Science fair project on gear

[jacimino 0]

I am in the 6th grade and working on an experiment involving parachutes. I constructed 4 small p-chutes;round, square, rectangle & triangle all w/same surface area. I have some basic ?s
1. What shapes are best and why?
2. How close to the ground can you fall and have the p-chute work
3. How often do they fail to open?
4. Do the dif. Branches of the Armed Forces use dif stlyes?
5. How much smaller is the back-up p-chute than the main p-chute? Thank you, James

[lisamariewillbe 1]

First thing is I would ask your parents permission and maybe provide the state that you live in. I assume there would be many instructors and skydivers willing to help you answer those questions and give you some advice.

Other then that good luck and post pictures of your parachutes, wed love to see them.

Sudsy Fist: i don't think i'd ever say this
Sudsy Fist: but you're looking damn sudsydoable in this

[skybytch 273]

You may find some of the articles here and here helpful.

1 - Which shape is best depends on the application.

2 - Depends on how fast the canopy opens.

3 - Often enough that we carry a reserve. Generally parachutes don't open due to a failure on the part of the jumper to activate them, not due to a failure of the canopy. Likewise, generally parachutes that malfunction do so due to a number of reasons that have little to do with the parachute and a lot to do with the person packing/operating it.

5 - Depends on the needs/desires of the jumper. Many people prefer that their reserve be larger than their main.

[nbblood 0]

Ok, I'm going to try and help out a little too.

1. First of all, the difference between square and round parachutes used in skydiving/military parachuting is more than just the shape. Round parachutes are simply a round piece of material, a single layer, that provides drag and slows descent. Modern square parachutes are much more complex. They have an upper skin and lower skin and are divided into cells. The front end is open allowing air to fill the cells and the tail is closed capturing the air and creating a pressurized wing. Square parachutes fly through the air instead of simply providing drag to slow descent. In military tactical jumps, round parachutes are better because they are less maneuverable in the air which prevents excessive canopy collisions during large tactical jumps. Ram air parachutes are more maneuverable and provide lift allowing a much softer landing. This makes them much preferred in sport skydiving.

2. How close to the ground a parachute will work depends on a lot of things. There are many things to do to slow down or quicken the opening of the parachute. This is probably a little too complex to explain at this point. However, skydiving parachutes typically open in 300-1000 feet of altitude. This is very rough and general figures. However, BASE jumpers use quicker opening parachutes and jump from altitudes less than 200 feet sometimes.

3. How often a parachute fails is difficult to determine. However, cutaway numbers in recent years have averaged roughly 1 in every 1000 skydives. That means for every 1000 jumps, 1 time a main parachute will malfunction to the point a skydiver cuts away and deploys the reserve. Again, this is very general and rough.

4. I'm in the Army. There are several parachutes that the Army has used over the years. The -10 model is the most common for tactical jumps. We also use steerable rounds such as the -1B and -1C but they are not generally used during large tactical jumps as they are more maneuverable and would likely lead to more canopy collisions with many people in the air. During High-Altitude/Low Opening (HALO) operations, jumpers use square ram-air parachutes such as found in sport skydiving. However, they are much bigger than typical sport parachutes to account for the additional weight of combat equipment. These are typically small unit insertions, generally special operations forces. I believe the other branches of the military use the same models for tactical jumps as the Army.

5. The reserve parachute is not necessarily smaller than the main. In many cases it is actually larger. Generally main and reserve sizes are roughly the same for a particular jumper, but it depends on that jumper's canopy selection.

Hope this helps you out some.

Blues,
Nathan

If you wait 'til the last minute, it'll only take a minute.

[teason 0]

Your first question is an interesting one. Unfortunately there is far too complex an arguement as different shaped canopies have different design charcteristics. For example a common round canopy in skydiving has only one layer of fabric while a square canopy has two layers which inflate and form a wing shape. The round canopy slows you down by generating drag while a square glides and generates lift like a wing. I'll assume you are constructing these parachutes like the common round (lines attached to the outside edge) in which case, there are other considerations. In round canopies, the line are typically twice the radius of the canopy to ensure stability. If the lines are to short, the canopy will not fly well. Round canopies also have a vent or hole in the top to adjust the critical opening velocity.
With all the variable that pertain to the different shapes, a better experiment maybe to find the optimum line length for stability, the effect of enlarging or shrinking the vent hole on opening times and the effects of tying a line to the center of the parachute to "flaten" out its profile. (This was done in the 60s with a parachute called the paracommander)

second question, A parachute's opening time can be effected by a skydivers body position, freefall speed, canopy size, etc. For example, a "base jumper" (a jumper who jumps off buildings) can open his parachute in a couple of hundred feet. I have also seen my own parachute open in 1500 feet. There is no firm answer exect that is could open in a couple hundred feet or not at all. (pretty crappy answer huh?)

Third. It's actually very seldom that the parachute "doesn't open". A more common situation is that the parachute opens but is not flying properly and is therefore unsafe to land. At our dropzone, we see a parchute malfunction about once for every thousand skydives. Although I know jumpers with thousand of skydives and no malfuctions, I had my first one after only 50 or so. Just the luck of the draw.

Fourth. The armed forces do use different types of equipment for different jobs. Specialized tactical missions would involve canopies with high glide ratios and forward speeds with square gliding canopies while mass troop deployments would use round canopies with little to no forward speed. When you have that many troops in the air, you don't want them flying into each other.

Finally, the reserve parachute is typically the same size as the main parachute (my main is 170 sq ft and my reserve is 181 sq ft). The big difference is the design of the canopies. The main is of a high performance design with fast landings in mind while the reserve has a design with a slower stall speed. This is because a malfuction will cost altitude and I may not be able to land in the nice open landing area. I may have to land near hazzards and in that case, a canopy with a more docile flight characteristic will suit me much better.

Hope that helps

I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

[tso-d_chris 0]

Quote

I am in the 6th grade and working on an experiment involving parachutes. I constructed 4 small p-chutes;round, square, rectangle & triangle all w/same surface area. I have some basic ?s
1. What shapes are best and why?
2. How close to the ground can you fall and have the p-chute work
3. How often do they fail to open?
4. Do the dif. Branches of the Armed Forces use dif stlyes?
5. How much smaller is the back-up p-chute than the main p-chute? Thank you, James

The difference between a round parachute and a square parachute extends beyond their shape. A round parachute simply catches a bunch of air, and uses a large amount of surface area to slow the descent. These usually fall close to straight down when there is little wind.

A rectangular parachute, often called a "square," works completely differently. It is an inflatable wing that actually produces lift, very much like an airplane wing. While this type of parachute, called a ram-air canopy, does not produce enough lift to allow the jumper to stay in the air, it does produce enough lift to slow the jumpers descent to allow a soft landing if flown properly.

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[councilman24 37]

Along with the above advice I might suggest you go to your library and look for a book by Dan Poynter, title Parachuting, the skydivers handbook. If they don't have it ask to get it by interlibrary loan. This will explain some of the things you've asked.

I'm old for my age.
Terry Urban
D-8631
FAA DPRE

[riggerrob 643]

Just to mess with the other posters ...
Heehee!
... there are round, square and triangular versions of "round" parachutes.

By "round" parachutes, I mean parachutes with equal-length suspension lines that are designed to go straight down.

Round "round" parachutes are still widely used by the military, but fell out fashion with skydivers about 20 years ago.

Square "round" parachutes have been built/sewn by the Russians since the 1930s and may still be found in a few ejection seats. The US Army recently experimented with a square "round" for static-line jumps.

Finally, there are a bewildering array of triangular parachutes, but only a couple of triangular "round" parachutes: the Hoffman Triangle (circa 1932) and a similar parachute, built (in small numbers, late in World War 2) for the German Army. However, the Hoffman Triangle had a hole in the rear corner, which gave it some forward speed, which gets us into the huge, complicated subject of steerable parachutes.

But steerable parachutes are a separate lesson.

[wmw999 2,587]

And, since the student is in the 6th grade, I'll bet that his parachutes are, in fact, 4 pieces of single-thickness fabric with lines sewn or tied to the outside perimeter.

Jacimino, when skydivers talk about different shaped parachutes, they're not talking about that kind of thing; the resources that they gave you will give you a lot of real-world information.

But if you want to find out what your 4 parachutes will do, you'll have to drop them and time them. It might be hard to get an exact time -- you might want to try it from the top of a gym or some other indoor place so that the wind doesn't hurt you. Good luck -- I judge science fair every year, and this one would be fun.

Wendy W.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)

[nbblood 0]

Quote

Just to mess with the other posters ...
Heehee!
... there are round, square and triangular versions of "round" parachutes.

By "round" parachutes, I mean parachutes with equal-length suspension lines that are designed to go straight down.

Round "round" parachutes are still widely used by the military, but fell out fashion with skydivers about 20 years ago.

Square "round" parachutes have been built/sewn by the Russians since the 1930s and may still be found in a few ejection seats. The US Army recently experimented with a square "round" for static-line jumps.

Finally, there are a bewildering array of triangular parachutes, but only a couple of triangular "round" parachutes: the Hoffman Triangle (circa 1932) and a similar parachute, built (in small numbers, late in World War 2) for the German Army. However, the Hoffman Triangle had a hole in the rear corner, which gave it some forward speed, which gets us into the huge, complicated subject of steerable parachutes.

But steerable parachutes are a separate lesson.

Yes, I'm aware that there are a ton of variations of these types. I just thought I'd keep it simple.....like kind of at the sixth grade level.

I also think Wendy's right This student's parachutes are surely single layer fabric in different shapes. The results should be interesting. But I took the question as he wanted to know about modern parachutes used in skydiving/military operations.

Blues,
Nathan

If you wait 'til the last minute, it'll only take a minute.

[peek 21]

This is not exactly an answer to your question, but is more for the skydivers reading this thread.

The Parks College Parachute Research Group web site creates so many inquiries from students about science projects related to parachutes, that we created a Student Area on the web site.

Feel free to mention it to any student that asks.

http://www.pcprg.com/student.htm