GREENHILL DRAWING

  • 2.8K Views
  • Last Post 08 January 2014
joeb33050 posted this 09 December 2013

There is a drawing of the standard bullet that Greenhill based his formula on. It has a diameter of 1 and the nose has a radius of 1. I can see this drawing in my mind, but can't find it in any book. Can anyone tell me where it is to be found? Thanks

Attached Files

Order By: Standard | Newest | Votes
joeb33050 posted this 09 December 2013

It seems that what I need is a drawing of an 1880 vintage Martini Henry bullet-particularly the nose. Thanks; joe b.

Attached Files

RicinYakima posted this 09 December 2013

Here is the best I could find. Ric

Attached Files

Ed Harris posted this 09 December 2013

I am not positive, but think it reasonable to believe that Greenhill's model was based on a profile not materially different than Ingall's G1, dimensions are in calibers.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

Attached Files

billglaze posted this 09 December 2013

Ed, I'm glad you brought up the Greenhill formula. I know it's set up for rifling twist, which relates to rotational velocity, but is there a formula that tells js the required rotational velocity for a specific bullet? I am sure that such exisfs for artillerists, but how about small arms?

Bill

In theory, there's no difference between theory and practice. In practice, there is. My fate is not entirely in Gods hands, if I have a weapon in mine.

Attached Files

Ed Harris posted this 09 December 2013

billglaze wrote: Ed, I'm glad you brought up the Greenhill formula. I know it's set up for rifling twist, which relates to rotational velocity, but is there a formula that tells js the required rotational velocity for a specific bullet? I am sure that such exisfs for artillerists, but how about small arms?

Bill

Donald Carlucci's book

http://books.google.com/books?id=pX9Tzs7VuSoC&dq=gyroscopic+stability+factor+s+g&source=gbsnavlinkss

The formula:

http://www.nennstiel-ruprecht.de/bullfly/gyrocond.htm The gyroscopic stability condition

Explanation

A spin-stabilized projectile is said to be gyroscopically stable, if, in the presence of a yaw angle d, it responds to an external wind force F1 with the general motion of nutation and precession. In this case the longitudinal axis of the bullet moves into a direction perpendicular to the direction of the wind force.

It can be shown by a mathematical treatment that this condition is fulfilled, if the gyroscopic stability factor sg exceeds unity. This demand is called the gyroscopic stability condition. A bullet can be made gyroscopically stable by sufficiently spinning it (by increasing w!).

As the spin rate w decreases more slowly than the velocity vw, the gyroscopic stability factor sg, at least close to the muzzle, continuously increases. An practical example is shown in a figure Go to figure.

Thus, if a bullet is gyroscopically stable at the muzzle, it will be gyroscopically stable for the rest of its flight. The quantity sg also depends on the air density r and this is the reason, why special attention has to be paid to guarantee gyroscopic stability at extreme cold weather conditions.

Bullet and gun designers usually prefer sg > 1.2...1.5, but it is also possible to introduce too much stabilization. This is called over-stabilization.

The gyroscopic (also called static) stability factor depends on only one aerodynamic coefficient (the overturning moment coefficient derivative cMa) and thus is much easier to determine than the dynamic stability factor. This may be the reason, why some ballistic publications only consider static stability if it comes to stability considerations.

However, the gyroscopic stability condition only is a necessary condition to guarantee a stable flight, but is by no means sufficient. Two other conditions - the conditions of dynamic stability and the tractability condition must be fulfilled.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

Attached Files

TRKakaCatWhisperer posted this 09 December 2013

ED - GOOD link on the stability! THANKS!

Attached Files

billglaze posted this 07 January 2014

Ed, thanks much for the cogent information and the links. I'm very sorry and embarrassed for the tardy reply, but i've been out of cir circulation due to the Christmas season until now,and focused on other things. It''s been way too cold here for this desert kid to go shooting, (they're forecasting a high of about 13 degrees tomorrow) and I've been going nuts to try out the new Savage heavy barrel .308 that Santa brought me. I'll begin working on the math as soon as the smoke settles from Christmas and a very recent family wedding have cleared.away.k Sometimes family stuff and business get in the way of the important stuff like shooting and loading! I'llt ry to do better, honest!

Bill

In theory, there's no difference between theory and practice. In practice, there is. My fate is not entirely in Gods hands, if I have a weapon in mine.

Attached Files

mckg posted this 07 January 2014

Has anybody tried the Miller stability factor?

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi>http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Attached Files

joeb33050 posted this 07 January 2014

mckg wrote: Has anybody tried the Miller stability factor?

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi>http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi Yes. Here's a workbook that calculates Greenhill, Dell/Bowman, Powley and Miller twist. 

Attached Files

mckg posted this 08 January 2014

Thanks Joe

Attached Files

Categories
Search
Popular Tags
This Weeks High Earners
Hot Topics
Close