WHAT IS: "Flying behind/below the power curve"

[LenM]

I've often encountered the phrase, "flying behind/below the power curve", I'm assuming this refers to cases where you want to increase height with elevators and not throttle? Or does it have another meaning?
Thanks.

[KFA]

It is the area of power vs. airspeed where our airspeed is very low(normally very close to the stall) but our power setting is very high(could be even full power). In essence we are using thrust not wing lift, to maintain altitude. Our nose is pitched up at such an angle that we maintain our altitude by keeping very high thrust with a very high angle of attack and very high drag. The advantage is that we have very low airspeed. The disadvantage is that if you loose the engine you are very likely to stall the plane, unless you have sufficient height to lower the nose and gain airspeed.

At best glide speed, the aircraft is in its lowest drag configuration, when you consider both parasitic and induced drag. So it takes more power to maintain level flight when either accelerating or slowing down from that speed, because you have increased drag. When this is plotted on a graph, it makes a more-or-less bell shaped curve, with best glide (lowest drag) at the peak.

So, technically, anytime you are maintaining altitude at a speed less than best glide speed you are "behind" (to the left side of) the power curve.

However in general pilot jargon, it means that you are far enough to the left of the peak of the curve that either full power will not accelerate the aircraft at all (in level flight) or that it takes quite a while to do so. This, obviously, can cause serious problems if you don't have much altitude to trade for airspeed and you need to climb and/or speed up.

So why would you venture there? The simple answer is - uneintentional or to get into those very tight bush strips.

[LenM]

KFA

Thanks for the detailled description, much appreciated!!

Len

[LenM]

It is the area of power vs. airspeed where our airspeed is very low(normally very close to the stall) but our power setting is very high(could be even full power). In essence we are using thrust not wing lift, to maintain altitude. Our nose is pitched up at such an angle that we maintain our altitude by keeping very high thrust with a very high angle of attack and very high drag. The advantage is that we have very low airspeed. The disadvantage is that if you loose the engine you are very likely to stall the plane, unless you have sufficient height to lower the nose and gain airspeed.

At best glide speed, the aircraft is in its lowest drag configuration, when you consider both parasitic and induced drag. So it takes more power to maintain level flight when either accelerating or slowing down from that speed, because you have increased drag. When this is plotted on a graph, it makes a more-or-less bell shaped curve, with best glide (lowest drag) at the peak.

So, technically, anytime you are maintaining altitude at a speed less than best glide speed you are "behind" (to the left side of) the power curve.

However in general pilot jargon, it means that you are far enough to the left of the peak of the curve that either full power will not accelerate the aircraft at all (in level flight) or that it takes quite a while to do so. This, obviously, can cause serious problems if you don't have much altitude to trade for airspeed and you need to climb and/or speed up.

So why would you venture there? The simple answer is - uneintentional or to get into those very tight bush strips.

KFA

Your description has been in the back of my mind since you posted it and I had the opportunity to try it with my instructor recently.
NOW the theory and practice matches up, thanks!!
Not a space I'm assuming you should be flying, but the benefit to landing in a tight strip now makes sense.

Once again, thank you!!

[Dobbs]

Another short description - the drag of the plane is = to or more than the thrust that the engine is able to produce. At low level the outcome is usually not pretty as you have no height to trade for speed.

Two typical phases of flight where this may occur is on take off where for weight or runway length reasons the trike gets into ground effect, but will not gain altitude because of the high angle of attack, read - bar too far out.

The other phase is coming in slow for a short field landing and you experience sink and you push the bar out and despite full power you may not gain altitude

I would strongly suggest that you practice this with an instructor where at a safe altitude you slow the plane down, push the bar way out and apply full power and watch both the altimeter and air speed indicator, and this will give you some feel for the plane's response under these conditions.

[Dobbs]

Sorry Len, I reread your post after submitting the above one, as I was referring to a trike, but the effect is excatly the same with a three axis - stick far back, high angle of attack, full power and nothing much is happening other than trouble looming

[Mogas]

As mentioned, this is useful in advanced flying techniques when needed for short-field work.
I have found that generally speaking the power to weight ratio on our LSA planes is much better than your average 40-50 year old blik airplane.
Ours (example 80-100 hp Bushbaby) can be hard to get to fly behind the power curve because they are so light but this situation must be constantly guarded against in the fore mentioned low powered TCA's when playing with slow flight close to the ground.