I love it and hope they are successful.

They seem to have some pretty good backing and partners. Much different then many other aviation start ups. And its going to happen some day by someone, you have to start somewhere.

Good for them.

Mike

I don’t want to see backing partners, I want to see a real product. They need significant gains in battery technology to do what they want to do. I am all for the pioneers, just tired of the hucksters. Other People’s Money scenario.

The interesting part here is not the plane, it's the proposed business model. As I said before, that's definitely the future if you can only make the plane cheap enough.


Get there much faster — and on your schedule.

Imagine leaving your doorstep in San Jose at 7 AM and making it to a 9:30 AM meeting in Pasadena. With Zunum Aero, simply drive to a nearby airfield and walk to your aircraft with bags in tow, for a trip that will take half the time and at a much lower fare. Or skip the meeting altogether, and be on the slopes in Tahoe by 8:40 AM for $100 round-trip, and back home the same evening.

We are a land of towns and communities, many with airports, but few with regular air service. Our stock of 13,500 airports is the largest in the world, yet just 140 of the largest hubs carry over 97% of air traffic. This has left many of us with long drives to catch a flight, while on shorter trips we skip air travel altogether. Communities without good air service also struggle to attract investment and create jobs.

Good question.

In theory, yes. It is just a shrouded propeller connected to an electric motor. Spin it fast enough with a big enough fan, and it will produce the thrust. Most of the power of a turbofan engine comes out in the fan as well, so that's not really different.

In practice, that's going to be one heck of an electric motor. The largest aircraft electric motor I know of is the Siemens 260 KW (~350 HP) which weighs 50 Kg (~110 lbs). That could produce roughly the same thrust as, say, a 900 lbf PW610F as used on the Eclipse which weighs 116 Kg (~256 lbs).

The Siemens motor is designed to drive a regular prop at fairly low RPM, so there may be some motor scaling advantages with a faster turning ducted fan engine, but even so, to build a little airliner will take an enormous motor. Let's say you need 3000 lbf thrust from each engine, that will be over 1200 HP electric motor, or about 2 megawatts total aircraft power at full power. To put that in perspective, it would be 1000 volts and 1000 amps for EACH motor. The wiring harness and controller will not be light, either.

Article on the Siemens motor:

http://www.flyingmag.com/aircraft/sieme ... raft-motor

Mike C.

Well, not really. When you put in bigger batteries, you get heavier and need bigger thrust, which needs bigger batteries, and so on.

You end up reaching a point where you can't do better no matter how many batteries you add.

Mike C.

Why does building a crippled electric plane enable that?

If this model works, why isn't anyone doing it now without an electric plane?

Mike C.

But that's a function of battery capacity, not thrust. Put bigger batteries in (or hybrid generator) and it will stay afloat much longer.

This is all just a function of battery density. If the battery density improves 10x, which it will at some point, just no idea when, the rest of the “problems” are not that hard to solve. I have used industrial electric motors in designs with crazy power ratings. To mike c’s point, they were not lightweight bc of all the power we had to push into them. Never compared that weight a turbine plus fuel weight though. My guess is that if you solve the battery weight problem, the other problems will get fixed quickly. Siemens has been working on the aviation electric engine for just a few years and they are making rapid weight savings and power increases.

All the focus should be on batteries though. Without a step function in density it will be tough to have anything much bigger than an all electric 172 flying is around.

I know that. I wasn't discussing whether you can do it today with current battery technology - I know we can't. I was simply pointing that the amount of time the machine can stay up in the air is not really related to the thrust that the engine is providing but rather to the amount of fuel that is consumed to generate that thrust.

Isn't it a matter of physics though? Don't they already know the wall that will be hit? Kinda like you can't fit 2 gallons of water into a 1 gallon jug. No amount of technology will change it.

The material is irrelevant - it's all about thrust to weight ratio. I had that discussion with my brother (heavy R/C flyer) and we've run some comparisons - turns out most of his toys have power to weight ration not that much different from more powerful GA airplanes (think extras, pitts etc).

The problem here is energy storage density - today's batteries are about 10x less energy dense than gasoline, which means you'd need about 1000lbs of batteries to provide the amount of energy that 100lbs of gasoline does. Untill we get there electric airplanes will be only suitable for some missions, mostly training.

But... the airplane seems to be a perfect target for a hybrid solution - let's work on a theoretical hybrid bonanza - you have 3 phases of flight:
1. takeoff where you need all the power you can get (~300HP)
2. cruise, where you normally don't use more than 65% (let's call it 200HP)
3. descend

Now if you put that Siemens motor up front and combine it with small battery capable of providing 100HP for the time needed to get to the altitude and gasoline powered 210HP generator working at constant RPM, fine tuned to operate at most efficient setting. You turn the generator on, throttle full forward and your engine produces 300HP for takepoff and up to your cruise altitude, at which point you level off, reduce power to 200HP and the remaining 10HP from the generator slowly recharges the battery to give you that additional 100HP for go around or cruise climb. Then during descent you can recapture energy from the propeller (turn your electric engine into generator) giving you great speed brake if you need it.

Now the question is - could the weight of tha electric motor and battery be offset by lighter engine/generator combo (should be lighter since we only need 210HP, not 300HP) and by smaller tanks/less fuel needed to fly (since our generator will operate at it's best efficiency all the time)? I don't know, I guess not right now, otherwise it would be flying already. But we will get there sooner than later.

I think you just said in 5 paragraphs what I said in 2 sentences.

The material is relevant..... That's where the weight comes from in your "thrust to weight ratio".

Not going to happen.

Basic physics/chemistry. You need sufficient anode and cathode material to generate the electron reaction. This is a mass overhead you cannot escape for any battery. Lithium batteries improve on this simply by using lighter materials (lithium in particular), but they still need cobalt, nickel, or iron in the cathode.


The battery weight problem is intrinsic, you can't "solve it" to improve by a factor of 10x. You can only work ever closer to the limits and each incremental step is getting harder and harder. Improvements are in single digit percentages now. The closer we get to the edge, the more negative effects (safety, manufacturing cost, rare materials) we start to have.

Mike C.

You've neglected efficiency of the electrical elements.

In the above design, the engine driven generator, wiring, and electric motor form an electric transmission coupling the shaft HP of the engine to the prop. The generator is perhaps about 95% efficient, and electric motor about the same, and the wiring harness perhaps 99% efficient. Net efficiency is about 90%. To get 200 HP at the prop, you need 220 HP at the engine. You could save that 20 HP by direct coupling the prop to the engine.


There is extremely little energy you can recover this way, basically zero. Even when a prop is producing drag, that may still be net positive torque (takes motor energy to turn it).

Case in point, on my airplane, a "zero thrust" setting is about 15% torque (~100 HP per engine). I hardly ever descend at 0% torque (0 HP, nothing to regenerate). I never descend at negative torque, and if I did it would last a handful of minutes at most (it would be basically an emergency descent rate, ~5000 FPM), and it would be trivial amounts of power, not worth the circuitry to regenerate the energy.


No, because you have losses you have not accounted for that trump the supposed efficiency gain of the smaller engine. The engine would also be operating at high power, basically 100%, all the time, so could be expected to have a short life.

Aircraft engines simply don't cruise in a low power mode like cars where hybrid makes sense, a high ratio of peak to average power.

Mike C.

Building a cheap plane enables that. I am totally not convinced that this plane will fulfill that promise, but I am pretty sure that the model will work if/when we figure out how to build cheap planes.