Pilots are cautioned about not getting behind the power curve, and I expect little instructional time is devoted to operating behind the power curve. Yet, I believe this situation can and has caused accidents when what pilots expect to happen, as a result of their control input, is not happening. Two common problems, one environmental and one poor technique, come to mind: High density altitude operations and mush/stall on takeoff and departure.

To get an idea of how a pilot could get behind the power curve at a high altitude, consider a takeoff from Leadville in a C-150 on a ninety degree afternoon. The math has the airplane at ceiling on the ground. Poor planning, but it happens without accident from time to time. The wind is often strong on hot afternoons providing pressure airspeed on the wing at zero ground speed, ridge lift is generally very good from westerly winds, we are above the treeline generally, the runway is unobstructed, and the drainage (Arkansas River to Mississippi River) would allow down hill flight all the way to the Gulf of Mexico.

Excess engine thrust for climb does not exist. The airplane will get off in low ground effect, but will not climb (except with ridge or thermal lift) out of ground effect. Vx and Vy are the same pitch attitude, which is necessary just to fly level. Gravity thrust is available all the way to the Gulf. But we are not thinking of going to the Gulf, or even just down to Buena Vista. We may want to cross the great divide and go west. We may want to go up, which cannot happen without ridge or thermal lift. We may pull back to increase pitch attitude and go behind the power curve. We will start to mush. We may bank to change our directed course, which will cause descent as no extra power is available to make up for lift lost in the bank. We may pull back on the stick to maintain altitude, but this cannot happen without ridge or thermal lift. We will start to mush in the attempt to maintain altitude.

When pulling back on the stick to increase pitch attitude results in no climb or even a mush, push forward on the stick a bit to possibly climb. It is time to look for orographic or thermal lift; and gravity thrust between the lifts.

Yes! We can avoid the high density altitude situation by going early or late in cooler times of day. I did not because I had to go anyway, and performance may be less with low powered airplanes in the cooler times of day in the mountain. Orographic and thermal lift can make that much difference.

Mush/stall on takeoff from much lower density altitude is the more common accident problem. Here, we expect that pulling back on the stick to pitch up will cause the airplane to climb (zoom) faster. Here even low powered airplanes have quite a bit of excess engine thrust for climb. Rejecting low ground effect energy for a too soon engine climb and commonly climbing at Vx pitch attitude often causes our going behind the power curve on takeoff and climb out. Climbing turns on takeoff and climb out or to stay in the pattern often causes our going behind the power curve.

When pulling back on the stick to increase pitch attitude results in no climb or even a much, push forward on the stick a bit to possibly climb.

But this time it is too late. Now we have to try to hit the obstruction in order to have enough pressure airspeed over the wing for it to work well. At high density altitude, we were probably somewhat prepared (spring loaded to) poor performance. This poor performance, at near sea level, is what causes accident pilots to report, “There was a power loss of some kind.” There was a power loss of some kind. It was the free low ground effect energy we left back on the runway and we now need to go over the obstruction. It was the nearer to Vy pitch attitude energy we could have had by not trying to clear the obstruction by so much unneeded altitude.

Given the above considerations and problems, why is the school solution “ALWAYS” to make climbing turns on takeoff and departure or to stay in the pattern after takeoff? What would be wrong with allowing the nose to drop naturally in the turn and then return to the climb when the wings were again level?

My guess is that 9 out of 10 pilots think the power curve has to do with your engine.

behindpropellers wrote:My guess is that 9 out of 10 pilots think the power curve has to do with your engine.

Yeah. That "powerband" thing that sometimes has to be replaced by a mechanic when it stops working.