Hydraulics are a game component as it effects how long you can maintain control in event of damage to your controls or hydraulic lines and it also powers gun turret control. Controls are not direct in modern aircraft, due to the amount of force required to move a large surface area on an aircraft weighing tons, human muscle has been replaced by a system of wires, pipes, pumps and actuators.
Pressure within this system is vital as it translates a pilots control movement into control surface movement, on a helicopter the cyclic (joystick) operates hydraulic servos that move a large ring under the main rotor called the "swashplate". Wikipedia (swashplate)
I digress.
To simulate damage to this system, we need a basic simulation that isn't too complex as it needs to work for all AI helicopters in our main update loop. If the hydraulic pressure drops then control response has to become "mushy", you should feel this if you're flying a damaged bird. Additionally this should give the AI flying as it's virtual control inputs lag potentially inducing poor looking oscillation. More experience AI crew having faster input response times should be able to handle emergency situations better.
From time of loosing pressure, we're going to give you around 20 minutes to land, your mileage will definitely vary. The ACCumulator stores around 3000psi and is a buffer that maintains the pressure of the primary (PRI) and utility (UTIL) system pressure. These two systems, PRI and UTIL are pressurised from the APU and used to start the engines.
This is reflected in the ENG page during startup. Start the APU, watch the pressures (there's a bleed metric for damage to the system and a fluid level as a percentage). As soon as the primary system reaches around 3000psi (there's a bit of fluctuation added for authenticity) you're good for engine start.
I think this is where the LOCK position of the rotor brake gets it's pressure from.
Almost everything in the Apache is automatic here, operation of this system is handled for you with some exceptions. We have a big Emergency Hydraulics button in the cockpit, pictured below. This allows fluid from the accumulator circuit to flow into the utility circuit. After that, you're on your own.
The things we have to do just to get three numbers up. Oh, and don't get me started on oil pressure ;-)
If you take any damage to a hydraulic system pressurised at 3000 psi you are going to lose all of the contents pretty quickly. I had a small leak from a hydraulic seal on 1 system and lost the contents of the whole system in 3 mins.
ReplyDeleteI dont know this for sure, but I would have thought the Apache has possibly more than 1 hyd system and a direct mechanical backup system. Losing a hyd system usually means losing your SAS and digital stabilisation systems. In short the thing will be a pig to fly, but it will still fly.
Basically, it would have to be a pin hole leak to last 20 mins.
Oil pressure - funnily enough engines will run a little longer if you dont adjust the power settings too much. i.e. acceleration and deceleration forces will decrease the time until the inevitible seizure.
Had a quick google search for info on AH-64 hyd systems. Not a lot I could find other than there is a primary and a utility system. No idea how these 2 systems interact and no mention of direct link backup. Anyone have a technical manual I can look at?
ReplyDeleteI have the dash 10 for the A model you can look at, pretty old now though but mechanically and specs wise I don't think the systems will have evolved that much except for the better by a margin.
ReplyDeleteYou can fly these things with no oil in the transmission for 20-30 mins. When it comes to pressure loss in your primary or secondary hydraulic system I would think it's a matter of landing as soon as is practical. You're probably right in that your flight time before your controls die will be measured in seconds to a good portion of a minute.
In video game land we want to make it a bit more exciting and let you fight the chopper back home if you want to risk it. You have numbers in front of you telling you how much pressure there is in left in each system so it's your call.
The HydPressureDemand() function can drop everything out in one go so it's easy to make it a 'realism' factor. Start giving users options though and you're giving them tools to take the fun factor away.
Less------Realism------More
More-------Fun---------Less
Although that's not always the case and the lines can be a bit blurred.
I completely agree that you can't have the player fail because a single bullet punched a hole in 1 of the hyd lines. I thought maybe with 1 remaining system or possibly direct flt ctrl linkage (does it exist?)you could just simulate the 1 system contents then pressure falling, followed by a warning, then the thing becomes a pig to fly. Common sense would dictate a RTB rather than "you have 20 mins to find somewhere to land". Obviously if you lose the second system then its all over.
ReplyDeleteIf the dash 10 is in electronic form then email it to me and I'll take a look at the schematics and description. I should be able to work out what powers what systems and the resultant implications of losing 1 or both hyd systems.
Also in my experience with fixed wing HYD systems, you will maintain system pressure at 3000 psi until you have lost most of the HYD contents & any accumalator pressure. (e.g. with less than 20% of HYD C contents remaining, there was still enough pressure to drop the landing gear on the 777).
The primary system is for loading and unloading only...no wait...that's Airplane the movie. The primary system is used for the flight controls.
ReplyDeleteThe utility system is pretty much everything else. Cannon, pylon articulation, brakes etc. I was instructed that if the primary system drops below 1650 psi then you're along for the ride, but the utility system has crossfeed valves that will maintain pressure in the flight controls dropping out the other systems.
Pushing the emergency Hyd button dumps the accumulator pressure into the utility system supposedly giving you around 40 seconds depending on how heavy handed you are on the controls.
So I'm going to have it work like that and make changes to the alert system in the process.
ok. Also maybe model the Hyd failure after the ah64 has taken some substantial damage rather than just a few hits by small arms fire. I would think the actual ah64 has got some reasonable shielding around its Hyd lines anyway?
ReplyDelete(e.g. with less than 20% of HYD C contents remaining, there was still enough pressure to drop the landing gear on the 777).
ReplyDeleteThe emergency landing gear extension is freefall on the Boeing 777...
The AH64 Bushmaster cannon mount is spring loaded on the vertical axis. In the unlikely event of the pressure going it gets a 'hard on' to stop it dragging into the dirt on landing.
ReplyDeleteI think the main components for the system are shielded by bigger ones, the hull has armor and ballistic protection in the form of a kevlar weave and a glass layered polyurethane ballistic foam. Safe as houses.
The real question is how likely is such a failure under various circumstances?
Recklezzz - Trouble is you made an assumption. Remember the old flight school saying "don't assume .. check".
ReplyDeleteI didnt use the emergency freefall. I lowered the gear normally when the contents reached 1/5th. There was sufficient pressure for the uplocks to disengage.
Flex, I'd say the failure is unlikely unless hit by a RPG or a SAM in the right place.
ReplyDeleteHard lessons were learned about hydraulic redundancy during the Vietnam war. F-105's had a particularly bad reputation for taking golden BB's and losing control response within seconds.
ReplyDeleteVery hard to imagine that they'd put together an attack chopper without redundant mechanical systems, or atleast heavily protect hydraulic lines.
20 minutes of flight with increasingly mushy controls combined with a button you can mash to buy some time sounds perfect. We're making a flight game not a milsim, the last thing we want is to get bogged down in endless pedantic detail. I want to blow stuff up.
Sounds like AD is gonna fly round with the Invincible option ticked, just so he can keep blowing stuff up. Maybe you'd better have endless ammo option there for him too. hehe
ReplyDeleteWasn't trying to be pedantic just offer an alternative which works equally well but is also closer to reality. But you're right, I look at the screenies and vids you boys push out & forget its a game. Just dont get too Hollywood on me AD.
Sorry, I wasn't having a go at anyone. Just getting worried about gravy. :-/
ReplyDeleteEveryone's input is appreciated and accuracy is a big part of the project. But we need to keep in mind the mayonnaise jar analogy. The golf balls have to go in before we can add in the pebbles and finally the sand.
Sim projects too often get side-tracked by detail and development times spiral out of control. The new Battle of Britain sim from Maddox is a prime example. They can afford that kind of detail because the Ruskie government just gave them a huge grant to build the SoW series. :(
Cheers
I didn't use the emergency free fall. I lowered the gear normally when the contents reached 1/5th. There was sufficient pressure for the unlocks to disengage.
ReplyDeleteThanks
Henry Jordan
Hydraulic Seal Kits