F15, engine fuel flow indicator and quantity indicator question

[fitness88]

The F15 engine fuel flow indicator is in pounds per hour. The indicator has a max reading of 100 pounds per hour which doesn't seem to make sense...unless the indicator numbers need to have a couple of zeros added on.

Does anyone know?

 

Can someone please explain in detail what all the readings represent on the F15 fuel quantity indicator. Also, does 'external fuel tanks' refer to the wing drop tanks?

 

Thank you.

[mvsgas]

The F15 engine fuel flow indicator is in pounds per hour. The indicator has a max reading of 100 pounds per hour which doesn't seem to make sense...unless the indicator numbers need to have a couple of zeros added on.

Does anyone know?

 

Can someone please explain in detail what all the readings represent on the F15 fuel quantity indicator. Also, does 'external fuel tanks' refer to the wing drop tanks?

 

Thank you.

 

1lbs pph x1000 AFAIK. Not sure

Edited October 26, 2013 by mvsgas

[104th_Maverick]

Yes the external tanks are your wing tanks and or the tank under the fuselage.

 

In the F-15C your external tanks are empty when your fuel gauge shows less than 13,440lbs of fuel.

 

The fuel flow gauges are in x100 the given reading, so if it displays 40 per engine you are burning 4000lbs per hour per engine.

 

Hope that helps

[fitness88]

;1915337']Yes the external tanks are your wing tanks and or the tank under the fuselage.

 

In the F-15C your external tanks are empty when your fuel gauge shows less than 13,440lbs of fuel.

 

The fuel flow gauges are in x100 the given reading, so if it displays 40 per engine you are burning 4000lbs per hour per engine.

 

Hope that helps

 

 

 

Let me see if I understand this:

1. The 'external fuel tanks' refer to the wing or fuselage drop tanks.
   
2. The Total LBS. digital indicator refers to the total of both internal and drop tanks.
   
3. Left and Right digital indicators refers to the left and right drop tank, is there no fuselage drop tank indicator?
   
4. 13,440lbs of fuel is the max the internal tanks can hold and at that amount or less indicates empty drop tanks, why does the fuel quantity needle only show 12,000 lbs?
   

Thanks for your feedback.

[TAW_Blaze]

I don't know where to find out how empty your droptanks are exactly, but as soon as your total fuel qty equals the left and right tank combined (that is usually around 13k lb as said above) that means they are empty so you can drop them off. As for fuel flow, look at the numbers on the gauge, it's easier :) ie if it shows 7000 then you're burning 7000 lb on said engine per hour. From my obervation the indicator is x1000 lb/hr but I'm not completely sure about this. I always look at the number only.

[fitness88]

I don't know where to find out how empty your droptanks are exactly' date=' but as soon as your total fuel qty equals the left and right tank combined (that is usually around 13k lb as said above) that means they are empty so you can drop them off. As for fuel flow, look at the numbers on the gauge, it's easier :) ie if it shows 7000 then you're burning 7000 lb on said engine per hour. From my obervation the indicator is x1000 lb/hr but I'm not completely sure about this. I always look at the number only.[/quote']

 

Thousand LBS per hour sounds right.

[TAW_Blaze]

Ye I think so. It was bumping around 5 when I was at 4300.

[fitness88]

Ye I think so. It was bumping around 5 when I was at 4300.

 

Confirming my previous post above :

1. The 'external fuel tanks' refer to the wing or fuselage drop tanks.
   
2. The Total LBS. digital indicator refers to the total of both internal and drop tanks.
   
3. Left and Right digital indicators refers to the left and right drop tank, is there no fuselage drop tank indicator?
   
4. 13,440lbs of fuel is the max the internal tanks can hold and at that amount or less indicates empty drop tanks, why does the fuel quantity needle only show 12,000 lbs?
   

[TAW_Blaze]

I'm confused as hell actually right now. I don't know! :megalol:

 

Been flying for most of the day, I'm starting to get tired :)

Edited October 26, 2013 by <Blaze>

[104th_Maverick]

Confirming my previous post above :

1. The 'external fuel tanks' refer to the wing or fuselage drop tanks.
   
2. The Total LBS. digital indicator refers to the total of both internal and drop tanks.
   
3. Left and Right digital indicators refers to the left and right drop tank, is there no fuselage drop tank indicator?
   
4. 13,440lbs of fuel is the max the internal tanks can hold and at that amount or less indicates empty drop tanks, why does the fuel quantity needle only show 12,000 lbs?
   

1. Yes

2. Correct

3. No, the left and right digital indicators are readings of your internal tanks (left and right side), there is no 'reading' for your external fuel amount, apart from taking 13,400 from your current total displayed on the fuel gauge.

4. You have burned off that fuel? try this....

 

Take off in F-15C fully fueled and with 2 or 3 external tanks, once airborne look at your fuel gauge.

Then press Lalt+R to drop your fuel tanks and watch what the reading drops too, it should be 13,440lbs (or close)

[fitness88]

Just did some testing below are my results. Tap the time accelerate several times to speed the testing up if you want to do it as well.

Z - LCtrl Time accelerate

Z - LAlt Time decelerate

Z - LShift Time normal

 

The fuel quantity needle is the sum of the left and right digital indicators. The fuel quantity needle and the left and right digital indicators indicate only internal fuel. They don't reflect fuel in the drop tanks. Fuel in the drop tanks are added onto the Total LBS indictor.

If you arm a fuel tank to the F15 with no fuel in the internal tanks you will see the quantity needle and the left and right digital indicators indicate an increase in fuel. This would seem is because the fuel in the drop tanks get transferred into the internal tanks if the internal tanks are not completey full.

Edited October 26, 2013 by fitness88

[fitness88]

;1915636']

 

1. Yes

2. Correct

3. No, the left and right digital indicators are readings of your internal tanks (left and right side), there is no 'reading' for your external fuel amount, apart from taking 13,400 from your current total displayed on the fuel gauge.

4. You have burned off that fuel? try this....

 

Take off in F-15C fully fueled and with 2 or 3 external tanks, once airborne look at your fuel gauge.

Then press Lalt+R to drop your fuel tanks and watch what the reading drops too, it should be 13,440lbs (or close)

 

1. wouldn't seem so after my test they respond only to internal fuel being added

Also why does the fuel quantity needle only have a max reading of 12,000 lbs when 13400 is the max?

Edited October 26, 2013 by fitness88

[104th_Maverick]

Your confusing me now, in your post above you confirm everything I said to you the last time. (sorry if I'm not understanding)

 

The 'fuel quantity' gauge shows you your total fuel on the aircraft, internal and external.

There is no separate gauge for the External only fuel amount.

 

The fuel needle will only move when you have less than 13,400lbs on board. Anything over that amount of fuel is stored in your fuel tanks. So the only way you can work out how much fuel is stored in your external tanks is subtracting 13,400 from what ever your current total is eg 24,500 - 13,400 = 11100lbs of external fuel.

 

If you refuel an empty aircraft you will see the needle move up to around 13,000lbs then stop even though the aircraft is still taking on fuel, then when you look at the digital gauge below that it tells you how much fuel is onboard all tanks eg 24,500lbs (once refuel complete)

 

Your aircraft will always use your external fuel first.

Edited October 26, 2013 by [Maverick]

[fitness88]

;1915650']Your confusing me now, in your post above you confirm everything I said to you the last time. (sorry if I'm not understanding)

 

The 'fuel quantity' gauge shows you your total fuel on the aircraft, internal and external which is internal.

There is no separate gauge for the External only fuel amount.

 

The fuel needle will only move when you have less than 13,400lbs on board. Anything over that amount of fuel is stored in your fuel tanks. So the only way you can work out how much fuel is stored in your external tanks is subtracting 13,400 from what ever your current total is eg 24,500 - 13,400 = 11100lbs of external fuel.

 

If you refuel an empty aircraft you will see the needle move up to around 13,000lbs then stop even though the aircraft is still taking on fuel, then when you look at the digital gauge below that it tells you how much fuel is onboard all tanks eg 24,500lbs (once refuel complete)

 

Your aircraft will always use your external fuel first.

 

Sorry to be confusing but I'm doing ongoing testing as we chat.

The left and right digital indicators will always = the fuel quantity needle exactly they are tied into the same source of fuel.

The use of external fuel tanks is a bit confusing, you say they are drop tanks and the manual says different

from the manual:

Fuel Quantity Indicator

The fuel quantity indicator is intended for indicating fuel quantity in the aircraft’s fuel tanks. The fuel

level needle shows the fuel quantity in the internal fuel tanks. The three digital indicators in the lower

part of the instrument show the total amount of fuel (both in internal and in external fuel tanks) and

the amount of remaining fuel in the left and right external fuel tanks respectively. Fuel amount is measured in pounds.

 

In red it's referring to left and right external tanks, so external tanks can't be drop tanks.

Edited October 26, 2013 by fitness88

[104th_Maverick]

"the amount of remaining fuel in the left and right external fuel tanks respectively."

 

Got spot!

 

To be honest, I'm not sure about that.

 

It's either a bug in the aircraft system or a typo in the manual.

 

I'm tempted to lean to the manual typo side but leave this with me and I will check it out and get an answer from someone very familiar with all the RW F-15C systems.

 

In the mean time though... everything else I said was true :D

[fitness88]

;1915661']"the amount of remaining fuel in the left and right external fuel tanks respectively."

 

Got spot!

 

To be honest, I'm not sure about that.

 

It's either a bug in the aircraft system or a typo in the manual.

 

I'm tempted to lean to the manual typo side but leave this with me and I will check it out and get an answer from someone very familiar with all the RW F-15C systems.

 

In the mean time though... everything else I said was true :D

 

Appreciate your thoroughness...for me when in doubt I lean toward what the aircraft tells me:pilotfly:

Thanks again

[fitness88]

Don't know why I didn't notice this before. On the fuel flow indicator there is a digital indicator that says exactly what the fuel flow pounds per hour are and the needle indicator below that.

[TAW_Blaze]

Don't know why I didn't notice this before. On the fuel flow indicator there is a digital indicator that says exactly what the fuel flow pounds per hour are and the needle indicator below that.

 

That is what I was telling you on the first page.

 

Don't worry you're not alone, sometimes I discover new gauges too despite having flown the plane for a long time. :D

[blkspade]

What actually confuses me about the fuel flow indicator is that it decreases in flow as you climb, which is expected, but as you shallow the climb or level out it just goes right back up. You would think that the decreased fuel flow associated with climbing would be consistent once you reach the desired higher altitude.

[howie87]

I noticed extreme efficiency with full afterburner at 65,000ft in level flight. I was just over Mach 1 with a ground speed of about 1000 knots.

 

Fuel consumption seems to act a bit weird in the F-15.

[fitness88]

I noticed extreme efficiency with full afterburner at 65,000ft in level flight. I was just over Mach 1 with a ground speed of about 1000 knots.

 

Fuel consumption seems to act a bit weird in the F-15.

 

Once the throttle is set I noticed that the fuel consumption indicator continues to increase, slowly. As well there is no reduction/increase in fuel burn no matter what stage afterburner you are in.

[howie87]

That's why I'm sticking to the A-10C! Seems to act much more realistically with regards to engine management/performance.

[sobek]

The F-15 is still SFM. Things are probably going to improve with the AFM for the F-15.

[GGTharos]

You'd have to ask the designers.

 

How much weight of fuel you actually have depends on the type of fuel you load. Some types of fuel would have your internals weighing in at 14500lbs or more, IIRC - but don't quote me on that. Some fuels would have the fuel quantity at a lower amount.

 

For the pilot, checking if he's at bingo fuel is seriously easy with the gauge, and remaining quantity is easier to read if the gauge is conveniently graduated.

 

Typical joker for an F-15 can easily be 6000lbs of fuel ... that's the needle pointing straight up. To the right of that, you're cool, to the left of that, you're probably looking for a gas station.

 

Also why does the fuel quantity needle only have a max reading of 12,000 lbs when 13400 is the max?

[strikeeagle]

The fuel gauge on all F-15's read 12,500 on the needle side. The totalizer reads how much gas is in the entire airplane. Why you may ask? Because MacAir said so.

 

As far as the quantity selector knob and its readings, when the knob is rotated to the far left and held, all 4 readings roll to zero for a BIT (built in test). FEED rolls the left and right indicators to see how much fuel is in the feed tanks (tanks 2 and 3). Next is INTL WING (self explanatory). TANK 1 is the largest tank. When the knob is rotated to that position, the right indicator reads zero and the left will read how much is in that tank. EXT WING, EXT CTR, and CONF TANK should be self explanitory.

Edited October 28, 2013 by strikeeagle