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Old 09-14-2019, 04:17 PM   #1
pcoud
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Join Date: Apr 2018
Posts: 6
Default Fuel management

Hi AV8B veterans,

Does anyone know:

1) if the basic drag index (BDI) that is shown on the VREST page is actually correct ? Is this BDI something calculated by the vrest computer or something that needs human input ? In DCS, the vrest BDI value changes when you load / unload either the gunpod or the litening pod, but does not change for any other loads (bombs, missiles, etc.) which does not seem to be correct (at least as far as I understand).

2) if the cruise and bingo pages are actually functional ? The right column (optimum cruise) in the cruise page seems somewhat correct to me, but not the left column (I don't even see the max range parameter decreasing over time).
Note: there's also a BDI value shown on the cruise and bingo pages, but it is stuck at 18.5

I'm currently working on fuel planning / management, bingo charts, etc. and any enlightment would be highly appreciated

PS: you can manually change the BDI value on the vrest page via the ODU, but not on the cruise / bingo pages.
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Old 09-14-2019, 05:43 PM   #2
Ramsay
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Join Date: Aug 2012
Location: UK
Posts: 2,152
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As you've noted, some of the VREST page is close to the expected values, whilst other parts seem to be placeholder or dummy values.

I've planned a basic flight plan using NATOPS performance charts and compared the VREST values to the actual flight.

I don't know if you'll find them useful but these are my rough Flight Plan Notes

Spoiler:
AV-8B VREST Cruise.txt

GTW = 22,560 lbs
VREST Drag Index = 18.5 = ~20

Nozzle Stop = 60 / NRAS = 63 KCAS
STOL Flaps = 450 ft ground roll

Climb = 350 KCAS / 0.74 mach
Climb to 35,000 ft = 5:12 min / 880 lbs fuel / 36 NM

Cruise = 35,000 ft / 0.74 mach/ 430 TAS
Cruise = 0.13 NM / lb = 2700 lbs / 350 NM = 55 lb/min @ 430 GS
Actual = 70 lb/min @ 450 GS = 450 NM /(70*60 ) = 450/4200 NM/lb = 0.11 NM/lb

Max Range Descent - flaps auto/throttle idle/speedbrake in
Descent = 230 KCAS / 0.74 mach
Descent = 11 min / 200 lbs / 52 NM

Landing + 500 lbs Reserve = 1200 lbs

Flight Plan
Distance 457 NM / 1 h 07 min

Fuel = 1200+200+2700+880 = 4980/7760 lbs

Idiot Check
Fuel = Landing + Climb + 10 lbs/NM = 1200+800+4600 = 6600/7760 lbs

350 KCAS / 0.80 mach seemed best i.e. 7 AoA, flaps at cruise
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Old 09-16-2019, 05:15 PM   #3
pcoud
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Join Date: Apr 2018
Posts: 6
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Thanks Ramsay, I appreciate. I am currently doing quite some testing too. It took me a while to understand those "bingo charts" that you can find in the natops performance charts, but now that I think I have understood it would be great to be able to use them :-) The only remaining small issue is the drag index since it is obviously not modeled properly, but when you are RTB, back from a mission, you generally not have much weapons left under the wings (or you can jettison them), and you can consider that the drag index is in the 20ish (or a bit more if you are carrying the tpod and/or the gunpod). Will continue testing :-)
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