Drag and Thrust of External Body Ducting

[BillTheRacer]

Is it possible for a properly engineered duct to produce a net thrust force on a vehicle?

For example many racing vehicles have Oil coolers and Radiators installed in a duct that has its inlet and exhaust located on the external surface of the body. My question is an issue of balancing the drag forces exerted on the inlet portion of the duct with the thrust generated by the exhaust.

I approached the problem using the Bernoulli principle for an irrotational, incompressible flow and mass conservation. Joseph Katz's book "Race Car Aerodynamics" (pg 100-102) both sparked my interest in and aided in my solving the problem so it may be a
helpful reference for those of you who own it.

I've spent several hours looking at the numbers and have personally rationalized an answer but I have been unable to convince my brother without the process on paper.

Any assistance on this problem is greatly appreciated.

 

[GregLocock]

Yes, in theory if you add heat to air in a correctly shaped duct it will generate thrust. Yer average 747 exploits this quite reliably, or perhaps more directly a ramjet is a good example.

The radiator duct design was claimed to add a few mph to the top speed of the P51.

So yes, it is a real effect. you need to establish whetether the skin drag of the more complex duct outweighs the thrust generated.

Cheers

Greg Locock


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

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

 

[thruthefence]

The Garrett/Honeywell TFE 731 series of turbofan engines have an annular oil cooler that supposedly adds energy to the fan duct bypass air flow, adding to total thrust. Seems a stretch to me, but every little bit helps, I guess.

 

[BillTheRacer]

Thanks for the input guys.