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Author Topic: Let's talk E20  (Read 58445 times)
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Yak 52
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« Reply #725 on: May 16, 2018, 07:34:41 AM »

Here's a couple of pics of my first 'Peterborough Open E20'. The rules allow any motor, battery or timer for an 8 second run.

This is a bit of a cobbled together model to try out a direct drive Racerstar 8520 drone motor on 1S, supposedly capable of 35g of thrust. The model came out at 32g and climb is similar to my Ferry 500, not quite vertical but pretty decent. The wings and tail are from my original 2014 E20 and use a 9% thick modified BE50 section. The wing mount has been taped on until correct the position is found.

Flying in the PMFC Ferry Meadows series yesterday was a bit tricky due to blustery turbulent conditions but the light model seems to have potential. I've ordered an even hotter 8mm motor and my next idea is to try a solid CLG/HLG style wing. This came out at 9g but has a little higher aspect ratio ie less wing area.

The other direction for the Open E20 class would be to go for much more thrust from brushless motors at a higher weight. It should be possible to make the 50-60g F500 style model with something like 2:1 thrust to weight ratio!  Grin Shocked I'm not sure how wise this would be however!

Jon
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dlasich
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« Reply #726 on: May 18, 2018, 09:10:08 PM »

My E-20 prototype #4 about ready for test flight.  For flight trimming I'll fly it with micro r/c assist with control over the throttle, and then switch out the r/c with the timer shown from microflierradio.com.
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flytyer96
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« Reply #727 on: June 14, 2018, 09:35:51 PM »

OK, I hope this isn't off topic. A few years back I bought a BSD E-20 timer/D/T "device". I have recently tried contacting BSD to get the instruction sheet for it since I have miss-placed mine. Seems BSD is no longer in business? Does anyone have the instructions that could send me a copy?
Any help would be greatly appreciated.
Thanks,
John
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wcstoddart
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« Reply #728 on: June 15, 2018, 06:45:06 AM »

Recent email address for Bob Selman is bselman@ecarthage.com .

Chris Stoddart
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flytyer96
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« Reply #729 on: June 15, 2018, 04:52:56 PM »

Thanks, Chris. Greatly appreciated.
John
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FF Bruce
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« Reply #730 on: September 10, 2018, 12:06:26 AM »

Things have been very quite here so I'll let you know that here in the fine state of Oregon we have had two contests with E-20 as one of the events. At the first one we had 7 fly and three put up 3 max's. They chose to do a 10 sec. motor run with a 2 min. max. This is a very fun way to find a winner . At the contest this weekend we had 8 flying and 3 with 3 max's and like the last it only took one flight to get a winner. E-20 has been a well participated event from the start for our club. A fun easy event with a 90 sec. max, helps keep the walking down.      Bruce 
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flytyer96
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« Reply #731 on: September 10, 2018, 09:36:24 AM »

Since things have been quiet here lately, I thought I'd trow my 2 cents in.
A couple of years back, I built Bob Aberle's Civy Boy E20 for my first E20. I brought it out to our field for a maiden and when it didn't perform very well, I just put it on the shelf were it sat until this spring.
On a whim, I decided to "rebuild" it the way Bob intended, not the way I thought it should have been built. Took it out to our field and spent a little time trimming it and it started to show some promise, which it somewhat of a miracle since I've never flown a "power" model in my life. Never had any interest, always been a rubber/glider person and didn't know a thing about "power" trimming/flying.
Anyway, I got it flying pretty well and entered it in the E20 contest at the Nats this year. Took fourth and felt mildly pleased with myself. This generated enough enthusiasm on my part that I went home and built Bruce's Mini-E. This one flew very well right from the start and I have been "hooked" ever since.
Lots of fun!

John
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Yak 52
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« Reply #732 on: September 11, 2018, 01:38:20 PM »

My observation from pager powered micro RC electric gliders is that the wind milling prop causes noticeable performance deterioration. When I've added a soft sponge brake slither to just clip the prop (akin to the old trick of putting a folded cigarette packed into the spokes of a bike wheel) I reckon the glide is improved. No numbers - just an observation. In ff mode this perhaps is not noticed at height or distance. 

Hi chaps, coming back to this (after 5 years  Shocked) but my 8mm coreless motor powered E20 has this issue. Can anybody give me opinions on the best way to brake the prop in the glide? It definitely impairs glide performance when freewheeling and seems to cause a strong left turn (CCW prop.) If the speed gets up this left turn initiates a faster spiral, which speeds up the prop and hence more turn, steeper spiral etc etc.

The motor is a Racerstar 8520 with a King Kong 65mm prop.

Thanks!
Jon
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flytyer96
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« Reply #733 on: September 12, 2018, 07:57:14 PM »

Went out and flew my Mini-E today. Got three beautiful thermaled flights except the last one, the D/T didn't trip and....that's right. OOS.
Oh, well. Time to build another.

John
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FF Bruce
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« Reply #734 on: September 12, 2018, 08:48:10 PM »

John I am sorry to hear this. If the DT did not work I would have lost mine a 100 times. Good thing is they are not to hard to build and don't cost an arm and a leg. If you had your name on it maybe it might come home.
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flytyer96
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« Reply #735 on: September 13, 2018, 02:14:44 PM »

Hi Bruce,
Not much chance of a recovery. Farm country all around. The last I saw, it probably came down in a huge bean field which looks to be ready for harvest in a week or two. Oh, well. Good thing I enjoy building as much as I like flying them. I've already got the electronics on order.
By the way, thanks for sharing your great design with the rest of us. I really like that plane.

John
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FF Bruce
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« Reply #736 on: September 13, 2018, 08:49:07 PM »

That is nice of you to say,I'm still flying the prototype model. Last time I looked  at the plan gallery the Mini E had like 450 down loads. I have 3 club mates that have built them and all are having fun with them. It is cool to see what all the others here on HPA have come up with. Have fun with your next build and post pic's, love to see how it's going.    Bruce       
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Yak 52
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« Reply #737 on: September 19, 2018, 04:46:07 AM »

Here's a photo of a selection of PMFC E20's at our last Ferry Competition of the summer, a mixture of Ferry 500 and Open class models. We also did a little 'demo' at the Flying Aces launching together.
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RalphS
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« Reply #738 on: September 19, 2018, 08:43:11 AM »

Hi chaps, coming back to this (after 5 years  Shocked) but my 8mm coreless motor powered E20 has this issue. Can anybody give me opinions on the best way to brake the prop in the glide? It definitely impairs glide performance when freewheeling and seems to cause a strong left turn (CCW prop.) If the speed gets up this left turn initiates a faster spiral, which speeds up the prop and hence more turn, steeper spiral etc etc.

I am not "into" E20 but years ago our club had "Speed 400" competitions.  Folding props greatly improved glide performance.  I don't know if they are allowed in the E20 rules or can be purchased in the size quoted.  I would think that Bert  Wink could come up with a solution.
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Yak 52
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« Reply #739 on: September 19, 2018, 09:43:16 AM »

Thanks Ralph.

In our PMFC Open rules anything goes so folding props would be allowed. The practical issue is these tiny 8mm motors with 65mm/2.5" props - there's no commercially available folder as far as I am aware.

Rod Brigginshaw and myself have been working on an electrical solution. The idea is to use another FET in the timer to short the motor wires after the motor run ends. Shorting the wires should provide enough braking to stop the prop. The tricky bit is making sure you short the motor and not the battery!  Shocked Roll Eyes

If you mean Bert W, some of the models in the photo are his - including the twin motor ones  Cheesy

Jon
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« Reply #740 on: September 19, 2018, 11:22:40 AM »

Jon

K&P did some folding hubs (2,3 & 4 blades) for their little KP00 some years ago and they were about 3" diameter - could be cut down.
Also as the blades were screwed into the hub, the pitch could be altered too.

Try Derek.

Regards John M
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Yak 52
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« Reply #741 on: September 19, 2018, 12:04:05 PM »

Thanks John. I have some KP props - this type:

http://www.samsmodels.com/index.php?route=product/product&product_id=126

But I get the impression they are design to fold to prevent damage rather than in flight as the hinge is fairly stiff and I doubt it would fold in the glide airflow.
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« Reply #742 on: September 19, 2018, 12:52:49 PM »

I suggest you include a time delay between switching the motor FET off and the brake FET on and vice versa to avoid component damage.

Have a look at Reply #616 which relates to an external magnetic brake. This worked reasonably reliably on a 7mm pager motor used in a pusher configuration. I can’t see why the principal wouldn’t work for the larger motor and might be further advantageous with a conventional prop configuration. If the motor has some axial play the powered prop will draw further away from the magnet but fall back to close the magnetic gap when unpowered. Worth further experimentation.
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« Reply #743 on: September 19, 2018, 01:20:21 PM »

Magnetic brake.

You might see if you can get in touch with Ralph Bradley.  I know that he tried a magnetic brake on his E20 and may still be doing it.  It seemed to work well. 
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Yak 52
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« Reply #744 on: September 19, 2018, 02:53:28 PM »

Thanks for that - I'd missed it somehow.

For reference: http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=14519.msg192889#msg192889

I'm not sure about a magenetic brake to be honest, with the amount of broken props you get it would mean a fair bit of work.

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« Reply #745 on: September 19, 2018, 04:29:56 PM »

Not all E-20 motors free wheel, mine doesn't but I felt that the glide was much better when it did. I'm on my second motor the first one had the lead brake off right at the back of the motor after a mid air, this one I'm using now doesn't seem to run as well but is good enough. I'm also on my third set of batteries they last about a year or so. The model is still as much fun to fly as it was on the first flight. 
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« Reply #746 on: September 19, 2018, 05:12:49 PM »

On my version the steel plate was glued to the rear of the prop hub with uhu-por if I remember correctly. Moving it to a replacement prop wouldn’t be too onerous a task. Alternatively, the plate could  be permanently attached to the motor shaft by soldering or bonding and the prop hub pushed on tight up to the plate.
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« Reply #747 on: September 20, 2018, 10:06:10 PM »

I have been traveling so I am a bit late replying to the prop brake question. As George noted, my brother Ralph uses a magnetic brake. Based on how effective that system has proven to be, I have adopted it for my E20 models as well. It is a simple setup and works really well. A 1/8" x 1/16" magnet is mounted under the motor just behind the prop. A small bar (3D printed but could be plywood) is mounted behind the prop on the prop shaft. The same size small magnets are mounted in each end of the bar. The distance between the magnets in the bar and the one under the motor is adjusted to provide a positive prop stop but not drag down the motor. The prop and bar geometry is easy to adjust so the prop can be stopped horizontally. Using a tachometer, no loss of motor rpm could be measured with our without the magnet bar in place.

Paul Bradley
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raggedflyer
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« Reply #748 on: September 22, 2018, 06:50:48 AM »

Paul, just wondered if you could explain please why it was necessary to have the 2 additional magnets on the prop side rather than a (shaped) ferrous plate. Agreed it’s desirable to stop the prop horizontally and to balance the rotating mass but the holding force to stop the prop wind milling is very low.

I found that an effective brake could be fashioned with just a piece of soft sponge rubber poking against the prop blade root which is at the other extreme to a magnetic brake with a clogging type action. Interested to hear your or Ralph’s rational please.
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« Reply #749 on: September 22, 2018, 08:07:48 AM »

Actually there are probably many ways to stop the prop on an E20.  Magnet-magnet works, so does magnet-steel.  Something rubbing on the back side of the prop should also work.  The key to any prop break is that it stops the prop at a desired location and does not reduce the climb performance of the plane.

I use the magnet-magnet approach because it is easier, for me, than trying to fashion a small piece of steel for the back of the prop.

I also am curious how Ralph came to his preferred approach. 
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