Ducted fan aircraft

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

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  1. Oct 12, 2013 #61

    deskpilot

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  2. Oct 12, 2013 #62

    DangerZone

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    Hey Malish,

    To answer your question why I was asking, well, I asked because I believe in you and your concept.

    I had a similar idea some five years ago and contacted many experts on the feasibility of such a ducted fan concept. Most advised to read a lot of literature on ducted fan design before ever starting anything, so I did. After reading all relevant information available at the time I realized that the challenges are enormous and decided not to go there and build another airplane instead. Even the literature available at the time had some contradictory information which can only be verified by experiments. So I am glad to see that you have done such a marvelous and challenging project which is a wish of many homebuilt airplane enthusiasts.

    The way I see it, you resolved most of the issues when building a ducted fan airplane. I saw some of the pictures on your Russian thread that remind of the book 'Ducted Fan Design' by Marc Piolenc and George Wright, which I am sure you already read. I am mentioning this because you seem to have quite some knowledge and courage to go where only a few have gone before. Sure, there will be some challenges but most of them can be resolved. And I agree with you that all that was written on ducted fans has some issues and that only true experiment can show how a ducted fan performs in reality.

    The biggest challenge of the ducted fan is to resolve the intake drag of the ducts. If I remember well, many have tried variable intakes, shape changing inlets, nozzles and variations, everything but to keep it simple and just accept the fact that there will be drag. By observing your design it seems that you have taken advantage of the 'channel' which is formed by the leading edge of the wing to assist air flow into the ducts by a smoother transition from turbulent to laminar airflow. Only experiment will show how this will perform in reality but somehow I have a good feeling about it.

    Please don't leave this forum, there is always some good information here even though sometimes communication might seem awkward due to the language and perspective differences. Even if you read some commentaries criticizing your airplane it does not mean this criticism has bad intentions. I see a potential in your airplane and it would be awesome if it would become a successful business in the future. When I pointed out that the MiG29 had intakes above the inlets it is a fact that might preserve your fan blades on the future models for those who would want to take off from grass runways. If there are any issues or challenges that could be resolved by different thinking, there are smart people here on this forum who might help with a perspective from a different angle.

    I anticipate that in time your project will expand and there will be other models. Thus if I seem like a critic it is simply because a different perspective might lead to some improvements in the future. The airplane that you are building is great, and it will be an awesome platform for experimenting on ducted fan. The Russians have built some awesome airplanes in the past like the MiG29 and the Su37 so you seem to keep up with the good tradition. Quite frankly, the jet-fighter-like piston engine ducted fan airplane is a dream of many, both here on this forum and pilots around the world. So please, keep up the good work and accept my best wishes for success. :)
     
  3. Oct 12, 2013 #63

    DangerZone

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    Talking about the actual flying examples, there was the Saunders JetHawk some 20 years ago, I believe it was built in the USA.

    2781d1231205131-saunders-jethawk-any-builders-jh2_2.jpg

    If I am not mistaken there was also the Smitty Airplane with a good looking ducted fan design but it did not meet the expectations of the builders but I can't remember where was the author of this fan from.
    Ductview.jpg

    iso1.jpg

    Apart from those, there was the German FanTrainer which was a shrouded prop certified aircraft and some said that it flew smoothly:
    0385369.jpg

    None of them shared anything similar to the Malish Piston Jet II project, apart from having some sort of duct or shrouded prop. Both the JetHawk and the Smitty airplane had some problems with the inlet duct design and it seems the PJ2 has resolved these issues by a rather clever positioning of the duct inlets.

    Thus, I join you in expressing the happiness to have someone like Malish (and Henryk) on this forum with wishes to learn something new. ;)
     
  4. Oct 12, 2013 #64

    DangerZone

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    Cute little airplane, is it made in Australia?
    21323d1355163371-experiamental-fighter-jet-style-aircraft-screen-shot-2012-12-10-9.02.14-pm.jpg
     
  5. Oct 12, 2013 #65

    rv6ejguy

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    I know of a couple ducted fan designs which flew but performance was so poor so as they were not practical. I have seen many more paper designs which were either never built or switched to true jet power along the design stage (we have a 60% CF-105 Arrow project at my airport underway for 15 years which will probably never fly).

    I don't consider shrouded fan designs in the same discussion as these can never have the cool visual appeal of ducted fan, fighter like designs and don't face the same challenges in design or execution.

    I think the Malish design is smart in several ways- short, large area duct and big hp with the centrally mounted engine staying out of the duct paths. Most ducted fan designs have had the engine blocking the duct and far too low hp, plus a long duct which increases internal drag.
     
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  6. Oct 12, 2013 #66

    henryk

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    -direct axial inlet generate much drag\big perpendicular surface\=moore power needed...
    I think,better solution are radial inlets=thay can have big surface,but paralel to the auter flow...BTW=they can suck boundary leyar=decreasing drag!

    Решотка.jpg +ejector ring for take off thrust incresing...
     
  7. Oct 12, 2013 #67

    DangerZone

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    I never understood why did the Canadians cancel the development of the CF-105 Arrow, it seemed like the first successful attempt of the modern jet fighter in the '50s. I got the feeling that this airplane inspired the Russians to make the MiG-25 and the Americans to do the F-15.

    I like the Malish design too, it's not only beautiful but rather cleverly done and I am curious about the performance. The internal drag might be reduced in the future by installing counter rotating fans which could also add dynamic thrust allowing better usage of the available horsepower at higher speeds.

    Henryk, could you please rephrase that for easier understanding what you wanted to say?
     
  8. Oct 12, 2013 #68

    Workhorse

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    [​IMG]

    I think Henryk is right. We are obsessed with ram air because we still think that a ducted fan is a propeller, and it is not.
    The pump jet doesn't care about an intake duct oriented to the airstream. It takes the needed water itself because the fan is more interested about the volume. That's why IMHO what is really needed is as much blades as possible, the thinner the wider the better avoiding spilling vanes. I don't mix fans and propellers, I see them totally different.
     
  9. Oct 12, 2013 #69

    Workhorse

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    I forgot to thank again Malish for his truly valuable project and data provided. Welcome Malish.
     
  10. Oct 12, 2013 #70

    henryk

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    Last edited: Oct 12, 2013
  11. Oct 12, 2013 #71

    henryk

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  12. Oct 12, 2013 #72

    LBarron

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  13. Oct 13, 2013 #73

    Vipor_GG

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    That Archon SF1 is a cool looking little plane. Scale it up to a two place and bump up the power and it would be a great little LSA, provided it flies well.
     
  14. Oct 13, 2013 #74

    rv6ejguy

    rv6ejguy

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    Political backroom meetings with the US sealed the fate of the Arrow and many of the Avro and Orenda engineers went to the US for jobs once it was canceled. Many Canadians are still sore about the decision and the way the government destroyed almost all traces of it. It took away much of the infrastructure and brainpower we had in aeronautics at that time.
     
  15. Oct 13, 2013 #75

    henryk

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    =auer Witold Kasper was mooved from Canada to Seattle too!

    http://koendu.pl/doc/Living with Inflation.pdf

    http://koendu.pl/doc/Polish resister, sister reunion here.pdf
     
  16. Oct 13, 2013 #76

    DangerZone

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    True, the pump jet does not care much about the losses of duct orientation up to a certain speed when the nature of water imposes an hardly breachable barrier. That is why we don't see speedboats with pump jets but rather propeller driven or fanjet engine powered. The water is a quite different fluid compared to air, it is incompressible and has a sticky/gluing element of fluid laminar flow. If you observe the bottom of modern fast speedboats you will notice dents/steps at calculated intervals which serve for the transition of laminar to turbulent flow so that the speedboat could slip over water. Without it, the sticking/gluing nature of water would not allow it to go that fast. This is the reason why every amphibian/seaplane has at least one step just slightly after the CG to be able to take off water. In other words, it is not an obsession but a necessity due to physics and the nature of fluids.

    The orientation of the pump jet intake does not matter for the 'slow' speeds of water vehicles. The nature and pressure of water along with hard compressibility assist the water jet to power a boat. Yet air is a different fluid and acts differently depending on the speed of the aircraft. Air is easily compressible and the pressure effect is influencing the flight of a ballistic object flying through air. A ducted fan is very efficient at static thrust yet with the augmentation of speed the dynamic thrust goes down exponentially. In other words, a ducted fan with many blades will be excellent for speeding up from 0km/h to around 130km/h but beyond that drag would overcome and the duct along with the fan becomes a massive air brake. It could be compared to an airplane that would pitch the prop in reverse to act as a brake if you'd want to dive from a couple of thousand meters down to a landing strip in a few seconds. The sooner people understand this the better, because there were many good looking projects in the past that had a ducted fan that was neglecting this fact and nature of air as a fluid. The Malish ducts and fans are well designed for a big airplane (meaning human flyable aircraft and not only RC models) that promise decent thrust at higher speeds because the channel is not obstructed by much and there are fewer blades to reduce drag. It's simple, more blades means more drag, more effort to rectify the swirl to thrust by installing vanes and less flying speed with the same power. If you need static thrust to let's say suspend something in air then yes, more blades would be a good thing. But if you want that airscrew to fly dynamically through air at a certain speed then the less blades the less drag. And drag is what slows the aircraft flying through air. That's why the JetHawk and some other airplanes didn't have the flying abilities that their designers thought they would have.

    Ok, now I understand what you meant and this is a great example of a static thrust ducted fan. So yes, it is very effective when it is static, installed in a box. At different Reynolds numbers such a ducted fan might even show good results in a ducted fan RC airplane. However, a big size ducted fan flying through air dynamically might experience a thrust ratio going down proportionally as the speed goes up. At around 130km/h the fan could have a significant drop in thrust and at speeds beyond that the duct would act as an air brake further decreasing the flying capabilities.

    The picture that is drawn with a comparison of STANDART and MOJ, is it showing two ducted fan versions for generating thrust as in a cooling fan (ventilator) or is this intended for flying? Because both might not be suitable in creating dynamic thrust for flying due to the drag they would create. The STANDART has an oversized leading edge duct nozzle which would be an aerodynamic brake and the MOJ might fly in the direction of the arrows but with major drag losses. At higher speeds the vanes would also act as an airbrake and the abrupt 90 degrees turn of the airflow would turn such an ducted fan into a powerless thrust source. It might work for a smaller RC model though, so if it intended for a toy or RC airplane there is a chance to have some results. In real airplanes the air flow has to be constant, as in Malish ducts where even the transition of rectangular to round shape is well balanced to reduce nozzle drag forming in the corners of the inlets.

    There is a simple way to see it yourself if this ducted fan performs the same both statically and dynamically. Make some sort of thrust measuring device behind the fan and put the whole setup on the roof of a fast car. Have a driver do the driving and evaluate the thrust at different speeds. You must not be the driver for safety reasons, it is not advised to be staring at the fan thrust results and driving the car at the same time simultaneously. Observe the data and notice how the thrust drops as the speed goes up. At some point you will even have reverse thrust when the dynamic air flow of the driving car speed takes over. The same would happen in a real size airplane if the ducts are not designed well and it might lead to a sudden loss of flying capabilities, not only sudden loss of thrust. If you lose thrust with a prop, no harm done, you could still land the aircraft with good aerodynamics. With a ducted fan that suddenly turns into a massive airbrake obstructing the aerodynamics of the aircraft? I am not so sure. I'm not trying to discourage you, I am merely suggesting that the best way would be to test it first to see what could be expected in real flight.

    Cool. Nice pics and cute airplane. There's only a slight little detail that seems to have passed their attention. The channel wing that they claim to have invented and named it FFA (flying fuselage aircraft) was built almost half a century ago and tested for many years by Custer, NASA and a bunch of others. Nevertheless, I like their F35 design, it looks 'mean' in a good way. :)
     
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  17. Oct 13, 2013 #77

    henryk

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    -greate thanks for yours good remarks...
    =some little difference between Sandauers,Malish\STANDART\...inlets and "my"\MOJ\=

    MOJ is located at the rear part of the Golschmid mode fuselage,wher neutral and overpressure exist=

    http://www.homebuiltairplanes.com/f.../23062-ducted-fan-blade-design-bowden-009.jpg
    \no auter propeller\...

    -boundary layer is "succed" throw inlet rings=allmost all fuselage has laminar flow...

    BTW="suction"-it is no such phisical phenomena,beqouse no pulling\gluing\ forces between air particles!!!
     
  18. Oct 13, 2013 #78

    DangerZone

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    You're welcome. I see that you have done quite a few interesting projects and it takes a while to understand the details. Is the MOJ (your) inlet project gonna have a shrouded prop or a ducted fan to generate thrust? Is this the propulsion of the egg shaped aircraft that you are building which looks sort of like a hang glider, the one that had Henryk written on the side?

    The MiG-29 had a similar diverging ramp inlet for take off from grass fields using the advantage of good static thrust and then closing the ramp and opening the front inlet for cruise. Thus the inlet opening was variable for the different speed needs and it reminds me of your MOJ project with the opening vanes. There is a big question whether a homebuilt ducted fan design would profit from variable inlets and outlets because the more complicated it gets the more drag there seems to be. For the speeds that most homebuilts fly of up to 500km/h it might be wise to keep things simple and uncomplicated.

    If I remember well, the Saunders JetHawk had problems with the inlets and the deflection of the air flow. Combine his poor fan efficiency with an underpowered engine and massive weight to get the picture how a beautiful idea can go down south easily. IMHO, the best way to design a ducted fan aircraft would be to build an engine and ducted fan assembly, test it, abuse it and then when satisfied with it all add a turbocharger on top to get even more power. Cause as much power as you have you'll always want more if the weight of the aircraft is close to a ton. It's like in the words of Skip Holm in the BD-10 video presentation: "A pilot can do a lot of stupid things in this airplane close to the ground, add power, and get out ok."

    The BD-10 was also a great concept and idea but the aircraft drifted away from the initial weight. The ViperJet had the same issues, it started with the same idea to have a ducted fan design with a piston engine. But as the weight went up they soon saw that the engine is underpowered so the later versions (that they build today) is jet powered. I love the idea of a ducted fan aircraft but it might be good to learn from other people's experiences than the hard way. So whatever we might build, it is always good to anticipate a more powerful engine just in case. It's better to have more power and not need it than to need more power to get out of something and not have it.

    What kind of engine did you plan to have and how would you install it in your ducted fan design?
     
  19. Oct 13, 2013 #79

    henryk

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    "Is this the propulsion of the egg shaped aircraft that you are building which looks sort of like a hang glider, the one that had Henryk written on the side?"
    =yes,it is rigid wing\KASPERWING\ "trike" with Mto <500kg...\in my case "motorbike"+2 training wheels\ with 80 HP SUZUKI G10 engine=direct fan drive,
    or 150HP KAWASAKI\similar weight\...

    "the best way to design a ducted fan aircraft would be to build an engine and ducted fan assembly, test it, abuse it and then when satisfied with it all add a turbocharger on top to get even more power."
    =yes,it is only possible methode to build effective thruster!

    BTW=thanks good L/D=25-30 we need little thrust for traveling\circa 20 kG\! +thermic "power"=very cheap transport...
     
  20. Oct 14, 2013 #80

    Aircar

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    Just got back to this thread - I don't have the designer/builder of the F80 Shooting Star scaled replica in front of me and will have to search my records -perhaps Head in the Clouds knows (it was in Queensland -about as far away as Moscow is from London ..)-it used a Mazda Rotary I seem to recall.

    Also reminds me of a design study done by Darrol Stinton in his excellent text book "design of the aeroplane" --his version of a jet fighter like homebuilt --it is featured on the cover and his preliminary specs are inside --not sure if it was to be turbine powered though .
     

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