What is the speed of, let’s say, a boeing 747 when it lands on the runway before the breaks are applied?
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.
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.
More info on point: What is the slowest a 747 can fly? - Factual Questions - Straight Dope Message Board
But what if it’s landing … on a treadmill ?!?
sorry - couldn’t resist
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%.
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.
Unless it’s a crash.
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.
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.
African or European? :rolleyes:
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!
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.
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!).
That’s the correct speed in Flight Sim, FWIW.
Sioux City, Iowa: United Airlines Flight 232.
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.
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.