Changing L/D of a previously released add-on aircraft?

[crewdog]

Hi all,


First I should mention that I've tried to contact the designer of the add-on aircraft I'm messing about with, but his email is no longer active. But I've been reading about a certain model, and the sink/glide rate in the model is too benign and (for my OWN USE ONLY!) I'd like to change it to try to more accurately reflect the real aircraft.

Is this a simple thing to do via changing a value or three in the aircraft.cfg file, or is there more to it?


TIA,

Steve

[gypsymoth]

I'm not an expert but a seeker of knowledge like your good self but a ? occurs to me...what's the aircraft  :-?

[crewdog]

[quote]I'm not an expert but a seeker of knowledge like your good self but a ? occurs to me...what's the aircraft

[JakesF14]

Hi, I am no expert, but yes, you have to play around with the CFG, especially with the following settings:

wing_area      wing_area = 176.0      Area of the top surface of the entire wing tip-to-tip (ft2).
wing_span      wing_span = 36.0      Wing span is the horizontal distance from wing-tip to wing-tip (feet).
oswald_efficiency_factor      oswald_efficiency_factor = 0.7      This is a measure of the aerodynamic efficiency of the wing.

[garryrussell]

The cfg will only change a few things. The flying characteristics are largely in the .air file

[JakesF14]

The cfg will only change a few things. The flying characteristics are largely in the .air file

Thanks Garry, I haven't gone there yet!  :-) some tutorials you can suggest??

[garryrussell]

Sorry Jake

Can't really advice the best tutorials as I have never looked for, or seen any.

I've never touched airfiles....but am well aware of the problems in getting dynamics to work correctly

Playing with that or the CFG setting can cause a lot of other probs unless it's done carefully.

Basically one thing can upset another so I leave that to those who know what they are doing.

You do need an airfile editor and an understanding of how dynamics interact in real life.

It's amazing how many FS models have incorrect engine positions and thrust lines or GC positions in the wrong place.

It's often the case that the problem is not where you first think it is. :-?

On one model I downloaded the tailplane was near the top of the fin intstead of the rear fuse where the tailplane is.

Another had the thrust line ten feet above the aircraft.


It's a bit of a minefield so best only work on copies.

Garry

[JakesF14]

Understand, and then you have to have a bit of understanding of aerodynamics as well.

Enjoy!

[nickle]

Agree that fundamental aero parameters are in the FDE.  If MS aero is wrong or the incorrect parameters applied, flight characteristics will be wrong.  However the aircraft config file contains vital aircraft parameters that do affect flight characteristics given the correct FDE choice.  Change the htail_pos_long to half of the stated value and test fly.  The major aero weakness MS FS is aircraft parameter entry.  Detailed dimensions and weights are available at a price for many aircraft but not generally available.  Most FSX prop aircraft are disappointing performers as issued.  Up to the user to test performance and attempt to verify aero dimensions.  For MOI see Abacus Flight Dynamics Engine tutorial on how to calclate bottom of the page.  Note the MS parsing of Data Reference Point aka Standard Center Point and Reference Datum in Aircraft Configuration Files, SDK.  Point is 1/4 chord.  Datum is referenced to Point. 0,0,0 means Acft CL, 1/4 chord, vertical.  Apex means tip of with respect to Point or Datum.  For htail_long it is the distance from 0,0,0 measured CL to a point perpendicular to the leading edge of the verical fin.