70

Because they are very lightweight and fragile. Therefore, thrust and propulsion mass must be distributed over span - a single, large propeller and motor would put too much force into the structure locally. Also, it would require a higher landing gear to give the larger propeller the required clearance. You are right about the higher losses. However, these ...


66

Short Answer Batteries would need to be somewhere around 16.7MJ/kg to give the same range and performance as liquid fuels, this is about 18.5 times the capacity of the best lithium-ion batteries. Price-wise it will cost about 30-35% to charge your airplane as opposed to fill it with liquid fuels at today's prices. Long Answer This is a good question ...


46

Short answer: No Long answer: No. Look at the solar impulse project, this is some of the best solar-electric technology that's out there, and it's barely able to carry one person, very very slowly. If you took an airliner, covered it in the best solar cells available and connected it to the best electric engines available it probably wouldn't even be able ...


38

Not yet. To look at a medium-range aircraft, let's base the engine on the CFM56 or the IAE V2500. Those engines produce between 100 and 150 kN static thrust. In cruise, their thrust is considerably lower due to the low density in cruise altitude and due to them moving at Mach 0.8. Let's use a value of 25 kN - this is enough so that two of them will ...


26

Was [towing unit or motors in landing gear] ever tested or assessed? Yes. 2014 Main Gear Using the Auxiliary Power Unit (APU) generator to power motors on the main wheels, the EGTS taxiing system allows aircraft to push back without a tug and then taxi without requiring the use of the main aircraft engines. One wheel on each main gear is equipped with ...


24

First, let's figure out how much power a 747 needs to takeoff: Assume: Engine thrust = 284 kN Takeoff speed = 170 knots Takeoff power = 90% max power Using $P=Fv$, converting the variables to SI units, we get $$Power=88,948,800 W$$ Or, in other words, around $90MW$. EDIT: This calculation is only correct if the engine efficiency is 100%, because it is ...


23

Even small 1 hp electrical motors can achieve that RPM Yes, but can it sustain that RPM when something tries to stop it, that is the question. 1 hp combustion engines can get to 2700 rpm as well, but you cannot attach a propeller to it, stick it in the air, and expect it to maintain the RPM. It takes a lot of torque to create aerodynamic thrust. It is a ...


20

How would you communicate with (and power) these motors? The main rotor is spinning constantly - Wires won't work, they would wrap around the shaft and be shredded. A slip ring and brushes (as used in some electically-actuated propellers) would work, but would also wear away quickly and require frequent maintenance as losing control of a helicopter's main ...


19

You're ignoring air resistance. A tiny electric motor can accelerate the prop to 2700 rpm in a vacuum. But at 1 bar, the prop moves against the air (effectively pumping air from one place to another), and this requires torque. An engine with less power won't be able to spin the prop at 2700 rpm. With a variable-pitch prop, you should be able to observe ...


19

There are experimental electric planes. Some are promising enough that they might end up useful as trainers and private GA flown for the love of flying. Long-range electric will not work. The electric equivalent of the Breguet equation is R=L/D*E/W*n/g, where E is stored energy and n is propulsive efficiency. For a 100% efficient L/D=20 aircraft that is 100%...


18

The lift augmentation has nothing to do with Magnus lift (or the Coanda effect). It is simply an increase in the dynamic pressure across the entire streamtube of the wing. At the low takeoff and landing speeds (slightly above a 61 knot stall speed), the induced velocity of the propeller almost doubles the velocity that the wing sees; and the lift is a ...


17

To cover a current-design airliner in solar cells and hook them up to electric engines spinning the fans will not work. Ever. Read @GdD's excellent answer for the reasons. But today's car is also not a horse buggy with a gasoline engine. It has evolved and adapted to the possibilities. The same needs to happen to the airliner. Now let's look at what is ...


15

An answer to your question can be found here. Advantages of ducted fans would be: reduced noise Better containment of broken blades protection of ground personnel when the engine is running Smaller size than a comparable propeller They look like a fancy jet engine. This is probably the main motivation of Airbus for their use on the E-Fan. For almost all ...


15

Variations on this kind of scheme and designs are currently being worked on. From what I remember, using electric motors are still pretty expensive, and also you're using them for a very short time frame, such that you're lugging around extra weight that is useful for a tiny portion of time(aka more fuel burn). Tugs of various sorts have been used at various ...


15

Propellers in some form are really the only option. It is currently the only efficient way to generate thrust with air as a medium. Even jet engines are in some sense just a very elaborate system of propellers. The reason for the turbine is to create an environment to efficiently burn fuel (suck, squeeze, bang, blow) to generate as much thrust as possible. ...


15

Usually an APU provides electricity and bleed-air, just like the aircraft engines do. An all-electric APU only provides electricity. This can be done in the Boeing 787 because of the bleedless architecture where systems that would normally require hydraulic or pneumatic pressure are fully electrified.


15

"Hard" is a matter of opinion. But installing an electric motor on a glider is quite doable. You don't want to put motors on the outside, though. Would make more sense to do what most manufacturers do, put the motor on a retractable pylon behind the cockpit, with doors that open and close as needed.


14

Assuming maximum altitude for the highest blimp is 74,000 feet, and the rail to be angled at 15 degrees, it gives us a rail length of 285,000 feet. The HiSentinel stratospheric airship flew that high, and was able to carry only 36 kg. The steel rail/rope would weigh roughly 5.5 million kg. Based on steel density and a good sized rope, to withstand the ...


14

Conventional commercial designs try to maximize kg-kms per dollar fuel cost or kg payload per dollar investment. Or minimize operating & maintenance cost. All these goals need an economy of scale that forces few large complex turbines. On the other hand, most solar planes focus on raw, dollar-agnostic performance / endurance metrics like max height ...


13

Because it would be too complicated (and failure prone) compared to the present system and would offer no great advantages. First, for all the complexity in the helicopter upper controls, the principle is pretty simple- Align the rotor plane with the (rotating) swash plate, and tilt (or rise) it according to requirements. Source: helistart.com This system ...


13

Engines are great as they are. Electric engines can be fast, powerful and effective. I see two problems: First - the sheer amount of energy consumed by the commercial airplane. With a single engine giving out 200kN you need a small power-plant attached to the aircraft. Even batteries would be 100% effective and could store enough energy, you need to burn ...


13

An all-electric craft similar to what you described has actually been created (IEEE Spectrum did a nice article about it). The batteries are described as 260 Watt-hours per kilogram with a power plant output ratio of over 5 kW/kg. The two-seat craft is designed for training flights, and the fuel for each hour of flight time costs less than one-eighth the ...


12

The jury (i.e. FAA) is still out on this question as of early June 2014. FAA has indicated it will not give a gasoline "fuel allowance" to be credited against weight for batteries. Given that fuel weighs 6 lbs. per gallon, or 30 lbs. for the maximum legal gas an ultralight can carry, it would be a somewhat negligible, but certainly welcome, allowance for ...


12

There is one important disadvantage that batteries will always have compared with fuel combustion for aviation propulsion: the weight remains constant. Airliners (especially those used for long-haul flights) burn off a large percentage of their take-off mass over the course of the flight. Batteries, however, retain their initial mass constantly. This is a ...


12

Don't forget the electrical advantages of multiple motors. No need to conduct all the current to a single place with long lengths of heavy wire, no need to control a large current. Also, many small motors and propellers provide redundant depth/graceful degradation in case of a failure(s).


12

It has been done! In 2008 an Edgley EA-9 Optimist glider was "converted" in very much this manner for a university project, by strapping eight pylons to the wings, each containing a battery pack and two electric motors - one pushing, one pulling - for a total of 16 motors. This might make it the aircraft with the most engines in history! It was test flown ...


11

That electric propulsion needs no oxygen is of little help for flying high. The composition of the atmosphere does not change too much with altitude, so it is the low atmospheric density which limits maximum altitude. We had this discussion before, and indeed solar-electric propulsion helped to reach record altitudes: The AeroVironment Helios set a record at ...


10

The main advantage would be similar to that of blown flaps. The flow around the wing will be slightly accelerated, so it operates at a higher effective dynamic pressure. This helps to prevent flow separation and allows to create more lift from the same wing area. This effect should be especially noticeable at low speed, when the relative speed increase in ...


10

I can't quickly find the necessary numbers for 747-8, so I'm going to go with the numbers for Rolls-Royce RB.211-524G-T, one of options on 747-400, taken from here. The engine can produce static thrust $$ T_s = 58,000\ \mathrm{lb}_\mathrm{f} = 258\ \mathrm{kN} $$ using mass flow rate of $$ \dot m = 1,604\ \mathrm{lb/s} = 727.5\ \mathrm{kg/s} $$ Now due ...


9

I went on a little search on my university library database, and found a review paper. I'm not sure if you can access it without paying. Active rotor control for helicopters: individual blade control and swashplateless rotor designs by Ch. Kessler. Link: http://dx.doi.org/10.1007/s13272-011-0001-0 There, I extracted three sources relevant to your question:...


Only top voted, non community-wiki answers of a minimum length are eligible