Possible new Air Force Osprey idea

[gtx2017]

My friend in the air force was complaining that the military Osprey was bulky, weak, and could be spotted from miles away. I have an idea that uses an electro-magnetic rotated turbine instead of the large and noisy propellers. it would include the encasement of the turbine to make the vehicle more slim and reduce the size of the Osprey. I'm not sure with the physics of the turbines or if it could work at all. I am a high school student looking to see if this is an idea worthy of prototyping.

 

[gtx2017]

By the way, just registered and not sure if I posted in the right place.

 

[boneh3ad]

So basically you want to replace the props with electric turbofans? What are you going to power the turbofans with? Current battery technology can't do anything like that, especially for such a heavy machine. Then you are left with saying "well okay, maybe I will just put an APU in there to generate power," in which case you now are powering an electric jet engine with the power generated by a regular jet engine, and at a loss, to boot.

 

[gtx2017]

What would be necessary to make it possible? it would be powered by batteries and solar panels and maybe a few bloom boxes. Is it the size of the magnets? I would like to research the tech required to start a prototype.

 

[Drakkith]

What would be necessary to make it possible? it would be powered by batteries and solar panels and maybe a few bloom boxes. Is it the size of the magnets? I would like to research the tech required to start a prototype.

I would suggest getting a degree in aerospace engineering. There's no possible way we could walk you through something like this here on the forums. There's simply too much you need to know.

Here's a link to a job related to this so you can see the requirements yourself: http://www.linkedin.com/jobs2/view/11572539?trk=job_view_similar_jobs

 

[Bandersnatch]

You need two engines of comparable power to those already incorporated, so that's about 9MW. The best solar panels can produce about 175W from a square metre in full sunlight. Assuming you could fit 10 square metres of panels onto the plane, you get a whooping 0.002% power requirements satisfied.
Even an imaginary, 100% efficient solar panel would only bring that number to about 0.01%.

As for the batteries, Lithium-ion batteries have specific energy of about 0.5 MJ/kg, meaning you'd need 18kg of batteries to power the engines for 1 second. An hour-long flight would require 65 metric tonnes of batteries to be carried on board, tripling the normal loaded weight of the craft, requiring three times more powerful engines, which in turn require three times as many batteries, and so on.

I don't know anything about bloom boxes, but I wouldn't expect them to be much of an improvement.

Heavy-duty electric-powered transports are just not very feasible with current technology.

 

[cjl]

Also, keep in mind that a lot of the noise simply comes from spinning a propeller in air with sufficient speed to lift the aircraft - replacing the engines with something silent wouldn't even come close to silencing the aircraft as a whole. Shrinking the props and putting them in ducts (similar to a jet engine) wouldn't solve the problem either - the smaller you make them, the more power will be required, and the higher the speed of the jet of air coming out the back will be (which creates a lot of noise as well). The best bet for making a quieter rotorcraft is probably to increase the size of the rotor, decreasing disk loading, decreasing power requirement, and decreasing the downwash velocity for a given amount of lift, but you obviously run into limits here too due to the physical constraints of the aircraft.

 

[mheslep]

Current battery technology can't do anything like that, especially for such a heavy machine...

The electric power required from both batteries and electric motors is readily available at that scale and much larger. What is not available via batteries is sufficient energy density storage to maintain such an aircraft in the air for any practical period of time.

 

[mheslep]

...maybe a few bloom boxes. ...

19.4 tons each for the 210 kW model, *not* including fuel.

 

[mheslep]

...

Heavy-duty electric-powered transports are just not very feasible with current technology.

I think it is more accurate say *long-range* electric-powered aircraft are not practical with current technology. If transport is not restricted to aircraft, there have been electric powered trains for decades, now even electric powered naval ships.

 

[russ_watters]

. If transport is not restricted to aircraft, there have been electric powered trains for decades, now even electric powered naval ships.

Er, hybrids, not direct electric power. And electric hybrid ships have been around for a century as well.

 

[mheslep]

Er, hybrids, not direct electric power. And electric hybrid ships have been around for a century as well.

I don't mean the old diesel-electrics. The Zumwalt class will (has?) have the propellers driven only by powerful electric motors (46 thousand HP), with the energy for the e-motors coming from combustion driven generators.

All electric propulsion system

Zumwalt will be the first US Naval surface combatant to feature all-electric propulsion. The DDG 1000 integrates an all-electric drive with an integrated power system (IPS) consisting of two Main Turbine Generators (MTG), two Auxiliary Turbine Generators (ATG) and two 34.6MW Advanced Induction Motors (AIM).

http://www.naval-technology.com/projects/dd21/

 

[russ_watters]

I don't mean the old diesel-electrics. The Zumwalt class will (has?) have the propellers driven only by powerful electric motors (46 thousand HP), with the energy for the e-motors coming from combustion driven generators.

http://www.naval-technology.com/projects/dd21/

Could you explain the difference?

 

[SteamKing]

I don't mean the old diesel-electrics. The Zumwalt class will (has?) have the propellers driven only by powerful electric motors (46 thousand HP), with the energy for the e-motors coming from combustion driven generators.



http://www.naval-technology.com/projects/dd21/

In the early years of the 20th century, steam turbines were directly connected to the propeller in large ships. This made the turbines into low-speed machines in order to prevent cavitation of the propeller. When combined with the low steam pressures of that era (less than 250 psi), a main propulsion steam turbine for a ship was a huge machine.

Then, someone hit on the idea of putting a reduction gear between the turbine and the propeller, so that the turbine could run at high RPMs without overloading the propeller. The problem was, cutting such large, high powered gears took a lot of machining resources and pushed the engineering envelope of the time.

General Electric, among others, hit on the idea to use the turbines in the ship to drive an alternator, which would supply current to a large AC motor connected to the propeller shaft. The turbine could not only be run at high speed, but it could also be run at a constant speed as well. The AC motor could be designed to turn at low RPMs which the propeller liked, and, by switching the polarity of the motor, could provide full backing power, unlike geared turbine vessels, which can only provide a fraction of ahead power when going astern.

The US Navy like the concept so much, they built a class of three colliers (coal carrying vessels) which were powered with the new turbo-electric power plants. Satisfied with these ships' performance, soon all large US naval vessels, like battleships and battle cruisers, were being designed and built with these new power plants.

http://en.wikipedia.org/wiki/Turbo-electric_transmission

After WWI, there was a cessation of large naval ship construction as the various disarmament treaties took effect. This 'holiday' allowed for more time to develop other improvements in naval ship propulsion, like high pressure boilers and double-reduction gears.

The turbo-electric concept was revived during WW II, when faced with constructing an enormous number of merchant and naval vessels, the US authorities had to make some hard choices about allocating the manufacturing resources available. The decision was to use turbine reduction plants as much as possible in new warship construction. Other types of plant were to be utilized for constructing the new merchant vessel designs.

In the Liberty ship class (over 2700 vessels constructed), a reciprocating steam engine was used to simplify construction. For its new tankers, the USN chose the T2 design (almost 500 built) which revived the turbo-electric power plant. These vessels could use a more modern steam turbine, but did not need to have reduction gears fabricated.

http://en.wikipedia.org/wiki/Liberty_ship

http://en.wikipedia.org/wiki/T2_tanker

Like the Liberty ships, the T2s remained popular after the war for new companies entering the shipping business. The vessels could be purchased rather cheaply, and were economical to operate. Many T2s were converted later in life, with the owners keeping the stern section where the power plant was located, and building and attaching new forebodies to the stern to extend the working life of these vessels.

 

[mheslep]

Could you explain the difference?

In reference to your hybrid reference, as I understand it, historically some marine propulsion systems made use of both the diesel or steam turbine drives connected to the shaft in tandem (clutch?) with an electric motor. This is not the case with the Zumwalt destroyer, in which the gas turbines run generators which drive electric motors, the only connection to the shaft.

Steam King does a nice job of describing the evolution of steam generated, electric drive. The Zumwalt is similar though the turbine is gas combustion, not steam driven.

 

[FactChecker]

My two cents:
1) It's hard to beat gasoline when it comes to specific energy unless you start talking about nuclear reactors.
2) Regarding inclosing the turbines, check out the ARES DARPA program that Lockheed Martin is doing: http://www.lockheedmartin.com/us/products/ares.html