Avanti Piaggio cabin noise measurements

For folks who’ve been beguiled by press releases from Otto Aviation, the Piaggio Avanti is a reminder that most of the great ideas in aerodynamics were implemented in the 1980s. The Piaggio designers threw out the rulebook on what an executive turboprop should look like and came up with a three-wing plane that goes 100 knots faster and 10,000′ higher using the same engines as a (two-wing) King Air.

The folks behind Piaggio have long claimed that the Avanti is exceptionally quiet inside, throwing out a 68 dBA number that never seemed credible.

A friend owns a 1992 Piaggio and graciously took me up to 17,500′ to make some measurements. Note that the company claims that the latest Evo model, which has a more advanced Hartzell propeller shape, is actually “20%” quieter. My friend says that a 2008 Piaggio that he flew was noticeably quieter than his 1992 model, so there may actually be three levels of Piaggio Avanti interior noise and the numbers below are the worst that one will ever see.

At Pilatus PC-12 speeds, i.e., 289 knots (222 indicated), sound at the pilots’ ears was about 72 dBA and up to 76 dBA in the passenger cabin (closer to the props spinning on the back of the main wings; closer to the door that whistles a bit (there is a trick to sealing it with a cloth that we didn’t apply for this short flight)).

At 311 knots (240 indicated), cabin noise was 1-2 dBA higher.

The owner says that the plane is noticeably quieter at its normal long-distance cruising altitudes so it is possible that the 68 dBA number is real at FL410! (He’s usually at FL370 and 370 true on 580 lbs/hour; against a headwind (and there is always a headwind because G*d hates pilots!), this is less fuel per mile than a single-engine PC-12.)

Should we all be envious of Piaggio Avanti owners? The plane is more complex to operate than the newest twin-engine turbojets that are certified for single pilots. There are switches to turn on the bleed air, for example, that typically should be thrown just before taking the runway (you’re probably taxiing with a tailwind and the result of leaving the bleeds on is some exhaust smell in the cabin). The steering has two modes, controlled by a switch on the yoke, and one is used for taxi while the other is used once 65 knots is reached on the takeoff roll. There is an autofeather mechanism that will reduce drag from a dead engine and it needs to be verified operational. Speeds are terrifying from a Pilatus PC-12 or even a Cessna Mustang pilot’s perspective. Rotate at 110 knots. Vmc is 100 knots (you can’t fly slower than this with one engine at full power and the other dead with prop feathered), final approach speed is 120-125 knots. The plane slows down very effectively with beta (twisting the prop blades to get some reverse thrust) and therefore a 5,000′ runway is plenty, but it will never compete with a Pilatus or King Air for short field performance. The Piaggio is also the wrong machine for grass, dirt, and loose gravel runways (see Burning Man for turboprop pilots for what a PC-12 can easily do if the Bay Area heroes are ever brave enough to gather again).

My friend says that the cabin is bigger than the PC-12’s (see diagrams below), but it felt smaller to me. Maybe it is the lack of a flat floor. Certainly you’ll never appreciate the genius of the Cirrus Vision Jet designers in making the pilot seats slide back 4′ until you’ve tried to get in and out of a Piaggio front seat. The pedestal extends all the way back to the seatbacks. Unless you’re a 5’2″ tall Italian yoga instructor, I’m not sure how it can be safe to get in and out during flight (without knocking a lever or switch). There is a bathroom all the way in the back, but it is not externally serviced (i.e., the owner-pilot of the $8+ million new Piaggio Avanti Evo will end up carrying a bucket out of the plane…).

The ice protection system is far better than on most newer planes. There is an automatic ice sensor that turns on the boots that protect the engine inlets. The main wing is heated via bleed air. The front wing is electrically heated. The tail is left alone and somehow the plane passed all of the certification tests and also has worked well in the real world (the Italian military operates some with more than 15,000 flights hours). (The HondaJet has a sensor-activated anti-ice system; most airplanes rely on pilots to use their eyes to notice ice building up and then set switches correctly.)

The pressure differential is 9 psi, enabling a sea level cabin up to 24,000′ and 6,600′ cabin altitude at FL410. Compare to 5.75 psi on the PC-12 and a cabin altitude of 10,000′ when the plane is at its service ceiling of FL300.

The older planes can be converted to dual Garmin G600TXi for primary flight display, but, due to the small number of eligible planes out there, there is no likelihood of Garmin certifying its modern engine instruments and GFC 600 autopilot. Below is my friend’s panel. Note the tall stack of warning lights right next to the tall stack of round dials for engine indications and remember that behind each warning light is a system that could suffer an intermittent failure that is challenging to troubleshoot. The old Collins autopilot is in the top center of the panel and the autopilot mode is currently indicated only on the lights above the switches (i.e., not on the PFD).

It would be interesting to see what could be done by upgrading the airplane with the latest GE turboprop (more fuel efficient and FADEC) and a lot more automation, e.g., changing the steering mode automatically, descending automatically in the event of depressurization (the latest planes with Garmin flight decks can do this), land itself if the old/rich guy in front croaks (trophy wife remains in middle seat and has reactivated her Tinder subscription before the flaps and gear are down), etc. If the number of switches and dials could be reduced to what you see in a Cirrus Vision Jet, and the service and support could be more like what the rest of the Jet A-powered world is used to, the Piaggio Avanti would live up to its revolutionary promise.

Some photos from our lunch-time excursion and the POH:

How does the above cabin cross-section compare to the PC-12?

If we assume 2.9′ as the mean radius of the Piaggio, that’s a cross-sectional area of 26.4 square feet. If we multiply the above numbers for the PC-12, we get roughly 24.2 square feet.

The PC-12 does seem to be longer in the back, 16’11” from the front of the passenger door to the rear of the cargo area. On the third hand, the Piaggio has a heated, but not pressurized, 67″-long baggage area behind the cabin.