An out of ground effect hover is when you are hovering about fifty feet off the ground. The rotor system is working pretty efficiently at this altitude. As I dredge through memories, I remember being pretty excited about this maneuver. Hovering high enough to see over the tree tops while holding the aircraft stationary over a spot fifty feet below. With a stiff wind, this was even more fun.
Here is why my instructor visibly relaxed when I completed this maneuver the first or second time I did it. I may not have noticed the first time, so this could have been my second. If the motor stops, we are too high off the ground to gently land the aircraft.
Here is why.
As soon as the motor stops, a Sprague clutch disengages the motor from the rotor system. This allows the inertia of the massive fan to keep the blades spinning. However, drag and friction are already slowing it down. At three feet, they don’t slow down enough to be an issue, and easily overcome the helicopters descent.
However, at fifty feet. Gravity has accelerated the helicopters fall and enough inertia bleeds off the rotor system so that it cannot effectively arrest the aircraft’s fall. What you get at the bottom of this fall is a pile of broken helicopter with two beaten up pilots inside.
We practiced out of ground effect hovers because it is what Army helicopters did. It was part of combat operations, but it was by far the scariest maneuver we did. An aircraft engine can fail at any time, and when you have only one, that is a problem. Most modern helicopters have dual engines. If one quits, most normal flight operations can continue to a safe landing spot. None of my training aircraft had that luxury.
By the time we got into tactics, we performed this maneuver in a manner we would perform it in combat. Helicopters, especially unarmed helicopters survived best in combat by hiding. If you were cruising along, and wanted to see what was on the other side of a tree line or ridgeline, you stopped, and peeked. Literally, you stopped, held the aircraft at a hover, pulled in a little power, and peeked over the tree line.
Most tree lines are easily thirty feet tall or more. We practiced this maneuver while flying NOE (Nap Of the Earth). What this entails is flying in the treetops, with just enough clearance to keep your rotors from trimming branches. It was great fun, a lot of work, a little nerve racking, but great fun. When we got to a clearing, we stopped, stabilized the aircraft, and took a peek.
I told my instructor as I pulled pitch and lifted the helicopter up so we could just see over the trees, that I was not a fan of this maneuver.
“Why is that?” He asked.
“What would the pile look like below us if the engine quits?” I replied.
“Oh, you mean the fact that by the time the dusts settles your asshole will be wrapped around your neck. That is why you don’t like OGH’s?”
“That’s exactly it Sir.”