Ducted fan aircraft

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by jthunt, Mar 17, 2012.

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  1. Oct 20, 2013 #101

    henryk

    henryk

    henryk

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    "Their designs are shown in Figure 1.4. The computa-tional analysis resulted in an increase in inlet lip suction and an increase in
    performance. However, the experimental thrust and power measurements,
    showed

    no di erence in performance

    of these designs when compared to their

    baseline duct"

    =no difference in performance=good too=no problems with duct stability!
     
  2. Oct 20, 2013 #102

    kenkad

    kenkad

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    Ducted fans! Please read the attachment before making quick judgments. Counter rotating fans are a requirement. Rear fan has to spin faster than front fan. Fan spacing is critical. Do not place the motor in the center so as to avoid excessive blockage. If blades are flexible, make sure groove/step can accommodate blade flexing. front and rear blade designs are different.
     

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  3. Oct 20, 2013 #103

    henryk

    henryk

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    Our Vision

    =look at bladetips placing\after inlet step!\
     
  4. Oct 20, 2013 #104

    kenkad

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    Henryk,
    Good luck with that. Too much fan blade blockage,too many blades. Large center blockage. No counter rotating so swirl in the exhaust that is inefficient. You must absolutely have counter rotating fans at the proper separation to remove swirl. That is why I suggested that paper to be read.
     
  5. Oct 21, 2013 #105

    ThadBeier

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    For GI JOE: Retaliation we built a couple of big dual-V8-powered fanboats. They had six-foot countrarotating Sensenich carbon-fiber propellers. The first propeller had much fatter blades than the second.

    Anyway, these looked completely awesome, but in the end the boat didn't go very fast. They finished construction the day before the shoot, and could have used some more time refining it. The fans had tremendous static thrust, but it takes more than that to make a fast boat.
     
  6. Oct 21, 2013 #106

    henryk

    henryk

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    =yes,right!=

    http://www.homebuiltairplanes.com/f...536-ducted-fan-blade-design-hall7-ejector.gif
    from=
    http://www.acoustics.org/press/148th/hall.html

    but...=

    Trek_Aerospace_Strategic_Alliances

    and=

    http://www.pegasusrotorcraft.com/specifications.pdf


    http://www.homebuiltairplanes.com/f...uel-system/13584-ducted-fan-blade-design.html

    http://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/12408-ducted-fan-aircraft-5.html

    http://www.sciencedirect.com/science/article/pii/S0376042109000347
     
    Last edited: Oct 21, 2013
  7. Oct 22, 2013 #107

    Malish

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    This is how, we're counter the swirl DSC07656 (Large).jpg DSC07657 (Large).jpg P9230097 (Large).jpg
     
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  8. Oct 22, 2013 #108

    DangerZone

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    Excellent work Malish! So it is five fan blades and 11 stator vanes to counter the swirl... I saw that you have positioned the exhaust pipe in the ducts upstream before the fan blades. Will there be some sort of diffuser at the pipe end so that the exhaust flow would not interfere with the air flow in the duct?
     
  9. Oct 22, 2013 #109

    Malish

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    Thanks. Yes, but letter. Right now we're getting airplane ready for final assembly and for test run's. It would be a lots of to to(I'm sure), for the fine tuning, after(hopefully) it will show proof of concept.
    Here some photos of first fan assemblies. On the test run the dust covers from drive shafts broke off and ruin the blades. P4060494 (Large).jpg P4060495 (Large).jpg P4060497 (Large).jpg
     
  10. Oct 22, 2013 #110

    Malish

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    Here the new one's P8300646 (Large).jpg PB020679 (Large).jpg
     
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  11. Oct 22, 2013 #111

    Jay Kempf

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    Malish, That is too bad. I guess you underestimated how strong the stuff in front of the fan needed to be. That is a good thing as it means you are getting more upstream low pressure than you planned meaning your static thrust was ahead of plan as well. I think the overall concept of the low angle V arrangement of driveshafts is very clever. And the modular tail end looks like a great design.
     
  12. Oct 22, 2013 #112

    Malish

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    Well, I was thinking, to remove those covers before anyhow. But didn't do it. This airplane is still in experimental stage. But you are right, this fan's will find anything to sac in in to the duct. We're swiping the ground in front of the intakes and poor some water in the area too, before we run the engine. And the intakes about 25' of the ground, still you can see small "tornado's" of water cumming into intakes. P6050577 (Large).jpg
     
  13. Oct 22, 2013 #113

    DangerZone

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    The first set looks like the glass or poly blades used in hovercrafts, or is it something you have made yourself? The second ones seem like carbon fiber with the titanium/steel reinforcement. Did you consider the wooden composite blades? The wooden ones seem to be very appreciated in hovercrafts cause they can resist more of hard abuse and in certain situations perform better than carbon or glass blades. This is a 'ground adjustable pitch' hub with 9 wooden blades made by Ales from Bufocraft:
    blades6.JPG blades7.JPG blades.JPG

    I know you need fast speed and high dynamic thrust and this is quite the opposite, high static thrust for low speeds, but maybe you could use some of the parts like the blades. You know, sometimes it saves time to buy a finished product instead of making your own. And these blades are small enough so they could be reformed to the desired shape by a small CNC machine. ;)

    It's a great project that you are doing, please keep up the good work. :)
     
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  14. Oct 22, 2013 #114

    henryk

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    =some intake "filters"?

    BTW=estimated versus practical thrust force?
     
  15. Oct 22, 2013 #115

    henryk

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  16. Oct 22, 2013 #116
  17. Oct 23, 2013 #117

    rv6ejguy

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    All the theory is great about fan design and tradeoffs but it is just theory and meaningless until validated in flight. When Malish or someone else comes up with a real, working example showing some good static thrust, ROC and speed numbers we can learn from their hard work. Nobody knows until they do it for real. This is hard stuff to model so as he said before, you have to build it, test it and improve it, not conjecture about it. Applying lessons learned in low speed applications may or may not be useful either, the dynamics at 200 knots are a lot different than 50 knots.
     
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  18. Oct 24, 2013 #118

    Doggzilla

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    Do any of these contested designs have nozzles? As the airspeed increases, the impulse thrust will be lower because the ambient flow of air is moving at a closer relative speed to the thrust...

    I don't think it has to do with drag of the housing, because it's drag is quite a bit less than an internal duct. The exterior surface has the advantage of the ambient air already being accelerated by the forward fuselage. You can see from a 2D vector graph that the laminar flow reduces the speed at the skin and gradually matches the indicated speed as it flow moves away from the skin.
    So the outside of the duct is at substantially lower drag than the inside of the duct, even with no thrust. When thrust is applied, the inside duct has vastly more drag. This was the issue with the xv-14, which could not take off with more thrust than its weight.... The internal ducts sapped the flow. So internal duct design should be priority number one.

    Im not positive, but a larger duct with a nozzle may have lower resistance due to a more gradual change in flow speed from the walls to the fastest part of the flow. Larger ducts are known to work substantially better in HVAC even though they have larger surface area...but the internal surface area is reduced by its square of its volume... A 10x10 duct has 100 square in cross section, while 12x12 is 144 sq... A 44% increase in volume for a 20% increase in area. The drag from a nozzle to accelerate the flow would be much lower than the drag of an undersized duct.

    Lastly, NASA is experimenting with "freeblades" for helicopters, a version of the freewing for propulsion. A freeblade in a ducted fan would automatically adapt to the incoming airflow and increase the impulse thrust.
     
  19. Oct 24, 2013 #119

    henryk

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    Last edited: Oct 24, 2013
  20. Oct 25, 2013 #120

    Aircar

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    Scrubbing losses on the intake trunk are not insignificant for sure --and separation is also a problem on a non contracting duct more than one with a non constant-decreasing, cross section and is one of the main differences between a ducted propeller (with a bell mouth creating a contracting duct in effect and accelerating the boundary layer by the airfoil effect when the stagnation point is on the outerside of the intake ) and a buried fan - without boundary layer bleeds on the intake and fairly clean flow into the intakes it could be hard to get the optimum blade loadings downstream at all times --the transition from a square section intake to a round disc face also introduces problems (even to standing vortices in the corners --it was Frank Whittle who foresaw this as a problem in centrifugal compressors and was found also in superchargers by Hooker --the Moller Slycar uses the reverse of a round intake to an expanded square exit and this is also a problematic geometry --few other homebuilts have used an internal shrouded propulsor so much will be learnt from this work .

    PS there was a Mazda rotary powered 'ducted propulsor' homebuilt flown at Mojave in the early 70s but I haven't heard of it since -any one know details ?
     

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