Aerodynamics

[Thanh33]

I'm not sure if i can ask for interviews but,

Can I have an Interview with an aerodynamics expert?

Dear Scientists,
Hi, I'm Matthew and I have been working on
a science fair project. I need an interview of a professional in the
field of my topic. Its energy and transportation, specifically
aerodynamics. Here are the outlines of my project: I am going to make
four different models of parachutes that are all different shape and
surface area. I am testing how long it takes for each to reach the
ground when dropped from a high elevation. If I can interview you,
please give me your name and email address either by posting it here or
by sending me an email to matthewthanhle33@yahoo.com If anyone can help or if
you know how i can get an interview that would be great too.
that would be great and i would greatly appreciate it. Please i have been searching for someone to interview someone for a week and it is due in 5 days.

From, Matthew

[barretttomlinson]

Hi Mathew,

I am sorry to hear you are having so much trouble finding someone to interview. Unfortunately Science Buddies policy forbids any “expert” working on this site from contacting you in any way except by posting on this site. The only way on this site for you to get an answer is to post the questions you want to ask and then for the “expert” to post their answers to your question thread. I know this is a poor way to conduct an interview from your perspective, but the policy is there for everyones protection.

So if you can’t get a face to face interview by some other means, post back a list of the questions you want answered and some of our experts will try to respond.

Best wishes for a great project,

Barrett Tomlinson

[peteryoung]

Matthew -
Write up your questions and I'll do my best to answer them. Have you started testing yet?

Regards

Peter Young

[Thanh33]

Yes, i have done all my testing

Here are my questions:

1. Which do you think will land first?
Parachute 1: Circle Canopy and SA= 347cm²
Parachute 2: Circle Canopy and SA= 707cm²
Parachute 3: Rectangle Canopy and SA= 347cm²
Parachute 4: Rectangle Canopy and SA= 707cm²

2. What is aerodynamics in your own words?

3. What plays a more important part in which will land first, shape or surface area?

4. Does air resistance have the same effect on all 2d shapes, as long as they have the same surface area?

5. Would there be a big purpose for the information found in this experiment?

That's is all i can think of right now, and thank you for anyone who answers my questions, it 's a big help!

[peteryoung]

Hello Thanh33,

Thanks for the questions which I think are excellent ones. I'll put my responses after your questions which are copied below:

1. Which do you think will land first?
Parachute 1: Circle Canopy and SA= 347cm²
Parachute 2: Circle Canopy and SA= 707cm²
Parachute 3: Rectangle Canopy and SA= 347cm²
Parachute 4: Rectangle Canopy and SA= 707cm²

There's no question that parachute shape and surface area are important design factors. There are however other engineering items that will determine how effectively a parachute will operate:
- payload mass - too light and the parachute may not be able to descend fast enough to be effective as a decelerator. If the payload is too heavy, the parachute may not be big enough to develop a reasonably slow and safe landing speed.
- parachute shroud lines - have to be a proper length to match the parachute size and the payload mass.
- other more subtle items are the weight of the parachute material and the "airtightness" of the parachute material. The first item, the parachute material weight, could determine how quickly it opens as it starts to open. The second item would be important for long duration flight and is probably not a factor for your tests. If you are using light cloth or plastic for your tests, then you're probably OK.

2. What is aerodynamics in your own words?

Aerodynamics is the science of understanding how air flows around objects to develop lift and drag in aircraft; there are other more specialized aerodynamics areas such as the parchutes that you're presently evaluating. Key aerodynamic knowledge areas include fluid dynamics, structural engineering, stability, control systems, and other elements needed to design safe and effective flying machines.

3. What plays a more important part in which will land first, shape or surface area?

As I noted above in the first question, there are other factors which can affect parchute performance. Surface area though, if the other items are reasonably good, is a dominant factor. An additional complicating factor is parachute stability during descent - if air starts to spill out one side of the 'chute, a rocking back and forth oscillation can result that could result in the parachute collapsing and thus failing to function. For that reason, some parachute designers add slits or vents in the parchute canopy to control airflow to prevent undesirable spillage; what's very common and quite readily seen in pictures is a small air exit hole in the very top of the parachute canopy.

4. Does air resistance have the same effect on all 2d shapes, as long as they have the same surface area?

Your statement is more true for rigid objects than for flexible shapes. Parachutes by their very nature are very flexible, quite important so they can be packaged into small containers prior to use. In the example of parachutes, air resistance and the drag it causes is influenced by downward velocity (where payload mass is a dominating item); and the final shape of the unfolded parachute (how flat or "cup-like" it is). "Full scale" parachutes are constructed of many pieces of fabric material, cut and joined together so that the final opened 3-dimensional shape is controlled to a very high degree.

So the answer to your question: while parachute surface area is an important item, there are quite a few other factors that determine how much air resistance is generated during a parchute's flight and thus, how effectively the parachute will function.

5. Would there be a big purpose for the information found in this experiment?

I think the biggest payoff is that you're exploring a very interesting aspect of engineering, and learning quite a bit as you do it with your hands-on testing. Parachutes date back many centuries to Leonardo Da Vinci who was the first, I believe, to originate the idea of an aerodynamic decelerator (= "parachute"). Today, NASA uses parachutes to decelerate very expensive and complex payloads through the atmosphere of Mars and other planets with atmospheres; the astronauts and cosmonauts returning from the International Space Station return to earth using very large parachutes that absolutely have to work properly. There are very complex and high performance parachutes used by the military services to lower people and equipment where the parachutes are designed to provide very good gliding performance in cross-wind or up-wind conditions.

One question that I've heard from students is whether there's anything new in parachute design. There are some very exciting and challenging new developments. One is very sophisticated computer codes to model the air flow into and out of complex shape parachutes. Another are lightweight, very strong fabric and shroud line materials, that take up less space and weight than older materials, but are more effective. The Army has developed parachutes that use Global Positioning Systems to accurately steer cargo parachutes into landing zones, all without human help. There are also a whole family of high-lift parachutes that are designed to act like wings - these are known as "parasails".

I hope this helps, good luck with your project!

Peter Young

[Thanh33]

Yes! this definetly helped. i feel like a whole load of stress has been lifted off of me. thank you again and remember i really, really appreciate ur help!