Joona From Finland, joined May 2001, 1038 posts, RR: 13 Reply 1, posted (11 years 2 months 4 weeks 11 hours ago) and read 2320 times:
I would say yes. What kind of departure do you mean? An engine failure during rolling or start moving with only one engine operating? If an engine failure occurs after V1, the plane is committed to takeoff. There are special speeds for this too, for example, BSEC (Best Single Engine Climb). I don't think a fully loaded Boeing 767 (at it's MTOW) could depart with only one engine, but a light Boeing 767 will, at least if it has both engines running during rolling and then have an engine failure after V1. I don't know if it can takeoff by using only one operating engine when they start rolling.
Jetpilot500 From United States of America, joined Nov 2000, 78 posts, RR: 0 Reply 2, posted (11 years 2 months 4 weeks 10 hours ago) and read 2293 times:
Even if there was enough power to allow the airplane to lift off, the yaw would be too great to overcome at low speeds with one engine at full power.
There is a speed called VMCG, or Minimum Control Speed on the ground with an engine out. Below that speed the rudder would not be able to over come the yawing force created by one engine at full power. Once you are faster than VMCG, the rudder has enough airflow over it to be effective in keeping the aircraft straight. VMCG is usually about 20-30 knots slower than rotation speed in most aircraft (I'm not sure about the B767), so typically around 100-120 knots.
Jetguy From , joined Dec 1969, posts, RR: Reply 3, posted (11 years 2 months 4 weeks 6 hours ago) and read 2260 times:
Tried it in the simulator and it wasn't a problem. Just slowly added power until VMCG was reached then went to takeoff power. Once V1 was achieved, it was just like any other "V1 cut". Used nearly 13,000 feet of runway!
Mit From United States of America, joined Dec 2000, 166 posts, RR: 0 Reply 4, posted (11 years 2 months 4 weeks 5 hours ago) and read 2250 times:
Kudos to jet guy for explaining that VMC does not prohibit a fully single-engine takeoff! (Given enough runway.)
On a humorous note, one of the events that lead to cockpit phraseology standardization involved the phrase "takeoff power." An airline captain needed maximum thrust in some urgent situation and began shouting "takeoff power, takeoff power." The FE interpreted this as "take off power" and promptly took off power by closing the throttles.
B787 From Australia, joined May 2005, 152 posts, RR: 0 Reply 5, posted (11 years 2 months 3 weeks 3 days 12 hours ago) and read 2186 times:
Modern big twins are certified to be able to climb at over 100 ft/min with one engine inoperative, this is how V1 gets set, and it also rolls into balanced feild length. so if one engine fails at V1 the twin takes off and can climb out to somewhere around 10,000 ft if need be to find an appropriate spot to land. This is why twins are normally overpowered and fun to fly.
Ambasaid From , joined Dec 1969, posts, RR: Reply 6, posted (11 years 2 months 3 weeks 3 days 11 hours ago) and read 2169 times:
B787
Go back to the research books, your information is wrong!
Rate of climb per minute is not a regulation, climb gradient is.
V1 is not primarily based on climb gradient.
Twins flying on one engine can climb beyond 10,000 feet.
Actually, you did get one thing right, twins are fun to fly.
Jetguy From , joined Dec 1969, posts, RR: Reply 7, posted (11 years 2 months 3 weeks 3 days 2 hours ago) and read 2146 times:
Ambasaid...
You too are partially right. Turbine twins can usually climb above 10,000 but it's not always a sure bet. Many piston twins often have single engine service ceilings sufficient to take them directly to the scene of the accident in the event of an engine failure - ie, Piper Apaches, etc. One thing is for sure, twin engine airplanes have two engines because they need two engines!
B787 From Australia, joined May 2005, 152 posts, RR: 0 Reply 10, posted (11 years 2 months 2 weeks 3 days 4 hours ago) and read 2090 times:
OK I admit I was not clear in my original comment I will try to make up for this now.
I stated that the climb gradient is how V1 gets set, and in part 25 we can read that
Sec. 25.107 Takeoff speeds.
(a) V1 must be established in relation to VEF as follows:
(1) VEF is the calibrated airspeed at which the critical engine is assumed
to fail. VEF must be selected by the applicant, but may not be less than VMCG,
determined under Sec. 25.149(e).
(2) V1, in terms of calibrated airspeed, is selected by the applicant;
and as for the takeoff climb gradient
Sec. 25.121 Climb: One-engine-inoperative.
(a) Takeoff; landing gear extended. In the critical takeoff configuration existing along the flight path (between the points at which the airplane reaches VLOF and at which the landing gear is fully retracted) and in the configuration used in Sec. 25.111 but without ground effect, the steady gradient of climb must be positive for two-engine airplanes
So I should have stated that Boeing chooses to set V1 based on an initial climb rate of 100ft/min until the gear can be stowed, without use of exceptional piloting skills.
I was not trying to write a dissertation about take-off power, just making general comments, I am sorry if I offended you and I will make a more concerted effort to get all my duck in a row the next time.
Ambasaid From , joined Dec 1969, posts, RR: Reply 11, posted (11 years 2 months 2 weeks 2 days 16 hours ago) and read 2068 times:
787,
Dont worry about offending anyone, we are all here to learn......
Anyway, Aircraft performance is a subject that i really enjoy, i therefore use every opportunity that i get to discuss subjects and enhance my knowledge.
It is with this in mind that i have to ask about the Boeing value of 100 fpm.
My understanding is that the distance from VLOF to V2 is determined from flight test by establishing the time to flare and multiplying by the average speed during the flare. The test points are faired to account for pilot techniques. (Note, its also called the flare distance on takeoff as well as landing.)
In this and the formulas associated with it i can't find any reference to a constant of 100 fpm.
Could you please tell me where this value came from?
My info btw, is from the Boeing Jet Transport Performance Methods manual published by the Boeing Flight Operations Engineering Department.
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