A320 Rudder Pedal behavior / RTLU

[marcom]

Hi folks,

I'm a little confused as to how the rudder pedals would behave in flight under normal conditions.
Here is what I know: the RTLU will limit the rudder surface deflection based on airspeed. This is reflected on the flight control page on the ECAM.

But what about the rudder pedals themselves? Do they always have full travel authority or is it limited as well?

The FCOM suggests so but I had the opportunity to test 3 different FFS and in 2 sims the rudder travel was limited at high speed whereas in the 3rd sim it wasn't! Airspeed was around 280 kts in each case.
All based on A320 CEO.
I'm very puzzled by this, especially that the sims would behave differently in this very fundamental aspect.

I'm aware that there aren't too many (alive) pilots who can actually testify as to how the real aircraft would behave!

Any thoughts on this? Any a reference would be very welcome!

Many thanks
Mark

[Sim25]

Since the A320 Airbus uses, at least for the ongoing A330/340 non electric rudder units (A380/350 and modern 330 use all electric rudder), RTLU systems that only limit the rudder travel and not the rudder pedal deflection. Opposed to the A310 for example which uses a fixed stop system limiting also the pedals. That’s the short answer…

if you are interested in more technical details: https://pdfcoffee.com/ata-27-4-pdf-free.html

Simon

[marcom]

Thanks for your input, Simon.

The PDF quotes:
"The mechanical input to the rudder servo control units is limited by the position
of the Rudder Travel Limitation Unit ( TLU ). The input rods will also act
against the Artificial Feel & Trim Unit."

Which does infer that input (which is coming from rudder pedals) is in fact limited. Perhaps the limiting is performed by the artificial feel unit and not directly by the RTLU?

Anyway, please don't take this the wrong way, but I am not yet fully convinced by your statement. This skepticism is also based on some false factual statements you made in the FBW control law thread (but you sound very convincing :-) ).

[Sim25]

I have to look that up again, but if I remember correctly (and quite frankly this is the only way it would make sense) the RTLU is placed downstream in the linkage system so after the trim and art. feel system (wich is "just" a spring and a screw displacing the sping and via the spring the complete linkage system, adding an offset, of course simplified, which also displaces the rudder pedals...)

One thing and I know that this can led to great ****storm, so now I ask you to pls don't get that wrong:

A FCOM isn't a technical absolute accurate reference... It's written in a way that it it describes sometimes pretty complex subsystems in a correct yet most as possible easy way. Which makes totally sense, as you don't need to know the details of all SAOs (the language when programming the flight control computers) like the cycle time of gain scheduling for alternate law pitch. Just as an example...
Back to rudder: The picture in the FCOM is OK and explains the principal but it isn't a detailed mechanical drawing.

Another example (and please if I missed it, correct me) while looking at the SAO for roll direct law on the 330/340 I noticed that the inner ailerons droop in direct, which isn't stated in the FCOM. Most likely it's only a small detail not worth mentioning but, if you stick brutally to FCOM you would say that I'm wrong, which according to the software! I'm not.

And as a last example: nobody needs to know how the maps in your cars's engine control look, and which functions are embedded to regenerate the exhaust system, just to drive the car. And I wouldn't compare the car's manual to a FCOM but the shop service manual you maybe can (details wise) compare to the FCOM and even there details of the above aren't mentioned. Same for AMM and the SAO stuff I wrote about... (and yes I know that driving a car is not flying a plane, and a plane is not a car and so on)

Hope you get what I mean and before this is somehow an argument later on: no I'm NOT a pilot, so aren't the engineers at Airbus, or most of them... and the thread you where referring to was a truly engineering topic where you need to go into details, like the guy who authored the paper I cited, which is then refuted with, sorry, abstruse arguments about how he (the author) has a phd in helicopter fbw?!?!? Sorry but there I'm out, this has nothing to do with scientific research or working principals.

Simon