Spins, Spiral Dives and Training

On Jul 2, 3:27*pm, "noel.wade" wrote:
I personally am of the opinion that a lot of people thermal too slowly
and put themselves in a position to have an inadvertent stall/spin
accident.

Most of us are aware that stall speed goes up in a banked turn. *But
the desire to fly slowly and stay in the thermal keeps us down in the
"danger-zone", just above the stall speed. *This is unnecessary and
can actually be a big hinderance! *Why?

1) There's no reason to fly below min-sink speed, as any good glider
handbook will tell you. *What they don't usually mention is that your
min-sink speed is higher in a banked turn than straight-and-level
flight! *The same G-loading that affects your stall speed also affects
your whole glide polar - just as added wing-loading does when you use
water ballast. *So in a thermal you should already be flying a bit
faster than the POH indicates for min-sink. *How much faster depends
on your bank angle, and the same calculations for stall speed in a
banked turn should be applicable to your aircraft.

2) The slower you go, the less control authority you have. *This means
upsets are tougher to avoid, recovery from an unusual attitude is
harder to achieve, and control deflections have to be bigger in order
to make normal corrections to maintain your bank & pitch angles.
Remember - bigger control deflections equal more drag!

3) Remember that your airframe and wings start to experience localized
areas of separated airflow long before you get down to true stall
speed. *_Any_ dirty or separated airflow is extra drag and can result
in a slower overall climb-rate (as you burn some of your energy
maintaining speed and countering the drag forces). *You want the
entire aircraft to be sliding through the air as cleanly as possible
to maximize the lift in the thermal!

4) Thermals contain unstable air - turbulence and wind gusts and the
shear around the edges of the thermal can all create assymetrical lift
conditions across the wings; or cause airflow separation on parts of
the wing (if the boundary layer is already close to seaparating). *The
closer you are to stall speed, the more likely this is to suddenly
occur due to gusts or shear effects.

(For those of you who are trying to fly fast, add in the effects of
your water-ballast to all of this, too)

Just some food for thought,

--Noel

For this reason and for safety is why I advocate an angle of attack
indicator. The AOA indicator will help determine the exact airspeed
for minimum sink for your wing loading and bank angle. Then, you can
use either instrument as your guide.

There's actually quite a large range of AOA between min sink and stall
so flying min sink AOA will keep you a safe distance from a stall.

I have to think that an AOA indicator 'might' have saved at least one
life this summer.

Our club's DG1000T has a stall warning device that sounds when a certain
angle of attack is reached. However I find the thing a distaction, as it
goes off every time you hit a gust (thermals tend to be gusty) and I can
comfortably circle at a speed where it is sounding all the time.

If Noel Wade came to visit the UK, he would probably not be able to climb
at all in our often tiny little thermals using the techniques he suggests.
The necessary skill is to be able to fly in accurate well banked turns at
not more than about 5 knots over the turning stall speed. Otherwise he
will be going round in the sink surrounding the thermal.

However I agree that you should not fly so slowly that the glider is
buffeting, as that is inefficient and dangerous.

By the way, my favourite spin entry for annual checks on our members is
out of a well banked turn. All you have to is slow the glider down in a
typical thermalling turn until it is just starting to buffet and then feed
in a bit of bottom rudder. The glider will depart instantly into a fully
developed spin. This demonstrates the need for accurate flying and for not
using too much rudder into the turn. If you put in a bit of top rudder it
is almost impossible to make the glider spin, however slowly you fly it.

Del Copeland


At 22:27 02 July 2009, bildan wrote:
On Jul 2, 3:27=A0pm, "noel.wade" wrote:
I personally am of the opinion that a lot of people thermal too slowly
and put themselves in a position to have an inadvertent stall/spin
accident.

Most of us are aware that stall speed goes up in a banked turn. =A0But
the desire to fly slowly and stay in the thermal keeps us down in the
"danger-zone", just above the stall speed. =A0This is unnecessary
and
can actually be a big hinderance! =A0Why?

1) There's no reason to fly below min-sink speed, as any good glider
handbook will tell you. =A0What they don't usually mention is that
your
min-sink speed is higher in a banked turn than straight-and-level
flight! =A0The same G-loading that affects your stall speed also
affects
your whole glide polar - just as added wing-loading does when you use
water ballast. =A0So in a thermal you should already be flying a bit
faster than the POH indicates for min-sink. =A0How much faster depends
on your bank angle, and the same calculations for stall speed in a
banked turn should be applicable to your aircraft.

2) The slower you go, the less control authority you have. =A0This
means
upsets are tougher to avoid, recovery from an unusual attitude is
harder to achieve, and control deflections have to be bigger in order
to make normal corrections to maintain your bank & pitch angles.
Remember - bigger control deflections equal more drag!

3) Remember that your airframe and wings start to experience localized
areas of separated airflow long before you get down to true stall
speed. =A0_Any_ dirty or separated airflow is extra drag and can
result
in a slower overall climb-rate (as you burn some of your energy
maintaining speed and countering the drag forces). =A0You want the
entire aircraft to be sliding through the air as cleanly as possible
to maximize the lift in the thermal!

4) Thermals contain unstable air - turbulence and wind gusts and the
shear around the edges of the thermal can all create assymetrical lift
conditions across the wings; or cause airflow separation on parts of
the wing (if the boundary layer is already close to seaparating).
=A0The
closer you are to stall speed, the more likely this is to suddenly
occur due to gusts or shear effects.

(For those of you who are trying to fly fast, add in the effects of
your water-ballast to all of this, too)

Just some food for thought,

--Noel

For this reason and for safety is why I advocate an angle of attack
indicator. The AOA indicator will help determine the exact airspeed
for minimum sink for your wing loading and bank angle. Then, you can
use either instrument as your guide.

There's actually quite a large range of AOA between min sink and stall
so flying min sink AOA will keep you a safe distance from a stall.

I have to think that an AOA indicator 'might' have saved at least one
life this summer.

On Jul 3, 12:00*am, Derek Copeland wrote:

If Noel Wade came to visit the UK, he would probably not be able to climb
at all in our often tiny little thermals using the techniques he suggests..
The necessary skill is to be able to fly in accurate well banked turns at
not more than about 5 knots over the turning stall speed. Otherwise he
will be going round in thesinksurrounding the thermal.

Derek -

Thanks for attacking my skills rather than arguing the point from a
logical perspective... I trained and fly in places that have both
weak lift and narrow lift, and I stay in them just fine - for the
record.

Now, to actually defend the point:

If your argument is that you have to fly slowly in order to stay in a
small thermal, you're ignoring an alternate solution: tighten your
bank angle. It is true that a slower speed gives you a smaller
turning radius at the same bank-angle, but it has a number of
drawbacks (many of which I touched on with my post - you're closer to
stall speed, you're possibly below min-sink - and therefore not flying
the glider as cleanly or efficiently as you could be). If you simply
keep your speed up and tighten your bank angle, you'll achieve a
smaller turning radius and you won't be in danger of stalling.

I urge you to do the math, as I have done (or at least look it up
online, there are webpages that illustrate this - such as:
http://www.soarns.ca/crclmotn.html)... Down around the speeds we're
talking about, you will have a _smaller_ turn radius at a 45-degree
bank-angle than at a 30-degree bank-angle, EVEN if you add 5 - 7 knots
of speed in the higher bank-angle turn. AND the additional G-loading
does not increase your sink rate by that much (around 20 ft/min in my
DG-300). Even in a small 2-knot thermal you're really only giving up
a small percentage of performance in order to be a lot safer. And
there are plenty of ways that the average pilot can "make up" that
performance, by flying more cleanly in other phases of flight.
Finally, if you _have_ been flying below min-sink speed (for a given
bank-angle), you may actually find _improved_ climb performance by
keeping your speed up and tightening your bank-angle.

Take care,

--Noel

Noel,

It was not my intention to attack your flying skills, but just to state a
fact of life about flying in UK conditions. The tighter you turn, the more
the stalling speed increases, due to the extra g loading, and the more the
sink rate increases. Our thermals can also be quite weak, so excessive
angles of bank can increase the glider's sink rate enough to cancel out
the thermal.

5 knots over the turning stall speed at a 35-40 degree angle of bank
usually works well in the UK, and that puts you at about the effective min
sink speed.

I have flown in central France, where the thermals are normally huge and
strong. In the UK you normally turn as soon as you encounter lift, but
there you had to wait for maybe twenty seconds before you reached the core
of the thermal. The French pilots seem to thermal at only about 15 degrees
angle of bank. One holiday I had over there consisted of a whole
fortnight of low inversion blue days, so somewhat UK like conditions with
small weak thermals. My syndicate partner and I where able to do a number
of 200-300k flights when most of the locals (with one exception, who was a
world class competition pilot) couldn't stay up at all. Maybe that is why
the UK has produced so many World Gliding Champions, although I am not
quite in that league myself.

Derek Copeland


At 23:06 05 July 2009, noel.wade wrote:
On Jul 3, 12:00=A0am, Derek Copeland wrote:

If Noel Wade came to visit the UK, he would probably not be able to
climb
at all in our often tiny little thermals using the techniques he
suggests=
..
The necessary skill is to be able to fly in accurate well banked turns
at
not more than about 5 knots over the turning stall speed. Otherwise he
will be going round in thesinksurrounding the thermal.

Derek -

Thanks for attacking my skills rather than arguing the point from a
logical perspective... I trained and fly in places that have both
weak lift and narrow lift, and I stay in them just fine - for the
record.

Now, to actually defend the point:

If your argument is that you have to fly slowly in order to stay in a
small thermal, you're ignoring an alternate solution: tighten your
bank angle. It is true that a slower speed gives you a smaller
turning radius at the same bank-angle, but it has a number of
drawbacks (many of which I touched on with my post - you're closer to
stall speed, you're possibly below min-sink - and therefore not flying
the glider as cleanly or efficiently as you could be). If you simply
keep your speed up and tighten your bank angle, you'll achieve a
smaller turning radius and you won't be in danger of stalling.

I urge you to do the math, as I have done (or at least look it up
online, there are webpages that illustrate this - such as:
http://www.soarns.ca/crclmotn.html)... Down around the speeds we're
talking about, you will have a _smaller_ turn radius at a 45-degree
bank-angle than at a 30-degree bank-angle, EVEN if you add 5 - 7 knots
of speed in the higher bank-angle turn. AND the additional G-loading
does not increase your sink rate by that much (around 20 ft/min in my
DG-300). Even in a small 2-knot thermal you're really only giving up
a small percentage of performance in order to be a lot safer. And
there are plenty of ways that the average pilot can "make up" that
performance, by flying more cleanly in other phases of flight.
Finally, if you _have_ been flying below min-sink speed (for a given
bank-angle), you may actually find _improved_ climb performance by
keeping your speed up and tightening your bank-angle.

Take care,

--Noel