You do lose airspeed in a downwind turn - trnshear.txt [1/1]
John T. Lowry
Here's a posting I came up with this afternoon which *SHOULD*
excite some discussion. At the moment, however, it is also
my genuine opinion.
John
You Do Lose Airspeed in a Downwind Turn
John T. Lowry, PhD
Flight Physics
Billings, Montana
(406) 248 2606
<jlo...@wtp.net>
June 1996
I came across a side reference to the infamous "downwind turn
controversy" in an Internet user group posting. Then I located a
reference to that conundrum, in Joe Christy's "Good Takeoffs
and Good Landings," 2nd edition. On page 11 Mr. Christy writes:
...there is no difference between downwind, upwind, or
crosswind turns in flight. They are all the same to the
airplane.
It seems that beginning flight students think that they will
need to add power or angle of attack when turning from upwind
to downwind because of the loss of airspeed inherent in the
reversal of direction. Later on they learn the more sophisti-
cated "truth." As expressed by Joe Christy farther down the
same page:
Remember, when airborne, you are carried *with* a moving
air mass independently of your movement *through* it.
His italics shown with *XX*. So the conventional wisdom is that
there is no difference, except for the name, between a turn from
downwind to upwind and one from upwind to downwind. Let's leave
it at that for the moment.
And let's change the subject; to that of horizontal wind shear,
or gusts. Say you're heading into the wind at 100 KTAS and at
first (Wind A) the wind is 40 knots. Suddenly (Wind B) there is
a slackening gust to only 10 knots. (All wind speeds are ground
speeds, speeds with respect to the earth just below them.) What
happens? Your airspeed suddenly drops 30 knots to 70 KTAS. (For
the moment, your 60 knot ground speed stays the same.) Let's say
you take no immediate pilot control action. If your airplane is
properly trimmed, the lower airspeed results in the airplane
both losing altitude and nosing over. Airspeed begins to
recover. When the original 100 KTAS is regained, you're back
into trim. Albeit at a lower altitude. The point is: your air
speed really did diminish. In fact there's a caveat to the
conventional wisdom in a figure caption on that same page of
Mr. Christy's book:
To an airplane in flight, there is no difference between
turning downwind, crosswind, or upwind, *except when
flying through a wind shear*.
This time, my (**) italics. So at this point we have it that
turning towards downwind does not result in loss of air speed
but flying into a slackening gust does result in loss of
airspeed.
But here's the kicker. *Turning to downwind is the same thing
as a slow wind shear*. Say you start a coordinated turn from
upwind towards downwind at standard rate, 3ų per second. At the
start, say you have a 30 knot headwind. A second later you have
a 30*cos(3ų) = 30*0.9986 = 29.96 knot headwind. It's not much
less, but it *is* less. After turning for 10 seconds you've
turned 30ų and the headwind has slacked off to "only"
30*cos(30ų) = 30*0.8660 = 25.98 knots. That's getting to be at
least marginally perceptible, but remember the effect has been
continuously spread over ten seconds. After a quarter turn from
headwind to crosswind, 90ų, which took 30 seconds, your relative
headwind has changed by 30 knots.
That 30 knots is almost precisely the size (50 ft/sec) of the
FAA's standard gust. But the FAA takes it that the gust develops
its full force over only one quarter second! There's the
difference. The same wind change, spread over a time interval
30/0.25 = 120 times as long and at a time while you've already
increased angle of attack to counteract your banked and
therefore off-vertical lift vector, and possibly also increased
power a little to counteract increased induced drag and
increased trim drag in the turn, is essentially imperceptible.
The time scales are vastly different.
So you do lose airspeed in a downwind turn. Only, normally, not
much.
I can imagine that students and instructors of aviation have
infused their hangar flying sessions on this subject with
several additional scientific red herrings. The Internet
posting I mentioned even got into general relativity. Here are
the more likely possibilities I can think of.
Possible Red Herrings in the Downwind Turn Controversy
1. The air mass in which the airplane is embedded is an inertial
frame and so . . . .
If the air mass is steady, that's so. But if you fly from Wind A
into slower moving Wind B, you're talking about two *different*
inertial frames. Your air speed is your speed through the air in
which you're currently flying, not your speed relative to the
air a mile back. An airplane can change air speed quite rapidly
because the speeds of air molecules can vary considerably from
one place to another place fairly near by. That is, gusts exist.
2. Air speed is air speed, so . . . .
Air speed is speed through that air *in the direction the
airplane is pointed*. Say I told you an airplane was progressing
northward against a 30 knot wind out of the north and its ground
speed was northward at 70 knots. You'd probably say its air
speed was 100 knots. But what if I told you, in addition, that
that airplane's nose was pointed directly to the *south*. (The
ultimate skidded flat turn.) Tilt! Unfair! Now the air speed has
suddenly become -100 knots. The concept of air speed takes a bit
more refinement than most of us give it.
3. The earth isn't actually an inertial frame of reference
anyway . . . .
True. But the non-inertial terms (due to rotation about its axis
and revolution about the sun) are known. And quite small. So for
all practical intents and short term purposes, the earth is an
inertial frame. Therefore, a force is necessary to change the
speed of the airplane relative to the earth. Even if the
airplane flew into a vacuum, it would *initially* still move at
the same speed in the same direction, just as does a tennis ball
you drop out the window of a speeding car. Then, as the changed
and unbalanced forces took over, the airplane would accelerate.
In summary, my answer to the downwind turn controversy is: You
do lose air speed in a downwind turn, but in a "noisy"
environment and only over a time span that renders that loss
almost imperceptible. Still, I think those beginning students
were right.
COMMENTS? CONTRARY VIEWS?
patterson,george r
In article <4qpoh3$9...@wtpprod1.wtp.net>, John T. Lowry <jlo...@wtp.net> wrote:
>and Good Landings," 2nd edition. On page 11 Mr. Christy writes:
>
> ...there is no difference between downwind, upwind, or
> crosswind turns in flight. They are all the same to the
> airplane.
>
> air mass independently of your movement *through* it.
>
>conventional wisdom in a figure caption on that same page of
>Mr. Christy's book:
>
> To an airplane in flight, there is no difference between
> turning downwind, crosswind, or upwind, *except when
> flying through a wind shear*.
No, there isn't. Wind shear is a change in the air mass in which you are
being carried and consequently affects your motion through it. "Downwind",
"Crosswind", etc. are all references to the wind's motion relative to the
ground and have nothing to do with the aircraft. Mr. Christy's original
statement is correct, and your "caveat" is wrong.
The remainder of your conclusions are similarly wrong, since they are
based on this.
-----------------------------------------------------------------------
| "In a way, things are worse than before the
| Marines came. The thieves know that we have no
George Patterson - | guns now, and they come and take what they like
| whenever they want."
| Somalia native (National Geographic interview)
-----------------------------------------------------------------------
Michael L. Murphy
Don Quitoxe rides again, to fight the unbeatable foe :)
It seems like this topic comes up every six months, it gets settled
after a long drawn out argument in which a few people finally agree
that the dangerous downwind turn *is* a myth and the rest give up(?),
only to turn up six moths later to be shot down again. Sigh.
One of these times when it comes around, I'll save all the postings,
list all the rebutttals on a web site, and simply direct people there :) .
In article <4qpoh3$9...@wtpprod1.wtp.net> jlo...@wtp.net (John T. Lowry) writes:
>This time, my (**) italics. So at this point we have it that
>turning towards downwind does not result in loss of air speed
>but flying into a slackening gust does result in loss of
>airspeed.
>
>But here's the kicker. *Turning to downwind is the same thing
>as a slow wind shear*.
No. A wind shear implies a change in the velocity of the wind.
A wind shear can affect your plane adversely turning either upwind
or downwind, depending on the direction in which the wind changes.
>Say you start a coordinated turn from
>upwind towards downwind at standard rate, 3ų per second. At the
>[...]
>headwind to crosswind, 90ų, which took 30 seconds, your relative
>headwind has changed by 30 knots.
Oh dear. You're not thinking about what wind is and what relative
motion is.
John, I want you to *seriously* answer the following two questions for me.
Suppose there was a 30-knot wind, but also suppose that the ground,
due to rapid continental drift :) , was also smoothly and silently moving
below you at 30 knots in exactly the same direction and speed as the wind
for as far as you could detect. Suppose also that you have no GPS, and
no stars are visible. How could you detect the wind? (In every
respect, your environment is indistinguishable from the no-wind case.)
What is the definition of wind? (If you answer "the motion of air",
you're not done yet - motion is always, always relative to something
else.)
>Possible Red Herrings in the Downwind Turn Controversy
>
>1. The air mass in which the airplane is embedded is an inertial
>frame and so . . . .
>
>If the air mass is steady, that's so. But if you fly from Wind A
>into slower moving Wind B, you're talking about two *different*
>inertial frames. Your air speed is your speed through the air in
>which you're currently flying, not your speed relative to the
>air a mile back. An airplane can change air speed quite rapidly
>because the speeds of air molecules can vary considerably from
>one place to another place fairly near by. That is, gusts exist.
A gust is caused by a change in velocity of an air mass. Typically,
your plane flies from one air mass which is moving at one velocity
(a certain speed and direction) into an air mass moving at another velocity
(a different speed and/or direction).
A turn does not change the velocity of the air mass in which you
are flying. A turn changes *your* velocity (specifically, your
direction of flight).
>
>COMMENTS? CONTRARY VIEWS?
>
Listen very carefully to what I am about to say. There is a law of
physics which is over 400 years old, and puts an end to the downwind
turn controversy once it is understood. It is called the "principle
of relativity", and was postulated by Galileo Galilei. It holds
true in every respect today.
Basically, it says: "All steady motion is relative and cannot be
detected without reference to an outside point".
What does it mean? Well, suppose you are driving smoothly along
in the back of a very large truck with no windows. As long as
the truck does not accelerate (speed up, slow down, turn - all are
accelerations) you cannot detect that you are moving. Agreed?
That's the principle of relativity - you can't tell that the truck's
in motion unless you refer to something *outside* the truck.
Suppose that the truck was *very* large, large enough to fly a plane
inside. You fly in circles in the back of the enclosed truck, and you
make perfect circles with respect to the floor of the truck, even though
the truck is moving along the highway at 30 mph. Your circles in the back
of the truck feel the same as circles over land in a no-wind situation, no
loss or gain of airspeed is detected. Are you still in agreement with me?
If not, refer back to the principle of relativity, read through this
paragraph, and keep thinking about this paragraph until it makes sense.
Continue when you're ready.
Ah, you made it. Good. Now, suppose that the truck is driving
at exactly the same speed and in exactly the same direction as the
wind - i.e. the truck is motionless with respect to the air mass
around it. Now, we open the (very large) rear door of the truck, and
the plane keeps making the circles. Of course, nothing changes at this
point - since the truck is moving along with the wind, the air seems to
be perfectly still outside the truck when the rear door is opened.
Now, the plane exits the truck and continues to make the same circles,
only behind the truck instead of inside of it. Does anything change?
No, of course not! The air inside the truck was moving at exactly
the same speed as the air outside the truck. There is no change.
Now, the truck takes the next highway exit, and the plane keeps turning
in steady circles. By this time, you've noticed that the path the
plane is flying with respect to the ground is actually a spiral.
But the pilot cannot tell that he is following a spiral path unless
he looks at the ground (or at a GPS). To him, and to his instruments,
he is holding a constant bank angle, keeping a constant rate of turn,
and holding a constant airspeed. This is no different a situation
than flying circles in a no-wind situation.
In sumarry, the steady motion of the air (i.e. a steady wind) is
undetectable to the pilot unless he refers to an outside point (the
ground, the stars, or an array of GPS satellites), in the same way that
the steady motion of the truck, or of *anything*, is undetectable without
judging that motion by some external reference.
All motion is relative to something else. And that is the principle
of relativity. An ancient, extremely useful princible of basic
physics, and something that I think everyone with a PhD in flight
physics should know intimately and take to heart. :)
--
+=And=the=Master=said=unto=the=silence,="In=the=path=of=our=happiness=shall=+
\ we find the learning for which we have chosen this lifetime." - R. Bach /
+=send=e-mail=to=<mur...@math.uiuc.edu>=====================================+
William Batchelor
Turning a plane down wind does not effect airspeed.
Turning a boat down river does not effect water speed.
Turning a car into the direction of the earth's rotation does not
effect ground speed.
Now, if the earth changed directions when driving (i.e. earth shear)
that would indeed effect your driving, but those are two different
issues.
nuff said.
Bob Noel
> Here's a posting I came up with this afternoon which *SHOULD*
> excite some discussion. At the moment, however, it is also
> my genuine opinion.
> John
>
> You Do Lose Airspeed in a Downwind Turn
>
> John T. Lowry, PhD
> Flight Physics
A PhD posted this?
[snip]
> But here's the kicker. *Turning to downwind is the same thing
> as a slow wind shear*.
wrong...and therefore the rest of your post is, well, nonsense.
--
Bob Noel aka Kobyashi Maru
my views are my own not MITRE's
(why use a disclaimer when people are
too --------- to understand it?)
Iain Clark
>But here's the kicker. *Turning to downwind is the same thing
>as a slow wind shear*.
No it is not. Not no way, not no how.
I could almost be persuaded that a turn was the same as a very slow
wind shear, but, it has nothing to do with whether the turn is upwind
or downwind.
>Say you start a coordinated turn from
>upwind towards downwind at standard rate, 3ų per second. At the
>start, say you have a 30 knot headwind. A second later you have
>a 30*cos(3ų) = 30*0.9986 = 29.96 knot headwind. It's not much
>less, but it *is* less. After turning for 10 seconds you've
>turned 30ų and the headwind has slacked off to "only"
>30*cos(30ų) = 30*0.8660 = 25.98 knots. That's getting to be at
>least marginally perceptible, but remember the effect has been
>continuously spread over ten seconds. After a quarter turn from
>headwind to crosswind, 90ų, which took 30 seconds, your relative
>headwind has changed by 30 knots.
This is a coordinated turn right? Where is the relative wind from in
coordinated flight? Is this a skidding turn or a slipping turn? I think
you are seriously in error here. You can fly uncoordinated turns if you
like but they will be unaffected by the wind's velocity with respect to
the ground.
Iain
Adam Wilt
You're flying with respect to the AIR MASS, not the ground; if the air
mass is all moving along at a given speed (no wind shear in the air mass
itself) then your turns are not going to affect airspeed at all (but your
groundspeed WILL change), assuming all else equal. i.e., a level turn with
sufficient power added to compensate for the increased drag due to the
tilted lift vector etc., etc....
If you're over a cloud deck that's moving with you, you won't be able to
see whether your ground speed has increased or decreased, right? Does your
airplane care? It can't even see!
Think of it this way: a fly, flying "crosswind" along a row of seats in a
cruising 747, turns "downwind" towards the rear of the plane. Does it
suddenly fall out of the air?
Sheesh!
Tom Turton
airmass is totally transparent to the airplane. Maybe I'm thinking
about this too much (or not enough!). What finally swung me over was
when I was considering a helicopter rotor blade. Most are familiar with
how the pitch of the rotor blade needs to change as it is flying through
the air. I thought for sure this would prove that a very fast turn
WOULD result in noticeable airspeed changes. THEN I realized I was
confusing the issue - to use the helicopter example, I would have to
consider either a helicopter hovering over one spot in a no wind situation
or a helicopter "hovering" in the same parcel of air as it is being
moved along with the wind. In both of these situations, I believe, the
helicopter blades would remain at the same pitch angle whether advancing
or retreating. Doesn't matter whether the copter is in a zero wind or
a 200 kt jetstream.
Vastly different would be a helicopter trying to 'hover' over a fixed ground
point in a 200 kt headwind (which would be the equivalent of flying at
200 kts in zero wind).
Anyway, I'll still be thinking about all of this, but I believe I was looking
at the downwind turn incorrectly. I know this subject comes up frequently,
but thanks to all those who posted rebuttals to John Lowry's post because
some of us (me, for example!) need to clear out some cobwebs occassionaly :)
----Tom T.
Konrad Kelley
suggest you go out to the local radio control modelers flying field
(call the hobby shop). You will be able to see the *airplane* flies in
reference to the air, but the *person* flies with reference to the
ground.
I suppose some folks could confuse changes in relative
airspeed with how the wind assists the (ground reference) turn when
turning from headwind to tailwind, and resists the tail to headwind
turn. Watching the R/C models you can see the different rates of turn
_with respect to the ground_ but the relative airspeed is the same
for both turns.
I recommend R/C flying for all pilots. It is an education on
how aircraft attitude, airspeed and control all relate.
Konrad Kelley
Leonard Wojcik
writes:
>That theory only holds if you consider the airplane is turning in a
>round circle relative to the ground. In reality, the plane describes a
>spiral over the ground.
> <SNIP>
here in lies the meat of the argument. If an aircraft flies constant radius
circles about a point on the ground in a steady hi-velocity wind (say 30 mph),
and the aircraft is flying at some given airspeed that does not change (say 90
mph), the ground speed of the aircraft will indeed have to change as it flies
its circles. Such changing ground speed implies a changing momentum. It
takes energy to change momentum. The engine provides the energy, but not
instantaneously, though in the turn about a point scenario, the direction
change is gradual Now make the turn quickly (such as
in a traffic pattern) and if the wind is large enough, and the airspeed low
enough, this can indeed affect the aircraft and cause an otherwise marginal
airspeed to decrease to the point of a stall. (since it takes some amount of
time for the aircraft to accelerate) This problem is analogous to the wind
shear problem, only it is pilot caused rather than weather caused.
The flaw in the "boat in a river" argument is that we fly traffic patterns
relative to fixed points on the ground (similar to the turns about a point).
Answer to the problem: always fly with enough airspeed so that wind gusts or
"downwind turns" do not present a hazard. Avoid abrupt turns in windy
conditions when low and slow.
Michael L. Murphy
>In article <4qssfu$c...@sol.sun.csd.unb.ca> eec...@umoncton.ca (Emile Cormier)
>writes:
>
>>That theory only holds if you consider the airplane is turning in a
>>round circle relative to the ground. In reality, the plane describes a
>>spiral over the ground.
>
>> <SNIP>
>
>here in lies the meat of the argument. If an aircraft flies constant radius
>circles about a point on the ground in a steady hi-velocity wind (say 30 mph),
>and the aircraft is flying at some given airspeed that does not change (say 90
>mph), the ground speed of the aircraft will indeed have to change as it flies
>its circles. Such changing ground speed implies a changing momentum. It
>takes energy to change momentum. The engine provides the energy, but not
>instantaneously, though in the turn about a point scenario, the direction
>change is gradual Now make the turn quickly (such as
>in a traffic pattern) and if the wind is large enough, and the airspeed low
>enough, this can indeed affect the aircraft and cause an otherwise marginal
>airspeed to decrease to the point of a stall. (since it takes some amount of
>time for the aircraft to accelerate) This problem is analogous to the wind
>shear problem, only it is pilot caused rather than weather caused.
No no no no no. Totally and completely incorrect.
Following a constant radius circle in a steady wind is *the same*,
aerodynamically speaking, as following a spiral path in a no-wind
situation. Your airspeed does change, but not because of the wind - it
changes because your rate of turn changes as you follow the circular
groundtrack (or spiral "airtrack"). Faster turn rates cause a higher
drag on the airplane, which slows the airplane down.
I can see I need to explain this one further. If an aircraft flies
constant rate circles in a steady high velocity wind, the following
is happening:
1) Its bank angle is constantly changing (steepest on the downwind,
shallowest on the upwind)
2) Its rate of turn is constantly changing (fastest rate of turn on
the downwind, slowest on the upwind)
These requirements for holding a circular path in the wind are well
known to every student pilot who has done turns about a point.
Naturally, the higher turn rate on the downwind portion of the
turns about a point requires a higher horizontal component of
lift (provided by increased back pressure), which generates more
induced drag. This *will* slow your airplane down. Also, the
higher G-loading associated with the steeper turn *increases* your
stall speed (double indemnity for steep turns at low airspeed).
Don't be fooled into thinking that the plane is slowing down
because it is turning downwind. Putting in the same control
inputs (varying bank angle & back pressure) in a no-wind situation
will result in a *spiral* groundtrack and the *same* airspeed
loss on the "tight" portions of the spiral path. The steady wind
really no affect aerodynamically on your airplane.
If you turn downwind with the same control inputs (same bank
angle, same amount of back pressure), you will get the exact same rate or
turn, and the exact same airspeed loss, if you make the same turn upwind.
Naturally, if you make tighter turns downwind than upwind, you're going
to lose more airspeed - but it is not caused by the wind, it is caused
by you.
>Answer to the problem: always fly with enough airspeed so that wind gusts or
>"downwind turns" do not present a hazard. Avoid abrupt turns in windy
>conditions when low and slow.
No. You should be *equally* careful turning upwind and downwind when
your are flying low and slow. Don't use steep bank angles, and always
coordinate your turns with rudder. Refer to your airspeed indicator,
not your eyeball estimate of the groundspeed, to judge your airspeed when
turning. Your groundspeed will be higher than your airspeed when turning
downwind, and unless you use your airspeed indicator, this can fool you
into hauling back on the yoke when you don't have any airspeed to spare.
Bill Chivers
This is one of the many 'old chestnuts' which lurk around in flying.
What I like to do is choose one every now and again and try and
prove/disprove it, or at the very least try and define it.
I agree with most of the postings here about the irrelevance of wind
speed, air speed unchanged etc. However, what is the origin of this
concept?
If we are going to discuss something, we need to state our assumptions /
experiment conditions precisely. Many people in this thread have done
so, but I have this sneaking suspicion that the origin of the 'downwind
turn = loss of air speed = danger' involved a different situation than
is generally considered.
Most people seem to discuss turns in general. But my theory is that the
origin of the statement is about *climbing* downwind turns, specifically
at low level (i.e. the circuit).
Let me give a very particular scenario, I accept it is a bit contrived
but that is to accentuate things:
Runway oriention North/South.
Met conditions: Very strong inversion at low level, say just below
circuit height at 900'. Therefore Windshear. Wind speed above inversion
Northish at 30 kts. Below inversion, due surface friction and no mixing,
Northish at 10 kts.
Circuit: Left hand, Taking off heading north, 1000' Oval pattern.
Aircraft: Generic Light Single, Vs 45 kts, Vy 70 Kts, R/H prop.
Imagine we were flying a circuit in these conditions.
In the initial climb out we would have Air Speed 70 kts, 10 kt H/W, G/S
60.
As we turn down wind, we would be tending towards Air Speed 70kt, 10 kt
T/W, G/S 80kt. But what happens as we pop through the inversion? G/S
still *instantaneously* 80 kt, 30 kt T/W, Air Speed now 50 kts.
Uh-Ooh! Not to worry though, still above Vs (45 kts).
But what happens if we are still turning? Say AOB=30, approximate 40%
increase in stalling speed (18 kts increase). Stalling speed now 63 kts,
Airspeed only 50 Kts. Ouch!
But thats not all. We've got full power on (because we are climbing) so
prop effect is going to yaw us to the left.
And if thats not enough, when we were turning crosswind, we might have
been caught out by a visual illusion of slipping to the left (due wind),
and may as a result already have been mishandling the aircraft by
applying left rudder, skidding the aircraft as we try to correct the
perception of slip.
So, we've got left rudder, left yawing prop effect, airspeed below
stalling speed. A nice little recipe for the aircraft to stall and start
to autorotate.
(No need to despair though. Quick as a flash we move the control column
centrally forward, applying opposite rudder to prevent further yaw, roll
the wings level after the buffetting stops and recover with minimum
height loss, all the while mentally thanking the CAA for those
cumpulsory 4 hours of stall/spin awareness training!)
So, my conjecture is that the origin of this 'downwind turn thing' is in
fact about circuit (or low level) flying specifically, rather than
turning in general. The problem is not so much turning downwind, but
*climbing* downwind. Since wind speed generally increases with altitude
at low levels then this *will* translate to a loss of airspeed. If we
are turning at the time then so much the worse due increased stalling
speed.
Now, since we generally take off into wind, it follows that we are
likely to be the turning downwind as we climb.
Opinions? Observations?
If you are bored with this thread, having seen it recur every few
months, try solving my stall turn problem, posted as a new thread :)
Bill Chivers
'Recently escaped from the groundschool department, dusting off log book - Yeee
Haaa!'
John Stephens
lwo...@vii.com (Leonard Wojcik) wrote:
[snip]
>The flaw in the "boat in a river" argument is that we fly traffic patterns
>relative to fixed points on the ground (similar to the turns about a point).
>
>"downwind turns" do not present a hazard. Avoid abrupt turns in windy
>conditions when low and slow.
Sure as hell hope you never fly my plane! You should make your turns in the
pattern at a fairly constant bank angle, and roll out on a heading that allows
for wind drift so that your pattern stays rectangular. You DO NOT try and
turn aroung a ground reference point with a constant ground radius. And you
NEVER let your airspeed decay to the point of approaching a stall. At least
not more than once. :-(
John
John Stephens
William Joseph Levenson <ss8...@den.mmc.com> wrote:
>John T. Lowry wrote:
>
>> You Do Lose Airspeed in a Downwind Turn
>>
>> John T. Lowry, PhD
>> Flight Physics
>> Billings, Montana
>> (406) 248 2606
>> <jlo...@wtp.net>
>> June 1996
>>
>>
>> In summary, my answer to the downwind turn controversy is: You
>> do lose air speed in a downwind turn, but in a "noisy"
>> environment and only over a time span that renders that loss
>> almost imperceptible. Still, I think those beginning students
>> were right.
>>
>> COMMENTS? CONTRARY VIEWS?
>
>
As I am one, I can say it...
Academic Degree Taxonomy:
B.S. (we all know what that is),
M.S. (more of the same), and finally,
Ph.D. (piled higher and deeper)
In this case, the higher and deeper are not in dispute!..
>No, John, there is no change in airspeed in a downwind, upwind,
>or crosswind turn...period. Wind shear is a totally different
>phenomenon. Think about it a little more.
>
>Bill Levenson
>PP-ASEL-IA
John Stephens
Ph.D. (Physics)
J.A. Dalton
>
>Think of it this way: a fly, flying "crosswind" along a row of seats in a
>cruising 747, turns "downwind" towards the rear of the plane. Does it
>suddenly fall out of the air?
Point taken. But wouldn't the fly have to turn towards the *front* of the
747 to be flying "downwind"??
William Lorimer
> But here's the kicker. *Turning to downwind is the same thing
> as a slow wind shear*.
No, it isn't.
> Say you start a coordinated turn from
> upwind towards downwind at standard rate, 3ų per second. At the
> start, say you have a 30 knot headwind. A second later you have
> a 30*cos(3ų) = 30*0.9986 = 29.96 knot headwind.
So? You're neglecting all the other forces acting on the airplane. For
example, there is now a cross-wind component of 30*sin(3ų). More
importantly, your aircraft velocity is continuously changing as a result
of the centripetal acceleration in the coordinated turn. This is *not* the
case in a wind shear, where the velocity of the aircraft changes only in
response to the change in the wind.
I don't have time for this. I have an M.Sc. in mathematics, I can't be
bothered continuing to lecture slack-minded know-it-alls who lock on to
one hazy idea and ignore everything else. If you're not prepared to do a
detailed mathematical analysis, don't try to snow us by concentrating
solely on one single vector.
--
WR Lorimer
Remember - your pride/ Is not worth your hide.
(PGP Key 0xF95EC559 available fm server)
(Standard Disclaimer applies.)
Bill Chivers
<Bi...@chivcons.demon.co.uk> writes
>
>Uh-Ooh! Not to worry though, still above Vs (45 kts).
>
>But what happens if we are still turning? Say AOB=30, approximate 40%
>increase in stalling speed (18 kts increase). Stalling speed now 63 kts,
>Airspeed only 50 Kts. Ouch!
Sorry folks, I must have been having a brain failure when I wrote this -
the figure are for an AOB of 60 (which is a bit big for the circuit!).
Correct figures should be an approximate 7.5% increase in stalling
speed, now 48 kts. So, not quite stalled but uncomfortably close.
Arguement still holds, especially if we are overbanked a little.
What an idiot!
Bill Chivers
'only a complete idiot has to correct his own postings!'
Jonathan Birge
credentials, but I think I know what he was getting at: you DO lose
speed in a downwind turn, but his argument doesn't really mention
anything special about downwind turns--he just considers a turn to be
somewhat analogous to a slow windshear. Period. This means that his
logic can be equally applied to an upwind turn. What's he's really
saying is that you lose speed in ANY turn, which is completely
reasonable. Given that he's got a Ph.D., I would be willing to bet
that the argument was somewhat tongue-in-cheek. I hope I'm right about
this, because it would otherwise be quite unsettling to my respect for
professors...
-Jonathan
patterson,george r
Jonathan Birge <bi...@garnet.engin.swarthmore.edu> wrote:
>Given that he's got a Ph.D., I would be willing to bet
>that the argument was somewhat tongue-in-cheek. I hope I'm right about
>this, because it would otherwise be quite unsettling to my respect for
>professors...
It shouldn't. Someone with a doctorate can be just as wrong as someone
who has a Masters, who can be just as wrong as a ditchdigger. People
with Ph.Ds *do* phrase it prettier. Your profs deserve your respect for
a vraiety of reasons, but they are not close imitations of God.
-----------------------------------------------------------------------
| I like long walks, especially when they are
George Patterson - | taken by people who annoy me.
| Noel Coward
-----------------------------------------------------------------------
Leonard Wojcik
>No no no no no. Totally and completely incorrect.
>Following a constant radius circle in a steady wind is *the same*,
>aerodynamically speaking, as following a spiral path in a no-wind
>situation. Your airspeed does change, but not because of the wind - it
>changes because your rate of turn changes as you follow the circular
>groundtrack (or spiral "airtrack"). Faster turn rates cause a higher
>drag on the airplane, which slows the airplane down.
sorry you miss the point.....
>1) Its bank angle is constantly changing (steepest on the downwind,
> shallowest on the upwind)
>2) Its rate of turn is constantly changing (fastest rate of turn on
> the downwind, slowest on the upwind)
>Naturally, the higher turn rate on the downwind portion of the
>turns about a point requires a higher horizontal component of
>lift (provided by increased back pressure), which generates more
>induced drag. This *will* slow your airplane down. Also, the
>higher G-loading associated with the steeper turn *increases* your
>stall speed (double indemnity for steep turns at low airspeed).
>Don't be fooled into thinking that the plane is slowing down
>because it is turning downwind. Putting in the same control
>inputs (varying bank angle & back pressure) in a no-wind situation
>will result in a *spiral* groundtrack and the *same* airspeed
>loss on the "tight" portions of the spiral path. The steady wind
>really no affect aerodynamically on your airplane.
So would you argue that there is no change in ground speed during the upwind
and downwind portions of the circle ???
>If you turn downwind with the same control inputs (same bank
>angle, same amount of back pressure), you will get the exact same rate or
>turn, and the exact same airspeed loss, if you make the same turn upwind.
>Naturally, if you make tighter turns downwind than upwind, you're going
>to lose more airspeed - but it is not caused by the wind, it is caused
>by you.
I'm not worried about loss of airspeed directly as a result of control
input.... only that arising from the momentum effect.... or do you
deny that there is a net change in ground speed as you fly around the circle?
Leonard Wojcik
>
>Sure as hell hope you never fly my plane! You should make your turns in the
>pattern at a fairly constant bank angle, and roll out on a heading that allows
>for wind drift so that your pattern stays rectangular. You DO NOT try and
>turn aroung a ground reference point with a constant ground radius. And you
>NEVER let your airspeed decay to the point of approaching a stall. At least
>not more than once. :-(
I sure hope not too. Don't think I could put up with your petty inuendo and
obvious superior attitude and inability to listen to what anyone else
says.
My point was that there is a definite diference between groundspeed when
flying the upwind leg and the downwind leg. Something has to make up for the
momentum diference (it takes energy input). Since acceleration is not
instantaneous there is a time after a downwind turn in which the plane must
accelerate to the new groundspeed (or decelerate after an upwind turn). If
the airspeed is too low to startwith, this can place the aircraft close to a
stall.
Charles H Miller
: In article <4qv3lh$7...@news3.digex.net> step...@pobox.com (John Stephens) writes:
I think it would be a good idea to fly patterns as outlined below:
: >
: >Sure as hell hope you never fly my plane! You should make your turns in the
: >pattern at a fairly constant bank angle, and roll out on a heading that allows
: >for wind drift so that your pattern stays rectangular. You DO NOT try and
: >turn aroung a ground reference point with a constant ground radius. And you
: >NEVER let your airspeed decay to the point of approaching a stall. At least
: >not more than once. :-(
My instructor recommends a 30 degree or so turn, followed by *crab* to stay
rectangular. Seems to work so far. And I've never lost airspeed *because* I
turned downwind, or upwind, or crosswind...it just doesn't seem to happen.
: I sure hope not too. Don't think I could put up with your petty inuendo and
: obvious superior attitude and inability to listen to what anyone else
: says.
If you think John is bad, just imagine what my instructor would say if you
tried turns around a point turning onto base. He wouldn't want you to
divide your attention that way!
: My point was that there is a definite diference between groundspeed when
: flying the upwind leg and the downwind leg. Something has to make up for the
: momentum diference (it takes energy input). Since acceleration is not
: instantaneous there is a time after a downwind turn in which the plane must
: accelerate to the new groundspeed (or decelerate after an upwind turn). If
: the airspeed is too low to startwith, this can place the aircraft close to a
: stall.
There is a change in momentum, all right, but not for the reason you think.
Because you change *direction* in a turn, the momentum (a vector quantity)
changes. The energy input comes from the pressure difference in the air
flowing around the banked wings. The air flows becuse the propellor
provides thrust.
The propellor provides thrust because the blades move through the air in
front (usually) of the aircraft. The blades move so fast the windspeed
from *them* is much more important than outside air movements, at least in most
cases that I've been in so far...
The airplane literally doesn't have *any* way of knowing groundspeed until
after the touchdown. Well, you *could* count ground effect, I guess, but
let's not. The plane does *not* have to "accelerate to the new groundspeed."
It is in the air, not on the ground. Groundspeed is meaningliss until the
touchdown, except that it determines how much time you spend in each leg
of the pattern. It does not affect *flight* dynamics because it is *ground*
speed.
Hopping off soapbox now....
--
Ecrasez l'infame!
Charles
Tim Long
> In article <4qv3lh$7...@news3.digex.net> step...@pobox.com (John
Stephens) writes:
>
> >
> >Sure as hell hope you never fly my plane! You should make your turns in the
> >pattern at a fairly constant bank angle, and roll out on a heading that
allows
> >for wind drift so that your pattern stays rectangular. You DO NOT try and
> >turn aroung a ground reference point with a constant ground radius. And you
> >NEVER let your airspeed decay to the point of approaching a stall. At least
> >not more than once. :-(
>
> I sure hope not too. Don't think I could put up with your petty inuendo and
> obvious superior attitude and inability to listen to what anyone else
> says.
>
> My point was that there is a definite diference between groundspeed when
> flying the upwind leg and the downwind leg. Something has to make up for the
> momentum diference (it takes energy input). Since acceleration is not
> instantaneous there is a time after a downwind turn in which the plane must
> accelerate to the new groundspeed (or decelerate after an upwind turn). If
> the airspeed is too low to startwith, this can place the aircraft close to a
> stall.
This is true for ANY turn, as EVERY turn is an acceleration. It just so
happens that in a homogeneous air mass, what the ground is doing relative
to the air mass has no effect on the aircraft, although it might have an
effect on the pilot's inputs. THAT can be a real effect of the wind. But
the acceleration is the same regardless of the turn relative to the wind
direction.
Reece R. Pollack
In article <lwojcik.13...@vii.com>, lwo...@vii.com (Leonard Wojcik) writes:
|>In article <4qv3lh$7...@news3.digex.net> step...@pobox.com (John Stephens) writes:
|>>
|>>Sure as hell hope you never fly my plane! You should make your turns in the
|>>pattern at a fairly constant bank angle, and roll out on a heading that allows
|>>for wind drift so that your pattern stays rectangular. You DO NOT try and
|>>turn aroung a ground reference point with a constant ground radius. And you
|>>NEVER let your airspeed decay to the point of approaching a stall. At least
|>>not more than once. :-(
|>
|>I sure hope not too. Don't think I could put up with your petty inuendo and
|>obvious superior attitude and inability to listen to what anyone else
|>says.
Ummm... the problem here is that John has listened to you, and found that
your belief is wrong.
|>My point was that there is a definite diference between groundspeed when
|>flying the upwind leg and the downwind leg. Something has to make up for the
|>momentum diference (it takes energy input). Since acceleration is not
|>instantaneous there is a time after a downwind turn in which the plane must
|>accelerate to the new groundspeed (or decelerate after an upwind turn). If
|>the airspeed is too low to startwith, this can place the aircraft close to a
|>stall.
Yes, there is a difference between ground speed. So? A wing generates
lift by moving through the air, not over the ground. I've flown in wind
strong enough to be able to hover in slow flight. Does this mean that
the moment I turn away from the wind I'm going to stall? Not a chance.
Any turn results in a decreased margin above stall. It doesn't matter
whether you're turning upwind or downwind, or towards the rotation of
the earth or away, or towards the motion of the universe or away. The
decrease in margin is exactly the same, because you're only concerned
with how the wing is moving through the air, not over the ground.
The one legitimate argument for being careful with a turn from upwind
to downwind has to do with pilot perception, not aerodynamics. In order
to make a pretty, square turn, a pilot may attempt to make the turn
from upwind to downwind tighter than he otherwise would. Tighter turns
further reduce the margin above stall. However, the reduction in margin
is no greater than with the same tight turn from downwind to upwind.
This thread will never die; if you can't convince everyone that the
earth is spherical and moves around the sun, you surely aren't going
to convince everyone that the downwind turn is a fallacy.
--
Reece R. Pollack
CP-ASMEL-IA -- N1707H Piper Arrow III (based GAI)
John R. Johnson
Jonathan,
Around a University, Ph.D.'s are rather like noses. Everyone has one,
so you don't pay much attention to it unless someone sticks it in your
face!
There is a common fallacy, shared by many people, both with and without
Ph.D.'s, that great expertise in one small area automatically lends
similiar expertise in ALL areas of knowledge. Unfortunately, this is
not true. Even Professors can be ignorant in some areas of knowledge.
Remember, ignorant means you do not know something. This is not the
same as stupid. Stupid means that you prefer being ignorant.
In this case, the "great downwind turn" business, is all based on a
misunderstanding of reality and a common misperception of pilots when
maneuvering close to the ground.
First, the "slow windshear fallacy."
Momentum is a VECTOR quantity. If you are moving a mass north at
100 miles an hour, to get it to move south at 100 miles an hour, you
have to accellerate it quite a bit. You have to essentially stop it
and reaccellerate in the opposite direction. If there is NO WIND and
you are going north at 100 mph, you will have a 200 mph CHANGE in
velocity when you turn south at 100 mph. This is also a CHANGE in
groundspeed of 200 mph. It is also a CHANGE in airspeed of 200 mph.
It is also a CHANGE in speed relative to the MOON of 200 mph. You
can't turn without making this change.
Now let's assume a wind of 80 mph straight out of the north. Boreas
is really huffing and puffing! Your airspeed is 100 mph NORTH. Your
ground speed is 20 mph NORTH. Now turn to the south at 100 mph. Your
change in AIRSPEED, from 100 mph north to 100 mph south is 200 mph.
EXACTLY like in the no wind condition. You ground speed CHANGES from
20 mph NORTH to 180 mph SOUTH. A CHANGE in ground speed of 200 mph.
Notice that this CHANGE is the same with NO WIND. It is the same as
the change in AIRSPEED, with or without WIND. The WIND makes NO
DIFFERENCE in the change in speed of the airplane OR in the RATE of
CHANGE in speed of the airplane. This is true whether you measure
your speed with respect to the airmass, with respect to the ground,
OR with respect to the MOON. The CHANGE in speed is always the same.
The accelleration required to make this change in speed is also ALWAYS
the SAME. This accelleration is required to make ANY turn. The direction
of the WIND and the strength of the WIND is irrelevant. Any CHANGES in
the wind must be summed vectorially with the CHANGES in airspeed, but
are normally a very small component of the CHANGE, and in anycase, do
not affect the airspeed, but merely affect the rate of change in direction
of the speed vector! Wheeewie. So much for that one. :-)
Now, about losing airspeed in turns, any turns! Clearly, to turn the
airplane has to accellerate. Accelleration requires a force. ( F=MA )
where F is force, M is mass ( not weight ), and A is accelleration.
That is one of Newton's great contributions to Physics. In an aircraft
this force is obtained by increasing and redirecting the lift vector.
(Bank the airplane and increase the back pressure a little to maintain
altitude.) If you maintain your altitude by increasing the back pressure
on the controls, and not by increasing the power delivered with the
throttle, then you do indeed pay for this accelleration by giving up
some speed. By reducing the speed slightly you reduce the power required
for level flight and allow the excess power ( you didn't reduce power also
did you? ) this makes available provide the energy required for the
accelleration. Alternatively, of course, you could keep the airspeed
constant and increase the power slightly to provide the energy required
for the accelleration. The energy required to alter the aircraft momentum
vector must come from somewhere, and it does require some energy flow.
Finally, the pilots misperception that originally gave rise to the great
"downwind turn" fallacy. When we fly an airplane we take our cues from
many places, many of them beneath the level of our conscious mind. When
we are close to the ground it is very difficult NOT to use the apparent
speed of the ground moving past us for a speed reference. To maintain a
constant airspeed, we often attempt to maintain a constant GROUNDspeed.
BUT, in a downwind turn, the GROUNDspeed must increase in order to keep
the airspeed constant. This provides conflicting cues to our subconscious
mind. These conflicting cues often results in, at least momentary,
incorrect responses to the apparent change in speed. This effect does
NOT happen when you are at any appreciable altitude because the distance
to the ground makes the speed cues you receive from the ground much less
intense. This incorrect response, caused by conflicting cues below the
concious level have caused many aircraft accidents over the years during
downwind turns, and will likely cause many more.
It is NOT because the change in momentum caused the airplane to slow down
and stall. It IS because the conflict in visual cues caused the PILOT to
slow down and stall.
John "Who also has a nose" Johnson
On 28 Jun 1996, Jonathan Birge wrote:
> I know people have been bashing this Ph.D.'s logic and questioning his
> credentials, but I think I know what he was getting at: you DO lose
> speed in a downwind turn, but his argument doesn't really mention
> anything special about downwind turns--he just considers a turn to be
> somewhat analogous to a slow windshear. Period. This means that his
> logic can be equally applied to an upwind turn. What's he's really
> saying is that you lose speed in ANY turn, which is completely
> reasonable. Given that he's got a Ph.D., I would be willing to bet
> that the argument was somewhat tongue-in-cheek. I hope I'm right about
> this, because it would otherwise be quite unsettling to my respect for
> professors...
>
> -Jonathan
>
>
R Wood
jlo...@wtp.net (John T. Lowry) wrote:
::Here's a posting I came up with this afternoon which *SHOULD*
::excite some discussion. At the moment, however, it is also
::my genuine opinion.
:: John
::
:: You Do Lose Airspeed in a Downwind Turn
:: John T. Lowry, PhD
:: Flight Physics
:: Billings, Montana
:: (406) 248 2606
:: <jlo...@wtp.net::
(clip)
::And let's change the subject; to that of horizontal wind shear,
::or gusts. Say you're heading into the wind at 100 KTAS and at
::first (Wind A) the wind is 40 knots. Suddenly (Wind B) there is
::a slackening gust to only 10 knots. (All wind speeds are ground
::speeds, speeds with respect to the earth just below them.)
I think you are complicating things uneccesarily by bringing windspeed
relative to the ground into the picture. If you throw out all of the
references to ground wind speed then it does not make any difference
if you turn upwind or downwind. The only factor that affect the wing
is the relative changes in the airspeed. All of the references to
what is happening relative to the ground are irrelevant.
I think the only relevancy the ground has is it's role in providing
the friction that will contribute to slowing the air closest to the
ground thus creating a vertical shear. That is, a difference between
horizontal layers of moving air that might have a bearing on the
downwind turn phenomena.
:: To an airplane in flight, there is no difference between
:: turning downwind, crosswind, or upwind, *except when
:: flying through a wind shear*.
I agree with this
::This time, my (**) italics. So at this point we have it that
::turning towards downwind does not result in loss of air speed
::but flying into a slackening gust does result in loss of
::airspeed.
True
::But here's the kicker. *Turning to downwind is the same thing
::as a slow wind shear*. Say you start a coordinated turn from
::upwind towards downwind at standard rate, 3ų per second. At the
::start, say you have a 30 knot headwind. A second later you have
::a 30*cos(3ų) = 30*0.9986 = 29.96 knot headwind. It's not much
::less, but it *is* less. After turning for 10 seconds you've
::turned 30ų and the headwind has slacked off to "only"
::30*cos(30ų) = 30*0.8660 = 25.98 knots. That's getting to be at
::least marginally perceptible, but remember the effect has been
::continuously spread over ten seconds. After a quarter turn from
::headwind to crosswind, 90ų, which took 30 seconds, your relative
::headwind has changed by 30 knots.
I don't understand this argument. Try it without the ground reference
and you don't have any airspeed changes. You don't have any IAS
changes even with the reference, just speed over the ground, the wing
doesn't care. The headwind component is irrelavent.
::That 30 knots is almost precisely the size (50 ft/sec) of the
::FAA's standard gust. But the FAA takes it that the gust develops
::its full force over only one quarter second! There's the
::difference. The same wind change, spread over a time interval
::30/0.25 = 120 times as long and at a time while you've already
::increased angle of attack to counteract your banked and
::therefore off-vertical lift vector, and possibly also increased
::power a little to counteract increased induced drag and
::increased trim drag in the turn, is essentially imperceptible.
::The time scales are vastly different.
I don't agree, the airspeed has not changed at all in your turn, only
the speed over the ground, which is irrelevant.
(clip)
::1. The air mass in which the airplane is embedded is an inertial
::frame and so . . . .
::If the air mass is steady, that's so. But if you fly from Wind A
::into slower moving Wind B, you're talking about two *different*
::inertial frames. Your air speed is your speed through the air in
::which you're currently flying, not your speed relative to the
::air a mile back. An airplane can change air speed quite rapidly
::because the speeds of air molecules can vary considerably from
::one place to another place fairly near by. That is, gusts exist.
Again reference to the ground is not necessary, you always lose
airspeed flying into an air mass moving relatively faster than the one
you are coming from. Headwinds, tailwinds and crosswnds irrelavent.
::2. Air speed is air speed, so . . . .
::Air speed is speed through that air *in the direction the
::airplane is pointed*. Say I told you an airplane was progressing
::northward against a 30 knot wind out of the north and its ground
::speed was northward at 70 knots. You'd probably say its air
::speed was 100 knots. But what if I told you, in addition, that
::that airplane's nose was pointed directly to the *south*. (The
::ultimate skidded flat turn.) Tilt! Unfair! Now the air speed has
::suddenly become -100 knots. The concept of air speed takes a bit
::more refinement than most of us give it.
This reasoning makes absolutly no sense at all. You'll have to try
harder to make your point!
::3. The earth isn't actually an inertial frame of reference
::anyway . . . .
::True. But the non-inertial terms (due to rotation about its axis
::and revolution about the sun) are known. And quite small. So for
::all practical intents and short term purposes, the earth is an
::inertial frame. Therefore, a force is necessary to change the
::speed of the airplane relative to the earth. Even if the
::airplane flew into a vacuum, it would *initially* still move at
::the same speed in the same direction, just as does a tennis ball
::you drop out the window of a speeding car. Then, as the changed
::and unbalanced forces took over, the airplane would accelerate.
I fail to see the similarity in elements of this argument nor it's
relevancy to the concepts your are putting forth. If an airplane flew
into a complete vacuum the only direction it would accelerate would be
toward the pull of a gravitational force. Motive force, lift and drag
would cease and the airplane would become part of the landscape.
::In summary, my answer to the downwind turn controversy is: You
::do lose air speed in a downwind turn, but in a "noisy"
::environment and only over a time span that renders that loss
::almost imperceptible. Still, I think those beginning students
::were right.
::COMMENTS? CONTRARY VIEWS?
You may lose airspeed but it has nothing to do with the wind relative
to the ground. It is probably a combination of perception of the
pilot and windshear.
Rhea Wood
N3489Y C-185
Alaska-Based Floatplane
Dennis Kodimer
>::COMMENTS? CONTRARY VIEWS?
This diatribe not only doesn't make it's point but it also rambles
into unrelated territory. Mr Lowry - I suggest you go back to the physics
of flight rather than trying to politic a new viewpoint into existence.
Once airborne, a plane flys AIR. The word "ground" shouldn't be there. Period!
All the ground does is ...
1) generate windshear & turbulence & handy-dandy places to land eventually
2) provide a huge moving map display which suggests what course you might want.
3) generate the gravitational downward force that the wings strive to balance
4) create confusion for those who would argue the case the way you did
That's not a viewpoint - it's the physics of the situation.
The words "downwind", "upwind" all connote ground reference, creating confusion.
The word "Inertial reference" just compounded the confusion so nothing made sense.
When a plane turns - it flys the speed the pilot sets it to fly. Period!
If he or she sets it at a certain speed - that's the speed it flies (sigh!)
But folks stare at the ground and when turning out of a strong headwind, think
they are accelerating downwind. They're not accelerating in the air, only against
the ground which cannot, does not, will not affect AIR speed.
The ground path simply becomes skewed toward downwind. The airpath is a circle.
Similar to the path of a bug on the rim of a wheel; viewed from the bicycle,
the bug is going around in a circle. Viewed from the roadway as the bike goes by,
the bug is following a "cycloid". So what? The bug is unaffected by the ground.
If the wind changes speed or direction, the inertia of the plane will keep
the same momentum albeit the IAS will change commensurately until forces balance.
But turning a plane does not affect the wind (unless the plane were truly gigantic!)
But that has nothing with airspeed whilst turning. The pilot controls that.
Amazing how many people got "snagged" into the illogic of this mess. Enough!
->Dennis<-
The true joy in life is the being used for a purpose recognized by yourself as
a mighty one. -Shaw These are my, but not my employer's, opinions.
Balthasar T. Indermuehle
Finally! Thanks for the clear words.
The facts are physics in its purest form.
The relations as discussed are psychological.
- Balthasar
LSZB
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* CEO / Geschaeftsfuehrer *
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