Mechanics of Elevator Trim. In Detail.

"Le Chaud Lapin" wrote in message
...
Hi All,

This post is primarily directed toward student pilots like myself.

First, I am not asking because I want to know the answer (I already
know), but do a little experiment. I have maybe 7 or 8 different
sources of flight information that I rely on for ground school
(Jeppesen, FAA Handbooks, etc), and none of them said _how_ it worked
in sufficient detail, they only said what one must do to make the
plane pitch up or downard.

Probably because there are several different ways to make it work -

I assume you are most familiar with the use of a servo tab. Can you name at
least two other ways that it is commonly done in light aircraft?


But it is good to understand how the aircraft systems work (and what can go
wrong) - so continue on with the discussion...

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

On Jun 8, 11:05*am, "Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way
D0t C0m wrote:
"Le Chaud Lapin" wrote in ...

Hi All,

This post is primarily directed toward student pilots like myself.

First, I am not asking because I want to know the answer (I already
know), but do a little experiment. *I have maybe 7 or 8 different
sources of flight information that I rely on for ground school
(Jeppesen, FAA Handbooks, etc), and none of them said _how_ it worked
in sufficient detail, they only said what one must do to make the
plane pitch up or downard.

Probably because there are several different ways to make it work -

I assume you are most familiar with the use of a servo tab. Can you name at
least two other ways that it is commonly done in light aircraft?

Nope.

But it is good to understand how the aircraft systems work (and what can go
wrong) - so continue on with the discussion...

Also, for the record, my assumption of what was going on with elevator
was invalid. The Jeppesen Private Pilot mentions the servo tab, and
technically, they do say what it does, but very briefly, so if student
is not paying attention, s/he might miss it.

-Le Chaud Lapin-

Capt. Geoffrey Thorpe wrote:

I assume you are most familiar with the use of a servo tab. Can you name
at least two other ways that it is commonly done in light aircraft?

The J-3 Cub has a moving stabilizer. Although you specifically said
"light aircraft" it's interesting to note that many airliners also us a
moving stabilizer.

This and another method are mentioned in this article:

http://flighttraining.aopa.org/learn...rticle_pf.html

On Jun 8, 9:17*pm, Michael Henry
wrote:
Capt. Geoffrey Thorpe wrote:
I assume you are most familiar with the use of a servo tab. Can you name
at least two other ways that it is commonly done in light aircraft?

The J-3 Cub has a moving stabilizer. Although you specifically said
"light aircraft" it's interesting to note that many airliners also us a
moving stabilizer.

This and another method are mentioned in this article:

http://flighttraining.aopa.org/learn.../articles/0209...

Yikes - that's it. The answer is in that link.

Since no other students responded...

...when I first started used/read about trim tab, I figured it was
"more of the same", meaning that there was some complex mechanism in
the aircraft where trim tab simply did more of whatever the elevator
was doing, but some how figured out how to release pressure on the
yoke.

Well that's true, but a more correct interpretation is that the trim
tab does not participate in elevating the aircraft really, but serves
to aerodynamically set the angle of the elevator, at which point the
elevator does its job. I learn this in MSFS by trying various
movements and watching outside the aircraft how control surfaces
responded. The trim tab was moving in opposite direction that I
thought it would. I also saw that on C172, there is an asymmetric,
with only one tab.

All obvious to pilots, but interesting for students, for me at least.

-Le Chaud Lapin-

On Sun, 8 Jun 2008 22:24:07 -0700 (PDT), Le Chaud Lapin
wrote:

On Jun 8, 9:17*pm, Michael Henry
wrote:
Capt. Geoffrey Thorpe wrote:
I assume you are most familiar with the use of a servo tab. Can you name
at least two other ways that it is commonly done in light aircraft?

The J-3 Cub has a moving stabilizer. Although you specifically said
"light aircraft" it's interesting to note that many airliners also us a
moving stabilizer.

This and another method are mentioned in this article:

http://flighttraining.aopa.org/learn.../articles/0209...

Yikes - that's it. The answer is in that link.

Since no other students responded...

...when I first started used/read about trim tab, I figured it was
"more of the same", meaning that there was some complex mechanism in
the aircraft where trim tab simply did more of whatever the elevator
was doing, but some how figured out how to release pressure on the
yoke.

Well that's true, but a more correct interpretation is that the trim
tab does not participate in elevating the aircraft really, but serves
to aerodynamically set the angle of the elevator, at which point the
elevator does its job. I learn this in MSFS by trying various
movements and watching outside the aircraft how control surfaces
responded. The trim tab was moving in opposite direction that I
thought it would. I also saw that on C172, there is an asymmetric,
with only one tab.

All obvious to pilots, but interesting for students, for me at least.

-Le Chaud Lapin-

if you ever read 'Stick and Rudder' by wolfgang langeweische you will
find that he refers to flippers for the majority of the book.
this is to prevent the mistake you make above where you thought the
elevator elevated the aircraft.

amazing, I never thought anyone actually made that mistake.
Stealth Pilot

Stealth Pilot wrote in
:

On Sun, 8 Jun 2008 22:24:07 -0700 (PDT), Le Chaud Lapin
wrote:

On Jun 8, 9:17*pm, Michael Henry
wrote:
Capt. Geoffrey Thorpe wrote:
I assume you are most familiar with the use of a servo tab. Can
you name at least two other ways that it is commonly done in light
aircraft?

The J-3 Cub has a moving stabilizer. Although you specifically said
"light aircraft" it's interesting to note that many airliners also
us a moving stabilizer.

This and another method are mentioned in this article:


http://flighttraining.aopa.org/learn.../articles/0209
...

Yikes - that's it. The answer is in that link.

Since no other students responded...

...when I first started used/read about trim tab, I figured it was
"more of the same", meaning that there was some complex mechanism in
the aircraft where trim tab simply did more of whatever the elevator
was doing, but some how figured out how to release pressure on the
yoke.

Well that's true, but a more correct interpretation is that the trim
tab does not participate in elevating the aircraft really, but serves
to aerodynamically set the angle of the elevator, at which point the
elevator does its job. I learn this in MSFS by trying various
movements and watching outside the aircraft how control surfaces
responded. The trim tab was moving in opposite direction that I
thought it would. I also saw that on C172, there is an asymmetric,
with only one tab.

All obvious to pilots, but interesting for students, for me at least.

-Le Chaud Lapin-

if you ever read 'Stick and Rudder' by wolfgang langeweische you will
find that he refers to flippers for the majority of the book.
this is to prevent the mistake you make above where you thought the
elevator elevated the aircraft.

amazing, I never thought anyone actually made that mistake.

First hour students do sometimes. I've also seen one guy actually tilt
his head back when IO told him to raise the nose on a first flight.

Flippers is an archaic term that predates Langeweisch by a couple of
decades! It was pretty much dropped mainstream during WW2, I suppose
because it didn't sound techie enough.


Bertie