How do to a full autoland

[Guest BeaverDriver]

I'm not sure how you turned this into an ego contest, but you are absolutely correct I'm sure. After all, what would nearly 50 years in aviation (including as a pilot and an Avionics Technician) that I have do for any expertise at all?? I'm sure it would count for nothing (in your world at least). I'm sure that your theory also strongly supports why every STOL aircraft is the world is a pure-jet and not a prop/turboprop machine... well, except for the Beaver (which I have a lot of time in), Otter, Twin Otter, Turbo Beaver, Dash 8 (100 thru 300 series), Dash 7, Porter, Kodiak... . On the jet side, we have.... oh wait, can't think of any. Maybe YOU can supply that info for me.

 

Since when are governed RPM's associated with A/T systems? That's a new one on me. According to that theory, the Dash 8 should have a A/T system. Interesting concept.

 

Anyway, as you mentioned, "I'm always up for being challenged or corrected..." . Perhaps there's a reason for this and maybe YOUR ego should take a back seat for once.

 

Have a nice day. Too bad you don't know the meaning of a meaningful dialogue.

[Bob650 31]

Sorry Q400_Flyer but Beaverdriver is absolutely correct.You are completely clueless my friend. I'd love to tell you why you're wrong but there isn't time or space on a forum to do so.

[Fabo 213]

This reminds me of a certain discussion on the NGX forums, where there was a gentleman that maintained his evidently wrong opinion until the very end of his opinion being disassemblet to the last nuts and bolts...

 

I will leave this here to you to figure out who is right and wrong though...

[3-2-1-Now 126]

No.

 

As per Post #2, no turbo-prop aircraft can be certified for an autoland capability, due to power responses being ineffective (too slow) to safely manage speed control, which is a core aspect of autolanding capability.

 

Jet aircraft are the only aircraft that possess autolanding capability, due to the constituent autothrottle / autothrust systems meeting the requirement for responsive automated speed control.

This is inaccurate. You can do an autoland with manual thrust - it is to do with the capability of the aircraft systems.

 

On several aircraft types it is permitted to do an autoland without auto-throttle (on the Airbus you can even go so far as engine out with manual thrust).

As an aside - there is nothing stopping a turboprop from doing autolands. Thrust response has nothing to do with it. It is all about automation capability and redundancy, and turboprops often do not meet the requirements.

 

I'm sure if the Q400 could have autoland capability, Bombardier would have added it.

 

Best regards,

Robin.

[Adam T Lutley 12]

There is no technical limitation that would preclude a turboprop from being certified and equipped with full autoland capability. Operationally, full autolands are relatively rare and if required by the prevailing weather conditions, the airport has to be CAT III certified as well. Most second tier airports, which are most likely to be served by turboprops aren't CAT IIIb,c certified at any rate. I find the previous discussion related to turboprop and turbojet throttle response to be amusing. Turboprop power output is measured as a function of torque while turbofans use N1 fan speed or even EPR (eng pressure ratio). I've held run/taxi certifications on various turboprops, and turbofan aircraft such as the JS3100, JS4100, ATR 42/72, EMB 145, CRJ700 and currently the Boeing 737CL and the NG. If anything, turboprops actually provide more throttle sesponse to given throttle lever movements than certainly earlier non FADEC equipped turbojets.

[Guest Q_flyer]

@@3-2-1-Now

 

@@Adam T Lutley

 

 .... can you please back up your theories with links to a single, solitary, certified airframe anywhere in the world, fitted with turbo-prop engines that is actually capable of a fully automated landing ........

 

....can't wait to read your findings.......

 

Cat III capable? ....yes, sure;  using a HUD.

 

Capable of autoland? .........nope.

 

Have a read of this discussion on the real world pilot pprune forum:-

 

http://www.pprune.org/archive/index.php/t-149522.html

 

......as an aside, I am here for the Majestic Q400 and discussions about it, not to engage with supposed armchair experts, and to play ego tennis .... so I'm sitting this thread out now, but all the best guys :wink:

[3-2-1-Now 126]

If you read my post carefully, you will see what I have to say about turboprops and auto-land.

Bottom line: they do not meet the requirements for systems redundancy and/or accuracy.

 

Look in JAR-OPS1 for Europe to see the requirements.

Best regards,
Robin.

[ESzczesniak 128]

Reasoning is telling me not to joint the discussion of prop vs jet spool speeds...but so much for reason. I agree that generally speaking props respond faster than jets. I said generally because there are going to be some high performance jets that respond better than poor performing props. It's an irrelevant argument though, as comparing the best to the worst is apples and oranges.

 

There are few key points being missed when arguing that a jet engine has less rotating mass and therefore reponds fast.

 

First, a turboprop typically has only a single compressor and generator. Turbojets have both high and low pressure compressors (and sometimes intermediate compressor), and generators. Each of these additional stages has several rows fans that are all rotating. While the diameter of each is smaller, there are many more of them and moving at a higher RPM. A single propellar can (and usually does) have a lower rotational moment than the sum of these multiple additional fans. So while considering rotational mass and force needed to impart rotational acceleration is correct and important, there is a fundamental misunderstanding of the additional parts in a jet versus prop.

 

Second, most large aircraft (and even small tactical jets now) are more accurately described as turbofans. The fundamental difference from a turbojet is that some mass of air bypasses the basic gas generator. The generator powers a large fan at the intake that moves a large mass of air at slower velocity that bypasses the generator core with the benefit of increased efficiency. The problem is that to increase power, the generator needs to respond, increasing the fan speed that then increases the bypass air. This just has an extra step.

 

Lastly, and in some parts following on from the last point, props are mechanically linked to the generator. Mechanical response is practically speaking instantaneous, while changing air pressures driving fans have a lag for pressures to build appropriately. A turbojet has less of these issues, as all thrust passes through the generator core like a turboprop, however is at higher pressure which takes longer to build up. A turbofan however does not have this same direct mechanical effect on speed. Yes, it's mechanical between engine parts, but the fan part of a turbofan needs time to build up that additional airpressure in the bypass core.

[Fabo 213]

Eric: Regarding the last point: That holds true to single shaft turboprops, like JS41s Garrets, however these are quite rare nowadays, at least for bigger planes. Dash 8 uses a free rotating turboprop, which basically works similar to a turbofan, in that the actual thrust generating part (prop or fan) is turned by a separate turbine, not connected to the compressor, moved by the means of exhaust gas.

[Adam T Lutley 12]

@@3-2-1-Now

 

@@Adam T Lutley

 

 .... can you please back up your theories with links to a single, solitary, certified airframe anywhere in the world, fitted with turbo-prop engines that is actually capable of a fully automated landing ........

 

....can't wait to read your findings.......

 

Cat III capable? ....yes, sure;  using a HUD.

 

Capable of autoland? .........nope.

 

Have a read of this discussion on the real world pilot pprune forum:-

 

http://www.pprune.org/archive/index.php/t-149522.html

 

......as an aside, I am here for the Majestic Q400 and discussions about it, not to engage with supposed armchair experts, and to play ego tennis .... so I'm sitting this thread out now, but all the best guys :wink:

I wasn't basing anything I said on theories. The Q400 and the SAAB 2000 both are certified for CAT III approaches using a HUD. As to your second point about no turboprops being fitted with an autothrottle, the C-130J is fitted with one and has full autoland capability.. Not equipping most turboprops with full autoland capability boils down to operational and cost factors not technical ones as you've suggested.

[kevinh 409]

First, a turboprop typically has only a single compressor and generator. Turbojets have both high and low pressure compressors (and sometimes intermediate compressor), and generators. Each of these additional stages has several rows fans that are all rotating. While the diameter of each is smaller, there are many more of them and moving at a higher RPM. A single propellar can (and usually does) have a lower rotational moment than the sum of these multiple additional fans. So while considering rotational mass and force needed to impart rotational acceleration is correct and important, there is a fundamental misunderstanding of the additional parts in a jet versus prop.

Turbofan gas generators are typically much larger and more massive than the gas generators in a turboprop and don't always spin at faster RPM.  A small turboprop engine core may well run faster.  Turbo prop cores are therefore faster to respond.  Also if the propeller is at governed RPM, typically around 1000, it doesn't need to spool up at all to respond to power demand.  All it needs is a blade angle change, so almost instant response.

 

As for the number of shafts, for free turbine turboprops the number is the same as for most turbofans: two.

 

I find it amazing that people in this thread are stating that there is something inherently problematic about a turboprop having autoland capability.  That is entirely to do with the capability and redundancy of the autoflight system and the redundancy of electric and hydraulic power supplies, not the engine type.  As has been said such very expensive complexity, not to mention the certification process, is not economically justified in turboprop regional aircraft.  However a HUD cost effectively provides the pilot with visual cues to manually fly to lower minima than the basic autoflight system is approved to do.

 

As for autothrottle systems, there is no technical reason why a turboprop can't have one.  The condition levers don't need to be automatically driven, so it's just a matter of driving the power lever (or commanding the FADEC with no lever movement, Airbus style).

[ESzczesniak 128]

 

 

Turbofan gas generators are typically much larger and more massive than the gas generators in a turboprop and don't always spin at faster RPM. A small turboprop engine core may well run faster. Turbo prop cores are therefore faster to respond. Also if the propeller is at governed RPM, typically around 1000, it doesn't need to spool up at all to respond to power demand. All it needs is a blade angle change, so almost instant response.



As for the number of shafts, for free turbine turboprops the number is the same as for most turbofans: two.

 

I apologize if I was less than clear.  I was stating that the gas core, prop or jet, runs at a faster RPM than the propellar a turboprop is driving.

 

Likewise, I was not trying to talk about the number of shafts at all.  I was talking about the additional rows and higher mass of the high pressure compressor blades in a turbojets and fans.

 

I was also staying very simple minded, so I was not delving in to RPM governers.  However, most turboprops do work this way and I also agree this response is even quicker since it is the propellars pitch that changes mechanically.  It is only limited by the time the gas core needs to generate the additional torque.

[kevinh 409]

I apologize if I was less than clear.  I was stating that the gas core, prop or jet, runs at a faster RPM than the propellar a turboprop is driving.

 

Likewise, I was not trying to talk about the number of shafts at all.  I was talking about the additional rows and higher mass of the high pressure compressor blades in a turbojets and fans.

 

I was also staying very simple minded, so I was not delving in to RPM governers.  However, most turboprops do work this way and I also agree this response is even quicker since it is the propellars pitch that changes mechanically.  It is only limited by the time the gas core needs to generate the additional torque.

The fan of a turbofan doesn't run that much faster than a propeller (the CF6 fan runs at about 3,600 RPM) and as with a turboprop runs slower than the core.  And it's not the actual speed but the acceleration required which is the issue.  You did mention the number of shafts in a turbojet though.  The number of individual stages aren't really important, it's the inertia of the shaft (and acceleration limits to avoid surge) that are important to response times.

 

Sorry, I should have made it clearer that my last two paragraphs weren't aimed at your post, they were about the thread in general.

[ESzczesniak 128]

 

 

The number of individual stages aren't really important, it's the inertia of the shaft (and acceleration limits to avoid surge) that are important to response times.

 

Ok fair enough...my point wasn't about the number of shafts though (I wasn't even thinking of this), but the larger amount of rotating mass that needs to accelerate.  So yes, I guess that pertains to acceleration through the shaft, I just hadn't been thinking that way.

[Pict 15]

As for the number of shafts, for free turbine turboprops the number is the same as for most turbofans: two.

 

Actually that only applies to the smaller pt6 series....the pwc100 series are all triple spool turboprops: low pressure spool (nl) high pressure spool (nh) and the free spool (connected to the propeller)

 

From my experience the single shaft turboprops respond quickly while the free turbines respond slower...I've never flown a jet but from riding jumpseat on CAL's 737s the cfms respond to throttle imputs much faster compared than when i'm flying a kingair (the garrets on the mu2s are near instantaneous)