Jump to content

i need discorver how i can calculate the Resistance of the fuselage of a rocket this for my college test(also i not english speaker)


Recommended Posts

Welcome to the forum. :D

Your thread has been moved since it doesn't appear to be a mod release. 

While we're here, could you expand upon the meaning of your picture? And it's relation to fuselage drag? 

Link to comment
Share on other sites

Putting hands together into a pointed shape definitely decreases their air drag resistance, but the rest of the fuselage on the picture looks too bulky to let this significantly decrease the total drag.

Edited by kerbiloid
Link to comment
Share on other sites

"Nonsense thread" is a harsh way of looking at it. Not everyone grew up speaking English, yet this person put the effort into posting in a foreign language. It costs us nothing to be encouraging. 

Link to comment
Share on other sites

1) Computational fluid dynamics simulations, something of which I have no familiarity.

2) Build it (or a scale model of it) and test it in a wind tunnel.

3) Guesstimate the ballistic coefficient based on published ballistic coefficients from similar-looking rockets.

There is no easy, analytical formula for drag: everything is either an approximation, or computationally demanding and an approximation, because differential equations are fun like that.

Link to comment
Share on other sites

10 hours ago, Vanamonde said:

"Nonsense thread" is a harsh way of looking at it. Not everyone grew up speaking English, yet this person put the effort into posting in a foreign language. It costs us nothing to be encouraging. 

But the person can at least post a picture of the project to understand what's given and what's needed.

(Not just the neko)

Link to comment
Share on other sites

I mean, how precisely do you need it? At subsonic speeds and in low supersonic regimes, to a good approximation, drag is FD = (1/2) CD ρ A v2, where ρ is density of the relevant fluid (air), A is cross-section area, v is velocity relative to the fluid (air), and CD is the drag coefficient. That last one is the hardest to estimate. For a rough order-of-magnitude estimate, CD tends to be close to 1 for subsonic flows. Wikipedia article on Drag Equation has a bit more detail.

If you need it more precisely than that, yeah, you'll need to either do a scale test in a wind tunnel, keeping Reynolds Number consistent, or do a numerical estimate of the drag by simulating the flow, which gets comically complex.

Lacking a wind tunnel, there are a few tricks you can play.

If we are talking about a model rocket, you can drop it and see how fast it falls. It's possible to estimate drag from timing the time of the fall very precisely. Of course, you'll want to have either a way to catch the rocket safely or be prepared to crash a few replicas.

For a real rocket, you can use the fact that Reynolds Number scales with density and test a toy-sized replica in water. That would let you measure drag forces at much lower speeds. If you get the size and speed correctly to have the same Reynolds Number, measure the drag force with a spring scale or similar, and compute CD for the model, it should be very similar to that of a real rocket.

Link to comment
Share on other sites

2 hours ago, kerbiloid said:

But the person can at least post a picture of the project to understand what's given and what's needed.

(Not just the neko)

- Please solve this college test for me!

- Ok, what test?

- Here’s a pretty picture! 

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...