Gliding lecture slides

[Richard Lancaster]

Hi,

I've put some lecture slides on the following topics:

* Principles of glider flight
* Glider instruments

onto the web site:

http://www.carrotworks.com/

Regards,

Richard

[Mike the Strike]

On Apr 14, 9:18*am, (Richard Lancaster)
wrote:
> Hi,
>
> I've put some lecture slides on the following topics:
>
> * Principles of glider flight
> * Glider instruments
>
> onto the web site:
>
> http://www.carrotworks.com/
>
> Regards,
>
> Richard

You might want to check on the accuracy of the oft-repeated myth that
wings develop lift because of the pressure difference between the
upper and lower surfaces. My understanding of the physics is that
this component is negligible compared to the second mechanism you
mention of the downward deflection of the airflow.

If you think I am mistaken, then please explain how symmetrical
airfoils develop lift!

Mike

[Tony[_5_]]

> If you think I am mistaken, then please explain how symmetrical
> airfoils develop lift!
>
> Mike

angle of attack.

[KevinFinke]

Richard and Mike, you're both a little bit wrong.

I like the slide showing the airflow around the airfoil section, few
illustrations show how the streamlines change on the lower surface. A
lot just keep them flat. However, if I'm to interpret the length of
the vectors as the local velocity in the flow field, then the vectors
on the lower surface look in error. They also typically accelerate to
a velocity greater than freestream. Which brings me to the problems I
have with the chart on page 8. The pressure forces on the lower
surface are not acting in the direction as shown. Because the air also
has to accelerate around the lower surface, it too is a lower pressure
than ambient and is therefore acting positive to the surface normal.
Or in the diagram, downward. However, the net difference between the
upper and lower surface yields a positive lifting force. This site has
very good diagrams that show the direction and magnitude of the
pressure forces on an airfoil. It also shows how the pressures react
for symmetric airfoils.

http://www.dynamicflight.com/aerodynamics/pres_patterns/

Mike, I think the common mis-understanding to which you are referring
to is the oft stated quote that because the surface is longer on the
top than the bottom, the air has to travel faster to meet at the end.
Geometrically, this difference is near 1%, and clearly any velocity
delta driven by the distance would not be significant. However, no
such rule requires that they meet at the end, and in reality they
don't.

There are two ways to look at how an airfoil creates lift. And both
are correct. The Pressure theorists look at the difference between the
upper and lower surface and calculate lift. If you integrate the
pressures on the airfoil you'll end up with the same calculation that
you get from momentum theory which looks at the imparted change in
momentum of the airmass which is deflected downward. Both are correct
and both happen. The difference is how you look at the problem. You
can examine it near field in which case you look at the pressures on
the surface, or you can examine it far field and examine the change in
airmass movement imparted by the airfoil as it moves through the air.

As for symmetric airfoils, they won't produce lift at an angle of
attack = 0. But as Tony says, change the angle of attack and it
produces lift. And now you know why.

-Kevin

[bildan]

On Apr 14, 10:18*am, (Richard Lancaster)
wrote:
> Hi,
>
> I've put some lecture slides on the following topics:
>
> * Principles of glider flight
> * Glider instruments
>
> onto the web site:
>
> http://www.carrotworks.com/
>
> Regards,
>
> Richard

Generally excellent for an introductory presentation. There are a few
very minor issues that only an engineer or aerodynamisist would
catch. One is the use of the Greek letter Alpha to label the AoA of
the fin in a skid - Beta is correct.

Another is the description of the secondary effect of roll with the
application of yaw inputs (Yaw to roll coupling). You are correct
that this is momentarily due to a spanwise difference in airspeed but
you failed to mention that the continued, and much larger, effect is
due to dihedral. Your description of 'adverse' yaw is correct but I
cringe at the negative connotation of the word. Adverse yaw is not
"bad" yaw - it's just what ailerons do. In fact, 'adverse' yaw can be
quite useful in soaring turns as well as in crosswind landings.

BTW, your description of how lift is generated is just fine for this
sort of presentation. Some will argue endlessly about it without
reaching a consensus but yours is more than good enough.

[Mike the Strike]

On Apr 14, 1:24*pm, bildan > wrote:
> On Apr 14, 10:18*am, (Richard Lancaster)
> wrote:
>
> > Hi,
>
> > I've put some lecture slides on the following topics:
>
> > * Principles of glider flight
> > * Glider instruments
>
> > onto the web site:
>
> >http://www.carrotworks.com/
>
> > Regards,
>
> > Richard
>
> Generally excellent for an introductory presentation. *There are a few
> very minor issues that only an engineer or aerodynamisist would
> catch. *One is the use of the Greek letter Alpha to label the AoA of
> the fin in a skid - Beta is correct.
>
> Another is the description of the secondary effect of roll with the
> application of yaw inputs (Yaw to roll coupling). *You are correct
> that this is momentarily due to a spanwise difference in airspeed but
> you failed to mention that the continued, and much larger, effect is
> due to dihedral. *Your description of 'adverse' yaw is correct but I
> cringe at the negative connotation of the word. *Adverse yaw is not
> "bad" yaw - it's just what ailerons do. *In fact, 'adverse' yaw can be
> quite useful in soaring turns as well as in crosswind landings.
>
> BTW, your description of how lift is generated is just fine for this
> sort of presentation. *Some will argue endlessly about it without
> reaching a consensus but yours is more than good enough.

I was maybe a little imprecise in my niggle, but Kevin has described
it very well. My main criticism would be that glider pilots don't
really need to know this. The rest of the stuff is fine.

Mike

[Brian Whatcott]

Mike the Strike wrote:
>> ... There are a few
>> very minor issues that only an engineer or aerodynamisist would
>> catch. One is the use of the Greek letter Alpha to label the AoA of
>> the fin in a skid - Beta is correct....
> Mike

Hmmm...beta is yaw angle, and alpha is AoA.
In referring to side forces generated by a vertical fin,
beta is not quite the controlling factor, is it, when the rudder effect
is included?

Brian W

[Bruce Hoult]

On Apr 15, 8:24*am, bildan > wrote:
> One is the use of the Greek letter Alpha to label the AoA of
> the fin in a skid - Beta is correct.

In mathematics variable names are without meaning and therefore
interchangeable, so I don't see how you can say that a particular
labeling is correct or incorrect, but at most that it follow or does
not follow some convention.

It is true that when considering an entire aircraft it is conventional
to use Beta for yaw, but if you are considering the fin as an airfoil
in isolation then Alpha is perfectly reasonable in order to use the
same equations as you would for other airfoils.

[Brian Whatcott]

Mike the Strike wrote:

> You might want to check on the accuracy of the oft-repeated /myth/ that
> wings develop lift because of the pressure difference between the
> upper and lower surfaces. My understanding of the physics is that
> this component is negligible compared to the second mechanism you
> mention of the downward deflection of the airflow.
>
> If you think I am mistaken, then please explain how symmetrical
> airfoils develop lift!
>
> Mike

Amusing how partisans grow zealous for their chosen explanation! :-)

Brian W

[Mike the Strike]

On Apr 15, 5:14*pm, brian whatcott > wrote:
> Mike the Strike wrote:
> > You might want to check on the accuracy of the oft-repeated /myth/ that
> > wings develop lift because of the pressure difference between the
> > upper and lower surfaces. *My understanding of the physics is that
> > this component is negligible compared to the second mechanism you
> > mention of the downward deflection of the airflow.
>
> > If you think I am mistaken, then please explain how symmetrical
> > airfoils develop lift!
>
> > Mike
>
> Amusing how partisans grow zealous for their chosen explanation! :-)
>
> Brian W

Actually, we physicists get annoyed when people get the science wrong.

Mike

[Richard Lancaster]

Thanks for the comments.

You wouldn't believe how much time I spent on the first few slides of the
Lift / Drag lecture, the bit covering how a wing generates lift, to try to
make them benign with respect to controversy but still say something
useful and meaningful.

Kevin, when I get a chance I will go back and review the streamline and
force diagrams on pages 7 and 8 of the Lift / Drag lecture. It does look
like they might be slightly erroneous, but I just want to check back
through the literature and dig out some experimental results before I make
any changes.

Bildan, with regard to yaw generating roll via dihedral effects I do
actually say that in the slide. However the section on the effects of the
controls is going to get a rework at some point. It's the only point in
all three lectures where the audience without fail zones out on you and
looses interest. So I need to think up some way of making it more
interesting.

Regards,

Richard

[Brian Whatcott]

Mike the Strike wrote:
> On Apr 15, 5:14 pm, brian whatcott > wrote:
>> Mike the Strike wrote:
>>> You might want to check on the accuracy of the oft-repeated /myth/ that
>>> wings develop lift because of the pressure difference between the
>>> upper and lower surfaces. My understanding of the physics is that
>>> this component is negligible compared to the second mechanism you
>>> mention of the downward deflection of the airflow.
>>> If you think I am mistaken, then please explain how symmetrical
>>> airfoils develop lift!
>>> Mike
>> Amusing how partisans grow zealous for their chosen explanation! :-)
>>
>> Brian W
>
> Actually, we physicists get annoyed when people get the science wrong.
>
> Mike


Hehe....good one, Mike! :-)

Brian W

[bildan]

On Apr 16, 5:10*am, (Richard Lancaster)
wrote:
> Thanks for the comments.
>
> You wouldn't believe how much time I spent on the first few slides of the
> Lift / Drag lecture, the bit covering how a wing generates lift, to try to
> make them benign with respect to controversy but still say something
> useful and meaningful.
>
> Kevin, when I get a chance I will go back and review the streamline and
> force diagrams on pages 7 and 8 of the Lift / Drag lecture. *It does look
> like they might be slightly erroneous, but I just want to check back
> through the literature and dig out some experimental results before I make
> any changes.
>
> Bildan, with regard to yaw generating roll via dihedral effects I do
> actually say that in the slide. *However the section on the effects of the
> controls is going to get a rework at some point. *It's the only point in
> all three lectures where the audience without fail zones out on you and
> looses interest. *So I need to think up some way of making it more
> interesting.
>
> Regards,
>
> Richard

You're right, I seem to have missed the section on yaw to roll due to
dihedral. I apologize.

Just a thought. This isn't exactly fair - it's clear you spent a lot
of effort on the graphics - but just repeating the same graphics style
with minor changes with different text can be boring. There's an easy
way to illustrate slides and get more color and realism by using a
flight simulator like Condor. I think Uros would grant you the right
to use the graphics if you give full credit.

The flight sim technique is to set up a situation you want to
illustrate and pause the simulator at just the right moment. Select
the outside view you like then take a JPEG screenshot. The resulting
JPEG file can then be edited with a graphics or photo-editor to add
additional graphics or text. The result can be quite pleasing.

[toad]

On Apr 15, 9:20*pm, Mike the Strike > wrote:
> On Apr 15, 5:14*pm, brian whatcott > wrote:
>
> > Mike the Strike wrote:
> > > You might want to check on the accuracy of the oft-repeated /myth/ that
> > > wings develop lift because of the pressure difference between the
> > > upper and lower surfaces. *My understanding of the physics is that
> > > this component is negligible compared to the second mechanism you
> > > mention of the downward deflection of the airflow.
>
> > > If you think I am mistaken, then please explain how symmetrical
> > > airfoils develop lift!
>
> > > Mike
>
> > Amusing how partisans grow zealous for their chosen explanation! :-)
>
> > Brian W
>
> Actually, we physicists get annoyed when people get the science wrong.
>
> Mike

Mike,

You might want to check your own physics, before making comments like
this.
Because us aerodynamicists get annoyed when people get the science
wrong :-)

Symetrical airfoils work the same way asymetric foils work. The air
is pushing up on the bottom, stronger than the air is pushing down on
the top. If the pressure was the same on the top and bottom surfaces,
there would be no lift.

Please, don't confuse pressure differential with the incorrect "equal
transit time" theory.

I have lost my favorite link to a well presented and complete theory
of lift, so I can't post it here. But the short version is:

angle of attack makes the air flow change direction
that change of direction makes
air pressure rise on the bottom ( but not by much )
air pressure drop on the bottom ( most of the change)

And it all happens because of the Kutta Condtion.
http://en.wikipedia.org/wiki/Kutta_condition

If you are going to berate people for their own incorrect knowledge,
you should be able to improve on that knowledge.

The original posters slides look like a pretty good explanantion. I
think that it is more information than a pilot really needs, but some
people won't relax and actually learn until they think they understand
"why" it works.

Todd Smith
Masters of Science Aerospace Engineering 1990

[Andy[_1_]]

On Apr 16, 1:18*pm, toad > wrote:

> If you are going to berate people for their own incorrect knowledge,
> you should be able to improve on that knowledge.
>


The only flight theory that most pilots need to know is that sustained
flight requires a continuous supply of money.

It is easy to prove that when the supply of money is exhausted flight
is no longer possible.

Andy

[Eric Greenwell]

toad wrote:

> The original posters slides look like a pretty good explanation. I
> think that it is more information than a pilot really needs, but
> some people won't relax and actually learn until they think they
> understand "why" it works.

That's probably the best reason I've heard for teaching pilots about
aerodynamics.

Despite my deep interest in aerodynamics, my observation and experience
is knowing the aerodynamics doesn't seem to be an asset to flying
correctly, and that it is really all about keeping the airspeed up and
horizon in the correct place on the canopy. When I fly, thoughts of AOA
and pressure distributions are not flitting through my mind, and things
happen too fast to be deriving your next action from first principles.

You definitely want the designer of your glider to understand
aerodynamics, but the pilot - completely optional!

--

Eric Greenwell - Washington State, USA (netto to net to email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz

[brianDG303[_2_]]

On Apr 16, 4:17*pm, Eric Greenwell > wrote:
> toad wrote:
> > *The original posters slides look like a pretty good explanation. I
> > *think that it is more information than a pilot really needs, but
> > *some people won't relax and actually learn until they think they
> > *understand "why" it works.
>
> That's probably the best reason I've heard for teaching pilots about
> aerodynamics.
>
> Despite my deep interest in aerodynamics, my observation and experience
> is knowing the aerodynamics doesn't seem to be an asset to flying
> correctly, and that it is really all about keeping the airspeed up and
> horizon in the correct place on the canopy. When I fly, thoughts of AOA
> and pressure distributions are not flitting through my mind, and things
> happen too fast to be deriving your next action from first principles.
>
> You definitely want the designer of your glider to understand
> aerodynamics, but the pilot - completely optional!
>
> --
>
> Eric Greenwell - Washington State, USA (netto to net to email me)
>
> - "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarmhttp://tinyurl.com/yb3xywl
>
> - "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
> you need to know tinyurl.com/yfs7tnz


I found the following website to be somewhat easy to understand and
extremely interesting, especially the last 1/2. The videos of lift and
pressure on a wing also good.

http://knol.google.com/k/why-it-is-possible-to-fly#

Brian

[toad]

On Apr 17, 10:14*am, brianDG303 > wrote:
>
> I found the following website to be somewhat easy to understand and
> extremely interesting, especially the last 1/2. The videos of lift and
> pressure on a wing also good.
>
> http://knol.google.com/k/why-it-is-possible-to-fly#
>
> Brian

If that website is easy to understand, I'm stupid. I'll spend more
time researching their topic, but from a quick scan it looks pretty
confusing.

Todd

[brianDG303[_2_]]

On Apr 17, 8:16*am, toad > wrote:
> On Apr 17, 10:14*am, brianDG303 > wrote:
>
>
>
> > I found the following website to be somewhat easy to understand and
> > extremely interesting, especially the last 1/2. The videos of lift and
> > pressure on a wing also good.
>
> >http://knol.google.com/k/why-it-is-possible-to-fly#
>
> > Brian
>
> If that website is easy to understand, I'm stupid. *I'll spend more
> time researching their topic, but from a quick scan it looks pretty
> confusing.
>
> Todd

Todd,
I was pretty confused by much of what was posted but started to get a
clue when I researched the whole Kutta Condition thing, which was from
your post. THAT made sense to me, and led to the site I referred to
which starts off disorganized but gets better I think, anyway it
worked for me so I posted it. Perhaps my sense of understanding is
just a more complex form of confusion. Anyway the movies of lift on an
airfoil at different airflow speeds are pretty.

Brian

[Brian Whatcott]

brianDG303 wrote:
> On Apr 16, 4:17 pm, Eric Greenwell > wrote:
>> toad wrote:
>>> The original posters slides look like a pretty good explanation. I
>>> think that it is more information than a pilot really needs, but
>>> some people won't relax and actually learn until they think they
>>> understand "why" it works. /snip/
>> You definitely want the designer of your glider to understand
>> aerodynamics, but the pilot - completely optional!
>>
>> Eric Greenwell - Washington State, USA (netto to net to email me)

>
> I found the following website to be somewhat easy to understand and
> extremely interesting, especially the last 1/2. The videos of lift and
> pressure on a wing also good.
>
> http://knol.google.com/k/why-it-is-possible-to-fly#
>
> Brian


I read this URL with interest.
While it is not a laughable piece about "I'm a physicist so I must be
right", it does suggest that they have their explanation right, and
everyone; Newton, Kutta, Bernouli, Uncle Tom Cobley an' all, have it
wrong. In a word, they exaggerate the value of their approach.
Still, it is interesting and helpful, in my view.

Brian W

[Martin Gregorie[_5_]]

On Sat, 17 Apr 2010 09:18:41 -0700, brianDG303 wrote:

> On Apr 17, 8:16Â*am, toad > wrote:
>> On Apr 17, 10:14Â*am, brianDG303 > wrote:
>>
>>
>>
>> > I found the following website to be somewhat easy to understand and
>> > extremely interesting, especially the last 1/2. The videos of lift
>> > and pressure on a wing also good.
>>
>> >http://knol.google.com/k/why-it-is-possible-to-fly#
>>
>> > Brian
>>
>> If that website is easy to understand, I'm stupid. Â*I'll spend more
>> time researching their topic, but from a quick scan it looks pretty
>> confusing.
>>
>> Todd
>
> Todd,
> I was pretty confused by much of what was posted but started to get a
> clue when I researched the whole Kutta Condition thing, which was from
> your post. THAT made sense to me, and led to the site I referred to
> which starts off disorganized but gets better I think, anyway it worked
> for me so I posted it. Perhaps my sense of understanding is just a more
> complex form of confusion. Anyway the movies of lift on an airfoil at
> different airflow speeds are pretty.
>
> Brian

http://www.av8n.com/ is a good, no-nonsense source.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[toad]

On Apr 17, 5:51*pm, Martin Gregorie >
wrote:
>
> http://www.av8n.com/is a good, no-nonsense source.
>
> --
> martin@ * | Martin Gregorie
> gregorie. | Essex, UK
> org * * * |

That's my favorite. Thanks for posting. I had lost the link.

Todd

[Alex Potter]

On Fri, 16 Apr 2010 14:32:58 -0700, Andy wrote:

> The only flight theory that most pilots need to know is that sustained
> flight requires a continuous supply of money.

How true...

Is that yours? or did you borrow it?

--
Alex