Aerodynamics of Hovercraft - Horowitz & Lopez

CLASSMATE QUESTIONS:
Samantha Goetz- How high do the hovercrafts usually hover, or does it depend on how big the craft is?
-we're not talkin' bout planes here, just a couple of inches.
Sonia Bansal- What is the usual efficiency of hovercrafts? (Lift power and height?)
-pretty damn efficient...
Sam Edwards - Are all hovercrafts fragile?
-If they are used on dangerous military operations, do you think they're fragile?!
Angad Sidhu - How much power would be required to lift a payload of X kg?
-to much math, ask another question....lol use website link it does all calculations.
Nauma Haider - Does any specific terrain affect the ability of the hovercraft? [i.e. terrain allows more lift?]
-it hovers, it doesn't even touch the terrain, try again.
James Song- In the future, would hovercrafts become more practical due to its efficiency? (i.e. outer space crafts)
-why would you hover in space, there is no gravity!
Brandon Siegenfeld-How do you stabilize a hovercraft in rough conditions Ex. waves in water?
-speed up grandma, the faster you go, the less rocking you will feel unless the waves are huge, like a tsunami.
Kevin Norris - What is the stopping distance of a hovercraft compared to a normal vehicle?
-no air friction so you never stop......never.....
Naveen Shetty - Can i go for a ride on your hovercraft?
-NO, paveeeen. You buggin.
William Chan - How practical are hovercrafts as compared to boats and trucks?
-very.
Greg Sturm - Does air resistance play a big role in hovercrafts since in the absence of friction it is the only backwards force on the hovercraft?
-Not really, greg, just put the petal to the metal and you will be fine...
Douglas Chin - Is a submarine/hovercraft hybrid vehicle possible? Could the body be depressed and the air supply cut off so it'll sink?


Hovercrafts

A hovercraft is a vessel that is capable of hovering over virtually any terrain, hence the name hovercraft.
Although it may seem straightforward, the physics involved make this simple concept much more complicated. The basic parts of a hovercraft are a given (i.e. body, engine, etc.), but the unique components are what separate this vehicle from everything else.
hovercraft2.jpgexternal image rc-hovercraft.jpg

The blueprints for a hovercraft call for several elements that are not traditionally used in vehicles.
The craft must have an open design in order to have a constant supply of air allowing it to maintain its hover and propel itself. The physics concepts for a hovercraft involve air pressure, lift, propulsion, volume, and friction. Categorizing these into upward lift and forward thrust is much easier; pressure, lift and volume relate to upward lift while friction and propulsion relate to forward movement.
The lifting of a hovercraft is the hardest part.
Many factors have to be taken into account in order to successfully lift the vessel several inches off the ground (check outhttp://www.rqriley.com/hc-calc.html to find out exact calculations). Movement starts by directing airflow underneath the craft which inflates a skirt, or air cushion. A ‘skirt’ is a flexible curtain attached to the outside perimeter of the craft. Once the air cushion is formed, the air escapes out of multiple holes at the bottom of the skirt. As excess air is pushed out from under the skirt, the downward force of the air produces an upward reaction on the craft, causing lift. The air pressure needed to lift the craft is different depending on the weight and area of each specific craft.

In order to find the air pressure needed, one can use the formula:

P = F/A with the values P, F, and A being the pressure of air cushion, the weight onboard the vessel (mass * gravity), and the area of the vessel, respectively. Then once this is calculated, one can find the volumetric flow rate as well as the lift power needed:
VFR = A*υ with the values VFR, A, and υ being volumetric flow rate, area of the vessel, and velocity of air discharge, respectively.
PL = P*VFR with the values PL, P, and VFR being lift power, pressure of air cushion, and volumetric flow rate, respectively. (More equations @http://www.arsp.sojo-u.ac.jp/acv/acv/design/lift.html)

It is important to know the air pressure needed for the lift of the craft. If too much pressure is applied, more lift will occur, causing the craft to tip.
If not enough pressure is applied, the craft will not lift at all, defeating the purpose.
Once the upward lift is in effect, how will the craft move?!
Well, because the craft is just floating over a surface and not actually in contact with it, there is practically no force of friction acting on the craft to hinder movement. With the elimination of friction, a second set of propellers, used for motion, will be sufficient to push the craft across surfaces. Devices such as turbines or blades provide the backward push on air to create the forward movement of the craft. In order to steer the vehicle, rudders are used to direct the airflow. Using kinematics equations, distance, velocity, and acceleration can all be determined. Equations from the upward lift section can also be used to find air pressure, volumetric flow rate, and power.
hovercraft1.gifexternal image activities_hovercrafts_clip_image001.jpg
The hovercraft is a very fascinating vehicle with a peculiar foundation.
The first commercial hovercraft was created by the inventor Sir Christopher Cockrell. By using two different sized cans, an industrial strength air blower and a pair of kitchen scales, Cockrell assembled his hovercraft. He placed the smaller can inside the larger can and used the hairdryer to blow air into the cans. The downward thrust produced was greatly increased when one can was inside the other rather than air just being blown into one can. He then designed and created a vehicle capable of hovering on a cushion of air. The first working example of a Hovercraft, known as the Saunders Roe Nautical, was shown to the public in June, 1959.

In the present day, hovercrafts have evolved into a large range of uses and activities.
Mainly, hovercrafts are used for transportation in cases where traditional vehicles are insufficient. They can replace boats because they are safer to use when navigating choppy waters and just faster in general. They can be used as ferries to transport people across bodies of water as well. Oil field companies use hovercrafts to transport equipment over mud and swamps that are too dangerous to cross otherwise saving time and money. Sometimes golf clubs even use hovercrafts to avoid the damage that ground cars make on their courses. Another use for a hovercraft is military and rescue missions. The coast guards for many countries use hovercrafts because they are quicker and safer than boats and can navigate any terrain, traveling from open water, to ice, to rough rapids, to pavement without difficulty in one easy step. The United States Navy uses hovercrafts as patrolling vehicles for land and water, which are fully armored and equipped with weapons. There are even entire fleets of tremendous hovercrafts holding several tanks and that are used in massive military operations, just recently as in Iraq in 2003. But that is not all, for the hovercraft can even be a recreational tool. Hovercrafts which hold one to two passengers are used for thrill and amusement rides across large fields or lakes. Yacht owners can use hovercrafts to transport people from their ship to the shore with ease. They can be used as scuba diving platforms that are more stable with their flat bottoms and they don’t require a dock or a boat slip. Hovercrafts can be used as a racing vehicle, and there are many competitions throughout the world. With hovercrafts becoming increasingly safer, quieter, and easier to use, the possibilities for this great invention seem endless.
hovercraftrace.jpgexternal image RM%20Iraq%20400.JPGexternal image mecosta.jpg









Works Cited:
http://www.quicktechhobby.com/Hovercrafts/what_are_hovercrafts.htm
http://en.wikipedia.org/wiki/Hovercrafts
http://www.sciencebuddies.org/science-fair-projects/project_ideas/Aero_p033.shtml
http://www.peterboroughhovercraft.com/ARTICLEmanyuses.htm
http://www.rqriley.com/hc-calc.html