Very often, I see people write that low-wing planes like my Piper Warrior have a longer flare (i.e. they float longer) than high-wing planes like the Cessna 172, usually based on the argument that lower wings benefit more from ground effect.
In fact, that does not seem to be the case: the numbers in the POH all indicate that the Warrior actually has a slightly shorter flare and shorter landing distance than the 172. My own personal experience is more dramatic: I find that the Warrior’s flare decays very rapidly at the end compared to that of the 172, and it took me a while to learn to land the plane smoothly without dropping a foot or two at the end. Other Piper owners have reported similar experiences, though, obviously, the differences are much smaller than going from either the Warrior or the 172 to a more heavily wing-loaded plane like the 182. The condition and rigging of any individual plane will also make a huge difference — if someone is flying battered, badly-rigged 172s and then switches to a clean, well-rigged Warrior, the Warrior will certainly flare better.
So what’s going on? Why would a plane with lower wings and about the same gross weight float less, when the wings are closer to the ground and should benefit more from ground effect? Here are two possibilities:
- The Warrior has a wing loading of 14.4 lb/ft^2, vs 13.8 lb/ft^2 for the 172P. That’s not a huge difference, but it will affect the plane’s floating ability. By comparison, the Cessna 182P has a wing loading of 16.9 lb/ft^2 (note that all of these apply at maximum gross weight, not with just one or two people on board).
- The Warrior’s wings have a lot more dihedral than the 172′s wings. Low-wing planes need more dihedral to get the same roll stability as high-wing planes, and the dihedral creates a lot of drag, as well as putting the wing tips (though not the roots) fairly high off the ground. Both the dihedral on the Warrior and the wing struts on the 172 cause drag, but I suspect that the struts produce only parasite drag, which is fairly constant, while the Warrior’s dihedral affects induced drag, which can increase dramatically near the stall (hence the abrupt end to a Warrior’s landing flare).
Basically, these two factors overwhelm any benefit gained from ground effect, increasing the Warrior’s stall speed and decreasing its flare and landing distance compared to the 172, as can be verified by the numbers in the POH. With no flaps, the 172P stalls at 51 kcas (44 kias), while the Warrior stalls at 56 kcas (50 kias); with full flaps, the 172P (with its huge fowler flaps) stalls at 40 kcas (33 kias), while the Warrior stalls at 50 kcas (44 kias) — since both planes have the same approach speed, a higher stall speed means a shorter flare.
As a final confirmation, the published landing distance over a 50 ft obstacle at sea level/ISA/maximum gross weight is about 50 ft longer for a 172P than a Warrior.