Ducted fan aircraft

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

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  1. Jul 31, 2013 #41

    JETMECHANIC

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    90% of the thrust of turbo fan engines come from the ducted fan. Example a Boeing 777 jet engine produces more than 100,000 pounds of thrust from the ducted fan but the hot section of the engine is making over 200,000 shaft horsepower. Hate to pay that fuel bill with a 2inch fuel line feeding that monster of a engine. The ducted fan has multi stages of rotors/fans, with the stators giving the airflow the proper angle of attack for the next stage rotor and straightening the air stream after the last stage rotor/fan. The multistage ducted fan is supercharging the ambient air, for example the inlet psia standard day sea level is 14.7 and after the last stage is somewhere around 50psia. giving you a Fan Engine Pressure Ratio (FEPR) of 50/14.7= 3.4 that more than triple the sea leve air pressure. So in order for your ducted fan to work you have to have multiple fan/rotor stages to bring down the diameter of the duct to around 4 feet, in say for example a ducted fan friendly scaled down size F15 aircraft configuration. Jet Mechanics Do It With More Thrust!:gig:
     
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  2. Jul 31, 2013 #42

    bmcj

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    All excellent points JetMechanic (and welcome to the forum by the way).

    So, about 1/2 pound thrust per HP, whereas a propeller gives maybe 6 (static) pounds per HP. Jets and turbofans are great for big and fast (and maybe even small jet replicas), but for the broader (small aircraft) GA market, props are hard to beat. (I think that is the same point you were making)
     
    Last edited: Jul 31, 2013
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  3. Oct 10, 2013 #43

    henryk

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  4. Oct 10, 2013 #44

    rv6ejguy

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  5. Oct 10, 2013 #45

    billyvray

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    It will have a single V8 running through a gearbox that splits and has two driveshafts to the fans. It's in the thread pics. Really cool.
     
  6. Oct 10, 2013 #46

    henryk

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  7. Oct 10, 2013 #47

    henryk

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    BTW=auer project of the flying scooter is based on the inner ducted fan too...

    Решотка.jpg
     
  8. Oct 10, 2013 #48

    rv6ejguy

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    I looked at all 12 pages on this project link. Amazing project and engineering.

    What happened with the one set of fan blades?
     
  9. Oct 10, 2013 #49

    Workhorse

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    I think the key for a ducted, not shrouded, fan is speed. In fact we already know they are very efficient at high speed. Perhaps we should think in terms of fan itself rather than propellers.

    Pump-jet - Wikipedia, the free encyclopedia
     
  10. Oct 10, 2013 #50

    henryk

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    Last edited: Oct 11, 2013
  11. Oct 10, 2013 #51

    DangerZone

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    Seems like a cool looking project...

    What performance does the builder expect from this aircraft? Cause it looks like the airplane might turn out to be slightly heavier than the ultralight class...

    I also noticed your assumption on a previous post about adding efficiency with the 'ducts'.

    It might be wise to distinguish two different concepts and two different ideas, the ducted fans are not the same as shrouded props and there's a difference between static and dynamic thrust. The assumption that you posted about an increase of a theoretical maximum of 40% thrust is most probably based on ducted fans from hovercraft racing. Yet there is a big difference between static thrust of the hovercraft fans and dynamic thrust needed by airplanes to fly through air. The initial impulse of the increase of static thrust when accelerating from zero up to a certain speed lasts quite short and after a certain speed it becomes a penalty in the form of excessive drag at speeds as low as around 100km/h. Thus using the principle might have some benefit for a hovercraft, a flying jetpack with shrouded props or ducted fans, anything that moves the duct very slowly through air. As soon as that speed becomes higher, drag and duct/shroud resistance augment exponentially. So a ducted fan would indeed be more efficient at slow speeds up to around ninety kilometers an hour but very inefficient beyond that. Most airplanes fly very shortly below that speed usually only during take off and landing.

    A shrouded prop also has some benefits of using the flow of air that would otherwise just slip from the sides but it depends on the design of the shrouds. The problem arises when the aircraft starts flying faster because the shroud becomes an air brake adding drag to the equation. There are some concepts that could use a sort of shroud to add lift like the Custer channel wing but it is far too complicated for the benefits they provide. The biggest challenge is to make an airplane that has a very low stall speed and very high cruise speed with minimal drag. This Russian airplane, however beautiful and sleek the lines, might not seem to be after that goal. The stall speed could be quite high above the range where the ducted fan would be more efficient and at a certain point the ducts could induce too much drag reducing the maximum and cruise speeds. I love the looks, the Sukhoi Su30 and MiG29 are beautiful and I hope the author of the aircraft has thought about all the advantages and disadvantages of the ducted fan concept.

    There was a brilliant Russiant guy who was making counter rotating ducted fans for hovercraft racing. After seeing the broken fan blades it seems the builder might use some additional advice from this expert. Anyway, I wish the builders good luck cause they gonna need it, it takes great courage and dedication to do such a complicated project.
     
    Last edited: Oct 11, 2013
  12. Oct 10, 2013 #52

    Jay Kempf

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  13. Oct 11, 2013 #53

    Aircar

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    Looks like only a matter of time before a homebuilder in his replica jet fighter (en route to Oshkosh say ) triggers a NATO nuclear alert, scrambles the USAF and who knows?-world war three ?? (only joking --at best a short tactical exchange of nukes would be likely:devious: ) - I guess that 'reaa.ru' equates to the Russian branch of EAA --it is notable that ,apart from the 'suitcase plane' and a Sukhoi aerobatic plane I don't know of any other Russian homebuilt type experimentals that have ever visited Oshkosh which is a shame given the evidence of unique and daring designs coming to light.

    Is the 'original' for this aircraft an F 15 or a Russian fighter in fact ? - only Jim Bede's BD 10 and one other semi replica fighter with a tail pusher prop have come close to being modern fighter counterparts from the homebuilder world (one Australian did a Lockheed Shooting Star with a ducted fan I believe ) --the view down the ducts reminds of my time crawling inside the F18 'centre barrel' sections on fatigue test here -- the three main spar carry throughs including the undercarriage attach and surrounding the dual engine intake ducts . I was a bit surprised that there was no boundary layer bleed internally after such a long entrance to the compressor. The cracking problem with the F 18 was due to the monolithic plates used to make the 'ring spars' in one piece but should have been pinned frames ( I suggested a fix involving through bolts that crossed the air intakes and tied the two sides of the frames together --relieving the bending of the open frames but the program was terminated in favour of buying newer F18s and the long awaited F35 --in the course of this the aerodynamics inside the duct were looked at and means to 'hide' the (airfoil shaped) spindles across the ducts by injecting air in their wake to make up for the drag . Still think it would work.

    I was surprised at how tall the landing gear was on the model --seems longer than needed but might not be scaled either. Why did the fan disintegrate BTW ? (haven't read back the thread yet ) -- this project is likely to attract the attention of a younger generation for whom a P51 is a museum piece and as far from their cohort as a world war one fighter is for the 'boomer' generation. I don't imagine that ultimate high speed is really that important for the 'mission' they have in mind.--it will be awaited with real anticipation .
     
  14. Oct 11, 2013 #54

    DangerZone

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    It seems like a smaller version of the MiG29 with some good influences of the Su30 design on some parts.

    The homebuilt:
    P4250064__Large_.jpg

    MiG29:
    mig29.jpg
    ap_mig-29ub_01.jpg
    mig-29n_tudm_0002.jpg

    However, there is one thing that is missing from the original MiG which would have been useful for such a homebuilt. The real MiG29 had inlets from above the ducts for taking off a grass stripway. Such a good solution would prevent debris, gravel and dirt to be sucked in by the duct inlets and damage the fan blades. Thus my asumption is that the engineer who has built this homebuilt had to make a taller landing gear to keep the blades safe and sound inside the ducts. At least that is simpler because a variable intake would complicate things a bit too much. It is evident that they read a great book about ducted fans called 'Ducted Fan Design' so they would not make the same mistakes as others have in the past, it's better to learn from other people's mistakes that on our own.

    The touble with ducted fans is that they have to be machined and adjusted to a tight fit, meaning that any deviation or bad tolerance might turn the fan inefficient. The materials used for hovercraft blades of ducted fans are usually wood, carbon fibers or glass, and all three are quite elastic compared to titanium or steel. This leads to a problem of CF/GF/wood deformation under heavy loads and high rpm and the closeness of the duct walls do not help creating a draft from laminar to turbulent airflow. This might lead to tear of the fan blades and it occurs quite often in ducted fans.

    There was a French guy who also played with the idea of a jet fighter but it seems he dismissed the whole idea of a ducted fan and planted a propeller on the tail. This is the French CC-02 which reminds a bit of the Javelin jet aircraft:
    cc02.jpg
    It's a very pretty design and it even flies well if you don't mind the high take off and landing speed. Copying a jet fighter looks has a certain cost and so far most of the successful homebuilts did have a higher than usual stall speed. I'm very curious what the performance of the Russian ducted fan airplane will be, it is certainly a very brave accomplishment.

    Jim Bede's BD10 was also a beautiful airplane and it seems the builder of this Russian aircraft had a great idea to make a similar 'jet' with good fuel economy with a piston engine. The biggest problem with BD10 and the ViperJet was that they too had a similar idea at first only to discover that the aircraft would be underpowered. More power meant a bigger engine, a bigger engine led to more weight and soon the airplane that was planned to be not heavier than 700kg ended up with a mass of more than a ton. It would really be interesting to see the weight and balance of this airplane, cause there is an option to have a more powerful engine which might be needed after the first flying tests. Real performance could show that even the 300 and something horspower might not be enough for such a ducted fan design. It would also be wise to anticipate such an event and plan forward for stiffer and stronger blades.

    Are there any pictures of this Australian Lockheed Shooting Star ducted fan design? It would be nice to see the achievements on the other side of the World, or is it 'Down Under' that people say? :)
     
  15. Oct 11, 2013 #55

    henryk

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    =PISTON JET II=prototype

    Взлетная скорость 150-160. Взлетный вес 1000кг. Топливо 280л. Дальность полета 1500км. Перегрузки +6/-4

    =Vtake off=150-160 km/h, Mtov=1000kg, gas=280l, flying distance=1500km, overloads=+6/-4...LS6 engine,airconversion.

    -proffesional aviaconstructor and workers...
     
  16. Oct 11, 2013 #56

    henryk

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  17. Oct 11, 2013 #57

    Malish

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    Hello everyone,

    Thanks to "henryk" you know about aircraft we're building in city of Volgograd, Russia.
    I will try to answer to your questions in English now on you forum. But you are welcome to go Russian EAA forum(links "henryk" provided).
    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 New Image 009 (Large).jpg
     
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  18. Oct 11, 2013 #58

    DangerZone

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    Hi Malish,

    Welcome to Homebuilt Airplanes and congratulations on such a beautiful and courageous design.

    One thing that might be good to include in the performance is the frontal drag of the aircraft, do you have that information?

    Keep up the good work. ;)
     
  19. Oct 11, 2013 #59

    Malish

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    To DangerZone,

    Thanks.
    If I remember right, the frontal area of airplane, is 0.65 But, this not including intakes. This area of experiment. I red, all could find on Ducted fan and NOTHING found 100% reliable. This is dark zone. Only experiment will show.
    BTW, why this question, of any how? Are you guy's is doing the same things, as on Russian forum? If so, I would live this forum. Thanks.
    NONE of manufactures including this information in performance.
    I don't expect performance of this airplane be competitive to jets and even to piston powered airplanes with same engine. But it will have something, that people will appreciate for fraction of the cost flying REAL jet aircraft.
    And I know it. I did visit many many airshows for many years. Including Oshkosh and Lake land . And I was there flying my own airplane: Yak-18T(photo I will attache later) I could say even more, but it's time to for the dinner. New Image 004 (Large).jpg
     
  20. Oct 11, 2013 #60

    rv6ejguy

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    I am not aware of anyone in North America building such an ambitious ducted fan aircraft as you. This is an amazing project and I think you have realistic performance goals. I think people might be interested once you get it flying and get the problems worked out. The airplane looks great!

    I think people don't realize how much work and experimentation is required for such a project and you have little information to go on. Like you say, you must design, build and test each part and it is a huge job.

    This forum tends to have more theoretical discussions and less actual flying examples of innovative aircraft. We can all learn something from you. Theory doesn't mean much until it's proven in practice so I like your approach.:) Happy to see you posting here.
     

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