Aerodynamics question

Archived from groups: alt.games.microsoft.flight-sim (More info?)

"Dallas" <Cybnorm@spam_me_not.Hotmail.Com> wrote in message
news:ADAke.5593$Lc1.3738@newsread3.news.pas.earthlink.net...
>
> For years I was comfortable with a concept I believe I read in a book that
> I
> now perceive as wrong:
>
> When you bank an aircraft to the right the ailerons create drag on the
> side
> opposite the turn and that causes the aircraft to yaw to the left.
> Because
> of this you apply right rudder to counter the yaw and thus create a
> coordinated turn.
>
> Except one thing... when you bank the aircraft one aileron is up and the
> other is down. The way I see it you've created roughly equal drag on both
> wings that would not cause you to yaw.
>
> So, what causes the yaw in a bank?
>
> Dallas
>
>

A short course in "Adverse Yaw" and ways to combat it:

http://www.nps.navy.mil/avsafety/a [...] %20yaw.htm

Google is your friend...

Jay Beckman
PP-ASEL / Sim Pilot
Chandler, AZ

Archived from groups: alt.games.microsoft.flight-sim (More info?)

On Tue, 24 May 2005 00:27:09 -0700, "Jay Beckman" <jnsbeckman@cox.net>
brought the following to our attention:

>"Dallas" <Cybnorm@spam_me_not.Hotmail.Com> wrote in message
>>
>> For years I was comfortable with a concept I believe I read in a book that
>> I now perceive as wrong:
>>
>> When you bank an aircraft to the right the ailerons create drag on the
>> side opposite the turn and that causes the aircraft to yaw to the left.
>> Because of this you apply right rudder to counter the yaw and thus create a
>> coordinated turn.
>>
>> Except one thing... when you bank the aircraft one aileron is up and the
>> other is down. The way I see it you've created roughly equal drag on both
>> wings that would not cause you to yaw.
>>
>> So, what causes the yaw in a bank?
>>
>> Dallas
>>
>>
>
>A short course in "Adverse Yaw" and ways to combat it:
>
>http://www.nps.navy.mil/avsafety/aero%20tips%20of%20the%20day/adverse%20yaw.htm
>
>Google is your friend...
>
>Jay


Another good question.. and how is this implemented in the Sim? If one
was to examine the AIR file by two authors of the same plane.. the Yaw
due to Aileron deflection moment could be of opposite sign. Example:

-- Yaw --

Cn_da Yaw Moment, Ailerons (+ = nose left)

AIR file #1 = 12 / [2048] = 0.005859 (FS2k INT Rec 1101)

AIR file #2 = -0.001697 (FS2k2 REAL Rec 1544)


See what's happening above for YAW in reaction to the Aileron
deflection? The pos (+) Cn_da yaws the nose outside the turn.. which
makes coord more difficult. The neg (-) Cn_da yaws the nose inside the
turn.. which makes coordination easier.


-- Roll --

Cl_da Roll Moment, Ailerons (+ = Right Aileron Down)

AIR file #1 = -112 / [2048] = -0.054688 (FS2k INT Rec 1101)

AIR file #2 = -0.092800 (FS2k2 REAL Rec 1543)



Supposedly.. modern aircraft have aileron deflection corrected
to minimize or eliminate effect. Not sure of this in a `first hand'
way however. As for AIR file SD's (stability derivatives).. have run
experiments and tested BOTH of the yaw moment signs.

Comments or corrections always welcome.
Having fun with dynamics!!


-Gregory

Archived from groups: alt.games.microsoft.flight-sim (More info?)

On Tue, 24 May 2005 10:14:55 -0600, "RandyL"
<rlink"nospam"@cableone.net> brought the following to our attention:

>Dallas
> I sometimes read the sci.aeronautics newsgroup, and once read a message
>from a poster who asked the simple question: "What causes lift?". You should
>have seen all of the contradictory, confusing, and mind-bogglingly technical
>answers

Randy.. one guy replied to a post (about 2-years ago) stating
that.. `gravity had nothing to do with it..!! ' :-]

the messages might still be in the Agent Outbox.


-Gregory

Archived from groups: alt.games.microsoft.flight-sim (More info?)

"Emilio" <emiliosan@tds.net> wrote in message
news:42936db3$1_1@newspeer2.tds.net...
>I must add that while you are in a turn outer wing sees higher wind speed.
> The inner wing is closer to the center of turn and its airspeed is slower.
> Since drag is a function of air velocity squared, this indifference alone
> will cause aircraft to yaw away from the turn.
>
> Anyway, B2 Bomber has no rudder. So they use split aileron to control
> unequal aileron drag while in a turn. I put in "B2" in google and found
> good B2 site http://www.bugimus.com/stealth/stealth.html There you can
> find
> many images with split aileron in flight.
>
>
> Emilio.
>
Emilio,
Absolutely right. The faster the airflow, the greater the drag. Another
way of roll axis control is to forget ailerons altogether and just use
spoilers on the tops of the wings. In a right bank, the spoiler is opened on
the top of the right wing. This interrupts the laminar airflow over the top
of the wing at that point, and kills part of the lift that the right wing is
generating. I was once building a homebuilt motorglider that used spoilers
on the tops of the wings for roll control.

Randy L.

Archived from groups: alt.games.microsoft.flight-sim (More info?)

"RandyL" <rlink"nospam"@cableone.net> skrev i melding
> Another way of roll axis control is to forget ailerons altogether and just
use
> spoilers on the tops of the wings. In a right bank, the spoiler is opened
on
> the top of the right wing. This interrupts the laminar airflow over the
top
> of the wing at that point, and kills part of the lift that the right wing
is
> generating. I was once building a homebuilt motorglider that used spoilers
> on the tops of the wings for roll control.
>
> Randy L.

And it also creates a little drag on the side of the downgoing wing yawing
the nose the same way.
Curious about the motorglider. Was it the American Eaglet?

Clamer

Archived from groups: alt.games.microsoft.flight-sim (More info?)

RandyL wrote:
> Dallas
> I sometimes read the sci.aeronautics newsgroup, and once read a message
> from a poster who asked the simple question: "What causes lift?". You should
> have seen all of the contradictory, confusing, and mind-bogglingly technical
> answers. There were as many "right" answers as there were people who
> replied! I don't know if this is the "right" amswer, as a matter of fact I
> am sure that someone will correct me, but I will tell you what I was told
> while taking flying lessons for my PPL. My instructor told me that the
> reason why one wing deflects upward when that aileron is moved downward is
> because the aileron in the down position increases the angle of attack of
> the wing at that point on the wing.

I think your instructor is exactly right about ailerons and flaps
generating lift by changing dramatically the angle of attack of the
wing. He apparently didn't study at Emery Riddle. By lowering the
trailing part of the wing you make a big change in the reference point
where the chord line is measured from. Dropping the trailing part of
the wing is not an efficient way to camber the wing, its more angle
than camber. Some more sophisticated flaps are much more efficient at
it than others. Take a wing section that has flaps lowered and
reposition it on the airplane at zero angle of attack and see how much
lift they make from inefficient under camber alone.

The "angle of attack" is the angle at
> which the mean chord of the wing intersects the relative wind. Mean chord
> is simply an imaginary line drawn between the leading edge and the trailing
> edge of the wing, right through the center of the wing. Relative wind is
> the direction that the air is coming from when it strikes the leading edge
> of the wing.

Relative airflow (relative wind sounds like your relative has a
flatulence problem) is not the direction that air is coming from when
it strikes the leading edge of the wing. Relative airflow does not
require the motion of air or a solid object only motion between the
two. Many times relative airflow is caused by the leading edge of the
wing striking still air. The simple and powerful concept of relative
motion is crucial in knowing the difference between drag and lift. I
have met a lot of private and commercial pilots but none that knew the
simple and single difference between the definition of lift and drag.
The potential direction of relative airflow and lift and drag is
infinite.

He told me that any time that you increase the angle of attack
> of an airfoil like a wing, or a propellor blade, you will generate more
> lift, since air has to move even faster over the top of the wing between the
> leading edge and the trailing edge of the wing.

If you increase angle of attack past the stall angle you will not
generate more lift.

The faster that air moves,
> the less dense it becomes. The less dense that the air becomes, the more
> pressure difference between the air on top of the wing, and the air on the
> bottom of the wing. This causes more lift to be generated on the wing that
> has the aileron in the down position.

The air moving over the wing in flight does not cause the lower
pressure, lower pressure causes the air to move over the wing. If this
were not true the air would separate more from the wing at the highest
point and not as much would make it down the other side. Take a spoon
and hold the back of it in a jet of air from an air hose, its tendency
to stick in the low pressure flow is quit dramatic. Knowledgeable
people will tell you that the low pressure is pulling the spoon into
the flow some will say that the low pressure allows higher atmospheric
pressure to push the spoon into the flow. People with learning
disabilities such as common sense and logic will say this is an easily
disproved crock that sheds some light on the skewed ideology of math
based text. Hold a knife blade in the flow of air (at zero angle of
attack ) and see how much lift you get.

The airfoil shape that generates the most lift at zero degrees angle of
attack is the one with the less pressure differentials on the top and
bottom. There is nothing better than using low pressure and the shape
of the top of the wing to divert the relative airflow except for using
low pressure and the shape of the bottom of the wing in addition to
divert the relative airflow. The distance over the top of an under
cambered air foil is closer the distance under the bottom compared to a
flat bottom airfoil yet it produces more lift at zero angle of attack.
Wat up wid dat dog.



The opposite wings aileron moving
> upward has the opposite effect. When that aileron is up, it decreases the
> angle of attack of that wing at that point. This causes less lift on that
> wing.
> While increasing the angle of attack increases lift, it also increases
> drag at the same time. The type of drag associated with increased angle of
> attack is called "induced drag." Since the aileron that is down is
> generating more lift than the aileron that is up because of being at a
> higher angle of attack, it is also generating more induced drag than the
> aileron that is up. This increased drag has a tendancy of making the
> aircraft want to yaw away from the direction of the turn. That is why you
> need to use the rudder in the direction of the turn, to counter act the
> induced drag that is being generated by the upward wing.
> You are correct in saying that drag is generated by both ailerons, its
> just that MORE drag is being generated by the aileron in the down position
> (because of its increased angle of attack) than the aileron that is in the
> up position. I hope this helps, and is not too confusing. Take care....
>
> Randy L.
>
> "Dallas" <Cybnorm@spam_me_not.Hotmail.Com> wrote in message
> news:ADAke.5593$Lc1.3738@newsread3.news.pas.earthlink.net...
> >
> > For years I was comfortable with a concept I believe I read in a book that
> > I
> > now perceive as wrong:
> >
> > When you bank an aircraft to the right the ailerons create drag on the
> > side
> > opposite the turn and that causes the aircraft to yaw to the left.
> > Because
> > of this you apply right rudder to counter the yaw and thus create a
> > coordinated turn.
> >
> > Except one thing... when you bank the aircraft one aileron is up and the
> > other is down. The way I see it you've created roughly equal drag on both
> > wings that would not cause you to yaw.
> >
> > So, what causes the yaw in a bank?
> >
> > Dallas
> >
> >

Archived from groups: alt.games.microsoft.flight-sim (More info?)

"Dallas" <Cybnorm@spam_me_not.Hotmail.Com> wrote in message
news:ADAke.5593$Lc1.3738@newsread3.news.pas.earthlink.net...
>
> For years I was comfortable with a concept I believe I read in a book that
I
> now perceive as wrong:
>
> When you bank an aircraft to the right the ailerons create drag on the
side
> opposite the turn and that causes the aircraft to yaw to the left.
Because
> of this you apply right rudder to counter the yaw and thus create a
> coordinated turn.
>
> Except one thing... when you bank the aircraft one aileron is up and the
> other is down. The way I see it you've created roughly equal drag on both
> wings that would not cause you to yaw.
>
> So, what causes the yaw in a bank?
>
> Dallas



Hey Dallas,

I remember thinking the same as you many years ago back when I was taking
flying lessons. I'm a stubborn cuss and insisted that my reasoning was sound
no matter what the books said. My flight instructor offered a chance to
test my theory. He had me sit with my feet on the back seat of my Mustang
convertible, my butt on the boot and my arms sticking out to either side.
He was going to drive and he wanted me to "fly' my hands like kids do out
the window.

"Get them both stable and equalized," he said, " then increase the angle on
one hand to fly it higher while at the same time decrease the angle on the
other hand so that it drops."

We pulled onto highway where he settled on about 45 mph. While bikers,
truckers and tourists roared past with amusement at the peculiar sight I
flew my hands and then, as instructed, lowered one "aileron" while raising
the other. Very small changes in pitch (a.k.a., angle of attack) made big
changes in both lift and drag. The hand that I had decreased the angle on
moved both down and forward as the other hand with a greater angle and
greater lift also created an amazing amount of drag. I was being literally
pulled around in the opposite direction of the roll I was trying to
simulate. I tried several variations of negative pitch on my descending
'wing' but the best I could manage was to keep the drag from reducing as
much as it did the first time but the drag on the hand going up was still
significantly greater than the hand going down.

When we got back to the airport cafe he went into the more detailed
explanations such as those offered by others in this thread but then he cut
to the bottom line.

"In straight and level flight BOTH wings are creating the SAME amount of
lift. When you roll the aircraft either into a turn or out of it one wing
is now during the roll creating more lift than the other. More lift equals
more drag, less lift equals less drag, period. Drag induces yaw. Rudder is
used to counter yaw to coordinate the turn."

I humbly conceded his well illustrated point

"And by the way," he added with a grin, "You caught a few bugs on the
front of your shirt."

Anyway, Dallas, this probably doesn't shed any new light on the discussion
but it brought back some funny memories.

Regards,
Rand