Does blowing hot or cold air over a wing increase lift?

[sid_galt]

pumping air over wing??

So if hot/cold air is blown over the top surface of a small sized wing inflight which has a medium angle of attack, will it help in the lift or will it be a disadvantage?

I can only think of two things

1) Advantage: It will reenergize the airflow and help in reducing turbulence. Higher speed of wind will decrease pressure and increase lift though temperature of hot air might render the effects of the increased lift negligible.

2) Disadvantage: It might detach the boundary layer and might increase the drag substantially. If the blow speed gets even a little bit uneven, it may destabalize the aircraft considerably. It will result in uneven distribution of lift across the wingspan unless the air is uniformly blown all over the wing. This will result in increased stress.

What do you think?

If it turns out to be a disadvantage, would blowing the air under the wing instead of the top result in increased performance/lift?


Also a question about winglets. Why are winglets oriented with a positive angle and not a negative one? What if one has two winglets with + and - angles? Would that help in performance especially in small aircraft?

 

[Speed]

The suggestion is not new. However the problem with pumping air through pores in the wing is that large amounts of complex ducting and pumps will be required. Space in the wing normally reserved for fuel tanks will also need to be cut down.

 

[sid_galt]

The suggestion is not new. However the problem with pumping air through pores in the wing is that large amounts of complex ducting and pumps will be required. Space in the wing normally reserved for fuel tanks will also need to be cut down.

Ducting, energy issues and pumps aside, will the suggestion actually work with either hot or cold air even on low Reynold number wings?

 

[Clausius2]

Ducting, energy issues and pumps aside, will the suggestion actually work with either hot or cold air even on low Reynold number wings?

I don't see any advantage, besides I don't understand the advantages you posted. Pumping air will increase turbulence instabilities and drag.

The fact is it has been a lot of research in sucking air through a porous wing wall. The suction of air delays the boundary layer point of detachtment, decreasing drag.

Some turbomachine blades are machined in such a way to have such porous wall.

 

[FredGarvin]

I was going to mention boundary layer control experiments using vacuums but Clausius beat me to it.

You may want to look at this link:
http://aerodyn.org/Drag/blc.html

It does talk about injection techniques.