Author Topic: whoever modelled the La7.... (Read 1711 times)

buzkill · « **Reply #30 on:** October 15, 2002, 05:01:48 PM »

just a note..have noticed my 51 reverses alot faster with 1 click down flaps and cut trottle when starting to pull out
Also the 38 WILL hang at low alt and speed with zeke:D

Spritle · « **Reply #31 on:** October 15, 2002, 05:53:22 PM »

funkedup,

Please break down your equation

Torque = Power / Angular Velocity

into it's base units of measure. Please show your work as this is for a grade.

Spritle

edit: Added words "of measure"

funkedup · « **Reply #32 on:** October 15, 2002, 06:02:46 PM »

Quote

Originally posted by Spritle
funkedup,

Please break down your equation

Torque = Power / Angular Velocity

into it's base units. Please show your work as this is for a grade.

Spritle

In SI units:

[N*m] = [N*m/s] / [1/s]
[N*m] = [N*m] * [1/s] / [1/s]
[N*m] = [N*m]

Show me your diploma(s), I'm taking this to the dean!!!!!!!!!

Spritle · « **Reply #33 on:** October 15, 2002, 06:07:13 PM »

funkedup,

[N*m] = [N*m/s] / [1/s]

WRONG!

What the hell is 1 in your equation?

You are saying 1/s = Angular Velocity !!!!!

1 what ? 1 needs a unit. In this case either degrees or radians.

You sure you want to take that to the dean? He will probably give you an F

funkedup · « **Reply #34 on:** October 15, 2002, 06:16:20 PM »

Spritle, if you are using natural units (radians) then you don't put a unit on angular measures.

For instance, the length "s" of an arc is:
s = theta * r
where theta is the included angle and r is the radius.

Analyze the units
[m] = [1] * [m]

Theta is dimensionless - measured in natural units (radians). So you use a 1.

If we explicitly put radians in there the dimensional analysis would look this:

[m] = [radians] * [m]

Which is an inequality.

And in case you you doubt the equation (s = theta * r ) is true, consider an arc with included angle 2*pi, also known as a circle

s = 2*pi * r = pi*D (where 2*r = D, the diameter)

The result is also known as the circumference of a circle. I'm sure you've seen circumference = pi*D in elementary geometry studies. If not, get something round, measure its diameter, then wrap a string around it, mark the circumference on the string, unwrap it, measure the circumference, and calculate the radio of the circumference to the diameter.

funkedup · « **Reply #35 on:** October 15, 2002, 06:21:20 PM »

Good intro to angular motion here: http://www.udallas.edu/physics/GP1/rotationalmotion_faqs.htm

Wilbus · « **Reply #36 on:** October 15, 2002, 06:26:03 PM »

CAT FIGHT!

Spritle · « **Reply #37 on:** October 15, 2002, 06:38:41 PM »

funkedup,

Consider a circle with a diameter X. How many radians are in that circle? How many degrees?

Angular velocity is NOT described as 1/s. It is expressed as degrees per second or radians per second.

You must be talking about theoretical math. No engineering text in the world uses your 1/s to define angular velocity. Sorry bub you lose.

1/s describes nothing. Give me the angular velocity of a 12 foot diameter prop turning 1200 rpm.

Nice try on the link too. It looks like you didn't understand what they were saying.

Here is a quote right from their page:

Do you always have to use units of radians per second for angular velocity?

There are many units for angular velocity. One of the most common is rpm, which stands for revolutions per minute (rev/min). In principle, any consistent set of units works for describing the kinematics of rotation. However, you will also want to describe the dynamics of rotation and to do that you must use radians per second (rad/s) for the units of angular velocity. Some advice: Get into the habit of immediately changing the units of all angular velocities to radians per second as the very first thing you do when you start to solve a problem.

Perhaps you were thinking rev was unitless. I'm not sure where you got that from 1 rev = 360 degrees = 2*pi*radians

Spritle

funkedup · « **Reply #38 on:** October 15, 2002, 06:45:03 PM »

Quote

Originally posted by Wilbus
CAT FIGHT!

It's a nerd fight actually.

funkedup · « **Reply #39 on:** October 15, 2002, 06:53:38 PM »

Quote

Originally posted by Spritle
funkedup,

Consider a circle with a diameter X. How many radians are in that circle? How many degrees?

Angular velocity is NOT described as 1/s. It is expressed as degrees per second or radians per second.

You must be talking about theoretical math. No engineering text in the world uses your 1/s to define angular velocity. Sorry bub you lose.

1/s describes nothing. Give me the angular velocity of a 12 foot diameter prop turning 1200 rpm.

Nice try on the link too. It looks like you didn't understand what they were saying.

Here is a quote right from their page:

Do you always have to use units of radians per second for angular velocity?

There are many units for angular velocity. One of the most common is rpm, which stands for revolutions per minute (rev/min). In principle, any consistent set of units works for describing the kinematics of rotation. However, you will also want to describe the dynamics of rotation and to do that you must use radians per second (rad/s) for the units of angular velocity. Some advice: Get into the habit of immediately changing the units of all angular velocities to radians per second as the very first thing you do when you start to solve a problem.

Perhaps you were thinking rev was unitless. I'm not sure where you got that from 1 rev = 360 degrees = 2*pi*radians

Spritle

Spritle - you can write the natural angles as radians but when you do dimensional analysis you ignore the radians, as I demonstrated with the arc length equation.

s = theta * r

[m] = [1 ]* [m]

If we do it your way, and use radians, we get:

[m] = [rad] * [m]

Which is an inequality, and therefore incorrect.

PS The 1/s notation is quite commonly used in textbooks for angular velocity and frequency measurements.

Badboy · « **Reply #40 on:** October 15, 2002, 07:09:50 PM »

Quote

Originally posted by funkedup

Show me your diploma(s), I'm taking this to the dean!!!!!!!!!

If it helps, I'm a college lecturer, and so far funkedup is 10/10

Badboy

udet · « **Reply #41 on:** October 15, 2002, 07:14:55 PM »

hehehe-lots of people got excited about this one.
I don't know much about the real La-7, but I figured this would get ppl fired up

None of my books about WW2 A/C has any info on it, only on the La5. But I still think that in AH, La-7 is faster than the Tempest in level flight at sea level.

Urchin · « **Reply #42 on:** October 15, 2002, 07:16:19 PM »

It isn't, it just accelerates faster, so it will catch a Tempest in a race starting from speed X to speed Y.

dtango · « **Reply #43 on:** October 15, 2002, 08:43:10 PM »

Here's an EM Diagram - La-7 vs. P-51D
(25% fuel, sea level alt, military power)

A lot of info there but the one thing I'd like point out above is the sustained turn rate curves. Note that the La-7 has a better sustained turn vs. the P-51D. One implication is at co-alt, co-speed the La-7 can be pulling near 3 g's sustained without bleeding any E while the P-51D would be losing E trying to match the La-7's turn at 3 g's.

The moral of the story is that just because you're burning E doesn't mean the other a/c is and that judging E states can be a really tricky thing leading to some nasty consequences.

Tango, XO
412th FS Braunco Mustangs

funkedup · « **Reply #44 on:** October 15, 2002, 09:21:44 PM »

Tango where did you get that? Is it based on AH empirical data, real world empirical data, or calculations?