leg5840 Posted July 16, 2023 Share Posted July 16, 2023 (edited) Problem: After cutting off the L/H engine, I accidentally moved the speed brake while cutting off the R/H engine. And at the moment hyd' pressure was lost, the speed brake was stopped and fixed during operation. principle of operation. : Originally, the Actuator Cylinder should be pressed and folded with the speed brake's own weight. Guess: It seems that the principle of operation is not properly implemented. Edited July 17, 2023 by leg5840 Link to comment Share on other sites More sharing options...
Scott-S6 Posted July 17, 2023 Share Posted July 17, 2023 (edited) I think this is correct behaviour. A loss of hydraulic system pressure won't cause the speed brake to collapse if the control valve is closed. The control valve for the speed brake on the F15 has return pressure sensing which closes and locks out the control valve in the event of hydraulic system pressure loss. Edited July 17, 2023 by Scott-S6 Link to comment Share on other sites More sharing options...
Tom Kazansky Posted July 17, 2023 Share Posted July 17, 2023 1 hour ago, Scott-S6 said: A loss of hydraulic system pressure won't cause the speed brake to collapse if the control valve is closed. seems to make sense. What leads to the question: shouldn't this valve be operational even after the loss of the hyd. pressure and if so, shouldn't the speed brake retract by opening the valve? Link to comment Share on other sites More sharing options...
Scott-S6 Posted July 17, 2023 Share Posted July 17, 2023 (edited) 55 minutes ago, Tom Kazansky said: seems to make sense. What leads to the question: shouldn't this valve be operational even after the loss of the hyd. pressure and if so, shouldn't the speed brake retract by opening the valve? Not in the case of the eagle and subsequent US aircraft. One innovation used in the eagle was the use of control valves that include a pressure sensor. If the sensor detects a drop in system pressure then the solenoid which actuates the valve is overridden, locking the valve closed. Edited July 17, 2023 by Scott-S6 Link to comment Share on other sites More sharing options...
Tom Kazansky Posted July 17, 2023 Share Posted July 17, 2023 19 minutes ago, Scott-S6 said: If the sensor detects a drop in system pressure then the solenoid which actuates the valve is overridden, locking the valve closed. Thanks for the explanation. I wonder whether there is a emergency retraction system of the speed brake in the Strike Eagle because a plane without hydraulic pressure might not want to have the speed brake extended. Link to comment Share on other sites More sharing options...
Scott-S6 Posted July 17, 2023 Share Posted July 17, 2023 (edited) 29 minutes ago, Tom Kazansky said: Thanks for the explanation. I wonder whether there is a emergency retraction system of the speed brake in the Strike Eagle because a plane without hydraulic pressure might not want to have the speed brake extended. The hydraulic system diagram doesn't show a flow regulator for the speed brake so unless there's something built into the actuator itself in that scenario you'd risk having the speed brake crash down if you could override the control valve lock. That could be pretty bad. You'd also get a sudden jet/spray of hydraulic oil from wherever the leak is which would also be less than ideal. If you no longer have functional control surfaces you probably have bigger concerns than the speed brake. (the control surface valves also have pressure sensors so losing both engines is pretty bad) Edited July 17, 2023 by Scott-S6 Link to comment Share on other sites More sharing options...
Tom Kazansky Posted July 17, 2023 Share Posted July 17, 2023 7 minutes ago, Scott-S6 said: The hydraulic system diagram doesn't show a flow regulator for the speed brake so unless there's something built into the actuator itself in that scenario you'd risk having the speed brake crash down if you could override the control valve lock. That could be pretty bad. You'd also get a sudden jet/spray of hydraulic oil from wherever the leak is which would also be less than ideal. If you no longer have functional control surfaces you probably have bigger concerns than the speed brake. (the control surface valves also have pressure sensors) thanks for the profound answers! will put that hydraulic behaviour on the wishlist for DCS 5.0 1 Link to comment Share on other sites More sharing options...
KlarSnow Posted July 18, 2023 Share Posted July 18, 2023 The Speed brake should in the case of a Util A hydraulic failure (hydraulic subsystem that powers the speedbrake) fail to a closed position. So if its remaining open with no hydraulic pressure right now that is a bug and it should get fixed. Now the corrolary to that is that if you've lost your UTIL A, for whatever reason, you also should have lost your: wheel brakes (emergency braking should still work) Landing gear normal extension and retraction (emergency extension would still work) Nose wheel steering (can also be re-enabled via pulling the Emergency brake handle) Radar Antenna (should freeze) Slipway valve Antiskid Left inlet (should be locked up) and the ability to retract your hook All of that is run off the UTIL A Hydraulic circuit powered by the L/R Util pumps 2 Link to comment Share on other sites More sharing options...
leg5840 Posted July 18, 2023 Author Share Posted July 18, 2023 21 hours ago, Scott-S6 said: I think this is correct behaviour. A loss of hydraulic system pressure won't cause the speed brake to collapse if the control valve is closed. The control valve for the speed brake on the F15 has return pressure sensing which closes and locks out the control valve in the event of hydraulic system pressure loss. Thank you for answer. This is my guess, but I would like to believe that it was not designed that way because it would cause a dangerous situation in which the speed brake would continue to create high drag in the air in an unfolded state. (Unless the speed is extremely low enough to not generate hydraulic pressure) And if the role of closing the control valve by sensing the pressure drop is actually performed as you say, maintenance personnel will not be able to open the folded speed brake on the ground. It will be able to operate after power and hydraulic pressure are applied in any way to unlock the locked speed brake control valve. However, in normal cases, the folded speed brake can be opened by hand. In addition, the speed brake of the F-15 is equipped with a restrictor, so when the speed brake is folded under its own weight, it is slowly folded. I remember seeing solenoids A/B in the speed brake schematic, but I can't remember exactly what they do. Can you provide evidence, data, or experiences to get accurate results? Link to comment Share on other sites More sharing options...
leg5840 Posted July 18, 2023 Author Share Posted July 18, 2023 19 hours ago, Scott-S6 said: Not in the case of the eagle and subsequent US aircraft. One innovation used in the eagle was the use of control valves that include a pressure sensor. If the sensor detects a drop in system pressure then the solenoid which actuates the valve is overridden, locking the valve closed. This is the emergency procedure for speed brake failure written in T.O 1F-15E-1. SPEED BRAKE FAILURE If either a hydraulic or electrical failure occurs, the speed brake is closed by air pressure. If the speedbrake does not retract, pulling the SPD BK circuit breaker removes electrical and hydraulic power and allow air load closure. 1. Speed brake circuit breaker - PULL -- How can the air pressure lock the speed brake if there is a hydraulic failure in midair, a drop in pressure is detected and the control valve is closed? 1 1 Link to comment Share on other sites More sharing options...
Not_G Posted August 3, 2023 Share Posted August 3, 2023 The speed brake doesn't lock without hydro/elec pwr and the switch in hold. It's a pretty heavy control surface so between gravity and air pressure it's not going to come up in flight without 3000 psi extending the actuator. Essentially with the switch in up, side "A" let's pressure through to raise the speed bk, with the switch in down side "B" gets pressure to retract and with hold selected they both get pressure to fluid lock the actuator. So with the absence of hydro or electrical power the speed brake will just fall down. I hope that answers your question. 2 Link to comment Share on other sites More sharing options...
leg5840 Posted August 3, 2023 Author Share Posted August 3, 2023 10 hours ago, Not_G said: The speed brake doesn't lock without hydro/elec pwr and the switch in hold. It's a pretty heavy control surface so between gravity and air pressure it's not going to come up in flight without 3000 psi extending the actuator. Essentially with the switch in up, side "A" let's pressure through to raise the speed bk, with the switch in down side "B" gets pressure to retract and with hold selected they both get pressure to fluid lock the actuator. So with the absence of hydro or electrical power the speed brake will just fall down. I hope that answers your question. thank you. sir. Link to comment Share on other sites More sharing options...
Solution leg5840 Posted August 17, 2023 Author Solution Share Posted August 17, 2023 patched. solved. 1 1 Link to comment Share on other sites More sharing options...
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