Ducted fan aircraft

[Malish]

WHAT IF ... duct and fan are 1 part. So, you let rotate the duct too. I guess it is not such a problem to do that. A central bearing at front and rear and a driving belt. No more blade tip clearance problems. But ... would it improve the performance?

I just can't imagine how much this unit will weight! Plus it need to be balanced to turbine tolerance...
Why we need to "invent bicycle if it's already was invented"? - Basic DF design is working just fine, if it's build right

 

[nestofdragons]

I just can't imagine how much this unit will weight! Plus it need to be balanced to turbine tolerance...
Why we need to "invent bicycle if it's already was invented"? - Basic DF design is working just fine, if it's build right

balance can be done like on a car wheel. Just add a few light weights to get it right. Reinventing the wheel? Hmmm ... maybe ... but i was thinking "this ducted fan thing doesn't get going for real. We might need to change it a bit to get more future for it." So ... i just launched a idea. Will it work? i don't know, but ... it would be a shame if we didn't consider it as a possibility to get things better for the ducted fans (which i like a lot).

 

[raytol]

-iff I understand
this "extra mass of the air" is ejected between duct and blade tips ring ?

-what is a crossection of this ring, its wide ? (airfoil or thin band )/ CF or GF ?

A flat plate carbonfiber "ring" was the easiest to make but it bulged between the 7 blade tips and caused some vibration.
A hollow airfoil worked a lot better as it was stiffer. Normally, the blades taper from the hub to tip but this was not necessary our case.
Our design called for reducing the diameter of the propulsion system so we could fit it into the design. We also used what we called a "mixed flow impeller" to increase static thrust but not affect the dynamic thrust. We had a lot more power than a duct could normally handle and the engine was attached to the fan without a gearbox.
I was quite surprised, during tuft testing, at how far from the front edge of the duct lip (on the outside of the duct) the air was being dragged backwards in to the prop!
I was working on a variable pitch unit when the project stopped.

 

[Malish]

balance can be done like on a car wheel. Just add a few light weights to get it right. Reinventing the wheel? Hmmm ... maybe ... but i was thinking "this ducted fan thing doesn't get going for real. We might need to change it a bit to get more future for it.

The car wheel is turning less then 1000 RPM, but DF speed is from 5000 RPM to 8000 RPM and sometimes even more. Fan unit must be balanced to turbine wheel tolerances in order not to fail. Plus, don't forget about gyroscoping loads - then heavier the fan unit then larger this load on the fan unit and it bearings. The fan unit must be made to weight as less as possible to cope with this potential problems(vibration), if this happens(vibration or bearings problem) - DF will destroy itself in matter of seconds

 

[Malish]

I was quite surprised, during tuft testing, at how far from the front edge of the duct lip (on the outside of the duct) the air was being dragged backwards in to the prop!

That is why the fan blade tip and fan shroud clearance should be very small - to prevent air flow from back of the fan to the front(back flow)...
If DF is working properly it's will create whirlpool of air coming from the ground into the intake duct - it's can be seen if some dust, water or light peaces of dirt on the ground under the duct intake...

 

[vhhjr]

As of a couple years ago NASA was funding a rotating duct arrangement in an effort to address the tip losses. It would seem to me that the large diameter bearings and high linear bearing speeds would be a design problem and would be expensive. Have you priced large diameter ultra thin bearings lately? Rotating the duct just transfers the tip loss problem to the stators.

Large comercial DFs are becoming available with thrust ratings in the usable range. They are all electric,. Maybe hybrid systems are the way to go an avoid transmissions, gearboxes and belts altogether. Alternators can be direct drive. With a hybrid system the engine/alternator can be located aywhere in the airframe and a realtively small battery pack can provide extra HP for takeoff and climb-out as well as short duration emergency power in the case the IC engine goes south.

See: VF-570 Standard


Vince Homer

 

[henryk]

don't forget about gyroscoping loads

=in CRFLIGHT mode NO gyroscopic momentum,
NO Reactional = REACTIONless drive !!!...

+RPMs of propellers/fans are circa 1/2 of motor RPM !

 

[Malish]

=in CRFLIGHT mode NO gyroscopic momentum,
NO Reactional = REACTIONless drive !!!...

It's doesn't matter CR props, CR fans or single fan/prop - they all have gyroscopic momentum, because they are gyroscope themself!
Even bicycle wheel is the big gyro too - if you lift bike front wheel of the ground and spin it fast, then try to turn it left or right - you will fill the resistance against the direction of the turn...

 

[Malish]

Large comercial DFs are becoming available with thrust ratings in the usable range. They are all electric,. Maybe hybrid systems are the way to go an avoid transmissions, gearboxes and belts altogether. Alternators can be direct drive. With a hybrid system the engine/alternator can be located aywhere in the airframe and a realtively small battery pack can provide extra HP for takeoff and climb-out as well as short duration emergency power in the case the IC engine goes south.

Hybrid system may working well in cars, but it's not very good for aircraft use, mainly because the extra additional weight of this system. The weight of hybrid system(IC engine/generator, electric motor(s), controller(s) and battery pack) may double the weight of IC engine/DF system it self...

 

[henryk]

they all have gyroscopic momentum, because they are gyroscope themself!

=right !

but in CR system Gyeoscopic Momentum are fully compensated...

+M =-M

 

[Malish]

but in CR system Gyeoscopic Momentum are fully compensated...

How it's can be?
It's not matter if you have CR or single gyroscopes - they're equally trying to hold their orientation in space. This principle is used in DG, Artificial horizon, turn & bank coordinator and autopilot construction

 

[Billrsv4]

As of a couple years ago NASA was funding a rotating duct arrangement in an effort to address the tip losses. It would seem to me that the large diameter bearings and high linear bearing speeds would be a design problem and would be expensive. Have you priced large diameter ultra thin bearings lately? Rotating the duct just transfers the tip loss problem to the stators.

Large comercial DFs are becoming available with thrust ratings in the usable range. They are all electric,. Maybe hybrid systems are the way to go an avoid transmissions, gearboxes and belts altogether. Alternators can be direct drive. With a hybrid system the engine/alternator can be located aywhere in the airframe and a realtively small battery pack can provide extra HP for takeoff and climb-out as well as short duration emergency power in the case the IC engine goes south.

See: VF-570 Standard


Vince Homer

One type of ducted fan used blades that extended into a ring that turned with the blades. That was fairly successful, with the problem being the weight of the ring. The ring was fitted into a tight fitting slot on the inside of the duct. It would be possible to make this setup with modern materials perhaps even hollow. (Carbon fiber?) Doing a version with those materials could be a solution that would work. The fact that ducted fans are most efficient at a narrow speed range, and the inability to have pitch change without a lot of complication is one drawback of ducted fans in general. It has always been tough to improve on a conventional prop!
Bill

 

[Malish]

The fact that ducted fans are most efficient at a narrow speed range, and the inability to have pitch change without a lot of complication is one drawback of ducted fans in general. It has always been tough to improve on a conventional prop!

As I said before - DF system should be used only on aircraft where others power plant systems(propeller or jet) will not work very well for some obvious reasons(cosmetic, layout or cost). This was the only reason we choose DF power plant system in our PJ-II "Dreamer" - it's should look(and fly) like real jet aircraft

 

[jedi]

How it's can be?
It's not matter if you have CR or single gyroscopes - they're equally trying to hold their orientation in space. This principle is used in DG, Artificial horizon, turn & bank coordinator and autopilot construction

Study physics. It does matter! Malish, you know what you are doing. Do not lower yourself to the level of other ass...ants on the internet.

 

[henryk]

DF system should be used only on aircraft where others power plant systems(propeller or jet) will not work very well for some obvious reasons(cosmetic, layout or cost).

=safety problem ...

+ in my case= low drag thruster in cruise regime=

BTW="physics. " =two high RPM tools, connected in opposite mode=NO gyro momentum !

 

[Malish]

Study physics. It does matter! Malish, you know what you are doing. Do not lower yourself to the level of other ass...ants on the internet.

I maybe missed something in the law of physics, please refresh it to me.
What I was saying that propeller or fan has gyroscopic momentum that will resist of turning this prop/fan disc against it's axis - creating bending load on the shaft and additional side loads on the bearings...
I'm wrong?

 

[Malish]

BTW="physics. " =two high RPM tools, connected in opposite mode=NO gyro momentum !

Maybe you talking about torque momentum?