A pilot who flew the Boeing 707 and 727 told me that ground effect on the 707 made it easy to do soft landings, "greasers" he called them. He thought the Boeing 727's triple slotted trailing edge flap arrangement did not produce as much ground effect and that it was harder to get soft landings. That and other reasons.
I never experienced a hard landing in my limited travels on the Boeing 707. I wonder whether the newer supercritical wings on modern jetliners and their various trailing edge flap arrangements produce ground effect like the 707.
I realize that ground effect is only one of a number of variables affecting the quality of landings and that firm landings are often the safest for existing field conditions.
Any thoughts on this subject?
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- BWIAirport
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Re: Ground effect during landing
I'm certainly no expert but I wonder to what extent the double-bogey nature of the 707 MLG contributes to the softer landings. In my experience (all newer aircraft than the 70/72), landings on double-bogey aircraft such as the 757 and A330 are always smoother than my 737 landings
Re: Ground effect during landing
convair880mfan wrote:ground effect on the 707 made it easy to do soft landings
convair880mfan, not 707, but on the KC-135, the potential to get a smooth landing had nothing to do with ground effect, but on the landing flap selection. The command standard for landings was Flaps 50 (full flaps) and as a result of the amount of drag associated with that flap setting, a firm landing was fairly common depending on when thrust was reduced to idle in the flare. There was nothing wrong with that--that is how Boeing designed the airplane to land. However, Flaps 40 landings were also permitted if required, i.e., gusty crosswinds or potential wind shear conditions, and it was much easier to get a smooth landing due to the reduced amount of drag. I knew some pilots who would intentionally select Flaps 40 landing if there were troops or Space A pax on board, conditions permitting.
You stated, "I wonder whether the new supercritical wings on modern jetliners and their various trailing edge flap arrangements produce ground effect like the 707."
You can get lots of discussion on this. I'm not sure it is accurate to say "produce ground effect like the 707." It is my understanding that various aircraft do not exactly "produce" ground effect; it is always there, equal to a distance from the ground up, half the length of the aircraft's wingspan. However, how aircraft react to the ground effect may vary depending on flap design or area ruling.
To be honest, I have never depended upon, or thought about, ground effect to help achieve a smooth landing. I just use standard visual cues and thrust reduction commensurate with the conditions.
e38
Re: Ground effect during landing
just to clarify my post above, which was very poorly worded,
aircraft experience ground effect when within a distance above the ground equal to half the length of their wingspan. How those aircraft react to that ground effect may vary based upon aircraft design.
However, having flown a couple of different types of aircraft, I have not been able to tell much difference on how those aircraft react to ground effect.
Perhaps other pilots have had other experiences.
I apologize for the confusion above.
e38
aircraft experience ground effect when within a distance above the ground equal to half the length of their wingspan. How those aircraft react to that ground effect may vary based upon aircraft design.
However, having flown a couple of different types of aircraft, I have not been able to tell much difference on how those aircraft react to ground effect.
Perhaps other pilots have had other experiences.
I apologize for the confusion above.
e38
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- dennypayne
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Re: Ground effect during landing
My stepdad flew both the KC-135 and the 727, and he always noted that it was inherently easier to drag an outboard engine pod on the former than it would be to have a wing strike the ground on the latter. So I'd say it was more incumbent on the 707 pilot to have a more gentle touchdown, however that might be accomplished, versus the 727 which could "get away" with a less stabilized arrival.
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Re: Ground effect during landing
I would say aspect ration, wing loading, and residual thrust at flight idle have more to do with a smooth landing than the airfoil profile. I've made really smooth and some firm landings in every type of airplane that I've flown.
Re: Ground effect during landing
The design of certain airplanes makes a difference in how conducive to smooth landings they are. The E Jet series seem to really be conducive to a smooth landing, while both the A32S and 737 get flown into the runway firmly. 787s seem to land ultra smoothly.
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