Airplanes and sailboats

[sailortonyb Allied Mis]

Henk....

We would land slightly behind the point at which we 'launched'. Although ' a body in motion tends to stay in motion unless acted upon by other forces' may seem to apply here, there are other less obvious forces at work, such as gravity. When you are sitting down, you are moving with the airplane and your relative position to the plane itself doesnt change. However, once you are in the air, gravity will pull you down from an imaginary point in the center of the earth to your actual position in 'space'. The plane is moving forward, so if all else remains the same, the plane is traveling in an arc around and parallel to the earth and therefore the gravitational forces are constantly changing their relative position since gravity will always pull from the imaginary center of earth to your position. Imagine a split second lag in your forward speed while in the air while gravity pulls you down from where you used to was and is continuing to pull you down from those tiny split seconds all the time the plane is moving forward. So, Its not like you jumped up and the plane moved ahead a small bit and you fell straight down on that spot. You will actually be dropping down in an arc shape. If that makes any sense, someone please re-explain it to me. Tony B

 

[sailortonyb Allied Mis]

Stu.....

The airplane wing needs 40mph to fly. It doesnt care how it sees it, as long as 40mph is passsing over the wing, it will fly. If it were possible to hook up a cable, you might could fly the plane like a kite if the headwinds were over 40mphLets take the reverse of that. Lets say there is a 40mph tail wind and ignore ground handling capabilities for arguements sake. OK, you taxi down the runway with 40mph tailwind, the wing dont see its needed 40mph head wind so it wont fly. You then increse your ground speed to40mph. Now the wing sees zero mph headwind and it still lacks the 40mph headwind to fly. So, now we have increased the ground speed to 60mph. The head winds "appear" to be only 20mph, because of the 40mph tailwind. So, now we have to go to 80mph ground speed in order for the wing to feel a 40mph apparent wind or relative wind speed in order for it to fly.For those of you non-flyers, the plane holds up the wings ONLY WHEN ON THE GROUND. Once in flight, the wings now hold up the planes fuselage. Tony B

 

[tom]

Angle of Attack

Part of the dynamics of flight is the angle of attack. This is hte angle of the wing to the on coming airflow. At high speeds the angle of attack is less because at high speeds you generate enough lift for level flight at lower angles. I have never measured it but think that the wings of most planes are more or less level with respect to the ground...low angle of attack when parked. So probably the lift generated by surface winds is minimal. We used to lock our plane's elevator in a neutral position and this would help keep the plane on the ground. Finally if you fly a kite you know that if you let go of the string the kits falls. Drag pushes the kite backwards. The same thing would happen to a plane. When a plane is gliding you are trading elevation for forward motion. A Cessna 172 can fly about 11' forward for 1 foot downward. The exact ratio depends upon trim and wing loading. For sustained gliding you have to find air rising faster than your sink rate. In the mountains on a windy day the air is usally rising on the windard side and falling on the leeward. My instruments have indicated me ascending at over 1500'/min because of mountain winds. You don't want to be on the leeward side of a mountain on a windy day in a light plane. Actually most light plane pilots avoid the mountains except in calm conditions. That may be why so many sailers are also pilots. Windy days you go sailing..calm days you go flying.

 

[sailortonyb Allied Mis]

My flying experience.....

My flying experience is limited to dumb enough to teach myself to fly and lucky enough to live through it.Just imagine, your first flight is unplanned....that is, you want to practice going up 3 to 4 feet than landing again, over and over again. Do as the book says. Only problem is , none of the books said that when it lifts off, it wants to stay flying. After all take off speed is only about 20mph and you have a 10mph headwind. Panic sets in at about 500 ft when you are supposed to be only 3 to 4 ft. up.Lets see.....hanglider frame, snowmobile engine, motorcycle throttle, small bicycle wheels, ropes and pulleys for rudder control and lets not forget the velcro on the wings.Oh yea, put feet down on runway for brakes and have resoled often and never wear tennis shoes, or a scarf for that matter, the prop is behind you.

 

[tom]

Ultralight Flying can Have a Powerful Pucker

The Pucker Factor of flying is always there. My wife was unconcerened as we were landing one day until she noticed that my forehead was covered in sweat. We were landing in a 15-25 knot crosswind that was gusty. It took everything I had to land but we did land safely.  My first flying experience was powered parachutes. Basically a little cart with a motor and fan attached to a large square parachute. Man the pucker factor was extreme as I flew over a tree that I could almost touch. Then the landing !!!! It seems like you are going to poop between your shoulders from the impact but it really is an easy landing. It's just the visual perspective. Actually powered parachutes are probably the safest way to fly. But you are really out there. Climb up to 2-3000' and then wind gets a little gusty and you start making like a big pendulum. It feels risky but is really fairly simple to fly. Heck a dead man landed one safely... he was older and had a heart attack and died while in the air. The chute flew until it ran out of gas and landed itself in a field.  I've never flown any other type of ultralight but they look fun.

 

[mortyd]

answers

this web site has gone a long way in showing why it took the world now many wrong answers before wilbur and orville. not one correct vision yet.

 

[sailortonyb Allied Mis]

I figured it out......I think

One thing I think we overlooked and maybe its a matter of symantics. I havent had a physics class in almost 40 years , but here goes.....Weight is a function of gravity. When a bird or fly is flying, it is using its energy to keep itself suspended. So while flying, it has zero weight (theoretically) or gravity would pull it down and it would fall. Its own generated energy has enough energy to keep it suspended. If a bird takes off into flight, does the earth weigh less....YES YES YES. It weighs less to the amount of the birds weight plus the air it displaced which is negligable. OK, so where did the weight disappear to? The earths atmosphere now weighs more , to the tune of the birds weight less the displaced air. That is why, as someone said earlier, you cant weigh an airplane flying over a scale. So, the bird sitting in the plane adds weight to the plane, but if it takes off into flight in the plane, the plane just got lighter. It is not the same as a particle in suspension, because the particle in suspension is not generating its own energy to stay in suspension as a bird in flight does.Therefore it is also not the same as a fish in a bowl. The bowl will weight the same whether the fish is at the top or bottom, but if the fish jumps out(flies) then the bowl will be lighter. This of course is negating the miniscule gravitational forces of the differences of distance to the center of the earth (The further you are from the center of the earth, the less gravitational force).So, energy makes the difference. If you are weightless in the space shuttle, does it weigh less...YES. Everything in space is weightless (more or less), meaning....no weight. Actually, there is some calculable weight, because all matter has gravity. So if muscle action by touching a wall and being able to push away from it makes it only appear to be weightless, but theoretically, if you never moved, you would be eventually pulled to the densest part of the shuttle where the most gravity would exist, providing you were totally free from the earths and suns gravity.

 

[Jeff]

easy

This thread is too long to read all so please forgive if this is a repeat.Plane: Doesn't matter how fast the tarmac is moving, it matters how fast the plane is moving through the air. IE: if the plane is stationary and is riding a really fast conveyor running the same speed that the engines are pulling the plane, it won't take off.The boat with 10k head current and 10k WATER speed will not make WATER headway. Speed over land is a different and drastically more complex calculation and likely has nothing to do with the spirit of the question. The plane question is easier, either it flies or it doesn't.BTW, I used to fly out of Santa Paula and have seen a Aeronca Champion tail dragger fly backwards (intentionally) in 40+mph winds 600 feet over the runway.

 

[Ross]

MortyD It is a sad day when a man decides that

knowledge is a noun and must be closely guarded and not permitted to be touched by the unwashed masses. When the religious leaders of this world 500 years ago heard that there were people teaching a new science they used strong measures to suppress such heresy. I have always believed that knowledge was a verb and only useful when it was in action.

 

[tom]

Never Weightless

If a mass is experiencing the effect of gravity it has weight. A satellite stays in orbit because it is traveling so fast that as it falls it goes over the horizon so to speak before it can hit. It's centrifugal force exactly equals the gravitational pull if the CF is greater than G it goes to a higher orbit. If it is less than G it sinks to a lower orbit. An object that is floating is not weightless it is being buoyed up by the weight of the water it displaces. Airplanes are not weightless. In straight level flight the lift of the wings exactly equal the pull of gravity. If the lift is greater than G the plane climbs if less than G it descends. That is why when flying you apply full power until you climb to cruising altitude. Then you can back off the throttle for constant speed without climbing. In a Cessna 172 I usually cruise at about 110 knots. It will fly a little faster but burns a lot more fuel. It's kinda like hull speed. A given airplane can only go so fast. Inexperienced pilots can die by turning a plane at slow speeds. When you are turning some of the lift is used to turn the plane. Turn too sharply the wing stalls and the plane falls. In flight training you deliberately stall the plane so that you can learn how to recover. That's how so many ultralight pilots get killed. They stall the wing and don't know how to recover. Usually the wing on the inside of the turn stalls first and the plane goes into a spiral. Many planes can't recover from a spiral. The lift pushes air downward as the plane flies. The energy of the downward forced air keeps the plane flying. the same for a bird or a fly. If a bird or fly is completely enclosed with a plane it is part of the plane's mass. It doesn't matter if it is sitting or flying.

 

[Ross]

But Tom our resident aeronautical engineer

has stated as a matter of fact "that an object in flight is weightless, period". So I am bewildered, knowing that sometimes airplanes crash.

 

[mortyd]

answers

back to high school, tom. weight is a force, not a color, a shape, nor a pattern ; a force. if an object that has static weight is in equilibium because it is also creating lift equal to its static weight, it is said to be weightless. ok? unfortunately neither archimedes nor bernoulli knew anything about wing theory, which was dicovered by the wrights, and the wrights alone, so referring to them is as useful as asking me how to hit pedro matinez.

 

[Ross]

That means that my driveway is creating

lift and all this time I thought is was just laying on the ground. It doesn't rise or fall so it is in equilibriun. If it is in equilibrium it is because it is creating lift. There can't be any other explanation for it.

 

[tom]

Getting into Semantics

In common language things are often called weightless. But in physics weight is the mass of an object being accelerated by gravity. All of the planet's behave as they do because of weight. The weight is created by the sun's and the planet's mass. We usually ignore the mass of a person or a fly because it is so much less than the mass of the earth. It is really cool that the mass of the earth isn't uniformly distributed. They can measure the difference. In the old days they placed a lot of mercury on a balance on a ship and sailed it around the world mapping these changes in gravity. The weight of the mercury changed as it was moved over the irregular distribution of mass in the earth. They have much more sensitive instruments today. Supposedly the creation of so many manmade lakes has changed the center of mass of the earth enough to slow down the earth's rotation a measurable amount. You may have noticed that an ice skater's rotation slows as they extend their arms. It's the same principle. The lakes have mass that is farther from the earth's center of rotation than it would be in the sea.For what it's worth I used to teach high school physics.

 

[Stu Jackson]

OK, I'll try and answer, which is why I

asked about the planes before.1. Floating around the Internet is this theory: if a plane is on a tarmac that is moving at the same speed the wheels are turning, will the plane take off?The ground and the plane's wheels has absolutely nothing to do with it being able to fly. As someone noted, consider the ground moving like a big conveyor belt. Regardless of the direction of the belt or the location of the wheels, the ONLY thing that makes a plane fly is the speed of the air over the wings, which is not included in the question. The pleasant discussion about the tops and bottoms of turning wheels was very enlightening and helpful, but doesn't seem to apply here. No real question, no answer.2. So I present to you: a boats speed is 10 knots heading into a 10 knot current. Will the boat make headway? Headway appears to mean over the ground. If that's the case, NOPE, zero, zilch, nada. Assumes directly to avoid vectors. It will be showing 10 knots on the speedo, because that's what it's doing against the water. This one is basic navigation 101.Have at it.

 

[Ross]

I have never seen a 10 knot current and

I hope I never do. The water going over the dam when they open the flood gates isn't current it is Niagara falls. The water below the dam is fast but I doubt it is ten knots. I have never seen a purple cow either.

 

[sailortonyb Allied Mis]

Most interesting thread............

This has turned out to be the most interesting and mentally stimulating thread I have seen since i joined this forum. The battle of the experts here will rival the battle of the experts on Court TV.Credentials are starting to fly like Mardi Gras beads. To keep up, I have to think back 40 years ago in school. And probably, some of those theories no longer hold water. Speaking of which.....If I open my fly.................?

 

[Ross]

Tonyb, not opening and not holding water

can be complicating. I wonder where neutral buoyancy fits into this discussion. I like to take mylar ballons and ballast them until they have neutral buoyancy and turn them loose in a very large room. They follow the air currents and almost never stay in a single place in the room.

 

[sailortonyb Allied Mis]

Ross

This was so much easier for me to grasp when i smoked grass. Everything made sense then.  Tony B

 

[Dan Johnson]

Hey Stu...

What does the scale read when the brick comes back down on your head? LOL!!!