Ducted fan aircraft

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

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  1. Oct 14, 2013 #81

    Malish

    Malish

    Malish

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    We never expect, that Ducted fan aircraft will outperform the propeller driven aircraft. Everyone know, that jet aircraft LOVE to fly at hi altitude. But fan there produce more drag then trust. It's good for slow airspeed flying. But everywhere is compromise.
     
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  2. Oct 14, 2013 #82

    DangerZone

    DangerZone

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    I liked the design of your rotary engine, if you could resolve the issues of overheating and friction it would be a great propulsion system for a ducted fan aircraft.

    Great book by Darrol Stinton, I heard he passed away last year or so, his work is outstanding. I have the first edition and am fishing on the internet for the second edition cause it has some additional information about electric aircraft which is something I will explore further in the future.

    I guess you meant this canard concept, right?
    5ccyfjwpr0370175568.jpg
    DarrolStinton01.jpg
    Did it ever evolve beyond plans? Cause I know a guy who is building a very similar aircraft in Germany but with a prop and a very light engine, the whole airplane is lighter than 120kg.

    Malish, I think you are doing a great thing and you never know where such a well done project might lead. The thing is that there are different perspective of what 'slow' flight might mean. For example, the BD-10 was intended for transonic flying but it never could fly successfully much faster than Mach 0.6 and even at those speeds it had problems with flutter. The ViperJet is also a great project but the speed is quite conservative compared to what was planned at first, a bit slower than the BD-10. Slow flying is our homebuilt territory, I don't think that it would be affordable to build anything faster than that.

    What speeds would you be happy with? What do you expect your stall, minimal, cruise, maximum and VNE speed to be when you finish the project? It really is a great concept, where could we find some more info in English about your airplane, how it all started, how come you decided to go that way, the whole story? I am sure that there are many more on this forum who would be interested... ;)
     
    Last edited: Oct 14, 2013
  3. Oct 14, 2013 #83

    henryk

    henryk

    henryk

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    "This is a sport two place aircraft PJ-II(pistonJet) utilizing "Ducted fan" system. Powered by "GM LS6" aeroconversion engine(by Team-38,Inc) via gearbox/multiplicator(ratio 1:1.4) witch turns two(69cm diameter)fan's. This engine provided 388hp at 5000rpm. We did run ground testing of the system. We're had static trust of 350+kg at 4000rpm. We're believe at airspeed 150-160km/hr(climb out speed), engine will turn 5000rpm.
    Cruise speed estimated 350km/hr(4000rpm) at 2000m.

    Aircraft spects:

    Length = 9.05m
    Wing span = 8.5m
    Height = 3.0m
    Mtow =1000kg
    Wing area =10m/sq
    Max fuel = 280liters"

    -BTW=extremal powerfull rotary engine is not optimized \fuel consumption\...
    it should be made from ceramic,not steel...=the work for another specialists!

    Zdjęcie181.jpg Obraz ++ 474.jpg +centrifugal/rubber clutsh...
     
  4. Oct 14, 2013 #84

    Malish

    Malish

    Malish

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    To DangerZone,

    I never expect this aircraft to fly supersonic. But I would like to fly at normal speed of GA aircraft.
    I'm pilot to. I would fly this aircraft( as projected) up to 350km/hr.
    I have experience of flying difference kind of aircraft. this aircraft not for everybody. It's don't have PROP WASH over the control serferces. And that mean, you have to FLY this aircraft like a jet(by numbers)
    If I will decide to write a book, Misha(my partner) said ,that I would be reach person by now.
    I will try to follow this link
     
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  5. Oct 14, 2013 #85

    Workhorse

    Workhorse

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    My point of view is that the fan act more as an extruder or an Archimedes screw.

    A4arcsM1.jpg

    You have a great benefit which is you can not worry very much about tip stall, vortices, loses if I'm correct. We can assume eficiency is lower given we have not an efficient turbojet driving the fan. The pump jet has about 1 atm pushing the water into the pump. In a ducted fan you have x atmospheres plus the ram air pressure for an airstream oriented duct, but what is really pushing the air into de fan is the atmospheric pressure which leads the air to the low pressure zone originated in the fan.

    A high vacuum axial pump: Turbomolecular pump - Wikipedia, the free encyclopedia
    Cut_through_turbomolecular_pump.jpg
    If this pump had fewer blades it could not reach the needed vacuum due to what I call 'spill loses' due to the low viscosity nature of air. This means that it works as a meat mincer, it needs to catch as much molecules as it can by having more blades.
    We can not think of fans as propellers because propellers are meant to 'fly' into the air meanwhile the fan is meant to 'grab' hunks of air, so again, the more the blades the better. I think the angle of attack is not much critical because they want to slice the air instead of letting the air flowing as a wing. You have plenty of air in front to grab, the limiting factor is the power you can give to this blades to do their work. This queueing air just need to be sliced and that's why a sharp thin blade is best for the job.

    The similarity between a pump-jet and Henryk's duct is that given a low pressure zone in the duct, the slipstream can do two things. 1.- If the pressure is lower it will happily flow into the fan inlet guided by the annular guide vanes. This vanes cancel any turbulence alowing a somewhat good laminar inlet flow. 2.-Upon reached max thrust in cruise i.e. there is not many vacuum for the atmospheric pressure to push air into. So the air just goes it's way rearwards in a by-pass manner so the duct doesn't add drag to the fuselage as a ram air inlet duct would.
     
  6. Oct 14, 2013 #86

    henryk

    henryk

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    NASA Hybrid Electric Hyper Efficiency Aircraft Concept - YouTube

    -read comments!

    "
    NASAPAV 1 rok temu
    Actually, the problem is not efficiency but simply how much thrust you can get out of the small nozzle. The BLI fuselage propulsor is optimally sized for cruise to achieve maximum efficiency, and therefore does not have nearly the thrust required for takeoff and climb. If you just try to throw more power, than the disk area is so small, that you would have to throw a LOT of power at it - and you would end up with a terrible solution.
    "
     
  7. Oct 14, 2013 #87

    DangerZone

    DangerZone

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    This is a quite realistic goal, it's great to have someone like you on this forum.

    When you say that you have to fly this PJ-2 aircraft like a jet, what did you mean exactly? The MiG-29 is made quite unstable so it could perform outstanding maneuvers. On the other hand your design seems to be very stable and the ducted fan will add quite a bit of stability. It is also remarkable that you positioned the fans at the outer side of the duct which is different than the point of view from the authors of the Ducted Fan Design book. Did you choose the position so you could add some sort of vectored thrust nozzles to the rear to have better maneuvring abilities in tight corners or will you leave the flow without variable duct exits?

    A book sounds good, it looks like there's a lot you could tell. Thumbs up on the wishes that you become rich someday, your project looks promising. ;)
     
  8. Oct 14, 2013 #88

    Workhorse

    Workhorse

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    He means that you have no propeller blast on the tail surfaces hence no low speed control authority.
     
  9. Oct 14, 2013 #89

    Jay Kempf

    Jay Kempf

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    And you don't have a climb prop to firewall and to get you out of trouble. You have to plan ahead. Momentum management. Sounds like he is going to have plenty of thrust though. And that LS6 will spool faster than an idling turbine :)
     
  10. Oct 14, 2013 #90

    DangerZone

    DangerZone

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    I believe you are quite correct regarding the compressors and the fans. However, a ducted fan does not act like a compressor or a jet engine. One of the problems with ducted fans is the nozzle effect it creates so without a good inlet design every project might end in a quite inefficient thrust generator. I've seen research by guys who had years and years of work on turbines and compressors give up after not being able to resolve this very challenging task of designing a good variable inlet which would serve to power an aircraft at low and high speeds both. Most of them gave up after some time so I admire every single person who has the time, guts, brains and money to take on that challenge.

    I've seen people judge Saunders saying his JetHawk was not good enough. But that's simply wrong. We have to admire every person taking on such a difficult challenge in the first place. Then, there were others, like the Smitty Hairplane guy, the Germans with the FanTrainer and a bunch of other people who have done something or at least fought for the idea. The way I see it, they all contributed to the development of the ducted fan design. It could be the future, sooner or later someone is gonna come up with a good solution, maybe an even more effective one than a propeller. For example, someone might see Henryk's rotary engine and suggest to try a different approach that would resolve friction and overheating issues while improving it's efficiency. Or someone might come over here with a brilliant new approach to a good and effective ducted fan blade.

    Whatever the case, there is a limit to the thrust that can be generated by such a small ducted fan. The technology is there, the knowledge, the methods, most of the information is available to those who wish to know. The obvious problem is the same one that the prop has without a variable pitch. If the ducted fan is well designed for low speeds, it will generate much drag at higher speeds. If it is good for high speeds then the airplane will need forever to take off and require quite a long runway. So it seems to be a sort of compromise, to reduce the thrust a bit to be able to enjoy both high speed and low speed thrust. Until someone else comes up with a better solution...
     
  11. Oct 14, 2013 #91

    DangerZone

    DangerZone

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    Yes, that one is obvious, this could be resolved with variable surfaces at duct exits as in hovercraft fans. If needed of course, that might only complicate things so the best would be to make them removable in case it turns out not to be that efficient. My question was more concentrated on the stability of the aircraft.
     
  12. Oct 14, 2013 #92

    Workhorse

    Workhorse

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    I think it is not so obvious. I landed once with a tailwheel in a really narrow strip with water both sides and my fear lead me where I was looking at, the water. Luckily I raised my head and slamed the throttle. The prop blast in the tail saved my day. Since then I carefuly remind what is the difference about having control authority and not.
    Jay, control happens before than lift.
     
    Last edited: Oct 14, 2013
  13. Oct 14, 2013 #93

    DangerZone

    DangerZone

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    I understand what you mean. But that is only one part of it, the stabilizing part of the ducted fan is another. In other words, imagine wanting to control the airplane and turn/pitch but the airplane continues to fly in the direction of the ducts. That's one of the reasons why most jet fighters are made to be inherently unstable, so they could maneuver better through air. And relying on roll and power thrust response to control the aircraft might be a bit hard to fly.

    By looking at the pictures the PJ-2 has cleverly positioned ducts which seem to be able to control pitch of the airplane by adding thrust. There are so many smart tiny little details on this airplane and the more I look at those pictures the more details appear. Whoever was designing and building this thing with (or for) Malish has either spent years thinking or is just a simple genius. Or Both. My question about the stability and flying 'like a jet' was simply asking for more information about what other goodies are hidden beneath the design, not visible to the naked eye at first...
     
  14. Oct 15, 2013 #94
  15. Oct 16, 2013 #95

    henryk

    henryk

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    Last edited: Oct 16, 2013
  16. Oct 16, 2013 #96
  17. Oct 17, 2013 #97

    henryk

    henryk

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  18. Oct 19, 2013 #98

    henryk

    henryk

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  19. Oct 20, 2013 #99

    DangerZone

    DangerZone

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    Is this the picture you wanted to extract?
    NotchedDuctedFan.jpg

    This paper might seem simple theoretical scientific research, are you aware that this is more theoretical than practical research?

    If it is electrical ducted fan research, it might be wise to see the results of projects that have the largest RC electric motor tests. Most tests with the Hacker 200 or Predator 37 in the 500mm to 700mm range fan/prop diameter might be useful to get an idea of advantages and limitations.

    http://turbomachinery.asmedigitalco...ls/JOTUEI/927772/turbo_136_02_021004_f001.png

    ASME DC | Journal of Turbomachinery | Tip Clearance Investigation of a Ducted Fan Used in VTOL Unmanned Aerial Vehicles

    The tip clearance might always be an issue unless the shape of the blades have a radical redesign. The Germans had some tests during WWII with a radical prop and impeller shape which could combine low losses during both low and high speeds which is hard to achieve. But that is beyond my knowledge, maybe someone else might have more information about tip votices loss in ducted fan impellers.
     
  20. Oct 20, 2013 #100

    AJLiberatore

    AJLiberatore

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    Think of that Duct as not notched, but maybe trenched. Look @ your Large and Biz Jet Turbofans. They either have an abrateable honeycomb aluminum for the blades to run into and wear away or they have a stepped trench. What the stepped trench looks like is if you took some lattice strips (lets say 1' x 1") and nailed them equi=spaced lengthwise along a 2" x 10" this is not all that dissimilar in layout to a "labby seal" found in the engine internals.
     

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