Ducted fan aircraft

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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.
 

DangerZone

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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...
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.

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 .
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.

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.
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... ;)
 
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henryk

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krakow,poland
"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.jpgObraz ++ 474.jpg +centrifugal/rubber clutsh...
 

Malish

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Russia. City of Volgograd
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
 

Workhorse

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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. :)
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.
 

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.
"
 

DangerZone

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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
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. ;)
 

Workhorse

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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?
He means that you have no propeller blast on the tail surfaces hence no low speed control authority.
 

Jay Kempf

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He means that you have no propeller blast on the tail surfaces hence no low speed control authority.
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 :)
 

DangerZone

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

View attachment 27489

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
View attachment 27490
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.
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...
 

DangerZone

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He means that you have no propeller blast on the tail surfaces hence no low speed control authority.
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.
 

Workhorse

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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.
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.
 
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DangerZone

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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.
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...
 

DangerZone

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http://www.personal.psu.edu/faculty/c/x/cxc11/papers/Double_Ducted_Fan_0903_Detailed_Description.pdf

=NOTCHED DUCTED FAN=
pic.1.4 on the page 12...no moore problems with blade tips and duct collision!!!

\I cant extract this pictures!?\
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.asmedigitalcollection.asme.org/data/Journals/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.
 

AJLiberatore

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Canton MI
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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