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Flight Dynamics Workbook, Airfoiltools and Table 404

Nater

Nater

Messages
460
Country
germany
Need some help gurus. Doing the FDE on the A350-900. Using the Flight Dynamics workbook, on the Data tab, I entered all the pertinent information about the wing. It is giving me an aspect ratio of 13.6 whereas if I google the aspect ratio, I get 9.6. Where is the disconnect? Am I missing something? So here comes the second part....Looking thru Airfoiltools, I found a couple of plans that look very similar to the airfoil shape of the A350's wing. I am having a hard time figuring out how to transpose the information from Airfoiltools to the custom airfoil section of the root and tip tabs in the workbook. I tried using some of the NACA airfoils and got it to take off around the speed I need, but at FL300 the drag was overcoming the thrust needed to stay airborne and reduced my airspeed to 0 from 270 knts. Any enlightenment would be absolutely helpful!
 
FSMuseum

FSMuseum

Messages
232
Country
us-kentucky
I'm not familiar with the flight dynamics work book but I may be able to help with your wing questions.

Aspect ratio is calculated as

b^2/S

where:

b = wing span
S = wing area (theoretical)

The theoretical portion may be what's throwing you off. For most aerodynamics applications, the wing area used in the mathematics includes the theoretical space inside the fuselage where the extended leading and trailing edges of the wings would be, and this extends to the fuselage centerline. In other words, the wings are treated as though the fuselage is not there with respect to area.

The numbers you find online for wing area should usually be the theoretical area you need, since this is usually the only wing area parameter released by manufacturers. Once you have confirmed accurate data for span and area, use the calculated result for aspect ratio. Relevant corrections to overall aerodynamics should be taken into account further in the process.

Using some figures I found online with a 10 second Google search:

b = 213 ft
S = 4770 sq ft

A = 213^2/4770
A ~ 9.511

Also, concerning your drag and thrust, check to make sure that the CD0 vs Mach table doesn't increase too rapidly. FS2004 and P3D unfortunately do not allow much fine tuning of this table so I usually set it to 0 except AFTER Mach 1 and then adjust the thrust tables to give the correct engine readings/performance during climb and cruise.
 
Last edited:
Roy Holmes

Roy Holmes

Resource contributor
Messages
1,803
Country
us-virginia
Regarding Mach and drag, what you said is true for FS2004, but P3D has the flexible mach intervals that were introduced in FSXA so you can accurately describe the mach drag coefficient shape between, typically 0.8 and 1.1 Mach.
Roy
 
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