Parasitedrag by blade comes out too big

[유민상]

I designed the UAM with openvsp and then checked parasitedrag.
Parasitedrag by blade comes out too big. It's even bigger than the main wing.
I don't know what the problem is with blade's drag analysis method. 

[Rob McDonald]

You should not include propellers in a parasite drag buildup.

During flight, they would be spinning -- and hopefully producing thrust and requiring power to spin them.

The parasite drag tool is treating them as wings -- with Swet, reference length, and t/c -- as-if they were aligned with the flow like a proper wing.

You need to understand what the parasite drag tool is doing to make effective use of it.

You also need to understand how you are going to do thrust/drag accounting for your aircraft.

Rob

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[유민상]

Thank you for the detailed explanation, Rob.
Then is there no function to calculate the drag of the propellers in openvsp?

2022년 11월 19일 (토) 오전 1:56, Rob McDonald <rob.a.m...@gmail.com>님이 작성:

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[Rob McDonald]

Propellers usually do not have drag -- instead they produce thrust and absorb power.

When a motor fails, a propeller may continue spinning -- in that case, it windmills and produces drag.

Alternately, you may feather the blades and it may stop spinning.  In that case, the drag would be similar to the drag you have calculated.

Or, you might fail in flat pitch (or a fixed pitch prop) and the blades are not spinning.  In that case, we would expect massive separation behind the blades and we would expect drag much higher than you have calculated.

You need to understand thrust/drag accounting.  You need to understand what state your propellers are in.  You need to understand how and what to calculate on them.

If you understand these things -- then it will probably be obvious what OpenVSP can and can not do for you.

Rob

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[유민상]

Thank you, Rob

2022년 11월 19일 (토) 오전 2:36, Rob McDonald <rob.a.m...@gmail.com>님이 작성:

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