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problems with Fuel Economy

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problems with Fuel Economy

Postby cain071546 » Fri Aug 15, 2014 12:52 am

i am using the Yak18T it is listed as having a range of 750km or 400 Nautical Miles or 373 Miles

it has 3 Fuel tanks that each hold 10 gallons (thats 30 gallons) (48 in the specs) i dont know were the other 18 went in the model

at 110 Knots at 6000 Ft at 24 Gallons per Hour of fuel being consumed by the engine i should be getting around 2 hours if i had 48 gallons at 24 gallons per hour and a range of about 220 Nautical mies or 407 Kilometers

i get aprox 23 Minutes per tank thats 69 Minutes of Flight time
i have the fuel mixture set to the lowest setting

at 110 knots + 9 minutes that is only about 213 Kms (i think)

what is wrong here, i even looked up the manuel for the plane and 24 gallons per hour is about right for 110-135 Knots at 50% throttle

and the size of the fuel tank is also close to spec, its listed as 700Kms on 180 Liters of fuel or 47.5 gallons so where do they get 700Kms from?

there is no way this aircraft can go 250Kms on the fuel available let alone 700!!!!!

that or i am seriosly messing up the math here
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Re: problems with Fuel Economy

Postby daveculp » Fri Aug 15, 2014 2:16 am

Is your cruise speed in knots indicated (KIAS) or knots true (KTAS) ? That could be the difference.
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Re: problems with Fuel Economy

Postby cain071546 » Fri Aug 15, 2014 4:05 am

it is in KIAS "Knots-Indicated Air Speed"

My father has also braught to my attention the Headwind/Crosswind along my route is slowing me down

i just dont know if that is enough of a factor to account for the lack of fuel economy, can that really cut 300Km off my range?
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Re: problems with Fuel Economy

Postby Gijs » Fri Aug 15, 2014 7:49 am

Hi,

this could very well be a badly tuned flight model. Not sure what Yak model you're using, but the one on the official download page (and in Git) has several issues. There's just a single tank for example and it holds only 9.33 (!) gallons of fuel. You can check the fuel consumption if you open the property browser and browse to /engines/engine/fuel-flow-gph.

Cheers,
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Re: problems with Fuel Economy

Postby sanhozay » Fri Aug 15, 2014 8:17 am

I'm just looking at the "yak18t" in Git and it has a single tank with 90 gallons. Hmm. That's different from OP and Gijs. In the property browser, I am seeing sim/aero as "yak18t-yasim"

i have the fuel mixture set to the lowest setting


I thought it might have been the mixture setting. Normally it's somewhere in the middle, based on Exhaust Gas Temp (EGT). I have the yak18t in the air and, although the mixture lever (which is blue) appears to be connected up (controls/engines/engine[0]/mixture), it doesn't seem to have any effect on fuel flow (engines/engine/fuel-flow-gph). The EGT gauge is present but not simulated.

Despite not being able to adjust mixture, fuel flow is pretty much a constant 24-25gph at 50% throttle, which gives about 3.5 hours from a 90 gallon tank, or about 420nm with no wind.
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Re: problems with Fuel Economy

Postby Gijs » Fri Aug 15, 2014 8:22 am

sanhozay wrote in Fri Aug 15, 2014 8:17 am:I'm just looking at the "yak18t" in Git and it has a single tank with 90 gallons.

That's apparently a bug. Try adjusting the slider to fuel by hand, then you'll see the "actual" number of gallons and pounds. In case of doubt, check the FDM file and you'll see that it's indeed set to 56 pounds (9.33 gallons) ;-)

EDIT: There's actually some Nasal stuff handling the fuel system. Looks like it is copy&pasted from another aircraft and not properly setup in relation to the FDM...
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Re: problems with Fuel Economy

Postby sanhozay » Fri Aug 15, 2014 8:34 am

Ah yes, it does drop to 9.3 gallons. So at least we are looking at the same aircraft.
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Re: problems with Fuel Economy

Postby cain071546 » Fri Aug 15, 2014 6:39 pm

yes its the same YAK18T that is available on the official Flightgear 3.0 Aircraft download page and in GIT

yes it has 3, 9.33 Gallon Tanks for a total of aprox 30 Gallons

it starts out with like 80 Gallons for some reason , when i reset or manually empty/refill the tank it immediatly switches over to 9.33 Gallons

there is a switch for the 3 tanks in the cockpit, it does not work, so when i switch i have to refill the tank myself anyway

(so i just imagine it has 3 tanks lol, and i work my way through all 3 as if they work right) so i dont feel like im cheating

either way this model does not fly ANYWHERE NEAR 700kms

i have had to shorten my jumps to compensate for the range

i am currently flying this airraft across the USA (watch me on the multiplayer map my callsign is _ cain _ ) i started yesterday afternoon around 2PM and made it all the way to Baker Montana around 2AM last night

i am flying manually this model has no autopilot
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Re: problems with Fuel Economy

Postby Buckaroo » Sun Sep 07, 2014 7:04 pm

The FDM currently used by the version on the Yak18T on the FG 3.0 download page appears to be the original place-holder FDM used by the author Emmanuel Baranger (helijah) when he built the model. It should not be regarded as anything close to accurate.

In early 2013 after some study of the Yak18T I offered Emmanuel a replacement FDM that is closer to the configuration of the aircraft. It may or may not be incorporated into the version in his hangar-- I could not say for sure. That FDM has the proper fuel quantity configuration (a pair of 25 gallon tanks and a 0.9 gallon sump tank).

Note that YASim will not give correct fuel consumption numbers even if the tank(s) have the right capacity, since the algorithms related to fuel burn are not particularly good. This can be handled via custom scripting, which is also necessary to make the fuel selection switch work. Even simple modification of the generic fuel script used by default in YASim aircraft can yield a significant improvement. As far as I know, the Yak18T uses the default fuel script (I merely reworked the FDM) . So unless someone has worked with the aircraft since then, I would not expect range to conform well with a pilot's handbook.

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Re: problems with Fuel Economy

Postby Oswald » Tue Jul 30, 2019 8:30 pm

Came across this old thread while trying to change settings in order to make fuel consumption more realistic. I'd like to fly the Yak 18T for a VA, therefore fuel consumption is an issue. With the help of different parts of Buckaroo's Yasim guides (thanks to you to make this available!) I tried to implement a variable pitch to the propeller (should be the right thing for this aircraft) or constant speed, this didn't give in any way realistic results. Guess there had to be changes in nasal scripting?

If anybody has an idea which I could try out please give me a hint - as easy to understand as possible.
It is a lovely machine! See my photo in SOTM July :)

Thanks,
Oswald

Little bit later: Simple possible solution: made manual mixture changes availabel:
<control-input control="MIXTURE" axis="/controls/engines/engine[0]/mixture" src0="0.0" src1="1.0" dst0="0.0" dst1="1.0"/>


changed dst0="0.8" dst1="0,8" to the above.

Might make things a bit more like reality, though probably very different from real flight dynamics.
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