I can't wait for electric/hybrid aircraft.

[BackPacker]

So you lug around all that dead weight just to be able to provide you with enough power for takeoff that you don't use after that.

So you argue that instead it's worthwhile to lug around an extra electric engine plus a significant amount of batteries for the duration of the flight, just to get a little oomph during take-off?

Don't get me wrong. IF we can get energy storage (batteries) sorted and IF we can get the grid updated so that it is able to deliver the power required to charge our batteries relatively quickly, I think 100% electric is the future. First for cars, later on for aircraft.

But hybrid aircraft, sort of like a Cessna Prius? I don't think so, particularly not if the electric bit has to be charged at some point from the fossil fuel bit of the aircraft somehow. Aircraft normally don't brake (so no regenerative braking possible) and they don't crawl along in traffic jams or city traffic - the places where hybrid cars can achieve the most fuel savings.

A hybrid car on a constant highway speed uses almost exactly the same amount of fuel as a normal non-hybrid car. And that scenario is by far the best comparison to an aircraft in flight. Minus one thing: The weight penalty for aircraft is much higher than for cars. So carrying around all these batteries will have more impact on energy required in airplanes than in cars.

[IO540]

As you yourself mentioned, you're carrying around a heavy cast metal thing for 100% power output when you in fact only use 70% of the power for 99% of your flight. So you lug around all that dead weight just to be able to provide you with enough power for takeoff that you don't use after that.

That assumes that the efficiency at 100% max rated power is any better. It won't be.

There's a fatal flaw in your calculus: only 20-30% of the energy in fuel turns into shaft horsepowers, whereas electric motors have 90% efficiency.

This changes a lot once one takes into account the theoretical maximum 40% efficiency of the steam cycle used to generate electricity (except a gas turbine driving a generator directly).

I don't think a hybrid plane makes any sense because the whole case for it in cars hangs on a) a car using little power most of the time and b) energy recovery from braking. Neither of these apply to planes.

[IanPZ]

I reckon hybrid will make sense in all forms of transport when

a) power density increases. LiPo is getting there, but the high density stuff is still in research labs, and a way off yet, and

b) when power generation comes from something much smaller than an engine, such as a fuel cell, whether methanol, hydrogen or lpg powered

I think pure battery power is a way off, partly due to the energy density mentioned, but more specifically due to the recharge capabilities. Even where batteries have been designed that can take a huge charge current to recharge quickly without boiling, the power infrastructure to get it to the charging point is not there. National grid would have to redig everyone's driveway and build new substations to make it possible!

Having said all that, I can imagine a day where a polymer based battery is used as structural components to the aircraft, as well as power. At that point, mass and power density take on a whole new meaning, as you are replacing more than just a power plant.

As for regenerative braking, it really isnt all that worth it! It helps a little, but I cant see it ever being of true value flying. It works for cars since they spend most of the time with very light loads, need a little push from the electric motors sometimes, and spend a lot of time coasting downhill. For boats, they are worth it since the wind is moving the boat, so you might as well tow a generator and get the water flow to work for you, but we are talking tens of watts, not hundreds or thousands.

From my limited experience of aircraft so far, except for gliders, when you turn the engine off or to idle, the thing heads down pretty darn quick. Even if you could generate hundreds of watts of power during that time, what you going to use it for?

Interesting discussion though!

[Mr Cessna]

Going off topic a tiny bit here but who an earth would fly an electric aeroplane, I personally couldn't think of anything worse... changing batteries like a bloody torch, humming along with an engine which feels like a fan. I agree it would be environmentally friendly but take all of the fun and what we know out of flying.

[BackPacker]

Well, other than a reduced noise level I don't think there's a lot of difference between flying electric or flying on fossile fuel. Especially if you fly FADEC equipped aircraft today already.

Yes, you only have one "load" lever instead of throttle, mixture, prop, carb heat, ignition and maybe a few other knobs and dials but I personally have never found those to be an integral part of the "fun" of flying.

Not to mention getting your hands dirty when refueling. Especially the smell of Jet-A can linger for hours.

(And electric aircraft can be turned upside down without needing inverted fuel/oil systems, header tanks and whatnot, so they're great for aerobatics - apart from the weight issue of the batteries.)

[Mr Cessna]

Point taken and I agree flying is flying wheather it be by glider, microlight, jet or even balloon, but I suppose people (including myself) fear change and disapprove in things they do not yet have knowledge about. But fossil fuel aeroplanes will always be needed surely to teach CPL students in complex singles and for ATPL training? Do you think fossil fuel engines/planes will one day be a thing of the past?

[IanPZ]

Yup, given that one day, fossil fuels will be a thing of the past too.

[FullWings]

Other factors when considering electric propulsion are instant availability, simple controls, lack of altitude effects, no icing or fuel contamination issues, very accurate range/endurance information and superior reliability. Also, not being surrounded by large amounts of flammable liquid in an accident is a bonus.

At the moment, as pointed out in this thread, battery tech. hasn't advanced to the stage where it is close to fuel in terms of energy density but the form factor is much better, i.e. you can put batteries anywhere, like the wings, whereas an engine is a big lump with aerodynamic and/or balance problems, wherever you put it.

[IO540]

It's very simple really.

An electric plane is trivial to do.

You could replace an IO540 with a brushless motor, a speed controller, and a load of bricks to make up the W&B, all off the shelf.

I reckon it would take under a week to do it all.

Might have to get a custom motor made, with a thick shaft, a prop flange, and a strong case, with IO-540-compatible mounting points.

Stick an "Experimental" sticker on it and off you go.

There's no contest.

The only issue are ................... the batteries

[Fuji Abound]

The only issue are ................... the batteries

I dont know, just do away with the pilot and pax and transfer to the model flying thread.

[AdamFrisch]

You're approaching a flying hybrid too traditionally. I'm not talking about adding a slightly larger starter that can "help" out during takeoff on a Rotax or Lycoming. No, the combustion engine has to go completely. I'm talking about a brushless electric motor in the front, nothing else. A battery and a turbine APU in the tail running a genset. Just like in the airlines.

The battery in this case made smaller and less heavy as it's only designed to be an energy storage device and be able to propel for maybe 30mins on its own. And the APU wouldn't have to be designed to excruciating standards as if it fails - you still have the battery that can execute a safe landing.

That would be lighter than a combustion setup and have all the benefits of electric and fossil. And even if it's the same weight, it's still much more desirable as it eliminates all the crap you to deal with with reciprocating engines.

As a side, and I say this owning two ancient Lycoming GO-435's on my AC520 (and I love they way the sound), but the problem is the combustion engine and the people that make them. They are the most traditionalist bunch I have ever come across and they've set aviation back 50 years. Let's talk some examples:

1. Why isn't the starter and generator combined to save weight? Ah, dunno, it works, don't mess with it...

2. Why are there still carburettors when the rest of the world moved to fuel injection years ago? Ah, dunno, it works, don't mess with it...

3. Fadec? Ah, dunno, it works, don't mess with it...

4. Will disintegrate if not fed ancient and eco unfriendly Avgas? Ah, dunno, it works, don't mess with it...

5. Magnetos that break mid flight when the rest of the world has had electronic ignition that doesn't brake ever for 20 years? Ah, dunno, it works, don't mess with it...

6. Exhaust Turbo that run the generator instead so you're not siphoning power from the engine? Ah, dunno, it works, don't mess with it...

The list just goes on and on. They're dinosaurs made by people why have had it far too comfortable and have not had to innovate. This is the drawback with type certification - once you're on paper as the engine that a type cert aircraft can use, they have you over a barrel. They don't need to do anything after that except cash your checks.

[IO540]

It's not so simple

1. Why isn't the starter and generator combined to save weight? Ah, dunno, it works, don't mess with it...

They do exist, on jets and turboprops. They are quite pricey... not your $300 starter and your $300 alternator. You are looking at $10k (TBM850)

2. Why are there still carburettors when the rest of the world moved to fuel injection years ago? Ah, dunno, it works, don't mess with it...

You do have the choice of FI so nobody has to fly with a carb anymore. I wouldn't if you paid me for it.

3. Fadec? Ah, dunno, it works, don't mess with it...

FADEC is fairly complex, requires sensors, electronics which have a poor history of reliability in GA (largely because there are very few competent electronics people in GA) and it would not deliver more MPG in cruise than a correctly leaned engine.

4. Will disintegrate if not fed ancient and eco unfriendly Avgas? Ah, dunno, it works, don't mess with it...

Engine efficiency is strongly dependent on the compression ratio...

5. Magnetos that break mid flight when the rest of the world has had electronic ignition that doesn't brake ever for 20 years? Ah, dunno, it works, don't mess with it...

Again, electronics reliability. A poor excuse, sure. But if you had electronic ignition it would need its own alternator. Unlike a car whose engine stops when the battery goes flat.

6. Exhaust Turbo that run the generator instead so you're not siphoning power from the engine? Ah, dunno, it works, don't mess with it...

That has been done, many years ago, but the energy recovery is tiny, for all the hassle you get. Also, making a generator which runs at tens of thousands of RPM is non-trivial. It has been done in recent years, for small turbine engines (look up Bladon Jets for example).

[AdamFrisch]

You do have the choice of FI so nobody has to fly with a carb anymore. I wouldn't if you paid me for it.

The new Skycatcher has a carb and carb heat. Don't think there's a FI option. This is on an aircraft that hasn't even been released yet - the newest of the new!

FADEC is fairly complex, requires sensors, electronics which have a poor history of reliability in GA (largely because there are very few competent electronics people in GA) and it would not deliver more MPG in cruise than a correctly leaned engine.

My dinosaur Aero Commander from 1953 has an autolean function - you never touch the mixtures as it leans itself by barometric pressure. This is 60 years ago and they still want me to believe it can't be done in this day and age electronically? They're just cheap and complacent, as simple as that.

[IO540]

The new Skycatcher has a carb and carb heat. Don't think there's a FI option. This is on an aircraft that hasn't even been released yet - the newest of the new!

Oh well, it was built to be cheap and light (flimsy) and I would not fly one anyway. Carbs are a little bit cheaper than fuel servos.

My dinosaur Aero Commander from 1953 has an autolean function - you never touch the mixtures as it leans itself by barometric pressure. This is 60 years ago and they still want me to believe it can't be done in this day an age electronically? They're just cheap and complacent, as simple as that.

Firstly, that system uses a diaphragm which is known to burst, and the resulting rich cut stops the engine (if at altitude) unless you are really on the ball and pull the red lever fast.

Secondly, the system might do a general form of altitude compensation but it won't do any kind of thermal engine management for say a climb from SL to the aircraft ceiling (constant EGT all the way up). It also won't give you the choice between best economy (peak EGT or slightly LOP) and best power (about 130F ROP); this is very relevant if trying to fly anywhere near the operating ceiling, and requires (in your case) a manual mixture control all the same.

Altitude compensated carbs have been around for yonks but they do only half the job, and in any case leaning manually is no hardship. It is a trivial non-event, if you have EGT and CHT instrumentation.

If there was some kind of magic bullet which would bring a dramatic improvement to the old engines, it would have been done long ago.

Sure one can do small improvements but the adoption would have been small.

An oxygen sensor in the exhaust would give you the potential for accurate peak-EGT control but it would not deal with the need to fly ~ 150F ROP during climb, for thermal management of an engine which for weight reasons cannot deliver 100% of max rated power while at peak EGT because it cannot dissipate the heat which would be thus generated.

Nothing short of a full FADEC is worth having, and the history of those working reliably is hardly good. In aviation electronics, one is kind of grateful to have a good working radio!

I drive a nice old 1995 Toyota import and while it is built like a tank, I have had two engine failures through alternator failures. In this case, you have maybe 10 mins (at night) before it stops. A bit like a DA40TDi then Would I buy one of those? What do you think?

[Jan Olieslagers]

Technically, nothing keeps us from having engine electronics with a degree of reliability acceptable for light/general/recreational aviation. And that would be a great improvement. Yet there is none on the market today, the development would be expensive and there is but little sales volume to make up for it.
For lack of anything better, we make do with automotive electronics, which have good reliability when compared to traditional automotive electrical systems, but aren't really good enough for us fliers.
For one example, I understand Rotax 4-strokers are often (or even as a standard?) equipped with electronic ignition from Ducati motorbikes.

[Jan Olieslagers]

other than a reduced noise level I don't think there's a lot of difference between flying electric or flying on fossile fuel

You might be surprised how small that difference actually is. I was much surprised on seeing an electrically powered trike demo'ed, and finding it quite as noisy as the others. The greater part of noise obviously comes from the prop.

[IanPZ]

Yeah, but you do have to be careful in case you dont hear them coming and they reverse into you....erm ?

[FlyingStone]

Originally Posted by AdamFrisch

The new Skycatcher has a carb and carb heat. Don't think there's a FI option. This is on an aircraft that hasn't even been released yet - the newest of the new!

Not any product that was made in 2011 and has a Cessna label on it is neccesarily good. Using the Continental O-200 instead of Lycoming IO-233 (which isn't yet certified) was one of the major mistakes in the design of Skycatcher. Using carbureted Lycontinental engines on new trainer in 21st century is just bad, you can't even lean them properly. OK, they do 100°F ROP without any problems, but if you want to get near optimum BSFC, most of them needs full throttle (well actually it's usually better to close it just a bit to create some turbulent airflow, which distributes fuel more evenly between cylinders), but for using full throttle at normal cruise powers (75% or below), you would need to climb to 5-6 thousand feet. As IO540 states, the altitude compensating carbs or fuel pumps do simplify things, but you lack the control over what kind of mixture do you want to have - best power for fastest cruise, deep LOP for maximum endurance, ... And using FADEC and "new" technology, such as diesel engines, the old engines remain competitive when comparing SFC, if you understand aircraft piston engine management and know how to lean properly. Besides, it's very difficult to destroy low-powered engines with leaning, especially if they are running a fixed-pitch prop: unless you don't see a problem with CHTs over 420-430°F.

Originally Posted by IO540

Engine efficiency is strongly dependent on the compression ratio

Agreed, but even then it's dependant on how much load you put on the engine. Thielert's Centurion 2.0 has a compression ratio of 18:1, but provides very little advantage in SFC over C172's "default" engine O320-D2J, which has a compression ratio of 8.5:1. I think the only really notable differences between the engines are: ability to use Diesel/Jet A-1 and constant-speed propeller, which gives a few knots increase in cruise speed, but FADEC has a very strange way of setting propeller RPM dependant on the load. I think if you set load below 20%, the RPM starts increasing (contrary to normal CSP), which actually means blades' pitch is going to very very fine and can indeed be felt with the aircraft slowing down significantly. Well speaking of electronics, Centurion 2.0 (one of the rare certified FADEC aircraft piston engines) doesn't have really the brightest history with clutch issues (although that was more of a problem on 1.7), the FADEC sometimes can't really decide on the RPM, especially when using somewhat medium loads with medium speeds on a C172 (say 45% load at 75 knots) and then it ends up by changing pitch and your passengers wondering (as well as you) what is going on

Basically, as was written lots of times: if there were any magic formula for creating mass of energy from nothing, it's likely that it would have already been developed, at least in some sorts of experimental version

[AdamFrisch]

My question goes beyond that: why do I have to lean at all? I should be able to just push a button that says LOP or GOP and automation takes care of everything else. Or there should be an Economy setting or a Sport setting, just like in my car...

[IO540]

The reasons for leaning the existing aero engines are not necessarily obvious. I have some notes here.

What you want could be achieved with a full FADEC box.