Power-Off Landings

[Joshrk22]

Thanks avbug!

 

[VNugget]

An approach with flaps does the same thing.

Well... true if you use a constant setting. But I should have qualified that I was referring to the commonly taught (at least here) method of adding a notch of flaps for each leg.

 

[avbug]

Vnugget,

I agree; I found that for the initial presolo training, I taught one airspeed for climb, approach and landing, and one power setting for landing, along with a single flap setting. As soon as the student became comfortable with that, we'd expand in each area, one step at a time. If an airplane had a best rate climb of say, 65 knots then the same speed roughly equated to the approach and landing speed. It was a good place to start.

Changing configuration (eg, adding flaps) during the approach phase is fine, but I feel it's best taught in stages after the student has learned basic handling of the airplane. Walk before running, that sort of thing.

I temper that by trying to integrate instruments into training right out the door, but heavily emphasize external cues, too. While this appears to add complexity to the learning experience, I think it helps clarify what the student is experiencing. When I introduce flaps and other features, the student has developed a sense of where to look, and what he or she is seeing when they look there, and can quickly correlate adding flaps at a given altitude or airspeed with the feel of the airplane, trim, position relative to the runway, etc.

I know others who introduce it right off the bat, and that's fine, too. Really it comes down to what the student needs; some need to progress faster or differently than others, and that's perfectly fine. I've never beleived in preaching a syllabus, but rather instead teaching a student. I think there's a difference.

 

[acaTerry]

Just my 2 cents worth. I have about 3000 dual given in airplanes, and another 2000 DG in sims from AST300s to the CRJ. Take my opinion for what it costs...
I find it helps alot to make sure they do slow flight really well before doing landings. I have them do slow flight descents toward the runway (no particular preference on flaps settings but usually go with 10 at first since they see a little of the effect without it being too much) closer and closer until it turns into a landing.
So far as power on or power off, it depends on the plane you fly. Light singles, as the FAA says, should be power off. Twins power on until nearly landed. This is especially true with higher flap settings because once you get to bigger planes, you are managing energy more than flying a plane. IOW, fly the plane you are in.
I think if you fly a Bonanza for example, that either method will work fine. However, initial students need to be able to learn power offs EARLY so that should they ever be alone with no engine....its just old hat to them.
Also, the "power off" term is really undefined. I mean, WHERE does the power off segment begin? For me, once the runway is made, its power idle. Properly executed I found it to be around 100-200 feetish. (Except engine failure training of course). I find that in the standard 152 and 172 (olders) that 1500 rpm, and one step of flap each leg with 80 DW, 70 base and 60 final will work well most of the time. In the 152 with the 110HP engine or the newer 172s that taking about 200 RPM less will work fair.
Anyways, keep in mind that the way the landing turns out is the result of how well the pattern was done.

 

[Waldom]

The bulk of MY private pilot lessons was taught by a 70 year old crop duster who earned his living flying Ag-Cats at 25 feet in West Texas.
[/quote]

When Cropdusting in West Texas, 25 feet is enroute altitude, not working altitude over the targeted field.

 

[satpak77]

The bulk of MY private pilot lessons was taught by a 70 year old crop duster who earned his living flying Ag-Cats at 25 feet in West Texas.

When Cropdusting in West Texas, 25 feet is enroute altitude, not working altitude over the targeted field.[/quote]

:laugh:

 

[avbug]

When I was eighteen and cropdusting, I didn't know any better...I remember one day running out of chemical, and my boss was still working the field. He said climb up 500' and wait for him, and we'd head back together. At the time, the idea of climbing that high scared the tar out of me. Seems funny looking back on it, but that was nosebleed altitude back then.

 

[Fearless Tower]

Avbug or anyone else with radial experience,

Sorry for the slight threadjack, but what exactly is it that makes radials more susceptible to shock cooling? Is it simlply the amount of air flow directly over the cylinders or is it just an old pilots tale?

 

[Waldom]

When I was eighteen and cropdusting, I didn't know any better...I remember one day running out of chemical, and my boss was still working the field. He said climb up 500' and wait for him, and we'd head back together. At the time, the idea of climbing that high scared the tar out of me. Seems funny looking back on it, but that was nosebleed altitude back then.

I remember that feeling when I was young and bulletproof too, Avbug. At the end of a spray season in North Carolina, we used to ferry Stearmans back to home base in Florida. After a summer spent over cotten and tobacco and under wires, climbing to 2000 agl for the flight south felt like being on the edge of space.

 

[avbug]

I've never heard of radials being more susceptable to shock cooling...but from a thermal point of view, radial engines have a lot more area generally exposed to the slipstream than a horizontally opposed or inline engines do. That's assuming a single row radial. When you're discussing twin row or four row radials (such as the R-4360), rear rows have major heating issues in that they don't change much with the power back, but don't get cooled much, either. (They also catch fire a lot, too).

In a radial arrangement, the lower cylinders are going to be operating cooler than the upper in a no-wind situation,such as on the ground, when heat rises. This is largely mitigated by the airflow from the propeller, and becomes effective upon shutdown. In flight, with airflow through the engine temperature changes can have a more pronounced effect overall on the entire engine because of the large frontal surface area. Some radials are tightly cowled and have relatively little airflow over the engine, whereas others are exposed to the airflow with nothing around them.

Think about the shock caused by rain...engines don't tend to crack when operating in the rain, yet we hear about cracking when the power is pulled back. Many are quick to point out this inconsistance in "shock cooling" theory, or the fact that upon shutdown engine temperature climbs in some parts of the engine while decreases in others, causing even more thermal differences. Or start-up...the engine warms quickly; this is a big thermal change that's often greater than the changes that occur with the power pulled back on a descent.

Radial engines, like some flat engines, are mostly geared engines. Geared on both sides, in most cases, with the front end driving the propeller and the back end driving an accessory section and supercharger. Windmilling (reduced power when the slipstream is driving the propeller and not the engine driving the prop) can be damaging, though this is also a hotly contested issue (see John Deaken from Avweb, who discusses this at length in his mythbusting series). I'm from the crowd that believes one should not put the engine in a position of having the slipstream drive the prop, and I do disagree with Deaken, though I respect his viewpoint.

Making a long story of a short, there's a lot more metal out there, exposed to a lot more airflow, in a radial engine, with a lot more disparity in thermal variance from some parts to others. Add to that the fact that most radials out there are older engines, often with cylinders that have been re-worked and re-worked, the engines have been often subject to a lot more abuse (or parts of them have) than what you may be flying now.

Shock cooling is only part of the issue with proper engine operation in a radial...one of many. But the principles are the same. I think a radial demands a little more respect. They're tough engines, but more parts and more potential for problems are present. If you think about the pontential for one single bad sparkplug on your Cessna 172 during a takeoff, think about 112 or 224 sparkplugs out there, each with it's own potential to go wrong...and that's just one small part of the engine. General engine operation practice and theory, and proper airmanship, demands that pilots of air cooled engines, regardless of w(h)eather they're inline, flat, or radially arranged, use judicious application of airflow and cooling during routine operation.

 

[Fearless Tower]

Thanks for the info...based on what you just said, I'm thinking the stories I've heard about handling radials probably have more to do with the gearing than shock cooling. I have not yet had had the pleasure of flying behind a round engine, but I've read in several different places a few rules of thumb such as not decreasing MP more than 1" per minute or 3" every 3 minutes. I've also heard similar guidance for geared engines such as the GO-300.

 

[nosehair]

Radials, schmadials, this isn't about engines that have to be catered to. This is about trainer airplanes with small 100 hp engines that do power off glides and landings all day long. Most every one says power off landings are good training and everyone agrees.

Enough with the 'big engine' talk that scares the beginner student pilot in his C-152.

 

[Big Dog]

Although it might take some amount of power to maintain airspeed & a proper glidepath in a given configuration to your aimpoint, the wheels should touch the runway with the throttles idle, I don't care what airplane you fly.

 

[avbug]

I'm one of those who do believe "shock cooling" is possible because I've changed out a lot of cylinders that have been cracked as a result. I've seen it happen.

You're talking about different things. Thermal issues are entirely different than issues related to backlash in a gearbox.

Smooth power management has more to do with detonation issues (pushing too high during a power transient on a boosted engine with a leaned mixture, typically) and engine longevity and balance (such as detuning a crankshaft), or merely keeping the engine operating (I had an engine failure in a J-3 cub when I applied power to go around for some deer on the runway, many moons ago...I pushed the power up too fast, and then I didn't have any power at all).

Graduated power reductions such as the inch per minute/inch per thousand feet rule of thumb are more grounded in tradition, but they're a nice, conservative way to operate the engine, be nice to the turbo and turbo bearings, and add to the long life of the engine.

When I was flying radial engines, we made a lot of big power changes; we'd reach the edge of a mountain and push over the top, following it's contours down, slipping the airplane like a cub (big four engine airplane), and use the power accordingly. The airplanes and the engines took a certain amount of abuse, though we tried hard to be as nice to them as we could (treat it like your life depends on it, because it does). No opportunity to wait a minute to reduce an inch of manifold pressure. What we did do was limit the lower end of our power reduction. We ensured that we had adequate power available to keep from driving the prop with slipstream. This in turn meant limited ability to control airspeed on a steep downhill run, which lead to slipping, use of flaps, and judicious use of terrain and planning where to roll into the run and minimize the airspeed buildup. In other words, we had to fly the airplane.

This is really what these rules of thumb are about; treat the airplane as well as you possibly can. You have a lot riding on it. You.

Places where this really shows up go beyond merely enroute climbs and descents. I see pilots who shut down their turbo'd and normally aspirated engines as soon as they reach the parking spot. We warm an engine up after it's started (we should), and we need to cool it down by running it after we stop. This is especially important of a turbo'd engine. In either case, the engine should be leaned back and cleaned up prior to shut down and most engine manufacturers recommend final checks prior to shutdown...things your flight instructor almost certainly never taught you, and that aren't in your aircraft flight manual...but are in the engine manuals from the manufacturer (which your instructor probably never showed you, or as seen him/herself).

Some of your biggest thermal changes take place in that engine upon shutdown, when oil stops flowing to carry away the heat, when it's no longer circulating but sitting on bearings where it can boil and coke, and where airflow no longer exists to put fresh, cooler air over cylinders and the engine in general. Preparation for that phase should include a cool down period, which is every bit as critical as a warm-up period after the engine is started. (Bear in mind that on exceptionally warm days, engines can overheat during ground operations, and excessive ground run time can do more harm than good). This is a good time to check idle mixture, too.

Closing the throttle in the flare isn't the same as a power off approach and landing. It's just part of a landing technique. Vary the technique as you need to at the time, considering the conditions that exist at the moment you land.

Although it might take some amount of power to maintain airspeed & a proper glidepath in a given configuration to your aimpoint, the wheels should touch the runway with the throttles idle, I don't care what airplane you fly.

You should care, because it can and does make a difference. With more experience,you'll learn this. Power may be carried for wind conditions, such as assymetrical thrust to compensate for a crosswind. It may be carried under particular soft field conditions (not the cheesy kind that everyone thinks they're doing in training. Real, genuine soft field conditions). Touching down with power is often prudent on skis, in snow, on mud, and other such scenarios. I've found it very prudent when settling onto a frozen muddy runway, as weight as slowly applied to ensure the aircraft won't break through. In turbine airplanes, it's often not only prudent but necessary, to have the engines partially spooled, and to carry the airplane until touchdown. Power may not be removed, in some cases until the airplane is firmly on the wheels. Some fields, the shortest ones in the world, require that the engine be spooled and coming to full power by the time you touch down...carrier landings.

Don't speak in absolutes so much, as you'll find as you gain experience that your absolutes of today don't mean much tomorrow. The more you learn, you'll learn that the less you know.

Radials, schmadials, this isn't about engines that have to be catered to. This is about trainer airplanes with small 100 hp engines that do power off glides and landings all day long. Most every one says power off landings are good training and everyone agrees.

Enough with the 'big engine' talk that scares the beginner student pilot in his C-152.

A student pilot asked about radial engines, and was given the courtesy of a reply.

The same principles apply to an 0-235.

 

[Big Dog]

Notice I classified my post with "wheels should touch the runway." For good reason I did not mention grass, mud, gravel, skis, carriers, ect. In your quest for unending detail you missed a minor detail. You need to learn to read closely before you tell people what they don't know.

I see way to many people people think wrongly that "power on" means touching down with the throttles other than at idle. It causes them to float way to far down the runway. My point is I would much rather see a firm landing on a designated spot than see a greaser 1000' beyond the captain's bars, that's all.

 

[avbug]

Again, this is not the case. I did read what you read.

The conditions dictate. In some cases, holding power on the airplane is necessary. Wheels slightly above the runway, on the runway, or weight on the wheels...power is not necessarily pulled to idle. The conditions dictate. Not every landing is power off.

 

[crazyaviatrix]

My CFI taught me power off landings from the begining. I do the same with my students. You need to learn to control the plane if you loose and engine. There nothing more embarassing than landing off airpot if you could have simply did a 180 and made the runway. Also if you plan to go anywhere in your flying career than you will have to do power off 180's for your commercial which is pretty much what you are doing now except most planes used for commercial training will most likely sink alot faster than your C-172

 

[avbug]

There nothing more embarassing than landing off airpot if you could have simply did a 180 and made the runway.

You say that as though it's based on experience.

Far better to land out safely than attempt a turn back and die trying. Is being dead embarassing?

 

[Flysher]

i think he meant a 180 from the downwind. a 180 on takeoff is suicide in most planes.

 

[crazyaviatrix]

thankfully no but I do know people who have. Ok so judgement counts but there are alot of dumbasses out there. If you loose and engine near an airport and you have enough altitude than landing in a fied or off airport can be far more dangerous. Just don't try it 10 miles out at 4,000 ft. There was one kid at another flight school on airport that lost his engine on downwind at TPA with happens to be 1200'AGL. The runway is slightly over 10,000 ft long yet he choose to land straight ahead.. He's dead now and it's too bad because he soo could have made it back with altitude and airspeed to spare.