being VERY careful not to heat for more than 2 - 3 seconds.

5. Hold the curl down with another tissue to protect the delicate paint and

6. let cool.

7. If that T.E. curls up again over time, additionally, or ALTERNATIVELY, make 2 identical down-curled thin cardboard forms, one each for the upper & lower surfaces of the outer third of the wing with the up-curled T.E., tape the rear of each form to the vacuum-formed black plastic shell in the box, and sandwich the wing btwn. them when the Avitron is stored in its box ....

[NOTE: birds curl the T.E. of their flexible wing feathers down by letting them roll/twist around their backs as they fold their wings when not flying]

This works better than adding weight to the opposite wingtip, since the mass of the wt. decreases the flap amplitude on that side, reducing its thrust, but which of course also reduces the overall thrust! Smarter to increase thrust on the weak wing when possible ....


Lee



*IFF = "if and only if"
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Old Oct 09, 2012, 08:35 AM
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Since I am now regularly flying the V1 and V2.0 sequentially for my bird [he likes the look of the old one, similar to his white/blue sister, while I love the performance and superb handling of the V2.0], I have to compare the V1 to a Volkswagen and the V2.0 to a Porsche! Volkswagens are very good cars, but Porsches ....!

Lee
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Old Oct 09, 2012, 01:10 PM
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Sounds like trimming via ballast is not such a good idea on these, due to the steering mechanism. More weight pulls the wing out of position at high power, that's obvious. Perhaps designing the tail with the ability to be rotated for trimming would work better? Would be a pretty simple mod I think, but I haven't been able to find hardly any modifications to the Avitron (other than kjell's frankenbirds).
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Old Oct 09, 2012, 03:16 PM
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The ballast does work, but adding weight always decreases performance a little bit. I have messed with tweaking the tail a little bit to trim the Avitron out as well. I haev 2 birds that have no lead ballast and both fly beautifully.
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Old Oct 09, 2012, 03:26 PM
Kjell Dahlberg
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This is an interesting experiment with the wings. The result is more speed and faster turns.
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Old Oct 11, 2012, 05:52 AM
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Quote:
Originally Posted by JerryScript View Post
Sounds like trimming via ballast is not such a good idea on these, due to the steering mechanism. More weight pulls the wing out of position at high power, that's obvious. Perhaps designing the tail with the ability to be rotated for trimming would work better? Would be a pretty simple mod I think, but I haven't been able to find hardly any modifications to the Avitron (other than kjell's frankenbirds).
As I mentioned above, it is the mass, NOT the weight, of the alu pieces which affects the thrust. The added mass slightly diminishes the amplitude [up/down movement] in both directions: i.e., both upwards AND downwards.

Twisting the tail is easily done with the tail removed and everything but the nylon front exposed, using a hairdrier. HOWEVER, this is best used only to correct a spiralling tendency in one circling direction, assuming the straight-ahead L/R wing trim is reasonable.

Lee
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Old Oct 11, 2012, 06:13 AM
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V2.0 piloting tip re: flt. in small places indoors

When flying slowly in high-tail position [I usually use notch 4 in my small livingroom], because of the V2.0's rapid authoritative steering, when I have to make a sudden bank-angle change while circling in my livingroom, I find I often need to quickly follow with a slight manual correction in the opposite direction to resume the same general flt. pattern. [having to make extremely precise livingroom circling (amidst my bird's, Avitron's and gentle non-blower convection-heating wind currents & turbulence), piloting from outside the circle, with NO room for error, I find it surest, quickest & easiest to tell myself to make such sudden corrections in the "inside" or "outside" (of circle) direction, instead of L/R. And of course this works in both clockwise and counter.clockwise circling].

However, for "normal" [not sudden] steering, the V2.0 controls are so precise & responsive that I just gently steer by actually flying it, smoothly guiding like a seasoned commercial airline pilot. And of course flying faster outside and in larger spaces the above is a total non-issue!


joyousLee

P.S. The V2.0 can (has!) actually make figure-8's in my livingroom .... but it is tight and a bit risky andI do want to keep this little jewel for a long time.
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Old Oct 11, 2012, 08:41 AM
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its very nice to see so many ppl interested in this bird ^^ uve semm to have alot of information and my tests are no longer required fortunatelly... when i started testing my old avitron v1 i noticed it wouldnt steer and make a loud squeeky noise when doing so, turns out the plastic cog at the steering mechanism was loose and it has pulverized its teeth or however u call them by some reason... so my tests are a failure and canceled, sorry guys.
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Old Oct 11, 2012, 01:07 PM
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Perhaps I'm wrong, but I think we are quibbling over terms, good old science class arguments over mass vs weight. What I'm trying to say can easily be shown with a piece of chewing gum and a couple of weights (or masses). Chew the gum to make it easily stretchable, then attach a light weight to it. If you then hold the gum and wiggle it, the weight will begin to move away. If you put a heavier weight on it, it will move away faster with all other parameters equal.

So adding weight to a wingtip will not only slow down it's beating frequency, it will also pull that wing further from the body, changing the CG of the entire model. Since these models turn via changes in CG, it would appear as if trimming via ballast is not the best idea. Perhaps attempting to trim via tail rotation is not a better idea either, can't wait to get mine to do some testing.
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Old Oct 12, 2012, 07:59 AM
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terminology and reality

Quote:
Originally Posted by JerryScript View Post
Perhaps I'm wrong, but I think we are quibbling over terms, good old science class arguments over mass vs weight. What I'm trying to say can easily be shown with a piece of chewing gum and a couple of weights (or masses). Chew the gum to make it easily stretchable, then attach a light weight to it. If you then hold the gum and wiggle it, the weight will begin to move away. If you put a heavier weight on it, it will move away faster with all other parameters equal.

So adding weight to a wingtip will not only slow down it's beating frequency, it will also pull that wing further from the body, changing the CG of the entire model. Since these models turn via changes in CG, it would appear as if trimming via ballast is not the best idea. Perhaps attempting to trim via tail rotation is not a better idea either, can't wait to get mine to do some testing.
Actually, as both a physicist and an engineer, I will quibble with your statements.

For ex., the added mass [weight is the name for the gravitational force downward, only, on a mass] on one wing, adds mass to the whole system and thus somewhat diminishes the frequency [for a given motor-voltage] of BOTH wings. But, of trimming importance, the amplitude of the wing with the extra mass added to its tip, is reduced and so its thrust. My experience as an engineer [with an MBA in Prdn Mgmt] suggests that the amount the affected wing will be "pulled out" is extremely negligable, esp because of the rigid attachment method of the carbon-fibre members. And these carbon-fibre members are far more rigid than chewing gum [even old, hard chewing gum ].

Finally, like living birds, and unlike so many of these toy ornithopters, the Avitron turns because of more thrust on one or the other side, the same as we use in steering a rudderless rowboat.

Regardless of any of the above, I am sure everyone will evt. figure out what trim method works best for them and really enjoy flying the Avitron V2.0 !


Lee
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Old Oct 12, 2012, 10:59 AM
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Thanks! I would have wasted time if you hadn't explained it so well. I didn't take into account the rigidness of the wing spars.

I am now confused as to why it's difficult on some of these to trim for both powered flight and gliding, I had thought the offset ballast was the reason.
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Old Oct 13, 2012, 07:48 AM
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Quote:
Originally Posted by JerryScript View Post
Thanks! I would have wasted time if you hadn't explained it so well. I didn't take into account the rigidness of the wing spars.

I am now confused as to why it's difficult on some of these to trim for both powered flight and gliding, I had thought the offset ballast was the reason.
Im no engineer or anything, but the reason for that is simple imo.

Lets consider this:

The left wing leaves a bit more gap than the right wing, i could confirm that by pushing the bird up and down at like 1kp/h by seeying the left wing makes more of a parachute shape than the right wing.

What Mr Kjell confirmed my idea with his own test, he had placed the holes further so it will stress the wings more, his conclusion was more speed.

So less gap = more rigidity which results in more speed.

But now is the problem, more rigidity means less parachute effect, which will make the bird glide less effective as it sinks forward faster.

Get the point?

When you are flapping quick you having the right wing beying more rigid produces better results than the left wing as that is loosing power by having to make a bigger angle untill it actually starts shifting the air, making the bird turn left at all times.

When you are gliding however, the left wing is now better, because it has a parachute effect larger than the right more rigid wing, so the right wing now sinks, this now makes the bird go right.

I have tested over 10 wings, ive only found 1 good pair of wings that actually made it glide properly and fly properly, unfortunatelly when the bird landed (hard) on the ground the wings broke long time ago (yeah u can actually break those wings).


Adjusting the direction with the alluminium tape is a not a good solution, because it will have the same problem at different speeds, lets assume u balance it so in full throtle it finally goes straigth, now u loose the gliding ability as now it turns even worse to the right in away it can be impossible to control the steering in that gliding mode.

This is what ive come up with, feel free to contradict me if im not right, im not here to show off i too want to get rid of this problem once and for all xD
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Old Oct 13, 2012, 08:47 AM
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Hi L_A:

You definitely hit the target! I find it easiest to consider each wing as a sailboat sail. Generally, the tighter the mainsheet, the tighter the sail, and the more force the wind can exert on the boat via the sail. Sailboats are passive, like gliders, whereas the ornithopter pushes against the air via the mechanics in the body.

The thrust in the Avitron is distributed between the wings via the directional servo in the rear, variably tightening one wing moreso than the other, and this has been significantly improved in V2.0. The Avitron wings have a tightness so engineered that the slightly tighter sail/wing will generally be able to gain thrust under power.

When gliding, the looser wing has a worsened aerodynamic shape for good L/D: in fact it has more drag vs lift than the flatter, but still curved, other wing and it will steer in the same direction in response to servo input.

Things in the real world are not simple, and one wing may have less thrust [servo neutral] because the spar is in fact longer and heavier, or the gear teeth & interaction has more resistance, etc. And the tail may be tilted more to one side than the other [how Tim, Timmy, I'm Fenice, etc., are steered]. However, I have found that the biggest reason for unbalanced thrust is that one wing/sail has been assembled TOO loose [as wrapped around spar], with then sub-optimal thrust [too large weaker pitch angle] .... and/or, the trailing edges of one of the wings has warped up [more than the other]. The latter was the subject of my "ballastless" trim tip above.

In general, an airplane which glides in one direction and turns the other way under power, indicates that one wing has too high an AoA and is stalling before the other, causing the glide to be opposite [stalled wing has more drag and less lift]. So the trick to get balanced gliding AND powered flight is to have both wings equally tight. That can also be influenced in flight by the trailing edge, which affects the curvature of the flexible wing, which is what the tightening process is all about, right?. AND to make sure that the tail is not skewed [as the tail experiences different oncoming airflow vectors in powered and gliding flight: best use a skew to correct for excessive spiralling in one direction].

I have been able to perfectly trim several Avitrons, both V1 and V2.0, without using any alu-wts on the tips [I mean masses ...wink].

Lee
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Old Oct 14, 2012, 06:56 AM
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effect of tail-skew/tilt

To be clear, air is a viscous fluid [sticky like molasses but much thinner], and it affects both the top and bottom surfaces of wings & tails moving through it. That noted, the net effect on the tail in powered, flapping ornithopter flt. is to push the tail down ["negative lift" vector pointing down] which raises the fronts of the wings so that they can provide [positive] lift. In such powered flt., if the left side of the tail is higher than the right, for ex., the down-pointing "neg-lift" vector is tilted slightly to the left .... pushing the tail left and the nose right (rotating around the CL & CG).

A right turn under power then.

But when gliding with the same tilted tail, the airflow comes more from underneath, and the tail either has a positive-lift vector, or ar least a less negative one. That means that the tail vector is in this case either tilted to the right or at least less tilted to the left .... The result is either a left turn or at least less of a right turn in the glide. But as noted in my previous post, there are of course also other factors involved in the flt. trim.

Further, with the same tail-tilt, if the orni is yawing too much to the right in a powered tight right circle or turn, the left-swinging tail acts a bit like a clockwise-rotating helicopter blade, and it will rise and help create a right spiral-dive [and the reverse in a left circle].


Lee
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Old Oct 14, 2012, 10:41 AM
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Thank you very much for ur comment, i will try to do that too and see if i can finally have a straight flight
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