Airplane Designs for Winglets

[deleted-249258]

My partner and I are doing an aerodynamics project, but we've come across a situation while writing up our experiment procedure. We're doing a project inspired by the Why Winglets project. We are to see if adding an extra winglet would improve the speed of an airplane. We were going to make 3 paper airplanes using a standard design. One would be normal (no winglets), the other with "regular" winglets (one on each wing folded up), and the third would have a split scimitar design (two winglets, one down and the other one up). While we can fold winglets on the planes, we can't do a split scimitar design using the standard airplane design.

Question: What design should we use for our airplanes? (This design has to be adaptable. It has to have a regular form and can be "tweaked" to form a winglet and split scimitar winglet.)

Alternative: If there isn't a design which can do the above, would it be a good idea to "make" the bottom part of the split scimitar and glue it on

[rmarz]

Must Finish - An interesting experiment, but let's consider the winglet argument for a moment. Winglets are designed into modern aircraft to reduce wing tip vortices. The vortex produced is the result of the significant pressure differences between the wings top and bottom surfaces recombining at the tip. The higher the wing loading, the more likely you will produce significant vortex energy. Here is why a paper airplane may no be the best platform to test your theories. Here are some typical wing loading figures from small and large airplanes.

Cessna 152. 10 pounds per square foot
Douglas DC-3. 25 pounds per square foot
AIrbus A-380. 136 pounds per square foot
Boeing 747. 152 pounds per square foot

Our paper airplane is probably made from a sheet of copier paper that weighs only 0.16 ounces. The wing area of the paper plane might be 0.4 square foot. The wing loading is a mere 0.026 pounds per square foot, insignificant compared to the larger aircraft that benefit from vortex reduction. Therefore, if there is no vortex production, winglets are not an appropriate mitigation solution. The Science Buddies experiment evaluated different wing configurations to see if flight length could be improved. Maybe you could base your experiment on these variables.

Rick Marz

[deleted-249258]

Thank you! My partner and I just did the Science Buddies experiment, but we calculated the length and speed of three airplanes (both with and without winglets). We increased the height of the winglets for each one (e.g. Plane #1's winglet = 1 cm, Plane #2's winglet = 2 cm). However, the results weren't what we expected. When the winglets were added, the planes didn't go as fast. Is that peculiar?

Note: Though I would love to get an answer back, my science fair is (May) Thursday 22nd and it's too late to change anything now.

[rmarz]

MustFinish_Project - The Science Buddy experiment uses distance flown as the measurement criteria. The procedure suggests that you must launch the airplane at the same angle and same force each time to get consistent results. That is probably difficult. You mentioned that you observed that the airplanes 'didn't fly as fast' with the winglets. How did you determine speed? What were the distances you measured between the 'winglet' and 'non-winglet' versions?

If you made the airplanes with a single sheet of paper as shown, and in the test cases bent up the end of the wing to create winglets, a couple of things happened. First, the area of the horizontal portion of the wing was reduced by the material that became the winglet. That may have changed the lift. When you bent up the winglets, they may not have been perfectly parallel to each other and could have induced new, parasitic drag (slowing the airplane).

I think this is an interesting experiment, but you have to make small incremental changes to the design, test the results in a controlled manner, and develop your hypothesis as to what introduced changes produced what effect. As I said, the paper airplane may not be the best platform for this analysis. Good luck.

Rick Marz

[deleted-249258]

Dear Mr. Marz, I read your reply soon after you answered, but for some reason, I haven't had the push to answer it until today (as I was looking through my inbox). Please accept my apologies.

My partner and I used the formula "Speed = Distance over Time" to determine how fast the paper airplanes went. Here were our results: http://goo.gl/bSNKoc We ultimately concluded, as we presented our board all day at the science fair, that even though winglets work on real airplanes, they do not work with paper airplanes. That's because the we decreased the size of the wing which, like you said, changed the lift. I also noticed that our winglets might not have been parallel (though my partner insisted they were and sometimes I thought they were as well). In my opinion, we could have been more careful and patient with the test flights and do the experiment once more to make sure results were more accurate. At the end of the day, the paper airplane wasn't, as you said, the best platform, but I felt pretty clever coming up with and executing the experiment. Unfortunately, I never got to see my official score for the science far, but I think I got a good grade. We did a great job and I'm glad we pulled everything off!

One more question though - Why did the Science Buddies experiment measure if higher winglets would lead to longer distance if the purpose of winglets are to make the airplane go faster easier (by reducing the drag)?

[rmarz]

MustFinish_Project - Your question is a good one. I don't know why the designer of the winglet experiment focused on distance flown as the basis of the experiment. That said, there certainly is a correlation between reduced drag and distance flown especially for a paper airplane. Glad you had a successful project.

Rick Marz

[deleted-249258]

Thank you for all your help Mr. Marz! Have a fantastic summer!