On Thursday, November 7, 2013 11:22:21 AM UTC-5, Sean F (F2) wrote:
On Thursday, November 7, 2013 10:31:19 AM UTC-5, wrote: On Thursday, November 7, 2013 8:16:56 AM UTC-5, wrote: Hank, I have heard the performance is degraded 1% at low speeds and 2% at high speeds from the factory. I have also heard as much as a 2-4% degradation was found on a recent non factory sponsored test. The airflow of the Lak17b FES is clearly disturbed at the nose and that turbulence very likely impacts the wing root slightly, more at higher speeds. I would take a bet that claimed only .1% performance impact. I am almost certain that it is much more than that. It just takes a simple look at the system itself to see the disturbance that is created by the root of the propellers when folded, not to speak of the 18 inch propeller blades lying on the fuselage nose when folded back in gliding flight. They have done a wonderful job trying to make it clean, but that folding propeller it is not perfect by any means. Here is a thought! If the ASG29 had FES as a standard offering I can bet the handicap adjustment would be under more serious consideration! A handicap adjustment for the Lak17b is absolutely needed in the US. The fact that their IS a performance impact IS NOT DEBATABLE. The only debate is how much. Here are some photo's that clearly show the structure of the folding propeller system and its impact to the airflow: https://www.google.com/search?q=fron...w=1706&bih=781 Good point on the article but the HC committee should be smart enough to figure these obvious things out on their own. It's as if they did not think about or research this glider in any way vs a pure glider. Having worked as part of the US handicap subcommittee for many years, I would as the writer where the data for this "obvious" thing would be located? The factory claims minimal loss of performance. I would be inclined to agree. If an owner was to request a review by the HC, and provide basis for requesting it, I'm sure it would be looked at. A rough guess would be it may reduce cross country speed by a tenth of a percent or two. That would make a scoring error of a couple points a day. UH

From the FES web site:
We developed a special very light carbon fibre foldable propeller. The propeller opens quickly using centrifugal force when rotation starts. It has 1.0m in diameter and each blade weighs only 240 grams. The blades are slightly bent to take the shape of the front surface of the fuselage. During propeller folding, pitch of blades is automatically reduced when they rotate closer to the fuselage. Additional drag of the folded propeller is really minimal as proved by accurate Idaflieg flight performance measurements.

Obviously it would be useful for an interested party to provide the Idaflieg data to the handicap committee so that an appropriate adjustment could be made.
That would certainly take my WAG or Sean's "I have heard" info out of the picture. It certainly is a cool approach to the sustainer issue.
UH