Author Topic: Ok, new question, DRAG and WEIGHT. (Read 1674 times)

hitech · « **Reply #15 on:** January 30, 2001, 01:26:00 PM »

You are correct jimdandy but just as top speed of a plane is when drag = thrust, in fscott's question of a plane no propler being droped you come up with the fowlling
F = M * A

Force = Weight - Drag

Mass = Weight / 32.2

Hence Accel. =
(Weight - Drag) / Mass or solving

Weight/Mass - Drag/Mass or in other terms
Accel = 32.2 - Drag/Mass

HiTech

Jimdandy · « **Reply #16 on:** January 30, 2001, 01:26:00 PM »

Quote

Originally posted by Jimdandy:
The weight is only a factor in wing loading. The drag is the biggest factor in the situation describe. In a vacuum a bowling ball and a feather fall at the same speed. It is wind drag that is that major player here. The terminal velocity is in direct proportion to the drag/frontal area of the aircraft. NO IF AND OR BUT'S! I say the P-51. The major reason the water cooled inline V engined plane were in vogue in WWII was FRONTAL AREA! Look at the level fight low alt speed of most of the WWII aircraft. Generally the inline V engined planes are the fastest at sea level.

I'm throwing down the gauntlet on the one HT! If I'm wrong I'll pay double my fee next month. If I'm right next month is free.

Signed,
Scott D. Barnes

Zigrat · « **Reply #17 on:** January 30, 2001, 01:26:00 PM »

hitech that does not make sense

a buff would win?no

in the initial dive will be the most pronoinced difference, since initially it is govered most greatly by weight( e at 100 mph little paracitic drag on any plane in ah)

at the end is is governed by drag to weight, terminal velocity reached when they are equal. since the p51 has the lowest FPA in the game and a moderate weight im sure it will win

compression effects neglected

fscott · « **Reply #18 on:** January 30, 2001, 01:28:00 PM »

Dingy, although you have gotten completely off my orginal question, you fail to see that the open parachute creates HUGE drag compared to it's weight, whereas the bowling balls have much less drag. That's why it's a drag/weight ratio.

My original question still no answer, only guesses. Assume no one really knows?

"America's 100,000 quotes the P51D with lke .0176 drag factor. I know it has the lowest drag, but does it's weight of 7100 lbs allow it fall faster than a P47D of 10,000 lbs and drag of .0213? Also, I heard someone say the Fw190a5 gad a drag coefficient of .0230, and I know it's a really fasdt diver too, although that's with the propellor. I am only interested in raw drag/weight without added thrust.

I thought HT would know this.

fscott

MANDOBLE · « **Reply #19 on:** January 30, 2001, 01:34:00 PM »

Quote

Originally posted by Dingy:
Sparing you the physics behind all this, its not a weight issue but a drag issue pure and simple.
-Ding

IMO, weight is also an issue. The drag forms a force "barrier" that fights against the force your plane has at a determinate point. This force increases with speed, and, at some point, the force is so big that you stop gaining speed. In this case, your mass and acceleration are constants, so, at any point, the heavier aircraft has most force than the lighter one. For same drag coeficient, the drag force should be greater to decelerate the heavier than the lighter, so, the heavier aircraft can gain speed for a longer time. Anyway, you usally will disintegrate your aircraft prior to getting to the point where drag force can compensate your 9.8 * M force to make your speed constant.

Zigrat · « **Reply #20 on:** January 30, 2001, 01:37:00 PM »

figure it out yourself i dont wanna do math

m*g=CD*.5*rho*u^2*a

m=mass (kg)
g=9.8 m/s^2
CD=drag coefficient
rho=density at terminal altitude(kg/m^3)
u=velocity(m/s)
a=planform area of wing

solve for u, convert to mph

Jimdandy · « **Reply #21 on:** January 30, 2001, 01:43:00 PM »

Quote

Originally posted by Jimdandy:
I'm throwing down the gauntlet on the one HT! If I'm wrong I'll pay double my fee next month. If I'm right next month is free.

Signed,
Scott D. Barnes

He's right folks. The man wins the $30 question. LOL!
HT I forgot buoyancy. Damn I it will be an expensive month next month. <S>

Your right.

Terminal velocity (vt) equals

vt=(mg/k)^1/2 where k= a proportionality constant that depends on the frontal area and the property of the fluid.

Damn damn damn I hate it when I flap my gums with out thinking first.

I'm going to go sulk now.

[This message has been edited by Jimdandy (edited 01-30-2001).]

[This message has been edited by Jimdandy (edited 01-30-2001).]

ljkdern · « **Reply #22 on:** January 30, 2001, 02:00:00 PM »

I would have to agree with Galileo on this one. If you remove the factor of thrust (propeller) than you are left with two falling objects. They will fall at the same rate regardless of mass. The only variable is drag. And I believe the Pony has the least amount of drag. When you add trust, the plane with the best thrust to drag ratio would have the highest top speed in a dive. And the plane with the best thrust to wieght ratio would have the best acceleration in a dive.

Dingy · « **Reply #23 on:** January 30, 2001, 02:04:00 PM »

Ok now Im really confused since all this goes against how I understood Galileos experiments. When he drop objects of different weight off the Tower of Piza, he showed that objects of different weight fall at the same speed, right? Or is what he showed incorrect. I think thats where Im getting hung up.

-Ding

[This message has been edited by Dingy (edited 01-30-2001).]

AKSeaWulfe · « **Reply #24 on:** January 30, 2001, 02:18:00 PM »

Quote

Originally posted by Zigrat:
figure it out yourself i dont wanna do math

m*g=CD*.5*rho*u^2*a

m=mass (kg)
g=9.8 m/s^2
CD=drag coefficient
rho=density at terminal altitude(kg/m^3)
u=velocity(m/s)
a=planform area of wing

solve for u, convert to mph

I'm not sure if you are saying HT is wrong or if he's right. If you are saying he's wrong, mass is weight so the gravitational pull of the earth on the object towards the ground would increase it's speed quicker (in an atmosphere). Wouldn't it?

Hmm I forgot my physics class and what the teacher told me for my response to Dingy.. oh well maybe some day it will resurface. ;-)
-SW

[This message has been edited by AKSeaWulfe (edited 01-30-2001).]

Jimdandy · « **Reply #25 on:** January 30, 2001, 02:21:00 PM »

Quote

Originally posted by Dingy:
Ok now Im really confused since all this goes against how I understood Galileos experiments. When he drop objects of different weight off the Tower of Piza, he showed that objects of different weight fall at the same speed, right? Or is what he showed incorrect. I think thats where Im getting hung up.

-Ding

[This message has been edited by Dingy (edited 01-30-2001).]

That's true if you jump to a vacuum. Think of it this way. Put the plane in oil. It will have buoyancy no mater where it is pointing straight down or not. The area displaces a small amount of air like a boat on the water. So even though the wing is thin and the nose of the plane is small it will try to support a small amount of weight do to the buoyancy of the fluid. Thus a heaver plain with a small frontal area will dive faster. The small area would be like putting a D9 Cat on a toy boat and expecting it to float. It wouldn't but the toy boat would non the less still be providing a small amount of buoyancy. In a vacuum there is nothing thus no buoyancy to contend with. Galileo holds true in a vacuum or for objects of similar drag at low speeds in air. A feather it truly the perfect example of this.

Now stop rubbing it in!

LOL

AKSeaWulfe · « **Reply #26 on:** January 30, 2001, 02:27:00 PM »

Okay I think this is what my physics teacher told me in H.S.> How fast an object falls in relation to another depends on the ratio of it's drag vs it's weight and the other objects ratio of drag vs weight.

Sound right?
-SW

Jimdandy · « **Reply #27 on:** January 30, 2001, 02:30:00 PM »

I'll say it again folks he is right. I just burnt some cash on my wrong answer so I wouldn't be agreeing if he weren't. He is right. You have to think of the falling plane as a really crappy boat in water. It is WAY to small to support the plane and keep it from falling (sinking) but it does still provide some flotation. Buoyancy is a function of mass and area. Thus the heavy plane with a smaller retaliative frontal area will fall a little faster. Just like a boat with to much weight.

Dingy · « **Reply #28 on:** January 30, 2001, 02:39:00 PM »

Im wrong...after blowing an entire afternoon researching this, I found this website:

Elephant and Feather

Basically I understand it such:

The downward force due to gravity is opposed by the upwards force of air resistance. Two objects of different weights have different downward forces due to gravity. An object dropped from a height will accellerate downwards until the upwards force of air resistance equals the downwards force of gravity. At this point the object has reached terminal velocity.

There are two factors that affect the upwards force of air resistance....the speed an object is travelling and its frontal area. Its this frontal area (among other things) which we think of drag in an airplane.

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

jedi · « **Reply #29 on:** January 30, 2001, 02:48:00 PM »

OK, say Norm from Cheers and Carla from Cheers go skydiving. Norm weighs more than Carla, and he's a lot "bigger" than Carla.

Norm wears a parachute, and Carla doesn't. Will they both hit the ground at the same time? I think not.