Raptor NG Discussion

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Malish

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I too found myself laughing out loud watching this.

At least it won't need a PSRU on it now...

Some folks never learn...
Ducted fan propulsion system will work only for slow flying aircraft(up to 200mph) and because thrust of Ducted fan based on "Mass flow" of the air pushing by fan, aircraft powered by this system can't fly at high altitude where air is thin and weight less. With Ducted fan aircraft will fly good only up to 12,000-15,000 feet of altitude. For PM picking this propulsion system - full utopia!!!...
 

speedracer

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They are called fanjets. They are everywhere.

John
A guy in the Portland, OR. area built a LongEZ with a ducted fan and 200 + HP Mazda. He messed with it for years and finally got the top speed up to 130ish. He finally gave up, cut off the fan and installed a 320. I hear it's a pretty good airplane now.
 

rv6ejguy

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I see lots of issues with the Raptor NG, even if the empty weight is reduced 500 pounds.

TO distance will be even longer.
ROC will be lower
Drag will be higher with the fan ducts there and second wing
Range will be less
Speed will be less

The low aspect ratio wing is a big killer here.

This must be for a different mission now. It will be struggling to do 200 knots and won't be going anywhere near 25,000 feet either. I predict another lame duck here based on what we've seen so far for concept.

Other challenges will be developing a lightweight 300Kw class Genset, battery cooling, the fans etc.

The trouble with hybid aircraft is they need a large percentage of power to climb and cruise compared to cars. They are more dependent on the IC engine to supply that power most of the time. You have an efficiency hit with the Genset, battery and motors and then a further one with the ducted fans. Cool maybe but not very functional for transporting folks efficiently.

Seems like another marketing concept with little basis in physics or reality.

Will be an interesting journey to watch...
 

Marc Zeitlin

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A guy in the Portland, OR. area built a LongEZ with a ducted fan and 200 + HP Mazda. He messed with it for years and finally got the top speed up to 130ish. He finally gave up, cut off the fan and installed a 320. I hear it's a pretty good airplane now.
Bob, I believe you're talking about Perry Mick and his Long-EZ with the Mazda and ducted fan. While he did get rid of the duct after a lot of modifications and testing (and crappy performance), he still has the Mazda installed. He's one of the few Mazda installs in EZ aircraft that's been relatively successful. Almost all others have been yanked for Lycomings, however, and maybe you're thinking of one of those, like Ron Gowan, although I'm pretty sure he was in TX.
 

BJC

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A guy in the Portland, OR. area built a LongEZ with a ducted fan and 200 + HP Mazda. He messed with it for years and finally got the top speed up to 130ish. He finally gave up, cut off the fan and installed a 320. I hear it's a pretty good airplane now.
Also Pushy Galore. Originally had a duct around the prop, but it later was removed to improve performance.

Ducted fans work great in the hangar to move lots of air across a work area.


BJC
 

JMyers1

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Alessandre

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One almost off topic question, if ducted fan are less efficient than regular propellers why the turbofan engines aren't converted to turboprop? I'm thinking about a auto conversion using a ducted fan where we could spin at the same RPM of the engine with a multi blade fan like the turbofan engines. We can see today the turbofans operating efficiently in low and high speeds without any mechanism of change blade pitch instead of a dominion of turboprops.
The experiences I saw in ducted fan was conventional propellers inside of a duct, but what about a turbofan powered by an auto engine direct drive?
 

rv6ejguy

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One almost off topic question, if ducted fan are less efficient than regular propellers why the turbofan engines aren't converted to turboprop? I'm thinking about a auto conversion using a ducted fan where we could spin at the same RPM of the engine with a multi blade fan like the turbofan engines. We can see today the turbofans operating efficiently in low and high speeds without any mechanism of change blade pitch instead of a dominion of turboprops.
The experiences I saw in ducted fan was conventional propellers inside of a duct, but what about a turbofan powered by an auto engine direct drive?
The Airbus E fan used two 40 hp motors and variable pitch fans if I recall and I think the latter feature is a requirement to get good overall performance across a wide speed range from TO to cruise on the limited power available here. Big gas turbines develop tens of thousands of hp. That's in a different realm.

The E fan didn't do anything better than a similarly sized aircraft with conventional prop and similar hp, in fact it was inferior. This is with real engineers and millions of dollars spent. I can't believe PM will be able to do better than Airbus here.

Driving 2 fans with one IC engine is relatively complicated and heavy, requiring a gearbox. Gearboxes are clearly not not PM's forte.

Direct driving a single prop means the engine is in the duct which impacts duct and fan efficiency to a high degree. A Wankel would be best here- small frontal area and high rpm capability.
 

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.
 

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.
 

wsimpso1

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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?
For starters, you convert fuel to high enough rate of energy in the engine, spin a big alternator to make it into AC of one frequency, then the electricity goes through one or two big power electronics converters so it is now at the right frequency for the motors. Losses (at best) will be a few percent. If you put any energy into a battery or take any out, you lose around 10% every J that converts in the battery.

Then there are end leaks, friction over the stators, and friction through the duct. Total losses in the duct are generally bigger than the tip losses of a prop until diameter gets big enough - think turbo fanjets on airliners big.

Billski
 
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