- 1.How does the Instrument Landing System (ILS) work?
- 2.EU Blacklist – Beware of these Airlines!
- 3.Flight Management System (FMS) – The Aircraft’s Brain!
- 4.Freedoms of The Air Explained – Can an Airline Fly Anywhere?
- 5.Winglets and Sharklets – Wingtip Devices Explained!
- 6.V Speeds – Aircraft Velocities Explained!
- 7.World’s Safest Airlines in 2018 Revealed!
- 8.Airbus A320 Cockpit – MUC to CGN Jumpseat Experience!
Howdy, dear readers. I hope, that all of you have had a nice Christmas among your beloved ones. Mine surely was great! After several days of feasting and unwrapping gifts, it’s time for some aviation knowledge again, don’t you think? That is why today’s article will be all about the so-called V Speeds in aviation. I will try to explain the most important aeroplane velocities to you. These are speeds such as the V1, the Vr speed, as well as the Vref speed. So, as always: Buckle up and enjoy the ride!
V Speeds Explained – V1: The Decision Speed!
Aircraft use, as all of you, should know already, runways to take-off and land. Unfortunately, those runways are not infinitely long. Moreover, pilots have to abort the take-off run every now and then for different reasons. That can be the case if an engine fails, a tire bursts or the captain decides that he needs more coffee ;).
If such an emergency occurs, the pilots decelerate the plane on the runway by using the plane’s brakes, spoilers and reverse thrust. This only holds true before the aircraft has reached one of the most known v speeds, namely V1!
V1: The Point of No Return!
V1 is the maximum speed at which a rejected take-off is still safe. After V1 is reached, the take-off run would be continued (almost) no matter what. Exceptions to that rule would be large system failures, or an uncontrollable aeroplane, e.g. because of a wing that falls off or a great fire, for instance.
A simple reason for not rejecting the take-off after V1 is that the aircraft cannot be brought to a full stop without the use of reverse thrust on the runway safely after having reached this v speed. Yes, you heard that correctly. It is safer to take-off with, for instance, only one running engine than to try to abort the take-off past the point of no return.
Modern aircraft have no trouble to safely fly and land with only one engine running. An aeroplane is, after all, built to fly and not to wheel over a narrow strip of concrete at ridiculous speeds! Furthermore, to break down the plane past V1 stresses the tires and brakes enormously. They can even catch fire quickly.
Vr Speed – The Rotation Speed!
The take-off run is in full swing, we are way past V1: Let’s rotate! But what does “to rotate” mean in aviation? This is very simple. “Rotating” describes the process in which the pilot gently pulls back the yoke (or side stick) of the aircraft to lift the nose gear off the ground. This “rotation” happens at the so-called rotation speed, or Vr.
In order to prevent a tail strike, the pilot flying should avoid pulling the yoke too abruptly. A good rule of thumb is to lift the nose by approximately 3° per second. This rate, of course, differs from plane to plane. The exact rotation point is reached when the nose wheel leaves the ground.
V2 Speed – The takeoff safety speed
We have already discussed two important V speeds in this article. V1 and Vr. Now it is time to get airborne. The V2 speed is the minimum velocity that is required to safely climb even with one engine off. Until a plane reaches the “acceleration altitude” this speed is, most of the time, V2+10 knots.
But when is the gear retracted? Simple as that: As soon as the Primary Flight Display (PFD) shows a positive rate of climb. The pilot not flying calls “positive rate”. Thereupon, the pilot flying orders “gear up”, what is then executed by the pilot not flying. By the way. All the speeds like V1, Vr and V2 depend on several factors like the aircraft’s weight, the wind conditions, as well as the airport elevation, for example.
V Speeds – The Acceleration Altitude
After lifting off the ground safely and at 1.000-1.500 ft above the ground (differs from airline to airline), the pilots reduce the thrust from take-off thrust to climb thrust. This climbing thrust is, in most cases, a bit lower than the thrust required for take-off. This has the purpose to go easy on the engines since they suffer quite a bit if they would operate at take-off thrust continuously.
At the same time, the pilot flying lower the nose of the aircraft a bit in order to accelerate from V2+10 knots, which is around 140-165 knots the most mid-sized airliners, to a maximum of 250 knots below 10.000 ft. While the aircraft accelerates, the pilots retract the flaps step-by-step, until the aircraft is in a “clean configuration” for cruise. A clean aircraft, in this case, does not mean a well groomed and shiny aluminium can. In a clean configuration, the aircraft’s flaps and gear are fully retracted.
The Vref Speed – The Final Approach Speed!
Time to get back on the ground again! The final approach speed is also denoted as the Vref speed. This speed is directly related to the aircraft’s gross weight since Vref is derived from the plane’s stall speed. But there are also other important factors to determine the final approach speed. Here are some of them:
- The plane’s Gross Weight
- The wind direction and speed
- The flap setting
- Weather conditions (e.g. icing)
- And some more!
The final approach speed is based on the reference speed, Vref. This speed is calculated in the following way:
After Vref is clear, one adds a correction component to the reference speed to compute the final approach speed. Those airspeed corrections take operational factors such as wind and icing conditions into account. By doing so, one achieves a great compromise between the distance needed for landing and the aircraft’s handling quality.
Not all corrections are added to the Vref at once, however. Pilots only take the largest correction into account and add it to the Vref for the final approach speed. I will not go into detail too much here. For further reference, this PDF offers a great read.
The Best Glide Speed (Vg)
Pilots have bad luck sometimes. Having said that, I can happen, that not only one, but all of your engines flame out. Fortunately, no plane will just fall off the sky like a rock immediately as a consequence. Modern aeroplanes can glide pretty long. But how can a pilot determine the speed with which he or she can glide as long as possible without engine thrust? That is where the “best glide speed” comes into play.
The faster an aircraft flies, the more lift it produces. On the other hand, the wing will also produce more drag, the faster it goes. Of course, the opposite does also apply. The slower the aircraft goes, the less drag and lift it produces. The best glide speed is, consequently, the speed with the optimum ratio of a drag as low as possible a lift as high as possible at the same time. By flying at the best glide speed, or Vg, the pilot makes sure to gain as much time as possible to find a place to land if all engines have failed.
Other V Speeds!
In the following, I would like to discuss some more important velocities that I did not mention before. Among those are, for instance, Vno, Va, as well as Vle!
Vno – The Speed of Normal Operation
The following V speeds mainly find application in smaller general aviation aircraft. Let us start with Vno or the Velocity of Normal Operations. The speed is the top of the green arc of an aircraft’s airspeed indicator. Vno is the so-called “maximum structural cruising speed”. Flying at or below this speed makes sure, that the aircraft can withstand strong gusts without any damage to the structure.
Vne – Never Exceed!
Take care! Vne is the velocity you never exceed! Going beyond One can become very dangerous, since going past Vne can result in destructive fluttering and cause serious damages to the aircraft’s structure and result in accidents.
Va – The Aircraft Maneuvering Speed!
Va is the aircraft’s maneuvering speed, or, more exactly, the velocity of acceleration. At this speed, the pilot flying should avoid too abrupt movements of the yoke. It is recommended to fly at or below Va in turbulence.
Vle – The Velocity of Landing gear Extended
One should not extend the landing gear when flying above the Vle velocity.
Cessna 172 V Speeds as an Example
In the previous sections, I have explained the most important and common V Speeds to you. Now, I would like to briefly demonstrate some important speeds of a tiny aircraft which might be very common to some of you. The Cessna 172. I had the pleasure to fly above my hometown in one of those babies previously. You can read more about this trip here!
- Vno: 129 knots
- Vne: 163 knots
- Enroute Climb Speed: 75-85 kts
- Vx (best angle of climb): 62 Kts
- Vy (best climb speed): 74 knots
- Vr: 55 knots
- Vg: The Cessna 172’s best glide speed is 68 knots
V Speeds: A Conclusion!
There are countless more V speeds in aviation, that help pilots to operate their aircrafts safely. This article just offers a quick overview of them. The author does not have the intention to provide all of them, since this would let the frame of this post burst a bit. I hope, however, that I could help you to get a nice overview over this interesting topic.
If you want to find out more about the aviation system and learn something new about the matter every week, feel free to subscribe to my newsletter.
Also, you might find some other articles of mine interesting.
- How does the instrument landing system work?
- What are the freedoms of the air?
- What does a working day of a Lufthansa 747 pilot look like?
Have a great day, Aaron