Bigger spinners !?

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Topaz

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Sure it is, if you're climbing at a constant airspeed and constant climb rate. But yes, it takes more thrust (power) to offset the fact that the gravity vector is no longer perpendicular to the direction of flight. But that's not the same thing as acceleration, which is defined as a change in velocity.

Dana
The issue here is gravity. In a turn, the acceleration is obvious, because there is no constant force imposing an acceleration in the horizontal plane. Vertically, it's a different story. An airplane is, in level flight, already accelerating at 32 ft/sec^2. While we call that "unaccelerated" in the pilot community, that's yet another case where we and the FAA get the facts completely wrong: the acceleration is not zero, it's actually 1g. In a climb - even a constant-rate one - the aircraft is accelerating vertically at a higher rate. If that weren't true, it wouldn't be climbing. The "g" loading is therefore higher than 1g, and that's the very definition of accelerated flight, even on the FAA's substandard terms.
 
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bmcj

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There is no such thing. While the airspeed may not be increasing, the total energy of the aircraft most certainly is, translated into a vertical velocity. This is no different than turning flight, where the increase in energy is expressed as a change in horizontal direction. In both cases, there is an increase in "g". If you are maintaining a constant positive vertical velocity against gravity, you are accelerating. If constant-rate-of-climb flight were non-accelerated, you could do it with the same power as level constant-airspeed flight. If you don't add extra energy, your vertical velocity will not be constant. It's the same as a turn, except that the acceleration is horizontal in the latter case. You can explicitly think of a turn as a "horizontal climb". The fundamental physics is exactly the same.

Look at it this way: In straight and level flight, you have added enough energy to the airplane (through the engine and prop) to counter a 32 ft/second^2 acceleration - that of Earth's gravity. In a constant-vertical-velocity climb, you have added more energy to create that climb. However, if you could magically increase the acceleration due to Earth's gravity, you could bring that climb back down to zero. Math being what it is, what you have done, even in a constant-rate climb, is accelerate away from the Earth at a rate that is higher than the rate imposed by gravity.

The only possible "non-accelerated" flight is straight and level at a constant airspeed.
Yeah, but gravity.jpg which means that gravity decreases as you move away from the Earth, so there! :pout:

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:)gig:)
 

Dana

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I see what you mean, but it's not acceleration. Gravity is a force that can cause an acceleration, unless opposed by an opposite force (e.g. lift).

A turn is acceleration because velocity is a vector, and you're changing the direction of the velocity vector. But in a constant rate climb, the force due to gravity is exactly opposed by lift (plus the small force added by the upward angled thrust line). Net force, and thus acceleration, are zero).

Dana
 

Topaz

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I see what you mean, but it's not acceleration. Gravity is a force that can cause an acceleration, unless opposed by an opposite force (e.g. lift).

A turn is acceleration because velocity is a vector, and you're changing the direction of the velocity vector. But in a constant rate climb, the force due to gravity is exactly opposed by lift (plus the small force added by the upward angled thrust line). Net force, and thus acceleration, are zero).

Dana
Check your physics books. An airplane in level flight is undergoing a 1g acceleration. Getting rid of the variables that confuse the issue, an airplane in level flight is undergoing an acceleration of 32 ft/sec^2. A climbing airplane is accelerating, in the vertical axis, at more than 1 g. You're acting as if an airplane in level flight (or constant climbing flight) isn't undergoing an acceleration, but it most certainly is.

Don't believe me? Look at the units in which gravity is expressed: ft/sec^2. That "squared" makes it an acceleration. You can express the weight (not mass) of something by the force imparted on it by the acceleration of gravity, but you don't express gravity as a force. It's an acceleration.

Take it another way: F = m*a. Weight is W = m*g. "g" and "a" are interchangeable because they're the same thing. "g" is just such a particularly common acceleration on Earth that we've given it it's own variable name, rather than defining the number every time.

Weight is a force.

Lift is a force.

Gravity is an acceleration.

Climbing requires that the airplane generate a higher acceleration in order for the airplane to move away from the Earth at more than the 32 ft/sec^2 acceleration which gravity imparts upon it in level flight.

Climbing, whether constant-rate or not, is accelerated flight, since the g-loading is more than 1. From a proper physics perspective, even level flight is "accelerated flight". Just because the bureaucrats at the FAA choose to call it something else doesn't make them right. Acting as if something magical happens when an airplane turns is disingenuous. The airplane is just accelerating more.
 
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bmcj

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I'm sorry Topaz, but I have to side with Dana on this one. AFAIK, in aviation terms, accelerated flight is flight in which the velocity vector changes, either in direction or magnitude (ignoring, of course, the curvature of the Earth or your distance from said mass). If climbing against gravity counts as acceleration (making it accelerated flight), then flying straight and level at a constant velocity should also be labeled as accelerated flight because you are still working against gravity, just not quite as much as you do when you climb. Climbing certainly adds potential energy to your equation, converted from the chemical energy in your fuel, but acceleration is generated by an imbalance of forces and you can balance your forces in a climb as easily as you can balance them in level flight. To argue that a steady-state climb is accelerated is, I think, a semantic argument at best.
 

Topaz

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I'm sorry Topaz, but I have to side with Dana on this one.
I'm sorry, too, because physics doesn't allow "sides".

AFAIK, in aviation terms, ...
There's the problem. The FAA came down and said "Level flight is unaccelerated." Unless that's happening in a straight line out in space somewhere, it's not true. The FAA doesn't get to define reality.

... If climbing against gravity counts as acceleration (making it accelerated flight), then flying straight and level at a constant velocity should also be labeled as accelerated flight because you are still working against gravity, just not quite as much as you do when you climb....
That description is exactly the case in the real world.

To argue that a steady-state climb is accelerated is, I think, a semantic argument at best.
No, it's an argument about reality versus an artificial definition imposed by bureaucrats. The latter bears no semblance to reality, and the difference is meaningful.

Again, I encourage you both to simply look at the units in which the quantities in question are couched. The only difference between "1G" and "2G" is that the latter is 32 ft/sec^2 faster acceleration than the former. A quantitative difference, not a qualitative one.
 
M

Manticore

Gravity is a force. The acceleration due to gravity is what you would get if the wings fell off.
 

Topaz

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Gravity is a force. The acceleration due to gravity is what you would get if the wings fell off.
Wrong.

If gravity were a force, it would be expressed in units of force: newtons, pounds-force, etc. It's not. It's expressed in ft/sec^2 or meters/sec^2. That means "distance per unit time, per unit time". Which is exactly the same units in which all other accelerations are couched. Weight is couched in terms of units of force, because F = mass*acceleration where, in the special case of weight, acceleration = "g" = 32 ft/sec^2, on Earth, anyway. Your planet may vary. Mass is an entirely different thing, independent of gravity, and has its own units: grams, kilograms, pounds-mass, etc.

Gravity is an acceleration, and what happens when the wings fall off is a change in the velocity vector due to the acceleration of gravity.

I'm done beating this horse, and this topic has gone completely off the rails because the FAA can't be bothered to stick to reality. Have fun guys, I'm out.
 
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bmcj

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Gravity is a force. The acceleration due to gravity is what you would get if the wings fell off.
Close, but no cigar!

Gravity is an acceleration (m/s**2)

Weight is a force generated by gravity acting on a mass

Wings falling off is a result of not mandating spin training (oops... didn't mean to go there! :gig:)



Topaz is right, this discussion has gone far off track from the original subject... we should split it off in its own thread.




I'm sorry Topaz, but I have to side with Dana on this one.
I'm sorry, too...
I know... we never disagree! Does this mean that the honeymoon is over? :(


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Sockmonkey

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Surprise, spinners are like every other part of the plane in that they need to be appropriate for it's speed, prop design, performance, and engine type.
 

Dana

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Actually gravity is a force of 32.2 lbf/slug. That causes an acceleration of 32.2 ft/sec². Acceleration is defined as the rate of change of velocity over time (ft/s per s). An airplane in level flight is no different from me standing on the floor. I'm not accelerating; my velocity is zero and it remains zero. The force of gravity acting on my mass is equal and opposite to the force of the floor pushing up on my feet.

Dana
 

StarJar

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...'cause you know, sometimes words have two meeenings.
I think Led Zeppelin wins. Maybe people who fly Zeppelins and hovercrafts are expert on this.
 
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mcrae0104

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Topaz is right, this discussion has gone far off track from the original subject... we should split it off in its own thread.
I present you with a new thread: Unaccelerated Climb

Topaz, I do very much hate bursting your bubble because I admire your tenacity. You are quite right that physics does not take sides; it only describes reality. I hope I have done so accurately in the new thread.
 

Retroflyer_S

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Biggest spinner could be made so that you look throught the spinner that is made outa plexi and prop would rotate around the fuselage like in Edson Fessenden Gallaudet seaplanes.

Wouldn't it be cool to be looking through the rotating spinner ?
 

Dan Thomas

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Biggest spinner could be made so that you look throught the spinner that is made outa plexi and prop would rotate around the fuselage like in Edson Fessenden Gallaudet seaplanes.

Wouldn't it be cool to be looking through the rotating spinner ?

The bugs would become a blur and not irritate me.

The rain would fly off nicely. Oh, wait, this has been done before. From Wiki:

A common alternative design used on ships, called a clear view screen, avoids the use of rubber wiper blades. A round portion of the windshield has two layers, the outer one of which is spun at high speed to shed water.

220px-Rotating_windshield_wiper.jpg
 

Retroflyer_S

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The bugs would become a blur and not irritate me.

The rain would fly off nicely. Oh, wait, this has been done before. From Wiki:

A common alternative design used on ships, called a clear view screen, avoids the use of rubber wiper blades. A round portion of the windshield has two layers, the outer one of which is spun at high speed to shed water.

View attachment 44408
Somehow I have a feeling you didn't quite get what I was after.
 
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