15B VNE

[Kevin Koch]

Hi

I own a 15B composite. It has the 15B fuse and 15 wings and tail.

I am having a great time flying it and now that I have some good hours up I decided to push it to VNE which according to the manual is 120 knots. Once I reached 90 knots all hell broke loose with major pitching. The CFI who was watching from the ground said that the wings were "flapping" up and down. Once I got the speed off, control was reagained and all was smooth once more except the top of my head.

Has anyone had a similar experience and/or does anyone have some advice as to what might have happened?

Cheers
Kevin

Post edited by: KFK, at: 2008/09/21 14:16

[Scott Alexander]

Oh SH1T!!!!

I just bought an ASW-15B last friday.  It scares me to think that this can happen going only 90!  That's really not that fast.

Here's a couple of questions.

Has the Balsa spar Fungus AD been complied with?  Maybe the structural integrity of the wing isn't too good.

Was the tail mounted on really really good and tight?

Are all your control cables solid?  Maybe something got loose.

How many hours do you have in yours?  I haven't flown mine yet.

[Scott Alexander]

Oh...one more thing....did you by chance hit a bump of turbulence?  Was it a smooth day?  Maybe you hit some turbulence going through 90 knots.

[Kevin Koch]

Hi Scott

Don't think you have anything to worry about. One of our club members has GN (picture above) and he has no problems at 120 knots. The engineers seem to think that it is in the aileron settings. I had the control bearings replaced last month and we aren't sure whether something has taken place at that stage.

The 15B glides beautifully and I had just completed a 2hr flight when I decided to have some excitement. We will find the answer. I'm sure it is something simple.

The glider is in excellent condition and yes the wings have ben inspected for mould etc and there are no issues with structural integrity. I only have around 15hrs in the 15B but I have 100hrs in various gliders including PW5's, Blaniks and k6's.

I did ask myself about turbulance but the "flapping" of the wings tends to rule that out. There was only little turbulance and it was light and occasional. I have flown in some wild rotor getting into wave and it was nothing like this

Post edited by: KFK, at: 2008/09/22 16:31

[Johan van Ravenzwaaij]

Hi Scott,

Congratulations with your ship! :woohoo:

You don't have to worry about kevins story, my 15 flies beautifully till Vne.

Kevin Koch wrote:

The engineers seem to think that it is in the aileron settings. I had the control bearings replaced last month and we aren't sure whether something has taken place at that stage.

Kevin, it looks like you have some space on the joints and/or connections of your ailerons. If you have any room at the hotellier connectors, they must be replaced. There is an AD for that.
Also, I noticed that the control system behind the backseat is fixed to the hull with small wooden blocks. These bocks can shrink in time due to dehydration. This will cause some slack. Just fasten the bolts to fix this.

Kevin, please keep us updated!

[Kevin Koch]

Thanks for that Johan

We'll certainly look at it

[Geoff Gaddes]

Hey Kevin!


 I have recently done up ASW 15 (A) ZKGGO! S/N 15069. I have managed to push it to 120 knots just about most flights and have never came accross any real flutter etc! Ive seen GKB a few times and it is tidy! So its got to be a minor issue, like control deflections etc!

Cheers

Geoff Gaddes

[Kevin Koch]

thanks Geoff

[Chris Norman]

I would wonder if it was Pilot induced ossolation. At 90kts I would brace my hand with the other hand. I suggest you check for play in your control runs and if all is well try again approaching 90 with care and be ready to ease the nose up if the pitching is not caused control input.