Finetuning the CG

How sensitive are Cessna 172s when it comes to maintaining proper CG*? It’s been a while since I have flown them, but I seem to remember from my past that small helicopters are way more sensitive to maintaining the CG within perimeters than airplanes are. However, I can imagine that the smaller the aircraft, the smaller the CG range will be. And I am open to learn more about it. Any CFIs in here?

I currently fly an aircraft which as an enormous CG range and doesn’t even have a chart for lateral CG. (Most helicopters I know not only worry about longitudinal CG but also lateral balance)
Although, like most aircraft I know, it prefers not to be in a high aft CG situation. Being out of aft CG is always bad from what I’ve seen or read (and experienced with my RC planes, LOL).
It would take A LOT of gum, however, to balance it with gum alone!

Or was Chuck just making excuses?

Not Chuck, I say! That would be a first 😉

*CG … Center of Gravity


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7 comments on “Finetuning the CG
  1. Karl Winters says:

    You should have worked Hans into a C.G. bit.

  2. Fbs says:

    Well, Cessna made the 172 very tolerant to CG and I’m sure it can even handle passengers (and pilots) like Hans – so the gum under the panel is definitely chuck’s reserve….and nothing to do with CG…

  3. DeanRW says:

    Since the advent of lead-free chewing gum, Chuck’s technique for controlling the CG must have been ineffective at best.

  4. Karel A.J. ADAMS says:

    Many thanks for the little footnote explaining the CG code – exactly what I have been clamouring for!

    About CG calculations: in my little bird (an Apollo Fox, similar to Eurofox, C42, Rans S6 & many more) it is no point of concern. The variables (humans and fuel and a tiny bit of luggage) are carried so near the main wing spar that it would be hard to load the bird outside CG limits. Still, one needs to carry a sheet of paper showing that the calculation has been done.

  5. Dopey says:

    The 172 isn’t that critical on CG, but, leaning forward and back a little bit will mess up trim–it can be fun to mess with a student by leaning forward in the middle of a steep turn to “check for traffic” and watch them lose altitude…this same technique can also be used to the pilot’s advantage when trying to keep tighter tolerances. (10 ft high? just lean forward a bit…)

  6. Franck Mée says:

    The C172 is quite tolerant to CG shift, but its balance still changes especially in situation like go-arounds.
    In 2017, my aeroclub had a C172 crash. The pilot, who had flown the 172 with an instructor only, was used to pull hard on the yoke during go-arounds. When he had to perform a go-around with three passengers (and the aft ones being not-than-thin), he pulled the yoke and stalled the aircraft. Fortunately, the left wing took most of the impact and though the aircraft was written-off, all four people escaped with minor injuries.
    Since then I’ve paid attention to this phenomenon and it’s actually quite obvious. The 172 (at least the R version we use) feels very nose-heavy without aft passengers nor luggage: you need to pull quite hard to take off and to transition from descent to climb. But at max weight and aft centering, you barely ever pull the yoke, even during take-off or go-around: as soon as you open the throttle, the nose rises quickly on its own.
    Other aircraft I’ve flown are more or less sensitive.
    The MCR4 gets off-balance way more easily (I do think putting a chewing-gum behind the panel would need you to re-trim it), but it’s always light on the controls so you keep watching your every move in any situation.
    The C177, TC160 and PA28 are less sensitive: they’re still pretty stable and nose heavy even with people and luggage in the back. (I actually loved flying the 177. It’s basically a 172 done right: less CG shift, better view during last turn, better performance…)

    Still, I’m pretty sure Chuck is not completely honest here. I mean, he got the CG right where he wanted, but it just needs a passenger getting a second slice of pizza to shift it again. 😀

  7. eekee says:

    I’m a Kerbal Space Program player who designs my own spaceplanes in the game, but I don’t feel experienced enough to design for CG range. Given that 70-80% of a typical Kerbal spaceplane’s takeoff mass is propellant and it’ll drain perfectly evenly from every tank, I don’t really have to.

    I’m not sure what I’m going to do in Juno: New Origins which drains tail tanks first. I guess I could divide tanks up so no one tank has too much of an effect and adjust fuel flow priority so some of the forward tanks drain first. It’s going to be a challenge when I also want the payload to be near the center of mass, but I think it’ll work.

    The real problem is that I don’t play with a joystick and thus want a plane which handles well enough to be flown on trim at high velocity. I really should just get a joystick. 🙂 Though having said that, it’s nice not to have too much drag from the tail when you’re trying to get as much speed as possible while using oxygen from the air.

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