Estimate winds aloft

nevermind I figured it out. essential just use your flight computer backwards.
 
No I am not talking about looking at duats and interpolating for my altitude. I was referring to actually calculating the winds while in flight.
 
Given airspeed, groundspeed, and heading, you can solve for the wind vector with these equations, or just use your whiz wheel. The G1000 and Dynon panels, among others, will also display the wind vector for you.

Interpolation is fine for textbook purposes, but appears to be considered harmful in real life; use a skew-t instead.
 
I tried to interpolate a young lady one time.
Man, did she slap me cross eyed.
 
Winds aloft without the need to interpolate is an easy to use function of the skew-t. Go to http://rucsoundings.noaa.gov/, put in the identifier of the airport in question (up to six allowed, three-letter identifiers only...no alphanumerics), and put 3.0 in the hours box. Hit java-based plots. On the resulting page, over on the right side, you will see a wind arrow for every 1000 feet of pressure altitude. Wind direction and velocity does not change instantaneously, so you can ignore the difference between pressure altitude and indicated altitude for all practical purposes. If I am wrong, Scott D will be along to straighten me out.

With the exception of true course, which you can measure on a chart with a plotter, all other flight planning elements are fuzzy, so don't expect extreme accuracy.

Bob Gardner
 
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How does one actually get their groundspeed vector while in the air?* Airspeed and heading is easy, but the second vector (groundspeed and course) needed to calculate the winds aloft vector isnt so easy to measure.

*I know technically how. Time and distance between 2 known points, plot that line, and measure course with plotter. easy on the ground, not so much in the air. Is this something a pilot is expected to do on his lap?
 
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jasc15 said:
How does one actually get their groundspeed vector while in the air?* Airspeed and heading is easy, but the second vector (groundspeed and course) needed to calculate the winds aloft vector isnt so easy to measure.

*I know technically how. Time and distance between 2 known points, plot that line, and measure course with plotter. easy on the ground, not so much in the air. Is this something a pilot is expected to do on his lap?
Click to expand...


On the contrary, it is easy to measure. Pick out easily identified landmarks with clearly defined boundaries, time as you fly between them, and use your whiz wheel to turn time and distance into groundspeed. You don't use your plotter to measure course while in flight...that is a ground planning action. You could, if you wanted to, measure the distance between checkpoints and write it next to each leg on the sectional during the planning process...then you wouldn't need the plotter in flight at all.

Pilots, including student pilots, have been making groundspeed calculations in the air for decades.

Bob Gardner
 
Thread hijack warning...

Looking at this map:

uvZvVUND


If one were to fly a Cessna 172 North-West through South Dakota, would the plane be exceeding Vne (100 knots normal cruise + 80 knots of wind)? If one flew South-East through the same area, would the 172 in level flight stall and drop out of the sky?
 
livitup said:
If one were to fly a Cessna 172 North-West through South Dakota, would the plane be exceeding Vne (100 knots normal cruise + 80 knots of wind)? If one flew South-East through the same area, would the 172 in level flight stall and drop out of the sky?
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No and no.
 
Will the airspeed indicator show 180 and 20 knots, respectively?

Edit to add the real question in my brain: Is it safe to fly a light single through that area?
 
livitup said:
Will the airspeed indicator show 180 and 20 knots, respectively?

Edit to add the real question in my brain: Is it safe to fly a light single through that area?
Click to expand...

Safe to fly, your indicated airspeed wouldn't be affected, but your ground speed would be. I wouldn't want to fly INTO that wind in a 172 (as you'd be going 20 knots across the ground), but I'd love to fly WITH that :yes:
 
livitup said:
Will the airspeed indicator show 180 and 20 knots, respectively?

Edit to add the real question in my brain: Is it safe to fly a light single through that area?
Click to expand...

No - the airplane moves through the air. The motion of the aircraft through the air is a function of the thrust, drag, lift, and gravity. In general, it doesn't matter how the air is moving relative to the ground.

It would be unsafe only if the interaction between the air and the ground results in unsafe levels of turbulence (that happens a lot in the mountains)
 
i used to do aerial photography work that sometimes involved extended n/s runs at 8000 ft. i had a lot of fun timing one mile runs and determining winds aloft based on that.
 
If facing a headwind, why wouldn't the IAS be affected? The pitot tube normally scoops up air forced into it by forward movement of the plane. Why wouldn't it scoop up air produced by forward movement of the plane and headwind?

Let's say it's perfectly calm, and you are tooling along at 100 KIAS on a course of 000. 1 second later a hypothetical wind appears from the middle of nowhere, blowing from 180 at 80 Knots.

I understand that the propeller is still pulling the plane along at a rate that would equal 100KIAS in calm air. But doesn't the 80 knot wind airflow somehow interact with the 100 knot airflow from the plane's forward motion, in effect "reducing" the lift to that of an airfoil with 20 knots of air speed?

I guess what is confusing me is that planes can shorten their takeoff roll by taking off into a headwind. The headwind component during the takeoff roll increases the lift beyond that produced by the plane's forward movement. Or is this a special circumstance because the plane is still on the ground?

Sorry I'm so dense about this, but it's cheaper to pick your brains than my CFI (when I pick a CFI... :))
 
The short answer to your question ("If facing a headwind, why wouldn't the IAS be affected?") is: it would be. But when you have a head wind, your plane is being pushed back at a rate equal to the headwind. Think of flying in a constant head wind like running on a treadmill. You have to move your legs fast enough to overcome that backwards motion of the treadmill or you get flung off the back. If you run faster than the treadmill, then you bump into the handrest. If the wind is blowing against you at 20 knots, your plane must generate 20 knots of thrust just to keep you stationary. If your plane can fly that slowly without stalling you would have an indicated airspeed of 20 knots, and a ground speed of 0. I personally have had a similar experience in flight training when the plane's garmin showed a ground speed of 0 (yes, we were essentially hovering in a plane), but we had an indicated speed of 70 knots. Obviously, we had a 70 knot head wind.

livitup said:
Let's say it's perfectly calm, and you are tooling along at 100 KIAS on a course of 000. 1 second later a hypothetical wind appears from the middle of nowhere, blowing from 180 at 80 Knots.

I understand that the propeller is still pulling the plane along at a rate that would equal 100KIAS in calm air. But doesn't the 80 knot wind airflow somehow interact with the 100 knot airflow from the plane's forward motion, in effect "reducing" the lift to that of an airfoil with 20 knots of air speed?
Click to expand...

In this situation, yes, you would lose lift as a result of the gust, and you might very well enter into an aerodynamic stall. But your plane would also begin to accelerate, as well, as the prop pushes against the body of air that has now also accelerated. Assuming you don't fall out of the sky completely, and you can regain control, eventually, your plane would return to it's original airspeed, even if the ground speed is much greater than before.

livitup said:
I guess what is confusing me is that planes can shorten their takeoff roll by taking off into a headwind. The headwind component during the takeoff roll increases the lift beyond that produced by the plane's forward movement. Or is this a special circumstance because the plane is still on the ground?
Click to expand...
Assume you have a headwind of 20 knots, and you need 55 knots airspeed to generate enough lift to take off. Standing still, you already have 20 knots indicated. You only need to accelerate an additional 25 knots. It takes less time (and therefore a shorter takeoff roll) to accelerate 25 knots than if you have to accelerate 55 knots.
 
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PPC1052 said:
But when you have a head wind, your plane is being pushed back at a rate equal to the headwind.
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:yes::yes::yes: Thanks, I think you broke the mental logjam for me.

The plane doesn't stall (or break into pieces due to overspeed) because the sum of the airflow from movement due to thrust and wind still equals 100 knots.

A plane which normally cruises at 100 Knots, when faced with a 80 Knot head wind, will still have the same lift as if it was in still air, but the ground speed is reduced because the wind is pushing you back?

In other words, Thrust + Wind = IAS. IAS below stall speed = falling out of the sky, but a headwind greater than the difference between stall and cruise just means you move slower compared to the ground... Your wing still makes lift, it's just less lift produced by the forward movement of the plane, and more due to the wind.

Did I get it right?

Can you hover a GA single, if you have enough wind? :D
 
livitup said:
In other words, Thrust + Wind = IAS.
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No. I used "thrust" imprecisely in explaining IAS above. Thrust is force, which is mass times acceleration (F=M * A). It is a measure of how quickly a particular mass will be accelerated. But as you fly, your plane has drag, which tends to decelerate the plane. (That is why you have to keep burning fuel to stay in the air, and you can't just coast forever.) As you increase thrust, the plane will accelerate to the point that thrust equals drag. At that point, it will have an equilibrium resulting speed. But as you can see, thrust is clearly related to speed, so you are not too far astray.

What is true is that ground speed +\- wind would give you IAS, assuming you are adding a head wind and subtracting a tail wind.

livitup said:
IAS below stall speed = falling out of the sky,
Click to expand...

Yes, unless you recover.

livitup said:
but a headwind greater than the difference between stall and cruise just means you move slower compared to the ground...
Click to expand...
I am not sure what you mean here. Assuming a constant wind, then ground speed would equal airspeed plus/minus wind. If you have gusty winds, the planes inertia will resist the change in speed from a gust, but it will accelerate or decelerate back to the equilibrium airspeed, although the ground speed would be different until the wind returns to what it was before the gust kicked up. Before the plane returns to the equilibrium airspeed for your power setting, you would see temporary spike or drop in the indicated airspeed.
 
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Remember, you can stall a planes wing at any airspeed or attitude... Just an aside and not necessarily related to the current flying thru a moving airmass discussion.
 
This is what I was referring to in post #10:


SEA(A) 1800 18Jan13
Op40 Analysis, valid 18-Jan-2013 18:00:00 (8.4nm/234° from SEA)

CAPE = 0.0 J/Kg, CIn = -1.0 J/Kg
TT = 12.0 KI = -38.0 LI = 20.0 SI = 12.0 SW = 93.0
LCL = 901.0

P_alt mb t/td w_dir/w_spd Time
(ft) (°C) (kts) (UTC)

128 1021 -1.1/-1.10 44°/001 1800
203 1018 -1.3/-1.30 56°/001 1800
348 1012 -1.4/-1.40 49°/001 1800
597 1002 -1.7/-1.70 199°/002 1800
653 1000 -1.6/-1.60 203°/002 1800
968 988 -0.8/-0.80 223°/005 1800
1467 970 5.0/4.500 260°/005 1800
2080 948 9.9/-6.80 276°/007 1800
2746 925 9.4/-17.6 271°/012 1800
2769 924 9.4/-18.0 271°/012 1800
3540 898 11.2/-23.9 273°/017 1800
4432 870 10.5/-31.0 279°/020 1800
5046 850 9.5/-35.0 281°/022 1800
5446 838 8.9/-37.6 283°/023 1800
6591 803 6.1/-39.8 287°/025 1800
7884 765 3.4/-36.4 288°/030 1800
9337 724 0.5/-33.1 288°/035 1800
10210 700 -1.4/-32.6 288°/037 1800
10971 680 -3.1/-32.1 288°/039 1800
12815 633 -7.1/-32.9 289°/043 1800
14882 583 -11.1/-35.0 293°/047 1800
17024 535 -15.5/-36.4 296°/049 1800
18701 500 -18.5/-35.4 297°/049 1800
19091 492 -19.2/-35.2 297°/049 1800
21073 453 -23.0/-34.4 295°/048 1800
22976 419 -26.9/-35.2 295°/048 1800
24039 400 -29.2/-36.6 296°/048 1800
24810 387 -30.8/-37.6 296°/048 1800
(I think that's high enough :wink2:)

Also note CAPE, at the top...it is a measure of instability. The atmosphere over Seattle today is so stable we can hardly see our hands in front of our faces.

Bob Gardner
 
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What advantage has to figure out the wind once you are airborne vs knowing the winds before you depart so you can choose the best altitude. Specially if you are going oceanic.

José
 
PPC1052 said:
livitup said:
but a headwind greater than the difference between stall and cruise just means you move slower compared to the ground...
Click to expand...
I am not sure what you mean here. Assuming a constant wind, then ground speed would equal airspeed plus/minus wind. If you have gusty winds, the planes inertia will resist the change in speed from a gust, but it will accelerate or decelerate back to the equilibrium airspeed, although the ground speed would be different until the wind returns to what it was before the gust kicked up. Before the plane returns to the equilibrium airspeed for your power setting, you would see temporary spike or drop in the indicated airspeed.
Click to expand...

I wasn't clear here...

What I mean is that the combination of:
  • airflow generated due to the movement of the aircraft due to thrust created by the engine -and-
  • airflow generated by wind
both added together will always equal the same IAS. So in still air, the engine will create enough thrust to move the plane through the air fast enough to have 100 knots of airspeed over the wings. And in the 80 knot headwind, the engine will produce enough thrust to indicate 100 knots, but the 80 knot wind will slow the plane to 20 knots, but the wind is also going over the wings at 80 knots, so the IAS is back up to 100.

In other words, in the second example: 100 Knots (engine) - 80 knots (speed lost by fighting the wind) + 80 knots (airflow over the wings from the wind) = 100 KIAS.

Am I thinking this through correctly?
 
Jeanie said:
Remember, you can stall a planes wing at any airspeed or attitude... Just an aside and not necessarily related to the current flying thru a moving airmass discussion.
Click to expand...

Absolutely true.
 
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