Help the Student Pilot

Factual Questions
1

I know I’ve PMed a bunch of you flight instructors and pilots already, but I’ve decided to just start a thread and get my questions out in the open. I intend for this thread to be a running, consolidated place for aviation questions. Other students, feel free to hijack with your own questions. CFIs and others, thanks in advance for your help.
Background: I’m currently on my sixth lesson (well, not currently currently) toward my Private Pilot certifcate. I’ve been playing MS Flight Sim since I was 10, though, so I’m coming at this with a lot of book knowledge and some simulated application of it.

First questions:

  1. Adverse yaw - It seems like this has a pretty minor impact on flight. If I don’t use any rudder to coordinate, say, a left turn, it seems like the nose only moves right for a second, then starts turning. Is it really that big of a deal? Why can’t I just not use any rudder while I’m turning?

  2. Turn coordination - I understand the concept but I can’t seem to connect the physical actions in the cockpit with the theory. When I first dip the wing into the turn, I need to apply some rudder to cancel the increased drag on the down aileron. I get that. But then what do I do in the turn? Do I ease up on the rudder? Quit using it entirely? Apply opposite rudder?

And how does the indicator work, anyway? It seems like, if I’m skidding, that the ball should go to the outside, not the inside, just like passengers in a car. In a hard-turning car, the passengers go to the outside until the car frame forces them into the turn. Shouldn’t the same thing happen to the ball?

  1. Why is final so short? It seems logical to have downwind and base at pattern altitude and then have final be the descending segment. Then you can monitor your glideslope easily and make adjustments as necessary. Yet we start the descent on downwind and continue it all the way through base and final. It seems like it’s intentionally set up to be complicated, what with flaps and turns having to be managed at the same time. Why do they do it that way?

  2. My instructor keeps having me set up on the right side of the runway on final. He says “now we’re on the centerline” and I’m looking out and seeing both edges of the runway slanting to the left. He says that’s an optical illusion and said “it’s called parallax”. Now, I’m quite familiar with parallax. So I googled “runway parallax” and got nothing useful. The term doesn’t seem to exist. I can’t, for the life of me, figure out what he’s talking about. What’s the illusion?

  3. Forward slip vs. sideslip. What’s the difference? They seem like the same thing, just facing the opposite way. Is one into the wind and the other’s away from it? If there’s no wind, aren’t they identical?
    Again, thanks for the help.

2

I took flying lessons back in 1979, and never quite finished to get my license, but I recall that I would naturally line up just to the left of the center stripe of the runway. I’ve thought that this was because if you’re driving a car (sitting on the left side) and you want to drive centered over a stripe, that stripe should be just to your right. But I also realize that in a small plane, you head is already very close to the center of the plane, and at the distance you are when you’re on final approach, you should just line up your head directly over the center stripe, but still I had this tendency to be just a little on the left side because then it “felt like” the plane would be centered.

Maybe your instructor, sitting in the right seat, thinks he’s lining up the plane’s center with the center stripe of the runway, not realizing that he’s really too far to the right?

3

1 and 2. Step on the ball to keep it centered. It becomes second nature very shortly.

  1. If final is too short, you turned base too soon. Once you master full flap landings, you’ll think nothing of a short final.

  2. I’ve never noticed. This all becomes so second nature you’ll hit the numbers every time without thinking about it. I always flew the center line, but you do what your instructor suggests.

The good news is that this all becomes second nature over the next 4 to 6 hours of flight time.
You’re not that far from the big day when your instructor tells you to pull over and let him out. I was scared and excited and damn, downwind seemed to take forever that day. You’ll do fine.

4

I don’t have time for a really thorough answer right now, but what type of airplane are you flying? I’d guess it’s a Cessna or a Piper, or something similar. They both have very little adverse yaw by design. Next time you fly, set yourself up at around 80 knots and run the ailerons back and forth to full scale deflection without using any rudder. When you get to full deflection, immediately begin a roll in the other direction. Before long, you’ll set up a situation where the nose is moving in the direction opposite to your aileron inputs. This is due to adverse yaw. Next, add just enough rudder that the nose stays pinned in one spot. You now have coordinated turns. The more aileron deflection you have, the more rudder deflection you should have. Next, make a medium banked turn, and note the position of your ailerons once established in the tuen. Almost no deflection, right? Same should go for your rudder. However, you need ailerons to roll back to wings level. Therefore, you’ll need rudder as well. I’ll be back this evening for more input.

5

It’s a Cessna 172.

We did that exercise already. It was easy enough. But it doesn’t seem useful for anything unless you want to make your passengers sick. If I’m just turning, then there doesn’t seem to be that much need for any rudder input.

6

I have just over 500 hrs in gliders, a handful in power.

Adverse yaw is minimal in a 172. It is a huge honking big deal in a sailplane. It varies between these extremes in other aircraft. Best to learn to deal with it instinctively now and make perfectly coordinated turns. This will make it far easier to transition to different aircraft. Adverse yaw is also more pronounced at low airspeeds and may be a factor in spin initiation.

Runway C/L: On a wide runway I prefer to stay just off the C/L, to where I can see it out the side. This is a tail dragger habit, as you often can’t see straight ahead over the cowl, and it makes it easier to stay aligned when the runway is very wide. On a narrower runway, you can use the runway edges as a reference instead of the C/L. On narrow runways I will often land to the downwind side of the C/L, expecting to weathervane a bit.

The main thing is to control with intention where you are on the runway, not just wherever you end up. Your instructor may want you exactly on the C/L because that is a clear target that you can both agree on.

Patterns: It is good to stay in a position where you can make the runway should the engine stop at any point in the pattern. This usually means a short final. A long final would mean you wouldn’t be able to make the runway if the engine stopped on or near the base leg.

When flying your patterns use the apparent position (angle) WRT to the end of the runway as a reference for where to make your turns, NOT local landmarks (hangers, water tanks, houses, etc.) None of those landmarks will be there when you land at a different airport.

Your instructor is getting you used to dealing with several things at once, an essential skill for an aviator. They will pile on the workload until you screw up. Eventually you stop screwing up even when they have you doing five things at once. Then they know you are getting close to being ready to solo. You can consciously handle only 2-3 things at once, so the others have to become ingrained enough that you can do them without needing to think about it. For example, at first it takes a great deal of attention to maintain heading and altitude, but eventually you can do it without conscious effort. By piling on the workload the instructor can asses how much of your attention these tasks are using up. When you finally solo, it will be much easier to fly without that SOB trying to make you screw up.
A slip is a slip is a slip. If the airplane is not yawed into the apparent wind, it is slipping. Save yourself some pain and adapt to your instructors terminology.

Slipping while turning is seldom desirable, and not for novices. Slipping toward the outside of a turn (AKA skidding) is a good way to spin, and probably a leading cause of spins in the pattern. Glider tow pilots will frequently use slipping turns to burn off altitude after releasing a glider, as it may be desirable to keep the throttle up to avoid shock cooling the engine.

IMO, side slip vs. forward slip distinction can only be made when on final.
A forward slip usually means you are aligned (in yaw) with the runway, AND the flight path is also aligned with the runway. It is one of the ways of dealing with a cross wind. By lowering the upwind wing, you can align the flight path AND the airplane with the runway. You normally maintain a forward slip (with adjustments) all the way to the ground, touching down on the upwind main first. For a given crosswind and final approach speed, there is one amount of forward slip that is just right. Too little or too much will result in some wheel skid at touch down, though IME it is much less critical and more forgiving than the “crab in and kick straight at the last instant” option. I would argue that a cross wind is required to perform a forward slip, but not with my instructor!

A side slip would yaw the airplane out of alignment with the runway, but also maintains the flight path along the centerline. It should also be done by lowering the upwind wing if there is any cross wind component. The goal here is different though. You are trying to shorten/lower your glide path. You would not maintain a side slip to the runway. You return to coordinated flight once you are back on your preferred glide slope. It is a way to make small to medium glide slope adjustments while leaving the throttle/flaps alone. The amount of side slip can be varied depending on how much you need/want to degrade the efficiency of the airplane

You could be in a forward slip, and need to burn off some altitude, so you could temperarily increase the slip a bit yawing the nose toward the downwind direction. So you would be doing a combined forward and side slip.

7

As some of you many know from other threads, I’m a professional (full-time) flight instructor. So…

As Stranger said, it’s subtle in many small aircraft. But yes, it’s a big deal. If the plane stalls and is coordinated, it just stalls. If the plane is yawed during an imminent stall entry, it will not just stall but spin. That yaw moment can be introduced through adverse yaw, so coordination is critical.

Here’s what I tell my students: If you are moving the ailerons, you should be moving the rudder too.

In a normal turn, you move the ailerons while simultaneously applying some rudder pressure in the same direction. I use the word “pressure” deliberately. It’s not really a big bootfull in most planes and at sensible airspeeds.

Once established in the turn you can usually release the rudder pressure. A lot of people don’t realize this. However, when leveling out of the turn, again use rudder pressure along with aileron in the same direction. A lot of people neglect to do that.

You’re over-thinking it. See this diagram from Rod Machado’s book.

Some people do land that way, keeping altitude until on final. There are advantages and disadvantages. The main disadvantage is it takes longer and can cause traffic problems. However, if you are not just aware of the wind condition, but utilizing it, you can fly in a continuous descent to the runway threshold, adding flaps as needed.

I tend to fly a tight pattern for safety, but I do begin a descent abeam the threshold unless I have a reason not to.

The illusion is you don’t know where the center line is and your instructor does. But I’ve never heard the term parallax used in this context.

I see this constantly with my students. Sitting on the left side of many aircraft if you put the airplane on the center line from your POV, you will actually be on the left. Best way to teach this is to position the plane by hand on a taxiway centerline, then get in and look.

Students invariably line up on the left side of the runway when they begin learning to land, and end up touching down on the left side of the centerline. I refer to this as “driving in England”.

The difference is the purpose, and sometimes the amount of control deflection. A forward slip is used to increase the rate of descent. A sideslip is to position the airplane on the runway centerline during a crosswind landing.

In a forward slip you would generally use a lot of rudder deflection, often a full throw. In a sideslip the amount of deflection depends on the wind speed and direction.

Hope this helps. Ask more and/or PM me if you’d like to.

8

Thanks for the help, but Wiki sez you have this backwards. Who’s right?

Another question: Weather - On a hot day, the pressure rises. This seems counter-intuitive to me, as I’d expect the air to expand in volume, not pressure. But when you’ve got gas in a container and heat it up, pressure (not volume) increases. Is the atmosphere really just one big container?

9

No, **Kevbo **and Wiki are both right. Unfortunately, there’s no easy way to remember which is which, but fortunately it doesn’t matter - to the airplane, they’re the same thing. A sideslip is what you do to land in a crosswind if you’re not crabbing - it keeps the fuselage aligned with the ground track. A forward slip is how you drop altitude if you’ve used up all your flap travel already (and, if you’re learning in a Cessna, you haven’t done it anyway).

Try this, if you want a memory aid - in a sideslip, your body is leaning to the side, and in a forward slip, you’re leaning forward.

Let me take a stab at your other questions: Coordinating a turn matters mostly because if you don’t, one wing will be slower and closer to stall than the other, and if you proceed to that point, it will be nastier than a straight-ahead stall and probably get you into a spin. Those take more altitude to recover from than you’ll be at in the pattern, IOW a too-slow slipping turn will kill you. Coordinating a turn also reduces drag because it keeps the nose pointing straight into the relative wind, without pushing the side of the fuselage into it. And, it eliminates side G loads that can be uncomfortable for passengers, if not you. The ball shows if you’ve eliminated those side G’s or not, and if not, by how much.

Finals are short so you can keep the airport in sight more easily, so you can make fine adjustments more easily, so less terrain or obstructions in the area come into consideration, and so fewer people on the ground are affected by your noise. That said, straight-in approaches are common too, and you’ll get to those eventually.

Your instructor has the optical illusion, not you. Put yourself, or, when you get a better feel, your right shoulder on the centerline and you’ll be fine. There’s a joke that when a certain haughty, perfectionist airline pilot made his final landing, the controller teased him “You were a little to the left of centerline on that one, Captain”. His reply: “Quite so, and my copilot was a little to the right”.

The other maneuvers you’re asking about, like most of the private pilot syllabus, are mainly about getting the feel of the airplane, so you’re not constantly thinking about what control to move where.

10

The lower atmosphere essentially is, yes - air pressure is just the total weight of all the air above you. If lower layers heat up but upper ones don’t, the weight of the upper layers, resting on the lower ones, will contain them and cause their pressure to rise.

11

I’m no expert, only a low-hours pilot (not far ahead of you, in other words), but a few things caught my attention:

I was taught to fly the downwind at constant height (decreasing airspeed and adding the first stage of flap by the end of downwind, while maintaining height) and only start to descend after turning base. I’m not saying that’s better, just saying that’s what I was taught, both in Ireland and the US. It’s interesting to see that others take a different approach.

You mention “flaps and turns having to be managed at the same time”. Assuming you literally meant “at the same time”, I think it’s better practice to adjust the flap when the wings are level. The way I configure for normal approach (into a short grass field) is “flaps 10, trim for 80 kt, turn base, level the wings, flaps 20, trim for 70, turn final, full flap as required, trim 60”.

12

I think you are right - in a Cessna 172 it doesn’t take much rudder input to keep the ball in the middle in a shallow turn. But I can think of a few reasons why it’s important. The most compelling (for me) is to remember that “slip + stall = spin”. (Do I have that right? I think a stall in either a skid or a slip condition risks a spin.) In other words if you are uncoordinated and stall a wing, better hope you have enough height for spin recovery.

Another reason is that steeper turns do need rudder input, so you might as well apply the right amount of rudder input anyway.

One piece of advice I got from an experienced pilot was to apply the rudder control slightly before deflecting the ailerons, anticipating rather than reacting to the ball.

13

And adding to that: Don’t even look at the ball. Adverse yaw is usually best judged by watching the horizon. The ball is more useful in sustained climbs when right rudder is needed for other reasons.

Let’s also stop for a moment and acknowledge that a great deal of flying technique varies from pilot to pilot. There are some techniques that are known to be “good” and some not-so-good. But a lot of them are arbitrary or have similar advantages / disadvantages, and depend on the person and how they were taught.

Example: Putting in flaps during the downwind leg vs. at the abeam point. I couldn’t care less how a student or pilot does that, as long as they do it consistently and it works for them.

I often inherit students from other instructors and I give them a little speech: “I might teach some things differently from what you learned before. That doesn’t mean your first instructor was wrong necessarily, but I might give you new ways to think about them. There are a few items which are mandatory for safety reasons. But for non-critical items if you prefer a different technique than mine, I’ll probably be OK with it as long as it is consistent.”

14

It remember what it was like learning to land: ‘Right rudder… RIGHT RUDDER! Hold it there! HOL… <thud> <thud> <THUD>’ :smiley: My problem was that I tended to get fixated at the area immediately ahead of the plane. Things got a little better when I tried to look farther ahead.

15

This is an excellent note.

Chessic Sense, I just wanted to come back to the adverse yaw point, because in my opinion this is a fundamental core skill that can NOT be overemphasized, and is severely lacking in many new pilots. All of the pilot examiners I interact with on a regular basis feel the same way. You are learning to fly in a 172, which is perfectly happy being bucked and yawed all over the sky. It can actually be a little bit difficult to get a 172 into an unaccelerated spin depending on CG location, and if you release pro-spin controls, it often pretty much recovers all by itself. This should tell you something about the inherent stability of the airplane you are flying. Many (most) airplanes are NOT that forgiving. Please, practice this until you are proficient and understand what you are doing. As an instructor, I use the pattern as my gauge. If my student is using the rudder to roll into and out of turns while they are busy picking out traffic, pitching for airspeeds, changing configurations, maneuvering relative to the runway, talking on the radio, etc., then I know they’re solid.

If you want to see the nose swinging as you are doing your coordination rolls, look to your left. Since the wing tip is much further from the CG that the nose of the airplane, any yaw will be amplified there. With only aileron input, you will see the wing tip trace an oval in the sky as you roll the wings back and forth. Add more and more rudder along with your aileron (leading the bank with rudder) until the wing tip is moving straight up and down. You now have coordinated turns. You can also do it the other way around, starting only with rudder, then adding aileron until the wingtip moves straight up and down. Either way, the effect is more apparent at higher angles of attack.

Last thing (semi-related): I’ve been lurking this board for a LONG time, and I just wanted to point out how many well-educated and very experienced airplane nerds we have here. Every thread about aviation gets a ton of people jumping in and adding their 2c. I love it.

16

Looks like I got the words backward from accepted definitions. My explainin of what you are doing and why was correct. The airplane doesn’t care what you call it, but learn what your instructor calls it so you can do what he asks you to.

17

Maybe your instructor wanted you to do, and think about, only one thing at a time. It’s easier to learn that way, obviously, but it can be hard to change later to a more efficient approach.

And that’s an example. I’ve gotten used to changing flaps while in the turn, while there’s pressure on the yoke anyway, and trimming when back level, so I spend less time overall manipulating the controls and leave more time to keep my attention outside the cockpit.

There are multiple right ways to do almost anything, really.

Me too, and probably almost everyone. Judging your height with peripheral vision only is just unnatural at first. You can be so focused on how high the wheels are off the runway that you forget to look at the far end of the runway instead.

For a while, I had a bad problem with touching down left wing low, because I was looking forward and down out the side window to judge my height vs. the rushing pavement. A refresher with an instructor who’d seen that many times fixed it in a few minutes.

That’s another point - you are never, or should never be, done learning. You might have heard that the most dangerous point in a flying career is at 100 hours, when you think you know everything, then at 500 hours, when you KNOW you know everything, and only after 1000 hours do you realize you can never know everything. Don’t ever be so wrapped up in your ego that you can’t go back and learn something, or get a problem identified and fixed.

18

Thread revival!

New question: Why do spins occur?

So I understand that a stall happens when the wing reaches the critical angle of attack and the airflow stops adhering to the top surface of the wing. The wing stops producing lift and the plane falls. I get that.

In certain situations, one wing stalls more deeply than the other, causing one to generate more lift and thus causing a roll along with loss of altitude. I get that.

What I don’t get is why wiki says:

Wait, what? Why would a wing dropping increase its angle of attack? The plan, for now, is still heading in the same direction. The relative wind is the same. The pitch of the wing is the same. What’s the change?

My ground school program, which needs some serious editing, says that the lower wing has a smaller angle of attack and even has a diagram where it shows a smaller, flatter angle because the wing is lower. Another site, which I’ve lost the link to, says that the wing is pulled backward and down. But if lift creates drag and airspeed creates drag, shouldn’t the high wing be the one with more drag?

ISTM that they should be saying that the lower wing, being inside the turn, has a lower airspeed and thus gets less lift. Am I just failing to imagine things in three dimensions?

Questions 2: Neutralizing ailerons.

Why can’t I use the ailerons to roll out of a spin? Is it because the ailerons usually work by changing the wing shape such that the lifted wing (aileron down) has a higher angle of attack, which normally generates lift but in this case, aggravates the stall? Even if that’s the case, it seems like I should just apply opposite aileron, then, and roll level.

Question 3: Why does recovery work the way it works?

Step 1 is to pull power to idle. Step 2 is to use rudder to get level. Step 3 is to go nose-down and then pull up out of the dive. Why does that work? Intuitively, I’d think you should first use rudder to get level, then apply power to pull yourself into the relative wind. That is, in the spin, the wind is hitting the bottom of the plane because you’re falling, not flying. Applying power should pull the plane forward, flattening the relative wind and thus reducing the AoA to something flight-worthy. Why idle power? Why the dive?

Thanks for all the help, aviators.

19

I’ve done a couple of thousand aerobatic flights in a Pitts Special, I’m fairly familiar with what works and what doesn’t but this was over ten years ago and I’m fuzzy on the finer points of theory. Please forgive any gross errors. I’m also running late for work; I’ll try to tidy things up and provide more detailed info when I get back.

The relative wind is not the same. While the wing that is stalled more deeply is in the process of dropping, it is moving down and the other one is moving up, that changes the relative wind between the two and the one that is dropping gets a higher angle of attack which further deepens its stall. The wing that’s going up gets a lower angle of attack and still generates some lift. It starts to fly itself around the inside wing.

I’m thinking your ground school notes are referring to a wing that is low, not a wing that is in the process of dropping. I’d need to refresh my memory as to whether a low wing does ave a lower angle of attack and why. I’m also not sure of the exact drag difference between a stalled and partially stalled wing. Airspeed doesn’t create much drag until at speeds significantly greater than the stall. The drag produced by lift decreases as airspeed increases. The drag produced by stalled and partially stalled wings is almost entirely due to the high angle of attack.

That is true once established in the spin but doesn’t help you picture why the spin starts in the first place. As the spin is being initiated the aircraft isn’t necessarily turning. Yes if you intentionally spin, you will be helping out with a boot full of rudder but they can also occur natural just by stalling, particularly in high performance aircraft that don’t have the docile stall characteristics of a trainer.

There isn’t enough airflow for the ailerons to work properly. If you use them in the correct sense, as you say, they will make the spin worse by increasing the effective angle of attack of the inside wing. You can use into spin aileron in a desperate attempt to recover from a particularly gnarly spin but you’re far better off using the rudder which is still a very effective control surface.

Remember that you are in a stalled aircraft and the way to recover from a stall is reduce the angle of attack. You also need to stop the rotation.

Are you familiar with the typical thrust/drag couple on an aircraft? Adding thrust will raise the nose of most aircraft because of the way the thrust vector is coupled with the drag vector. Adding power to a spinning aircraft will likely raise the nose which flattens the spin and increases the angle of attack of the stalled wings. You end up in a worse situation. It would be like holding full up elevator to recover from a stall, it doesn’t work.

You need to use rudder first because it is the most effective control surface and you are better to stop the rotation before recovering from the stall.

The “dive” is standard stall recovery. Once you’ve stopped the rotation, you’re still stalled and need to reduce the angle of attack. You do this by lowering the nose.

Incidentally, a well behaved aeroplane will recover from a spin if you take your hands and feet off the controls. If you get into serious trouble and nothing seems to work, try that. (That is of course not a recommendation to try spinning without adequate training.)

20

Thanks, Richard. As always, you’ve helped get my head on straight. I withdraw my statement about my ground school program conflicting with wiki. I took a second look at it, and they do, indeed, match up. The lower, inside wing has a greater AoA. I get now that I shouldn’t be calling it a lower wing, but a falling wing, and that makes it all clear.