Ducted Fan Pseudo-Jets

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Malish

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You guys said this was bad - that having more distance between tip & duct leads to more turbulence losses.

Their fans look thicker and heavier, different than PJ-2 fan-blade pictures shown by Malish.
Blades look wider. Even hub of fan looks much larger.
Is there some advantage to this?

Looks like this fan is some kind of "cooling" fan - not designed and made to be used as DF in aviation. Also it's made of some material not designed for hi rpm and aerodynamic loads - it look like this fan came from some automotive field(radiator cooling fan?) :(
49482999_2409642409076958_5471583516703588352_n.jpg
 
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henryk

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Riggerrob

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Just like helicopter rotor blades provide little lift, I suspect that ducted fan roots also provide little thrust.
Just look at most helicopter blade roots and you will find that the inner 20 percent are not even airfoil shaped.
When Rohr' 2-175 added an internal spinner its' rate of climb doubled.
 

Malish

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F thrust=?

I think UL-39 ALBI has problem not only with fan design, but also with air duct intakes - very sharp turns in front of the fan.
Fan should be farther away from intakes and intakes ducts should be more shallow to avoid airflow separation and turbulence of air in front of the fan...
dalsi-aktivity-ul39.png pohon05.jpg ul-39-albi-fuselage-cutaway-588883369ba71237544046_orig.png
 

BBerson

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So the pseudo-jet could hide the larger prop under the upper duct only. The prop would be unducted on the bottom. The prop/fan could be a much larger diameter with this scheme. Ingesting rocks would be an issue, but same as any other pusher.
 

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Malish

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=intakes shold be placed in region,where pressure is higher as sorraunding atmosphere !

For fighter jet - yes! They often fly at high angle of attack, that is why their air intakes located under the wings or fuselage. For DF aircraft this is unnecessary - what is most important, air duct should be made as strait as possible(without sharp turns), particular for air intakes!
Ducted fan design 024 (Large).jpg Ducted fan design 025 (Large).jpg
And fan should be located close to the end(exhaust) part of the duct...
 
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Blackhawk

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Please don't shoot the messenger; I'm only looking at the engine layout.

I was looking at our Aus Gumtree site and came across this vintage GI Joe Storm Eagle which I have never seen before.

The inlet ducts are below the wings and the outlet is above the wings and don't interfere with the fuselage, the landing gear folds into the back of the inlet ducts below the wing.

The outboard wings could be folded for storage, I think it's cool; GI Joe does it again.

Gi Joe Storm Eagle.jpg
 

Malish

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For fighter jet - yes! They often fly at high angle of attack, that is why their air intakes located under the wings or fuselage. For DF aircraft this is unnecessary - what is most important, air duct should be made as strait as possible(without sharp turns), particular for air intakes!
And fan should be located close to the end(exhaust) part of the duct...

It's was a big mistakes designers of UL-39 ALBI made by placing the fan next to sharp turning air intakes - airflow to the fan there is terrible :oops:
ul-39-albi-fuselage-cutaway-588883369ba71237544046_orig.png
 

Toobuilder

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Please don't shoot the messenger; I'm only looking at the engine layout.

I was looking at our Aus Gumtree site and came across this vintage GI Joe Storm Eagle which I have never seen before.

The inlet ducts are below the wings and the outlet is above the wings and don't interfere with the fuselage, the landing gear folds into the back of the inlet ducts below the wing.

The outboard wings could be folded for storage, I think it's cool; GI Joe does it again.

View attachment 119954

looks like a "stylized" Northrop YF-23
 

Malish

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Just like helicopter rotor blades provide little lift, I suspect that ducted fan roots also provide little thrust.
Just look at most helicopter blade roots and you will find that the inner 20 percent are not even airfoil shaped.
When Rohr' 2-175 added an internal spinner its' rate of climb doubled.

Helicopter rotor, regular aircraft propeller(open prop) don't have much to do with DF theory and I don't know what kind shape of blades fan on Rohr 2-175 had, but DF blades have larger "twist" and root of the blade almost parallel to the axis of the hub and airflow to minimize air resistance. Because of that "flat"(almost no "twist") fan blades are not used in DF.
Good designed DF blades:
113.JPG 004.JPG
And bad one:
ul39-004 (Large).JPG
 

pylon500

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Helicopter rotor, regular aircraft propeller(open prop) don't have much to do with DF theory and I don't know what kind shape of blades fan on Rohr 2-175 had, but DF blades have larger "twist" and root of the blade almost parallel to the axis of the hub and airflow to minimize air resistance. Because of that "flat"(almost no "twist") fan blades are not used in DF.
Good designed DF blades:
View attachment 119979 View attachment 119980
And note also the flow straighteners behind the strongly twisted fans. This is almost as important.
 

henryk

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flow straighteners behind the strongly twisted fans.


=+ noise problem !
 

Blackhawk

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Below is the Polish Military trainer "EM-10 Bielik" (White Tailed Eagle) single engine jet; first flown in 2003

It would be perfect for a single engine ducted fan Pseudo-jet, maybe scaled down to 85%

Doesn't have a complicated duct system having the inlet below the fuselage and engine/ducted fan system would be an easy installation.

em-10-bielik 1.jpg

General characteristics

  • Crew: 2
  • Length: 9.00 m (29 ft 6 in)
  • Wingspan: 6.60 m (21 ft 8 in)
  • Height: 2.50 m (8 ft 2 in)
  • Wing area: 11.90 m2 (128.1 sq ft)
  • Aspect ratio: 3.7
  • Empty weight: 1,700 kg (3,748 lb)
  • Max takeoff weight: 2,500 kg (5,512 lb)
  • Fuel capacity: 850 kg (1,870 lb)
  • Powerplant: 1 × General Electric CJ610-6 turbojet, 13.5 kN (3,000 lbf) thrust prototype; production aircraft 12.75 to 17.65 kN (2,870 to 3,970 lbf) turbojet / turbofan
Performance

  • Maximum speed: 1,100 km/h (680 mph, 590 kn)
  • Maximum speed: Mach 0.9
  • Stall speed: 165 km/h (103 mph, 89 kn)
  • Ferry range: 2,500 km (1,600 mi, 1,300 nmi) with auxiliary tanks
  • Rate of climb: 45 m/s (8,900 ft/min)
  • Wing loading: 210.1 kg/m2 (43.0 lb/sq ft)
 

sanman

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Thanks for that link - visually this style looks quite nice - similar to F-5/F-20, with twin intakes, but the ducts are much shorter, since this is a ducted fan design:


image.png


I admit ducts would look a little nicer if they could be longer, but ducted fan perhaps doesn't allow too much of that.

I bet it would even be possible to also fit that Custer-style Channel wing underneath the central fuselage, as a ducted fan intake that looks similar to F-16's smileyface intake.


Alternatively, here is an image of the JF-17, which is built by Chengdu Aircraft Corporation of China. It's based on the F-7 airframe, which is itself a knockoff of MiG-21:

337106_800.jpg


Note the twin intakes on either side of the fuselage, which extend above and below the wing level.
Each inlet features a DSI shock bump meant to divert the mach wave away from the central turbine engine.


I think UL-39 ALBI has problem not only with fan design, but also with air duct intakes - very sharp turns in front of the fan.
Fan should be farther away from intakes and intakes ducts should be more shallow to avoid airflow separation and turbulence of air in front of the fan...
View attachment 119913 View attachment 119914 View attachment 119915


How do you mean more shallow? You just mean shorter ducts? How does that keep intakes farther away from fan?
 
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