Electric Airplanes

[ERD50]

The first impact will be general aviation- your basic Cessna 172 engine with all the associated hoses, etc weighs about 390 pounds and makes 150HP. A Tesla motor weighs 70 lbs and makes 375HP. A British company makes a 300HP motor that weighs 20 lbs - still experimental though.

One advantage is charging the batteries during decent. I’ve also thought that there might be some sort of super capacitor used for take off and dropped at the end of the runway - or wireless charging along the runway.

Very exciting to watch this technology take-off! (Pun alert)

It's a good point that when talking batteries versus fuel, we should include any weight savings of motor vs engine.

Though I'm not sure the 375HP 70# Telsa motor vs 150HP 390# Cessna engine is a fair comparison. I'm assuming the Cessna is rated 150HP continuous, and the Tesla 375HP would be intermittent (acceleration for a few seconds)?

-ERD50

 

[skyking1]

very true that. The parts in a plane are continuous ratings. Hook the Tesla motor up to a semi trailer and put it on a 10 minute pull up a mountain pass to simulate what that means. It cannot cool itself as it is to survive that.
The functional weights will be a little higher, but not a whole bunch. The really cool thing about propellers and electric power is the RPM. It is so easy to engineer for the best revs for an application, with electric.

 

[Koolau]

It's a good point that when talking batteries versus fuel, we should include any weight savings of motor vs engine.

Though I'm not sure the 375HP 70# Telsa motor vs 150HP 390# Cessna engine is a fair comparison. I'm assuming the Cessna is rated 150HP continuous, and the Tesla 375HP would be intermittent (acceleration for a few seconds)?

-ERD50

The HP of the Cessna is essentially continuous, though you'd be unlikely to use it in that fashion for long periods of time - not that you couldn't. ALL take offs (and theoretically) all climbing is done at full power. That CAN be done for quite some period of time. My C-150 took the better part of 25 minutes to reach 10500 feet MSL at full power with a full (ahem and then some) gross weight. But once you reach cruising altitude, using "full power" buys you relatively little in top speed. 65% to 75% power is kind of the sweet spot for most piston aircraft because their engines are then matched with the aerodynamics of the airframe. As usual, I've told you more than I actually know about the subject though I did fly and did see the reality of what I've mentioned here. YMMV

 

[NW-Bound]

I am not an electric motor designer, but will venture that it is not hard to design in enough cooling to allow continuous operation for an electric motor. In fact, this is already done with the current electric planes that have VTOL capability. Hover is the most power-demanding phase of flight.

The hard part remains how to get a battery to provide the motor with continuous power for a flight of several hours in duration.

 

[Walt34]

The hard part remains how to get a battery to provide the motor with continuous power for a flight of several hours in duration.

The guy who did this ten hour R/C flight also posts over on rcgroups.com, and what he did to achieve this is probably not scalable to full size and certainly not with any useful load. But it does show that it is possible.

ETA: BTW this is all off-the-shelf hardware, nothing exotic about it.

 

[NW-Bound]

The guy who did this ten hour R/C flight also posts over on rcgroups.com, and what he did to achieve this is probably not scalable to full size and certainly not with any useful load. But it does show that it is possible.

ETA: BTW this is all off-the-shelf hardware, nothing exotic about it.

The above feat is impressive. RC gliders are very efficient with low drag. And if they catch a thermal to ride, can stay aloft for hours with no power, not unlike manned gliders.


But 20 years ago, an RC with a glow plug engine made it across the Atlantic, covering 1900 miles in 39 hours. It sported a specially built carburetor to make its 5 lbs of fuel last (it weighed 6 lbs empty). It had a special tiny alternator to generate electricity for its electronics, which included a GPS, autopilot, and telemetry transmitter via satellite.

A man in the team helped launch it from Newfoundland, then went home to catch a commercial flight to Ireland to catch the plane as it arrived over the ocean.

See: https://en.wikipedia.org/wiki/The_Spirit_of_Butts'_Farm

 

[travelover]

I have no doubt that I know less about this than most here, but I can't shake the thought that we don't know what we don't know.

Critics of early steam locomotives thought that humans were not designed to go at 50 mph, and that it would be impossible to survive such speeds.

Thinking about how we went from the advent of heavier-than-air powered flight to walking on the moon in less than 66 years lets me stay optimistic.

I tend to agree. In my old j*b, I was tasked with solving complex systems problems. When we had a big issue, we'd call in all the design engineers for the components of the greater system. One one by one they would sadly tell us there was nothing they could do to help - sorry. Generally, a solution was created by someone from outside the design and release community and a change was forced onto one or more of the "sorry" design engineers. It is always easier to say it can't work than to look for a solution.

 

[Koolau]

High-speed rail seems like the most efficient option for inland people transport. The US needs to get "on board" with developing high-speed rails. Save the jet fuel for crossing the oceans.

In my elementary opinion, it seems that hydrogen would be the best bet for powering airliners in the future.

Any idea of the capital costs of the infrastructure to have high-speed rail? We (Honolulu) are building a light rail of about 20 miles. It's already established that it will not accomplish its stated goals and it will perhaps average 20 mph due to the various stops. BUT with all those issues, it's already up to $13 Billion and will likely be $20 billion before it's finished.

High speed rail? The right of way will cost many 10s or 100s of billions and that's before the first shovel goes in the ground or first cubic yard of (very energy intensive and CO2 intensive) concrete is poured. And, of course, "high speed" is in the eye of the beholder. Compared to 550 mph in an old 747, HS rail will be considered a step backward.

Other than that, yes, I think H2 might be a fuel of the future - but it will NOT be cheap. Maybe it will be cheaper than $10/gallon equivalent (2060 priced) hydrocarbon fuel, but it won't be "cheap." All SWAGs so YMMV.

 

[mpeirce]

One advantage is charging the batteries during decent. I’ve also thought that there might be some sort of super capacitor used for take off and dropped at the end of the runway - or wireless charging along the runway.

Very exciting to watch this technology take-off! (Pun alert)

I'm very much looking forward to airliner takeoffs using scaled up aircraft carrier catapults. Should be fun!

 

[Walt34]

But 20 years ago, an RC with a glow plug engine made it across the Atlantic, covering 1900 miles in 39 hours. It sported a specially built carburetor to make its 5 lbs of fuel last (it weighed 6 lbs empty). It had a special tiny alternator to generate electricity for its electronics, which included a GPS, autopilot, and telemetry transmitter via satellite.

A man in the team helped launch it from Newfoundland, then went home to catch a commercial flight to Ireland to catch the plane as it arrived over the ocean.

See: https://en.wikipedia.org/wiki/The_Spirit_of_Butts'_Farm

Those were interesting times. I was in the same R/C club as Maynard Hill (Walt Good was also a member) and it was fascinating to hear those guys talk about what they had done and were doing. The trans-Atlantic flight was after I retired and moved to WV, but I did see the prototypes in club meetings before they were launched and lost at sea. Maynard specifically polled the club members for anyone who had an early model of O.S. Engines' four strokes, that were still new at the time. The early four stroke glow engines didn't develop as much power as later designs but they were very fuel efficient, hence Maynard's interest in them. His work was truly bleeding-edge stuff at the time. I was still learning the basics so when they were around I just STFU and listened.

Walt Good and his brother William (Bill) were two of the pioneers in the development of radio control airplanes and of course the military was always interested in what they were doing.

 

[Koolau]

I'm very much looking forward to airliner takeoffs using scaled up aircraft carrier catapults. Should be fun!

I've wondered for a long time why commercial aircraft could not be assisted by a catapult. I'm not talking about the neck-snapping steam or electric devices used on aircraft carriers. Simply adding enough catapult "oomph" such that maximum power required by jet engines could be reduced perhaps 15 or 20% might well dramatically reduce FF use (and CO2) emissions. Once "launched" jet aircraft tend to be most efficient at near full power. The need for that extra take-off power more or less "dooms" modern aircraft to carrying around larger - less efficient jet engines which are only needed for a few seconds on the ground. 20% less powerful engines would be significantly more efficient during the 98% of the time they are just used for "flying" - not taking off.

Another way to reduce FF use/CO2 would be to use "mules" that now "push" aircraft back from their gate to get aircraft to their runway. Think of the inefficient use of jet fuel to taxi a huge (heavily laden) aircraft to their take-off point using their own jet engines. Instead, a diesel - or preferably battery powered mule could drag each aircraft out to the "launch" point. These could be unmanned with radio controls from the cockpit. At the runway, the mule would return for its next load while the aircraft started its engines in preparation for launch. Mules currently used are good (efficient) at what they do which is to shove or pull aircraft around on the ground. Doing that job with ground-bound jet aircraft is very inefficient - especially when the aircraft is 15th in line for takeoff.

No idea on the economics or even energy balance on this approach. BUT I am aware that jet aircraft are NOT good on the ground at fuel efficiency. YMMV

 

[REWahoo]

I've wondered for a long time why commercial aircraft could not be assisted by a catapult. I'm not talking about the neck-snapping steam or electric devices used on aircraft carriers. Simply adding enough catapult "oomph" such that maximum power required by jet engines could be reduced perhaps 15 or 20% might well dramatically reduce FF use (and CO2) emissions. Once "launched" jet aircraft tend to be most efficient at near full power. The need for that extra take-off power more or less "dooms" modern aircraft to carrying around larger - less efficient jet engines which are only needed for a few seconds on the ground. 20% less powerful engines would be significantly more efficient during the 98% of the time they are just used for "flying" - not taking off.

Ever heard of a plane losing an engine in flight? Or an aborted landing requiring a go-around? 20% less powerful engines would equate to an 80% (or greater) chance of disaster.

 

[NW-Bound]

I've wondered for a long time why commercial aircraft could not be assisted by a catapult. I'm not talking about the neck-snapping steam or electric devices used on aircraft carriers. Simply adding enough catapult "oomph" such that maximum power required by jet engines could be reduced perhaps 15 or 20% might well dramatically reduce FF use (and CO2) emissions. Once "launched" jet aircraft tend to be most efficient at near full power. The need for that extra take-off power more or less "dooms" modern aircraft to carrying around larger - less efficient jet engines which are only needed for a few seconds on the ground. 20% less powerful engines would be significantly more efficient during the 98% of the time they are just used for "flying" - not taking off...

Military aircraft occasionally use rockets to assist their take offs.

Would that not raise some eyebrows at the FAA if proposed for commercial airliners? Maybe passengers will pay extra for the experience?

Here's a laden C-130 struggling to get off the ground despite rocket assistance.

Another video of a C-130 in JATO shows the rockets not being lit off until late into the take-off roll. I wonder what happens if the rockets misfired. Is there time to abort the take off?

 

[NW-Bound]

And here, I found a video of an attempt at short landing via reverse thrust with rockets.

The rockets were fired off early, and the aircraft stalled and crashed.

 

[NW-Bound]

Here are some successful rocket-assisted short takeoffs and landings, plus a spectacular rocket-assisted short landing at the end.

You are not supposed to play with fire, let alone rockets.

 

[REWahoo]

Not a catapult but during the Cold War the USAF had a way to enhance thrust during takeoff on the original KC-135a tanker. Here's a short description:

Your high school science teacher lied to you-water does burn. KC-135A Pratt & Whitney model J57 engines produce thirteen thousand pounds of thrust by injecting water into inlets and combustion chambers. Six hundred and seventy gallons of demineralized water burns in about 125 seconds during a "wet thrust" takeoff.

The additional thrust was roughly equal to having a fifth engine during those two minutes.

 

[schenbew]

And here, I found a video of an attempt at short landing via reverse thrust with rockets.

The rockets were fired off early, and the aircraft stalled and crashed.

This was the aircraft used to test the ability of a C-130 to land and takeoff in a Tehran stadium to assist in the rescue of the American hostages held in Tehran, Iran. The reverse thrusters were fired too early, causing the aircraft to descend quickly, land hard, break the wings and catch fire. The crew all survived.

Code name for the project was “Credible Sport”

 

[NW-Bound]

This was the aircraft used to test the ability of a C-130 to land and takeoff in a Tehran stadium to assist in the rescue of the American hostages held in Tehran, Iran. The reverse thrusters were fired too early, causing the aircraft to descend quickly, land hard, break the wings and catch fire. The crew all survived.

Code name for the project was “Credible Sport”

Thanks. That makes sense.

In the video I linked earlier, it is impressive to see the aircraft literally jumped off the ground with rocket assistance. It's at 1:06.

 

[schenbew]

Thanks. That makes sense.

In the video I linked earlier, it is impressive to see the aircraft literally jumped off the ground with rocket assistance. It's at 1:06.

Absolutely. Read the Wikipedia entry on Credible Sport to get an idea of how much rocket power was strapped onto the mighty C-130 to perform like this.

Proves that anything will fly, and stop on a dime, given enough thrust....

 

[NW-Bound]

Proves that anything will fly, and stop on a dime, given enough thrust....

True that. Even RC builders know this.

 

[Koolau]

Ever heard of a plane losing an engine in flight? Or an aborted landing requiring a go-around? 20% less powerful engines would equate to an 80% (or greater) chance of disaster.

Don't follow your 20/80 math but understand your point. Full power is needed in these situations. 80% power would either be enough or it wouldn't be approved by FAA. I don't know if 80% would be enough or not. Oh, and 80% engines would weigh less as well, so there's that.

The good news on a go-around is that by the time a plane lands, its used up most of its fuel which can be as much as half the take-off weight. 80% would then be more than enough for a go-around.

This was one of my "flights of fancy" anyway so YMMV.

 

[Koolau]

Not a catapult but during the Cold War the USAF had a way to enhance thrust during takeoff on the original KC-135a tanker. Here's a short description:

Quote:
Your high school science teacher lied to you-water does burn. KC-135A Pratt & Whitney model J57 engines produce thirteen thousand pounds of thrust by injecting water into inlets and combustion chambers. Six hundred and seventy gallons of demineralized water burns in about 125 seconds during a "wet thrust" takeoff.



The additional thrust was roughly equal to having a fifth engine during those two minutes.

Here is the rest of the article. As you will notice, the water does NOT burn. It is used for two reasons. It cools the engine, allowing for more fuel burn without damage - heat is the limiting factor in most jet engines. Too much heat means damaged turbine blades. (There ARE problems of smoke caused by flame quenching due to water injection.)

The second thing water injection does is to increase the mass accelerated by the engines leading to more thrust.

The article quickly points out that water injection is no longer needed because we now have materials that can "take the heat" (my words/emphasis). BUT, what if you DID want to create more take-off thrust? Why wouldn't water injection still work? Especially as a way to accelerate more mass? Yet another flight of fancy, so YMMV.

Water Injection

 

[jeffmete]

Interesting thread. I fly electric rc and have had a lipo battery explode and burn when pushed too hard in a ducted fan (jet), batteries really don’t like to be used hard and discharged too far. Flight time is roughly 3 minutes.

There are full scale electric powered gliders for sale now. I’ve never seen one, but assume battery power is just for take off https://www.dg-flugzeugbau.de/en/ls8-e-neo

When I was in college, in the 70’s, we had to read books that said we’d be out of oil and starving due to over population by the late 80’s, In actuality we never run out of anything, it just gets more expensive until we switch to something else!

 

[Safe Harbour]

A gallon of gasoline weighs 6.3 lbs, and holds 33.7 kWh. That's 5.3 kWh/lb.

The battery in a typical EV weighs 1,200 lbs, and stores 85 kWh. That's 0.07 kWh/lb.

Don't expect electric planes, it's not the technology for clean flight. Think something more like hydrogen power.

In electrical terms, the energy density of hydrogen is equal to 33.6 kWh of usable energy per kg, versus diesel which only holds about 12–14 kWh per kg. What this really means is that 1 kg of hydrogen, used in a fuel cell to power an electric motor, contains approximately the same energy as a gallon of diesel.

Hydrogen blasted the space shuttle into orbit!

 

[NW-Bound]

When I was in college, in the 70’s, we had to read books that said we’d be out of oil and starving due to over population by the late 80’s, In actuality we never run out of anything, it just gets more expensive until we switch to something else!

Yes, this.

Eventually, when fossil fuel gets too expensive, only rich people can afford to take long-haul flights. The rest of the masses either stay home, or take forever to go somewhere with electric planes that can fly only short hops. Going from San Diego to NYC will involve 15 hops. Or perhaps this inconvenience of air travel will spur the development of rail travel, which of course is most easily powered by electricity.

For trans-oceanic flights, perhaps there will be half-way stations in the middle of the ocean for electric planes to swap out their batteries. Of course, this means the planes will be seaplanes, unless they know how to build VTOL planes with better ranges.

All this will be beyond my lifetime, I think. Too bad I will not be around to see how things evolve.