Welcome back! I'm Jacob and in this video I cover the Height-Velocity Curve, also known as Deadman's Curve.
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Just about every operator's manual has a diagram that depicts airspeed in relation to altitude and calls it either the Height-Velocity Curve, the Avoid Region, or Deadman's curve. Generally it outlines the area of certain altitude and velocity combinations that you want to stay away from because, if an engine fails, the likelihood of safely landing is unlikely. Each chart should be tailored to a specific aircraft. The reason you want to avoid operating in this region is because there simply isn't enough kinetic or potential energy in the form of airspeed and altitude, respectively, to safely autorotate. In this video I'd like to outline what the curve is based on, what isn't mentioned or explained, and some considerations.
First off, the chart is based on a few factors. To be certified, the curve must e demonstrated under the helicopter's maximum gross weight. This is so the worst-case scenario is what is depicted. Anything lighter weight would be a shrinking of the curve. Second, the curve is based off of the average pilot. This doesn't mean a pilot or training but instead a proficient pilot who can perform basic emergency procedures. Above the knee part of the curve, there is usually a 1 second delay factored in between onset of engine failure and the pilot inputing the corrective action. That said, highly experienced pilots have been known to "beat the curve" and safely recover the helicopter despite being inside the curve. I wouldn't recommend ever pushing your luck here because this is done by trained pilots who know the exact indications and symptoms of an engine failure (usually seconds before it happens) and react instantly with the corrective action as if they'd been spring loaded to do so.
Moving on to what the chart doesn't show. Most of this testing to determine the curve involves a run-on or roll-on landing to a suitable landing area. If you're not over a flat runway, theres no guarantee your autorotation will be survivable. Furthermore, just because you are outside the curve doesn't mean you're necessarily safe either. While being outside the curve you could still have an engine failure over a wooded area, lake, or rocky terrain. Being outside the curve just means you have the potential to make it to the earth's surface in a controlled fashion instead of an uncontrolled plummeting. Lastly, not all charts account for pressure altitudes. In fact, many are based on sea level altitude. By flying in higher altitudes, the curve expands right and up to cover higher airspeed and altitude combinations.
The last thing I want to cover is other considerations such as the high-speed low-altitude region that is sometimes present. This is for pilots operating so low and fast that a pilot might not have enough time to safely react to an engine failure and recover in time. Also, dual engine helicopters usually have a smaller curve depicted. If 1 engine fails, the helicopter may still maintain flight if outside of the dual engine curve. But if the second engine fails (for instance because of a fuel issue) the helicopter would still need to be outside the single engine curve. Lastly, some federal regulations outline that intentionally operating in this avoid region is breaking an aircraft limitation and therefore should be avoided at all times. But this usually applies to larger, heavier, multi-passenger helicopters and not your typical commercial one.
That wraps up this video. The Height-Velocity Curve or Deadman's Curve is simply an area that you may want to avoid or not linger in because its unlikely you can safely recover the helicopter if you lose an engine.
Be sure to hit like and subscribe below. Once again, I'm Jacob and this is Helicopter Lessons in 10 Minutes or Less. Safe flying.