For those still following this thread I recently switched to the Horizon Hobby 25-46 rotating electric retracts for my Top Flight F4U ARF. The Horizon retracts have been through several flights and worked perfectly. Although they are longer than the opening it is only 1/16th of an inch and I was able to take that off the leading edge side leaving the spar untouched. Previously I had some plastic retracts that didn't work worth a darn. They would not extend in the airstream or failed to retract when the end point sensor was not working. I'll admit to being one of those that does not want to invest more in the retracts than the entire plane so some of the options here seemed excessive. I'm sure they work but don't seem practical from a cost perspective. For the money and the simplicity of use (no air equipment required) the Horizon retracts work well and seem to be holding up just fine after several flights.