Airways Posted June 28, 2019 Report Posted June 28, 2019 Yesterday I took my M20K up for its first flight since purchase. What drew my attention was how much louder the cabin noise was compared to a ‘90s M20J. I’m not referring to the difference in engine sound, but the general noise level in flight. I still have the original 1987 interior (and thus insulation). Has there been a significant evolution in materials being used nowadays ? Could I significantly reduce cabin noise by replacing insulation with the newest kind available ?
Parker_Woodruff Posted June 28, 2019 Report Posted June 28, 2019 This is an interesting observation as I first owned a 1990 M20J-AT and then a 1987 M20K and did not find any appreciable difference in noise. The M20K "felt" quieter due to lower vibration... If your door seals are bad, that could be a good place to start.
Shadrach Posted June 28, 2019 Report Posted June 28, 2019 10 hours ago, Airways said: Yesterday I took my M20K up for its first flight since purchase. What drew my attention was how much louder the cabin noise was compared to a ‘90s M20J. I’m not referring to the difference in engine sound, but the general noise level in flight. I still have the original 1987 interior (and thus insulation). Has there been a significant evolution in materials being used nowadays ? Could I significantly reduce cabin noise by replacing insulation with the newest kind available ? I can’t speak for what they were using for insulation in the late 80s. I can’t tell you but the fiberglass we pulled out of our 67F was as near to useless as makes no difference. We did the entir cabin in Super Sound proof. https://m.aircraftspruce.com/catalog/appages/soundproofinstall.php?clickkey=59594 If you were to remove the side panels in my aircraft the fuselage looks like a black closed cell foam tunnel. I fabricated the soft headliner pieces from the same material by covering them in Ultrasuede. Understand that a decibel or two is a huge improvement in an aircraft. We did ours over a decade ago, So no before/after decibel readings. I will do a reading this weekend with my phone app and see what it says. Once I have a number you can compare yours using the same app. It seemed quieter to us but “seeming” is not scientific. one thing that was dramaticly different was how it evened out cabin temperature. Most Fmodels have tremendous heaters. Before re-insulating we could keep the entire cabin warm but the front seat occupants would be cooking. After re-insulating I’ve had no complaints from backseat passengers even while cruising in the subzero OATs.
Skates97 Posted June 28, 2019 Report Posted June 28, 2019 43 minutes ago, Shadrach said: I can’t speak for what they were using for insulation in the late 80s. I can’t tell you but the fiberglass we pulled out of our 67F was as near to useless as makes no difference. We did the entir cabin in Super Sound proof. https://m.aircraftspruce.com/catalog/appages/soundproofinstall.php?clickkey=59594 If you were to remove the side panels in my aircraft the fuselage looks like a black closed cell foam tunnel. I fabricated the soft headliner pieces from the same material by covering them in Ultrasuede. Understand that a decibel or two is a huge improvement in an aircraft. We did ours over a decade ago, So no before/after decibel readings. I will do a reading this weekend with my phone app and see what it says. Once I have a number you can compare yours using the same app. It seemed quieter to us but “seeming” is not scientific. one thing that was dramaticly different was how it evened out cabin temperature. Most Fmodels have tremendous heaters. Before re-insulating we could keep the entire cabin warm but the front seat occupants would be cooking. After re-insulating I’ve had no complaints from backseat passengers even while cruising in the subzero OATs. I did the same thing with my plane. I don't know about the improvements in sound but the temperature improvement was significant, both in staying warmer in the winter and cooler in the summer. I think it is worth it for that factor alone, even if there is no sound improvement. 1
LANCECASPER Posted June 28, 2019 Report Posted June 28, 2019 In '94 when Mooney went with the Fiberglass interior panels over the old Royalite that made a difference in sound. Maybe it was better insulation behind the panels or just one less noise competing (plastic vibration, metal vibration, wind, engine), but it definitely was better.
Airways Posted June 28, 2019 Author Report Posted June 28, 2019 I didn’t even think about temperature control. Good point ! Door seal might need some replacing as well...
bradp Posted June 30, 2019 Report Posted June 30, 2019 Also note that 1) the majority of the decibels originates at the firewall. This is very difficult to insulate and access. 2) the floor is not insulated with the exception of carpet on the early models at least. This is a giant heat sink.
M016576 Posted June 30, 2019 Report Posted June 30, 2019 On 6/28/2019 at 11:47 AM, Parker_Woodruff said: This is an interesting observation as I first owned a 1990 M20J-AT and then a 1987 M20K and did not find any appreciable difference in noise. The M20K "felt" quieter due to lower vibration... If your door seals are bad, that could be a good place to start. I had the same experience going from my M20J with a 2 blade to a Missile with a 3 blade prop.
carusoam Posted July 1, 2019 Report Posted July 1, 2019 Inviting Phil @pmccand to stop by this thread. It may be interesting to him... Best regards, -a-
bradp Posted July 4, 2019 Report Posted July 4, 2019 Guy I used the same foam just no velcro - I cut it to shape and it sits nicely behind the steel cage and in front of the fuselage skin
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