Headwinds, always

Mike Weller wrote:
Consider the old example taught to students (or should be):

1. 100kt airplane (no wind)
2. 50kt. wind from the west (270)
3. Round trip 400 nm (point A to point B and return)
4. Course from point A to point B is 270

Round trip time with no wind is 4 hours.

With a 50kt headwind the time from point A to point B is 4 hours.
Sure, you've got a tail wind going back, but you will never make up
for the headwind.

Why not? Ginsberg's Theorem, which paraphrases the three fundementals
of thermodynamics. may be a clue.



Of course, the real reason is with the higher groundspeed in the tailwind,
you're not in it as long. Headwinds always hurt more than tailwinds help, if
you're going round trip.



--
Mortimer Schnerd, RN

VE

(Paul Tomblin) wrote in
:

I once made 144Kt GS in a Warrior II and another member of the group
had 160Kt earlier this year. Mostly I'm lucky to get 100Kt :-(

Well, I made 200kt GS in a Dakota once, but I still think it was magic
pixies or really good gas.

How did you fly with my butt out the window?

Should of went the other way around.
"Paul kgyy" wrote in message
oups.com...
I just returned from an 8-day tour of the midwest. This was a 6-leg
circular route west to Des Moines from Chicago, then up to the Dakotas,
back through Duluth, Green Bay. We mostly flew at 7000 ft. We had
20-30 knot headwinds on 5 of the 6 legs and never once a tailwind.

In a previous article, Judah said:
(Paul Tomblin) wrote in
:
Well, I made 200kt GS in a Dakota once, but I still think it was magic
pixies or really good gas.

How did you fly with my butt out the window?

You have magic pixies coming out your butt?

--
Paul Tomblin http://xcski.com/blogs/pt/
"To announce that there must be no criticism of the president, or that we
are to stand by the president, right or wrong, is not only unpatriotic and
servile, but is morally treasonable to the American public." -- Teddy Roosevelt

On Mon, 6 Jun 2005 10:58:57 -0700, "Peter Duniho"
wrote in
::

"Larry Dighera" wrote in message
.. .
[...]
The point I'm making is, that of the 360 degrees available for winds
to intersect the intended course, only about 15% are able to result in
a net ground speed increase.

This is from memory, so I'm sure someone will correct me with a more
detailed analysis.

Of course.

It depends on the strength of the wind.

For example, if you are flying 100 knots, a 20 knot wind from 10 degrees aft
of a direct crosswind gives you a 1.5 knot boost in speed, but a 40 knot
wind from the same direction slows you by 1.1 knots.

The stronger the wind, the more directly behind you it can be and still slow
you down.

That said, your statement that only 15% of the available degrees result in a
true tailwind is plainly false. That would be an arc of only 7.5% degrees
to either direction of straight aft of your heading, when in fact modest
wind speeds even only slight aft of your heading result in a net increase in
groundspeed. And it ignores the fact that it's not simply the direction of
the wind, but also the speed.

It's true that more than 50% of all wind directions and speeds result in a
headwind, but it's only *slightly* more than 50%. Certainly not nearly
enough to explain the original poster's experience.

Pete


Around 1998 or so, The High Ground column in Plant & Pilot contained
an article titled Estimating Surface Winds. It provided five
paragraphs each dealing with a different aspect of winds, and four
figures. Figure C is titled Estimating Tailwind Component. It shows
wind from astern (0 degrees), 30 degrees off the tail, 60 degrees off
the tail, and wind from off one wing tip (90 degrees). Here are the
captions of each:

0 Degrees: Estimate tailwind component at full wind velocity.

30 Degrees: Estimate tailwind component at full wind velocity.

60 Degrees: Estimate tailwind component at three-quarter wind
velocity

90 Degrees: Estimate tail wind component at one-half wind
velocity.

So I appears that my recollection was faulty. But it seems counter
intuitive, that a 90-degree crosswind contributes half its velocity to
a tailwind component.


Here is the text of the article:

ESTIMATING SURFACE WINDS

An awareness of the surface wind is all-important to successful
mountain arrivals and departures. A few rules of thumb are
useful.

1 Estimating Headwind Component. If the wind sock is swinging
within 30 degrees of your runway's alignment, consider the
headwind component at three- fourth the wind velocity.
(Mountain winds are seldom steady; a direction and velocity one
moment may change the next.( Allow one-half the wind's velocity
as your component when the sock swings 30 to 60 degrees off the
runway. And, when the sock's angle to the runway exceeds 60
degrees, count the headwind zero.

2 Estimating Crosswind Component. If the wind lies within 30
degrees of runway alignment, estimate your crosswind component at
one-half the wind's velocity. Estimate your component at
three-fourths the wind's velocity if the wind crosses your runway
at 30 to 60 degrees. If the wind angle exceeds 60 degrees,
estimate your crosswind component to equal the velocity.

3 Estimating Tailwind component. If the wind is blowing within
30 degrees of your tail, consider the wind's full strength as your
tailwind component. A wind 30 to 60 degrees of the tail calls for an
estimated component of three-fourths the wind's velocity. Estimate
your component at one-half the velocity if the wind angle exceeds 60
degrees.

4 Estimating wind velocity. Most wind socks used at small airports
are designed to stiffen at 15 knots. Estimate lesser velocities by
the sock's angle of droop. A sock drooping at a 45-degree angle, for
example, shows a velocity of seven or eight knots.

5 Estimating Wind Correction Angle. Knowing at the outset the
approximate wind correction needed on final approach or initial
climbout is helpful. At typical light plane liftoff or approach
speeds of 55 to 65 knots, correct one degree for each knot of
crosswind component. Thus, an approximate 10-degree correction should
keep you on track when lifting off or landing into a 10-knot crosswind
component.

Dan Luke wrote:

Flew round trip Mobile - Baton Rouge Saturday, with a 30-minute stop at BTR.

6,000' there, 7,000' back, course 270, 090.

Headwinds both ways.

Had some really nice winds off the gulf Saturday if you were flying
north here in LA...

"Larry Dighera" wrote in message
news
[...]
So I appears that my recollection was faulty. But it seems counter
intuitive, that a 90-degree crosswind contributes half its velocity to
a tailwind component.

That's because you need to take into account the application of that
particular resource. Applying that sort of thinking to cruise flight IS
counter-intuitive, because it's not correct in that context.

It's not even literally correct in the context of the article you quoted,
but nevertheless the article you quoted has useful information in it.
First, it's a discussion of landing, not cruising. Second, it's a
collection of rules of thumb, not a precise analysis of reality.

It is easy to show that mathematically, a 90 degree crosswind results in no
tailwind component. Without a correction, it results in no headwind
component as well.

But when dealing with mountain flying, and in particular landing on a short
runway, assuming a tailwind component for a 90 degree crosswind is
conservative approach. That is, a 90 degree crosswind clearly doesn't add
half the wind speed to your groundspeed, but the crosswind does create other
effects that could result in a lengthening of the room required to land,
roughly equivalent to a similar increase in groundspeed.

Note that while a tailwind is estimated at full strength, when coming from
within a 30 degree angle, a headwind is estimated only a 3/4 strength, even
when coming from the same angle (in the other direction, of course).

I believe that is the true nature of the article you've quoted: to provide
rules of thumb that offer safe guidance to pilots landing in constrained
areas, especially when the landing area is defined not by prevailing winds
but by terrain restrictions, preventing the pilot from taking best advantage
of the current winds. Where the winds increase the landing distance, they
are assumed to be greater than actual, and where the winds might shorten the
landing distance, they are assumed to be lesser than actual. In neither
case do the estimates provide any assistance in judging the effects of winds
aloft during cruise flight.

Hope that helps.

Pete

The ADDS forecast is excellent but I don't usually have access to it
when travelling on vacation, particularly in the evening when I'm
planning tomorrow's flight in the hotel room.

(Paul Tomblin) wrote in news:d82mvl$q35$1
@allhats.xcski.com:

In a previous article, Judah said:
(Paul Tomblin) wrote in
:
Well, I made 200kt GS in a Dakota once, but I still think it was magic
pixies or really good gas.

How did you fly with my butt out the window?

You have magic pixies coming out your butt?


Had you flown with me, you would know.

In fact, had you flown for a while after me, you would know.

"Darrel Toepfer" wrote:

Flew round trip Mobile - Baton Rouge Saturday, with a 30-minute stop at
BTR.

6,000' there, 7,000' back, course 270, 090.

Headwinds both ways.

Had some really nice winds off the gulf Saturday if you were flying
north here in LA...

That was the problem.
--
Dan
C-172RG at BFM