This is way off the topic of FS98 and I'm sorry you all had to read this it
just struck me as funny! I'll probably get flamed. If you do be gentle my
feelings get hurt easy.
Kind Regards, Michael
>Oh ..... pfffttt! Another vacuous comment, always from the nameless
>ones. Kids !!
>Dear Mr 727-jerkoff-pilot, there are more informed simmers posting here,
>with far more enthusiasm and real interest in learning the real nuts and
>bolts, Basic Aeronautical Knowledge and Principles of Flight than many
>students or fellow pilots I've known with in the last twenty years. Do
>not be afraid to actually do a bit of learning yourself.
>The unfortunate fact of the matter it is that many enthusiasts posting
>herein or just simming along solo and unaware of this forum may never
>have the resources or opportunities to follow their passion through into
>real life. Hands-on flight and theory training is something many would
>obviously attack with great passion, zeal and discipline, and I hope
>like hell most manage it because the rewards are huge (in a personal
>sense, that is). Those simmers with those qualities and real passion
>will likely do whatever it takes to realise that goal.
>Mr 727-jerkoff-pilot, I'll even bet you there's many a copy of
>"Aerodynamics for Naval Aviators" (pretty dry reading) on the
>bookshelves of more deskbound simmers than there are in licensed pilot's
>bookshelves. That book is a definitive read if you really want to
>wrestle aerodynamic theory.
>'What flaps do' was funny even if not so intended. That thread was
>interesting but for the most part it was hot air. I think the average
>balloonist could have used all that heat.
>747-400 Precision Simulator pilot
>WOD ndb 20d west of EGLL on Airway G1, United Kingdom
The Bernoulli effect is more like the result of how a wing works, notQuote:> The force, "lift" is derived from an airfoil through a principle often
> referred to as Bernoulli's Principle. As air flows over the upper surface of
> an "airfoil", the curvature of the airfoil causes an increase in the speed
> of the airflow. The increased speed of airflow results in a decrease in
> pressure on the upper surface of the airfoil. At the same time, airflow
> strikes the lower surface of the airfoil at an angle, building up pressure.
Air moving across a wing will tend to follow the contour of the wing
(if the flow is laminar). As it's accelerated downwards, the air's
to this acceleration (momemtum) will result in a lower pressure above a
and somewhat higher pressure below (most of the lift in a wing is due to
pressure above the wing). The surrounding normal pressure air will
towards the lower pressure area above the wing, from every direction
because the wing blocks this flow path, resulting in a net downwash
is flowing in all directions but "up", and also in lift on the wing
since it's preventing the higher pressure air from below from flowing to
the lower pressure
above (pressure differential). So basically lift, corresponds with
The low pressure area above the wing also causes the air to accelerate
a fairly high speed as it flows over a wing. I've read that the air flow
wing can be actually moving backwards faster than the forward air speed
wing (at the leading edge this makes sense, not sure about the effects
the trailing edge, where is the trailing edge boundary of the lower
area...) I've also read that this increased air flow speed due to the
lower pressure area above a wing also complies with Bernoulli's
but as the effect, not the cause.
>>Bet you can't get one to fly without an engine - and I'm not talking about
>>gliding down from 10,000 feet :-)
>>747-400 Precision Simulator pilot
>>WOD ndb 20d west of EGLL on Airway G1, United Kingdom
Bernoulli is indeed an effect not a cause. The reason
that the air is going faster is that it went down a pressure
gradient; it isn't that the pressure drops when the air
goes faster. If this canard were true, you would have
to pick out what coordinate system to measure speed in,
and you could get any pressure you wanted by changing
the names of pieces of air.
The principle is that the sum of the pressure head and
the velocity head are constant in steady state flow
along a streamline. So if the velocity is less the
pressure is more, but the reason that the
air accelerates up and down preexisting pressure gradients.
It would be like saying that the valleys are caused by
bicycles going faster and hills by bicycles going slower, so
the way to get a better view is to slow down bicycles.
The art of designing a wing is to throw air downwards without
throwing it much forwards, and the wing is an efficient design
to do that, while for example a flat plate is not.
On the internet, nobody knows you're a jerk.
I have been tempted to jump into these threads before! I will try andQuote:
>The Bernoulli effect is more like the result of how a wing works, not
>the cause. Ultimately, Newtonian physics apply, lift from a wing
>to downwash of air, or force equals mass times acceleration, in this
>the force (lift) is equal to the amount of air mass moved downwards, and
>the rate of acceleration.
Bernoulli is not a result of how a wing works it is a part of it.
If Bernoullis' 'laws' were changed then lift would be changed! It is
true that lift will not be generated on a finite wing unless the air is
deflected dowmwards but the amount of deflection wand the pressure
distribution on the wing would not be the same.
We meet again! You cannot say that Bernoulli is an effect not a cause.Quote:>Somebody else replied first!
>Bernoulli is indeed an effect not a cause. The reason
>that the air is going faster is that it went down a pressure
>gradient; it isn't that the pressure drops when the air
>goes faster. If this canard were true, you would have
>to pick out what coordinate system to measure speed in,
>and you could get any pressure you wanted by changing
>the names of pieces of air.
True that is a fair statement.Quote:>The principle is that the sum of the pressure head and
>the velocity head are constant in steady state flow
>along a streamline.
You lost me again! Potential flow theory by itself leads to zero lift,Quote:> So if the velocity is less the
>pressure is more, but the reason that the
>air accelerates up and down preexisting pressure gradients.
So viscosity changes the flow and results in circulation which causes
the air to be deflected around the aerofoil. In an infinite span wing
the air would not be deflected. (Because if the wing is infinite, finite
lift can be developed with no deflection.)
Exactly what would be like saying that?Quote:>It would be like saying that the valleys are caused by
>bicycles going faster and hills by bicycles going slower, so
>the way to get a better view is to slow down bicycles.
OK I'll accept that one but please come into line with the rest of theQuote:>The art of designing a wing is to throw air downwards without
>throwing it much forwards, and the wing is an efficient design
>to do that, while for example a flat plate is not.
> Exactly what would be like saying that?
The sum of potential energy and kinetic energy is constant
for the bicycle (let's say). The sum of pressure head and
velocity head is constant for a piece of air.
That is, the air speeds up as it moves from high pressure to
low pressure, and slows down again when it moves from low
pressure to high pressure, ``running down and up'' the pressure
This is the sense that faster moving air goes with lower pressure,
the same way that faster moving bicycles go with valleys.
Yet faster moving bicycles do not cause valleys!
On the internet, nobody knows you're a jerk.
>> Exactly what would be like saying that?
>Height = pressure, velocity = velocity.
>The sum of potential energy and kinetic energy is constant
>for the bicycle (let's say). The sum of pressure head and
>velocity head is constant for a piece of air.
>That is, the air speeds up as it moves from high pressure to
>low pressure, and slows down again when it moves from low
>pressure to high pressure, ``running down and up'' the pressure
>This is the sense that faster moving air goes with lower pressure,
>the same way that faster moving bicycles go with valleys.
>Yet faster moving bicycles do not cause valleys!
However since you _seem_ to agree that Bernoulli operates within
streamlines (this applies only outside the boundary layer because within
the boundary layer energy is lost to heat) then how do the streamlines
get to be the shape they are?
The pressure and velocity between the streamlines depends on the shape
of the streamlines does it not? So the question is not just whether the
_bicycle_ changes the hills but what does change the shape of the hills?
You are not I take it saying that the shape and position of streamlines
is always the same? So in a way yes, the air itself and its properties
is interconnected with the streamlines and your bicycle does interact
with the hills! :-)
Notice that I am saying 'between' streamlines and not along them. You
can say nothing about the changes of pressure and velocity if all you
have is a single streamline.
Can you calculate the shape of the streamline field by using only your
All these arguments that give the idea that there is a basic reason for
lift and that all the other physical phenomena are a consequence of that
do, in my opinion, no good service to the advancement of understanding.
There are a number of factors that are connected with lift and they are
all interconnected with one another in the actual physical world that we
inhabit. They do not exist in isolation.
Some of them are:
1 The shape and surface of the aircraft.
2. The gas equations.
3. The velocity with which the aircraft is moving.
4. The Mach number at which is is flying.
5. The density of the air.
6. The viscosity of the air.
7. The laws of statics and dynamics.
8. Conservation of momentum.
8. The Conservation of energy.
9. Bernoulli's Law.
10. Mechanical equivalent of heat.
11. Reynolds Number.
13. Vortex flow.
14. The flexibility of the aircraft structure.
and probably others that I have missed.
These are are all interconnected, some can be deduced from some of the
others. None of them are _wrong_. Starting from knowledge of different
parameters there are various ways of showing that the laws of physics
are obeyed and of carrying out simple calculations that relate to lift.
All of the 'laws' are useful in calculating and predicting the result of
of various physical circumstances.
One thing is certain and that is that lift must appear as pressure
changes and shear forces on the surface of the aircraft. Unless anyone
can think how else the forces can be transferred to the aircraft?
In supersonic flow the balance of forces and theories is different but
the same theories and parameters are involved.
The thing is that there is no physical intuition for pressure
and there is physical intuition for throwing air downwards.
So for what you can use throwing air downwards for (eg. calculating
induced drag in your head) it is the superior method. It doesn't
give you the airflow field but the wonderful thing is that you
don't need it to figure out induced drag. The interrelation of
all the laws you listed has an interesting property, that one
law (well, two laws, conservation of momentum and conservation
of energy) is sufficient to tell you what the induced drag is.
The gas equations must obey this constraint.
The aircraft throws air downwards, is how momentum is transferred to
it. If you throw stones downwards, you don't speak of pressure
as doing its work on you. Why does it change with air? It's
just throwing away a physical intuition that's perfectly good
in favor of a bit of mathematics that you can't do in your head.
Pressure doesn't even show up in the laws of incompressible flow
except as an artifact. That is, you can compute the full dynamical
velocity of the fluid without ever figuring out the pressure.
On the internet, nobody knows you're a jerk.
It seems to me that a wing "disturbs" the air, and Bernoulli'sQuote:> 9. Bernoulli's Law.
How is Bernoulli's law applied to wings? Is the airflow
relative to the wing or to the surrounding air? The
low pressure area above a wing exists, regardless of
what reference point (the wing or the still air that the
wing is passing through), the surrounding normal
pressure air accelerates towards this low pressure
area (except it can't flow through the wing itself resulting
in downwash), again independent of the frame of reference.
In my opinion, the frame of reference shouldn't matter in
explaining how a wing generates lift.
Relative to the surrounding still air, it's the flow above
the wing that's moving more slowly, and the flow below
that's moving quicker (closer to the wings speed).
In this case, it's the slower moving (relative to the
surrounding still air) air that has the lower pressure.
It's a lot easier to think of a wing as an "air pump",
as the air follows the contour of a wing, the wing deflects
the air downwards, mostly by "sucking" the air from above,
and a little by "pushing" from below.
Just to stir things up even more, consider how downforce
is created underneath a car. Which frame of reference do
you use to measure the speed of air flow in this case, the
road or the underbody of the car? Note that two "opposite"
approaches are both succesfully used. Cars like the McLaren
F1 channel air (horizontally) to increase air flow relative
to the car, and Nascar cars use air dams up front to to
reduce (prevent) air flow underneath and relative to the car
(along with spoilers above the trunk for downforce at the rear).
The F1 uses the "Bernoulli" effect (partially, see below), and
the Nascars simply create a "void" (lower pressure area) behind
the air dam since the dam is litterally accelerating the
surronding still air from 0 to about 200mph, higher pressure
in front of the air dam, lower behind, all due to the air's
resistance (momentum) to the accleration by the air dam.
The channeling of air in an F1 also creates a "void"
in the areas outside of the channel, so this channel
also has some "air dam" properties. The F1 also
cheats by using "exhaust" fans on it's channel, but
other cars succefully use underbody channeling without
Hi to all,
I'm a roboticist thinking of competition events for a robotic version of
an indoor flying airplane. The envisioned robotic indoor flyer I'm
designing would fly, takeoff, land and detect walls/ceilings/obstacles
using several sensors (infrared LEDs, ultrasonic sensors and perhaps
That said, I want to design a competition event to showcase what such a
flying robot could do. The event should challenge teams to do test and
design sensor-based algorithms, but be easy enough that some teams can
A Google Search for "Indoor Flying Competitions" didn't provide much help.
By reading about existing conventional competitions, I hoped to get good
ideas (beyond pylon races).
Some ideas for robotic indoor flyers I thought of are:
2. Roundtrip flight from one office room to another
3. Perch-and-stare: takeoff and land on an elevated stage and
Your thoughts/leads for a competition events are much appreciated,
- Paul Oh
4. error type 1