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Author Topic: Let's talk E20  (Read 63423 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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flytyer96
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« Reply #756 on: December 04, 2018, 11:08:44 AM »

Well, I'm starting to make some progress on Mini-E #2. Ya, I'm a slow builder. Thought I'd post some pics of the build.
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PaulBrad
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« Reply #757 on: December 04, 2018, 09:35:17 PM »

Your new Mini-E is looking good. I look forward to seeing the finished model.

Paul Bradley
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flytyer96
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« Reply #758 on: December 06, 2018, 10:55:08 AM »

Thanks, Paul.

Attached is a pic of the horizontal stab. If I keep going at this rate, I should be able to "maiden" by the end of the year.

John
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FF Bruce
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« Reply #759 on: December 06, 2018, 09:23:28 PM »

You look like you know what you are doing. Nice job, I love flying mine must have a couple hundred flights on it.
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flytyer96
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« Reply #760 on: December 06, 2018, 10:36:29 PM »

Thanks, Bruce. I know I sure enjoyed flying mine during the short time I had it. Hopefully I will still have this one for next years Nats.

John
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Pappy
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« Reply #761 on: December 10, 2018, 04:12:16 PM »

Tachometer sensor test set up for a planned E-20 power train analyzer.
The goal is to evaluate motor and battery performance over 20 second
and 10 second intervals. It is apparent that not all E-20 motors and
batteries are created equal. Hopefully the analyzer will help pick out
the best motors and batteries on hand before each E-20 contest.
The “ticks” on the scope in the photo indicate the test motor was turning
about 14,500 RPM on a somewhat discharged battery. Initial RPM is typically
16,300 using a freshly charged battery with a stock motor and prop.

 -Pappy
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Yak 52
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« Reply #762 on: December 14, 2018, 09:29:04 AM »

I've just found the Cliché plan: http://www.parmodels.com/cliche-e20
I was very interested in this as I've been developing a similar 'CLG style' wing, so thanks for drawing it up Paul and Ralph Smiley

I've just about solved the electronic prop stopper so I'm starting to get on with E20 design again...

Jon
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flytyer96
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« Reply #763 on: December 31, 2018, 03:53:29 PM »

Well, the weather being uncooperative(for flying), I've made headway towards finishing my Mini-E. This is a shot of the vertical stab being glued on.
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flytyer96
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« Reply #764 on: December 31, 2018, 04:01:32 PM »

Here's some shots of the covered wings and fuse. The wing was covered with Litespan, the horizontal stab with domestic tissue and the fuse with polyspan. Everything has been sprayed with a coat of 30/70 Eze-Dope/water. Tomorrow, I'll give her 2 more coats and call it done.
Right now, it's "toddy-time". Happy New Year everyone!
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skyrocket
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« Reply #765 on: January 02, 2019, 08:18:55 AM »

nice to see this blog...new E20 attached...#2 of this design for me
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Yak 52
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« Reply #766 on: January 02, 2019, 09:20:02 AM »

Two nice models there guys!

Skyrocket, is this your own design?

Flytyer, I'm interested in the motor mount - is that alloy tube in the middle? If so can you tell me what size it is please?

I've been working on some fully adjustable motor mounts for E20, possibly looking at 3D printing something. It's one of the most awkward aspects of design in my opinion, ie how to get a solid but fully adjustable mount.

I've been building wings for some lighter models. Photo below shows a CLG style wing at about 9 grams and a 7% thick flat bottomed built up wing, 4 grams uncovered. The airfoil is modified from an Eggleston catapult section and looks decent in XFLR5. I'm using a fairly high dihedral and less of a pylon.

I've also been doing quite a bit of motor thrust testing on small brushed and brushless set ups for our PMFC Open class.


Jon
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flytyer96
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« Reply #767 on: January 02, 2019, 10:53:15 AM »

Jon,
That's some nice looking work you're doing as well.

Yes, the "motor sleeve" is an aluminum tube, 3/8" O.D. x .014W. It's a slightly loose fit on the O.D. of the motor which I will shim to a tight fit with cellophane tape. The nose block of course, is the usual laminated block fitted into the fuse in the typical rubber model fashion. This lends itself to shimming for thrust adjustment. My previous model of the same design, required very little thrust change.

John
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flytyer96
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« Reply #768 on: January 02, 2019, 10:58:18 AM »

Skyrocket,
Very nice looking plane. Is this a published design or something of your own? I would certainly be interested in building one myself if plans are available.
It looks to have a tapered, rolled fuse. If so, what did you use for a mandrel?

John
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Yak 52
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« Reply #769 on: January 02, 2019, 11:08:54 AM »

Yes, the "motor sleeve" is an aluminum tube, 3/8" O.D. x .014W. It's a slightly loose fit on the O.D. of the motor which I will shim to a tight fit with cellophane tape. The nose block of course, is the usual laminated block fitted into the fuse in the typical rubber model fashion. This lends itself to shimming for thrust adjustment.

Thanks John, I had identified this size might make a good motor tube (from K&S p/n: 9409) but I can't get it on this side of the pond at the moment :/

I used the same noseblock method on my lightweight E20 but with the motor CA'ed straight in to the balsa. Works fine but making the motor removable would be nice.

Cheers,
Jon
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flytyer96
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« Reply #770 on: January 02, 2019, 01:23:46 PM »

Jon,
I would be happy to mail you a couple of tubes if you could PM me your address. Do you think it would cause a ruckuss at the post office if I put them in a 1" PVC pipe?

John
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skyrocket
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« Reply #771 on: January 02, 2019, 01:50:11 PM »

The fuselage is a rolled tube of 1/32" on the upper half of a pool cue and the pylon is let into the front. The motor mounts are 1/8" square basswood and the motor is held in with small D/T bands. It does fly great with a slow flat glide. My own design. I went with a lower A/R because of the 20" span limit and a under-cambered airfoil. The first one came out at 28.5 grams but was lost. This one is 22.5 grams. I'm not ready to release any plans right now. I'm working on an all-sheet version
to simplify construction, much like a HLG glider.
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Yak 52
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« Reply #772 on: January 02, 2019, 04:38:30 PM »

Jon,
I would be happy to mail you a couple of tubes if you could PM me your address. Do you think it would cause a ruckuss at the post office if I put them in a 1" PVC pipe?

John

John, that's a very generous offer, thank you. Let me just have a dig around and be sure I can't get it locally before I put you to any trouble and I will get back to you. Thank you very much!

Jon
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Yak 52
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« Reply #773 on: January 09, 2019, 04:40:38 AM »

I just came across this video of a little folding prop for E20:
https://www.facebook.com/ross.jahnke/videos/1992702144116589/

The motor mount - using a brushless 'pole' mount is and idea I also had but have yet to try. The common 24g 'blue wonder' motors have an 8mm diameter mount which could be drilled or filed out slightly.

http://robotbirds.com/catalog/images/20gmdraw.jpg

https://rajeshkovvuri.files.wordpress.com/2013/05/20130507-101645.jpg
Let's talk E20
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Ross J
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« Reply #774 on: January 28, 2019, 12:16:14 AM »

This is a prototype 3D printed motor mount I designed and had printed at Shapeways. The black plastic is stronger than the white and the printing was much more accurate (I only show the white one because it's easier to see in photos). The bolts are 1-72 nylon.

The motor is glued into the front flange, and the  "firewall" fits a 4mm carbon rod fuselage. The wires run through the large offset hole in the firewall. There is a recess, not visible in the photos, sufficient for the wires to pass from the motor out that hole. It could also be adapted to a built up fuselage and the wires routed through the center hole instead.

There are some subtle changes that I want to make to the design that should get the weight closer to 1 gram. The material is more than strong enough, the limitation is the capability of the printer. For comparison, the aluminum mounts I've made were all about 1.5 grams.

BTW the folding prop is made from an old Harbor Freight electric model and some Delrin. The diameter is 3.25" so it's not legal, just a proof of concept.
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