parasite drag

[Rishab Gupta]

HI ,

In VSP Aero and Parasite drag calculation, whenever we select from model option and we have 2 wings which should be our reference wing or do we need to calculate for both the wings seprately \

Thank you

Rishab

[Brandon Litherland]

For the reference areas, it really doesn't matter.  You can use a value of 1.0 if you only want to scale by dynamic pressure.  The point is to use the same reference area between your comparisons so you aren't artificially favoring one over another.

For this case, because the wings are identical, you can easily use the planform area of one or the other.

[Rishab Gupta]

Ok so I use either of the two wings for the reference

Thanks ☺️

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[Rishab Gupta]

So , the coefficient of lift and drag of both the wings would be same? 

[Jing Men Carol Ma]

Hi,

How about if the wings are not identical? Does it mean that we can find the calculation of two different wings by selecting specific wing model in reference area ?

gupta....@gmail.com 在 2020年8月6日 星期四下午10:33:11 [UTC+1] 的信中寫道：

[Rishab Gupta]

Do we need to calculate lift and drag for one wing and then say it's the same for other through parasite drag and vsp aero , or just  one time calculation gives the whole calculation of lift and drag ( that is , we don't need to say separately) 

On Thu, Aug 6, 2020, 9:42 PM Brandon Litherland <litherlan...@gmail.com> wrote:

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[Brandon Litherland]

There are several posts about this topic on the Group.  You can search for "reference area" in the search bar to find them.

In short, the reference area value really doesn't matter as long as you use the same value for your comparisons.  To compare Drag force to Drag force, you should scale the CD back up using dynamic pressure (Q) and reference area.

So if you want to compare between design iterations, just make sure that you are using the same area to calculate CD.  

[Brandon Litherland]

It won't be the same between the two wings because the flow from the forward wing can interact with the flow over the aft wing.  From a parasite drag perspective, you'll be using the same reference speed so if the wings are identical, you should be getting the same value.  It's just a flat plate area calculation with some extra fun under the hood. (See documentation).  The induced drag will not be the same and you should run VSPAERO with both wings in place to capture that interaction.

[Rishab Gupta]

So the reference area really doesn't matter if the wings are similar as we get similar results so just choose one reference area and do the analysis 

Thanks a lot ☺️☺️

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[Brandon Litherland]

To clarify: pick one reference area and use that across all of your models being compared.   Otherwise, upscale the CD to Drag force and compare that.