Jump to content


Photo
- - - - -

Do heavier objects accelerate better than lighter objects?


  • Please log in to reply
30 replies to this topic

#1 ACE-OF-ACES

ACE-OF-ACES
  • Posts: 24

Posted 18 May 2014 - 16:34

Nope!

Sorry, I know this topic has most likly come up before, and one would think it would be put to rest by now, but just the other day online the topic of diving away from your enemy as a tactic came up, and as usual (almost expected) someone mentioned the P-47 ability pull away from (read better acceleration) the enemy plane in a dive due to the P-47 being heavier.

I had just landed, and resting and I figured I would point out that the P-47 being heavier (read more mass) has nothing to do with the P-47s ability to pull away from the enemy plane, due to the fact that gravity is (for all intents and purposes) constant. I went on to point out the values that are affected by more mass is the momentum and kinetic energy of the P-47 relative to lighter fighters.

I than attempted to explain the P-47 dive acceleration myth by pointing out the P-47 was a very structurally sturdy aircraft, which allowed the pilots to push the P-47 to the edge of its envelope in speed in a dive without worry. Where as other planes would have started to shake prior to this point enough that the pilot would have stopped chasing, or at least pulled back on the throttle in fear of his plane breaking up. Which I will come back to later (see below)

By this time in the chat, several people (most notably Panthera) disagreed with me and stated a heavier (read more mass) plane will accelerate faster than a lighter plane. Panthera gave an example of how a bowling ball will drop faster than a balloon of the same size. I was quick to point out that a bowling ball and a balloon both hit the ground at the same time in a vacuum, which is a classic test used to show heaver objects hit the ground at the same time as lighter objects. Which means they both fell at the same rate (read speed) and therefore both had equal accelerations, which is to be expected due to gravity being a constant and acting equally on all objects.

Which is the whole purpose of the bowling ball vs balloon in a vacuum test. I went on to explain what does affect the acceleration of an object in the atmosphere is it's surface area which causes drag, and in an airplanes case, it's thrust. To which Panthera responded with:

All objects, regardless of surface area, will drop at the same rate in a vacuum.

Note he said 'surface area' which shows he is confused about the purpose of the vacuum drop test. The purpose of the vacuum drop test is to show

All objects, regardless of mass, will drop at the same rate

But don't take my word for it!

Light and heavy objects fall at the same rate

And keep in mind here that Galileo does not qualify it by saying in a vacuum. Galileo conclusion came from rolling balls of different size (read mass) down a angled slide and made note of the fact that they all reached the bottom at the same time.

Granted, there are other factors in play in Galileo's test, and he was comparing like objects (balls) but his conclusion was correct. On that note, the modern vacuum test is a extension of Galileo's test to show that once you remove the forces of drag due to an atmosphere all objects fall at the same rate. And the only way two objects can fall a the same rate is if they both have the same acceleration, in our case, Earth's gravity.

Now back to the P-47, in my example above, where I pointed out the P-47 was a very sturdy aircraft, which allowed a pilot to push it to the edge of it's speed envelope in a dive. I believe this is where the P-47 gets its reputation from, with regards to diving away from an enemy plane. As shown above, we know the P-47's dive acceleration is NOT due to it being a heavier object, therefore if two planes, say a P-47 and Fw190 were to start a dive from the same initial velocity and dive angle, the plane with more thrust and less drag would be the one that accelerates (read dives) better.. It is not until you get near the planes max speed that this 'could' change, where a sturdy aircraft like the P-47 could continue on and a less sturdy aircraft may not be able to continue on in fear of breaking up. As a mater of fact, that is exactly what was found in a test performed in WWII where they compared a P-47 to a captured Fw190 in a dive.. Initially the Fw190 pulled away (read better acceleration) from the P-47, but eventually the P-47 caught up and passed it.

So, in summary, take two identical WWII planes, fill one up with 100% fuel, and the other with 25% fuel, dive them side by side at the same angle, same throttle settings (read thrust) and they will both accelerate equally which in turn means they will both dive at the same rate (read speed). The only time the extra mass will assist is once the planes reach their terminal velocity.. Assuming they do not fall apart, the plane with more mass (more fuel) will be able to go faster due to a bigger force (F=ma) countering the drag.. But chances are it will be so small, relative to the thrust (read force) it may go un-noticed, that and the chances are high that poorly constructed planes would break upon reaching terminal velocity, which is why this case is seldom considered, except for free falling objects with no thrust. The P-47 was an exception to the rule, it was a very sturdy aircraft, which is probably why it was used after WWII for high speed dive testing new propeller types.

Hope this helps!

For those who are not convinced, feel free to Google it NASA has some nice high school examples on the subject, but here is one I think is helpful

http://www.physicscl...1DKin/U1L5e.cfm" onclick="window.open(this.href);return false;">http://www.physicscl...1DKin/U1L5e.cfm
  • 0

#2 =HillBilly=

=HillBilly=
  • Posts: 5605
  • LocationSouthern Ozark Mountains

Posted 18 May 2014 - 18:08

Acceleration of a object is dependent on the force acting on the object.
Two objects with the same force on both, but one has more mass than the other, the one with less mass will accelerate faster than the other with more mass, look at drag racing.
  • 0

     So Long, and Thanks for All the Fish

 
 


#3 ACE-OF-ACES

ACE-OF-ACES
  • Posts: 24

Posted 18 May 2014 - 19:14

Acceleration of a object is dependent on the force acting on the object.
Not the way I would put it, but good enough.

Two objects with the same force on both, but one has more mass than the other, the one with less mass will accelerate faster than the other with more mass,
Again, not the way I would put it, but good enough.

look at drag racing.
No need, F=ma applies to more than drag racing..

Thanks for your input Billy..

Just not sure what it has to do with the topic at hand?

Your statement is talking about how the acceleration must change if the force is constant..

Which I think is clear based on the F=ma equation, at a glance anyone can (should) see if the force is constant, changing the mass will force (no pun intended) you to change the value of the acceleration to keep the force constant.

Which as far as I know no one is debating!

Where as my statements is talking about a constant acceleration (read gravity) and how varying the mass has no effect on the acceleration (hence the word constant) and therefore the force will have to change..

Long story short, you said nothing that would disprove anything I said, thus I can only assume you agree with what I said.
  • 0

#4 Gadfly21

Gadfly21
  • Posts: 1081

Posted 18 May 2014 - 19:24

So, in summary, take two identical WWII planes, fill one up with 100% fuel, and the other with 25% fuel, dive them side by side at the same angle, same throttle settings (read thrust) and they will both accelerate equally which in turn means they will both dive at the same rate (read speed). The only time the extra mass will assist is once the planes reach their terminal velocity.. Assuming they do not fall apart, the plane with more mass (more fuel) will be able to go faster due to a bigger force (F=ma) countering the drag.. But chances are it will be so small, relative to the thrust (read force) it may go un-noticed

You're technically correct on a lot of what your wrote, but "chances are so small" and "may go unnoticed" aren't very good arguments for your case.

The internal fuel capacity of the P-47 was 375 US Gallons. Fuel weighs in at 6 pounds per gallon (this is the figure used in weight and navigation planning). That's 2,250 pounds from full to empty. The loaded weight of the plane is 13,300 lbs according to Wikipedia (close enough), which is a change of 17%. That's not insignificant.

Furthermore, when people say the P-47 was a good diver, they are comparing to planes like the Bf-109 and Fw-190. It is true that the FW-190 had better TWR, giving an initial acceleration boost, but in a prolonged dive, the P-47 would catch up. Again, the loaded weight of the P-47 is 13,300 lbs and the Fw-190 is 9,735 lbs (27% diff). A Bf-109 is only 6,940 lbs loaded (48% diff).

It is entirely reasonable to argue that the P-47 could dive faster because of its much greater weight, thereby providing greater terminal velocity. Structural strength is a factor in top speed, but it certainly isn't the only one as you seem to be saying.

Secondly, and this is unrelated to the topic at hand, I think it is unfair to assume that people do not already know the basics of the speed of falling objects. At worst, it makes you sound pretentious.

EDIT- typos
  • 0

#5 ACE-OF-ACES

ACE-OF-ACES
  • Posts: 24

Posted 18 May 2014 - 19:38

You're technically correct on a lot of what your wrote, but "chances are so small" and "may go unnoticed" aren't very good arguments for your case.

The internal fuel capacity of the P-47 was 375 US Gallons. Fuel weighs in at 6 pounds per gallon (this is the figure used in weight and navigation planning). That's 2,250 pounds from full to empty. The loaded weight of the plane is 13,300 lbs according to Wikipedia (close enough), which is a change of 17%. That's not insignificant.

Furthermore, when people say the P-47 was a good diver, they are comparing to planes like the Bf-109 and Fw-190. It is true that the FW-190 had better TWR, giving an initial acceleration boost, but in a prolonged dive, the P-47 would catch up. Again, the loaded weight of the P-47 is 13,300 lbs and the Fw-190 is 9,735 lbs (27% diff). A Bf-109 is only 6,940 lbs loaded (48% diff).

It is entirely reasonable to argue that the P-47 could dive faster because of its much greater weight, thereby providing greater terminal velocity. Structural strength is a factor in top speed, but it certainly isn't the only one as you seem to be saying.

Secondly, and this is unrelated to the topic at hand, I think it is unfair to assume that people do not already know the basics of the speed of falling objects. At worst, it makes you sound pretentious.
So you agree with everything I said..

And the only thing we differ on is how big is big?

That is to say we both agree more mass will increase the terminal velocity, its just a question of how much. You seem to feel the 17% mass will mater, where as I think the squared term of velocity with regards to drag will be the driving factor..

Thus all that is left is for someone with enough time on their hands to plug in the numbers! At which point we will have a real velocity value to argue about.. if it is big or not.

As you reply, keep in mind that the myth here is the P-47 could accelerate faster than other planes because it weight more.

As I showed above, that is not the case!

Thus I attributed the myth about the P-47 dive tactics stems from the P-47 construction which allowed it to fly at faster speeds without concern of falling apart..

Thus making good use of it top speeds up to and including terminal velocity, where terminal velocity is something most pilots in most plane avoided, in that it could be as deadly as a bandit on your six.. Where as the P-47 was an exception to this rule, the pilots had no fear getting near the edge of the envelope.

In summary, the P-47 better acceleration due to weight is a myth, which I believe stems from the P-47s ability to fly at speeds near it envelope with ease where other planes feared to go. Which in turn allowed the P-47 to put distance between it and the plane on it's six, or catch the plane it was chasing.. And some incorrectly concluded this speed delta was due to acceleration when in fact it is just a top speed (terminal) delta.
  • 0

#6 Panthera

Panthera
  • Posts: 462

Posted 19 May 2014 - 03:55

ACE-OF-ACES,

Sadly you didn't pay attention in the classroom on the day this was explained.

1) Any object, regardless of mass AND surface area (i.e. density) will drop at the same rate in a vaccum

This is true because in a vacuum there is no atmosphere and therefore no drag to slow down the acceleration of the object, and therefore in a vacuum the acceleration of ANY object falling, irrespective of size, weight or surface cleanliness, will be equal to what'ever gravitational pull is present.

Hence a balloon and a bowling ball of exactly the same dimensions and surface cleanlines will fall at exactly the same rate on the Moon where there is no atmosphere. Infact regardless of any disparity in size, weight or surface cleanliness, ALL objects fall at the same rate on the moon.

This is NOT the case on Earth or any other planet with an atmosphere, here's why:

2) Objects of similar size but different weight (i.e. different density) will NOT fall at the same speed on Earth or on any other planet with an atmosphere.

This is true as on Earth, which has an atmosphere, surface friction & buoyancy will suddenly come into effect, acting on the objects and causing what is known as terminal velocity.

The terminal velocity of a falling object is the velocity of the object when the sum of the drag force and buoyancy equals the downward force of gravity acting on the object: http://en.wikipedia....rminal_velocity" onclick="window.open(this.href);return false;">http://en.wikipedia....rminal_velocity

In other words, since the bowling ball weighes more than the balloon it is also a lot denser, and the higher the density of an object the less the bouyancy. In short this means that on Earth the bowling ball's higher density and therefore lower bouyancy will make sure that it will accelerate faster as its greater mass will help it better overcome the surface friction (drag) caused by the atmosphere, resulting in the bowling ball having a much higher terminal velocity than the balloon.
  • 0

#7 Panthera

Panthera
  • Posts: 462

Posted 19 May 2014 - 04:16

Remember however that, everything else being equal, if the density of the atmosphere is low and the falling distance is short as in a couple of meters, then the difference in density needs to be significant in order to be able to observe the difference in acceleration of two similar sized objects with a different mass.

Hence why I chose the bowling ball & balloon example, as this is something which all of us here on earth will be easily able to test and observe even at a short falling distance.

For example, if we were instead to take two bowling balls with exactly the same dimensions (surface area) and drag coefficient (surface cleanliness), but with only a small weight difference of say 6 vs 7 kg. Then we wouldn't be able to discern any difference in the time it took each ball to hit the ground from a height of just 1.5 to 2 meters.

HOWEVER, were we to drop these two balls from a skyscraper 500 meters high, then we would be able to observe the heavier ball hit the ground before the lighter one, simply because the heavier ball is more dense and therefore has a higher terminal velocity.

The difference in falling speed of two objects of different density is more easily observed the higher the density of the atmosphere. A good example would be to take a very dense medium such as water, fill up an aquarium with it, and then drop two perfect 1x1cm balls into it; one made of a dense material such as lead and another made of a less dense material such as glass. What you'll be able to observe is the lead ball plummit to the bottom a lot faster than the glass ball, and that because its higher density will help it better overcome the drag & bouyancy as it moves through the water.
  • 0

#8 Panthera

Panthera
  • Posts: 462

Posted 19 May 2014 - 04:27

It couldn't be demonstrated better than in this video:


  • 0

#9 Panthera

Panthera
  • Posts: 462

Posted 19 May 2014 - 04:36

So in short, the P-47 was known as such a fast diver because it was in effect a lot denser than other aircraft, which meant that in a dive its greater mass made sure it could more easily overcome the exponential increase drag for every increase in speed.

Hence why lighter aircraft such as the FW190 could only just about keep up in a dive with the P-47 for the initial few seconds until the force of the drag overcame the 190's lighter mass, where'as the P-47 just kept going.
  • 0

#10 steppenwolf_

steppenwolf_
  • Posts: 245

Posted 19 May 2014 - 13:37

So the car would've pulled away from the tire if the fall was longer, right? So in a vacuum Galileo is right? But on earth Aristotle's theory is right too? Truth is so subjective.
  • 0

#11 Panthera

Panthera
  • Posts: 462

Posted 19 May 2014 - 14:22

So the car would've pulled away from the tire if the fall was longer, right? So in a vacuum Galileo is right? But on earth Aristotle's theory is right too? Truth is so subjective.

Since I don't know the density and drag coefficient of either object I can't tell you that for sure.

However it seems you've got the jest of it.

In short and simple terms there are 4 things that will influence the speed at which an object falls in an atmosphere such as on Earth:

1) Mass (Weight)
2) Surface area (Size)
3) Surface cleanliness (Drag coefficient)
4) Gravitational pull (Gravity)

Whilst in a vacuum, like on the Moon, only one thing matters: Gravitational pull (Gravity)

So both Galileo and Aristotles had it wrong.
  • 0

#12 JoeCrow

JoeCrow
  • Posts: 4146

Posted 19 May 2014 - 14:56

So the car would've pulled away from the tire if the fall was longer, right? So in a vacuum Galileo is right? But on earth Aristotle's theory is right too? Truth is so subjective.

Since I don't know the density and drag coefficient of either object I can't tell you that for sure.

However it seems you've got the jest of it.

In short and simple terms there are 4 things that will influence the speed at which an object falls in an atmosphere such as on Earth:

1) Mass (Weight)
2) Surface area (Size)
3) Surface cleanliness (Drag coefficient)
4) Gravitational pull (Gravity)

Whilst in a vacuum, like on the Moon, only one thing matters: Gravitational pull (Gravity)
That is correct unless it has a lift-vector. To apply that principle to an aircraft you would have to assume that the lift-vector and angle-of-attack were zero and we know that the lift ratio is never zero unless the aircraft is at rest (parked). To keep the lift vector at zero in the air the pilot would have to switch off the engine and keep the nose level until the speed also dropped to zero, but we know that a stall would intervene and the aircraft would begin to fall, thus raising the lift vector again. An aircraft always tries to return to the level-flight speed for which it is trimmed even if the engine is off and it does that by trying to change its angle-of-attack (porpoising).

All of this is much more complicated than it sounds but we should remember that the thrust/weight/lift/drag ratios are all part of a single equation, so if you change one ratio then they all change proportionately (that is not quite true but near enough). In effect it means that, generally speaking, an aircraft with the low lift-ratio and angle-of-attack will dive faster than an aircraft with a high lift ratio if all else is equal.

That is actually just scratching the surface of aerodynamics which is a very complicated subject and fills many books. Fortunately, a pilot is usually only concerned with the parts that keep him safely in the air. There is a saying that if you want to know how a plane really flies ask a mechanic and not a pilot.
Cheers.
  • 0

#13 Panthera

Panthera
  • Posts: 462

Posted 19 May 2014 - 17:22

So the car would've pulled away from the tire if the fall was longer, right? So in a vacuum Galileo is right? But on earth Aristotle's theory is right too? Truth is so subjective.

Since I don't know the density and drag coefficient of either object I can't tell you that for sure.

However it seems you've got the jest of it.

In short and simple terms there are 4 things that will influence the speed at which an object falls in an atmosphere such as on Earth:

1) Mass (Weight)
2) Surface area (Size)
3) Surface cleanliness (Drag coefficient)
4) Gravitational pull (Gravity)

Whilst in a vacuum, like on the Moon, only one thing matters: Gravitational pull (Gravity)
That is correct unless it has a lift-vector. To apply that principle to an aircraft you would have to assume that the lift-vector and angle-of-attack were zero and we know that the lift ratio is never zero unless the aircraft is at rest (parked). To keep the lift vector at zero in the air the pilot would have to switch off the engine and keep the nose level until the speed also dropped to zero, but we know that a stall would intervene and the aircraft would begin to fall, thus raising the lift vector again. An aircraft always tries to return to the level-flight speed for which it is trimmed even if the engine is off and it does that by trying to change its angle-of-attack (porpoising).

All of this is much more complicated than it sounds but we should remember that the thrust/weight/lift/drag ratios are all part of a single equation, so if you change one ratio then they all change proportionately (that is not quite true but near enough). In effect it means that, generally speaking, an aircraft with the low lift-ratio and angle-of-attack will dive faster than an aircraft with a high lift ratio if all else is equal.

That is actually just scratching the surface of aerodynamics which is a very complicated subject and fills many books. Fortunately, a pilot is usually only concerned with the parts that keep him safely in the air. There is a saying that if you want to know how a plane really flies ask a mechanic and not a pilot.
Cheers.

Quite right, I was merely addressing the subject in a very simplified way in order to explain why, all else being equal, heavier objects do fall faster than lighter ones in an atmosphere.

If we were to look at aircraft then ofcourse both thrust and lift should be accounted for as-well, eventhough I'd argue that one might as-well just count lift as one component of the drag, the two being directly related.
  • 0

#14 JoeCrow

JoeCrow
  • Posts: 4146

Posted 19 May 2014 - 20:45

If we were to look at aircraft then ofcourse both thrust and lift should be accounted for as-well, eventhough I'd argue that one might as-well just count lift as one component of the drag, the two being directly related.

That is also correct. If you simply push the stick forward in level flight the lift-vector is still directly opposing gravity. If you invert the lift vector and point it in the same direction as gravity (and add them together) you will dive whether you want to or not. So what happens to your dive speed if you roll the lift vector 45 degrees in a dive or 90 degrees? What happens to weight, drag, thrust and velocity? Nothing about 3-dimensional flight is ever as simple as it first seems. The answers fill volumes.
Cheers.
  • 0

#15 Panthera

Panthera
  • Posts: 462

Posted 20 May 2014 - 06:59

If we were to look at aircraft then ofcourse both thrust and lift should be accounted for as-well, eventhough I'd argue that one might as-well just count lift as one component of the drag, the two being directly related.

That is also correct. If you simply push the stick forward in level flight the lift-vector is still directly opposing gravity. If you invert the lift vector and point it in the same direction as gravity (and add them together) you will dive whether you want to or not. So what happens to your dive speed if you roll the lift vector 45 degrees in a dive or 90 degrees? What happens to weight, drag, thrust and velocity? Nothing about 3-dimensional flight is ever as simple as it first seems. The answers fill volumes.
Cheers.

Again quite right.

Calculating such instances is never an easy feat, however in this case of a straight vertical dive one would then have to figure out the lift/drag coefficient of each wing at full up & down aileron deflection and then use this information along with how long the 45 or 90 degree roll took in order to figure out the speed/acceleration lost in this time period. Acquiring such figures is no easy feat though as you will need access to all the necessary windtunnel figures.
  • 0

#16 gavagai

gavagai
  • Posts: 15542

Posted 20 May 2014 - 10:00

Misconceptions about dive acceleration are the least of it. I've heard people claim again and again that a P-47 will have a better zoom climb because of its mass.
  • 0

#17 =HillBilly=

=HillBilly=
  • Posts: 5605
  • LocationSouthern Ozark Mountains

Posted 20 May 2014 - 12:11

"I've heard people claim again and again that a P-47 will have a better zoom climb because of its mass."
Wait a minute,it is true that the P47 is big and heavy compared to the FW190 but aerodynamically it is the the smaller lighter plane. The P47 wing loading 44.33 lb\ft squared,FW 190 49.4 lb\ft squared and the power loading is close on both.
  • 0

     So Long, and Thanks for All the Fish

 
 


#18 Raine

Raine
  • Posts: 232

Posted 20 May 2014 - 13:19

Galileo took this debate on in 1589 by dropping two balls of different masses from the leaning tower of Pisa, a distance of 100 "braccia" [arm's lengths]. They landed about the same time, leading Galileo to debunk Aristotle's belief that velocity in a fall was a function of mass.

But because the larger ball touched an instant before the smaller due to air resistance, other academics claimed that Aristotle's belief had won out. Galileo's response was: "You find, on making the test, that the larger ball beats the smaller one by two inches. Now, behind those two inches you want to hide Aristotle's ninety-nine braccia and, speaking only of my tiny error, remain silent about his enormous mistake."
  • 0

#19 dirk

dirk
  • Posts: 63

Posted 20 May 2014 - 14:06

Galileo had a beautiful argument to confound those who argued that heavier objects fell faster than lighter ones (this was a belief popular at the time and often attributed to Aristotle). Galileo said: "Suppose you have one object with a mass of say 1kg and another of mass 2kg." You say that the 2kg mass will fall faster than the 1kg mass, but if you attach the two masses together, at what rate will the combined mass fall." The believer will almost certainly reply that the combined mass of 3kg will fall faster than the 2kg mass, to which Galileo replied: "But surely the lighter mass, which wants to fall at a lower rate, will slow down the 2kg mass, so that the combination will fall at a lower rate than the 2kg mass alone?" At this the believer in Aristotle's theory retires baffled.
  • 0

#20 JoeCrow

JoeCrow
  • Posts: 4146

Posted 21 May 2014 - 07:02

"I've heard people claim again and again that a P-47 will have a better zoom climb because of its mass."
Wait a minute,it is true that the P47 is big and heavy compared to the FW190 but aerodynamically it is the the smaller lighter plane. The P47 wing loading 44.33 lb\ft squared,FW 190 49.4 lb\ft squared and the power loading is close on both.
That is a good example. Mass does help to conserve energy but, again, we cannot consider mass (weight) as a separate entity without also including the effect of velocity on the combined thrust/lift/drag to weight ratios in a zoom-climb. You can shuffle the forces any way that you like as long as you include all of them.
Cheers.
  • 0

#21 ACE-OF-ACES

ACE-OF-ACES
  • Posts: 24

Posted 21 May 2014 - 14:52

Well.. it looks like Ill have to eat crow on this one!

Panthera, please accept my apology! You are right and I was wrong!

I want to thank you for the challenge, because it forced me to dig a little deeper and find the error in my thinking.

On that note, I use to think as you did, but somewhere along the line someone changed my mind, and I have been operating under this false impression for several years now. So, thanks for setting me straight!

While we are on the subject, I found several sights covering this issue, but I think the NASA sight had the best one, here:

http://www.grc.nasa....lane/termv.html" onclick="window.open(this.href);return false;">http://www.grc.nasa....lane/termv.html

Where in summary it says

The terminal velocity equation tells us that an object with a large cross-sectional area or a high drag coefficient falls slower than an object with a small area or low drag coefficient. A large flat plate falls slower than a small ball with the same weight. If we have two objects with the same area and drag coefficient, like two identically sized spheres, the lighter object falls slower. This seems to contradict the findings of Galileo that all free falling objects fall at the same rate with equal air resistance. But Galileo's principle only applies in a vacuum, where there is NO air resistance and drag is equal to zero.

So thanks to all for the input and sorry if I confused anyone!

As for the P-47, I still feel the 'myth' has more to do with the sturdy design.. Based on the real world test results, we know that the extra weight of the P-47 did NOT cause the P-47 to acc faster than the Fw190, as in the P-47s extra weight did not make up for the Fw190s better trust to weight ratio.. The P-47 did over take the Fw190 at ~3,000ft but if I remember correctly, the test made no mention of either planes speed at that point.. My gut tells me that neither plane was at it terminal velocity, thus I suspect at some point in the dive, the Fw190 cut back on the throttle to 'stay away' from the terminal velocity point, probably due to vibrations, where as the P-47 had no issues and was able to go faster than the Fw190 and eventually overtake it, as it did. Just my theory, but ill check the test again and see if it mentions what the speeds were of either plane at the point the P-47 overtook the Fw190 at 3,000ft.

S!
  • 0

#22 Panthera

Panthera
  • Posts: 462

Posted 22 May 2014 - 10:46

Apology accepted ACE-OF-ACES :)

You have my outmost respect for owning up and directly apologizing, something way too few people are capable of these days, just shows you're an honest and righteous individual :S!:

We're all here to learn and it's important to remember that everybody gets it wrong now and then, even the experts, so its important to be patient and remember that it takes courage to openly admit it when it happens. God knows we've all been in that situation before.
  • 0

#23 JoeCrow

JoeCrow
  • Posts: 4146

Posted 22 May 2014 - 20:51

We're all here to learn and it's important to remember that everybody gets it wrong now and then, even the experts, so its important to be patient and remember that it takes courage to openly admit it when it happens. God knows we've all been in that situation before.

I'll second that.

ACE is probably a far better pilot than I am. The only difference is that a pilot needs to know what works and a mechanic needs to know how it works, and mechanics are usually afraid of heights.
Cheers.
  • 0

#24 Gadfly21

Gadfly21
  • Posts: 1081

Posted 23 May 2014 - 02:14

I saw the page count on this thread had continuing to grow, and I came in expecting to see a pie slinging contest. I'm glad to have been shown otherwise.
  • 0

#25 WF2

WF2
  • Posts: 1485

Posted 23 May 2014 - 11:26

Finally something well worth reading on this forum. Good show to all.

Induced drag decrease with acceleration while parasite drag increases with acceleration. So how aerodynamically clean an aircraft is factors in on all this too.

Great debut guy's!
WF2
  • 0

#26 JG1_Butzzell

JG1_Butzzell
  • Posts: 1380

Posted 23 May 2014 - 14:03

S!

To qu0te Arty Johnson "Vaaaaaary intersting".


Has anyone bothered to solve the drag equations for the P47 and the FW190 to determine their terminal velocities?

Just wondering?
  • 0

sig9.png


#27 ACE-OF-ACES

ACE-OF-ACES
  • Posts: 24

Posted 23 May 2014 - 21:49

Apology accepted ACE-OF-ACES :)
Thanks Bud! S!
  • 0

#28 ACE-OF-ACES

ACE-OF-ACES
  • Posts: 24

Posted 23 May 2014 - 21:55

Has anyone bothered to solve the drag equations for the P47 and the FW190 to determine their terminal velocities?
That should be easy to do, all we need is the drag coefficients (Cd) of each plane.. I know I have the Cd values for 'a' Fw190 and 'a' P-47 somewhere.. Just not sure it would be for the exact versions used in that real world test? The frontal area of the P-47 didn't change much during the war, thus I think any Cd value would be good to go.. but the frontal area of the Fw-190 changed a lot, thus one would have to insure they get a Cd value close to the version of the plane used in the real world dive test..

Than just set D = W and solve for vel, i.e.

V = sqrt ( (2 * W) / (Cd * r * A)

Now just pick the altitude you want to find the terminal velocity and use the corresponding value of atmospheric density value ®.. Do it for several altitudes and than connect the dots..

I was really interested in trying to find the thrust and/or acceleration of each plane from the real world test data.. Of which we know the following:

  • Starting altitude
  • Initial Speed of both planes
  • The dive angle of both planes (roughly)
  • The altitude at which the P-47 passed the Fw190

  • But I don't 'think' that will be enough information?

    If we had the vel of each plane at a few altitude points I think we could have solved for (created) a thrust v.s. alt curve.. The assumption here is they were not flying at terminal velocity in the real world test
    • 0

    #29 Panthera

    Panthera
    • Posts: 462

    Posted 24 May 2014 - 23:00

    "I've heard people claim again and again that a P-47 will have a better zoom climb because of its mass."
    Wait a minute,it is true that the P47 is big and heavy compared to the FW190 but aerodynamically it is the the smaller lighter plane. The P47 wing loading 44.33 lb\ft squared,FW 190 49.4 lb\ft squared and the power loading is close on both.

    Err.. what?

    The P-47 is a much larger plane than the FW190, period.

    As for wing loadings, the P-47D-25's wing loading was 237 kg/m^2 at a gross weight of 6,622 kg (14,600 lbs), where'as the wing loading of the heaviest FW190, the A8, was 234 kg/m^2 at a gross weight of 4,300 kg.

    As for why you are even mentioning wing loading I have no idea, seeing as that is in no way an indication of size.
    • 0

    #30 =HillBilly=

    =HillBilly=
    • Posts: 5605
    • LocationSouthern Ozark Mountains

    Posted 25 May 2014 - 00:26

    I think you need to check your figures, and the key word is AERODYNAMICALLY. True the P47 is larger heaver and has more wing area than the FW190,and less drag. Even with the more powerful inline engines the FW190 was slower than the P47.
    Why I mentioned wing loading is to show mass to size.
    • 0

         So Long, and Thanks for All the Fish

     
     


    #31 Panthera

    Panthera
    • Posts: 462

    Posted 25 May 2014 - 03:04

    I think you need to check your figures, and the key word is AERODYNAMICALLY.

    My figures are fine, and there is no such thing as an "aerodynamic size".

    True the P47 is larger heaver and has more wing area than the FW190,and less drag.

    Less drag? I don't think so, if that were the case the P-47 wouldn't have needed 2,800 hp to reach the same speed as a 2,050 hp FW190.

    Even with the more powerful inline engines the FW190 was slower than the P47.

    I don't recall the P-47 ever achieving a top speed of 710 km/h with a 2,000 hp engine. No the P-47 needed a whopping 2,800 hp to achieve such performance, so logically it couldn't have been less draggy.

    Why I mentioned wing loading is to show mass to size.

    Which wing loading gives us no clue about what'so'ever as it completely neglects the size of the rest of the aircraft.

    Wing loading is simply just weight divided by wing area, or in other words a stupendously simple exercise in elementary arithmetics (division) which is way too often used on internet forums in an effort to figure out the agility of different aircraft relative to each other; for which purpose it is completely worthless btw as neither lift coefficients or aspect ratios are considered.
    • 0


    0 user(s) are reading this topic

    0 members, 0 guests, 0 anonymous users