Angle of incidence

On May 28, 11:16*am, Roel Baardman wrote:
First of all: thanks for all the replies!
I find it incredibly interesting to ponder about these subjects, so more info is
better :-)
I also like the Ls-6 story!

My tendency with the B4 is to approach with too much velocity, often 100 km/h.
This gives me the feeling I have proper aileron control, so it's intentional.
When I approach the deck and slowly start to bring the nose up, I encounter the
ground effect that the B4 has. I either float for a long time before touching down
with a two-point landing, or I make a touchdown on the main wheel only (sometimes
with a slight jump after that).
What happened yesterday, was that I was so busy compensating for crosswind (I
don't want to have a traversed landing), that started floating again and gained
some altitude (1 meter roughly).
Knowing that the fault is probably in the velocity, I approached the instructor to
learn from his B4 experience.
I agree that the B4 is very friendly and benign. I will put effort in bringing my
approach speed down to 90 in the upcoming flights.

Slightly too much airspeed at the start of the flare will have a large
effect on float distance. The big culprit is ground effect which can
as much as double the glider's L/D just as you are trying to land
making it hard to get rid of that extra airspeed.

I choose a small airspeed increment over the yellow triangle according
to the gustiness of the day and use that for my "over the fence" (OTF)
airspeed. In the pattern, I'll use whatever airspeed give me a good
gust-stall margin then slow down to the "OTF" airspeed on short final.

2cents from a partially reformed sinner...

I learned to fly in Bergfalkes that have all the penetration of a well
thrown tissue. So I learned to approach with lots of speed - because it
will disappear fast once the nose comes up, and because any lack will
have you running out of energy very fast.

Transition to a big, heavy, slippery single and there is still the
tendency to want an extra few kt on the dial - and then it floats
forever in ground effect.

Have learned to bring the big Kestrel in a lot slower and the landings
are a lot less exciting. Still have a way to go. She can be landed in an
incredibly short distance if you have that approach speed nailed.

In my case the magic number is 45kts - Stall at 32-34Kt *4/3 is
42-45kt. Now that feels just WRONG but in still air it is perfect.
At 55kt (90km/h) you are carrying a massive 47% extra energy - that
takes a lot of distance to dissipate at 1:40+ - check it - set the
logger at 1s intervals, get it all stable at ~2m AGL over the numbers on
a long runway an see how long you can keep the wheel off the ground for.
Use the traces and try at a couple of approach speeds to see what your
achieved L/D is in landing configuration. At 55kt the Kestrel is still
in the air 100m later - and that is with landing flap and half airbrakes.

At low speed the ailerons are less powerful, but a little airbrake
increases effectiveness by diverting airflow over the controls so you
should have more than enough control - you are trying to fly straight -
not do aerobatics.

On 2012/05/29 3:55 AM, Bill D wrote:
On May 28, 11:16 am, Roel wrote:
First of all: thanks for all the replies!
I find it incredibly interesting to ponder about these subjects, so more info is
better :-)
I also like the Ls-6 story!

My tendency with the B4 is to approach with too much velocity, often 100 km/h.
This gives me the feeling I have proper aileron control, so it's intentional.
When I approach the deck and slowly start to bring the nose up, I encounter the
ground effect that the B4 has. I either float for a long time before touching down
with a two-point landing, or I make a touchdown on the main wheel only (sometimes
with a slight jump after that).
What happened yesterday, was that I was so busy compensating for crosswind (I
don't want to have a traversed landing), that started floating again and gained
some altitude (1 meter roughly).
Knowing that the fault is probably in the velocity, I approached the instructor to
learn from his B4 experience.
I agree that the B4 is very friendly and benign. I will put effort in bringing my
approach speed down to 90 in the upcoming flights.

Slightly too much airspeed at the start of the flare will have a large
effect on float distance. The big culprit is ground effect which can
as much as double the glider's L/D just as you are trying to land
making it hard to get rid of that extra airspeed.

I choose a small airspeed increment over the yellow triangle according
to the gustiness of the day and use that for my "over the fence" (OTF)
airspeed. In the pattern, I'll use whatever airspeed give me a good
gust-stall margin then slow down to the "OTF" airspeed on short final.

--
Bruce Greeff
T59D #1771

At 07:16 29 May 2012, BruceGreeff wrote:

Have learned to bring the big Kestrel in a lot slower and the landings
are a lot less exciting. Still have a way to go. She can be landed in an
incredibly short distance if you have that approach speed nailed.

In my case the magic number is 100m later - and that is with landing flap
and half airbrakes.

At low speed the ailerons are less powerful, but a little airbrake
increases effectiveness by diverting airflow over the controls so you
should have more than enough control - you are trying to fly straight -
not do aerobatics.

In my 19m Kestrel used to use full landing flap and full negative flap
(separate levers!) More than enough drag from the inboard flaps plus
brakes and plenty of roll control from the outers until it came to a halt.

That is indeed the way to do it - then the negatice flap puts the
ailerons at low angle of attack and you have excellent roll control.

Landing flap and positive flap is a recipe for - don't be pointing at
something you were hoping to reuse...

On 2012/05/29 11:14 AM, Z Goudie wrote:
At 07:16 29 May 2012, BruceGreeff wrote:

Have learned to bring the big Kestrel in a lot slower and the landings
are a lot less exciting. Still have a way to go. She can be landed in an
incredibly short distance if you have that approach speed nailed.

In my case the magic number is 100m later - and that is with landing flap
and half airbrakes.

At low speed the ailerons are less powerful, but a little airbrake
increases effectiveness by diverting airflow over the controls so you
should have more than enough control - you are trying to fly straight -
not do aerobatics.

In my 19m Kestrel used to use full landing flap and full negative flap
(separate levers!) More than enough drag from the inboard flaps plus
brakes and plenty of roll control from the outers until it came to a halt.



--
Bruce Greeff
T59D #1771