They take the power from the small aux. motor in the back of the plane and drive the plane with.
Airplanes are step by step becoming more electrical. I read that all in all, there is something like 500 kW of power distributed by a 115/200V 400 Hz system in upcoming airplanes. It's just a question of time before you will be asked to do the rough in on a 787.
Maybe we should ask Winnie in chorus how this little motor can move a big airplane?
Ever think of why they haven't done it before? Thats 10-50 jobs at every airport in the world. Most major commuter aircraft already have reverse thrust deflectors. Big scoops that fold back over the exahst that enable the same thing for push back, so long as jet wash areas are clear. There are usually baggage handlers there.... They could automate that too, but they haven't.
Mark Heller "Well - I oughta....." -Jackie Gleason
#62469 - 02/16/0611:55 PMRe: OT: Electric airplane
I'm not sure how much I can say, since there is quite a bit of proprietary data involved
The Chorus technology is my personal baby; I spend my day trying out different winding designs and control approaches, and trying not to blow up transistor arrays. (I've gotten pretty good at this, our last failure was not a transistor, but a 900V capacitor bank letting go at 1200V, ooops)
The whole reason for Chrous in this application is _overload_ operation. These motors are not used at their continuous rating, but instead at their 5-15 minute rating, and are expected to go from ambient (40C) to maximum winding temperature (180C) over the course of operation. Chorus motors work very well in this sort of operating regime.
I will say that the power levels involved in an airplane are causing things to move to 480V electrical distribution, and because the alternators are a 'parasitic' load on the jet engines, there is a strong push to 'wild frequency' power.
Air conditioning is currently done with 'bleed air'. Air is compressed at the front of the jet engine, mixed with fuel, burnt in the center and shot out the back. Air for the AC is 'bled' off prior to being mixed with fuel. This, of course, means that the air is not available for thrust production, so one goal is to get rid of bleed air, instead using electric power for air conditioning and cabin pressurization. This is a very large electrical load.
Compared to all of the other loads, actually moving the plane at low speed is pretty small.
BTW, bringing this back on the electrical topic, this was the project that got me looking at impedance grounded systems. For the demo system, we were not covered by NEC, but we wanted to maximize safety and minimize any chance of damage to the aircraft in the event of a ground fault. In particular, in the event of a ground fault, we didn't want however many hundreds or thousands of amps flowing through the aircraft chassis until a breaker tripped. So we powered the system from a 277/480V wye source with a 50 ohm resistor between neutral and ground. We used a ground fault relay set at 2A tied to a shunt trip on the main breaker. A bolted ground fault would cause about 6A to flow, and as soon as a fault was detected we would trip out the source. The major point that was not NEC compliant was that there were a few line to neutral loads.
#62470 - 02/17/0606:56 AMRe: OT: Electric airplane
The airplane business industry is conservative, that's for sure...
Winnie, Aha, I suspected that you would run the motor hot.
I can see the point of "wild frequency". It was the way power plants were built before the concept of "power grids" was introduced. Small plants, like wind mills, are now using it. (Again)
Could this mean the end of 400 Hz?
Raw "wild frequency" power from the engines, used for various aircraft system while all cabin loads (lights, outlets, galleys, entertainment system) will run on ordinary 120V 60Hz or 230V 50Hz ground power? (A coffe machine or a TV screen for an airplane is EXPENSIVE)
#62471 - 02/18/0601:55 PMRe: OT: Electric airplane
OK, I only fly small airplanes with a Cherokee Six being the biggest. Powered towbars on the nose wheels of small aircraft are nothing new. I started losing track when A/C and bleed air and reverse thrust started coming up.
My understanding of jet HVAC is that high temp bleed air from the compressor section is mixed with low temp (around -50 C) outside air to provide make-up air under control of the cabin pressurization system. I think bleed air would have a minor impact on modern high bypass turbofan aircraft engines.
As far as pushing back is concerned, I can't imagine using the clamshells or beta thrust to do that except under some strange emergency. Are we talking about attaching these motors to a landing gear bogey? If we are talking about a connector nearby to power something that stays on the ground, I'm all for it. If it's an assembly that stays on the bogey, no thanks. We've had 2 incidents in the last year where we watched airliners that couldn't get three in the green, make fantastic precautionary landings. The more things that get hung on the gear, the more components to fail. Joe
#62472 - 02/18/0602:51 PMRe: OT: Electric airplane
These things will become a _permanent_ part of the nose gear assembly.
There isn't enough room on the main gear; they are full of brakes.
Some airlines have experimented with using the thrust reversers to pushback from the gates. Bad idea; you blow lots of stuff up that then gets sucked into the engines. 'Foreign object ingestion' is a big baddie on jet engines. Using the nose gear for pushback offers another safety benefit: when a transport aircraft is moving in reverse, you really _don't_ want to use the main brakes to stop it; the CG is way too close to the main gear, and there is a significant risk of tipping. If you use the nose gear for breaking as well, then you can't tip back.
I don't know the details of bleed air effect on the engines...I just know that the engineers who work with it despise it.
The jet engines are very inefficient for ground operations. The estimate is that using APU power to move the aircraft through nose gear will save upwards of 200lb of fuel per flight.
The increase in APU power is significant but small. The hotel load on a modern transport aircraft is tremendous.
#62474 - 02/18/0609:05 PMRe: OT: Electric airplane