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Richard McDonald Woods

Brake temperatures on heavy RTO

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I have been practicing my RTO procedures with a fully loaded 747-400 under Vista, FSX and PMDG 747-400X. I feel that the indicated brake temperatures are too low.My RTOs took place at EGLL RWY27R with OAT 15C, flaps 20 and a dry runway. Aircraft had a ZFW 264.5 tonnes and a GTOW of 437.1 tonnes. With V speeds of 154/170/191, I accelerated to 154 to execute the RTO. But for 10 minutes after coming to a halt, the brake temperatures all showed only 2. Surely this is not realistic?Cheers, Richard

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Hello Richard-Actually at 337.1T (which I'm guessing is what you meant) you really aren't THAT heavy. Try it at 397T (60T heavier) and I'll guarantee higher temps ;)It would be interesting for our RW drivers to give us typical brake temps at 330T and 390T RTOs. Anyone?Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png| XP Pro SP3 | 2 x APC UPS | Coolermaster Stacker 830 SE | Gigabyte P35 DS3R | e8500 @ 4gHz | Tuniq Tower 120 | EVGA 8800GT 512MB | Creative X-Fi Fatal1ty | 2 x 1 GB Corsair XMS2 | 2 x 320GB WD Caviar RAID 0 | Corsair HX620W PS | CH Products Yoke-Pedals-Throttle Quadrant | Aerosoft 747MCP-EFIS-EICAS |

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Richard-Carl's feedback is correct- you have to get pretty heavy and pretty fast before you'll see things get excessively hot.Also keep in mind that the autobrakes are targeting a decel rate. On the real airplane if you have spoilers out and reversers screaming- you are going to see a lower brake temperature than you would if you reject the takeoff and leave the engines at idle. In the case where you use reverse thrust you are reducing the amount of energy that must be absorbed by the brakes (which is always a good thing...)

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Hi Carl and Robert!I have now rechecked my figures, and have to report the same brake temperatures of 2 all round, even under Vista/FSX/PMDG 747-400X V2.1 (10.0.61355.39)I have maxed the numbers in the Load Manager. This gives ZFW 264,337 kgs, and Fuel of 132,553 kgs. The PMDG Aircraft Fuel option set to max then alters Fuel to 173,600 kgs.So I RTO with ZFW 264.5 tonnes, plus Fuel of 173.5 tonnes, giving GTOW of 438.1 kgs. The brake temps then show 2 on all wheels.I understand that these figures are above MTOW, which the PMDG manual sets at 396,893 kgs (MTW is 397,800 kgs). But surely this should only make the brake temperatures even higher!Or am I missing something?Cheers, Richard

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Richard-I just ran tests in both the FS9/FSX 747-400s. Conducted at MGTW with the abort at 140 KIAS, no spoilers, no reverse.In both platforms I saw the temps reach 5 and 6 respectively.If you are only getting to 2, I'd suspect that something in your setup is tripping off the autobrakes before the decel is completed.This could be caused by a couple of different things, such as not bring the throttles all the way back, manually stowing the spoiler handle during braking, etc.Note that these actions could also be triggered by spiking in hardware being interpreted as the above actions...We chased a problem with some hardware toe brake assignments tripping the autobrake when we didn't want it to- but this was resolved many many months ago and was pretty thoroughly tested.So- not sure what to recommend to you- but on my tests here both platforms worked as expected...

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Robert, are you sure he never got the new carbon brakes on his? If so I feel a bit ripped off. I still got the steel!

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Hi Robert!Thanks for your prompt reply. I shall reserve further judgement on this until I have a little more experience of the update.Thanks, Richard

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Richard- speaking for the FS9 version, I can say that Robert's temps are echoed in my RTOs..........let us know- you've got me "curiouser and curiouser" ;)Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png| XP Pro SP3 | 2 x APC UPS | Coolermaster Stacker 830 SE | Gigabyte P35 DS3R | e8500 @ 4gHz | Tuniq Tower 120 | EVGA 8800GT 512MB | Creative X-Fi Fatal1ty | 2 x 1 GB Corsair XMS2 | 2 x 320GB WD Caviar RAID 0 | Corsair HX620W PS | CH Products Yoke-Pedals-Throttle Quadrant | Aerosoft 747MCP-EFIS-EICAS |

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Guest hangar744

Hi there,Caution. Autobrake RTO circuit does NOT target deceleration. The control circuit that monitors the pressure on/off ramp rates is bypassed. Maximum braking effort is commanded without time delay.The autobrake functions should be separated in three totally different groups. Autobrake selection 1, 2 and 3 haven't got much in common with selection 4 and MAX AUTO. RTO is also from a different planet. Only the 1, 2, 3 and MAX AUTO are designed to increase and decrease the brake pressure to maintain the preset decelerations. Circuit 1, 2 and 3 will try (runway friction) to command 4.0, 5.0 and 6.0 ft/sec2 deceleration with 0.2 sec delay at the maximum control pressure of 1500, 1750 and 2000 PSI.Circuit 4 and MAX AUTO will try to command 7.5 and 11.0 ft/sec2 deceleration with 0.2 sec delay at the maximum control pressure of 2400 and 3000 PSI. However the deceleration command is initially limited to 6.0 ft/sec2, and it's ramped to the final value within approximately 5 sec of braking initiation.We calculate with some additional delays like wheel spinup detection, filling up the brakes with hydraulic fluid. Some kind of braking action is provided after autobrake initiation, but a controlled deceleration rate is only achieved after approximately 1.2 sec. If the runway friction is not sufficient (wet, ice, patchy, etc.) to maintain the commanded deceleration, the autobrake pressure will be maintained at the maximum control pressure for each deceleration setting respectively, so the a/c deceleration due to braking will be pretty much the result of the antiskid system performance only. That's why we use some additional aerodynamic drag (spoiler, T/R). With the help of those drags we can produce a/c deceleration in excess of the selected deceleration, so the autobrake system will reduce brake pressure. One can understand immediately, in case of RTO the brake pressure is not reduced at all...so actual deceleration depends on a/c weight and rwy condition.Let's stay with RTO, and take a look at some numbers.Conditions: MGTW, brakes on speed 140 KIAS, no slope, no wind, press alt 0 ft, OAT 15 deg C. Most of the a/c kinetic energy is converted to thermal energy by the brakes. In this case the brake energy per brake will be 53.4 millions of foot pounds, heating up the brake core to a temp of 1750 deg F. This is not sensed by the temp sensor. The a/c has came to a stop. It will transmit a lot lower value of approximately 250 deg F. That temperature is still only a white 0 EICAS indication. In the next minute the core temp will spread causing the sensor to transmit higher values. Passing 350 deg F (EICAS white 1), 487 deg F (EICAS white 2), 625 deg F (EICAS white 3), 762 deg F (EICAS white 4). Probably within 3 minutes it will reach 900 deg F triggering BRAKE TEMP EICAS ADVISORY MESSAGE and also change the color to amber 5. The sensed temperature of the brake will keep rising, however the core temp of the brake is already decreasing. Sensed temp will rise to 1037 (amber 6), 1175 (amber 7), 1312 (amber 8), and in our test it will not reach the 1450 deg F (EICAS amber 9). The temp indication system will not provide accurate temperatures for the first 15 minutes after the a/c has come to a complete stop, and it will sense and transmit approx 400 deg F lower temperature than the actual core temperature for the next 2 hours. You don't wanna be near that gear for sure.So this test (MGTW/ 140KIAS) should result an EICAS amber 8.Cpt. Randazzo did his tests and reached temp 5 for the FS9. According to my calculations, 108 KIAS brake on speed would do a "low" 5 indication with MGTW. 116 KIAS would still get away with 5.Carl asked for RTO temp at 330T. With 140 KIAS brake on speed would do 46.2 million foot-pound brake energy per brake. A new brake assy, with high heat sink mass value will cause about 1225 deg F core temperature. Reading should be 4.Hope I did not write anything insane, wasn't my intention.regards and happy RTO's,delcom

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Delcom:Thanks! Wow- THIS is why I love this forum!Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png| XP Pro SP3 | 2 x APC UPS | Coolermaster Stacker 830 SE | Gigabyte P35 DS3R | e8500 @ 4gHz | Tuniq Tower 120 | EVGA 8800GT 512MB | Creative X-Fi Fatal1ty | 2 x 1 GB Corsair XMS2 | 2 x 320GB WD Caviar RAID 0 | Corsair HX620W PS | CH Products Yoke-Pedals-Throttle Quadrant | Aerosoft 747MCP-EFIS-EICAS |

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Someone on another forum calclulated the energy dissipation for stopping at 100Kt and MTOGW to be 756 Megajoules. The decision to reject or to continue the takeoff becomes more and more critical at higher speeds, due to the enormous energies involved. The increasing risk of wheel fire, or tire or wheel loss obviously needs to be weighed against the severity of the fault or failure requiring the decision to be made. Indeed, in many cases, it is often safer to take an otherwise serviceable and controllable aeroplane into the air and deal with the problem there, before dumping fuel and returning. For this reason, Boeing has made 80kts a cutover point for B747-400 RTO. Below 80 kts, the takeoff would normally be aborted for engine failure, any fire or fire warning, system failure, master caution, abnormally slow acceleration, takeoff config warnings, predictive windshear alerts, unusual noise or vibration, or if the aircraft is unsafe or unable to fly. Above 80kts and prior to V1, the takeoff is generally only aborted for fire/fire warning, engine failure, predictive windshear or if the aircraft becomes unsafe or unable to fly (in the Captain's opinion).

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Well quoted. Thanks!Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png| XP Pro SP3 | 2 x APC UPS | Coolermaster Stacker 830 SE | Gigabyte P35 DS3R | e8500 @ 4gHz | Tuniq Tower 120 | EVGA 8800GT 512MB | Creative X-Fi Fatal1ty | 2 x 1 GB Corsair XMS2 | 2 x 320GB WD Caviar RAID 0 | Corsair HX620W PS | CH Products Yoke-Pedals-Throttle Quadrant | Aerosoft 747MCP-EFIS-EICAS |

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