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View Full Version : Re A340 "limited by the all engine case"


jalbert1
10th Sep 2010, 17:59
Regarding takeoff performance what does this mean?
Also the V1/VR split against the twin(ie 330) . Can someone explain how these are connected?
Many thanks.

galaxy flyer
10th Sep 2010, 18:11
Under FAR/JAR 25 certification rules, take-off performance is limited by the most restrictive case of engine-out performance (climb, obstacle, brake energy, structure, field length OR 115% of the all engines operating take-off run to 35 feet above the runway elevation. Four engine planes can be limited by all engines case more frequently than twins. Reason being the four-engine planes lose only 25% of their thrust while twins lose 50% and probably something on the order of 80% of their excess thrust making the OEI case more restrictive for twins.

Need more detail to answer the second question.

GF

Did I do OK, J_T?

john_tullamarine
11th Sep 2010, 15:13
GF - that sounds like the guts of the matter

V1/VR - the OP doesn't give us much to go on. However, I presume he/she is looking at the effect of V1/VR on whether OEI or AEO conditions are limiting. If so, then consider the two extreme cases for either 4 or 2 motor jobs ..

(a) V1=VR where we would expect the minimum difference in TOD between the OEI and AEO cases. In this situation, the AEO case is most likely to be the limiting case - not guaranteed to be so but most likely compared to any other V1/VR.

(b) V1/VR at the minimum value, whatever that might be for a particular aeroplane. This results in the greatest speed delta to be achieved during OEI operation to get to VR .. as well as the final flare to screen contributing. In this situation, the TOD will most likely be OEI limited.