10/23 Raptor Video

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rv6ejguy

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PredragVasic

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Motor and controller are not 100% efficient nor is the Genset.
Are you saying that the electric motor in that ducted fan is not efficient? That is it less efficient than an ICE engine driving a propeller?

While we know that the ICE engine in an aircraft generally runs near its most efficient regime (versus in an average car, where it is more often than not far from optimal), ICE engines convert massive amount of energy into heat, rather than kinetic energy, and because of that are significantly less efficient than electric motors.

I can possibly accept that an electric motor, powered by an ICE generator (and a buffer battery) together could be less efficient (as a complete system) than just an ICE engine driving a propeller (ducted or not), but that wasn't the original statement (it didn't mention how the electric energy is obtained). Electric motor, driving a ducted fan, converts very little energy into heat, delivering almost all of it to the fan, so I'm sure it is considerably more efficient than an ICE engine.

The only challenge is energy storage (batteries).
 

BBerson

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They work but require more power than comparable propeller driven aircraft to achieve the same performance.
Right. The RC electric jets run about 3-4 minutes, so about half the flight time of a typical propped RC.
It's a combination of small disc area and duct drag. They do sound nice.
 

Vigilant1

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Are you saying that the electric motor in that ducted fan is not efficient? That is it less efficient than an ICE engine driving a propeller?
How are you defining 'efficient'?

If we are talking about converting mechanical HP to thrust, the 300 HP ICE engine with a typical size constant speed prop at a 250 knot cruise will be more efficient than two electric motors turning ducted fan units.

If you are instead talking about partial system efficiency (turning the available chemical energy in batteries or fuel into thrust), then the electric motors will probably be better (due to the large waste heat from the IC engine). But this last measure is of nearly zero practical importance. And, if we did a complete system audit (including losses in the production of the energy used to charge the batteries), the efficiency of the hybrid system with ducted fans will be quite poor.
 
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Rataplan

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Are you saying that the electric motor in that ducted fan is not efficient? That is it less efficient than an ICE engine driving a propeller?

While we know that the ICE engine in an aircraft generally runs near its most efficient regime (versus in an average car, where it is more often than not far from optimal), ICE engines convert massive amount of energy into heat, rather than kinetic energy, and because of that are significantly less efficient than electric motors.

I can possibly accept that an electric motor, powered by an ICE generator (and a buffer battery) together could be less efficient (as a complete system) than just an ICE engine driving a propeller (ducted or not), but that wasn't the original statement (it didn't mention how the electric energy is obtained). Electric motor, driving a ducted fan, converts very little energy into heat, delivering almost all of it to the fan, so I'm sure it is considerably more efficient than an ICE engine.

The only challenge is energy storage (batteries).
well and the needed energy you get from a generator who gets its energy from ?
 

PPLOnly

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Maybe the company that bought the Martin jetpack is involved.
The ducted fans used on it were supposedly very efficient.
2 fans could produce over 700lb of thrust with 200hp
I’m really surprised none of us know the company yet. He’s not going to an area known for engineering or aviation. There can’t be many candidates.
 

Rhino

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Good one.

If you thought this whole thing couldn't have gotten much worse... well, it now has.
I think lots of people have one premise wrong though. His project has been incredibly successful. It was designed to get him attention, and it has succeeded dramatically.
 

rv6ejguy

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Why would an electric motor driving a ducted fan require more power than an ICE motor driving a propeller? Where is the loss of energy?
This isn't a straight battery to motor design but rather a hybrid with a small battery so the IC engine will be driving a big generator to charge the battery to supply electricity to the electric motor. At every step in energy conversion, there is a loss.
 

Rataplan

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about efficiency of the complete drive till propulsion (prop / fan /duc or not) we should think in airplane efficiency. Not necessary the same as conventional efficiency. like an electric motor is more efficient than an ICE engine . but in a plane I care more about how much energy (hp * time) I can deliver per weight "fuel + engine". a very inefficient ICE can be for me more efficient than a very efficient electric motor with its heavy batteries.
 
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