DUCTED FAN vs TURBOJET

[harrisj]

I am looking at the feasibility of a light (100 kg) low-speed (100 kt) unmanned aircraft, similar to those used by the military for drones, reconnaissance etc.

Most of these use small turbojets but I am considering using a ducted fan driven by a 4-stroke IC engine. What are the pros and cons? I guess fans are bigger diameter, but I don't know enough about limiting factors such as tip speed.

Can anyone point me to a useful source of data?

 

[insideman]

I can design such a fan for you. But it will be more complex and less effective than a propeller.

 

[pyro]

Ducted fan = high static thrust. Turbojets operate more efficiently at higher Mach # due to the "free" compression from the ram effect. You'll want to keep the tip speeds below the critical Mach # for the airfoil you choose for the blade.

 

[harrisj]

Insideman:

We may be interested in getting you to help with the feasibility study / design. Please email your details to:

john.harris@marshallsv.com .

 

[Wittenborn]

Here is a link you may be interested in:

http://www.aurora.aero/gallery.html

They have built a ducted fan drone (I think they call it "Golden Eye&quot, with pretty impressive "advertised" performance. I have seen pictures that they have built one, but not actually flown it. The concept is a ducted fan, driven by a rotary engine.

Let me know what you think.

Regards,
Grant Wittenborn
Aerospace Engineer

http://www.darcorp.com

 

[tbuelna]

harrisj:

Here is a good reference, US patent #4,996,839. It's a patent for a ducted fan driven by a piston engine. Teledyne was evaluating such a configuration for long range, subsonic cruise missile propulsion.

You can also try this link:

http://patimg1.uspto.gov/.piw?Docid...ageNum=&Rtype=&SectionNum=&idkey=CB4439462A15

Regards,
Terry