fsx cessna 185 thrust issue

[airgreg]

I downloaded and installed the c-185 found on this site by Lucariny and found it to be an a usable and flyable aircraft. That is until I looked at the aircraft.cfg file and found this....

cylinder_displacement=137.4132627
compression_ratio=6.00
number_of_cylinders=12
max_rated_rpm=3000.00
max_rated_hp=1735.00
fuel_metering_type=0
cooling_type=1
normalized_starter_torque=0.0350
turbocharged=1
max_design_mp=66.0
min_design_mp=1.00
critical_altitude=34000.00
emergency_boost_type=3
emergency_boost_mp_offset=10.00
emergency_boost_gain_offset=0.6500
fuel_air_auto_mixture=0
auto_ignition=0
max_rpm_mechanical_efficiency_scalar=1.100
idle_rpm_mechanical_efficiency_scalar=1.00
max_rpm_friction_scalar=1.00
idle_rpm_friction_scalar=0.800

[propeller]
thrust_scalar=1.0
propeller_type=0
propeller_diameter=11.300
propeller_blades=4
propeller_moi=65.00
beta_max=65.00
beta_min=20.00
min_gov_rpm=1700.00
prop_tc=0.100
gear_reduction_ratio=2.0800
fixed_pitch_beta=0.00
low_speed_theory_limit=80.00
prop_sync_available=0
prop_deice_available=0
prop_feathering_available=0
prop_auto_feathering_available=0
min_rpm_for_feather=0.00
beta_feather=0.00
power_absorbed_cf=0.00
defeathering_accumulators_available=0
prop_reverse_available=0
minimum_on_ground_beta=0.00
minimum_reverse_beta=0.00

I highlighted a few areas that stood out to me right away. Such as the engine being rated at 1735 HP. A little excessive don't you think for this aircraft? Yeah that is what I thought as well.....

So I took it upon myself to rectify this 'error' and altered the specs to this.....

[piston_engine]
power_scalar = 1.0
cylinder_displacement=90.0
compression_ratio=8
number_of_cylinders=6
max_rated_rpm=3000.00
max_rated_hp=375.00
fuel_metering_type=0
cooling_type=1
normalized_starter_torque=0.0350
turbocharged=0
max_design_mp=0
min_design_mp=0
critical_altitude=0
emergency_boost_type=0
emergency_boost_mp_offset=0
emergency_boost_gain_offset=0
fuel_air_auto_mixture=0
auto_ignition=0
max_rpm_mechanical_efficiency_scalar=1.100
idle_rpm_mechanical_efficiency_scalar=1.00
max_rpm_friction_scalar=1.00
idle_rpm_friction_scalar=1.20
BestPowerSpecificFuelConsumption=0.49

[propeller]
thrust_scalar=1.5
propeller_type=1
propeller_diameter=6.9
propeller_blades=2
propeller_moi=5.00
beta_max=0
beta_min=0
min_gov_rpm=1200
prop_tc=0
gear_reduction_ratio=1
fixed_pitch_beta=20.00
low_speed_theory_limit=80.00
prop_sync_available=0
prop_deice_available=0
prop_feathering_available=0
prop_auto_feathering_available=0
min_rpm_for_feather=0.00
beta_feather=0.00
power_absorbed_cf=0.00
defeathering_accumulators_available=0
prop_reverse_available=0
minimum_on_ground_beta=0.00
minimum_reverse_beta=0.00

Much more realistic but now it is so underpowered that it refuses to get to takeoff speed much less climb .
I altered the weight and balance sections as well because they were way out of wack too. The only way I have been able to get reasonable real world performance out of this is by at least doubling the thrust and power scalar values which I think is a a major fudge. This aircraft should be able to takeoff with a 375HP engine no problem. There must be other serious flaws in this design for the original builder to have to put a 1735 HP engine in this aircraft.

And yes, I looked at the drag values in the air file. They seem to be reasonable numbers.

So, why does this thing perform like a lead balloon? Beats me....... Obviously I have not copied over the entire aircraft.cfg file to this forum. There may be other tweaks that I am missing but at this point I am somewhat stumped. Paradoxically, the aircraft performs closer to real world levels with the 1735 HP engine which tells me that the drag numbers are all messed up somewhere.

Help please........

[tgibson_new]

Many aircraft authors just copy over flight dynamics that work well for a plane with the performance of their plane. Then they tweak it a bit. Just because the HP is wrong (etc.) doesn't matter, as long as it *flies* correctly.

[airgreg]

OK, I understand that in many cases it is easier to simply copy over the flight dynamics from another aircraft and tweak them. But still, putting a 1735 HP engine in an 1800 LB aircraft should make that airplane perform like the space shuttle on launch. I know that Microsoft was'n perfect in modeling the flight dynamics for many aircraft but this is ridiculous.

[StringBean]

... putting a 1735 HP engine in an 1800 LB aircraft should make that airplane perform like the space shuttle on launch.

Does it?

The question isn't "what's in the .cfg?" it's "does the plane fly right?".

If it does then all you're doing is chasing your tail.

peace,
the Bean

[airgreg]

What is contained in the cfg and .air files is a digital model of that aircrafts flight characteristics. If the original real life aircraft had a 375 HP engine then so should the simulated version. Is it reasonable to expect the same performance levels from the simulated aircraft as the real world version? No, but it is reasonable to expect something fairly close. I just want to know what it is about this particular design that requires a 1735 HP engine.

[StringBean]

What is contained in the .air and .cfg files are values that work together to provide the end-user with a flight model that (hopefully) compares to what one would experience in the real world.

This particular package is a plane with roots in FS2002 that has been modified to work in FSX. Maybe that's why it needs a 1735 HP engine.

As you have learned changing one parameter requires changing others to keep the same flight characteristics.

There is a file in the library (c185dgl.zip) that is the original model. It contains an aircraft.cfg that has correct numbers for the plane.

Maybe you should try using the .air and .cfg file from that download and see if it works any better in FSX.

BTW, if you want your C185 to be real-world accurate it would have either a 260 or 300 HP engine, not 375.

peace,
the Bean

[airgreg]

OK, you got me there. I was looking at the GTSIO-520 that was used on the cessna 404(and others). I will have a look at c185dgl.zip and see what happens. Still though converting from fs2002 to fsx should'nt require such drastic measures. There are only 4 primary forces that act on an aircraft(lift,weight,thrust,drag). I tweaked the cfg and the .air file to bring these values back to where I think they should be for this aircraft and it flew like a lead balloon. There were entries in the .air file refering to CFS and fs2002 but I deleted them since they had no bearing on the flight dynamics for a FSX airplane. I can go look at the cfg and .air file again but I will admit I am running out of places to tweak.

The original .air file had a text line in it that mentioned that the aircraft had 12 cylinder merlin engine. Those engines were used in WWII warbirds that weighed 3-4 times more than a c-185. Besides that, according to wikipedia a typical merlin engine only generated 1290 HP at sea level. Where the original developer got 1735 HP is beyond me. Is this the way aircraft design should proceed? Just plug any old numbers into the flight dynamics until you the performance specs you want?

[StringBean]

Just plug any old numbers into the flight dynamics until you the performance specs you want?

A lot of the time, this is how FS works.

[faostube]

1,735 BHP! Just send it over to me, I can probably go 6 seconds in a quarter mile with it! :-]

[airgreg]

There was another entry in the .air file that I missed the first time. The designer had set the empty weight at 7000 lb and on top of that it had 3 fuel tanks(center, left ,right)holding a total of 400 gallons of fuel. You can check my math on this.....

7000 lbs empty weight
400 gallons of avgas @ 6 lbs per gallon= 2400 lbs
4 passengers @ 150 lbs each= 600 lbs

total= 10,000 lbs

No wonder a 300 hp engine could'nt move this thing.