fpas

[colubridae]

just a quickie...

 

 

if i'm flying at low altitude and I use the FPAS to check range. it gives (amongst other things) a range at optimum altitude, usually in the 30000' level.

 

 

Does that range include fuel burnt whilst climbing to that altitude?

 

 

please.

 

:)

[Harker]

AFAIK it gives the maximum range you can cover if you fly at the optimum altitude, using optimum speed, based on your current (and likely projected) weight. I think of it like "if you flew that profile, you'd go that far", so, unless I'm mistaken, it doesn't take the fuel required to climb into account, but it will adjust itself as you burn it.

[RaiderOne]

...

... range at optimum altitude ...

 

...

 

Does that range include fuel burnt whilst climbing to that altitude?

...

No, this "Overall Optimal Maximum Range" displayed on the bottom part of the FPAS page, is there to give you a better idea of what range you could get at that optimal altitude ... take it as a "Maxi Max range" !

 

If you want to optimise your climbing profile to reach the best compromize between best altitude to transit with low fuel flow and the minimum kerozen to use to reach that target altitude, then you have to do those steps :

 

 

- push full MIL Power (limit of afterburner),

 

- use the "Climb" mode on the FPAS page to display the optimal climbing speed on your HUD (on top of your IAS),

 

- follow this recommended speed without moving your throttle (climb more to decelerate, climb less to accelerate),

 

- stop climbing when you reach the "Overall Optimal Altitude" if you have enough range to travel to stay quite a long time at that high altitude, but if your remaining travel range is shorter, then stop climbing at an altitude where you could stay at least the same time it took you to climb.

 

 

 

I hope it is clear enough to help you to understand what to do ... ?!

Edited September 24, 2019 by RaiderOne

[colubridae]

Yessir. Going to give it a test.

 

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[Zyll]

Are you sure that the climb profile is the best compromise if climb rate and fuel burn? I always assumed it was the fastest climb at a certain fixed throttle, but never saw a proper explanation myself. How can it be both the best climb rate and fuel efficient at the same time?

[Flamin_Squirrel]

Are you sure that the climb profile is the best compromise if climb rate and fuel burn? I always assumed it was the fastest climb at a certain fixed throttle, but never saw a proper explanation myself. How can it be both the best climb rate and fuel efficient at the same time?

 

What do you mean by 'fastest', climb rate, or airspeed? Fuel burn drops off considerably at altitude, so climbing around best climb rate is generally the most fuel efficient.

 

Max throttle is also best, because fuel flow drops off faster as you climb than you'd have saved by being at a lower throttle setting.

[RaiderOne]

Are you sure that the climb profile is the best compromise if climb rate and fuel burn? I always assumed it was the fastest climb at a certain fixed throttle, but never saw a proper explanation myself. How can it be both the best climb rate and fuel efficient at the same time?

 

It is not the best climb rate or the fastest. I am pretty sure.

 

But I did some tests (a lot more should be done to clarify everything) and it appears to me that :

 

- if you want to go from point A to point B (with B quite far away from A),

- and if at point A you are lower than the "Overall Optimal Altitude for Range",

then the best way to travel to B (I mean with the smallest amount of fuel used) is to climb from A to that "Overall Optimal Altitude for Range" at Mil Power and with the speed recommended by the "Climb Mode of FPAS Page" ... and then once done, to stay at this high altitude up to near the point B !

 

 

But just like you, I did not found anywhere a clear enough explanation to be definetly sure of the perfect trajectory to save the maximum of fuel !

Edited September 24, 2019 by RaiderOne

[Harker]

AFAIK, the below procedure is correct (please correct me if I'm wrong):

1) Select CLIMB on the FPAS page, push throttle to MIL.

2) Adjust your pitch/climb rate so your airspeed is equal to the one indicated above the airspeed box on the HUD.

3) Keep doing that (adjusting the pitch to match the indicated speed) until you reach Optimum (or desired) altitude.

4) Once you stop climbing, adjust airspeed so that you achieve the best Mach for your altitude, indicated in the CURRENT tab. If your altitude is the same as the Optimum altitude, the CURRENT and the OPTIMUM tabs should match, more or less (so CURRENT best Mach would be equal to OPTIMUM best Mach).

 

Use the OPTIMUM tab to figure out the best altitude for max range or max endurance, use the CURRENT tab to figure out the best Mach for each case, for your altitude (which may or may not be one of the two optimum altitudes).

 

Disclaimer: I think the following works like that, but I'm not 100% sure. Please verify (and please let me know if you do).

To get the best descent profile, use the HSI. Below the Waypoint (or TACAN) name, you have a few rows of data, such as distance and bearing, time to arrive, calculated remaining fuel upon arrival and below that, a number counting down, that shows in how many NM you should start descending. Once that number reaches zero, place the throttle to IDLE and descent, placing your FPM on the waypoint location.

[RaiderOne]

AFAIK, the below procedure is correct (please correct me if I'm wrong):

1) Select CLIMB on the FPAS page, push throttle to MIL.

2) Adjust your pitch/climb rate so your airspeed is equal to the one indicated above the airspeed box on the HUD.

3) Keep doing that (adjusting the pitch to match the indicated speed) until you reach Optimum (or desired) altitude.

4) Once you stop climbing, adjust airspeed so that you achieve the best Mach for your altitude, indicated in the CURRENT tab. If your altitude is the same as the Optimum altitude, the CURRENT and the OPTIMUM tabs should match, more or less (so CURRENT best Mach would be equal to OPTIMUM best Mach).

 

Use the OPTIMUM tab to figure out the best altitude for max range or max endurance, use the CURRENT tab to figure out the best Mach for each case, for your altitude (which may or may not be one of the two optimum altitudes).

 

Disclaimer: I think the following works like that, but I'm not 100% sure. Please verify (and please let me know if you do).

To get the best descent profile, use the HSI. Below the Waypoint (or TACAN) name, you have a few rows of data, such as distance and bearing, time to arrive, calculated remaining fuel upon arrival and below that, a number counting down, that shows in how many NM you should start descending. Once that number reaches zero, place the throttle to IDLE and descent, placing your FPM on the waypoint location.

 

 

Yes Man, I do agree with everything except the very end ... if the ending point is a TACAN source, not a waypoint, then for my descent, I put the throttle on Idle, OK, but I adjust my speed with the one indicated by the "Climb Mode" again !

I sounds weird but it seems to work correctly !

I stop descending this way when I cross the Angel 3 or 4 Level.

[colubridae]

Thanks all.

 

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[Harker]

Yes Man, I do agree with everything except the very end ... if the ending point is a TACAN source, not a waypoint, then for my descent, I put the throttle on Idle, OK, but I adjust my speed with the one indicated by the "Climb Mode" again !

I sounds weird but it seems to work correctly !

I stop descending this way when I cross the Angel 3 or 4 Level.

Interesting. Why would a TACAN station be any different that a waypoint though, assuming you want to descent to the same altitude? Both are points in space, as far as the FPAS is concerned.

[RaiderOne]

The only difference is that the TACAN point is not showing itself on the HUD like the Waypoint does. So you cannot put your FPM on it to adjust your descent rate ...

[KittyVCAW-1]

The only difference is that the TACAN point is not showing itself on the HUD like the Waypoint does. So you cannot put your FPM on it to adjust your descent rate ...

 

i've seen a page on the ddi somewhere that give the gps coordinates of every tacan station on the map. If you want to plug them into the UFC for that kind of thing. I can't recall exactly where they are located atm. I might do a flight this evening if I do i'll look for it. They might be on the kneeboard pages too I can't remember.

 

edit* HSI>DATA>TCN : use PB 12 & 13 to cycle up and down the list

Edited September 25, 2019 by Jonnie2Bad

[Weasel]

i've seen a page on the ddi somewhere that give the gps coordinates of every tacan station on the map. If you want to plug them into the UFC for that kind of thing. I can't recall exactly where they are located atm. I might do a flight this evening if I do i'll look for it. They might be on the kneeboard pages too I can't remember.

Seems to be in the HSI page where you can find the GPS coordinates of the tacan stations

[RaiderOne]

The only difference is that the TACAN point is not showing itself on the HUD like the Waypoint does. So you cannot put your FPM on it to adjust your descent rate ...

And - I forgot this one - the TACAN station can be mobile ... The Carrier (Stennis) for instance.

 

So in this case, it is useless to create a waypoint with the GPS coordinate of the TACAN station.

And anyway, in the case of the Carrier, you don't have to aim directly to the Carrier itself (for your descent) but you have to manage your descent to be compliant, at the end, with the Recovery Procedure declared (CASE I, II or III).

[Switch625]

According to the Bingo Profile charts, descents are all done at: "250 KCAS idle thrust decent". The distance to start decent varies based on weight and drag index.

[Flamin_Squirrel]

According to the Bingo Profile charts, descents are all done at: "250 KCAS idle thrust decent". The distance to start decent varies based on weight and drag index.

 

Multiply your attitude in thousands by 2 to get a distance and you should be there or there abouts. E.g. 25,000ft, descend with 50nm to go.

[Preendog]

Mind that the refueling hose is pretty quick, so doing a faster than standard approach will save time if you are doing a rearm and refuel.

 

I think the refueling is even faster than afterburner flow.