Important Lesson: Don't Use Angle of Attack to Pick Landing Spot

VWGhiaBob

VWGhiaBob

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VWGhiaBob
:D I'm sure this is old hat and seems stupid to many, but I wanted to share am important lesson I learned today from my instructor and a Sporty's video. I'm about 15 hours into my return to aviation after a break of decades and total hours only around 100.

Intuition would tell you that if you're a little low, increase the angle of attack a bit, and you will go farther. And vice versa.

Wrong! This is especially important during emergency landings.

How far ahead you land is a function of many things. But primary among the factors is whether or not you are near the best glide angle speed.

So if you're a bit low at 75knts in a C712 pulling the nose up actually makes you drop faster, because it decreases your speed to...say...65knts, which results in a less efficient glide and a faster descent.

OK, call me dumb, but this lesson made my landings much better today. Even when high, I resisted the temptation to lower the nose. Instead, I raised it. This decreased my efficiency and brought me down faster but at a lower airspeed. Just have to watch it so the airspeed isn't TOO low.

Lesson learned! :yes:
 
You're right about the relationship between A of A and airspeed, and the relationship between airspeed and glide distance, but it's really not about rate of descent so much as glide ratio (horizontal distance for a given vertical distance).
If you look at the POH, you may see a glide ratio noted... this is the ratio you get at Vbg at max gross.
Unless you are stalled or slipping, going slower is not going to make your vertical speed greater; in fact you should descend more slowly, up to a point (your minimum-sink airspeed). But it may shorten the distance you can cover, if it is below the appropriate best-glide speed for that weight.
And because all V-speeds increase with weight, the only thing different about a glide at low weight vs. high weight, assuming you have nailed the right best-glide airspeed for your weight, is the time it will take for you to reach the touchdown target. You'll be going forward faster or slower and descending faster or slower, but the ratio of height/distance will stay the same.


It is true that in a normal final approach in a 172, with flaps out, you may well be flying below Vbg, so you may descend faster, and slipping will also slow you way down and make your vertical speed increase. Vbg is not vital when the engine is working, so flying below the actual Vbg for your weight, with that "elevator going down" effect, is normal.
But in an engine-out scenario, you will have to fly at Vbg, or you just won't get the most distance for every foot of altitude lost. Obviously, sometimes you want to steepen the approach, like when you have to get over obstacles onto a short runway or emergency-landing site, but when you are looking to get the most mileage for your altitude without using power, Vbg, and no slower or faster, is the secret. Even if Vbg for your plane is 300 kts, you won't go any farther if you go at 310 kts. You'll come up short, and get there faster.

To descend as slowly as possible, you need to fly at minimum-sink speed, which is a little slower than Vbg, and again, dependent on weight. But if you go any slower or faster than that, you will descend more rapidly. In fact, you won't have to slow down much at all from min-sink speed before you stall the wing, in which case you will descend very rapidly! :D

You can look all this up, or trust a pilot whose last few hundred approaches and landings were made without power. And I wouldn't have gotten my PP-G or the commercial rating if I couldn't roll to a stop within 200 feet of a pre-determined target, without rolling past that target. ;)

But you obviously get the important idea: that you usually won't get the desired result by simply pointing the nose at some point on the ground.
 
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Welcome to applying the axioms of gliding to powered flight.
 
Well put, rotty! That's what I was trying to say, but better said. If you're high, and potentially headed to a point too far down the runway, raising the nose HELPS, if you slow to a speed that's below your best glide speed. You land closer to the threshold and slower.

The opposite is true. If your're short and slow, raising the nose without power makes the situation worse.

My intuition told me that if I'm high, push down the nose so it's pointed where I want to land. That turns out not to be true.

Knowing this, my landings were MUCH better yesterday.

I too love the physics of this. I was a math nerd in high school, and loved the relationship of math and flight. Still do! :yes:
 
You can use pitch to adjust the aim point if you're high. Unfortunately, you'll be much too fast when you get there. The part new student pilots miss is that you must control position AND airspeed. That means elevator and throttle simultaneously.
 
MAKG1 said:
You can use pitch to adjust the aim point if you're high. Unfortunately, you'll be much too fast when you get there. The part new student pilots miss is that you must control position AND airspeed. That means elevator and throttle simultaneously.
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Pitch down throttle down. If throttle is full out, slip if allowed by poh for your flap configuration or go around.

Or if you are like me, drop it on the runway too fast :confused:
 
This kinda sorta sounds like; "Nose attitude controls airspeed, power controls rate of descent."
 
VWGhiaBob said:
Well put, rotty! That's what I was trying to say, but better said. If you're high, and potentially headed to a point too far down the runway, raising the nose HELPS, if you slow to a speed that's below your best glide speed. You land closer to the threshold and slower.

The opposite is true. If your're short and slow, raising the nose without power makes the situation worse.

My intuition told me that if I'm high, push down the nose so it's pointed where I want to land. That turns out not to be true.

Knowing this, my landings were MUCH better yesterday.

I too love the physics of this. I was a math nerd in high school, and loved the relationship of math and flight. Still do! :yes:
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Yes, this is true. BUT it puts you on the wrong side of the L/D curve and will be much harder to recover from when you're back on glide.

A much better technique (IMO) would be to LOWER the nose and accept the increase in airspeed. That increase will bleed off once you're back on glide and you raise the nose again.

If you're engine out and WAY too high for a simple pitch down to fix it there are still several tools. Slips and S turns can easily take care of excess altitude.

If you're engine out and WAY WAY too high then a simple 360 will get you back in the funnel.

Long and short, I can't imagine a situation where I was high and would feel like pitching up to near stall would be the way I'd get rid of altitude. I know it would work...but I also know there are many other options available that I'd prefer.
 
Interesting posts. I learned in a Piper Cherokee 180, but am now in a C172 180. The 172 seems to float forever, so I like a bit of a slower approach, but nowhere near a stall. My experience: Come in a little fast in a 172, and then wait, wait, wait to finish the flare. Come in slower, and there's still plenty of float left if you need it.
 
Recommend the OP read Stick and Rudder. A must have for all training/new pilots.

Good on you OP for putting together the relationship! Putting that knowledge to work in the real world is a lot harder. :yesnod:
 
VWGhiaBob said:
Well put, rotty! That's what I was trying to say, but better said. If you're high, and potentially headed to a point too far down the runway, raising the nose HELPS, if you slow to a speed that's below your best glide speed. You land closer to the threshold and slower.

The opposite is true. If your're short and slow, raising the nose without power makes the situation worse.

My intuition told me that if I'm high, push down the nose so it's pointed where I want to land. That turns out not to be true.

Knowing this, my landings were MUCH better yesterday.
Click to expand...

I figured you had it... but I zeroed in on the whole rate of descent thing, and it got me worried. :D
Glad to hear you are doing better. This is typical for student pilots; you seem to hit a wall with some task, then you break through, half by understanding, and half by plain old practice. Approaches and landings are just the beginning of that, but once you can land the airplane consistently well, the other walls will not seem so hard to break through.
Be sure to spend some time exploring the airplane's best glide and stall speeds whenever practical (and at a safe altitude, with an imaginary "glass runway" at a healthy altitude AGL). I really didn't make much progress with mastering my final approaches until my instructor had me do that. I found it easier to take it all in without worrying about actually approaching the runway. Obviously, there's no substitute for the real thing, but this exercise can do wonders for your understanding without risking anything or scaring yourself or your instructor.
I didn't learn about minimum sink speed until I got into soaring, but every airplane has one, even if it's not published. It's somewhere between Vs and Vbg, and knowing what it is could be important some day.
 
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numl0ck said:
Recommend the OP read Stick and Rudder. A must have for all training/new pilots.

Good on you OP for putting together the relationship! Putting that knowledge to work in the real world is a lot harder. :yesnod:
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+1

I highly recommend this. I read it as I got back into flying and it was much better for me than the Sporty's videos I bought. That's not to say that the Sporty's videos were bad, just that the book was much much better.
 
I am going to post a review of Sporty's. I bought the complete PP course and felt it was poorly designed. I got a refund. I bought Stick and Rudder and am about to dive into it.
 
Captain said:
A much better technique (IMO) would be to LOWER the nose and accept the increase in airspeed. That increase will bleed off once you're back on glide and you raise the nose again.
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Leighton Collins describes exactly that technique in his book "Takeoffs and Landings" in the section "Too High, Too Fast" of Chapter 7. But only advised when done far enough away; not in close. Also says the speed will bleed off fairly quickly even in a clean airplane once the nose is held level and the power off.

He also suggests not doing this on a license test or biennial review - "for when nobody is looking and you don't want to have to go around."
 
VWGhiaBob said:
Interesting posts. I learned in a Piper Cherokee 180, but am now in a C172 180. The 172 seems to float forever, so I like a bit of a slower approach, but nowhere near a stall. My experience: Come in a little fast in a 172, and then wait, wait, wait to finish the flare. Come in slower, and there's still plenty of float left if you need it.
Click to expand...

If the 172 floats significantly, you're too fast on approach. 60 KIAS solo, 65 heavy, at full flap.

Same for an Archer.

If you want to minimize float, look at the short field landing procedure, not the normal one.
 
deltafox said:
This kinda sorta sounds like; "Nose attitude controls airspeed, power controls rate of descent."
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I prefer to think in terms of "The pilot controls altitude and airspeed using a combination of power and elevator inputs.
 
I think a more important lesson to be learned from this thread is how there appears to be a broad misconception that your pitch angle in regards to the horizon is equivalent to your angle of attack.

It's not
 
Slowing down to get away from L/Dmax has the added benefit of letting a headwind have more time to effect you, thus further steepening your descent. Speeding up to get away from L/Dmax gives the headwind less time to act on you. Reverse if you're trying to get down with a tailwind.

I've used both of these methods to get away from L/Dmax and descend. Both can work, however I prefer to use other methods to get down. Ideally, you realize that you're high when you're far enough out that only minor adjustments result in the change you need. For instance, dropping flaps a bit sooner than you normally do, pulling out the power sooner. If I'm closer in, though, I typically slip. It's fun.
 
VWGhiaBob said:
I am going to post a review of Sporty's. I bought the complete PP course and felt it was poorly designed. I got a refund. I bought Stick and Rudder and am about to dive into it.
Click to expand...

I am a new private pilot (check ride last October) I have just finished reading "Stick & Rudder" if I have one regret it was not reading it during my training, I honestly believe it would have helped me be a better student.
 
75Kts approach is waaay to fast in a 172. My 172S (heavier than other models) will fly fine in slow flight with flaps up at 50kts.

Try a final approach speed at 60Kts full flaps. Trim for 60 and adjust power to meet your touchdown point. Smooth everytime.
 
Actually, any time you're flying the wing (re: all the time unlss you're flying one of those god awful helos, which I can't even begin to explain the aerodynamics of), you're using AOA to make the plane do what you want it to do. Coming up short, reduce the AOA to gain more energy (Pitch=performance). Gonna be long, increase the AOA to lose some energy.
 
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