PDA

View Full Version : Dive physics questions

Grey_Mouser67
10-07-2005, 06:26 PM
I've been following Targets roll rate graphs with great interest. I realize, as do most rational people, that there simply is no way to accurately model aircraft given current technology completely...so I really never got caught up in the "this plane isn't as fast as that plane" but rather looked at it from a relative standpoint to other aircraft...anyways...since roll rate is off, I got to wondering about dive modelling...I have always felt that E and Dive were the worst modelled aspects...rate of roll aught to be pretty easy to model, but it is way off in many aspects so...some questions about physics for the physics buffs.

As I think about climb rate, I am under the impression that power to weight ratio...probably better thought of as "thrust to weight" since power is only a part of the equation...rpm's and propeller efficiency play a big part too. Drag and gravity are the primary resisting forces to overcome and drag increases as angle of attack increases on the wing....I would conclude that the better the thrust to weight ratio, the better the plane could overcome gravity. The lower the wingloading, the more efficient the climb would be at lower speeds and the higher the wing loading the higher the speed for efficient climb since a high wing loaded aircraft requires a larger angle to produce the same lift...am I thinking about this right?

Now reversing the thought and moving to dive...thrust to weight is no long relevent since gravity is not a resisting force but rather a propelling force...drag is your primary resistance...so thrust plus weight (mass might be more appropriate) are the propelling forces with drag being resistance...now I'm thinking the dive angle is a big deal here and wingloading should also factor in because the steeper the dive, the less angle of incidence...because gravity wants to pull the aircraft straight down, the propeller is moving it forward and the wings are providing lift which is resisting the gravity...on top of that throw in drag. I've read before that parasitic drag increases with speed...does it increase at an increasing rate as air density thickens? I'm thinking it does because with throttles off I am under the impression that planes can and will reach a terminal dive speed and actually decelarate without engines propelling them forward...the propeller will also create drag. I was imagining a free body diagram and trying to understand the forces involved....

So, having stated all that, If I'm remotely close then the weight and thrust should be additive in nature...so heavy aircraft with high horsepower should accelerate faster than light aircraft with lower horsepower. High wingloaded aircraft will out dive low wingloaded aircraft and high drag aircraft will not accelarate nor maintain their dive speed as well as low drag aircraft. Shallow dive angles will favor a high wingloaded aircraft over a low wingloaded aircraft...is that thinking correct? What other significant factors are there?

Now I wouldn't know the math, but if we had an idea of how drag was calculated, I'd think we should be able to calculate the relative difference in accelaration in a dive...what I'm really trying to understand is given an aircraft's weight, horsepower/thrust, drag and wingloading...how fast should it accelerate in a dive relative to an aircraft with different specifications? Does anyone know the math?

If we can do that, maybe we can understand how the dive is modelled or not modelled...I know a Wildcat can outdive a zero...a P-47D outdive a Bf-109 in real life, but I get the impression that the diving ability (in game) of an aircraft is more related and proportional to its top speed, and accelaration...if is accelarates fast and is faster than another plane then it will outdive it...regardless of engine horsepower, weight and wingloading. I haven't been able to figure out a test and I'm not sure how I'd hold dive angle consistant but based on the feedback received, maybe there would be a way to test.

Your thoughts? I only have a very rudimentry and basic understanding of physics, statics & dynamics and virtually no knowledge of aeronautical engineering....but I bet there are some here that do!

Grey_Mouser67
10-07-2005, 06:26 PM
I've been following Targets roll rate graphs with great interest. I realize, as do most rational people, that there simply is no way to accurately model aircraft given current technology completely...so I really never got caught up in the "this plane isn't as fast as that plane" but rather looked at it from a relative standpoint to other aircraft...anyways...since roll rate is off, I got to wondering about dive modelling...I have always felt that E and Dive were the worst modelled aspects...rate of roll aught to be pretty easy to model, but it is way off in many aspects so...some questions about physics for the physics buffs.

As I think about climb rate, I am under the impression that power to weight ratio...probably better thought of as "thrust to weight" since power is only a part of the equation...rpm's and propeller efficiency play a big part too. Drag and gravity are the primary resisting forces to overcome and drag increases as angle of attack increases on the wing....I would conclude that the better the thrust to weight ratio, the better the plane could overcome gravity. The lower the wingloading, the more efficient the climb would be at lower speeds and the higher the wing loading the higher the speed for efficient climb since a high wing loaded aircraft requires a larger angle to produce the same lift...am I thinking about this right?

Now reversing the thought and moving to dive...thrust to weight is no long relevent since gravity is not a resisting force but rather a propelling force...drag is your primary resistance...so thrust plus weight (mass might be more appropriate) are the propelling forces with drag being resistance...now I'm thinking the dive angle is a big deal here and wingloading should also factor in because the steeper the dive, the less angle of incidence...because gravity wants to pull the aircraft straight down, the propeller is moving it forward and the wings are providing lift which is resisting the gravity...on top of that throw in drag. I've read before that parasitic drag increases with speed...does it increase at an increasing rate as air density thickens? I'm thinking it does because with throttles off I am under the impression that planes can and will reach a terminal dive speed and actually decelarate without engines propelling them forward...the propeller will also create drag. I was imagining a free body diagram and trying to understand the forces involved....

So, having stated all that, If I'm remotely close then the weight and thrust should be additive in nature...so heavy aircraft with high horsepower should accelerate faster than light aircraft with lower horsepower. High wingloaded aircraft will out dive low wingloaded aircraft and high drag aircraft will not accelarate nor maintain their dive speed as well as low drag aircraft. Shallow dive angles will favor a high wingloaded aircraft over a low wingloaded aircraft...is that thinking correct? What other significant factors are there?

Now I wouldn't know the math, but if we had an idea of how drag was calculated, I'd think we should be able to calculate the relative difference in accelaration in a dive...what I'm really trying to understand is given an aircraft's weight, horsepower/thrust, drag and wingloading...how fast should it accelerate in a dive relative to an aircraft with different specifications? Does anyone know the math?

If we can do that, maybe we can understand how the dive is modelled or not modelled...I know a Wildcat can outdive a zero...a P-47D outdive a Bf-109 in real life, but I get the impression that the diving ability (in game) of an aircraft is more related and proportional to its top speed, and accelaration...if is accelarates fast and is faster than another plane then it will outdive it...regardless of engine horsepower, weight and wingloading. I haven't been able to figure out a test and I'm not sure how I'd hold dive angle consistant but based on the feedback received, maybe there would be a way to test.

Your thoughts? I only have a very rudimentry and basic understanding of physics, statics & dynamics and virtually no knowledge of aeronautical engineering....but I bet there are some here that do!