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Struggling to keep speed in headwind

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I'm at FL370 with a headwind of 242/40. My speed is 225 but should be .825. N1 is 101.3 on each engine. PFD is THR REF/LNAV/VNAV SPD

 

the speed is right on the red lines, any advice on what to do?

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Check flaps and gear???  Calibrate your throttle quadrant?  Disengage AP and see what occurs when you take manual control.


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Flaps and gear are up. Its on autothrottle at the moment. I am using AS2012.

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I'm at FL370 with a headwind of 242/40. My speed is 225 but should be .825. N1 is 101.3 on each engine. PFD is THR REF/LNAV/VNAV SPD

 

the speed is right on the red lines, any advice on what to do?

Hi Chris,

Your speed maybe showing 225, but this is Knots. Above FL 240  The mach No comes into play and Knots is not valid.  I agree, .825 sounds about right. What does the bottom of the PFD show, as this is where you will find the mach Number directly under the speed tape. Also, are the red bricks climbing from the bottom on the speed tape, indicating you have a speed problem developing? 

 

It also sounds like the weather engine is giving you some very unkind winds, which is very common. Do you have a registered version of FSUIPC? as this is often used to restrict winds. Maybe the winds displayed are 'only' 40 knots, but possibly, the weather engine is generating a lot more.

 

What temps do you have outside, as some times the weather engines create a high temp which reduces air speed.

 

The easy test is to remove all weather(which you can do while flying) and check what results you get. If now ok, its indicating you have a high head wind issue

 

Hope this helps.

 

Regards


Geoff Bryce

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por930, on 17 Mar 2013 - 12:56, said:

Hi Chris,

Your speed maybe showing 225, but this is Knots. Above FL 240 The mach No comes into play and Knots is not valid. I agree, .825 sounds about right. What does the bottom of the PFD show, as this is where you will find the mach Number directly under the speed tape. Also, are the red bricks climbing from the bottom on the speed tape, indicating you have a speed problem developing?

 

It also sounds like the weather engine is giving you some very unkind winds, which is very common. Do you have a registered version of FSUIPC? as this is often used to restrict winds. Maybe the winds displayed are 'only' 40 knots, but possibly, the weather engine is generating a lot more.

 

What temps do you have outside, as some times the weather engines create a high temp which reduces air speed.

 

The easy test is to remove all weather(which you can do while flying) and check what results you get. If now ok, its indicating you have a high head wind issue

 

Hope this helps.

 

Regards

Hi thanks for the explanation. i was having a headwind issue as its now 213/23 with my heading at 239. My speed is now .827.

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If we are talking 747, Mach .827 is inside the normal range for some cost indexes. I like things a touch quicker myself (cost index 100, mach .84 to .86 depending on altitude) but .827 will get ya there.

 

Some weather generators have an issue of too high a temperature at altitude, in which case you will struggle to maintain altitude itself. Sometimes 'turbulence' generation in the sim is a bit unrealistic (the entire air-mass of the planet moves left and right at random in millisecond intervals.)

 

Headwind on it's own shouldn't change anything except ground speed. Mach .827 with a 150 knot headwind requires the same amount of thrust as Mach .827 with a 40 knot tailwind, or 80 knot crosswind, or no wind. The only time anything becomes a problem is if the wind is shifting in speed or direction. FSUICP can limit the wind direction shift so that the weather generator doesn't do the silly and turn a 150kt tailwind into a 90 knot headwind in 2 seconds (which would be impossible in real life, and leads to a 240kt change in airspeed in an instant in the sim).

 

Airspeed is not the same as speed over the ground.


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Trent Hopkinson, 2015 Crewmember of www.mangrove.com.au WorldFlight sim

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Hi thanks for the explanation. i was having a headwind issue as its now 213/23 with my heading at 239. My speed is now .827.

 

Chris,
 
Wind should not affect your airspeed, it affects ground speed.  Also a 40 knot headwind is not excessive, it's quite realistic.  What sounds very strange is your IAS of 225 corresponding to a Mach number of 0.825.  225 is really quite low for a cruising speed.  It's getting near the point you'd need to extend flaps!  At Mach 0.825, IAS should be approximately 270 knots.
 
I've seen the PMDG 747 suddenly lose thrust and have speed drop quite low, and then it struggles to accelerate again.  But if that had happened Mach number would decrease too.  Are you flying online with VATSIM?  FSInn is notorious for computing odd atmospheric conditions at high altitude and that might be part of the cause.  It's normal to disable FSInn weather at high altitudes.
 
Some screenshots of the panel would help.  An offline test flight with no weather program running and with zero wind would be worth trying to see if the 747 flies normally with no weather effects.

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