New Door Seal Humming

[0TreeLemur]

We installed the new door seal on our M20C yesterday afternoon.    We used the Knots2U seal based on what I read in  @Marauder's New Door Seal thread.  We bought their adhesive and remover. 

This evening we took her for a test flight with a short hop for a $100 enchilada plate and some cheap avgas.  The new door seal is working better.   The old HD seal was so poor that the front seat passenger shirt tail would get sucked out under the door.   That doesn't happen any more.  However...

On final approach to our destination we noticed a baritone hum coming from the door.  The pitch and intensity changed slightly with airspeed, and the sound became intermittent when encountering turbulence.  Definitely a new sound, which means it is the door seal- that is all we have changed.

On the trip back the noise was a bit louder- happening over a wider range of airspeeds, seems like whatever is vibrating is getting better at it.

Upon landing, we inspected the seal and it is still adhered to the door.  No obvious changes there.  

We installed it according to the instructions, which was to install the "L shaped" seal with the thick part adjacent to the a/c skin.  Abut the door frame except near the hinge, when the seal shall be installed as near to the hinge as possible.    The sound seems to be coming either from the area of the door hinge or maybe from the seal at the bottom of the door.    Anyone dealt with this?   I don't think that the seal is quite thick enough for our a/c.  My guess is that the part of the L we installed by the hinge, that is not next to the skin or the door frame, is what is vibrating.  My gut tells me to either backstop it with some intermittent beads of silicone, or thin HD door seal material.

Please, somebody has to have troubleshot a solution for this issue already??? 

[hypertech]

I also think this seal might be a little too thin in places and/or my door on my M20R has a larger gap than it is supposed to.  I didn't have a buzz but I did have a leak after installation.  I wouldn't put a bead of silicone on anything.  That sounds like a mess and/or way too accidentally glue your door shut.  Something like this might help:

 

https://www.amazon.com/gp/product/B078H8Y95X/ref=oh_aui_search_asin_title?ie=UTF8&psc=1

[LANCECASPER]

I'm impressed. I've never had one really even seal, let alone hum, much less hum baritone. That seal may have been trained at Sea World.

[Bryan]

I had a hum in my previous 231 but it turned out to be the door keeper/slide (sorry don’t know the official name) but the metal slide that keeps the door from opening all the way. It would vibrate against the door jam at certain harmonic RPMs of the engine. Took several flights to figure it out.

[0TreeLemur]

11 minutes ago, Bryan said:

I had a hum in my previous 231 but it turned out to be the door keeper/slide (sorry don’t know the official name) but the metal slide that keeps the door from opening all the way. It would vibrate against the door jam at certain harmonic RPMs of the engine. Took several flights to figure it out.

Huh- I didn't consider that.   The frequency I'm hearing seems like it would be most likely a seal.

[DXB]

On 3/10/2019 at 9:59 PM, Fred₂O said:

This evening we took her for a test flight with a short hop for a $100 enchilada plate and some cheap avgas. 

On the trip back the noise was a bit louder- happening over a wider range of airspeeds, seems like whatever is vibrating is getting better at it.

Are you sure the "vibration" wasn't a physiologic response of your passenger's digestive tract to the enchilada plate?  

FWIW, I didn't have this problem after the door seal was changed but the door sure was tough to close for a while.  Whatever pressure point is causing the vibration may resolve as the seal compresses.

[LANCECASPER]

Here's what seals sound like when they are humming. . . 

 

[0TreeLemur]

IT SOUNDS JUST LIKE THAT!!!   Especially when the wind noise picks up and accompanies the seal humming.

[Andy95W]

32 minutes ago, Fred₂O said:

IT SOUNDS JUST LIKE THAT!!!   Especially when the wind noise picks up and accompanies the seal humming.

That's great that you identified the problem!  Now you just have to get the humming seal out of your baggage area...

[0TreeLemur]

Followup- After a weekend of trial-and-error work, the source of the buzzing was identified as the thin (0.025") aluminum angle trim that was fastened to the bottom of the door frame with screws about 4" o.c.  High speed air leaking out through the gap between the door frame and door, past the lower-aft corner of the door was causing it to vibrate between screws.   Inserting something thin like a credit card into the gap there would stop the hum/vibration/buzz. 

Tried a layer of gasket material under the aluminum to decrease the gap, negative effect.   Inserted about 8" of the stuff recommended by @hypertech and it worked- mostly.   On the fourth flight test it only made noise intermittently when turbulence would flex the craft and change the gap/airflow under the door- then it would buzz for a short time.   After that flight, I peeled off the paper and stuck the black high-density seal strip/tape to the aluminum before screwing it down.   I'm thinking that the added mass of the elastomer will damp the vibrations of the metal.  Next flight will tell.  

In summary- changing the door seal was a good idea.  What was there was a CB HD POS seal installed by the PO, and it just didn't work very well at all.   The new seal has cut the air flow considerably.   The buzzing problem that resulted was a nasty problem requiring trial and error.   The location where the buzzing/humming sound was being created was hard to detect with just ears alone.  It required feel.  Inserting a thin plastic item like a credit card into the gap really allowed us to narrow down the source.  As an added benefit, the interior of the cabin is slightly less noisy.   Still really loud when the ANR headphones are removed.

Thanks to @hypertech  and @Bryan for the positive suggestions and @LANCECASPER for the humor!

[LANCECASPER]

1 minute ago, Fred₂O said:

Followup- After a weekend of trial-and-error work, the source of the buzzing was identified as the thin (0.025") aluminum angle trim that was fastened to the bottom of the door frame with screws about 4" o.c.  High speed air leaking out through the gap between the door frame and door, past the lower-aft corner of the door was causing it to vibrate between screws.   Inserting something thin like a credit card into the gap there would stop the hum/vibration/buzz. 

Tried a layer of gasket material under the aluminum to decrease the gap, negative effect.   Inserted about 8" of the stuff recommended by @hypertech and it worked- mostly.   On the fourth flight test it only made noise intermittently when turbulence would flex the craft and change the gap/airflow under the door- then it would buzz for a short time.   After that flight, I peeled off the paper and stuck the black high-density seal strip/tape to the aluminum before screwing it down.   I'm thinking that the added mass of the elastomer will damp the vibrations of the metal.  Next flight will tell.  

In summary- changing the door seal was a good idea.  What was there was a CB HD POS seal installed by the PO, and it just didn't work very well at all.   The new seal has cut the air flow considerably.   The buzzing problem that resulted was a nasty problem requiring trial and error.   The location where the buzzing/humming sound was being created was hard to detect with just ears alone.  It required feel.  Inserting a thin plastic item like a credit card into the gap really allowed us to narrow down the source.  As an added benefit, the interior of the cabin is slightly less noisy.   Still really loud when the ANR headphones are removed.

Thanks to @hypertech  and @Bryan for the positive suggestions and @LANCECASPER for the humor!

The credit card comes in handy for all things aviation.

[Yetti]

The door was leaking a bit 4 years ago.   Installed a couple of strips in strategic places.   Still good 4 years later.  https://www.homedepot.com/p/M-D-Building-Products-5-16-in-x-17-ft-All-Climate-Auto-and-Marine-D-Profile-Weatherstrip-01025/202066509