Teaching pitch for a short field approach

[jrh]

I've been having a bit of a problem lately in trying to teach short field landings to a couple students, and I'm hoping somebody here on JC can help me out.

Both of these students can't get the approach stabilized, and I'm looking for a better way to describe how the downwind/base/final legs should look. I don't think they're seeing how a slower approach will affect the pattern and the pitch, especially on final.

First, a quick description of the way I fly short field appoaches (in a C-152): Abeam the numbers, reduce power to 1500 RPM. Maintain level flight until 70 knots. As soon as the airspeed is in the white arc, 10 degrees flaps. Turn base at the usual 45 degree point. Judge height and set 20 degrees of flaps at an appropriate time. Allow the plane to slow to 60 knots. As soon as wings roll level on final, set full flaps and make any fine adjustments to pitch for the aiming point. Use power to maintain 55 knots. Ideally the power should not need to be added. Either no adjustment to power or a slight reduction.

There are two common problems I keep seeing. On the base leg, the student pitches for 60 knots, and chases the airspeed. Therefore, they usually bring the nose too high, almost to a level pitch, in an effort to control airspeed, and we roll onto final a couple hundred feet too high. When I try to get them to visualize the descent to the runway, pitch for that profile, and use power for airspeed, they pitch too low and reduce the power in order to maintain 60 knots. That leaves us too low on final, needing to add power to maintain airspeed. I don't mind a very small addition of power, but I teach that approaches should ideally have only reductions of power.

The next problem comes from the basic idea of pitching for a point, keeping it stationary in the windshield, then using power for airspeed. Both of these students tend to pitch too low initially on final, reduce the power to maintain 55 knots, then recognize they will come up short of their aiming point as they get close to the runway. They pitch up, but don't add power for a second, so we get behind the power curve, then bump the power up to about 1800 RPM, so we wind up doing slow flight for the last few hundred feet of final. Not exactly a stabilized approach. Essentially, I don't think they see what "pitching for a point" looks like at 55 knots, rather than the 65 knots for a normal landing.

I've demo'd a couple of approaches and it seemed to help, but both still have trouble. I've also talked to them about how the pitch will appear shallower at slower airspeeds on approach, just like how the nose is higher flying level at 55 versus level at 70. It is the same deal during a descent on final. For one of the students I tried talking about AoA needing to be increased with a reduction in airspeed, but I think I lost him on that explanation.

Another instructor suggested breaking it down to being as simple as "The point is two inches above the cowling on a normal approach and one inch above the cowling on a short field approach," but I shy away from that explanation because I don't like aircraft-specific references (what happens in aircraft with a different shape to the cowling?) and it doesn't teach the student why the view is different. But maybe I'm overcomplicating it for student pilots. Wouldn't be the first time I was accused of overcomplicating something.

So what other ways can I teach the correct pitch on base, rather than pitching for airspeed, and the correct pitch for a point on final?

[MidlifeFlyer]

I don't like airplane-specific references either. But I think a "bring the nose up another 1/4" and let's see what happens" is an effective technique for the pilot to find his own way and useful for all airplanes.

Since I can't see it, these are only guesses.

1. I think the problem is the new airspeed on base. It sounds like you are using different airspeeds than a normal landing on al three legs rather than only on final. It's not "wrong" but I think it adds an unnecessary level of complexity to the procedure. You mention that the first sign of the problem occurs on base. Makes sense. That's a pretty short time period for which to learn a new configuration. If you do everything else normally and leave the final short field configuration change for final, there's only one view out the window that needs to change.

2. If the student is still chasing airspeed, it might be that the student is trying to fly the ASI instead of pitch. You know that it's all about "pitch and power and wait" until the airplane catches up to the canges you make. Cover the ASI.

[jrh]

[ QUOTE ]
1. I think the problem is the new airspeed on base. It sounds like you are using different airspeeds than a normal landing on al three legs rather than only on final. It's not "wrong" but I think it adds an unnecessary level of complexity to the procedure. You mention that the first sign of the problem occurs on base. Makes sense. That's a pretty short time period for which to learn a new configuration. If you do everything else normally and leave the final short field configuration change for final, there's only one view out the window that needs to change.

[/ QUOTE ]

I see what you're saying about learning a new configuration. However, I teach the pattern is normally flown with 70 knots on downwind, 65 on base and final, and slowing to 60 on short final is fine.

If I tell the student to use 65 knots on base for a short field approach, I don't think they'll have time to slow the plane to 55 and get stabilized after turning final. 10 knots makes such a difference in a 152. Five knots is more manageable because they can lose 5 just by extending full flaps, whereas 10 knots will make them be slowing all the way down final, rather than sticking an airspeed and flying it.

What configurations/targets do you use throughout a short field approach?

[MidlifeFlyer]

[ QUOTE ]

I see what you're saying about learning a new configuration. However, I teach the pattern is normally flown with 70 knots on downwind, 65 on base and final, and slowing to 60 on short final is fine.

If I tell the student to use 65 knots on base for a short field approach, I don't think they'll have time to slow the plane to 55 and get stabilized after turning final. 10 knots makes such a difference in a 152. Five knots is more manageable because they can lose 5 just by extending full flaps, whereas 10 knots will make them be slowing all the way down final, rather than sticking an airspeed and flying it.

What configurations/targets do you use throughout a short field approach?

[/ QUOTE ]Based on old experience in 152s (I will not teach in one in Colorado except on a =very= cold day with a =very= small person), I never found it to be a problem getting rid of that extra 5 knots or so on final.

For the airplanes I do teach in I use the same speeds on downwind and base for a short field as I do for a normal landing. It hasn't been a problem for any of them. It's just a matter of bringing the nose up a little further on final.

Yes, it will take a bit longer for the airplane to slow down that extra 5 knots, but that just means that you will end up higher than a normal landing glidepath. And once you reach the short field landing target speed, you'll more than make up for it with a steeper descent. (Biggest error I see on short field landings is thinking you need to put the nose =down= to get down in a shorter space).

Isn't that what the short field landing is really all about anyway? Slower airspeed and steeper descent so that you can land in a confined space?

To the extent that slowing down more on final does present a problem, I'll just extend the downwind a bit so I can have more time to stabilize on final without messing around with my view out the window on downwind and base. I teach tight patterns but am not religious about it.

[mtsu_av8er]

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Isn't that what the short field landing is really all about anyway? Slower airspeed and steeper descent so that you can land in a confined space?

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Not neccesarily in steeper, just the confined space. If there's an obstacle, then it becomes steeper. no reason to have a steeper final approach to land on a flat runway in a flat area with no obstacles!

[MidlifeFlyer]

[ QUOTE ]
Not necessarily in steeper, just the confined space. If there's an obstacle, then it becomes steeper. no reason to have a steeper final approach to land on a flat runway in a flat area with no obstacles!

[/ QUOTE ]
The slower short field airspeed will automatically give you as steeper approach unless you purposely drag it out with extra power. If you drag it out with extra power, then you have more potential energy to dissipate. That means you will have a longer landing roll. No?

[MikeD]

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Not necessarily in steeper, just the confined space. If there's an obstacle, then it becomes steeper. no reason to have a steeper final approach to land on a flat runway in a flat area with no obstacles!

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The slower short field airspeed will automatically give you as steeper approach unless you purposely drag it out with extra power. If you drag it out with extra power, then you have more potential energy to dissipate. That means you will have a longer landing roll. No?

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I suppose if you were landing on a short field runway with absolutely no obstacles around it, you could conceivably fly a shallower approach with power while still maintaining short field airspeed and managing the aimpoint. Best technique to do? Maybe; though it would feel a little "dragged in" to me if not managed correctly. But that's one of the ways I can think of it being done.

[MidlifeFlyer]

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I suppose if you were landing on a short field runway with absolutely no obstacles around it, you could conceivably fly a shallower approach with power while still maintaining short field airspeed and managing the aimpoint. Best technique to do? Maybe; though it would feel a little "dragged in" to me if not managed correctly. But that's one of the ways I can think of it being done.

[/ QUOTE ]You (and probably 20 other people here) probably know more about the physics of it than I do, but won't 61 KTS at 2200 RPM produce a longer landing roll after touchdown than 61 KTS at 1000 RPM?

I've seen the "drag it in" method and it usually involves a higher power setting coupled with a lower than book airspeed, with the goal of producing even =lower= potential energy shortening the landing roll even further. But I don't think the non-PTS version of the maneuver, even if done in the real world, is what the poster was asking about.

[MikeD]

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You (and probably 20 other people here) probably know more about the physics of it than I do, but won't 61 KTS at 2200 RPM produce a longer landing roll after touchdown than 61 KTS at 1000 RPM?


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Generally, I'd think so even though 61 kts is 61 kts. You'd probably have to time pulling the power earlier, but with a shallower approach and slower speed, that doesn't leave much room for error, IMO.

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I've seen the "drag it in" method and it usually involves a higher power setting coupled with a lower than book airspeed, with the goal of producing even =lower= potential energy shortening the landing roll even further. But I don't think the non-PTS version of the maneuver, even if done in the real world, is what the poster was asking about.

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Same. The drag-in method, though it works, like I was saying above IMO it leaves a far smaller margin for error with the potential for touching down short of the runway/aimpoint. Sure, we've digressed from the original thread intent, so to track it back, I agree with the helpful methods to teaching the steeper, obstacle approach.

[mtsu_av8er]

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But that's one of the ways I can think of it being done.

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That's how I do it! Of course, it has to be done correctly . . .

[ QUOTE ]

You (and probably 20 other people here) probably know more about the physics of it than I do, but won't 61 KTS at 2200 RPM produce a longer landing roll after touchdown than 61 KTS at 1000 RPM?


[/ QUOTE ]

If you land with power . . .

[ QUOTE ]

I've seen the "drag it in" method and it usually involves a higher power setting coupled with a lower than book airspeed, with the goal of producing even =lower= potential energy shortening the landing roll even further. But I don't think the non-PTS version of the maneuver, even if done in the real world, is what the poster was asking about.

[/ QUOTE ]

Where does the PTS say "dive-bomb"?

OK, just checked the AFH, and it doesn't say anything about a "steepre than normal" approach, except for the part that talks about obstacles.

[MidlifeFlyer]

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Where does the PTS say "dive-bomb"?

[/ QUOTE ]Beats me. Did somebody other than you say "dive bomb?"

[mtsu_av8er]

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[ QUOTE ]

Where does the PTS say "dive-bomb"?

[/ QUOTE ]Beats me. Did somebody other than you say "dive bomb?"

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Nobody at all . . .

So, please allow me to correct myself.

Where in the PTS does it say "steep" approach?

[bluelake]

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Where does the PTS say "dive-bomb"?

[/ QUOTE ]Beats me. Did somebody other than you say "dive bomb?"

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Nobody at all . . .

So, please allow me to correct myself.

Where in the PTS does it say "steep" approach?

[/ QUOTE ]

i believe the current PTS refers to the short field landing as a "confined area", but there is (no longer) any reference to clearing a 50' obstacle or anything like that.

SO. slow and precise - YES. Steep descent - N/A

[kellwolf]

I think "confined area" refers to seaplane takeoffs and landings.

[jrh]

Here's the basic physics of any approach, and I think about this as I fly all types of approaches:

At a given airspeed, there is a given amount of drag. To maintain stabilized flight with that amount of drag, there has to be a given amount of thrust. The drag vector and the thrust vector must be equal. It doesn't matter if the aircraft is climbing, descending, or flying straight and level.

During a descent, there are two sources of thrust--the engine and the forward component of weight. Just like how the rearward component of weight slows an aircraft down during a climb (increases drag), the forward component of weight will increase speed during a descent.

So let's say you are at cruise, level flight, and everything is stabilized at 100 knots. Then you push the nose down and hold it a set distance below the horizon. The aircraft will accelerate because there is now a forward component of weight acting as added thrust. As speed increases, so does parasite drag. In other words, the drag vector is increasing. Once the thrust and drag become equal, the aircraft stops accelerating and flies in a descent at the new airspeed, maybe, 120 knots.

Ok, so transfer that idea to an approach. The speed for a short field approach is already set at say, 55 knots, for a C-152. That means the total thrust has to equal the drag associated with 55 knots. Come in steeper, there is a greater percentage of total thrust coming from the forward component of weight. That means there needs to be less thrust from the engine (lower RPM) to get the same total thrust. Come in shallow, less thrust from the weight, and there needs to be more thrust from the engine.

Ok, so here's my point with all this: I don't want to add power during an approach if at all possible. Only reduce it or leave it where it is. So if I initially pull the power back to 1500 RPM, I don't want to get into a spot where I need to bump the power up to 1800 RPM in order to make the runway. If I have to bump the power up, that means I was too low. Because I was too low, the approach was shallower and the forward component of weight + the given engine thrust (1500 RPM) was not enough to equal the amount of drag for the airspeed.

Of course, this principle also explains how an aircraft can get too high and a forward slip or go around are the only good options. If the aircraft is so high that setting the power to idle and pitching for the aiming point does not allow the aircraft to slow to the approach speed, the forward component of weight alone is providing too much thrust. The only way to reduce the forward component of weight is to fly a shallower approach, and the only way to do that is to forward slip for a bit. Well, you could also pitch for an airspeed on the back side of the power curve and let the added drag bring you down, but I wouldn't ever teach that to a student pilot...

Anyway, my idea of a good "steepness" to a short field landing is whatever steepness allows you to maintain 55 knots with the power set somewhere between idle and 1500 RPM (in a C-152).

Does this make sense to anyone but me?

[kellwolf]

Let me try to give it a shot. Someone tell me if I'm way off here.....

[mtsu_av8er]

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SO. slow and precise - YES. Steep descent - N/A

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Thank you. It's just kinda silly to demand that students do this precision power-off dive towards the numbers . . . (not saying that you demand that, midlife....take it for what it's worth).

[mtsu_av8er]

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Let me try to give it a shot. Someone tell me if I'm way off here.....



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Ummm....

you forgot to square the difference in root parameters.

[Grabo172]

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Does this make sense to anyone but me?

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Actually... Yes it does, for me.

[jrh]

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Let me try to give it a shot. Someone tell me if I'm way off here.....

[/ QUOTE ]

Not really. Although your diagram does show a forward component of lift, which I hadn't thought about until just now...

Unlike the forces of lift, thrust, and drag, which can change the direction they are "aimed", the force of weight always acts straight down.

Therefore, if the flight path of the aircraft is inclined upward (in a climb), the weight is still pointed straight towards the center of earth, and you can draw a vector to show how it has a rearward component in a climb. In other word, the weight vector is aimed more towards the rear. The rearward component of weight adds to drag, which is why aircraft slow down during climbs.

In a descent, the opposite happens.

Reference the Pilot's Handbook of Aeronautical Knowledge, page 3-2, figure 3-2, and see if that helps.

[kellwolf]

Ah, I figured that "forward component of lift" and the term you were using were more or less interchangeable. Hadn't heard the weight one. So basically, what you're talking about would almost be the same as the "lift vector" but on the underside of the wing since weight is pulling downward?

[jrh]

Yeah...sort of...pretty much...I think.

The one very important distinction is that the weight vector is always acting straight towards the center of the earth. The direction never changes, regardless of the flight path or attitude of the aircraft.

Lift, on the other hand, acts perpendicular to to the flight path. Lift is never able to contribute to thrust (or more broadly defined as forward forces).

With the way you're describing it, it almost sounds like in a steep descent, because the wings are angled downward, a "forward component of lift" is what is keeping the aircraft moving forward. That isn't the case. It is the weight.

As a demonstration of this, think of an aircraft with the power set at idle, doing slow flight, right before a stall. The pitch attitude will be nearly level, maybe even slightly nose up. If you were to draw an arrow perpendicular to the wings, it would be going straight up, not forward. However, visualize the flight path. It will be a descent (obviously, because the power is at idle). It is that forward component of weight in the descent that is providing the thrust needed to keep the aircraft moving forward.

Whenever I think about these principles, it helps if I take something to an extreme.

Therefore, another example is of an aircraft in a power off dive, straight down. If the flight path is vertical, and the nose is pointed straight down, obviously the airspeed will be very high. In order to have a high airspeed, you have to have a lot of thrust, right? So where is that thrust coming from? The lift? I don't think so...the lift is pointed at the horizon. But where is the weight vector? Straight down, parallel to the flight path. That's how you can make any aircraft have a 1:1 thrust to weight ratio...point the nose at the ground. It might not be thrust from the engine, but it's still thrust, in the broader sense of the term.

Does that make things any clearer?

[MidlifeFlyer]

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Where in the PTS does it say "steep" approach?

[/ QUOTE ]Nowhere.

Interesting discussion and a rehash of one that went on when the 50' obstacle disappeared from the PTS. A large camp read it not only as "not required" but as "don't do it." Others looked at

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3. Considers the wind conditions, landing surface, obstructions, and selects the most suitable touchdown point.
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in the private pilot task description as meaning that the conditions are optional and don't see anything that would prevent a DPE from saying, "Okay, for this one, lets assume there is an 100' obstacle and the first 500' of the runway has potholes" (or heading over to the nearest airport that =had= those conditions.

Me, I looked at it and didn't see any reason to stop using the same method as before - the POH target airspeed, a stabilized descent, a marginally steeper descent, and a slightly firmer touchdown that gets all the wheels planted with reduced forward momentum.

Works fine for short fields, short field with obstacles, runways with only one turn-off at the approach end to minimize back-taxi, and the occasional ATC request to "make short approach and turn off at the first taxiway for inbound traffic" on the 10,000' runway I usually land on.

I don't claim it's the One True Way to teach a short field landing. I thought I said so in my initial response to jrh. If you need to believe yours is, be my guest.

[MidlifeFlyer]

[ QUOTE ]

Anyway, my idea of a good "steepness" to a short field landing is whatever steepness allows you to maintain 55 knots with the power set somewhere between idle and 1500 RPM (in a C-152).

Does this make sense to anyone but me?

[/ QUOTE ] FWIW, it makes complete sense to me.