Angle of incidence

After speaking with an instructor about my Pilatus B4 landings, he argued that
the angle of incidence on this glider has a great influence on the landing
characteristics.
I looked it up, and it was only 1.5 degrees. With the tailplane oriented at -3
degrees.

However, I cannot figure out what other gliders have as the angle of
incidence. I have 6 degrees in my head somehow, but I'm not sure where I get
this from. Searching on Google does not give me figures, only stories about
changing it (from Ls6 to Ls8 for example).

I'm therefor wondering: can you tell me the angle of incidence on your glider
if you know it? And how does it effect take-off and landing characteristics?
For example: some people in my club argue that the Discus2 take-off
characteristics are also to be blamed on its angle of incidence.

regards,

Roel

On May 27, 11:21*pm, Roel Baardman wrote:
After speaking with an instructor about my Pilatus B4 landings, he argued that
the angle of incidence on this glider has a great influence on the landing
characteristics.
I looked it up, and it was only 1.5 degrees. With the tailplane oriented at -3
degrees.

However, I cannot figure out what other gliders have as the angle of
incidence. I have 6 degrees in my head somehow, but I'm not sure where I get
this from. Searching on Google does not give me figures, only stories about
changing it (from Ls6 to Ls8 for example).

I'm therefor wondering: can you tell me the angle of incidence on your glider
if you know it? And how does it effect take-off and landing characteristics?
For example: some people in my club argue that the Discus2 take-off
characteristics are also to be blamed on its angle of incidence.

regards,

Roel

Roel,

According to the manual for my Mini Nimbus C the wing incidence is .7
deg and the tail incidence is 0 deg set to the rear fuse center line.

I use to rent a B4 and found it to be a nice handling sailplane, never
had a problem with landings.

Mike

On Monday, May 28, 2012 1:21:35 AM UTC-4, Roel Baardman wrote:
After speaking with an instructor about my Pilatus B4 landings, he argued that
the angle of incidence on this glider has a great influence on the landing
characteristics.
I looked it up, and it was only 1.5 degrees. With the tailplane oriented at -3
degrees.

However, I cannot figure out what other gliders have as the angle of
incidence. I have 6 degrees in my head somehow, but I'm not sure where I get
this from. Searching on Google does not give me figures, only stories about
changing it (from Ls6 to Ls8 for example).

I'm therefor wondering: can you tell me the angle of incidence on your glider
if you know it? And how does it effect take-off and landing characteristics?
For example: some people in my club argue that the Discus2 take-off
characteristics are also to be blamed on its angle of incidence.

regards,

Roel

What exactly is your problem with your landings in the B4? I remember flying the B4 our club had and it was one of the most benign and dorcile gliders to land.
Uli

On May 28, 12:21*am, Roel Baardman wrote:
After speaking with an instructor about my Pilatus B4 landings, he argued that
the angle of incidence on this glider has a great influence on the landing
characteristics.
I looked it up, and it was only 1.5 degrees. With the tailplane oriented at -3
degrees.

However, I cannot figure out what other gliders have as the angle of
incidence. I have 6 degrees in my head somehow, but I'm not sure where I get
this from. Searching on Google does not give me figures, only stories about
changing it (from Ls6 to Ls8 for example).

I'm therefor wondering: can you tell me the angle of incidence on your glider
if you know it? And how does it effect take-off and landing characteristics?
For example: some people in my club argue that the Discus2 take-off
characteristics are also to be blamed on its angle of incidence.

regards,

Roel

Angle of incidence does vary from glider to glider, and it's a useful
point to note when making transitions to new gliders. Trainers like
the ASK21 have a fairly high angle of incidence. Duos and standard
class gliders have much lower angle of incidence, the latest (28, D2)
especially. That, along with c.g. much further behind the main gear,
is worth reflecting on and preparing for in a transition.

Low angle of incidence in unflapped gliders means the fuselage is more
aligned with the airflow at high speeds. Good for high speed
performance, but it means that the nose points way up to achieve a
high angle of attack at low speed. They can't achieve a stalling
angle of attack even with the tail wheel on the ground. Thus, they
have to take off at substantially higher airspeeds. There is a
tendency to roll down the runway forever on the first few flights. One
answer is to take off with the fuselage at a much higher pitch
attitude in order to produce the same angle of attack at takeoff.
Similarly, If you land close to a stall you will hit the tail wheel
first and then plop down on the main.

That's also why the nose is very high on tow and while thermaling.
Some pilots find themselves thermaling at too high speeds early in the
transition. Part of the reason is that the nose needs to be much
higher on the horizon at thermaling angles of attack. If you put the
nose at the ASK21 pitch attitude, the duo or a standard class glider
will be screaming along.

It's also useful to note that where the nose is pointing is not where
the glider is going. That's what's going on with the feeling that the
nose is high on takeoff, tow, and thermaling -- the nose is pointing
up though the glider is gliding down. The converse issue happens at
high speed. The wings are very efficient at high speed, so putting the
nose down and pointing at the runway just means you speed up to 90
knots and keep going flat. Glider looks like this: (moving left to
right) \ \ \ . That's part of the feeling that "spoilers don't
work." No, you're not using them! To an eyeball approximation, the
glide angle is always the same, but pointing the nose up or down just
changes the airspeed.

More than you asked for, but I've learned a lot about these sight
angles while helping new pilots transition to our duo discus and asw24
lately

John Cochrane

On Sunday, May 27, 2012 10:21:35 PM UTC-7, Roel Baardman wrote:
After speaking with an instructor about my Pilatus B4 landings, he argued that
the angle of incidence on this glider has a great influence on the landing
characteristics.
I looked it up, and it was only 1.5 degrees. With the tailplane oriented at -3
degrees.

However, I cannot figure out what other gliders have as the angle of
incidence. I have 6 degrees in my head somehow, but I'm not sure where I get
this from. Searching on Google does not give me figures, only stories about
changing it (from Ls6 to Ls8 for example).

I'm therefor wondering: can you tell me the angle of incidence on your glider
if you know it? And how does it effect take-off and landing characteristics?
For example: some people in my club argue that the Discus2 take-off
characteristics are also to be blamed on its angle of incidence.

regards,

Roel

I remember a long final glide that I made with a friend (both flying LS-6's). We were dead even, flying best L/D, we had to make it over a lake with enough altitude to clear the ridge. After a few minutes my buddy said; "Watch this" and slowly, but surely, he started gaining altitude on me. After 10 miles he was a good 50 feet above me. So, I asked, "OK, what did you do"? He replied, I went to one notch of positive flap. Why did that work? Because the wing on the LS-6 is attached at zero incidence so as to make the fuselage align with the relative wind when flying fast, but at best L/D, the nose was up and selecting +1 flaps brought the nose down a tat and alighned it better into the relative wind. Good trick to remember.
JJ
JJ

[quote=Mike C;815406]On May 27, 11:21*pm, Roel Baardman wrote:
After speaking with an instructor about my Pilatus B4 landings, he argued that
the angle of incidence on this glider has a great influence on the landing
characteristics.
I looked it up, and it was only 1.5 degrees. With the tailplane oriented at -3
degrees.

However, I cannot figure out what other gliders have as the angle of
incidence. I have 6 degrees in my head somehow, but I'm not sure where I get
this from. Searching on Google does not give me figures, only stories about
changing it (from Ls6 to Ls8 for example).

I'm therefor wondering: can you tell me the angle of incidence on your glider
if you know it? And how does it effect take-off and landing characteristics?
For example: some people in my club argue that the Discus2 take-off
characteristics are also to be blamed on its angle of incidence.

regards,

Roel

I would be interested in exactly what problems you are encountering on landing. I am interested in the Pilatus B-4 for its aerobatic capabilities. While it would not necessarily be a good cross country airplane, cross country does not interest me all that much.

Having read the B-4 manual I was surprised to see that it did not discuss the landing process to any degree. I fly a SGS 1-34 which recommends a high energy landing and the manual specifically recommends against landings resulting in a tail first or tail strike landing. Somewhat nonintuitive for someone trained in powered taildraggers recommending a full stall, three point type landing in otherwise non windy conditions. Essentially the 1-34 is flown onto the ground and then flown to a stop as mentioned in the manual. I had the good fortune to talk to several pilots with extensive experience in the 1-34 prior to flying it. I would think this would always be advisable as we transition into other aircraft.

Walt

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.

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.

Hi Walt,

Although my opening post starts with the B4 and landing, this does not mean it's
tough to land. Not at all.
I have a tendency to fly fast on final, and the ground effect of the B4 makes it
float when I do that.

In my experience it is a great glider to fly. I can compare it with an ASK-23 and
SZD Junior, both being gliders which are flown by pilots with some solo starts. In
fact, the B4 has been used for this purpose in The Netherlands in the past. The
glider is generally responsive and very friendly.

Pitch is somewhat sensitive, but nothing you can't get used to. The same applies
for rudder control. On my first flights I tended to put too much rudder in during
thermaling.

In terms of aerobatics I think the glider is a nice follow-up for the ASK-21 (on
which I learned to fly aerobatics). The pitch-sensitivity requires more precise
inputs during rolls. Also since the rudder is so effective, you can actually stall
the rudder when flying knife-edge at 3/4 of the roll. After some practice I could
do very nice rolls without having to pitch up 20 degrees.

Stall-turns are not hard, especially if you side-slip a little on the vertical
line up.

It warns before you spin (I can hear the airflow get turbulent over my wings, and
there's a *shoop* when it drops), the spin rotates quickly but can be stopped in
1/4 turn with rudder and then forward-stick. The glider then swiftly drops to 90
degrees down. Pretty perfect for competitions I would say.

Tailslides have a tendency to drop canopy-down/wheel-up (due to the wing-profile I
was told), so you should keep those a little positive if you want to drop
canopy-up/wheel-down.

I have tried inverted spinning, but am not sure how stalled the glider was during
this maneuver. It can perform the figure though.

I haven't tried snap-rolls, since I hear this will make the rivets in the tail pop
and give the tail play.

I have some videos with flights from start (tow) until landing. Drop me an e-mail
if you're interested.

Roel

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