0TreeLemur

Thanks Anthony! That is one of the best written patents I've ever read. Extremely easy to understand. No need to take one apart now. Still impressive- those jewel bearings are pretty darn low friction!

Resurrecting this important thread because I'm planning to install new side window and door window before it gets too hot... This thread is full of good information.

It would be mucho fun to take one apart and see what makes it tick. Anybody have an old non-working one they want to get sacrifice in the name of inquiry? I'd post photos of the disassembled unit.

Can anyone point to a link showing the internals of a card compass? I find it to be a quasi-magical device and would like to know more about how it works. How can they connect a shaft to a magnet that produces enough torque to turn a shaft subject to the ridiculously weak strength of the Earth's magnetic field, all in a turbulent/vibrational frame? A whiskey compass I get. The card compass seems to good to be true. Like there must be some hidden wire importing electrons to run some kind of amplifier and stepper motor.

Applying lube to the socket can only help. And the collar. And the other socket too. Take a can of lube with you and a helper next flight, or do it when next on jacks.

That's slooow. If you think to, please let me know who that is, and how it turns out when finally done. I'm going to have to find a new person/shop to do my next annual in Dec.

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!

When we calibrated the senders last year, the data don't show that effect. The first 3/6 data points are pretty much on a straight line.

Follow up: Investigation found no signs of mud in pitot tube. Drain is open. Whatever it was is gone now.

Also- Be careful when you switch it on. That Turbo Encabulator functionality was ultimately discontinued because of the risk it was determined to pose to the local space-time continuum.

My 67C has a footwell light. When I added a dome light switch, I discovered that the power for that light actually goes up to the dimmer in the headliner then back down to the footwell. Surprise! That switch seems like an add-on. I'm guessing it enables the Turbo Encabulator "synchronized cardinal grameter" function. That was a thing in the 60's. Google it.

I was trying to figure out what the units of at "gozinta" are....

Which reminds me of my favorite sociology joke: I only hate two kinds of people. Those who are intolerant of other cultures- and the Dutch.

nerds.

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

Last year we put in an EDM900 in our M20C and took out a bunch of redundant stuff. Items removed included: Garwin instrument cluster, MP/FP gage, tach, carb temp gage, EGT gauge and switch. We went through the wiring and removed a pound or so of disused wiring and connectors. The Hartzell prop gov was replaced with the compact and lighter PCU5000. I was certain that in the process of all this change/modernization we would gain useful load. My A&P Dave (RIP) was pretty certain not. No wager was placed, but I would have lost if a wager were made. The a/c w&b logs gave the accumulated/calculated useful load of 986 lb. We drained the tanks by removing the sump valves. Then we carefully leveled the a/c according to the Service & Maintenance Manual. The recently purchased digital scales were double checked. The result said that the UL was 945 lb after subtracting out the weight of the oil. Leaving in 8 qts of oil, the UL is 931 lb. As a card carrying engineer, I verified the level and performed the moment calcs following the procedure in the SMM. Why was the a/c 41lb heavier? A discussion ensued around the shop about the difference. Maybe we left a few lb of gas in the tanks when we pulled the sump drains. The sump drains are located so that when the plane is sitting at normal ground angle they are very near the bottom of the tanks, so we probably left no more than maybe 1/2 gal per side. So that's maybe 6 lb gained back. Looking at the logs, when the a/c was painted in 2004 they stripped the paint off the removable cowl parts and rough sanded the rest before repainting. The paint that they left on could easily weigh 20-30 lb, maybe a bit more depending on thickness. Also, I had put on Michelin tires that are about 1 lb each heavier than the originals. An a/c will gain 1/2 oz of weight per year by accumulated grease, dust, residue, mud dobber nests (e.g. Since weighing I've excised 0.5 to 1 lb of mud-dobber nests discovered since then. That gain can add up to a few pounds over 50+ years of "if a little grease is good, a lot is better". Paint. Tires. Mud dobbers. It all adds up.

Good job! The previous owner of my M20C went through the same process as you with the same result. The PC system w/ Accutrak II is amazing.

Yeah, yesterday my wife deduced that the dobbers where getting in there. Should be a seal there! Ours has decayed to nothingness. Don't see anything on LASAR.com

For those who like the smell of old airplane enough to want to sleep with it??

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

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???

After my flight instructor complained about getting cold sitting next to the door, we put a new door seal on yesterday. The old, leaky HD door seal was installed a few years ago by that same instructor, but that is another matter... In the process we took the door interior door liner off to avoid messing it up any more than it's 50+ year old self is already messed up. Look what we discovered inside the door! This huge mud-dobber nest (how did they get in there???) weighs about 1/3 of a pound. Judging from its roundness, has been rolling around inside the door frame for years. Taken together with the large one I found last annual behind the rat sock in the main wheel well, I've removed more than a pound of mud dobber nests. This one would not fit through that hole, requiring screwdriver-assisted disassembly and vacuum extraction.

"Free" is an optional interpretation. I donate, don't you? Anything to not see advertisements for @Marauder's ladies.

The pudding:

Not in the same thread. One in General Mooney Talk, and the other in Miscellaneous Aviation Talk. Search result: