Hello, Guys!

 

See in picture given and tell me how is it possible that Thai Airways is on 36,975 Ft Height with 501 Knots Speed? Another plane I saw at the same place of KLM Boeing 747-400 was going on 39000 Ft Height and approximately 500 Knots speed?

 

You can see this plane in the picture in yellow highlight and web site is planefinder.net.

 

On FSX, When I fly B747-400, Its speed decreases as its Height increases and vice versa. My speed on FSX B747-400 is 274 Knots on 39000Ft Height. Very simple, when I decrease the Height, Speed automatically increases.

 

So how is it possible in real Thai and KLM? Why I cannot go on FSX as Thai and KLM going?

 

There using true air speed TAS What you see in your sim is Indicated air speed IAS on the PFD display

While flying bring up your GPS, there you will see letters GS and some three numbers behind it, for example GS501

 

The number you see behind GS is your groundspeed which i think is the speed shown also on planefinder.

If you're not already familiar, I would definitely take some time to go through the difference between IAS and TAS. It call comes down to IAS being measured based on pressure...which all-in-all decreases with altitude. Also never forget about the possibility of headwinds and tail winds. These don't affect IAS/TAS, but do affect ground speed which can exceed 700 kts on a 747 with a hefty tail wind.

Hello, Guys!

 

 

 

There using true air speed TAS What you see in your sim is Indicated air speed IAS on the PFD display

 

 

While flying bring up your GPS, there you will see letters GS and some three numbers behind it, for example GS501

 

The number you see behind GS is your groundspeed which i think is the speed shown also on planefinder.

 

 

If you're not already familiar, I would definitely take some time to go through the difference between IAS and TAS. It call comes down to IAS being measured based on pressure...which all-in-all decreases with altitude. Also never forget about the possibility of headwinds and tail winds. These don't affect IAS/TAS, but do affect ground speed which can exceed 700 kts on a 747 with a hefty tail wind.

 

You are all right but I still have not reached where real plane reaches. Real plane on planefinder.net has 33000ft plus 539Knots True Speed. Some have 558Knots on True Speed 35000ft and some have 550ft True Speed on 39000ft. All plane including, B747, A380 and B737-800 etc....

 

But I, YOU can see in picture below: I have 523Knots True Speed on 20,000ft. If I'll increase height then, True Speed will reduce more. What can I do now?

Edited November 17, 201213 yr by firehawk44
Image removed. Exceeds 400KB limit by two times.

Uhmm first I think your settings are set incorrectly, it seems like your airspeed indicator isn't showing indicated airspeed like supposed but something else. Try to change that from your settings, 430 knots if IAS would be total overspeed by far.

 

Also your ground speed depends from winds too.

... I have 523Knots True Speed on 20,000ft. If I'll increase height then, True Speed will reduce more. What can I do now?

 

That's actually not necessarily true. IAS always decreases as altitude increases as a function of they way it is measured. True airspeed is a calculated number accounting for the decrease in ambient pressure as your altitude increases. It actually tends to increase as you gain altitude due to decreased drag in the less dense air.

 

You also need to understand what speeds are being reported on the sites you are referencing. Flight tracking sites almost universally report ground speed, not TAS. I'm not familiar with planefinder itself, but would venture to guess this applies to them as well. Ground speed encompasses any effect of wind, which at these flight levels is almost always 60-80kts and can exceed 120kts. Depending on the flight direction (with or agains the wind), this either gets added or subtracted to TAS.

That image of the real aircraft shows true speed, true speed is exactly that, the true speed of the aircraft in relation to the ground. In relation to it's environment however that speed will likely be much less, even more less the higher you go as the air becomes much less dense. It is possible to travel at 500kts true airspeed but the environment around the aircraft is more like flying at sea level at 250-300 kts.

 

In aviation we aren't interested in the true airspeed because the aerodynamic forces acting on the aircraft are never the same as if we were travelling on the ground and to prevent damage to the aircraft we work in indicated airspeed which takes into account the outside environment. It's impossible to straight convert the true airspeed from that image into indicated airspeed within FS because we do not know the conditions such as temperature that are being experienced.

 

To replicate the scenario you are seeing, at cruising altitude most aircraft will use mach as a means of setting speed because we know it as a constant no matter what the environment, mach always represents a fraction of the speed of sound. A 747 will usually cruise at around mach .85 to .87 with a slight leeway around that, in your image you are at mach .89 which is 8.9/10ths the speed of sound. At 20,000 ft your travelling far too fast for the air density and outside conditions, hence the overspeed.

 

If you climb to 36,000ft and set mach as .85-.87, your ground speed will thereabouts read what you see in the Thai aircraft on planefinder however it is totally dependant on the conditions being experienced.

Besides the obvious problem of the op not understanding basic aviation terms, using the default 747 will never give any realistic results.

That image of the real aircraft shows true speed, true speed is exactly that, the true speed of the aircraft in relation to the ground. In relation to it's environment however that speed will likely be much less, even more less the higher you go as the air becomes much less dense. It is possible to travel at 500kts true airspeed but the environment around the aircraft is more like flying at sea level at 250-300 kts...

 

That's really not accurate.

 

Indicated Airspeed (IAS): Airspeed displayed by the gauge. It is derived from the pitot-static system based on calibrated differences in pressure readings between a forward facing pitot tube and a flush mounted pressure sensor. Since this relies on air pressure, the decreasing density at higher altitudes will lower the pressure (and thus the displayed speed).

 

True Airspeed (TAS): True airspeed is a calculated number based on IAS that at minimum adjusts for density and tempurature. However, it typically will also use either mach number or compressibility quotients to account for the compression of air at higher speeds. It is the speed of the aircraft relative to the air mass through which it is traveling. Since it is defined as speed relative to the air mass, wind speed does not alter this calculation. It is already accounted for in "relation to the air mass", which in the case of wind is moving at it's own defined rate.

 

Ground Speed (GS): The speed in relation to the ground. Since the reference frame is to the ground that is not moving (ignoring the earth's rotation), it does not automatically account for wind. A rough, but very close, approximation is TAS +/- tail/head wind component.

 

TAS is essentially the effective speed seen by the airframe (while IAS is probably a better marker of the effective aerodynamic speed affecting the control surfaces). Since the force of drag is reduced in less dense air, the structure of an aircraft can typically tolerate higher TAS at higher altitudes. As you referenced, this is usually flown as mach number above a certain cross over altitude (based on you planned climb speed). While a 744 can cruise at mach 0.85-0.90 at cruise altitude, at lower altitudes this speed would cause catastrophic structural damage in the denser air.

 

...It is possible to travel at 500kts true airspeed but the environment around the aircraft is more like flying at sea level at 250-300 kts...

 

This relationship is essentially reverse. While indicating 250-300 kts at altitude, the enviroment around the aircraft is moving at 500 kts. True airspeed should not be viewed as a relationship to speed at sea level, it should be viewed as a corrected value of indicated airspeed based on a limitation in the way IAS is measured.

Guys! You all are right. It was my error not anyone esle's. Actually, I was using a downloaded 747, made by any user. When I used Microsoft-made (built-in with game) B747-400 then I found that speed slowly slowly reaches at 500Knots.

 

I was at 39000ft and on clear weather, I just gave one flap (1) by pressing F7, then speed started slowly increasing and then I give another flap at (5) then speed started to decrease fastly. Then again I reduce flap to 1 by F6 then again speed started to increase again. So question is, at 39000ft, why only 1 flap works? Why 5 not works? and if weather is Fair, then flap 1 don't work too and plane starts to do like up-low, up-low, up-low, its nose does this. Why it happens in a little heavy air (Fair Weather)? and why it doesn't happen in clear weather?

 

So at Clear Weather, Flap 1 works well, means speed increases and plane remain in stable position.

But if there is a Fair Weather or little bad weather, then flap 1 doesn't work too. So What we should do here to increase speed and to make plane in stable position?

 

Again Thanks to all for helping me.

 

Best Regards,

AP,

There is no reason to apply ANY flaps at that flight level.

 

Regarding the rest of your question, the higher you fly the less resistance on the airframe leads to higher and more economic speed. The drawback comes when the IAS (Indicated airspeed) shows less speed due to the change in barometric pressure at high flight levels.

Flaps is only used to increase the lift the wing produces during landings and departures. It allows the plane to fly slower without stalling. It is never used during cruise, as it would increase drag (which increases fuel usage), and besides, the wing is perfectly capable of providing enough lift to carry the plane at cruise speeds anyways

Why are you using flaps? In other words, what problem are you encountering that you are trying to remedy with flaps? Any level of flaps adds drag. They will decrease speed due to this added drag at any time in flight, making them wasteful and inefficient in cruise. During takeoff and landig where speeds are already low, the added left outweights this increased drag.

If you are talking about the default 747, flaps set to 1 might indeed help, because otherwise the airplane has a totally wrong attitude in level flight (if I recall correctly, it's about 5 degrees pitch up), and thus it's quite possible, that with zero flaps the thrust of the engines doesn't allow the plane to accelerate exceeding a certain speed. (I'm not sure, but it seems likely to me.)

 

Regards,

Flo