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#1
Old 05-28-2008, 12:02 AM
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How fast are airplanes going when they land?

What is the speed of, let's say, a boeing 747 when it lands on the runway before the breaks are applied?
#2
Old 05-28-2008, 12:25 AM
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You may want to start here.
#3
Old 05-28-2008, 02:19 AM
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Between 130-160 knots according to this message board. Note that the speed depends greatly on the aircraft weight. The landing reference speed (Vref) is calculated prior to conducting the approach and is based on an estimated landing weight. A heavy B747 will have a much higher landing speed than a light B747.
#4
Old 05-28-2008, 04:31 AM
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Yup - about 150mph is a reasonable guess, but there are many factors already mentioned. Weight (and hence fuel load) is the main one.

Rule of thumb: to convert knots to mph, add 15%. Edit to add: if you don't need precision. It's a decent approximation, though.

Last edited by PaulParkhead; 05-28-2008 at 04:33 AM.
#5
Old 05-28-2008, 06:21 AM
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More info on point: http://boards.academicpursuits.us/sdmb/...d.php?t=290268
#6
Old 05-28-2008, 06:47 AM
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But what if it's landing ... on a treadmill ?!?









sorry - couldn't resist
#7
Old 05-28-2008, 07:13 AM
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Some relevant points:

It's brakes.

As noted, landing airspeed depends on mass. The ratio of airspeeds will be the square root of the ratio of masses (so, for example, twice the mass leads to a 41% increase in speed).

The work that thrust reversers and brakes must do is proportional to the square of the groundspeed. Any headwind will reduce the reduce the aircraft's groundspeed - which is of course why aircraft land into wind when possible. In the case of a 747 landing at 130 kts, the effect of a paltry 10-kt headwind will be to reduce the energy that must be dissipated by 15%.
#8
Old 05-28-2008, 08:24 AM
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As luck would have it, I landed last night on a flight from Atlanta to Hartford. 757 that had the TV in the seat back. I was watching the flight tracking, and as the wheels touched down, we were at 153 mph.
#9
Old 05-28-2008, 08:50 AM
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Quote:
Originally Posted by Xema
It's brakes.
Unless it's a crash.
#10
Old 05-28-2008, 10:51 AM
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Little airplanes can land at a much lower speed. Someone will correct me if I'm wrong, but I believe a typical single-engine four-seat plane lands somewhere around 85-100 mph.
#11
Old 05-28-2008, 10:54 AM
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Quote:
Originally Posted by kunilou
Little airplanes can land at a much lower speed. Someone will correct me if I'm wrong, but I believe a typical single-engine four-seat plane lands somewhere around 85-100 mph.
As low as 40 mph for a very wee aircraft, e.g., Piper Cub.
#12
Old 05-28-2008, 10:56 AM
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Quote:
Originally Posted by kunilou
Little airplanes can land at a much lower speed. Someone will correct me if I'm wrong, but I believe a typical single-engine four-seat plane lands somewhere around 85-100 mph.
My flight training days are from about 7 years ago (with no flying since then, alas) but I believe the landing speed on the Cessna 172 I trained on was 65 Knots.

J.
#13
Old 05-28-2008, 11:41 AM
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Quote:
Originally Posted by TeddyLee
What is the speed of, let's say, a boeing 747 when it lands on the runway before the breaks are applied?
African or European?

ahem.

In the neighborhood of 100-150 mph.

The importance of speed (or lack thereof) in landings:

Several years ago, a DC-10 had to crash land in Kansas (Nebraska?) after an engine failure blew out all its hydraulics. It nearly made it, but the problem was it was coming in way too fast (the number 250 knots comes to mind). The pilots were controlling this plane just with the engines. It hit the ground slightly off-runway, flipped over, broke apart, and parts burned. Several people were killed, but many people made it.

A small plan has a much lower landing speed. I've been in a Cessna 172 several times where the pilot literally had to dive the airplane into the ground in order to land. The headwind speed plus the minor speed of the airplane was keeping it in the air like a kite!
#14
Old 05-28-2008, 12:14 PM
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Quote:
Originally Posted by 633squadron
A small plan has a much lower landing speed. I've been in a Cessna 172 several times where the pilot literally had to dive the airplane into the ground in order to land. The headwind speed plus the minor speed of the airplane was keeping it in the air like a kite!
What do you mean by the "minor speed of the airplane"? It'd be pretty unusual to have to dive the plane at the ground in order to land, normally that would indicate that you're just travelling too fast. A gusty headwind may cause that temporarily but a steady headwind won't.

Landing too fast and trying to force the aeroplane on to the ground rather than letting the aeroplane settle as the speed decays can lead to this kind of landing (youtube link.)
#15
Old 05-28-2008, 12:23 PM
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Quote:
Originally Posted by 1920s Style "Death Ray"
What do you mean by the "minor speed of the airplane"? It'd be pretty unusual to have to dive the plane at the ground in order to land, normally that would indicate that you're just travelling too fast. A gusty headwind may cause that temporarily but a steady headwind won't.

Landing too fast and trying to force the aeroplane on to the ground rather than letting the aeroplane settle as the speed decays can lead to this kind of landing (youtube link.)
He might be referring to a slip which can be a legitimate technique.
#16
Old 05-28-2008, 02:39 PM
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Quote:
Originally Posted by bikebloke
As low as 40 mph for a very wee aircraft, e.g., Piper Cub.
And even lower (like, 25-35 mph) for a specially-designed STOL plane like the Fieseler Storch (Hi! I'm the Fieseler Storch! You may remember me from such STOL flights at the rescuing of Benito Mussolini from his mountaintop prison!).
#17
Old 05-28-2008, 02:41 PM
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Quote:
Originally Posted by jharvey963
My flight training days are from about 7 years ago (with no flying since then, alas) but I believe the landing speed on the Cessna 172 I trained on was 65 Knots.

J.
That's the correct speed in Flight Sim, FWIW.
#18
Old 05-28-2008, 02:48 PM
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Quote:
Originally Posted by 633squadron
The importance of speed (or lack thereof) in landings:

Several years ago, a DC-10 had to crash land in Kansas (Nebraska?) after an engine failure blew out all its hydraulics. It nearly made it, but the problem was it was coming in way too fast (the number 250 knots comes to mind). The pilots were controlling this plane just with the engines. It hit the ground slightly off-runway, flipped over, broke apart, and parts burned. Several people were killed, but many people made it.
Sioux City, Iowa: United Airlines Flight 232.
#19
Old 05-28-2008, 10:11 PM
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Quote:
Originally Posted by 1920s Style "Death Ray"
What do you mean by the "minor speed of the airplane"? It'd be pretty unusual to have to dive the plane at the ground in order to land, normally that would indicate that you're just travelling too fast. A gusty headwind may cause that temporarily but a steady headwind won't.

Landing too fast and trying to force the aeroplane on to the ground rather than letting the aeroplane settle as the speed decays can lead to this kind of landing (youtube link.)


As I understand it, small planes have to approach the runway with a nose-down attitude in order to maintain lift at their lower landing speeds because they don't have the extra lift surfaces that larger planes do, such as slats. They pull up in time to touch down (one hopes!)

For a passenger, this could be felt as a "dive", especially if they are used to feeling pushed back into their seats from a nose-up landing in a larger aircraft.
#20
Old 05-28-2008, 11:11 PM
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Quote:
Originally Posted by 633squadron
African or European?

ahem.

In the neighborhood of 100-150 mph.

The importance of speed (or lack thereof) in landings:

Several years ago, a DC-10 had to crash land in Kansas (Nebraska?) after an engine failure blew out all its hydraulics. It nearly made it, but the problem was it was coming in way too fast (the number 250 knots comes to mind). The pilots were controlling this plane just with the engines. It hit the ground slightly off-runway, flipped over, broke apart, and parts burned. Several people were killed, but many people made it.

A small plan has a much lower landing speed. I've been in a Cessna 172 several times where the pilot literally had to dive the airplane into the ground in order to land. The headwind speed plus the minor speed of the airplane was keeping it in the air like a kite!
While the speed of United 232 for sure did not help, it was not the cause of the plane breakup. After the loss of all hydraulics, the plane was barely controllable via the use of the engines.
The pilots via some skill beyond that of mere mortal men, managed to regain some semblance of control and the ability to steer. The issue was that the plane was porpoising up and down over about 5,000 vertical feet. As they approached the runway, the plane decided to head down into another cycle. As they were way less than 5,000 feet up, they hit the ground short of the runway. Had they made it to the runway, the plane might have run off the runway and crashed, or might have run out of runway and crashed, or they might have been just fine, but this is unknown.
#21
Old 05-29-2008, 02:48 AM
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Quote:
Originally Posted by mnemosyne
As I understand it, small planes have to approach the runway with a nose-down attitude in order to maintain lift at their lower landing speeds because they don't have the extra lift surfaces that larger planes do, such as slats. They pull up in time to touch down (one hopes!)
Um... that's not the way I do it... (Well, I do touch down nose up...)

First of all, small airplanes are not somehow deficient in lifting surfaces - they weigh a LOT less and need less wing area. In fact, sometimes small airplane pilots use techniques like slips which reduce lift.

Lowering the nose actually maintains airspeed at low power, it does not reduce lift.

Fowler flaps as seen on Cessna 150's and 172's (as examples) they increase the wing area so yes, they do have devices to increase lift at low speeds.

Actually, if you didn't reduce lift from what is being produced at climb or cruise you won't come down, and coming down is an important part of landing, the trick being to do it in a controlled manner.

(As I am posting this at 2am I have a dreadful feeling this post won't look nearly as clear by light of day...oh well...)
#22
Old 05-29-2008, 05:02 AM
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Quote:
Originally Posted by mnemosyne
As I understand it, small planes have to approach the runway with a nose-down attitude in order to maintain lift at their lower landing speeds because they don't have the extra lift surfaces that larger planes do, such as slats. They pull up in time to touch down (one hopes!)

For a passenger, this could be felt as a "dive", especially if they are used to feeling pushed back into their seats from a nose-up landing in a larger aircraft.
There is no fundemental difference between how a large aeroplane and a small aeroplane is landed. They both need to be flown towards the ground and then "flared" so as to land a little nose up. Most common small aircraft have flaps that provide for plenty of lift, they also already have relatively high lift wings compared to a jet airliner. It happens that commercial pilots are generally taught to fly a 3 degree approach which is somewhat flatter than what a single engine pilot might fly, but a Cessna 172 can be flown on a 3 degree approach and many probably are. Another factor is that wing flaps alone will result in a lower nose attitude because they effectively increase the angle of incidence which is the angle of the wing against the fuselage, slats on the other hand result in a higher nose attitude because, although they increase lift like flaps do, they actually lower the angle of incidence. For this reason, a jet with a high speed wing that requires a lot of high lift devices including slats for approach and landing, does have quite a high nose attitude on approach compared to a light single engine aircraft with flaps only.

So your basic premise is correct, a normal approach in a light aircraft may feel steep compared to a larger aircraft, but it is not because the headwind is holding it airborne like a kite and it is not because they need to lower their nose to maintain lift at a lower speed (that's contrary, the nose needs to be raised to increase lift, not lowered.)
#23
Old 05-29-2008, 08:20 AM
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Quote:
Originally Posted by Broomstick
if you didn't reduce lift from what is being produced at climb or cruise you won't come down
It's true that you briefly reduce lift to start a descent. But during a normal descent, lift is exactly the same as during cruise or a steady climb - it's equal to the weight of the aircraft.


Quote:
sometimes small airplane pilots use techniques like slips which reduce lift.
When used during landing, the principal purpose of a slip is to increase drag, yielding a steeper approach.
#24
Old 05-29-2008, 11:15 AM
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Quote:
Originally Posted by 633squadron
A small plan has a much lower landing speed. I've been in a Cessna 172 several times where the pilot literally had to dive the airplane into the ground in order to land. The headwind speed plus the minor speed of the airplane was keeping it in the air like a kite!
Despite the other replies to this statement, I know what you mean. If the pilot of a small plane is approaching a runway in the presence of high and gusty headwinds, he rightfully SHOULD be flying much faster than a normal approach speed.

If I'm flying a "normal" approach speed of 65 knots in these conditions, what would happen if the wind speed dropped 20 - 30 knots ("gusty", remember?)? All of a sudden, I'm falling, not flying: I've stalled because my airspeed has just fallen below my stall speed. So I'm GOING to come in hot and steep and only reduce air speed when I'm over the runway.

I learned to fly in Sedona, AZ where strong winds are common. There were many times when I had to apply lots of power on final approach, where, in calmer wind conditions, I'd have had the engine at idle.

J.
#25
Old 05-29-2008, 06:53 PM
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Quote:
Originally Posted by 1920s Style "Death Ray"
There is no fundemental difference between how a large aeroplane and a small aeroplane is landed. They both need to be flown towards the ground and then "flared" so as to land a little nose up. Most common small aircraft have flaps that provide for plenty of lift, they also already have relatively high lift wings compared to a jet airliner. It happens that commercial pilots are generally taught to fly a 3 degree approach which is somewhat flatter than what a single engine pilot might fly, but a Cessna 172 can be flown on a 3 degree approach and many probably are. Another factor is that wing flaps alone will result in a lower nose attitude because they effectively increase the angle of incidence which is the angle of the wing against the fuselage, slats on the other hand result in a higher nose attitude because, although they increase lift like flaps do, they actually lower the angle of incidence. For this reason, a jet with a high speed wing that requires a lot of high lift devices including slats for approach and landing, does have quite a high nose attitude on approach compared to a light single engine aircraft with flaps only.

So your basic premise is correct, a normal approach in a light aircraft may feel steep compared to a larger aircraft, but it is not because the headwind is holding it airborne like a kite and it is not because they need to lower their nose to maintain lift at a lower speed (that's contrary, the nose needs to be raised to increase lift, not lowered.)

Ok, so I messed up the physics of it

I work near the airport, and pretty much watch airplanes land all day long, and without a doubt the smaller planes (business jets and smaller) have a nose down attitude on approach. They are still nose down as they pass over Hwy 13 (Autoroute Chomedy: seen here The Q-series Bombardiers tend to look relatively level or slightly nose-up, and CRJs, Airbuses and Boeings are definitely nose up.

A Bombardier employee (retired engineer) also once told me that the lack of slats is why the Challenger 605s and 300s approach nose-down.

I just put that together and wrote my above post. Clearly incorrectly, but still based on some facts! I think it does explain the feeling of "diving" towards the runway, though.

Thanks (and to the other posters too!) for the clarifications... I love learning about this stuff, but I admit I really don't know much!
#26
Old 05-29-2008, 07:22 PM
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Quote:
Originally Posted by mnemosyne
Thanks (and to the other posters too!) for the clarifications... I love learning about this stuff, but I admit I really don't know much!
No worries. Some small aircraft do have slats by the way. This NZ built de Havilland Tiger Moth* has leading edge slats on the outboard sections of the top wing that deploy automatically at low speeds.

*Tiger Moths were built by several countries during WWII including Canada, Australia, New Zealand, and of course the United Kingdom.
#27
Old 05-30-2008, 10:05 AM
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Years ago I took some flying lessons with an eye toward getting my private pilot license. I started off flying a Piper Tomahawk which is a very small, low-wing aircraft. Landing it pretty much involved cutting power, lifting the nose to scrub speed and drop like a rock, then levelling off to touch down for the landing.

Sometime later I switched to a high-wing Cessna 172. I tried to land it the same way, but it just would not come down with a nose-up attitude. Those things generate so much lift, you have to point the nose at the ground and fly it all the way down, then level off to land. Different planes, different configurations, totally different approach techniques.

The thing is, in all cases, your landing speed depends on the flight characteristics of your aircraft (ie stall speed) plus current wind conditions. Your airspeed as you come in for landing MUST be a little bit above your stall speed+maximum headwind gust speed because, as mentioned above, any slower than that and if the wind suddenly dies down, you fall out of the sky.

My dad was once flying into New Orleans just ahead of an incoming hurricane. Windspeeds were in the 50-60mph range at the time with higher gusts, and he was on a jet with a normal landing speed in the 150mph range. They had to land at over 200mph indicated airspeed just in case they hit a sudden calm. He claims it was rather exciting to come in that hot.
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