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Guest theonlyamrad

TO/Climb performance change

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Hello Gentlemen,I've been using the B744 in conjunction with Christian Grille's TOPCAT tool and also with Boeing's own data - especially for all takeoff calculations. Up until upgrading to the B744F - I've only ever noticed minor inconsistencies between the Queen and Boeing's own data when calculating RTOD, thrust derates etc.However, since installing the B744 cargo, performance on takeoff seems to be a good bit out of whack. For example, At ATOW of 697,000lbs, wind 2 kts headwind, 36 deg C, 1002 hPa, runway length 13,800 feet. I get a max derate of T0-1 and +68deg C - giving 13,600 feet required, and that climb limit is 699,000lbs. On take off with either passenger or cargo versions, I'm already airborne at 50 ft after less than 10,000ft. Climb performance seems to be similarly "strong", even when TOW is higher than climb limit!I've also been able to take off from shorter runways at weights which should be both field and climb limited with ease - leaving lots to spare! Again, for example, conditions giving field limit of 760619lbs at rw 28 EIDW(8652ft) - at 820000lbs I was airborne with over 2000ft of rw left.I enjoyed being able use the real data for flight planning and in failure scenarios - and being able to trust that the Queen's performance would match the real bird's performance pretty accurately. Wondering if anyone else has noticed/expeienced the same thing - or found a solution or if PMDG could give me a pointer.Patrick Roe

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We're getting into some serious nitty-gritty here. Real performance calculation is a real brain burner. However a quick observation might propose that being airborn 10,000 feet down the runway might seem in the ball park. V1 happened a while back. Whatever was left from V1 to that 13600 might just leave a V-Liftoff at ~ 10,000 down the strip. That 13600 not about the field legnth needed to take off. It's the field legnth needed to stop the beast if something goes wrong before V1.But stay with this. Vspeed / Field legnth performance is an area thatis extremely complicated, but critically important to real world ops. And to speak of a 'just this weekend' real world example . . . What happened with that Challenger. Any one know yet?

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> That 13600 not about the field legnth needed to take off. It's the field legnth needed to stop the beast if something goes wrong before V1.Or to accelerate the aircraft to Vr on only three engines if one quits after V1...Martin

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VR is just rotation and V lift-off can be considerably later. If the engine fails after V1, the airplane will continue the takeoff, but VR and VLO will all happen well before the 13600 is reached even with just 3 engines. Obstical avoidance can be, but is generally not the fence. Now consider: If the RW was 25R at LAX, the departure is right off a cliff and then directly over the ocean. In this case, the obstical IS the fence. If this was LAX, might this 13600 be entirely about stopping if a motor fails (before V1) or can it be about clearing the fence? Anyone getting dizzy? I am!

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>VR is just rotation and V lift-off can be considerably later.>If the engine fails after V1, the airplane will continue the>takeoff, but VR and VLO will all happen well before the 13600>is reached even with just 3 engines. Obstical avoidance can>be, but is generally not the fence. >>Now consider: If the RW was 25R at LAX, the departure is right>off a cliff and then directly over the ocean. In this case,>the obstical IS the fence. If this was LAX, might this 13600>be entirely about stopping if a motor fails (before V1) or can>it be about clearing the fence? Anyone getting dizzy? I am! You must clear the departure end of the runway by 35' with an engine out and also clear any obstruction within the airport boundaries by 35' vertically and 200' horizontally. Just avoiding and clearing the fence doesn't do it according to the regs.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpg

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But in the case described, the only obstacle is the fence. Still though, the runway must be longer than 13600. If the 13600 is TO roll distance, the airplane still has to climb to that 35 feet by the end of the runway.The question remains: Is 13600 the TO roll required for obstacle avoidance or the roll needed just to get off by the end of the runway. I'm leaning toward the former.

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>The question remains: Is 13600 the TO roll required for>obstacle avoidance or the roll needed just to get off by the>end of the runway. I'm leaning toward the former. >If 13,600' is the balanced field length then it includes the 35' altitude requirment at the departure end of the runway. I can't see a 13,600' T/O roll even in the most severe case.IF the roll is 13,600', you will need almost 14,600' of runway to meet the 35' requirement. Not many runways that long in the entire world.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpg

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Hi guys,Thanks for all the replies.Just to try to clarify my example a bit more. The level of derate I used for my first example was at the extreme for me to test things out. Previously, even when I tried an engine failure at v1 - I always made the stop in time using the normal procedures "by the book".The same applies to the V1 cut and continuing the TO. Also, the Queen behaved according to real world climb limits. Now, in terms of balanced field length, things seem to be a bit too much on the high power side - such as really good climb performance - even when considerably over the climb limit.As for my second example, c.760,600lbs put me at field AND climb limit. Yet I was able to do the TO case and climb (c.3000 ft/m) at 820,000 with loads rw left. I havn't tested RTO yet - but suspect that with fail at V1 - I can make the stop in this overweight condition. As far as the 35' requirment is concerned - any "tests" I did previously were done in obeyance of the relevant regs.I really believe there's been a performance change from passenger only version installed to having the cargo version also. Personally, right now it seems to me that the difference pulls away from realistic behaviour - but would like to hear other people agree OR make the counter-arguement.

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Good. Making progress. So that 13600 is about being able to stop if an engine quits before V1. Now how about another variable. We just got a Notam advising that a 300 foot tall crane has just been moved in to finish up a construction project just 100 yards off the departure end of this runway. It's temporary, but it's there. This is the only runway this airport has. We gotta use this runway. Can we still use the same Weight/V1/VR numbers on this runway? Now the go/no-go decision point (V1) it's not just about accelerate / stop runway length, but also about obstacle avoidance with an engine out. What kind of decision matrix must I now use to guarantee that I can liftoff and climb to 335 feet within 100 yards of the end of the runway if an engine fails at V1 + 1 knot. A V1 speed will still be my decision point, but how do I calculate this. What do we do now?

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>Good. Making progress. So that 13600 is about being able to>stop if an engine quits before V1. Now how about another>variable. >>We just got a Notam advising that a 300 foot tall crane has>just been moved in to finish up a construction project just>100 yards off the departure end of this runway. It's>temporary, but it's there. This is the only runway this>airport has. We gotta use this runway. >>Can we still use the same Weight/V1/VR numbers on this runway?>Now the go/no-go decision point (V1) it's not just about>accelerate / stop runway length, but also about obstacle>avoidance with an engine out. What kind of decision matrix>must I now use to guarantee that I can liftoff and climb to>335 feet within 100 yards of the end of the runway if an>engine fails at V1 + 1 knot. A V1 speed will still be my>decision point, but how do I calculate this. >>What do we do now? > That's actually an unrealistic scenario. Most airports that are capable of supporting a 744 have ILS LOC transmitters that are normally 150 yards past the end of the runway with the perimeter fence being farther than that by at least 50 yards. If this were a real situation the airport would actually reduce the runway length to allow for approach clearance at the crane end resulting in a severely displaced threshold. I don't have the regs handy for approach obstacle clearances but I'm sure the ratio that's required for safe approach clearance would effectively shut most runways down to all but the smallest traffic. More than likely the runway would be NOTAM'd closed for landings and takeoffs over the tower end if it were that close to the runway.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpg

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It may seem like we're veering off your topic, but step 1 will be to really nail down what the performance should be. What should a 744-XYZ be able to do and how do we calculate it. So let

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>It may seem like we're veering off your topic, but step 1>will be to really nail down what the performance should be.>What should a 744-XYZ be able to do and how do we calculate>it. So let?s seriously think about this. "That's unlikely">just avoids the question . . . and this about takeoffs, not>landings. >>This may be (and was intentionally presented as) an>exaggeration, but it is still an example of what flight>planners deal with every day. >>So, like I asked, what do we do now?>>To properly answer your question, the displaced threshold has to be determined and that's done by the airport due to the obstacle in quesion. The airport cannot lagally allow the entire length of the runway to be used and will displace the threshold. The most restrictive clearance being the approach end WILL result in a greatly reduced runway length(a few thousand feet from the obstacle, at least). Your hypothetical question can't be answered unless the reduced runway length is known and since that's an unknown variable, it can't be answered.I still believe that in your hypothetical, the runway would be closed at the obstacle end.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpg

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>However an operator might certainly, still be able to use the runway. >There may be no need to abandon the operation or close the airport.>Cheers,I think your understanding of airport operations is clouding your speculation. The reality is that the operators who use the airport have no choice but to use the reduced length due to the obstruction and cannot use the entire length for their calculations. No if's, ands, or buts. The airport has the final say and will reduce the runway length to provide an adequate approach clearance by temporarily displacing the threshold. This reduces the overall allowable runway length regardless of whether you're taking off or landing so you need to know how much runway you're working with.Recently at the airport I work at, they were doing some resurfacing work at one end and closed 2200' of a 12000' runway. All takoff calculations had to be based on a 9800' surface. In essence this is what would happen with an obstruction at the end of a runway like you speculate although the closed portion would be more than 2200'. You have to use what the airport lets you use in these situations. In the end your hypothetical situation still requires variables that are not known to get what you're looking for.JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpg

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