Questions tagged [airspeed]

The speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed ("IAS"), calibrated airspeed ("CAS"), true airspeed ("TAS"), equivalent airspeed ("EAS") and density airspeed.

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80
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14answers
40k views

What is the slowest fixed-wing airplane?

It's easy to find information about the fastest airplanes, in different categories (e.g. X-15, SR-71, the Concorde etc), but what is the slowest one? Which powered, manned airplane is capable of ...
35
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8answers
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What happens if you exceed the maximum speed on a C172?

The airspeed indicator has a red marking that means: "never exceed this speed" ($V_{NE}$, around 160 KIAS). Why can't you exceed that speed?
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6answers
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Why does Airbus not display the exact airspeed on the PFD?

On every other PFD (I know), the exact airspeed is displayed as big number on the PFD. To clarify what I mean, here are two pictures: Source, added square, Boeing PFD Source, added square, D10A EFIS ...
29
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3answers
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How does a Mach Meter determine the speed of sound at a given altitude?

By my understanding, the Mach Number at a given altitude is calculated by dividing IAS by the speed of sound at that altitude. So how is this speed of sound calculated to display the Mach Number on ...
28
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8answers
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Does a sudden drop of the velocity of the headwind affect the airspeed by lowering it?

I had a discussion about air speeds with one of my instructors recently. He is claiming that there is a sudden drop in the wind velocity as you get closer to the ground (which is absolutely true, due ...
27
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1answer
14k views

Is there any equation to bind velocity, thrust and power?

I am designing a remote controlled airship. I will tune it so that the lift given by Archimedes' Principle will exactly balance the weight of all the structure. It will be propelled by brushless ...
26
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3answers
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Why are planes slower at higher altitudes?

On many flight simulators, I have noticed that planes tends to get slower with increasing altitude. For example, I can reach 1100 knots just above the sea level in Google Earth flight simulator(F16), ...
24
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1answer
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Do Air Traffic Controllers have to remember stall speeds for different aircraft?

While dealing with Takeoffs and Landings controllers provide speeds to pilots for different phases of the flight, specially during a landing approach. How do they know which speeds are safe for all ...
22
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1answer
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How does exceeding the critical Mach number of an aircraft affect its operation?

If an aircraft exceeds its critical Mach number, does it affect the way the aircraft is handled? Are there any significant changes to performance or the safety of the aircraft when above this speed? ...
20
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5answers
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Why is there a difference between GPS Speed and Indicator speed?

I just played with flight simulator and noticed that the GPS shows different speed from the speed indicator in the cockpit. Also, GPS speed is higher than the Indicator. Any Idea why?
20
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2answers
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What is a jet (unit) shown in Windows 10 calculator? [closed]

From Windows 10's calculator: What is a "jet" (physical unit)? And why does it equal 480 knots or 888,88 km/h, if a jetliner's cruising speed is around 950 km/s? Or why does it equal 0.73 M, if a ...
20
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5answers
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Why do fighter jets land faster than Jumbo commercial aircraft?

From my own understanding, the bigger (and heavier) aircraft, the higher approach speed it needs to keep itself from stalling. According to this site, the approach speed of an A380 is 140 knots, and ...
20
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2answers
15k views

When can spoilers be used on airliners?

On airliners, are spoilers used in any part of flight other than landing?
20
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3answers
4k views

What is the reference used when measuring flight speed?

I'm a physicist who was amused by the argument in the comments of this question about gravity. The correct answer about the affect of the accelerating reference frame of the plane on the apparent ...
19
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2answers
40k views

What is the reason for changing the speed reference (IAS or Mach number) with altitude?

Inspired by that question: How is the airspeed-Mach number transition handled in modern airliners? When pressure and density decrease IAS also decreases. When temperature and pressure/density ...
18
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6answers
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Would a slower speed and lower altitude reduce fatal incidents?

If it became plausible to fly commercial aircraft much lower in the future (due to developments in technology and airway regulations permitting it), say at a standard height of 5,000ft, but with a ...
18
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5answers
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Why does the speed of commercial airliners fluctuate, sometimes as high as 1,060 km/h or as low as 800 km/h?

I've noticed that (long-haul) airliners sometimes travel at as high as 1000 km/h (I believe I've even seen 1040 km/h), but usually they fly closer to 800 km/h, for most of the trip. This seems odd ...
18
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5answers
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What aircraft fly faster than 250 knots indicated airspeed under 10,000 feet for safety reasons?

14 CFR 91.117 limits aircraft to 250 knots indicated airspeed below 10,000 feet, but 91.117(d) allows aircraft to fly a higher speed if the minimum safe speed is higher. What aircraft and aircraft ...
18
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2answers
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Why did the Solar Impulse flight take so long?

The Solar Impulse just made big news for flying from Japan to Hawaii on a solar-powered plane in five days. But five days seems really long. Let's do the math on that. The distance from Japan to ...
18
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3answers
8k views

Why do some military aircraft use variable-sweep wings?

There are a couple of American military aircraft (the retired F-14 and the B-1 come to mind immediately), that have variable swept wings. I know that they keep the wings full out (roughly ...
17
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7answers
6k views

Is it possible to accurately measure airspeed without pitot tube?

This is a follow-up to my previous question: How does this IMU work and how to convert its output into meaningful information? for which many people asserted that I need a pitot tube and a static ...
17
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1answer
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SR-71 flew 2193 mph. How can this mathematically be Mach 3.3?

Virtually every time I read about the Lockheed SR-71 (including other threads on this forum), I see that its speed record is listed as approximately 2193 mph. The same blurb will invariably say this ...
16
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3answers
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What are CAS and EAS used for?

What are calibrated airspeed (CAS) and equivalent airspeed (EAS) used for? When would a pilot need to know these?
16
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1answer
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Why are speed restrictions imposed for flights flying below 10,000 ft?

I know that restrictions do not always apply and ATC can cancel them or pilots can request for speed restriction being canceled. But why is there such a speed restriction in first place? Are there any ...
15
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6answers
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Why is indicated airspeed rather than ground speed used during the takeoff roll?

My instructor asked me this question during my lesson and I couldn't come up with any answers. He asked why do I need to look at the indicated airspeed rather than ground speed when in takeoff roll or ...
15
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6answers
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What is the commercial passenger aircraft top speed record?

Aircraft manufacturers claim that commercial passenger aircrafts cruise at the speed of 400-500 knots. But, is the top speed of a commercial passenger aircraft recorded (while in air)? If so, what is ...
15
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1answer
4k views

Why is a 737 Original speed-restricted below 10 kft with inoperative windscreen heating?

According to this page on the 737's operational limitations, the Original 737s (737-100/-200) are limited to 250 KIAS below 10 kilofeet if the windscreen-heating system is inoperative: Anti-Ice & ...
15
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3answers
2k views

Is trimming for constant speed equal to trimming for constant angle of attack?

My understanding of trim: When you say you have trimmed an aircraft for a constant speed, say 100 mph, you are actually trimming the horizontal stabilizer so that there are no forces on stick (or tail ...
14
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4answers
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Why would 2 aircraft fitted with the P&W PT6 Engine have different top speed?

Why can the Quest Kodiac and Cessna Caravan not exceed 200 knots? PT6 from Pratt and Whitney in other implementations like Epic E1000 and Pilatus PC12 can cruise at over 300 knots. The Kodiac and ...
14
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3answers
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Why must Vr be set so precisely?

Why must VR (Rotation Speed) be set so precisely? I mean why can't they just say: Rotate the Aircraft at 120 to 150 knots And then, the pilot thinks: OK, I have a full plane and half full tanks,...
14
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5answers
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Is the Mach number shown by an Air Data Computer considered a “true” Mach number?

I am trying to find more information on "true" vs. "indicated" Mach number (not airspeed). I've found older fighter aircraft manuals online that have a conversion chart from one to the other, but the ...
14
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2answers
7k views

How does an energy variometer work?

In a comment to an answer regarding instrumentation complexity, an "energy variometer" was mentioned, labeled in knots. What does this dial actually show, and how does it work? The image accompanying ...
13
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9answers
70k views

Does a plane have brakes to stop or slow down while flying?

Does a plane have brakes to stop or slow down while flying? For example, if the pilots see a large flock of birds at some distance in front of the airplane, and they want to reduce speed suddenly. ...
13
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7answers
7k views

What is the fastest possible transatlantic flight today?

I'm working on a novel that, as part of the backstory, requires samples of a biological agent to be flown from Incirlik Air Base to labs across Europe, and then finally from the UK to the US. In the ...
13
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3answers
13k views

How to determine aircraft altitude and speed, as a passenger?

Is it possible for a passenger to determine the aircraft's altitude and or speed or location using any mobile apps. Not all airlines have displays with constant info about this. I had tried using ...
13
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5answers
5k views

What will the pilot do if all the airspeed indicators fail?

Are there any alternate instruments to indicate the airspeed in case of pitot tube failures?
13
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2answers
844 views

Is there a surface of a commercial jet exposed to air flow at speed near Mach 1?

With commercial aircraft flying slightly above Mach 0.8, is there any surface exposed to speed of air significantly larger, e.g. near Mach 1? ignoring: The engine components, The boundary layer as ...
13
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2answers
7k views

What is the actual air speed over and under a wing due to Bernoulli's Principle?

Bernoulli's Principle states that as a fluid speed increases, its pressure decreases, and vice versa. Air flowing over the wing of an aircraft flows faster than its neighboring air flowing under the ...
12
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3answers
2k views

Is it possible for a plane to accelerate easily from 30 to 45 mph in flight while it struggles to reach 30 mph (the engine runs at constant power)?

In two letters sent to Dr. G. A. Spratt (an aviation enthusiast), Wilbur Wright reported the progress he and his brother had made, up to September 10, 1904, regarding Flyer II, a plane powered by a 16-...
12
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2answers
3k views

Is it quiet in the cockpit when flying faster than the speed of sound?

Is it quiet in the cockpit when flying faster than the speed of sound or is the noise from air resistance just too loud? Similar question: is it quieter at the front of an airliner flying faster ...
12
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1answer
17k views

Are there limits to speeds at certain altitudes?

Are there speeds that cannot be exceeded at certain altitudes?
12
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1answer
7k views

What protection does Vno provide?

VNO, the airspeed where the green and yellow arcs meet on the airspeed indicator, is the "maximum structural cruising speed" (FAR 1.2). An airplane should only be flown above VNO in calm air. ...
12
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3answers
2k views

Why do aircraft have a crossover airspeed, and why does it increase at higher vertical load factors?

According to the NTSB accident report on the crash of USAir Flight 427, all commercial aircraft have a crossover speed (the speed at which the maximum rolling force from the aircraft’s ailerons and ...
11
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2answers
2k views

Why is the initial short-field climb below Vₓ in a Cessna 172?

Short-field takeoff procedure for a Cessna 172R is Wing Flaps – 10°. Brakes – APPLY. Throttle – FULL OPEN. Mixture – RICH … Brakes – RELEASE. Elevator Control – SLIGHTLY TAIL LOW. ...
11
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2answers
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Is there a maximum airspeed to deploy a ram air turbine?

Is there any airspeed limit for deploying a ram air turbine? Can airspeed be determined from the rate of its propeller rotation? Could that data be used to determine altitude?
11
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3answers
3k views

When a plane flies faster than the speed of sound, does the distance between plane and sound increase?

I had this discussion with my dad about a question he had asked. Basically he said: If a plane flies faster than the speed of sound, will he be able to overtake his own sound and hear itself? (let'...
11
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2answers
3k views

What is the fastest recorded backward flying plane?

It is a well known fact that some planes like the Antonov An-2 can fly backwards since their stall speed is lower than the speed of the winds they can stably fly into. My question is what is the ...
11
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2answers
6k views

How (and why) does engine thrust change with airspeed?

I'm interested in how the thrust of a turbofan engine is affected at higher airspeeds (TAS). I know (I believed) that engine thrust(at constant N1) was relatively constant like in the following graph (...
11
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2answers
2k views

What alternatives to pitot static systems are available or in development?

Air France 447 is a powerful example of what a serious situation unreliable air data indications can be if not handled properly by a crew. Still, whether crews are properly trained or use that ...
10
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6answers
4k views

How does it feel like to be outside a flying airplane?

Riding a motorcycle on a freeway at over 200 kph you surely feel the rush of air around you. A typical commercial jet airliner travels at approximately 3-5 times that speed at cruise altitude. ...

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