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martin-w

Flap15 approach too fast.

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Just got the PC-12 the other day, so far liking it.

 

Certainly very pleased that the characteristic 2-3 degree pitch down on approach is correct.

The only issue I've spotted is approach speed at flap 15, according to my research, I suspect it's 15-20 knots too fast. Flap 30 and flap 40 are correct.

110knots is the correct approach speed for zero flaps, not flap 15.And at max landing weight, not 8500lbs.

The PC-12 in the sim is 8500lbs, at that weight, at flap 15 it shouldn't be 110 knots.

I could be missing something of course, I wouldn't be surprised.

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Hi Felix.

 

The landing experience is realistic except, hypothetically at this stage,  for flap 15 approaches.

 

The mods you mention are in the flap.0 section, so they will impact all flap settings. Flap 40 is correct, as is flap 30, it's just flap 15 that's too fast. Pitch is correct at flap 15, 2-3 degrees down]   AoA indicator is correct, just approach speed too high.
 
The other point of course is that modifying drag scalars impacts other parameters, for example engine power. More power will be required to counter the drag, and thus more inaccuracy is introduced.
 
I believe the guys were trying to overcome what they perceived as excessive pitch down on approach. My tests tell me that the pitch on approach is correct. as confirmed by two real world PC12 pilots and video evidence. I commented in that thread actually.


More drag will merely be countered by engine power and not impact pitch on approach, so not sure why they added that parameter.

 

If I am correct [still not definitive] then what would be required is modifications that impact flap 15 approaches only. A quick glance of the cfg and I see there is only a flap.0 section. My experience tells me that to impact flap 15 only would require an additional flap section. Not sure if that's feasible without corresponding air file entries.

 

At this stage though, I'm just trying to determine if I am right or wrong, if flap 15 approaches are too fast.


My logic here [or lack of] is based on information on the Pilatus website. Stall speeds were available at various flap settings and weights. From that information I determined approach speed, which is 1.3 times stall speed, or 30% higher in other words. 

 

We have to remember of course, that the Carenado bird is at 8500lbs, not max landing weight, and many of the resources available apply to max landing weight. Hence why I calculated approach speed from stalls speeds that were available.

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http://www.pilatus-aircraft.com/#196

 

Weight in the sim is 8500lbs.

 

 

Stall speeds.

 

Flap 40 = 59

Flap 30 = 63

Flap 15 = 66

 

Approach speeds should be + 30%

 

Flap 40 = 77

Flap 30 = 82

Flap 15 = 86

 

At flap 15 I see 110 knots.

 

 

if I'm missing something anybody know what?

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Thanks Greg, certainly does, that's a great help. I see from your normal procedures checklist...

Flap 15

Vfe 163

Vref 98

Vref Ice 108

 

 

It's not clear at what weight though, I suspect it would be max landing weight, so 9921lbs. So at 8500lbs in the sim, that would suggest we are seeing an approach speed that is way too high.

 

In the sim we are 14% lighter than max landing weight, so that would equate to 85 knots at 8500lbs. Close to what I estimated above. This is looking more definitive.

 

I see Vref at 0 flaps is 118. Haven't tested that yet. Would be less at 8500lbs of course.

 

It's not a huge deal to me in the sim, as I usually land Flap 30 or 40, but you would think something so fundamental would be right.

 

We are talking a huge 25 knots too fast!

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I see from your normal procedures checklist...

 

That's a real world checklist...not mine.  Perhaps there's more info out there somewhere.

 

Gregg

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That's a real world checklist...not mine.

 

 

 

 

Yes I thought it was Greg, I meant "yours" in terms of you posted it. It was very useful.

 

Hell of a cock up if I'm right.

 

We may not land Flap 15 that often, but when we do, it'sonly reasonable to expect a semblance of realism.

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We may not land Flap 15 that often, but when we do, it'sonly reasonable to expect a semblance of realism.

 

Can you not reduce power to get the right approach speed?  Does it throw AOA way off? 

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Well, we are talking about 25 knots too fast, which is a lot, so if you simply reduce power and fly at what should be the correct approach speed, lift is reduced and thus angle of attack increases, pitch would then be higher than is realistic for the PC-12. And yes, the angle of attack indicator on the PFD would indicate inaccurately.

 

What most of us would like as simmers, is of course something as fundamental as approach speed to be correct.

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Might be worth a try to increase the 'flaps 15' setting to flaps 18 or 20 (in the config file)...just to see what happens.  Truly, if you think about it, flaps are nothing more than 2 pieces of metal that are stuck out at a particular size, position and angle.  The fact that they work well at 2 settings and not at a third seems weird and something wrong with the way FSX is crunching the numbers.  I suspect it has more to do with FSX than this airplane.

 

Gregg

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I think you need to get an experienced PC12 captain into this discussion to arrive at anything substantial... doing this from checklists, tables, and youtube videos is going to be inconclusive at best.

 

As you mentioned, this is all going to depend on weight and balance in the airplane, so I would suggest that you fly the airplane, and learn to handle it the way it behaves with different loads - just like in the real world.

 

I always land this plane with 15 degrees of flaps (no modifications) and find that it handles nicely..

 

Now, I fly by the seat of my pants mostly, and let it bleed off speed from 90 knots over the runway lights.. just hold it off the runway, until it settles.

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I think you need to get an experienced PC12 captain into this discussion to arrive at anything substantial... doing this from checklists, tables, and youtube videos is going to be inconclusive at best.

 

Truly, that would be ideal.

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I suspect it has more to do with FSX than this airplane.

 

Gregg

Well no, not really. It's not an FSX issue, it's the flight model. I know of no other add on that is on the numbers at all but one flap setting.

 

 

I think you need to get an experienced PC12 captain into this discussion to arrive at anything substantial... doing this from checklists, tables, and youtube videos is going to be inconclusive at best.

 

As you mentioned, this is all going to depend on weight and balance in the airplane, so I would suggest that you fly the airplane, and learn to handle it the way it behaves with different loads - just like in the real world.

 

I always land this plane with 15 degrees of flaps (no modifications) and find that it handles nicely..

 

Now, I fly by the seat of my pants mostly, and let it bleed off speed from 90 knots over the runway lights.. just hold it off the runway, until it settles.

Landing isn't an issue Burt, I have no issue landing. This is about realism.

 

Weight and balance isn't the issue when it's smack on the numbers at 30 and 40 flap. Weight is a variable I have accounted for.

 

If it complies with the tables and POH at 30 and 40 but not 15, then I'm suspicious.

 

There may be something I'm missing, but as yet nothing has surfaced.

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I understand your frustration, but I think you might as well put this issue aside,

and enjoy flying the airplane..

 

Just my opinion.. B)

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We may not land Flap 15 that often, but when we do, it'sonly reasonable to expect a semblance of realism.

 

There is indeed a significant difference between specified and actual speed with flaps 15, which I hadn't really noticed, as I hardly ever land with this setting. Most common is flaps 30 or, for short-field operation, flaps 40. But with strong crosswind flaps 15 or even zero flaps (up to 30 kts crosswind!) should be used.

 

Modifications of the aircraft.cfg cannot correct this discrepancy. I agree with you that this should rather be done in the airfile, i.e. by Carenado. Maybe you could give Carenado such proposal.

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How exactly do you measure "actual speed"?

 

I just flew an approach with the PC12.. at glideslope intercept, I lowered the gear and Flaps to 15.

 

Reduced speed to a comfortable 110 kts.

 

At decision height, disconnected the autopilot, reduced throttle to idle.

 

Crossed the threshold at about 90 kts.. held the plane off the runway to about 65 knots

and settled down on the gear.

 

Nice landing, very comfortable... what was not right about the above?

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Bert, in response to your previous reply to me...

 

I think it was you, in an earlier thraed I was reading this morning, that said keep reporting any bugs you find to Carenado. When I'm sure this is an error on their part I will do exactly that.

 

I am not frustrated and I am enjoying the airplane. It's about spotting a potential error, discussing it with fellow simmers, and reporting it if significant, just like you and others have done with previous issues.

 

 

How exactly do you measure "actual speed"?

 

I just flew an approach with the PC12.. at glideslope intercept, I lowered the gear and Flaps to 15.

 

Reduced speed to a comfortable 110 kts.

 

At decision height, disconnected the autopilot, reduced throttle to idle.

 

Crossed the threshold at about 90 kts.. held the plane off the runway to about 65 knots

and settled down on the gear.

 

Nice landing, very comfortable... what was not right about the above?

Bert, this isn't hard.

 

Tha angle of attack indicator gives you the speed. The IAS indicator tells you the speed. Pitch on approach tells you your speed is correct, Theres plenty of documentation that tells you Vref at 15 Flap for a given weight... and it's not 110 knots.

 

Whats "wrong with that" is that on a 3 degree glidesope, and thus 2.5 degrees negative pitch, at 15 flap, at 8500 lbs, you should not be at 110 knots.

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OK, I am still grasping here..

 

If atc tells me to hurry up and maintain 110 knots, is there anything wrong with flying the

approach at that speed?

 

I am used to picking my own speed, as long as I am not dropping below Vref..

 

As far as the AoA indicator goes, it does not have to be centered, as best I know..

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As a follow on, the Carenado code has the AoA indicator centered when the Incidence Angle is zero.

 

Is that the way the real airplane is calibrated?  

 

I am beginning to wonder if the AoA indicator in the real airplane is more sophisticated in it's function..

and if that might explain part of the issue at hand..

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If atc tells me to hurry up and maintain 110 knots, is there anything wrong with flying the

 

approach at that speed?

You aren't understanding this Bert.

 

Of course there is nothing wrong with flying the approach faster if ATC tell you to...

 

but you aren't doing that in the Carenado plane, you are flying at what Carenado perceive as Vref for Flap 15 [110 knots]. Which is at a speed that is 25 knots faster than the aircraft should be for that weight and subsequent angle of attack. As published in the POH.

 

And of course, you wouldn't maintain a faster speed than Vref all the way down, you would decelerate prior to landing, back to Vref. And when you did so, you would see the AoA indicator centred, the pitch correct on approach, and you would be at the speed specified by Pilatus for that weight... 85 knots at 8500 lbs. Not 110 knots.

 

 

As far as the AoA indicator goes, it does not have to be centered, as best I know..

 

Correct, I have seen approaches with it  a tad lower... but when it is centred it tells you that you are at Vref. That's the point of the AoA indicator.

 

 

As a follow on, the Carenado code has the AoA indicator centered when the Incidence Angle is zero.

 

 

 

Is that the way the real airplane is calibrated?

 

 

 

I am beginning to wonder if the AoA indicator in the real airplane is more sophisticated in it's function..

 

and if that might explain part of the issue at hand..

 

 

 

Except that pitch on approach, is correct. That tells us that the add-on has been coded with 110 knots as Vref for Flap 15 at 8500 lbs. If it were just the AoA indication that was in error, then we would see greater lift due to the excessive speed, and thus a very significant pitch down on approach... not just the -2.5 degrees which is correct for the PC12. If it were just the Aoa indicator, I would expect to see maybe 7 degrees pitch down or more, as an estimate.

 

As I'm sure you know, when manufactures build a new aircraft they test them for stall speed. Vref for each flap setting, plus 0 flaps is calculated from that figure. Vref is 1.3 times the stall speed, so 30% higher.

 

Thus, flying at Vref for all flap settings should result in the AoA indicator being centred, and pitch on approach being correct.

 

My hypothesis, is that perhaps Carenado have looked at the wrong chart. I find it quite a coincidence that 110 knots happens to be the correct Vref [or thereabouts] for max landing weight in icing conditions. It could simply be an error as a result of taking the figures from the wrong chart.

 

I may be utterly wrong of course.

 

And as I said... Flap 30 and 40 is bang on the correct speed, specified by Pilatus.

 

I must say I am even more convince it's wrong. The stall speeds for a given weight, are clearly stated in the Pilatus graph I posted a link for. That's direct from pilatus themselves, and Pilatus should know, it's their aircraft. And as we have said, Vref is calculated from stall speed.

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You may very well be right, and it would indeed be something to report to Carenado.

 

I'm still not convinced that you can rely on the AoA indicator in this airplane, given the simplistic coding,

but you make a persuasive case based on pitch and speed..

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BTW, have you tried the proposed fix in the other thread:

 

lift_scalar = 0.7     // three lines added to Flaps section as modification
drag_scalar = 1.9
pitch_scalar = 0.8

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BTW, have you tried the proposed fix in the other thread:

 

lift_scalar = 0.7     // three lines added to Flaps section as modification

drag_scalar = 1.9

pitch_scalar = 0.8

 

Does this go only under flaps.0 ?

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As best I know, that is where it goes.

 

But, because of the added drag, the approach speed with 15 degree flaps goes up even further..

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