Mechanist Posted May 1, 2012 Posted May 1, 2012 (edited) Well i'm not a physicist or expert in aerodynamics but i think the dragforce of weapons in the Su-25T are a bit inacurate. Lets say I have some "bricks" (Vikhr or LLTV) on my wing and the plane start to shake near 660 km/h TAS at near ground level altitudes. I think it is fine. But when I climb to 6000 meters and the plane start to shake exactly the same TAS (arround 660) it is a bit unbeliveable. So in the first scenario (near ground level) the air which come against me, produces nearly 660 IAS, because it is thicker and everybody knows you get a harder resistance from thicker air or water. Just try to run in water and you will see :D. But in the second case the IAS is arround 450 and the air is much sparse then in ground level so you collide less air with your payload. My point is basicaly if you collide your "bricks" with less air particles because you are higher and the air is not as thick as in ground level (IAS shows nearly this) you will get a lower drag force or shake force, therefor you can travel faster between your base and your target if you get higher. So it would be nice to change some parameter and base the shaking effect on IAS, because I feel that part of the FM is based on TAS. Also if someone can prove i'm wrong with fact / charts base on fact etc., and the dragforce / shakeforce is same in any altitude I would except it because I base this on common sence. Edited May 1, 2012 by Mechanist "Fighters make movies, bombers make history."
Dr_Arrow Posted May 4, 2012 Posted May 4, 2012 Well i'm not a physicist or expert in aerodynamics but i think the dragforce of weapons in the Su-25T are a bit inacurate. Lets say I have some "bricks" (Vikhr or LLTV) on my wing and the plane start to shake near 660 km/h TAS at near ground level altitudes. I think it is fine. But when I climb to 6000 meters and the plane start to shake exactly the same TAS (arround 660) it is a bit unbeliveable. So in the first scenario (near ground level) the air which come against me, produces nearly 660 IAS, because it is thicker and everybody knows you get a harder resistance from thicker air or water. Just try to run in water and you will see :D. But in the second case the IAS is arround 450 and the air is much sparse then in ground level so you collide less air with your payload. My point is basicaly if you collide your "bricks" with less air particles because you are higher and the air is not as thick as in ground level (IAS shows nearly this) you will get a lower drag force or shake force, therefor you can travel faster between your base and your target if you get higher. So it would be nice to change some parameter and base the shaking effect on IAS, because I feel that part of the FM is based on TAS. Also if someone can prove i'm wrong with fact / charts base on fact etc., and the dragforce / shakeforce is same in any altitude I would except it because I base this on common sence. Well it is not about TAS/IAS, it is about critical Mach number. It is modeled well.
Mechanist Posted May 4, 2012 Author Posted May 4, 2012 Quite interresting, I never heard about it before. Read about this critical mach number and if I assume right the higher you get the slower speed (TAS) this will happen? Assuming that the mach speed decreses with the altitude. So in higher altitude you can reach the speed of sound slower and that means you can exced this critical mach number easier? "Fighters make movies, bombers make history."
Dr_Arrow Posted May 5, 2012 Posted May 5, 2012 Quite interresting, I never heard about it before. Read about this critical mach number and if I assume right the higher you get the slower speed (TAS) this will happen? Assuming that the mach speed decreses with the altitude. So in higher altitude you can reach the speed of sound slower and that means you can exced this critical mach number easier? yes, that's how it works. See figure 3 on the following link: http://www.rfcafe.com/references/electrical/ew-radar-handbook/mach-number.htm 1
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