Fuel Flow/Burn
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Hi,
I thought I noticed this yesterday but wasn't certain.
This morning I flew EGNM-LEAL. The centre tank burns away in the climb but once in the cruise the actual fuel burn figures are around about 1/2 of the simbrief predicted burn.
I was estimated to land into LEAL with 3.0T of fuel remaining and a burn of 5.9T. The actual figures were as attached - a burn of 3.06 and fuel remaining approx 6.0T.
I am flying LEAL - EGGW now and monitoring more closely and will report back. All SOP and checklists followed. So far predicting similar.
Real weather etc - which is currently showing on the way back at ISA +3 so that shouldn't affect the fuel burn and my OFP was showing an overall ISA +2 for the entire flight, and winds are so far pretty much bang on the forecast.
Ian.
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@genista descending now into LUTON, I clicked the "fuel total weight" figure on the tablet (which was much higher than it should have been for this stage of my flight) and it updated (reduced quickly including the fuel gauges) to what I expected it should be.
Justflight FYI.
Ian.
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Actually - clicking the fuel weight box as above resulted in a low fuel situation when turning final due to a huge change in the fuel amount.
Flight LEAL-EGGW predicted fuel burn (most recent simbrief profile) was 6.1 with an actual from the fuel totalisers of 3.2. Pushed with 8.4 and landed with 0.9 (!) which should have been from the OFP around 2.5 to allow diversion/holding. This was after clicking the EFB as above. If I take fuel burned off the fuel I pushed with I'd have landed with 5.2 which is obviously just over double the OFP suggests (and my fuel burn is around 1/2 of what it should have been).
Unless I'm missing something!
Ian.
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I’m also seeing far less fuel consumption than predicted by the default SimBrief profile for the -300. Is there a reference somewhere we can use to figure out whether the simulation or the SimBrief profile is wrong?
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@systemdefault I've seen the same thing, but with the old simbrief profile from a few days ago. I'll try the new one tomorrow.
But there is a big element that aircraft programmers must be having nightmares about, which is that MSFS still has a major issue with increasing drag with airspeed, and the corresponding affect of engine power on speed (and corresponding fuel flow and consumption).
Example from just this evening, in the BAE146, you might be cruising along with throttles at 70%, and you realize you are doing 290 KIAS, and slowly accelerating. You back off the throttle just a hair, like down to 69%. Look at your airspeed 10 minutes later, and you've slowed down to 200 knots.
It's teven worse with Aerosoft's CRJ (which also does not have an autothrottle) - you are constantly having to manually adjust the throttles - either you are heading into overspeed, or the slightest adjustment will slow you down to the point you can't even maintain altitude.
After nearly 2 years, I hope Asobo is looking at fixing this. According to their priority list, popcorn clouds seem more important than a monumental failure in flight dynamics.
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@dreadnought1906 interestingly though this doesn’t seem to be an issue with with WT CJ4.
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What do the profile options mean?
LIke... High Speed I assume is is maximum Thrust (using VS or IAS mode)? Long Range I guess is a lower power climb (ie 500-1000fpm). For descent I guess High Speed it essentially just an idle throttle high FPM descent over a shorter distance while Long Range is just that, idle or near idle descent over a much larger distance than the High Speed one?
For Cruise profiles, M70 is just maintain Mach .70 I guess, not to hard to work out. MCR is setting the TMS to Max Cruise Thrust, and just flooring it and riding the barber pole? LRC is low power cruise for max distance, like I'm guess .5 Mach or something?
Would be nice to get more information on what these meant, haha.
I haven't really had the issue with maintaining speed like some folks here have mentioned. It can be a little fiddly at the start with initial cruise, but after that its generally fine, usually letting me wander away or watch some Youtube while flying along.
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@melon Unfortunately some parts of SimBrief at a black box, profiles like that included. As far as I'm aware users can't change or add those profiles, and I made an OFP with the High Speed climb and Descent profiles and didn't get anything helpful for figuring out what my speeds should be.
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@dreadnought1906 Indeed, same annoying behavior. Engine N1 increases as we build up more speed, therefore generating more thrust, but without drag increase, meaning the speed just tend to increase slowly but exponentially if we do not find the exact sweet spot where speed is stable.
It is hard if not impossible to be accurate with speed between 250 and 300KIAS. As long as I am in that range, I don't touch the throttle otherwise it'll either slow down to 200 or overspeed lol
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@plhought The new profile at least for the -100 variant, is better, but not by much.
On my most recent flight from KDAL to KLEX with 50 pax, no cargo, at FL270:
Old Simbrief (B463 profile with adjusted weights to work with -100) Trip Fuel : 9052 lbs
New B461 profile Trip Fuel: 8476 lbs
Actual fuel used: (Gate to gate): 5452 lbsSo still way off, and frankly I think the Simbrief profile is not the problem - the sim is. If the sim's fuel burn is accurate, that means the -100 has around 3,500 nm effective range. I don't f'ing think so.
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@dreadnought1906 Guys, I found a trick that seems to solve the problem of trying to micro-control your throttle lever at cruise.
Set the TMS to TGT (target) mode, and enter 600 in the TGT window. The system will try to maintain all engines at that power setting. I found that 600 results in a cruise speed somewhere between 255 and 260 KIAS. And it's pretty stable. I'm lightly loaded and have to experiment with higher settings, but this is a nice discovery for me.
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@dreadnought1906 Another Simbrief performance reference:
Flight from KEUG to CYVR. Simbrief ordered 34,000 feet, so that's what I did. Can the -100 really fly that high? Anyway...
Simbrief Trip Fuel: 4973 lbs, plus 500 for Taxi
Actual: 3057 lbs Gate-to-gate, including 461 for taxi, so 2596 flight usage.
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@dreadnought1906 this is a genius solution. I’ll give it a try. Thank you.
