V2 Speed - Definition?
 

Does anyone have a concise definition for the V2 safety speed?
Just as a reply to an interview question or something like that.

The airspeed an aircraft is at 35 feet on Takeoff.

Why is it there? It is at which speed, following an engine failure at V1, the aircraft must be capable of climbing and retracting the gear.

That's the concise version!

nice one Lancer,

I really didn't fancy digging out my Performance file to dig that up.

ta.

It's the speed at wich an aircraft must be when arriving at screen height to be able to continue climb on one engine in take off climb configuration.

Screen height can be lower or higher than 35 ft depending on conditions and type of aircraft....

Courtesy of the pprune search engine!!

read this

I seem to recall a definition of 'Minimum free air safety speed', ie, the lowest speed in TO configuration that you can suffer a worst case engine failure and still retain directional control. I don't have my 'Handling the Big Jets' tome (good one DP Davies, RIP) to look up.

The Interview Answer
 

V2, the Take Off Safety Speed, is the lowest speed at which the aircraft complies with the handling criteria associated with climb after take off, following the failure of an engine.

V2 is also defined as the target speed to be attained at the screen height with one engine inoperative and is maintained to the point where acceleration to Flap Retraction Speed is initiated. :ok:

Notso,

Sounds like you're thinking Vmcg and Vmca - minimum control speeds ground/air. Vmcg MUST be before V1 for obvious reasons.

V2
 

126.9, You almost got it,change the word INITIATED to ATTAINED.
There ye go.

There is a whole Thesis envolved ,the big question is,what happens between just after V1, and not yet "Attaining" V2.

:ok:
Now where's my pint.

Crack
 

You've got to stop smoking that stuff mate! Perhaps your time with Iosopata has confused you even more on the green & gold island..? The words INITIATED and ATTAINED were both used correctly, in the correct places and I've personally checked my thesis to confirm that! To answer your question: Vr comes between those two along with a possible host of other performance dependant speeds. Cut back on the pints mate, you can see where it's got me and it's not pretty ... :}

TAKEOFF safety speed.

Yes, V2 is thus.

Some with more distant memories (and experience) will recall that all piston engine powered transports, as well as many turboprops, attained V2 prior to rotation...ie; while still on the runway.
In addition, the screen height was fifty feet, not 35.

The change made for transport jets was made to CAR4b (leaving aside the Comet and the ARB fiasco attached thereto) for one very simple reason...V2 while still groundbound, and the 50 foot screen height were absolutely not achieveable in the early underpowered jets of yesteryear, without excessive speeds (and the associated tire problems)...not to mention the large runway requirements (length) attached thereto.

And yes, speaking BOEING jets here.
Specifically the early -121 series 707's
A heap 'o cr@p, if there ever were any...for sure.:yuk:

V2-green & gold.
 

126.9: Green & Gold, Green & Gold???????you did say Tarawa?.
Your Thesis, WHO marked it?
Maybe you could point out to ALL of us,just where V2 begins and ends, and how do you get there.
Initiated Vs Attained.
411A,747FOCAL,& BOAC,love you guys.

Now I will go and have another pint mate?and you where never pretty.:ok:

Crack
 

1. Green & Gold - YES! Vic Bitter = Green & XXXX = Gold! :p

2. UNSW - Sydney.

3. V2 begins and ends at V2 for any particular departure. Any deviation from the SELECTED V2, is a V2 plus or V2 minus deviation. Considering that V2 is the speed to which the aircraft, with one engine inop, must accelerate after rotation at Vr and lifting of at Vlof appropriate to the prevailing conditions, then V2 selection may begin at V2min which is the lowest speed that V2 may be in any ambient conditions or any configuration. In terms of CAS V2min may not be less than:

i) 1.2 Vs for:
a) Two and three-engined turbo-prop a/c and,
b) Turbo-jet a/c without provisions for obtaining a significant reduction in the one engine inop stalling speed.
ii) 1.15Vs for:
a) Four-engined turbo-prop a/c and
b) Turbo-jet a/c having provisions for obtaining a significant reduction in the one engine inop stalling speed.
iii) 1.10Vmc. JAR 25.107(b)

V2max (if you will) may be selected under the correct prevailing conditions, and would then be, V2 at Flap 0 taking into account all of the above: therefore the CONFIGURATION criteria is stated. It is of course worth bearing in mind that regardless of which V2 is selected for a particular departure, it needs to meet the above criteria AND then remains V2 for that take-off.

4. Once Flap retraction is commenced, the acceleration segment (and the basic principles of flight on most large aircraft) does not allow for V2 to be maintained. Therefore, V2 is also defined as the target speed to be attained at the screen height with one engine inoperative and is maintained to the point where acceleration to Flap Retraction Speed is initiated.

5. It is nice to see some male-bonding come out of the closet so openly!

6. On this point you are absolutely correct!

:}

Never mind the love bit, 'Crack'. Just give me some of what you are on.:D

what about Vmu ,anyone can explain it to me?

cheers.
RMM

minimum unstick speed .... absolute minimum speed at which the aircraft can be dragged off the ground ... tests normally done with a something suitable bolted to the tail ... lots of sparks and scraping noises ...

Have a look at this set of slides ... one shows a demo on 727.

Vmu:
Minimum Unstick: The minimum demonstrated speed at which it is possible for the aircraft to become airborne.

Screen Height:
The minimum height to be achieved by the aircraft over the end of the take off distance available.
Props: 50 feet
Jets Dry: 35 feet
Jets Wet: 15 feet

By the way, What does this mean?
"without provisions for obtaining a significant reduction in the one engine inop stalling speed"

Um, definition of screen height is??

Was this thread recently censored to exclude exchanges of trivial niceities? I notice at least two postings missing? Odd...

:}

yes if you want to e-mail each other feel free. Nobody else is interested.

(d) VMU is the calibrated airspeed at
and above which the airplane can safely
lift off the ground, and con- tinue
the takeoff. VMU speeds must be selected
by the applicant throughout the
range of thrust-to-weight ratios to be
certificated. These speeds may be established
from free air data if these
data are verified by ground takeoff
tests.

phnuff,

"Screen Height" is the prescribed certification height above the runway at which runway aspects of the takeoff (ie distances) are deemed to be completed. Sometimes used in respect of landing in a similar way - the height at which the landing distance measurement commences.

Originally 50 ft was chosen for both - reputedly a figure plucked out of the air by the early antecedents of the FAA. Supposedly this was based on some then recent military trials of an early biplane which had been demonstrated in/out of a particular parade ground which happened to be surrounded by trees of height approximating 50 ft. .. and why not ? .. as good a place to start the regulatory ball rolling as any.

Can't recall just when the 35 ft came into vogue for takeoff without digging into the dusty drawers but probably it was when the performance PAMC which predated CAR 4b surfaced. The extra distance associated with the more complex takeoff analyses was a bit too penalising were 50 ft to be retained. Those of us who have little hair, and/or significant grey portions of whatever hair we may have left will recall that the performance PAMC came in during the early days of the F27 and similar aircraft. The document marked a change from "simple" takeoff analyses to the more complex protocols we follow today which are based on a more rational and sound approach to risk management. I know I have a copy of that document somewhere in the archives ... somewhere.

Subsequently, wet runway screen heights nominally half the normal screen (rounded to 15 ft) came into the equation and the whole exercise continues to become more complicated but, at the same time, far more sensible.

Thanks John

Understood

747FOCAL, considering you would burn a large hole in the hull, is it really defined as "safe" ?