Aerospace Parts Example丨Why Are Aircraft Engine Blades Designed As Loose Structures?

Aerospace Engines Are Known As The Jewel In The Crown Of Modern Industry. Their Output Power Is Amazing. An Aircraft Engine Weighing Only A Few Tons Can Propel Passenger Aircraft Weighing Tens Hundreds Of Tons. Generally Speaking, The Manufacturing Cost Of An Aircraft Engine Accounts For About 30% Of The Manufacturing Cost Of The Entire Aircraft, Its Importance Is Self-Evident.

The Internal Structure Of An Aircraft Engine Is Very Precise Complex, The Connections Between Parts Should Be Tight. But When Passing By An Aircraft Engine, You Can Hear A Clicking Sound Coming Inside. Is It Possible That The Fan Blades Inside The Engine Are Loose? Yes, It Is Loose, But Don't Be Afraid, It Is Designed To Be Like This.

In Aircraft Engines, Blades Are Responsible For Compressing Expanding Gases Generating Powerful Power With The Highest Efficiency To Propel The Aircraft Forward. Blades Are A Special Type Of Parts That Are Numerous, Complex In Shape, Have High Requirements, Are Difficult To Process.

The Curved Surface Configuration Of Aircraft Engine Blades Is Extremely Complex. They Transmit Considerable Torque Extremely High Combustion Temperature. Therefore, The Blades Are Generally Made Of High-Temperature Resistant High-Strength Materials. The Original Material Was A Polycrystalline Nickel-Based High-Temperature Alloy. Later, Polycrystalline Blades With Oriented Grain Boundaries Were Made. The Crystallization Direction Is Consistent With The Force Direction, The Performance Is Greatly Improved. Finally, Titanium Alloy Materials Are Widely Used For Processing. At Present, People Use The Whole Blade Processing Technology.

As The Load-Bearing Parts Of The Engine, The Blades Of These Fans Are Firmly Fixed On The Engine, But Are Stuck In The Tenon Of The Fan Disc Through The Tenon. There Is A Gap Between The Tenon The Tenon. When The Fan Rotates Slowly, Under The Action Of Gravity, Each Blade Will Slide Towards The Axis When It Is Close To The 12 O'clock Position, Will Slide In The Opposite Direction Of The Axis When It Is Close To The 6 O'clock Position. As A Result, The Fan Blades Collide With Each Other In The Process Of Sliding Back Forth, Making A Rattling Sound.

The Mortise Tenon Structure Connecting The Fan Blades The Fan Disk Is Called A "Vertical Tree Type" Mortise Tenon Because It Looks Very Much Like A Vertical Tree A Fir Tree, With A Toothed V-Shaped Tenon A Clear Gap Between The Tenon Groove, Which Allows The Tenon To Slide Freely Within A Certain Range.

Why Are Aircraft Engine Blades Designed As Loose Structures?

When The Engine Fan Rotates Rapidly Exceeds The Critical Speed, The Shaft Begins To Approach Its Geometric Center Due To Its Elasticity, Then Passes The Geometric Center Approaches Its Unbalanced Position. At This Time, The Centrifugal Force On The Blades Starts The New Shaft Passes Through The Position The Blades Are Located. The Component Along The Tangent Direction Of The Turbine Disk Points To The Opposite Direction Of The Unbalanced Position, Causing The Blades To Deviate In This Direction, Thereby Readjusting The Unbalanced Position, Making The Center Of Gravity Close To Its Geometric Center, Reducing Vibration.

This Process Is Dynamic, So The Vibration Of The Fan At Any High Speed Can Be Dynamically Reduced, The Angle Of The Blade Relative To The Tangential Direction Of The Turbine Disk Changes Periodically, So The Blade Needs To Swing Left Right.

In Order To Allow The Blades To Swing Freely To A Certain Extent, The Blades Are Completely Fixed On The Turbine Disk, But There Is A Gap, The Shoulder Cannot Completely Fit The Adjacent Blades, Which Is Also To Allow The Blades To Swing. It Can Be Determined That Only The Fan Blades Are Loose, But Also The Blades Of All Levels Of The Compressor Are Loose.

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