Lancair crash at SnF

On Apr 25, 10:48*am, Stefan wrote:
WingFlaps schrieb:

Try reading the statement again, here it is:

"Now we add in the energy losses from having to accelerate with the
wind and to glide speed."

Now perhaps you would like to revise some physics and try to critcise
it for us?

It's the "having to accelerate with the wind" part which is complete BS
unless I completely misunderstand what you are trying to say.

The latter I think. The imposed accelerations associated with the
change in direction (from upwind to downwind) require control inputs
that add drag and increased energy loss (from drag).

To summarise your missed point, the pilot control inputs cost energy
that is not factored into simple glide/time analysis.

Cheers

WingFlaps wrote in news:80a95935-4492-4d7d-95c1-
:

On Apr 25, 10:48*am, Stefan wrote:
WingFlaps schrieb:

Try reading the statement again, here it is:

"Now we add in the energy losses from having to accelerate with the
wind and to glide speed."

Now perhaps you would like to revise some physics and try to
critcise
it for us?

It's the "having to accelerate with the wind" part which is complete
BS
unless I completely misunderstand what you are trying to say.

The latter I think. The imposed accelerations associated with the
change in direction (from upwind to downwind) require control inputs
that add drag and increased energy loss (from drag).

To summarise your missed point, the pilot control inputs cost energy
that is not factored into simple glide/time analysis.

Nope, the wind is going to help you in almost every way if you're
turning back. Firstly, your climnb gradient will have improved from the
headwind, leaving you higher for a given distance from the field. Also,
your glide is going to be improved by the tailwind when you do turn
downwind. also, your best LD speed is going to occur at a lower
airspeed, which will give you a couple of extra seconds if you have the
presence of mind to take advantage of it. You'll probably be a little on
the slow side after having made the turn anyway, so that's a help there.
If there is any crosswind element to the wind, you have another plus if
you turn towards the wind. The x-wind will minimise the radius of the
manuevering turns you will have to make.
There is no inertia involved in making a downwind turn. None. What does
cause trouble during a climbout is twofold. the wind gradient can cause
trouble, as it will for any tailwind/climb situation because inertia
does play a role there, and two, the perceived acceleration to the
eyeball can cause the pilot to do some untoward things. That's how that
particular old wive's tale came about.
However, the gradient is also your friend in the turnback/tailwind on
approach situation. the decreasing tailwind will bump your airspeed up
on approach and cut your G/S as you descend back to the runway.
I'd consider a turnback with some headwind on takeoff and the calmer it
is the less consideration I'd give to that avenue, depending of course
on the other circumstances.


Bertie

Hold on while I try to correct some nits in what Bertie said and see
what happens

Bertie the Bunyip wrote:
Nope, the wind is going to help you in almost every way if you're
turning back.
[ many good points supporting this assertion, but... ]
also, your best LD speed is going to occur at a lower
airspeed,
Well, technically, your best LD speed is related to angle of attack, and
not the groundspeed, so that won't change. Your best glide speed
certainly will be less...

There is no inertia involved in making a downwind turn. None.

Here's why I wonder about that. Let's suppose 65 KAS before and after a
180 turn from a 10 KT headwind. OK, before the turn, your groundspeed
is 55KTS and after the turn your groundspeed is 75KTS. Your intertial
frame of reference is tied to the g/speed, not the a/speed. So -- the
kinetic energy of the aircraft and contents is about 33% higher
(75/55)^2. That energy is only going to come from one place with no
power -- trading in altitude (potential energy) for kinetic energy.

tman inv@lid wrote in
:

Hold on while I try to correct some nits in what Bertie said and see
what happens

Bertie the Bunyip wrote:
Nope, the wind is going to help you in almost every way if you're
turning back.
[ many good points supporting this assertion, but... ]
also, your best LD speed is going to occur at a lower
airspeed,
Well, technically, your best LD speed is related to angle of attack,
and
not the groundspeed, so that won't change. Your best glide speed
certainly will be less...

OK, not the LD, you're right. but your best glide speed is realted to
your ground speed. To take an extreme example to illustrate this point,
imagine that your published best glide is 70 and you're trying to glide
into a 70 knot headwind. You're going nowhere. Increase your speed and
you will make headway.
In the tailwind scenario, your best glide distance over the ground will
be better at a lower speed than published. the stronger the wind, the
lower the speed required until you arive at your min sink speed.

There is no inertia involved in making a downwind turn. None.

Here's why I wonder about that. Let's suppose 65 KAS before and after
a
180 turn from a 10 KT headwind. OK, before the turn, your groundspeed
is 55KTS and after the turn your groundspeed is 75KTS. Your intertial
frame of reference is tied to the g/speed, not the a/speed. So -- the
kinetic energy of the aircraft and contents is about 33% higher
(75/55)^2. That energy is only going to come from one place with no
power -- trading in altitude (potential energy) for kinetic energy.

Nope, your inertial frame of reference owes nothing to the ground
whatsoever. None. Zero, nil zilch zippo. You ar entirely a creature of
the air and owe nothing to the ground whatsoever ( except in the
vertical, of course) The earth simply isn't that important in the bigger
scheme of things! If it were, you'd have trouble making left or right
hand tunrs in your car....


Bertie

On Apr 24, 6:41 pm, tman inv@lid wrote:
Hold on while I try to correct some nits in what Bertie said and see
what happens

Bertie the Bunyip wrote:

There is no inertia involved in making a downwind turn. None.

Here's why I wonder about that. Let's suppose 65 KAS before and after a
180 turn from a 10 KT headwind. OK, before the turn, your groundspeed
is 55KTS and after the turn your groundspeed is 75KTS. Your intertial
frame of reference is tied to the g/speed, not the a/speed. So -- the
kinetic energy of the aircraft and contents is about 33% higher
(75/55)^2. That energy is only going to come from one place with no
power -- trading in altitude (potential energy) for kinetic energy.

See the previous post. There's a change in kinetic energy, but
very, very little. Many people make the mistake of thinking that the
earth has an effect on the airplane. It does, but only vertically, by
gravity. Gravity has no horizontal Component. Like a gyroscope, which
is rigid with respect to space and cares not one bit about the earth,
the airplane's mass, as it moves in the horizontal, is affected only
by its relationship to space and the air it flies in.
That isn't to say that the earth isn't going to get in the
way a little harder. Landing downwind, as with landing into the wind,
involves transferring the weight from the wings to the wheels, and
downwind means much more groundspeed and maybe loss of control as the
roll continues at higher speed while the flight controls feel a
decreasing airspeed, or maybe the airplane will run out of runway.
Bang.
We do illusions created by drift turns with students, usually
in a strong wind and at around 500 feet, so that they can see that the
ball stays centered in the turn while they get the visual impression
that the airplane is skidding or slipping on the downwind and upwind
sides of the turn. The airspeed does not change. Not so's you could
read it. If we put the student under the hood and make him fly on
instruments while we do this, he can't tell us when he's turning into
the wind or out of it. Can't feel anything, can't see any performance
changes on the gauges.

Dan

On Apr 24, 6:41 pm, tman inv@lid wrote:
Here's why I wonder about that. Let's suppose 65 KAS before and after a
180 turn from a 10 KT headwind. OK, before the turn, your groundspeed
is 55KTS and after the turn your groundspeed is 75KTS. Your intertial
frame of reference is tied to the g/speed, not the a/speed. So -- the
kinetic energy of the aircraft and contents is about 33% higher
(75/55)^2. That energy is only going to come from one place with no
power -- trading in altitude (potential energy) for kinetic energy.

In your world, it's gonna be pretty hard for a sailplane to circle in
a drifting thermal. In my world, it's not a problem.

In rec.aviation.student tman inv@lid wrote:
Here's why I wonder about that. Let's suppose 65 KAS before and after a
180 turn from a 10 KT headwind. OK, before the turn, your groundspeed
is 55KTS and after the turn your groundspeed is 75KTS. Your intertial
frame of reference is tied to the g/speed, not the a/speed. So -- the
kinetic energy of the aircraft and contents is about 33% higher
(75/55)^2. That energy is only going to come from one place with no
power -- trading in altitude (potential energy) for kinetic energy.

This simply does not make any sense.

Kinetic energy, like velocity, is a relative quantity. You cannot look at
an object and say, "it has X joules of KE". You can only talk about KE
relative to some frame of reference. Just like velocity.

So forget about KE. It's in the same boat as velocity, so look at
velocity. You make a turn and suddenly you gain a bunch of groundspeed.
Where does the extra speed come from? It comes because you're maneuvering
relative to a medium, the air, which is itself moving. Your KE relative to
that medium is exactly the same as it was, so no energy has to come from
anywhere.

--
Michael Ash
Rogue Amoeba Software

"tman" inv@lid wrote

Here's why I wonder about that. Let's suppose 65 KAS before and after a
180 turn from a 10 KT headwind. OK, before the turn, your groundspeed
is 55KTS and after the turn your groundspeed is 75KTS. Your intertial
frame of reference is tied to the g/speed, not the a/speed. So -- the
kinetic energy of the aircraft and contents is about 33% higher
(75/55)^2. That energy is only going to come from one place with no
power -- trading in altitude (potential energy) for kinetic energy.

You should try to get your money back from your CFI.
--
Jim in NC

On 2008-04-25, tman inv@lid wrote:
is 55KTS and after the turn your groundspeed is 75KTS. Your intertial
frame of reference is tied to the g/speed, not the a/speed.

That is so wrong it's not even wrong. The ground isn't even relevant.

If it was right, thermalling a glider would be an utter nightmare.

--
From the sunny Isle of Man.
Yes, the Reply-To email address is valid.

WingFlaps schrieb:

Try reading the statement again, here it is:
"Now we add in the energy losses from having to accelerate with the
wind and to glide speed."

To summarise your missed point, the pilot control inputs cost energy
that is not factored into simple glide/time analysis.

This is absolutely correct. But then, I dont understand the connection
to your first statement regarding the wind. Additioinal drag by control
input is completely unrelated to the presence or non-presence of wind.

BTW, here's an example of a successful turn back from an engine failure
at 400ft! Mind you, this was *not* in a glider, but in an Antonov An-2,
pretty much a flying airbrake.

And before you ask: Yes, this is an accident report. But it only was an
accident because the ground was covered with soft snow so the plane
flipped over at touch down. Otherwise, the maneuvre would have been
successful. Even so, everybody walked away and the plane is flying again.

Here's the link to the report: http://www.bfu.admin.ch/common/pdf/1826_e.pdf