Automobile engines are very challenging because the power demands are highly variable and they can’t be optimized for any specific load.
I never checked mpg while taxiing but the motor would be almost idle.
I said GALLONS PER HOUR. If you're taxiing for hours, you're doing it wrong.
The Piper Cherokee PA-28-140 weighs a petite 2150 pounds (max loaded weight) and burns 10 gallons an hour and would do about 115 KIAS, which translated to roughly 130 miles per hour ground speed, which is 13 miles per gallon.
It would do even better if you flew for efficiency, but since rental was by hours of engine time wet (I didn't pay for fuel and would be reimbursed for fuel purchased), there was really no reason to not throttle that baby up to full rental power.
The reason is to reduce pollution, but that's obviously no concern at all for most GA pilots and passengers.
There's nothing magical about flight. Take-off takes a bunch of energy. Maintaining that energy, not so much. Planes are pretty aerodynamic, imagine that :) Some are much lighter than cars since every pound counts. To the point that people often opt to not have AC (if it's even an option) to save a few pounds.
They will cover a lot of ground in the same amount of time. That helps even more.
Not all planes are that economical, of course. But some are indeed hilarious. Check ultralights (or microlights as they are known in Europe).
Yep, take-off and ascent burns a lot of fuel, much more for the time duration than cruising. It's too bad there isn't a way of recovering some of that energy when descending, similar to how electric cars recover energy when braking.
A descent is a pretty efficient conversion between potential energy (altitude) and kinetic energy (speed/horizontal distance) so you get it back. Your RPM difference between cruise and descent is a proxy for your recovered energy. An engine out glide/landing is the extreme demonstration of this.
But that's exactly what happens already. Point the aircraft down and it will pick up speed.
Nearer the airport, I’ll make a power reduction and continue to convert that potential energy to forward travel, eventually putting out gear and flaps.
There’s more than enough drag for any reasonable descent profile to allow the potential energy to be used to move forward without gathering excessive speed.
Power off, I can glide around 1.5 nautical mile for every 1000’ of elevation I have to use.
Additionally, planes tend to fly at constant and pretty high speed for most of their operation, while a car has a lot of acceleration and deceleration going on. Planes can also use wind thermals to change altitude (sail planes can only use that!) or can stay at the same altitude while a car driving below it is stuck with the geography (i.e. it has to follow and climb hills).
I don’t view an 11% spread as “horribly inefficient” given the need for many redundant systems, air-cooling, high diameter pistons, and relatively low RPM.
0-https://michaelsoroka.com/2014/03/26/are-airplane-engines-in...
They are 60's or maybe 80's car engines that are still made since nobody in GA wants to pay for better ones.
Since nobody wants to pay to certify better ones.
The engine in a Cessna 172 is going to run you $20-40k (20k rebuilt, 40k new afaict - check out [0]) - far more expensive than an automobile engine with 'equivalent' performance. The difference is that the Lycoming is certified by the FAA for use with your airframe. (And it'll work in whatever conditions you care to name, and with a car engine that's only a 'probably')
Yeah unfortunately the weight and size of those systems is prohibitive for most light aircraft. Plus catalytic converters and oxygen sensors for closed loop efi can’t be used with leaded fuel.
> They are 60's or maybe 80's car engines that are still made since nobody in GA wants to pay for better ones.
The Lycoming and continental engines in most of the fleet were certified in the early 50s. A few were in the early 60s. That means they were designed in the 40s and 50s!
A Cessna 172 burns about 8 gallons per hour and travels at 125 knots, or about 140 mph. That's the equivalent of about 18 mpg.
There's been an enormous improvement in automobile engine efficiency in the past 30 years, and most of that has come from optimizing engines and transmissions to minimize their fuel consumption under light load, while still giving them enough peak power capacity to accelerate quickly, tow a heavy load up a hill when needed, etc.
In comparison, an aircraft engine spends very little time "idling" and sees very little change in load over the course of a flight. It just runs at a fixed speed and power setting for most of the time. There isn't that much to optimize or improve.
Timing is a big one; magento fired engines have fixed timing. The engines can't remove or add timing to get more power.
Fuel ratios are determined by the pilot with current Lycoming and Continentals. Why should the pilot need to worry about this? EFI has been around for 40 years now and would help decrease the cognitive load on the pilot. Like, how many engines have cooked valves because the pilot (or student) forgot to richen the mixture before descending?
Cooling is a huge one. There are a few liquid cooled aircraft engines and they just make everything easier. The engines are more reliable, and it also removes a carbon monoxide poisoning risk due to corrosion in the exhaust cuff.
Yeah, a Cessna can get better fuel economy than a car traveling at 140mph but it could be _so much better_ than what it is. And not just better fuel economy, but better all around experience for the pilots (lower cognitive load), and owners (lower cost of living, more reliable engines).
Modern engine monitors have given us more insight than ever into engine operation and I don’t find the engine management particularly taxing.
After initial takeoff, I’m likely to set the power (throttle, RPM, and fuel mixture) at 1000’ above the ground and not touch it again for 4 hours (when it’s time to transition to landing).
GAMI got their start selling more balanced fuel injectors, but there's only so much you can do when you squirt gas into a tube and hope that it makes it equally to all cylinders.
There's a _lot_ on the table in terms of efficiency and it puzzles me why there has been almost zero progress on this front.
The SDS EFI people claim up to a 20% fuel effiency gain by going to multipoint fuel injection on existing engines.
If you have consistent cooling (hey, guess what, those rear cylinders on an O-540 are running hotter than the fronts), you can run more timing and more compression.
More timing, more compression, less fuel = more efficiency. Basically everything I'm talking about is more cruise power efficiency!
I have GAMIs; they are one per cylinder, just like the factory injectors were, but provide closer matched air-fuel ratios. I also have per-cylinder EGT and CHT instruments and have measured less than 0.3gph spread (about 2%) between the leanest and richest cylinder. Modern cars are rarely measuring per-cylinder fuel, but rather measuring the average of half or all the cylinders and using that to adjust short and long term fuel trims.
Also, I dont know that you want to increase the compression on the hot cylinder. If anything Id run rich to make sure it doesnt knock
Can you elaborate further on this? Is this lower cognitive load because the engine is more reliable?
In the gallery here: https://cessnaowner.org/pilots-perspective-cessna-340/ The red controls are the mixture and have to be manually adjusted by the pilot, so you could potentially remove 1/3 of the controls from that area
It's still early days with short flying time, but electric planes are a thing: https://en.wikipedia.org/wiki/Pipistrel_Velis_Electro
Flight training is seemingly the first market:
"The eDA40 will compete with Bye Aerospace’s new all-electric eFlyer 2 and eFlyer 4 aircraft, which have been securing significant preorders in the flight training market."
https://www.futureflight.aero/news-article/2021-10-13/diamon...
I'm still rooting for electrification there too. I can't imagine an electric drive train to cost as much as a Lycoming/Continental engine overhaul.
variable valve timing also helps.
EDIT: This comment is about automobile engines.
CVTs are fairly recent and people managed to stifle it by adding simulated gears.