Scheny
Well-Known Member
Hi!
I was already starting building my scale model (fortunately the wings where the design is already frozen), when I noticed I had one small error in my CoG calculation (CoG of fuselage estimated too much in the front, as front half has almost twice the carbon as the rear half). Now I did not want to take any risk and tried to verify the project three times more:
This would mean that my static margin for CoG = 25% would be 59%!!! (SM=NP-XCg).
I checked this against other aircraft, but they look similar... CoG in the right spot at 25%, but the NP is way rear. I am now a little insecure about the static margin and hoped for some of your insights.
BR, Andreas
*VLM = vortex lattice method
**the viscous drag is not calculated by VLM, so it only adds a factor for it which is tuned for model aircraft
I was already starting building my scale model (fortunately the wings where the design is already frozen), when I noticed I had one small error in my CoG calculation (CoG of fuselage estimated too much in the front, as front half has almost twice the carbon as the rear half). Now I did not want to take any risk and tried to verify the project three times more:
- I calculated the weight again with formulas from Raymer and guess what: 158,6kg (Raymer) vs. 160kg (my guess)
- I made a detailed analysis using VLM2 algorithm with a detailed fuselage panel model --> everything to my expectation
- I calculated everything with CFD and compared to VLM* data --> perfect match except for drag** (VLM)
- the CoG should be located between 18-30% MAC
- be in any case in front of the NP
- static margin should be around 10% MAC
This would mean that my static margin for CoG = 25% would be 59%!!! (SM=NP-XCg).
I checked this against other aircraft, but they look similar... CoG in the right spot at 25%, but the NP is way rear. I am now a little insecure about the static margin and hoped for some of your insights.
BR, Andreas
*VLM = vortex lattice method
**the viscous drag is not calculated by VLM, so it only adds a factor for it which is tuned for model aircraft