This is a subject I have been very confused with lately about thrust coming from downwash on a propeller and helicopter, but to understand how the downwash increases thrust is to know how it forms and works on a regular aircraft wing. A picture of downwash on a wing would be helpful. And also how does downwash make thrust on a propeller and helicopter wing?

  • $\begingroup$ @RedGrittyBrick Not a duplicate none of the answers in that question explained downwash. $\endgroup$ – Ethan Sep 23 '15 at 22:43
  • $\begingroup$ Did you try to search "downwash" on this site? $\endgroup$ – mins Sep 24 '15 at 4:58
  • $\begingroup$ It is the words you are confused about. As others have said before in your many questions on this topic, a helicopter rotor blade, a propellor blade and a wing are all the same. They generate a force from air moving over them. The only difference is the direction in which the force they generate normally points. The downwash on a propellor normally goes backwards, not down. The downwash from wings and rotors go down. They do not increase thrust, they are the thrust, according to Newtons 2nd, which causes the propellor to pull, and the rotor blade or wing to lift. $\endgroup$ – Simon Sep 24 '15 at 5:54
  • $\begingroup$ It is only called downwash on a wing or a rotor. On a propellor, it is called prop wash (or other terms) but the only reason to use different words is because the prop wash does not go down. Therefore calling it downwash would be confusing. Your confusion stems from wherever you read or assumed that the airflow moving back off a propellor is called downwash. Just understand that propellors, rotors and wings are all just aerofoils and work in exacactly the same way. Speed of relative airflow and angle of attack to produce a force. $\endgroup$ – Simon Sep 24 '15 at 5:57
  • $\begingroup$ Newtons 2nd law tells you why downwash produces thrust. If you accelerate air downwards (which is what downwash is) there must be an equal and oppopsite force upwards. This is lift (wing or rotor) or thrust (propellor). $\endgroup$ – Simon Sep 24 '15 at 6:04

Having in mind a typical flow around an airfoil, the flow over the wing flows much faster than the one under the wing. This faster particles arrive first to the trailing edge and are "projected" against the rest of the flow, creating that additional thrust. Moreover, the difference between the free stream and the flow after the trailing edge is the downwash angle. I hope it helped.

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