Electric Power Plants

[steveinindy]

On a great note, both the "visionaries" and the OEMs are seriously looking at electric airplanes. There IS a future.

There is, but for the immediate future (<20 years) it's going to likely be very limited applicability. If you knew half the crap the OEMs are investigating at any given time in terms of propulsion systems that never gets mentioned in the press, you'd probably not put so much faith in the fact that they are "seriously looking" at any given topic. Until it's on the assembly line, it's all just bloody speculation and theorizing.

Ron, I'll even offer to buy you a steak at Oshkosh if they put an electric airplane into production that can best 150 kts in cruise flight before 2020. Actually, you know what, if you'll be at Oshkosh next year, I'll buy you a steak anyhow. I am always up for a lively exchange of ideas and it's always best to surround yourself with folks who aren't in creative lockstep with you.

[Frank Giger]

Wow...I knew they were slow but dang. All the more reason why I've never understood the fixation some folks have with the new generation of aircraft geared towards that market. If I want to putter around, I'll be more than happy to get an Aeronca or a vintage Cub (which I plan on doing anyhow). I guess my mindset is more towards "Point A" to "Point B" rather than what transpires (beyond the safety and cost aspects) between the two.

Too funny - I have the exact opposite mindset. If I really want to get from Point A to Point B reliably I'll either drive or call Delta.

Probably why I'm building a single seat, open cockpit biplane that cruises at 55 MPH.



Seriously, I think the focus on LSA (1,320 gross weight limit, 120 kts cruise, two seats only) in electric powerplants is more about ready-made production platforms that have lower engine requirements than anything else. Add in composite material construction, advanced electronics, etc., and it's a good way to start out.

This is why electric cars focused on sub-compacts as development beds. Personally, I'd of opted for a light truck or mini-van and loaded up the batteries for greater range; clearly they did the math and the lower power demand trumped power storage capacity.

LSA's also fit another handy design parameter - range (or, more precisely, duration of flight). The FlightDesign CTLS, for example, carries 34 gallons and burns 5.5 gallons of mogas an hour, for a flight time of six hours (total, without taking off the 30 minute required reserve). The CTLS actually cruises at the max allowable - 120 kts - for a nominal range of 660 NM. This is pretty typical for LSA's, and while pretty steep for electrical aircraft gives a nice benchmark goal to shoot for.

In a different direction, I have serious doubts that a hybrid aircraft would be desireable. Beyond the weight penalties of having one engine required to make another engine work, I would not want my soft pink flesh relying on a combustion engine that had to automatically start, shut down, and restart in irregular intervals to keep the batteries up to snuff.

All of this avoids the net negative environmental impact of electric aircraft, which seems to be actively overlooked. To achieve zero emmissions at the end of the pollution stream it's upsourced the supply chain and then dumped down once the plane is on the ground.

The materials for composite aircraft and in manufacturing the batteries are far more demanding on the environment than aluminum skinned (or fabric covered) aircraft using an internal combustion engine. Electric generation is our single greatest area of emissions (40% of the USA's total GHG production comes from coal fired electric plants), and the alternatives for generating even more are unworkable or politically difficult.

On the downstream, batteries that have outlived their life cycle are environmentally nasty. And they're going to need to be replaced on aircraft far more frequently than in cars. I take the cue of ELT's - expect the FAA to mandate replacement at 50% of the expected life expectancy. Even if they're recycled there's a huge amount of toxic waste generated.

I hate to be the naysayer, but pound-for-pound nothing beats the power storage capacity of liquid hydrocarbons....

[steveinindy]

Seriously, I think the focus on LSA (1,320 gross weight limit, 120 kts cruise, two seats only) in electric powerplants is more about ready-made production platforms that have lower engine requirements than anything else. Add in composite material construction, advanced electronics, etc., and it's a good way to start out.

I would tend to agree, although I don't think the advanced electronics are really necessary for anything that is day VFR only. An airspeed indicator, altimeter, maybe an attitude gyro, radios and a fuel gauge are all that's necessary. Plugging a glass cockpit into one of these LSAs is a bit like my urge to plug one of the higher end, 1200 hp PT6As into my design: it'd be nice, but it's not essential for the mission of the aircraft. That's why I'm going with a much lower horsepower engine (most likely either a Rolls Royce or GE engine) that will do the job at a much lower fuel consumption rate.

In a different direction, I have serious doubts that a hybrid aircraft would be desireable. Beyond the weight penalties of having one engine required to make another engine work, I would not want my soft pink flesh relying on a combustion engine that had to automatically start, shut down, and restart in irregular intervals to keep the batteries up to snuff.

As a safety researcher, I am in complete agreement with you there, but then again I also feel the same way about mogas engines in aircraft and electric powerplants too.

The materials for composite aircraft and in manufacturing the batteries are far more demanding on the environment

On a somewhat related note, welcome to one of the toughest problems in composite design: finding a way to make the stuff not either burn or not be as toxic when it does burn in a crash.

[Ron Blum]

Guess it's my turn to "speak". First, Steve, I'll email you privately with other information ... somehow I can't believe that you're an engineering student.

A hybrid airplane is just a bad idea ... it's good for a car, though. Car and airplane engines have totally different operating environments. A car's engine is up and down all the time (equates to inefficiency), so making it a hybrid makes sense because the engine can run at peak efficiency all the time it is running. (except for airplanes doing aerobatic routines) Airplane engines run at high (efficient) power all the time, and they rarely change RPM (another good thing for efficiency).

Yes, liquid hydrocarbons have a 72:1 weight advantage over current batteries, but that ratio is starting to come down. In addition, electric propulsion systems can be made more efficient than engines (for multiple reasons). I like Frank's comment about 6 hours of range. Who ever uses that? (rhetorical question). Even the mid-range capable Citation IIIs (Cessna Model 650s - not CJ3s), The mean flight time is 1:15, and modal flight time is 0:42. In other words, 150-200 NM trips.

My background is supervising/managing OEM Flight Test Engineering departments ... and running DO-160 labs. The Hawker Beechcraft composites pass all the FAA requirements.

I hate to be the naysayer, but pound-for-pound nothing beats the power storage capacity of liquid hydrocarbons....

Although I currently agree with this, the Prius would be a total flop. Sorry to say, but green sells ... and that keeps people employed.

[steveinindy]

My background is supervising/managing OEM Flight Test Engineering departments ... and running DO-160 labs. The Hawker Beechcraft composites pass all the FAA requirements.

Still don't want to inhale what result when you burn it. Even if the "usual suspects" of incomplete combustion (CN, CO, HS, etc) don't get you, then you wind up with a nasty pulmonary fibrosis from the inhalation of the fibers.

[Frank Giger]

Burning composites is a tiny problem environmentally.

On the issue of fire safety, they beat the next lightest covering - fabric - all to heck.

Manufacturing them is where the pollution comes from. Not to say that they aren't a good trade off for heavier materials in the long run when energy requirements for aircraft over a thirty year (if not more) lifespan of an aircraft are taken into account.

Recycling a typical GA aircraft today is simple - gut it, chop it up, and melt down the aluminum. Not so much for composite aircraft, AFAIK.

Both hybrid and electric cars sell because they are fashionable and the illusion of savings. They cost more and are ultimately more polluting than internal combustion ones. In the future the price will come down, but the pollution for the increased demand for electricity will go up. One is simply trading emissions from a tailpipe for one coming out of the stack of a coal fired plant - and due to wasteage of electricity over lines in the grid much more is required.

On glass panels, it's hard to find an LSA on the market that doesn't have one, and from a marketing standpoint it is almost required for any aircraft that bills itself as high tech.

[steveinindy]

Burning composites is a tiny problem environmentally.

I'm not thinking environmentally outside of the immediate 'environment' of the cabin for purposes of survivability and the health of my brother and sister firefighters who have to respond to crashes.

On the issue of fire safety, they beat the next lightest covering - fabric - all to heck.

This is very true although that is no reason to rest on one's laurels and not try to improve things, which is all I am advocating for.

Manufacturing them is where the pollution comes from.

Take a look at the pollution associated with aluminum production since it involves large amounts of electricity.

On glass panels, it's hard to find an LSA on the market that doesn't have one, and from a marketing standpoint it is almost required for any aircraft that bills itself as high tech.

Point taken, but maybe it's the nostalgia buff in me that find something appealing in old steam gauges when flying low and slow. That's one of the reasons I want to own an L-bird some day. Stick and rudder, basic instruments and cheap to operate. No need to shell out more money for something that's "high tech" but low speed.

[Ron Blum]

Point taken, but maybe it's the nostalgia buff in me that find something appealing in old steam gauges when flying low and slow. That's one of the reasons I want to own an L-bird some day. Stick and rudder, basic instruments and cheap to operate. No need to shell out more money for something that's "high tech" but low speed.

If there ever is a practical electric airplane, the first one should be done with "steam" gauges. Cheaper, easier and requires less (no) power (and failure modes are well known). Flying IFR, in icing or at night is a much different story ... and power requirements are significantly higher.

Steve - I think you're giving me enough inspiration to go after some ideas that I have been thinking about for years now to make air data systems better. Thanks. ... ah, after the 1911 is done.

[steveinindy]

Steve - I think you're giving me enough inspiration to go after some ideas that I have been thinking about for years now to make air data systems better. Thanks. ... ah, after the 1911 is done.

Not a problem. Can I help?

[shadow738]

I'm also a pilot and electrical engineer. With regard to horsepower, an electric motor can deliver much more than its rated power, BUT there is no such thing as a free lunch. The reason is that you can put up with short term heating as long as you don't fry the motor. You will be taking the power from the battery.

This means you can size the motor for cruise, and overload it short time for takeoff and initial climb. When speed and altitude permit, you throttle back to "cruise climb"/MECO power just like any other airplane.

Electric heating effects are proportional to the SQUARE of the current: "Twinkle, twinkle little start, power equals I (current) squared R (resistance)."
A motor on low voltage will put out the same power, but it will draw more current and usually fry itself. I work in a hardware store and we sell big, 240-volt air compressors; if you try to run them on 120 the thermal breaker in the motor will trip--that's the good news. The motor is trying to draw twice times the amps resulting in four times the heat.

--- Doug Drummond