Drag over wing span

[Agustin Buffa]

Hi,

I started to doubt a bit about this result I got with Cd over wing span ("drag" photo). It is a rectangular wing with flap at 20°. What it seems odd is the drag at the wing tips, shouldn't be very high because of induced drag like in "Spanwise-drag-distribution-for-the-S45-wing" photo?

Thanks,

Agustin

[Brandon Litherland]

Let's take a step back.  Do your comparisons here both include flaps at 20?  Are they fairly similar models?  Are you asking if the tip drag per unit length should be higher or lower?  You're also comparing force per length to a normalized force coefficient (c/cref) per length so the plots won't necessarily look the same.  

[Agustin Buffa]

Hi Brandon,

Both refer to different wings, I should have taken that into account. What it seemed odd to me was the low drag over the wing tip in my model. Shouldn't be the highest cd over there? 
I ran the same model on xflr5 to validate, and it's quite the same than VSPAero, heres what I got ("xflr5" photo), so physics is telling me I was wrong.

Also, I compared this flapped wing with a clean one ("comparison" photo) and the drag on flap it is much higher than the drag over the tips, so it appears very low in this condition. I attach the "clean wing" photo, where it shows clearly the induced drag maximizing over the tip, just like I learned at college haha.

[Agustin Buffa]

Now, I have another question. It's about the clean wing, when I ran it on VSPAero I get a kind of spikes over the curve, while on xflr5 I didn't. I am aware that VSPAero takes into account every drag whereas xflr5 only induced.  Are reliable the results of VSPAero regarding to cd?

Thanks,

Agustin.