On 9/27/2011 9:54 PM, Beryl wrote:
Richard wrote:
On 9/27/2011 12:13 AM, Beryl wrote:
Richard wrote:
Do you know what would happen if the elevator were rigged for zero
trim at 500 mph?
...
What's the tradeoff?

Less efficiency at the speeds where most airplanes spend most of their
time, cruising along at ~70% power.


How about a 200 MPH landing speed?

X-15? What lands at 200 mph?

Not exactly a taildragger, is it?
Well, actually it sorta is - skids rather than wheels.
LOTS o drag on that there tail.


Are you saying that the Galloping Ghost, or Strega, couldn't be rigged
for minimum drag at 500 mph because they'd then have to land at 200?

Minimum drag, sure.

Zero drag, no.


Note that I never said the Stabilizer produces no nose-down force at 500
mph. I'm only doubting that the Trim Tab/Elevator are doing much work
there, at all. Set the Stabilizer to do the work, and lift (downward)
comes by way of Angle of Attack. But set the Trim Tab and Elevator to do
the work, and lift (downward) comes by way of Camber. And not even a
good camber, it's all zig-zagged and creased.

It's still drag.

And you can calculate how much will be there under any given conditions.

On 9/27/2011 10:04 PM, wrote:
On Tue, 27 Sep 2011 19:54:59 -0700, wrote:

Richard wrote:
On 9/27/2011 12:13 AM, Beryl wrote:
Richard wrote:
Do you know what would happen if the elevator were rigged for zero
trim at 500 mph?
...
What's the tradeoff?

Less efficiency at the speeds where most airplanes spend most of their
time, cruising along at ~70% power.


How about a 200 MPH landing speed?

X-15? What lands at 200 mph?

Are you saying that the Galloping Ghost, or Strega, couldn't be rigged
for minimum drag at 500 mph because they'd then have to land at 200?

Note that I never said the Stabilizer produces no nose-down force at 500
mph. I'm only doubting that the Trim Tab/Elevator are doing much work
there, at all. Set the Stabilizer to do the work, and lift (downward)
comes by way of Angle of Attack. But set the Trim Tab and Elevator to do
the work, and lift (downward) comes by way of Camber. And not even a
good camber, it's all zig-zagged and creased.


The elevator - and the trim tab - do a LOT of work on a race plane at
500mph. And a lot at 200 too.

Absolutely.

Add to that there is a lot of speed changes as the aircraft hits the turns.

TANSTAAFL...

wrote:
...
The elevator - and the trim tab - do a LOT of work on a race plane at
500mph. And a lot at 200 too.

Explain! I haven't seen any explanations here, just claims. Richard
claims the nose must forcibly be held down at 500 mph.

The airplane is nose-heavy already, it must be held up. If it takes 200
lbs of downforce at the tail to hold the nose up at 200 mph, it also
takes 200 lbs of downforce to hold the nose up at 500 mph.

We want that 200 lbs of force to come with as little drag as possible at
500 mph. Can anyone explain how full nose-down trim tab deflection +
pushing the stick forward will produce the necessaty 200 lbs of
downforce at the tail?

It will do it because the stabilizer incidence is all wrong for 500 mph.
The stock stabilizer rigging is a compromise, to work acceptably through
the whole speed range. At 500 mph it's pushing the tail down too hard,
so Richard has to trim, and push the stick, to help hold the tail back
up. The tail surfaces are working against each other. Pitched up/down
crap hanging out in the wind.

Richard wrote:
....
The elevator - and the trim tab - do a LOT of work on a race plane at
500mph. And a lot at 200 too.

Absolutely.

Add to that there is a lot of speed changes as the aircraft hits the turns.

The winning pilot minimizes speed loss and G forces through the turns.

TANSTAAFL...

That's why to optimize the airplane for top speed, the slow speed
performance suffers.

Richard wrote:
On 9/27/2011 9:54 PM, Beryl wrote:
Richard wrote:
On 9/27/2011 12:13 AM, Beryl wrote:
...
Are you saying that the Galloping Ghost, or Strega, couldn't be rigged
for minimum drag at 500 mph because they'd then have to land at 200?

Minimum drag, sure.

Zero drag, no.

You're the only one who specified Zero, wasn't me.


Note that I never said the Stabilizer produces no nose-down force at 500
mph. I'm only doubting that the Trim Tab/Elevator are doing much work
there, at all. Set the Stabilizer to do the work, and lift (downward)
comes by way of Angle of Attack. But set the Trim Tab and Elevator to do
the work, and lift (downward) comes by way of Camber. And not even a
good camber, it's all zig-zagged and creased.

It's still drag.

Well then, why ever point the nose up to climb? Just lower the flaps and
add power, it's only drag.

And you can calculate how much will be there under any given conditions.

Really?

Richard wrote:
Beryl,

One last try and then I'll go away and leave you alone.

Bye!

Forget "nose heavy".

Think "pitch", aka deck angle, or preferably, angle of attack.


Within limits of course, angle of attack directly controls the amount of
lift generated by the wing. Yes, other parameters are also involved
but this angle is what the pilot has control of via the stick.

For straight and level unaccelerated flight, lift equals weight.

Wrong. Lift equals weight PLUS tail downforce. You can't "forget nose
heavy" as you suggest.

(thrust equals drag too, but that's another story)

As speed increases _so will lift_, unless something is done to keep that
from happening. THAT trick is simply pushing the nose down.

Wrong. That trick is lessening the tail surfaces' angle of attack, and
letting increased airspeed assume the task. There must be downforce at
the tail, always. You only think you're "pushing the nose down" because
you're fighting the stabilizer angle of attack, which, at 500 mph, is
far overdoing its job of holding the nose up.
Maybe you need to think Stabilator to make the light bulb come on.

(Airliners often pump fuel forward(!) but that's a bit over the top for
light aircraft)

By lowering the nose, the angle of attack is decreased, thereby
decreasing the coefficient of lift, and, if done right, maintaining
a constant altitude (the level part of straight and level)

Ok?

That's the whole of it.


So...

Quote
Of course trim needs chsnge. Richard apparently believes that
some nose-down is ALWAYS needed, and only the /amount/ of nose-down
changes as speed changes.

So for the discussion of a racer at 500 MPH, Yeah, True, Si, Da...

When landing, no.

On 9/28/2011 12:28 AM, Beryl wrote:

Explain! I haven't seen any explanations here, just claims. Richard
claims the nose must forcibly be held down at 500 mph.

The airplane is nose-heavy already, it must be held up. If it takes 200
lbs of downforce at the tail to hold the nose up at 200 mph, it also
takes 200 lbs of downforce to hold the nose up at 500 mph.


Not on this planet...

Richard wrote:
On 9/28/2011 12:28 AM, Beryl wrote:

Explain! I haven't seen any explanations here, just claims. Richard
claims the nose must forcibly be held down at 500 mph.

The airplane is nose-heavy already, it must be held up. If it takes 200
lbs of downforce at the tail to hold the nose up at 200 mph, it also
takes 200 lbs of downforce to hold the nose up at 500 mph.


Not on this planet...

You actually think the airplanes mass balance changes with speed?!!

John B. fired this volley in
:

You are forgetting that as speed increases so does lift. As the main
source of lift is forward of the elevators as lift increases so does
the nose up tendency.

Stop for a moment and think about what you wrote. CL is aft of CG (must
be for it to be "nose heavy") -- and besides, CG aft of CL loading is
unstable and unsafe.

As the lift increases with airspeed, the CG doesn't change, so the nose-
DOWN tendency increases with increased lift. That's just the opposite of
what you wrote.

Also, if nothing else changed, a tendency to point nose-down would
depress the effective angle of attack of the tail, creating more down-
force at the H-stab. So what would really happen is that the nose would
tend to depress a little with increased speed, until it was counteracted
by the more negative angle of attack of the horizontal stabilizer; It
would reach a point where the forces were balanced.

For maximum "slippery-ness", you want the surfaces set up so everything
is more or less neutral at the speed you're intending to go. To repeat
my old saw, anything sticking out in the wind is just an air brake.

For a given target speed, these high-end racing guys aren't going to fly
anything less than a fully optimized aircraft. They'll settle for less-
than-optimum at approach speed to get the extra knots. That's a given.

Lloyd

"John B." wrote in message
...
On Tue, 27 Sep 2011 23:23:50 -0700, Beryl wrote:
Richard wrote:
On 9/28/2011 12:28 AM, Beryl wrote:


No an aircraft's mass changes as fuel is consumed or something falls
off. But you seem to be forgetting that lift changes. Note also that
the CL moves as lift changes. You seem to be thinking of a static
device when you talk about 200 lb. to hold the tail down at 200 mph
then it only takes 200 lbs at 500. That is wrong, the forces acting on
an aircraft change, rather radically, with changes in speed; among
other variables.

If your thesis was correct there would be no need of trim tabs at all.
Just built it in and away we go.
John B.

http://www.av8n.com/how/htm/aoastab.html

The Mustang's wing is symmetrical top and bottom, as you can see by sighting
down it from the wing tip.
http://www.aviation-history.com/theory/lam-flow.htm

jsw

John B. wrote:
On Tue, 27 Sep 2011 23:23:50 -0700, Beryl wrote:

Richard wrote:
On 9/28/2011 12:28 AM, Beryl wrote:

Explain! I haven't seen any explanations here, just claims. Richard
claims the nose must forcibly be held down at 500 mph.

The airplane is nose-heavy already, it must be held up. If it takes 200
lbs of downforce at the tail to hold the nose up at 200 mph, it also
takes 200 lbs of downforce to hold the nose up at 500 mph.

Not on this planet...
You actually think the airplanes mass balance changes with speed?!!

No an aircraft's mass changes as fuel is consumed or something falls
off. But you seem to be forgetting that lift changes. Note also that
the CL moves as lift changes.

Yes, the center of lift moves aft as speed increases. Which makes the
nose become even heavier, calling for more nose-up trim, not nose-down.
Which counters Richard's got-to-push-the-nose-down reasoning.

You seem to be thinking of a static
device when you talk about 200 lb. to hold the tail down at 200 mph
then it only takes 200 lbs at 500. That is wrong, the forces acting on
an aircraft change, rather radically, with changes in speed; among
other variables.

I'm ignoring other variables. There could be thousands, can't discuss
what they all may be doing without losing focus on what the tail
feathers do. Pressure on the canopy may force the nose down, while
pressure on the cowl forces the nose up, while pressure somewhere else
forces the nose down, while... up... down... up... etc.

If your thesis was correct there would be no need of trim tabs at all.
Just built it in and away we go.

That's Richard's thesis. He just said I should forget about the airplane
being nose-heavy. Forget that, and, as you say, the whole trim problem
dosappears, at any speed.

John B. wrote:

But, if you set the incidence of the horizontal stabilizer at
sufficiently high an angle, i.e., build in nose down trim, will you be
able to get the nose up high enough at low speed to fly?

I hesitate to call it nose-down trim (or incidence). I still call it
nose-up trim (or incidence, rigging, whatever) at any speed, but less of
it at 500 mph.

When you can't get the nose high enough at low speed to fly, then you
need to abandon your old "low speed" and accept a higher one.

I have not much more than 200 hrs in my logbook, almost all of it in
152s. And I haven't flown in 25 years. Richard has far more experience,
I'm sure, and is more current. So what?

"Jim Wilkins" wrote

The Mustang's wing is symmetrical top and bottom, as you can see by
sighting down it from the wing tip.
http://www.aviation-history.com/theory/lam-flow.htm

jsw

Isn't symmetrical when you can fold it in half along one plane, and two
sides match?

Steve

"Steve B" fired this volley in
:

"Jim Wilkins" wrote

The Mustang's wing is symmetrical top and bottom, as you can see by
sighting down it from the wing tip.
http://www.aviation-history.com/theory/lam-flow.htm

jsw

Isn't symmetrical when you can fold it in half along one plane, and two
sides match?

Steve


And where does it say in that site that the Mustang's airfoil was
symmetrical? Symmetrical airfoils are used predominantly for aerobatics
where extended inverted flight or strong negative Gs need to be pulled,
but they aren't very effective for range and speed. One has to maintain
a significant angle of attack to develop lift (either way, up or down).

The site you quoted was talking about NACA-designed lamilar flow
airfoils. That doesn't translate directly to "symmetrical".

LLoyd

Some interesting Mustang trivia from a UK site:
http://www.historylearningsite.co.uk...51_Mustang.htm



It would have been more complete if you mentioned that the P51 was
designed by North American Aviation, and production was started in
California. The P51A had two problems: First was that Allison promised
NAA and Larry Bell a 1,150 hp supercharged V12 power plant for both the
P51 and the Bell P39 Aerocobra but tried and failed to copy the front
mounted gear driven supercharger that Rolls Royce had designed into the
Merlin Engine.

Both companies were forced at the start of production to use the
naturally aspirated 750 Hp version of the same engine, which was great
on fuel and reliability, but was too weak for both planes.


The second problem with the P51 was the wing air foil design which was a
modification of a 1933 design. The air foil actually created drag at
speeds over 200 mph that require tremendous increases in horsepower to
overcome, and the faster the wing flew, the worse the problem became.
The solution came from Cal Tech or U. of Southern California with a new
air foil called lamilar flow air foil which allowed the air behind the
wing to "knit" back together without creating excessive drag. It also
allowed the centre of lift to be set to the centre of gravity of the
plane, and the two stayed together as speed increased unlike the
original air foil where the two centrelines separated making handling of
a tail heavy plane at high speed nearly impossible. Boeing was given the
air foil design and used it on the B29 with great success.

(note: NACA 66 series airfoil and a slightly thinner wing than that used
by earlier Mustangs)

As for the engine in the Mustang, all but the P51A engines were made by
Packard Motor Car Company in Detroit, Michigan as Rolls did not have the
engine building capacity to supply the needs of their own planes, much
less the Mustang and the Bell King Cobra. A real fight broke out
between Packard and Rolls as at the time, the Merlin was only 1350 hp.
Packard interviewed British and American pilots who had flown the engine
who repeatedly told Packard that the engine was not even "trying" when
at full power.



Packard made small modifications to the fuel system and produced 2,000
hp on their first try. Rolls said no-way were they going to have their
name on that engine as it would not hold together. Packard had collected
info that the average British fighter plane was shot down with only 97
hours on the engine. Rolls demanded 2,000 hours with only normal oil,
fuel, and air filter changes and valve adjustments. Finally the War
Department picked a number of 1,650 Hp and that was what went into
production at Packard. Spare engines were sent to England to support the
P51B and C. Spitfire pilots got hold of a few then demanded that Rolls
at least match the Americans engines, which they finally did.



I grew up in Chicago and two of my neighbours flew Mustangs as bomber
escort in Europe and in Korea against Yaks and Migs. The other fellow
flew his against Japan from March 1945 on until the end of the war in
the pacific. Both men loved their Mustangs. As Chuck Yeager said; it is
not an airplane, it is more like a well tailored suit that you put on it
fits so well you can’t believe it! It goes where you point it. Just fly
it fast and use the see-kill-go combat approach.

I have flown a Mustang back in 1964 after I first got my licence and
fell in love with it. This one had a 2,000 HP Rolls post war engine and
could screw itself right into the sky.



The Mustangs only rival was the Bell P63 King Cobra which used the same
engine but mounted it mid ship allowing faster turns with less wing
area, and it used the lamilar flow air foil also. While it had almost
the same profile as the much smaller P39, it had over 40% more wing area
and over 200% more horsepower. Since the P39 was such a failure (under
powered and wing loading too high), the War Department promised 100% of
the production of the P63 to the USSR before even seeing it. I worked
for a man who flew them over to Russia as part of the lend / lease
program. He said it was the best plane he had ever flown.



Most of the Mustangs were built in Texas near Dallas.

The Mustang I flew had been converted to have two seats. A second fully
functional seat had been added after removing the big radio and the 85
gallon fuel tank behind the pilot. I had learned to fly in a 1947 Piper
Cub J3. After take off and climb to 8000 feet in the Mustang, the pilot
offered me the controls. My Cub required about 6" of stick to the right
or left turn the airplane. Using the same on the right side of the
Mustang stick caused the view above my head to turn from sky blue to
green corn fields with no more effort that it takes to wink your eye.

There I sat hanging from my belts as amazed as the instructor was.
Finally he asked if I intended to continue inverted as we were not
cleared for aerobatics. The plane rolled back to level.

One problems with the P51D was that on take-off with a full load of fuel
(with drop tanks and ammo) the plane at maximum weight AND was tail
heavy.

Instructors in the US trained the new pilots to burn off their drop
tanks FIRST, then begin burning off fuel from the tank behind the pilot
in order to get maximum range.


The problem was that if a problem came up that meant returning to the
field to land, the plane could not be landed in the tail heavy
condition: it would flip upside down on its tail on approach. Many
green pilots were killed.


The experienced pilots quickly retrained the green kids to take off on
the wing tanks, then at about 2000 feet switch the tank behind the
pilot to burn off the 85 gallons that was making the plane tail heavy
during the remaining time it took to climb to 30,000 ft plus. That way
if they did have to drop the wing tanks to go after BF 109s for FW 190,
the Mustang would not have to fight in a tail heavy configuration,
which would mean sure death.


Landing the Mustang had some Do's and Don'ts. The plane required itself
to be flown onto the runway with ample power. Too many green pilots
would find themselves "short" of the runway and at just above stall
speed, trying to add a big burst of power from the Merlin. The Merlin
is not a high rev engine, but it IS an extremely high torque engine.

Opening the throttle would cause an immediate increase of torque to be
applied to the massive 4 bladed propeller which reacted slowly causing
reaction torque causing the plane to roll in the opposite direction of
the propeller rotation, usually causing a stall and crash since there
was no time to apply opposite stick to correct. Most experienced
Mustang drivers landed well above stall speed and slightly long to
assure that they would not be caught with this problem.

"Steve B" wrote in message
...

"Jim Wilkins" wrote

The Mustang's wing is symmetrical top and bottom, as you can see by
sighting down it from the wing tip.
http://www.aviation-history.com/theory/lam-flow.htm

jsw

Isn't symmetrical when you can fold it in half along one plane, and two
sides match?

Steve

Yes, for a paper rib pattern.
http://farm5.static.flickr.com/4143/...f1d7e89e10.jpg

A real one:
http://www.warbirdinformationexchang...c.php?p=312144

jsw

On Tue, 27 Sep 2011 22:28:05 -0700, Beryl wrote:

wrote:
...
The elevator - and the trim tab - do a LOT of work on a race plane at
500mph. And a lot at 200 too.

Explain! I haven't seen any explanations here, just claims. Richard
claims the nose must forcibly be held down at 500 mph.

The airplane is nose-heavy already, it must be held up. If it takes 200
lbs of downforce at the tail to hold the nose up at 200 mph, it also
takes 200 lbs of downforce to hold the nose up at 500 mph.

We want that 200 lbs of force to come with as little drag as possible at
500 mph. Can anyone explain how full nose-down trim tab deflection +
pushing the stick forward will produce the necessaty 200 lbs of
downforce at the tail?

It will do it because the stabilizer incidence is all wrong for 500 mph.
The stock stabilizer rigging is a compromise, to work acceptably through
the whole speed range. At 500 mph it's pushing the tail down too hard,
so Richard has to trim, and push the stick, to help hold the tail back
up. The tail surfaces are working against each other. Pitched up/down
crap hanging out in the wind.
The trim TAB is a servo mechanism that causes a small amount of
force to control a large amount of force. The little trim tab is what
makes the control input neutral. At 500mph, the force produced by a
couple degrees of "angle of incidence" on a tab 20 inches wide and 2
inches long - just as an example is VERY SIGNIFICANT - Stick your hand
out the window at 50mph and change the angle - feel the force. Now
remember aerodynamic drag increases at the cube of speed increse. The
lift and drag work directly in concert.Double the speed - 4X the
force. You are going to go 10 times as fast. What does that do to the
forces? And that tab is aerodynamically a lot cleaner than your hand.
It is also SIGNIFICANTLY more area - A few degrees of tab trim will
input a lot of force - particularly at the trailing edge - up to
several feet from the pivot. That trim makes the elevator (in this
case) follow along at the correct angle of incidence for straight and
level flight with no control input force (stick pressure).
Now, let that trim tab come loose at one end and start flapping in
the breeze, 2 feet farther back from the pivot than where it should be
- or simply 15 degrees or more off from where it should be - and all
of a sudden LARGE AMOUNTS of control input are required to hold the
elevator at the right position for level flight. Several hundred
pounds of force on the stick would be required INSTANTLY to correct
for the separation - and if that correction is not made INSTANTLY, the
quick movement of the elevator control surface through a significant
degree of movement causes a dangerously violent change in attitude -
forcing the tail surface down - and on a LONG lever - the down force a
LONG way back from the center of lift - which acts as the fulcrum. It
does not take a lot of force that far back to really toss the aircraft
out of straight and level flight. The up-pitch of the plane cuased by
the quick drop of the tail in this case caused well over 12 G's of
force on the plane- and the pilot - making it virtually impossible for
him to correct and control the plane - particularly when that close to
the ground.
The probability is VERY high that the 12 Gs of force caused the
(average)20 lb human head to weigh 240 lbs plus - instantly snapping
the pilot's neck in the process.

Anyone who doubts the effect of a trim tab at speed has never looked
seriously at aerodynamics or the flight characteristics of an
airplane. (and has likely never been at the controls of an airplane)

On Tue, 27 Sep 2011 22:34:05 -0700, Beryl wrote:

Richard wrote:
...
The elevator - and the trim tab - do a LOT of work on a race plane at
500mph. And a lot at 200 too.

Absolutely.

Add to that there is a lot of speed changes as the aircraft hits the turns.

The winning pilot minimizes speed loss and G forces through the turns.

TANSTAAFL...

That's why to optimize the airplane for top speed, the slow speed
performance suffers.
And the speed change through the turns in a race is NOT that
significant. Ground speed - yes, but not airspeed. That's why a lot of
turns are a "diving " turn. Trade altitude for airspeed in the turn so
you don't need to waste power getting the airspeed back after the
turn. You don't want to loose enough airspeed in the turn (heavily G
loaded) to stall the flight surfaces - or even get anywhere close.

fired this volley in
:

Trade altitude for airspeed in the turn so
you don't need to waste power getting the airspeed back after the
turn. You don't want to loose enough airspeed in the turn (heavily G
loaded) to stall the flight surfaces - or even get anywhere close.


Clare, you didn't think that out. Diving into a turn will gain you the
advantage of not losing airspeed, but what do you do in the next turn --
dive again?

How many turns do you execute before you meet the ground.

If you dive into a turn, you must climb on the straights. If you climb
during straight-ahead flight, you're "wasting airspeed" gaining altitude.
Ain't no other way it works.

It's a closed system -- you cannot maintain an "average" level flight
without expending a certain amount of power over the whole course. It
doesn't matter (on average) where you spend it if everything is
perfect... of course, things aren't 'perfect' in turns; the airplane is
"dirty" in turns, so you use less power regaining altitude in straight
flight than you would maintaining in in a turn.

But you _still_ "waste airspeed" gaining altitude. You can't not.


LLoyd

On Tue, 27 Sep 2011 23:03:48 -0700, Beryl wrote:

Richard wrote:
Beryl,

One last try and then I'll go away and leave you alone.

Bye!

Forget "nose heavy".

Think "pitch", aka deck angle, or preferably, angle of attack.


Within limits of course, angle of attack directly controls the amount of
lift generated by the wing. Yes, other parameters are also involved
but this angle is what the pilot has control of via the stick.

For straight and level unaccelerated flight, lift equals weight.

Wrong. Lift equals weight PLUS tail downforce. You can't "forget nose
heavy" as you suggest.

(thrust equals drag too, but that's another story)

As speed increases _so will lift_, unless something is done to keep that
from happening. THAT trick is simply pushing the nose down.

Wrong. That trick is lessening the tail surfaces' angle of attack, and
letting increased airspeed assume the task. There must be downforce at
the tail, always. You only think you're "pushing the nose down" because
you're fighting the stabilizer angle of attack, which, at 500 mph, is
far overdoing its job of holding the nose up.
Maybe you need to think Stabilator to make the light bulb come on.

(Airliners often pump fuel forward(!) but that's a bit over the top for
light aircraft)

By lowering the nose, the angle of attack is decreased, thereby
decreasing the coefficient of lift, and, if done right, maintaining
a constant altitude (the level part of straight and level)

Ok?

That's the whole of it.


So...

Quote
Of course trim needs chsnge. Richard apparently believes that
some nose-down is ALWAYS needed, and only the /amount/ of nose-down
changes as speed changes.

So for the discussion of a racer at 500 MPH, Yeah, True, Si, Da...

When landing, no.
Another way of looking at air racing - to go fast you need to reduce
LIFT to the absolute minimum required to keep the plane at the desired
altitude - so the LIFT REQUIRED is only the weight of the plane. The
lift PRODUCED increases dramatically with airspeed. The only way to
correct for the massively inreased lift at speed is to CHANGE the
angle of attack of the lifting surface(wing)- and the way to do that
is to raise and lower the elevator/horizontal stabilizer hanging out
back at the end of the "lever" that is the fuselage. Changing and
controlling that angle of attack takes significant force - produced by
the lift of the "elevator" - which is controlled by changing the angle
of attack of the elevator. The angle of attack of the elevator is
"trimmed" by the trim tab to neutralize the control input required to
produce straight and level flight - so only CONTROL input is required
by the pilot. If he wants to lower the tail - he provides input to
lower the tail. If he wants to raise the tail, he provides input to
raise the tail - he does not raise the tail by reducing the input that
is keeping the tail down - nor does he lower the tail by reducing the
input keeping the tail up. He just says "tail up" or "tail down" and
the plane follows his instructions.

And some planes have "flying tails" that constantly provide positive
lift in level flight - while other planes have "reverse flying tails"
that contantly provide down-force in level flight. Just look at the
airfoil configuration of the rear stabilizer/elevator on, say, a
Zenith 701 and compare it to, say, a cessna 172.

On Tue, 27 Sep 2011 23:23:50 -0700, Beryl wrote:

Richard wrote:
On 9/28/2011 12:28 AM, Beryl wrote:

Explain! I haven't seen any explanations here, just claims. Richard
claims the nose must forcibly be held down at 500 mph.

The airplane is nose-heavy already, it must be held up. If it takes 200
lbs of downforce at the tail to hold the nose up at 200 mph, it also
takes 200 lbs of downforce to hold the nose up at 500 mph.


Not on this planet...

You actually think the airplanes mass balance changes with speed?!!
No. but the LIFT BALANCE sure does!!!!

On 9/28/2011 6:15 PM, wrote:

Another way of looking at air racing - to go fast you need to reduce
LIFT to the absolute minimum required to keep the plane at the desired
altitude - so the LIFT REQUIRED is only the weight of the plane. The
lift PRODUCED increases dramatically with airspeed. The only way to
correct for the massively inreased lift at speed is to CHANGE the
angle of attack of the lifting surface(wing)- and the way to do that
is to raise and lower the elevator/horizontal stabilizer hanging out
back at the end of the "lever" that is the fuselage. Changing and
controlling that angle of attack takes significant force - produced by
the lift of the "elevator" - which is controlled by changing the angle
of attack of the elevator. The angle of attack of the elevator is
"trimmed" by the trim tab to neutralize the control input required to
produce straight and level flight - so only CONTROL input is required
by the pilot. If he wants to lower the tail - he provides input to
lower the tail. If he wants to raise the tail, he provides input to
raise the tail - he does not raise the tail by reducing the input that
is keeping the tail down - nor does he lower the tail by reducing the
input keeping the tail up. He just says "tail up" or "tail down" and
the plane follows his instructions.

And some planes have "flying tails" that constantly provide positive
lift in level flight - while other planes have "reverse flying tails"
that contantly provide down-force in level flight. Just look at the
airfoil configuration of the rear stabilizer/elevator on, say, a
Zenith 701 and compare it to, say, a cessna 172.


I wonder what he'd think about a flying wing?
Is it still "nose heavy" if it has no nose?
Or tail??

Clare Snyder wrote this wierdosity....

nother way of looking at air racing - to go fast you need to reduce
LIFT to the absolute minimum required to keep the plane at the desired
altitude - so the LIFT REQUIRED is only the weight of the plane. The
lift PRODUCED increases dramatically with airspeed.

Clare... (sigh...) When, exactly, did you encounter any situation in
straight and level flight were one needed more lift than the weight of
the plane (or less)?

Level flight _describes_ a situation where lift is equal to weight.

It doesn't matter what speed range you're considering... you don't
"reduce lift" to fly level, you keep it constant.

The only part of what you said that made any sense at all was that you
may have to reduce the angle of attack to keep the lift constant at
higher speeds.

????

LLoyd

On Wed, 28 Sep 2011 18:06:13 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

fired this volley in
:

Trade altitude for airspeed in the turn so
you don't need to waste power getting the airspeed back after the
turn. You don't want to loose enough airspeed in the turn (heavily G
loaded) to stall the flight surfaces - or even get anywhere close.


Clare, you didn't think that out. Diving into a turn will gain you the
advantage of not losing airspeed, but what do you do in the next turn --
dive again?

Nope, you climb to the next one - means you don't "need to hold the
nose down" as much!!!

How many turns do you execute before you meet the ground.

If you dive into a turn, you must climb on the straights. If you climb
during straight-ahead flight, you're "wasting airspeed" gaining altitude.
Ain't no other way it works.

You do NOT want to loose too much speed when in highly loaded flight -
like a turn. Rather have to climb slightly in the straights than be
too close to the ground, too "heavy" and too slow in the corners.

It's a closed system -- you cannot maintain an "average" level flight
without expending a certain amount of power over the whole course. It
doesn't matter (on average) where you spend it if everything is
perfect... of course, things aren't 'perfect' in turns; the airplane is
"dirty" in turns, so you use less power regaining altitude in straight
flight than you would maintaining in in a turn.


Eaxactly
But you _still_ "waste airspeed" gaining altitude. You can't not.


LLoyd
It takes power to fly - - - and a LOT of power to fly fast!!

On Wed, 28 Sep 2011 19:23:49 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Clare Snyder wrote this wierdosity....

nother way of looking at air racing - to go fast you need to reduce
LIFT to the absolute minimum required to keep the plane at the desired
altitude - so the LIFT REQUIRED is only the weight of the plane. The
lift PRODUCED increases dramatically with airspeed.

Clare... (sigh...) When, exactly, did you encounter any situation in
straight and level flight were one needed more lift than the weight of
the plane (or less)?

Level flight _describes_ a situation where lift is equal to weight.

It doesn't matter what speed range you're considering... you don't
"reduce lift" to fly level, you keep it constant.

Yes, but lift increases with airspeed - to a point - and if trimmed
for level flight at X000 feet at , say 300 mph, if you do not change
trim you will NOT be at X000 feet at 500MPH

The only part of what you said that made any sense at all was that you
may have to reduce the angle of attack to keep the lift constant at
higher speeds.

????

Hey LLoyd - what part of "so the LIFT REQUIRED is only the weight of
the plane. The lift PRODUCED increases dramatically with airspeed."
didn't you catch? You increase speed, you increase lift - so as you
speed up you need to - get this - REDUCE LIFT - to stay at the same
level.

LLoyd

In the Formula One racing, Tom Cassutt, the legend goes, was obsessive
about getting his racer around the pylons as fast as possible, if not
faster...

He was getting near 250 MPH out of a Continental O-200 engine (100 HP in
a Cessna 150 - at 80 knots!)

Back in the 1950's He did the math to compare routes. Close in and a
tight turn for the shortest distance flown, or out farther with a
lighter turn and higher airspeed. He seemed to favor the longer route
at higher speed as the best course.

Before he finally quit racing (dementia setting in) he was muttering
about completely eliminating cooling drag from his racer. At those
speeds air going through the engine to cool it account for fully 1/3
of the total drag on the airplane. 33% decreases in drag don't come
easy or cheap though!

Tom figured that the heat (punny) lasted 8 minutes, and the engine
would run full power for 10 minutes before seizing.

And it only takes him 15 minutes to change engines.

wrote:
On Tue, 27 Sep 2011 22:28:05 -0700, Beryl wrote:

wrote:
... The elevator - and the trim tab - do a LOT of work on a race
plane at 500mph. And a lot at 200 too.
....
The trim TAB is a servo mechanism

Nitpick - there are servo tabs, too. They work like trim tabs, except
they're not independently controlled by a trim wheel. They move with
elevator movement, in the same direction a trim tab would move, and
reduce stick forces.

that causes a small amount of force to control a large amount of
force. The little trim tab is what makes the control input neutral.
At 500mph, the force produced by a couple degrees of "angle of
incidence" on a tab 20 inches wide and 2 inches long - just as an
example is VERY SIGNIFICANT - Stick your hand out the window at 50mph
and change the angle - feel the force. Now remember aerodynamic drag
increases at the cube of speed increse. The lift and drag work
directly in concert.Double the speed - 4X the force. You are going to
go 10 times as fast. What does that do to the forces? And that tab is
aerodynamically a lot cleaner than your hand. It is also
SIGNIFICANTLY more area - A few degrees of tab trim will input a lot
of force - particularly at the trailing edge - up to several feet
from the pivot. That trim makes the elevator (in this case) follow
along at the correct angle of incidence for straight and level flight
with no control input force (stick pressure). Now, let that trim tab
come loose at one end and start flapping in the breeze, 2 feet
farther back from the pivot than where it should be - or simply 15
degrees or more off from where it should be - and all of a sudden
LARGE AMOUNTS of control input are required to hold the elevator at
the right position for level flight. Several hundred pounds of force
on the stick would be required INSTANTLY to correct for the
separation - and if that correction is not made INSTANTLY, the quick
movement of the elevator control surface through a significant degree
of movement causes a dangerously violent change in attitude - forcing
the tail surface down - and on a LONG lever - the down force a LONG
way back from the center of lift - which acts as the fulcrum. It does
not take a lot of force that far back to really toss the aircraft out
of straight and level flight. The up-pitch of the plane cuased by the
quick drop of the tail in this case caused well over 12 G's of force
on the plane- and the pilot - making it virtually impossible for him
to correct and control the plane - particularly when that close to
the ground. The probability is VERY high that the 12 Gs of force
caused the (average)20 lb human head to weigh 240 lbs plus -
instantly snapping the pilot's neck in the process.

Anyone who doubts the effect of a trim tab at speed has never looked
seriously at aerodynamics or the flight characteristics of an
airplane. (and has likely never been at the controls of an airplane)

That was pretty good.
It didn't support "The elevator - and the trim tab - do a LOT of work on
a race plane at 500mph" one bit, except for the unfortunate case when
the tab comes off. If that happens, it does do a LOT of work.

wrote:
...
And some planes have "flying tails" that constantly provide positive
lift in level flight - while other planes have "reverse flying tails"
that contantly provide down-force in level flight. Just look at the
airfoil configuration of the rear stabilizer/elevator on, say, a
Zenith 701 and compare it to, say, a cessna 172.

The 701 does not have a lifting tail. You're nuts.
The 701 tail pushes down to hold the nose up, just like the 172 tail does.

I see on their website
http://www.zenithair.com/stolch701/7-design-tail.html
they're calling the stabilizer an "inverted stabilizer". Just silly words.

On Wed, 28 Sep 2011 19:46:04 -0700, Beryl wrote:

wrote:
On Tue, 27 Sep 2011 22:28:05 -0700, Beryl wrote:

wrote:
... The elevator - and the trim tab - do a LOT of work on a race
plane at 500mph. And a lot at 200 too.
...
The trim TAB is a servo mechanism

Nitpick - there are servo tabs, too. They work like trim tabs, except
they're not independently controlled by a trim wheel. They move with
elevator movement, in the same direction a trim tab would move, and
reduce stick forces.

that causes a small amount of force to control a large amount of
force. The little trim tab is what makes the control input neutral.
At 500mph, the force produced by a couple degrees of "angle of
incidence" on a tab 20 inches wide and 2 inches long - just as an
example is VERY SIGNIFICANT - Stick your hand out the window at 50mph
and change the angle - feel the force. Now remember aerodynamic drag
increases at the cube of speed increse. The lift and drag work
directly in concert.Double the speed - 4X the force. You are going to
go 10 times as fast. What does that do to the forces? And that tab is
aerodynamically a lot cleaner than your hand. It is also
SIGNIFICANTLY more area - A few degrees of tab trim will input a lot
of force - particularly at the trailing edge - up to several feet
from the pivot. That trim makes the elevator (in this case) follow
along at the correct angle of incidence for straight and level flight
with no control input force (stick pressure). Now, let that trim tab
come loose at one end and start flapping in the breeze, 2 feet
farther back from the pivot than where it should be - or simply 15
degrees or more off from where it should be - and all of a sudden
LARGE AMOUNTS of control input are required to hold the elevator at
the right position for level flight. Several hundred pounds of force
on the stick would be required INSTANTLY to correct for the
separation - and if that correction is not made INSTANTLY, the quick
movement of the elevator control surface through a significant degree
of movement causes a dangerously violent change in attitude - forcing
the tail surface down - and on a LONG lever - the down force a LONG
way back from the center of lift - which acts as the fulcrum. It does
not take a lot of force that far back to really toss the aircraft out
of straight and level flight. The up-pitch of the plane cuased by the
quick drop of the tail in this case caused well over 12 G's of force
on the plane- and the pilot - making it virtually impossible for him
to correct and control the plane - particularly when that close to
the ground. The probability is VERY high that the 12 Gs of force
caused the (average)20 lb human head to weigh 240 lbs plus -
instantly snapping the pilot's neck in the process.

Anyone who doubts the effect of a trim tab at speed has never looked
seriously at aerodynamics or the flight characteristics of an
airplane. (and has likely never been at the controls of an airplane)

That was pretty good.
It didn't support "The elevator - and the trim tab - do a LOT of work on
a race plane at 500mph" one bit, except for the unfortunate case when
the tab comes off. If that happens, it does do a LOT of work.
And that's EXACTLY what happened on the plane in question (P51
Mustang bases Reno Racer)

On Wed, 28 Sep 2011 21:23:39 -0700, Beryl wrote:

wrote:
...
And some planes have "flying tails" that constantly provide positive
lift in level flight - while other planes have "reverse flying tails"
that contantly provide down-force in level flight. Just look at the
airfoil configuration of the rear stabilizer/elevator on, say, a
Zenith 701 and compare it to, say, a cessna 172.

The 701 does not have a lifting tail. You're nuts.
The 701 tail pushes down to hold the nose up, just like the 172 tail does.

I see on their website
http://www.zenithair.com/stolch701/7-design-tail.html
they're calling the stabilizer an "inverted stabilizer". Just silly words.
No, you need to understand how an airfoil works - then LOOK at both
the Cessna and the Zenith. The Cessna has the camber on the top - and
the bottom is flat. The airfoil causes LIFT in the upward direction.
The 701 has the camber on the bottom - and the top is flat - meaning
the LIFT is in the DOWNWARD direction. Forget about angle of attack
and just look at the AIRFOIL. The airfoil creates lift on the side
that accellerates the air-flow - following Bernouli's principal.

It is plainer than the nose on your face when you know what you are
looking for. But you are RIGHT - the 701 does NOT have a Lifting tail
- but the Cessna DOES.

wrote:
On Wed, 28 Sep 2011 21:23:39 -0700, Beryl wrote:
...
The 701 tail pushes down to hold the nose up, just like the 172
tail does. ...
The Cessna has the camber on the top - and the bottom is flat. The
airfoil causes LIFT in the upward direction.

Where did you see this 172 airfoil? Elevator, or stabilizer?

... the 701 does NOT have a Lifting tail - but the Cessna DOES.

No way. It would be tail heavy, unstable, with computers driving it.
An F-16.

On Thu, 29 Sep 2011 17:17:59 -0700, Beryl wrote:

wrote:
On Wed, 28 Sep 2011 21:23:39 -0700, Beryl wrote:
...
The 701 tail pushes down to hold the nose up, just like the 172
tail does. ...
The Cessna has the camber on the top - and the bottom is flat. The
airfoil causes LIFT in the upward direction.

Where did you see this 172 airfoil? Elevator, or stabilizer?
Stab. I'll have to take a closer look next time I'm at the airport
The camber is not much, compared to the fat stabilizer on the 701, but
from what I remember it is opposite in format from the 701

Many planes have pretty well symetrical stabilizers.

I guess "lifting tail" isn't totally accurate - but a lot less of a
downforce tail. Different hacks for different tracks - a faster plane
gets more downwash from the wings thet forces the tail down much more
at speed. A slow-flying plane like the 701 and Pegazair depends more
on the reversed airfoil for the downforce.
On a very fast plane like the p51 the stabilizer is almost like a
knife blade or a plank - not much camber either way.

On Sun, 25 Sep 2011 18:05:58 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

fired this volley in
:

Sounds like a classic side slip - pull the nose up to peal off speed,
then drop one wing and let it slide a few hundred Or thousand) feet,
drop the nose to catch back a few knots, and hit the runway, instead
of doing another 2 circuits around lake meade to get down.

It was standard approach practice for the Aussie pilots flying Caribous
in 'Nam. They wanted to avoid ground fire, so they'd do what amounts to
a side-slipping stall right above the threshold, and drop in like a rock,
recovering just enough airspeed to flare near the end.

On 1100' PSP runways, that actually looks like an attractive way to make
an approach!

Hey, I've got no problems with it at all - that is, with a little
advance warning about what's going to happen. And "Informed Consent"
comes into play too.

"Okay people, we're shaving 20 minutes off our approach. Face
forward, heads up and well back in your seat, and here we go..."

You don't DO that with a full commercial passenger aircraft without
giving the passengers a heads-up. Or at least an apology if you did
it inadvertently, "No, that wasn't your imagination."

-- Bruce --