13 Stability: 3D modes

[@giovannigiorgio0]

when i was running the analysis i got ''Unsuccessful attempt to compute eigenvalues for Control= 0.200 - skipping.'' can u help why this happening and how can i fixed it ?

[@katnap8354]

Hi, I just have a couple of questions! What is the Vinf (speed to balance the weight)? What if the Vinf is not located on a curve? Is it okay to run this static analysis with the plane set at a certain velocity? Also, do you know why following the static analysis, only one point is plotted?

[@NashidHazakat]

What if there is a mismatch between the zero-moment angle in the log v/s polar curve?

[@willwood8337]

Did you ever manage to find out a solution to this? I am having the same issue

[@Cynthialove99]

@@willwood8337 me too

[@edo_far]

this is very useful, thank you very much!

[@1938_NAYYARASAYYAD]

While doing stability analysis on xflr5 I'm facing some errors that's why the modes for longitudinal and lateral stability are not operating could you plz guide me through this?

[@1938_NAYYARASAYYAD]

Like which parameters should I consider for generating the view of root locus graph

[@aerokemankes]

Hi. What should be the sign of the resulting angle of attack for the stability analysis?Positive or Negative. (you found -0.159 deg). I don;'t really understand that resulting a.o.a. is the glide angle or aerodinamic a.o.a. For example, I have best L/D ratio at +1 degree a.o.a. Should i adjust the cg for the positive a.o.a results... Thanks in advance...

[@techwinder]

+alpay demircan -0.159° is the aoa for which Cm=0. This can be seen as its natural balanced position, but this angle has no reason to be the aoa for which L/D is optimal. You can run some sensitivity analysis (video 16) to check the influence of the design parameters and decide if you need to move the CoG forward or backward.

[@edo_far]

but, then, this means the aircraft is going to fly with this aoa?. I think the alpay's question is because of this. thank you

[@techwinder]

Yes, if the plane was capable of flying in perfect horizontal attitude, that would be the aoa. In practice, the plane will enter the phugoid mode, keeping this aoa all the way through.

[@edo_far]

thanks for the answer

[@arthurmellobatista8802]

What can I do when my Cm x Alpha has a positive slope and when alpha = 0, Cm is negative?

[@bikashkunwar2877]

Actually there are a couple of things you can play around to get trim in pitch. 1) increase the tail volume ratio( either by increasing moment arm or increasing the elevator area). 2) Bring the CG towards the LE of the wing(i.e.before the neutral point of the aircraft). 3. Adjust Cm at alpha=0 by giving a negative tilt angle for elevator and/or positive tilt angle for the wing.

[@K_SE_NikhilRawat]

I’m getting unstability at the 3rd mode what yo do?

[@darshitdesai]

Found a negative lift for Alpha=-14.23846.... skipping the angle... Unsuccessfull attempt to trim the model for control position= 0.00 - skipping. Sir I am getting this error please help

[@aerokemankes]

Firstly you need component weights for inertia calculations. Then set your cg between 25-40 percent of your wing chord. Probably coordinate axis is passing through the leading edge of your root chord. and cg is on the origin (leading edge). inertia and cg position is everything for stability analysis.

[@MuhammadHanif-yr4jv]

what is this software?

[@Quatuux]

XFLR5