Flap15 approach too fast.

[Flyfox 114]

 

 

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.

[Bert Pieke 7,584]

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?

[martin-w 3,234]

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.

[Bert Pieke 7,584]

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..

[Bert Pieke 7,584]

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..

[martin-w 3,234]

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.

[Bert Pieke 7,584]

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..

[Bert Pieke 7,584]

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

[Boeing or not going 578]

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 ?

[Bert Pieke 7,584]

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..

[martin-w 3,234]

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

 

Hi Bert. I haven't tried those settings no, I don't believe they apply to the issue I'm highlighting.

 

I believe the guys tried those setting because they were unhappy about the pitch down on approach.

 

I have two objections to those settings to be honest...

 

Objection 1. Pitch is correct on approach, so no adjustment is necessary. I had the opportunity some years ago, to ask that very question of two real world PC12 pilots. The first pilot said he recalled pitch down was about three degrees, the second pilot actually checked for me on his next flight, he confirmed that pitch down is -2.5 degrees.

 

The above is on a 3 degree glideslope, at the correct Vref for the flap setting and weight.

 

In addition, there is a rather excellent video available from Flight Video Productions. There's a nice close up of the PFD as they land on a three degree glideslope, confirming 2.5 degrees pitch down. there's also plenty to read on the internet regarding the PC-12's characteristic slight nose down attitude on approach.

 

Objection 2. I don't agree with the settings suggested. I'm not sure why drag_scalar adjustments were made, or pitch_scalar. Adjusting drag_scalar settings will simply necessitate higher engine rpm to compensate for the drag, thus adding more inaccuracy to the equation, and drag adjustments won't correct the pitch issue that they perceived at all. And personally, when I've tried pitch_scalar adjustments in the past, they are ineffective in the cfg without corresponding airfile adjustments.

 

I've modified many add-ons in this respect, and all that's required I've found is an adjustment to the lift_scalar.

 

I read in the other thread, that the guys were much happier with a "flat" approach, that's fine in my opinion if they are happy... but it's not realistic. The PC-12 is famous for it's slight nose down attitude on approach. And this is one aspect of the flight model that Carenado have got right.

 

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..

 

 

 

If anyone wanted to try those settings, then yes, it goes in the flaps.0 section. But to be honest, I would advise against it.

 

If there is an adjustment to be made in regard to pitch it's only slight, and as I said above... lift_scalar= is the parameter that would need adjusting, nothing else.

 

I would also be surprised if Vref went up due to the drag. Engine RPM yes, but not Vref.

 

Again... my advice is if you think it does need a slight tweak, lift_scalar only! And you are aiming for 2 - 2.5 degrees pitch down, on a three degree glideslope, at the correct Vref for that flap setting and weight. Anything else is not as per the real world.

 

There is a possibility of course that as the settings are in flaps.0, they will impact lift at all flap settings, and that includes stall speed and take-off, but in my experience it's not significant enough to be an issue.

[martin-w 3,234]

To add to this...

 

If anyone would like to report this to Carenado, I would appreciate it.

 

Unfortunately I can't, as I bought the product from Just flight, not Carenado, so I have no facility to submit a ticket.

[Flyfox 114]

Hi Martin, I fully understand your concerns and I widely agree with your points. However, I would like to add two comments:

 

1. My proposal to modify the flap parameters in the aircraft.cfg was not meant to correct the too high flaps 15 approach speed, but to slightly reduce the (according to my observations) somewhat too accented nose-down attitude. In addition, even with flaps 40 setting, it seems unrealistically difficult to slow down during flare. With the original setting the risk for a nose-wheel landing is quite significant (unlike the RW PC-12) and the mentioned mods somewhat reduce this tendency. BTW, I finally ended up with the following settings: lift_scalar = 0.8, drag_scalar = 1.4, pitch_scalar = 0.9. This improves my flight experience with this bird. Thanks to FSX's open structure we are free to experiment!

 

2. We all try to have a simulation which meets the reality as good as possible, but there are a lot of limitations, mainly given by the imperfect flight dynamics simulation of FSX (and P3D...). Matching the perfect function of an AOA indicator for all possible flap settings seems particularly difficult. Not even Flight1 got it right with their PC-12 (which I still like a lot!). And we all know that Carenado offers superb graphics, but does leaves the user with some lack of system depth and RW match. It's great if we are aware of the RW data, but we always need to compromise: It's still just a (already quite aged) flight simulator.

[martin-w 3,234]

My proposal to modify the flap parameters in the aircraft.cfg was not meant to correct the too high flaps 15 approach speed, but to slightly reduce the (according to my observations) somewhat too accented nose-down attitude.

Yes, I realised that Felix, as I said in the other thread. But actually, all you require in that case is a slight tweak to the lift_scalar. Try something like lift_scalar=0.8 As for pitch on a approach, it absolutely should be minus 2.5 degrees down, on a three degree glideslope, at the correct Vref. your setting throw out the AoA indicator and result in a flat approach, which is not realistic.

 

No less than two real world PC12 pilots confirmed this for me, not to mention a rather excellent video by Flight Video Productions that provided all the variables like glideslope, weight and Vref, and clearly demonstrated a two-three degree pitch down tendency. This is something the PC12 is famous for, and if you adjust settings to eliminate this tendency it is indeed wrong, not realistic. but of course, we are free to do what we like in the sim if we want to.

 

I also have a graph, presented to me by a different PC12 developer, that also clearly demonstrates a 2.5 degree pitch down characteristic on approach. I can PM you that if you are interested.

 

 

even with flaps 40 setting, it seems unrealistically difficult to slow down during flare.

 

I did some serious testing yesterday, the results are in the other thread. I see no issue with deceleration in the flare. In fact it lands beautifully, one of the easiest I've landed in the sim. It's your technique Felix.

 

 

 

With the original setting the risk for a nose-wheel landing is quite significant (unlike the RW PC-12) and the mentioned mods somewhat reduce this tendency

 

I've not had any issues like that at all. From what I've read from real world test flights, powering back at 15 feet is pretty common, the PC12 is quite a big bird for a single engine turboprop, it has quite a bit of inertia. I have found it very easy to flare and land with a reasonable degree of pitch up. Treating it like a Cessna and powering back too late might be the issue you experienced, in addition turboprop engines spool down slowly and also generate quite a lot of residual thrust from the exhaust gasses. I have to say also, I have seen quite a few landings in the PC12 where it pretty much narrowly avoids a nose wheel first landing. But as I say, I've not found that a problem at all, with a well known tendency to have a nose down attitude you can expect to have to pay attention in the flare and adjust the height where you power back accordingly.

 

Like this one...

 

 

 

 

 

BTW, I finally ended up with the following settings: lift_scalar = 0.8, drag_scalar = 1.4, pitch_scalar = 0.9. This improves my flight experience with this bird

 

 

I tested your settings yesterday and commented in the other thread.

[martin-w 3,234]

Firstly Felix, I mean no disrespect by challenging your settings and assumptions about the PC12. So apologies for doing that, but we are enthusiasts, and it is "simulation" so the truth of the matter is important, and I hope you would critique my notions if you had a better understanding.

 

 

But this is my conclusion when I tried your settings...

 

Edit: Okay, I've just tested the changes recommended in this thread.

 

Modifying the cfg in this way has the following effect...

 

At flap 40, at 8500lbs, at the correct Vref specified by Pilatus, on a three degree glideslope it results in... zero degrees pitch up This is wrong! Pitch should be 2.5 degrees down.

 

In addition, the settings throw out the AoA indicator. If you follow the AoA indicator, and fly faster than the correct Vref, it centres, and pitch is closer to being correct, but Vref is then wrong. Engine rpm is also higher.

 

 

 

Without the settings mentioned in this thread...

 

 

 

Stall speeds are correct for all flap settings.

 

AoA indicator is correct.

 

Pitch on approach is correct.

 

The only issue is the one mentioned in the other thread, namely Vref is too fast at Flaps15.

 

 

In short Carenado got it right for stall speeds, they are bang on, they got it right for pitch on approach, and I suspect they got it right in regrd to the inertia and residual thrust of a bigger heavier turboprop aircraft. Not surprising if indeed Bernt Stolle did the FDE.

 

 

 

---------------------------------------------------------------------------

 

You might find this video interesting Felix.

 

There's yet another landing by a PC12 that's nose gear and main gear touching down simultaneously.

 

In addition, the presenter mentions how massive the aircraft is [lots of inertia] and at 2:28 he mentions the extra thrust from the exhaust. All of this adds up to a requirement to power back sooner than you would in a smaller piston prop.

 

 

 

 

The problem is it's easy for we enthusiastic simmers to dive in and assume things are wrong and start altering files, but we need to be sure that's indeed the case.

 

The Carenado PC12 really does land great Felix. You should try it with the default [realistic] settings and power back earlier.