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VNAV at FL310 and climbing fast

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Hello everybody I haven't posted in a long time so here goes:The plane is at FL310 and I want to leave 310 for 360. She climbed hard and fast at 5000 fpm. This reminds me of the days with fs2k2 PSS 777-200. I am using the service pack 1, so my version is 1.1. Can anybody help me?ThanksWilson HinesMy Blog: http://www.wilsonhines.com --------------------------------------http://www.precisionmanuals.com/images/forum/747400.jpghttp://online.vatsimindicators.net/837438/3074.png

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Hi Wilson,Sounds like you're lightly loaded but I could be wrong.Some questions:Using any weather addons?Was the climb up to 310 as fast?What is your optimum altitude on the VNAV page of the FMS at the time you start the climb?

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The normal Vnav climb mode is VNAV SPD. This is a 'speed on pitch' climb mode. That means that thrust simply drives up to, and then holds at whatever EICAS thrust limit is in effect. The airplane will overspeed, but just for a nanosecond. As the AFS (autoflight system) sees the overspeed, it will rock the nose back (pitch up) to arrest this impending overspeed. The airplane will then control airspeed by pitching up or down as necessary to keep the airplane at the commanded airspeed. . . thus the name, "Speed on pitch." You will also hear it called speed "On the Elevetor." The point is that the rate of climb (in this mode) is not directly controlled at all. It'll be what ever it will be. If you are light, thrust will accelerate you like a race car. The AFS will then rock the nose back to control it . . and you will then climb like a rocket ship on steroids. 5000 fpm is not unusual at all. Current versions of the CF6 engine are at ~62,500 lbs/thrust. That's potentially ~250,000 lbs/thrust at TO. I spoke to a Boeing 747 post-production test pilot that said it can take 28 degrees of deck angle to control airspeed on a spankin' new 747-400 (TO pitch mode is also that speed on pitch thing) to just V2+10 during a non-derated, full power takeoff. These are massively powerful machines. 5000 fpm ROC? Even in the real world, that ain't nothing.

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True Sam, still I'm impressed that this guy is seeing a sustained 5000FPM at FL310, that's pretty huge! Certainly not impossible though, as you correctly point out!

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Hey, can we do formation flying in VatSIM. I'm a LOMAC fan too . . . and we chase each other around over there like crazy all the time (on Hyperlobby). -- Ahhh, with a slightly different goal! -- Can we load up to different weights and do formation, "Time to altitude trials?" That'd be fun.

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That actually sounds kinda cool. I normally constrain my flying to FTG routes so it's not often I take the 744 out for a non-standard operation.

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Kinda off topic, but some 747-400 pilots have said that in a lightly loaded 744, when holding for take-off on the runway, there is so much residual thrust generated that they can't hold it with the toe brakes. It's SOP to set the parking brake so she won't creep.That said, can you imagine a similar situation with a snow cluttered runway? Even with the parking brakes set, the residual thrust could skate the aircraft across a runway!

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>Hi Wilson,>>Sounds like you're lightly loaded but I could be wrong.>>Some questions:>>Using any weather addons?>>Was the climb up to 310 as fast?>>What is your optimum altitude on the VNAV page of the FMS at>the time you start the climb?>Loaded out @ 540,768 - almost a full load. All pax stations are loaded and only 12 cargo stations are empty.ASWXR was used, but I don't have problems like this.The climb up to 310 was perfect.365 was the optimal on the vnav. I am very careful about following that guidline.Wilson HinesMy Blog: http://www.wilsonhines.com --------------------------------------http://www.precisionmanuals.com/images/forum/747400.jpghttp://online.vatsimindicators.net/837438/3074.png

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For all Mx-hi power runs, we have to have a minimum fuel load (or ballast) to get the airplane heavy enough so it won't skid at TO power. Your are very right. It's a very real deal. Even at that, it can be kind of a hazard. Everyone's got their head down watches the gauges. Sometime the MIC (mechanic in command) will have to say: "Will someone please keep an eye out the window!?" They just don't get it. Something could go wrong . . . or like you said, the airplane could really, just skid away. If it starts skidding with the parking brakes set, getting on the toes isn't going to help . . . or visa-versa. Watch the wind direction for all this too. Compressor stalls are especialy (no) fun. Boom . . . boom, BOOM!The other thing I miss in the model is all that 'shakin' going on' during a brakes set, high power run. The airplane shakes like crazy. You have to double check your (written down) numbers after a run just to make sure they aren't just a bunch of squiggles. Real world pilots often don't see this because they generally don't advance to final, TO power until they have at least some forward airspeed. Maybe in the next patch. Hey Wilson, Chime on in. We're just chattin'. Was that ROC before or after FL310? Then, what was your pitch mode and what was your EICAS thrust limit set to?

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Gave it a try at a GW of ~540k, FL310, .83 mach and TAT of -25. I got a speed on pitch climb of about 2500fpm with CLB thrust, then about 3000 fpm when I raised the EICAC thrust limit to CON. I think you are right 5000fpm at this altitude/GW/etc is too much . . . . except I could (easily) get 5000fpm with V/S, that is until I ran out of airspeed and stalled!Couple of things didn't track though. I got an OPT of ~ FL390 at this very light GW. All (but 12) lower lobe spots filled and full pax is about 540K without any fuel. Regardless of loadout (in any case) 540 is very light.What was your pitch mode, AT mode, EICAS limit, TAT, And to double ck the weight, how about fuel load, CG and stab trim?

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Hi all,To make a note here, a 747 will not climb 5,000 fpm at 31,000 feet at around 300 knots at max thrust. You could push 5,000 feet per minute if you nose up but your airspeed would drop faily rapidly and you would stall. According to my 747-400 flight performance chart, here is the real world performance. This is the lightest weight the chart indicates:Gross Weight: 440,000lbsAirspeed: 290 knots IASAltitude: FL300Rate of Climbe: 2,900 fpm. Of course, this is at a fairly light weight. What was the weight of your airplane at the time this occured? Ken.

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>For all Mx-hi power runs, we have to have a minimum fuel load>(or ballast) to get the airplane heavy enough so it won't skid>at TO power. Your are very right. It's a very real deal. Even>at that, it can be kind of a hazard. >>Everyone's got their head down watches the gauges. Sometime>the MIC (mechanic in command) will have to say: "Will someone>please keep an eye out the window!?" They just don't get it.>Something could go wrong . . . or like you said, the airplane>could really, just skid away. If it starts skidding with the>parking brakes set, getting on the toes isn't going to help .>. . or visa-versa. >>Watch the wind direction for all this too. Compressor stalls>are especialy (no) fun. Boom . . . boom, BOOM!>>The other thing I miss in the model is all that 'shakin' going>on' during a brakes set, high power run. The airplane shakes>like crazy. You have to double check your (written down)>numbers after a run just to make sure they aren't just a bunch>of squiggles. Real world pilots often don't see this because>they generally don't advance to final, TO power until they>have at least some forward airspeed. Maybe in the next patch.>>>Hey Wilson, Chime on in. We're just chattin'. Was that ROC>before or after FL310? Then, what was your pitch mode and what>was your EICAS thrust limit set to? ROC was like between 1200 fpm and 1700 fpm before 310. In fact, when I got the gear up and took it up to 3000 ft, I was sitting there thinking "this is going to be a great flight (as far as the model goes) because usually if it takes it a while to hit 3000 ft agl (just like in the videos) everything from there out just flat out rocks. I mean, listen, this sim is so #### good when I start to throttle up and I hit the landing lights my freak'n heart starts to pump as if I were "there." Pitch Mode - that is a good question, because if it was on the wrong mode, that could have been the whole problem. EICAS T/L: Again, I can't remember.I am about to land at LOWW. When I do, I am going to set her up just like I had it. And I am going to look for the following:Pitch Mode, EICAS T/L, ZFW is going to be max that she will hold for the length of the trip and required fuel. Wilson HinesMy Blog: http://www.wilsonhines.com --------------------------------------http://www.precisionmanuals.com/images/forum/747400.jpghttp://online.vatsimindicators.net/837438/3074.png

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Anybody want to request any information FSUIPC settings, ACARS (Fs Flight Tracker), particulars for this test flight to try to replicate this problem?I am getting ready to prep for this flight.LOWW-Somewhere! LOLWilson HinesMy Blog: http://www.wilsonhines.com --------------------------------------http://www.precisionmanuals.com/images/forum/747400.jpghttp://online.vatsimindicators.net/837438/3074.png

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RESULTS:ZFW: 540,768 with 250,416 fuel on time off.CLB1 and VNAV SPD: Anywhere from 900 fpm to 1800 fpm through FL290 then from 290 to 310 it crawled up with a range from 200fpm to 800. Fl310 was optimal, but VATSIM controller called and asked for me to get FL350 if able. Well, my max was FL358 so it was a strecth, but if you can, you should I guess. To make it do that, I had to hit the V/S pitch mode and carry it up manually, it didn't want to go on VNAV SPD. So, it was 1000 fpm to FL350. This test is a failure LOLI may need to do this test at a later time with a whole lot less traffic. Wilson HinesMy Blog: http://www.wilsonhines.com --------------------------------------http://www.precisionmanuals.com/images/forum/747400.jpghttp://online.vatsimindicators.net/837438/3074.png

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Is it possible that your cruise speed in the FMC was set a fair bit higher than your FMC climb speed? For example cruise set at m .84 and climb set at m .78. Wouldn't the a/c generate a rather high initial ROC as it slows to capture the FMC "climb" speed? Since the altitude change was only 4000 feet you may have arrived at the new altitude before capturing the climb speed and therefore miss out on the a/c reducing to a more typical ROC. (am at work right now so can't test it out and, sad to say, haven't had much time in the Queen lately so can't speak with much authority, just ask questions).Hope you get it sorted.

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I just have no clue. I am going to test this in a more controlled environment. I don't have to work until Friday afternoon. So, I will have the time to get the low-down by then. Maybe even first thing in the morning. Everybody please don't give up on this quite yet.Wilson HinesMy Blog: http://www.wilsonhines.com --------------------------------------http://www.precisionmanuals.com/images/forum/747400.jpghttp://online.vatsimindicators.net/837438/3074.png

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Ahhh, Better. Now you're good and heavy. (Sorry, I didn't get that the 540 was a ZFW.) This really doesn't sound too bad. As we were discussing, VNAV SPD is a speed on pitch climb mode. Again, if a VNAV SPD climb is selected, the first thing that happens is that thrust just moves up to whatever EICAS limit is in place. That's the thrust mode "THR REF." The airplane overspeeds - just enough for the AFS to see it -- then the AFS reacts by pitching the nose up to control the speed. The more power the AT 'lays into it', the more pitch the AFS is going to need to control the airspeed. A higher pitch will result in a higher ROC. So now it become apparent that the ROC is completely dependant on how hard the AT mashes on the gas peddle when a VNAV SPD climb is commanded. Now I can say: "A higher EICAS thrust limit will provide a greater ROC a in VNAV SPD climb." Also, (just FYI) this the same way the pitch mode FLCH works, except ROC is the target. FLCH activates the thrust mode "THR." With this thrust mode, thrust doesn't just mash up to an EICAS limit. It moves around, actively targeting a ROC (up to an EICAS limit max). FLCH's ROC is determined by how much climb you have selected. Below a ~2000 request, thrust targets 1200 fpm. From ~2000 to about an (~)8000 ft request, thrust targets an increasing ROC. Above ~8000 ft, thrust just goes to the EICAS limit and you get a max available ROC. (Just like VNAV SPD will do for ANY amount of climb selection.) The thrust mode "THR" is the 'smartest' of the thrust modes. FLCH is a good alternatice to a VNAV PATH climb mode. Now you know why it's important to know what EICAS limit you were using for your VNAV SPD climb . . . . and another reason why a lot of these over the shoulder videos show RL ops with an EICAS thrust limit of CLB while in cruise.Careful of V/S mode . . . but only because there's no airspeed protection. If you are reverting to VS to climb, you are almost certainly trading off airspeed for altitude. Are you sure you want to do this? It's OK. Just be aware. IMO, cruise airspeed is close enough to a stall as it is (~V1.3g. That means that if I pull .3 gs, I will stall). There are other ways and I just would not what to mess with it. I love to test fly, but I

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>Is it possible that your cruise speed in the FMC was set a>fair bit higher than your FMC climb speed? For example cruise>set at m .84 and climb set at m .78. Wouldn't the a/c>generate a rather high initial ROC as it slows to capture the>FMC "climb" speed? Since the altitude change was only 4000>feet you may have arrived at the new altitude before capturing>the climbSimple calculations shows it is impossoble because of physics. The difference between 0.84M and 0.78M is only about 20 m/sec - you would bleed this amount of speed in just a few seconds whereas the change of altitude of 4000 ft would take a minute or more.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

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There on the other hand, ztimbe makes a very astute observation. In the scenario he describes there could indeed be an initial trade off of airspeed for a potentially increased ROC. The principal is entirely correct and the math, far from simple. (On thing though, does airspeed shift for a cruise climb? I

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The speeds listed were conservative because I was at work and could not recall with certainty typical climb and cruise speeds. Regardless, on further testing, my theory turns out to be incorrect.To the OP, I've duplicated your flight conditions re: weight on an ISA day, and get nearly the same max FL of 358. Unfortunately, even if I set the VNAV climb speed artificially low and the VNAV cruise speed artificially high, I still cannot reproduce what you're seeing. If, once stabilized in cruise @ mach .880 and FL310, I select a new cruise level of FL530 via VNAV, VNAV adopts the cruise speed during the "second" climb, and does not revert to the original (slower) climb speed. This results in a climb of approx. 800 fpm.If I manaully roll the speed back via speed intervention (VNAV still engaged -not FLCH), I can momentarily produce a ROC of approx. 3000 fpm. Once speed reaches the revised speed, however, the ROC climb reduces to approx 500-800 fpm. I could not in any case in VNAV produce a ROC of 5000 fpm with the weights you described. Sorry, but good luck to you anyway!regards.

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