Does a small aircraft fly slowly than a bigger one while landing/takeoff?

Question

If you observe, a huge plane like Boeing 747 looks like its floating in the air just before landing or soon after take off; while a small ATR plane looks like its flying so fast after take off...
Does the speed differ or is it just an illusion?

Answer 1

In most cases they do. Landing speed is determined by the weight of the aircraft and the design of the wings and flap system. It's always a trade-off.

But what you see is differing airspeeds combined with the perceived "bulk" of the airframe...so it's partly an illusion. Even going the same speeds, the ATR would appear to be going faster because its "bulk" appears to pass a fixed point in space in a shorter time.

Theoretically you could design a wing that would allow a fully loaded B-747-400 to approach and land at say, 60 knots...which would be slower than an ATR. But the wingspan would make it all but unmangageable on the ground, (it wouldn't fit at terminal gates, etc.) and the weight and drag penalty for cruise speed and fuel efficiency would be enormous.

The amount of lift needed to keep an airplane in flight is a combination of the wing shape / design and the forward airspeed. Generally, during design, the builders want to create an airliner that can operate safely and efficiently from a typical commerical airport runway which are usually between 7,500 to 10,000 feet in length.

Consider the Space Shuttle. it has a very small wing for it's weight...which is about 1/3 that of a 747. The Shuttle's approach speed is well over 200 knots whereas a 747's is typically more like 160 knots.

The infamous and fairly small F-104 Starfighter had extremely small wings...although was supersonic and fairly fuel efficient for its day and time. It was quite a bit smaller than an ATR but the F-104's approach speed was notoriously high...and a lot of overrun or wing-stall accidents were the result of this design.

The opposite case might be comparing a 4-place Piper Cherokee to a 3 times larger DHC-6 Twin Otter. The Twin Otter is designed for using short runways and can actually land at a slower speed than a Cherokee. But the Twin Otter has a relatively low cruise airspeed compared to other aircraft of its size and weight because of its large and bulky wing and strut design.

Answer 2

The simple answer to your question is yes....typically the larger an aircraft, the faster the take-off/rotation and landing speeds are. But also, a lot of the speed/lift relationship has a lot to do with the actual shape of the wing. Let me try to explain.

Different aircraft have different landing/take-off speeds. These speeds are determined during the aircraft's certification process through a series of many hundreds of tests and different weight and wing/flap configurations.

The flapsmain function is to alter the aerodynamic shape of the wing.

During take-off, a small amount of (take-off) flaps are employed to generate a slight amount of extra lift during take-off. These are then retracted as the aircraft climbs because the characteristics of the air change with altitude and the wing is essentially designed for efficient cruise flight with maximent lift co-efficent.

During the landing phase, the landing flaps (a larger amount are employed) are then deployed to;

1. Decrease the stalling speed (permitting a lower approach speed),
2. Create a steeper flightpath,
3. Lower nose attitude and finally,
4. Shorter hold-off (shorter landing run because of increased drag and lower airspeed).

As I said int he 2nd paragraph, lift has a lot do do with the shape of the wing. For example, an ATR has a long slender wing, almost glider like. It's VERY lift efficient and thus the ATR can land in very small airfields/runways. Contrast that to the F15 fighter. It's smaller than an ATR, but the wing is a BIG delta wing. Not very lift efficient for short field take-offs, but deadly in the event of a dog fight as it's inherently unstable (the fundamental requirement of a fighter).

The Boeing 747 also has long wings, but they're again shaped differently than the ATR because they're built for flying at higher altitudes and cruise speeds (around Mach 0.84) than the ATR. Hence the sweepback on a modern jetliner is the best efficient form of lift for these aircraft. Hence they have more slats and flaps and some also have higher approach speeds than, say, an ATR. But here's an interesting point. There is not much in it when comparing the approach speeds of a B747 vs a B737, the lift co-efficient being very similar, the only difference being the weight of the aircraft having an effect on the amount of lift required and thus the speed needed on final approach.

My answer might be a bit long-winded, but I hope it helped explain the need for speed/flap/weight considerations when determining landing speeds.

Claython

Answer 3

When you say fly on, I guess you mean be a passenger. There is no question I would much prefer to fly commerical over flying in a small plane as a passenger. Commercial aircraft generally better weather capability, performance, and crew training. When you fly on a small plane, you put you life in the hands of someone who's qualifications to fly and airplane can be marginal, and who have not had enough experience to make the proper decision at times (not to fly at all). I cannot see any private pilot who would rather fly a nasty IFR approach, single pilot, in a Cessna 182 over flying the same approach as a passenger with a professional crew who trains all the time to make that type of approach, in an airplane that is designed to fly in really bad weather. Even then you will see commerical flights canceled for weather. If I can fly the small aircraft myself, then yes, that will be the choice almost all the time. If for some reason, there was a total loss of power (much, much more likely on a small single engine aircraft as compared to a multi-engine commerical aircraft), the small airplane is where you would want to be. With a good pilot, it would be very rare not to survive an engine failure in a small aircraft. Notice I said good pilot. There have been more than a few perfectly flying small aircraft contact the ground in uncontrolled flight after an engine failure. An aircraft does not need an engine for controlled flight. Loss of aircraft control in an emergency landing, would be fatal almost 100% of the time. If you gotta crash, hit the softest, cheapest thing you can find with the aircraft still flying under your control, at the lowest speed that positive control of the aircraft can be maintained.

Answer 4

Has to do with wing-loading. A Piper Cub can rotate or land at about 35 knots, because it has very light wing-loading (the ratio of weight to wing area), as opposed to a 747, which has to be around 120-130 to lumber off the ground.
A lot of it is illusion, because of the size differences, but there are also real speed differences as well.

Answer 5

Partly it's an optical illusion, and partly, larger aircraft TEND to be designed for faster landing speeds, though that's not always true.

For instance, the immense H-4 Spruce Goose was airborne at 70 NMPH, but the small F-18 Hornet needs 134 NMPH for landing approach.

Answer 6

its an illusion. its like when you are driving and you look out the window. things closer go seem to go faster and things farther seem to go slower. speed does differ though. a 747 will land at about 170 - 200 knots and smaller prop driven aircraft will come in anywhere from 80 knots to 120 knots depending on aircraft.

Answer 7

yes the speeds differ i used to be a pilot on General aviation or light aircraft i only used to fly single engined but the climb out and approach speeds were both 70knots but on something like a Jumbo i believe the take off speed is about 170 mabey even 200 knots i am sure i see on a documentary where it said it was 170 knots it also all depends on wing type as well like delta wing for instance but its only usually fighters and very high performance aircraft that have that set up with concorde being the exception

Answer 8

The first 2 answers are very good.
If I recall correctly, the landing (or over the fence) speed on a 737 is faster then the 747

Answer 9

most of the time, yes

Answer 10

............... the difference is not as much you feel ....... which is an illusion ........... the bigger the airplane, the slower it will seem ........