Experimental Ducted Fan Aircraft Designs

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Blackhawk

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Some of you would probably remember the Davis Cold Jet from the late 70's.

I really think this design type could be explored again, especially with the lightweight
materials available today which weren't around 40 years ago


"D 340 Cold Jet
The Davis D-340 Cold Jet was a single staged high-pressure ratio axial flow compressor driven by
an internal combustion engine. Its maximum rpm was just over 18,000. The maximum tail pipe
velocity was just over 500 mph. The rotor blades were stainless steel and made to a tolerance
of .005 inches, with 350 hp, at 18,000 feet, it would be able to reach 300 mph."
 

Vigilant1

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It would be useful to know the thrust it produced. I didn't see that online.

Slightly related:. I'm always amused by the stickers on the leafblowers at Home Depot. "120 MPH blast!" Etc. That tells me nothing about how much air it is moving, the overall KE of the stream, and how well it will move leaves.
 
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I think some additional efficiency can also be fairly easily obtained by moving the motor outside of fan and have it driven by belts. The last thread had some rough designs talking about this.
 

cluttonfred

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The key here would be developing a complete powerplant that can be integrated with multiple airframes. Like with electric aircraft, the problem is the lack of off-the-shelf solutions.

If you look through https://machdiamonds.com/ or https://minijets.org/, you'll find that the Turbomeca Palas sparked the largest number of light jets that were more than self-launched sailplanes. The Palas was rated at 160 kg/353 lb thrust for takeoff and 130 kg/287 lb continuous.

An equivalent ducted fan would be heavier but should also have better fuel consumption and so need to carry less fuel. With that in mind, I think a ducted fan and engine combination that could produce about 150 kg/331 lb would be ideal for a two-seat sport plane, maybe 100 kg/220 lb thrust for a two-seat microlight or single-seat sport plane. To my knowledge, no one is offering such a package off the shelf.
 

Vigilant1

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Just to say it:
There's a pretty good but basic overview of ducted fan/shrouded prop considerations in this old post by Orion. In general (and rough) terms, a designer will need about 3 times the power for a ducted fan to equal an open prop. That's largely due to the lower efficiency of making thrust by accelerating a smaller volume of air (relatively small fan face vs a prop disk).
The physics can't be overcome with clever engineering or new production technology.
If someone accepts the inefficiencies (using much more power to make the same thrust) and wants a ducted fan/shrouded prop anyway, then that's fine. IIRC, Malish is producing approx 800 lbs of thrust using two 69cm dia fans driven by a single GM LS6 engine in a very nice design. The considerable fan area helps improve his efficiency. The Cold Jet in the OP looks like it is exactly the opposite approach.
 
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henryk

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Malish is producing approx 800 lbs of thrust using two 69cm dia fans driven by a single GM LS6 engine in a very nice design.

it exist formula for propeller drive comparison ,(Koefficiant of propeller finesse," Kf"

Kf=( Fthrust /N) * [ sqr (Fthrust/ S )]

for AEROSYSTEMS Ducted Fan=
D=0.55m S=0.24 m^2
N=30 HP, Ft=70 kG ,

Kf= 40 !!! (very good result)

for Malish DREAMER=
N=380 HP, F thr.=400 kG ,S=2*0.785*0.69^2=0.75 m^2
Kf=24

for comparation=1.7 m propeller, 70 HP, 180 kG thrust=
Kf=23
 

Vigilant1

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it exist formula for propeller drive comparison ,(Koefficiant of propeller finesse," Kf"

Kf=( Fthrust /N) * [ sqr (Fthrust/ S )]
Thanks.
So, Kf describes the efficiency per unit of prop area, but shouldn't/can't be used as a measure of overall efficiency to compare props/fans of different areas.
 
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henryk

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Thanks.
So, Kf describes the efficiency per unit of prop area, but shouldn't/can't be used as a measure of overall efficiency to compare props/fans of different areas.
=exactly,
Duct lips can anhance (amplifie) thrust force 0-40 % !
 
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Malish

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"D 340 Cold Jet
The Davis D-340 Cold Jet was a single staged high-pressure ratio axial flow compressor driven by
an internal combustion engine. Its maximum rpm was just over 18,000. The maximum tail pipe
velocity was just over 500 mph. The rotor blades were stainless steel and made to a tolerance
of .005 inches, with 350 hp, at 18,000 feet, it would be able to reach 300 mph."
But it never worked in real life and probably never will have such performance.
Ducted fan will work best at low altitude and relatively low flying speed - below 150-180 mph.
 

Malish

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it exist formula for propeller drive comparison ,(Koefficiant of propeller finesse," Kf"

Kf=( Fthrust /N) * [ sqr (Fthrust/ S )]

for AEROSYSTEMS Ducted Fan=
D=0.55m S=0.24 m^2
N=30 HP, Ft=70 kG ,

Kf= 40 !!! (very good result)

for Malish DREAMER=
N=380 HP, F thr.=400 kG ,S=2*0.785*0.69^2=0.75 m^2
Kf=24
This formula is for propeller ONLY and can't be used for Ducted fan performance.
 

Malish

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It would be useful to know the thrust it produced. I didn't see that online.

Slightly related:. I'm always amused by the stickers on the leafblowers at Home Depot. "120 MPH blast!" Etc. That tells me nothing about how much air it is moving, the overall KE of the stream, and how well it will move leaves.
Ducted fan has different "thrust theory" - it's "mass flow" and this have BIG difference with propeller theory. It's like two different "animals".
 

henryk

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Where you get this data?
AEROSYSTEMS, Josef Dusek, Chech Republik

(M-18 opposite,30 HP +0.55m fan)

BTW=formula for Kf can help in comparation betwen
two DF with different dimensiones...

(better,as Specific Thrust [kG/kW] )

 
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