limit of trim = limit of travel?

On Tue, 6 May 2008 07:16:07 -0700 (PDT), WingFlaps
wrote:

On May 7, 12:56*am, Stealth Pilot
wrote:
On Mon, 5 May 2008 23:54:37 -0700 (PDT), WingFlaps

wrote:
On May 6, 3:36*pm, Bertie the Bunyip wrote:
WingFlaps wrote :

OK, then if the AOA of the stabilator is constant, and the elevator
angle is constant, why does the lift reduce when the trim tab is
deflected in the opposite direction?

because the elevator angle isnt bloody constant. what is constant is
the stick force which you maintain at the same pressure by
unconsciously moving the stick as you change the trim tab position.

It's as I said, the effect is as
if the _effective_ area is reduced.

no it bloody isnt. the area remains the same the lift force is what
varies and guess what, that's why the tailfeathers have the hinges in
the middle.

You could say that CL is altered
but then it gets more messy as you have to consider different CL's and
areas for each section of the stabilator. It's much simpler to just
subtract the area taken by the trim from the calculation and that will
give a very good first order approximation for longitudinal stability
calculations.

you have basically started out with a faulty understanding and for the
last 100 posts have misinterpreted everything written because you keep
relating the information to the original faulty premise.


Nope. I understand it perfectly. As defined in any good book on
aeronautical design, stabilator effectiveness is _defined_ by the
horizontal tail volume coefficient which is the product of tail moment
and area divided by the wing area and it's mean chord.

From the style of you reply I can see you will have a hard time
understanding this this it really is correct -look it up.

Cheers

no I'm afraid that it is you who do not understand it.
you take a rule of thumb approximation and then try to apply it as a
hard and fast aerodynamic concept.

brother have you got it wrong.
Stealth Pilot

On Tue, 6 May 2008 07:29:10 -0700 (PDT), WingFlaps
wrote:



if you had studied and passed the BAK you wouldnt be so perpetually
stupid regarding the questions you ask.


Perhaps it is you who does not understand the depth of the questions I
ask? But I'm sure you must be right, I can't possibly have any
understanding of the interplay of trim and trimmed surface with the
airflow over them because I'm not a pilot in your world.


no genuinely you do not understand how this works in practise.

if you are designing an aircraft forget the trim tab in the
calculations. the pilot will set it to where ever he needs it.

your questions dont have that much depth btw.
just a lot of misunderstood aerodynamics.

Stealth Pilot

On May 8, 12:17*am, Stealth Pilot
wrote:


your questions dont have that much depth btw.
just a lot of misunderstood aerodynamics.


Naysaying is the mark of a troll wihen no facts are given to back it
up.

Cheers

wrote:
On May 5, 5:55 pm, WingFlaps wrote:

Does the elevator lift force and stall angle reflect trim setting at
all?
Cheers

Probably to some rather minor degree. The government just demands
that the airplane behave in certain ways in various configurations and
maneuvers, so the designers have to build their airplanes to fit
within those specs. An elevator should never stall before the wing,
for example, or the whole machine could flip over onto its back. The
rising tail, rising because the stab/elevator stalled, would
experience an even higher AOA as it rose and things would get very
nasty. The certification guys want the nose to drop gently as the wing
stalls, which couldn't happen if the stab let go too soon. Some
airplanes (I.E. Ercoupe) had limited up-elevator to prevent wing stall
and therefore the stall/spin scenario that killed so many in the '40s
and '50s. The nose didn't drop because the wing stalled but because
the stab/elevator ran out of nose-up authority. It could easily have
been modified to get the stall. There was plenty of area there. Only
problem was that guys would get slow on final and pancake into the
ground and break their backs with compression fractures. Don't
necessarily need to stall to get killed.
The Cessna Cardinal had a problem early on with the stabilator
stalling in the landing flare and smashing the nosewheel on pretty
hard, and they fixed that with a slot in the leading edge of the
stabilator. IIRC the ground effect had something to do with the stab
stall problem. I never had any such thing happen at altitude in the
'68 (non-slotted) Cardinals.

Dan

Usually, in conventional aircraft, the tailplane force is a download.
When this download is suddenly reduced, as in a tailplane stall, there
is a sudden and probably fairly violent nose down pitch. How you
determine whether it is an elevator stall, or tailplane stall, without
special instrumentation, is beyond me.
Cheers

nospam wrote in
newsbmdnXqirNejAr_VnZ2dnUVZ_sednZ2d@internode:

wrote:
On May 5, 5:55 pm, WingFlaps wrote:

Does the elevator lift force and stall angle reflect trim setting
at
all?
Cheers

Probably to some rather minor degree. The government just demands
that the airplane behave in certain ways in various configurations
and
maneuvers, so the designers have to build their airplanes to fit
within those specs. An elevator should never stall before the wing,
for example, or the whole machine could flip over onto its back. The
rising tail, rising because the stab/elevator stalled, would
experience an even higher AOA as it rose and things would get very
nasty. The certification guys want the nose to drop gently as the
wing
stalls, which couldn't happen if the stab let go too soon. Some
airplanes (I.E. Ercoupe) had limited up-elevator to prevent wing
stall
and therefore the stall/spin scenario that killed so many in the '40s
and '50s. The nose didn't drop because the wing stalled but because
the stab/elevator ran out of nose-up authority. It could easily have
been modified to get the stall. There was plenty of area there. Only
problem was that guys would get slow on final and pancake into the
ground and break their backs with compression fractures. Don't
necessarily need to stall to get killed.
The Cessna Cardinal had a problem early on with the stabilator
stalling in the landing flare and smashing the nosewheel on pretty
hard, and they fixed that with a slot in the leading edge of the
stabilator. IIRC the ground effect had something to do with the stab
stall problem. I never had any such thing happen at altitude in the
'68 (non-slotted) Cardinals.

Dan

Usually, in conventional aircraft, the tailplane force is a download.
When this download is suddenly reduced, as in a tailplane stall, there
is a sudden and probably fairly violent nose down pitch. How you
determine whether it is an elevator stall, or tailplane stall, without
special instrumentation, is beyond me.
Cheers


You can't, and the reason you can't is because it's all one unit.
There's no difference because you can't seperate their functions.

Bertie

WingFlaps wrote:
On May 6, 2:19 am, Bertie the Bunyip
wrote:
On May 5, 6:06 am, WingFlaps wrote:





On May 5, 8:48 am, Bertie the Bunyip wrote:
WingFlaps wrote :
On May 5, 3:19 am, Bertie the Bunyip wrote:
Stealth Pilot wrote
innews:u8kr141dp0o1e
:
On Fri, 2 May 2008 12:32:28 -0700 (PDT), WingFlaps
wrote:
On May 3, 12:40 am, Stealth Pilot
wrote:
On Wed, 30 Apr 2008 00:12:54 +0000 (UTC), Bertie the Bunyip
wrote:
WingFlaps wrote in
news:ad8fc9c9-57cb-4733-9e97-
:
On Apr 30, 9:37 am, wrote:
On Apr 29, 2:24 pm, WingFlaps wrote:
I don't follow this. The trim surface operates in the
opposite direction to the trimmed surface and takes area
away from it.
-----------------------------------------------------------------
^^^
^
Explain
please?
What area stuff?
Cheers
that area stuff. ...which shows a total lack of aerodynamic
understanding.
Still don't know what you're talking about! Most of that thread has
spooled off my main server now..
He's trolling.
Cheers
He's not, he's right. Deflecting a tab in the oppostie direction doesn't
remove area.
It reduces effective area.
No, it doesn´t. The area is stil there. The tab isn´t "hiding" because
it´s going the other way, it´s just doing something different. it may
be reducing the effectiveness of the surface, but that isn´t the same
thing as reducing the area.

Nope. Effectiveness is proportional to area -from the old lift
equation.

Cheers
Oh I get it, if I am flying along and select an AOA which gives the
aircraft zero total lift, I have effectively reduced the wing plus tail
area to zero.
Don't know why you don't just say that the tail coefficient of lift is
affected by tab angle (any tab).
Cheers

Bertie the Bunyip wrote:
nospam wrote in
newsbmdnXqirNejAr_VnZ2dnUVZ_sednZ2d@internode:

wrote:
On May 5, 5:55 pm, WingFlaps wrote:

Does the elevator lift force and stall angle reflect trim setting
at
all?
Cheers
Probably to some rather minor degree. The government just demands
that the airplane behave in certain ways in various configurations
and
maneuvers, so the designers have to build their airplanes to fit
within those specs. An elevator should never stall before the wing,
for example, or the whole machine could flip over onto its back. The
rising tail, rising because the stab/elevator stalled, would
experience an even higher AOA as it rose and things would get very
nasty. The certification guys want the nose to drop gently as the
wing
stalls, which couldn't happen if the stab let go too soon. Some
airplanes (I.E. Ercoupe) had limited up-elevator to prevent wing
stall
and therefore the stall/spin scenario that killed so many in the '40s
and '50s. The nose didn't drop because the wing stalled but because
the stab/elevator ran out of nose-up authority. It could easily have
been modified to get the stall. There was plenty of area there. Only
problem was that guys would get slow on final and pancake into the
ground and break their backs with compression fractures. Don't
necessarily need to stall to get killed.
The Cessna Cardinal had a problem early on with the stabilator
stalling in the landing flare and smashing the nosewheel on pretty
hard, and they fixed that with a slot in the leading edge of the
stabilator. IIRC the ground effect had something to do with the stab
stall problem. I never had any such thing happen at altitude in the
'68 (non-slotted) Cardinals.

Dan
Usually, in conventional aircraft, the tailplane force is a download.
When this download is suddenly reduced, as in a tailplane stall, there
is a sudden and probably fairly violent nose down pitch. How you
determine whether it is an elevator stall, or tailplane stall, without
special instrumentation, is beyond me.
Cheers


You can't, and the reason you can't is because it's all one unit.
There's no difference because you can't seperate their functions.

Bertie
Well, even without instrumentation, one can determine if the elevator
power is sufficient to do a landing flare at say 1.3 Vs minus 5kts at
forward CG. Increasing elevator area may be one method of increasing
elevator power. Also you cannot treat the elevator and tailplane as one
unit where elevator hinge moments are needed to be of a particular
(algebraic)sign ie stick free longitudinal static stability measurement.
Cheers

nospam wrote in
news:bYydndxV96btLr_VnZ2dnUVZ_vCdnZ2d@internode:

Bertie the Bunyip wrote:
nospam wrote in
newsbmdnXqirNejAr_VnZ2dnUVZ_sednZ2d@internode:

wrote:
On May 5, 5:55 pm, WingFlaps wrote:

Does the elevator lift force and stall angle reflect trim setting
at
all?
Cheers
Probably to some rather minor degree. The government just demands
that the airplane behave in certain ways in various configurations
and
maneuvers, so the designers have to build their airplanes to fit
within those specs. An elevator should never stall before the wing,
for example, or the whole machine could flip over onto its back.
The
rising tail, rising because the stab/elevator stalled, would
experience an even higher AOA as it rose and things would get very
nasty. The certification guys want the nose to drop gently as the
wing
stalls, which couldn't happen if the stab let go too soon. Some
airplanes (I.E. Ercoupe) had limited up-elevator to prevent wing
stall
and therefore the stall/spin scenario that killed so many in the
'40s
and '50s. The nose didn't drop because the wing stalled but because
the stab/elevator ran out of nose-up authority. It could easily
have
been modified to get the stall. There was plenty of area there.
Only
problem was that guys would get slow on final and pancake into the
ground and break their backs with compression fractures. Don't
necessarily need to stall to get killed.
The Cessna Cardinal had a problem early on with the
stabilator
stalling in the landing flare and smashing the nosewheel on pretty
hard, and they fixed that with a slot in the leading edge of the
stabilator. IIRC the ground effect had something to do with the
stab
stall problem. I never had any such thing happen at altitude in the
'68 (non-slotted) Cardinals.

Dan
Usually, in conventional aircraft, the tailplane force is a
download.
When this download is suddenly reduced, as in a tailplane stall,
there
is a sudden and probably fairly violent nose down pitch. How you
determine whether it is an elevator stall, or tailplane stall,
without
special instrumentation, is beyond me.
Cheers


You can't, and the reason you can't is because it's all one unit.
There's no difference because you can't seperate their functions.

Bertie
Well, even without instrumentation, one can determine if the elevator
power is sufficient to do a landing flare at say 1.3 Vs minus 5kts at
forward CG. Increasing elevator area may be one method of increasing
elevator power. Also you cannot treat the elevator and tailplane as
one
unit where elevator hinge moments are needed to be of a particular
(algebraic)sign ie stick free longitudinal static stability
measurement.
Cheers



Sure you can, one without the other is notreally much of anything. they
work together.

Bertie

"Bertie the Bunyip" wrote in message
.. .
nospam wrote in
news:bYydndxV96btLr_VnZ2dnUVZ_vCdnZ2d@internode:

Bertie the Bunyip wrote:
nospam wrote in
newsbmdnXqirNejAr_VnZ2dnUVZ_sednZ2d@internode:

wrote:
On May 5, 5:55 pm, WingFlaps wrote:

Does the elevator lift force and stall angle reflect trim setting
at
all?
Cheers
Probably to some rather minor degree. The government just demands
that the airplane behave in certain ways in various configurations
and
maneuvers, so the designers have to build their airplanes to fit
within those specs. An elevator should never stall before the wing,
for example, or the whole machine could flip over onto its back.
The
rising tail, rising because the stab/elevator stalled, would
experience an even higher AOA as it rose and things would get very
nasty. The certification guys want the nose to drop gently as the
wing
stalls, which couldn't happen if the stab let go too soon. Some
airplanes (I.E. Ercoupe) had limited up-elevator to prevent wing
stall
and therefore the stall/spin scenario that killed so many in the
'40s
and '50s. The nose didn't drop because the wing stalled but because
the stab/elevator ran out of nose-up authority. It could easily
have
been modified to get the stall. There was plenty of area there.
Only
problem was that guys would get slow on final and pancake into the
ground and break their backs with compression fractures. Don't
necessarily need to stall to get killed.
The Cessna Cardinal had a problem early on with the
stabilator
stalling in the landing flare and smashing the nosewheel on pretty
hard, and they fixed that with a slot in the leading edge of the
stabilator. IIRC the ground effect had something to do with the
stab
stall problem. I never had any such thing happen at altitude in the
'68 (non-slotted) Cardinals.

Dan
Usually, in conventional aircraft, the tailplane force is a
download.
When this download is suddenly reduced, as in a tailplane stall,
there
is a sudden and probably fairly violent nose down pitch. How you
determine whether it is an elevator stall, or tailplane stall,
without
special instrumentation, is beyond me.
Cheers


You can't, and the reason you can't is because it's all one unit.
There's no difference because you can't seperate their functions.

Bertie
Well, even without instrumentation, one can determine if the elevator
power is sufficient to do a landing flare at say 1.3 Vs minus 5kts at
forward CG. Increasing elevator area may be one method of increasing
elevator power. Also you cannot treat the elevator and tailplane as
one
unit where elevator hinge moments are needed to be of a particular
(algebraic)sign ie stick free longitudinal static stability
measurement.
Cheers



Sure you can, one without the other is notreally much of anything. they
work together.

Bertie

Of coarse you can Bertie Buttlipp, you know everything, you know everyone,
you've done everything. Gotta link?

Bertie the Bunyip wrote:
nospam wrote in
news:bYydndxV96btLr_VnZ2dnUVZ_vCdnZ2d@internode:

Bertie the Bunyip wrote:
nospam wrote in
newsbmdnXqirNejAr_VnZ2dnUVZ_sednZ2d@internode:

wrote:
On May 5, 5:55 pm, WingFlaps wrote:

Does the elevator lift force and stall angle reflect trim setting
at
all?
Cheers
Probably to some rather minor degree. The government just demands
that the airplane behave in certain ways in various configurations
and
maneuvers, so the designers have to build their airplanes to fit
within those specs. An elevator should never stall before the wing,
for example, or the whole machine could flip over onto its back.
The
rising tail, rising because the stab/elevator stalled, would
experience an even higher AOA as it rose and things would get very
nasty. The certification guys want the nose to drop gently as the
wing
stalls, which couldn't happen if the stab let go too soon. Some
airplanes (I.E. Ercoupe) had limited up-elevator to prevent wing
stall
and therefore the stall/spin scenario that killed so many in the
'40s
and '50s. The nose didn't drop because the wing stalled but because
the stab/elevator ran out of nose-up authority. It could easily
have
been modified to get the stall. There was plenty of area there.
Only
problem was that guys would get slow on final and pancake into the
ground and break their backs with compression fractures. Don't
necessarily need to stall to get killed.
The Cessna Cardinal had a problem early on with the
stabilator
stalling in the landing flare and smashing the nosewheel on pretty
hard, and they fixed that with a slot in the leading edge of the
stabilator. IIRC the ground effect had something to do with the
stab
stall problem. I never had any such thing happen at altitude in the
'68 (non-slotted) Cardinals.

Dan
Usually, in conventional aircraft, the tailplane force is a
download.
When this download is suddenly reduced, as in a tailplane stall,
there
is a sudden and probably fairly violent nose down pitch. How you
determine whether it is an elevator stall, or tailplane stall,
without
special instrumentation, is beyond me.
Cheers

You can't, and the reason you can't is because it's all one unit.
There's no difference because you can't seperate their functions.

Bertie
Well, even without instrumentation, one can determine if the elevator
power is sufficient to do a landing flare at say 1.3 Vs minus 5kts at
forward CG. Increasing elevator area may be one method of increasing
elevator power. Also you cannot treat the elevator and tailplane as
one
unit where elevator hinge moments are needed to be of a particular
(algebraic)sign ie stick free longitudinal static stability
measurement.
Cheers



Sure you can, one without the other is notreally much of anything. they
work together.

Bertie
They only work "together", as you put, after a lot of careful
engineering of the individual components and the interaction between
them. Even then, testing often shows that further refinements are
necessary.

Take, for example 4 tails all of the same planform and aerofoil section.

1. An all flying tail hydraulically operated.
The pivot point can be almost anywhere, hinge moments don't matter much
if sufficient hydraulic power is available. No tabs are required and
control feel can be as simple as a set of springs.

2. An all flying tail manually operated.
The pivot point position has to be placed to achieve correct control
feel throughout the tail range of motion at all angles of attack the
tail will "see" in service. A anti-balance tab will be required - this
will affect the tail lift curve. A trim tab will be required, depending
on the aerodynamic problems this may or may not be incorporated in the
anti-balance tab operation.

3. A fixed tail with an elevator.
The hinge positions can be comparatively easily calculated to achieve
the correct hinge moments for feel and stick fixed stability. To have
the same power as the two above more area is required. A trim tab is
required and an elevator down spring may be necessary to achieve the
same stable CG range as the above 2.

4 A fixed tail with an elevator which requires a geared balance tab to
either increase or decrease elevator hinge moments and therefore control
feel.

Similar to above but will be more or less powerful depending on the
direction of operation of the geared balance tab.


Sure it all works together but has to be designed to do it.

For those who were wondering about tab effect, or indeed elevator effect
on total tail lift the following may help;
Each item can be considered separately.
There will be a basic tail camber lift component which in many cases is
zero.
Then find the tailplane AOA and from the lift curve slope find tail Cl -
put that into the normal lift equation.
At that particular tailplane AOA, select the elevator AOA and again find
the Cl from the lift curve.
Then do the same for the tab.
Add the 3 solutions to get total tail lift.
Do this for the complete range of angle of attack for each component and
you will know the total range (and direction) of tail lift.
Cheers