Take off calculations - require help

[zubart 5]

Whats your takeoff thrust set at? Is the STAB TRIM set properly?Are the flaps set properly?Floyd

[N520AT 3]

What I do, for the -700 is for runways longer than 9,000 feet use flaps 5, and for runways shorter than 9,000 feet use flaps 10:-)

[Guest A32X]

Hi Don,I suspect the take off data is for flap 5, but I used flap 10 for the reduced take off roll and still didn't make it into the air.OAT was 22 degrees Celsius, I calculated my MTOW allowable, loaded the 737 up to that weight then I found the V-speeds by line selecting the FMC, just as they'd be more accurate than a rounded value from the tables.Has anyone else tried this calculation for short runways? You'll need manual 01 - Take off PerformanceEDITORS NOTE TO USER A32X: I'm Posting this here in hopes you will see it. I deleted a handful of other posts based on the fact that they were not signed... Please please please sign your posts in this forum in accordance with forum policy.... Thank You! RSRandazzo

[Donstim 109]

Hi Paul,Okay, after a couple of attempted test flights, I'm tending to agree with you. I tried taking off out of Renton Municipal, shutting down an engine at the V1 callout. Although I could successfully get off the ground, I was unable to continue climbing after takeoff. This indicates a climb problem (not enough thrust or not enough lift/drag), rather than a ground run issue. But, although I haven't tried to reject the takeoff, I was left with the impression that there would not be enough runway left to do that. (I would have tried it, but it takes so long to reset each flight that I ran out of time.)I'll continue the testing when and if I can find the time. For my testing, I'm using runway 33 at KRNT (5382 feet long), zero wind, 79 degrees F with the 737-700. I tried the takeoff with flaps 5, 10, and 15, all with generally the same result.Since the performance tables included in the PMDG documentation do not indicate what flap setting they are for (nor the takeoff altitude), they are pretty much worthless anyway. The incorrect directions on how to use them don't help either.Good thing nearly all of my flights are from long runways and I have the failures turned off.Don S.

[Donstim 109]

Okay, I conducted some rejected takeoffs and could not get the airplane stopped on the runway. I tried one at flaps 5 and one at flaps 25, and in the latter case still went into Lake Washington at over 65 knots. I used the RTO autobrake setting, failed an engine at V1, throttled back the other one, and raised the spoilers. No reverse thrust, just like what the field lengths are based on.(Note: I don't really find this a big drawback to PMDG's 737NG. I don't know what it would take to achieve more accurate takeoff performance in FS2004, or how closely it could be made to match the real world. I find the sim to portray the "feel" of a normal all-engines-operating takeoff pretty well. The only reason I conducted these test flights was to respond to Paul's concerns.)Don S.

[Donstim 109]

How did you determine that flaps 10 is the proper flap setting for your takeoff? The PMDG manual does not indicate what flap setting their data is meant to be good for.Can you provide the details of the takeoff you are attempting -- i.e., airport, runway, OAT, V speeds, N1 setting, etc.?Don S.

[zubart 5]

Is that a -700,-800 or -900 MTOW?Also, was the correct OAT set in your simulation that you were using for the takeoff chart?Anyway, I'll try it tonight. I thought I saw a post a while back about the -800/-900 on this same subject.Floyd

[Donstim 109]

Hi Paul,I tried one quick takeoff out of Renton Municipal Airport (KRNT) in Renton, WA. The runway is 5382 feet long. Using the 737-700, I loaded it up to about 136,700 lb. for an OAT of 79 degrees F (26 degrees C). Using flaps 10, the V speeds were around 122-124-132 (within a knot anyway - I let the FMC fill them in, but forgot to write them down), and N1 for a full rated takeoff was 95.5%. I used a trim setting of about 7 3/4.I ran the engines up to full thrust with the parking brakes set, then let 'er rip. I reached Vr well before the end of the runway and lifted off with pavement to spare. I don't know how it would have done in an engine out situation, or even if the PMDG takeoff weight tables are for flaps 10 (I doubt it and agree with you that they are probably for flaps 5), but at least I was able to successfully complete this takeoff.Hope this helps.Don S.

[Guest A32X]

Hi,Could someone please confirm this situation for me?Go to any airport with a short runway say around 6,000feet long, set the temperature and don't bother with the wind to keep it simple. Then calculate your MTOW from the tables provided by PMDG.Now load up your 737 to it's MTOW allowable. I find I am reaching vR at the end of the runway and I fail to get airborne before running onto the grass.Can someone else try this so I can figure out if I'm just doing the calculations wrong?Thanks!Paul

[rsrandazzo 6,353]

Paul-(Please see my note in one of your other posts in this thread! Thanks paul!)The performance of the airplane and engines is nearly flawless in terms of performance... The problem you are experiencing is due to a lack of proper and complete information....For starters, 5300 feet is a SHORT runway for a maximum weight takeoff in an airplane of this size. The NG is absolutely perfectly capable of it- but from an airline captain perspective- this runway length is "getting a bit hight" on the pucker scale because there is so little margin for error.(That's fun in simulators- but in real life...not so fun.... But hey- it's a sim- so lets have some fun, right?)I loaded the airplane to 130,000lbs, and loaded up at KRNT at standard temperature.I had looked at the Runway Limit Weight table and found that I should have plenty of ability to get off this runway, in spite of the fact that it would be close.As per your scenario, there was no wind- so I ignored the wind table and continued on... (BTW: If you mess with the wind table- look it over carefully... the table is actually giving you output that describes the effect of wind on your runway lenght...so read the legends carefully because a headwind will have a lessening effect on your takeoff distance...)I set flaps to 15 because this runway is not long, and adjusted the trim backward by holding the trim up key for about three seconds. (forgot to write down the resulting number, sorry....)Released the brakes and opened the throttles for a max N1 of 93.x%. Thrust set, everything looks good... V1... Rotated at 3 degrees per second and was climbing through 400 feet be the time i cleared the end of the runway.....Now.....If you try this procedure at flaps 10- you get much closer to the end of the pavement.... Flaps 5 and you might be swimming.....(BTW: Rejected the takeoff on the flaps 15 just for fun- and had no problem stopping before the end. Would have qualified for a brake inspection- and more than likely would have melted a tire plug....)So how did i select flaps 15 instead of 5? Experience and a but of guesswork....In the real world, we have dispatch offices who provide very detailed tabular data for every runway you will operate on/off of. The tabulated data will suggest flap configurations and "balanced field length" data to ensure that V1 will occurr within stopping distance of the end....If it is put into printed form- this type of data for a small airline can run over 1000 pages.... and obviously it varies by every airport and runway- so there is simply no way to compile it and provide it to MSFS users....(The data service from companies like Jeppesen costs many hundreds of thousands of dollars....)So there really is no "hard and fast" information to tell you what flap setting to use- but I have used the following guestimates when testing this airplane:<6500: Flaps 156500-7500: Flaps 107500+: Flaps 5You will find that each airplane behaves a bit differently, so you can get away with lower flap settings in the 700 than in, say, the 900!A great fun experiement is to fly the same departure in each of the airplanes and see how different they accelerate, rotate and climb away....Oh- on a side note: The V1 listed in our tables is a "balanced field length assumptive V1." By this, the V1 figure assumes that "all other things being equal, a balanced field length will exist to accelerate to V1 and stop on remaining runway." Obviously- if you were flying a 900 out of KRNT, you wouldn't want to load the airplane to max takeoff weight because you will certainly go swimming after V1 but before rotation.... In real life- a dispatcher (or detailed book) would tell you that!So- next time you wander through airline ops: Hug your dispatcher.... ;-)

[Guest A32X]

Thanks for the reply; I guess we need a virtual dispatcher! ;)Also, maybe you could include much more accurate tables for the 747 (perhaps even airport specific) as we're only going to be flying to say 10/20 major airports around the world.Cheers,Paul

[Donstim 109]

Hi Robert,It's great to see you post in this thread. You seem to have been responding to my testing at KRNT though you directed your response to Paul. If you don't mind, I'd like to address some of your comments below:>The performance of the airplane and engines is nearly flawless>in terms of performance... The problem you are experiencing>is due to a lack of proper and complete information....Hmm...I don't think so. But then again, I don't expect any MSFS 2004 airplane/engine simulation to be "nearly flawless in terms of performance." But I agree that there is a lack of proper and complete information (as well as some misleading instructions on how to use the information that was provided). As I said in a previous message, however, within certain bounds the PMDG simulation certainly provides a realistic enough feel performance-wise for a good simming experience!>For starters, 5300 feet is a SHORT runway for a maximum weight>takeoff in an airplane of this size. The NG is absolutely>perfectly capable of it- but from an airline captain>perspective- this runway length is "getting a bit hight" on>the pucker scale because there is so little margin for error.What Paul was questioning was the performance at the maximum takeoff weight allowed for the runway length when the runway length limits the takeoff weight and the allowable takeoff weight is from the PMDG documentation. If I, as a captain, am going to trust the PMDG documentation, I ought to be able to show that it accurately portrays the capability of the sim. Unfortunately, for the situation I tried, it did not.>(That's fun in simulators- but in real life...not so fun.... >But hey- it's a sim- so lets have some fun, right?)>>I loaded the airplane to 130,000lbs, and loaded up at KRNT at>standard temperature.>>I had looked at the Runway Limit Weight table and found that I>should have plenty of ability to get off this runway, in spite>of the fact that it would be close.>In other words, you are not at the runway limit weight for that runway. For your scenario, the takeoff weight tables you provide say that the airplane should be able to take off at around 139,000 lbs. So you are not testing the critical case.>As per your scenario, there was no wind- so I ignored the wind>table and continued on... (BTW: If you mess with the wind>table- look it over carefully... the table is actually giving>you output that describes the effect of wind on your runway>lenght...so read the legends carefully because a headwind will>have a lessening effect on your takeoff distance...)>It's a good thing we're using zero wind and ignoring the wind correction table, because the instructions for using the table are wrong. (You cannot take off in 40 knot tailwinds.)I set flaps to 15 because this runway is not long, and>adjusted the trim backward by holding the trim up key for>about three seconds. (forgot to write down the resulting>number, sorry....)What flap setting is the runway limit weight data in the PMDG documentation based on? The trim setting should come from the table in the takeoff data document, not just be arbitrarily set.>>Released the brakes and opened the throttles for a max N1 of>93.x%. >>Thrust set, everything looks good... V1... Rotated at 3>degrees per second and was climbing through 400 feet be the>time i cleared the end of the runway.....>>Now.....>>If you try this procedure at flaps 10- you get much closer to>the end of the pavement.... Flaps 5 and you might be>swimming.....With all engines operating, I don't think you will have a problem even with flaps 5. The maximum runway length limited takeoff weight is based on failure of an engine just prior to V1. Did you try continuing the takeoff with an engine failure (at the maximum weight for that runway length and environmental conditions)?>>(BTW: Rejected the takeoff on the flaps 15 just for fun- and>had no problem stopping before the end. Would have qualified>for a brake inspection- and more than likely would have melted>a tire plug....)>I was also able to successfully reject the takeoff for your scenario. However, as you noted, you were not at the limiting weight. I was unable to avoid going into the drink at the limiting conditions of 136,600 lb at 79 degrees F at KRNT using flaps 15 on the 737-700. (BTW: You don't get to use reverse thrust for this test as the field length limits don't include it.)>So how did i select flaps 15 instead of 5? Experience and a>but of guesswork....>And because the takeoff data provided in the PMDG documentation does not indicate what flap setting it is for. Actually, the best flap setting for your scenario would have been flaps 25.>In the real world, we have dispatch offices who provide very>detailed tabular data for every runway you will operate on/off>of. The tabulated data will suggest flap configurations and>"balanced field length" data to ensure that V1 will occurr>within stopping distance of the end....>>If it is put into printed form- this type of data for a small>airline can run over 1000 pages.... and obviously it varies>by every airport and runway- so there is simply no way to>compile it and provide it to MSFS users....The level of detail you are describing is unnecessary for MSFS users. However, tabulated data can be provided in a much more abbreviated format similar to what was provided in the PMDG documentation. All that would be needed would be to augment it by providing separate tables for each takeoff flap setting and a small set of different airport elevations. Users can then approximate or interpolate for specific runways (i.e., play dispatcher!). Otherwise, why provide any data at all? Maybe it would have been better just to provide the general guidance that you provide below.>>(The data service from companies like Jeppesen costs many>hundreds of thousands of dollars....)>>So there really is no "hard and fast" information to tell you>what flap setting to use- but I have used the following>guestimates when testing this airplane:>><6500: Flaps 15>6500-7500: Flaps 10>7500+: Flaps 5>>You will find that each airplane behaves a bit differently, so>you can get away with lower flap settings in the 700 than in,>say, the 900!>>A great fun experiement is to fly the same departure in each>of the airplanes and see how different they accelerate, rotate>and climb away....>>Oh- on a side note: The V1 listed in our tables is a>"balanced field length assumptive V1." By this, the V1 figure>assumes that "all other things being equal, a balanced field>length will exist to accelerate to V1 and stop on remaining>runway." Obviously- if you were flying a 900 out of KRNT,>you wouldn't want to load the airplane to max takeoff weight>because you will certainly go swimming after V1 but before>rotation.... In real life- a dispatcher (or detailed book)>would tell you that!>But you can load the airplane to the maximum takeoff weight allowed for the KRNT field length. And the data in the PMDG documentation implies that you can use it to determine the maximum takeoff weight that will keep you from swimming. If not, what was the purpose for including it?>So- next time you wander through airline ops: Hug your>dispatcher.... ;-)>That's for sure! :-)

[Guest hlm65]

Hi Paul,I flew out at KJAC (runway length about the same as airport elevation !) with a 737-700 at almost max TOW weight, +25 C and no wind and did it flawlessly with runway to spare at flaps 5. I lined up, opened the thottles to the computed N1 and held the plane on the brakes till attaining the desired N1. Got 5.5 up elevator trim.If you want more infos, try to download and print the graphs at:http://www.boeing.com/assocproducts/aircompat/737.htmThey are very usefus.Happy takeoffs !

[Guest A32X]

Great Link Enrico, can you please explain this chart to me;Thanks,Paul

[teropa 4]

An Interesting thread.Just a small side-note here WRT documentation and performance. I'm not addressing PMDG with this, but I feel this is something of an issue in FS addon developing. Thing is, more and more detailed, even actual aircraft documentation is being attached to FS addon aicraft. Very nice indeed. But... when done so, the user expects that documentation to be usable with the addon he/she is using. I'm referring to the message above. If the documentation doesn't correspond to the product/aircraft, it's useless.Without knowing the actual details of this event, whether or not correct procedures were used or not, if everything was loaded up correctly and information from the tables used correctly, I will not say anymore, but I guess I just want to get this message through to all developers (not just PMDG):- the documentation should correspond the aircraft in every aspect- the documentation should be detailed enough to provide for ALL the _needed_ information so the user can accomplish the most basic flight planning & normal flying tasks- if there are certain parts in the documentation that will state conflicting information (or information that SEEMS conflicting but is not anyway), they should be removed or explained thoroughly why this or that is like it isIf the documentation provided is there just to provide countless hours of entertainment for the user, without the correspondence to the product itself, it should be clearly stated within the docs to avoid confusion.Tero