POH performance charts - C172

Discussion in 'Pilot Training' started by jaymark6655, Nov 26, 2018.

  1. jaymark6655

    jaymark6655 Pre-takeoff checklist

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    So, being from IN I never really worried too much about high altitude operations. Today I was reading the POH and started wondering why do the takeoff and landing charts stop at 8000'? Are you not supposed to operate this plane out of strips above that height due to lack of climb performance? (8000' on an 104 F day is close to 4615' takeoff with only a 285fpm climb)
     
  2. Tantalum

    Tantalum En-Route

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    Pretty much. It is amazing how pitiful the performance is of some of the basic trainer fleet.

    Out here (Southern Californa) Big Bear is a popular destination.. but there are many days in the summer where it is pretty much a no-go destination for many club 172 and Cherokee planes.. the airport elevation is high enough near 6K, and you throw in a hot day and your density altitude goes to crap.. plus you have terrain so you can't really afford to tool around at 200 fpm
     
  3. Cap'n Jack

    Cap'n Jack Final Approach

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    Interesting question. How many airports are higher than that? Leadville, CO (KLXV) is 9933' MSL and the highest I know about. KGNB (Granby-Grand County, CO) is 8200', 33V is 8125' MSL. There are a few more, such as Telleride, but they seem to be concentrated in the Rocky Mountains in CO.

    I'm pretty sure they operate C-172s from some of those places. Maybe they calculate density altitude and work from that?:dunno:

    They probably operate them with little load; a C-172 becomes a 2-seat plane up there.
     
  4. jaymark6655

    jaymark6655 Pre-takeoff checklist

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    I think there are only 8 pave fields above 8000', probably all in CO (Angelfire in NM). Unpaved strip, no idea, a lot. Telleride, you just get airborne and the fall off the cliff right :rolleyes:. I would love to fly into Leadville, but probably should do it on a really cold day. Right now my DA is -1000' last weekend :D.
     
  5. MauleSkinner

    MauleSkinner En-Route

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    There’s nothing that says you need charted performance for a takeoff in a light plane...if AFM performance data isn’t required by certification (I’m pretty sure the 172 doesn’t require it), 91.103 simply requires
    Personally, I’ve always liked the takeoff performance computer from Sporty’s. It takes way more into consideration than your airplane chartsmdo, anyway, and it has he added benefit of being able to adjust to your technique and aging airplane’s performance.
    https://sportys.com/pilotshop/takeoff-performance-computer.html
     
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  6. luvflyin

    luvflyin Final Approach

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    Seems to me I remember reading somewhere not to ‘extrapolate’ above the highest altitude in the Charts in the POH. I think it was in a POH. I would be reluctant to do it. Extrapolating between say 6000 and 8000 and then continuing that angle, curve, formula or whatever you call it beyond 8000 could give bad information. The actual performance changes could get real ‘steep’ after 8000.
     
  7. jaymark6655

    jaymark6655 Pre-takeoff checklist

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    I had seen a chart somewhere that did a best fit curve to the POH data and it an e^x shape (gets really steep at the end) look to it. I will try to find it again and attach it. Edit: Not as steep as I remember from last night, but not all that great either.
    chart.png
     
  8. luvflyin

    luvflyin Final Approach

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    Yeah.
    Yeah. Kinda like that. If you go beyond 13000, not only will the curve continue to steepen, but it could steepen at a ‘rate’ that is not apparent in what you already see.
     
  9. Clip4

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    Maybe they don’t want to encourage anyone crazy enough to takeoff in 172 when the density altitude is greater than 13,000ft.
     
    Last edited: Nov 27, 2018
  10. alfadog

    alfadog En-Route

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    Leadville airport. I drove over there on a skiing trip. Ski Cooper is my go-to slope and we stay in Leadville. There was this old gal that was teaching mountain flying out of Leadville in a 172. No doubt in cool weather only.

    S1052591.JPG
     
  11. Dan Thomas

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    "Basic trainers" are necessarily relatively inexpensive airplanes. Performance has a cost, and if basic trainers all had turbochargers and larger engines there would be very few flight schools. Few enough now already.
     
  12. Tantalum

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    The SkyHawk is a uniquely pitiful airplane though. If you look at the light sport market then there are some very capable and modern machines out there that do not have turbo chargers and big engines
     
  13. Pilawt

    Pilawt Final Approach

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    The 172 does better than other certified "four-seaters" with similar power, though. And with 180 hp it's a decent performer even in the high country.
     
  14. Dan Thomas

    Dan Thomas En-Route

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    The 172 is no hotrod, for sure, but any airplane that is built to haul four people at 100 knots or so on 150 hp is going to act very much like a 172. The light sport is no comparison and has no magic; those airplanes are over 1000 pounds lighter (at gross) and have lower stall speeds, meaning that their wing loading is lower. There have been many homebuilts with far better performance at high altitudes without turbos, but they're all light and rather slow, or have awesome power-to-weight ratios. Higher stall means a higher takeoff speed, which means much longer runways at altitude and lower climb rates.

    Every airplane design is a collection of compromises.
     
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  15. Tantalum

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    The Sling 4 does 120 knots on 115 hp with 4 people in it, or a roughly 1,000 lb useful load.. Compromises exist, but the Skyhawk is built solely to be a docile and forgiving trainer, and it accels at that, but any "performance" it has is purely accidental to the main design goal
     
  16. jaymark6655

    jaymark6655 Pre-takeoff checklist

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    Not to dump more on the C172 (I do like it), but checked out the DA-40 and it seems to be better than the Cessna. Goes about 20 knots faster at a 75% cruise with an 1 hour difference in endurance due to carrying less fuel (17 gallons less! I think there is an ER version), shorter takeoff, higher ceiling, slightly wider cabin, and rear door. Only places that C172 is close is they almost have the same useful load, stall speed on the DA is 9 knots faster and the DA lands about 75' longer. A lot of schools are getting the DA-40s, I think they might be $100K more. Unfortunately there isn't one near my location to rent, 2 hour drive to the only one I could find.
     
  17. Tantalum

    Tantalum En-Route

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    I have plenty of time in 172.. even recently. @RudyP had the pleasure of flying in one with me just a couple weeks ago. BUT, I don't feel bad dumping on it. Outside of having two doors the plane has zero redeeming qualities (not true about the 182). It's sad to me that most people's first flying experience is on one, and many will never get to fly anything else. Grievances:

    *trim wheel up front and totally out of the way of the pilot, this means that you have to be constantly moving forward and backward in your seat to adjust it, each time slightly changing your CG so you never quite get the trim right

    *no rudder trim.. get a good leg cramp going, or fly uncoordinated. I know some have rudder trim, I've yet to fly on one that actually does something useful.. pretty sure it's just attached to a 50 year old stretched rubber band

    *God knows how much fuel you actually have in either tank.. is that left tank showing 3 gallons while the right shows 30? Switch the tank and fly on the other for an hour.. now you suddenly have MORE fuel in that tank? wtf?

    *vernier knobs for throttles

    *rip your skin off turning on the defroster

    *air vents that fall out

    *a nose wheel that is -sort of- attached to the rudder pedals

    *a nose wheel that loves to shimmy to death

    *why should you be able to strain the nose fuel sump alone?

    *YAY, 13 fuel sumps!!

    *pathetic visibility.. constantly leaning forward to look for traffic, and hope you guessed your base to final turn right

    *struts!

    *smash your head into the wings

    *am I the only who who's vision is distorted looking out the front window?

    *the yoke feels dinky.. don't break it off!

    *have a cool 180 conversion? Nice! Enjoy the ghetto piece of metal screwed to the panel so you can't put flaps past 30

    *pathetic looking vacuum gauge

    *I hope you like turbulence

    *enjoy the "I'm a student!" look you get on any ramp you fly into

    *strut missing that piece of sandpaper? I hope you brought a ladder to mount the plane and check the fuel

    *enjoy sucking on the stall horn

    *did the door shut right? Did that top pin go all the way in? Slam it a little harder just to be sure

    *oh, your baggage door handle ripped off? Or it is just permanently bent?

    *did it snow last night? Plane is probably sitting on its ass

    *is your seat locked?
     
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  18. JAWS

    JAWS Line Up and Wait

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  19. jaymark6655

    jaymark6655 Pre-takeoff checklist

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    Yeah, saw that last night. I was search for DA-40 videos and I guess it took DA to mean density altitude.
     
  20. will44s

    will44s Filing Flight Plan

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    A bit off topic but anyone have an explanation for this. Rpm redline in the skyhawk I fly is 2600 but the cruise performance tables go to 2700. Why is it so? It's a continental o300.
     
  21. dmspilot

    dmspilot En-Route

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    Sounds like a mismarked tach, the POH and TCDS both say 2700.
     
  22. Dan Thomas

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    Much of that is maintenance issues. That can apply to any airplane. 13 fuel sump drains are due to the wet wing and liability. The vernier throttle thing is a stupid mod. Rudder out of whack is a misrigging issue, probably compounded by a worn or broken rudder bar spring. More maintenance shortcomings. Trim? Are you using the trim like an elevator, or trimming the pressure off? Use the Attitude-Power-Trim procedure, and any airplane will trim out nicely. Out of all the time flying and instructing in 172s, and all the years maintaining them in a flight school, I never had these issues. Sure, the doors were always a pain, but a lot of aircraft doors are a pain too.

    We sold a mid-70s 172 when it hit 13,000 hours and the engine was coming due and a lot of other stuff like the paint and interior needed refurbishing. It made more sense, for a flight school with the need for good dispatchability, to find a low-time airframe and spend the money on it instead. The guy that bought the old one had been renting 172s, and couldn't believe his luck at getting this one. He said it flew like a new airplane. Started and ran smoothly. Flew straight. No slop in the controls. Everything, including the seats and locks, worked well. Nosewheel never shimmied. Even the doors worked nicely.

    So much of it is maintenance. Poor maintenance means cancelled flights, disappointed students, lost revenue and maybe lost customers; it's just not worth it to cheap out on it.
     
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  23. Tantalum

    Tantalum En-Route

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    Totally agree with you there
     
  24. Clip4

    Clip4 En-Route

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    When can we expect the Sling 4 to progress beyond a purely experimental airplane and over 44,000 being produced?
     
  25. Tantalum

    Tantalum En-Route

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    The objective of my post was in response to another poster to show that the Skyhawk is not the epitome of performance for 150 hp and four seater plane.. that there are much faster planes with similar useful loads flying with much smaller engines. The technology is out there, it's just hampered by regulations, and a very small (and shrinking) market that makes investment from people like Cessna and Piper into a clean sheet design not viable

    But if we're going to talk numbers, then production numbers show that Vans alone there are close to 10,000 of those flying around, that's more than there are Cirrus.. that's an impressive figure considering these planes have to be handbuilt at home by owners.. the fact that you can build something in your garage with a smaller engine that flies faster with the same useful load as a Skyhawk for a quarter of the cost (new) is incredible, and really paints a dire picture for the legacy manufacturers (and puts the cost of certification into perspective). Cirrus gets away with it because they have a niche "high end" product.. but even Cirrus struggles to sell the SR20 which is priced (new) on par (ish) with the Archer and Skyhawk.. might not be as good of a trainer (this is debatable), but it's faster and a much more comfortable product
     
  26. Walboy

    Walboy Line Up and Wait

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    That's kind of neat. I would like to be able to check it out before I bought one though...see how it compares to actual data, see what the underlying assumptions are.

    Maybe one of the more useful things from Sporty's
     
  27. MauleSkinner

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    It does take a little getting used to what defines some of the parameters, like the difference between turf, grass, and long grass. Beyond that, I’ve found it to be very accurate when “calibrated” for my actual technique. One takeoff I distinctly remember had me pretty close to runway available on my farm strip...I lifted off within 100 feet of where it said I should.
     
  28. Pilawt

    Pilawt Final Approach

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    Nobody here has said the C-172 was "the epitome of performance." Nor, on the other hand, is it a "uniquely pitiful airplane."

    The 172's performance is comparable to other certified, production aircraft of similar (non-turbo) horsepower -- better than some in some respects, worse than some in others. A 150- or 180-hp C-172 has better takeoff, climb and altitude performance than a fixed-gear PA-28, AA-5x or BE19/23 of like power. It's faster than some PA-28 models, slower than others, and invariably faster than the Baby Beeches. And guess which 180 hp airplane is faster and has a better useful load -- a 172 or a fixed-gear Mooney (the rare M20D Master of the mid-1960s).

    More 172s have been sold than any other type in the history of general aviation, not because it blows the socks off everything else in the sky, but because it gets the job done competently and economically, boring though it may be. It's sort of aviation's Toyota Corolla.

    Full disclosure ... I own a 172. And a Corolla. :)

    The design goal of the 172, and its predecessor 170 back to 1948, was as an entry-level family cruiser and personal airplane. The 172 was never marketed as a trainer until after the demise of Cessna's 2-seat loss-leader trainer (150/152).
     
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  29. Tantalum

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    someone up thread insinuated that its performance was the best you can get based on its power and useful load and I used some modern-day examples to show that there is more performance to be had with the setup possible

    Something about the airplane always just uniquely irritated me, even though it climbs nicely I just never felt like it flew that well or was fun or enjoyable to fly, but I get that it gets its job done well

    I would buy a mid 70s Mooney any day over any Skyhawk, and it would probably save money..

    But different strokes for different folks, I get that

    No personal animosity towards any Skyhawk fans, I just never liked the plane
     
  30. Clip4

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    Yes, those pesky safety regulations keep a lot of experimentals off the market, some for good reason.
     
  31. Tantalum

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    some are good, and necessary. There's a reason the US has such a good aviation safety record, and I like knowing that the instruments in the airplane I fly are going to work especially when at night or IMC

    but there's also a lot of streamlining and clean up that could be done with the process.. pretty incredible that you have to almost quadruple the cost of something to put it in the certified world (new)
     
  32. Sundancer

    Sundancer Pattern Altitude

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    I have a lot o' time in 172s, though all with 180hp or more - the T-41, with 210hp was a far, far superior climber, compared to a 182. And handled much better. Then again, a wheel barrow handles better than a 182. . .
     
  33. Dan Thomas

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    I'm not a 172 fan either. I defend them because they can stand the student's ham-handedness and the Lyc is nearly bulletproof. They are a much more stable IFR training platform than the 150, especially on those hot and turbulent days. They are easy to maintain and there are plenty of aftermarket parts available, though that doesn't mean that a lot of flight school airplanes couldn't do with a lot more maintenance and some new aftermarket parts. 172s perform OK on their power. I wouldn't buy one because I'd prefer a taildragger like my Jodel. The Maule M4 appeals more to me. I like tube and fabric. And steam gauges. Simple airplanes are much more affordable for the average dude, but an awful lot of pilots want beauty and speed and will go up to their eyebrows in debt to get them.

    Cessna is owned by Textron, a huge company with deep pockets. That makes them a target for way too many lawsuits where the pilot went and did something dumb but the lawyers find ways to convince the juries that the fatalities were all Cessna's fault. So Cessna sets aside something like a third of the price of a new piston single to pay for insurance on that airplane for the 18-year liability period. That's one reason a 172 costs so much more than it should. Another is that the FAR 23 rewrite in the '90s demanded a bunch of stuff like the 26G front seats and 19G rear seats, and those cost way more to build. Fuel injection costs more.

    Sure, you can build an experimental for a quarter of the 172's price. But bill out your time and overhead at reasonable factory levels and see if it's still cheaper. And never forget that much of an experimental's performance comes at a cost of safety. They are more sensitive and their stall/spin behavior can sometimes be nasty, and they're not usually built with crashworthiness in mind. The average PPL is going to be in trouble real quick with some of those; not so with the 172.