Frise ailerons on sailplanes

At 08:30 24 February 2005, Mark James Boyd wrote:
Neat on the Duchess and the Aero Commander (twin engine
planes)
but haven't heard of it in competition gliders.
Also haven't heard of rudder-aileron interconnect for
gliders.


The Nimbus 4 has a mechanism whereby full rudder operates
a small portion of aileron at the tip so as to counteract
the adverse yaw at the expense of a reduced roll rate.

I have heard that some big jets, perhaps 737 and such,
use spoilers
for additional roll authority as well.
And the U-2 was rumored to have twisting trailing edge
landing gear,
so landing in a crosswind in a crab was fine.

Don't know about the U2 but I believe the B52 incorporates
both of these features, it has no ailerons at all,
entirely relying on differential spoilers for roll
control. Allows a lighter wing with less torsional
stiffness at the expense of awful handling 'feel' and
all of the wheels steer to allow crabbing on the ground,
both for taxying through small (small is a relative
term when you've got a 56m wingspan) gaps and landing
in cross winds.

Nimbus 3/4 have these spoilers because otherwise the rudder would need to be
substantially larger to provide sufficient yaw authority. Larger rudder =
more drag all the time, little spoiler = a little more drag only during the
beginning of a turn.

--
Bert Willing

ASW20 "TW"


"Andrew Warbrick" a écrit dans le
message de news: ...
At 08:30 24 February 2005, Mark James Boyd wrote:
Neat on the Duchess and the Aero Commander (twin engine
planes)
but haven't heard of it in competition gliders.
Also haven't heard of rudder-aileron interconnect for
gliders.


The Nimbus 4 has a mechanism whereby full rudder operates
a small portion of aileron at the tip so as to counteract
the adverse yaw at the expense of a reduced roll rate.

I have heard that some big jets, perhaps 737 and such,
use spoilers
for additional roll authority as well.
And the U-2 was rumored to have twisting trailing edge
landing gear,
so landing in a crosswind in a crab was fine.

Don't know about the U2 but I believe the B52 incorporates
both of these features, it has no ailerons at all,
entirely relying on differential spoilers for roll
control. Allows a lighter wing with less torsional
stiffness at the expense of awful handling 'feel' and
all of the wheels steer to allow crabbing on the ground,
both for taxying through small (small is a relative
term when you've got a 56m wingspan) gaps and landing
in cross winds.

Some people that own Nimbus 3's do not connect the tip spoilers because
they say the effect is negligible. I connect them on mine, but I can't
really say how effective they are - they only come up in the second
half of stick input. I believe the Nimbus 4 arrangement with the tip
spoilers connected to the rudder makes much more sense as I almost
always use much more rudder than aileron when turning into a thermal.

More effective than the tip spoilers is to minimize adverse yaw in the
Nimbeast 3 with easy, patient roll rate - in other words, the faster
and farther I move the ailerons, the quicker I run out rudder - at
thermal speeds.

Once settled into the thermal, it's easy to keep on an even keel, but
it does like to overbank if you let it.

Occasionally, on bad thermal days I can move the ailerons and rudder as
much as I want and the beast just does not want to go where I want it
to!! Swearing seems to help. Other days, it's easy as pie. Probably
more to do with the control system located between the headsets than
anything else.

In any case, a little adverse yaw, overbanking and leg exercises
(rudder dancing) are a small price to pay for the horsepower available
in this glider. Someday I'll learn how to use it's potential - and I
have a lot to learn.

Jim




Bert Willing wrote:
Nimbus 3/4 have these spoilers because otherwise the rudder would
need to be
substantially larger to provide sufficient yaw authority. Larger
rudder =
more drag all the time, little spoiler = a little more drag only
during the
beginning of a turn.

--
Bert Willing

ASW20 "TW"

The use of spoilers as roll control on a sailplane has two major drawbacks
compared to ailerons with adverse yaw. These comments are based on flight
test of a roll spoiler equipped flying wing glider.

First, the relationship of drag to reduction in lift produced by the roll
spoiler changes dramatically with airspeed. There is only one airspeed
where the drag and roll produce a perfectly coordinated turn entry.
(Remember that drag increases with the square of airspeed.)

At airspeeds above the coordinated airspeed, the spoiler will produce too
much drag and the turn entry will skid unless outside rudder is used. This
is called proverse yaw.

At airspeeds below the coordinated airspeed, the roll spoiler will not
produce enough drag and the turn entry will be a slip unless into-the-turn
rudder is applied. (Adverse yaw)

The second major problem with roll spoilers is during a steady turn where
one would normally use top aileron to oppose overbanking. If the pilot
attempts to oppose overbanking with roll spoilers, the drag of the spoiler
will cause the glider to yaw away from the turn. The pilot will then use
into-the-turn rudder to center the yaw string which will cause the
overbanking to resume unless still more top spoiler is used. This will
quickly progress to the point where full top spoiler and full into-the-turn
rudder is applied. This is hardly conducive to a low sink rate.

The lession here is that adverse yaw is actually needed for steady state
turns. In a turn the airspeed and angle of attack varies across the full
span. This results in the outside wing having more drag and lift than the
inside wing causing overbanking. Top aileron restores spanwise symmetry of
lift and drag neatly taming the overbanking.

Adverse yaw is also useful for crosswind landings. Into the wind aileron
produces a down wind yaw that helps align the fuselage with the direction of
flight.

Another way to look at it is that differential spoilers produce a control
response that is not unlike the rudder. If the glider is equipped with both
rudder and roll spoilers it has, in effect, two rudder systems and therefore
lacks true 3-axis controls.

That said, differential spoilers actuated through the rudder control curcuit
can significantly augment a weak rudder.

Bill Daniels

If you want to see what can happen when you have no ailerons as all go to
this web site and scroll down to the B-52 crash.

http://www.alexisparkinn.com/aviation_videos.htm


"Andrew Warbrick" wrote in message
...
At 08:30 24 February 2005, Mark James Boyd wrote:
Neat on the Duchess and the Aero Commander (twin engine
planes)
but haven't heard of it in competition gliders.
Also haven't heard of rudder-aileron interconnect for
gliders.


The Nimbus 4 has a mechanism whereby full rudder operates
a small portion of aileron at the tip so as to counteract
the adverse yaw at the expense of a reduced roll rate.

I have heard that some big jets, perhaps 737 and such,
use spoilers
for additional roll authority as well.
And the U-2 was rumored to have twisting trailing edge
landing gear,
so landing in a crosswind in a crab was fine.

Don't know about the U2 but I believe the B52 incorporates
both of these features, it has no ailerons at all,
entirely relying on differential spoilers for roll
control. Allows a lighter wing with less torsional
stiffness at the expense of awful handling 'feel' and
all of the wheels steer to allow crabbing on the ground,
both for taxying through small (small is a relative
term when you've got a 56m wingspan) gaps and landing
in cross winds.

On Thu, 24 Feb 2005 07:50:23 -0800, "Gary Boggs"
wrote:

If you want to see what can happen when you have no ailerons as all go to
this web site and scroll down to the B-52 crash.

http://www.alexisparkinn.com/aviation_videos.htm

In fact this is going to happen with any aircraft that you stall in a
steep turn close to the ground.


Bye
Andreas

I flew a Javelin J-4 way back in the mid 70's at the old Vacaville
gliderport. Odd little glider, nice big cockpit, lousy drag spoilers,
horrible control feel throught the roll spoilers. OK performance as
long as maneuvering wasn't called for.

It crashed the day after I flew it - stall spin on base to final. I'm
convinced the accident was partially due to the poor glidepath control
and poor roll control - pilot probably got high on final, tried a 360,
then got low and lost it.

Interesting concept for a mid performance low cost glider, and with
conventional ailerons and better spoilers it might have worked - would
have been a nice club-class metal ship for clubs and FBO's.

Kirk