Debunking Glider Spoiler Turns Causing Spin Thinking

It would take a lot of writing to totally describe the pattern. Of
course I make allowances for cross wind (crab), lift/sink (altitude),
head/tail wind (airspeed, flap setting), thermal/sink (dive brakes,
shifted touchdown point), etc. It's a dynamic process. Most pilots can
do it some can't. What I described is the nominal method. I do not fly
by rote as some pilots apparently do or are instructed to do...

On 6/2/2015 5:34 PM, son_of_flubber wrote:
On Tuesday, June 2, 2015 at 6:31:07 PM UTC-4, Dan Marotta wrote:
I can see the
landing area slightly over my shoulder as I begin the turn and I
keep my eyes on that spot with occasional glances inside and out on
final for other aircraft.
So you initiate the turn from downwind at the right time/point regardless of sink/wind conditions?

With your one turn method, the length of the glideslope to touchdown is set when you initiate the turn from downwind and so you make all corrections to touchdown point with more/less airbrakes (keeping airspeed constant)?

--
Dan Marotta

How come nobody ever states that these G loading increases are for level
flight? Since the glider is always descending, wouldn't it be better to
include something about the descent rate being maintained? What about a
climbing turn? Maybe some trig including the flight path angle?

Curious minds... And it's a slow morning before going to tow at the
Moriarty encampment.

On 6/2/2015 11:48 PM, Surge wrote:
On Wednesday, 3 June 2015 01:37:42 UTC+2, Bruce Hoult wrote:
I think you'll find that's more like 58 knots.

In a 45 degree turn, the G loading is 41% higher, but it only takes 20% more speed to produce that G loading, not 41% more speed.
You're right.
G-loading would be 1.41G in a 45 degree bank but the stall speed would increase by 1.19 so that would make it 58 knots (107km/h).

--
Dan Marotta

The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.

Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.

S

On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
How come nobody ever states that these G loading increases are for
level flight?* Since the glider is always descending, wouldn't it be
better to include something about the descent rate being
maintained?* What about a climbing turn?* Maybe some trig including
the flight path angle?



Curious minds...* And it's a slow morning before going to tow at the
Moriarty encampment.

On Wednesday, June 3, 2015 at 4:58:36 PM UTC+3, Dan Marotta wrote:
How come nobody ever states that these G loading increases are for
level flight?* Since the glider is always descending, wouldn't it be
better to include something about the descent rate being
maintained?* What about a climbing turn?* Maybe some trig including
the flight path angle?

The speed at which the wing stalls depends only on the G loading, not on the attitude with respect to gravity or the earth. Of course if you're in an unusual attitude then your speed may be changing.

As long as you keep the angle of attack constant (which pretty much means the elevator and therefore stick position), you don't have to think about how the speed or the G loading are changing -- they'll change together in sync. As long as you stay below the speed at which the G loading will break your wings off anyway.

On Wednesday, June 3, 2015 at 10:32:35 AM UTC-7, wrote:
The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.

Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.

S

On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
How come nobody ever states that these G loading increases are for
level flight?* Since the glider is always descending, wouldn't it be
better to include something about the descent rate being
maintained?* What about a climbing turn?* Maybe some trig including
the flight path angle?



Curious minds...* And it's a slow morning before going to tow at the
Moriarty encampment.



It doesn't matter if the glider is descending - the wing loading is the same. The only thing that will change that is accelerated flight. That is an increasing or decreasing rate of descent (not constant) or a change in velocity (that includes turns which are a change in velocity by definition). A sustainer glider will have the same wing loading in level (unaccelerated) flight as it does in a glide.

It is best not to think of the "speed at which the wing stalls". That can be anywhere from 0 to beyond redline, depending on a bunch of conditions. You should think of "the angle of attack at which the wing stalls" which is for all intents invariant on a glider. The only way to unstall a wing is to reduce its angle of attack, fortunately that is usually easy. This may have consequences (normally, an increased rate of descent) which may have to be dealt with later, but at least you are in control of it.

Thanks! Most appreciated.

On 6/3/2015 11:32 AM, wrote:
The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.

Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.

S

On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
How come nobody ever states that these G loading increases are for
level flight? Since the glider is always descending, wouldn't it be
better to include something about the descent rate being
maintained? What about a climbing turn? Maybe some trig including
the flight path angle?



Curious minds... And it's a slow morning before going to tow at the
Moriarty encampment.



--
Dan Marotta

PS that's for level flight-- for a turn the effective glide ratio is worse than the L/D and so the trig is more complicated and there's more unloading of the wing (compared to horizontal flight at the same bank angle) than you'd have at the same L/D in level flight, but the unloading is still quite small until we start talking about really steep bank angles or really poor L/D ratios.

Examples: G-load (lift / weight) at various bank angles and L/D ratios:

L/D Infinite-- 0 deg 1.00 30 deg 1.15 45 deg 1.41 60 deg 2.00
L/D 10:1-- 0 deg .995 30 deg 1.15 45 deg 1.40 60 deg 1.97
L/D 5:1-- 0 deg .981 30 deg 1.13 45 deg 1.36 60 deg 1.87
L/D 2:1-- 0 deg .894 30 deg 1.00 45 deg 1.15 60 deg 1.41
L/D 1:1-- 0 deg .707 30 deg .756 45 deg .817 60 deg .894

(if my math is right....)

S

On Wednesday, June 3, 2015 at 12:32:35 PM UTC-5, wrote:
The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.

Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.

S

On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
How come nobody ever states that these G loading increases are for
level flight?* Since the glider is always descending, wouldn't it be
better to include something about the descent rate being
maintained?* What about a climbing turn?* Maybe some trig including
the flight path angle?



Curious minds...* And it's a slow morning before going to tow at the
Moriarty encampment.

I might've paid attention in math class if I had known it could save lives

On Thursday, June 4, 2015 at 5:50:31 AM UTC-7, wrote:
PS that's for level flight-- for a turn the effective glide ratio is worse than the L/D and so the trig is more complicated and there's more unloading of the wing (compared to horizontal flight at the same bank angle) than you'd have at the same L/D in level flight, but the unloading is still quite small until we start talking about really steep bank angles or really poor L/D ratios.

Examples: G-load (lift / weight) at various bank angles and L/D ratios:

L/D Infinite-- 0 deg 1.00 30 deg 1.15 45 deg 1.41 60 deg 2.00
L/D 10:1-- 0 deg .995 30 deg 1.15 45 deg 1.40 60 deg 1.97
L/D 5:1-- 0 deg .981 30 deg 1.13 45 deg 1.36 60 deg 1.87
L/D 2:1-- 0 deg .894 30 deg 1.00 45 deg 1.15 60 deg 1.41
L/D 1:1-- 0 deg .707 30 deg .756 45 deg .817 60 deg .894

(if my math is right....)

S

On Wednesday, June 3, 2015 at 12:32:35 PM UTC-5, wrote:
The fact that the glider is descending only "unloads" the wing by a tiny amount, if we are talking about a steady-state constant-airspeed descent rather than an acceleration. The exact amount is cosine (arctan (D/L)). At a 10:1 L/D, you have over 99% of the loading that you'd have in level flight. The same would be true at a 10:1 powered climb angle-- there would be an unloading of the wing, but it would be slight.

Now, if you are pushing the stick forward to "unload" the wing and make the flight path curve toward a more steeply downward trajectory and make the airspeed increase, that's a different story from the steady-state case described above.

S

On Wednesday, June 3, 2015 at 8:58:36 AM UTC-5, Dan Marotta wrote:
How come nobody ever states that these G loading increases are for
level flight?* Since the glider is always descending, wouldn't it be
better to include something about the descent rate being
maintained?* What about a climbing turn?* Maybe some trig including
the flight path angle?



Curious minds...* And it's a slow morning before going to tow at the
Moriarty encampment.



Are you saying that the wing loading goes down in a turn because the glide ratio deteriorates?

That is incorrect. Wing loading and glide ratio, as you are using them here, are unrelated.

In steady state, unaccelerated flight, Lift = Mass and the wing loading is constant. It does not matter what your sink rate is. The wing loading is the same with flaps, gear, and spoilers out as it is clean. If Lift Mass then the glider is accelerating, either up, down or by changing direction. If Lift Mass then the wing loading is higher, for example a turn or pull up. If Lift Mass then the wing loading is lower, for example a push over..

We have one old timer instructor in my club who insists on airbrakes fully in during turns. The only good reason I can think of for doing this is if you have a student who is in the early stages of learning the circuit and landing. Early on they may have trouble reliably determining whether they are above or below glidepath while turning or may be overwhelmed by adding the modulation of the brakes to the demands on their attention during the base and final turns.

If you are flying the pattern at the approach speed recommended by the manual for an approach in which full airbrakes might be deployed (which in my opinion is every approach) you should have a safe margin above the stall speed in the sort of well banked turns you should be using in the circuit whether the brakes are in or out. The brakes are there to put you on your desired glide path. Use them as necessary, you paid for them!

As an experiment try this at altitude: trim to the recommended approach speed with full airbrakes or recommended approach speed found in the AFM (or if it's not specified use the formula you were taught for choosing an approach speed), roll the glider into a good coordinated 40 degree bank turn then move the elevator progressively back. In every glider I've flown the elevator hits the stop without provoking a stall. I tried this after reading a Derek Piggott article suggesting it.