V2 & V2+15
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Pretty sure RAT5 is on the spot, regarding the original question. These limitations become very apparent when one is flying TPīs for instance the ATR has a very outspoken speed philosophy regarding the limitations on bank angle in respect of airspeed.
Found this in the FCOM for 73 classics as well....
Cheers W
Found this in the FCOM for 73 classics as well....
Cheers W
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Hmmm... it seems V2+15 represents 2 things:
1. Minimum speed for full manoeuvrability; and
2. Minimum speed for all-engine takeoff (V2+15 to V2+25).
I wonder which one it is?
1. Minimum speed for full manoeuvrability; and
2. Minimum speed for all-engine takeoff (V2+15 to V2+25).
I wonder which one it is?
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I wonder which one it is?
There is also a third criterion. It is a speed that incorporates the speed increment that inevitably occurs, before the speed and flight path angle can be stabilized, when the airplane is rotated at VR at a normal rate with all engines operating, just as V2 incorporates the inevitable speed increment when rotated at VR with one engine inoperative.
P.S.
An additional consideration may result from FAR Part 36: Noise Standards, Appendix B:
(4) The takeoff reference speed is the all-engine operating takeoff climb speed selected by the applicant for use in normal operation; this speed must be at least V2+10kt (V2+19km/h) but may not be greater than V2+20kt (V2+37km/h). This speed must be attained as soon as practicable after lift-off and be maintained throughout the takeoff noise certification test.
Last edited by Gysbreght; 7th Jul 2015 at 07:51. Reason: improved wording
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I'd always thought V2 is a performance issue with all Perf A a/c. It is 'never below speed'; takeoff safety speed in old speak. Is it not related by various % to Vr & VMCA and perhaps many other speeds? It is a certification & performance speed for many types, as it is a concept.
Now for B737, and perhaps others, >V2+15 = full manoeuvrability.
One is vertical for all aeroplanes, the other is lateral for B737.
Now for B737, and perhaps others, >V2+15 = full manoeuvrability.
One is vertical for all aeroplanes, the other is lateral for B737.
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Yeah, bit of both....
Assuring margin for lift capacity enough during turn at a relatively low airspeed. Applies to different aircraft types t (wing planforms etc.) and different additives in airspeed, seems the norm is 10-20kt in this eg. B737 =+15 (less than +15 then a lower bank angle has to be used to not induce to much drag)
As for the increment just for climb (obstacle avoidance etc.) The all engine should give a better climb gradient compared to v2 only... as per briefing notes below...
Assuring margin for lift capacity enough during turn at a relatively low airspeed. Applies to different aircraft types t (wing planforms etc.) and different additives in airspeed, seems the norm is 10-20kt in this eg. B737 =+15 (less than +15 then a lower bank angle has to be used to not induce to much drag)
As for the increment just for climb (obstacle avoidance etc.) The all engine should give a better climb gradient compared to v2 only... as per briefing notes below...
Last edited by winterOPS; 6th Jul 2015 at 14:38.
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RAT 5:
This may refresh your memory:
This may refresh your memory:
Part 25 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
Subpart B--Flight
Performance
Sec. 25.107
Takeoff speeds.
(a) (...)
(b) (...)
(c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by Sec. 25.121(b) but may not be less than--
(1) V2 MIN;
(2) VR plus the speed increment attained (in accordance with Sec. 25.111(c)(2)) before reaching a height of 35 feet above the takeoff surface; and
(3) A speed that provides the maneuvering capability specified in Sec. 25.143(h).
Subpart B--Flight
Performance
Sec. 25.107
Takeoff speeds.
(a) (...)
(b) (...)
(c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by Sec. 25.121(b) but may not be less than--
(1) V2 MIN;
(2) VR plus the speed increment attained (in accordance with Sec. 25.111(c)(2)) before reaching a height of 35 feet above the takeoff surface; and
(3) A speed that provides the maneuvering capability specified in Sec. 25.143(h).
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Guys: This is a copy from B737 FCTM; as the original question was about this a/c. Note the comment that would suggest an ETP can be flown at the speed attained when the engine fails if >V2 & <V2+20.
See also the notes about bank angles v V2 (+15)
2 Engine normal takeoff.
V2 + 20 knots is the optimum climb speed with takeoff flaps. It results in the maximum altitude gain in the shortest distance from takeoff. Any speed between V2 + 15 and V2 + 25 knots results in approximately the same takeoff profile.
Note: A maximum bank angle of 30° is permitted at V2+15knots with takeoff flaps.
Engine failure during takeoff.
Adjust pitch attitude, as needed, to maintain desired airspeed of V2 to V2 + 20 knots.
The initial climb attitude should be adjusted to maintain a minimum of V2 and a positive climb. The flight director commands a minimum of V2, or the existing speed up to a maximum of V2 + 20 knots.
The initial climb attitude should be adjusted to maintain a minimum of V2. If an engine fails at an airspeed between V2 and V2 + 20 knots, climb at the airspeed at which the failure occurred. If engine failure occurs above V2 + 20 knots, increase pitch to reduce airspeed to V2 + 20 knots and maintain V2 + 20 knots until reaching acceleration height.
If an immediate turn is required, maintain V2 to V2 + 20 knots with takeoff flaps while maneuvering.
Note: Limit bank angle to 15° until V2 + 15 knots. Bank angles up to 30° are permitted at V2 + 15 knots with takeoff flaps. With LNAV engaged, the AFDS may command bank angles greater than 15°.
Thus: for B737 you will see that V2 - V2+20 (+25) is a general climb thing, while V2+15 bank angle limit is very specific. They are 2 different items. No doubt the manoeuvrability criteria was designed so that it combined well with the climb performance envelope. Sensible engineering.
See also the notes about bank angles v V2 (+15)
2 Engine normal takeoff.
V2 + 20 knots is the optimum climb speed with takeoff flaps. It results in the maximum altitude gain in the shortest distance from takeoff. Any speed between V2 + 15 and V2 + 25 knots results in approximately the same takeoff profile.
Note: A maximum bank angle of 30° is permitted at V2+15knots with takeoff flaps.
Engine failure during takeoff.
Adjust pitch attitude, as needed, to maintain desired airspeed of V2 to V2 + 20 knots.
The initial climb attitude should be adjusted to maintain a minimum of V2 and a positive climb. The flight director commands a minimum of V2, or the existing speed up to a maximum of V2 + 20 knots.
The initial climb attitude should be adjusted to maintain a minimum of V2. If an engine fails at an airspeed between V2 and V2 + 20 knots, climb at the airspeed at which the failure occurred. If engine failure occurs above V2 + 20 knots, increase pitch to reduce airspeed to V2 + 20 knots and maintain V2 + 20 knots until reaching acceleration height.
If an immediate turn is required, maintain V2 to V2 + 20 knots with takeoff flaps while maneuvering.
Note: Limit bank angle to 15° until V2 + 15 knots. Bank angles up to 30° are permitted at V2 + 15 knots with takeoff flaps. With LNAV engaged, the AFDS may command bank angles greater than 15°.
Thus: for B737 you will see that V2 - V2+20 (+25) is a general climb thing, while V2+15 bank angle limit is very specific. They are 2 different items. No doubt the manoeuvrability criteria was designed so that it combined well with the climb performance envelope. Sensible engineering.
Last edited by RAT 5; 6th Jul 2015 at 15:24.
