Lancair crash at SnF

On Apr 25, 10:48 am, Stefan <stefan@mus._INVALID_.ch> 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

Stefan <stefan@mus._INVALID_.ch> wrote in news:9f9a3$481106d6$54487369
$14456@news.hispeed.ch:

> WingFlaps schrieb:
>
>> (the stall is now damn close -better
>> hope there's no significant wind)
> ...
>> Now we add in the energy losses from having to
>> accelerate with the wind and to glide speed.
>
> Arrrgh! Not the old "turn into downwind" legend again! Better work out
> your understanding of physics before publicly reasoning about turns.
>
>> There is nearly always somewhere flat to put the plane
>
> The operative word in this sentence is "nearly".


so you've done this, have you?


Bertie

> Why two turns? At 500' why not one turn and land with wind up
> derriere? And, at 500 ft I wouldn't be too worried about the radio.


When you turn back for the runway, you will not be lined up with it! Still
air, you have to turn in excess of 180 deg to get back on or near the RW
centerline and then, you need to make on in the opposite direction to line
up.


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.

gatt <admin@godhateskansas.com> wrote in
news:T-Sdnb-eo8vLtIzVnZ2dnUVZ_tWtnZ2d@integraonline:

> Buttman wrote:
>> On Thu, 24 Apr 2008 17:05:06 +0200, Stefan sayeth:
>>
>>> Brian schrieb:
>>>
>>>> Your right in that many aircraft it is possible. But the problem is
>>>> it isn't possible for many pilots when the engine quits. It is not
>>>> a maneuver that is routinly practiced.
>>> Now this problem could be solved.
>>
>> You're suggesting instructors practice engine failures with their
>> students on takeoff? Oh boy, better hope Dudly doesn't see this...
>
> One way to practice this would be to establish a "runway altitude" at,
> say, 1000ft AGL, get the airplane into takeoff configuration on
> heading at that altitude over a road or something, simulate a failure
> at a specified altitude--say, 1,500 feet--and see what altitude you're
> at when you get back to your reciprocal heading. If it's above your
> starting altitude, you made it.
>
> Wind, density altitude and aircraft weight are significant variables.
>
> Of course, a proficient pilot will have considered all these variables
> as well as the terrain downrange before takeoff, so they already know
> what they will do if the engine quits at a specific altitude. On
> probably as many checkrides and flight reviews as not, the instructor
> has asked me what I will do if I lose power on takeoff so I already
> know
> where there transmission lines are, about how far it is to the lake,
> etc.
>
> -c
>

More importantly, perhaps, is the fact that if you make nice gentle
turns in an average lightplane, you simply won't make it. You have to
make the turn at a very high angle of bank to have even a hope of making
it in time. If you make it at say, 30 deg of bank at about 65 you're
going to lose the guts of 800 feet just manuevering to line up with the
runway if you fly the airplane accurately. You're going to be very low
at the end of this manuever to say the least. The best way to do it is
with a steep bank. Very steep. This will, of course, mean a high sink
rate, but the time required to make the turn will be cut drastically and
you'll be closer to the centerline when you've come about, so less time
and alt wasted trying to get lined up. To do this you must be absolutely
completely comfortable doing a steep power off turn at a reltively low
airspeed when you do it. Not imagining you can do it based on experience
doing steep turns with the power on, you have to be able to
simultaneously offload the wing at a rate that won't get the nose too
low as to get an excessive alt loss and make this drastic turn at the
same time without stalling. All this while your brain has become akin to
that of a lizard looking a rather big snake. IOW, you have to have
practiced this and other aerobatic manuevers so that they are second
nature. It can be done and it can be done in almost any airplane, but it
requires a lot of practice, experience, careful planning and a lot of
luck. Better to go straight ahead if you can.


Bertie

In rec.aviation.student WingFlaps <Moreflaps@> wrote:
> On Apr 25, 3:12?am, Dylan Smith <dy...@vexed3.alioth.net> wrote:
>> In gliders, every glider pilot is taught "the impossible turnback" from
>> 200 feet (which, in the typical low performance training glider, is
>> about equal to turning back at 600 feet in a C172).
>
> It's the L/D that makes it much harder in a typical powered plane.
> This means that all manouvers lose energy much faster. The turn back
> needs at least 2 turns as well as acceleration if there is any wind.
> You will note that nearly all the accidents are stall spins -a moments
> thought about the situation will make you realize why this is. The
> turns are made tight because there is not enough height/time for a
> lazy turn.
>
> Let's work some real numbers for a 172 at 500'. Say climb was a Vx 59
> knots. The plane must first be accelerated to 65 for best glide. The
> pilot carries out some trouble checks say 10s. Calls on the radio =10
> s and plans his return. Note that 20s have probably elapsed. The plane
> has already travelled ~0.4 miles and at a 10:1 glide ratio has lost
>>200' (assuming he did get it to best glide in the first place). Can
> he make 2 turns and land back -no way!

It's worse than just the L/D difference would make you expect in a few
ways.

The glider's best glide speed is considerably lower. Typical best glide
speeds are 50-55kts. Also, for best performance while doing a 180 you want
to fly at min sink speed rather than best glide speed, which in a typical
glider will put you down at 40-45kts.

This speed difference has two effects, neither of them good. First, your
sink rate will be considerably higher. At 10:1 and 65kts you're sinking at
650fpm. At 30:1 and 55kts you're sinking at under 200fpm. Second, a turn
done at lower speed is smaller and faster, so you're spending more time at
that 650fpm sink rate than the glider is spending at under 200fpm.

Another speed-related effect is that the glider is taking off much faster
than his best glide speed. A typical glider tow may be at 65kts. The extra
speed is energy to be burned off in the turn. A modern medium-performance
glider will come out of a 180-degree rope-break turn at the same altitude
he started! In the Cessna in your example you have the opposite problem,
you have to trade altitude for speed just to get *up* to best glide, and
then you keep losing it at an extremely high rate.

Rope breaks are also extremely obvious when they happen, so reaction time
is essentially instantaneous. There are other glider launch emergencies
which aren't so obvious, such as the tow plane losing power, where things
can get more difficult. In the case of the piece-of-cake 200' rope break
you'll have the controls deflected in less than a second from the event
unless you really screwed up your pre-takeoff mental preparation.

In conclusion: fly gliders, it's safer!

More serious conclusion: these things are much easier in gliders because
they're basically made for it. Don't carry it over to powered flight.

--
Michael Ash
Rogue Amoeba Software

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 Apr 25, 10:45 pm, Stefan <stefan@mus._INVALID_.ch> wrote:
> WingFlaps schrieb:
>
> > Itls a turn upwind to downwind. That involves 2 direction changes, one
> > to reverse course and the the other to line up the runway. If there's
> > wind there will be an effect on line up. Try thinking about more
> > factors that cost altitude OK?
>
> All good and fine, and I'm thinking about a lot of factors, btw. also
> about human ones which are usually the weak link, but you still have not
> explained what you meant when you wrote: "Now we add in the energy
> losses from having to accelerate with the wind."

Yes, I did. I'll explain it one last time. A direction change in a
plane is always due to acceleration (and that means more drag). That's
Newtonian physics. You go from up wind direction (takeoff is usually
up wind) to turn in the wind direction to land down wind. There's an
acceleration, it is a change in _velocity_ it creates drag, it costs
height and that's the important bit. Now do you understand -TURNS are
not free, they cost more height than the distance covered. Get it
now?

Cheers