Mark Ravinski wrote:

I'm not much familiar with these engines but it is not too appropriate to compare them with piston engines at low altitude.

Unfortunately for the turbines, it is a fair comparison.  An aircraft has to take off from low altitudes.  It has to descend to low altitudes and at a minimum muddle along in a pattern.  If IFR, it will have to hang around down there longer and if IMC, longer still.  

If there is a practical use for these engines, it's probably more for the long range, high altitude flights and comparisons should be made over the whole flight profile.

You are right.  The fair comparison is to compare the two types of engines in a realistic environment and that includes climb, cruise, descend and reserves.  If the turbine uses so much fuel getting up to altitude and then coming back down from there that it can cruise for only 1 hour, then it is unfair to compare its cruise performance against a piston's, which can cruise for 3 hours on the same fuel capacity.  It is the 45 minute reserve portion of the fuel consumption that will take a huge bite from the range.

I suspect that when you add the actual block to block performance, the turbine will shine only over a very limited range of distance; distances that are close to (but just under) the aircraft's maximum range and its multiples.  For other distances, the slower piston will get there sooner because it will not have to spend time for a fuel stop.  

It is not very obvious at first, but when you think about it, in many cases, increasing an aircraft's fuel capacity is the most effective speed mod you can add to your airplane!

Hamid