To be honest the entire two years of flying turbo props I never worried about fuel efficiency, except when trying to takeoff from JFK when you single engine taxied a turboprop with no nose wheel steering that was never designed to taxi single engine.
it was always Max ITT for the power settings and Vmo for the airspeed. Vmo for approach and landing on the glide slope to 3 mile final.
For climb out I think it was 140kts to get up to cruise as fast as possible or 180kts for cruise climb to go as fast as you could while still having a positive climb rate. Or 160kts between the two extremes.
if I knew I had a tail wind at cruise, I’d fly 140 to try to get into the tailwinds as soon as I could. If I knew I was going to get into headwinds, then I’d fly 180.
probably (definitely?) not the most efficient way to fly and/or not the most comfortable flight for the passengers.
fuel efficiency was never a thought or goal.
Fuel for a typical 20-40 min flight segment was always about 1200-1600lbs including the 45min reserve. At Max payload Max fuel you could take was 1900-2000lbs
But I had no idea how little I knew (basically nothing) about flying the first two years and 2400hrs of my career until I left the turboprop airline and in hindsight and every time I reflect on that time in my career am always amazed that I didn’t make a smoking hole in the ground during that time.
TL-DR.... I guess you could try to find the fuel efficient profile, but how much would/could you save? When the amount of fuel being discussed in total for an entire flight amounts to what is taxi fuel for a turbojet.
Of course it’s nitpicky and one vector down at 3000 will throw all of it out the window, it’s just the kind of thing I ponder at 3 AM watching the top of descent creep closer on the moving map. We do also on occasion have a leg length/wind combination that pushes the airplane especially if you need an alternate.Anecdotally climbing at the manufacturer recommended profile (fast) a Vy profile (slow) and a company-recommended profile (in between) seems to have no detectable difference in block times. Despite manufacturer claims if it’s warm and I’m heavy I’m usually at Vy the last couple thousand feet anyway.
Some considerations for the climb...
Altitude over Airspeed:
-Blackhawk marketing shows how quickly the -67 KA350 will get to altitude and into the thin air.
-ATC might get you on course quicker when you reach altitude
Airspeed over Altitude:
-passenger comfort (EMS)
-leg length and final altitude
I known you were discounting wind, but you really can’t discount the wind. Are you climbing into a 100 kt headwind or tailwind? Of course, I’d want to capture that big push ASAP.
For the descent, the approach of staying as high as long as possible works. You can even delay the descent beyond the planned 300/1 to 1500 AGL/5nm prior to the airport. Use 400 or more — just watch the 91.117 limits. In EMS, this was more challenging because the patient’s head was forward and holding a prolonged nose-down attitude could make things uncomfortable.
I flew with one pilot who did the 1500/5 prior without fail, until I mentioned we’d be going another couple of miles beyond the airport to come back in to land. There’s another 5 miles of low fuel flow. If you’re flying with an FMS, you’ll see your fuel at destination increase during the descent. I’d think the idle vs zero thrust would be airframe specific, ie RX-12X vs. Piaggio.
Didn’t AirNet have an idle descent profile for their Lear 35s?
Pax comfort-the Pilatipus doesn’t really have enough grunt to get an uncomfortable deck angle.
Certainly where we operate the first 6000’ it’s important to get up to MVA so we can get a direct on course.
On descent I’ve fiddled with it a bit and you can easily do 5-6° with no tailwind. You’ll lose the vertical track below you for the first 6-8k feet because you’re MMO limited but once you’re down in the teens if you keep it Vmo minus 10-15 depending on turbulence you’ll catch it by 5-6k easy. Patient comfort could definitely become an issue between the nose down attitude and hauling butt through any turbulence (as you know the PC rides bumps like an empty 1-ton pickup).
Thinking about power settings, I guess you would actually want a small positive torque because you want the engine to be doing the work of turning the prop, otherwise it’s a big drag device and that would kill fuel efficiency. But then again maybe not? What does the fuel flow vs torque curve look like? You’re burning x pph just to keep the engine running, maybe bumping it up to x+50 actually gives you a return? On one hand it means you spend more time lower, on the other it means you spend longer at your descent speed. But then again, you’re usually cruising fast enough that you don’t gain a lot of TAS in the descent. So maybe absolute minimum fuel flow while still letting the engine drive the prop is the name of the game. I guess it depends on airframe/engine rigging-the Caravans I flew both Pratt and Garrett would definitely give you drag if you pulled enough power. Something about the way the Pilatus installation is rigged it doesn’t feel like it does, except momentarily coming into the landing flare.
It’s interesting to me because there’s all kinds of stuff out there about turbojets because airlines analyze it down to the smallest decimal place but turboprops there’s a much higher bias toward “eh, whatever helps you fit in with traffic”. Which of course isn’t as much of a concern at 0300 or going into a 1 in, 1 out airport. It is fun on short legs (for example yeeting across the cascades from BFI to YKM or EAT) to see how high you can get on a parabolic type altitude profile and see if you can beat the fltplan fuel numbers.
I also wonder at what point of bypass ratio turbofans start to act more like turboprops from a fuel efficiency standpoint. Or maybe straight wings vs swept matters more. But probably not, because most turbojet stuff is based on the idea that fuel flow is related to thrust production, and at some point the bypass ratio becomes so high that the performance of the fan at different altitudes and airspeeds starts to be more propeller-like.