Ducted fan aircraft

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Lendo

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I love the idea of a Ducted Fan, I've seen some attempts but all seemed to end up less efficient than an open prop, I've never really understood why. I've spoken to one Aeronautical Engineer who is redesigning an aircraft his Dad designed here in Australia some years back, he says it can be done well for specific applications - he should know, but I think there are too many variables.
George
 

henryk

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Thrust per fan, or for the two of them?
I love the idea of a Ducted Fan, I've seen some attempts but all seemed to end up less efficient than an open prop, I've never really understood why. I've spoken to one Aeronautical Engineer who is redesigning an aircraft his Dad designed here in Australia some years back, he says it can be done well for specific applications - he should know, but I think there are too many variables.
George
=ducted fans are lower surface as open propellers are...
(greater surface load,lower specific thrust !)

-EJECTOR duse can help,aspatially at low speed (taxi,climbe...)

http://www.reaa.ru/yabbfiles/Attachments/hustawka_multiplikatorwidelec_016_001.jpg
 

Doggzilla

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It’s likely because we have been using the wrong sizing on older ducted fans.

Compare the PJ-2 to other ducted fans and the other fans are far too large for their power.

The PJ has almost 200hp per small fan. Many other ducted fans have 200hp with a very large fan. Yet the PJ is much faster despite having a very similar power to weight ratio, and probably similar drag.

It’s very obvious that older ducted fans were using far too large fans.
 

jbiplane

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Jan 29, 2014
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Krasnoyarsk, Russia
A complete and proven ducted fan unit to suit a common paramotor engine like the VIttorazi Moster 185 would be very attractive for ultralight/microlight aircraft. I might even dust off that idea for a "profile scale" ultralight jet inspired by the general lines of the BAE Hawk.... ;-)
My customer on paramotor testing my 2-stroke 294cc boxer engine in ducted fan. Cannot spread photos without his permission. What trust do you need?
 

cluttonfred

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Just a concept at this point, but looking for something comparable to what the same 25 hp engine can do through a full-size prop and redrive but in a smaller package.
 

Doggzilla

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Good work Malish!

If you have any problems with the plastic attachment flange, I have seen people 3d print with metal inserts. You should be able to add an insert to mimic the steel base of your carbon blades.

Also, I wonder what will happen if you change thickness to allow higher angle of blades before compressor/fan stall. May allow different RPM range if that’s something you are interested in.
 

henryk

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Shrouded propellers and ducted fans are not exactly the same thing.
It's my understanding there are certainly advantages to contra-rotating blades. But I didn't consider the idea for my project due to the weight cost and complexity.
https://www.dropbox.com/s/ky1z5jc9g3srohq/Dym - zwolnione tempo.mp4?dl=0
https://www.dropbox.com/s/htftd6ttj1b2emj/Dym.mp4?dl=0

=auer experiments with CR differentially drived propellers=>25 % thrust gain...

<10 % weight increase.

I think,ducted CR should be better, NO stator need ! (see smoke trajectory...)
 

Doggzilla

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Very interesting. It appears to be squeezing the exhaust like turbine exhaust squeezes during shock diamonds.

It’s like a Venturi caused by the different inertia of the air flow and still air. The flow is very fast but surrounded by still air. This pulls the still air inward and squeezes the flowing air into a tight well controlled flow.

But why this only happens with twin props I do not know. It must be how it affects the center of the flow.
 

Lendo

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henryk, Good find, the Ligeti -Stratos (ducted-fan) was the one I mentioned previously, his Son is reverse engineering the concept as all documents were lost when he was killed. A modification to the design tested at low altitude, as directed by CASA.
George
 

henryk

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Very interesting. It appears to be squeezing the exhaust like turbine exhaust squeezes during shock diamonds.

It’s like a Venturi caused by the different inertia of the air flow and still air. The flow is very fast but surrounded by still air. This pulls the still air inward and squeezes the flowing air into a tight well controlled flow.

But why this only happens with twin props I do not know. It must be how it affects the center of the flow.
=this aiflow is focused/concentrated and so powerfull=no possibility to stay in it
for thrust force read !!!
(I should read =235 kG=in lying position !)

https://www.dlr.de/bt/desktopdefault.aspx/tabid-8196/14020_read-35636/

=CR FAN

https://slideplayer.com/slide/3853756/13/images/3/Thrust+Augmenting+Ejector.jpg

=EJECTOR for thrust augmentation...
 
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henryk

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krakow,poland
Could it be they were testing the parachute system to determine aircraft safety during canopy deployment..?

Although, the nose down position does not look good for a parachute safety system design. There are better ways to save an aircraft with a foil canopy.
https://innowacjablog.files.wordpress.com/2019/11/flaris229237.pdf

=polish 5-place jet with BRS (rocket) + 6 ? auter airbags for soft landing !!!

-another polish patent=dynamic breake for pataschute=allmost ZERO speed landing...

https://airsafe.pl/

BTW= iff Vlanding=5 m/s and distance 0.05 we get deceleration

a=V^2/2s=25/0.1=250 m/s^2 ( circa 25 "G" !!!)

=for 7 m/s = 50 "G"
 
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