Electric planes

[Tdave]

Perhaps bringing this thread down to earth and off on a new heading...

I have heard about adding electric propulsion for taxiing, firing up the jet engines just before takeoff and shutting them down immediately after touchdown. That seems to make a lot of sense.

Is there enough time at the gate to recharge the batteries if only used for that purpose?

[doug]

I think only the most recent Harrier has achieved both vertical launch and supersonic flight in the same aircraft.

I think you mean the F35. One of the most awesome planes I've ever had a chance to see in person.

I have heard about adding electric propulsion for taxiing, firing up the jet engines just before takeoff and shutting them down immediately after touchdown. That seems to make a lot of sense.

If that's all it's going to do, you might be better off just using some kind of EV to tow the plane to and from the runway. (Might have to take more precautions to avoid ground collisions, though.)

[dpeilow]

Very interesting, but 50-60 min run time is pretty limited.

However, wasn't the 2 x 745 kW for the DC-3 engines? According to Wikipedia (ultra reliable, I'm sure) the Dash 8 has 2 x 1800 shp turboprops. So 2686 kW would be required instead of 1490 kW, reducing the run time from 60 min to only 33 min.

You are right, but the Dash 8 does have a much faster cruise speed than a DC-3 so it needs the extra power. I was looking at that plane as an example of the masses that could be saved if one around that size was made electric, just to see if this idea would fly (ahem). I suppose that the advantage of an electric design would be that you could have 2MW motors for take off if needed and still throttle back to a lower speed only using the power talked about above.

As for the usefulness, well around the UK and Ireland there are plenty of turboprops flying routes well under 150 miles and I'm sure that is the case with other island nations too. So if this can significantly lower running costs, there could be a market there. It's worth a closer look I think.

I have heard about adding electric propulsion for taxiing, firing up the jet engines just before takeoff and shutting them down immediately after touchdown. That seems to make a lot of sense.

I believe that the original PML Flightlink pancake motors were developed for aircraft landing gear. Was this the intended purpose?

Is there enough time at the gate to recharge the batteries if only used for that purpose?

Well, having a high power charger in that environment is more likely to be approved than on the street, and if the fuel saved in taxing more than offsets the mass, then this could be an application for the AltairNano battery (hey, if EEstor come through, that would be excellent for this discussion).

I think you mean the F35. One of the most awesome planes I've ever had a change to see in person.

The friend at Rolls Royce that I mentioned in the Lotus EV thread is working on the lift fan for that. But he said that the vertical take-off done by the prototype was basically a stunt that only that plane could do - the production F-35B spec will be short take-off/vertical landing.

But I agree, it is awesome.

If that's all it's going to do, you might be better off just using some kind of EV to tow the plane to and from the runway. (Might have to take more precautions to avoid ground collisions, though.)

Not sure if it is with EVs, but Richard Branson proposed doing this.

[TEG]

I believe that the original PML Flightlink pancake motors were developed for aircraft landing gear. Was this the intended purpose?

Were you thinking of Chorus?
Electric motor propels Boeing 767 - on the ground : August 2005
Electric WheelTug System to Move Planes on the Ground - 2007-11-19 00:00:00 - Design News
http://www.teslamotorsclub.com/techn...html#post14690

[dpeilow]

That's the same - but I remember reading it on PML's site that they were proposing that 30 years ago. (BTW it was trying to find that again that I saw the bad news.)

[GSP]

I suppose that the advantage of an electric design would be that you could have 2MW motors for take off if needed and still throttle back to a lower speed only using the power talked about above.

As for the usefulness, well around the UK and Ireland there are plenty of turboprops flying routes well under 150 miles and I'm sure that is the case with other island nations too. So if this can significantly lower running costs, there could be a market there. It's worth a closer look I think.

Ah.... Island hopping. I hadn't thought of that. My midwest US mentality just assumed that I could drive 150 mi and be at my destination faster and cheaper than flying, and have my car, luggage, etc! Doesn't work to well once you get to land's end (a concept that I've read about, but rarely experienced).

I don't understand the 2 MW motor comment though. If the motors were any more powerful than needed for takeoff, wouldn't that add a *lot* of unnecessary weight?

GSP

[dpeilow]

Well, I know that in some other applications, double the output for a short time is possible. It was only in answer to whether that much power was needed for the Dash 8-sized airframe. There must be a runway length / engine power trade-off and this is where we have to go off and do some proper engineering

By the way, I've recently read that for sustained output, just over 1kW/kg is a good number for a state-of-the-art motor. How does that compare with Tesla's?

[TEG]

By the way, I've recently read that for sustained output, just over 1kW/kg is a good number for a state-of-the-art motor. How does that compare with Tesla's?

Tesla eMotor:
~185kW, ~35kg. ~5kW/kg. Not bad. And that isn't even the sport motor.

[dpeilow]

Tesla eMotor:
~185kW, ~35kg. ~5kW/kg. Not bad. And that isn't even the sport motor.

Hmm... I thought circa 200kg seemed a tad on the heavy side.

Well, I guess that calls into question the claims of the other source, although they would have to run flat out at very high power levels for hours at a time (and it is a well respected electrical engineering company).

More investigation required...

[TEG]

Maybe ~35kg is a bit on the low side.

I see a fair amount of variation in reported motor weight...

Tesla Roadster

The Tesla Roadster runs on a 3-phase, 4-pole electric motor that weighs a mere 70 lbs.

Green Car Congress: Tesla to Use Interim Transmission to Get Production Roadster Out the Door

they managed to build a 248 hp electric motor that weighs only 70 lbs.

Medieval's Blog!: The Tesla Roadster

...it weights 70 lbs.

apr 07 business | The Global Intelligencer

No larger than a watermelon, the whole motor weighs around 70 lbs.

Tesla Motors - think

(70 lbs for the motor, ~160 lbs for the motor, differential and transmission).

Thermal Systems: Tesla Motors

The Tesla Roadster motor is a 3-phase, 4-pole electric induction motor. The motor is equivalent to the size of a large watermelon and weight about 100 lbs.

Tesla Motors - under the skin (Motor section)

The Tesla motor weighs less than 115 pounds...

The Tesla Roadster - the perfect Elise? (by The Racing Geek)

The electric motor spins up to 13,500 rpm and produces 248 bhp and 200 ft/lbs of torque while weighing just 125 lbs.

So, depending on where you look the motor weighs between 70 and 125lbs (32-56kg). Perhaps the old/lower number was without cooling fan shroud? I don't know why the weight would have gone up over time.