Factors affecting V1

[Canadian Beech]

I am searching for info on this subject... however I'm having problems with the search function on this site (not allowing me to search 'V1').
Anyone with a link to a thread would be greatly appreciated.
I am especially confused with certain factors that affect the accel in a negative way, but decel in a positive way (ie upslope)... would this increase, or decrease V1, and why?

Thanks in advance!
:ok:

[HotDog]

V1 adjustments:

Wet runway Reduce by 10 KTS
Slope Add 1 KT/1% UP Sub. 2 KTS/1% DN
Wind Add 1 KT/15 KT HW Sub.4 KTS/10 KT TW.

[BOAC]

CB - search characters on PPrune need to be more than 3. Try 'Vspeeds' or 'Runway Slope' and there should be loads of links for you.:D

[Keith.Williams.]

Many JAR ATPL students have a little bit of difficulty with this subject. The best way of approaching it is to start by going back to the definition of V1 then consider the implications.

If an engine failure is recognised at speeds below V1 the take-off must be aborted. To do this it must be possible to bring the aircraft to a stop within the remaining accelerate-stop distance available. The greater the V1, the greater will be the distance required to stop.

If an engine failure is recognised above V1 then the take-off must be continued. To do this it is neceassry to accelerate to V2 and reach screen height within the remaining take-off distance available. The greater the V1, the less will be the increase in speed that is required to reach V2 and the less the distance required to achieve this speed increase.

The above requirements mean that V1 markes the demarkation between being required to stop and being required to go in the event of an engine failure. This means that at V1 the aircraft must be equally capable of stopping or going within the remaining distances available.

Any factor (such as an upward slope) that decreases acceleration rate will increase the distance required to get from V1 to V2. If spare distance is not available then V1 MUST be increased making it closer to V2. This makes an increased V1 NECESSARY.

Any factor that increases decelertaion rate decreases the distance required to stop. So V1 may be increased and still permit the aircraft to stop. This makes an increased V1 POSSIBLE, but does NOT MAKE IT NECESSARY.

So an upward slope means that V1 MUST be increased to complete the take-off and MAY be increased without preventing an abort. The overall effect is that V1 MUST be increased.

The effects of other factors such as headwinds or tailwinds can be deduced in the same manner. After a bit of practice most students find this easier than trying to remember a long list of effects.

[mutt]

Hot dog...

V1 adjustments: Wet runway Reduce by 10 KTS

I presume you are talking only about the Classic B747?


Mutt.

[HotDog]

Yes, the data I quoted were for the 747 classic.

[corporal klinger]

has anybody knowledge about a consideration of the reaction time of the pilot?
I heard 1 second is implemented..

[dartman]

On a/c with an approved engine failure warning system, certification allows one second for the pilot to recognise the failure, and commence the RTO. On a/c that do not have a engine failure warning system, the allowance is 3 seconds. i.e. 727-100 / 707 etc. It must be stressed however, that this 1 (or 3 as the case might be) second allowance is not to allow the line pilot more time to assess the situation at V1. During certification, test pilots typically commence the abort 0.3-0.5 seconds after the failure. These are reaction times unlikely to be repeated in a line situation, so the times are built up in recognition of the fact that RTO's are a rare occurance, and line pilots not as spring loaded as the test pilot,

dartman

[tired]

Actually, dartman, I think I'm right in saying that the Europeans (ie JAA) changed it to 2 seconds some years ago. The FBW Airbusses were all certificated on 2 secs anyway. Don't know about the FAA.

[dartman]

I actually was thinking of FAA rules, but they should be similar, so I stand corrected. Too lazy last night to look it up....

d.

[macadam]

Jar 25.107 (a)
The time between Vef and V1 is 2 seconds.

[oldebloke]

actually gents the time for VEF prior to V1 is 'established' by the constructor....As you say this can be up to 3seconds in the failure of the Centre eng(slow recognition due to no Yaw)..VEF first issued in the AFM in 1978 due to insistance by the pilot conmunity(it had always been evident to the test /certification pilots),is about 1 second prior to V1..
And as FAR25-107 says must be recognized and reacted to prior/by V!(about 5knots acceleration)
AGAIN the 2seconds reaction time is built into the DISTANCE allowed for the ACC/stip runway case,not in the handling of the Stop case..:ok:
JAR25.107(a)(1)

For the FAA case go to FAA.GOV.go to AC25-7a for the flight test information
Aircraft Performance Theory by Stanton is good for JAR stuff:ooh:

[lomapaseo]

KW your reply makes perfect sense (to me) if I change a few words based on F=MA or

acceleration = F/M where both M and F are pretty much constant after you set power.

thus

Many JAR ATPL students have a little bit of difficulty with this subject. The best way of approaching it is to start by going back to the definition of V1 then consider the implications.

If an engine failure is recognised at speeds below V1 the take-off must be aborted. To do this it must be possible to bring the aircraft to a stop within the remaining accelerate-stop distance available. The greater the V1, the greater will be the distance required to stop.

If an engine failure is recognised above V1 then the take-off must be continued. To do this it is neceassry to accelerate to V2 and reach screen height within the remaining take-off distance available. The greater the V1, the less the acceleration (time) required to reach V2 and the less the distance ***********

The above requirements mean that V1 marks the demarkation between being required to stop and being required to go in the event of an engine failure. This means that at V1 the aircraft must be equally capable of stopping or going within the remaining distances available.

Any factor (such as an upward slope) that decreases acceleration *** will increase the distance required to get from V1 to V2. If spare distance is not available then V1 MUST be increased making it closer to V2. This makes an increased V1 NECESSARY.

Any factor that increases decelertaion rate decreases the distance required to stop. So V1 may be increased and still permit the aircraft to stop. This makes an increased V1 POSSIBLE, but does NOT MAKE IT NECESSARY.

So an upward slope means that V1 MUST be increased to complete the take-off and MAY be increased without preventing an abort. The overall effect is that V1 MUST be increased.

The effects of other factors such as headwinds or tailwinds can be deduced in the same manner. After a bit of practice most students find this easier than trying to remember a long list of effects.

From JAR 25.367

.........
(b) Pilot corrective action may be assumed to be initiated at the time maximum yawing velocity is reached, but not earlier than two seconds after the engine failure. The magnitude of the corrective action may be based on the control forces specified in JAR 25.397 (b) except that lower forces may be assumed where it is shown by analysis or test that these forces can control the yaw and roll resulting from the prescribed engine failure conditions.


For V1 cuts, I don\'t see how an assumption of a quicker response time can be made and I was under the impression that the more typical assumption was 4 seconds. Obviously some automated systems, ala B777 rudder kicks may alleviate some of the control reaction times but may not affect V1 stop assessments.

[Keith.Williams.]

Lomapaseo,

Thank you for the correction. But I think that the term "increase in speed" is probably more appropriate than "acceleration time". I have amended my earlier post accordingly.