I built one of these a few years back. I modified it to take a Dynamax fan and an OS.77. It had spring air retracts. Dry weight was 9.5#. It performed very well. But I always wonderered what the performance would have been like with a Turbax and OS.46 or K&B.45. It would have been a pound or so lighter, which would have improved the wing loading. Ivan Muninghoff scratch built a similar sized F-15 and he used the Turbax sized fan with great success and he is from Colorado also.