View Full Version : Turboprop performance
13th Nov 2003, 18:01
Lots of books have been written on the subject of aircraft performance. However; I'm lookin for some more documentation on "Performance in practise". This would be like; should you increase/decrease climb speed according to head-/tailwind. If so - how much? And every time, regardless of wind strength? Which is the better climb mode to use in turbulent air? Certainly not VS, but Pitch or IAS? On short legs, say around 30-45 minutes, is it better to increase climb speed and go for a lower FL, with TOC/TOD spaced close to eachother, thus giving a shorter sector time?
I have my own thoughts on this, but it's always hard to prove/argue when my CDR always "knows" he is right! (and he could very well be...). And then there's always the standard argument over "the step", even though we are limited to FL250.
I fly the DHC8 100/300, but most performance books deal with jet aircraft - quite a different cup of tea.
All kinds of inputs - book references - private messages a.s.o. on turbo prop performance / techniques in practise, are welcome. Thank you!
13th Nov 2003, 18:25
We used to use a fixed climb speed, (210kts IAS) variation for head/tail seems a bit too much like hard work :D It was pretty close to turb air speed as well. Generally the efficency of higher levels outweighs the time saving of increased IAS, except on friday night trying to get in before the pub shuts when all bets are off and METO all the way home!
Step climb in turboprops is IMHO generally a waste of time. Because the fuel burn is so low on shorter sectors the weight change is so little that you could climb straight up to optimum level anyway. I have used it but only on long sectors (5 hours plus)
cant think of any refrences of the top of my head, but you could always read "handling the big jets" backwards!:ok:
13th Nov 2003, 20:11
...and that's the problem with most of these books. "Flying the big jets" is just like the other ones; it says a little about everything, but nothing really worthwhile on anything... But hey, perhaps I'll try to read it backwards. Could be a sublime message in there somewhere! :-)
13th Nov 2003, 22:32
There is probably a gap in the market, hmm wonder how quickly i could write a book to have it out for christmas:8
15th Nov 2003, 02:55
If you follow the normal speed schedules, if I remember the dash 8 correctly 160 til somewhere around 20,000 feet and then decrease it gradually until you level off you can't go wrong. Adjusting this speed for whatever case will not make "much" difference. A minute or two does not make a difference in the whole scheme of things.
On jets we climb at a speed somewhere around 300 kts and transition to somewhere around Mach .80 which is close if not exacty the cruise speed. These speeds are automatically adjusted for by the flight management system which takes into account the price of fuel, weight of aircraft, and wind.
By the way there is no "step" for speed or altitude on an airplane, that is unless you are flying floats.
As for which mode to use (v/s, ias etc) it is best to use ias for climb. Never use v/s unless you watch it like a hawk. In some windshear conditions it is possible to overspeed or even stall when using v/s in a climb. In really severe bumps try to hold your attitude to carry out the task (climb descent level)
15th Nov 2003, 05:24
Always a subject for debate but for these <1 hour sectors there is so little to be gained that it's not worth the funny look from your CDR.
Whether a cruise climb, high speed cruise climb or best rate climb is best can easily be worked out when you out flying. The argument usually goes on about efficency but in the real world (the european airline industry) what matters is ground speed. You're not paying for the fuel and the deciding factor on how much fuel you actually use is air traffic control.
Also, you may find the cabin attendants complaining if you topple their trolleys with too steep a climb after releasing them.
'The Step' is no longer an issue with turboprop engines. You accelerate to whatever speed you get with climb power then reduce to cruise power and the speed falls back to what it falls back to.
A friend ofmine did some experiments and found that it pays to go as fast as you can in a head wind but there is almost no benefit in flying slower with a tailwind. Isn't that always the way; -40kts out, +15 kts back!!!
If you're not heading in the direction you want to go on a SID climb as best you can.
15th Nov 2003, 12:09
Ummm . . . . . is it possible that there is some confusion between two books in the above discussion? Daysleeper refers to one, and Crossunder possibly to another. It's a mistake that I've made a few times so I recognise it. One of the books is great.
Handling the Big Jets, is by D P Davies. Published back in 1971 (3rd edition). It is a real test pilot's/outstanding technical book. Davies was Chief Test Pilot of the UK Airworthiness Authority, and it shows. The book covers, in immense depth, the differences between propellor and jet, and there is one heck of a lot in there that can be taken away for turboprop operation. If I come across as highly impressed by the book and the author, then I make no apologies - if I could write half as well as Davies, then I'd be an outstanding writer on technical subjects. Oh well, stick to the day job.
Flying the Big Jets, by Stanley Stewart is a very different book and, IMHO, is lightweight. I've got both books. No idea where Stewart's is - don't care. Davies is in the primary shelf of my 41 shelves of textbooks which itself is guarded by an alarm.
Davies is probably out of print; Stewart is available widely (such as Amazon). But I tracked down copies of Davies from a couple of places (possibly secondhand):
Hopefully there are others.
15th Nov 2003, 16:53
Twas Davies i referred to , the gag being that he takes Heavy piston/Turboprop pilots through jet theory. as we are all trained by JAR as jet pilots perhaps reading it backwards would take the Jet pilot back to the turboprop.
Loses something when you have to explain it.:hmm:
15th Nov 2003, 19:58
Thanks guys! I had the "Flying" not "Handling" book, but Amazon just sold me a seconhand copy of the real stuff for $99 :-)
18th Nov 2003, 21:26
I have a little experience with recips and jets, but no experience with turboprops.
I've a question:
- What's the power setting you use for descent, and why?
- Do you use some kind of cruise power descent, as the recips do, or you do the idle (and more efficient too) descent the jets do?
My main concern is the minimum torque I can set without increasing the drag. In my A36 Bonanza I usually set 16 inches of manifold and 1800RPM, wich is, I think, the minimum manifold set I can fly without creating propeller drag and freezing the engine.
What about the turboprops? What's the minimum torque for minimum thrust and minimum drag?