Ducted Fan Design .pdf
Ducted Fan Design (2001Ed.) Return to Mass Flow page Return to Autodidactics Home Page Email Link. How to order:Send check made out to 'Mass Flow' for $49.95 + $3 s&h ($6 outside North America) to: Mass Flow. 917 Sandpiper St. West Covina, Calif. Return to Mass Flow page Return to Autodidactics Home Page. Fans Malcolm J. McPherson 2 10.1. INTRODUCTION A fan is a device that utilizes the mechanical energy of a rotating impeller to produce both movement of the air and an increase in its total pressure. The great majority of fans used in.
There is no easy way to get it accurately.You need to define: static thrust or at what speed do you want the thrust. The inlet lip radius has a huge static thrust effect; does the duct converge,diverge or is it straight? Those also have an effect.Martin Hollman's book on ducted fans gets into this. 98 -Thrust in lbs= 9.35 x ( hp x D)2/3 powerhp = horsepowerD= rotor diameter, ftinside the partrentheses is raised to the 2/3 powerOptimum blade number, chord, angle of attack of the blades, and the tolerance between the blade tip and the shroud all have major effects. The there's compressibility effects as the tips get over 0.80 Mach. It's a bitch to design one of these suckers.Chasbo RE: Ducted Fan (Industrial) 5 Sep 03 04:53.
RobWard,I will attempt a (partial) answer your question.1. A fan usually has a higher pressure ratio across its face than a propeller, and a fan often has more blades.2.
A fan and shroud unit will have a smaller overall diameter than an ordinary airplane propeller for a given horsepower, mostly because the shrouded fan blades have a higher and more uniform loading along their span.3. A ducted fan will be quieter for a given power level; because sideline noise, which is the worst part of a fan's or propeller's noise signature, is largely captured by the shroud.4. A ducted fan usually runs at higher rpm than a bare propeller, which helps to make the ducted fan a good match for a high speed engine.5. Static and low speed thrust for a ducted fan are typically higher than for a bare propeller at a given power level, because pressures induced on the shroud by the fan flowfield add to the thrust. However, the static and low speed thrust advantage of the ducted fan is lost if its diameter is too small.The thrust of an ordinary propeller at low speeds (under 50 knots)is generally poor. Ultralights could gain both thrust and noise benefits from a well designed ducted fan, if the weight can be kept low - a major challenge.6.
At higher speeds (above 100 knots, depending on the details of the overall fan & duct design, the duct drag exceeds the duct thrust gain.7. Duct weight is considerable, because the low internal and leading edge pressures can result in very high loads.8. The weight and high speed drag penalties are the main reasons you don't often see ducted fans, except on jets.9. Jet engines with bypass fans always use ducts, despite the weight and drag penalties.
Ducted fans are not essential for fanjets, however. Douglas Aircraft did tests on a DC-9 with 'unducted fan' engines. Their fan blades were fewer in number and larger in diameter than the fan blades on an equivalent ducted fanjet engine.
The unducted fan engine was a somewhat more efficient propulsion system; but it had noise issues. (On a typical fanjet engine, the duct helps contain the fan noise, plus the fan duct exhaust is mixed with the core jet exhaust to reduce jet noise as well. The unducted fan can do neither of these.) There may also have been certification issues due to extreme unbalanced forces resulting from loss of a large fan blade.
RE: Ducted Fan (Industrial) 8 Sep 03 07:21. I am hoping DORD2002 sees this post.I am in need of a copy of R. Hovey's book, 'Ducted Fans for Light Aircraft' or at least copies of critical pages on how to calculate static thrust from a ducted fan.If you could scan and e-mail to me the critical calculation pages, I'd be most appreciative. I also desire the title page with ISBN.I have done searches at amazon.com and bibliofind with no luck. There must not have been many copies published.Any help from anyone regarding this matter is appreciated!Phil RE: Ducted Fan (Aeronautics) 23 Oct 03 18:40. A further very usefull reference fot those interested in designing ducted fans or shrouded propulsors is'Aerodynamics of VSTOL flight', MxCormick,B.W.
Academick press. Library of congress no 66-30093 chapter 9A low pressure ducted fan, usually called a shrouded propulsor, can be designed in the same way as a free propellor with the adition of the flow from a series of ring vortices to simulate the duct as well as the flow field from a fuselage or nacelle.I designed one for a twin engined amphibian and compared it with a free propellor. Both using the same high rpm engine (suzuki 993 cc). The smaller diameter fan had benefits in lower off set thrust line and higher low speed thrust at take off float hump speeds. The weight of the ducts was more than compensated by the shorter propulsor supports and by the lack of need for a reduction drive for the shrouded propulsor.May i thank miper for his very succinct replyhappy new year to everyonemotorglider RE: Ducted Fan (Mechanical) 2 Oct 04 20:39. I've been reading this thread with interest and I would like to know what the ideal duct shape would be, tapered or straight in front and behind the fan?
Will a small (5%)reduction in cross section behind the fan increase thrust as I seem to recall an idea that it would? Can anyone help with the calculation for the ideal bellmouth radius and shape?
I'm looking at an 1100mm fan (number of blades to be tried between 2 and 12)with a maximum tip speed of 165 m/s using 50HP - 80Hp. Maximum operating speed would be aroung 100km/h so I'm mainly interested in static/low speed thrust for acceleration. Keeping it as quiet as possible would be nice.Motorglider, have you any further info on the twin engined amphibian as this sounds close to what I need? I also intend to use a Suzuki motor albeit 658cc and with a reduction drive. RE: Ducted Fan (Aeronautics) 2 Oct 04 21:11. I am looking for similar help. We are building a remote control car w/ a ducted fan in the middle for the possibility of going up walls.
The fan will suck air in at a high velocity from the undercarriage and spit it out the top creating a suction effect. I need a ducted fan that is approimately 5' in diameter. If anyone has any advice(on a type of ducted fan, or if we should use a reducing duct to increase the air velocity) I would greatly appreciate it. RE: Ducted Fan (Aeronautics) 23 Oct 04 17:10. Hi Jon8088,I have seen the drawings for the Jetpack, it is quite alarming and a very amature design, tho I am sure someone will try to kill themselves with one probably quite successfully.
The fans are chain driven from a single engine, failure of one chain would spin the occupant into the ground before he realised there was a problem. If the engine fails this machine cannot autorotate like a helicopter, it will simply fall to the ground. If anyone does intend to fly one of these machines I would recommend an explosively deployed parachute. Scanwizard 5 v7.220 macintosh. Even with a parachute an engine failure between 20ft and 300ft altitude would almost certainly be fatal. Having seen footage of the test flights for the origional jetpack, I would imagine serious injury or death would result long before anyone managed to master the control of this thing.Karl RE: Ducted Fan (Automotive) 12 Oct 05 02:15.
2 feet is a bit exaggerated, when you see him standing in profile he leans a bit forward, I 'd say a few inches.Seems to me that, or the thing is actively stabilized, or you 'll need weeks of practice to learn how to fly it because it can not be naturally stable. Also a landing with more than 125 lb on your shoulders seems to me almost impossible to achieve. A chair or some other stand might have helped to take the weight of the pilot's shoulders.Nevertheless, I think it looks nice and it would be fun to fly it although I would never do it.Checking if it has enough power to lift 330 lb:From the Rankine-Froude Momentum Theory of Propulsion:1. Power = (Thrust). (Air Speed of the accelerated air mass):P = T.
(V + v)2. Thrust = Flow of accelerated air Mass. (Final Air Velocity Increase of this mass flow):T = ?.
A. (V + v). (2. v)Note: a.
The air mass being accelerated by the fan disk will increase speed before passing the fan disk,when it reaches the disk the speed increase is v, then it continues to increase behind the disk until it reaches a total increase of = 2.v.b. In hovering conditions V = 0.When we consider hovering conditions, the Thrust (T) equals the aircraft Weight (W), and using this in the 2 above equations by eliminating v you get:For T = W, P = SQrt((W^3)/(2.?.A))In reality P will be higher (for a ducted fan, probably about 10%) because in the above equations there are no losses considered like for example the energy lost in rotational momentum.Doing the calculation P necessary for hovering at sea level is about 51 HP. With all losses included let's say about 20% more is about 61 HP. In other words, he can not even lift 330 lbs.Maybe it is a bit insane, but I like it anyway, and it could undoubtedly find useful utilities, maybe in the army or so.
RE: Ducted Fan (Aerospace) 24 Jan 06 02:33. GregLocock, where could I find information on fan efficiencies? Specifically speaking fan blades/impellers. I’ve purchased the book mentioned in this thread (Marc de Piolenc) and gives great information, but I would like to see graphs.I have lots of info on DF’s since my master’s thesis was related to them.
Ducted Fan Design Pdf
But in it I’ve always treated impellers as another component that only reduced efficiency and never looked at it. I was evaluating the losses due to obstructions inside high speed air ducts.It would be nice to see a graph with ‘x’ number of blades, ‘y’ fan swept area and ‘z’ fluid speed (air).
Maybe throw in ID and OD, RPM and or blade angle also. Any combination would be interesting to see.See ya.BTW. RE: Ducted Fan (Automotive) 23 Feb 06 18:07.
While I'm not as lofty as aero eng I do mech stuff. Here is the end of the line in small ducted fans for model airplanes. A few years ago they were the ultimate rage. Some got over 200 mph!!
Ducted Propeller Design
They are vastly complex models. However thay have been of late surpassed by the turbine engine. These are very fast. Easly 200 mph straight and level. Honest ingen. You get a pretty nice car for the cost of these.
Ducted Fan Design Pdf
And yes they do crash. Some even leave a smoking hole.literaly.Check this site for ducted fansRE: Ducted Fan (Aeronautics) 29 Mar 06 13:33.