Landing techniques: turboprop/jet vs.piston?

[MarkH]

I'm still getting to grips with the Turbine Toucan, and especially figuring out how to land it. Leaving aside the finer points, I have adopted a more or less dead-stick approach, carrying an excess of speed. I have found it unhelpful to use the throttle actively on approach as the engine takes so long to respond, and it occurred to me that this must be a problem generally with turbine engines. So, for example, where I might blip the throttle in a piston-engined aircraft to recover a bit of speed in the flare, this isn't appropriate with a turbine.

This has made me consider my general (er) approach to flying the approach in such an aircraft, and one consequence might be that I need to fly it onto the ground rather than stall it on, so I'm always carrying a bit of excess speed to get me out of trouble (a bit like flying a flapless approach in gusty conditions in a piston aircraft). I have no experience of turbine aircraft in FSX or real life, so I'd be interested to hear if I'm on the right track. I'd be interested in other pointers people might have about flying turbines and turboprops too!

[wiltzei]

Perhaps folks at PMDG´s forum might help you, if you dare to post your name: AVSim (http://forum.avsim.net/topic/313503-manual-landings/)

Turboprobs can be handful. I do usually fly the PMDG JS41 to ground firmly, with smallish flare and exactly at VREF.

The Dash 8 Q400 is particularly tricky according to real world stories I´ve heard. Luckily, PMDG is developing that particular plane.

[bstolle]

That's mostly a designer and/or FSX problem.
Jet engines accelerate IRL slow at low RPM but they respond to throttle changes immediately at high RPM. The limit is normally 8sec and e.g. on the CRJ 100 the engine does need the full 8sec.
When you advance the thrust lever from idle exactly nothing happens for the first 1-2sec.
That's e.g. one of the reason for some jet engines to have a flight idle (higher) and ground idle RPM setting to keep the engines spooled up a bit during the approach.
The other way too keep the engines spooled up used earlier was to use large flap settings which produced a lot of drag and hence needed a high power setting on approach.
Interestingly the Aces guys screws up because in the default jets like the 737 the engines spool up rather quick and accelerate slower at higher RPM. That way it's almost impossible to fly an approach with big thrust changes.
But that's an easy air file fix.
On a turboprop with smaller jet engines like the PT-6 I never experienced any significant lag.
Problem is with big turboprops like the Dash-8 300 and 400 that you can't make tiny smooth adjustments as every small throttle adjustment result in a rather large sudden power changes.

[MarkH]

On a turboprop with smaller jet engines like the PT-6 I never experienced any significant lag.
I think the Toucan has a PT6 or something like it. Trouble is it does need to be more or less idling just to descend, as the aircraft has such an outrageous thrust-to-weight ratio and no flaps or spoilers to dirty it up. In fact the only effective spoiler is the prop, which at idle causes a huge amount of drag. The amount of drag ought to be controllable, as the prop pitch can be set all the way to feathered. We should be able to fly the approach like a glider with some control over descent rate, but in practice varying the prop doesn't seem to make any/much difference.

[bstolle]

>In fact the only effective spoiler is the prop, which at idle causes a huge amount of drag.

That's already the sign for a good flight model

>The amount of drag ought to be controllable, as the prop pitch can be set all the way to feathered

Nope. At idle you are most likely in the beta range which means not the prop pitch lever but the throttle is controlling the pitch. There's no way to control the prop pitch at idle.

On this plane you have the Dash8-400 problem magnified times 100, LOL. Either nothing and a huge amount of drag or way too much power.

[MarkH]

Nope. At idle you are most likely in the beta range which means not the prop pitch lever but the throttle is controlling the pitch. There's no way to control the prop pitch at idle.

Ah, okay. I found a great reference (http://www.pilotoutlook.com/airplane_flying/split_shaft_free_turbine_engine) on turboprops, and re-reading the page on beta and reverse operations I realise it does say this.



On this plane you have the Dash8-400 problem magnified times 100, LOL. Either nothing and a huge amount of drag or way too much power.

That sounds like a perfect description of what I have! I have wondered about getting a registered FSUIPC and trying to create a throttle profile that's much flattened near the idle end. But this relies on the power setting actually having sufficient resolution - i.e. it assumes there are actually intermediate settings between 'idle' and 'too much' that could be selected if only the throttle control was sensitive enough.

[bstolle]

>it assumes there are actually intermediate settings between 'idle' and 'too much' that could be selected if only the throttle control was sensitive enough.
Can you imagine how funny it is to have the same problem IRL ?
It's similar in the F-15 but in that plane you don't have to worry about passenger comfort, LOL

[rvn817j]

In the 'Real World' in that type of equipment you would use a side slip, float in ground effect and then wheel land (tail (and tail wheel) remain up) until you are slow enough to gently lower the tail. I don't have the Turbine Toucan so I can not test this method (but I have been thinking about getting it....so many airplanes and sceneries, so little time and money).

[pilottj]

Mark I recommend trying out Bill's Epic LT or Kodiak to get some good turboprop time. I have the Toucan too and it is quite a touchy airplane. With the Epic I find that the marks on the throttle quadrant are good reference points (1/4,1/2,3/4...etc)...ie full flaps, gear down, and throttle at the 1/2 mark gives me about 105kts and a nice controllable decent rate. As you and Bstolle have pointed out, there is a bit of lag power lag. If you have reference points or throttle percentages to fly by you can just set the throttle to those approximates and make minor adjustments from there.

[Bone]

I have found it unhelpful to use the throttle actively on approach as the engine takes so long to respond, and it occurred to me that this must be a problem generally with turbine engines.


so I'm always carrying a bit of excess speed to get me out of trouble (a bit like flying a flapless approach in gusty conditions in a piston aircraft). I have no experience of turbine aircraft in FSX or real life, so I'd be interested to hear if I'm on the right track. I'd be interested in other pointers people might have about flying turbines and turboprops too!

The gas generator section (Ng) is always spooled up in turbo props during flight, so there is no lag time when you adjust the torque lever. Turbo props are generally known for their quick ability to generate thrust.

In pistons it's called the throttle, but in turbo props it's called the torque lever (in jets it's called the thrust lever). It's called the torque lever in TP's because it adjusts the blade angle to generate or reduce thrust, and the fuel control unit automaticly adds or reduces the fuel to keep the Ng section running at a constant speed. When you push the torque lever forward the blades increase angle of attack, thrust is generated, a load is put on the prop, and in turn a corresponding load is put on the Ng section (the prop and Ng section are connected by a reduction gear box, except PT-6's, which are free turbines). The Ng section doesn't bog down because fuel is added to keep it spooled up. The rpm of the prop doesn't change either, because it's a constant speed prop, and it's speed is maintained relative to the Ng speed. This is where the torque is generated. You have an increase in thrust, but the Ng and prop speed (Np) stay the same. If you pull the torque lever back, the blade angle is decreased, less thrust is generated, load is reduced, and the fuel control unit decreases fuel to keep the Ng section from increasing rpms...percent rpms to be exact, but I'll confuse you if I try to explain that one.

In pistons the prop rpm guage is what you measure power with. In turboprops it's the torque guage that you measure power with, because you are not changing rpm to get more or less power, you are changing torque. If you want to change prop rpm (Np), you have to either adjust the rpm levers or condition levers...depending on what type of turboprop engine it is. Condition levers are combined rpm and fuel control levers...and are usually on larger turboprops. If you are in a turboprop that has rpm levers, there will be a separate set of fuel control levers....think PT-6's, which is probaly what your Toucan most likely has.

If the turbine Toucan is anything like a Pitt's, it doesn't have flaps. The Pitt's is flown in a side-slip on final to keep the speed down and descent rate high. Just in case someone here doesn't know what a side-slip is, a side-slip is where you would put in left rudder and right aileron, or right rudder and left aileron...ie cross controlled.

[bstolle]

In pistons it's called the throttle, but in turbo props it's called the torque lever (in jets it's called the thrust lever)

Man I'm getting really old. In the old days on the Dash 7 (turbo prop) it was also throttle and on the 767 (jet) it's still called and labeled autothrottle.

Cheers

Bernt

[MarkH]

The gas generator section (Ng) is always spooled up in turbo props during flight, so there is no lag time when you adjust the torque lever

Well there is a very pronounced lag in the Toucan, so something doesn't seem right. If Ng is the same as N2 (the power turbine speed) then yes, it does stay spooled up even with the torque lever pulled to idle, but there is still a lag. Anyway, thanks that detailed explanation, it helps me understand things a lot better!

[MarkH]

Mark I recommend trying out Bill's Epic LT or Kodiak to get some good turboprop time.
Thanks, I will consider those.

[Bone]

Man I'm getting really old. In the old days on the Dash 7 (turbo prop) it was also throttle and on the 767 (jet) it's still called and labeled autothrottle.

Cheers

Bernt

I never flew the Dash 7, but I have alot of time spread out between the EMB-110 Bandierante, EMB-120 Brasilia, and ATR-72. If you want to be "old school", fine, but we're close to the same age. MarkH asked a question, so I tried to throw in something for his knowledge base. Since I still have a valid CFIIMEI, I decided to use the proper term "torque lever" instead of "doohicky" or "thinga-ma-jig".

Alot of guys would call the torque levers "throttles", as I have many times myself. But, it's merely flying slang that's easier to say than torque levers. Maybe your Dash 7 called them throttles, but they're called torque levers in the Dash 8. Whatever, you know what I'm talking about.

If you want to put a spin on the term "autothrottle", then go ahead. Autothrottles are just the subsystem that will automaticly adjust the thrust levers if you have it engaged...they had to call it something, and autothrottles made sense.




When you advance the thrust lever from idle exactly nothing happens for the first 1-2sec.



You know what I'm talking about, you're well aware of the term Thrust Lever.



Cheers

[PRB]

ADCS: Automatic Doohicky Control System...

This has been a very informative thread! I've had some of the same questions about many of the stuff covered here. Thanks!

[MarkH]

MarkH asked a question, so I tried to throw in something for his knowledge base.
It is appreciated here, thanks! Sometimes we get our wires crossed and all that, but good info stands out as good info regardless.

[MarkH]

In the 'Real World' in that type of equipment you would use a side slip, float in ground effect and then wheel land (tail (and tail wheel) remain up) until you are slow enough to gently lower the tail. I don't have the Turbine Toucan so I can not test this method (but I have been thinking about getting it....so many airplanes and sceneries, so little time and money).

Oops, missed this first time. Yes, the Toucan will dump height with a side-slip, although at idle it already requires an alarmingly steep descent to maintain speed, so side-slipping too tends to lead to extreme maneouvering. It's also hard to keep it in a controlled slip without rolling in or out, as it is very sensitive to aileron inputs (has full-span ailerons on the lower wing and very-nearly full-span on the top.

[bstolle]

If you want to put a spin on the term "autothrottle", then go ahead. Autothrottles are just the subsystem that will automaticly adjust the thrust levers if you have it engaged...they had to call it something, and autothrottles made sense.

that's inconsistent...if it's 'thrust', and 'thrustlevers' how about calling it 'autothrust'...like Airbus ;)

Correction on the Dash7...looked it up in my old manual and it's called power levers there as in the Dash8...and in the Metro. Torque lever is new to me...but as I said...I'm getting old... ;)
Don't know why some companies etc... feel the need to re-invent the wheel every now and then...

[Bone]

that's inconsistent...


...I'm getting old...

1. As was pointed out years ago: people park on the driveway, and drive on the parkway.


2. If you say so.