RASAero II CENTER OF PRESSURE REGULAR vs. Barrowman

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ColumbiaNX01

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In RASero what is the difference between the regular center of pressure and the Rogers Modified Barrowman center of pressure. In my application is the difference of 2 inch. The Barrowman is 2 inched further aft then regular.
 
Let me ask you a question- have you ever read the Barrowman paper? Strongly suggested.

Barrowman has a few assumptions. A large one that is commonly ignored today is that Barrowman is really only valid for rockets that are traveling under about 0.7 Mach.

I also believe that it does not handle base drag correctly.

Rogers corrected takes some of that into account.
 
Let me ask you a question- have you ever read the Barrowman paper? Strongly suggested.

Barrowman has a few assumptions. A large one that is commonly ignored today is that Barrowman is really only valid for rockets that are traveling under about 0.7 Mach.

I also believe that it does not handle base drag correctly.

Rogers corrected takes some of that into account.

I have not read it. So if a rocket is flying mach you should just leave the default setting on the software?
 
Does anyone know if RASaero runs on Windows 10 or some of the latest MAS OS? When I look at the download page it mentions some old Windows versions, but no MAC OS.
 
Thanks Mark. I hate fiddling around with a download only to find out it is not made to run on the platform I was expecting to use it on.
 
In RASero what is the difference between the regular center of pressure and the Rogers Modified Barrowman center of pressure. In my application is the difference of 2 inch. The Barrowman is 2 inched further aft then regular.

"Rogers Modified Barrowman" from what I can tell is nothing more than Galejs's "Extended Barrowman" calculation that Chuck decided to implement then put his name in front of it.

Galejs's paper can be found here. (warning, PDF)
https://argoshpr.ch/joomla1/articles/pdf/sentinel39-galejs.pdf

OpenRocket also has this option available and references Galejs's work in the documentation under the heading "Effect of body lift".

TLDR; extended Barrowman takes into account AOA and the resultant lift generated by the body tube which Barrowman chose to ignore.
 
I think Rogers extends Galejs' modification of Barrowman past the high subsonic? I'm often wrong though.
 
I think Rogers extends Galejs' modification of Barrowman past the high subsonic? I'm often wrong though.
I don't believe that's the case. In the manual Chuck refers to it as "the Rogers Modified Barrowman Method for subsonic center of pressure". See below from the RASAero II User manual.

Under the Options Tab on the RASAero II Main Screen the option is available to select the Rogers Modified Barrowman Method for subsonic center of pressure...
The Rogers Modified Barrowman Method includes a more accurate body normal force slope with angle of attack (CNalpha) at low angles of attack by including the influence of the body tube cylinder (left out of the Barrowman Method), includes the body in the presence of the fins interference factor (Kbf) (left out of the Barrowman Method), and includes body viscous crossflow using the Jorgensen Method for the forward movement of the rocket center of pressure with angle of attack (not included in the Barrowman Method).


That said I'm unsure if the inclusion of the fins interference factor or the Jorgensen Method are included in Galejs's calculations of if that's what makes it the "Rogers Modified Barrowman Method".
 
As noted in the excerpt from the RASAero II Users Manual, the differences between the Barrowman Method and the Rogers Modified Barrowman Method are:

1) The CNalpha of the combined Nose Cone and Body Tube at low angles of attack is included, versus the Barrowman Method where only the Nose Cone is included. Again, this is the CNalpha through zero degrees angle of attack. The effect of adding the Body Tube to the Nose Cone at low angles of attack is the CNalpha is increased, and the Center of Pressure of the Nose Cone/Body Tube combination at low angles of attack is moved aft towards the bottom of the Nose Cone/top of the Body Tube. Note this is not the increased CNalpha with angle of attack from viscous crossflow (Galejs), which is covered below.

2) The Body in the presence of the Fins Interference Factor (Kbf), which was left out of the Barrowman Method, is included.

3) The viscous crossflow increase in CN with angle of attack is included. This is what was described by Galejs in What Barrowman Left Out. In fact we used some of the Galejs Planform Areas and Planform Area CP's. (Thanks you Galejs.) We used a more advanced method, Jorgensen Viscous Crossflow, for the CN calculations.


Charles E. (Chuck) Rogers
Rogers Aeroscience
 
That said I'm unsure if the inclusion of the fins interference factor or the Jorgensen Method are included in Galejs's calculations of if that's what makes it the "Rogers Modified Barrowman Method".

As noted in the earlier post, Rogers Modified Barrowman is not just Barrowman with Galejs (What Barrowman Left Out) added. The addition of the effect of the Body Tube added to the Nose Cone at low angles of attack is a key difference. And a more accurate method to calculate the viscous crossflow for the viscous CN. And putting back in Kbf, which Barrowman removed.

Note that the Rogers Modified Barrowman Method is used for Subsonic only. For Supersonic a combination of USAF DATCOM and Missile DATCOM methods are used, for Hypersonic Modified Newtonian Theory and Missile DATCOM methods are used.


Charles E. (Chuck) Rogers
Rogers Aeroscience
 
And a further note. We used the Jorgensen Viscous Crossflow Method, but we added the Missile DATCOM modified Viscous Crossflow Drag Coefficient data, where Jorgensen's original model was modified for Missile DATCOM to better match wind tunnel data.


Charles E. (Chuck) Rogers
Rogers Aeroscience
 
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