Author Topic: Show me some factual info  (Read 934 times)

Offline TequilaChaser

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Re: Show me some factual info
« Reply #15 on: February 12, 2020, 07:49:16 AM »
I guess I've lost the use of more gray matter than I thought, because the physics are not adding up in my brain to see that, LOL

Edit: initially yes! If your TAS hits a head wind of a 100 knots, for a little bit the plane will be able to push forward at a rate of 450 KTAS, but it will slow down depending how long the plane continues to fly into the head wind..... I can not see the "TAS Indicator" continue to say 450 knots when in reality the 100 knot head wind (drag) has slowed it down to 350 knots.... <---- that is your TAS(corrected)

Explain to me what I'm missing, I can not see the gauge saying the plane is doing 450 KTAS, when it is not....how does that help the pilot in any way giving a false reading saying that your doing 450, but you're actually a 100 knots slower
« Last Edit: February 12, 2020, 08:41:12 AM by TequilaChaser »
"When one considers just what they should say to a new pilot who is logging in Aces High, the mind becomes confused in the complex maze of info it is necessary for the new player to know. All of it is important; most of it vital; and all of it just too much for one brain to absorb in 1-2 lessons" TC

Offline Oldman731

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Re: Show me some factual info
« Reply #16 on: February 12, 2020, 08:42:28 AM »
I guess I've lost the use of more gray matter than I thought, because the physics are not adding up in my brain to see that, LOL

Edit: initially yes! If your TAS hits a head wind of a 100 knots, for a little bit the plane will be able to push forward at a rate of 450 KTAS, but it will slow down depending how long the plane continues to fly into the head wind..... I can not see the "TAS Indicator" continue to say 450 knots when in reality the 100 knot head wind (drag) has slowed it down to 350 knots.... <---- that is your TAS(corrected)

Explain to me what I'm missing


Best explanation I ever read was in Langewiesche's "Stick and Rudder."  He likened a plane moving through an air mass to a man walking through a train car.  Regardless of how fast the train is moving across the landscape, the relative motion of the man within the car was the same.

- oldman

Offline TequilaChaser

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Re: Show me some factual info
« Reply #17 on: February 12, 2020, 09:03:08 AM »
To add, if we are talking modern fighter jets..... Lets say starting back with the F4 phantom II (one that I'm very familiar with and have done high-powered turn qualifications in among other jets)

Then they have the thrust-to-weight ratio to overcome head winds, or the F-15 etc....

If we are talking prop planes and/or passenger jets, they don't have the ability
"When one considers just what they should say to a new pilot who is logging in Aces High, the mind becomes confused in the complex maze of info it is necessary for the new player to know. All of it is important; most of it vital; and all of it just too much for one brain to absorb in 1-2 lessons" TC

Offline TequilaChaser

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Re: Show me some factual info
« Reply #18 on: February 12, 2020, 09:07:22 AM »

Best explanation I ever read was in Langewiesche's "Stick and Rudder."  He likened a plane moving through an air mass to a man walking through a train car.  Regardless of how fast the train is moving across the landscape, the relative motion of the man within the car was the same.

- oldman

I actually have that old book in my collection but haven't opened it in over 30 years, heh

I understand what you're saying there, but in a plane or jet, you are strapped in.....like a stationary part of the cockpit
"When one considers just what they should say to a new pilot who is logging in Aces High, the mind becomes confused in the complex maze of info it is necessary for the new player to know. All of it is important; most of it vital; and all of it just too much for one brain to absorb in 1-2 lessons" TC

Offline toasted

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Re: Show me some factual info
« Reply #19 on: February 12, 2020, 04:21:22 PM »
"but in a plane or jet, you are strapped in.....like a stationary part of the cockpit"
physics doesn't care if your strapped in to the cockpit or riding free in the hold.it works the same.

its why you can throw a ball from one hand to the other while riding in an airplane(car,train) without the ball immediately bouncing off the rear bulkhead.
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Offline Mister Fork

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Re: Show me some factual info
« Reply #20 on: February 13, 2020, 04:17:38 PM »
Let me get this straight - TAS takes into account of your altitude in addition to your IAS? Same speedo dial as it does in Aces High?

Ground speed would only be available through GPS or through radar navigation systems?
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Offline Busher

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Re: Show me some factual info
« Reply #21 on: February 13, 2020, 05:28:22 PM »
Let me get this straight - TAS takes into account of your altitude in addition to your IAS? Same speedo dial as it does in Aces High?

Ground speed would only be available through GPS or through radar navigation systems?

Correct. IAS becomes less reliable as an airplane climbs due to air density. Private pilots are taught very early in their training, how to covert IAS to TAS based on altitude and temperature.

And ground speed can also be displayed by DME (distance measuring equipment) used by airplanes not GPS equipped. ATC can also provide groundspeed in a radar environment on pilot request.
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Offline Mongoose

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Re: Show me some factual info
« Reply #22 on: February 13, 2020, 09:57:09 PM »
  Ok, let's say I'm at 20,000 feet flying west at an indicated airspeed of 100 mph.  According to a little conversion calculator I found, my true airspeed is 154 mph.  This can vary depending on air temperature.  But this mean that I am actually traveling through the air at 154 mph.  If there is no wind, then my ground speed is 154 mph.  If the wind is blowing west to east at 10 mph, then I have a 10 mph headwind, and my ground speed will be 144 mph, even though my true airspeed is still 154 mph.  I am still traveling through the air at 154 mph, but that air is traveling in the opposite direction at 10 mph, so I lose 10 mph in ground speed.

If the wind is blowing east to west at 10 mph, then I have a 10 mph tailwind, and my ground speed will be 164 mph.  I am still traveling through the air at 154 mph, but that air is traveling in the same direction I am, so I gain 10 mph in ground speed.

Now let's say my stall speed is 80 mph.  Stall speed is indicated air speed, regardless of my true air speed.  The less dense air means that I need more of it to provide the lift I need.  So if I slow down to 80 mph indicated air speed, I will stall, even though my true air speed is 123 mph.

Offline hitech

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Re: Show me some factual info
« Reply #23 on: February 14, 2020, 04:05:40 PM »
  Ok, let's say I'm at 20,000 feet flying west at an indicated airspeed of 100 mph.  According to a little conversion calculator I found, my true airspeed is 154 mph.  This can vary depending on air temperature.  But this mean that I am actually traveling through the air at 154 mph.  If there is no wind, then my ground speed is 154 mph.  If the wind is blowing west to east at 10 mph, then I have a 10 mph headwind, and my ground speed will be 144 mph, even though my true airspeed is still 154 mph.  I am still traveling through the air at 154 mph, but that air is traveling in the opposite direction at 10 mph, so I lose 10 mph in ground speed.

If the wind is blowing east to west at 10 mph, then I have a 10 mph tailwind, and my ground speed will be 164 mph.  I am still traveling through the air at 154 mph, but that air is traveling in the same direction I am, so I gain 10 mph in ground speed.

Now let's say my stall speed is 80 mph.  Stall speed is indicated air speed, regardless of my true air speed.  The less dense air means that I need more of it to provide the lift I need.  So if I slow down to 80 mph indicated air speed, I will stall, even though my true air speed is 123 mph.
100% correct.
Only thing I could add is some visualizations. And definition of CAS Calibrated air speed.

IAS is a measure of the pressure change as a result of putting a tube pointed into the wind at speed. So when you go higher, there is less pressure differential do to less atoms going into the tube. In the same way less atoms are striking your wing causing less lift, and  hence you will need to fly at a higher AOA to maintain the same lift. Since a give plane stalls at the same critical AOA, your "Stall Speed" will always be the same IAS.

Now since your tube can not always be pointed directly forward as your AOA changes, you will be presenting a cross section of the tube into the air stream. This will cause your Air speed indicator to read slower than if it was pointed directly into the wind. CAS is the IAS adjusted for this error.

HiTech

Aces High does the inverse calculation from CAS (used to determine all forces)  to IAS which is only used to display on the gauge.

HiTech


Offline Mongoose

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Re: Show me some factual info
« Reply #24 on: February 14, 2020, 07:00:32 PM »
100% correct.
Only thing I could add is some visualizations. And definition of CAS Calibrated air speed.

HiTech

Yay!  I got it right!  And thanks for the explanation of CAS.  That part always left me a little puzzled.

Offline Denniss

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Re: Show me some factual info
« Reply #25 on: February 14, 2020, 08:49:27 PM »

Offline TyFoo

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Re: Show me some factual info
« Reply #26 on: February 14, 2020, 10:30:54 PM »
Recent example of a major difference between IAS and TAS
https://www.nytimes.com/2020/02/09/world/british-airways-subsonic-flight.html
https://www.bbc.com/news/uk-england-london-51433720

Those articles are an example of the difference between TAS and Groundspeed. The Aircraft TAS remains unchanged and relative to their filed Flight Plan speed (somewhere around 490 - 510kts). While they attained a top Groundspeed of 825mph for 24 minutes. 

Offline mikeWe9a

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Re: Show me some factual info
« Reply #27 on: February 18, 2020, 01:55:04 PM »
I guess I've lost the use of more gray matter than I thought, because the physics are not adding up in my brain to see that, LOL

Edit: initially yes! If your TAS hits a head wind of a 100 knots, for a little bit the plane will be able to push forward at a rate of 450 KTAS, but it will slow down depending how long the plane continues to fly into the head wind..... I can not see the "TAS Indicator" continue to say 450 knots when in reality the 100 knot head wind (drag) has slowed it down to 350 knots.... <---- that is your TAS(corrected)

Explain to me what I'm missing, I can not see the gauge saying the plane is doing 450 KTAS, when it is not....how does that help the pilot in any way giving a false reading saying that your doing 450, but you're actually a 100 knots slower

True airspeed isn't an independent or direct airspeed measurement - it is simply indicated airspeed corrected for air density, sometimes just by dialing in the pressure altitude on the instrument itself.  Not all aircraft even have a true airspeed gauge, as it isn't a required instrument for flying the aircraft.  Indicated airspeed is simply a measurement of static and dynamic pressure at the location of the pitot tube (or whatever actual pressure sensor is used).  If you are encountering wind shear or turbulence that makes your indicated airspeed fluctuate, then your true airspeed reading will fluctuate as well.  So if the true airspeed indicator reads 450 knots, then that simply means that the pressures (actually the difference in pressures) measured by the pitot tube is such that would be produced by a wind of the set air density passing at a speed of 450 knots.  It doesn't matter if the pressure is steady state, or if it caused by a malfunction of the pitot tube (icing, a bug in the inlet, etc).  It is simply an indication of the pressures that the instrument is "seeing."  There is no logic in the airspeed indicator to determine if the measurement is useful, or even if it is correct.

Mike

Mike

Offline Vulcan

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Re: Show me some factual info
« Reply #28 on: February 18, 2020, 05:00:39 PM »
But what if your plane is on a conveyor belt?

Offline Drano

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Re: Show me some factual info
« Reply #29 on: February 18, 2020, 06:04:17 PM »
But what if your plane is on a conveyor belt?
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