Fly-By-Wire Flight Controls

Benjamin Gawert wrote:
Eunometic schrieb:

The PA200 Tornado is fully FBW with a mechanical linkage backup system...

Benjamin


Then why does it need a thermal backup battery to remain airborn?

Because besides power for certain important instruments and the radio
the EPS battery also powers an electric motor that powers a hydraulic pump.

"Mechanical linkage" does not mean that the stick is connected to
pushrods and levers that move the control surfaces (which would be silly
on a fighter/bomber aircraft with up to ~55000 pounds weight).

Which means that PA200 Tornado when using 'mechanical' backup is
actually fully power opperated as opposed to power assisted (power
assisted can be designed to connect into a fully manual system with
limited movement). Given the need for power it doesn't seem to make
much sense to bother to use a mechanical system at all. An additional
layer of redundancy and an 'analog' backup would be better use of the
weight. Perhaps Panavia was worried about Electromagnetic Pulse or
Weapons. I believe F-16 uses fiber optics.

When in
so-called "mech mode" the stick is connected to several hydraulic valves
that control the hydraulic actuators. So you need hydraulics pressure,
and in cases of double engine out this hydraulic pressure comes from an
electric pump that powered by the EPS battery.

In normal operation the potentiometers connected to the stick submit
stick position data to the flight control system (CSAS and SPILS) which
calculate the necessary control surface deflection and control the
corresponding actuators.

They use potentiometers? I though LVDT were normally used.

The mechanical linkage is inactive (in
emergencies the stick gets linked to the mechanical controls through a
honeycomb block which gets squeezed by the stick movement applied by the
panicing pilot ;-)

This applies to the GR versions (bomber), I don't know if the F versions
are somewhat different.

Benjamin

Eunometic schrieb:

"Mechanical linkage" does not mean that the stick is connected to
pushrods and levers that move the control surfaces (which would be silly
on a fighter/bomber aircraft with up to ~55000 pounds weight).


Which means that PA200 Tornado when using 'mechanical' backup is
actually fully power opperated as opposed to power assisted (power
assisted can be designed to connect into a fully manual system with
limited movement).

correct.

Given the need for power it doesn't seem to make
much sense to bother to use a mechanical system at all.

The mechanical linkage backup is there if the 2x redundant fly-by-wire
system fails or gets damaged. When in "mech mode" (FBW dead but engines
are running) the aircraft is fully controllable (but of course reacts
more sensible due to the lack of CSAS and also lacks things like spin
prevention and AOA limiter etc). Loosing the FBW does not mean the
aircraft can't return safely...

An additional
layer of redundancy and an 'analog' backup would be better use of the
weight. Perhaps Panavia was worried about Electromagnetic Pulse or
Weapons.

Correct. Thanks to the mechanical linkage the aircraft is still operable
even when suffering from an EMP or with a damaged electronics system.
Even 4x redundant FBW wouldn't provide this safety, and the weight
penalty isn't really big.

I believe F-16 uses fiber optics.

The Eurofighter Typhoon uses fiber optics. The F-16 used a wire harness
(don't know if that has been changed in a later block but I doubt that).

In normal operation the potentiometers connected to the stick submit
stick position data to the flight control system (CSAS and SPILS) which
calculate the necessary control surface deflection and control the
corresponding actuators.


They use potentiometers? I though LVDT were normally used.

No, it's some sort of potentiometer, but of course a bit more
sophisticated than what you can find in consumer electronics ;-)

Benjamin

On Mon, 19 Dec 2005 19:59:21 +0100, Benjamin Gawert
wrote:

Eunometic schrieb:

"Mechanical linkage" does not mean that the stick is connected to
pushrods and levers that move the control surfaces (which would be silly
on a fighter/bomber aircraft with up to ~55000 pounds weight).


Which means that PA200 Tornado when using 'mechanical' backup is
actually fully power opperated as opposed to power assisted (power
assisted can be designed to connect into a fully manual system with
limited movement).

correct.

Given the need for power it doesn't seem to make
much sense to bother to use a mechanical system at all.

The mechanical linkage backup is there if the 2x redundant fly-by-wire
system fails or gets damaged. When in "mech mode" (FBW dead but engines
are running) the aircraft is fully controllable (but of course reacts
more sensible due to the lack of CSAS and also lacks things like spin
prevention and AOA limiter etc). Loosing the FBW does not mean the
aircraft can't return safely...


Hmm sounds sensible in a Cold War environment with buckets of canned
sunshine being thrown around.

But now a question to pilots or folks in the know:
Do they train flying "mech mode" and if so how?
Just in the sims or sometimes for real as in.
"IP to student: I flipped the switch to mech mode. Show me how you
smooth you can land this baby"?

And if a pilot can apparently fly safe in "mech mode" does that mean
that the Tornado is not inherent unstable like the F16? Or at least
not very inherent unstable?

Because flying a F16 in "mech mode" (if that beast would exist) THAT
would be a real challange.

Greetz Mu




Greetz Mu

Mu schrieb:

Hmm sounds sensible in a Cold War environment with buckets of canned
sunshine being thrown around.

Well, the PA200 is a aircraft from the cold war aera...

But now a question to pilots or folks in the know:
Do they train flying "mech mode" and if so how?
Just in the sims or sometimes for real as in.
"IP to student: I flipped the switch to mech mode. Show me how you
smooth you can land this baby"?

No real training in mech mode (mech mode is an emergency system and not
selectable by a switch, and having it activated once means that after
the aircraft is back on the ground it has to go to service for having
the honeycomb package replaced). You can train that in the simulator,
but usually there is no special training for flying in mech mode...

And if a pilot can apparently fly safe in "mech mode" does that mean
that the Tornado is not inherent unstable like the F16? Or at least
not very inherent unstable?

No, it's not. The PA200 is a very stable aircraft, there are no real
surprises for the pilot when in mech mode. There is a little yaw
tendency that gets suppressed by the yaw damper in CSAS and that shows
up in mech mode, and you loose functions like auto rudder or SPILS (spin
preventer/AOA limiter), stick feel simulation and such. Nothing which is
really a problem for emergency operation...

Benjamin

On Tue, 20 Dec 2005 13:52:11 +0100, Benjamin Gawert wrote:

And if a pilot can apparently fly safe in "mech mode" does that mean
that the Tornado is not inherent unstable like the F16? Or at least
not very inherent unstable?

No, it's not. The PA200 is a very stable aircraft, there are no real
surprises for the pilot when in mech mode.

A bit sensitive in pitch maybe? :-)

Theres a video at the link below of a GR1 doing a mech-mode approach,
although thats not what the vid is about, hehe. Scroll down to 'Bonus' and
its the 'Near miss' video. A hairy situation.

http://www.fromtheflightdeck.com/videos/index.htm


--
Steve.

Steve wrote:

Theres a video at the link below of a GR1 doing a mech-mode approach,
although thats not what the vid is about, hehe. Scroll down to 'Bonus' and
its the 'Near miss' video. A hairy situation.

http://www.fromtheflightdeck.com/videos/index.htm

Don't you just hate people who don't have their checklists completed
when the take the active? ;


Jack

Steve schrieb:

No, it's not. The PA200 is a very stable aircraft, there are no real
surprises for the pilot when in mech mode.


A bit sensitive in pitch maybe? :-)

With wings at 25 degrees the Tornado is quite sensitive in pitch, even
with FBW. Especially since approaches and take offs are done with
deactivated SPILS...

Theres a video at the link below of a GR1 doing a mech-mode approach,
although thats not what the vid is about, hehe. Scroll down to 'Bonus' and
its the 'Near miss' video. A hairy situation.

http://www.fromtheflightdeck.com/videos/index.htm

Nice video. This btw happened in Decimomannu/Italy when the tower
"forgot" about a italian Tornado waiting for T/O clearance and allowed a
German Tornado to land...

Benjamin

On Sat, 24 Dec 2005 21:21:50 +0100, Benjamin Gawert wrote:

http://www.fromtheflightdeck.com/videos/index.htm

Nice video. This btw happened in Decimomannu/Italy when the tower
"forgot" about a italian Tornado waiting for T/O clearance and allowed a
German Tornado to land...

Ah, didn't know it was at Deci. Thought it happened in UK but with an
Italian exchange student in the front and moaning mini in the back. :-) Did
the GR see the F2 in time or was it a red flare job? Heard the F2 crew had
to scrub due to shock.


--
Steve.