14.15 Is there a "rule of thumb" as to when to turn the base leg?
From FlightSim
IS THERE A "RULE OF THUMB" AS TO WHEN TO TURN THE BASE LEG? IN OTHER WORDS, HOW FAR PAST THE END OF THE RUNWAY DO I EXTEND MY DOWNWIND LEG? AT WHAT POINT DO I BEGIN MY DESCENT...IN THE DOWNWIND LEG OR AFTER I TURN TO THE BASE LEG? IS THERE A STANDARD PATTERN HEIGHT, I.E., 1000 AGL? HOW FAR SHOULD I EXTEND MY CROSSWIND LEG...IN OTHER WORDS, HOW FAR SHOULD I BE FROM THE RUNWAY WHILE I AM FLYING PARALLEL TO IT ON THE DOWNWIND LEG?
"Rule of thumb:" First, most airports will have a published traffic
pattern altitude that can vary because of terrain/obstruction
considerations. Barring this, a good altitude would 800 - 1000 ft.
above field elevation. Decrease power abeam the intended touch down
point while on downwind leg and hold altitude to decrease speed. When
flap extension speed is reached (white arc on the AS indicator) lower
flaps one notch and establish a 300 - 500 fpm descent using the
vertical speed and airspeed indicators as cross reference. When at a
position where the end of the runway is 45 degrees behind you turn
base and lower another notch flaps. At this point, you should be
about 300 ft below pattern altitude. Continue descent until you reach
a point where you can turn directly onto final without over or
undershooting the extended runway centerline. Evaluate your
situation as regards to altitude, airspeed and position relative to
the runway and make corrections as necessary. Use the VASI, it helps.
You should be constantly evaluating your aircraft's position and
performance throughout the pattern. I must admit that in a real
airplane that this is easier than in FS 98! You can see more of what
you need to see (if flying a Cessna!) You're right about this being
important. At airports with parallel runways proper pattern flying is
critical.
Dave W. Manes
Flying crosswind, you will fly about a half mile from the runway,
turn downwind....at midfield (I'll make this with a simple airplane
like a 152 for an example since it's just easy) reduce power to 2000
RPM and a flow check (fuel on, mixture full rich, prop full RPM if
applicable, carb heat as required or as applicable and fuel boost
pumps on as applicable...I don't think I missed anything). Once you
reach the numbers on the approach end of the runway, reduce RPM to
1500...continue downwind until you can look back and the end of the
runway looks as though it's 45 degrees off your wing. Then turn your
base...oh, I forgot...you can start descending when you cut power to
1500....ok, now you're on base, check final for incoming aircraft,
then turn your final and land as usual. Let's see...Oh, I forgot to
say that yes, usually you'll find a standard pattern altitude to be
1000 AGL. Also, on downwind, after you make your first power
reduction, you should be at about 20 kts airspeed more than your
final approach speed. Then you can drop 10 kts on base and you'll be
at your final approach speed shortly after turning final.
Aaron
Aircraft up to Large Turbo Props usually use 1000 ft Circuit Height.
Jets that I have flown F-28 - MD83 and A-300/310 Airbuses use 1500
ft. Keep in mind for the Circuit, the WIND will affect your timing
for turns. If the wind is across the strip you can fly longer into
the wind say on cross wind to keep you out wide enough. With Jets --
you use the stop watch (FS - press the button on the bottom left) to
time your Down Wind past the end of the Runway --- say
400 ft bad weather 20 Seconds 1000 ft 30 Seconds 1500 ft 45 seconds
Bill B.
Flying a tight pattern is a wonderful goal, really necessary in the
real world. It is more difficult in a sim, because you don't have all
the instant, smooth viewing capabilities available in the real world.
At a tower controlled field, you are less likely (with ATC in the
picture) to be able to fly a complete pattern, though often you do
(but they may not let you keep it tight, depending on traffic).
Ideally, you'd be no more than 1/2 mile from the runway on downwind (speaking of light aircraft now -- larger aircraft are another story) often a bit closer, at 800 to 1000 feet (most airports publish a recommended pattern altitude as, for example, 5454 MSL (Mean Sea Level). A crutch I've used for students in 152/172 type aircraft is to turn base when you see the runway at a 45 degree angle behind you. Ensure that you are at the correct approach speed. Again, a crutch for my 172 students is:
- Reduce power to 1500 RPM when opposite the point of intended touchdown.
- Maintain altitude until reaching 65 kts., then add 10 degrees of flap. Retrim.
- When the touchdown point is at the 45 degree point behind you, start a turn to base leg, add 10 more degrees of flap (20 total), maintain 65 kts. Retrim.
- Turn final, add remaining flaps, slow to 60 kts. Retrim. Align with the runway. Power should still be at 1500 RPM, if you've done it all correctly.
- Slight power changes should be all that is needed until you are "over the fence," at which point smoothly reduce to idle, start easing the nose up for the flare. As the aircraft slows, rate of back pressure increase becomes more rapid.
It takes a lot of practice, and is more difficult in FS98, due to not enough visual cues -- it is really surprising to many how much we depend on turning our heads, on peripheral vision, etc.
Note that the retrimming I constantly mention is actually "retrim until you do not have to hold forward or back pressure." In other words, let the aircraft do the work. A human hand is a wonderful sensor of pressures CHANGES, but is poor at detecting absolute pressures. That's one of many reasons that, TO ME, a programmable joystick is a major asset in flying a sim -- one of the first things I program is elevator trim.
Hope this helps you, and perhaps others wondering the same things.
Larry N.
I would fly it like this (and I recognize this is just my opinion)
power to 1500 rpm, carb heat on abeam point of intended landing.
Maintain altitude until airspeed less than 110 kts IAS. Flaps to 10.
Maintain 80 kts. This should set up about a 500 fpm descent. Once the
point of intended landing is 45 degrees behind, turn base. Judge your
height (too high, too low) and determine if now is the right time to
go to 20 flaps, ideally it should be time to go to 20. Maintain 75
kts. Turn final. Again judge height. Add flaps 30 (sometimes add 30
flaps prior to final if high on glide path. Turn to final should be
made 400-500ft agl. Maintain 65 kts +- 5. Whether to use pitch/power
to control airspeed/altitude is subject for a hugh debate, but as far
as flight sim goes, hold 65 approx. on airspeed, add/subtract power
for altitude as necessary and flare. I have found that flight sim
seems to lengthen the float compared to the real world, so err on the
side of low airspeed.
Ray
I might as well throw my advice in here. Pattern altitudes are
generally either 800' or 1000' AGL for the little guys--check the
A/FD to be sure. If nothing is specified I prefer 1000'--no point in
giving up altitude until you have to. If the runway is short it might
help to fly the pattern at 800'. Here are the target altitudes I
use: After takeoff, don't turn onto the crosswind leg until reaching
pattern altitude minus 300', unless you're climbing really slowly.
Fly the downwind leg at pattern altitude and at a distance of 3/4
mile to 1 mile (A rule of thumb I've heard is to fly the downwind at
a distance that puts the runway halfway down the wing strut on a
Cessna). When you're abeam the touchdown point pull back power and
begin your descent. Make your turn to base when the touchdown point
is 45 degrees past abeam. Continue the descent on base. When you
make the turn to final you should be passing through the halfway
point (500' or 400'). Adjust the timing on your pattern to meet
these targets. Of course, no pattern ever comes out perfect and you
have learn when to make adjustments.
MDK
According to my AIM, traffic patterns range from 600 ft to 1,500 ft AGL. 1,200 ft to 1,500 ft is common for turbojets. Section 4-3-4 says, "1000' AGL is recommended pattern altitude unless established otherwise".
Note it says recommended there is no requirement in the FARs or elsewhere to fly a standard pattern at any altitude. You can make straight ins, base entries downwind entries if you wish. The 45 degree downwind entry at pattern altitude is only the recommended one. Thankfully, most people use it so some sanity prevails at uncontrolled airports. The A/FD will tell you actual pattern altitude for a given runway (some airports with multiple runways will have different pattern altitudes for different runways).
Rayh
I guess it's rather obvious by now that different instructors teach
different rules of thumb -- and that's all they are. For me, your
method makes the pattern a bit too wide, meaning that folks behind
who normally fly tighter patterns have considerable adjustment to
make. Engine reliability improvements over the years have left a lot
of folks not so concerned about "What happens if the fan stops?" Of
course if you were learning in a 182 or bigger, then the larger
pattern makes more sense.
Hope everyone here that had questions gets the idea that there are a number of different "rules of thumb" taught in the real world, and that the common thread among them is to establish a CONSISTENT method of learning to judge for yourself (and it IS an individual judgment in each case) how you are doing in relation to getting to the runway safely and at the right speed -- the most important thing is to always use the same speed for the same configuration, have the speed and rate of descent stabilized so that you can judge visually how you are doing.
Another trick, one that is a bit tougher to use in FS than in the real world, is to realize that, given a stable approach, there is a point on the ground (hopefully on the runway) ahead of you that is not moving either up or down in the windshield. That is the point at which, with no adjustments, the nose will plow into the ground. A good rule of thumb is to have that point be just short of your intended point of landing, then as you start your round out the aircraft will actually land a bit beyond that stationary point.
Larry N.
