Friday, March 9, 2012

Replacing Paper: Future of Back-of-the-Envelope Analysis

Will the computer replace paper for rapid conceptual design & analysis?

Back in the day, if someone asked you a "quick" question or you had a brilliant idea (perhaps one that would change the world), the first thing to do is to move objects around your desk until you find a pencil and a piece of paper (the thought is fleeting and you will not remember if not immediately committed to paper).

Next, you feverishly sketch drawings and write down equations until you realize "ah, this will work! (or not)". This activity is the beginning of the conceptual analysis process. If your idea is really-really good, the piece of paper that you will randomly find is an envelope (perhaps from a bill or unsolicited advertisement).

The reason for the back-of-the-envelope calculation is to jot down your ideas using a medium that is totally familiar (and responsive) before you forget (or misinterpret) the volatile thought.

No matter how well you can draw or how quickly you can perform algebra, the back-of-the-envelope lacks robust computation power. It is often tucked into an ajar desk draw or between the pages of your favourite fluid dynamics text until you can find more time to complete the thought.

However, while we were sharpening our pencils, someone was trying to "improve" the back of the envelope process. The video below shows how a computer can be used to sketch drawings on a surface and the "paper" will actually solve the problem.

This can work for aerodynamics as well. The video below shows Hanley Innovations' MultiElement Airfoils as a conceptual analysis tool for deciding the position and orientation of a group of airfoils. The software can generate the lift, drag and moments for any configuration. It can save the configurations and export the shapes and positions to a .dxf file. More information can be found at

Paper is indeed changing. The video below shows Autodesk ForceEffect on the iPad. The program allows drawing on the screen to solve statics problem using free body diagrams.

Do you think that the computer will replace the back of the envelope?

For more information about Hanley Innovations' interactive aerodynamics analysis software, please visit:

Thanks for reading, Patrick.


  1. Patrick:

    I recall seeing a TED video about a tabletop system where you set an object on the table and it automatically shows the streamlines around it. It was literally a tabletop wind tunnel.

    As for your question, the proverbial envelope (or napkin) is all in the head anyway. So yes, it will be replaced by the computer. But that computer will contribute as much as the envelope did.

    1. John,

      Thanks for your comments. Yes, I agree. In the final analysis, the user of both the envelope and computer is the instrument of the creativity and innovation.