F-15C Technical Discussion

[strikeeagle]

I feel that the game F-15 closely represents the RL plane

 

.

 

Trust me...it doesn't.

[GGTharos]

It says that it can be used for the purpose in the emergency procedures in the -1. In Section 3-11, emergency procedure for double engine stall/stagnation/failure:

 

JFS can be used to provide flight control and maintain a min descent rate of 210kts.

 

I take this to mean that the JFS keeps an engine spooled up at a speed sufficient to provide the hydraulic power for flight control and emergency generator while maintaining best glide ratio.

Edited December 2, 2014 by GGTharos

[strikeeagle]

It says that it can be used for the purpose in the emergency procedures in the -1. In Section 3-11, emergency procedure for double engine stall/stagnation/failure:

 

JFS can be used to provide flight control. I assume this means that the JFS is spooling an engine to a speed that allows that engine to charge the hydraulics, but is not done directly by the JFS itself.

 

Ummmm...I still disagree. The JFS would be used to maybe attempt a restart or cool the motor. There is a limited amount of time that the JFS can run at 100%. The JFS cannot supply hydraulic power and there is no such thing as charging the hydraulic system.

 

Now the engines can be motored (wind milled) to recharge the JFS accumulators if need be. In flight these accumulators provide hydraulic pressure to start the CGB/JFS and to provide pressure to open the forward landing gear doors. That's about it.

[strikeeagle]

If you maintain sufficient airspeed, the motors will wind mill provided that they haven't seized. Thus will provide power to the emer gen and pressurize the utility hydraulic system. The utility system provides pressure to the PC's if there is a leak in certain PC circuits (A or B).

[GGTharos]

TO-1F-15A-1 Emergency procedures, 3-11.

 

The JFS can be used to provide flight control power in an emergency situation. Whether it does so by itself (and I have no reason to not believe you when you say it cannot), or by spinning the engine in conjunction with wind-milling below the recommended 350KIAS is not important when you are flying the aircraft.

 

Again, Emergency Procedure.

 

And yes, I'd be interested to know exactly how/why it works, and I think I'm well within my rights to assume it does since it is part of the double engine failure emergency procedures.

Edited December 2, 2014 by GGTharos

[strikeeagle]

TO-1F-15A-1 Emergency procedures, 3-11.

 

The JFS can be used to provide flight control power in an emergency situation. Whether it does so by itself (and I have no reason to not believe you when you say it cannot), or by spinning the engine in conjunction with wind-milling below the recommended 350KIAS is not important when you are flying the aircraft.

 

Again, Emergency Procedure.

 

And yes, I'd be interested to know exactly how/why it works, and I think I'm well within my rights to assume it does, when it is part of the double engine failure emergency procedures.

 

 

What's the date on that tech-data again?

 

The idea behind maintaining the 350 is to wind mill. The JFS cannot provide hydro. Do you know how the JFS/CGB work?

[GGTharos]

It's from '86, but mentions specifics for both -100 and -220. I suspect that the JFS and engine operation hasn't changed since. Could be wrong of course, or emergency procedures may have been amended. But unless there's a new TO to go by, what's available is what I'll go by. I have 90's TOs as well, but not handy.

 

I have only a bit of an idea of how the JFS works, don't know what the CGB is. I know that charged hydraulic accumulators will spin up the JFS. I assumed it will burn fuel after this, but that's an assumption on my part :) I also know you can charge the hydraulics to run the JFS manually if necessary.

 

The JFS then provides power/air to spool up the engines, and the power comes on when the 50% switch trips on the engine generator.

 

That's the extent of my knowledge regarding this piece of equipment.

Edited December 2, 2014 by GGTharos

[strikeeagle]

It's from '86, but mentions specifics for both -100 and -220. I suspect that the JFS and engine operation hasn't changed since. Could be wrong of course, or emergency procedures may have been amended. But unless there's a new TO to go by, what's available is what I'll go by. I have 90's TOs as well, but not handy.

 

I have only a bit of an idea of how the JFS works, don't know what the CGB is. I know that charged hydraulic accumulators will spin up the JFS. I assumed it will burn fuel after this, but that's an assumption on my part :) I also know you can charge the hydraulics to run the JFS manually if necessary.

 

The JFS then provides power/air to spool up the engines, and the power comes on when the 50% switch trips on the engine generator.

 

That's the extent of my knowledge regarding this piece of equipment.

 

 

No no no....

 

The JFS and CGB are connected together. When the pilot has both engine master switches "ON", and the JFS control switch "ON", he/she pulls the JFS control handle in the cockpit. When they pull the handle this is what happens:

 

1. Hydraulic pressure w/a nitrogen pre-charged is released from the upper accumulator, through the accumulator manifold, and to the CGB hydraulic start motor.

 

2. The start motor turns, thus turning the CGB which is connected to the JFS, so if the JFS GCU is getting power from the CGB PMG, the JFS lights off.

 

3. Pilot raises the #2 finger lift

 

4. A electrical signal is sent to a couple relays and 50 percent switch.

 

5. The CBG clutch plate releases, oil pressure is sent to the isolation decupler that extends the decupler into the AMAD pawl carrier

 

6. Once in the carrier...the JFS accelerates to 100% spinning the decupler, that is rotating the AMAD pawl carrier, that is rotating the AMAD, that is turning the PTO shaft, that is connected the engine gearbox, that is turning the tower shaft, that is spinning the N2 compressor.

 

7. At 20% engine RPM, the throttle is moved from off to idle.

 

8. The motor lights off at about 23-25%

 

9. Once the JFS reaches a overspeed condition, the 2-speed switch decelerates the JFS back to idle retracting the decupler.

 

10. Same thing happens when starting the #1 motor except, there is a signal being received from the #2 50% switch saying "the other motor is running" causing the JFS to shutdown

 

The only thing the JFS/CGB does is start the engine...that's it.

[cofcorpse]

Trust me...it doesn't.

 

Could you be more specific? Please, PM, if you want.

[strikeeagle]

Oh...the only way to manually charge the JFS accumulators is if the Crew Chief uses the JFS hand pump. It's done by hand...not running the JFS.

[GGTharos]

Yes, that's what I meant. I imagine it's quite tiring.

[Haukka81]

Oh...the only way to manually charge the JFS accumulators is if the Crew Chief uses the JFS hand pump. It's done by hand...not running the JFS.

 

Are you real pilot or what :)

[GGTharos]

Then I would suggest you are better connected to explain why the emergency procedure says what it does. It could also mean something else than it seems to mean - it's not like mistakes or poor writing doesn't happen in a -1 :)

 

The only thing the JFS/CGB does is start the engine...that's it.

[strikeeagle]

Could you be more specific? Please, PM, if you want.

 

-Start sequence

-Having a electrical power "switch"

-Speed brake fully extends above .85 Mach

-Speed brake has 3 positions

-External lighting

-JFS sounds

-Ramp dropping sequence is slow

-Canopy closes too fast

-No JFS chimney texture

-Bitch'n Betty

-Cockpit lighting

-The BIT panel on the left rear console

-Switches that are off should be on

-etc

[strikeeagle]

Are you real pilot or what :)

 

That I am, but I crewed the 15 for 9 years and taught its systems for my last 4 years on active duty.

[cofcorpse]

-Start sequence

-Having a electrical power "switch"

-Speed brake fully extends above .85 Mach

-Speed brake has 3 positions

-External lighting

-JFS sounds

-Ramp dropping sequence is slow

-Canopy closes too fast

-No JFS chimney texture

-Bitch'n Betty

-Cockpit lighting

-The BIT panel on the left rear console

-Switches that are off should be on

-etc

It's very interesting. Some of this "errors" are current limitations of FC level model, but others can be fixed.

Edited December 2, 2014 by cofcorpse

[GGTharos]

How about

-engine spool-down time (it seems really slow, and yes it's important - in particular in the idle-to-80% regime)

-Throttle axis becomes strangely compressed when climbing in altitude (you will notice the upper part of MIL power acquires a 'dead zone' that gets larger and larger and does nothing).

 

This stuff affects flight.

[strikeeagle]

Then I would suggest you are better connected to explain why the emergency procedure says what it does. It could also mean something else than it seems to mean - it's not like mistakes or poor writing doesn't happen in a -1 :)

 

It's all good. I'd have to personally look at the procedure. You guys do a bang-up job, but I'm still partial to my F-15 :smartass:. I had many-a-good times working the jet.

[strikeeagle]

It's very interesting. Some of this "errors" are current limitations of FC level model, bit others can be fixed.

 

:thumbup:

[strikeeagle]

How about

-engine spool-down time (it seems really slow, and yes it's important - in particular in the idle-to-80% regime)

-Throttle axis becomes strangely compressed when climbing in altitude (you will notice the upper part of MIL power acquires a 'dead zone' that gets larger and larger and does nothing).

 

This stuff affects flight.

 

I noticed that too. You guys know all the game model programer stuff. I can point out whats wrong.:lol:

 

Spool down is a little slow.

[GGTharos]

Not so much directed as clarification :)

[strikeeagle]

Not trying to argue with you as you're probably right.

 

How ever what I think Tharos was getting from and what I would think reading those emergency procedures is that once the JFS is running [if it can be started] that it could spool up one engine enough to provide hydraulic pressure.

Tharos wasn't referring to the jfs actually providing direct hydro pressure but rather spooling an engine to where it can then provide hydraulic pressure. This also comes in if the engine are not siezed. As you have said that the jfs can't run at 100% for very long but it could be an option to provide power to an engine just long enough to get the plane to the ground at a non lawndarting fasion.

 

Hey I could be wrong. I also wouldn't think the jfs could run with 0fuel unless the engines will shut down before 0fuel and there is enough fuel and the jfs fuel is sumped from the very bottom of the tanks or has it's own fuel reserve.

 

Roger that, but the ability for the JFS to run at 100% to motor a engine to get it on the ground is VERY unlikely. The F-15E-1 only refers to the JFS to attempt to start a motor. The book also says that when both PC's reach zero PSI, eject. IIRK, the JFS can only run a 100% for 60 seconds.

[GGTharos]

Here's a question for you: As I understand it, the engines are probably continuously charging the hydraulics that run the JFS. What if the windmilling + JFS can keep an equilibrium that will keep the JFS going - the 210kts (this is what the JFS helps with) glide provides less RPM than the 350kts, but 210kts + JFS might be able to keep it spinning just a bit faster. Or maybe the JFS doesn't need to work as hard to keep the engine going since part of the power is provided by the airflow, and so the JFS can run longer - what is the possibility of this?

[strikeeagle]

Here's a question for you: As I understand it, the engines are probably continuously charging the hydraulics that run the JFS.

 

The engine doesn't continuously recharge. There are 4 hydro pumps. 1 for each PC and 2 for the utility system. These pumps are connected to the AMADS: 2 pumps per AMAD. Since the engine is turning the AMAD via a PTO shaft the pumps rotate. The utility hydraulic system supplies the hydro fluid for the JFS accumulators. So, if I have to manually pump-up the JFS bottles (there is a upper and lower bottle), I'm "sucking" the fluid from the utility hydro reservoir.

 

 

What if the windmilling + JFS can keep an equilibrium that will keep the JFS going

 

Hydraulic fluid does not keep the JFS running, the JFS is a jet engine so it uses fuel from tank 3.

 

JFS: The front of it is facing the Crew Chief doing the safety wiring.

 

 

CBG: Front looking aft. The right side of the picture is LEFT side of the jet. That green thing is the left utility pump/manifold.

 

 

 

- the 210kts (this is what the JFS helps with) glide provides less RPM than the 350kts, but 210kts + JFS might be able to keep it spinning just a bit faster. Or maybe the JFS doesn't need to work as hard to keep the engine going since part of the power is provided by the airflow, and so the JFS can run longer - what is the possibility of this?

 

If there is ample RPM >12%, there is no need for the JFS. The emergency generator would supply hydraulic power to the utility system that would power the flight controls.

 

Edited December 2, 2014 by strikeeagle

[strikeeagle]