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I have always considered taking off over tall grass,corn,or small trees,would take more power.As an ag pilot I have always reduced my loads to compinsate for this.

Talking to another ag pilot,he says that he thinks anything vertical stops the lateral movement of air and actually helps.I am almost certen I had the look on my face like the amish at circut city.

So he takes his 47 and hovers over corn,then moves over to short mowed grass an says that there is no manifold diff.

So what the heck is going on.Have I been wrong all these years? Has it been all in my head? Is there any proof? and how about taking off over water

I do know this, the taller the crop I am spraying, the less drift I get and always figured it was taller crops slowed lateral movement of air. This would make sense for his defense.

Edited by spraypilot
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I've always felt that the difference in hover power requirements over vegetation, water, etc., were due to altitude issues. It's harder to tell exact height over the ground over tall grass, and especially hard over water, so it's really hard to gauge differences in power required regards them and a ramp, for example. But, I've read that the rotor wash moving the grass or rippling the water absorbs energy, and this increases hover power required.

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I've always felt that the difference in hover power requirements over vegetation, water, etc., were due to altitude issues. It's harder to tell exact height over the ground over tall grass, and especially hard over water, so it's really hard to gauge differences in power required regards them and a ramp, for example. But, I've read that the rotor wash moving the grass or rippling the water absorbs energy, and this increases hover power required.

 

 

I was taught that the irregular surface affects the cushion of air you normally have under you in a hover which in turn requires the additional power to hover.

 

In practical experience (of which I have not a lot since I'm still working on my private rating but, I'll relate what I have experienced):

 

I did some approaches at a small RC landing strip (we're talking tiny, but pretty level) so that some of my hovers from approach ended over non-pavement areas (about 1' or less of vegetation - similar to my front yard but just a bit more manicured :D). I could definitely tell a difference between ending in a hover over pavement and over the grass. It was significant enough that I mentioned it to my CFI.

 

Hovering over grass felt 'softer'. I don't know that it took more sustained power, but at least the initial stop did and it felt like I had to work more to keep the hover at a consistent height above the ground.

 

Anyway, that's my .002th.

 

Kelly

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