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What are the differences between interference drag and form drag? And which factors affect them?

Pondlife
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Chetan Gowda
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    Does this answer your question? There are a lot of questions here about drag, have you read through them? Please add some detail about what, exactly, you're confused about, or this may get closed for being far too broad. – FreeMan Nov 07 '20 at 13:09

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Form drag is caused by the body itself travelling through a medium, such as air. The more streamlined the body is, the less form drag it causes. For example a cube has high form drag compared to a droplet shaped body.

Interference drag arises in places where two forms join each other, such as wing - body joint. It is caused by the pressure rises especially on the rear half of both bodies combining and causing earlier separation, as well as turbulence at discontinuities of a shape; the more abrupt the change is, the more interference drag is caused. It can be made smaller by blending the joining bodies into each other with a rounded fillet or such.

Jpe61
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    Might want to put your last sentence in a comment instead? – 60levelchange Nov 07 '20 at 10:43
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    Interference causes the pressure rises especially on the rear half of both bodies to combine, causing earlier separation. It is not just turbulence or discontinuities (although those have their fair share, too). – Peter Kämpf Nov 07 '20 at 11:08
  • I removed my comment altogether. We'll see how this q makes it.... – Jpe61 Nov 07 '20 at 16:48
  • @PeterKämpf I infused your comment into the answer, could you please see if I got it right. I modified your sentence some, and might have "broken" it.... – Jpe61 Nov 07 '20 at 18:51
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    Looks good. A fillet reduces wetted surface area and draws out the pressure rise. In order to reduce interference drag, it is advisable to separate the areas where pressure rises; that is why horizontal and vertical tails often are not at the same lengthwise station. This also reduces blanketing of the vertical in spins, so it has multiple benefits. – Peter Kämpf Nov 07 '20 at 21:52