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Do Aircraft Become Airborne Before V2?  
User currently offlineXXXX10 From United Kingdom, joined Jan 2000, 777 posts, RR: 0
Posted (12 years 4 months 2 weeks 3 days 20 hours ago) and read 2726 times:

Can anyone help?

Do aircraft leave the runway before reaching V2 speed, if so do you allow the speed to build up to V2 before pitching up any further

While at take off power would an aircraft continue to accelerate if the pitch angle was not increased?

Many thanks for all replies

6 replies: All unread, jump to last
 
User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 1, posted (12 years 4 months 2 weeks 3 days 19 hours ago) and read 2690 times:

Dear XXXX10 -
V1 is the speed at which the decision is made to abort the takeoff, and stop the airplane on the remaining length of the runway... or continue the takeoff.
VR, is "rotation speed", the speed at which the pilots move the nose in the "up position" some 8 to 10 degrees initially, depending type of aircraft to achieve lift and leave the ground...
VLOF is lift-off speed, a few knots higher than VR, say some 5 knots or so, when the aircraft leaves the ground... and further increase of nose up...
V2 is reached by 35 feet above the runway on departure... It is the speed to climb out at, if an engine failed after the V1 decision speed...
In a "no problem takeoff" the target climb-out speed is V2+10 kts initially...
xxx
To give you an idea about "speeds", this is for a 747-200/300 series, the V1-VR-V2 are, with 10 flaps -
167 - 178 - 188 at maximum gross weight of 377,000 kg (833,000 lbs)
132 - 142 - 160 at a light weight of 290,000 kg (640,000 lbs)...
In the examples given, I would say, the lift-off speed would be probably some 180-182 knots for the heavy takeoff, and 145 kts in the instance...
And yes, the speed would increase if the pitch is not increased...
xxx
xxxx10, a fellow countryman of yours, D.P. Davies of the CAA, wrote a masterpiece, titled "Handling the big jets", it has been my bible for most of my airline pilot career... I acquired my "third edition" at Foyle's, Charingcross Rd, near Trafalgar Sq.. London... If you wish to educate yourself in the flying and handling of airplanes, that gentleman is a scholar, and when in doubt, I read his lines. It is the best book ever written, on the subject of airliners, let the Yanks educate theirselves with "Sporty Pilot Shop" academy (McDonald style) textbooks... Cheers...
(s) Skipper



User currently offlineBroke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 2, posted (12 years 4 months 2 weeks 3 days 15 hours ago) and read 2649 times:

While I am not a professional pilot, I endorse "Handling The Big Jets". The name makes it sound (to me) more like a child's book , but it gives the reader an excellent idea of what it takes to fly a jet transport and the differences between the jets and the props. It is an important book in my library.
A note on V2. It is predicated on Vmc, which is the minimum control speed with the critical engine failed that an airplane can be flown. In flight, and airplane has 3 Vmc's; the lowest is with the airplane banked away from the failed engine, next is the speed with the wings level, third is the speed required to maintain control with the airplane banked in the direction of the failed engine. This third speed is the speed that the airplane should be flown at in order to be able to meet all circumstances.


User currently offlineXXXX10 From United Kingdom, joined Jan 2000, 777 posts, RR: 0
Reply 3, posted (12 years 4 months 2 weeks 3 days 14 hours ago) and read 2638 times:

many thanks, I had borrowed the book you mentioned but must have forgotton that passage.

User currently offlineTAA_Airbus From Australia, joined Nov 1999, 726 posts, RR: 0
Reply 4, posted (12 years 4 months 2 weeks 3 days 13 hours ago) and read 2633 times:

Am I right in saying that V2 is the speed at which the plane will fly and climb, where as VLOF will get you off the ground, but is more attributed to ground effect?

And do you yell out V2? Or is V2 confirmed by checking for +ROC?

TAA_Airbus hasnt bothered to read CAO 20.7.1 Bravo yet.


User currently offlineJetguy From , joined Dec 1969, posts, RR:
Reply 5, posted (12 years 4 months 2 weeks 3 days 12 hours ago) and read 2630 times:

Skipper,

It seems that, as with most things associated with aviation, there is some room for at least a little discussion. It seems that the definition of V1 is based on geographical considerations. There is the FAA definition and the JAA definition - and they are very different.

Thanks to the miracle of "cut & paste", I've inserted the definition of V1 as contained in Part 1 of the FARs (OK, I know that they are now known as 14 CFR...):

V1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

Here's the reference so you can check it out yourself: http://ecfr.access.gpo.gov/otcgi/cfr/otfilter.cgi?DB=3&query=14000000001®ion=BIBSRT&action=view&SUBSET=SUBSET&FROM=1&SIZE=10&ITEM=1#Sec.%201.2
Scroll down to Section 1.2

The point is that if V1 is the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance, then the decision to abort or continue the takeoff must be made at some point prior to reaching V1 in order to allow for pilot reaction time.

For the rest of the world, the JAA definition is very simple: "V1 - Takeoff decision speed"

The actual calculation however, in terms of Accelerate-Stop distance (JAR 25.109), is that the aircraft may:

"...continue acceleration for 2 seconds after V1 is reached with all engines operating (and) come to a full stop from the point reached at the end of that acceleration assuming that the pilot does not apply any means of retarding the aeroplane until that point is reached."

So under JAR a two second gap is permitted on reaching V1 before the pilot does anything, to allow for the decision to be made. The continued acceleration of the aircraft from that point is also allowed for, with both engines operating, for 2 seconds (a long time in aviation).

We're talking more than semantics here. By regulation, U.S. pilots, flying U.S. registered aircraft are required to comply with the MORE restrictive of either the FARs or the local regulations, if they are operating outside of domestic U.S. aiarspace. I think that it could be argued that the FAA definition is more restrictive, hence this is the one that I am compled to use. For Skipper and the other pilots flying for non-U.S. companies, I would assume that the JAA definition would apply.

TAA Airbus...
VLOF is merely the speed at which the airplane becomes airborne. As far as the flightcrew goes, it's not even "part of the takeoff equasion". In other words, it just happens. What the flightcrews do call is VR. When the "Rotate" call is made the PF (pilot flying) simply raises the nose. The airplane will liftoff when it achieves a sufficient angle of attack.

V2 (Takeoff Safety Speed) is the speed that you will have at 35' agl - in the event of an engine failure at or before V1. You maintain that speed until you have 400' agl and are clear of any immediate obstacles. (However, if you manange to have a speed faster that V2 you wouldn't want to allow it to bleed off - would would maintain whatever you had.) Once you are clear of the obstacles you enter the 3rd segment or acceleration phase of the where the aircraft is allowed to accelerate Vfto or Final Segment Takeoff Speed. As the aircraft is accelerating it is cleaned up appropriately as the various speeds are achieved. Under normal operations (all engines operating) V2 is of little interest to the crew - the airplane is acelerating like the proverbial "raped ape" - and it blows through V2 in very short order.

Jetguy


User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 6, posted (12 years 4 months 2 weeks 3 days 8 hours ago) and read 2577 times:

Dear Jetguy -
The original question was about airplanes "flying" before V2, I thought XXXX10 would like to have known about these V1, VR and V2 speeds, and give him some speeds from my pilot manual... obviously we all can make a simple one line few words definition of V1... and what you do with that value in practice. Put a question on that subject, it will never run out of answers... or discussions... During classroom recurrent training I avoid the subject of V1 as, each time we would spend the rest of the afternoon discussing it, dismissing the class a hour too late, and not making it on time for happy hour...
xxx
I just stated that indeed, airplanes leave the ground shortly before V2...  Wink/being sarcastic
(s) Skipper


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