Dual Trim Switches?

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?

They're not just unnecessary -- they're dangerous. That is 13
separate points of failure that should not be in that wing.

I've had several quick drains leak over the years -- one quite badly
-- now imagine 13 of them! All plumbing fittings, by their very
nature, will eventually leak. These will, too.

There's really no other way to put it: Cezzzna really screwed the
pooch with their wing design.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Recently, Jay Honeck posted:

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?

They're not just unnecessary -- they're dangerous. That is 13
separate points of failure that should not be in that wing.

I've had several quick drains leak over the years -- one quite badly
-- now imagine 13 of them! All plumbing fittings, by their very
nature, will eventually leak. These will, too.

There's really no other way to put it: Cezzzna really screwed the
pooch with their wing design.

Our club's 172 SP had those drain points. As I recall, only 10 of them
were in the wing, with the other 3 on the cowling. I can only imagine the
pretzel fuel flow that made that many drains necessary. I agree with the
OP that suggested that Cessna's lawyers designed that aspect of their
planes.

Neil

On Tue, 02 Oct 2007 09:56:00 GMT, "Neil Gould"
wrote:

Recently, Jay Honeck posted:

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?

They're not just unnecessary -- they're dangerous. That is 13
separate points of failure that should not be in that wing.

I've had several quick drains leak over the years -- one quite badly
-- now imagine 13 of them! All plumbing fittings, by their very
nature, will eventually leak. These will, too.

There's really no other way to put it: Cezzzna really screwed the
pooch with their wing design.

Our club's 172 SP had those drain points. As I recall, only 10 of them
were in the wing, with the other 3 on the cowling. I can only imagine the
pretzel fuel flow that made that many drains necessary. I agree with the
OP that suggested that Cessna's lawyers designed that aspect of their
planes.

AIUI, it's because they're bladders and folds on the bottom could
gather water. If it was a wet wing they wouldn't need as many, like
the older models.

Help

I flew a 'Top Hat' four way trim switch for thousands of hours and
never saw a second one. Anyone know where it was located?

Our emergency procedure for run away trim was to pull the circuit
breaker(s).

Big John

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


On Fri, 28 Sep 2007 09:43:28 -0700, "Robert M. Gary"
wrote:

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

Big John wrote in
:

Help

I flew a 'Top Hat' four way trim switch for thousands of hours and
never saw a second one. Anyone know where it was located?

Our emergency procedure for run away trim was to pull the circuit
breaker(s).



Switches like that are illegal now. You have to have passive fail systems
on trims and autopiots nowadays.



Bertie

Bertie

I'm going to the "Wings over Houston" Air Show at Ellington this week
end. Besides getting some cockpit time in the P-40 and P-51, I'll talk
to some of the current Heavy Iron drivers, with birds on display,
about what the trim is on the birds newer than I flew. From past shows
expect to see at least the F-15, F-16, F-117 and also Navy jets, Blue
Angels, etc. Probably some Chinese Migs that were kept at Ellington.

Its 62 years since I flew the P-40 and 58 years since I flew the P-51
so need the cockpit time to refresh where all the controls, etc.,
were/are )

Big John
************************************************** *****88

On Sun, 30 Sep 2007 07:47:28 +0000 (UTC), Bertie the Bunyip
wrote:

Big John wrote in
:

Help

I flew a 'Top Hat' four way trim switch for thousands of hours and

----clip----

Switches like that are illegal now. You have to have passive fail
systems on trims and autopilots nowadays.

Bertie

Big John wrote in
:

Bertie

I'm going to the "Wings over Houston" Air Show at Ellington this week
end. Besides getting some cockpit time in the P-40 and P-51, I'll talk
to some of the current Heavy Iron drivers, with birds on display,
about what the trim is on the birds newer than I flew. From past shows
expect to see at least the F-15, F-16, F-117 and also Navy jets, Blue
Angels, etc. Probably some Chinese Migs that were kept at Ellington.

Its 62 years since I flew the P-40 and 58 years since I flew the P-51
so need the cockpit time to refresh where all the controls, etc.,
were/are )


Have fun!

Ask 'em if they have any LeBlond valve springs while you're there.

Bertie

If the switches are in parallel and one of them develops an internal short
circuit, you will still have trim runway; if they are in series, both must
be closed simultaneously. Sounds like a dumb idea to me, but check with a
mechanic or radio shop for a knowledgeable answer...I'm not sure that I
would expect the Chief Pilot to be the expert on electrical questions.

Bob Gardner

"Christopher Brian Colohan" wrote in message
...
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.")

On Sep 28, 1:30 pm, "Bob Gardner" wrote:
If the switches are in parallel and one of them develops an internal short
circuit, you will still have trim runway; if they are in series, both must
be closed simultaneously. Sounds like a dumb idea to me, but check with a
mechanic or radio shop for a knowledgeable answer...I'm not sure that I
would expect the Chief Pilot to be the expert on electrical questions.

Bob, I'm curious why you think it's a dumb idea? As far as I know
they are in series and it seems like a fairly clever idea to me since
it greatly reduces the possibility of a malfunctioning switch causing
runaway trim. I'm not sure if it's a solution looking for a problem
or if that's a legitimate concern, but given how simple and cheap it
is to implement, why not?

My memory isn't what it used to be, and though I flew a lot of planes with
trim switches I don't remember there being two. I must have a "two separate
actions" thing going on in my thinking machine.

Bob

"tjd" wrote in message
ups.com...
On Sep 28, 1:30 pm, "Bob Gardner" wrote:
If the switches are in parallel and one of them develops an internal
short
circuit, you will still have trim runway; if they are in series, both
must
be closed simultaneously. Sounds like a dumb idea to me, but check with a
mechanic or radio shop for a knowledgeable answer...I'm not sure that I
would expect the Chief Pilot to be the expert on electrical questions.

Bob, I'm curious why you think it's a dumb idea? As far as I know
they are in series and it seems like a fairly clever idea to me since
it greatly reduces the possibility of a malfunctioning switch causing
runaway trim. I'm not sure if it's a solution looking for a problem
or if that's a legitimate concern, but given how simple and cheap it
is to implement, why not?