Helicopters

[sparks]

I was wondering if there is any sort of concensus in the community on which helicopter model 'style' is preferred in FS - and why. As far as I can tell, at the end of the day, the only functional difference is the engine type and which set of gauges it drives.

[jcomm]

I was wondering if there is any sort of concensus in the community on which helicopter model 'style' is preferred in FS - and why. As far as I can tell, at the end of the day, the only functional difference is the engine type and which set of gauges it drives.

Basically the Bell206 and add-ons derived from it are based on a highly tweaked C182 FM. It all started far back when someone tried to use flaps with irrealistic lift scalars to model airships with VTOL capabilities. By fs98, if I am not wrong, MS introduced the Bell, but it was internally tweaked in a similar way.

Things have changed specially after fs2002. Turbine model changes introduced with fs2000 and a few new records were added to the Bell airfile, but it was/is still a C182 with strange aerodynamical capabilities :-)

On the R-22 arena things are considerably different. The core code of FS deals with r-22-based airfiles specifically. The engine model (it's supposed to model a recip helo...) has several problems, and the correlator code is not what I could call ... "very clean". Also, although apparently you could get rid of a correlator and operate your helo using twist-grip as in the old models (B47, SChweizer, etc...) setting it's availability to NILL has no effect :-(

I have invested on r-22-based FMs. Tweaked JustFlight's Cbi300, and I am now working on their upcoming R-44. The base models are designed by Rob Young, so, I do have a sound basis to start with... All I have to do is to use silly "inflow", "weight 2 MOI", "collective on torque..", "torque_scalar" and stability parameters to turn the helicopters into much more unstable machines (like their RW counterparts are) and allowing for some sort of auto-rotation, which is not possible with the default r-22 on either fs9 or fs10. Changing control scalars also helps.

Things are changing, though ;-) There are some surprises for the future...

Speaking of auto-rotations in MSFS, they're, of course, completely out-of-sync with reality in as far as speed and collective are concerned... There is actually no "rotor load" in the FM, so, after lowering the collective all the way down, at a pace wich strongly depends on the tweaking I mentioned above, you do not have to worry about over RRPMs. In RL we have to keep working the collective in order for the needle to stay in the "greens". It will gladly over-rev.

And since, on another thread someone asked about this, I'll take the liberty of posting here a few parameters that when used with the default fsx (I think fs9 too...) R-22 will allow for sustained rear flight, autos, etc...

=========== tweaking the default R-22 in fsx/fs9 ===========
[piston_engine]
...
idle_rpm_friction_scalar= 0.7 //1.0
...

[Helicopter]
reference_length = 21.58
reference_frontal_area = 17.7
reference_side_area = 44.5
side_aero_center = -12.5
right_trim_scalar = 1.0
correlator_available = 1
governed_pct_rpm_ref = 1.04
governor_pid = 0.4, 0, 0.1, 0, 0.2
rotor_brake_scalar = 1.0
torque_scalar = 8.0 //1.0 but I set it to 18.0 now
cyclic_roll_control_scalar =1.0
cyclic_pitch_control_scalar =1.0
pedal_control_scalar =1.8 //1.2
collective_on_rotor_torque_scalar = 0.9 //1.0

[fuselage_aerodynamics]
drag_force_cf = 1.15 //0.55
side_drag_force_cf = 2.5 //10.0
pitch_damp_cf = -2.0
roll_damp_cf = -2.0
yaw_damp_cf = -2.0 //-0.1
yaw_stability_cf = 0.15 //0.27

[MainRotor]
...
Weight_per_blade = 26.0
Weight_to_moi_factor = 0.78 //0.58
inflow_vel_reference = 36.0 //34.0
============================================


Many aerodynamical phenomena based on the interference of various structures that together affect flows, drags, lifts etc... are also not modelled in MSFS.

To be honest, so far the only three very realistic helicopter flight models I have been able to experiment are ELITE's Evolution S623 simulator:

http://www.flyelite.com/support/forums/index.php?topic=1291.0
http://www.flyelite.com/hardware.php?product_id=78

X-Plane (on the games market...)

and a very interesting "home" project being developed to suite the needs of Portuguese Airforce and a few flying schools. The models so far created do a tremendous job in replicating the Robinson-22 and Robinson-44 models, as well as the EH-135.

Loong post, I know, and not really answering what Jerry has asked, objectively... but I love talking about this passion of mine ;-). But, all I can say is that, definitely, it is the R-22-based FM that makes the ideal base for more serious helicopter modelling in FSX (and upcoming products...).

BTW: http://www.elsevier.com/wps/find/bookdescription.cws_home/699635/description#description is an excellent text for people willing to get more into the world of rotary wing aircraft...

[sparks]

Hi jcomm

Thank you for the reply and the links - I'll have to spend more time on those.

I agree that the R-22 style model seems fairly simple and they certainly are easy to modify.

Basically the Bell206 and add-ons derived from it are based on a highly tweaked C182 FM. It all started far back when someone tried to use flaps with irrealistic lift scalars to model airships with VTOL capabilities. By fs98, if I am not wrong, MS introduced the Bell, but it was internally tweaked in a similar way.

Things have changed specially after fs2002. Turbine model changes introduced with fs2000 and a few new records were added to the Bell airfile, but it was/is still a C182 with strange aerodynamical capabilities :-)



There are those who have a very different opinion on this subject:

http://www.hovercontrol.com/artman/publish/article_51.shtml

One of the problems I have with the Helo-turbine type is the undocumented helicoter sections in the air file. The best info I have is a paper written in 2001 by Steve Baugh. I've never really tried to test it, but it seems to have a lot of good info. If anyone is interested I'll put a copy up on my web site.

[jcomm]

...The best info I have is a paper written in 2001 by Steve Baugh. I've never really tried to test it, but it seems to have a lot of good info. If anyone is interested I'll put a copy up on my web site.

Jerry, please do! ;-)

I've heard mixed oppinions about the "unknown" records in the Bell206 airfile. They have certainly changed things after fsx, one of the effects being that it brought back auto-rotation capabilities, but it is still a very limited model, unless in fact there are hiden parameters that could be used in the air or cfg files...

[sparks]

Here's a link to Steve's paper:

http://www.mudpond.org/Helo_Air_Report.txt (http://www.mudpond.org/Helo_Air_Report.txt)

Bear in mind that this paper was written in 2001, FS2000 was the current version of FS, and many of the 400-series air file sections were still 'unknowns'.

[jcomm]

Here's a link to Steve's paper:

http://www.mudpond.org/Helo_Air_Report.txt (http://www.mudpond.org/Helo_Air_Report.txt)

Bear in mind that this paper was written in 2001, FS2000 was the current version of FS, and many of the 400-series air file sections were still 'unknowns'.



Many many thanks Jerry!!! :jump:

[jcomm]

Just a note to report that most of the records mentioned on Steve's paper are gone from both helo FMs in fsx, moved inside the core code, making it even more difficult to tweak.

OTOH, the new r-22 model is more promissing, and still being "tweaked", so, there is hope that in the future the helicopter FM will improve.