Why Do Biplanes Struggle Aerodynamically Compared to Sailboats?

[redfax]

My understanding is that biplanes are pretty awful aerodynamically, the two wings interfere with each other, and the reason they persisted as long as they did was the fact that box girders are easier to make strong than cantilevered wings.

But when I learned how to sail, they told me that a ship with a mainsail and jib (a sloop) is much faster than one with just a larger mainsail, and that this was due to airflow in the slot between the two sails.

Why do stacked airfoils work for sailboats, but not aeroplanes?

 

[russ_watters]

The mainsail and jib are not stacked, they only overlap partially.

The proper airfoil comparison is to leading edge slats. The slot helps keep flow attached at high angles of attack.

 

[SteamKing]

Biplanes have more drag than monoplanes, but with the extra wing surface, they can turn on a dime, so to speak, even more so with triplanes like the Sopwith Camel or the infamous Red Baron Fokker.

I'm not sure that you could consider biplane wing construction as a 'box girder' since you are missing the sides. The wings are held together with a few flimsy struts and some wires, hardly a robust method of construction. I think that biplane construction persisted for so long because early aircraft powerplants were so heavy and underpowered. Since low power also implies low speed, in order to be able to carry a useful load beyond the weight of the aircraft, a large wing area is required to generate the necessary lift. Biplanes provide this large wing area without exacting too significant a weight penalty.

In the 1920's and 1930's when more powerful aircraft engines came along, particularly the air-cooled radial engine, aircraft designers could explore new aircraft construction techniques because the wings did not have to be so big to keep the aircraft flying. Thus, monoplanes began to replace biplanes, and metal began to replace wood and fabric as construction material for the airframe and wings. Watercooled inline engines persisted for a time, mostly in single seat fighters, but until jets matured, the air-cooled radial engine was what led to the development of very large airframes in the 1930's and 1940's.

 

[Integral]

Nitpick the Sopwith Camel is a biplane.

The early multiwing planes had a lot of lift, had to because of their slow speed. The tight turn radius was only to one side that due to the huge torque of a massive radial engine. You could turn on dime as long as you turned the direction your engine wanted you to turn. The other direction was a different story.

 

[SteamKing]

Nitpick the Sopwith Camel is a biplane.

The early multiwing planes had a lot of lift, had to because of their slow speed. The tight turn radius was only to one side that due to the huge torque of a massive radial engine. You could turn on dime as long as you turned the direction your engine wanted you to turn. The other direction was a different story.

You're right about the Sopwith Camel. The Sopwith Triplane was unofficially known as the Tripehound, or simply Tripe, by its pilots.