Rolls Royce M250 BLISK (bladed disk) for helicopters

Reference example of integral blade-disc construction for weight savings on helicopter engines.

I should have looked at the blisk on the web. The web's getting better and better — I did this morning. Here's a nice graphic of a turbine disk that is not a blisk. Here's your root, where the vane has to attach to the big heavy flange. With a blisk you can make the whole thing integral, which they do for the M250 engines of Rolls-Royce. The integral version is a lot lighter than this great big mass right here. So you'd like to do that because there's collateral weight savings.

The only commercial-production blisk Tom knows — Rolls-Royce M250, used on helicopters and small aircraft. Cast, not welded. Probably the highest-production jet engine in the world.

There's only one engine I know of in commercial production that uses a blisk, and it's a cast blisk. I wish I could get one — it's about this big around. It's made by Rolls-Royce, it's the M250 engine, used on helicopters and small aircraft. It's probably the highest-production jet aircraft engine in the world. But it's a small helicopter or a small plane like a Lear jet. I don't know if it's on a Lear, but that's one example of blisk, and it's a cast part.

The only commercial BLISK Tom knows of — Detroit Diesel Allison (now Rolls Royce) M250, ~10,000 made. Cast as one unit, superalloy. Used to anchor the weight-savings-cascade argument.

One of these is called a bladed disk, or a BLISK. You'd love to be able to take the turbine disk, which right now has this complex geometry to join the turbine blade to the disk, and you have this heavy structure right in here. If you could weld these things together or cast them together, you could reduce a lot of weight. And that's exactly what has been done in some cases. The only commercial BLISK that I know of happens to be on the Detroit Diesel Allison, now Rolls Royce, M250 engine, which they've made something like 10,000 of. They go in helicopters and other things. They cast the blades to the superalloy, all cast as one unit. It's a small turbine engine for helicopters and small planes, but not for great big commercial planes. People can't cast with the quality they need in the big disk. People are trying welding. The Air Force has spent tens, if not hundreds, of millions of dollars trying to figure out how to weld blades to disk, because there's tremendous value.

Used to illustrate sprung-vs-unsprung-weight logic and to set up the Air Force friction-welding ambition. Cast blisk eliminates the Christmas-tree root structure that consumes 60-70% of rotating-assembly weight.

One of the best examples I have is when I talk about welding, and friction welding, I talk about the blisk. A blisk is a bladed disc. They've built about thirty or forty thousand Rolls-Royce M250 engines that go in helicopters and small aircraft like Cessnas. It's a small turbofan engine, and it has a cast blisk about this big. It's a single blisk of nickel-based superalloy, and the blades are cast directly onto the disc. You don't have all the weight that you have in a typical turbine blade in a bigger engine, where you have to join the blade — which is a simple little airfoil — to the disc. Blades and vanes are airfoils generally; blades rotate and stators don't.

The only production aircraft engine Tom knows with cast integral disc-and-blade — M250 Detroit Diesel Allison (now Rolls Royce). 30-year-old design, all-cast technology, 10–20K units, in helicopters and small business jets.

The Air Force would love to make a blisk and they still have big programs to do it. The only aircraft that I know that actually has a cast integral disc and blade — and I'd like to get one — is an M250 Detroit Diesel Allison, which is now Rolls Royce. They make like 10,000 or 20,000 of these engines; they go in helicopters and small business jets. Very high volume engine. It's a cast technology, everything is cast. It's not as fancy as these single-crystal blades. It's a 30-year-old engine, but they do use blisk technology.

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