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Cessna 172SP Performance

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#1 Jimm

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Posted 17 February 2017 - 06:42 AM

I have a report to present to the furm as well as a request for information dealing with the performance of C172SP in Xp11.  So far, this aircraft has treated me well, and up until using XP, I wasn't a huge fan of the default Cessna.  Now that I've been using it almost all the time now, I've been getting used to how it handles, how it operates through all phases of flight, but last night, something strange happened, that I believe may be beyond a bug, but something not modeled.

 

Last night, I performed a 2-hour or so flight from KTRM to KSBP.  The plan was to visit a couple of other airports that GPB500 has put together (great scenery, btw), and so with that, I loaded up the C172SP, set my airport and position, set the weather to auto download, confirmed the time ans set off.  The weather in general, was rather pleasant at KTRM, and during the first 1/3 or so of the flight, I only experienced periods of intense wind, with heavy cloud cover to follow at around 8000 feet.

 

Somewhere northeast of KSBA, I had to increase altitude to 9000 feet and it was at this time, that I flew into a storm system in the area.  The OAT was reading around 34F, but started to decrease rapidly.  I was starting to see rain (a first for me in XP11) and the winds were very strong.  As the autopilot was struggling to hold my heading, I started to hear the faint stall warning sound and as I glanced down at my pitch indicator, the aircraft was starting to roll to the left.  My altimeter was beginning to fall, so I re-checked the autopilot and it was disabled. As I did a quick check of all systems, they showed normal, but I was still losing altitude.  I took the controls, applying a firm back pressure on the yolk, to attempt to maintain level flight, but the aircraft was all over the place.  I re-checked the OAT and it read 28F, so obviously I was in very cold conditions.  Within about 10 minutes time, I did the right thing and dropped my altitude back down to 8000 feet, and during that time, the OAT rose to 34F, the aircraft was a little easier to control, the winds weren't as strong, and I was able to re-engage the autopilot.

 

It wasn't until this morning, as I thought about that flight again, that I realized that no carb heat control has been modeled in this aircraft.  I'd looked for it before, in the past, and recognized there wasn't a control knob for it, so I didn't give it a second thought.  I also never flew into a storm system like that before (with a single prop aircraft), but in hidnsight, I believe what happened was that the carb heat would have helped prevent the aircraft from wanting to stall.  During that rough patch of weather, my KIAS was around 60 and no matter what I did, i couldn't get the aircraft to speed up, until i was below the flight level i was at.

 

I've experienced carb heat issues before in another sim, using a different aircraft that had carb heat modeled, so it was a simple mistake to correct as a pilot, but for the C172SP, no carb heat control can be found on her.  If carb heat was the issue and the solution, would this be a candidate for a bug report, or is it something I should petition LR to model?  I took a look at an old 1978 POH for the Cessna 172N, and I do see it was equipped with a carb heat knob.  In fact, under normal procedures, section 4, carb ice can form, and it is recommended to use it, though can cause a richer mixture, so re-adjusting the mixture with carb heat on is tuned manually (trial and error), throughout the flight.

 

I may have gotten a little long-winded here, but if anyone wants to chime in with thoughts, experiences and recommendations, that's fine.  I honestly don't recall anyone reporting the missing carb heat knob in XP11, in fact, I don't remember off hand if the Cessna had it or not in XP10.

 

In any case, I recovered the aircraft and landed safely at KSBP, where the weather was much more pleasant.

 

*Shameless plug:  please check out GPB500 (Greg) airports and consider the small donation fee he requests, because for what you get it, it is worth every penny.  He's always hard at work, perfecting his airports, with new ones planned in the future.


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#2 Jimm

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Posted 17 February 2017 - 07:04 AM

I further researched this issue, and I realized that the POH I originally referred to was for the 'N' model, not the 'S' or 'SP'.  In the latter, the carb heat knob is in fact, not present, so now I believe this was all pilot error on my part, in not leaning the mixture properly, but I can't help but think that the carburetor heat is an issue.


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#3 SouthPawPaul

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Posted 17 February 2017 - 07:33 AM

I'm not sure if what you experienced was airframe icing too. I'm not sure if the X-Plane 11 C172SP models icing, but I'd consider that.

 

I'd also consider reading up on leaning the engine using the CHT guage. There's some great articles out there on how to get the best performance out of the engine whilst still treating the engine well. There's quite a good article here (if a little involved)

 

https://www.aopa.org...ng-lean-of-peak


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#4 Jimm

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Posted 17 February 2017 - 07:47 AM

I'm not sure if what you experienced was airframe icing too. I'm not sure if the X-Plane 11 C172SP models icing, but I'd consider that.

 

I'd also consider reading up on leaning the engine using the CHT guage. There's some great articles out there on how to get the best performance out of the engine whilst still treating the engine well. There's quite a good article here (if a little involved)

 

https://www.aopa.org...ng-lean-of-peak

Hey thanks Paul, you may be right about that too.  I'd been reading up on the POH of the C172S, and it gives some pretty helpful info on proper leaning of the engine, so I'll give that a go later on to see what happens.  All I need now is some really bad weather.  :smile:

 

I don't typically fly with failures on, as I am still learning, so I don't know if failures can still occur, but that may be a dumb question in of itself.  Obviously, XP doesn't coddle the pilot, and you don't have the ability to select easy or hard for difficulty, which I don't mind so much because of that happened last, night, I'm a little more informed and know what to watch out for later.


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#5 strider1

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Posted 17 February 2017 - 08:39 AM

The SP is fuel injected, no carb. Probably ice on the wings.
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#6 Jimm

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Posted 17 February 2017 - 09:02 AM

The SP is fuel injected, no carb. Probably ice on the wings.

Good, this is good info that I never normally considered.  I do appreciate the feedback from you guys, it will help.  :smile:


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#7 19dcavscout

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Posted 17 February 2017 - 09:21 AM

The environmental conditions you described are an ice rich environment. Sounds to me like you were in icing. A general rule of thumb is icing conditions exist where there is visible moisture (clouds are considered visible moisture) with a temperature of less than +5 degrees C. My experience in piston aircraft is rather limited, but if you had carb icing you would not have systems normal as the engine begins to starve for fuel. Bottom line is do not fly an aircraft into icing conditions unless it has been certified for it. 


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#8 Jimm

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Posted 17 February 2017 - 09:52 AM

The environmental conditions you described are an ice rich environment. Sounds to me like you were in icing. A general rule of thumb is icing conditions exist where there is visible moisture (clouds are considered visible moisture) with a temperature of less than +5 degrees C. My experience in piston aircraft is rather limited, but if you had carb icing you would not have systems normal as the engine begins to starve for fuel. Bottom line is do not fly an aircraft into icing conditions unless it has been certified for it. 

Well I kinda figured it was icing, just not sure what was icing up.  Fortunately, after decreasing my altitude, everything got warm enough that I could retake control properly.  I'd say Strider had the right assumption, as I found the control surfaces were a real bear to control.

 

I didn't "plan" this flight, as I am still testing out different scenarios in the beta, so i never expected that type of weather at 9000 feet over California, but that's what I get for assuming. :)

 

Thanks again guys for the input, I appreciate it.


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#9 Paraffin

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Posted 17 February 2017 - 11:11 AM

Just chiming in here to agree this sounds like a classic case of X-Plane's icing effect. The conditions were right for it. There is no visual indication. You just have to infer it by the way the plane starts to feel heavy, the controls get sluggish, and eventually the plane just stops flying. 

 

I appreciate the realism, but I also wish there was a setting to disable this as an option. Sometimes the weather won't let you escape, and it can ruin a virtual airline flight. As far as I know, it's one of the few failure modes like helicopter VRS that isn't exposed in a ,prf file you can edit. 


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#10 Jimmy RFR

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Posted 17 February 2017 - 11:53 AM


I appreciate the realism, but I also wish there was a setting to disable this as an option.

 

Well... there kind of is - remove the icing conditions altogether via the weather panel. From my point of view, if you want realistic weather (or what passes for realistic weather) in the sim, then currently, the aircraft behaves realistically. So the choice is simply different than you'd expect - instead of turning off the realism in the aircraft, you're turning off the realism in the weather (by changing it to something that might not match RW conditions.)

 

To debate it otherwise, is an argument for greater user control in X-Plane 11, which really seems like an argument that no-one is going to win given LR's current design philosophy. :smile:


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#11 Jimm

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Posted 17 February 2017 - 12:37 PM

Well... there kind of is - remove the icing conditions altogether via the weather panel. From my point of view, if you want realistic weather (or what passes for realistic weather) in the sim, then currently, the aircraft behaves realistically. So the choice is simply different than you'd expect - instead of turning off the realism in the aircraft, you're turning off the realism in the weather (by changing it to something that might not match RW conditions.)

 

To debate it otherwise, is an argument for greater user control in X-Plane 11, which really seems like an argument that no-one is going to win given LR's current design philosophy. :smile:

Good point.  For example, last night, when I started up X-Plane, I went to the weather section to download the latest data, and it kept failing.  After a couple of clicks and getting the same message, I exited out of XP and got back in, then it was fine.  I probably should have given the report a closer look, due to my icing incident, but honestly, I appreciate that there is this level of realism available.  In my own opinion, it should be left as is, because it is a flying simulator and if you opt for real world weather, then the experience should remain whole.  As far as any argument on how to control the weather aspect, it's pretty much clear cut.  You can either get real-world weather or manually configure it.  By choosing a manual config, you start with a blank slate, and if you leave it like that, then you have no weather. :smile:


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#12 Adrian123

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Posted 17 February 2017 - 12:41 PM

A few days ago, I had a 727 fall out of the sky due to icing. Should learned how to activate the anti icing. :shok: So it's somewhat realist.


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#13 Mountain Man

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Posted 17 February 2017 - 01:04 PM

I appreciate the realism, but I also wish there was a setting to disable this as an option. Sometimes the weather won't let you escape, and it can ruin a virtual airline flight.

 

You can always change the weather settings. I recently did that mid-flight when the real-world weather conditions became far too dangerous for a Cessna 172. The plane started wildly pitching and rolling by 30-degrees or more and became extremely difficult to control (I would have been a dead man in real life), so I opened weather settings and chose something a bit calmer. Problem solved, and I was able to finish my flight.


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#14 Paraffin

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Posted 17 February 2017 - 01:17 PM

Well... there kind of is - remove the icing conditions altogether via the weather panel. From my point of view, if you want realistic weather (or what passes for realistic weather) in the sim, then currently, the aircraft behaves realistically. So the choice is simply different than you'd expect - instead of turning off the realism in the aircraft, you're turning off the realism in the weather (by changing it to something that might not match RW conditions.)

 

Its not that simple. With real weather injection, you don't know what you might be flying into when the weather updates. Might be fine now, might start icing in 20 minutes after a weather injection update. If I'm flying something like an FSEconomy assignment where the whole point is to complete the flight and I'm wasting my time otherwise, it requires an overly cautious approach. It means never using real weather, when there is even the slightest chance of icing that would ruin the flight. 

 

The real issue (see below) is that like helicopter VRS, it's a failure mode that's inconsistent with other failure modes that can be turned off by the user. 

 

To debate it otherwise, is an argument for greater user control in X-Plane 11, which really seems like an argument that no-one is going to win given LR's current design philosophy.  :smile:

 

It's an inconsistent design philosophy. Why give the user control over whether control surfaces are damaged with over-G, or bird strikes are a hazard, and not let the user turn off the chance of in-flight icing? Why isn't this on the failure menu like everything else? Bird strikes are just as much of an environmental hazard as icing.

 

And yeah, I know this is probably just p..., er talking into the wind. Laminar does things their own way, and it isn't always logical.


You can always change the weather conditions.  I recently did that mid-flight when the real-world weather conditions became far too dangerous for a Cessna.  The plane started pitching and rolling by 30-degrees or more and became extremely difficult to control (I would have been a dead man in real life), so I opened weather settings and chose something a bit calmer.  Problem solved, and I was able to finish my flight.

 

Sure, that's the escape method. But it breaks immersion to have to pause the flight and go into the weather menu like that.

 

It would be so much simpler to just turn off that failure mode before flying a FSEconomy flight, so I can enjoy the look, if not all the effects of real weather. And then turn it back on when I'm doing a less mission-critical flight, where I might want to cope with the dangers. It just baffles me why we can turn off other failure modes and not this one.


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#15 Jimm

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Posted 17 February 2017 - 01:26 PM

There is always the option of using the in-sim map (tap the M key), then click on the closest airport to get the METAR.  I've used it and it helps a bit.

 

Not to be a Debbie-downer, but we're starting to stray off the path a little folks.  As far as the scenario I flew last night, and given that I handled the flight as best I could, despite not interpreting the weather in time, would a better course of action been to fly around the affected area, since my aircraft was not capable of handling the icing issue?


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