Airframes, Engines, and Systems

champThis is an Aeronca 7AC “Champ”. If you learned to fly in the 1950’s, you probably learned in one of these.  Or perhaps one of these: the classic Piper J-3 “Cub.”

j3Notice that when flying a Cub solo, you have to be in the back seat.

These airplanes had only 65 horsepower, so they weren’t going to win any speed or climb contests. But they were a delight to fly. If I had the choice I would teach all beginning students in airplanes like these.

champbareThis is what these airplanes look like without their clothes. You can see the welded steel fuselage, the wooden wing spars, and the metal wing ribs.

champfuselageHere is a Champ fuselage mostly covered, with fabric! It used to be cotton (or silk!) but these days is a stronger artificial fabric called Ceconite.

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In this photo you can see the wood spars and metal ribs that form the wing structure.

In contrast, here is an all metal wing without the skin.

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There are a number of ways to build aircraft structure. Because of the strength requirements, wings are usually built around two spars (front and rear) and ribs.

The fuselage can be built in a similar way, around a steel frame as seen above. But lighter structures can be made using monocoque (roughly, single-shell) or semi-monoqoque design, where the external skin bears most of the loads.

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Here is a detail of a metal structure during construction. Along the bottom of the photo you can see six rivet clamps, used during assembly. Each clamp is then replaced by a rivet.

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This is a replica of the aircraft the Wright brothers flew. They used wing-warping for roll control. As you can see, the elevators were on the front, ahead of the pilot.

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Through many flights (and some crashes) the Wright brothers got very good at flying what (by today’s standards) would be called a very bad airplane.

The Wright brothers invented wing-warping and three-axis control and then discovered the need for stability the hard way. Fortunately, the flying speed of their airplanes was about 30 mph, so they walked away from their crashes.

All this is leading up to WHY most modern airplanes look like this:

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The first thing to notice is that the airplane is like a dart: there is weight up front (engine) and there are tail feathers at the back. This is to make the dart or airplane fly nose first. If you throw a dart sideways, it will straighten out in flight as the center of mass takes the lead and the tail surfaces, on their lever arm, orient the system for the least drag.

The wing, of course, is the largest aerodynamic surface, because it has to generate lift equal to the weight of the airplane. The ailerons (green) move in opposite directions to roll the airplane around the longitudinal axis. 

The tail surfaces, out on their lever arm from the center of gravity, make the airplane fly nose-first, as we have seen. The attached control surfaces allow the pilot to change the way the airplane meets the air. The rudder (red) lets the pilot make the airplane fly slightly sideways, or to straighten it out if necessary.

The elevators (blue) require a few more words.  They control the airplane in pitch (they move the nose up and down), but they also (over a slightly longer term) control the angle at which the wing meets the air.  That angle is called the Angle of Attack, or AoA. 

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This is an airplane in a glide. Here you can see what I mean by “over a slightly longer term”.  Pull back on the wheel or stick, and the nose goes up and the airplane goes up – for a few seconds. Then it goes down again, at a lower speed and at a higher angle of attack.

 

These are the slides from the Airframes, Engines, and Systems Presentation of Nov 3 & Nov 10,  2015.

Following are 3 links to  .pdf’s of the slides on this page.

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PPLAircraftSystems2

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Nov 3 slides go here.

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