Backup for dropping the gear

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I've been reading the POH for my club's 182RG, and I find myself surprised.
The manual gear extension replies upon the same hydrolic pressure system as
the powered mechanism.

Isn't that insufficiently redundant?

I'm not sure what I expected - perhaps something purely mechanical. But I
didn't expect a lone pressure system to be a single point of failure.

Is this normal?

- Andrew

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In a previous article, Andrew Gideon said:
I've been reading the POH for my club's 182RG, and I find myself surprised.
The manual gear extension replies upon the same hydrolic pressure system as
the powered mechanism.

Isn't that insufficiently redundant?

The P32R Lance that I'm currently checking out in uses hydraulic pressure
to hold the gear *up* against springs and gravity - lose the hydraulic
pressure and the gear goes down. As a matter of fact, sometimes in
turbulence you get a gear unsafe light and you have to quickly cycle the
gear lever to repressurize the hydraulics.


--
Paul Tomblin http://xcski.com/blogs/pt/
"Maybe if your vcr is still blinking 12:00 you shouldn't be using Linux."
-- Slashdot poster

Piper gear PIREP

The nose gear on the Seminole and many other similar Pipers has a coaxial
pair of springs.
In my case the inner spring failed, jamming the outer spring and resulting
in a nose idiot light not coming on.
Expecting a collapse, I landed the Seminole like a tail dragger and walked
away.

The springs are a few dollars. Replace them periodically.
My Seminole was on leaseback,
I was scheduled between two renters.
Better me than them.

Old pilots have paid attention to detail.
So said one.

Blue skies.
H.



"Paul Tomblin" wrote in message
...
In a previous article, Andrew Gideon said:
I've been reading the POH for my club's 182RG, and I find myself
surprised.
The manual gear extension replies upon the same hydrolic pressure system
as
the powered mechanism.

Isn't that insufficiently redundant?

The P32R Lance that I'm currently checking out in uses hydraulic pressure
to hold the gear *up* against springs and gravity - lose the hydraulic
pressure and the gear goes down. As a matter of fact, sometimes in
turbulence you get a gear unsafe light and you have to quickly cycle the
gear lever to repressurize the hydraulics.


--
Paul Tomblin http://xcski.com/blogs/pt/
"Maybe if your vcr is still blinking 12:00 you shouldn't be using Linux."
-- Slashdot poster

"Andrew Gideon" wrote in message
online.com...
I've been reading the POH for my club's 182RG, and I find myself
surprised.
The manual gear extension replies upon the same hydrolic pressure system
as
the powered mechanism.

I'm not sure there's enough standardization in gear retraction/extension
systems to say what's "normal". However, certainly the lack of redundancy
is common enough on light planes. In fact, not only is the gear on my
airplane designed similarly, the flaps and elevator trim use the same
hydraulic system. A failure in the hydraulic system that takes out certain
lines, and/or results in a loss of fluid would affect all three systems
simultaneously.

Occasionally you might find a "fail safe" system like the one on the Lance
that Paul mentions, but as he even points out, those systems come with their
own issues. Aircraft designers often come to the conclusion that the extra
complexity, cost, and weight isn't worth the marginal increase in safety.

Especially when one considers just how dangerous a gear-up landing *isn't*,
it's not hard to see why that conclusion is reached so often. As far as I
know, such "insufficiently redundant" systems are more common than
"sufficiently redundant" ones.

Pete

"Andrew Gideon" wrote in message
online.com...
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I've been reading the POH for my club's 182RG, and I find myself
surprised.
The manual gear extension replies upon the same hydrolic pressure system
as
the powered mechanism.

Isn't that insufficiently redundant?

I'm not sure what I expected - perhaps something purely mechanical. But I
didn't expect a lone pressure system to be a single point of failure.

Is this normal?

The Cessna 172RG is similar.

Hydraulic pressure is used to hold the gear up. The pump runs every few
minutes to maintain hydraulic pressure. Unfortunately, if the pump or
another part of the hydraulic system fails, the gear will come down only
part way, streaming behind the airplane like a duck with broken legs.

The manual system is just another pump, only it is only capable of lowering
the gear. If you lose hydraulic pressure the manual system will provide
enough pressure to lower the gear and lock it in place if there is any fluid
in the system at all. You would have to spring a leak at the bottom of the
sump to lose all your hydraulic fluid.

If someone absolutely cannot get the gear down and locked it is nearly
always because of some fracture at the pivot point. No backup system would
salvage that -- the landing gear is physically broken.

I personally have seen the gear system work with no hydraulic fluid left in
the reservoir -- just a little bit left in the lines. The emergency
extension lever was not even needed.

The landing gear system is not all that critical anyway. If more redundancy
is required, the weight penalty is better applied to other systems.

"Peter Duniho" wrote in message

I'm not sure there's enough standardization in gear retraction/extension
systems to say what's "normal". However, certainly the lack of redundancy
is common enough on light planes. In fact, not only is the gear on my
airplane designed similarly, the flaps and elevator trim use the same
hydraulic system. A failure in the hydraulic system that takes out
certain
lines, and/or results in a loss of fluid would affect all three systems
simultaneously.


I suppose you could also run the brakes off the same hydraulic system as the
gear, too. After all, if the gear fails you won't be needing any brakes. :-)

Not sure what you mean by "normal"...? It certainly is for
all the Cessna retractable singles - yours hasn't been singled
out for special treatment. As to whether it's a good idea, well
no, it sure doesn't seem so. But that's the way it is.

I've had to hand-pump mine once, when a switch in the
pump circuit failed. It's a nasty moment when the gear doesn't
go down, and a very pleasant feeling when that green light
comes on. Failure of a seal anywhere in the hydraulics means
you'll be using a lot of power to taxi off the runway. According
to Aviation Consumer it's rare (amongst failures) but not unknown.

John

"Andrew Gideon" wrote in message
online.com...
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I've been reading the POH for my club's 182RG, and I find myself
surprised.
The manual gear extension replies upon the same hydrolic pressure system
as
the powered mechanism.

Isn't that insufficiently redundant?

I'm not sure what I expected - perhaps something purely mechanical. But I
didn't expect a lone pressure system to be a single point of failure.

Is this normal?

- Andrew

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If by "normal" you mean "does everyone else do it this way", then no it's
not normal. Piper arrows have an override which releases hydraulic pressure
so that the gear can free fall into position. Older moonies have a "johnson
bar" which is a purely manual system. Yet other planes have an emergency
tank for blowing the gear down (beech maybe?).

For the 182RG, I believe the hydraulic system provides for "up pressure"
meaning that if you spring a leak the gear should drop. So if only the pump
fails, out comes the handle, otherwise the gear are coming down anyway. And
now for the bad news: because the main gear fold backward into the fuselage,
they likely won't drop all the way on a hydraulic failure. There are
various anecdotes about pilots reaching out the door with the towbar to pull
the gear all the way down.

Folding legs on the high-wing Cessnas have always been a bit of a black eye,
usually due to maintenance issues.

cheers,
mark

"Andrew Gideon" wrote in message
online.com...
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I've been reading the POH for my club's 182RG, and I find myself
surprised.
The manual gear extension replies upon the same hydrolic pressure system
as
the powered mechanism.

Isn't that insufficiently redundant?

I'm not sure what I expected - perhaps something purely mechanical. But I
didn't expect a lone pressure system to be a single point of failure.

Is this normal?

- Andrew

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In article ,
"C J Campbell" wrote:


I suppose you could also run the brakes off the same hydraulic system as the
gear, too. After all, if the gear fails you won't be needing any brakes. :-)

The B-24 I used to fly is like that. Brakes, flaps, landing gear and
bombbay doors all on the same system. There is one engine driven pump
(#3 engine), an electric pump and a hand-pump. There are also 2
accumulators. If you have pressure in the accumulators you will have
one shot at the brakes...release the brakes and you release the
pressure. The copilot will be pumping like crazy on the handpump about
then. G The gear will freefall into position (the nose gear has to be
manually thrown out), and the flaps can be pumped down using the
handpump.

I only had one problem with the hydraulics. The main feed line from the
engine driven pump cracked at an elbow filling the bombbay with
hydraulic fluid...took less than a minute to pump all the fluid out
rendering us helpless. Luckily we had just landed and were taxiing to
parking when it failed. Mixtures to "cutoff" and coasted to a stop.
Had just enough time to say "WHEW!" before the airplane started rolling
backward due to a very slight grade on the taxiway. NOT a good feeling.
G The crewchief was scrambling trying to get out to throw himself
under the wheel as a chock when we came to a stop. If the crack had
opened just a minute or two before I probablyl would've parked the
airplane in the same gas station Southwest did a few years back.

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

There are a lot of things that are not redundant.

The lesson to learn is to know the systems of your plane very, very, well.
This is not an easy task, nor is it common between planes.

You should know all the systems, and the what-if scenarios that go with
them. This includes the mechanical systems. Like how the cables and
pushrods are run through the plane.

For example: What if you pump down the gear but do not get a green
light? Do you cycle the gear? Answer - it depends. You need to give
thought to the possibility that cycling the gear may lose what little
hydraulic fluid you have left. When the hydraulic system runs more
than one thing, you need to worry about what else you might lose.
There is no one pat answer that fits all planes. Reading the emergency
procedures is great - except the emergency procedures have difficulty
determining which combination of failures has happened. You really
need to understand the systems.




In article ne.com, Andrew
Gideon wrote:
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I've been reading the POH for my club's 182RG, and I find myself surprised.
The manual gear extension replies upon the same hydrolic pressure system as
the powered mechanism.

Isn't that insufficiently redundant?

I'm not sure what I expected - perhaps something purely mechanical. But I
didn't expect a lone pressure system to be a single point of failure.

Is this normal?

- Andrew

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