Header Bar Graphic
Shuttle Image and IconAerospace HeaderBoy Image
Spacer TabHomepage ButtonWhat is NASA Quest ButtonSpacerCalendar of Events ButtonWhat is an Event ButtonHow do I Participate ButtonSpacerBios and Journals ButtonSpacerPics, Flicks and Facts ButtonArchived Events ButtonQ and A ButtonNews ButtonSpacerEducators and Parents ButtonSpacer
Highlight Graphic
Sitemap ButtonSearch ButtonContact Button
 

Aerospace Team Online

ATO#126 Designing a Mars Airplane - March 23, 2001

Part 1: Upcoming Chats
Part 2: Contest
Part 3: Pushing, Pulling and Twisting
Part 4: Designing a Mars Airplane ____________________________________________________

UPCOMING CHATS

Enter these chats from the Common Events page
http://quest.nasa.gov/common/events/

NOTE: TIME CHANGE

Aerospace Team Online Chat with Chris Lockwood
Tuesday, March 27, 2001 12 AM PST - 1 PM EST
Chat with Chris Lockwood the lead engineer in the balance calibration lab. Chris knows about wind tunnel testing and wind in sails too. Read his bio at http://quest.nasa.gov/aero/wright/team/clockwood.html

NOTE: DATE CHANGE
Atmospheric Flight 2 with Steve Smith
Thursday March 29, 2001 10 AM PST
Students have a second chance to ask Steve Smith questions about flight in Earth's and Mars' atmosphere. Go to http://quest.nasa.gov/common/events/ to attend.
Atmospheric Flight is important to understand in order to design for planetary flight. Visit the archive of Atmospheric Flight http://quest.nasa.gov/aero/events/atmos.html

Aerospace Team Online Chat with Kelly McEntire
Wednesday, April 4, 2001 10 AM PST - 1 PM EST
Chat with Kelly McEntire the branch chief for Turbo Machinery. Have you been wondering about whether to use a Turbo Jet engine for your Mars Airplane Design? Kelly knows propulsion. Read his bio at http://quest.nasa.gov/aero/team/mcentire.html

Aerospace Team Online Chat with Joe Kolecki
Tuesday, April 17, 2001 10 AM PST - 1 PM EST
Chat with Joe Kolecki a physicist specializing in space environment effects. His speciality is the planet Mars. Do you have a question for him about what the environmental effects on a Mars airplane? Read his bio at http://www.lerc.nasa.gov/WWW/K-12/CoE/JoeKolecki.htm ____________________________________________________

NEW CONTEST

Planetary Flight Book Jacket: March 26 to April 26, 2001

Grades 5-8

Contest Description:

This contest invites students to create a book jacket for a novel about planetary flight. The book jacket should include the title, author, and illustration on the cover. The binding should include the title of your story and the author's name. The back of the jacket should include a brief description about the characters, setting, and plot of the story.

For more information visit: http://quest.nasa.gov/aero/planetary/contest.html ____________________________________________________
[Editors Note: Chris is a mechanical engineer who invented a robotic balance calibrator. His work is to make sure that the balance measures strains correctly. Read his bio at http://quest.nasa.gov/aero/wright/team/clockwood.html ]

PUSHING, PULLING AND TWISTING

by Chris Lockwood

March 23, 2001

My name's Chris Lockwood and I work in the balance calibration lab. The last time I did a web chat was during the Wright Flyer effort here at NASA Ames Research Center. I explained a little about wind tunnel balance at that time too You can check that info out on the web at: http://quest.arc.nasa.gov/aero/wright/team/fjournals/lockwood/index.html

A wind tunnel balance (or just balance) is a thing that looks like the cardboard tube from a paper towel roll with the cone part an ice cream cone, stuck in one end. The "cone" part fits into the end of a long pipe called a sting. The sting is mounted in the wind tunnel so the tip - the balance - is pointing up stream. The balance has electronics inside to measure forces. If you were to hang on the balance, it would tell you how much you weigh, where you were hanging and which direction. Now of course gravity only goes down so the direction would be down, but if you put your feet the floor and push up on the balance it would tell you how hard you were pushing, and the new direction.

So what? Well now if you mount a model of an airplane on the balance and blow some are air across the wings, the balance will tell you how much lift the wings are generating and which direction. In fact the balance tell you every thing that the wind is doing to the model, in all directions - pushing, pulling and twisting. The thing to remember about a wind tunnel is this: if the model is stationary, and you blow air over it at 100 miles per hour, model thinks it's flying at 100 miles per hour even though it's going nowhere (models don't really think, but you get the idea). A wind tunnel simulates flight without having to first make something fly. It's a tool for experiments.

The last few weeks have been very busy. We have had a company that builds airplanes here testing a model of a plane that already exist. Companies like this always want to improve the gas mileage of their planes. To do that, they make them as smooth and sleek as possible. During this test, they are looking at one thing in particular called "fillet drag". A fillet is a rounded corner where two surfaces meet. Like at the bottom of some swimming pools. Well the question is, how round do you make the joint were the wings meet the body (fuselage) of an airplane? This company brought lots of different fillet panels, each shaped slightly different from the others. They will test them all to find out which one will create the least drag (backward push from the wind). The more drag you have the harder the plane's engines have to push and the more gas you use.

We had to calibrate 6 different balances for this effort because of all the different model pieces they wanted to test (see the previous journal web site to find out what we do when we calibrate a balance). The biggest balance was high strength steel, as big around as a large plastic soda bottle, and twice as long. It will measure up to 8000 pounds of lift. That's the weight of about 3 cars!

____________________________________________________
[Editor's Note: Steve Smith is an aeronautics engineer at NASA Ames Research Center. Read his bio at http://quest.nasa.gov/aero/team/ssmith.html ]

MARS AIRPLANE DESIGN

by Steve Smith

March 23, 2001

We were pretty excited when we were asked to help design an airplane to fly on Mars. This was a chance to use our aeronautics knowledge on a completely new challenge with some very special problems. Several of the team members had some experience with flight at very low atmospheric pressure from working on airplanes to fly at extremely high altitudes on Earth. But we had never tried to design an airplane that had to meet some really special requirements. It was my job as the Project Leader to understand the requirements and limitations on the design and make decisions about how we would meet the requirements.

The first requirement was that our airplane would have to fold up inside a small container that would carry it to Mars and protect it during a fast, hot atmospheric entry. this container, called an aero-shell, has a special heat shield called a thermal protection system on it to protect it and its contents from the intense heat during entry. You can read about other researcher's work on thermal protection systems at http://quest.nasa.gov/aero/events/thermal.html Once the aeroshell was slowed down and descending in the lower atmosphere, it opened a parachute, and then the heat shield was released. At this point, our airplane would be dropped out of the aeroshell, and unfold and start to fly.

We were very worried about getting the airplane to unfold correctly. suggested that the fewer the folds, the better. So we picked a design with just 3 folds: two wing folds and a fuselage fold. Some other people have tried designs with many more folds, as many as ten. But they did not always unfold properly.

Even with the airplane folded up, it still had to be pretty small to fit in the aeroshell. Not only that, but the mission planners gave us a maximum weight limit for the airplane, because the spacecraft that was to carry our airplane and aeroshell to Mars could only carry so much weight. Part of the weight allowance was used for guidance and communication equipment on the spacecraft, basically a computer, a radio, and an antenna. Then, there was the weight of the aeroshell itself, with its heat shield and parachute. So we were given a mass allowance of 20 kg for the airplane. On Earth, 20 kg weighs 44 pounds, but on Mars, it would only weigh about 15 pounds because there is less gravity on Mars. The inside diameter of the aeroshell was about 0.65 meters, or just over 2 feet. So with the airplane all folded up, it had to be less than 2 feet in any direction. With the wings unfolded, the wing span would be about 6 feet, since we had two folds.

One thing we did not know the answer to was which of these two requirements would be the controlling limitation. In other words, if we made an airplane that would just fit into the aeroshell, would it weigh more than 44 lbs on Earth? If so, we would have to make it smaller to stay within the weight limit, even if we had more space. I decided that we would go through the design process trying to make the airplane as big as possible, and see if we exceed the weight limit. As it turned out, it weighed just a little bit less than 44 lbs. so the size constraint was the controlling limit, but it was very close. If the aeroshell was just a little bigger, it might have turned out that the weight constraint would have become more of a limit.

Another challenge that we did not know very much about was all the equipment that the airplane would have to carry. The scientists that want to use an airplane to explore Mars told us the kind of instruments they would like to carry, but they did not know very much about how small they could be made. They also did not know how we would get the information from the instruments sent back to Earth. So I formed a group to concentrate on the instrumentation and data communication back to Earth.

The mission planners told us that the best way to get the information sent back to Earth was to first send it to the spacecraft that took us to Mars, and then that spacecraft would relay the information back to Earth. But this is really not very good, because after the spacecraft drops the aeroshell off on the way to Mars, it just keeps flying off into space. It is only in a good position to relay data from Mars for about 20 minutes. So even if our airplane could fly for longer than 20 minutes, no information would come back from it after the spacecraft flew past Mars.

The instrumentation and data communication group decided what instruments the airplane would carry, and what kind of radio and antenna would be needed, and what the data-management computer would need to store the data and send it back to the spacecraft. This group also studied the flight control computer problems too. In order to fly all by itself on Mars, the airplane needs some sensors and a computer to work as an autopilot. Once this group told the airplane design group what the instruments were, how much they weighed, and how big they were, then the airplane design could really begin.

We also had to decide how we would power the airplane. For our first airplane, we decided it would be simple to use an electric motor and batteries to power the airplane using a propeller. The other ideas we considered were using a rocket, and using a special turbine motor that burns rocket fuel but turns a propeller. The turbine motor would be similar to a jet engine, except that with no oxygen in the atmosphere, it won't work like a jet on Earth that breaths intake air. Instead, we would use rocket fuel that has its own oxygen mixed in. In the long run, this choice is probably the best. But no such motor exists, so for now, we would use an electric motor, and when a new motor becomes available, we could switch.

We had to make sure there was room in the fuselage for all the sensors, instruments, antenna, computer, plus the motor and batteries for the airplane. We were careful to position the various items in the fuselage so that the center of gravity was in the right place to get the airplane to balance for stability and trim.

While all this was happening, other people in the group were studying the best wing shapes and airfoils. Others were estimating how much the wings and fuselage would weigh, and what the folding mechanisms would be like. You can read Andy Hahn's Field Journal to get more ideas on what this part of the project was like. Finally, we put everything together and evaluated the performance of our design. To do that, we had to be sure it would make enough lift to carry its weight, estimate the drag of the airplane, make sure there was enough thrust to equal the drag, and then see how long the batteries would last. After a few tries, we found we could fly for more than 20 minutes, so our airplane was a success. We also decided that we would try to make it fly longer using the turbine motor and rocket fuel. We found that it could fly much longer, almost two hours. So in the future, this will be a good way to power airplanes on Mars.

Now, with the new planetary aeronautics web site, http://quest.nasa.gov/aero/planetary/ , you can try to design your own Mars airplane. You can make choices about what instruments to carry, what kind of fuel and propulsion system to use, what the wings should look like. The web applet will tell you if your design will work, and how long it will fly. See how long a flight time you can get! Good Luck.

 
Spacer        

Footer Bar Graphic
SpacerSpace IconAerospace IconAstrobiology IconWomen of NASA IconSpacer
Footer Info