Archive for February, 2010

Not a lot of difference…

Friday, February 26th, 2010

I am in the process of updating Prop Designer and part of that is to use what is claimed to be an improved model to model the propeller blades. The model is the Adkins and Leibeck model which is claimed to be better than the Larabee and Glauert models I have been using. The models are generally similar but the Adkins and Leibeck model does not use approximations.

I have implimented the design of low induced loss designer and on first inspection there seems to be not a lot of difference between the 2 models. The results are similar enough that most users will not find  any difference worth worrying about.

I am in the process of modifying the main calculation routine and I will then move on to the off-design routine.

There are a number of other improvements I am thinking about making. If I can find the time and figure out ways to impliment the features they will be added otherwise I will release a version with only slight improvements.

Wortmann FX 63-137

Sunday, February 7th, 2010

It was pointed out to me that the lift v angle and Cm v angle graphs were wrong for the FX 63-137 characteristics. For some reason I had put the wrong graphs on the page so I took the opportunity to not only correct the page but to double check the coordinates for the section.

This is where the trouble started! I scanned in what I consider the original section coordinates from “Man Powered Flight” and converted them to a .dat file format. Running them through JavaFoil to check how good they were I noticed that the results were not as good as they could be so I then used QFLR5 0.04 to check and I could get it to smooth the profile by moving the coordinates and add some more points. I chose 101 points and the output was fine as soon as I made the angle step 0.25 degrees. I could have used that section coordinates for the smoothed  version of the FX 63-137 but I didn’t. I went to the UIUC airfoil database at http://www.ae.illinois.edu/m-selig/ads/coord_database.html and checked out their versions of the FX 63-137. They are slightly different from each other which makes me think their smoothed version could be renamed FX 63-137 modified. Also on the site is a link to a report http://www.ae.illinois.edu/m-selig/uiuc_lsat/vol4/NREL-SR-500-34515.pdf which contains what I hope is better quality coordinates for the FX 63-137 than the site itself.

Why am I checking all these various sets of coordinates for the FX 63-137? I don’t know. It is a very difficult section to build as you have to modify the trailing edge for structural reasons and the accuracy of construction with lightweight methods uses by HPAs means there are likely to be inaccuracies. As I always suggest, it is best to build a test section and try it for yourself first.