# Tag Info

Accepted

### How would adding a wind deflector in front of roof-mounted solar panels affect drag on an RV?

The concept of what you're doing is sound, and as Russell McMahon notes the efficiency gains could be significant enough to justify the change. I'd strongly suggest that you consider adding a ramp to ...
• 1,966
Accepted

### How does the pressurized suspension of the Hyperloop not affect the tube pressure?

The air used for the air cushions will come from the air still in the tube pressurized by the pod itself. Thus the system remains closed (all air that is released is sucked out of the environment).
• 5,666
Accepted

### Below what Froude number can I neglect wave-making resistance on a vessel?

Your intuition is correct, those are high. However, you would need to be moving very slowly for wave-making resistance to be negligible. And since it is typically higher than skin-friction I don't ...
• 917

### Anomaly in viscous force - vs - velocity relationships

The examples you mentioned both occur due to turbulent flow of a gas. However in a lot of mechanical systems damping often occurs due visco-elastic deformation or due to shearing of the lubricant ...
• 1,603

### Is the drag coefficient/velocity of of a vehicle based on frontal area?

The drag coefficient $C_d$ is defined as: $C_d = \dfrac{2F_d}{\rho u^2A}$ where: $F_d$ is the drag force, which is by definition the force component in the direction of the flow velocity; $\rho$ is ...
• 7,481

### Is the drag coefficient/velocity of of a vehicle based on frontal area?

No Cd is not directly related to the frontal area, it has to do with how much that frontal area moving against the stream of air has to fight drag. For example, consider the old semi trucks' trailers. ...
• 21k

### Does more downforce affect the acceleration and top speed?

You do not want to overcome the force of static friction when accelerating because that's when the dynamic friction takes over and your wheels slip. That means that the force applied on the edge of ...
• 3,230
Accepted

### Does the aerodynamic force qualify as a viscous damping force in the Mechanical Harmonic Oscillator

The equation $F_{\textrm{A}} = C_{\textrm{D}}A\rho\dot{x}^2/2$ doesn't tell you that drag is proportional to the square of velocity. In itself, that equation doesn't tell you anything at all about ...

### Below what Froude number can I neglect wave-making resistance on a vessel?

Whether these are sensible Froude numbers or not depends on the length of the vessel in question. For a 100 m ship these are probably high but for a 5 m dinghy these would be quite low numbers. Speed-...
• 1,025

### How would adding a wind deflector in front of roof-mounted solar panels affect drag on an RV?

Stress on panel mounts needs considering. This can be greatly reduced by a "ramp" that fully protects the panel from air impact in the forward direction. Flat plate drag for a panel will be <= ...
• 3,824

### Is there a way to simulate the drag effect created by acceleration while in a stationary object?

The rides in Disneyland do a great job of combing the visual cues of the ride with actually accelerating the vehicle or boat or rocket but in a carefully designed short span giving the impression of ...
• 21k

### How would adding a wind deflector in front of roof-mounted solar panels affect drag on an RV?

I can remember this being discussed during a fluids lecture in my student days a long time ago, when the subject of car roof racks and truck fuel scoops was raised. The panel will increase the drag ...
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### Below what Froude number can I neglect wave-making resistance on a vessel?

"Hull speed" is actually the ratio of speed to the square root of length. To make things even more confusing, length is in feet, and speed is in knots. That's how the constant 1.34 arises. (ProTip: ...

### What is the area when calculating the drag coefficient for a race car wing?

When $C_d$ is an appropriate parameter for discussion, road vehicle aerodynamics uses the planform area of the wing. That's the area formed by the chord (see below) and total width of the wing. You'd ...
• 1,966
Accepted

### RC drone rotor air access

In the 50's the DARPA designed such a craft but due to aerodynamic instability it was a complete failure and abandoned. The problem you have is maintaining 4 separate intakes which have a greater ...
• 844

### How long does it take and how far does it travel a sphere in free fall before reaching a percentage of the terminal velocity?

I suggest using the relationship below to derive the equations you are looking for. $F = ma$ $W = mg$ $D = \dfrac{C_d\rho V^2A}{2}$ $C_d$ = Drag Coefficient (Shape dependent) $\rho$ = Atmospheric ...
• 7,481
Accepted

### Is there a way to simulate the drag effect created by acceleration while in a stationary object?

"the drag from acceleration" This isn't called drag. It's just called force or perhaps inertia. No you can't, not completely stationary anyways. The body detects forces based on ...
• 3,230
1 vote

### Drag coefficient of a complex object made using simple objects (with known drag coefficient) in small Re?

At such very low Reynolds numbers, skin friction drag will (Landau and Lifshitz, 1987, Fluid mechanics, Butterworth-Heinemann, section 45) dominate over pressure drag (this is despite the sharp edges ...
1 vote

### Is the drag coefficient/velocity of of a vehicle based on frontal area?

The $C_D$ is a convenience factor used by engineers to simplify fluid mechanics for cars and aerodynamics. A simplified explanation is that the $C_D$ normalises the aerodynamic drag to the frontal ...
• 22.6k
1 vote

### Does more downforce affect the acceleration and top speed?

TL;DR: I will expand on DKNguyen answer, which provides all the salient points. i.e. (my interpretation) the downforce is desirable to provide a better interface/grip between the car and the ground.) ...
• 22.6k
1 vote
Accepted

### How long does it take and how far does it travel a sphere in free fall before reaching a percentage of the terminal velocity?

TL;DR: the time required to reach a $p$ percentile of the Terminal velocity $$t_p= \sqrt{\frac{2\rho_{sphere}r}{g \cdot C_D \rho_{air}}}arctanh\left(p \right)$$ the distance travelled required to ...
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1 vote
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• 3,425
1 vote
Accepted

### Boat Hull Drag in Shallow Water

I found some possibly applicable explanations here. The figure referred to in the quote below is The attached plot [Hofman 2000] illustrates the basic principles of added drag due to shallow ...
• 4,033
1 vote

### What is the area when calculating the drag coefficient for a race car wing?

The area is named "reference area". As long as it is defined by someone, you are free to choose any arbitrary value for A. To make comparisons easier among different designs for a certain project, ...
• 896
1 vote

### How can i calculate drag on an Angled area?

I believe under Results>Reports>Forces, you can calculate the force on a chosen surface in a particular direction vector (by providing x,y,z coordinates). Does that help?
• 151
1 vote
Accepted

### Coefficient of Drag (Cd) Question

So the formula you need is Density = P /(R*T) and the value of R you have been given is for air. Once you have re-worked your answer then you should calculate the Reynolds number and then you can ...
• 13.9k
1 vote

### Could car waste heat be used to lower drag?

I see how you're thinking: the car is a "piston" and if you heat the air behind this "piston", it will push it forward. Now think how inefficient this "engine" is - you are adding fractions of a ...
• 291
1 vote

### Could car waste heat be used to lower drag?

The thermic energy output of a car is too small to make a difference. Also the technical implemention would be very difficult. Did you ever hold your hand near to the exhaust. Its really not that hot ...
• 111

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