DCS F-18 - Hydraulic System

[VBF-12 Gosling]

Chaps

This is no where near as bad as it looks. It’s really quite simple...

There are TWO main system (Hyd1, Hyd2) each with TWO channels (A, B) at the top left and top right of the diagram.

The diagram is in TWO half’s. Top is Flight Control Surfaces, bottom is ancillary systems. Just follow the lines from the items back to the Hydraulic pumps at the top. From the top:



Leading Edge Flaps (LEF) - Left fed by Hyd1B, backup if pressure in 1B lost = Hyd2A
Leading Edge Flaps (LEF) - Right fed by Hyd2A, Backup if pressure in 2A lost = Hyd1B

Aileron - Left fed by Hyd2B, Backup Hyd1B
Aileron - Right fed by Hyd1A, Backup Hyd2A

Trailing Edge Flap (TEF) - Left fed by both Hyd1A & Hyd2B in tandem. Internal configuration in the jack will avoid hydraulic lock in the case of a failure of either system.
Trailing Edge Flap (TEF) - Right fed by both Hyd1A & Hyd2B in tandem. Internal configuration in the jack will avoid hydraulic lock in the case of a failure of either system.

Stabilator - Left fed by the higher pressure system of Hyd1A or Hyd2B AND higher of Hyd1B or Hyd2A, in tandem. So TWO of any of the FOUR systems.
Stabilator - Right fed by the higher pressure system of Hyd1B or Hyd2A AND higher of Hyd1A or Hyd2B, in tandem. So TWO of any of the FOUR systems.

Rudder - Left fed by higher of Hyd2B or Hyd1A
Rudder - Left fed by higher of Hyd1B or Hyd2A

Now the bottom half:

Pretty much the whole system is driven by Hyd2A with some systems backed up by Hyd2B if selected.

Hook - Hyd2A only
Speed Brake - Hyd2A only
- Can be selected both OFF

Gun - Hyd2A only
Refuel Probe - Hyd2A. Backup Hyd2B if selected
Main Landing Gear - Hyd2A when selected down
Nose Landing Gear - Hyd2A when selected down
- Landing Gear Backup = Higher pressure of Hyd2B or Brake Accumulator if selected
Launch Bar - Hyd2A only
Nose Wheel Steering - Higher of Hyd2A or Hyd2B
Parking Brake - Hyd2B by selection
Brake - Hyd2A via Anti-Skid. Backup by higher of Hyd2B or Brake Accumulator but without Anti-Skid
Anti-Skid - Hyd2A but only when the gear is down

During start, there is a APU Pump and accumulator which charges the Brake Accumulator and powers the Brakes and Nose wheel steering before engine start.

Finally, for the Chockheads there is a Hand Pump that also charges the brake accumulator. This allows recharge of the brakes if the aircraft is standing for long periods. Onboard it would be used if respotting the aircraft on deck.

The only part I am struggling to understand is the purpose of the Trickle Charge (Centre of bottom half of diagram) link between the Hyd1A and Brake Accumulator. Seem to me a leak in and around the brake accumulator would lead to a slow leak of the whole Hyd2 system!!!! I cant see the reason behind this connection

See, not so bad....

[VBF-12 Gosling]

Yep - I hear you load and clear.... “But Gos, SO WHAT!!!”

Well obviously it’s all good when everything is working. In fact it’s all pretty good even with a singe channel failure. Well, all but Hyd2A that is! Loss of Hyd2A causes a few issues with ancillaries, but they are all overcome with a bit of cockpit procedure switching.

It’s when we get Double Channel and Triple Channel failures that things start to get tricky and, to be honest a bit confusing... What is still driving and what it is driving is not immediately obvious. So, in the Emergency Checks is the following diagram that decodes failures to loss of flight surfaces...



The lost surfaces should be reflected on the FCS page on the DDI as XXXs

There are pages and pages of Hyd system failure emergency checks so I am trying to boil it down to something basic and memorable. Thankfully there are no immediate actions, so things can be done in slow time.

ANY CHANNEL FAILURE - Single or AA or BB
1. Airspeed ... ... ... ... ... ... ... ... ... Maintain below 350Kts
2. Land as soon as practical.

SINGLE SYSTEM (Both Channels) = Left (HYD1A & 1B) or Right (Hyd2A & 2B)
1. Affected side Engine ... ... ... ... IDLE
2. Airspeed ... ... ... ... ... ... ... ... ... Maintain below 350Kts
3. Land as soon as practical.

ANY CROSS CHANNEL FAILURE = Hyd1A & Hyd2B or Hyd1B & Hyd2A
1. Airspeed ... ... ... ... ... ... ... ... ... Maintain below 300Kts
2. AoA ... ... ... ... ... ... ... ... ... ... ... Maintain below 10 degrees
3. Land as soon as practical.

ANY TRIPLE FAILURE - All of it...
1. Affected double side Engine ... ... IDLE
2. Airspeed ... ... ... ... ... ... ... ... ... Maintain below 300Kts
3. AoA ... ... ... ... ... ... ... ... ... ... ... Maintain below 10 degrees
4. Land as soon as practical.

Into this is the need to avoid FCS resets if the LEFs are Xs - See the Left of the diagram and all the dead LEFs!!!!

So let’s look at it another way... What check is the result of what failure. There are only 3 checks really and I have put them in priority order...
- Engine = Idle for any whole system, 1 or 2
- Airspeed = Below 350 for everything, below 300 for anything on both sides
- AoA = Below 10 for anything with an A and a B in it
And of course, LASAPrac = for everything

I know this is hard to memorise.... Try this...
- Any Hyd - Bugger, that will slow me down.... if I get another on the other side it will slow me down even further!
- One side - Wow, that Hyd system is having a lazy day (Idle)
- A & B - Now that makes me CROSS as its going to be difficult to get back on deck with the AOA limit
Best I head home and see what else is not working...

Summary:
Single = 350 / LASAPrac
Double Same Side = IDLE / 350 / LASAPrac
Double Cross Channel = 300 / 10 / LASAPrac
Triple = IDLE / 300 / 10 / LASAPrac

There is a load of other stuff mainly to do with conditions on approach and use of ancillary systems, for which reference to the cards will be essential, but that can be done in slower time once on the way home or diverting....

Now pick a box in the diagram above and see if you can workout the initial checks without looking at the above text....