Reverse Thrust System and Interlocks

[farrokh747]

Hi all –

my Throttle Quadrant has a set of 4 thrust reverser interlocks, and the microswitch assy mounted just fwd of the throttle lever pack – the function of the interlocks is to prevent travel of the reverser levers beyond 50 degrees of travel until the thrust reverser is in "null thrust position", after which the interlock retracts to allow the reverse levers to travel the full 89 degrees... The interlocks are solenoids, and I guess would be driven by relays. The microswitch assy is a set of 4 plunger switches, which are activated by the detents in the edges of the throttle lever pack. From what I can tell, these control functions dealing with the reverser system, and some autobrake systems. (bit foggy about this)

The steps, breifly..( as explained by an ame to me)
1. Reverse lever inhibited by a latch in the lever when thrust lever is more than 2 degrees forward of idle (mechanical)
2. At 3. When rev thrust is selected, the eec sends a signal to the interlocks to move from retract to extend, which inhibits TR lever movement beyond 50 degrees of travel
4. When Thrust reverser moves to the the null thrust position, the EEC signals the interlocks to retract and allow levers to move all the way to 89 degrees.
5. When the Thrust Reverser is in the null thrust position, the EEC sends the appropriate signal to the fuel valves based on the TR lever position.

My question is: are the interlocks (and the Thrust Reverser Sequencing) modeled in PSX? Right now in FS we're using the standard –4096 to +16384 values, without using the interlock function, or any of the logic described above.  I'm in the process of re wiring the quadrant, and was wondering if I should include all the available outputs / relays to the I/O

Also, not clear what "null thrust position" is.... And, with the above, is the actual range of Thrust Reverse power limited to 50 to 89 degrees of lever travel, with the 0 to 50 degree portion restricted to controlling the actuation of the physical reversers?

The info above may be incorrect/incomplete in parts, as I'm writing from memory...

Any thoughts would be helpful!

Thanks!

Farrokh.

[John H Watson]

4. When Thrust reverser moves to the the null thrust position, the EEC signals the interlocks to retract and allow levers to move all the way to 89 degrees.
5. When the Thrust Reverser is in the null thrust position, the EEC sends the appropriate signal to the fuel valves based on the TR lever position.

I can't say I've heard of the expression "null thrust position". The EECs simply generate a signal to unlock the interlocks when the reverse thrust cowling has moved more than 60% (CF6/RR/PW)

You would have to discuss with Hardy, the depth of modeling required. Perhaps interlock relay status would be required if you are implementing interlocks. There may not be a big demand for this.

The system, of course, will be modelled with the latest wiring amendments (to prevent inadvertant retraction of LE flaps during takeoff).

Rgds
JHW

[farrokh747]

Thanks John = do you know if the Reverser in transit period is linked to the amber REV before it goes Green...? If so, I assume that the interlock release and change from amber to green would occur simultaneously..

I agree this is not going to be an in demand feature... :-)

No rush here, will wait for word on this from Hardy when comes to this section, if he hasn't already...

Is this the mod you're referring to?

http://www.skybrary.aero/index.php/B744,_Johannesburg_South_Africa,_2009_(LOC_AW)  

http://flightsafety.org/asw/jul10/asw_jul10_p56-63.pdf

cheers

FC

[farrokh747]

from the OM:

Thrust Reverser Indication:
Displayed REV (amber) - reverser in transit.
Displayed REV (green) - reverser fully deployed.

Amber to green REV annun and Interlocks release when reverser fully deployed.

On pushing the levers forward and down again, the indication goes back to amber, and  is removed when reverser is stowed and locked. I don't believe there's any interlock activity on reversers OFF.

[Hardy Heinlin]

Hi Farrokh,

yes, the reverser interlock system will be modelled. The mechanical side of the model is already implemented, -- EEC not yet.


Cheers,

|-|ardy

[John H Watson]

do you know if the Reverser in transit period is linked to the amber REV before it goes Green...? If so, I assume that the interlock release and change from amber to green would occur simultaneously..

As far as I know, the REV indications are unrelated to interlock. There are simple proximity sensors & targets on the strut and reverser cowling for generating these indications. The prox sensors can only sense stowed/not stowed and fully deployed/not fully deployed (i.e. logic 1 or logic 0).
For the interlock at the 60% value (and greater , for engine thrust control), this requires a continuous range of position feedback (provided by other sensors).  

Is this the mod you're referring to?

http://www.skybrary.aero/index.php/B744,_Johannesburg_South_Africa,_2009_(LOC_AW)  

http://flightsafety.org/asw/jul10/asw_jul10_p56-63.pdf

Correct )
There was an earlier mechanical modification which was tried many years ago to help prevent the unintentional retraction of LE flaps. However, the earlier modification was not designed to safeguard against the improper rigging of stow position sensors on two different engines (which seemed to be the case in the 2009 incident)

Regards
JHW

[farrokh747]

Thanks Hardy, John... that's good news...

So re. the thrust lever travel, raising the reverse thrust levers till the idle detent just actuates the reverser system, and once the reversers are deployed, the rest of the lever travel arc controls the amount of reverse thrust... does this seem right? This would be of some importance to builders...

Q: how long does it take for the reversers to travel to 60% and then full deploy? From the landings I've seen, this seems pretty fast.... maybe a sec or so....

cheers

fc

[John H Watson]

once the reversers are deployed, the rest of the lever travel arc controls the amount of reverse thrust... does this seem right?

I have no details on angle versus thrust, but the interlock is at 46 degrees lever angle (full rev thrust at 89.25deg). Interlock is idle reverse, but how far beyond interlock thrust increase begins, I'm not sure. Note, operationally, that if the levers are stowed overly-quickly, the engine may be still at high rpms (and produce high forward thrust after stowing). The reversers must be stowed relatively slowly.

Q: how long does it take for the reversers to travel to 60% and then full deploy? From the landings I've seen, this seems pretty fast.... maybe a sec or so....

Yes, full deployment takes only a second or so : )

[farrokh747]

The Levers on the TQ are linked to position resolvers via the brake assy (which supplies the friction) - The position resolvers receive a signal from the EEC and transmits the Thrust Lever Angle to the EEC - now the interesting thing is that for the full 50 degrees of forward lever movement, the resolver readout is mapped to 50 degrees. However, for the 89.25 degrees of reverse lever travel, the resolver is mapped to appx 30 degrees..

Most builders would be using pots for throttle lever control. IN my case, the pot would read 89 degrees for reverse, and 50 degrees for fwd.... I would be using phidgets 8/8/8 cards for this.. FS2Phidgets maps the travel to FS values... will have to see how this works out with PSX...

Reverser Stowing: maybe there's a logic that stows the reversers only after the rpm is below a value or at idle...

I'll see if I can find out something more about the actual thrust control in rev....

[delcom]

Reverser Stowing: maybe there's a logic that stows the reversers only after the rpm is below a value or at idle...

No interlock exists when stowing the reverser. Advancement of
the forward thrust levers is possible as soon as the reverse levers are in
the fully down position. The thrust limiting logic of the EEC again
controls the amount of thrust which the pilot can command. When the
throttle position (TRA) indicates that forward thrust has been
commanded, the EEC will assume that the reverser has been commanded
stowed but will limit thrust to idle if the reverser is less than 85% stowed.
When the reverser is more than 85% stowed, the thrust is allowed to
increase linearly so that at 90% stowed, maximum forward thrust is
permitted.

EDIT: this is for the blown Commercial Fan, I don't remember how it's done on the Roller and the fluid powered PW. I assume it's more or less the same.

cheers,
delcom

[delcom]

Zero thrust or null thrust position is a condition during reverser half translation. It exists for a friction of a second when the blocker doors are about "half way" directing half of the horses run backwards the other half of the herd sideways through the cascade vanes. That's the ideal moment to remove the lock command from the interlock mechanism. Is that really 50 percent? No! 100 percent reverse thrust does not really exists, since there are some gaps between the blocker doors and the sleeve. That's why the unlock command is further displaced towards 60 percent.    
Since the two T/R halves are not synchronized, the EEC will wait for the lazy T/R half to reach its null thrust position in order to retract the interlock actuator for that engine.

cheers,
delcom

[delcom]

Make no mistake...the EEC is not looking for this "null thrust condition" by means of sensors. It's not that important. It's waiting for position value only. Engineers recommended the programmers of the EEC to set this approximate value, knowing their own blocker door design is far from perfect. They know if you scare 100 horses with the reverser fully deployed...95 (something in this range) of them will go through the side door (reverse thrust), the rest will find their way trough the main gate (forward thrust).

 
delcom

[farrokh747]

Thanks, Delcom
http://www.youtube.com/watch?v=dZ-wh8Kuh1M&feature=related

767 tho, but you see the time taken for travel...

And -400 http://www.youtube.com/watch?v=eqQcg7e8eYc&feature=related

you can see a 2/3 second delay after the reversers transit to engine spool up...

[farrokh747]

Another Q: So after the interlocks open to allow levers to travel to reverse, at what point do they close/reset again for the next cycle? When the thrust levers are moved to fwd? Or when the TR moves back to it's stowed position? Im thinking the latter...

cheers,

fc