MrBens Zephyr XL Build Log

[MrBen]

cofg too far back usually comes with nose diving down with slightest down elevator and hard to fly level and land,especially into wind.Could be weak servos or loose control rods also.

sure could tell on video which way wind was blowing.lol

servos have 7kg torque Im using HS645MG, there is zero slop in the control linkages but a tiny bit on the servo arm itself, I have minimised the  effect this has by moving the pushrod to the hole closest to the servo, I asked Mark to check my old zep2 and he said there was a little bit on that one too which is pretty much the exact build of this (I sold my old one to him)

[MrBen]

was this the first atempt or second mate?

3rd

[MrBen]

Ben, I believe your using single Elevon's, are your servos adequate?, slop in linkage??
That's the only thing I can think of that might cause that...

Filled mine yesterday, sanding down then spray glue today, Paint tomorrow, might be ready by end of week, maybe...

What weight Lam did you use on the Elevon's?

I used 3mil (75micron) on the elevons, I think the servos have enough power as they have 7kg torque, plus it does it at all speeds

Latest video has a preflight look at the plane and a post flight analysis

zxl4thflight

[bigMouse]

No slop to worry about in that linkage!

The wide angle lense is distorting the wing shape, can't tell if those vertical stabs are upright or leaning out as per build videos.

Is the bobbing up and down visible from the ground! I mean is it subtle or really obvious large movements?

The only difference with yours and the ritewing video example is the wider opening at center to accept the 13" prop, and one servo per elevon, neither of which should cause anything like your experiencing!

[MrBen]

Final flight of the Zephyr XL

Zephyr XL splits in mid air : Gopro footage

[Dusty]

bad luck Ben, that's proper shitty mate.

did you find the current sensor and batteries?

You could see it starting to wobble up and down just before it tore apart.

[mark1975]

shame ben was a sweet looking wing,scary to think that something like this can happen so quickly and before you know it you have no plane .

[Dusty]

this might have happened http://www.youtube.com/watch?feature=player_detailpage&v=aZQlmxrmjXQ#t=114s

[Ant]

Damn it ! That's a real shame mate ! Wonder what happened ?

I studied that bridge as part of my degree - not really flutter but simple harmonic motion - ant the geek !

[Dusty]

no, i mean later in the vid.

at 2.25 it's almost exactly what could have happened to the ZXL

[bigMouse]

Ben, I'm really sorry about this! Hopefully it can go back together!
Looked like severe flutter to me!. Think I'll do my first test without the vertical stabs, they might be resonating with the larger prop! Can you remember if it porpoised with the throttle cut?

[MrBen]

it still did it with throttle cut and that last flight was without the vertical stabs

[MrBen]

bad luck Ben, that's proper shitty mate.

did you find the current sensor and batteries?

You could see it starting to wobble up and down just before it tore apart.

current sensor was recovered, one of the batteries was found burnt out and the other 2 lost, everything else recovered and working including rvosd

[Cupid Stunt]

Bummer
I assume whatever the cause it was something to do with the nose bobbing and the fluttering

Know how you feel Ben, my latest pride and joy (Sport Jet on 5 cell) now looks like it's a 3 year old beat up plane

[bigMouse]

If we can apply some constructive criticism, you seemed to be giving it some wellie! at least for a wing it seemed fast from the video! As an example, on my Vega to make it go faster than it's happy maximum, say 40mph. takes a load of amps, you were flying more or less straight when it looked as though the entire wing had gone into some kind of flutter/resonance. The center section on the zep's is the weakest area, almost entirely battery bay cut-outs, would suggest they need more reinforcement. Perhaps the cause of the original problem was the entire wing twisting, rather than just the control surfaces. Going back in history, the Horten wing suffered the same fate! Long slender wings were never rigid enough in flight, Some of their beautiful high aspect ratio designs never left the drawing board. Probably need to limit the speed, and add reinforcement (or use a  lower aspect ratio as in the zII)