what is that noise?

[gregv]

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-v2HmN4A&feature=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

[[email protected]]

It may be as simple as your fiberglass seat back rubbing against some part of the fuselage interior. Can you duplicate the sound while sitting in the cockpit on the ground?

[gregv]

Le lundi 22 juillet 2019 13:22:57 UTC+2, a écritÂ*:
> It may be as simple as your fiberglass seat back rubbing against some part of the fuselage interior. Can you duplicate the sound while sitting in the cockpit on the ground?

I don't think it is the seat back, no sound while sittin in the cockpit on the ground. Maybe I will try with somebody else moving /shaking the wingtip while sitting on the ground to check if I can hear that noise...

[[email protected]]

Another possible source of the noise might be the wing spars rubbing against each other. My Pegase made that sound, and then just to try to isolate it, I put a very light coat of cooking oil on any part of the spar that looked like it had been rubbed. Creaking noise was gone immediately, so I quit worrying about it.

[Ross[_3_]]

Sounds like the wings are about to come off.

Kidding, I would be looking for signs of rubbing anywhere. Canopy is always a good place to start as they expand and contract the most.
Spars are a possibility.
Seat back.
After that the options become less. Good luck hunting

[Michael Opitz]

At 10:39 22 July 2019, 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-v2HmN4A&feature=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
>
Possible rubbing of the canopy frame? The plastic canopy will
shrink when the temperature falls after flying for a while, especially
at higher altitudes in the mountains. You may only be able to
replicate the noise on the ground in cooler temperatures.

RO

[Tim Taylor]

Likely the canopy or spar. Clean the canopy rail and the area where it touches on the fuselage. A light coat of wax or a very thin open cell foam seal may help on the canopy. Check the spar for rubbing and wax any possibility areas.

[son_of_flubber]

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.

[gregv]

Le lundi 22 juillet 2019 16:07:24 UTC+2, Tim Taylor a écritÂ*:
> Likely the canopy or spar. Clean the canopy rail and the area where it touches on the fuselage. A light coat of wax or a very thin open cell foam seal may help on the canopy. Check the spar for rubbing and wax any possibility areas.

ok thanks, I think it is spar related, I will wax and check for rubbing

[[email protected]]

On Monday, July 22, 2019 at 4:01:58 PM UTC+1, gregv wrote:
> Le lundi 22 juillet 2019 16:07:24 UTC+2, Tim Taylor a écritÂ*:
> > Likely the canopy or spar. Clean the canopy rail and the area where it touches on the fuselage. A light coat of wax or a very thin open cell foam seal may help on the canopy. Check the spar for rubbing and wax any possibility areas.
>
> ok thanks, I think it is spar related, I will wax and check for rubbing

I used to have a Nimbus 2c. It was a long time ago but I still remember what I think is the same cracking sound you are describing. Quite loud and sharp. It never bothered me. Like you I thought it came from the spar stub area when there was a bit of turbulence.

[Mike C]

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-v2HmN4A&feature=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. ;^)

[Glidingstuff[_2_]]

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

[Delta8]

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

[Craig Funston[_3_]]

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

[Charlie M. (UH & 002 owner/pilot)]

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.....

[[email protected]]

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-v2HmN4A&feature=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

[ian]

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-v2HmN4A&feature=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.

[Bob Kuykendall]

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.

[Vaughn Simon[_2_]]

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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[[email protected]]

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-v2HmN4A&feature=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

[[email protected]]

I've heard that in hundreds of videos, more often in two seaters. Watch a few Duo Discus vids, you'll see what it mean. I believe it's almost certainly the spar stubs rubbing.

[gregv]

Le lundi 22 juillet 2019 12:39:11 UTC+2, gregv a écritÂ*:
> 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-v2HmN4A&feature=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

Ok so I checked carefully the glider on the ground and I seems I could reproduce the noise.

Lift Pins and bearings are ok, no rubbing clue on the spar neither on the fuselage. The noise is not related to outer wings.

When the airbrakes are open, there is no more noise... so it must be related to airbrakes... I can hear the noise coming from the airbrakes / flaps, and if I put my hand on them as they are closed and that I put the wing for and aft I can hear and feel the noise with my hand. When I inspect the airbrakes mechanism everything seems ok. Strange thing is that the noise is symetrical on both wings.

[Martin Gregorie[_6_]]

On Sat, 27 Jul 2019 06:32:03 -0700, gregv wrote:

> Ok so I checked carefully the glider on the ground and I seems I could
> reproduce the noise.
>
> Lift Pins and bearings are ok, no rubbing clue on the spar neither on
> the fuselage. The noise is not related to outer wings.
>
> When the airbrakes are open, there is no more noise... so it must be
> related to airbrakes... I can hear the noise coming from the airbrakes /
> flaps, and if I put my hand on them as they are closed and that I put
> the wing for and aft I can hear and feel the noise with my hand. When I
> inspect the airbrakes mechanism everything seems ok. Strange thing is
> that the noise is symetrical on both wings.
>
If that was my glider (I'm in the UK) I'd being asking the inspector who
does my Annual Inspection to take a look at it. Doing that in the past
has both found problems I've missed and shown that things I asked him
about were non-problems.


--
Martin | martin at
Gregorie | gregorie dot org

[[email protected]]

> > if I put my hand on them as they are closed and that I put
> > the wing for and aft I can hear and feel the noise with my hand. When I
> > inspect the airbrakes mechanism everything seems ok. Strange thing is

I'm reading this as you pull/push the wing tips for and aft and feel the noise in the airbrake system. If so, how much force, how much do the wing tips move and is there a spec limit for this in the poh or maint manual?

[Charlie Quebec]

On my DG200 fore and aft play in the wings is eliminated by shimming the lift pins. If a shim has come loose, and dropped of it could cause such issues.

[[email protected]]

What, if anything is supposed to hold the shims in place when the glider is in the unassembled state?

On Monday, July 29, 2019 at 11:00:28 PM UTC-5, Charlie Quebec wrote:
> On my DG200 fore and aft play in the wings is eliminated by shimming the lift pins. If a shim has come loose, and dropped of it could cause such issues.

[[email protected]]

On Tuesday, July 30, 2019 at 8:53:21 AM UTC-4, wrote:
> What, if anything is supposed to hold the shims in place when the glider is in the unassembled state?
>
> On Monday, July 29, 2019 at 11:00:28 PM UTC-5, Charlie Quebec wrote:
> > On my DG200 fore and aft play in the wings is eliminated by shimming the lift pins. If a shim has come loose, and dropped of it could cause such issues.

Gliders with removable lift pins have the shims under the shoulder of the pin.
UH

[John Wells[_2_]]

My Mini Nimbus creaks on hot days -- more if it's been left out in the sun

before launch. It sounds like flexing plastic to me, and I've always put it

down to the canopy expanding/contracting a different amount to the fus. I
think it goes away eventually in flight (or at least, I tend to only notice
it at
first).

Your video sounds more like a banging noise, but it's hard to tell from the

video... it could be the same creaking perspex noise I hear.

J

At 13:52 30 July 2019, wrote:
>On Tuesday, July 30, 2019 at 8:53:21 AM UTC-4,
wrote:
>> What, if anything is supposed to hold the shims in place when the
glider
>is in the unassembled state?
>>
>> On Monday, July 29, 2019 at 11:00:28 PM UTC-5, Charlie Quebec
wrote:
>> > On my DG200 fore and aft play in the wings is eliminated by
shimming
>the lift pins. If a shim has come loose, and dropped of it could cause
such
>issues.
>
>Gliders with removable lift pins have the shims under the shoulder of the
>pin.
>UH
>

[[email protected]]

I agree with a earlier poster that I would look in the airducting system Sounds like a vent cover or something hard but loose in the airflow.

[[email protected]]

The howling in the tail boom might be from air pressure coming in and it doesn’t have a escape.

You can try leaving the wing tape off at the trailing edge about one inch. It helped on my Lak.
W7

[Charlie Quebec]

On none removable lift pins, the shins are lightly glued on to the fuse wing fillet with contact cement or similar.
Be warned, too tight shims can make rigging very difficult in hot weather.

[[email protected]]

My Libelle has a floating shim on one of the lift pins and I'm afraid it will slide off and get lost during assembly/disassembly. Sounds like cementing it on may be the trick.

On Thursday, August 1, 2019 at 6:42:11 PM UTC-5, Charlie Quebec wrote:
> On none removable lift pins, the shins are lightly glued on to the fuse wing fillet with contact cement or similar.
> Be warned, too tight shims can make rigging very difficult in hot weather.