naw, props are fine
If the public are happy to sit in a prop for 60 minutes when a fan would do it in 45....
Props deliberately target 66seats but most of the fans congregate around 120 seats hoping to carry more people over more sectors per day. The prop does not seriously start to compete until it can spend a lot of its cruise time above 13000ft pressure altitude because its burn gets leaner and its comfort gets better and it can speed up a bit.
A bash at the figures but I think this resume is a maybe a little thirsty.
Notwithstanding the differences in first cost. Suppose we have a sector of 200nm as Ozzy suggests and a battle of the twins.
A lightweight turboprop of 50000lb all up weight is competing with a bigger turbofan at 10000lb. The turboprop ascends to 13000ft pressure altitude but the turbofan 29000ft. I know I know but just wait. David and Goliath.
If the former has 650sq ft wing area (ATR-72/Dash 8 ish) the latter has 1000 (DC/MD ish). Both have about the same lift coefficient and a guesstimate of the parasite drag coefficients is turboprop 0.025 (ATR72) and the turbofan 0.020 (DC9).
The turboprop has an effective aspect ratio of 9 (from 12 absolute) and the turbofan may be 8 (from 11 absolute), the reductions in each case being a matter of aerodynamic efficiency.
So the turboprop chugs along at 480ft/sec and a lift:drag ratio of 13.5 to 1 whereas the turbofan flits along at 720ft/sec and L/D of 15.
The turboprop has little compressibility drag and its drag coefficient is about 0.03 compared to the turbofan which does suffer compressibility drag of say 6% raising its figure to almost 0.03 (remember these are referred to wing planform areas and not total wetted surface). I just need reasonable figures to estimate fuel burn.
If the prop efficiency is 85% the turboprop needs 3800ehp to provide the thrust to push it along. The turbofan needs 6600lbf of straight thrust.
Each ehp-hr consumes 0.45-0.50 lb of fuel and each lbf-hr consumes 0.60 lb of fuel. The trip is about an hour in the turboprop and 45 minutes in the turbofan burning 1800 and 3900 lbs fuel each. But the turbofan can carry twice the pax load and fly more sectors a day. But its more expensive to buy and operate.
But what if the load factors aren't high enough to justify the jet and if the prop can get at least half the trip done at a much higher pressure altitude, say 23,000ft?
The turbofan advantage starts to erode, that's what, as long as folks don't mind being thrummed along in a prop.
As hinted earlier big turboprops would really rather be jets and the A400M is the way it is because military and civil markets differ. And a ducted fan beats an unducted fan anyway and is easier to certificate. Remember blade shedding anyone?
PS my example FUBO figures turn out to be on the high side. If I'd guessed nearer 12kg/min for the prop and 1100kg/hr/engine for the fan it'd be better. But as the underlying assumptions are roughly the same for each it's still cox's pippins for garnny smiths and all good fun. Until the fans shrink and the weight plummets. All change!
Best Rgds from the "E" and KO Sally on tour. Caribbean next to see the relos.
And get sailing