SpainCub
Well-Known Member
Howdy all, it’s been a while… I was looking at some of the data I have collected in the ~3K hour I have been flying my Cub. On it, I can see that I can consistently land my Cub at around ~32mph airspeed, since most of my landings have been at 900ft elevation… I was trying to see how well I did when I was flying at nearly ISA sea level, and I was consistently still landing at 32mph, Ok, here is the question… I was calculating Cl at my landings and I was surprised… is this math correct?
Formula for lift coefficient (Cl) for the given values:
Cl = 2 * Weight / (ρ * V^2 * A)
Datapoints
Cl = 2 * Weight / (ρ * V^2 * A)
Substituting the values into the equation:
Cl = 2 * 800 kg / (1.225 kg/m³ * (13.8 m/s)^2 * 16.58 m²)
Calculating the expression inside the parentheses:
Cl = 2 * 800 kg / (1.225 kg/m³ * 190.44 m² * 16.58 m²)
Simplifying further:
Cl ≈ 1,600 kg / (1.225 * 190.44 * 16.58) kg·m⁴/m⁶
Cl ≈ 1,600 / (49,853.55) m⁻²
Cl ≈ 0.0321
Am I getting this completely wrong? I‘m landing my cub under 300ft consistenly, and I’m not pushing the breaks much… this surprised me as I have data points to tell me the Stall is reach very, very close to this value, less than 15% variance… with a +- 5% instrument error… am I doing the math completely wrong
or is is a self realization that I’m a terrible flyer ? 
The lift coefficient (Cl) for the given values is approximately 0.032 which is substantially less than Cl_max of 1.8 for the USA 35B MOD? I don’t have AOA data for the landings, lets say, is high from my pov, I do however have really good data for the wind speed at touchdown with an arduino and a giro to align the wheels touching down to the two PCE-HWA-30 anemometer at each of the wings, 75% from root of wing. I am flying the airplane near maximum loads, and if the weight decrease, so should the Cl at landing… what gives?
Formula for lift coefficient (Cl) for the given values:
Cl = 2 * Weight / (ρ * V^2 * A)
Datapoints
- Weight of the airplane: 800 kg * i’m sus ing the max load I ever put on my cub, and I have practiced landings on this weight to support my assumptions.
- Wing area: 16.58 m²
- Stall speed: 13.8 m/s
- no air preasure data, we still need the air density (ρ), assuming standard sea level conditions, which is approximately 1.225 kg/m³
Cl = 2 * Weight / (ρ * V^2 * A)
Substituting the values into the equation:
Cl = 2 * 800 kg / (1.225 kg/m³ * (13.8 m/s)^2 * 16.58 m²)
Calculating the expression inside the parentheses:
Cl = 2 * 800 kg / (1.225 kg/m³ * 190.44 m² * 16.58 m²)
Simplifying further:
Cl ≈ 1,600 kg / (1.225 * 190.44 * 16.58) kg·m⁴/m⁶
Cl ≈ 1,600 / (49,853.55) m⁻²
Cl ≈ 0.0321
Am I getting this completely wrong? I‘m landing my cub under 300ft consistenly, and I’m not pushing the breaks much… this surprised me as I have data points to tell me the Stall is reach very, very close to this value, less than 15% variance… with a +- 5% instrument error… am I doing the math completely wrong
or is is a self realization that I’m a terrible flyer ? The lift coefficient (Cl) for the given values is approximately 0.032 which is substantially less than Cl_max of 1.8 for the USA 35B MOD? I don’t have AOA data for the landings, lets say, is high from my pov, I do however have really good data for the wind speed at touchdown with an arduino and a giro to align the wheels touching down to the two PCE-HWA-30 anemometer at each of the wings, 75% from root of wing. I am flying the airplane near maximum loads, and if the weight decrease, so should the Cl at landing… what gives?
