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About Center of Gravity

All Terrain Vehicle Performance Chart

Hovercraft Center of Gravity

The Principals of a hovercraft are very similar to that of an airplane. There is a roll, yaw and pitch associated with a hovercraft. It is not critical to use the dynamics of math for the design since it does not fly high enough to matter in a roll, yaw, or pitch scenario! However, due to the lack of experience, it is possible to cause severe damage to the craft and other objects, and possibly death to the pilot and passengers.

As in the book by James Perozzo, "Hovercrafting as a Hobby," he uses the term “center of lift” instead of “center of gravity.” These terms are very similar, and we will use the term CG or center of gravity, clarified since Alaska has the largest concentration of small airplanes in one location in the world and these terms are more easily I cannot emphasize the importance of CG enough. I have seen many hovercraft’s flying characteristics fail in performance due the builder not recognizing the CG and not following the basic rule to keep it where it belongs on the hovercraft. As you build the hovercraft, check the position of the CG. See if it is following the manufacturer’s recommendation. The correct calculations can be found on page. 23 of Mr. Perozzo’s book.

To simplify some of the flying characteristics of a hovercraft is to simply adjust the cargo load to the correct moment by a calculation formula. In easier language, move cargo, fuel or persons to a slightly different location to correct for better performance. A hovercraft flies with a normal nose-up attitude or slightly higher angle of attack to the planning surface, this can be from a 3 to 6 degree nose-up attitude for correct cruising of the hovercraft. As the hovercraft increases in size so will adding a horizontal stabilizer will help perform this task. There are many other variations.

Generally the CG is a precise spot give or take a 1 inch or 2. The design of a hovercraft is built on this basic rule, which gets over looked really easy. Try to get the CG within an eighth of that recommended spot.

Here is what can help: Instead of using a 2x4 for the CG or balance point use a quarter inch dowel rod. This reason for this is it will help tremendously with anything you may want to add to the hovercraft. As you add in the front of the line of CG, so must you add in the back of that line? It will help to consider carefully what things you want to put on the hovercraft and how much weight you really do or don’t want to add.

Let’s say you add a pound to the rear of the craft, you will then need to add double or triple that weight to the front depending on where it is put. Remember, the closer to the CG the more you will need to add to correct the center of lift. The further away from the CG the less weight it will require less, but yet, still a lot more to stay within the correct moments of weight. A rough estimate is approximately 1/3 the distance from the rear of the hovercraft, much like finding the cord in a wing on an airplane for the CG or balance point. There are large values that were designed into that hovercraft that you don’t want to alter, since it will affect the flying characteristics. If the basic rules are followed and the hovercraft is kept as light as possible, flying will be more fun.

A hovercraft's proportions are generally a 2 to 1 in size relationship, meaning it is twice as long as it is wide.  A wider hovercraft is generally much more stable. On the other hand, as the hovercraft becomes longer, and without changing the width, it generally becomes more of a racer, or speedier craft and the stability decreases.

Air flow of a hovercraft

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