I am new to OpenVSP and VSP Areo

[Janik Walker]

Hello everyone.
As you probably read in my title, I am new to OpenVSP and VSPArero.

Now I have some general questions about OpenVSP and VSPArero that I still have after watching all the GroundSchool videos.
What is a good airfoil for a high-decker?
Should a winglet point up or down?  

Where in VSPArero should I look and what graphs should I look for?
How can I influence them and what are some good values for them?

 
I have heard about the CMy value, what does it mean and what are some good values for it?
And the L/D, where should all this be?

Sincerely
Janik Walker

[Tim Swait]

I guess a little more information is needed about what you're trying to achieve with the software is needed to answer most of those questions. Aircraft design is all about compromises, there is no 'best' wing section, different sections are best in different situations.

To get started, CMy is the pitch moment coefficient, i.e the moment about the spanwise, y axis. This needs to have a negative slope as alpha changes, i.e. if the nose pitches up then CMy goes negative to push it back down and vice versa. The steeper the slope the more stable. Again there is no 'right' answer for how stable your aircraft needs to be, it all depends on situation. Also the point at which the graph of CMy versus alpha crosses the axis (i.e. where CMy = 0) is the alpha that the aircraft will trim at. You can then look up the CL at that alpha and use that to calculate the trim speed (all these coefficients are relative to Sref which you set in the VSPAERO window, or allow it to calculate from your model). L/D is Lift/Drag ratio, the ratio of CL to CD. In steady flight since L=W and D=T then this is also the Thrust/Weight ratio, so it will tell you the power requirement at each alpha, which you can relate to speed through the CL versus alpha plot.

[Janik Walker]

hello
First of all, thank you for your quick reply.

It is good to know that there is no best in airplane modelling.
Your explanations for CMY and L/D were really good, but you said I could calculate something out of it, but how?


Ok, I will try to give you as much information as I can.

As the OpenVSP Hangar does not work for me, why I do not know ,I get this error message. I'm using Joanthan's model some threads below, as it looked cool, for testing and getting used to OpenVSP. Now I have data and dont know what all this means.  

I probably also fixed one of his bugs by accident, as my CMy values now look very different to his. Now I want to know what I can do better, what all this data means and how I can use VSPAREO to know how my plane is performing.

Sincerely
Janik Walker

[Tim Swait]

Just calculate using the standard formulae: https://en.wikipedia.org/wiki/Lift_coefficient

For example, to find trim speed then look at your CMy versus alpha graph to find the alpha at which CMy=0. Then look up the CL at this alpha. Now use the defining equation from Wikipedia to find out the speed using the knowns; L=W, rho = air density at the altitude for the design point, S = the reference area that the CL was calculated for (be sure to use the correct reference area, the one that was used in the VSPAERO set up window), and then solve for speed. You can also divide the weight by the L/D ratio at the trim alpha to find the thrust requirement for that case.

[Janik Walker]

Thank you for you fast answer

do you think this CMy is ok 
 

and this Cl

but thank you for your help and have a great day 
Janik