spoilers vs. ailerons

[[email protected]]

There are two old Senecas at my airport with the Robertson STOL mod -
full span flaps w/spoilers in place of conventional ailerons. I've seen
one of them take off with a brutally short roll, and it went up as if
on an escalator. My question is, how would one of these land in a stiff
x-wind? Is the pilot limited to crabbing approaches with a kick-out in
the flare just above the runway? Or is there no appreciable difference
with ailerons?

I'm hoping Mike R. will weigh in with his Shmoo experience. IIRC the
MU-2 has the same configuration.

Will

[Mike Rapoport]

Spoilers function the same as ailerons at low angles of attack and better
than ailerons at high angle of attack. The primary advantage of spoilers
instead of ailerons is that it enables full span flaps. Spoilers also
reduce or eliminate adverse yaw.

Mike
MU-2




> wrote in message
oups.com...
> There are two old Senecas at my airport with the Robertson STOL mod -
> full span flaps w/spoilers in place of conventional ailerons. I've seen
> one of them take off with a brutally short roll, and it went up as if
> on an escalator. My question is, how would one of these land in a stiff
> x-wind? Is the pilot limited to crabbing approaches with a kick-out in
> the flare just above the runway? Or is there no appreciable difference
> with ailerons?
>
> I'm hoping Mike R. will weigh in with his Shmoo experience. IIRC the
> MU-2 has the same configuration.
>
> Will
>

[[email protected]]

OK, but if spoilers "spoil" lift over the wing isn't that an
undesirable condition when low & slow such as a crosswind landing where
the upwind wing is dropped? Does that make airspeed control even more
critical, or is that not a consideration? Is a x-wind landing done the
same way?

[Ron Natalie]

wrote:
> OK, but if spoilers "spoil" lift over the wing isn't that an
> undesirable condition when low & slow such as a crosswind landing where
> the upwind wing is dropped?

What do you think an aileron does in the same situation?

[ShawnD2112]

Just as a comparison, for what it's worth, the B52 doesn't have ailerons but
relies on spoilers for it's roll control.

Shawn
> wrote in message
oups.com...
> There are two old Senecas at my airport with the Robertson STOL mod -
> full span flaps w/spoilers in place of conventional ailerons. I've seen
> one of them take off with a brutally short roll, and it went up as if
> on an escalator. My question is, how would one of these land in a stiff
> x-wind? Is the pilot limited to crabbing approaches with a kick-out in
> the flare just above the runway? Or is there no appreciable difference
> with ailerons?
>
> I'm hoping Mike R. will weigh in with his Shmoo experience. IIRC the
> MU-2 has the same configuration.
>
> Will
>

[Darrell S]

wrote:
> There are two old Senecas at my airport with the Robertson STOL mod -
> full span flaps w/spoilers in place of conventional ailerons. I've
> seen one of them take off with a brutally short roll, and it went up
> as if on an escalator. My question is, how would one of these land in
> a stiff x-wind? Is the pilot limited to crabbing approaches with a
> kick-out in the flare just above the runway? Or is there no
> appreciable difference with ailerons?

Minor differences. The spoiler spoils lift on the side of the raised
spoiler. This normally causes a roll toward the raised spoiler much the
same as aileron movement. Some people always land by trying to get about a
foot above the runway and keep it there by continually raising the nose as
speed decreases. If you actually stall the wings it only drops a foot.
That's with an aileron aircraft. With a spoiler controlled aircraft, when
you stall the wings it makes the spoiler ineffective. It can no longer
spoil lift that is no longer there. So if you were cross-controlling a wing
low for crosswind you'd lose the roll control but still have the rudder
input. A perfect example of that is the B-52H that crashed in Spokane, WA,
maneuvering at low altitude for a fly-by the airport. He got it into
almost 90° of bank and stalled the wings. Pictures taken just prior to the
crash show the upper wings spoilers fully extended as he rolled the control
column to try to roll out of the bank. Useless attempt. If the wing lift
is already gone the spoiler now does nothing to control the roll. If he'd
quickly pushed top rudder he might have been able to yaw the aircraft
towards wing level, reducing G force and making the wing fly again.

As long as the spoiler is at or close to the center of lift, deploying a
spoiler will not also cause a pitching tendency. If it is aft of the center
of lift (as in the B-52H) it also produces a pitch up. During airport
traffic flying we usually moved the airbrakes to position 4 (if I remember
40 years ago right). This way rolling the wheel caused the downward moving
wing spoiler to move up more and the upward moving wing spoiler to move down
some. This eliminated the pitch up/down while manuevering. The extra drag
required more power, putting the throttles into a more responsive range. It
also caused the speed to bleed off more rapidly when retarding the thottles
for landing.

--

Darrell R. Schmidt
B-58 Hustler History: http://members.cox.net/dschmidt1/
-

[Jackal24]

wrote in news:1122393811.505648.264850
@g49g2000cwa.googlegroups.com:

> There are two old Senecas at my airport with the Robertson STOL mod -
> full span flaps w/spoilers in place of conventional ailerons. I've seen
> one of them take off with a brutally short roll, and it went up as if
> on an escalator. My question is, how would one of these land in a stiff
> x-wind? Is the pilot limited to crabbing approaches with a kick-out in
> the flare just above the runway? Or is there no appreciable difference
> with ailerons?
>
> I'm hoping Mike R. will weigh in with his Shmoo experience. IIRC the
> MU-2 has the same configuration.
>
> Will
>

Why not just land across the runway. :)

[[email protected]]

I think the difference in this instance is that ailerons deflect
airflow upward wheras spoilers actually interrupt lift

[[email protected]]

ISTR reading that about the Buff, but with that aircraft the landing
gear is aligned with the runway during an xwind landing and it lands in
a crab. For planes with spoilers and conventional gear I'm curious if
there's a different procedure for xwind landings

[[email protected]]

IIRC in this case an up aileron deflects airflow upward wheras a
spoiler interrupts or "spoils" the lift of the wing. I'm curious if
that represents an unsafe situation when down low

[[email protected]]

Right, but the B52 also has gear that can be aligned with the runway so
it lands in a crab. I'm asking if there's a different method for xwind
landings for conventionally gearly acft with spoilers. Maybe I didn't
phrase the question clearly enough... Mike R whaddya think?

[Peter Duniho]

"Ron Natalie" > wrote in message
m...
> wrote:
>> OK, but if spoilers "spoil" lift over the wing isn't that an
>> undesirable condition when low & slow such as a crosswind landing where
>> the upwind wing is dropped?
>
> What do you think an aileron does in the same situation?

The difference is one of degree, as well as of mechanism.

To address the previous question...

For a given roll rate, a certain amount of force needs to be applied.
Ailerons provide this force in a balanced way, by increasing the angle of
attack on one wing and reducing it on the other. A spoiler, rather than
reducing the angle of attack, simply disrupts the airflow and reducing lift.

So, compared to ailerons, the spoiler is more like using only a single
aileron on the opposite wing to induce the roll (which would put that wing
closer to the stalling angle of attack).

Of course, that all ignores a bunch of other aspects of the situation.
Ailerons, even as they increase the angle of attack, also change the shape
of the wing, which can change the stalling angle of attack. Also, many
ailerons are configured for asymmetric deployment, to help reduce adverse
yaw; the aileron on the down-going wing is deflected more than the aileron
on the up-going wing.

Another element that is actually in favor of spoilers (the previously
mentioned ones are, IMHO, pro-aileron) is that if for some reason deployment
of the spoiler should cause a stall, all that will happen is that the wing
going down will go down faster. The pilot's instinctive response will be
just fine, as reducing or reversing aileron input will simply restow the
spoiler, allowing that wing to generate the required lift again. Contrast
that to slow flight with an aileron, in which not only does the wing stall
induced by aileron input cause a reversal of the rolling moment, but the
pilot's natural reaction would be exactly opposite that required.

Of course, being able to put full-span flaps on a wing also helps compensate
for any potential risk of a stall due to roll control input. It seems
likely to me that, given the situations in which spoilers are often found
for roll control, it's a net gain for the spoilers.

One should not forget that in reality, at typical approach speeds (even
those required for a short-field approach), one ought not to be close enough
to risking a wing stall due to roll control input, whether it's spoilers or
ailerons that are being used. Obviously, spoilers work "well enough" and in
fact in many cases may be a superior solution to ailerons.

Pete

[Matt Whiting]

Mike Rapoport wrote:

> Spoilers function the same as ailerons at low angles of attack and better
> than ailerons at high angle of attack. The primary advantage of spoilers
> instead of ailerons is that it enables full span flaps. Spoilers also
> reduce or eliminate adverse yaw.

I assume there must be some disadvantages of spoilers for roll control
as you see them so rarely. What are the drawbacks? Cost??

Matt

[Mike Rapoport]

"Darrell S" > wrote in message
news:BavFe.49931$4o.24620@fed1read06...
> wrote:
.. With a spoiler controlled aircraft, when
> you stall the wings it makes the spoiler ineffective. It can no longer
> spoil lift that is no longer there. > --
>
> Darrell R. Schmidt
> B-58 Hustler History: http://members.cox.net/dschmidt1/
> -

This isn't true. Spoilers provide effective roll control even on a stalled
wing while ailerons do not. lift does not disappear when the wing stalls.

Mike
MU-2

[Mike Rapoport]

You guys are overthinking this. Aircraft with spoilers have *better* low
speed roll control than those with ailerons.

Mike
MU-2


> wrote in message
oups.com...
> Right, but the B52 also has gear that can be aligned with the runway so
> it lands in a crab. I'm asking if there's a different method for xwind
> landings for conventionally gearly acft with spoilers. Maybe I didn't
> phrase the question clearly enough... Mike R whaddya think?
>

[Mike Rapoport]

I think that the main disadvantage is probably cost and perhaps complexity
or weight, I really don't know. Many jets use spoilers as their primary
roll control. Guys are overthinking this one. If spoilers were really
different then a type rating would be required on a MU-2 and if they were a
problem at low speed they wouldn't be used on a Helio.

Mike
MU-2


"Matt Whiting" > wrote in message
...
> Mike Rapoport wrote:
>
>> Spoilers function the same as ailerons at low angles of attack and better
>> than ailerons at high angle of attack. The primary advantage of
>> spoilers instead of ailerons is that it enables full span flaps.
>> Spoilers also reduce or eliminate adverse yaw.
>
> I assume there must be some disadvantages of spoilers for roll control as
> you see them so rarely. What are the drawbacks? Cost??
>
> Matt

[[email protected]]

>>>Why not just land across the runway. :) <<<

Why indeed? Just fly off a carrier... those Navy guys never have to
deal with crosswinds when flying off the boat Hmmphh... What's so
darn hard about grabbing a three-wire anyway? : )

[Mike Rapoport]

Actually with it large vertical stabilizer and relatively small rudder, the
Helio has fairly poor crosswind performance. Most experienced Helio pilots
compensate for this by landing diagonally across the runway

Mike
MU-2


> wrote in message
oups.com...
>>>>Why not just land across the runway. :) <<<
>
> Why indeed? Just fly off a carrier... those Navy guys never have to
> deal with crosswinds when flying off the boat Hmmphh... What's so
> darn hard about grabbing a three-wire anyway? : )
>

[Darrell S]

Mike Rapoport wrote:
> "Darrell S" > wrote in message
> news:BavFe.49931$4o.24620@fed1read06...
>> wrote:
> . With a spoiler controlled aircraft, when
>> you stall the wings it makes the spoiler ineffective. It can no
>> longer spoil lift that is no longer there. > --
>>
>> Darrell R. Schmidt
>> B-58 Hustler History: http://members.cox.net/dschmidt1/
>> -
>
> This isn't true. Spoilers provide effective roll control even on a
> stalled wing while ailerons do not. lift does not disappear when the
> wing stalls.
> Mike
> MU-2

Not so, Mike. Spoilers spoil lift. You can't spoil lift that ain't there
as in a stalled wing.

--

Darrell R. Schmidt
B-58 Hustler History: http://members.cox.net/dschmidt1/
-

[Skywise]

"Darrell S" > wrote in news:NrVFe.51930$4o.23949@fed1read06:

> Mike Rapoport wrote:
>> "Darrell S" > wrote in message
>> news:BavFe.49931$4o.24620@fed1read06...
>>> wrote:
>> . With a spoiler controlled aircraft, when
>>> you stall the wings it makes the spoiler ineffective. It can no
>>> longer spoil lift that is no longer there. > --
>>>
>>> Darrell R. Schmidt
>>> B-58 Hustler History: http://members.cox.net/dschmidt1/
>>> -
>>
>> This isn't true. Spoilers provide effective roll control even on a
>> stalled wing while ailerons do not. lift does not disappear when the
>> wing stalls.
>> Mike
>> MU-2
>
> Not so, Mike. Spoilers spoil lift. You can't spoil lift that ain't there
> as in a stalled wing.

But is not the definition of a stalled wing one that is
producing less lift than necessary to maintain flight?

That seemed to be quite a topic not too long ago re spins.

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism

Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html
Blog: http://www.skywise711.com/Blog

Sed quis custodiet ipsos Custodes?

[Peter Duniho]

"Skywise" > wrote in message
...
>>> [...]
>>> This isn't true. Spoilers provide effective roll control even on a
>>> stalled wing while ailerons do not. lift does not disappear when the
>>> wing stalls.
>>
>> Not so, Mike. Spoilers spoil lift. You can't spoil lift that ain't
>> there
>> as in a stalled wing.
>
> But is not the definition of a stalled wing one that is
> producing less lift than necessary to maintain flight?

Actually, the definition of a stalled wing is one that has exceeded the
critical angle of attack. The critical angle of attack is the point at
which the wing has the greatest lift coefficient.

It is true that a stalled wing still has lift, and it is also true that a
stalled wing can be provided with *some* roll control with spoilers, when in
the same situation ailerons would be useless.

I might dispute the use of the word "effective", just because often it's
used to imply some semblance of quality. But I think in this context, as
long as it's understood that "effective" simply means that the spoiler do
have an effect, there's no need for debating those semantics.

Pete

[Mike Rapoport]

A stalled wing is still producing lift.

Mike
MU-2


"Darrell S" > wrote in message
news:NrVFe.51930$4o.23949@fed1read06...
> Mike Rapoport wrote:
>> "Darrell S" > wrote in message
>> news:BavFe.49931$4o.24620@fed1read06...
>>> wrote:
>> . With a spoiler controlled aircraft, when
>>> you stall the wings it makes the spoiler ineffective. It can no
>>> longer spoil lift that is no longer there. > --
>>>
>>> Darrell R. Schmidt
>>> B-58 Hustler History: http://members.cox.net/dschmidt1/
>>> -
>>
>> This isn't true. Spoilers provide effective roll control even on a
>> stalled wing while ailerons do not. lift does not disappear when the
>> wing stalls.
>> Mike
>> MU-2
>
> Not so, Mike. Spoilers spoil lift. You can't spoil lift that ain't there
> as in a stalled wing.
>
> --
>
> Darrell R. Schmidt
> B-58 Hustler History: http://members.cox.net/dschmidt1/
> -
>
>

[Mike Rapoport]

"Peter Duniho" > wrote in message
...
> "Skywise" > wrote in message
> ...
>>>> [...]
>>>> This isn't true. Spoilers provide effective roll control even on a
>>>> stalled wing while ailerons do not. lift does not disappear when the
>>>> wing stalls.
>>>
>>> Not so, Mike. Spoilers spoil lift. You can't spoil lift that ain't
>>> there
>>> as in a stalled wing.
>>
>> But is not the definition of a stalled wing one that is
>> producing less lift than necessary to maintain flight?
>
> Actually, the definition of a stalled wing is one that has exceeded the
> critical angle of attack. The critical angle of attack is the point at
> which the wing has the greatest lift coefficient.
>
> It is true that a stalled wing still has lift, and it is also true that a
> stalled wing can be provided with *some* roll control with spoilers, when
> in the same situation ailerons would be useless.
>
> I might dispute the use of the word "effective", just because often it's
> used to imply some semblance of quality. But I think in this context, as
> long as it's understood that "effective" simply means that the spoiler do
> have an effect, there's no need for debating those semantics.
>

In the MU-2 roll control is pretty good in a stall. It takes more yoke
movement to get the same effect but control is still very positive.

Mike
MU-2

[[email protected]]

That's a key statement. The definition of stalled, as the FAA and the pilot
see it, is not an aerodynamic definition. It is a definition based on
aircraft
handling and controllability.

Nobody here has yet defined spoiler or aileron either. If the "spoilers" are
located far aft on the wing, and are hinged at their leading edge, would
you call them ailerons? How about if the ailerons go up only, are they
spoilers? There are plug type spoilers, hinged at the leading edge spoilers,
vented spoilers, spoilers at the front of the airfoil, spoilers at the rear
of the
airfoil, spoilers in the slot between the wing and flap and the variations
go on
and on. Their characteristics vary widely. There are lots of reports done a
long time ago by NACA on spoilers. One of the characteristics I remember
reading from these reports was the location on the airfoil was a compromise
between control response delay and control effect. Forward locations had
more effect and more delay. Aft locations went the other way. The conclusion
I came to was that the best location and size to have the good
characteristics
of ailerons was the same size and location as ailerons.

The Mead Adventure started life with spoilers, no ailerons. The Durand Mark
II
biplane had full span spoilers on the lower (forward) wing, no ailerons. The
Adventure was converted to ailerons very quickly. The spoilers were quite
unacceptable, located forward on the airfoil. The Durand biplane worked
quite
well according to Bill Durand. As I recall, they were located aft on the
airfoil, in
front of plain flaps. I once flew an R/C model specifically to test
spoilers in
combination with full span flaps. The spoilers were part of the flap gap
area, so
that the optimum lift over the flap would be destroyed with spoiler
deflection. We
started the testing by taping a spoiler to one wing of an existing
aircraft. When it
took about half aileron to fly level, we quit changing the size and
deflection of the
temporary taped-on spoiler, knowing that a wing with similarly sized
spoilers
would be controllable enough to fly (no flaps). After I completed the wing
(we used
the same aircraft that we used to test the taped-on spoilers), I estimated
that
control response should be the most similar to ailerons with the flaps down
about
10 to 20 degrees. This turned out to be right on the button. With flaps up,
the roll
rate was considerably slower than with ailerons. With flaps full down, the
roll rate
was extremely high. So much so that only a couple of landings were
attempted.
With the flaps up, roll response was just adequate both INVERTED and
upright.
Kind of neat seeing an aircraft with spoilers instead of ailerons make a
low inverted
pass. BTW, this was done around 1970. I still have the wing. Never
crashed.

My conclusion was that spoilers make good spoilers, ailerons make good
ailerons
and flaps make good flaps.


Mike Rapoport wrote in message ...
>A stalled wing is still producing lift.
>
>Mike
>MU-2
>
>
>"Darrell S" > wrote in message
>news:NrVFe.51930$4o.23949@fed1read06...
>> Mike Rapoport wrote:
>>> "Darrell S" > wrote in message
>>> news:BavFe.49931$4o.24620@fed1read06...
>>>> wrote:
>>> . With a spoiler controlled aircraft, when
>>>> you stall the wings it makes the spoiler ineffective. It can no
>>>> longer spoil lift that is no longer there. > --
>>>>
>>>> Darrell R. Schmidt
>>>> B-58 Hustler History: http://members.cox.net/dschmidt1/
>>>> -
>>>
>>> This isn't true. Spoilers provide effective roll control even on a
>>> stalled wing while ailerons do not. lift does not disappear when the
>>> wing stalls.
>>> Mike
>>> MU-2
>>
>> Not so, Mike. Spoilers spoil lift. You can't spoil lift that ain't
there
>> as in a stalled wing.
>>
>> --
>>
>> Darrell R. Schmidt
>> B-58 Hustler History: http://members.cox.net/dschmidt1/
>> -
>>
>>
>
>

[Mike Rapoport]

Well it is certainly possible to screw up the design of anything. However I
stick to my orginal premise that spoilers (as installed in a properly
designed aircraft) have far superior roll response at low speed and vastly
better roll response when the wing is stalled.

Mike
MU-2


" > wrote in message
...
> That's a key statement. The definition of stalled, as the FAA and the
> pilot
> see it, is not an aerodynamic definition. It is a definition based on
> aircraft
> handling and controllability.
>
> Nobody here has yet defined spoiler or aileron either. If the "spoilers"
> are
> located far aft on the wing, and are hinged at their leading edge, would
> you call them ailerons? How about if the ailerons go up only, are they
> spoilers? There are plug type spoilers, hinged at the leading edge
> spoilers,
> vented spoilers, spoilers at the front of the airfoil, spoilers at the
> rear
> of the
> airfoil, spoilers in the slot between the wing and flap and the variations
> go on
> and on. Their characteristics vary widely. There are lots of reports done
> a
> long time ago by NACA on spoilers. One of the characteristics I remember
> reading from these reports was the location on the airfoil was a
> compromise
> between control response delay and control effect. Forward locations had
> more effect and more delay. Aft locations went the other way. The
> conclusion
> I came to was that the best location and size to have the good
> characteristics
> of ailerons was the same size and location as ailerons.
>
> The Mead Adventure started life with spoilers, no ailerons. The Durand
> Mark
> II
> biplane had full span spoilers on the lower (forward) wing, no ailerons.
> The
> Adventure was converted to ailerons very quickly. The spoilers were quite
> unacceptable, located forward on the airfoil. The Durand biplane worked
> quite
> well according to Bill Durand. As I recall, they were located aft on the
> airfoil, in
> front of plain flaps. I once flew an R/C model specifically to test
> spoilers in
> combination with full span flaps. The spoilers were part of the flap gap
> area, so
> that the optimum lift over the flap would be destroyed with spoiler
> deflection. We
> started the testing by taping a spoiler to one wing of an existing
> aircraft. When it
> took about half aileron to fly level, we quit changing the size and
> deflection of the
> temporary taped-on spoiler, knowing that a wing with similarly sized
> spoilers
> would be controllable enough to fly (no flaps). After I completed the wing
> (we used
> the same aircraft that we used to test the taped-on spoilers), I estimated
> that
> control response should be the most similar to ailerons with the flaps
> down
> about
> 10 to 20 degrees. This turned out to be right on the button. With flaps
> up,
> the roll
> rate was considerably slower than with ailerons. With flaps full down, the
> roll rate
> was extremely high. So much so that only a couple of landings were
> attempted.
> With the flaps up, roll response was just adequate both INVERTED and
> upright.
> Kind of neat seeing an aircraft with spoilers instead of ailerons make a
> low inverted
> pass. BTW, this was done around 1970. I still have the wing. Never
> crashed.
>
> My conclusion was that spoilers make good spoilers, ailerons make good
> ailerons
> and flaps make good flaps.
>
>
> Mike Rapoport wrote in message ...
>>A stalled wing is still producing lift.
>>
>>Mike
>>MU-2
>>
>>
>>"Darrell S" > wrote in message
>>news:NrVFe.51930$4o.23949@fed1read06...
>>> Mike Rapoport wrote:
>>>> "Darrell S" > wrote in message
>>>> news:BavFe.49931$4o.24620@fed1read06...
>>>>> wrote:
>>>> . With a spoiler controlled aircraft, when
>>>>> you stall the wings it makes the spoiler ineffective. It can no
>>>>> longer spoil lift that is no longer there. > --
>>>>>
>>>>> Darrell R. Schmidt
>>>>> B-58 Hustler History: http://members.cox.net/dschmidt1/
>>>>> -
>>>>
>>>> This isn't true. Spoilers provide effective roll control even on a
>>>> stalled wing while ailerons do not. lift does not disappear when the
>>>> wing stalls.
>>>> Mike
>>>> MU-2
>>>
>>> Not so, Mike. Spoilers spoil lift. You can't spoil lift that ain't
> there
>>> as in a stalled wing.
>>>
>>> --
>>>
>>> Darrell R. Schmidt
>>> B-58 Hustler History: http://members.cox.net/dschmidt1/
>>> -
>>>
>>>
>>
>>
>
>

[Ron Natalie]

wrote:
> I think the difference in this instance is that ailerons deflect
> airflow upward wheras spoilers actually interrupt lift
>
You don't think deflecting the airflow upward doesn't decrease the
lift?

[Ron Natalie]

Darrell S wrote:

>
> Not so, Mike. Spoilers spoil lift. You can't spoil lift that ain't there
> as in a stalled wing.
>

What part of "a stalled wing still generates lift" don't you understand.
A stall occurs at the critical angle of attack. This is the point where
further increase in angle of attack generates no further increase in
lift. The lift goes down, it doesn't disappear.

[Ron Natalie]

wrote:
> That's a key statement. The definition of stalled, as the FAA and the pilot
> see it, is not an aerodynamic definition. It is a definition based on
> aircraft
> handling and controllability.
>
Says who?



>

[Peter Duniho]

"Ron Natalie" > wrote in message
m...
> wrote:
>> I think the difference in this instance is that ailerons deflect
>> airflow upward wheras spoilers actually interrupt lift
>>
> You don't think deflecting the airflow upward doesn't decrease the
> lift?

I think it's fair to say that there's a difference between using the word
"interrupt" and using the word "decrease".

[[email protected]]

The certification requirements. They do not mention in any way a specific
aoa.
They define stall by how the aircraft acts. Like reaching a stick limit, or
responding in a
direction other than that of a control input. Or, on bigger aircraft, when
the computers
say that the plane is stalled. Back to little planes. The stall varies
widely, mostly
depending on weight and cg position. For example at forward cg, the stall is
often
determined by running out of elevator travel. The airplane isn't really
stalled, but the
certification requirements say it is. Reaching a control limit is a limit.
At aft cg, the
airplane nose may stop rising and may even start dropping with increased
elevator
position. This is a limit, because the aircraft is not responding in the
direction of input.
The same things apply to aileron action. The airplane must respond in the
direction of
control input at conditions above stall speed. Stall characteristics get
into this at the
same time. Even though the aircraft may respond in the proper direction, if
the angle
of bank exceeds a rather small number (15 degrees, as I recall) the stall
characteristics
are deemed unacceptable. Addressing all these problems results in
compromises.

I'm sure that I have not covered the issue well at all. It would be a good
exercise pull
up the certification requirements for light aircraft and read them. After a
month or two
of full time study, a person could come up with a lot of questions on just
how the heck
can you certify any plane.

One other thing. Stall speeds vary considerably with entry rate. The regs
specify a 1
knot per second entry rate. At slower entry rates, the stall speed is
higher. At higher
entry rates, the stall speed is lower. Very, very few instructors do 1 knot
per second
entry rate stalls. It's much more difficult to do than the "bring the nose
up and recover
when it breaks" type. This is my most favorite pet peeve. Many instructors
are avoiding
one of the most insidious parts of the envelope. "There I was, turning final
above stall speed and the plane dove into the ground." Turning flight. Slow
speed
decline. It adds up.


Ron Natalie wrote in message
>...
wrote:
>> That's a key statement. The definition of stalled, as the FAA and the
pilot
>> see it, is not an aerodynamic definition. It is a definition based on
>> aircraft
>> handling and controllability.
>>
>Says who?
>
>
>
>>

[Peter Duniho]

" > wrote in message
...
> Ron Natalie wrote in message
> >...
wrote:
>>> The definition of stalled [...] is a definition based on
>>> aircraft handling and controllability.
>>
>>Says who?
>
> The certification requirements. They do not mention in any way a specific
> aoa.

They don't even define stall. What makes you think they define it based on
handling rather than AOA?

Perhaps you are confused (for example) by the wording of 23.49(a). When
they say "VSO and VS1 are the stalling speeds or the minimum steady flight
speeds, in knots (CAS), at which the airplane is controllable", that means:

"VSO and VS1 are (the stalling speeds) or (the minimum steady flight speeds,
in knots (CAS), at which the airplane is controllable)"

Or perhaps you are mistaking the FAA's requirement for how to *identify* a
stall for a definition of one. See 23.201(b). You'll note that the
requirement in 23.201(b) even applies to airplanes that don't actually stall
under the conditions described, such as the Ercoupe. The FAA is well aware
that those airplanes are not stalling.

The FAA uses the same definition for stall that everyone else does.

> [...] Back to little planes. The stall varies widely, mostly
> depending on weight and cg position.

True.

> For example at forward cg, the stall is often determined by running out
> of elevator travel.

False. Unless by "often" you mean "rarely".

> The airplane isn't really stalled, but the certification requirements
> say it is.

Also false. Even for the rare airplane where a forward CG means the
elevator doesn't have enough authority to create a stall, the FAA doesn't
call that situation a stall. They simply use that situation to define a
specific speed.

Don't be confused by the fact that the speed defined is often referred to as
the stall speed. It's not the stall speed, it's Vs0 and Vs1 (as
appropriate).

> [...] I'm sure that I have not covered the issue well at all.

I can certainly agree with that.

> It would be a good exercise pull up the certification requirements
> for light aircraft and read them.

I can agree with that as well. Perhaps you should try it again, this time
reading them correctly.

> [...]
> One other thing. Stall speeds vary considerably with entry rate. The regs
> specify a 1 knot per second entry rate. At slower entry rates, the stall
> speed is higher.

So, you're saying as the entry rate approaches 0 knots per second, the stall
speed goes to infinity?

Um, seems to me you have this backwards.

> [...] "There I was, turning final
> above stall speed and the plane dove into the ground." Turning flight.
> Slow
> speed decline. It adds up.

Perhaps, but your post doesn't.

Speaking of which, maybe you could look into your whole line-lengths thing.
It is customary to either limit your line lengths to 72 characters or less,
or to not limit them at all. The former is much more common, but at least
with the latter the post is still readable in *some* newsreaders.

Pete

[[email protected]]

I said:

>> For example at forward cg, the stall is often determined by running out
>> of elevator travel.
I made an error. I should not have used the word determined.
I should have been more clear. The point is that with the elevator limited
based on the stall at aft CG, the forward cg case can be compromised.
You tend to run out of elevator which make the approach speeds
higher etc, etc.

You said:
>False. Unless by "often" you mean "rarely".

I reply:
Indirectly, stall can be changed by what has happened at forward cg.
The compromises of elevator throw and cg position will change
the published speeds.
---
snips:
---
I said:
>> One other thing. Stall speeds vary considerably with entry rate. The regs
>> specify a 1 knot per second entry rate. At slower entry rates, the stall
>> speed is higher.
>
You replied:
>So, you're saying as the entry rate approaches 0 knots per second, the
stall
>speed goes to infinity?
>
>Um, seems to me you have this backwards.

I reply:
I made no such inference that the stall speed grows infinitely. What I said
is correct. Try it. It's not easy to do. Count down from 10 to 1 at the same
time
you are reducing the airspeed that last 10 knots. One knot per second.
The stick input will probably be very non-linear in order to do this.
Now do the last 10 knots in 5 sec. Now do it as slowly as possible.
It takes multiple runs, since the "last" 10 knots will be redefined
depending
on the stall speed at each entry rate. The most difficult part is that last
second. That's the part that counts for data.
Touching the elevator stop, rolling off, or nose reacting in a direction
opposite
elevator input all count as stall.


Enough of this - the thread was about spoilers.

Dennis

[Blueskies]

"Matt Whiting" > wrote in message ...
> Mike Rapoport wrote:
>
>> Spoilers function the same as ailerons at low angles of attack and better than ailerons at high angle of attack. The
>> primary advantage of spoilers instead of ailerons is that it enables full span flaps. Spoilers also reduce or
>> eliminate adverse yaw.
>
> I assume there must be some disadvantages of spoilers for roll control as you see them so rarely. What are the
> drawbacks? Cost??
>
> Matt
>

What happens when the wing is inverted? If you are pushing negative Gs then the roll control will be reversed?

[Mike Rapoport]

" Blueskies" > wrote in message
m...
>
> "Matt Whiting" > wrote in message
> ...
>> Mike Rapoport wrote:
>>
>>> Spoilers function the same as ailerons at low angles of attack and
>>> better than ailerons at high angle of attack. The primary advantage of
>>> spoilers instead of ailerons is that it enables full span flaps.
>>> Spoilers also reduce or eliminate adverse yaw.
>>
>> I assume there must be some disadvantages of spoilers for roll control as
>> you see them so rarely. What are the drawbacks? Cost??
>>
>> Matt
>>
>
> What happens when the wing is inverted? If you are pushing negative Gs
> then the roll control will be reversed?
>

It would work the same. The wing doesn't know that it is inverted, all it
knows is AOA.

Mike
MU-2

[Blueskies]

"Mike Rapoport" > wrote in message hlink.net...
>
> " Blueskies" > wrote in message m...
>>
>> "Matt Whiting" > wrote in message ...
>>> Mike Rapoport wrote:
>>>
>>>> Spoilers function the same as ailerons at low angles of attack and better than ailerons at high angle of attack.
>>>> The primary advantage of spoilers instead of ailerons is that it enables full span flaps. Spoilers also reduce or
>>>> eliminate adverse yaw.
>>>
>>> I assume there must be some disadvantages of spoilers for roll control as you see them so rarely. What are the
>>> drawbacks? Cost??
>>>
>>> Matt
>>>
>>
>> What happens when the wing is inverted? If you are pushing negative Gs then the roll control will be reversed?
>>
>
> It would work the same. The wing doesn't know that it is inverted, all it knows is AOA.
>
> Mike
> MU-2
>

The wing does know, the AOA is negative. Right side up, the spoiler is deflected and the wing drops. Turn it upside down
and deflect it, the wing still drops.

[Mike Rapoport]

" Blueskies" > wrote in message
m...
>
> "Mike Rapoport" > wrote in message
> hlink.net...
>>
>> " Blueskies" > wrote in message
>> m...
>>>
>>> "Matt Whiting" > wrote in message
>>> ...
>>>> Mike Rapoport wrote:
>>>>
>>>>> Spoilers function the same as ailerons at low angles of attack and
>>>>> better than ailerons at high angle of attack. The primary advantage of
>>>>> spoilers instead of ailerons is that it enables full span flaps.
>>>>> Spoilers also reduce or eliminate adverse yaw.
>>>>
>>>> I assume there must be some disadvantages of spoilers for roll control
>>>> as you see them so rarely. What are the drawbacks? Cost??
>>>>
>>>> Matt
>>>>
>>>
>>> What happens when the wing is inverted? If you are pushing negative Gs
>>> then the roll control will be reversed?
>>>
>>
>> It would work the same. The wing doesn't know that it is inverted, all
>> it knows is AOA.
>>
>> Mike
>> MU-2
>>
>
> The wing does know, the AOA is negative. Right side up, the spoiler is
> deflected and the wing drops. Turn it upside down and deflect it, the wing
> still drops.
>
No. The wing is pushing the air down to keep the plane up. If the spoiler
is extended on an inverted wing, turbulence is created behind the spoiler
and air is not pushed down as effectively. Although I have never flown
inverted, I have pushed the nose over to the point of negative Gs and roll
control is not reversed.

Mike
MU-2

[Mike Money]

The first spoiler I ever saw was on the Navy's RA-5C. Found the concept
quite interesting. It's a complex system and quite pricey. The RA also
utilized full moving vertical and horizontal stabalators in lieu of
rudder and trailing vertical control surfaces on the tail of the
aircraft. The "Vigi" was years ahead of its time in design.