wolit@alice.UUCP (Jan Wolitzky) (02/15/85)
While I'm no expert, here's my two cents worth: I was taught to fly nice, squared-off approaches (i.e., downwind leg extended about 1/2 mi past the end of the runway, then a 90-degree turn to base, then a 90-degree turn to final) with partial flaps applied as soon as I reduce power (approx. opposite the end of the runway), and full flaps applied on base, with about 1500 rpm carried throughout (for a PA-28-140, PA-28-160, AA-5A, ...). This technique has the advantage of producing pretty-looking patterns in the sky, (not such a bad thing, since others can guess where I'm going) and a good amount of time to "stabilize" the approach -- nothing happens too quickly, the rate of descent isn't too great, and the technique carries over fairly well to instrument training: the descent angle is pretty much like an ILS approach, but with the two right angle turns thrown in. I fly like this with nervous passengers and FAA inspectors on board. I don't like it, though. I don't like being strung way out on final at about 500' AGL with all that flap hanging out, just waiting for the engine to cough or for someone flying a tighter pattern to cut me off without looking. I would feel real bad flying all the way from point A to point B, always (well, almost always) having a field in mind for a soft landing should the engine quit, and then having to land in the trees with my destination airport in sight. As long as there's no one in the pattern ahead of me (I don't want to cut anyone else off, either), I like to fly a power-off approach, which means about a 180-degree turn from downwind to final. Since I also like to land as slow as possible to save on tires, which means using full flaps, this means flying a pretty steep descent, which means having to flare rather assertively. It means having to use a different technique when I'm under the hood, or flying with my wife, but it also clears me out of the pattern fast and gives me a little more peace of mind. -- Jan Wolitzky, AT&T Bell Laboratories, Murray Hill, NJ; (201) 582-2998
ark@alice.UUCP (Andrew Koenig) (02/15/85)
I expect different airplanes respond best to different techniques. I fly single-engine high-wing Cessnas (150, 172, 177RG), and, like others, I have had different instructors tell me different things. From these various things, I have evolved the following guidelines that work well for me in the airplanes I fly: 1. Avoid power-on approaches unless you use at least 20 degrees of flaps. I know that's not always possible in a busy pattern. The reason for avoiding power-on approaches without flaps is that if the engine quits you can pick up the flaps and at least still have a shot making the field. 2. The fixed-gear Cessnas I fly all have 40 degrees of flaps available. The airplane flies more or less like a brick with all the flaps on. I have become increasingly suspicious of full-flap landings in those airplanes on a long runway, because the steep nose-down attitude makes the flare a touchy matter and because I don't know what I'd do if I needed to go around and the flap motor failed. The 177RG has only 30 degrees and the flaps are less effective, so I always land that airplane with full flaps unless it's really gusty. Because of these two things, I find my most satisfying landings in the 150 and 172 are made with 20 degrees of flaps.
kiessig@idi.UUCP (Rick Kiessig) (02/18/85)
Getting back for a moment to the question at hand
about high/low power/no power, here is some refresher
info (paraphrased from VFR Flight Review by Avram Goldstein):
1. When abeam the numbers, reduce power from
(say) 2300rpm to 1700rpm. Carb heat. 10 deg
flaps, opposing nose-up tendancy with some
forward yoke. You should slow from (say)
90 kts to 80 kts, and have dropped about
200 feet by the time you're ready to turn
base.
2. As you turn base, add another 10 deg of flaps,
again opposing the nose-up tendancy with
some forward yoke. The additional drag
will slow you another 10 kts - say to 70.
Now you start to control your decent carefully
with throttle - more if you're too low, less
if you're too high. Trim if needed.
3. Apply full flaps as you turn from base to
final. Try to lead this turn neatly, so
taking the wind into account, so you roll
out exactly in line with the runway. Many
stall-spin accidents happen during this
turn. If you never exceed 20 deg bank
and keep the nose down at all time, it
is virtually impossible to stall the airplane
at approach airspeeds. But you could be
distracted, then if you're not well-trimmed
for a nose-down attitude, as soon as you
relax pressure on the yoke, the nose goes
up, the airspeed falls off, and if you are
in a speep bank, you are suddenly in trouble!
If you do things right, you apply full flaps
as you turn final, you keep the nose down,
you trim for nose-down, and you use whatever
power is needed to control the decent. Your
right hand should be on the throttle continuously
from the moment you turn final until you taxi
off the active. Your eyes should be looking
over the nose the whole time. If you can't
see the ground over the nose, you're in big
trouble because your nose is too high and
your airspeed is too low. You should glance
at the airspeed indicator occasionally out
of the corner of your eye. The extra drag
of full flaps should slow you to (say) 65 kts
on long final, and you'll lift the nose
slightly on short final to 60 kts, ready
for the flare.
4. At all phases of the final approach, you should
concentrate on keeping the airspeed constant with a
constant pitch attitude, and control your decent with
power. Reducing to idle power, with full flaps, results
in a very efficient decent, and if needed the decent
can be increased further by slipping without a change
in airspeed.
My teaching has been slightly different than the
book recommends: I was taught to always do one thing at
a time - therefore don't apply 20 deg 1laps until you've rolled
out on base. And where I fly, the downwind leg can be VERY
long, resulting in a very long final (3mi or more). Therefore,
I was also taught not to apply full flaps until short final,
rather than on long final as the book suggests.
I have always been told that putting on full flaps
on base or before is VERY bad news. As the book says, many
pilots get killed stalling and spinning on the turn from
base to final. Bad news. Not to mention the problems of
engine failure. Much better to wait until almost the last
minute before putting on full flaps. This solves problems
of tire/landing gear wear while at the same time keeping you
safe. Suggestions of making a 180 deg turn from downwind to
base or of making sharp 90 deg turns with full flaps - COME ON!
If you can't make a nice-looking 90 deg turn without
full flaps, or if you can't make a nice square base leg
without them, watching for traffic like you should, then you
shouldn't be flying! A short approach is one thing; a well-
flown pattern is another.
I suggest that all pilots periodically fly the
pattern with no flaps. Use slips and engine control instead -
which is of course what you have to do on aircraft that
don't have flaps (yes, some planes don't have them!), or
what you would have to do if your flaps were broken.
--
Rick Kiessig
{decvax, ucbvax}!sun!idi!kiessig
{akgua, allegra, amd, burl, cbosgd, decwrl, dual, ihnp4}!idi!kiessig
Phone: 408-996-2399cfiaime@ihnp4.UUCP (Jeff Williams) (02/18/85)
This question of flaps or not is about as personal a question as possible in
aviation. However, I am quite willing to put my two cents worth into the
discussion.
I teach my students the following procedure in a Cessna 152, 172, PA-28
series, Grumman AA-5 series, and the like.
1. Downwind is flown about 3/4 of a mile out from the runway, at a
speed of Vfe-5 knots (80 knots in a C-152/C-172).
2. Halfway down the downwind leg, add carb heat if the aircraft manual
calls for it.
3. At the point on downwind abeam of the touchdown point, add the first
increment of flaps, power at 1700 to 1500 depending on the
temperature, ect.
4. A nice, square pattern, with base about 1/2 mile from the threshold
of the runway.
5. Second notch of flaps on base leg. Still keep 1500 - 1700 rpm.
Speed is touchdown speed +10 to 15 (70 to 75 knots in a 152
or 172.)
6. Full flaps on short final when the runway is made. Power off at
a point where a comfortable landing will be made 500 feet down
the runway (big runways) or 100 feet down (short runways).
In a Cessna, it is either FULL flaps or NO FLAPS depending on the wind.
If the wind is over 25 knots, or over a 15 knot crosswind, the flaps are
up. Otherwise, the flaps are down all of the way. Touchdown is at Vso*1.1
or at the recommended speed. The stall warning horn is just starting to make
it's mournful bleat.
So, why this technique? Why not power off like one would fly a taildragger?
Simple. First, this is a predictable pattern, both for the student and for
following traffic. Next, it is possible from any point in the pattern to
make the runway if the engine quits (after turning crosswind, natch). Third,
we don't shock cool the engine, which causes a LOT of EXPENSIVE wear.
By keeping the touchdown point somewhat down the runway, there is a built in
"ooops factor" for an undershoot, especially if the engine were to die in
the pattern. As for the flaps, take a look in a Cessna owner's manual at
the stall speeds with and without flaps. You will notice that the first
20 degrees give a large amount of lift, while the last 10 or 20 degrees give
mostly drag.
As an example, lets look at the book figures for a 1971 Cessna 182. (I
could find this manual, my wife filed some of the newer manuals when she
moved my library to make a bedroom for our new kid. However, this will
illustrate what I am talking about.)
Power off stall, 0 degrees of bank = 66 mph CAS.
Power off stall, 20 degrees of bank = 59 mph CAS.
Power off stall, 40 degrees of bank = 57 mph CAS.
Note, for the first 20 degrees of bank, the stall speed decreases 7 mph,
a bit better than 10% decrease in stall speed. In the last 20 degrees,
the stall speed decreases only 2 mph, under 5% stall speed decrease.
So, picture this. The 182 pilot comes in with 10 knots extra for wife and
kids, and partial flaps. The 182 pilot will float into the next county
because the wing is much more efficient in ground effect, the 20 degrees of
flap are providing more lift than a clean wing, but not a large amount of
drag. By the way, a 182 is an acceptible airplane for the illustration
by virtue of the wing being the same airfoil as the 150/152/172 series, that
is a NACA 2412.
Can pilot technique with full flaps get an airplane in trouble? Sure, if
the pilot does not fly the attitude of the airplane and watch what the
airplane is doing. With full flaps, the airplane wants to slow up much more
quickly than when flown with no flaps. Pitch attitude is important, just as
power setting is important. But, as an instructor, I have seen more pilots
get into trouble by not using flaps than by using flaps.
I, however, will not use full flaps in a Cessna O-1 Birddog, because the flap
at 60 degrees can cause some problems. I also had problems getting full flaps
on in a Cessna 180/185 because of where the flap handle was located, and where
I have to sit to reach the rudder pedals in that airplane. After the first
20 degrees, I couldn't get my arm moved around to get the last 20 degrees.
But, that's ok, because I would wheel land the thing and not play with the
flaps until it was totally stopped. (By the way, the 185 is a blast to fly!)
Oh well, the question is non-existant in a REAL airplane anyway. I mean,
who ever wanted flaps in a Champ, Cub, or Taylorcraft?
Jeff Williams
AT&T Bell Laboratories - Naperville, Ill
ihnp4!cfiaime