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After reading a very interesting interplay between two writers attempting to answer this question of helicopter downwash velocity, it occurred to me that, although this calculation:

$V_i = \sqrt{\frac{F_n}{2 \rho S}}$

may be accurate, it would not take into account the vertical velocity of the air entering the disk.

When a helicopter is in a hovering state, is it not in its own vortex? I am not sure if the helicopter pilot can compensate by adjusting the blade AoA to the relative wind of the downflow, but in forward flight blade AoA must be changed for forward and trailing wind components to keep lift constant on either side.

Does it take a lot more power to hover? Can we predict the velocity of the inflow into the disk to determine the outflow velocity (which should be the inflow + the calculated downwash).

We would expect lower net downwash in forward flight, but how does that compare to power required in hovering flight?

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  • $\begingroup$ aviation.stackexchange.com/questions/45631/…. $\endgroup$
    – Pilothead
    Commented Jan 20 at 19:00
  • $\begingroup$ It seemed that agreeing to "split the difference" of two downwash velocity calculations required further examination. Let's please keep working on this. $\endgroup$
    – Robert DiGiovanni
    Commented Jan 20 at 20:58
  • $\begingroup$ The power required for hover is plainly answered in the linked question. You may be able to rephrase your question but it needs more than just a title modification. $\endgroup$
    – Pilothead
    Commented Jan 20 at 21:37
  • $\begingroup$ @Pilothead this question is about the formula applied for downwash velocity in the referenced question. Why are you stuck on Power? (BTW, the reference provided by the moderators is excellent). Why not take a try at an answer? $\endgroup$
    – Robert DiGiovanni
    Commented Jan 20 at 21:58
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    $\begingroup$ @RobertDiGiovanni, the induced velocity is a delta, so it's w.r.t to the incoming velocity, see for example this link $\endgroup$
    – ROIMaison
    Commented Jan 25 at 9:40

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