# Why does adding more blades to a propeller/fan not show a decrease in efficiency?

According to this answer increasing blade solidity increases the blade area by either enlarging chord or increasing blade count both of which reduce efficiency via reducing the lift coefficient and increasing friction.

However, in fan maps of turbofans the efficiency of the fan is as high as 90%.

The word efficiency seems overloaded, meaning different things in the case of lightly loaded propellers compared to highly loaded fans.

What exactly are we measuring the efficiency of then? If it's just measuring the efficiency of compression, how can we relate the "efficiency" of highly loaded fans to that of lightly loaded propellers?

• Well, if you want to compare, you'll need the fan map of an engine with a high solidity and a different one with a low solidity. You can't make any conclusion based on just one number. That's like saying "I heard 8 cylinder engine car engines weigh more than 6 cylinder car engines, but here's a 8 cylinder engine that only weighs 450 pounds, and that seems small to me, so therefore 6 and 8 cylinder engines weigh the same". Apr 21, 2022 at 16:46
• @DanielK That wasn't what I was going for, I improved the question. Thanks. Apr 21, 2022 at 18:15
• Well, to me, the question is even less clear now. I would suggest you start a new question, delete everything referring to the linked answer about solidity, and just ask a new question of "How is efficiency defined for a fan map for a turbofan", and then a second question "how is efficiency defined for a propeller". I think that gets at what you are really trying to ask. Apr 21, 2022 at 19:55