Sunday, January 17, 2010

Top Speed RC Contest

John and I are competing in an unofficial "top speed" construction contest. Only rules are that the aircraft needs to be electric powered, and must be flying after the top speed attempt. The contest will take place on March 1st 2010, at a place to be determined.

I am designing and building my own entry. So far my chosen configuration is a flying wing with dimensions modeled after the Ritewing Demon 40, with a HS522 airfoil. My initial design had a 40" wingspan. I'm thinking that I will build the 40, but perhaps with a better low speed airfoil, and use the first airplane for a test bed. I'll probably use a lower powered drive system for the initial build.

I selected the HS522 airfoil based on data found on this german (english language) website:
http://www.aerodesign.de/english/profile/profile_s.htm
http://www.aerodesign.de/english/profile/profile_s.htm

Translating Airfoil section co-ordinates to Solidworks Model:
This is fairly easy to do, but takes a few steps:
1) copy x,y coordinates from source website.

2)  paste into text file. If you try to directly paste into excel, you'll lose the data columns. Save the text file.

3) Import into excel. The data is delimited with spaces, it should be a straightforward import process. 
4) remove column headers. Add a third "z-axis" column- also without a column header. Fill this column with all "0", since you want the airfoil cross section to be in the same datum plane. Save first as excel file. Then, save as a txt file. Only save this workbook sheet.

5) Open Solidworks. Create a new part file. Insert a "curve through XYZ points". Click on "browse", select your text file. Once the curve is selected, you'll have create a new sketch, select the 3D curve you created, click on the curve, copy the curve into the sketch, then scale the curve to the size you need for your design.


Phew!






Initial "Speedwing" Power System:

  • Turnigy 2836 3200kv motor
  • Rhino 2150 mAh 4s pack
  • Turnigy Plush 80A speed control
  • 6x4 Prop
  • This system yields a maximum pitch speed of 179 mph

I've been modeling the aircraft in Solidworks, and trying to keep the calculated CG within the recommended location for the Ritewing Demon. I've been having a hard time keeping it far enough forward, so I've cut lightening holes in the wing and vertical stabilizers.

Density Assumptions: (all from web searches)

Bluecore foam density: 2.2 lb/ft^3   - NOTE: I discovered this density isn't accurate, see later post for measured value
Balsa density: 10 lb/ft^3
Carbon fiber density: 115 lb/ft^3

Next I'm going to try and calculate the center of lift for the wing and make sure it matches up with the recommended CG location from the reference Ritewing Demon design.



No comments:

Post a Comment