ANITIX87 From United States of America, joined Mar 2005, 3233 posts, RR: 14 Reply 3, posted (3 years 5 months 3 weeks 5 days 14 hours ago) and read 3934 times:
Along similar lines, is weight still calculated using "average weight of a human" or whatever they call it? I recently saw a show about a situation where the weight in a turboprop (which is, admittedly, more important than in a 300-person widebody) was wrong and the plane crashed because it was over MTOW. Or do aircraft nowadays have a better way of obtaining true total weight (whether it's a sensor in the landing gear to measure it's compression, or something else...).
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Buckfifty From Canada, joined Oct 2001, 1314 posts, RR: 21 Reply 4, posted (3 years 5 months 3 weeks 5 days 13 hours ago) and read 3921 times:
Generally, the speeds are calculated manually (via charts in the cockpit), or by a system at an airline's home base, where the data can be accessed from the aircraft by ACARS.
The V speeds are extrapolated from a database created during the aircraft's flight test program, using variables which include the TODA, ZFW, TOW, QNH, airfield temperature and wind speed. The aircraft's basic weight is already taken into account as a constant, and the system will calculate the takeoff thrust required, optimal flap configuration, and the V speeds.
We input the V speeds manually into the computers. Personally, I don't know of any aircraft that will calculate them on it's own, but I could be wrong...
CosmicCruiser From United States of America, joined Feb 2005, 2211 posts, RR: 16 Reply 5, posted (3 years 5 months 3 weeks 5 days 13 hours ago) and read 3917 times:
Quoting Buckfifty (Reply 4): I don't know of any aircraft that will calculate them on it's own, but I could be wrong...
The FMC in the MD-11 does calculate the V speeds and they can be modified manually as well. Often we see V1 calculated by our perf comp differ from the FMS V1 so it will be modified. In the MD-10 system all V speeds are manually inserted.
GLEN From Switzerland, joined Jun 2005, 199 posts, RR: 2 Reply 6, posted (3 years 5 months 3 weeks 5 days 10 hours ago) and read 3872 times:
V-Speed calculated by the FMC like on the MD11 are pure aerodynamical speeds, based on the actual weight entered into the FMS, i.e. they have a mathematical relation to the stall speed.
On newer aircraft like Airbus (I don't know Boeing, but I think it is similar) the calculation of V-Speeds is more sophisticated. They are not only depending on weight, but also optimized for runway length, obstacle situation at a specific airport, runway condition and atmospheric conditions. The calculation is done via tables for each specific runway or via a certified performance program on a separate laptop.
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CosmicCruiser From United States of America, joined Feb 2005, 2211 posts, RR: 16 Reply 7, posted (3 years 5 months 3 weeks 5 days 10 hours ago) and read 3849 times:
Quoting GLEN (Reply 6): are pure aerodynamical speeds, based on the actual weight entered into the FMS, i.e. they have a mathematical relation to the stall speed.
I won't challenge you because our manual doesn't get that specific EXCEPT for a reference that Vcl is based on wgt AND manuvering requirements. But I would have said the Vspeeds are based on wgt AND runway length since a specific rnwy must be entered before any V speeds are generated. As your post below references our perf laptop "trumps" the FMS V speeds because it does consider wx., rnwy conditions and MEL/CDL items.
Quoting GLEN (Reply 6): via a certified performance program on a separate laptop.
A346Dude From Canada, joined Nov 2004, 1198 posts, RR: 8 Reply 8, posted (3 years 5 months 3 weeks 5 days 10 hours ago) and read 3845 times:
Quoting ANITIX87 (Reply 3): I recently saw a show about a situation where the weight in a turboprop (which is, admittedly, more important than in a 300-person widebody) was wrong and the plane crashed because it was over MTOW.
I watched that episode too (Mayday/Air Crash Investigation on Air Midwest Flight 5481) and I think it was somewhat misleading. Even though the aircraft may have been slightly over MTOW, it was the overly aft CG coupled with inadequate elevator authority caused by improper maintenance that caused the accident. The fact that the use of average passenger weights resulted in the aircraft being operated overweight probably had nothing to do with the accident - it was the "balance" portion of weight and balance that was the problem.
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DashTrash From United States of America, joined Aug 2006, 1314 posts, RR: 4 Reply 9, posted (3 years 5 months 3 weeks 5 days 7 hours ago) and read 3792 times:
In the Dash 8 you get the Vspeeds from the speed cards, or other info provided by the operating company or manufacturer. It is based on weight. If the runway requires a lower V1, you would get that info from the flight release provided by the dispatcher.
Flying the Citation X with the FMZ, legally you must get you perf data from the flight manual. In reality it comes from the FMZ based on the runway, aircraft weight, flap setting and antiice on or off. Those speeds are then posted to the airspeed tape automatically and cross checked with the flight manual numbers.
After getting the ATIS, we enter the runway, approach, altimeter setting, temp, and wind. The FMS will ask you to verify that the a/ice is on or off, and what flap setting you will use. After that is entered, it will calculate runway requirements, wind vectors, and Vspeeds.
Tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81 Reply 10, posted (3 years 5 months 3 weeks 5 days ago) and read 3730 times:
Quoting Jayeshrulz (Thread starter): I want to ask that in the FMC or Airbus or Boeing, does the pilot manually enter the Vref speed such as V1, Vr, V2 or it is automatically calculated?
It depends on the aircraft. The ability to calculate v-speeds in the FMC is usually a customer option, because some airlines like it and some airlines hate it. If you have an FMC with V-speed calculation disabled, you get the data from dispatch.
Quoting GLEN (Reply 6): On newer aircraft like Airbus (I don't know Boeing, but I think it is similar) the calculation of V-Speeds is more sophisticated.
Depends on how the options are purchased. On a Boeing, really sophisticated V-speed calculations need some other computer (e.g. an EFB or performance laptop) since the FMC can't do improved climb, wet runway, etc.
The defaults are also different...I believe Airbus defaults to an improved climb while Boeing defaults to a balanced field.
CosmicCruiser From United States of America, joined Feb 2005, 2211 posts, RR: 16 Reply 14, posted (3 years 5 months 3 weeks 4 days 13 hours ago) and read 3609 times:
Quoting Jayeshrulz (Reply 13): Is it possible for the aircraft to calculate the exact speed...is the Approach speed also done my FMC?
I'm speaking only about our MD-11, No the exact V speeds for t/o cannot be calculated because the FMS doesn't know the airport conditions eg. clutter nor wind, nor any MEL/CDL conditions, those parameters are all considered in the perf. laptop.
Yes the Vref & Vapp are calculated by the FMS since it's only weight generated. Any additions due to wind or eng out conditions must be edited by the pilot.
As I posted earlier the MD-10 requires pilot input for V1, Vr & V2 all others are FMS generated.
Quoting Jayeshrulz (Reply 13): How is the rate of descend calc by the pilot?...i mean if the airport is 10 miles 12'o clock, at 2500. how is it calculated?Any formulaes
We use the 3:1 ratio. For a 3 deg app path you descend 300' for every 1 mile. If you turn a 5 mi final you should be 1500' agl. You can also use this for a rough estimate of a descent point from altitude adding or subtracting miles for hdwind/tlwind.
Thegreatchecko From United States of America, joined Mar 2004, 1110 posts, RR: 3 Reply 17, posted (3 years 5 months 3 weeks 4 days 10 hours ago) and read 3558 times:
Quoting Jayeshrulz (Reply 13): How is the rate of descend calc by the pilot?...i mean if the airport is 10 miles 12'o clock, at 2500. how is it calculated?Any formulaes?
These easy mental math formulas will give you a pretty close idea.
Altitude to be lost / 10 * 3 = Distance from point to start descent
Ground Speed / 2 * 10 = Rate of Descent
Cruising Altitude: 25,000 ft
Airport: 5,000 ft
Ground Speed: 380 knots
Altitude Difference = 20,000 ft
20,000/10 = 20 * 3 = 60 miles
380 / 2 = 160 * 10 = 1600 Feet per minute
In other words, one would start the descent 60 miles from the field and maintain an approximately 1600FPM descent to the field.
Keep in mind that one would need to take into account the change in ground speed as the aircraft accelerated or decelerated in the descent (this is very important if meeting a crossing restriction!!) and the possible need to level out to slow down and configure the aircraft for landing.
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CX flyboy From Hong Kong, joined Dec 1999, 6341 posts, RR: 56 Reply 18, posted (3 years 5 months 3 weeks 3 days 14 hours ago) and read 3471 times:
For the FMC, in CX on the 747 and 777 the FMC calculates the Vspeeds automatically, however we ignore these and use the company system calculated speeds which are deemed to be ore accurate. We do refer to the calculated FMC ones and if they vary greatly to the company-generated ones then it is a clue to investigate why.
Jayeshrulz From India, joined Apr 2007, 1000 posts, RR: 4 Reply 19, posted (3 years 5 months 3 weeks 1 day 21 hours ago) and read 3295 times:
Quoting CX flyboy (Reply 18): For the FMC, in CX on the 747 and 777 the FMC calculates the Vspeeds automatically, however we ignore these and use the company system calculated speeds which are deemed to be ore accurate. We do refer to the calculated FMC ones and if they vary greatly to the company-generated ones then it is a clue to investigate why.
hmm...can anyone please tell me how to calc the Vspeeds?..tks!
Goldenshield From United States of America, joined Jan 2001, 5427 posts, RR: 12 Reply 20, posted (3 years 5 months 3 weeks 1 day 18 hours ago) and read 3264 times:
Quoting Jayeshrulz (Reply 19): hmm...can anyone please tell me how to calc the Vspeeds?..tks!
Well, one option is to pay a company (AERODATA, etc.) lots of money to make you data, as they take into account local variables, such as mountains, etc., and then provide a fairly nice, straight-forward way to calculate other possible variables. Other way is to find an aircraft's performance manuals, and go through the spaghetti charts to find the appropriate number.
I, for one don't have that kind of money, and I hate dealing with spaghetti charts.
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Tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81 Reply 22, posted (3 years 5 months 2 weeks 2 days 8 hours ago) and read 2933 times:
Quoting Jayeshrulz (Reply 21): i'm asking how do you know the fuel quantity added+ pax wt.
Fuel quantity comes directly from the gauging system (it reads out in pounds/kilos). Pax weight is usually estimated as # of pax times some average weight (for large numbers of pax, that's valid). Small airplanes will weigh passengers individually. That data should go to the flight crew via the dispatch paperwork.
Not really. It's a bunch of lookup tables. The FMC is basically doing the same thing as you do with the spaghetti charts. What's really going on is you're calculating a bunch of V-speeds for various conditions (obstacle clearance, minimum climb gradient, max braking energy, balanced field, etc.) and they taking the most conservative speeds from each situation to come up with a final V1/Vr/V2 that meets all the requirements. It's specific to thrust, runway length, temperature, wind, obstacles, weight, CG, etc. Throw improved climb into the mix and it gets even more complicated.
Fabo From Slovakia, joined Aug 2005, 1111 posts, RR: 1 Reply 23, posted (3 years 4 months 4 weeks 1 day 3 hours ago) and read 2352 times:
You can get a nice little program called TOPCAT for your PMDG 747 - it does basically the same thing dispatch does for real pilots - you get a really real looking loadsheet off it, complete with weights, CoG data, or, say, instructions for spoiler trimming. Then, another part, is take-off performance calculator, which will do exactly what you need - it takes into account all the different things, like load, runway data (length, obstacle clearance, even engine-failure-after-v1 scenario on some airports), wind, temperature, packs on/off, etc. etc. and will blow out a pretty comprehensive bunch of data, including, of course, v-speeds, but also FLEX temperatures, optimal flap settings (Forget Flaps 5 on 737, you DO get anything from 1 to 15 on regular basis)
Say I had a pretty full 747 of holidaymakers wanting to go from Moscow to Turkey (not that it is any good idea in middle of December, but whatever) - so I set TOPCAT up, and let it compute my data, for now, just for RWY20 in VKO.