Tuesday, June 28, 2011
USAF DATCOM: Lesson #1 (2)
Datcom_1-2
If you forget to put a decimal, your datcom file would not run.
figure
another rule, always put a comma after the value, except maybe for the last variables value in a namelist, which you could simply end the value with dollar sign ($). Along with this explanation, many rules will emerge. For the complete writing rules, see here.
So now we have finished our wing input. What next? We just input the wing planform geometry. With only that, a wing cannot produce enough lift. It requires its cross section to be defined, the Airfoil! Lets use the most simple way to input Wing-1 airfoil using a control command, NACA. As explained before, our Wing-1 airfoil is NACA2412, a simple yet good airfoil for low speed aircraft. DATCOM, with the use of NACA control command, have a large collection of NACA airfoil, especially those that been created in the early years. You can see Datcom collection of airfoils here. We define our airfoil simply as follows.
kode
This sintax represented parameters as follows:
picture
The W after the control command NACA defined the naca controler to be used by Wing. You will find later that we can change this with H or V, which refers to the horizontal tail and vertical tail.
And now, our wing dimension is ready to be analyzed.
What we need to do next is to define the reference point for our calculation, then input our wing position from it. Usually we use the aircraft nose point for the reference point. However, we only have the wing, no fuselage. So lets just use our wing's root chord leading edge, as shown in the following picture:
figure
Then, we use the chord line as the reference line. From the defined reference point and line, we define the position of our center of gravity, lets just put it at 25% point of root chord and exactly on the chord line. We also need to define the wing root chord leading edge, which in this case, is zero horizontally and vertically. To input those positions, we use the namelist 'SYNTH', which mean synthesis. The code of this namelist are as follows. I assume you can guest each variable name meaning.
kode
Are we done yet? Nope. We need one more namelist for our simplest wing before we could analyze it. We need to define the wind/air properties, in which our wing-1 operates. For this we use the the FLTCON namelist, which mean flight condition. The required air property for datcom could vary, the simplest one is as follows:
kode
The code above includes the angle of attack, mach number, and reynolds number (you certainly could guest which one which). Notice there are variable NALPHA and NMACH, which is the number of angle of attack, and the number of the mach number respectively, in which we want to analyze our wing-1. Right now we input 1.0 for each of them, because we just want to analyze our wing at 0 degree angle, and at 0.2 mach. DATCOM could accomodate up until 20 angle of attack and 20 mach number on one runtime. I'll show you how to do this on our next analysis.
