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Diesel Engine vs. Electric Motor

11/09/2017 1:54 PM

Gentlemen,

I need your input on a project I'm working on. To keep it simple, I want to determine what it would cost in dollars and pounds (weight) to replace a propulsion system that used 4 diesel engines.

Here's the breakdown on what was originally used:

4 diesel engines

max hp = 1350 each

cruise hp = 900 each

weight = 4300 lbs each

Each diesel engine drove a 4 bladed propeller via a transmission that reduced the rpm's 2:1

For the upgrade, I need to know if the following is possible and what the costs would be in dollars and pounds (weight):

  • Replace the diesel engines driving the propellers with electric motors having the same capability (hp range).
  • Provide the electrical power for the 4 electric motors from 2 generators driven by 2 diesel engines.
  • Assume the thrust output from the propellers will remain the same.

Initially, I considered the option of replacing the 4 diesel engines with turboprop engines, however the fuel consumption of the turboprop counterpart causes operational costs to skyrocket.

In addition, based on my research turboprop engines are most effective in an application that utilizes high speed and high power to weight ratios. They can offset their fuel consumption by reducing travel time.

Ours is a low speed application ~ 80 mph cruise speed.

For your reference, please review the Hindenburg's specs at the following link:

http://www.airships.net/hindenburg/

I appreciate any feedback and guidance.

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#1

Re: Diesel Engine vs. Electric Motor

11/09/2017 2:07 PM

Well the motors would have to be designed specifically for this airship, so no specs available....The costs would be quite high, probably well into the 10's of millions....

..."

NASA Electric Aircraft Testbed[edit]

NASA Electric Aircraft Testbed

NASA research agreements (NRA) are granted to develop electric-propulsion components. They will be completed in 2019 and the internal NASA work by 2020, then they will be assembled in a megawatt-scale drive system to be tested in the narrowbody-sized NASA Electric Aircraft Testbed (NEAT) at Plum Brook Station, Ohio.[60]

The University of Illinois is developing a 1-megawatt permanent magnet synchronous motor spinning at 18,000 rpm to drive a Rolls-Royce LibertyWorks' Electrically Variable Engine turbofan from a battery for taxiing, takeoff and idle descent in a parallel hybrid. Ohio State University is building 300-kW and 1-megawatt prototype motors, a 2,700 rpm, 1-m (3.3-ft) diameter, 2.7-megawatt liquid cooled ring induction motor and designed a 5,000 rpm, 10-megawatt turbofan integrated ring motor. These electric machines target 13 kW/kg and over 93% efficiency, while NASA Glenn Research Center is developing a superconducting electric machine with a 16 kW/kg goal and above 98% efficiency: a 0.4-m-dia, 6,800 rpm, 1.4-megawatt wound-field synchronous motor using a self-cooled, high-temperature superconductingrotor winding.[60]

The highest voltage used now is 540 (±270) volts, but distributing megawatt-scale power will require higher voltage to reduce current for smaller, lighter electric cables. One megawatt over 150 ft (46 m) need 900 kg at 540 V but would be reduced to 200 kg at 2,000 V DC. A near-term hybrid would need 1,000–3,000-volt and a fully turboelectric large aircraft 5,000–10,000-volt, like ship power systems but arcingoccurs at much lower voltages at low pressures than at sea level.[60]

While a battery power source would use a direct current distribution, a gas turbine power source would also allow alternating current which would need power converters, mainly inverters to convert DC to controlled, variable-frequency AC to regulate a motor speed and torque. Silicon carbide [SiC] and gallium nitride [GaN] switches can operate at higher frequencies with lower losses, increasing efficiency. GE is building a 2,400-volt DC, 1-megawatt inverter with SiC switches and its 1.7-kW MOSFETs power modules. The University of Illinois is building a 1,000 volts DC, 200-kW “flying capacitor” scalable to a 1-megawatt with GaN-based field-effect transistor switches. Both are liquid cooled and target 19 kW/kg at 99% efficiency but Boeing is developing a cryogenically cooled 1-megawatt inverter for 26 kW/kg and 99.3% efficiency with off-the-shelf silicon semiconductors, and is currently fabricating a liquid-nitrogen-cooled 200-kW inverter before a 1-megawatt one.[60] "...

https://en.wikipedia.org/wiki/Electric_aircraft

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#2
In reply to #1

Re: Diesel Engine vs. Electric Motor

11/09/2017 2:28 PM

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#4
In reply to #2

Re: Diesel Engine vs. Electric Motor

11/09/2017 2:55 PM

SolarEagle

Great video!

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#3
In reply to #1

Re: Diesel Engine vs. Electric Motor

11/09/2017 2:32 PM

Thanks for your post, but this is for an airship application not an airplane so the requirements aren't nearly as demanding.

It can easily be satisfied with off the shelf products currently available. The trick is determining what the requirements are and what products can meet those requirements.

As an example, an airplane, I believe it was a Dornier model, was outfitted with off the shelf electric motors and lead acid batteries in the 1970's and test flights performed.

Thanks for the post.

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#5

Re: Diesel Engine vs. Electric Motor

11/09/2017 2:56 PM

Consider this: will you be wanting to change the rpm's and the prop pitch also?

Will your power system be DC, pulsed DC, or AC? If AC, how many phases, etc.

I suspect the maximum horsepower ratings of the electric motors should be at least 120% of the diesel maximum horsepower rating, but never operated above 100%, and as such you may run into some weight penalty for the overall power system.

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#6
In reply to #5

Re: Diesel Engine vs. Electric Motor

11/09/2017 3:10 PM

James Stewart

Thanks for the post!

We definitely want variable pitch propellers.

I would prefer AC over DC as it's my understanding that most commercial aircraft already utilize AC and it's easier to produce. That said, if I want to store some of the AC for future use, I'll have to get creative for our application. The real question is what are the efficiency and weight differences between an AC vs DC motor with the same specs?

If the diesel engines could provide 850 to 1300 hp, will I look for electric motors of the same hp rating, or is there a difference? From research, it's my understanding that when comparing electric motors to gas or diesel, just comparing hp ratings isn't correct as we're not comparing apples to apples. I need clarity on this point I think in order to go forward.

Also, I would be willing to take a slight hit on the weight side in order to gain something on the efficiency side. Increasing build cost slightly to reduce operating cost.

Again, thanks for the post!

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#7
In reply to #6

Re: Diesel Engine vs. Electric Motor

11/09/2017 3:49 PM

Yes the torque curves are quite different....

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#9
In reply to #6

Re: Diesel Engine vs. Electric Motor

11/09/2017 4:34 PM

Advices: Listen carefully to senior engineers on this site, such as Solar Eagle.

Some of these fellows here know a great deal more about electric motor performance than I.

For sure, AC motors are less heavy than DC ones of the same torque, I suspect, especially when you get into large HP values.

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#8

Re: Diesel Engine vs. Electric Motor

11/09/2017 4:33 PM

I just searched for 1000hp ac electric motors and everything I saw was over 6000lbs.

Surely you can get the same hp with a lot less weight with a diesel engine.

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#10
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Re: Diesel Engine vs. Electric Motor

11/09/2017 4:48 PM

Nice catch, brother. It is true that electric motors are not necessary light weight, nor small in stature.

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#11
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Re: Diesel Engine vs. Electric Motor

11/09/2017 4:50 PM

JPool,

Thanks for the post!

When I did my initial research on this subject, I found the same to be true when comparing hp to hp. The electric counterpart was much heavier. However, comparing hp to hp values between gas power engines and electric motors is not a correct comparison. There's more involved and it's in that realm that I need greater understanding.

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#12
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Re: Diesel Engine vs. Electric Motor

11/09/2017 5:14 PM

What's wrong with hp to hp?

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#13
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Re: Diesel Engine vs. Electric Motor

11/09/2017 5:47 PM

Tornado,

As SolarEagle pointed out above, there's a major difference in the torque curves when comparing a reciprocating engine to an electric motor.

If I have an application that requires 800 hp at continuous load I would utilize an electric motor that provides 800 hp at continuous load, but the reciprocating engine would have to be at a higher hp rating as reciprocating engines are rated at peak load. So a reciprocating engine capable of operating at 800 hp continuous load would rated in the neighborhood of 1200 hp give or take.

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#38
In reply to #8

Re: Diesel Engine vs. Electric Motor

11/13/2017 11:08 AM

Impractical. The weight of a diesel generator engine, the generator, fuel, 4 electric motors at ~1,350 HP, medium voltage distribution gear with VFD's or eddy current speed controls will really reduce payload and cargo volume.

Though pushing technology, perhaps a larger number of shaft-mounted rotary engine propellers fueled by https://www.physicsforums.com/threads/lithium-hydride-as-energy-source-for-combustion-engines.698803/ or wait for motor-applied linear/ring technology . . . https://www.researchgate.net/publication/3929998_Propulsion_control_in_a_linear_electrodynamic_motor_with_two_degrees_of_freedom

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#14

Re: Diesel Engine vs. Electric Motor

11/09/2017 6:29 PM

For your weight estimate, you'll need to look at total system weight, comparing both power sources and their fueling and support systems sized to sustain some defined flight time duration.

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#15

Re: Diesel Engine vs. Electric Motor

11/09/2017 6:46 PM

I think a more important point as far as weight is concerned is storing the energy, i.e., the weight of batteries vs the weight of a fuel tank with the equivalent amount of fuel energy.

Battery
Type
Cost
$ per Wh
Wh/kgJoules/kgWh/liter
Lead-acid$0.1741146,000100
Alkaline long-life$0.19110400,000320
Carbon-zinc$0.3136130,00092
NiMH$0.9995340,000300
NiCad$1.5039140,000140
Lithium-ion$0.47128460,000230

http://www.allaboutbatteries.com/Battery-Energy.html

Energy density of diesel fuel = 11.6 KWh/kg = 11.6 x 3600 x 1000 = 41,760,000 J/kg vs 460,000 J/kg for Lithium-ion

https://hypertextbook.com/facts/2006/TatyanaNektalova.shtml

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#16

Re: Diesel Engine vs. Electric Motor

11/09/2017 8:55 PM

https://en.wikipedia.org/wiki/Lockheed_Martin_P-791

@$40 million each....

https://www.hybridairvehicles.com/aircraft/airlander-10

https://en.wikipedia.org/wiki/Hybrid_Air_Vehicles_HAV_304/Airlander_10

@$25 million each....

..."‘Hybrid airships’ – some prefer the term ‘hybrid aircraft’ – are the modern versions of the great vessels that, for a brief period in the 1930s, seemed as though they were the shape of future air travel. The dreams of their proponents came to a sudden halt after the destruction of several in devastating fires, caused by their use of highly-inflammable hydrogen to create lift.

Compared to those vessels the new-generation designs are, effectively, inflated flying wings that produce a sizeable percentage of their lift from their aerodynamic shape. And by the end of this decade a Dubai-based company, Airships Arabia, plans to have bought examples of two different hybrid aircraft. One, Lockheed Martin’s P-791 Hybrid Airship, will have a 10ft x 10ft x 60ft cargo bay capable of carrying a 21-tonne payload and 19 passengers.

A British counterpart, the Airlander 10, has a smaller payload of 10 tonnes, but space for 48 passengers. And the latter’s manufacturer, Hybrid Air Vehicles, plans rapidly to follow up its initial model with the substantially larger Airlander 50, which will have a payload of 50 tonnes, or six standard ISO shipping containers.

Airship enthusiasts have been predicting for at least 30 years that airships were on their way back, focusing on their abilities to deliver people, but primarily cargo, to remote spots that lacked surface transport infrastructure.

In the early years of this century, for example, a German company, CargoLifter, got quite far down the road to developing a leviathan that could lift a 160-tonne payload. However, it ran out of funding before it could get the craft into production. And Zeppelin, the most famous name in airships, is still in business, but only in a modest way, flying tourists on pleasure trips around southern Germany.

This time, however, say airships’ supporters, everything is in airships’ favor to make a comeback. Airships use considerably less fuel than conventional aircraft, which will give them good operating economics when fuel prices rebound in the next few years. They don’t need much in the way of ground support or basing facilities. And they can deliver outsize, heavy loads to remote areas that do not have airstrips.

Airships Arabia sees several different roles for its new vehicles. One is transporting fresh flowers from Kenya, a major growing region for blooms, up the East African coast to Dubai, which is a distribution point for fresh flowers all over Europe. "....

https://airwaysmag.com/industry/new-airships-get-second-wind-dubai/

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#17
In reply to #16

Re: Diesel Engine vs. Electric Motor

11/09/2017 9:21 PM

..."Propulsion

The Airlander 10 is powered by a total of four Thielert Centurion 325 hp V8 diesel engine which drive sets of three-bladed ducted propellers to provide the thrust for both flight and manoeuvring.[14][17] These engines are positioned in pairs, one set being located towards the rear of the airship, while the other are positioned alongside the sides of the forward fuselage, mounted on stub wings. Each engine is furnished with a 50KW generator, which provides electrical power for the airship and its mission systems.[17] The assembly for each of the side-mounted engines can be pivoted 20 degrees in either direction, vectoring the thrust to provide flight control, particularly during landing and taking off; the rear-mounted engines are fixed.[6][17] By employing thrust vectoring, the engines can direct their thrust downwards to provide additional lift during takeoff.[6] A series of four triangular-shaped variable vanes are positioned behind the engines to provide further control authority; such as by re-directing thrust from the rear engines over the tail fins.[17]

While cruising at altitude, propulsion can be switched to a more efficient electric drive fed from the airship's central generator. Due to the hybrid aerostatic/aerodynamic lift approach, fuel can be expended without entering a state of positive buoyancy that would necessitate routine helium venting in order to land, a costly weakness present upon conventional airships.[6][5] Fuel is primarily contained within the 40-ft.-long main fuel module housing up to nine tons of fuel; the main tank is supplemented by separate rear and forward tanks, containing up to 4 tons. To optimise cruising efficiency, the angle of incidence can be adjusted by pumping fuel between the fore and aft tanks.[17]"...

https://en.wikipedia.org/wiki/Hybrid_Air_Vehicles_HAV_304/Airlander_10

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#18
In reply to #17

Re: Diesel Engine vs. Electric Motor

11/09/2017 9:34 PM

..."The 75° V8 DOHC 4 valves per cylinder was initially equipped with two turbochargers and weighting 283.5 kg (625 lb) dry for 228 kW max (310 hp) till FL80 at 2300 rpm at the propeller, and 176 kW (250 hp) in cruise for 29.5 l (7.8 US gal)/h and 25 l (6.6 US gal)/h at best economy, for 208 g/kW/h (0.342 lb/hp/h), it was planned for a production of 600 per year.[3]

Designed as a larger engine to replace the 300 hp (224 kW) gasoline engines and developed from the Mercedes-Benz OM629 automobile engine, it produced 350 hp (261 kW) later with a larger single turbocharger."....

https://en.wikipedia.org/wiki/Thielert_Centurion

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#19
In reply to #18

Re: Diesel Engine vs. Electric Motor

11/09/2017 10:42 PM

SolarEagle,

Thanks for the posts!

If you've done your research on any of the current hybrid offerings then you're already aware that the 3 prototypes, Airlander 10, P791, Dragon Dream (actually a fully rigid airship) have been in development for at least 15 years and have cost the US taxpayers somewhere in the neighborhood of $300 million.

Aeroscraft's Dragon Dream unfortunately met its demise when its hangar roof collapsed and destroyed it.

The 2 remaining prototypes have no real capabilities and at $40 million each for the full scale version are overpriced to the point of impossibility.

There's a better more economical way, one that has resiliency.

As for the diesel aircraft engines, their technology is still in development. They were developed to replace the reciprocating engines in smaller aircraft as there's a fear that the environmentalists are eventually going to succeed in the extinction of certain aviation fuels. In their early stages, they had issues dealing with higher altitudes and several of the companies involved in their development went belly up. However, a couple still remain and are making slow progress but as you can see they're only in the 300 hp range.

Here's the specs on the diesel engines used in the Hindenburg:

· Main powerplant: 4 Daimler-Benz 16 cylinder diesel engines

o 1320 hp @ 1650 RPM (maximum power)

o 850 hp @ 1350 RPM (cruise setting)

o 900 hp @ 1480 RPM

Reference website: http://www.airships.net/hindenburg/size-speed/

Thanks again for the posts.

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#20
In reply to #19

Re: Diesel Engine vs. Electric Motor

11/09/2017 11:41 PM

You did catch this part?

..."While cruising at altitude, propulsion can be switched to a more efficient electric drive fed from the airship's central generator."...

...and you realize the airships shown here have a different shape than the Hindenburg in that they are shaped as an airfoil ....this decreases the amount of power needed to propel the airship greatly, that and lighter material construction together with attitude adjustment through fuel location manipulation and vectoring ....The Airlander 10 is said to have a cruising speed of 92 mph and a ceiling of 20k ft.... So matching power requirements to a 70 year old design may not be the way to go...

Performance

  • Cruise speed: 148 km/h (92 mph; 80 kn)
  • Endurance: 5 days manned
  • Service ceiling: 6,100 m (20,000 ft)
    Loiter speed 20 knots (37 km/h)

http://www.bbc.com/news/uk-england-beds-bucks-herts-40272708

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#24
In reply to #20

Re: Diesel Engine vs. Electric Motor

11/10/2017 9:45 AM

SolarEagle,

Thanks for the posts.

I'm hoping if I keep digging and you guys keep contributing we'll eventually get the design fleshed out and can take an honest look at its capabilities and costs.

As for the 3 prototypes (Airlander 10, P791, Dragon Dream), I've been following their development for several years and I'm always amazed by the advertising of their capabilities yet they remain only prototypes. No discredit to the men and women who have worked so hard to develop and build them.

I must mention that the 3 prototypes have been in development for nearly 20 years and have cost the American tax payers literally over $300 million in development costs. The US gov. has spent in excess of $1.4 billion pursuing the technology in general. That's a lot of $$ for very little return.

The German's however, started their technology from virtually nothing, perfected it, built 120 airships, used the technology to bomb England during WWI, flew thousands of missions, were the first in nonstop transatlantic flight, carried thousands of passengers injury free, were the first to fly passengers around the world, set the early standards for commercial aviation, and did it all in less than 40 years.

Now that's an accomplishment!

Please keep digging and posting, the knowledge is out there we just need to piece it together and then take an honest look to determine if it's something that will work or just another Frankenstein.

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#26
In reply to #24

Re: Diesel Engine vs. Electric Motor

11/10/2017 10:51 AM

Yes but the 5k airships that Germany built all eventually crashed and burned, not an insignificant detail...

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#27
In reply to #26

Re: Diesel Engine vs. Electric Motor

11/10/2017 11:18 AM

2 November, 2017 - 14:12 By Tony Quested

Luxury travel company to trial hybrid giant of the clouds

..."British luxury travel pioneer. Henry Cookson Adventures (HCA), will create a world first taking the hybrid Airlander 10 – the largest aircraft on the planet – on its maiden international flight in 2018.

This will be the precursor to the low carbon aircraft’s adoption for use in the luxury travel and adventure market; the Airlander is the brainchild of Hybrid Air Vehicles (HAV) in Bedford.

HCA is working alongside a team of scientists and engineers to ready her for launch. From ski races to the Magnetic North Pole to taking private submersibles to the Antarctic, the HCA team have been pushing the boundaries of high-end travel for over a decade.

On completion of the trial flight next year, HCA ultimately plans to take the type-certified Airlander 10 to a range of destinations at client request, experiencing landscapes that vary as diversely as the North Pole, Bolivian Salt Pans and Namib Desert.

The ability to stay aloft for days at a time, in virtual silence, with floor-to-ceiling windows and fresh air make Airlander perfect for cruising in exceptional locations.

Using innovative technology, Airlander 10 is the first in a new breed of hyper-efficient aircraft. Though potentially capable of staying in the air for weeks at a time, it is the Airlander’s ability to land anywhere that truly sets her apart from traditional aircraft. These twin assets make it perfect for exclusive adventures, bringing guests to hard-to-reach locations in unprecedented levels of comfort.

In a further development, HAV and Design Q have been awarded a £60,000 Design Foundations Round 2 grant by the UK’s Innovation Agency, Innovate UK. This funding is going to be used in a unique and original ‘Airlander Luxury Tourism Design Development Project’.

Design Q is one of the leading independent design consultancies with automotive and aviation clients throughout the world, including BAE Systems, Bombardier and Virgin Atlantic.

Design Q will become Hybrid Air Vehicles’ preferred supplier for design and manufacture of the luxury cabin interiors created as a result of the project...."

https://www.businessweekly.co.uk/news/travel-and-transport/luxury-travel-company-trial-hybrid-giant-clouds

https://www.hybridairvehicles.com/news-and-media/in-the-news

This doesn't seem to be a failed project to me....on the other hand....

This from the article....

The Hindenburg Disaster

..."But while airships like USS Akron (on which 73 died) crashed at sea, and the British R-101 (on which 48 were killed) crashed in the darkness of night — both far from witnesses or cameras — the crash of the Hindenburg was captured on film. Millions of people around the world saw the dramatic inferno which consumed the ship and its passengers. Oh, the Humanity!

At least, that’s the conventional wisdom about why the age of the zeppelin died that rainy day at Lakehurst.

But perhaps after 35 years of accidents and disasters — the crashes of LZ-4, LZ-5, Deutschland, Deutschland II, Schwaben, R-38, R-101, Shenandoah, Akron, Macon, and the list goes on — perhaps the public had just had enough.

And more importantly, despite its romance and grandeur, Hindenburg was obsolete before it ever flew."...

Now that's a fail...!!

http://www.airships.net/hindenburg/disaster/

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#21
In reply to #19

Re: Diesel Engine vs. Electric Motor

11/10/2017 12:46 AM

Heavy earth moving equipment and tug boats of late use diesel engines, generators and E-Motors instead of the old system of mechanical gearing as demand for power and speed variation is large and frequent. Also no rigid connection between engine and propeller or driven wheels as the case may be is required. Electric cables can be easily placed and go around corners.

For an airship of your application power demand is much more steady and a fixed transmission is likely adequate.

With every conversion of energy losses are unavoidable.

For all of above reasons diesel engines with a gear box is likely the most economical set up for your needs. Combined with variable pitch propeller this drive set up provides adequate variability. It is simple, no heavy E-motors, no electrical control system in addition to the engine controls. The trick is to find the 'right' diesel engines for the job. Large 4 cylinder types are likely lighter and more suitable than 12 cylinder units. Find long stroke modes as used in earth moving equipment for higher efficiency.

However, in today's political climate some sort of electric hybrid drive is perceived to be most economical but I have my sincere doubts if that is true. You do not have 'breaking' power recovery in an airship.

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#23
In reply to #21

Re: Diesel Engine vs. Electric Motor

11/10/2017 9:11 AM

Floram,

You make some good points, thanks for your post!

As you so aptly pointed out, there are definitely loses involved in the conversion process. I would like to explore this design more and try to determine what those loses would be and how much they would effect overall operating costs. There's some features and flexibility about the design that are appealing for reasons I can't go into at the moment. For those reasons, I must explore this further and develop some solid data I can sink my teeth into.

I need someone with the expertise to help me find my way in this conversion process. I think we have to start at the thrust end and work backward.

If you have any further insight, please don't hesitate to share it.

Thanks

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#22
In reply to #19

Re: Diesel Engine vs. Electric Motor

11/10/2017 9:03 AM

I hate to re-hash, but now that I went and started, I will continue:

The Hindenberg failed not as much due to the flammability of hydrogen as the almost explosive nature of the nitrocellulose (yes, the same material as smokeless gunpowder) used as either a layer or the entire skin of this positive buoyancy aircraft.

If Hindenberg would be re-engineered or reverse-engineered, I would begin as follows:

(1) keep the diesel engines, or replace with one larger and more powerful one, or with a gas turbine engine of lighter weight/horsepower rating.

(2) keep the aluminum frame, even use lighter composite frame

(3) use a non-flammable (tested) skin, and better hydrogen containment bags

(4) utilize a fore/aft fuel transfer system to maintain attitude

(5) double contain all hydrogen bags and high pressure vessels with an outer bag/vessel containing nitrogen or even Argon shell gas to limit or eliminate contact of flammable gas to atmosphere to below the explosion limit.

(6) install seal-less compressors to transfer hydrogen from bags to pressure bottles, with tested transfer tubing with zero leakage fittings.

(7) gas separation equipment on board to purify the shell gas supply, and to re-capture hydrogen from shell gas.

The end result would be a safe, reliable hydrogen lift ship, with renewable supply. She would only need to take on water, diesel/jet fuel. Looking at some of the new Boeing aircraft designs, I would want to get my hands on the new boundary layer jet, to put one at the aft of this ship to make her faster.

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#25
In reply to #22

Re: Diesel Engine vs. Electric Motor

11/10/2017 10:04 AM

James Stewart,

Thanks for the post!

Good points on the design.

However, I want to clear up a popular misconception. I'm always amazed at the assumption that the German's weren't smart enough to test their doping product for flammability. On the contrary, the Germans refused to us the doping product the US Navy used on the Akron and Macon because after extensive testing they discovered their own product less flammable. If you watch the films on Youtube of the Hindenburg fire, you will notice the airship is burning from the inside out and the skin is the last part of the structure to catch fire. That's an interesting reality.

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#28
In reply to #25

Re: Diesel Engine vs. Electric Motor

11/10/2017 11:51 AM

from this link: http://www.airships.net/hindenburg/lz129-hindenburg-detailed-history/ , I offer the first reply as an excerpt. {start} William T. Klapper | June 9, 2017 at 10:22 am | Reply

The design of Hindenburg had a fatal flaw. The gas exit shafts were designed to conduct the mixture of hydrogen and air to the outside to reduce the lift of the airship. This mixture is exceedingly easy to ignite and the result of ignition would be a detonation. This detonation ruptured adjoining hydrogen gas cells or broke the gas valves on the gas bag resulting in hydrogen leakage, ignition and destruction of Hindenburg. This hydrogen and air mixture can be ignited with as little as 20 millijoules of energy and once ignited it cannot be stopped. The process of venting large quantities of hydrogen into a gas exit shaft had been done many times before , giving airship captains the impression that this was a safe way to handle hydrogen. The German was to protect the gas exit shafts from a static spark originating withing and around the gas shafts. No protection was given from a hydrogen gas flame that was burning on the outside of the airship. Apparently on May 6, 1937 the vented mixture of hydrogen and air was ignited outside the airship by an atmospheric condition and this ignited the mixture of hydrogen and air in the gas exit shaft resulting in the fatal explosion.
The Germans covered up this design weakness by inventing all sorts of stories and calling the destruction “mysterious”. They further covered the possibility of a gas explosion in a gas exit shaft by simply not talking about the gas exit shaft at all. There was nothing mysterious about explosion. It was a design flaw. A much safer design for the gas exit shaft for the gas exit shaft would be to use cooled down exhaust gas from the diesel engines as a diluant for vented hydrogen instead of using air as a hydrogen diluant.{end}

I am pretty clear in saying that, no dilution with engine exhaust cooled, when mixed with hydrogen is a safe mixture. There would still be sufficient oxygen present in the exhaust of any working diesel engine to remain within the explosive limits, unless the ratio of diluent gas to hydrogen were sufficiently high to bring that concentration below the lower explosion limit. At any rate, a foolish, and totally unsafe practice.

As to ship's outer skin material, no solid material (short of brissant explosive) might exceed the flame velocity of hydrogen in air.

In common with other airships of the era, the cotton outer skin was varnished with ‘dope’, a plasticised lacquer. This made the woven fabric airtight and kept it taught, reducing flutter and aerodynamic drag. The silver colour of the Hindenburg was a result of aluminium powder mixed with the dope and painted onto the outer surface to reflect sunlight to prevent the hydrogen warming up, expanding and escaping. A layer of iron oxide was applied to the inside top half of the outer skin to absorb ultraviolet radiation and prevent it destroying the cotton gas bags inside. credit - outer skin of Hindenburg - doped cotton with aluminum powder

This article was found on the Royal Society of Chemistry's website.

"Dope" - was a nitrocellulose lacquer typically applied to cotton to make it the outer skin of airplanes in the early 1900's.

Typical doping agents include nitrocellulose, cellulose acetate and cellulose acetate butyrate. Liquid dopes are highly flammable; nitrocellulose, for instance, is also known as the explosive propellant "guncotton". Dopes often include colouring pigments to facilitate even application, and are available in a wide range of colors. - Wikipedia.

In spite of this, the photographic evidence appears to support that only hydrogen was responsible for the ship's destruction. The inside of the skin was coated with a type of iron oxide to protect against UV damage of the skin or the gelatin/cotton gas bags. - Surely a disaster looking for the scene of the incident.

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#29
In reply to #28

Re: Diesel Engine vs. Electric Motor

11/10/2017 12:15 PM
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#30

Re: Diesel Engine vs. Electric Motor

11/11/2017 4:21 AM

My guess is 2 large diesels will weigh nearly as much as 4 smaller ones, for the same total power. So unless the 2 generators + 4 motors (maybe + some control gear, depending on the system) weigh about the same as the 4 gearboxes, you're out of pocket weight-wise.

I know that system is used in diesel-electric locomotives, and is more efficient than, say hydraulic transmission, but weight is less of a concern there.

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#31
In reply to #30

Re: Diesel Engine vs. Electric Motor

11/11/2017 8:52 AM

Codemaster,

Thanks for the post.

I agree, we're definitely going to be heavier than just 4 diesel engines.

I'm in the process of determining how much heavier.

I want to weigh the advantages in flexibility vs. the weight increase to determine if it would be doable.

Once I have some solid data, I'll be sure to post my findings so you guys can take a look.

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#32

Re: Diesel Engine vs. Electric Motor

11/11/2017 8:55 AM

Gentlemen,

Does anyone have insight on permanent magnet AC motors?

It's my understanding that they are smaller in size and more efficient than their AC induction counterparts.

I need to know if they make them in the 400 - 500 hp range?

Obviously, we have a low voltage application.

Thanks

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#33

Re: Diesel Engine vs. Electric Motor

11/11/2017 1:50 PM

Bear in mind that for an airship application, with combustion propulsion the vehicle gets lighter over time, which is not the case with electric propulsion.

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#34
In reply to #33

Re: Diesel Engine vs. Electric Motor

11/11/2017 4:29 PM

Not so! If diesel engines are used to generate, then liquid fuel will also be expended.

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#35
In reply to #34

Re: Diesel Engine vs. Electric Motor

11/12/2017 11:33 AM

Ahem - if <...diesel engines are used to generate...> then it is a combustion-powered vehicle and therefore <...Not so...> would be incorrect.

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#36
In reply to #35

Re: Diesel Engine vs. Electric Motor

11/12/2017 8:02 PM

The OP'er wanted to replace 4 diesels with 2 diesels driving electric motors, so there would also be a reduction in weight through loss of fuel.

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#37

Re: Diesel Engine vs. Electric Motor

11/13/2017 11:03 AM

Cruz2017,

Reading #15 by Rixter and #22 by James Stewart I spotted an opportunity. One of my guiding technological philosophies stolen from the natural world is: for any design, try to throw away as much as possible. Usually this means make what is left perform the function of the things you want to discard.

Rixter points out the outstanding energy density(per volume and weight) of diesel fuel and James Stewart points out that since technology has advanced one might consider a re-engineering of the Hindenberg. Basically, what if you made the airship frame perform the function of internal combustion engine is the overall concept. From nature one might look at the jellyfish as inspiration. Slow squirting of fluid from the canopy yields fantastic efficiency of operation at approximately neutral buoyancy. The traditional diesel engine has fast movement, high mass, and high temperatures, all of which are undesirable if one wants to be a jellyfish. As someone else pointed out, conversions (diesel-electric) works well on trains but trains are well-suited to carry lots of weight.

Airships have large surface area and rapidly moving any large percentage of that will destroy efficiency with drag so our redesigned diesel should not move pistons or cylinders or anything large. That basically leaves valves. Consider several bilaterally symmetric, large bore tubes that are part of the stiffness of the airship fore to aft. Inject(spray) some fuel(maybe diesel,propane,butane,hydrogen,or...) at the 1/4 region from the bow in two of the bilaterally paired tubes. When the fuel hits the proper stoichiometric ratio, ignite it. Oops ! It does its rapid volume and rapid temperature increase but it blows out forward as well as backward. Put a flapper check valve at the bow end of the tube. Try again. OK, it now blows out backward but even with some inertial action it still does not suck in enough fresh air for the next stroke. After the burn, put a fine water spray in the pipe where it is the hottest to abruptly cool the gases and suck in some fresh air. Oops! it sucks fresh air in the aft end as well as the bow end. Put a flapper valve in the aft end. Now we do not have to be moving forward to drive in enough fresh air for the next burn. We also should use just enough water to get the inhale and perhaps a water to steam expansion advantage after the first cooling burst and the steam helps remove the excess heat from the pipe and thus the airship. Voila! We have an airship jellyfish internal combustion engine. Various enhancements might include an outer tube around each pipe to serve as a venturi to implement a force matching(transmission-like) element. Observe that this "engine" works well in a flying wing airship as well as a teardrop shape. The venturi may run the entire length of the ship or just be an aft end accessory. There are no pistons, crankshafts, camshafts, and control is by off-the-shelf temperature, mass air flow, and O2 sensors(perhaps resistor heated.) The cylinders, as previously mentioned, stiffen the ship.

I do not know if anyone else has experimented with similar engines except perhaps the German V1 rocket engine but it was going fast to bring in the fresh air rather than using the water spray rapid cooling. I saw the water spray cooling method proposed for solar energy applications before as an HVAC air mover. The water spray may gain some advantage if it leads the slug of hot exhaust down the long pipe. The initial spray cools the hot gases quickly, the trailing spray generates steam from the thermal inertia of the pipe from exhaust gases not adequately cooled by the first short "inhale" squirt. The water for the "inhale" squirt is the coolest and the water temperature forms a gradient of higher temperatures reaching 100°C just before arriving at the end of the tailpipe. Research should be done to optimize the amount of water carried vs any steam-engine-like advantages since water is heavy. Flapper valves are to describe the concept and may be replaced with a smart (perhaps powered) valving system but remember that the valves and the water and fuel atomizers are the only moving parts of this system to save energy so avoid big energy-hog valves or any other big rapidly moving parts. A great deal of advantage might be available by carefully timing everything perhaps even resonating the pipes(be careful to not generate obnoxious or structurally fatiguing noise) for maximum flow. Driven progressive linear combustion is also worth a look. Either of these may be better than continuously running the water spray respiration.

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#41
In reply to #37

Re: Diesel Engine vs. Electric Motor

11/13/2017 3:20 PM

Jellyfish Airship(post #37) Comments

Just to preemptively clarify:

1. This airship internal combustion engine does almost no intake compression, it uses spark ignition, so it is by no means a diesel.

2. The V1 rocket was really not a rocket but a pulsed ramjet.

3. The airship has some density technique for achieving neutral buoyancy which I was not discussing. Perhaps helium, perhaps hydrogen with safety mods. With some development it may be able to fly without special gases but it would still need to be very large to be practical.

4. One would need to somehow make sure that the overall craft did not accumulate heat. The tubes would need to be additionally heat tolerant.

5. The whole scheme is just a concept and would need a proven implementation.

6. There are likely sound and vibration issues which need to be addressed. The V1 had sound issues. This airship would likely have very low frequency vibrations which could easily cause problems if not anticipated.

7. There are no pistons. The accelerated exhaust exits the rear, propelling the airship forward in long slow pulses from many combustion tubes fired in a symmetrically balanced fashion unless one wants to deviate from traveling straight forward. (Have you ever lit a little fuel in a bottle to hear the whoosh?)

8. Steering is broad and slow. It may be inadequate for docking maneuvers.

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#42
In reply to #41

Re: Diesel Engine vs. Electric Motor

11/14/2017 10:30 AM

Rather than all this hazardous flames being shot out the back, why not use the Bernoulli effect shrouded fan design, where the tail fan pulls air from the boundary layer of the air frame, thus lowering the drag, as is proposed for some jet liners?

If you want the greatest fuel economy, this also means less initial load lifting at the outset for the same range of travel.

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#43
In reply to #42

Re: Diesel Engine vs. Electric Motor

11/14/2017 1:06 PM

Shrouded Fans are Pretty Good BUT...

I like the shrouded fan and the entire airship could be that shroud but I was eliminating the traditional engine you are still using to drive the fan. A traditional engine has a large mass and fast moving metallic parts in intimate contact with the explosion losing(what becomes in that case) waste heat which would be good to minimize. The up side is that it is well understood and readily designed.

The point of emphasizing the length of the combustion tubes is that complete combustion can be achieved before the exhaust leaves the tube so "hazardous flames" are not shooting out of the back. This puts it close to an isobaric operation which gets work out of the fuel proportional to (Vf - Vi) which shrinks the vertical dimension of this engine cycle and expands the work out horizontal dimension:

https://cdn.miniphysics.com/wp-content/uploads/2011/12/Engine-cycle.png

The expansion of the exhaust and the surrounding air it heats becomes a gas piston driving the airship forward efficiently while adding no piston mass to the weight of the airship. The tube should be large enough and the fuel injected low-central enough that little heat ends up as waste heat in the airship cylinder wall. Most of the energy of the fuel then gets expended expanding the volume of gases headed eventually(all combustion complete and expanded volume cooled some with that expansion and heating of surrounding extra air in the tube with its resulting expansion) in rolling gas vortices out the aft end. This exiting whoosh of gases is inherently rather well matched to the speed of the airship unlike a traditional piston which does not move even close to the speed of the explosion wavefront inside the cylinder(thus the desire for slower burning hi-octane fuels in conventional engines.) The traditional engine sucks far more "waste-heat" out of the fuel into the engine solids requiring radiators and such just to discard it. The jellyfish airship internal combustion engine uses far more of the heat produced by the fuel to actually do work accelerating expanding gases out and pushing the airship forward.

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#44
In reply to #43

Re: Diesel Engine vs. Electric Motor

11/15/2017 8:50 AM

So has anyone ever built such an engine, or is this a pigment of someone's imagination? The fruit of a low-hanging fantasy branch?

Build it, and the world will be on your doorstep (one way or the other).

Are we talking about a valve-less ram jet?

How do you plan to prevent this thing from lighting off your hydrogen?

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#45
In reply to #44

Re: Diesel Engine vs. Electric Motor

11/15/2017 3:46 PM

Valves, Glory, Grins, Giggles, and truly Great Goslings

James Stewart: "Are we talking about a valve-less ram jet?"

I got rid of pistons, camshafts, and crankshafts but explicitly mention valve use.

thewildotter: "..but it blows out forward as well as backward. Put a flapper check valve at the bow end of the tube. Try again. OK, it now blows out backward but even with some inertial action it still does not suck in enough fresh air for the next stroke. After the burn, put a fine water spray in the pipe where it is the hottest to abruptly cool the gases and suck in some fresh air. Oops! it sucks fresh air in the aft end as well as the bow end. Put a flapper valve in the aft end."

It is a ram-jet but one modified to operate slow speed, large scale.

JamesStewart: "How do you plan to prevent this thing from lighting off your hydrogen?"

I prefer the helium I mentioned. I only included hydrogen because others espoused schemes for adequate containment which I just chose not to disparage. The atomic mass of H2 being 2 is attractive relative to He at 4 but four is adequate at large scale considering the atomic mass of N2 at 28 so I would not use hydrogen unless someone else's scheme proved it safe.

JamesStewart: "The fruit of a low-hanging fantasy branch?"
Since you thought it had no valves, I can understand why you might consider it a fantasy. I have concepts for better valves than flappers but opted to leave that description out since I do realize that my posts are long and obviously some people's eyes glaze over well before that level of detail.

JamesStewart:"Build it, and the world will be on your doorstep (one way or the other)."

Why would I want the world on my doorstep(any which way) ? I love mankind, it's people that I can't stand. I have implemented many successful things for many decades now in nearly complete obscurity, and except for throwing stuff over the fence for someone else to use as their road to glory(should they want such a ridiculous thing), I am happy to leave it that way. Vicarious glory is more than enough and there is no compelling impetus even for that, just a few grins and giggles to be had along the way.

I find that new goslings, after one success(especially the more intelligent goslings) start to pick and choose from the breadcrumb memes I dribble out to them. I find it amusing(I call it incremental imprinting) when they return time and again to ultimately retrieve most or all of the memes they originally left behind. Some of them even realize it, grin(culturing great goslings is something really worthwhile.) Feeling progressively more mortal(one of my all-time-best goslings recently passed), I have converted the bulk of my dribbling to more of a firehose blast. It is not going all that well. All but a few, rare people need time to piecewise assimilate and acclimate.

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#39

Re: Diesel Engine vs. Electric Motor

11/13/2017 1:04 PM

Coming from the hovercraft side of the field it is a little closer to the air ship design in that lift is created separately from thrust (to a point.)

A good starting point would be to work the other way and get prop size then work through HP requirement for that prop.

We designed with a 60" prop in mind due to the fact anything larger looked way out of proportion but the bigger the better to a point.

I don't see why an 26' blade would be an issue and this would give a tip speed of .90 mach at 750 rpm which is on the maximum end of the performance spectrum for blades.

The larger diameter would give you a sweep area of 1134 with the 19' blade as designed and 2123 with a 26' blade.

The best thing about using an electric motor is it's torque is in the higher range when it's RPM is around 750 and this is easy to do with a drive so no gear reduction is required.

If you are going to power the system directly from a single diesel gen set then you could set the frequency there and control fan output with variable pitch on prop or just generate 60 HZ and use drive to control.

Getting the voltage as high as possible in the HP range is the trick. You will have to take into account the weight of the cabling so keeping voltage high will greatly reduce it's size.

I would do thrust with two larger fans and then control pitch adjustments with two/4 much smaller fans or directional vents from primary thrust.

Here is the calculator I use on fan designs for our crafts!

www.warpdriveprops

A Baldor G5810 frame 700 HP motor draws 90 amps at 4000V, produces 4100 ft/lb torque and can be ordered stock at around 800 RPM which could be direct driven at 60 HZ. It is 41" long and has rough diameter of 32" and weighs around 1400 lbs from the little info I could find about weight ( a call to Baldor could confirm this.)

When compared with specs from the site you sent it shows the nominal HP was 850 at 1350 RPM which is 3310 ft/lb of torque so you could almost get by with a 500 HP Baldor.

Once a fan layout is determined you could get the prop designer to give you a true required torque for your desired pitch/diameter.

You could also surround the hull with a ring of smaller props using individual small motors in say the 50 HP range, the good thing about your type of craft is surface area is not a problem. A ft/lb of thrust whether it comes from one 40' fan or 32 5' fans is still a ft pound of thrust.

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#40
In reply to #39

Re: Diesel Engine vs. Electric Motor

11/13/2017 2:15 PM

Mistyped 1400 lbs, should have been 4100 lbs.

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#46

Re: Diesel Engine vs. Electric Motor

11/20/2017 7:03 PM

Just a bit of brainstorming here, instead of two Diesel engines powering two generators to power the four electric motors how about using a fuel cell? Perhaps the fuel cell could power the four motors along with the rest of the ship. While I have no idea how much the fuel cell would weigh the tanks of compressed hydrogen should weigh less than the tanks of Diesel fuel.

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#49
In reply to #46

Re: Diesel Engine vs. Electric Motor

11/21/2017 10:26 AM

Truly an elegant answer. If they use hydrogen for most of the lifting bags, sheathed in helium, or even CO2 thin shell, the potential for hydrogen explosion drops off amazingly low. Fuel cell is far lighter, and also more efficient in the same or greater power range which is a huge plus.

Water ballast, and the use of proper electrolysis cells with PV could provide make up hydrogen on an as-needed basis, or at minimum extend the range. Other option:

Use liquid hydrocarbons, and strip off the hydrogen only, or have fuel cell(s) that runs off CO and H2. I prefer a multi-layered redundant system myself, although having fuel tanks on board surely takes care of much of the issue.

I do not care if the thing sprinkles carbon on the ocean, or keeps it as retained ballast. Hydrogen re-compression from the lift bags is useful if no leaks exist, and ship mass is decreasing.

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#47

Re: Diesel Engine vs. Electric Motor

11/20/2017 11:50 PM

You could consider diesel + generator @ e.g. 400 or 800 Hz and ditto electrical motors.

Your additional weight coefficient will be less than 1/3 of conventional 50 or 60 Hz systems. Commercial airplanes also have a higher frequency pack. You might look into plane supplies.

For the diesels MTU, MAN, MERCEDES have this power (1200HP) in the +$400,000.00 range and have a good weight/power range (12 cyl.)

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#48
In reply to #47

Re: Diesel Engine vs. Electric Motor

11/21/2017 8:31 AM

High weight seems to be the problem.

A good power/weight range is preferable

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