A Level 1 AOA clarification

[Ramapriya]

If my understanding is correct, an aircraft stalls beyond that AOA
which, when increased any further, produces no (further) lift. If
correct, would it be logical to infer that an aircraft's stalling AOA:

a. is dependent on its airspeed, and is independent of its weight and
weight distribution, and
b. varies, for a given airspeed, with the air density (altitude)

I know these are way elementary, but please help out.
Cheers,

Ramapriya

[Paul Tomblin]

In a previous article, "Ramapriya" > said:
>If my understanding is correct, an aircraft stalls beyond that AOA
>which, when increased any further, produces no (further) lift. If
>correct, would it be logical to infer that an aircraft's stalling AOA:
>
>a. is dependent on its airspeed, and is independent of its weight and
>weight distribution, and

Close. The AOA required to maintain altitude at a given airspeed varies
with the aircraft's weight, so a more heavily loaded aircraft will reach
the stalling AOA at a lower speed than a more lightly loaded one.

Also, the tail produces a downforce which is used to maintain stability in
the plane. If you load the CG further forward, the downforce needs to be
greater to counter balance it fore and aft, so you need more upforce from
the wings as well to put the up and down forces in balance, so that
increases the AOA required to maintain lift.

There are good diagrams of this in any decent aviation text book.

--
Paul Tomblin > http://xcski.com/blogs/pt/
"GNU is not Linux - Linux has a kernel that boots" - Chris Thompson

[Andrew Sarangan]

"Ramapriya" > wrote in news:1104029481.765015.34960
@c13g2000cwb.googlegroups.com:

> If my understanding is correct, an aircraft stalls beyond that AOA
> which, when increased any further, produces no (further) lift. If
> correct, would it be logical to infer that an aircraft's stalling AOA:
>
> a. is dependent on its airspeed, and is independent of its weight and
> weight distribution, and

No, the stall AOA is independent of both airspeed and weight.


> b. varies, for a given airspeed, with the air density (altitude)
>

No the stall AOA does not vary with density.


The stall AOA is determined by the shape of the wing. It is independent of
weight and airspeed. However, the airspeed vs AOA relationship depends on a
variety of factors, such as weight and density. This is why stall speed is
somewhat a misleading quantity. AOA would be a better quantity.
Unfortunately there is no direct way to measure the AOA in most aircraft,
so we use the airspeed as an indirect indication of the AOA.

[Ramapriya]

Andrew Sarangan wrote:

> > a. is dependent on its airspeed, and is independent of its weight
and
> > weight distribution, and
>
> No, the stall AOA is independent of both airspeed and weight.

Too confusing :(

Getting back to basics, wings produce lift only when wind hits them,
i.e. when the aircraft starts moving. This keeps increasing until the
airspeed is adequate enough to produce a total lift that can levitate
the aircraft. Since the angle of the wings can't be varied, ignoring
flaps momentarily, I can't see how the stall AOA can be independent of
airspeed. What then is 'stall speed' of an airplane?

If stalling AOA is reached, adding engine power before the plane goes
into a stall will prevent the stall by increasing airspeed, right?

> > b. varies, for a given airspeed, with the air density (altitude)
>
> No the stall AOA does not vary with density.
>
> The stall AOA is determined by the shape of the wing. It is
independent of
> weight and airspeed. However, the airspeed vs AOA relationship
depends on a
> variety of factors, such as weight and density. This is why stall
speed is
> somewhat a misleading quantity. AOA would be a better quantity.
> Unfortunately there is no direct way to measure the AOA in most
aircraft,
> so we use the airspeed as an indirect indication of the AOA.

Don't know much yet about this but I'm sure I saw the AOA indicated in
an A320 cockpit recently. I thought the pitch itself indicated AOA but
when the captain showed me the actual AOA reading, it varied by a wee
from the aircraft's pitch. He had to punch some buttons into the flight
computer to get the AOA reading.

Need to read up John Denker's book and the FAA material a lotttt more,
I guess :\

Ramapriya

[Ramapriya]

Andrew Sarangan wrote:

> > a. is dependent on its airspeed, and is independent of its weight
and
> > weight distribution, and
>
> No, the stall AOA is independent of both airspeed and weight.

Too confusing :(

Getting back to basics, wings produce lift only when wind hits them,
i.e. when the aircraft starts moving. This keeps increasing until the
airspeed is adequate enough to produce a total lift that can levitate
the aircraft. Since the angle of the wings can't be varied, ignoring
flaps momentarily, I can't see how the stall AOA can be independent of
airspeed. What then is 'stall speed' of an airplane?

If stalling AOA is reached, adding engine power before the plane goes
into a stall will prevent the stall by increasing airspeed, right?

> > b. varies, for a given airspeed, with the air density (altitude)
>
> No the stall AOA does not vary with density.
>
> The stall AOA is determined by the shape of the wing. It is
independent of
> weight and airspeed. However, the airspeed vs AOA relationship
depends on a
> variety of factors, such as weight and density. This is why stall
speed is
> somewhat a misleading quantity. AOA would be a better quantity.
> Unfortunately there is no direct way to measure the AOA in most
aircraft,
> so we use the airspeed as an indirect indication of the AOA.

Don't know much yet about this but I'm sure I saw the AOA indicated in
an A320 cockpit recently. I thought the pitch itself indicated AOA but
when the captain showed me the actual AOA reading, it varied by a wee
from the aircraft's pitch. He had to punch some buttons into the flight
computer to get the AOA reading.

Need to read up John Denker's book and the FAA material a lotttt more,
I guess :\

Ramapriya

[G.R. Patterson III]

Ramapriya wrote:
>
> Andrew Sarangan wrote:
>
> > > a. is dependent on its airspeed, and is independent of its weight
> and
> > > weight distribution, and
> >
> > No, the stall AOA is independent of both airspeed and weight.
>
> Too confusing :(

I'll try to simplify it a bit. An angle of attack is the angle at which the wing
"attacks" the air. If the air is relatively stable and you raise the nose, you
have just increased the angle of attack. Lower the nose, the angle decreases.

Ok so far?

Now. The stall angle of attack is the angle at which the airflow over the wing
won't follow the curve of the wing anymore. The wing is tilted up too steeply
relative to the airflow. If I undrestand him correctly, Andrew is stating that
the angle of attack at which this occurs is the same regardless of airspeed. I
believe he is incorrect in this - definitely my aircraft will stall at a much
lower angle of attack at 50 mph than at 60 mph, and I've never been brave enough
to get the nose high enough to stall it at higher airspeeds.

Now, there *is* a misconception that stall airspeeds are constant, and this is
not true. The way the truth is usually phrased is "an airplane can stall at any
speed." You can exceed the stall angle of attack while flying perfectly level at
a pretty fair speed if you fly into a wind that is blowing up a steep slope.
There are also "high-speed" stalls caused by attempting to maneuver too rapidly
at high speed.

The true airspeed at which a stall occurs also increases with density altitude.
This is not usually a factor for light aircraft, since the indicated airspeed
for a given true airspeed decreases at the same rate. In other words, if your
plane has a pitot tube and stalls at 60 knots indicated, it will stall in that
configuration at that speed at any altitude it can reach. If the aircraft is
equipped with an indicator that reports true airspeed, however, stall speed is
not constant.

I do not know whether or not the stall angle of attack changes with weight, but
the stall airspeed in any configuration increases as weight increases. Paul's
points on the effects of loading and the downforce produced by the tail surfaces
are also good.

George Patterson
The desire for safety stands against every great and noble enterprise.

[Radio Flyer]

"Ramapriya" > wrote in message
ups.com...

Depending on what kind of plane you are flying, you may get good use out of
your shoulder harness if you add power just before or during a stall. While
you probably could delay the stall by adding power, it will eventually
happen if you do not lower your attitude. In most cases, that is.
> Don't know much yet about this but I'm sure I saw the AOA indicated in
> an A320 cockpit recently. I thought the pitch itself indicated AOA but
> when the captain showed me the actual AOA reading, it varied by a wee
> from the aircraft's pitch. He had to punch some buttons into the flight
> computer to get the AOA reading.

That is because the aoa depends on the relative wind. The relative really
does not have much to do with where the ground is, or what your attitude is.


>
> Need to read up John Denker's book and the FAA material a lotttt more,
> I guess :\
>
> Ramapriya
>
>

[Peter Duniho]

"G.R. Patterson III" > wrote in message
...
> I'll try to simplify it a bit. An angle of attack is the angle at which
> the wing
> "attacks" the air. If the air is relatively stable and you raise the nose,
> you
> have just increased the angle of attack. Lower the nose, the angle
> decreases.

To elaborate a bit: Ramapriya's assertion that "the angle of the wings can't
be varied" is incorrect. The angle of the wings can be and is varied, by
using the elevator control to adjust the pitch attitude of the aircraft, and
thus of the wings.

This is what George means by "raise the nose".

> [...] If I undrestand him correctly, Andrew is stating that
> the angle of attack at which this occurs is the same regardless of
> airspeed. I
> believe he is incorrect in this - definitely my aircraft will stall at a
> much
> lower angle of attack at 50 mph than at 60 mph

You understand Andrew correctly, but not stalling.

Since you mention stalling at two different airspeeds, let's look at those
as examples. Let's assume that at the lower airspeed, you are stall in
unaccelerated flight. There are two ways to stall the airplane at a higher
airspeed then: one is to pull hard on the yoke to increase loading and pitch
attitude to stall before the airplane slows further; the other is to have
the flaps out at the slower airspeed, but not the higher.

In the first case, the pitch attitude appears higher, but the angle of
attack is the same. The airplane, because of the higher pitch angle, is
accelerating upward, which changes the direction of the relative wind
somewhat downward, making a given angle of attack occur at a higher pitch
angle.

In the second case, the pitch attitude appears higher, but the angle of
attack is the same (sound familiar? :) ). When the flaps are extended, the
effective chord of the wing changes, essentially pitching the wing upward
and increasing angle of attack. This increases the angle of incidence of
the wing (the angle between the wing chord and the fuselage), causing a
given angle of attack to occur at a lower pitch angle, compared to a
no-flaps stall (at a higher airspeed).

The flaps might also change the stalling angle of attack subtly, but a) most
of the perceived change in angle of attack comes from the change in
effective angle of incidence, and b) the change in AOA in that case is due
to the change in shape of the wing, not the change in airspeed.

> [...]
> Now, there *is* a misconception that stall airspeeds are constant, and
> this is
> not true. The way the truth is usually phrased is "an airplane can stall
> at any
> speed."

You forgot the other half of that: an airplane can stall at any attitude.
Pilots often mistake pitch angle relative to the ground for angle of attack.
In level, 1-G flight this is the case. But you can exceed the critical
angle of attack with the nose pointed down (pulling out from a high-speed
dive for example), and you can have the nose pointed quite high (during a
climb in a high performance airplane, especially at lower weights), without
exceeding the critical angle of attack.

> [...]
> I do not know whether or not the stall angle of attack changes with
> weight, but
> the stall airspeed in any configuration increases as weight increases.

Weight does not affect the stalling angle of attack.

Pete

[Peter Duniho]

"Ramapriya" > wrote in message
ups.com...
> Getting back to basics, wings produce lift only when wind hits them,
> i.e. when the aircraft starts moving. This keeps increasing until the
> airspeed is adequate enough to produce a total lift that can levitate
> the aircraft. Since the angle of the wings can't be varied,

See my reply to George. The angle of the wings CAN be varied, and doing so
is essential to the art of flying.

> ignoring
> flaps momentarily, I can't see how the stall AOA can be independent of
> airspeed. What then is 'stall speed' of an airplane?

The stall speed of an airplane is the airspeed at which the airplane will
stall, assuming straight and level unaccelerated flight. Any published
stall speed is actually specific to a certain weight (most popular stall
speeds to know are for maximum weight), and for a specific configuration
(for example, gear and flap extension both can change stall
speed...especially flaps).

> If stalling AOA is reached, adding engine power before the plane goes
> into a stall will prevent the stall by increasing airspeed, right?

Sort of. By the time you are down to stall speed, what additional engine
power actually does is to allow you to fly at *lower* airspeeds. However,
yes...commonly when one is near stalling and doesn't want to be, increasing
engine power is one part of the recovery. If not combined with a reduction
in pitch attitude, all that more power will do (assuming everything else is
held constant) is to cause the airplane to climb.

Pete

[Ramapriya]

Peter Duniho wrote:
> "G.R. Patterson III" > wrote in message
> ...
>
> To elaborate a bit: Ramapriya's assertion that "the angle of the
wings can't
> be varied" is incorrect. The angle of the wings can be and is
varied, by
> using the elevator control to adjust the pitch attitude of the
aircraft, and
> thus of the wings.

My bad. What I intended saying was that the wings on their own can't be
tilted about, barring use of flaps; they're after all rigid structures.
Cheers,

Ramapriya

[Andrew Sarangan]

"Ramapriya" > wrote in
ups.com:

> Andrew Sarangan wrote:
>
>> > a. is dependent on its airspeed, and is independent of its weight
> and
>> > weight distribution, and
>>
>> No, the stall AOA is independent of both airspeed and weight.
>
> Too confusing :(
>
> Getting back to basics, wings produce lift only when wind hits them,
> i.e. when the aircraft starts moving. This keeps increasing until the
> airspeed is adequate enough to produce a total lift that can levitate
> the aircraft. Since the angle of the wings can't be varied, ignoring
> flaps momentarily, I can't see how the stall AOA can be independent of
> airspeed. What then is 'stall speed' of an airplane?

I see where you are getting the misconceptions from. You are thinking of
the takeoff and landing as the start and end of flight. Just because an
aircraft is on the ground does not mean it is stalled. Instead, picture
an aircraft in mid flight. Then imagine what happens if you increase the
angle of attack. The airflow over the wings will start to break up. This
is the start of stall.This point is only related to the angle at which
the airstream strikes the wing.

Think of the AOA as the difference between the angle where the aircraft
is pointing and where it is going.



>
> If stalling AOA is reached, adding engine power before the plane goes
> into a stall will prevent the stall by increasing airspeed, right?
>
>> > b. varies, for a given airspeed, with the air density (altitude)
>>
>> No the stall AOA does not vary with density.
>>
>> The stall AOA is determined by the shape of the wing. It is
> independent of
>> weight and airspeed. However, the airspeed vs AOA relationship
> depends on a
>> variety of factors, such as weight and density. This is why stall
> speed is
>> somewhat a misleading quantity. AOA would be a better quantity.
>> Unfortunately there is no direct way to measure the AOA in most
> aircraft,
>> so we use the airspeed as an indirect indication of the AOA.
>
> Don't know much yet about this but I'm sure I saw the AOA indicated in
> an A320 cockpit recently. I thought the pitch itself indicated AOA but
> when the captain showed me the actual AOA reading, it varied by a wee
> from the aircraft's pitch. He had to punch some buttons into the
> flight computer to get the AOA reading.

True, some of the larger aircraft and military jets have an AOA
indicator. Most small aircraft do not have an AOA indicator. There is a
good reason for this. In a large aircraft, the weight can vary
substantially over its flight envelope. This will result in a large
variation in stall speed. In a small aircraft, the stall speed variation
is rather small, and a single stall speed can be used safely.




>
> Need to read up John Denker's book and the FAA material a lotttt more,
> I guess :\
>

No, you need to take a couple of flying lessons.

[Hilton]

Andrew Sarangan wrote:
> True, some of the larger aircraft and military jets have an AOA
> indicator. Most small aircraft do not have an AOA indicator. There is a
> good reason for this. In a large aircraft, the weight can vary
> substantially over its flight envelope. This will result in a large
> variation in stall speed. In a small aircraft, the stall speed variation
> is rather small, and a single stall speed can be used safely.

IMHO, there is no good reason for not having an AOA indicator on GA
aircraft. Stall/spin is a leading cause of death among GA pilots and
passengers. Best glide (potential emergency situation) is determined by
AOA. Put an AOA sensor on GA planes with a hand that smacks the pilot on
the head when the AOA approaches the critical AOA and a lot fewer people
will die while having fun on the weekends.

Hilton

[tom418]

"Hilton" > wrote in message
link.net...
> Andrew Sarangan wrote:
> > True, some of the larger aircraft and military jets have an AOA
> > indicator. Most small aircraft do not have an AOA indicator. There is a
> > good reason for this. In a large aircraft, the weight can vary
> > substantially over its flight envelope. This will result in a large
> > variation in stall speed. In a small aircraft, the stall speed variation
> > is rather small, and a single stall speed can be used safely.
>
> IMHO, there is no good reason for not having an AOA indicator on GA
> aircraft. Stall/spin is a leading cause of death among GA pilots and
> passengers. Best glide (potential emergency situation) is determined by
> AOA. Put an AOA sensor on GA planes with a hand that smacks the pilot on
> the head when the AOA approaches the critical AOA and a lot fewer people
> will die while having fun on the weekends.
>
> Hilton
>
>
The April, 1973 (yeah, that's a while ago) issue of FLYING had a great
article about Safe Flight's AOA indicator. Peter Garrison described it as
"phenomenally useful", after flying a Beech Sierra equipped with one.

[Greg Esres]

<<Stall/spin is a leading cause of death among GA pilots and
passengers. >>

Caused by the pilot not paying attention. Will having another
instrument that he's not paying attention to really help?

<<Best glide (potential emergency situation) is determined by AOA. >>

A few knots either way isn't going to make much difference. Plus, how
often is maximum glide range critical in an engine out situation? How
closely is the pilot really maintaining one airspeed (or AOA) during
an emergency?

<<Put an AOA sensor on GA planes with a hand that smacks the pilot on
the head >>

Some studies I've seen have shown that pilots are often oblivious to
warning horns and lights, though stick shakers are effective.

My prediction: put an AOA indicator on every airplane in the fleet
and you won't see much change in the accident rate due to stall spin.

[G.R. Patterson III]

Peter Duniho wrote:
>
> You understand Andrew correctly, but not stalling.

Well, yes I do, but not that late at night or with that much "Christmas cheer",
obviously.

Rama, in my post, I forgot that at a higher airspeed, the plane is likely to be
climbing, therefore the relative wind will be coming from above. You will reach
the same angle of attack at a steeper pitch angle at higher airspeeds.

George Patterson
The desire for safety stands against every great and noble enterprise.

[Peter Duniho]

"Ramapriya" > wrote in message
oups.com...
> My bad. What I intended saying was that the wings on their own can't be
> tilted about, barring use of flaps; they're after all rigid structures.

Even without the use of flaps, you can change the angle of the wings.
That's what the elevator control does.

[CV]

Ramapriya wrote:

> If my understanding is correct, an aircraft stalls beyond that AOA
> which, when increased any further, produces no (further) lift. If

A _wing_ (not an aircraft) is considered stalled whenever the
AOA is greater than the AOA of maximum lift. Beyond that point an
increase in AOA produces less lift, not more. There is still _some_
lift being produced, all the way up to 90 degrees AOA.

(If this was what you meant with "no (further) lift" then you
have the general idea right)

> correct, would it be logical to infer that an aircraft's stalling AOA:

The stalling AOA of a _wing_, not of an aircraft. When an aircraft
stalls the AOA will of course be somewhere close to the stalling AOA
of the wing, but they are still different concepts.

> a. is dependent on its airspeed, and is independent of its weight and
> weight distribution, and
> b. varies, for a given airspeed, with the air density (altitude)

The stalling AOA of the _wing_ is generally constant, typically
around 15 degrees, and does not depend on any of those factors.

The _speed_ at which the _aircraft_ stalls does depend on factors
like weight, but the stall will still happen at an AOA somewhere
close to the stalling AOA of the wing.
CV

[CV]

Peter Duniho wrote:

> "Ramapriya" > wrote in message
>>If stalling AOA is reached, adding engine power before the plane goes
>>into a stall will prevent the stall by increasing airspeed, right?

By reducing the AOA actually, which happens as a consequence of
increasing airspeed. But see below also.

> Sort of. By the time you are down to stall speed, what additional engine
> power actually does is to allow you to fly at *lower* airspeeds. However,

And it is interesting how that actually happens. The vertical component
of thrust takes a bit of the load off the wings which helps reduce the
AOA and keep it under the limit of the stall. Part of the weight is
in fact hanging by the propeller, like a helicopter.
CV

[Andrew Sarangan]

I agree that AOA is a nice instrument to have, but I am not convinced if
that is going to reduce the number of stall spin accidents. Most stall spin
accidents despite all stall indications, such as low airspeed, buffet and
descent rate. Having another instrument on the panel is not going to change
the situation.



"Hilton" > wrote in news:5_Azd.10136$9j5.3520
@newsread3.news.pas.earthlink.net:

> Andrew Sarangan wrote:
>> True, some of the larger aircraft and military jets have an AOA
>> indicator. Most small aircraft do not have an AOA indicator. There is a
>> good reason for this. In a large aircraft, the weight can vary
>> substantially over its flight envelope. This will result in a large
>> variation in stall speed. In a small aircraft, the stall speed variation
>> is rather small, and a single stall speed can be used safely.
>
> IMHO, there is no good reason for not having an AOA indicator on GA
> aircraft. Stall/spin is a leading cause of death among GA pilots and
> passengers. Best glide (potential emergency situation) is determined by
> AOA. Put an AOA sensor on GA planes with a hand that smacks the pilot on
> the head when the AOA approaches the critical AOA and a lot fewer people
> will die while having fun on the weekends.
>
> Hilton
>
>

[Peter Duniho]

"CV" > wrote in message
...
> By reducing the AOA actually, which happens as a consequence of
> increasing airspeed. But see below also.

No. Increased airspeed happens as a result of reduced angle of attack, not
the other way around. Airspeed has no direct effect on AOA, though it does
have indirect effects (since changes in airspeed affect what AOA you need
for a given performance goal, whether that's turning, climbing, descending,
or whatever).

> And it is interesting how that actually happens. The vertical component
> of thrust takes a bit of the load off the wings which helps reduce the
> AOA and keep it under the limit of the stall. Part of the weight is
> in fact hanging by the propeller, like a helicopter.

Thrust does contribute, yes. But the primary reason for requiring
additional power is that, while the wing is capable of generating the
necessary thrust at a lower airspeed, higher angle of attack (all the way up
to the stalling AOA of course), the higher angle of attack results in higher
drag, requiring higher thrust.

Pete

[Hilton]

G.R. Patterson III wrote:
> Rama, in my post, I forgot that at a higher airspeed, the plane is likely
to be
> climbing, therefore the relative wind will be coming from above. You will
reach
> the same angle of attack at a steeper pitch angle at higher airspeeds.

What?

Hilton

[Hilton]

Greg Esres wrote:
> <<Stall/spin is a leading cause of death among GA pilots and
> passengers. >>
>
> Caused by the pilot not paying attention. Will having another
> instrument that he's not paying attention to really help?

Yes, *if* the AOA is effectively communicated to the pilot. I'm not
suggesting we just stick a few LEDs on the panel. I would want to see some
audio piped into the headset, and/or a stick-shaker etc. I find it amazing
that everyone jumps all over this new GPS whizbang stuff - is it going to
increase or decrease the accident rate? I don't know. But a simple AOA
detector that will directly reduce the number of accidents and fatalities
goes completely ignored.


> <<Best glide (potential emergency situation) is determined by AOA. >>
>
> A few knots either way isn't going to make much difference. Plus, how
> often is maximum glide range critical in an engine out situation?

Take a look at the fuel exhaustion/starvation accidents - they always seem
to 'land' a mile or two from their destination.



> How
> closely is the pilot really maintaining one airspeed (or AOA) during
> an emergency?

I don't know - I haven't seen any research on this one.


> <<Put an AOA sensor on GA planes with a hand that smacks the pilot on
> the head >>
>
> Some studies I've seen have shown that pilots are often oblivious to
> warning horns and lights, though stick shakers are effective.

Lights are useless - the Arrow's stall light is embarrasing. Stall
'buzzers' are OK. So, let's figure out something new, or how about stick
shakers on GA aircraft. Just throwing up our arms while people continue to
die is not good enough.


> My prediction: put an AOA indicator on every airplane in the fleet
> and you won't see much change in the accident rate due to stall spin.

I completely disagree (if done correctly - see above).

Hilton

[Denny]

Well, not to dispute the thrust of your argument, but your statistics
are wrong... CFIT is the leading cause of injury and death in GA...
Stall/spin crashes in vfr flight are down the list a ways..

Now, if the pilot is incapable of noticing the air speed indicator well
down into the white arc, or is incapable of noticing that the nose is
well up, or that he is pulling G's while stomping top rudder, what
makes us suspect that he will notice the AOA needle in the red?

Denny

[CV]

Peter Duniho wrote:

> "CV" > wrote in message
> ...
>
>>By reducing the AOA actually, which happens as a consequence of
>>increasing airspeed. But see below also.
>
> No. Increased airspeed happens as a result of reduced angle of attack, not
> the other way around.

Be that as it may, flying faster allows us to use a smaller AOA,
which is what prevents the stall.

We can stall at any speed, and at any attitude, but it always
happens at the same (or very close to the same) AOA.

CV

[Greg Esres]

<<Yes, *if* the AOA is effectively communicated to the pilot. >>

You're really just talking about a more effective stall warning
system. Fine.

<<But a simple AOA detector that will directly reduce>>

Hypothesis. Skydivers point out that in spite of all the new safety
equipment they have these days, the fatality rate stays about the
same. People will always push the limits to achieve what they
consider an "acceptable" risk.

Consider that the unstallable airplanes such as the Ercoupe didn't
show any improvement in accident rates.

<<Just throwing up our arms while people continue to
die is not good enough.>>

The sure-fire way to reduce the fatality rate is to add ballistic
parachutes to our aircraft....no, wait, that hasn't worked either.
;-)

I don't know the solution to the problem. It may be an unavoidable
aspect of our freedom to fly.

[Greg Esres]

<<Andrew is stating that the angle of attack at which this occurs is
the same regardless of airspeed. I believe he is incorrect in this >>

Andrew is 100% correct on this.

<<my aircraft will stall at a much lower angle of attack at 50 mph
than at 60 mph, and I've never been brave enough>>

That sentence doesn't make any sense at all. You may be confusing
pitch angle with angle of attack.

The only means you have of determining your AOA is your airspeed
indicator. At 50 mph, you are at a higher AOA than at 60 mph.

<<You will reach the same angle of attack at a steeper pitch angle at
higher airspeeds.>>

Same AOA = Same airspeed.

[Frankster]

>> You will reach the same angle of attack at a steeper
>> pitch angle at higher airspeeds.
>
> What?
>
> Hilton

He's saying that, by definition, the AOA is the wing's angle to the
*relative* airflow. Pitch is relative only to the ground, and really has no
bearing on this entire discussion.

-Frank

[Hilton]

Frankster wrote:
> >> You will reach the same angle of attack at a steeper
> >> pitch angle at higher airspeeds.
> >
> > What?
> >
> > Hilton
>
> He's saying that, by definition, the AOA is the wing's angle to the
> *relative* airflow. Pitch is relative only to the ground, and really has
no
> bearing on this entire discussion.

Frank,

The sentence above read: "at a higher airspeed, the plane is likely to be
climbing, therefore the relative wind will be coming from above."

I don't understand the first part (higher speed and climbing?) and the
second part is wrong.

Hilton

[Hilton]

Greg Esres wrote:
> <<Yes, *if* the AOA is effectively communicated to the pilot. >>
>
> You're really just talking about a more effective stall warning
> system. Fine.

Both really (indicator and stall warning), but yes, a more effective stall
warning system would literally be the life saver.


> <<But a simple AOA detector that will directly reduce>>
>
> Hypothesis.

Are you contradicting your previous comment: "Some studies I've seen have
shown that pilots are often oblivious to warning horns and lights, though
stick shakers are effective."?


> The sure-fire way to reduce the fatality rate is to add ballistic
> parachutes to our aircraft....no, wait, that hasn't worked either. ;-)

I see the parachute guys got a mention on CNN. I wonder if/when the
research will start about the effect they have on a pilot's thinking,
decision making, and risk assesment. I know one was 'fired' when an aileron
became detached - was the plane really uncontrollable? Maybe, I'm not going
to doubt the pilot's remarks. But what about the other ones, and the
accidents where a pilot *perhaps* fly into 'unsuitable' conditions. BTW:
I'm also writing this in future tense.


> I don't know the solution to the problem. It may be an unavoidable
> aspect of our freedom to fly.

I'd like to think it's a solvable problem, or at least reducable.

Hilton

[Hilton]

Denny wrote:
> Well, not to dispute the thrust of your argument, but your statistics
> are wrong... CFIT is the leading cause of injury and death in GA...
> Stall/spin crashes in vfr flight are down the list a ways..

You got a source for these assertions?

Hilton

[G.R. Patterson III]

Hilton wrote:
>
> I don't understand the first part (higher speed and climbing?) and the
> second part is wrong.

If I leave the flaps at 0 degrees in my aircraft, bring the power back to
decelerate, and maintain level flight, she will stall at about 53 mph indicated.
The relative wind will be essentially horizontal, since that is the direction in
which the aircraft is actually traveling.

If I leave the flaps at 0 degrees, slow down to 60 mph indicated and raise the
nose enough to stall, the aircraft will be climbing just prior to the stall. The
relative wind will be "coming from above", since that is the direction in which
the aircraft is traveling.

George Patterson
The desire for safety stands against every great and noble enterprise.

[Greg Esres]

<<Are you contradicting your previous comment: "Some studies I've seen
have shown that pilots are often oblivious to warning horns and
lights, though stick shakers are effective."?>>

No, the discussion has vacillated between AOA indicators and warnings;
there is more justification for improved warnings than for indicators
which won't be used.

BTW, I do agree that AOA indicator would be *useful* in the right
hands (precise short field landings, e.g.), but I don't think it will
make much of a dent int he stall/spin accidents.

<<I'd like to think it's a solvable problem, or at least reducable.>>

Planes that fly themselves? ;-)

[Greg Esres]

<<The relative wind will be "coming from above", since that is the
direction in which the aircraft is traveling.>>

The relative wind doesn't ever "come from above" while the aircraft
has a positive angle of attack..by definition. ;-) Nor will the
aircraft stall with the relative wind "essentially horizontal."
Sounds like you think there is a zero angle of attack in that
situation? Cannot be true.

When not pulling a g-load, an aircraft climbs because the *flight
path* is inclined relative to the horizon; the AOA depends on the
chord line angle with the *flight path*.

If your level flight stall speed is 53 and you're stalling at 60,
you're probably achieving an accelerated stall.

The flight testing guys try to decelerate 1 knot per second; oddly,
decelerating at a greater rate produces a *lower* stall speed, which
must be normalized during the data processing. (I'm sure this only
occurs up to a point.)

[Hilton]

Greg Esres wrote:
> The flight testing guys try to decelerate 1 knot per second; oddly,
> decelerating at a greater rate produces a *lower* stall speed,...

Why?

Hilton

[Peter Duniho]

"Greg Esres" > wrote in message
...
> The relative wind doesn't ever "come from above" while the aircraft
> has a positive angle of attack..by definition. ;-) Nor will the
> aircraft stall with the relative wind "essentially horizontal."
> Sounds like you think there is a zero angle of attack in that
> situation? Cannot be true.

I am sure that George means "coming from above relative to the horizon".
Which is a fine statement to make, IMHO. I do find it odd that you were
apparently unable to make this inference, given your next paragraph:

> When not pulling a g-load, an aircraft climbs because the *flight
> path* is inclined relative to the horizon; the AOA depends on the
> chord line angle with the *flight path*.

Yes, the flight path IS inclined relative to the horizon, and this causes
the relative wind to also become inclined relative to the horizon.

> If your level flight stall speed is 53 and you're stalling at 60,
> you're probably achieving an accelerated stall.

Yes, he certainly is, and he said as much.

Pete

[CV]

G.R. Patterson III wrote:
>
> Hilton wrote:
>
>>I don't understand the first part (higher speed and climbing?) and the
>>second part is wrong.
>
>
> If I leave the flaps at 0 degrees in my aircraft, bring the power back to
> decelerate, and maintain level flight, she will stall at about 53 mph indicated.
> The relative wind will be essentially horizontal, since that is the direction in
> which the aircraft is actually traveling.
>
> If I leave the flaps at 0 degrees, slow down to 60 mph indicated and raise the
> nose enough to stall, the aircraft will be climbing just prior to the stall. The
> relative wind will be "coming from above", since that is the direction in which
> the aircraft is traveling.
>
> George Patterson
> The desire for safety stands against every great and noble enterprise.

I think I see a lot of confusion happening in this thread due to
the use of fuzzy and unnecessary concepts like "relative wind",
"pitch angle", "from above" and a couple of others.

Angle of Attack is simply the angle at which the airflow meets
the wing. There is no need to complicate matters by calling the
airflow "relative", especially as some posters seem to be confused
about what is _relative_ to what.

If we must use "relative" then it would be better to say exactly
what we mean "relative to the wing/aircraft" or "in relation to
the wing/aircraft", but as this is the only relation that makes
sense when discussing AOA it shouldn't be necessary to mention
it at all.

And "wind" is positively misleading as it makes you think of
movement of an airmass in relation to the ground. "From above"
is similarly meaningless, unless we specify whether we mean it
in relation to the wing/aircraft or the horizon.

Cheers CV

[Greg Esres]

<<I am sure that George means "coming from above relative to the
horizon". Which is a fine statement to make, IMHO. I do find it odd
that you were apparently unable to make this inference, given your
next paragraph:>>

That is possibly what he meant, but I think you're trying to interpret
what he said in light of your own understanding. That's a common
mistake that instructors make and it hides the fact that the student
really *doesn't* understand.

Odd words or phrases used to explain something can often give a clue
that the mental model is wrong. This "relative wind coming from
above" sets my detectors going off. Where the relative wind is coming
from relative to the horizon is irrelevant.


<<[an accelerated stall.] Yes, he certainly is, and he said as
much.>>

Where?

[Greg Esres]

<<Why?>>

I don't know. None of the books explain it. They just descibe
methods of correcting for it. (Test pilots seem the practical sort,
rather than theoretical.)

My suspicion is that it's due to the "dynamic stall" concept. When an
aircraft is rotated rapidly to a high AOA, it can generate a much
higher lift coefficient than steady state. Apparently it takes some
finite amount of time for the adverse pressure gradients to do their
magic and cause the airflow to separate.

[Greg Esres]

<<If we must use "relative" then it would be better to say exactly
what we mean "relative to the wing/aircraft" or "in relation to
the wing/aircraft", but as this is the only relation that makes
sense when discussing AOA it shouldn't be necessary to mention
it at all.>>

That's why it's almost impossible to discuss a subject meaningfully
with someone unless he has the basic vocabulary down. For the CFIs I
have taught, my first step is have them read an entry-level
aerodynamics book. Much of our discussions after that is making sure
they use the correct words and have a clear idea of what they mean.

Words like "pitch", "angle of attack", and "climb angle" all have
different meanings, but the distinction is so fuzzy in most pilots'
minds that it's no wonder that people get confused.

Now, "relative wind" is a standard aerodynamics term and is as
ordinary to me as the word "chair". Surely all pilots understand what
relative wind is?


Yes, "wind" probably isn't the ideal word to use; vast numbers of
pilots out there still think that the motion of the airmass relative
to the ground affects the aerodynamics of the aircraft, and it's very
difficult to rid them of that notion.

[David CL Francis]

On Tue, 28 Dec 2004 at 03:56:41 in message
>, G.R. Patterson III
> wrote:

>If I leave the flaps at 0 degrees, slow down to 60 mph indicated and raise the
>nose enough to stall, the aircraft will be climbing just prior to the stall. The
>relative wind will be "coming from above", since that is the direction in which
>the aircraft is traveling.

I think the question here is "Above What?" If the aircraft is flying
then the relative wind will be coming from a direction in which the
velocity vector of the aircraft is pointing (assuming we are talking
still air).

But it will not be coming from "above the aircraft". A normal angle of
attack sufficient to satisfy the required lift vector must still exist.
The lift required when climbing is normally somewhat less than that
required in steady horizontal flight.
--
David CL Francis

[David CL Francis]

On Sun, 26 Dec 2004 at 21:58:05 in message
>, Peter Duniho
> wrote:
>Thrust does contribute, yes. But the primary reason for requiring
>additional power is that, while the wing is capable of generating the
>necessary thrust at a lower airspeed, higher angle of attack (all the way up
>to the stalling AOA of course), the higher angle of attack results in higher
>drag, requiring higher thrust.

I think Peter that an aircraft will climb if trimmed to the same angle
of attack that it was using in level flight. It does this as long as
the lift is slightly less and the speed drops to produce _less_ drag
and lift, leaving more engine power and thrust to climb.

When climbing extra work must be done against gravity. That extra work
can come from increasing power or from reducing speed and therefore
drag.

Nitpicking point: wings do not create thrust! :-) You meant lift of
course.
--
David CL Francis

[G.R. Patterson III]

Greg Esres wrote:
>
> <<The relative wind will be "coming from above", since that is the
> direction in which the aircraft is traveling.>>
>
> The relative wind doesn't ever "come from above" while the aircraft
> has a positive angle of attack..by definition. ;-)

The relative wind always comes from the direction in which the aircraft is
actually traveling. If the aircraft is climbing, the relative wind comes from
above the horizon; ie. it is not horizontal.

> Nor will the
> aircraft stall with the relative wind "essentially horizontal."

It certainly will if the aircraft is neither climbing nor descending, is not
banked, and the pitch angle exceeds the stall angle of attack.

> Sounds like you think there is a zero angle of attack in that
> situation?

No, I don't.

George Patterson
The desire for safety stands against every great and noble enterprise.

[G.R. Patterson III]

CV wrote:
>
> "From above"
> is similarly meaningless, unless we specify whether we mean it
> in relation to the wing/aircraft or the horizon.

Yes. I meant above the horizon and failed to say so.

George Patterson
The desire for safety stands against every great and noble enterprise.

[Peter Duniho]

"David CL Francis" > wrote in message
...
> I think Peter that an aircraft will climb if trimmed to the same angle of
> attack that it was using in level flight.

Well, ignoring for a moment that I never meant to suggest anything about
what happens if you simply increase power without changing anything else
when just above stall speed... (my comments were simply about what
additional power *allows*...not what it *causes*)

You can't make that generalization. Changes in power affect elevator
authority (affecting trim), as well as necessary rudder input (changing
drag). It is entirely possible that when just above stall speed, an
increase in power will result in an increase in angle of attack, an increase
in drag, or both.

What you can say is that if the pilot maintains the same angle of attack,
but increases power, then the airplane will climb (I don't believe that
added drag from rudder will ever be MORE than the added thrust, but I could
be wrong about that). But that's not really what I was talking about.

> It does this as long as the lift is slightly less and the speed drops to
> produce _less_ drag and lift, leaving more engine power and thrust to
> climb.

At an airspeed just above stall, a reduction in speed results in MORE drag.
There is a reduction in parasitic drag, but there is a greater increase in
induced drag, with a net increase in total drag (and that's ignoring drag
caused by the rudder and any other control surfaces that require a change in
position).

> When climbing extra work must be done against gravity. That extra work can
> come from increasing power or from reducing speed and therefore drag.

The extra work comes ONLY from a net surplus of power. A reduction in speed
is only guaranteed to produce a net increase in power available if the new
airspeed is higher than Vbg. It can sometimes also produce a net increase,
if the old airspeed was sufficiently higher than Vbg, and the new airspeed
is close enough to Vbg, even if less than, but you need to know more about
the old and new airspeeds in that case to say for sure what happens. More
importantly, a reduction in speed is guaranteed to produce a net decrease of
power available if the OLD airspeed is lower than Vbg (as it is when just
above stall speed).

> Nitpicking point: wings do not create thrust! :-) You meant lift of
> course.

Yes, of course. Thank you.

Pete

[Greg Esres]

<< A reduction in speed is only guaranteed to produce a net increase
in power available if the new airspeed is higher than Vbg. >>

I think you mean higher than the airspeed for minimum power, which is
lower than Vbg.

Even that's not really true, since the power available curve isn't
flat. Vy is maybe closer to the truth.

[Peter Duniho]

"Greg Esres" > wrote in message
...
> << A reduction in speed is only guaranteed to produce a net increase
> in power available if the new airspeed is higher than Vbg. >>
>
> I think you mean higher than the airspeed for minimum power, which is
> lower than Vbg.

Yes...sorry, I use Vbg as a nice "landmark", since it's very close to the
actual speed in question. I guess I should be more explicit about that,
especially in this context.

[Greg Esres]

<<Yes...sorry, I use Vbg as a nice "landmark", since it's very close
to the actual speed in question. I guess I should be more explicit
about that, especially in this context.
>>

I thought so. You couldn't be right about so much and get that one
wrong. ;-)

[David CL Francis]

On Tue, 28 Dec 2004 at 16:55:05 in message
>, Peter Duniho
> wrote:
>> It does this as long as the lift is slightly less and the speed drops to
>> produce _less_ drag and lift, leaving more engine power and thrust to
>> climb.
>
>At an airspeed just above stall, a reduction in speed results in MORE drag.
>There is a reduction in parasitic drag, but there is a greater increase in
>induced drag, with a net increase in total drag (and that's ignoring drag
>caused by the rudder and any other control surfaces that require a change in
>position).
>
HI Peter. How easy it is to get slightly confused on Usenet! What I was
trying to say is that if you maintain the same AoA then the lift drag
ratio remains the same, but because the lift required when climbing is
less than when flying level you can climb at a reduced speed but with
less drag. So under some conditions if you just raise the nose a little
you can find a new steady state where speed is slightly reduced but with
the same thrust you can climb at the same AoA..

There is a maximum lift drag ration at a modest angle of attack. Above
_and_ below that angle of attack that ratio worsens.

>> When climbing extra work must be done against gravity. That extra work can
>> come from increasing power or from reducing speed and therefore drag.
>
>The extra work comes ONLY from a net surplus of power.

I agree with that. However that net surplus can come from either more
engine power or reduced drag. Because even in a modest climb the engine
thrust vector plus the lift vector combine to match the weight. Put
another way if you are flying below the maximum lift drag ratio and you
increase the AoA to the optimum whilst keeping the same power the
aircraft should climb. This is self evident if you are flying level at
high speed and at a climbing power setting. Bring the nose up increasing
the AoA and your aircraft will definitely climb. Agreed?

> A reduction in speed
>is only guaranteed to produce a net increase in power available if the new
>airspeed is higher than Vbg. It can sometimes also produce a net increase,
>if the old airspeed was sufficiently higher than Vbg, and the new airspeed
>is close enough to Vbg, even if less than, but you need to know more about
>the old and new airspeeds in that case to say for sure what happens. More
>importantly, a reduction in speed is guaranteed to produce a net decrease of
>power available if the OLD airspeed is lower than Vbg (as it is when just
>above stall speed).
>
I think that is another way of saying what I have just said? I cannot
remember if we started off with an assumption that the aircraft was only
just above stall speed? If so then you are correct of course.

Even in a steady glide the required lift is less than that needed in
level flight! That is easier to see because the drag vector helps the
lift match the gravity vector.

--
David CL Francis

[Peter Duniho]

"David CL Francis" > wrote in message
...
> [...] So under some conditions if you just raise the nose a little you can
> find a new steady state where speed is slightly reduced but with the same
> thrust you can climb at the same AoA..

Your theory sounds wonderful, but I doubt it holds water in practice.

Thrust does not reduce the required lift by much, especially not in the
light planes we tend to fly. Steady-state pitch angles in climbs tend to be
modest, meaning a tiny fraction of the thrust vector is the downward
component. Just 17% of the total thrust, for a 10 degree pitch angle.
Given how little thrust a light plane has in the first place (only a
relatively small fraction of the total weight of the airplane in the first
place, less than 10% in at least some cases, perhaps most cases), even
taking 20% (or even 34%) of that and applying it to lift just isn't going to
help that much.

Even assuming an airplane with a thrust-to-weight ratio of 1.0 (a rare
occurrance, but they do exist...some F-16s, for example), I'm not sure your
theory holds up very well. You might think that you could simply increase
thrust as you slow the airplane in order to allow a smaller AOA to suffice
to provide the remaining necessary lift. But there's a problem with that
idea.

If the AOA is kept small, then the increased thrust will prevent the
airplane from decellerating. To have a vertical component high enough to
support the airplane will require a horizontal component so high that the
airplane won't slow. If the AOA is allowed to increase, then what the
increased thrust is actually allowing is for the wing to stall without the
airplane being pulled downward by gravity (the wing WILL stall at the
appropriate AOA, regardless of airspeed). It's not demonstrating anything
about some "new steady state".

The above thought experiment should also illustrate another problem with
your theory: it ignores the change in the portion of lift actually
contributing to counteracting gravity that occurs due to pitch changes. See
below for more commentary on that.

Of course, to me the biggest problem intuitively with your theory is that I
am sure that aerodynamics involves only continuous functions. Given that,
if you assume more than one steady state, you are claiming that there are
multiple local minima/maxima between which are apparently "lower efficiency"
areas. And of course, if there's more than one, I see no reason to believe
that there are only two. This would then imply that the flight envelope has
numerous of these local minima/maxima points.

Given that in more than 100 years of study, this concept has never shown up
as a noted element of the relationship between speed, drag, and lift, I'm
inclined to believe that it's just not true (just as the idea of "cruising
on the step" is not true).

I admit that I have not brought out the equations and proved my point
irrefutably. Someone like Julian Scarfe or Todd Pattist would probably do a
better job discussing this, since they seem to be more "math oriented" (that
is, they don't mind crunching some equations now and then :) ). But I still
feel reasonably confident that there's no secondary "new steady state" one
can achieve by increasing AOA and taking advantage of thrust.

>>The extra work comes ONLY from a net surplus of power.
>
> I agree with that. However that net surplus can come from either more
> engine power or reduced drag. Because even in a modest climb the engine
> thrust vector plus the lift vector combine to match the weight.

I assume by "the engine thrust vector" you really mean "the vertical
component of the engine thrust vector". Assuming that, I agree with your
statement, but I don't find it informative. The engine thrust vector has a
non-zero vertical component even during level cruise flight, and yes it does
contribute to counteracting gravity, reducing the lift required.

But when you ask the question about HOW MUCH it does this, the answer is
"not enough to change the fundamentals". Not for the airplanes we fly, and
I think probably not for any airplane.

> Put another way if you are flying below the maximum lift drag ratio and
> you increase the AoA to the optimum whilst keeping the same power the
> aircraft should climb. This is self evident if you are flying level at
> high speed and at a climbing power setting. Bring the nose up increasing
> the AoA and your aircraft will definitely climb. Agreed?

I never said anything to the contrary. If you are at an angle of attack
lower than the best L/D AOA (and thus at an airspeed higher than the L/Dmax
airspeed), increasing pitch angle without a change in power will result in a
climb, yes.

But that has nothing to do with what happens at an airpseed near stall,
which occurs below the L/Dmax airspeed, and well above the best L/D AOA.

> I think that is another way of saying what I have just said?

Well, since I seem to disagree with what you said, I sure hope not. :)

> I cannot remember if we started off with an assumption that the aircraft
> was only just above stall speed? If so then you are correct of course.

Yes, this part of the discussion was entirely about the regime of flight
near the stalling speed and AOA. Reducing drag by pitching up while above
L/Dmax airspeed is uninteresting, since that's a direct consequence of
slowing to an airspeed closer to L/Dmax airspeed.

> Even in a steady glide the required lift is less than that needed in level
> flight! That is easier to see because the drag vector helps the lift match
> the gravity vector.

This seems like a good point at which to mention something else you've left
out and which I alluded to earlier...

Lift is always generated perpendicular to the wing's chord. Some people
like to call just the vertical component of this force "lift", but the
amount of force acting through the wing is the force perpendicular to the
chord.

However you label things, you cannot avoid the fact that when you change the
angle of the lift vector, the portion of the force created by the wing used
to counteract gravity is also changed. In particular, in the low-airspeed,
power-on example, even as thrust is helping support the airplane, you are
using your lift less efficiently, which means that the wing needs to
generate more total lift just to provide the necessary vertical component.

This is similar to the required increase in lift while in a turn, but due to
redirecting the lift vector in a different way.

Since the lift vector points slightly aft in level flight, even at high
airspeeds when the angle of attack is low, it's easier to see how this
negates at least some of whatever contribution thrust might make as the
angle of attack is increased. However, in gliding flight, the vector is
pointed forward, helping counteract the contribution drag makes to lift.

I wrote "at least some" up there, but it should be apparent from the
disparate magnitudes of the lift and thrust vectors that you get a much more
significant change in lift than you do in thrust.

The bottom line here: even though thrust does contribute at least a little
to counteracting gravity, it does not do so in a way significant enough to
change the fact that, as you slow the airplane from any airspeed at or below
L/Dmax airspeed, you experience increased drag.

Pete

[Greg Esres]

<<relatively small fraction of the total weight of the airplane in the
first place, less than 10% in at least some cases, perhaps most
cases)>>

Lift in a 10 degree climb should be reduced about 1.5%.

<<I'm not sure your theory holds up very well.>>

"His" theory is mentioned in a number of aerodynamics books.

Although I agree that a small increase in AOA would not contribute
enough vertical component of lift to overcome the initial increase in
induced drag, there are ways to get into this regime of flight. If
you had enough unused AOA left to generate a load factor, you could
change the flight path then return the AOA to its original value. The
aircraft may be able to stay on a steeper flight path due to the
reduced parasite drag and reduced effective weight. Don't forget that
thrust will increase slightly with a lower airspeed.

<<To have a vertical component high enough to support the airplane
will require a horizontal component so high that the airplane won't
slow. >>

Not really clear on what you mean by that. The only component of
thrust that accelerates the airplane is that parallel to the flight
path. If the angle of climb remains the same, then increasing thrust
will obviously accelerate the airplane. However, as thrust increases,
the angle of climb increases up to the point that the component of
aircraft weight along the flight path is equal to the increase in
thrust.


<<Of course, to me the biggest problem intuitively with your theory is
that I am sure that aerodynamics involves only continuous functions.
Given that, if you assume more than one steady state, you are claiming
that there are multiple local minima/maxima between which are
apparently "lower efficiency" areas. And of course, if there's more
than one, I see no reason to believe that there are only two. This
would then imply that the flight envelope has numerous of these local
minima/maxima points.>>

All of the above is very vague. What I hear you say is "I don't want
to believe you." ;-)

There are an infinite number of steady states; every time I move the
elevator, I create a new steady state.

<<Given that in more than 100 years of study, this concept has never
shown up >>

I doubt you're familiar with even 1% of the 100 years of aerodynamic
research and thought. I'm certainly not.

You should realize that "I've never heard of it so it must be false"
is a weak argument.

<<Lift is always generated perpendicular to the wing's chord. >>

No, for subsonic flight, it's perpendicular to the *local* relative
wind, the relative wind that is modified by wingtip vortices. If lift
were perpendicular to the chordline, you would have induced drag in a
wind tunnel, and you don't.

<<you cannot avoid the fact that when you change the angle of the lift
vector, the portion of the force created by the wing used to
counteract gravity is also changed. >>

This is based on your mistaken notion above.

<<Since the lift vector points slightly aft in level flight, >>

Only because of induced drag.

<<However, in gliding flight, the vector is pointed forward, helping
counteract the contribution drag makes to lift.>>

No, the lift vector is perpendicular to the local relative wind
causing it. There is a rearward component (called "induced drag"),
but there is no component forward along the flight path.

[Peter Duniho]

"Greg Esres" > wrote in message
...
>
> <<relatively small fraction of the total weight of the airplane in the
> first place, less than 10% in at least some cases, perhaps most
> cases)>>
>
> Lift in a 10 degree climb should be reduced about 1.5%.

Yes. So? Not relevant to the statement you quoted (which was about
thrust).

> <<I'm not sure your theory holds up very well.>>
>
> "His" theory is mentioned in a number of aerodynamics books.

Fantastic. It would have been nice of you to provide the name of one
popular (i.e. easy to find) one, so that I can read up on it.

> [...] If
> you had enough unused AOA left to generate a load factor, you could
> change the flight path then return the AOA to its original value. The
> aircraft may be able to stay on a steeper flight path due to the
> reduced parasite drag and reduced effective weight. Don't forget that
> thrust will increase slightly with a lower airspeed.

I admit, I didn't consider scenarios where one is taking advantage of
transient changes in drag and lift. Still, there's not much "unused AOA" in
the regime of flight we're talking about, nor did David suggest that might
be required (his implication, to my reading, was that his suggestion applied
generally, not with very specific pilot techniques and situational
characteristics).

> <<To have a vertical component high enough to support the airplane
> will require a horizontal component so high that the airplane won't
> slow. >>
>
> Not really clear on what you mean by that.

Yeah, I was posting pretty late. That wasn't clear at all. My point is
simply that I don't see how you can increase thrust enough to support the
airplane significantly, while still managing to slow the airplane down to
theoretically lower-drag steady state. Perhaps the zoom maneuver you
described is the answer to that.

> All of the above is very vague. What I hear you say is "I don't want
> to believe you." ;-)

Yes, I admit that readily. But the reason I don't want to believe is that
the proposal bears no resemblance to the behavior of any airplane I've
flown, not while I've been flying it anyway.

I agreed up front that my response is as much hand waving as anything else.
But then so is David's. I'd be more than happy to see someone step in with
some real math that shows the answer one way or the other. I don't happen
to be patient enough with the math. There's a reason that, when I was
working on my math degree, I focused on theory and stayed away from numbers.
:) Topology was my favorite class, differential equations my least.

> There are an infinite number of steady states; every time I move the
> elevator, I create a new steady state.

It seems to me that in this context, my qualification of "new steady state"
(and David's for that matter) should have been clear. That is, he's
proposing that at the same speed, there are multiple steady states that
produce different amounts of drag.

> <<Lift is always generated perpendicular to the wing's chord. >>
>
> No, for subsonic flight, it's perpendicular to the *local* relative
> wind, the relative wind that is modified by wingtip vortices.

Mea culpa. Still, in a climb (or descent), lift is not being applied
entirely to counteracting weight.

> If lift
> were perpendicular to the chordline, you would have induced drag in a
> wind tunnel, and you don't.

I understand my error regarding chord versus relative wind. Still, I'm
boggled by the lack of induced drag in a wind tunnel. If the wing's not
creating lift (0 AOA), I can see how there wouldn't be induced drag. But
this would happen in the real world too. If the wing is creating lift,
shouldn't there be a measurable force parallel to the relative wind? Even
in a wind tunnel?

You can measure lift in a wind tunnel. Why not induced drag?

Pete

[Greg Esres]

<<Yes. So? Not relevant to the statement you quoted (which was about
thrust).>>

The issue under discussion was how much less lift was needed when
thrust supported some of the weight of the aircraft. The reduction in
necessary lift could accommodate a lower airspeed at the same AOA, or
a lower AOA at the same airspeed. But, as you said, the reduction in
lift is not a whole lot.

<<It would have been nice of you to provide the name of one popular
(i.e. easy to find) one, so that I can read up on it.>>

It's not always easy to find a reference to something I've read; I
often lose hours doing so. Anyway, here's one: "Introduction to
Flight", by John D. Anderson. p. 290. Quote:

"As seen in this example, for steady climbing flight, L (hence Cl) is
smaller, and thus induced drag is smaller. Consequently, total drag
for climbing flight is smaller than for level flight at the same
velocity."

<<Still, there's not much "unused AOA" in the regime of flight we're
talking about, nor did David suggest that might be required (his
implication, to my reading, was that his suggestion applied ??

True

<<But the reason I don't want to believe is that the proposal bears no
resemblance to the behavior of any airplane I've flown, not while I've
been flying it anyway.>>

If the effect exists, I agree that it would probably be small and
might well be lost in the wash.

<< I'd be more than happy to see someone step in with some real math
that shows the answer one way or the other. >>

Anderson shows some numbers. I hate trying to depict the math in this
forum, because it looks so ugly.

<<I don't happen to be patient enough with the math. There's a reason
that, when I was working on my math degree, >>

I only delve into math when the concepts are not clear. Putting some
numbers to the theory makes things real sometimes.

<<That is, he's proposing that at the same speed, there are multiple
steady states that produce different amounts of drag.>>

There are precedents. A banked aircraft at a given airspeed will have
a larger AOA than a non-banked one, and thus incur larger amounts of
induced drag.

I envision that a climbing airplane is essentially a lighter one,
since thrust will support a small amount of weight.

<<Still, I'm boggled by the lack of induced drag in a wind tunnel. If
the wing's not creating lift (0 AOA), I can see how there wouldn't be
induced drag. But this would happen in the real world too. If the
wing is creating lift, shouldn't there be a measurable force parallel
to the relative wind? Even in a wind tunnel?>>

I should qualify that. The great body of wing sections that NACA
tested in the early part of the last century were placed flush against
the walls; no wingtips. It is the wingtip vortices which cause the
local relative wind to be different from the "real" relative wind.
Absent that, the total aerodynamic force is perpendicular to the
incoming freestream.

They did this intentially, since the actual induced drag on a real
wing will depend on its aspect ratio. Better to make their data
"pure" and allow builders to adjust it to fit their specific
planforms. There is still drag, of course, but just not induced drag.

[Hilton]

Greg Esres wrote:
>
> <<relatively small fraction of the total weight of the airplane in the
> first place, less than 10% in at least some cases, perhaps most
> cases)>>
>
> Lift in a 10 degree climb should be reduced about 1.5%.

How did you arrive at 1.5%?


> <<Lift is always generated perpendicular to the wing's chord. >>
>
> No, for subsonic flight, it's perpendicular to the *local* relative
> wind, the relative wind that is modified by wingtip vortices. If lift
> were perpendicular to the chordline, you would have induced drag in a
> wind tunnel, and you don't.

Come on Greg, you're telling me that wings in wind tunnels have no induced
drag? That's ridiculous. How about if the wind tunnel was 1000 miles long
by 10 miles high - would the wings in that wind tunnel have induced drag?
(I seem to remember this same argument a few months ago)

Hilton

[Hilton]

Hilton wrote:
> Greg Esres wrote:
> > No, for subsonic flight, it's perpendicular to the *local* relative
> > wind, the relative wind that is modified by wingtip vortices. If lift
> > were perpendicular to the chordline, you would have induced drag in a
> > wind tunnel, and you don't.
>
> Come on Greg, you're telling me that wings in wind tunnels have no induced
> drag? That's ridiculous. How about if the wind tunnel was 1000 miles
long
> by 10 miles high - would the wings in that wind tunnel have induced drag?
> (I seem to remember this same argument a few months ago)

Just to follow-up my own post, here is a line from the NASA web site:
"During the winter, with the aid of their wind tunnel, they began to
understand the role of high induced drag on their aircraft's poor
performance."

http://www.grc.nasa.gov/WWW/Wright/airplane/drag1.html

Sorry Greg, "no induced drag in a wind tunnel" is simply not true.

Hilton

[Greg Esres]

<<How did you arrive at 1.5%?>>

L = Wcos(theta)


<<Come on Greg, you're telling me that wings in wind tunnels have no
induced >drag? That's ridiculous. How about if the wind tunnel was
1000 miles long by 10 miles high - would the wings in that wind tunnel
have induced drag? >(I seem to remember this same argument a few
months ago)>>


Argument? No, Todd Pattist and I attempted to educate you on this
subject, but apparently failed.

The size of the wind tunnel is irrelevant. What matters is that the
wing tips are flush against the walls of the wind tunnel. This
produces 2-D airflow, rather than 3-D. In 2-D flow, there are no wing
tip vortices and thus will have no induced drag.

(If you would read something other than Aerodynamics for Naval
Aviators, you'd understand this.)

[Greg Esres]

<<Sorry Greg, "no induced drag in a wind tunnel" is simply not true.>>

Once again, you don't understand.

If you put a 3-D wing in a wind tunnel, you will get induced drag.

The article you posted even documents the effect:

<----------snip-------------->
This drag occurs because the flow near the wing tips is distorted
spanwise as a result of the pressure difference from the top to the
bottom of the wing. Swirling vortices are formed at the wing tips, and
there is an energy associated with these vortices.
<----------snip-------------->


See that? Flow "near the wing tips is distorted"....vortices are
formed at the wing tips


2-D flow is achieved when the wing tips are flush against the sides of
the wind tunnel. No wing tips => no pressure leaking around the wing
tips => no wingtip vortices => no induced drag.

[Peter Duniho]

"Greg Esres" > wrote in message
...
> "As seen in this example, for steady climbing flight, L (hence Cl) is
> smaller, and thus induced drag is smaller. Consequently, total drag
> for climbing flight is smaller than for level flight at the same
> velocity."

I'm not questioning whether thrust contributes to lift, and thus reduces the
total lift requirement. It is patently obvious to me that a force directed
at least partially downward contributes to lift. That quote says nothing
more than that. What I am questioning is whether for a given performance
scenario there are multiple drag scenarios.

> <<That is, he's proposing that at the same speed, there are multiple
> steady states that produce different amounts of drag.>>
>
> There are precedents. A banked aircraft at a given airspeed will have
> a larger AOA than a non-banked one, and thus incur larger amounts of
> induced drag.

It's clear that I continue to fail to state my objection properly. Let me
try again...

David's post implies that for a given performance scenario (straight and
level flight, for example) you can nudge the airplane into a "new steady
state" where drag is lower. Your examples of climbing and turning don't
address that issue; they are entirely different performance scenarios (that
is, the airplane is doing something different) than the scenario to which
drag is being compared.

According to David's original post (if I read it correctly), there are
multiple drag scenarios for a given path of flight. Each time you come up
with an example, it starts out by assuming a new path of flight compared to
the "base case".

> I envision that a climbing airplane is essentially a lighter one,
> since thrust will support a small amount of weight.

Seems reasonable to me. But what if you don't want to climb? And in
particular, if we're talking about comparing one airplane in straight and
level flight to another in straight and level flight, introducing a climb to
the discussion doesn't help much.

Pete

[Hilton]

Greg Esres wrote:
> <<How did you arrive at 1.5%?>>
>
> L = Wcos(theta)

*If* you assume level and climb airspeeds are the same.


[zap: induced drag disagreement]

> (If you would read something other than Aerodynamics for Naval
> Aviators, you'd understand this.)

Yeah, I also hate it when people use decades of research, hours of wind
tunnel testing, and accepted aerodynamic principals in these newsgroups. :)

Hilton

[Greg Esres]

<<According to David's original post (if I read it correctly), there
are multiple drag scenarios for a given path of flight.>>

I didn't pick up on that, but if so, I agree with you. That scenario
seems unlikely.

[David CL Francis]

On Fri, 31 Dec 2004 at 02:06:08 in message
>, Peter Duniho
> wrote:

Peter, I am sorry that this reply is a bit delayed as we have had
visitors over the last three days. I have gone back to basic equations
and looked again at them! I now have to confess that you are, at least
in part correct. I offer my apologies.

>"David CL Francis" > wrote in message
...
>> [...] So under some conditions if you just raise the nose a little you can
>> find a new steady state where speed is slightly reduced but with the same
>> thrust you can climb at the same AoA..
>
>Your theory sounds wonderful, but I doubt it holds water in practice.
>

My statement above was wrong as written. It is true in the sense that
you can find a new steady state at the same AoA and a slightly reduced
speed but only by applying more thrust. You apply more thrust and if the
AoA stays the same the velocity will initially increase and the flight
path will curve upward arriving at a new steady state where there is a
climb, but at a slightly reduced speed.

Theta is the angle of climb in degrees.

If the L/D is fixed at 10 then here is a little table. I hope it comes
out not too screwed up by different fonts and line lengths:

weight Lift/ Theta Drag Thrust Lift Lift
Velocity
lb. drag deg lb. lb. lb.
% %
10000 10 0 1000 1000 10000 100 100.00
10000 10 1 1000 1174 9998 100 99.99
10000 10 2 999 1348 9994 100 99.97
10000 10 5 996 1868 9962 100 99.81
10000 10 15 966 3554 9659 97 98.28
10000 10 30 866 5866 8660 87 93.06
10000 10 45 707 7778 7071 71 84.09
10000 10 60 500 9160 5000 50 70.71
10000 10 90 0 10000 0 0 0.00

In practice aircraft cannot be controlled at zero velocity and more
thrust would be needed at the higher angles of climb to maintain a
controllable airspeed. Note that lift is reduced to zero in a vertical
climb as it must be.

I freely admit that these equations give only a simplified
demonstration. There are many refinements to be added but the basics are
generally accepted I believe.

For example at the same power setting thrust is not independent of
velocity, the thrust is not always exactly opposite to drag and control
deflections also have an effect on drag and total lift.

Weight is the gravitational force on the aircraft and points to the
centre of the earth. Thrust is defined, in this simplification as a
force along the flight path and drag is a force in the opposite
direction. Lift (you seem to have got this wrong further down in your
post) is defined, in the usual way, as acting at right angles to the
flight path.

Drag acts along the flight path in the opposite general direction to
thrust. It has two components. One is the standard parasitic drag and
the other is induced drag which can be looked at as the drag component
due to the tilting back of the force vector to allow for the deflection
of the air stream by the generation of the lift. By making a few
assumptions about the size of the airflow that is actually deflected
this can be shown to be proportional to the square of the lift
coefficient.

>Thrust does not reduce the required lift by much, especially not in the
>light planes we tend to fly. Steady-state pitch angles in climbs tend to be
>modest, meaning a tiny fraction of the thrust vector is the downward
>component. Just 17% of the total thrust, for a 10 degree pitch angle.
>Given how little thrust a light plane has in the first place (only a
>relatively small fraction of the total weight of the airplane in the first
>place, less than 10% in at least some cases, perhaps most cases), even
>taking 20% (or even 34%) of that and applying it to lift just isn't going to
>help that much.
>
The thrust must be equal to the drag or the aircraft will not fly at
all! If the thrust is smaller than 10% of the weight then that implies
that the lift/drag ratio is better than 10 for it to even fly at best
lift/drag ratio. A motor glider requires little thrust to fly but may
not climb very well. Note that the pitch angle, depending on how it is
defined, is not normally the same as the angle of climb

>Even assuming an airplane with a thrust-to-weight ratio of 1.0 (a rare
>occurrance, but they do exist...some F-16s, for example), I'm not sure your
>theory holds up very well. You might think that you could simply increase
>thrust as you slow the airplane in order to allow a smaller AOA to suffice
>to provide the remaining necessary lift. But there's a problem with that
>idea.
>
See the table above. I think you are using what you call 'my theory' in
a strange way in the above. If an aircraft is capable of climbing
vertically and steadily then thrust must always be greater than weight
so that a velocity can be maintained sufficient to maintain control
Under those circumstances the situation requires that lift is zero.

>If the AOA is kept small, then the increased thrust will prevent the
>airplane from decellerating. To have a vertical component high enough to
>support the airplane will require a horizontal component so high that the
>airplane won't slow. If the AOA is allowed to increase, then what the
>increased thrust is actually allowing is for the wing to stall without the
>airplane being pulled downward by gravity (the wing WILL stall at the
>appropriate AOA, regardless of airspeed). It's not demonstrating anything
>about some "new steady state".
>

I do not understand the above and in particular your remark that the
'aircraft will not slow'. If AoA is not changed then increased thrust
will increase speed and increased speed will increase lift. That, unless
checked, will lead to the flight path curving upward and a climb
beginning until a new state is reached. The gravity component then also
plays its part in speed reduction.

>The above thought experiment should also illustrate another problem with
>your theory: it ignores the change in the portion of lift actually
>contributing to counteracting gravity that occurs due to pitch changes. See
>below for more commentary on that.
>

Again I am not sure what you mean there. If you mean it ignores the
effect of a climbing flight path then it does not. I have no special
theory - just an attempt to explain basics in the simplest reasonable
way using the simplest possible static equations. AFAIK there are an
infinite number of different possible steady states in the flight of an
aircraft.

>Of course, to me the biggest problem intuitively with your theory is that I
>am sure that aerodynamics involves only continuous functions. Given that,
>if you assume more than one steady state, you are claiming that there are
>multiple local minima/maxima between which are apparently "lower efficiency"
>areas. And of course, if there's more than one, I see no reason to believe
>that there are only two. This would then imply that the flight envelope has
>numerous of these local minima/maxima points.
>
I certainly agree that aerodynamics is a series of continuous functions
with changes of those functions at certain values.

I am not sure about the rest of your paragraph above. An aircraft can
fly at any speed and angle within its capabilities. Change any of the
basic 4 forces and a new situation that can be maintained may or may not
be possible.

>Given that in more than 100 years of study, this concept has never shown up
>as a noted element of the relationship between speed, drag, and lift, I'm
>inclined to believe that it's just not true (just as the idea of "cruising
>on the step" is not true).
>
What concept are you talking about? I am just using simple balance of
forces equations - apart from when I get it wrong of course! :-(

>I admit that I have not brought out the equations and proved my point
>irrefutably. Someone like Julian Scarfe or Todd Pattist would probably do a
>better job discussing this, since they seem to be more "math oriented" (that
>is, they don't mind crunching some equations now and then :) ). But I still
>feel reasonably confident that there's no secondary "new steady state" one
>can achieve by increasing AOA and taking advantage of thrust.
>
I would welcome Todd's participation, he has corrected me a few times
but we have often agreed.

>>>The extra work comes ONLY from a net surplus of power.
>>
>> I agree with that. However that net surplus can come from either more
>> engine power or reduced drag. Because even in a modest climb the engine
>> thrust vector plus the lift vector combine to match the weight.
>
>I assume by "the engine thrust vector" you really mean "the vertical
>component of the engine thrust vector". Assuming that, I agree with your
>statement, but I don't find it informative. The engine thrust vector has a
>non-zero vertical component even during level cruise flight, and yes it does
>contribute to counteracting gravity, reducing the lift required.
>
Fair enough and I have made a part of that point above somewhere. It is
a part of the simplification involved.
>
>> Put another way if you are flying below the maximum lift drag ratio and
>> you increase the AoA to the optimum whilst keeping the same power the
>> aircraft should climb. This is self evident if you are flying level at
>> high speed and at a climbing power setting. Bring the nose up increasing
>> the AoA and your aircraft will definitely climb. Agreed?
>
>I never said anything to the contrary. If you are at an angle of attack
>lower than the best L/D AOA (and thus at an airspeed higher than the L/Dmax
>airspeed), increasing pitch angle without a change in power will result in a
>climb, yes.
>
I am glad we agree on that!

>But that has nothing to do with what happens at an airpseed near stall,
>which occurs below the L/Dmax airspeed, and well above the best L/D AOA.
>
Agreed. You cannot decrease drag by increasing AoA near the stall. This
is part of where we were at cross purposes. I was not thinking
specifically about near the stall.
>
>This seems like a good point at which to mention something else you've left
>out and which I alluded to earlier...
>
>Lift is always generated perpendicular to the wing's chord. Some people
>like to call just the vertical component of this force "lift", but the
>amount of force acting through the wing is the force perpendicular to the
>chord.
>
That is wrong. Lift is always defined as perpendicular to the free
stream velocity of the aircraft. In the same way lift is not defined
relative to gravity either except that in steady level flight it just
happens to be exactly opposite and balancing gravity.

>However you label things, you cannot avoid the fact that when you change the
>angle of the lift vector, the portion of the force created by the wing used
>to counteract gravity is also changed. In particular, in the low-airspeed,
>power-on example, even as thrust is helping support the airplane, you are
>using your lift less efficiently, which means that the wing needs to
>generate more total lift just to provide the necessary vertical component.
>
Insofar as I understand it, I disagree still with that statement. If
thrust is providing a vector in the lift direction then in steady flight
less lift is required as my table does show.

>This is similar to the required increase in lift while in a turn, but due to
>redirecting the lift vector in a different way.
>
No, it is different to that because the increased force required in a
turn is needed to produce an acceleration which is felt as 'g'. That
does not apply in steady level, climbing or gliding flight when just the
normal 1g is felt.

>Since the lift vector points slightly aft in level flight, even at high
>airspeeds when the angle of attack is low, it's easier to see how this
>negates at least some of whatever contribution thrust might make as the
>angle of attack is increased. However, in gliding flight, the vector is
>pointed forward, helping counteract the contribution drag makes to lift.
>
The lift vector points at right angles to the line of flight no matter
what. Lift and drag coefficients are measured like that unless things
have changed a lot since my long ago student experiments in a wind
tunnel.. The only time you consider a backward shift of the 'lift'
vector is in calculating induced drag using a simplified method. By
including a separate term for induced drag proportional to Cl^2 that
effect is allowed for. Lift and drag coefficients for an airfoil are
determined for infinite aspect ratio.

This is getting too long to deal with like this! It has got to the point
where we would need to discuss this face to face to achieve much more
and come to a common understanding of terms and simple equations.

>I wrote "at least some" up there, but it should be apparent from the
>disparate magnitudes of the lift and thrust vectors that you get a much more
>significant change in lift than you do in thrust.
>
Not at small angles of climb as my correction and table indicates. Small
angles of climb mean a small change of the lift vector component in the
truly vertical direction vector.

>The bottom line here: even though thrust does contribute at least a little
>to counteracting gravity, it does not do so in a way significant enough to
>change the fact that, as you slow the airplane from any airspeed at or below
>L/Dmax airspeed, you experience increased drag.
>
That is true and I do agree with that and apologise for the confusion.
Only if the L/D increases with AoA do you get a benefit of reduced drag.
Although the L/D of an aircraft may be 10 or more at maximum. at full
speed in level flight it will be much lower, perhaps as low as 2 or
less. At the zero lift AoA the Lift/drag ratio is also zero but you
cannot then maintain level flight!!!.

I hope that helps to clear some of the misunderstandings between us. My
only excuse is my great age!

I repeat my apology for my error.

I always enjoy your posts even if I don't quite agree!
--
David CL Francis

[David CL Francis]

On Fri, 31 Dec 2004 at 21:23:58 in message
>, Peter Duniho
> wrote:
>I understand my error regarding chord versus relative wind. Still, I'm
>boggled by the lack of induced drag in a wind tunnel. If the wing's not
>creating lift (0 AOA), I can see how there wouldn't be induced drag. But
>this would happen in the real world too. If the wing is creating lift,
>shouldn't there be a measurable force parallel to the relative wind? Even
>in a wind tunnel?
>
>You can measure lift in a wind tunnel. Why not induced drag?

Peter,

After posting another long article with a correction I am a bit
reluctant to step in again here. However the explanation is fairly
simple.

Induced drag and wing tip vortices are almost one and the same thing.
Very roughly induced drag is proportional to

(Lift coefficient)^2/(aspect ratio)

The higher the aspect ratio then the smaller is the induced drag until
when the Aspect Ratio is infinite it is zero. Airfoil sections always
used to be tested in wing tunnels by taking them right across the tunnel
so that there are no tip effects. A correction has to be made for the
tunnel wall but the effect is to test a two dimensional section. Of
course there is still the parasitic drag component to be measured and
that is the Cd that is quoted for the particular wing section.

You can try to measure induced drag but you need a large tunnel and a 3d
model of the aircraft sufficiently far from the walls so that the flow
is not too distorted.
--
David CL Francis

[Greg Esres]

<<David CL Francis>>

David, I think you mentioned that you were retired aeronautical
engineer of some sort. Can you relate something about your
background? I'm just curious

[David CL Francis]

On Wed, 5 Jan 2005 at 01:56:52 in message
>, Greg Esres
> wrote:
><<David CL Francis>>
>
>David, I think you mentioned that you were retired aeronautical
>engineer of some sort. Can you relate something about your
>background? I'm just curious

You remember correctly Greg! Who is this guy eh?

I took a degree in Aeronautically engineering many years ago and got
involved mainly in missile design at Filton (It was Bristol Aeroplane
Company then). I did a lot of structural work and then moved into
Engineering management. As the years passed I moved into more and more
other management type jobs but I was delighted that for the last two
years of my career I was able to move back into engineering management.

I have now been retired some years and a lot of my earlier detail
knowledge has drifted away from me. At my age that is not surprising!

I did start learning to fly, went solo but then I gave it up, partly I
was not sure I had the abilities that I thought I should have and also
because I felt I would never be any good at radio work! That tells you
something about how long ago it was because the aircraft I flew had no
radios despite sharing the airfield with a modest number of commercial
flights! One of the highlights of my instruction was a brief spell of
spin recovery training in a Tiger Moth (which does it for you unless you
are quick).

I did a lot of model work later with radio controlled models but
eventually dropped that and found flight simulators.

My first ever flight was with my father in WW2, would you believe, when
he
smuggled me up in a DH Dragonfly! It was being used as a communication
aircraft. My father was a full timer in the RAF and flew in Hendon Air
Displays in 1928-30. My Uncle was also a full time RAF pilot who ended
his flying career as an Instructor in Canada in WW2.

More recent highlights were a successfully take off, circuit and landing
at Hong Kong in the REAL Concorde Simulator at Filton (with just a
little help from the 'instructor') and a ride in the jump seat of a
747-400 flying into Kennedy on the 6th Sept 2001. I'll never get the
chance to do that again! We drove away from New York to Philadelphia on
the 10th Sept 2001 and found all about it in there in company with my
friend who is a regular and respected contributor to this newsgroup. My
wife and I stood on top of the South Tower on Sept 8th 2001.
--
David CL Francis

[Greg Esres]

<<Who is this guy eh?>>

Very interesting, thank you! Surprising that you could spend your
life in this field, yet never get the pilot certificate. I'm not sure
I would be interested in the subject if I were not able to fly.

[David CL Francis]

On Fri, 7 Jan 2005 at 05:02:30 in message
>, Greg Esres
> wrote:
><<Who is this guy eh?>>
>
>Very interesting, thank you! Surprising that you could spend your
>life in this field, yet never get the pilot certificate. I'm not sure
>I would be interested in the subject if I were not able to fly.
>
Just me I guess Greg. We are all different.

My son was working in South Africa some years ago and he won his Private
Licence out there. In 1989 my wife and I were out there and he took us
for a flight over Johannesburg. Later back here he hired a Warrior and
after a check ride from Filton we made a tour of the district.

Before he left South Africa he checked out on a Cherokee 6 300 and with
three friends (none of them were pilots) went on a touring cruise. They
flew from Johannesburg to the mouth of the Orange River then north
across the Namibian desert to Swakopmund. Then to the airport of
Windhoek to Maun and then across Botswana to Francistown before heading
back to Rand Airport In Johannesburg. Two desert crossings (Namibian and
the Kalahari) 22.4 hours flying and 1012 litres of fuel. He no longer
flies - it is very expensive in the UK and he has his own business to
run. Anyway where in the UK can you fly for 3 hours without being able
to even contact anyone on the radio?

So my son, I am glad to say, has done many things that his father has
not!

If you wish to go to email my reply address should work OK.
--
David CL Francis