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A Blisk is a bladed-disk, all one monocoque component.

enter image description here

So the blades do not have to be inserted and secured, and they are not removable. No nuts and bolts either.

The downside is that any serious damage to one blade, and the whole blisk must be replaced. The upside, I have heard, is that they save weight. Wikipedia says "efficiency improvements of up to 8% are possible." but I'm not interested in aerodynamic efficiency right now. I'm interested in weight savings.

So the question is, how much weight can you save? Is it really significant? Interested in compressor and turbine blisks and I would not be surprised if the answer varies between them.

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Very significant.

A research on blisk cost estimation with funding and data provided by Rolls-Royce states:

Integrally bladed discs, commonly known as blisks, are currently found in axial-flow compressors of gas turbine engines. Fig. 1 shows that blisks require significantly less material because the dead weight from the blade roots, disc lugs, and the disc structure required to support these features, is no longer required. This leads to a weight saving of up to 30% (Rolls-Royce, 2005), permitting higher blade speeds and consequently higher pressure ratios per stage (Steffens, 2001). A blisk compressor therefore requires one third fewer rotor stages to achieve the same total pressure ratio as a conventional design (Steffens, 2001). [emphasis added]

enter image description here
Fig. 1. Blisk weight saving.

Langmaak, Stephan, et al. "An activity-based-parametric hybrid cost model to estimate the unit cost of a novel gas turbine component." International Journal of Production Economics 142.1 (2013): 74-88. (PDF)

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  • $\begingroup$ Wonder what that does to the repair costs from fod damage? $\endgroup$
    – John K
    Commented Feb 16, 2021 at 3:22
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    $\begingroup$ @JohnK: I would think that most FOD damage is to the first disc - quite a few objects would disintegrate on the first hit. But even with 1/3rd less rotor stages, you'd still have quite a few blisks after a first conventional disc. $\endgroup$
    – MSalters
    Commented Feb 16, 2021 at 10:19
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    $\begingroup$ @JohnK This is just a guess - I know nothing about turbine engine maintenance - but I imagine that the cost of the fix includes having the aircraft out of service and the effort to dismantle and reassemble the engine, in which case the cost of replacing one blisk instead of n blades per damaged disk might not be significant - plus there's no judging which blades need replacing, no dismantling/reassembling the disk, testing the disk integrity, balancing it (if those are issues...) $\endgroup$
    – sdenham
    Commented Feb 16, 2021 at 18:43
  • $\begingroup$ WOW thirty percent. and that's spinning. $\endgroup$
    – Fattie
    Commented Feb 16, 2021 at 18:48
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    $\begingroup$ replacing a whole blisk would seem to be incredibly, amazingly, cheaper than fooling around with traditional assembly-style $\endgroup$
    – Fattie
    Commented Feb 16, 2021 at 18:49

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