what is that noise?

On Monday, July 22, 2019 at 4:39:11 AM UTC-6, gregv wrote:
Hello, I fly a 1979 Nimbus 2 carbon, and since a few years I hear a cracking noise behind me. That noise occurs more often after a few hours of flight, maybe related to temperature change with altitude. You can hear the cracking noise in this video:

https://www.youtube.com/watch?v=pke-...ature=youtu.be

Did you already hear that noise? how do you think I can fix this ? do you think it is dangerous?

Thank you for help and advice

Sounds like the rain I was thermalling in on Saturday. ;^)

Check the incidence pins and bearings on the wings and fuse. They may have worn and are allowing the wing to move fore and aft as well as slightly up and down. We had the same issue with an ASH 25. Sounded exactly the same. After replacing worn pins on inner panel noise disappeared.

Paul

What a bunch of hypochondriacs it's the gear door slapping . Change the damn bungees .

On Monday, July 22, 2019 at 7:29:40 AM UTC-7, son_of_flubber wrote:
On Monday, July 22, 2019 at 6:39:11 AM UTC-4, gregv wrote:
Hello, I fly a 1979 Nimbus 2 carbon, and since a few years I hear a cracking noise behind me.

Count your blessings. I have a howling banshee in my tail boom.

Flub, what are you flying. I removed the V seals in my Nimbus 3 rudder one year and the banshee took up residence at speeds over 90 kts. Once they were replaced, the banshee was banished.

Cheers,
Craig JN

They usually change sound if you "rudder it a bit" in straight flight. More often than not, one bungee fails/weakens before the other. A yaw will tend to suck a door open if the bungee is weak.

Sorta like figuring out a failing wheel bearing in a car. Wide open road, do big S turns to load each side.....the loud side has the bad bearing.....

On Monday, July 22, 2019 at 5:39:11 AM UTC-5, gregv wrote:
Hello, I fly a 1979 Nimbus 2 carbon, and since a few years I hear a cracking noise behind me. That noise occurs more often after a few hours of flight, maybe related to temperature change with altitude. You can hear the cracking noise in this video:

https://www.youtube.com/watch?v=pke-...ature=youtu.be

Did you already hear that noise? how do you think I can fix this ? do you think it is dangerous?

Thank you for help and advice



I would agree to take that noise off your hands if you can give me those views along with it. :-)

Gary Osoba

On 7/22/19 12:39 PM, gregv wrote:
Hello, I fly a 1979 Nimbus 2 carbon, and since a few years I hear a cracking noise behind me. That noise occurs more often after a few hours of flight, maybe related to temperature change with altitude. You can hear the cracking noise in this video:

https://www.youtube.com/watch?v=pke-...ature=youtu.be

Did you already hear that noise? how do you think I can fix this ? do you think it is dangerous?

I used to fly a Nimbus, original II (without b or c). It was noticeably
noisy but maybe not the same sounds as yours. I would start by looking
for the obvious, check every piece of tape on the glider, over joints,
control surface hings and U/C doors etc.

One thing to try is applying rudder each way during straight and level flight, and see if that causes the noise. If so, the noise might be caused by the lift pins working in their sockets.

There is also remote chance chance that it might be a loose joint between the steel mid-fuselage cage and where it attaches to the composite fuselage shell. It's unlikely unless the ship has a damage history involving a very hard landing or a ground loop. But you might have your mechanic or tech take a good look at it during the next condition inspection.

--Bob K.

I always that that one of the advantages of airplanes over gliders is
that an airplane engine masks those potentially-concerning noises that
virtually all airframes make as they deal with normal flight loads.

Vaughn


On 7/22/2019 6:39 AM, gregv wrote:
Hello, I fly a 1979 Nimbus 2 carbon, and since a few years I hear a cracking noise behind me. That noise occurs more often after a few hours of flight,

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On Monday, July 22, 2019 at 6:39:11 AM UTC-4, gregv wrote:
Hello, I fly a 1979 Nimbus 2 carbon, and since a few years I hear a cracking noise behind me. That noise occurs more often after a few hours of flight, maybe related to temperature change with altitude. You can hear the cracking noise in this video:

https://www.youtube.com/watch?v=pke-...ature=youtu.be

Did you already hear that noise? how do you think I can fix this ? do you think it is dangerous?

Thank you for help and advice

The sound does not seem to me to be the usual lift pin type noise. I could not associate with apparent changes in loading of the ship.
For the heck of it I'd look for something in the ventilation system.
UH