Power loading vs the percentage increase of total static thrust in a ducted prop with a lip?

[Key200]

Hi! Just want first to say I am not a complete beginner in aerodynamics.

I have been searching for an answer to this question I have had for a while now w/o luck.

Will you still get huge benefit of huge added extra lift force from the duct lip even if you have huge power loading?, like say, a big shrouded helicopter-rotor sized propeller with relatively low power input. Or, as- I suspect- will the extra increased lift from the duct lip here in this case be very tiny due to the high powerloading? Will this percentage increase of total thrust thus still continue to decrease as you decrease the input power to the propeller?

I read a lot of papers and pdfs about tests , I didnt get any real answer. I got however a rough general idea/guestimate that only-in ducted fans with very high discloading and low power loadings -that the total thrust can be significantly increased or doubled compared to the same unshrouded propeller, i.e. only in highly powered "inefficient" systems with very low power loading that the percentage increase of total thrust is high, around 100% more than without the shroud.
Am I understanding this right?


I really dont need an exact answer but a rough aproximate answer from a very solid experienced person/source to the problem will make me very very happy. As I said I have a huge hunch of the answer but I fear I may be very wrong and thus I need to be confirmed.


Thanks
Best regards Regards

 

[GregLocock]

I'd lay off the text formatting if i were you.

Looking around I found no ducted fans with a Figure of merit much above 50%, that's pretty low.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Key200]

Thanks, sorry, I changed that now.
....
Indeed the ducted fan has a relatively low efficiency but what about big ducted propellers/rotors? The thrust of all low-disc area high-powered systems can be doubled or more by installing a suitable ductlip but of course as you know the original thrust of the ductless fan is pretty small anyway compared to the power consumed and thus even if that thrust is doubled the F.G is still low. Hence my question: will the thrust of a big diameter low powered rotor theoretically also be dramatically increased with a duct lip just like the small ducted fans?

For clarification on risk of being too repetitive in fear of my question wasnt clear. A typical Model unshrouded highly discloaded and highly powered propeller may only give 1 kg of thrust and 2 kg with a suitable ductlip. For this same power a bigger diameter rotor w/o ductlip may give 10kg of thrust but will this thrust increase be anywhere near to 20kg after installing a ductlip or not? does percentage of increased thrust stay the same as you increase the powerloading, that is my wondering.

Thanks, sorry, I changed that now.
....
Indeed the ducted fan has a relatively low efficieny but what about a big ducted propellers/rotors? The thrust of all low disc area high powered systemes can be doubled or more by installing a suitable ductlip but ofcourse as you know the original thrust of the ductless fan is pretty smallanyway compared to the power consumed and thus even if that thrust is doubled the F.G is still low. Hence my question: will the thrust of a big diameter low powered rotor theoretically also be dramatically increased with a duct lip just like the small ducted fans?

For clarification and high on risk of being repetitive if my question wasn't clear. A typical Model unshrouded highly discloaded and highly powered propeller may give 1 kg of thrust and 2 kg with a suitable ductlip. For this same power a bigger diameter rotor w/o ductlip may give 10kg of thrust but will this thrust increase be anywhere near to 20kg after installing a ductlip or not? does percentage of increased thrust stay the same as you increase the powerloading, that is my wondering.

Thanks