Engine Systems Instrumentation and Fuel Systems

[PAWPAWPAW]

I am currently researching aircraft system philosophy and was wondering if anyone has any suggestions or sources that could indicate WHY certain systems and instruments are not included with different aircraft.

 

1. So with the F/A-18C, one omission that stands out is the oil temperature.

A) Can one of the other indicated variables on the DDI Engine page be used to indicate Oil temperature behaviour (even if indirectly)?

B) Does the internal computer have a way of measuring it (even without it being indicated)?

C) If all of the above answers are “NO”, why does the F/A-18C NOT have instrumentation for that variable?

 

2. Another set of instruments that are missing are related to the APU. Why is it not considered important in the F/A-18C (green light only) whilst in the A-10C there are at least indications for APU EGT and RPM?

 

3. Also, what Fuel Quantity gauging method does the F/A-18C use?

The NATOPS flight manual mentions that it uses a float system during refueling and for fuel-redistribution with the control valves. It also mentions in a few sections that the fuel quantity indicators do not necessarily account for pressure and temperature effects (hence the “more or less” statements). It even looks like it does not account for density changes. Does it not use a capacitance measuring system?

 

Any answers will be greatly appreciated and I thank you in advance for your time.

[drallabco]

Oil temp is indicated on the IFEI. Can't address the other questions.

[PAWPAWPAW]

Thank you for your quick response drallabco.

 

Maybe I have misunderstood the manaul, but I thought the IFEI displays only EGT (usually determined with thermocouples positioned into the gas stream at some point downstream of the combustion chamber and not via oil temp from the turbine bearings)?

 

Could you be more specific?

[luft]

The oil temperature is not shown in the IFEI. The indication there is is oil pressure.

 

RPM Displays engine N2 rpm from 0 to 199%. TEMP Displays turbine exhaust gas temperature (EGT) from 0 to 1,999°C.

FF Displays main engine fuel flow only (afterburner fuel flow is not displayed). Range is 300 to 199,900 pounds per hour with 100 pound per hour increments. When fuel flow is less than 320 PPH, zero is displayed.

NOZ Displays exhaust nozzle position from 0 to 100% open in 10% increments.

OIL Displays engine oil pressure from 0 to 195 psi in 5 psi increments.

 

 

In the DDI, the oil temperature is not shown either

 

 

INLET TEMP Engine inlet temperature in °C. N1 RPM Fan speed in % rpm. N2 RPM Compressor speed in % rpm. EGT Exhaust gas temperature in °C.

FF Fuel flow in pounds per hour.

NOZ POS Nozzle position in %.

OIL PRESS Oil pressure in psi.

THRUST Thrust in %.

VIB Engine vibration in inches per second.

FUEL TEMP Engine inlet fuel temperature in °C.

EPR Engine pressure ratio (ratio of exhaust pressure to ambient inlet pressure). On aircraft 161925 AND UP with weight off wheels, EPR is a ratio of exhaust pressure to ambient total inlet pressure. On all aircraft, EPR is valid only during ground static conditions.

CDP Compressor discharge pressure in psia.

TDP Turbine discharge pressure in psia.

 

 

 

About fuel see the attachment

Edited June 28, 2018 by luft

[PAWPAWPAW]

Thank you luft for that excellent bit of information on the fuel system (I had not seen that document before).

 

I still feel that even with all of the information on the DDI page (which I assume was retrieved from the NATOPS document), that the oil temperature data is a critical bit of information that is missing. I am not sure how the Oil Temp could be deduced from the DDI page information?

 

Am I wrong and Oil Temp is now considered superfluous information with regards to maintaining an engine within correct operating conditions? Any thoughts?

[luft]

Thank you luft for that excellent bit of information on the fuel system (I had not seen that document before).

 

I still feel that even with all of the information on the DDI page (which I assume was retrieved from the NATOPS document), that the oil temperature data is a critical bit of information that is missing. I am not sure how the Oil Temp could be deduced from the DDI page information?

 

Am I wrong and Oil Temp is now considered superfluous information with regards to maintaining an engine within correct operating conditions? Any thoughts?

There is an oil temperature sensor in both AMADs, producing the caution in the DDI, L / R AMAD, when it is too high.

 

Enviado desde mi SM-G950F mediante Tapatalk

[Midnightzulu]

Modern aircraft design has progressed to the point that the pilot has been gifted the ability to focus almost entirely on the mission. Today’s aircraft will typically alert you when something’s wrong with the systems.

[Drotik]

alert you when something’s wrong with the systems.

 

That's the point. There is no need to constantly watch such parameters as sophisticated monitoring systems take of that for you. And therefore there is no need to constantly display them. To be alerted when something exceeds its normal parameter is more than enough. You should also consider that the temperature of the oil in a gas turbine engine is of somewhat other importance than in a reciprocating one. Since the oil encounters very high temperatures (as cooling is one of its main functions) only full synthetic high performance lubricants may be used. In comparison to normal lubricants that are used in piston engines or other machinery it's viscosity is very low, almost like water when it reaches normal operating temperature. It is designed to maintain that viscosity through a very large temperature range (from about -40 to 300 deg Celsius) without losing its features. So a hot oil condition in a jet engine is not treated like in a piston engine where more or less immediate action is required. Can't speak for the Hornet but in the Tornado for example it is considered an “Amber Caution”. Something out of the ordinary but not outright dangerous. There is absolutely no benefit in displaying that value as long as a simple computer keeps watch, which is the case in all more or less advanced aircraft. I am quite sure the Hornet's engine does measure oil temp and gives a warning if the temperature reaches a critical level. Resistance type detectors are normally used for that task. You may find it interesting that the engine oil in jet engines is almost never changed but refilled after nearly every flight. The Tornados engines devour about 2-3 liters of oil pH each.

Edited June 29, 2018 by Drotik

[mvsgas]

I am currently researching aircraft system ....

I think is just different engineering teams philosophies and design.

1 For the oil temp omission;

It is not unique, IIRC, neither the F-16, F-15 nor the AV-8, etc. have oil temp gauges. I think Drotik describe it best. In some engine (Pratt & Whitney) F-16 do not even have a light to indicate oil temp.

 

2 For the APU;

Again, IIRC, is used differently. For example, APU on the A-10 can be used for maintenance and to power system on the ground. So it can run for longer periods under load. APU For the F/A-18 is only used for start or to help ECS on the ground. The F/A-18 APU can rotate the AMADS, for maintenance (giving hydraulic pressure and power) but it does that through bleed air, the A-10 APU can do all that as a unit with its own generator and hydraulic pump.

[Drotik]

but it does that through bleed air, the A-10 APU can do all that as a unit with its own generator and hydraulic pump.

 

Kinda like in an airliner then. I find it interesting that the APU in the FA-18 can be started in flight. On our european jets, the Tornado and the Eurofighter, the APU cannot be started without weight on the wheels. In the Eufi it even switches off at a certain taxi speed.

 

Edit: As far as I remember even the old F-104 did not have an oil temp indicator for the engine. Not sure if it had a warning light.

Edited June 29, 2018 by Drotik

[mvsgas]

Kinda like in an airliner then. I find it interesting that the APU in the FA-18 can be started in flight. On our european jets, the Tornado and the Eurofighter, the APU cannot be started without weight on the wheels. In the Eufi it even switches off at a certain taxi speed.

 

Edit: As far as I remember even the old F-104 did not have an oil temp indicator for the engine. Not sure if it had a warning light.

 

In the F-117, the APU ran the entire flight. It was started before the engines and shut down after. Every aircraft is different I guess.

[PAWPAWPAW]

Apologies for my late reply and thank you to everyone for you interesting comments (loving the APU discussion and comparison with European aircraft).

 

There is an oil temperature sensor in both AMADs, producing the caution in the DDI, L / R AMAD, when it is too high.

 

 

For those who are curious, the information regarding the oil temp warnings for the FA-18C AMADs can be found on pages V-12-1, V-12-2 & primarily V-12-7 of the NATOPS guide.

 

If I may be so bold as to ask one final question regarding the oil temp warning on the DDI...

 

Has this oil temp warning system currently been implemented in the DCS aircraft? And if so, does this L/R AMAD warning appear on a specific page or does it flash up as a major caution on the LDDI overriding other page information?

 

Thanks again in advance

 

 

EDIT: Think my question has already been answered in this thread: https://forums.eagle.ru/showthread.php?t=214797

 

Thanks

Edited July 4, 2018 by PAWPAWPAW