Lancair crash at SnF

On Apr 27, 8:18*am, Bertie the Bunyip wrote:


I'm still not sure what you mean when you say the aircraft has to
accelerate. Are you saying that turning downwind will cost more in
acceleration than any other type of turn?

No, that's not what I'm saying.

Cheers

WingFlaps wrote in news:167e4f31-1a4a-4bfa-98d0-
:

On Apr 27, 8:18*am, Bertie the Bunyip wrote:


I'm still not sure what you mean when you say the aircraft has to
accelerate. Are you saying that turning downwind will cost more in
acceleration than any other type of turn?

No, that's not what I'm saying.


OK

Bertie

In rec.aviation.student Bertie the Bunyip wrote:
45 degrees isn't enough unless you have a very nice gliding airplane or
are starting from a good height to begin with.

A 45 degree bank will give you the minimum turn radius and thus minimum
altitude lost for any heading change done with a steady state turn. Are
you suggesting that there are more... interesting techniques which can be
used to turn around, or just that sometimes you are doomed?

--
Michael Ash
Rogue Amoeba Software

In rec.aviation.student WingFlaps wrote:
On Apr 27, 8:22?am, Michael Ash wrote:
In rec.aviation.student WingFlaps wrote:

On Apr 27, 6:04?am, wrote:
? ? ? ? Lots of people had the impression you were talking about the
dreaded downwind turn, with all the talk about the energy required to
accelerate to maintain airspeed. The energy required, as pointed out
in a much earlier post with several very good references, is so tiny
that it's not worth fooling with at all.

Perhaps you could put a number on that? Could you try a gliding turn
with stopwatch and altimeter and compare that to a straight glide?

In the optimal 45-degree-banked turn the load factor will be about 1.4.
Your best glide speed and min sink speed will increase by the square root
of that, or 20%. The glide angle remains the same if you increase your
airspeed appropriately, so your sink rate will also increase by 20%. So
instead of 650fpm you'll be coming down at 780fpm. At 78kts (65kts best
glide speed from previous post plus 20%) and a 45 degree bank you're
making a circle a bit over 500ft across which will take you 13 seconds to
complete half of. The extra sink rate from the turn will therefore cost
you 30 feet over what you would have experienced in a straight glide for
the same amount of time.

You'll also lose about 80 feet to accelerate from 65kts to 78kts. But
you'll gain this back at the end, so as long as the end of your turn ends
at a reasonable height it can be ignored.

The numbers will, of course, vary between aircraft but it would appear
that the extra energy loss due to the turn itself isn't all that
significant. If 30 feet is the difference between making it and not making
it you probably should not be turning around in the first place.

I make the turn diameter bigger than that using the formula
rad=(knots^2)/(11.26 x tan(bank)) (assuming it's right) or about
1080'?

You're right, I gave the radius, not the diameter, but worded it as though
it were the diameter. My 13 seconds is based on v/(pi*r) though so it
ought to be correct.

On a side note, these equations are generally vastly more comprehensible
if you leave out unit conversions altogether. Turn radius in any circle
caused by acceleration is v^2/a, and here the acceleration is
9.8m/s^2*tan(bank). Anyway, the result is the same, I just find it easier.
Moving on....

So, what would you consider the minimum height taking decision
time into account and a 225 degree turn followed by a 45 to line up
back on the runway?

I really haven't a clue. I don't fly these things and thus don't have the
experience to comment on this. I've heard that you need to be quite high
to be reasonably safe doing it. The physics only gives you a raw minimum.
You need a hefty safety margin on top of that, plus knowledge of your
personal ability to perform close to the ideal, obstacles which may modify
your options, and other such things. Wind, density altitude, engine
performanc, aircraft weight, and other such things will all contribute as
well to change the answer.

My personal decision height for the analogous glider launch emergency is
*usually* a shade under 200 feet. Conditions, performance, obstacles, and
landing opportunities ahead can all modify this value. The physics would
tell you that the altitude required is around 35% of your wingspan,
because the energy from the extra speed you carry is theoretically
sufficient to zoom slightly, make the turn at min sink speed, and roll out
lined up with the adjacent taxiway at the same altitude you started. (If
you don't lose altitude then you just need to be high enough to avoid
hitting your wingtip on the ground, thus the 35%.) In reality you'd have
to be completely nuts to try this maneuver starting from an altitude of
20ft at normal takeoff speeds. And as I mentioned before, this has very
little bearing on the options available to a typical powered airplane.

--
Michael Ash
Rogue Amoeba Software

Michael Ash wrote in
:

In rec.aviation.student Bertie the Bunyip wrote:
45 degrees isn't enough unless you have a very nice gliding airplane
or are starting from a good height to begin with.

A 45 degree bank will give you the minimum turn radius and thus
minimum altitude lost for any heading change done with a steady state
turn. Are you suggesting that there are more... interesting techniques
which can be used to turn around, or just that sometimes you are
doomed?


Sure, a steeper bank than will get you around more quickly and the altitude
loss will be lower, mostly because the displacement form the centerline
will be minimal. I'm not theorising here. I used to do it as did most
people at the place. This was what worked from the lowest altitudes, but it
was dangerous and when one of the more experienced guys actually had an
engine failure and crashed badly turning around, we decided it might not be
such a good idea after all..
Typically I considered about 300' minimum for things like a T-cart or my
Luscombe, and about 400' for a Cherokee or 172 or something. In excess of
60 degrees is neccesary to do that. That, of course, is going to bring you
over the stall speed if you allow the wing to load up, so a brisk lowering
of the nose is required as you come around. The situation has to be assesed
moment to moment as you come around and you will be absolutely on the edge
of stalling the whole way. If you screw it up you will hit the ground hard.
Same is true of the 45 deg method you're proposing. In my experience that's
not going to be enough unless you're high enough to have turned crosswind
anyway. Most guys aren;t even proficient at doing steep turns at a constant
altitude with the power on. Also, probably few turnbacks are planned before
departure, that's why the tiny success rate..


Bertie

On Apr 27, 11:23*am, Michael Ash wrote:


My personal decision height for the analogous glider launch emergency is
*usually* a shade under 200 feet. Conditions, performance, obstacles, and
landing opportunities ahead can all modify this value.

What's your glide ratio? If it were 40:1 would that equate to 800' in
a 10:1 Cessna?

Cheers

In rec.aviation.student WingFlaps wrote:
On Apr 27, 11:23?am, Michael Ash wrote:

My personal decision height for the analogous glider launch emergency is
*usually* a shade under 200 feet. Conditions, performance, obstacles, and
landing opportunities ahead can all modify this value.

What's your glide ratio? If it were 40:1 would that equate to 800' in
a 10:1 Cessna?

The things I fly regularly range from 20:1 on the low end to 37:1 on the
high end. The 200ft number remains the standard for all of them. Glide
ratio can adjust it but it's more a matter of having a comfortable safety
margin. I once talked to an instructor who did a 180 in a 34:1 machine at
only 100ft, and he said it was a piece of cake. With that kind of
performance the turn costs no altitude at all so the decision height is
basically all safety margin. Flying something with reasonable performance
out of an airport where the landing sites ahead look deadly then I
probably would reduce the decision height to something like 100ft.

A direct multiplication isn't going to work here for several reasons.

First because of the safety margin. You don't need four times as much of
that.

Second because of speed differences. The power plane needs to go
significantly faster to maintain best glide or min sink, resulting in a
larger turn, more altitude lost in that turn, and more corrective action
to regain the runway centerline after it. The power plane starts out
either around best glide or slower than it, whereas the glider generally
has extra speed which means extra energy. (This will of course depend on
the performance speeds of the plane in question, but most power planes
have faster performance speeds.)

Third, reaction time. When you hear a bang and your rope goes away it
makes the situation obvious instantly. Engine trouble can take more time
to diagnose. (One of the more difficult scenarios for a glider is when
this happens to the tow plane. You could end up low and slow before
realizing what's going on and 200ft may very well not be enough in that
case.)

Overall I don't think it makes sense to extrapolate from the glider case.
From what the power guys are saying, it sounds like you want at least
several hundred feet, with the exact number depending heavily on the skill
of the pilot and the performance of the airplane.

--
Michael Ash
Rogue Amoeba Software

On Thu, 24 Apr 2008 15:40:55 -0700 (PDT), WingFlaps
wrote:

On Apr 25, 10:16*am, Stefan wrote:
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.


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?

I await your stumbling analysis of my words with mild amusement.

Cheers
*****************************************
Long time ago in the 30's I saw on a couple of occasions a Cub take
off in a strong head wind 25+ mph and make a 180 degree turn to down
wind. They then started losing altitude and mushed into the ground
nose high. Any idea why? Pilot's said they had full throttle and
proper RPM showed on engines until impact.

Big John
Big John

Big John wrote in
:

On Thu, 24 Apr 2008 15:40:55 -0700 (PDT), WingFlaps
wrote:

On Apr 25, 10:16*am, Stefan wrote:
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.


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?

I await your stumbling analysis of my words with mild amusement.

Cheers
*****************************************
Long time ago in the 30's I saw on a couple of occasions a Cub take
off in a strong head wind 25+ mph and make a 180 degree turn to down
wind. They then started losing altitude and mushed into the ground
nose high. Any idea why? Pilot's said they had full throttle and
proper RPM showed on engines until impact.



Wind gradient. As they climbed, the wind would increase and they'd lose
some airspeed until they were on the backside of the power curve.same
thing would happen if you took off with strong tailwind in the first
place. Also, the poorer climb angle even without the wind gradient would
cause many to get the nose up a bit too much as well if they were not
used to it.

Bertie

"Alric Knebel's Rack" wrote in message
...
On Fri, 25 Apr 2008 11:06:42 +0000 (UTC), Bertie the Bunyip wrote:

It's not so much the loss of altitude that will get you in this
manuever. it's the probable loss of control trying to manuever around
back towards the field.
Firstly, in any emergency that hasnt been drilled, you will have a
moment where you will be sitting there with your mouth open in utter
disbelief of what has just happened. in fact, even if you have drilled
for it you will still have this moment, but if it's been practiced the
moment you begine to do something about it will be sooner coming.
While you're sitting there wondering what's going on, the speed will be
bleeding off. Not good.

Nothing you do is useful. You very rarely even come up with a good
idea, and when the blind squirrel principal does kick in (astoundingly,
you've seem to even defeat random chance with your incompetence), you
manage to cock it up so badly that what might have been a useful thing
in a normal person's hands turns to low-grade fertilizer.

Those are your two claims to fame. Being a complete flake who can't
keep even the simplest of things on track for any significant period of
time, and being an absolute moron when it comes to understanding what's
useful to the piloting community, and implementing it.


No, actually he has proven himself a failure and dozens of things, wannabe
troll, pilot, motorcycle mechanic, and others. I think it might be fair to
label him a "complete" or "master" failure.