Power n' pitch...

I would hope that your instructor could provide a good answer here. Buuut, here is the correct one. The actual correct answer is it depends on which side of the power curve you're on. If you're on the backside of the power curve (slow), as you get slower, induced drag increases, so you need more thrust to counteract. Long story short, pitch directly controls airspeed, and power controls airspeed. If you're at a normal cruise speed (on the front side of the power curve), pitch controls altitude, and power controls airspeed. As you slow towards best glide speed, the transition occurs, so usually at your landing approach speed in a light piston single, both pitch and power affect altitude and airspeed equally.

I've had a beer or four, so clear as mud?

This is what the examiner was after on the CFIA checkride.
 
@killbilly,


Let's consider some situations where this would apply. If you're descending on an ILS at 3 degrees, and you're 5 knots fast, what happens if you try to pitch up to lose that airspeed? You get high on the ILS, and now you need to not only drop the nose, but pull out power to get back on the glide slope. Would pitching for airspeed be the best solution? No, reducing power a little bit would be your best solution.

In the same manner, if you're at 500' on your base leg, and you lose 10 knots. What's the quickest way to regain that airspeed? By dropping the nose a little bit. If you just tried to power out of this situation, you may find that you don't have enough power to do what you want, and the engine (even with a piston engine) won't provide the immediate response that reducing the angle of attack will.

The problem is that when we're teaching folks how to fly airplanes, and EVERYTHING is foreign, there are certain truisms that are taught. Are they always 100% applicable? No, but they likely won't get you killed. Reducing AOA to regain airspeed not only works when you need to regain airspeed quickly, but applies doubly when it comes to stall recovery. If we taught the fundamental as power for airspeed, you'd see guys holding pitch attitude while trying to power out of stalls.
 
I know that both can be correct - my real question is twofold - 1. Why is one way taught, and then another taught? 2. Should I be choosing one over the other in instrument flying or is that incidental? What's going on here?

Simple reason. Flying an ILS, staying on the glideslope is the most important thing. So you trim for that, and adjust pitch to stay on it no matter what. In a light single, speed isn't all that critical to the approach***. If you are centered on the needles and 10 kts fast, well, being fast isn't a huge deal right that second. Since power is the only thing you can change, you cut some power, stay on the glideslope, and eventually the speed will decay. If you are slow, well, you don't pitch down since you don't want to fly into the ground. So you add power, which eventually brings your speed up.

*** in bigger airplanes, it is much more important. But in the cessna that you normally fly 90kts on approach, nothing bad happens if you fly 110kts instead. At busy airports, you are going to be asked for best forward speed on the approach fairly often anyway :)
 
I think people often get hung up on these rule-of-thumb issues because they don't recognize a difference between 1) a rule of thumb and 2) fundamental aerodynamic principles.

Fundamental aerodynamic principles are complicated and rarely useful when it comes to actually flying. Airspeed and climb rate are complicated functions of pitch, power, and many other variables such as your airspeed regime, drag profile, excess power, pitch/trim sensitivity, etc. etc.

A rule-of-thumb is a simple rule/relationship that allows a pilot to organize and structure their control inputs in order to achieve accurate, predictable performance. It has no value or inherent truth beyond its ability to achieve that goal.

Given that all my experience is in light pistons, I find pitch for airspeed, power for climb rate to be useful most of the time. However, anytime you have to control your altitude/climb rate very carefully, such as an ILS or doing a low approach over the runway for fun, I swap the rule to pitch for altitude/climb rate, power for airspeed. Eventually you develop intuition and habit patterns and start using a bit of both without thinking about it.

If you find another approach that works for you and allows you to fly the plane accurately and safely, I don't see how anyone could fault you.
 
I've heard lots of people mention that they fly an ILS one way and fly a visual landing another way. Here is a thought to ponder. What does the lack of visibility have to do with how the plane flys? In other words, the airplane doesn't care if it is IMC or VMC and why do we, as pilots, think we have to change our method of piloting based on the conditions?
Another fun fact that most people know, but not everyone so it is worth bringing up. Trim holds an airspeed. Set a speed, trim for it and then the airplane will always seek that speed out. In this case, power would control altitude as the pitch would set itself to the attitude required to hold that speed.
 
What does the lack of visibility have to do with how the plane flys? In other words, the airplane doesn't care if it is IMC or VMC and why do we, as pilots, think we have to change our method of piloting based on the conditions?
Because different conditions demand different performance and one method may be more applicable in one regime vs. another. And it's not the IMC vs VMC; it's the need to precisely control GS. If you want to fly a PAPI very precisely in VMC you may also want to use the pitch for glideslope/power for airspeed method.

But you want to fly using different rules of thumb, go nuts, I won't care as long as you get good results.
 
I've heard lots of people mention that they fly an ILS one way and fly a visual landing another way. Here is a thought to ponder. What does the lack of visibility have to do with how the plane flys? In other words, the airplane doesn't care if it is IMC or VMC and why do we, as pilots, think we have to change our method of piloting based on the conditions?

Another fun fact that most people know, but not everyone so it is worth bringing up. Trim holds an airspeed. Set a speed, trim for it and then the airplane will always seek that speed out. In this case, power would control altitude as the pitch would set itself to the attitude required to hold that speed.

Because a newly IFR rated pilot needs to learn very precise control of an aircraft when in IMC. And that control starts WAY before the approach does.

As to your 2nd point. That is only true in airplanes that are inherently stable.

My train of thought? Power always controls airspeed with a few exceptions. You have either full (or fixed) power or no power at all.

If we all could just teach students that the ONLY way to recover from a stall is to lower the AoA we wouldn't have this problem. But I agree, it blends to both as you progress and eventually doesn't matter.
 
I would hope that your instructor could provide a good answer here. Buuut, here is the correct one. The actual correct answer is it depends on which side of the power curve you're on. If you're on the backside of the power curve (slow), as you get slower, induced drag increases, so you need more thrust to counteract. Long story short, pitch directly controls airspeed, and power controls altitude. If you're at a normal cruise speed (on the front side of the power curve), pitch controls altitude, and power controls airspeed. As you slow towards best glide speed, the transition occurs, so usually at your landing approach speed in a light piston single, both pitch and power affect altitude and airspeed equally.

I've had a beer or four, so clear as mud?

Edit in bold. Beer...
 
@killbilly
Let's consider some situations where this would apply. If you're descending on an ILS at 3 degrees, and you're 5 knots fast, what happens if you try to pitch up to lose that airspeed? You get high on the ILS, and now you need to not only drop the nose, but pull out power to get back on the glide slope. Would pitching for airspeed be the best solution? No, reducing power a little bit would be your best solution.

Ah but an instrument rated pilot who has done a few ILS approaches knows that if they are 5kts fast and on glideslope, and they reduce power to fix their airspeed, they also need to trim (pitch nose up) to maintain the glideslope. If they just reduce power and don't add some back pressure, they will still be at 95kts but below glideslope. Students may not have this relationship 100% down yet. Hence, pitch for airspeed power for altitude :) Or more accurately (on an approach) trim for airspeed, power for glideslope. As you can see either way you think about it the actions are the same (reduce power and add backpressure) and the end result is the same.

So why teach 'pitch for airspeed' instead of the other way around? Because in other phases of flight like slowflight or stalls, pitch really is more important than power. If the student gets into the mindset of using pitch for airspeed, that will help them out with other things like commercial maneuvers.

By the time they get to a transport category aircraft that actually has some power, they should understand the principles and not need the rules of thumb anymore.
 
Well, this has sure been fascinating. (no sarcasm - I really have liked hearing the mental processes here - very enlightening.)

You guys have definitely answered my questions as to why the two methods are taught the way they are - and they do make sense to me. I do realize that both pitch and power have their effects on flight, and at a tender 150 hours TT, I don't really think of flying the airplane in those specific terms anymore...I've got enough "air sense," I guess, to apply power/pitch changes as needed when I'm flying, and I'm learning to combine the two practices to make the airplane do what I want it to. Tailwheel flying has helped with that quite a bit.

I also suspect that I am overthinking this IR stuff right now - at least at this phase where I am working through CBT-based ground training and doing a lot of supplemental reading. I don't know what I don't know yet. I believe I am probably just hypersensitive right now to what I perceive as anomalies (that probably aren't) because I want very badly to be very good at this particular aspect of aviation.

Once again - thank you to everyone. I surely appreciate the discussion (and feel free to keep going with it) and I think I have the answers to my initial questions.
 
When I was teaching people to fly small airplanes I taught the pitch for airspeed, power for altitude method because it was easier for them to control the airplane that way. In an airplane with limited power and no autopilot you trim for airspeed, and leave it set, then you use power to set the desired vertical speed rate and the airplane is very predictably easy to control that way.

In a swept wing jet with 20000 pounds of thrust, a trim switch on the yoke and an a dual axis autopilot you use the power levels to achieve the desired speed and trim the pitch for altitude. Most of the time. That being said there are times in each where you would use the other method. For example, in a piston single in cruise you're setting your power accordingly and making slight elevator or trim adjustments to maintain altitude. And in a jet on final I'm trimming for ref+ and using power to set my descent rate.
 
Because different conditions demand different performance and one method may be more applicable in one regime vs. another. And it's not the IMC vs VMC; it's the need to precisely control GS. If you want to fly a PAPI very precisely in VMC you may also want to use the pitch for glideslope/power for airspeed method.

But you want to fly using different rules of thumb, go nuts, I won't care as long as you get good results.

You should be flying with the same level of precision whether you are VFR or IFR, at least attempting to anyhow.
 
Agreed, to add, the DPE was asking what side of the power curve I was on for a short field landing.

Trimming for an airspeed (at least in a 172) is something that was also new to me.
 
I recommend the book "Stick and Rudder". It has a great way of explaining how airplanes fly in "normal" terms.

It's all about visualizing the flight path or objective you desire and making the proper control inputs to make the plane do what it needs to (oversimplified as Pitch + Power = Performance).
 
You should be flying with the same level of precision whether you are VFR or IFR, at least attempting to anyhow.
I would never argue against the ideal of trying to fly precisely at all times.

But different conditions, maneuvers, and regimes of flight do demand different standards of precision. An ILS requires a high degree of precision because you are maneuvering the airplane VERY close to the ground without visual references and clearing visually obscured obstacles by very small margins. The localizer and GS give very sensitive needle deflections, and we adjust piloting technique accordingly with a faster scan and smaller corrections. Try flying at cruise with only 5 degree heading corrections, AI bar width pitch corrections, and immediately going after any small deviation? You'll tire yourself out and quickly realize you don't need the same level of precision at cruise.
 
I would never argue against the ideal of trying to fly precisely at all times.

But different conditions, maneuvers, and regimes of flight do demand different standards of precision. An ILS requires a high degree of precision because you are maneuvering the airplane VERY close to the ground without visual references and clearing visually obscured obstacles by very small margins. The localizer and GS give very sensitive needle deflections, and we adjust piloting technique accordingly with a faster scan and smaller corrections. Try flying at cruise with only 5 degree heading corrections, AI bar width pitch corrections, and immediately going after any small deviation? You'll tire yourself out and quickly realize you don't need the same level of precision at cruise.
I try to fly with the same precision at cruise, especially if I'm scud running through the mountains in a mile vis with no autopilot.
 
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