Ok, new question, DRAG and WEIGHT.

[F4UDOA]

Just as a little side bar to this conversion.

The P-38L when tested had the best initial dive acceleration. Followed by the F4U and P-51D tied and then the P-47D.

Of course this was with power on but none the less my money is on the P-38. It had the wing loading of a cement truck.

[Jimdandy]

 

Originally posted by Dingy:

Still dont quite follow what Galileo proved given this but the sources backing up HT are out there.

Now as far as what plane acclerates fastest, I would have to say, whatever is on my 6.

-Ding

Galileo proved the above AND that in the absence of drag things will fall at the same rate no matter the weight.

[fats]

You all are doing this the wrong way, take out the Ol' ping pong balls. One empty and the other filled with sand. They have always done the trick of turning any aerodynamics thread into a long brain damaging experiment in torture if you try to read one.


// fats

[Jimdandy]

 

Originally posted by fats:
You all are doing this the wrong way, take out the Ol' ping pong balls. One empty and the other filled with sand. They have always done the trick of turning any aerodynamics thread into a long brain damaging experiment in torture if you try to read one.


// fats

That is a great example fats. Thx.

[miko2d]

 Gallileo used objects of different weight but of the same aerodynamic properties to demonstrate that weight(mass) does not have anything to do with acceleration. If I remember correctly (we were both pretty drunk at a time), he dropped a cannon ball and a musket bullet - both round objects.

 Even then the objects would evantually fall at different speed due to difference in density (lead is more dense then iron) and weight to crossection ratio (crossection is proportional to square of size while weight is proportional to cube).

 Since the height of the tower was much lower then what would be necessary for such objects to reach terminal velocity (where resistance of air equals the force of gravity), there was no noticeable difference. Since the common wisdom of the times was that an object ten times as heavy would fall ten times as fast, he made his point very convincingly.


 When an object is falling at it's terminal velocity, the force of gravity which is proportional to it's mass is equal to the force of drag which is proportional to crossection area, aerodynamic coefficient and approximately a square of speed.

 So of two objects (planes) with the same crossection area and aerodynamic properties, the heavier one will reach higher speed before the drag equalizes the force of gravity (weight) and it stops accelerating.

miko

[Jimdandy]

Miko2d hit it on the head.

[PakRat]

 

Originally posted by hitech:
Dingy you are incorect it's not just a drag issue, is a combination of drag and weight.

This is very simple. Weight is involved because we are talking about forces - mass * acceleration for the airplane and the retarding force of drag.

The drag force will depend on speed, profile, surface roughness, etc. and the force pulling the airplane down is the product of the aircraft mass times the acceleration due to gravity.

A very light airplane of the same dimensions as a very heavy one will fall slower. It is the same as the bowling ball / feather thing. In air they fall at different rates. In a vacuum they will fall at the same rate as the retarding force is 0.



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Rape, pillage, then burn...

[PakRat]

 

Originally posted by Jimdandy:
HT I forgot buoyancy. Damn I it will be an expensive month next month. <S>       Your right.

Bouyancy has nothing to do with it. In the very extreme it might have an exceptionally minor effect but with the density of almost every single airplane part being so much greater than air, bringing bouyancy into this is ludicrous.

Did that many here sleep through their science and physics classes?

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Rape, pillage, then burn...

[ljkdern]

This is getting silly. Galileo did not do his experiments in a vacuum. Weight does NOT effect a falling objects ACCELERATION. Weight and drag determine an objects terminal velocity or top speed while falling and NOT its acceleration. A feather reaches terminal velocity almost immediately, while a bowling ball takes much longer. The P47 was known as the best diving airplane not because of its acceleration in a dive but because of the tremendous speeds it could reach. This is because of its high terminal velocity (due to weight) and relatively low drag and high thrust. You take a p47 with a full tank of gas and a p47 with 1/4 tank of gas and race them in a dive.....the 1/4 tank will initially pass the full tank because of its superior thrust to weight ratio .... however it will reach terminal velocity(TV) sooner than the full tank because of its lighter and therefore less drag is required to equal its lighter weight. When the 1/4 tank reaches TV the full tank will catch up and pass the 1/4 tank, because it still has gravity working for it, until it also reaches TV. The full tank will also increase its lead because it will reach its excess thrust limit at a higher velocity than the 1/4 tank.

[fscott]

ljkdern, the last thing I wanted to do was argue on this, all I wanna know is which dern plane has the best drag/weight ratio!

You need to look at it this way. Take a sopa bubble the size of a bowling ball, and take a bowling ball. The drop them both on a zero windless day. The bowling ball will accelerate significantly quicker because it has more weight. The greater weight allows it to push through the air quicker.  Whereas the bubble will reach terminal velocity almost immediately. No need to argue weight is a factor.

fscott

[Moose11]

Wow.

[ljkdern]

Wow is right...sigh... the soap bubble and the bowling ball accelerate at the same rate- the soap bubble reaches terminal velocity almost immediately while the bowling ball continues to accelerate until it reaches terminal velocity. Until one or the other reaches terminal velocity they are accelerating at the same rate. The bowling ball doesnt accelerate faster...it accelerates longer. The bowling ball will hit the ground first because it has a much higher terminal velocity.

PS   I would also like to know which aircraft has the best drag to weight ratio.

[F4UDOA]

FScott,

If your looking for the affects of drag vrs weight then maybe dive isn't the question you should be asking. If you want the best idea of drag(parasite drag at high speed) then you should look at sea level HP+ weight + drag = Vmax. This should give you the best idea of the profile drag for each A/C based on how much HP is available versus top speed. Drag then becomes the limiting factor.

I may be way off in what your looking for but it's just an idea.

[funked]

ljkdern I say this with all due respect - you are dead wrong.

[Jigster]

We all know a human being broke the sound barrier without a aerodynamic body (as in some form of shell to reduce drag of some form -- including wings, or otherwise) surrounding him? Enclosed in nothing more then a pressure suit.

"I thought, hey this is pretty weird, I've got shockwave forming off my arms and legs!"

 

Just an example of the effects of drag, weight, and acceleration, and atmospheric pressure.

Btw Ding I think I found the equation for why Wolvie is so damn short. There's only 1 extranous root...

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