As I type this I’m in a 250ish mile flight and I’m currently in cruising altitude/configuration. Prior to SU5 I have always been able to peg the throttle at 75% and lean the engine 50 deg rich of peak for 2200-2300 RPM in this region of the US and that would afford me 100-105 knots. I’m currently at 9000ft and I’ve been noticing I have to bump up the throttle to over 80% with proper leaning and even then this only affords me 85-90 knots. Had I kept it at 75% throttle the speed would have crept down and AOA would have been excessive like the plane is struggling to stay up.
EDIT: I just ran it on full throttle for a couple minutes without changing altitude or mixture and was only able to get it to teeter between 106-107 knots where as before it would go to 120-125 at full throttle.
Am I doing something wrong or is this an issue with the plane?
You aren’t doing anything wrong, you have the wrong expectations
75% throttle isn’t the same as 75% power at higher altitudes.
At 9000ft you need almost 100% throttle to achive 75% power.
According to the manual 2320RPM at this altitude means slightly more than 50% power at ~104ktas.
So the MSFS version is actually very close.
106kias at 9000ft means 121ktas, the manual shows ~123ktas at full throttle.
So these numbers are matching nicely as well.
Ah, thanks for clearing that up. I got the 75% throttle at cruise figure from the checklist because it says no more than 75% throttle. So would it make sense than to cruise in this plane at lower altitudes? (Given terrain allows it) This is an IFR flight and the built-in ATC has made it quite clear in the past it can’t distinguish between a 747 and a single engine Cessna with it’s commands, that’s why I ask.
That’s incorrect. Where did you get this checklist from?
You simply use the power settings from the POH tables, regardless of the resulting throttle position.
edit: that’s a copy & paste from a 172 manual
NORMAL PROCEDURES
CRUISE
Power - 2100 - 2700 RPM (No more than 75% power is recommended)
Concerning your cruising altitude question. The performance tables are available up to 12000ft.
This is a modified checklist that I dropped in my community folder (includes emergency procedures). I feel like the stock one may have said 75% throttle at the bottom as well although they both say 75% power at the top. The inconsistent language may have lead me to stick with “75% throttle all this time”. Again thanks for the clarification. Would you have a link to the appropriate POH? This one says 172S although no year is given https://www.flygoodyear.com/images/downloads/Cessna%20CE-172SP%20POH.pdf and this one says 172 skyhawk (N) but is year 78. https://wayman.edu/files/Cessna-172N-POH.pdf
What about 1000 feet altitude? In MSFS I have 90 knots and dropping at 2100 RPM. What airspeed shall I expect at 2100 RPM, clean configuration at 50%fuel tanks + 2 standard pilots? For fully-loaded C-172S, according to POH, I expect at sea level 75% power 114 knots, at 4000 feet 119 knots, and at 8000 124 knots. At 65% - 108/112/117 accordingly and at 55% - 101/104/107.
When I transit from climb to horizontal flight (after take-off at pattern altitude 1000 feet, for example) and accelerate to 100 knots and reduce RPM to 2100 my RPM is not rising to 2200-2300, it drops often or rises to 2120-2130. Is this OK or my expectations (rising from 2100 to 2200-2300) are wrong and my memory is wrong?
Hahaha. Thank you for posting this! I’m struggling to get my 172 up to FL16 when doing IFR flights. I did a 2 hour flight last night and requested ATC to lower my flight level to 8,000. I’m still pretty new to some of these concepts, but I couldn’t get my plane to the cruising speed of 124 knots. I had my throttle at full and my mixture to about 30%. The max I got out of it was about 100 knots.
I’ll have to look at the POH. Thanks again for posting about this.
FL160 is totally unrealistic in a C172. Even FL80 is very high. Your ears would hurt like hell, you’d feel very light headed and possibly even pass out. I’m talking about a scenario when you take off from sea level. I have never flown that high in an unpredsureized cockpit, but I have clibmed 10000 ft mountains and remember feeling much weaker. And that was after a full day climb, so you could get used to it.
I fly the C172 regularly and 99% of the time it’s 2000-3000ft.
No, 8000 ft is a perfectly achievable altitude to fly a 172 on a long range flight without any negative side effects. If someone’s ears are hurting or they are easily getting light headed flying a 172 at that altitude it is likely an indication of an underlying health issue.
That was about FL160, assuming it’s even possible to climb that high. But FL80 is also very high. It would take ages and a lot of fuel to climb to that altitude.
From Sea level to FL080,14 minutes and 3.0 US Gals of Fuel, if you’re climbing that high it’s normally to make use of a good tail wind that will more than offset that. To FL160, that’s just not happening.
What are some of the specs when you’re climbing? In the sim, I look at RPM, fuel output, airspeed, and vertical climb. I’ve noticed that a VC of 500 fnm gives me a decent climb and keeps the airspeed in a positive rate. I’ve tried 600 fnm and it slowly lowers the airspeed to stall. I believe I read in the POH that climbing roughly uses 15 gal per nm so I’ll set the mixture to that. I also try to keep the RPM at 2500 and cruise at 2300.
Would love to see how more experienced pilots and simmers do it. I wasn’t a big fan of the 172 at first, but with my interests in gas gauges and very little glass cockpiting this bird has really grown on me. I see there’s a C182 in the marketplace. It looks like that model has more horsepower. Do you think it’s worth purchasing? I’m in the Xbox.
You can climb at Vx, Vy, and VCC - Cruise climb (Vcc - “enroute climb speed”). The cruise climb for most of GA single engines is about +16 knots to Vy. The 172’s sea-level Vy is published at 74 knots. Enroute climb (Vcc) is published at 75-85 knots. The task is not to overheat your engine and/or to save as much fuel as you can. Vertical climb depends on your weight and altitude/temperature (pressure altitude). In cruise climb, I lean mixture for the best climb on Vy or VCC but within temperature limits, C-172 with NGX is good for this as she has an assistance regime for leaning, and my best climb - vertical speed is always different. Normal enroute climbs are performed with flaps up and full throttle and at speeds 5 to 10 knots higher than best rate-of-climb speeds for the best combination of performance, visibility, and engine cooling.
There is also one thing IRL we have to revise from time to time to decide “to lean on peak or not to lean” - what is more expensive, fuel or spare parts or time to the destination?
I’m not a real pilot so I’ve only been exposed to these concepts, but wonder how much impact they really have? My overall understanding is if you’re trying to save on fuel and parts wear-and-tear then you always LEAN. If you’re trying to get to your destination as fast as possible then just floor it! Is that an oversimplification of that concept?
A leaned engine will run hotter, hence provide a faster cruise speed. But also, because it runs hotter it’s more wear and tear. Full rich runs cooler, but burns more fuel and will take longer.
Genuine considerations for a real plane, since wear and tear isn’t an issue in our simulated plane, leaning is your best bet.
Oh my goodness. That makes so much sense. I’ve been really enjoying the learning process of flying. It’s so fascinating! This wear-and-tear is why it’s such a debate whether to lean or not. I’m with you now.
Well; thank you for that insight. Eventually; I plan to get my private pilot’s license so I want to use my time in the sim to practice real procedures. Make it more of a habit than something to always think about.
Yes, the POH from the first link is perfectly fine!
I did a 2 hour flight last night and requested ATC to lower my flight level to 8,000. I’m still pretty new to some of these concepts, but I couldn’t get my plane to the cruising speed of 124 knots. I had my throttle at full and my mixture to about 30%. The max I got out of it was about 100 knots.