The Cessna 120-140 Association Forum

What is a C-140’s glide ratio?

Unlike the later Cessna models, the C140 POH is rather sparse for technical data, including glide ratio data. However, the C140, C150, and C152 all used the NACA 2412 airfoil. Since the wing generates significant drag (because it generates significant lift), I would think the C140's glide ratio approximates that of the C150 and C152, which is about 9:1.

For reference, the NACA 2412 section L/Dmax of the plot for lift coefficient vs. drag coefficient is about 88:1 at Re = 3,000,000 (Re calc based on assumption of 60 mph best glide speed), but this is just for the two-dimensional wing (REF: Abbott & Von Doenhoff, Summary of Airfoil Data, NACA Report 845, 1945).

Seems like as many 120/140 s that are out there Cessna would have an updated POH

8337 wrote: ↑Thu Dec 06, 2018 6:52 am Seems like as many 120/140 s that are out there Cessna would have an updated POH

When the plane was certified, the only requirement was a one page "manual" Form ACA-309. The fact that there is a manual at all is unusual for planes of the era. Cessna added the manual in 1947. See Cessna Service Letters SLN-32 and SLN-40. Here's my ACA-309.

That’s pretty cool. ForeFlight seems to think the glide ratio is 10:1

That may be possible, but I suspect, in the real world, it's pretty optimistic.

6896 wrote: ↑Thu Dec 06, 2018 12:24 am However, the C140, C150, and C152 all used the NACA 2412 airfoil. Since the wing generates significant drag (because it generates significant lift), I would think the C140's glide ratio approximates that of the C150 and C152, which is about 9:1.

I apologize for my ignorance... how did you came up with that conclusion. I got this approx. glide ratio from the POH
C150 = 8.5 (14NM / 10k')
C172 = 9.1 (15NM / 10k')
C152 = 9.7 (16NM / 10k')

Or you can do a little testing

Horizontal Distance Traveled

Change in Altitude in Feet

Divide the Distance Traveled by the Altitude Loss

For example:

5 miles Traveled with a loss of 3,000 Feet
(*change the distance of 5 miles to feet-26,400 feet)

Use the formula - 26,400/3000=Glide Ratio of 8.8
Therefore, if you lost power at 3,000 feet you will travel approximately 9 feet for ever loss of 1 foot

If you experiment with the aircraft at different weights remember that the glide ratio will be approximately the same, but at a heavier weight the glide will need to be made slightly faster. Wind will also make a difference; therefore, you can experiment with different indicated airspeed values in different amount of wind, i.e. 0 - 10 knots for example, to see how much distance you an can cover. You probably will find that around 65-70 mph will give you a pretty good glide ratio.

maverick_fa wrote: ↑Mon Mar 21, 2022 2:48 pm

6896 wrote: ↑Thu Dec 06, 2018 12:24 am However, the C140, C150, and C152 all used the NACA 2412 airfoil. Since the wing generates significant drag (because it generates significant lift), I would think the C140's glide ratio approximates that of the C150 and C152, which is about 9:1.

I apologize for my ignorance... how did you came up with that conclusion. I got this approx. glide ratio from the POH
C150 = 8.5 (14NM / 10k')
C172 = 9.1 (15NM / 10k')
C152 = 9.7 (16NM / 10k')

Interesting numbers I’m skeptical because a 150 is a lot less draggy airframe than a 152. That omnivision rear window is a lot of drag. The 150 ought to have a better glide ratio than the 152.
Just realized newer 150’s had the window.
The 140 ought to have the least drag as it has no nose wheel and a lower drag fuselage (no rear window). it’s not the window, it’s the shape.

a64pilot wrote: ↑Thu Dec 06, 2018 12:24 am Interesting numbers I’m skeptical because a 150 is a lot less draggy airframe than a 152.

Take a look at the POH