Never run out of altitude and airspeed simultaneously..

[vintage1]

http://news.bbc.co.uk/1/hi/world/8150639.stm

[MCarlton]

"so, I'm virtually stalled, heading down, if I pull this back REALLY hard, will that help?"

http://i67.photobucket.com/albums/h300/NariaAmore/Random/double-facepalm.jpg

[JetPlaneFlyer]

As a regular cyclist i've had to take avoiding action on a number of occasions when cars have pulled out accross the road in front of me, and once or twice with a bus... but i've never had that problem with a plane!

I think those cyclists should consider themselves VERY lucky...

Steve

[GeeW]

I dont know about the cyclists. I think the pilot was bl***y lucky. I believe he got out alive but damaged.
Not many outlive a virtual spin-in....


Gordon

[vintage1]

I wonder if that clip is viewable outside the UK?

Perhaps it was a 'downwind turn' ;).. it certainly looked like he suddenly ran out of airspeed when he didnt expect to..the nose is way up coming out of the dive..

[Montag DP]

I wonder if that clip is viewable outside the UK?

Perhaps it was a 'downwind turn' ;).. it certainly looked like he suddenly ran out of airspeed when he didnt expect to..the nose is way up coming out of the dive..I could view it fine, at work no less.

[HerkS]

Looked to me as if the spin went flat.

Very difficult to recover from a flat spin.

[kcaldwel]

And then a high speed stall trying to hurry the pull-out.

Kevin

[bwalt822]

It sounded like his engine didnt power up which could have contributed. Hitting belly first is better than nose first.

Also I think he went around 1 more time than he wanted to.


Edit:
Wait I just read vintage's comment, definitely the downwind turn.

[Work in Progress]

This is the guy in the Pitts in Germany. He spins more turns than he ought to, for whatever reason, and then has insufficient recovery height. Almost certainly in the pre-stall buffet all through the pull-out, and mushes in. The 'pull' instinct is not your friend in these matters.

[vintage1]

This is the guy in the Pitts in Germany. He spins more turns than he ought to, for whatever reason, and then has insufficient recovery height. Almost certainly in the pre-stall buffet all through the pull-out, and mushes in. The 'pull' instinct is not your friend in these matters.

I agree..the angle of attack was vilely large as he approached the deck. I am surprised that the engine didn't have enough power to pull him out.

[Work in Progress]

Let us analyse...

The Pitts family comes in myriad variations but let's assume it is a fairly typical single-seat Pitts, of which the Lycoming AEIO-360 powered (nominally 180 hp) S1-S is the most common big-engined version.

Weight probably 1100 lb. The nominal 180 hp Lycoming generally gives between 165 and 170 flat out when dyno'd, and it's a fixed pitch prop so unlikely to be at full power RPM during the manoeuvre. But if we say 164 hp output that's a handy 120 Kw. 109 watts / lb, equivalent to 145 watts / lb input on a 75% efficient electric setup. Not all that much really, given that it is a very draggy aeroplane with a pretty high wing loading (around 11 lb per square foot).

I haven't flown an S1 but have flown the 200 hp S2A and 260 hp S2b with constant speed props. They are fun machines impressive by the standards of the average lightplane but every Formosa at the modelling field is way overpowered by comparison. With its higher wing loading and low aspect ratio wing your Sharkface actually flies in a fairly Pitts-like way. Keep the AoA modest and it will climb to the stars but get it slow and pull hard and I can imagine that doing the same as the Pitts in the film, at least on the props I fly it on.

[BMatthews]

I know we're all arm chair quarterbacks in this but I have to agree that it sure looks like the spin suddenly got more serious than he wanted it to get and that delayed his pullout. From that point he was in the toilet and it was just a case of minimizing the damage. Yeah, he pulled too hard and stalled it but really what choice did he have? No room to let it dive for speed as far as I can tell although a little LESS pull at the first part may have let him pull harder as he got near the ground...... like I say, we're armchair quarterbacks on this one..... If he had let it get speed back by not pulling up so soon maybe he would have just dove in sooner instead of stall/pancaking it. And it's hard to say if the engine acted up due to the extra spin or if he was late adding throttle or if it's just the delay in the sound reaching the mic on the camcorder.

[Work in Progress]

Fair point, Bruce: as I said in my first post, the root cause of the crash was that he spun more than he had safe height for, and once he stopped the spin his available recovery height may well have been inadequate regardless of pull-out technique.

[vintage1]

Put a 6x5.5 on that sharkfish WIP.. Fully vertical, and pretty fast too. Probably 60-70mph. Which is enough for 22" of assorted balsa sticks.

[Work in Progress]

I will do when I fly it next. It is in the rare and heavenly "not broken" state at the moment so likely to get a go next weekend, if it stops raining for five minutes.

[fhhuber506771]

The news report says he hit a CAR.
The video looks like he hit people on bicycles...

It appeared to me that he saw he was going to hit someone in his pull out and grabbed more elevator to get the nose higher.
That probably kept the prop from hitting someone which would have been MUCH worse for the people he hit but guaranteed he was going to crash rather than potentially make a touch and keep going.

I think he kept his wits and did the right thing after the over-rotated spin.

************

Yes, we are armchair quarterbacking... and a lot of this is guesswork with bennefit of hindsight. (and the limited single camera viewpoint...)

[Work in Progress]

I think you are reaching a bit there.

At high AoA in a Pitts you can't see anything ahead within about 25 degrees of the centreline - the outside world ahead is invisible behind that big flat engine - so you are in no position to be making decisions about individual pedestrians, cyclists, cars or whatever. At that stage pretty much all he could do was wait to see what happened.

His ability to influence matters diminished greatly once he had decided to enter the spin at low level and diminished a big step further when he failed to recover cleanly.

Speaking generally rather than about this specific case the Pitts S1 / S2 family are known as some of the the cleanest and most predictable spinning aeroplanes in the world - they are perfect for demonstrating the various erect, inverted, flat and accelerated spin modes responding normally to all the classic control variations in terms what you do with the ailerons and power on / off. They come out very quickly with either the classic recovery technique or with the last-resort Beggs - Mueller recovery. But, being small and highly loaded, they do rotate fairly quickly and it is not unknown for people to lose the picture in terms of how many turns they have done, or even to confuse a normal spin with an inverted spin, and take the wrong recovery action.

[biber]

I've seen discussions popping up all around the internet on this particular crash
and rarely has it been dealt with as proficiently as in this small and special corner of the online world.
Lots of expertise meeting here, honestly.
I think you have pretty much nailed it.

biber

[funfly2]

This one was not a spin and the power seemed to be set to WOT...
Yet, less lucky.
R.I.P.

http://www.youtube.com/watch?v=2vOUUT3FNx4&feature=related

[Work in Progress]

A well known case, the fatal loss of the Rolls-Royce owned Spitfire XIVc, G-AGLT / RM689

Hot day, higher density altitude than in previous similar displays and a higher fuel load than normal for display flying, so performance was reduced. Failed to make the go / no-go threshold height at the top of the loop, and carried on round anyway. The usual escape plan if the height and speed are wrong at the top of a low-level loop is to unload to zero G at the top, and simply half-roll out. If too slow, wait for the nose to float down a bit as the speed builds gently and then roll out.

[bwalt822]

or maybe it was a downwind loop...

[JetPlaneFlyer]

The Spitfire crash is very tragic..

Even so I could not help but snigger at the 'downwind loop' quip.. nice one!

Steve

[JaRaMW]

or maybe it was a downwind loop...

If you weren't from over the pond, I'd say british humour at its finest :D
Seriously, as if the death of the pilot would not be disastrous enough, it hurts to see such a beautiful plane go in. Happens way too often IMHO...
I see no need for low alt aerobatics in such machines, after all their handling is quite tricky. It is amazing enough to experience a low pass of such a plane or just watch them do some mild mock dogfights up there.

Back to the Pitts crash. I think it is really pointless to speculate here. The time from realizing that it won't work to the crash is way too short to think about some cool alternatives. Either you already have a backup plan or you just revert to basic instincts and pull like a maniac, hoping that somehow everything goes well.

[funfly2]

or maybe it was a downwind loop...
or maybe not...
But a strong head wind at the end of the loop might have saved the plane and pilot's life...

[Brandano]

not enough airspeed means not enough airspeed regardless of the way the wind is blowing

[funfly2]

not enough airspeed means not enough airspeed regardless of the way the wind is blowing
That's obvious but doesn't prove my statement untrue.
A strong head wind at the end of the loop might have prevented the crash, whereas a strong tail wind at the end of the loop might have caused it.

[Montag DP]

That's obvious but doesn't prove my statement untrue.
A strong head wind at the end of the loop might have prevented the crash, whereas a strong tail wind at the end of the loop might have caused it.Only if it was a gust. If it was a steady wind that was present the whole time, it wouldn't have made a difference.

[fhhuber506771]

That's obvious but doesn't prove my statement untrue.
A strong head wind at the end of the loop might have prevented the crash, whereas a strong tail wind at the end of the loop might have caused it.

Only a strong GUST of headwind would have had any effect...

He had inadequate airspeed and altitude to complete the loop... only something that altered airspeed could have helped.

When a plane is flying in a constant speed air mass... ground speed has no effect on aircraft performance. the aircraft's "relativity sphere" is based on the air mass, not the ground. The only effect the ground has is that it provides a hard limit on minimum altitude.

[funfly2]

Not only a gust, a sudden change in flight direction may give the same result as a gust.
A gust results in a sudden change in airspeed.

The plane is not carried by the mass of air as a balloon is.
If a plane were flying at say 300mph ground speed and the air suddenly disappeared it would keep moving at that speed (due to inertia) while gradually falling to the ground due to gravity, like a bullet or a rocket.
Just assuming that a plane is always carried by a mass of air regardless its manoeuvres is an oversimplification.

What carries a bullet? Would a bullet or rocket suddenly stop moving or fall to the ground if the air suddenly disappeared? No.
The bullet tries to keep its ground speed, the air is just a brake that slows the bullet down.

The same principle applies to the plane, it needs air to keep altitude but it doesn't need air to keep its ground speed if you use rocket propulsion.

[fhhuber506771]

Not only a gust, a sudden change in flight direction may give the same result as a gust.
A gust results in a sudden change in airspeed.

The plane is not carried by the mass of air as a balloon is.
If a plane were flying at say 300mph ground speed and the air suddenly disappeared it would keep moving at that speed (due to inertia) while gradually falling to the ground due to gravity.
Just assuming that a plane is always carried out by a mass of air regardless its manoeuvres is an oversimplification.

What carries a bullet?

a sudden change in flight direction will always mean a sudden increase in drag due to control deflections and the G load on the wings needed to produce the change in the "velocity vector" Thei invariably means a REDUCTION in airspeed.

A gust can potentially increase or decrease airspeed.

and the argument that if the air suddenly dissapeared is just pure bull.
Create such a condition.

Once the space shuttle is in orbit the direction it is orbiting the earth is of no consequence... except in the "east to west" path being typically used being convenient for aiding in reducing potential collisions with other orbiting objects. So once again ground speed becomes irrellevent.

[funfly2]

a sudden change in flight direction will always mean a sudden increase in drag due to control deflections and the G load on the wings needed to produce the change in the "velocity vector" Thei invariably means a REDUCTION in airspeed.That's just One of the factors.

So what carries a bullet?
The bullet tries to keep its ground speed, the air is just a brake that slows the bullet down.

The same principle applies to the plane, it needs air to keep altitude, but it wouldn't need air to keep its speed if you used rocket propulsion.

[fhhuber506771]

That's just One of the factors.

So what carries a bullet?
The bullet tries to keep its ground speed, the air is just a brake that slows the bullet down.

The same principle applies to the plane, it needs air to keep altitude, but it wouldn't need air to keep its speed if you used rocket propulsion.

The bullet is carried by momentum and SLOWED DOWN by air reistance. What the ground is doing under it does not matter... wind direction will affect its flight path.

When a sniper takes his shot from 800 meters he has to take WINDAGE into account. he doesn't have to take potential ground movement into account unless the TARGET is going to be moved by it.

Sorry all of your false arguments will fail.

[funfly2]

The bullet is carried by momentum and SLOWED DOWN by air reistance. What the ground is doing under it does not matter... wind direction will affect its flight path.
So why don't you accept the fact that the plane also has momentum?



When a sniper takes his shot from 800 meters he has to take WINDAGE into account.Yes, the bullet is affected by the wind but it is not carried by the air.


.

[Brandano]

I'll delete this post since apparently it was considered trolling... no great loss seen it's quoted in it's entirety below...

[funfly2]

Look, please take some flight lessons. And a physics course. However, I have little faith that any explanation of how the world actually works will be enough to move you away from your prejudice (from wikipedia: "any unreasonable attitude that is unusually resistant to rational influence." http://www.worldofquotes.com/topic/Prejudice/index.html ).The fact that you don't fully understand physics doesn't give you the right to spew derogatory comments, which by itself proves your lack of education.


.

[fhhuber506771]

The fact that you don't fully understand physics doesn't give you the right to spew derogatory comments, which by itself proves your lack of education.


.

We are pointing out that YOU don't understand physics.

You are the one lacking education.

[bwalt822]

hahaha, look what ive done.

Funfly, If I am going up an escalator and you are going down the other side, if I stop and start running down the side going up, does it effect you in any way?

Guys, until funfly can realize that energy and momentum are properties of motion and that they do not determine motion it is hopeless.

The only thing that can influence motion is a force. Until funfly can show me how simply having momentum or energy imparts a force of any kind his argument is completely ridiculous.

Another question funfly, do you believe that the only thing that can influence the motion of an object is a force? My definition of influencing motion means to give it an acceleration of some kind.

[Brandano]

Incidentally, check the direction of the smoke as the firetrucks reach the scene. The plane was doomed the second the pilot got to the apex of the loop. He probably watched the runway and judged his groundspeed to be too fast to complete the loop, so he cut down on thrust.

[funfly2]

We are pointing out that YOU don't understand physics.

You are the one lacking education.Instead of addressing my question in a proper and civilized manner you chose to start with accusation and personal attack.

Again:
Why don't you accept the fact that the plane also has momentum?


I've debunked you and you're too proud to admit you're wrong and I'm right.

.

[JetPlaneFlyer]

Funfly,
We have been here before and I know that there is no argument (no matter how well supported by science, or how well argued by highly qualified persons) is going to change your belief that motion of ground somehow effects planes in flight.

So I'm not even going to try to convice you otherwise but it really would be best if you dont go accusing people of not understanding physics (especially in capitals).. because it only makes you look foolish to those who do understand.

Steve

[vintage1]

Once upon a time, there was a man, who used to go around in south America, reading loudly from many books he had, and gathering a crowd, none of whom could read and all of whom were very impressed.

One day a man from the city came by and stopped to listen and walked up to the man and noticed that he had the book upside down. 'You are not reading that book : Its upside down' There was a deathly hush..then..'What difference does it make to which way up the book is, to a man who can READ?!'

:D

[fhhuber506771]

Instead of addressing my question in a proper and civilized manner you chose to start with accusation and personal attack.

Again:
Why don't you accept the fact that the plane also has momentum?


I've debunked you and you're too proud to admit you're wrong and I'm right.

.

I responded to and debunked EVERY one of your claims...

And any physics instructor worth his degree will back me up... and tell you to go back to 3rd grade

[bwalt822]

Funfly, why do you always ignore my straightforward statements and questions? I will give them again below.

Nobody is denying that a moving object has momentum.

The only thing that can influence motion is a force. Until you can show me how simply having momentum or energy imparts a force of any kind your argument is completely ridiculous.

Another question funfly, do you believe that the only thing that can influence or CHANGE the motion of an object is a force? My definition of influencing motion means to give it an acceleration of some kind.


Instead of addressing my question in a proper and civilized manner you chose to start with accusation and personal attack.

Again:
Why don't you accept the fact that the plane also has momentum?


I've debunked you and you're too proud to admit you're wrong and I'm right.

.

[JaRaMW]

Not only a gust, a sudden change in flight direction may give the same result as a gust.
A gust results in a sudden change in airspeed.

The plane is not carried by the mass of air as a balloon is.
If a plane were flying at say 300mph ground speed and the air suddenly disappeared it would keep moving at that speed (due to inertia) while gradually falling to the ground due to gravity, like a bullet or a rocket.
Just assuming that a plane is always carried by a mass of air regardless its manoeuvres is an oversimplification.

What carries a bullet? Would a bullet or rocket suddenly stop moving or fall to the ground if the air suddenly disappeared? No.
The bullet tries to keep its ground speed, the air is just a brake that slows the bullet down.

The same principle applies to the plane, it needs air to keep altitude but it doesn't need air to keep its ground speed if you use rocket propulsion.

"A strong head wind at the end of the loop" is the same as a gust, so what's the problem? A strong constant wind, no matter what speed and direction, wouldn't have prevented the crash unless you get picky about wind gradients which, in this case, would probably be of very little noticeable effect for any non-hurricane wind conditions anyway. I guess this has been clarified to death already in many downwind-turn discussions. The same would be the case if for whatever reason the ground would start moving around while the Spit was maneuvering.

The plane's maneuverability doesn't care about its momentum relative to the ground. Why? Because you can just as well calculate energy and momentum relative to any other inertial system (i.e. any coordinate system which does not change its state of motion) and always obtain the same physics. It's just a matter of convenience. Take the ground if you like as long as there's no earthquake (this oscillation turns it into a non-inertial system). Take the surrounding air as long as its velocity vector does not change. Take the sun as long as the observed time interval is small enough to neglect earth rotation and curvature of it's path around the sun. Take any imaginary point moving at whatever constant speed. Same result: you get completely different values for energy and momentum and the plane still behaves the same because its change in motion is affected only by the aerodynamic forces which are given by its motion through the air and gravity, which is constant. The ground is only for the crash.

[bwalt822]

Most of us know that you are right but it is surprising that so many pilots will disagree and think that a planes momentum relative to the earth effects its fight characteristics.

I guess its because a not instrument rated pilot's main input is their eyes so they try to relate the behavior of the aircraft to what they see which is the ground and not the air. I wonder why there are no downwind turn incidents under instrument conditions...

[funfly2]

Funfly, why do you always ignore my straightforward statements and questions? I will give them again below.

Nobody is denying that a moving object has momentum.

The only thing that can influence motion is a force. Until you can show me how simply having momentum or energy imparts a force of any kind your argument is completely ridiculous.Whenever you say motion, unconsciously or not, you have a reference point.
So, the plane is in motion in relation to what?
The air is in motion in relation to what?

In our case we have the ground, the air and the plane, and when the plane is in motion in relation to the ground it's usually also in motion in relation to the air, but not always.

In a strong head wind the plane is in motion in relation to the air but may be motionless in relation to the earth.
Also when we say "strong wind" we mean that the air is in motion in relation to the earth.

Well, I assume this is quite obvious for everyone so far...

If a plane is moving in relation to the earth it has momentum in relation to the earth - you may also call it a reference frame.
The plane may have a certain momentum in one frame of reference, but a different momentum in another frame of reference, let's say a different momentum in relation to the air.

Momentum is the plane's mass in motion and is defined as the mass times the velocity.
Momentum= m*v

A model airplane of 1 kg travelling at 1 m/s in straight and level flight has a momentum of 1 kg m/s in relation to the ground.

Now you have inertia, which is the plane's resistance to changes in motion or the plane's resistance to changes in momentum.
Inertia is proportional to the plane's mass.
The larger the plane's mass the greater the "resistance" to changing its state of motion in response to a force.

Inertia (mass) may be determined by applying a force to an object and measuring the acceleration that results from that force.
An object with small inertial (mass) will accelerate more than an object with large inertia (mass) when acted upon by the same force.
So, one may say that the body of greater mass has greater inertia.

Another form of inertia is rotational inertia (moment of inertia), which refers to the fact that a rotating rigid body maintains its state of uniform rotational motion. Its angular momentum is unchanged, unless an external torque is applied; this is also called conservation of angular momentum.




Another question funfly, do you believe that the only thing that can influence or CHANGE the motion of an object is a force? My definition of influencing motion means to give it an acceleration of some kind. According to Newton's second law, the rate of change of the momentum of a particle is proportional to the resultant force acting on the particle and is in the direction of that force.
In the case of constant mass, and velocities much less than the speed of light, this definition results in the equation: Force = m*a

A model airplane of 1 kg accelerates from rest to a velocity of 1 m/s in 1 s. The thrust (Force) required to produce this acceleration is 1 newton.
The change in momentum is 1 kg m/s.
It keeps accelerating until the thrust equals the drag (opposite Force).

.

[bwalt822]

Ok, Everything you have said there is correct.

So assuming that mass is constant do you agree that the only thing that can change a planes direction or velocity is a force then? (yes or no)

[funfly2]

Ok, Everything you have said there is correct.

So you agree that the only thing that can change a planes direction or velocity is a force then? (yes or no)
Yes.

[bwalt822]

Ok, now, what are the only possible forces acting on an aircraft in ANY type of flight regime.

Hint: There are only four of them (well technically only two or three depending on how you look at it but its easier to divide those into four)

[funfly2]

Ok, now, what are the only possible forces acting on an aircraft in ANY type of flight regime.

Hint: There are only four of them (well technically only two or three depending on how you look at it but its easier to divide those into four)
Well, you have the gravity, thrust, drag and lift, and you have also the forces caused by deflection of the moving surfaces like ruder, elevator and ailerons, and you have centripetal and centrifugal forces...
And you have also the plane's inertia that opposes changes in motion or the changes in momentum caused by other forces.


.

[bwalt822]

Inertia is not a force and according to what you agreed to earlier it cannot CHANGE motion because the only thing that can change motion is a force.

Forces from the rudder, elevator and ailerons can be included into lift and drag.

Centripetal and centrifugal "forces" aren't forces, they are a type of acceleration.

So that leaves us with the only forces being thrust, drag, lift, and gravity.

Agreed?

[funfly2]

Inertia is not a force and according to what you agreed to earlier it cannot CHANGE motion because the only thing that can change motion is a force.

Forces from the rudder, elevator and ailerons can be included into lift and drag.

Centripetal and centrifugal "forces" aren't forces, they are a type of acceleration.

So that leaves us with the only forces being thrust, drag, lift, and gravity.

Agreed?
No.
Because inertia, which opposes changes in motion or changes in momentum caused by other forces, must also be a force.
You can only oppose a force by applying another force...

Check out:
http://www.learniacs.com/inertia

.

[bwalt822]

Inertia is not a force it is a property of having mass. I have inertia while sitting here but there is no force besides gravity and the normal force from the chair acting on me.

The space station has inertia but the only force acting on it is gravity. its inertia keeps it moving forward but there is no force on it to keep it moving forward.

That website is wrong and is just trying to simplify things. Inertia is what wants to keep your body going the direction that it is going and the normal force from the roller coaster seat is what causes you to be pushed down.

Can you provide a university website that says that intertia is a force?

[bwalt822]

Here are some questions from a grade school physics class. Note parts 1-3.

http://www.glenbrook.k12.il.us/gbssci/phys/reviews/63reviews/u2/u2ans1.html

[funfly2]

Inertia is not a force it is a property of having mass. I have inertia while sitting here but there is no force besides gravity and the normal force from the chair acting on me.

The space station has inertia but the only force acting on it is gravity. its inertia keeps it moving forward but there is no force on it to keep it moving forward.

That website is wrong and is just trying to simplify things. Inertia is what wants to keep your body going the direction that it is going and the normal force from the roller coaster seat is what causes you to be pushed down.

Can you provide a university website that says that intertia is a force?
Here's another one:
http://www.vangani.co.za/articles/article_roller.html

Sorry, but right now I've no time to search for a more reliable source.

However, Newton's first law is often referred to as the law of inertia:
"A body persists its state of rest or of uniform motion unless acted upon by an external unbalanced force."

I think that we came to the core of our disagreement...
I don't want to persuade you on anything, just give yourself some time to think about this and search for other sources.

For me there's no doubt about the fact that inertia, which is linked to a body's mass, is a force that counteracts other forces that might change a body's state of motion.

Thanks for a civilized conversation.

.

[fhhuber506771]

inertia is NOT a force... it is STORED ENERGY

If you fire a bullet out of a gun, at the point it leaves the barrel it will have some inertia value.

As it passes throught he air the DRAG of the air it is passing through will SLOW THE BULLET. It hits the target at a lower speed han it had when it left the barrel.

DRAG (friction) converted some of the stored energy (inertia) into heat.

Inertia NEVER changes the motion of the object... Something ELSE changes the motion and affects the amount of inertia and/or its direction.

Inertia is a VECTOR PROPERTY of an object in motion. It is not a force.

********************

You don't have time to find a RELIABLE source to support your claim that inertia is a force because no reliable source supports you... The search would take infinite time.

[bwalt822]

Sorry, fhuber, you are wrong about this. Inertia is not energy in any way shape or form and has nothing to do with vectors. Inertia is simply the resistance to the change in motion.

The fact that a moving object has intertia is what allows energy to be stored though.

[bwalt822]

Alright how about this funfly.

Inertia by itself does not change motion it only resists the change in motion. Surely you agree with this.


Here's another one:
http://www.vangani.co.za/articles/article_roller.html

Sorry, but right now I've no time to search for a more reliable source.

However, Newton's first law is often referred to as the law of inertia:
"A body persists its state of rest or of uniform motion unless acted upon by an external unbalanced force."

I think that we came to the core of our disagreement...
I don't want to persuade you on anything, just give yourself some time to think about this and search for other sources.

For me there's no doubt about the fact that inertia, which is linked to a body's mass, is a force that counteracts other forces that might change a body's state of motion.

Thanks for a civilized conversation.

.

[Montag DP]

For linear motion, inertia = mass.

For circular motion, inertia =(equivalent to) moment of inertia.

It is a scalar property.

I think people are confusing inertia and momentum here.

Momentum is the net result of a force acting on an object over time. In a way it is a measure of how much an object's motion has been changed by a force, which is the complete opposite of what funfly seems to be saying.

[bwalt822]

I was on a good track guys, let me have at it for a bit.

[funfly2]

Alright how about this funfly.

Inertia by itself does not change motion it only resists the change in motion. Surely you agree with this.That's right, inertia by itself does not change motion, it only resists the change in motion.
You have to apply a force to change the motion of an object and the greater the object's inertia the greater the force has to be applied.

Now you have the Newton's third law: law of reciprocal actions:
''To every action there is always an equal and opposite reaction''

The Newton's third Law means that all forces are interactions, and thus that there is no such thing as a unidirectional force.
(e.g., if the road exerts a forward frictional force on an accelerating car's tires, then it is also a frictional force that Newton's third law predicts for the tires pushing backward on the road).

.

[bwalt822]

Ok so if inertia cannot change motion then it cannot be a force. If you dont agree to this then you have contradicted yourself because you said earlier that the only thing that can change motion is a force.



Originally Posted by bwalt822
Ok, Everything you have said there is correct.

So you agree that the only thing that can change a planes direction or velocity is a force then? (yes or no)

Yes.

This leaves us with the four fundamental forces on an airplane, lift, drag, thrust and weight... Agreed?

[funfly2]

Ok so if inertia cannot change motion then it cannot be a force.That's your own conclusion, not mine.

I said that inertia by itself does not change motion, but inertia resists the change in motion.
Thus inertia is a force in the opposite direction to the force that changes the motion.

For example:
Let's say that you push your car with a force of 15kg, this means that your car pushes back on you with 15kg too, that's the same force but on the opposite direction.

If you pull a bag with a force of 10kg it means that the gravity pulls the bag down with a force of 10kg too.

This because there is no unidirectional force, it's not possible by nature.


Now it's rather late in the evening here and I've to go offline.

.

[bwalt822]

You agreed with my conclusion that inertia cannot change motion and you agreed that only a force can change motion. Since inertia cannot change motion then it cannot be a force. You have made or agreed to three statements, one of which cannot be true:

1. Inertia by itself cannot change motion

2. A force is the only thing that can change motion

3. Inertia is a force

Which of those three statements is not true?

A mathmatical representation of this would be

1. A does not equal C
2. B equals C
3. A equals B

One of those cannot be true.

[funfly2]

You agreed with my conclusion that inertia cannot change motion and you agreed that only a force can change motion. Since inertia cannot change motion then it cannot be a force. You have made or agreed to three statements, one of which cannot be true:

1. Inertia by itself cannot change motion

2. A force is the only thing that can change motion

3. Inertia is a force

Which of those three statements is not true?

A mathmatical representation of this would be

1. A does not equal C
2. B equals C
3. A equals B

One of those cannot be true.You still don't get it.

Let's put it in other words:
Inertia is a force that reacts upon another force.
The force of inertia only takes place when other force changes an object's state of motion.

While traveling in a car, you will notice when the car starts, you will feel a force pressing you against the seats, in opposite direction to the motion of the car. This is the force of inertia.
At the end of the journey, when the car stops, the passengers lean forward. This is again the force of inertia.

http://www.commonsensescience.org/pdf/articles/inertial_mass.pdf

.

[Cory]

Wrong again. When you accelerate in a car the force you feel is the back of the car seat pushing forward on you. It takes a force to get you going, otherwise you could get up to the speed of light with just the force of the thought of moving. As stated before, inertia is a property of mass, not a force.

Here are definitions from some pretty reliable sources in my book:

Caltech: "Inertia A descriptive term for that property of a body which resists change in its motion. Two kinds of changes of motion are recognized: changes in translational motion, and changes in rotational motion." http://web.ipac.caltech.edu/staff/jarrett/LiU/resource/misused_glossary.html

Harvard: "inertia The tendency of an object to continue in motion at the same speed and in the same direction, unless acted upon by a force. " http://chandra.harvard.edu/resources/glossaryI.html

NASA: "Inertia: A property of matter that causes it to resist changes in speed or direction (velocity)." http://science.nasa.gov/newhome/help/glossary.htm

Notice that none of these define inertia as a force, but as a property of matter.

[JetPlaneFlyer]

Funfly,
Inertia as all the others have said is an intrinsic property of matter not a force, it's quantified by an objects mass.

The 'force' you are referring to is the reaction force that is generated when you apply an acceleration to an object that has inertia (not a 'force of inertia' itself). The force is equal to: mass (a.k.a inertia) x acceleration.

This must be true because otherwise, if the force you are referring to was 'purely' inertia, then this 'force of inertia' would always be the same value because inertia is an unchanging fixed value for any object of fixed mass.

Using your example; if the 'force' your body generates pushing back against the seat of your car was purely 'inertia' then it would be constant regardless of your car's acceleration, because the inertia (mass) of your body is constant.. Obviously this is not how it works. It is only when you apply acceleration to your body that you get the reaction force pushing back and the force generated is proportional to acceleration.

agreed?

[Jurgen Heilig]

Wow, you guys have strayed far from the initial subject. ;)

The cause for the accident is still being investigated. Once the results are being published, I will post them here.

And we may put an end to the discussion about inertia ;):

http://en.wikipedia.org/wiki/Inertia

:) Jürgen

[funfly2]

Wrong again. When you accelerate in a car the force you feel is the back of the car seat pushing forward on you. It takes a force to get you going, otherwise you could get up to the speed of light with just the force of the thought of moving. As stated before, inertia is a property of mass, not a force.
Well, you are just denying Newton's Third Law of Motion!

What force acts against you when you start pedalling your bicycle?



Here are definitions from some pretty reliable sources in my book:

Caltech: "Inertia A descriptive term for that property of a body which resists change in its motion. Two kinds of changes of motion are recognized: changes in translational motion, and changes in rotational motion." http://web.ipac.caltech.edu/staff/jarrett/LiU/resource/misused_glossary.html

Harvard: "inertia The tendency of an object to continue in motion at the same speed and in the same direction, unless acted upon by a force. " http://chandra.harvard.edu/resources/glossaryI.html

NASA: "Inertia: A property of matter that causes it to resist changes in speed or direction (velocity)." http://science.nasa.gov/newhome/help/glossary.htm

Notice that none of these define inertia as a force, but as a property of matter. NASA: "Inertia: A property of matter that causes it to resist changes in speed or direction.

How can something resist changes in speed or direction without the exertion of a force?!!

Do you really claim that the force that changes a body's speed or direction has no corresponding force in the opposite direction?

Yes or no?

.

[Jurgen Heilig]

...
What force acts against you when you start pedalling your bicycle?
...

F = m x a

F = Force (N)
m = mass (Kg)
a = acceleration (m/s²)

The force you need to apply to the pedal is lowered by the gear-ratio and raised by friction losses.

:) Jürgen

[JetPlaneFlyer]

Funfly,
in my post #68 above i attempted to explain the relationship between inertia, which is a property of matter, quantified by mass....and the reaction force due to acceleration of an objects that has inertia.


The difference between inertia and the reaction force you are referring to is very similar to the difference between 'mass' and 'weight'
Mass is not a force in itself, but mass results in a force which we call 'weight' when subject to the gravitational field of the earth.

Steve

[Brandano]

..
NASA: "Inertia: A property of matter that causes it to resist changes in speed or direction.

How can something resist changes in speed or direction without the exertion of a force?!!


You fail to understand a basic concept. Were it not for inertia, all objects would move in a chaotic way, since there would be no need of a force for them to change speed or direction. This paradox is what made Newton's intuition so revolutionary. Why should an apple fall downward, and not, say, sideways?

[Cory]

Jetplaneflyer summed it up better than me. Consider my answer to be his answer.

[funfly2]

Funfly,
in my post #68 above i attempted to explain the relationship between inertia, which is a property of matter, quantified by mass....and the reaction force due to acceleration of an objects that has inertia.


The difference between inertia and the reaction force you are referring to is very similar to the difference between 'mass' and 'weight'
Mass is not a force in itself, but mass results in a force which we call 'weight' when subject to the gravitational field of the earth.

SteveThat's not the answer to my question. Stop sidestepping the issue.

Inertia is resistance to motion changes regardless if the body is subject to gravitational field or not.


I repeat, can't anyone of you answer this simple question:
Do you claim that the force that changes a body's speed or direction has no corresponding force in the opposite direction?

Yes or no?

.

[Montag DP]

That's not the answer to my question. Stop sidestepping the issue.

Inertia is resistance to motion changes regardless if the body is subject to gravitational field or not.


I repeat, can't anyone of you answer this simple question:
Do you claim that the force that changes a body's speed or direction has no corresponding force in the opposite direction?

Yes or no?

.You're trying to argue that inertia in itself is a force. You therefore disagree with basic (middle school) physics. You are either a revolutionary genius or a troll. I can't decide which it is.

As others have said, there is a force of inertia which is equal to the object's mass times acceleration. That's what you feel when you accelerate or decelerate in you car. But that is not the same thing as inertia; it is due to inertia. Also, this force is a result of motion (Newton's 3rd Law reaction) and not a cause of motion. In most dynamic analyses it is not actually drawn in as a force, but instead is written as the sum of all outside forces.

[JetPlaneFlyer]

That's not the answer to my question. Stop sidestepping the issue.

Inertia is resistance to motion changes regardless if the body is subject to gravitational field or not.


I repeat, can't anyone of you answer this simple question:
Do you claim that the force that changes a body's speed or direction has no corresponding force in the opposite direction?

Yes or no?

.
I'm not dodging anything.. Yes of couse there is an 'equal and opposite' reaction to any unballanced force.

This reaction force is equal to the object's mass (inertia if you insist) multiplied by it's acceleration. (F = m x a)..

Note that you need to apply an acceleration to produce a force, inertia on it's own is not a force it's a property.

[funfly2]

I'm not dodging anything.. Yes of couse there is an 'equal and opposite' reaction to any unballanced force.

This reaction force is equal to the object's mass (inertia if you insist) multiplied by it's acceleration. (F = m x a)..

Note that you need to apply an acceleration to produce a force, inertia on it's own is not a force it's a property.So what's your problem? you seem splitting hairs now…

As I’ve said before to bwalt822 in my post #62 (http://www.rcgroups.com/forums/showpost.php?p=12983278&postcount=62)
Inertia by itself does not change motion, it only resists the change in motion.

Inertia is the plane's resistance to changes in motion or the plane's resistance to changes in momentum.

Now if you wish to call it another name it’s not so much relevant, my point is that the plane’s inertia (or force of inertia) plays a role during its manuevres both in the air and on the ground.

.

[pmackenzie]

It sounded like his engine didnt power up which could have contributed. Hitting belly first is better than nose first.

Also I think he went around 1 more time than he wanted to.


Edit:
Wait I just read vintage's comment, definitely the downwind turn.

Pretty clear that he hit "go" on the way down and the motor didn't respond.
The extra turn in the spin was probably the time it took fiddling with the throttle, or perhaps turning the mag switch back on or something.


Pat MacKenzie

edit - didn't see how old the OP was :o

[pmackenzie]

That's not the answer to my question. Stop sidestepping the issue.

Inertia is resistance to motion changes regardless if the body is subject to gravitational field or not.


I repeat, can't anyone of you answer this simple question:
Do you claim that the force that changes a body's speed or direction has no corresponding force in the opposite direction?

Yes or no?

.

No. The unbalanced force produces an acceleration. This is pretty much the basics of Newtonian dynamics.

It can sometimes be viewed as a fictitious force, as in the case of "centrifugal" force, but it is not a real force.

Pat MacKenzie

[funfly2]

No. The unbalanced force produces an acceleration. This is pretty much the basics of Newtonian dynamics.

It can sometimes be viewed as a fictitious force, as in the case of "centrifugal" force, but it is not a real force.

Pat MacKenzie
Yes, but when you say unbalanced force it implies another force which it is unbalanced to, you are comparing two forces.
What is the other one?

.

[pmackenzie]

The "unbalanced" force is the vector sum of all the applied forces.
If it adds to zero then the body does not accelerate.
If it sums to a non-zero vector then the body accelerate in the direction of the vector.




Pat MacKenzie

[funfly2]

The "unbalanced" force is the vector sum of all the applied forces.
If it adds to zero then the body does not accelerate.
If it sums to a non-zero vector then the body accelerate in the direction of the vector.




Pat MacKenzieYes, now assume that you were pedalling your bicycle on an level pavement and when you sudden stop pedalling you noticed that your bicycle kept moving forward.
What is the force that makes the bicycle keep moving forward after you stopped pedalling?

.

[pmackenzie]

There is not one.
There is however drag that slows it down.

Pat MacKenzie

[funfly2]

There is not one.
There is however drag that slows it down.

Pat MacKenzieOk, so drag was a force that acted upon the bicycle, right?

Now you want to stop and apply brakes and notice that the bicycle didn't stop but resisted for a while your braking force.
What was the force that opposed your braking force?

.

[pmackenzie]

There is no force opposing your braking force.
What you, the rider, will feel is the force of the bike pushing back on you. Which is the same force (less the mA of the bike) that the ground and drag is exerting back on the bike.

The correct way to do these problems is by drawing the free body diagram and working out the motion equation (F=mA).
If you start off by imagining some force and then trying to rationalize its existence you are leading yourself astray.


Pat MacKenzie

[funfly2]

There is no force opposing your braking force.
What you, the rider, will feel is the force of the bike pushing back on you.

The correct way to do these problems is by drawing the free body diagram and working out the motion equation (F=mA).
If you start off by imagining some force and then trying to rationalize its existence you are leading yourself astray.Which is the same force (less the mA of the bike) that the ground and drag is exerting back on the bike.


Pat MacKenzieI can't agree, you have to apply a force to brake the bicycle.
Either using the brakes or another object that exerts a force upon the bike.

You said above that the drag slows down the bicycle and you know that the drag is a force.
Your claims are contradictory.

.

[pmackenzie]

No contradiction at all.
I said that drag acts to slow down the bike.
When you apply the brakes the force is between the road and the wheel.
The road pushes back on the bike.

You are looking for some force that "keeps the bike moving" or "opposes the braking". There is no such force.

Pat MacKenzie

[funfly2]

No contradiction at all.
I said that drag acts to slow down the bike.
When you apply the brakes the force is between the road and the wheel.
The road pushes back on the bike.

You are looking for some force that "keeps the bike moving" or "opposes the braking". There is no such force.

Pat MacKenzie
I do not agree with you.
The brakes do the same as drag does and you know that the drag is a force.

You've been debunked and are not worth my time.

.

[pmackenzie]

I do not agree with you.
The brakes do the same as drag does and you know that the drag is a force.

You've been debunked and are not worth my time.

.
The brakes do produce a force, but the force results in the bike slowing down, not opposing the slowing down. As I have said twice already.

Your last comment, I am in complete agreement with :)

[Brandano]

The bike will keep rolling indefinitely, since it possesses mass and therefore inertia, until you apply a force to slow it down. In this case drag from the air and the asphalt and wheels. however, if you eliminate these forces, the bike will go on. It's a steady state. If the bike had no inertia it would be incapable of holding a steady state. Its position and/or speed and direction would be completely unpredictable and not subject to Newton laws of motion.

[pmackenzie]

If the bike had no inertia it would be incapable of holding a steady state. Its position and/or speed and direction would be completely unpredictable and not subject to Newton laws of motion.
And every serious bike racer would pay a small fortune to get one :D

[Brandano]

Now, little thought experiment, take that bike and run circles with it on the deck of an aircraft carrier at a constant speed and radius. Would you have to alter your bank angle through your turn to maintain the same speed and radius? And what if the carrier was turning too at the same time?

[pmackenzie]

Is that an African or a European aircraft carrier?http://www.getsmileyface.com/sm/evil/751.gif

As soon as the aircraft carrier starts circling things will get "interesting"

[JetPlaneFlyer]

What is the force that makes the bicycle keep moving forward after you stopped pedalling?

.

Forgetting drag and friction for a moment...The bike does not need a force applied to keep it moving.

Newton's first law of motion:
An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

The bike obays Newton's first law.. it stays in a state of motion, moving forward at the same speed BECAUSE no force is applied to it.

If we include drag then the bike will slow down and the rate it will slow down will be = mass / combined force of drag and friction.

[Brandano]

You Sir seem to understand what a frame of reference is, and what does constitute a steady state. Bravo!

[bwalt822]

Funfly,

You did not answer my question below. You have agreed to or said three statements below which are in contradiction. Which of the three is not correct.


You agreed with my conclusion that inertia cannot change motion and you agreed that only a force can change motion. Since inertia cannot change motion then it cannot be a force. You have made or agreed to three statements, one of which cannot be true:

1. Inertia by itself cannot change motion

2. A force is the only thing that can change motion

3. Inertia is a force

Which of those three statements is not true?

A mathmatical representation of this would be

1. A does not equal C
2. B equals C
3. A equals B

One of those cannot be true.

[funfly2]

Funfly,

You did not answer my question below. You have agreed to or said three statements below which are in contradiction. Which of the three is not correct.All my statements are correct.

When you started pedalling your bike on a level pavement you noticed that you had to apply greater force on the pedals in the beginning, when the bike started moving you noticed that the effort (force) needed to keep it moving was much less than the effort (force) in the beginning.

What do you call the force that acted against you requiring greater effort from you in the beginning?


Another one:
Assume that you were pedalling your bike on a level pavement and when you stopped pedalling you noticed that your bike kept moving forward without needing you to apply any force. However, a certain force was opposing friction and drag that both slowed your bike down (decelerate).
While still not pedalling you suddenly hit a brick wall, which abruptly halted your journey.
At the moment of impact you felt your body being thrown out of the bike and your face hit the wall breaking your nose, your teeth, your glasses as well as your forehead (you didn't have helmet).

What do you call the force that thrown you out of the bike?

After the impact you also noticed that the bike's front wheel was badly distorted and the fork was bent backwards.

Why didn't the bike just stop when it met the wall without taking any damage?
You may say that the force of impact caused the damage... But what caused such a force?


Now ponder this:

Forces always come in pairs - action-reaction force pairs.

The action-reaction force pairs are quite evident in the nature.
Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards.
Since forces result from mutual interactions, the water must also be pushing the fish forwards, moving the fish through the water.
The force on the water equals the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards). Action-reaction force pairs make it possible for fish to swim.

Newton's Third Law of Motion:
For every action, there is another and opposite (in direction) reaction force.


Now comes the most exciting part of the truth:

If the fish wants to swim faster (accelerate) it has to apply a force that overcomes the force of its inertia (+ the friction on water).
If you want to move your bike faster (accelerate) you have to apply a force that overcomes your and your bike's force of inertia (+ the friction and drag).
If you want to move slower (decelerate) you have to apply a force that overcomes your and your bike's force of inertia too.
The force that you need to apply depends on your and your bike's mass and how much you want to accelerate or decelerate.
Force = m*a (+ friction and drag when applicable)




Game Over.

.

[pmackenzie]

All my statements are correct.

When you started pedalling your bike on a level pavement you noticed that you had to apply greater force on the pedals in the beginning, when the bike started moving you noticed that the effort (force) needed to keep it moving was much less than the effort (force) in the beginning.

What do you call the force that acted against you requiring greater effort from you in the beginning?
You have this backwards. You provide the force and the bike accelerates. The action reaction force is the bike pushing on the ground and the ground pushing forward on the bike.


Another one:
Assume that you were pedalling your bike on a level pavement and when you stopped pedalling you noticed that your bike kept moving forward without needing you to apply any force. However, a certain force was opposing friction and drag that both slowed your bike down (decelerate).
While still not pedalling you suddenly hit a brick wall, which abruptly halted your journey.
At the moment of impact you felt your body being thrown out of the bike and your face hit the wall breaking your nose, your teeth, your glasses as well as your forehead (you didn't have helmet).

What do you call the force that thrown you out of the bike?
There is no force that throws you off the bike. You are unable to provide enough force on the bike to produce enough acceleration to keep you on the seat. When you hit the wall it is capable of producing enough force to stop you.

[JetPlaneFlyer]

Funfly,
If you define your 'force of inertia' as 'mass x acceleration' than yes i just about agree with most of your points in the previous post, even though i dont like the term 'force of inertia' much... (inertia itself is not a force)

As poined out already no 'force' threw you off the bike.. Due to inertia your body simply maintained it's speed and as i think we all agree maintaining speed requires no 'force' (Newton's first law).

The critical point is that an object keeps moving at a constant speed unless a force acts upon it. The object does not need the application of 'force' to keep it moving... I think we are now all agreeing on this :D

I cant even recall whet the relevance of any of this is to this thread :rolleyes:

Steve