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Author Topic: Let's talk E20  (Read 57633 times)
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PaulBrad
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« Reply #750 on: September 22, 2018, 07:29:12 PM »

As George has noted, there are a variety of ways to stop your E20 prop. Ralph did look at alternative methods. The issue was prop run down time. The goal was to get the prop to stop quickly and reliably every time. The use of magnets in a bar rather than a strip of material that is attracted to a magnet provided a more positive prop brake. When the motor is shut off the prop stops almost immediately regardless of the slip stream strength.

Paul Bradley
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Ralph B
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« Reply #751 on: September 22, 2018, 11:21:25 PM »

As Paul pointed out I went with the magnetic brake for it's ability to stop the prop quickly during my experiments with his 3D printed folding prop. The folder operated reliably with the magnetic brake and I used it at the 2017 US Nationals. Late last year I tried the 65 mm RJX or King Kong prop and retained the magnetic brake. I got a little better climb on the RJX and found the glide to be as good as the folder. That is what I used at the US National this year.

I use a home made prop adapter on my models. I start with a commercial brass threaded push rod end that is then drilled out to fit the 1MM motor shaft. The brass comes with a 1/32" through hole from the package. I machine an aluminum back plate for the prop that gets bonded to the brass with red Loctite. After cutting the adapter to it's final length I machine a small aluminum spinner to retain the prop and magnet bar. Adjusting the stopped position of the prop is very easy with this arrangement. The prop hub is drilled out to slip on to the prop adapter and the hub is also machined flat on the front and back sides. The prop adapter is bonded to the motor shaft with red Loctite. The attached photos probably make more sense than my description. The motor mount in the photos was cut from an old Horizon 4-Site gearbox. It has since been replaced with a 3D printed part but the function is exactly the same. The magnet in the motor mount is 1/8" X 1/16". The magnets on the prop bar are 1/16" X 1/16". I know what you are thinking and yes this does add a few tenths of a gram of weight but it's on the nose and can be offset with the battery placement. Two of my three E20 models needed some ballast to reach the 30 gram minimum weight so the extra weight of the prop adapter and magnets were not an issue. The model I flew at the last two Nats weighed 31.4 grams. I have not had an opportunity to fully trim out the lighter models yet.

Ralph Bradley
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raggedflyer
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« Reply #752 on: September 23, 2018, 12:33:28 PM »

Thanks Ralph, I enjoyed the explanation.
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Yak 52
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« Reply #753 on: September 23, 2018, 04:46:29 PM »

Interesting stuff about the magnet prop stopper, the pre-determined stop position sounds useful.
My electric circuit solution works as planned but I need to tune the timings a little...

Jon
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FF Bruce
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« Reply #754 on: October 02, 2018, 11:14:46 PM »

Well the 2018 flying season in the Northwest ended last weekend. We had three contest E-20 was flown at each meet. Had a told of 9 different fliers and I ended up with the highest total time. Was able to get three maxes at each meet and won one fly off. At this last meet I was the only max out, many had 2 maxes but came up short on there third flight. As with most Free Flight it came down to picking the right time to fly. All the E-20's had good climbs,most are built up balsa and tissue but we have had a few all foam models. One was what I'll call a ultra high thrust with the motor about 1 1/2'' above the wing, it was very impressive. We all had fun and now look forward to next year.
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wcstoddart
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« Reply #755 on: October 04, 2018, 10:06:18 AM »

FF Bruce

Congratulations on your E20 contest results.

Please provide contact information or further details on the "all foam" and "ultra high thrust" line E20 designs.

Chris
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