Dual Trim Switches?

After flying Tomahawks and Citabrias, I took my first lesson in a
Cessna 172 last night. I asked many questions, but I had one question
which nobody in my flying club (including the chief pilot) knew the
answer to when I was the Why does the electric elevator trim have
two switches (both of which must be depressed) on the yoke instead of
one?

The best theory I could come up with was "to avoid runaway trim if one
switch stuck", but that is not very satisfying...

Anyone know why?

Chris

(Another question: 13 fuel drains? What were they thinking??? But I
am pretty sure the answer is "the lawyers designed that part, not the
engineers.")

Christopher Brian Colohan wrote in
:

After flying Tomahawks and Citabrias, I took my first lesson in a
Cessna 172 last night. I asked many questions, but I had one question
which nobody in my flying club (including the chief pilot) knew the
answer to when I was the Why does the electric elevator trim have
two switches (both of which must be depressed) on the yoke instead of
one?

The best theory I could come up with was "to avoid runaway trim if one
switch stuck", but that is not very satisfying...

That's it. It's the one and only reason.




Anyone know why?

Chris

(Another question: 13 fuel drains? What were they thinking??? But I
am pretty sure the answer is "the lawyers designed that part, not the
engineers.")


There's 13 places where water gets stuck in that system.

Bertie

On Sep 28, 9:26 am, Bertie the Bunyip wrote:


There's 13 places where water gets stuck in that system.

I seriously doubt that.

-Robert, CFI

"Robert M. Gary" wrote in news:1190997921.453348.284760@
22g2000hsm.googlegroups.com:

On Sep 28, 9:26 am, Bertie the Bunyip wrote:


There's 13 places where water gets stuck in that system.

I seriously doubt that.


Kay.

Bertie

That is exactly what I was taught learning the Mooney M20C meny years ago!

Ron Gardner

"Robert M. Gary" wrote in message
ups.com...
On Sep 28, 9:26 am, Bertie the Bunyip wrote:


There's 13 places where water gets stuck in that system.

I seriously doubt that.

-Robert, CFI

"R. Gardner" wrote in message
.. .
"Robert M. Gary" wrote in message
ups.com...
On Sep 28, 9:26 am, Bertie the Bunyip wrote:


There's 13 places where water gets stuck in that system.

I seriously doubt that.

-Robert, CFI

That is exactly what I was taught learning the Mooney M20C meny years ago!

Ron Gardner


Drains cost money and add points of failure, weight, and (nearly always)
drag. They are *only* placed where the manufacturer is convinced that water
might otherwise be trapped.

Peter

P.S.: Nevertheless, when this thread began, I really was tempted to suggest
that the multitude of drains was to collect enough fuel to run a
lawnmower--since we no longer throw it on the ground and most pilots don't
put it back in the aircraft. :-)

Peter

Using drained fuel for lawn mower.

When using 115-145 fuel I always filled up my Zippo when preflighting
and draining water out of tanks. We didn't have the plastic jars to
drain into so let fall to ground under bird (in old days). Had to be
careful and shake excess out of lighter (Zippo) or first couple of
times when lit, would get a 6 inch flame and could singe your eye
brows lighting your cigarette or pipe. )

Of course we never worried about the lead (TEL) in the gas (lots in
the high octane fuel) and inhaling it when lighting the tobacco (
Probably part of the cause of my lung problems today.

Big John

************************************************** ***


----clip----

P.S.: Nevertheless, when this thread began, I really was tempted to
suggest that the multitude of drains was to collect enough fuel to run
a lawnmower--since we no longer throw it on the ground and most pilots
don't put it back in the aircraft. :-)

"Christopher Brian Colohan" wrote in message
...

(Another question: 13 fuel drains? What were they thinking??? But I
am pretty sure the answer is "the lawyers designed that part, not the
engineers.")

Cessna was offered the Monarch fuel tanks when the went back into
production. But, according to Bill Barton, Cessna never even acknowledged
the offer.

There are 13 drains because they NEED them. The Monarchs need only one, ALL
water is drainable, and they never leak. Cessna has particularly poor fuel
tank engineering.
http://www.sumpthis.com/imagescourte...er17274599.htm

You should always test the trim switches according to the POH to prevent
runaway trim.

KG

On Sep 28, 9:15 am, Christopher Brian Colohan
wrote:
After flying Tomahawks and Citabrias, I took my first lesson in a
Cessna 172 last night. I asked many questions, but I had one question
which nobody in my flying club (including the chief pilot) knew the
answer to when I was the Why does the electric elevator trim have
two switches (both of which must be depressed) on the yoke instead of
one?

I assume this is a recent model 172. To avoid a stuck switch (or
shorted switch) from running the trim. In the preflight checklist that
Cessna provides one of the tests under the "trim test" section is to
ensure that the trim does not move with either of the switches is
moved by itself. Additionally you should ensure that the electric trim
does not work at all when the auto-pilot cut-off is held down.

The best theory I could come up with was "to avoid runaway trim if one
switch stuck", but that is not very satisfying...

Anyone know why?

Chris

(Another question: 13 fuel drains? What were they thinking??? But I
am pretty sure the answer is "the lawyers designed that part, not the
engineers.")

No one really knows. Some believe that there is one for every lawsuit
someone brought against Cessna because they forgot to drain the tanks.
Few actually believe that Cessna designed the tanks to collect water
at that many points. In anycase, we just drain them all.

-Robert, CFII

"Robert M. Gary" wrote

No one really knows. Some believe that there is one for every lawsuit
someone brought against Cessna because they forgot to drain the tanks.
Few actually believe that Cessna designed the tanks to collect water
at that many points. In anycase, we just drain them all.

From the pictures provided (by a link) in an earlier post, it is obvious
(with the help of some added color agent) that there are, or could be, some
very big problems if the tank is not drained at all of the provided drains.

Everyone knows that the airplane is a group of compromises flying in close
formation. It seems as though the tank design is a _big_ compromise, for
some reason.

It is hard for me to understand how Cessna could come up with such a poor
design. I do realize that a wet tank has to have internal structures in
place, with weight and strength being two of the most important design
criteria, but it does seem like it should be possible to leave some pass
through areas to let gas and water flow freely from bay to bay.

It might have cost a little more, but when you are spending, what, over 200
AMU's to buy an airplane, should it not be possible to include some design
improvements that costs a little more, than take the easy way out with
nearly a dozen added (should be) unnecessary drains?

If a tank design like that is Cessna's normal way of dong things, I would
think Columbia's future owners have some genuine concerns.
--
Jim in NC