Spoilers or Airbrakes - Whats in a name?

Bill Daniels wrote:

Both common sense and aerodynamics say that if the G-meter says 1.0 then
lift = weight. Applying 'spoilers' doesn't change that. Spoilers do not
'reduce lift' if the G-meter continues to say 1.0 - they increase drag.
The general formula is lift = weight x G

There is a nuance he opening the spoilers on most gliders does
diminish the lift of the wing section near the spoilers. To compensate,
the outer panels have to carry more of the weight of the glider. You can
clearly see this on an ASW 20 or open class ship, when the wings bend up
noticeably after the spoilers are open. So, in a steady state condition,
the lift is *decreased* over a significant fraction of the wing, but the
overall lift remains the same.

The reverse is true for flaps used for glidepath control: the lift in
the flapped section is increased. I can see this clearly on my ASH 26 E,
because now the outer panels are bent down slightly when landing flaps
are selected. So, in a steady state condition, the lift is *increased*
over a significant fraction of the wing, but the overall lift remains
the same.

Now, I'd say a true divebrake is what some fighters have: a panel(s)
that pop out of the fuselage, so they only add drag, and don't affect
the lift of the wing. Maybe we should consider our retractable landing
gear our "divebrake".

Of course, we glider pilots are a sloppy bunch and lump divebrakes in
with spoilers, and airbrakes. We pretty much stick with calling flaps,
well, flaps.

--
Eric Greenwell - Washington State, USA
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On May 16, 12:46*pm, Brian wrote:

Take a glider at approach speed about 5 feet off the runway in steady
state (at least for a glider) level flight with all drag devices
retracted..

If you deploy the spoilers and do not change attitude the glider will
drop onto runway, speed will change very little.

if you deploy airbrakes the glider will slow and settle to the runway.

If you deploy flaps the glider will balloon up.

Maintaining a constant attitude in the test you describe will require
a pitch control input and that input controls what happens to the
glider as the devices are deployed. To put it another way,
maintaining pitch attitude is an arbitrary choice. You could have
specified constant sink rate, constant glide path, constant airspeed,
etc etc. That close to the ground my intent is to control sink rate
and the controls interact to achieve that.

In my experience deploying my top surface devices with stick free
results in nose down pitch, increased sink rate, and airspeed remains
essentially constant. Who can define the name of the device that
causes that?

Andy

On May 16, 4:34 pm, Eric Greenwell wrote:
Bill Daniels wrote:
Both common sense and aerodynamics say that if the G-meter says 1.0 then
lift = weight. Applying 'spoilers' doesn't change that. Spoilers do not
'reduce lift' if the G-meter continues to say 1.0 - they increase drag.
The general formula is lift = weight x G

There is a nuance he opening the spoilers on most gliders does
diminish the lift of the wing section near the spoilers. To compensate,
the outer panels have to carry more of the weight of the glider. You can
clearly see this on an ASW 20 or open class ship, when the wings bend up
noticeably after the spoilers are open. So, in a steady state condition,
the lift is *decreased* over a significant fraction of the wing, but the
overall lift remains the same.

The reverse is true for flaps used for glidepath control: the lift in
the flapped section is increased. I can see this clearly on my ASH 26 E,
because now the outer panels are bent down slightly when landing flaps
are selected. So, in a steady state condition, the lift is *increased*
over a significant fraction of the wing, but the overall lift remains
the same.

Now, I'd say a true divebrake is what some fighters have: a panel(s)
that pop out of the fuselage, so they only add drag, and don't affect
the lift of the wing. Maybe we should consider our retractable landing
gear our "divebrake".

Of course, we glider pilots are a sloppy bunch and lump divebrakes in
with spoilers, and airbrakes. We pretty much stick with calling flaps,
well, flaps.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly


An aerodynamicist would say that a spoiler changes the lift vs angle-
of-attach curve of a wing section. It will also change the drag curve
of that wing section.

I don't think there are universally accepted definitions of these
terms.

A side note, just about any kind of device on the wing will affect
both lift and drag, but depending on the location and type, will
affect lift and drag in different proportions. This can lead to
confusion of the terms.

Todd Smith
3S

snip
Maintaining a constant attitude in the test you describe will require
a pitch control input and that input controls what happens to the
glider as the devices are deployed. *To put it another way,
maintaining pitch attitude is an arbitrary choice. *You could have
specified constant sink rate, constant glide path, constant airspeed,
etc etc. *That close to the ground my intent is to control sink rate
and the controls interact to achieve that.

In my experience deploying my top surface devices with stick free
results in nose down pitch, increased sink rate, and airspeed remains
essentially constant. Who can define the name of the device that
causes that?

Andy

Yes, I specified constant attitude simply because I can obviously stop
the descent by pitching back up. I was just trying to Isolate the
effects of the various drag devices which as you point out is simlar
no matter what the initial steady state is.

One other feature I have noticed on Spoilers is they tend to be ON/OFF
as opposed to Airbrakes that tend to be more proportional. I.E. in my
example if you slowly apply the Spoilers at a certain point the glider
will just drop. Where as the Airbrakes will tend to gradually become
more effective.

Brian

On May 16, 10:43 am, Bob Kuykendall wrote:
Launch Robert Mudd post on glidepath control nomenclature on my mark:
three... two... one...

Bob K.

LOL!

I set Robert up once calling the DG's divebrakes spoilers, after
seeing the term in my DG's manual. The response was as expected. I
then had the pleasure to show him the term in the manual. He told me
he would have to have a talk with Herr Dirks about this the next time
he saw him.

noel.wade wrote:
On May 16, 12:59 pm, "jonathan"
PLEASE.REMOVE.THIS.PREFIX.jonathan.go...@ntlworld .com wrote:

Sort of visualise the difference between a wing (spoiler) on a racing car
creating downpressure and throwing a dirty great parachute out the back to
assist braking?

Jim.

Oh, boy - where to begin?

First: In the automobile world, the difference between a "spoiler"
and a "wing" is very important. A wing is a device that allows air to
flow over both top and bottom surfaces, and is typically used to
create down-force (just like the horizontal tail on your glider). A
spoiler actually has the leading edge fixed to the auto in such a way
that air flows over the top surface only. It, too, creates down-
force, but it also creates a lot more drag than a wing.

Second: Technically "spoilers" are supposed to be there to change the
airflow over the _wing_. By "spoiling" the airflow such that it
cannot follow the curves of the airfoil, it changes the glide-path and/
or drag of the aircraft. "Airbrakes" are technically a device
_anywhere_ on the aircraft that increases drag.

Now here's where most people fall down: They want to categorize every
device as one or the other type. But the plain truth is that most
devices on sailplanes do BOTH.

Have fun debating spoilers and airbrakes! I don't think this one will
ever be fully settled...

I think it's fair to say that the debate is of little significance, but
much concern. ;-)


Shawn

I'd continue to use them interchangeably until we have a glider with
independent controls for spoilers and airbrakes. However, if you like
precision, I'd opt for spoilers. I can't recall having seen a modern glider
that didn't have upper surface spoilers when equipped with lower surface
airbrakes. If during a positive control check the pilot corrects your call
of "spoilers," look under the wing for the extra control surface.

"ContestID67" wrote in message
...
I spotted the following statement in Wikipedia.

http://en.wikipedia.org/wiki/Spoiler_%28aeronautics%29
http://en.wikipedia.org/wiki/Air_brake_%28aircraft%29

"Spoilers differ from airbrakes in that airbrakes are designed to
increase drag while making little change to lift, while spoilers
greatly reduce lift while making only a moderate increase in drag."

I had always used the terms spoilers and airbrakes interchangeable.
This statement makes it seem like they are not. So what does the
typical sailplane have? Spoilers or airbrakes?

- John "67" DeRosa

user wrote:
I'd continue to use them interchangeably .....
If during a positive control check the pilot corrects your call
of "spoilers," look under the wing for the extra control surface.

Yes, I've seen at least 2 books (FAA Glider Flying Handbook and Russell
Holtz's Glider Pilot's Handbook of Aeronautical Knowledge)where the
writer claimed that if the ..um.. "device".. extended top surface only
it was a spoiler and if it extended from both survaces it was an air
brake. Seems dubious to me.

Tony V LS6-b "6N"

user wrote:
I'd continue to use them interchangeably until we have a glider with
independent controls for spoilers and airbrakes. However, if you like
precision, I'd opt for spoilers. I can't recall having seen a modern glider
that didn't have upper surface spoilers when equipped with lower surface
airbrakes. If during a positive control check the pilot corrects your call
of "spoilers," look under the wing for the extra control surface.

FWIW I always thought of my Ventus and Mosquito "Approach Control
Devices" (at least the top part) as air brakes. Doesn't seem like much
lift spoiling going on all the way back there.


Shawn

Spoilers American Heritage Dictionary –

A long, narrow hinged plate on the upper surface of an airplane wing
that reduces lift and increases drag when raised.

Brakes American Heritage Dictionary

A device for slowing or stopping motion, as of a vehicle, especially
by contact friction.
Something that slows or stops action.