Microlight wing "snaps" during takeoff

[gertcoetzee]

This morning after flying in the direction of Altona, I decided to land, to tighten a shoe-lace. There was a light crosswind, and I touched down, tied the laces, and immediately took off. A second or two after wheels-up I felt the wing gave a "snap". I momentarily thought of landing, then felt all is OK, opened throttle, looked briefly (as if checking whether the wing was there) and continued to Wintervogel, where I did a landing on 02 (into wind), and examined the wing. I looked at the jesus bolt, the hangblock, the tension cables, etc. and could not find anything wrong.

Off to the sea, and back to Morningstar, where the wind was straight down 20 and the landing was somewhat labour intensive (see the video on http://www.zu-dve.com videos.

Some time ago, on this forum, someone else experienced something similar, and I cannot recall whether a solution was found. This afternoon I remembered the "snap" and ran through the video.

The result is for all to see in the following video. I have loaded it onto the website :

http://www.youtube.com/watch?v=2FILeqUP ... e=youtu.be

My landing at Altona .... tying my laces, and then takeoff....at 1:05 the snap - see what happened? The keelpocket does not "tense" uniformly, and then it does, snapping to the back. I looked at the landing but cannot see where the shift takes place.

I've looked at my Morningstar and Wintervogel take-offs, and in both the keelpocket tense uniformly and does not snap or shift.

Explanations!?

(I have better quality video if you want me to post it)

[DarkHelmet]

I had the inner batton ropes in the prop a while ago in some bad turbs

[DarkHelmet]

Is there any possibility of movement on the hang block?

[gertcoetzee]

No, I think the cause of the "snap" is clear in the video - the keelpocket "unfolds" and shifts back. There is no backward-forward movement of the hangblock as far as I can see.

I have downloaded the essential 7 seconds in high resolution to the website - (7MB)

http:/www.zu-dve.com/videos/keelpocket.mov

Loop it & keep eyes on keelpocket, wheels up..

No, I do not think it is movement of the batton ropes, or the tension cables.

Also have a look at a subsequent takeoff - note where the wing and keepocket becomes taut - when I press the bar out. (1.2MB)
http:/www.zu-dve.com/videos/wintervogel.mov

On the "snap" occasion, the wing does not become taut immediately - did I get airborne too close to stallspeed?

[bobthebuilder]

Is this a new problem, or something that occurs fairly often?

[gertcoetzee]

No, first time. Three takeoffs in this flip, only occured once. Numerous landings for months since I got the wing back for "Solowings".

[John Young]

Hi Gert,

Spreader bar cable was stuck under a bolt - gives an almighty "twang" when going back to normal.

Obviously on the ground you can't see what happened.

Regards
John

[Sad-Ham]

Had the same experience while flying my previous Aquilla.... turned out to be the spreader bar tensioner cable hooking on a bolt and then slipping back into place during flight. Not a nice feeling!!

[Gannet]

Gert, it looks like the aft end of the centre bar (keelbar?) is not carrying the weight of the sail until the snap, then it it fully supports the sleeve under the bar. This is very clear in your still pic above. Right after you pass the tree, after the the snap, you can see the full weight being carried.

Hope this helps you in narrowing down the area to examine more closely.

[Biggles]

I'm with SAD HAM and John. Something got caught and then released. The sudden push forward on the bar probably did it. I am not familiar with these wings so check what possibly could get caught like that and take weight of the keel pocket.

[Petrodactyl]

Hi Gert

Something which I have had happen to me on an Aquilla is where the top surface of the wing hooks up on (and then pops loose from) the 2 plastic guides for the spreader bar tension strings on the bottom of the kingpost. This would explain the keel pocket tightening up as well. When it happens, your nought tries to eat your underpants!

Check it out

[BOATCH]

I agree with Sad ham and John Young

[Gadget]

Hi Gert.

I had this problem on a couple of occasion on my aquilla 1 wing. It was caused on seperate occasion by two different faults. When the snap effect first came about it was due to a bent shock that got stuck. After my instructor and I nearly crapped ourselves and he said he is not flying the bird again until I find the problem and rectify it, i took the shocks off and recreated the problem. Once this was fixed it was quite for a time.

Now as you know I have packed up and deployed that wing a couple of times and shortly after one of these deployments the snap was back, albeit more pronounced. After doing something to the effect of 50 take off's etc I found that the spreader cable got stuck on the two hooks on the king post, and sometimes it slipped past them. In my understanding they should not be able to go past the hooks but they did. The hooks also looked quite worn. I replaced them and have not had the same issue since.

Good luck in finding yours.

Gadget

[lamercyfly]

Hi Gert.

Yes, the snap is not lekka.

Happens when the spreader bar cable hooks under the J bolt head, and then anytime from lift off till about 5 seconds later at about 100 feet this terrible 'snap'. You hear it, and feel it.

Has happened plenty times.

Your keel pocket will be loose as the wing has not 'risen' to its 'inflight position'. The wing also 'rolls' forward on the frame in full flight configuration, so there will be a forward movement noticed when the spreader bar cable releases and the wing progressess to 'full flight configuration'.

I solve the problem by using a bungee to loop around the two spreader bar cables so that they cannot drop drop below the J bolt.

Happens when you taxi. I always look up to make sure they are not hooked before I start my take-off run, but even then, while accelerating for rotation, the cable has hooked. Happens especially on rough runways.

Sometimes I have had the cabler hook under the butterfly nut on the J bolt. There it stays for good, and the only way you will suspect it is that your wing handles kak! Huge dynamics come into play when the root of the wing does not rise to it's correct camber position. The 2 lugs on the kingpost are what set the rise of the spreader bar and in turn the 'rise' of the root section of the wing. Some kingposts no longer have the lugs, but 2 guide through which the cables run.

I have witnessed very, very loose rear upper rigging, and were these aircraft to have very slack flying wires(whilst on the ground), this combination could quite easily lead to an inflight situation described above.

A very important fact this, as the kingpost can be pulled up and off the keel by the upward force imparted by these spreader bar cables, if the upper rigging is not standard. This will result in a fatal accident.

Fortunately there is a downward force on the Kingpost, exerted by the reflex cables. All in all, EVERY COMPONENT MUST BE IN STANDARD CONFIGUATION for the aircraft to be airworthy and safe. My sad experience is that not many folk understand the dynamics of flex wings, and aircraft are passed fit that come to me in shocking state..

Cheers.

[gertcoetzee]

Dave

Thanks for the explanation.

Yes, I am one of the guys doing the flying, with little thinking about the dynamics of the wing. This wing has been re-done and tested by Solowings after my crash last year, so I have no reason to believe it is anything other than the spreader cables over the J bolt as you explained. Will check that and do the bungee thing. Thought it quite nice to have the event on camera and to share with others.

Gert