Weights again.

[Guest venquessa]

OK I have multiple values for maximum take off weights.In the Limitations PDF that comes with the CD, I have the MTOW of .. em.. from memory 133,000lbs for the 737-700.If I use this weight if it is lower than the max runway weight, then all works OK, rejected take offs etc.However in the Max weight for runway length there is the figures in excess of 150,000lb and I just downloaded the Fuel planner and it shows the MTOW at 150,000 something.If I use the numbers for the max weight for runway length from the tables in the Takeoff performance sheet, then the plane will barely get off the runway, and will NOT stop on a V1 abort, nor will it get off the runway with an engine out at Vr. Even at flap 15 110% N1 on the remaining engine it just wont happen.Can someone please confirm this? What is the correct Max take off weight?I don't need a dispatcher type detail, I just need a few figures, or even which manual to take a gospel and which to ignore.Thanks.

[Guest wee_davie_2612]

Hey Paul,A simple answer is to use the weights in the fuel planner as gospel. I've checked them against the real life weight limits from Boeing and they're real close to being spot on (an average had to be taken due to different class layouts etc.).Can't find the link just now but I'll have a look.Hope it helps,David

[zubart 5]

Weight Limmitations from an Operations Manual(These might vary slightly with different airlines operations)Max Taxi Weight is 155,000 pounds.Max Takeoff Weight(MTOW) is 154,500 pounds.Max Landing weight is 129,200 pounds.Max Zero Fuel Weight is 120,500 pounds.Floyd

[Donstim 109]

Hi Paul,Let me give it a try. The maximum weights shown in the limitations section are the maximum weights that the airplane can be operated at regardless of the runway or environmental conditions. These weights are normally considered the structural limit weights, though often simply reflect the maximum weight capability that the airline has purchased.I don't know where PMDG got their maximum weight limitations from. The maximum takeoff weight limit that has been certified for the 737-600 is 143,500. (You can find this information here: http://www.airweb.faa.gov/Regulatory_and_G...FILE/A16WE.pdf) As I said, though, different airlines may purchase different maximum weight capabilities (but not more than the maximum that has been certified). PMDG may have gotten their information from an airline that purchased a lower weight capability.In addition to the maximum weight that can ever be used, there are performance requirements that can affect the maximum weight that can be used for any takeoff. One of these is based on runway length, another is based on the climbout after takeoff. There are others, but these are the only two that we can hope to address with the PMDG documentation. The maximum weight that can be taken off from a specific runway length is provided in the PMDG takeoff data tables, as is the maximum weight that meets the climb requirements (the numbers is yellow).Now, you must meet all of these requirements for every takeoff. So, if your maximum weight based on runway length and the climb limit weight are greater than the maximum takeoff weight from the limitations section, then the maximum allowable weight for that takeoff is the maximum weight from the limitations section. Since the runway limit and climb limit weights are higher, you know that you will not have a problem taking off in that runway distance, nor will you have a problem climbout out after the takeoff.Just remember, the maximum weights in the limitations section have nothing to do with airplane performance. They apply to every takeoff (and landing), regardless of where you are taking off or landing. From a performance standpoint, however, the airplane should be perfectly capable of taking off above those weights as long as you meet the maximum runway and climb limit weights. So, if you want to do a flight test to check the PMDG 737's runway and climb performance, ignore the weights in the limitations section. They serve no purpose in MSFS 2004. If you trying to simulate airline flying, however, obey them (or pretend that you purchased a higher weight option).For your information, the requirement that determines the maximum wieght for a given runway length is that you must be able to safely stop the airplane on the runway after rejecting a takeoff at V1 (without the use of thrust reversers), and be able to continue the takeoff and reach a height of 35 feet by the end of the runway after an engine failure occurring just before V1. (This slightly simplified explanation ignores consideration of clearway and stopway, which we needn't concern ourselves with here.)For the climb limit weights, the airplane must be able to achieve a 2.4 percent climb gradient with the landing gear retracted after a takeoff where the engine failed just before V1.I hope this helps.Don S.

[rsrandazzo 6,353]

Paul-You've been given a few replies to your question that are misleading- so I'll add a bit more information to tie them together and hopefully present you with a clearer answer!There are two weight figures being commonly confused in the Sim Community.Maximum Certificated Weight and Limitation Weight.Maximum Certificated Weight is a figure that appears in the aircraft's Type Certification, and represents the results of significant engineering and testing by the manufacturer. It indicates to the governing authorities the maximum weight at which the airplane was found to be capable of meeting regulatory requirements for certification, OR the highest weight at which tests were conducted given the current state of the airplane and equipment.Limitation Weight is the weight published by the manufacturer and given to the operators of the airplane as a "Do Not Exceed" limitation. This figure may vary slightly, or significantly from the certificated figure based on subtle differences in the structure of the airplane, landing gear/brakes, or may be related to fatigue and cycle life issues for the airplane's logevity.As an airline purchasing an airplane, Boeing will give you a series of options on an airplane such as thrust limits, landing gear strength, etc... The mix of options you choose will determine the Limitation Weight of YOUR airplane.... (Boeing has a long history of then expanding the capability of it's airplanes by improving structural components and landing gear/brakes, etc. The 777 for example, has seen a significant increase in MTOW during the past 10 years.)So- what happens in the sim community is this: Users sometimes get confused because they see different weights attributed to an airplane type.... The information used to produce PMDG's airplane was provided by Boeing. The weight figures presented as limitations in our manuals represent the weight limits published by Boeing for it's "typical" airframe in each hull design.In performance manuals, it is common to find higher figures listed than those for which your airplane is certified... That is because Boeing has done the engineering and performance testing for heavier weights already.When flying the line (my other job!) one of my responsibilities as a Pilot in Command is to ensure that my airplane is NEVER alowed to taxi or take off at a weight that is higher than the listed Aircraft Maximum Takeoff Gross Weight. The MTOW is called a LIMITATION because it is restrictive in nature. Even if performance figures state that my aircraft will take off at a higher from a given runway, it does not imply that I have approval to ignore a weight limitation that is published in the Aircraft Operating Manual....So the weight limitations published in PMDG's manuals represent the maximum weight limits that you should respect when flying the airplane... Using those weight limits will give you the performance predicted by the manuals, and ensure you don't see the runway end lights up close and personal- at hight speed. ;-)I hope that helps to tie some of the information to gether for you. ;-)

[Guest wee_davie_2612]

Hey Paul,The [a href=http://www.boeing.com/assocproducts/aircompat/acaps/7376sec2.pdf]link[/a] as promised. The different weight columns correspond to the different class configs that are detailed later on in the .pdfHave a good one.David

[Donstim 109]

Robert --I would be interesting to know which part of my explanation you found misleading. Like you, I pointed out that a given operator's maximum weights may be less than the maximum certificated weight of the airplane. I also pointed out that all of the weight requirements must be met for every takeoff -- whether it be the structural limitation weight, the takeoff runway limit weight, or the climb limit weight.Where we appear to differ, and where I find your response to be misleading, is that you seem to imply that the structural limit weight has something to do with airplane performance. It does not. And as I and others have shown, you may see those runway end lights (and whatever is beyond) up close and personal in the PMDG 737NG even when operating within all of the weight limitations if you have an engine failure near V1 speed.I don't really find that to reduce the enjoyment I get in any way from your team's excellent simulation, though. I don't know if it is even possible nor worth the time and effort to try to match the actual airplane's performance capability that accurately in a pretty darn inexpensive product built on a pretty darn inexpensive piece of flight simulation software.One other thing I recently noticed that maybe you could clear up. Although your limitations documentation notes the maximum weights of the -600, -700, -800, -900 to be 127,000 lb, 133,500 lb, 174, 200 lb, and 174,200 lb, respectively, the config files have the maximum weights set at 144,000, 153,500, 173,000, and 174,500 lb, respectively. Why are these different?Thanks,Don S.

[Guest venquessa]

OK I was aware that the 2 weights could be as you outline, but I didn't expect them to be that much apart.Anyway. Testing again, I already know that at the Limitations manual MAX weights I can stop from V1 and I can also climb out on 1 engine from a loss at V1. But...Test conditions:Model: 737/600 Weight: 149,9xxlbsRunway: 6000ft (DRY)OAT 15 degreesPress. 29.92Wind 0/0 (FS2004 Clear, confirmed with FSNav)No Derate.MAX throttle with no A/T (about 105%).Flaps 15.V 1 125, R 126, 2 132Generic Procedure:Brakes on, autobrakes in RTO.No horn, everything green ready and waiting.Full power... wait... till 95% N1 or when it rolls anyway (about 90+)Normal departure:Rotate at 125, lift off just about V2, very limited climb, but successful. About 50ft AGL by end of runway.Early Abort:At 120 throttle back, engage speed brakes, full brakes on. No reversers. I got stopped literally 2 foot from the end of the runway.V1 Abort:At 125 (V1 call) cut thottle, engages speed and foot brakes. No reversers, I stopped about 20 foot off the end.V1 Engine Fail:Rotate and pull fuel cutoff in No.2 engine at same time. Kick left rudder to center on runway, keep rotation angle, (tail skid just off the tarmac). No joy. It stayed put on the ground at 125kts and ploughed into someones house. At one point it lifted the main gear, but even though I had almost full back stick in, it set back down. I tried full back stick, I tried racking in lots of trim and inversely I tried lowering the deck angle and use the rest of the runway to accelerate, still ended up spoiling somones garden and sunday dinner.V2 Engine Fail:Killed the engine just as the main gear departed terra firma. It almost instantly stopped climbing and held 10ft AGL for about 10 seconds before settling back down again. Nothing would keep that baby in the air, NOT EVEN GROUND EFFECT, at 149,9xx lbs!If I use the 600s figures in the 700 for max take off weights from the performance sheet as above it just gets airborne and able to maintain about 200fpm ascent.So. While I think the Limitations manual weights of 128,000 for the 600 are a little on the safe side, the MAX performance for temperature, wind and runway length are out somewhat. I don't see how any pilot, Boeing test or not, could get that plane in the air, or climb with 1 engine out, with the 150.1 listed for the 6000ft runway under those conditions.So I will revert my performance take offs to the Limitations manual limits, or interpolate them with the Performance manual for test flights.

[Donstim 109]

Hi Paul,Interesting results. Note that the 150.1 lb weight in the takeoff performance document is a climb limit weight, and is independent of runway length. It does not matter whether the runway is 6000 feet long, or 12,000 feet long.The climb limit weight for an airplane depends on thrust, flap configuration, speed, and OAT. The PMDG documentation only provides info on two of these variables -- OAT and speed (V2 speed). We do not know what thrust level or flap configuration the 150.1 lb weight corresponds to. (This make the performance data provided by PMDG pretty worthless.) It very well could be that the data are for flaps 5, which would have better climb performance than flaps 15. You are probably above the climb limit weight for flaps 15, which explains why you cannot even maintain level flight. It could also be that the thrust level is for full rated thrust with the air conditioning bleeds turned off. By not taking bleed air off the engines, more takeoff thrust is provded (if PMDG models this effect).Another aspect is that PMDG may have decided that matching the climb performance at weights above the maximim limitation weight was unnecessary since you should not be operating there anyway.If you want to do any more testing, may I suggest you try your takeoff at 50 degrees C OAT at the climb performance limit weight of 123,000 lb? This is within the limitations weight. You can try different flap settings (lower is better) and turning the air conditioning bleeds off to get better climb performance. With an engine cut at V1, you should just barely be able to climb away (about 316 feet/minute climb rate at a V2 of 130 knots, for example). This is not a runway limit test, so feel free to use a longer runway.For a runway limit test, you will need to find a runway where the runway limit weight is lower than the climb limit weight. For example, at 50 degrees C, you can use a 5000 foot runway, which has a limit weight of 121,300 lb. The runway limit weight also depends on the flap setting and the thrust level, with higher flap settings providing better performance.Best of luck,Don S.