Amazing that the only thing you hear is the wind rustling by.
Silent planes would be welcomed by many people living in densely populated cities with high air traffic.
They're almost giving away apartments near Pearson Airport in Toronto, for example.
The price per square foot in that area is ~10x lower than the rest of the city and for good reason. (You are constantly bombarded by the sound of jet engines passing by).
Props still make significant noise, especially at takeoff RPM.
A friend of mine owned a house under the approach path to a medium-volume reliever airport (KBED). All of the piston airplanes that flew overhead were perfectly pleasant (at least to me), but the jets were notably more annoying.
Carrying more power/noise, more speed, and more disturbance to stay flying while dirtied up, the difference was night and day. I suspect the PT-6 powered C208 would already fall on the “not so annoying” side of that spectrum (closer to the piston props than the turbojets’ noise profile), so changing fuel might not provide that much relief to those who bought houses near airports.
I have a theory that we'll be able to reduce the RPM and increase the torque of these engines, versus conventional gas turbines and piston engines, thereby reducing the tip speed of the blades
Maybe. The PT6A already has a gearbox, so the engineers are presumably able to choose a reduction ratio and prop RPM quite independently of the gas and power generator rotational speeds. (There are still torque limits in the gearbox output, though it seems the same constraints would face an electric motor.)
In most planes, pilots are already able to chose their propeller RPM somewhat independently of torque by varying the pitch of the propeller. However, pilots typically optimize for rate of climb and not noise in order to get out of the low altitude / low airspeed danger zone as quickly as possible.
Yes. What GP is talking about though is changing the range of speeds available for pilot selection by changing the prop length, airfoil, maybe number of blades, and other design parameters. IOW, the design elements, not so much the operational element. Similar to how the C421 cruises at 1800-1900 prop RPM to give a(n eerily) quieter cabin.
Considering the rate at which the general aviation fleet turns over (~none in ~forever), and that the typical Cessna is flying around with a World War 2 engine or its closely related descendant, I predict that it will be roughly infinity years before people who live at the ends of airports stop cursing the noises.
Of course, if they just outlaw 100LL avgas and pass some noise regulations the problem will solve itself.
I was never clear on why leaded avgas wasn't banned long ago. I know I've run across information on the internet about aircraft engines that can run on unleaded.
You can read these other replies, but the shorter explanation is that the AOPA is in all relevant respects the NRA but with aircraft instead of guns, and the owners have achieved cold-dead-hands status with their obsolete planes.
Not accurate. The AOPA typically takes positions that protect public safety, such as opposing Trump’s attempted giveaway of our ATC to the airlines.
However, the GA industry should be condemned for its failure to face the writing on the wall about leaded gas, which has been obvious since the ‘70s. On the other hand: Until recently, stifling certification requirements made it nearly impossible for these low-volume manufacturers to innovate.
Nobody wants leaded gas.
The other sham being perpetrated is advertising some plane engines as running on “automotive” gas. This is BS, because that means only PURE gasoline, not gasohol. I challenge you to find a gas station selling 100% gasoline. I haven’t seen that in decades. So the touted “mogas” is nearly as much of a niche fuel as 100LL.
I’m not entirely sure I buy this argument. Ban it effective on a fixed date in a few years and introduce a favorable regulatory regime to help with replacements. If some planes won’t be able to fly, so be it.
Alternatively, introduce a Pigouvian tax: charge an obscene and increasing amount to burn leaded fuel.
This is kind of like the regulations that permit grossly polluting old collectible cars to operate. Sure, they have history, but that’s not a sufficient excuse to allow them to operate unmodified near other people.
Most piston engine aircraft in the country require, by regulation, 100LL. Oil companies and the FAA have been working for years to develop a replacement and came very close a couple years ago, but since the FAA strongly favors safety and reliability over almost any other consideration it takes a very long time to collect enough data to have confidence a potential replacement is truly equivalent. We have ~80 years of safety data for 100LL.
Generally speaking, airports are reluctant to spend money on a second set of tanks, pumps, etc. required during a transition period; though some have - particularly in the midwest where there are a lot of less regulated homebuilt aircraft that can burn alternative fuels.
A lot of pilots would love to burn something else. 100LL is relatively nasty and builds up in engines, shortening their life. It's even actively discouraged to burn 100LL in some more modern small aircraft engines like the Rotax 912 and pilots like myself who run that engine look for non-leaded fuel whenever practical because it's healthier for the engine. But well maintained aircraft last just about forever and the legacy fleet is absolutely enormous.
"...it takes a very long time to collect enough data to have confidence a potential replacement is truly equivalent. We have ~80 years of safety data for 100LL"
It sounds odd to put it this way, because leaded gasoline started being phased out over 40 years ago. In an alternate universe, we would now have 40 years of safety data for unleaded and for leaded.
> we would now have 40 years of safety data for unleaded and for leaded.
When lead was banned in auto gas, it was replaced by MTBE, which itself was banned in most states by 2007. The alternative to MTBE is Ethanol, which is currently used in auto gas. But Ethanol is incompatible with aircraft because it is corrosive to aluminum (and tends to cause more serious vapor-lock problems in fuel lines).
In other words, there's no widely-used blend of fuel that could even potentially have 40 years of safety data. Pilots are already used to paying a lot for fuel (more than auto gas), so there's money at stake if someone can come up with an unleaded alternative. It's just that someone has to invent that safe alternative first.
On top of that, fuel is a particularly sensitive issue to the FAA because fuel and engine malfunctions are currently the 3rd and 4th leading causes of aircraft accidents (and this is after the FAA has spent decades on safety programs to reduce fuel-related accidents).
I was generally aware of MTBE, but I didn't know it was universal since the 70s nor necessary for all grades of fuel. What about iso-octane?
Also, I happen to have a car from the 80s and in looking for information about the consequences of using fuel with ethanol, some say it can be a problem while other people say at that point in time it was designed to handle it. So I'm not clear on what diversity there was in the types of fuel available over time.
Piston airplane engines typically (but not universally) have high compression ratios, so they require fuel with a high octane rating. In fact, the only avgas that contains lead today is 100LL (100 octane, low lead).
If you want to have a discussion about lead in avgas, you're having a discussion specifically about 100 octane fuel.
> What about iso-octane?
Definitionally, 100 octane fuel has anti-knock properties similar to 100% iso-octane. You may be able to make an approximately-100% iso-octane blend for lab tests, but it's not really possible to manufacture it in commercial quantities.
Keep in mind, "premium" auto gas is usually less than 93 octane, and even that has ethanol.
The problem is there hasn't been a suitable 100-octane unleaded replacement until very recently (see: G100UL or UL102), and lower octane fuels cause detonation. Last I checked, how well the replacements perform is still an open question.
Everyone in aviation wants to get off 100LL fuel, we're just waiting for the FAA to certify one of the replacements as safe.
We also know that 100LL is shelf-stable for years and is compatible and safe (from the perspective of those riding in the plane) to use with just about every piston aircraft engine in existence. We don't yet have enough data to know if that's the case for the potential replacements. Automotive gasoline is too low-octane and not stable enough to be used most aircraft, which for some aircraft results in engine failure in flight. There are ongoing efforts to develop an alternative aviation fuel blend, but as I mentioned previously - this takes time.
A couple years ago we got close to having an approved alternative - Swift Fuel's UL94. However as an example for why this is hard: one of the objections to that fuel was that it didn't weigh the same as 100LL, meaning its use would alter weight and balance designs of the aircraft that use it. For most airplanes that's not a big deal, for some it is.
We have 80 years of aircraft flying around designed more or less around the characteristics of one specific fuel blend and most of those aircraft have decades of life left in them. We all want to get off 100LL, but we also don't want aircraft falling out of the sky as a result.
But in aviation you're not only worried about the knowns, but also the unknowns. Example: JAL 123, BA 38, TWA 800 and other cases where you believed things to be safe but in reality they were a ticking time bomb and/or would trigger in very weird conditions.
I’m an owner and pilot of one of the previously mentioned planes that run on leaded fuel. The current issue with your plan is that for a vast chunk of the GA fleet there is no certified alternative to leaded fuel. Some planes have supplemental type certificates (STC) available that allow them to burn unleaded fuel, but many do not (such as my Grumman Tiger). It’s not just the engine, it’s the fuel system in the plane that must be certified- this is not just a paperwork drill, there have been failed certification attempts because the fuel system couldn’t deliver enough fuel pressure at certain temperatures.
The FAA is required to evaluate the impact of new regulations on the existing fleet. A change that would eliminate or place a prohibitively high tax on leaded fuel would likely be shown to eliminate half of the GA fleet. This will not be approved until the impact can be reduced. Developing and certifying new engines and fuel system components for all the different aircraft type certificates is totally infeasible; a new fuel substitute is pretty much the only option.
The FAA has made huge regulation changes before but there has always been an alternative. The recent ADS-B mandate requires about $5k of new equipment before a plane is allowed to fly where Mode C transponders were previously sufficient. This is/was expensive for many private pilots, but was deemed to be acceptable for the safety benefits gained. Some owners have chosen not to add the ADS-B equipment and haven’t been allowed to fly in some parts of the country, but they can still fly most places. A fuel regulation that grounds half the fleet with no alternative regardless of the price is a completely other level of impact.
The FAA and most pilots want an alternative to leaded fuel (at least for the assumed cost savings if not for the environment). Energy companies are working on unleaded substitutes but current options still require an STC to burn. You probably won’t see leaded fuel going away until there is a universally approved replacement that can just take the place of 100LL at every airport in the country. Edit: or barring a complete drop-in replacement, at least an option that can be shown to work in existing engines and fuel systems without requiring major R&D.
It doesn't seem like you're addressing the pollution/health effects to the population caused by burning leaded gas and the relative harm of that versus the benefit of keeping the existing fleet flying. Is that because the pollution is so small or that the pollution just is not relevant in your opinion?
For the vast majority of the population, the number of cars passing by their house each day will be many times the number of planes burning leaded fuel flying overhead.
The vast majority of the population will never fly in a leaded gas powered plane, so I'd think the harm is much more than the gain. Said in another way, it probably wouldn't take much convincing to get a proposition passed to ban leaded gas for aviation.
There's a number of essential services that rely on small aircraft, even if you're not personally flying on them as a passenger.
Lab specimens, search and rescue, law enforcement, aerial photography for the "satellite" maps on your phone, power line surveying, transportation to remote parts of the country. Not to mention training for both future airline and military pilots.
Just because they're not economical for passenger service, doesn't mean they don't have an important role.
And again, I don't think you'll find many people in aviation who wouldn't like to move away from leaded gasoline. They're just waiting for the FAA to certify a replacement.
On the other hand, the amount of leaded fuel burned is tiny compared to automotive fuel. Roughly 0.1% of all fuel sold in the United States.
Yes it's bad. Yes we need to get away from it. Yes it's being worked on and will happen eventually. Also please at least recognize that it's a hard problem.
Is the slow turnover because you don't have the same fatigue because the cabin isn't pressurized, older Cessnas are already decent, airframes haven't gotten that much better, and it's pretty easy to add modern Garmin avionics to an old plane?
As much of a dick move as it is, it's not uncommon for homeowners to band together and work through local government to take down sources of noise that long predate them. When the source is a small airport or a local racetrack they often win.
The date the airport was built is nor always important. People in my area are upset because FAA nextgen approaches always fly precisely over the same guy's house every time, where they used to be a bit more scattered. Now the Oakland airport was built in 1927 and most of these houses date from the 1940s, but air travel has increased a lot on the intervening decades.
You should not be able to hear a small plane at idle on landing approach, and VFR final approaches are not charted (can substantially vary in ground track.)
So talk to a local FBO owner and work out an alternate landing for that "same guy's house."
The angry neighbor club isn't upset about GA on approach, they're mad because the new WNDSR TWO arrival into OAK flies a tight corridor right along the ridgeline where people live in the Oakland hills. Here's the flight that most recently flew it: https://flightaware.com/live/flight/SWA743/history/20200531/...
That's all got nothing to do with why GA is irritating. GA is irritating because their little mosquitoes are low and slow and have piston engine sounds and their pilots have a tendency to loiter.
Or maybe people could stop buying houses next to an airport that has been around for 80 years and arriving surprised that people fly airplanes around airports.
Not true; the only aircraft that does what you describe is a glider. Any propeller will generate a lot of noise, the tips of the blades get close to the sound barrier. Disclaimer: pilot here, I did fly gliders and I fly propeller planes regularly.
Well, even in a glider all the air moving by does quite some hissing, so its not completely silent (judging from the two flights I took as a passenger in a Blanik and Super Blanik respectively). Still much quieter than a small prop aircraft & you can talk with the pilot just fine.
On the other hand from the ground - yeah, a glider is pretty much silent. You might sometimes hear some rather earie whistling from some types when they are directly above, but thats it.
He said the wind is the only thing you hear. Yes, in a glider you hear the air moving, but adding a propeller adds a huge amount of noise over that base sound.
For all that you read about people complaining about airplane noise, I grew up only a mile or two from an airport and never thought about it nor do I remember anyone else complaining. But one of my recurring dreams/nightmares for most of my life is of watching a plane overhead and realizing at first something is wrong and then that it's going to crash in the back yard.
Silent planes would be welcomed by many people living in densely populated cities with high air traffic.
They're almost giving away apartments near Pearson Airport in Toronto, for example.
The price per square foot in that area is ~10x lower than the rest of the city and for good reason. (You are constantly bombarded by the sound of jet engines passing by).