Frans wrote:
What does JMB want with that? Isn’t it just a pure overkill of engine power for a UL?
The biggest benefit of the 916iS in my opinion is that it has lower fuel consumption giving it even more range. The extra power is only for take-off, in cruise the available power is about the same.
At the end these engines when powered up further will start to cost as much as a good old IO520….
There is no replacement for displacement…I like the Risen concept though its all about aerodynamic efficiency for speed with limited power fuel burn…
Vref wrote:
There is no replacement for displacement
It is, and it’s called RPM 
It’s what makes turboprops move btw. Another replacement is boost (more torque).
A 916 iS costs around €50k. The newest and lightest Carbon Cub is built around this engine, which is pretty cool, but it also makes it very expensive.
On the lag thing. On a multi shaft engine like the PT6 you squirt in more fuel, the gas generator accelerates and produces more gas. The power turbine accelerates and the prop governor increases the pitch to maintain prop rpm. But the gas generator has to accelerate first.
On a single shaft engine when you squirt in more fuel as the single shaft tries to accelerate the prop pitch immediately increases to maintain prop rpm and hence much less lag.
