Emergency Glide Ratio
Hello folks,
I've reached a crossroads on an important matter and want to know your opinion on this.
When I was training an engine failure procedure on a C152 that started on the base leg of the traffic circuit, the aircraft was already configured with 20º flaps.
The flight instructor then discussed with me if I should or should not retract the flaps to reach the runway. Quickly I tried to explain to him that in theory and my intuition told me that you should retract it - thinking that the best glide speed is obtained with flaps up - but I've heard many times people say that once you're configured for landing, you don't change the configuration, even in an engine failure.
So he said "Ok, let's see if we can reach the runway." I maintained the best glide airspeed, but quickly it became obvious that we wouldn't reach the runway: we were losing altitude quickly.
Then I told him we couldn't reach it, and he just retracted the flaps.
Without power or anything, just maintaining the best glide airspeed, the aircraft reached the runway safely.
He then explained to me that the additional drag from the flaps makes it impossible to reach it, and that's why you should retract the flaps immediately after an in-flight engine failure under these conditions.
So I was happy to know that what you learn in theory is applied in real life.
Some days later, I was talking to a far more experienced flight instructor, with many more hours than the previous one, and I explained to him that situation.
He told me the exact opposite, that what happened was pure luck, that atmospheric conditions helped the aircraft and in other circumstances I wouldn't reach the runway.
He then told me a recent case on that same runway that a similar aircraft had a real engine failure on final approach. The pilot judged he could not make it to the runway, so he dived in steeply to gain airspeed, going below the runway height (this runway is located on a higher ground than the sorroundings), and pulled up while lowering almost full flaps (I don't think it was full flaps). So - the instructor said - the aircraft 'inflated' when the flaps were lowered, quickly gaining altitude, and went above the runway, reaching it and landing safely.
As you can see, the two stories contradict each other. In one occasion, you should retract flaps, in the other, you should deploy flaps after diving.
I remember back in my aerodynamics class when I learned that maintaining the best glide speed was the only way to reach the farthest place possible. If you try to dive to gain more speed, and then pull, you're going to decrease your range. It was said that's what some people do when they get desperate.
Now I don't know what to make of this, the theory says one thing, I saw it working in practice, but then a far more experienced pilot, and former instructor, tells me the opposite.
In the aircraft's manual, it references to the best glide speed with flaps up. It doesn't mentions best glide with flaps down, so you assume that the best glide is always with flaps up.
Please, anyone who can shed some light on this would be greatly appreciated, even referencing books or some other source.
Thanks in advance!