jayeshrulz
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A Question For Pilots.

Wed Nov 25, 2009 10:53 am

Hi there,

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?
And what about a/c such as Dash 8 or ATR?

thanks.
Keep flying, because the sky is no limit!
 
swiftski
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RE: A Question For Pilots.

Wed Nov 25, 2009 11:43 am



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's calculated, but relies on the data inputs for weight.

Quoting Jayeshrulz (Thread starter):
Vref

Don't get confused - Vref doesn't mean "reference speeds". Vref is an approach speed. Expect this to be something like (1.3Vso+5),
 
jayeshrulz
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RE: A Question For Pilots.

Wed Nov 25, 2009 11:55 am

sorry i meant Vr! :P

So is it calculated by FMC, hmm....can you please elaborate, meaning how is the wt calculated?
Like ZFW+pax wt+cargo wt + fuel wt...anything else?

[Edited 2009-11-25 04:03:19 by jayeshrulz]
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ANITIX87
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RE: A Question For Pilots.

Wed Nov 25, 2009 1:57 pm

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
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RE: A Question For Pilots.

Wed Nov 25, 2009 2:27 pm

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
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RE: A Question For Pilots.

Wed Nov 25, 2009 2:37 pm



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.
 
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glen
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RE: A Question For Pilots.

Wed Nov 25, 2009 5:10 pm

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
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RE: A Question For Pilots.

Wed Nov 25, 2009 5:49 pm



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
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RE: A Question For Pilots.

Wed Nov 25, 2009 5:58 pm



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
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RE: A Question For Pilots.

Wed Nov 25, 2009 8:46 pm

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
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RE: A Question For Pilots.

Thu Nov 26, 2009 3:28 am



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.

Tom.
 
pilotpip
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RE: A Question For Pilots.

Thu Nov 26, 2009 4:17 am

We get our numbers via ACARS (or speed cards in the aircraft) but enter them manually. The problem with setting Vapp, is that it really doesn't take gust factors or personal preference into account.
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Mir
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RE: A Question For Pilots.

Thu Nov 26, 2009 5:23 am



Quoting Jayeshrulz (Reply 2):
So is it calculated by FMC, hmm....can you please elaborate, meaning how is the wt calculated?
Like ZFW+pax wt+cargo wt + fuel wt...anything else?

Empty weight + pax + cargo + fuel is what the system I'm working with uses. Then you have a temperature and CG input, and the runway that you plan to use. From this, the FMC calculates the speeds.

So yes, the actual calculations are automatic, but if you put something in wrong in the initial setup, you're going to get bad data at the end - garbage in, garbage out.

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jayeshrulz
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RE: A Question For Pilots.

Thu Nov 26, 2009 2:11 pm

thanks guys.


I thought mostly they were to be automatically calculated, like in my pmdg 747, i just confirm my speeds :P

Is it possible for the aircraft to calculate the exact speed...is the Approach speed also done my FMC?

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?
tks!
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CosmicCruiser
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RE: A Question For Pilots.

Thu Nov 26, 2009 2:42 pm



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.
 
Woodreau
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RE: A Question For Pilots.

Thu Nov 26, 2009 3:31 pm



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?

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A346Dude
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RE: A Question For Pilots.

Thu Nov 26, 2009 4:00 pm



Quoting Woodreau (Reply 15):
Mk 1 Mod 0 Eyeball with or without corrective lenses and/or tinting

Plus the assistance of a glideslope, most of the time (not that it's necessary in VFR conditions).
You know the gear is up and locked when it takes full throttle to taxi to the terminal.
 
thegreatchecko
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RE: A Question For Pilots.

Thu Nov 26, 2009 5:50 pm



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

Example:

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.

Happy Flying!

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CX Flyboy
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RE: A Question For Pilots.

Fri Nov 27, 2009 1:18 pm

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
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RE: A Question For Pilots.

Sun Nov 29, 2009 6:03 am



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!
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Goldenshield
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RE: A Question For Pilots.

Sun Nov 29, 2009 9:45 am



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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jayeshrulz
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RE: A Question For Pilots.

Sat Dec 05, 2009 1:00 pm

hi,

i'm asking how do you know the fuel quantity added+ pax wt.

there must some formula to calculate the V speeds.
And how does the pilot know CG%
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tdscanuck
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RE: A Question For Pilots.

Sat Dec 05, 2009 7:44 pm



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.

Quoting Jayeshrulz (Reply 21):
there must some formula to calculate the V speeds.

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.

Quoting Jayeshrulz (Reply 21):
And how does the pilot know CG%

On most planes, dispatch tells them (from the fuel & pax load + airplane data). Some planes compute it, especially freighters, using sensors.

Tom.
 
Fabo
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RE: A Question For Pilots.

Wed Dec 23, 2009 12:02 am

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.

APT PRWY POAT PWIND PQNH PMRTW FLP CONF THRUST V1 VR V2 PTOW
UUWW 20 -15°C 160/02 1019 252796 FLAPS 20 D-TO2 +45°C 110 131 143 252475

RMKS SPEED/FLAPS SCHEDULE: VREF30=144 F10=164 F5=184 F1=204 UP=224 CLEAN=244



--------- ------ --------- ----- ----------- ----- ----- ----- ---------------------
RWY/INT OAT WIND QNH RWY COND V1 VR V2 THRUST/FLAPS CONFIG


------- REDUCED - 6MM WATER - OPT FLAPS - OPT THRUST - A/C ON - A/I ON OR OFF ------
RWY 20
3060 M
TO2 HW02
AT EPR FLAPS 20
+49 1.37 244278 F10-30-41
+47 1.37 248465 F10-31-43
/+45 1.38 252796 F10-32-44
+43 1.38 257134 F10-33-45
+41 1.39 261471 F10-35-46
HW/10 KT +3860
TW/15 KT -26147


--------- FULL - 6MM WATER - OPT FLAPS - OPT THRUST - A/C ON - A/I ON OR OFF -------
RWY 20
3060 M
TO HW02
OAT EPR FLAPS 20
-11 1.76 293329 F25-37-56
-13 1.76 293329 F25-37-56
/-15 1.76 293329 F25-37-56
-17 1.76 293329 F25-37-56
-19 1.76 293329 F25-37-56
HW/10 KT +25844
TW/15 KT -29332


Pretty good, huh? Although I liked the old format better.
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Fabo
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RE: A Question For Pilots.

Wed Dec 23, 2009 12:03 am

Example of old report.

--- AIRPORT/RUNWAY ---------------------- CONDITIONS ------------------------

LZKZ 19 (KOSICE)
T.O.R.A. = 2600M WIND = 240/5 (3 HEAD)
T.O.D.A. = 2600M QNH = 1018
A.S.D.A. = 2600M TEMP = +9 °C
ELEV. = 753FT (230M) WEIGHT = 50673 KG
HEADING = 189°
SLOPE = +0.0%

SPEED SCHED : VREF 40=121 CLEAN=191

--- REMARKS -----------------------------------------------------------------

TEMPO RWY SHORTENING 500M FROM RWY HEAD

--- FLAPS 1 - D-TO2 - RWY DRY - AIR COND ON - ANTI ICE OFF ------------------

* INDICATES OAT OUTSIDE ENVIRONMENTAL ENVELOPE

TEMP°C N1 LIMIT CODE V1 VR V2 MARGIN
47 * NOT AUTH *
-> 45 80.9% 50748 CLIMB 123 123 126 759M
43 81.1% 51794 CLIMB 123 123 126 820M
41 81.4% 52840 CLIMB 122-123 123 126 878M
39 81.6% 53899 CLIMB 122-123 123 126 936M

--- FLAPS 1 - TO2 - RWY DRY - AIR COND ON - ANTI ICE OFF --------------------

TEMP°C N1 LIMIT CODE V1 VR V2 MARGIN
11 86.2% 59539 CLIMB 120-121 121 126 1222M
-> 9 85.9% 59577 CLIMB 120-121 121 126 1231M
7 85.6% 59608 CLIMB 120-121 121 126 1240M

--- OBSTACLES - LZKZ - RWY 19 -----------------------------------------------

NONE
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