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.