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Author Topic: Electric Wright Stuff trial event for Div. B or C?  (Read 4599 times)
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Little-Acorn
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« Reply #50 on: May 18, 2018, 01:03:21 PM »

Lee, yup, that's pretty much it. I coached (rubber-powered) Wright Stuff at my son's middle school last season, and learned a whole lot. Meaning, I started while not knowing nearly enough to do a good job. Thankfully we survived anyway ;-) , and the WS team even came in 7th at our state tournament this year. The kids seemed to have a pretty good time, and (I hope) learned a lot too. I guess we'll find out when we see how many come back for next year's WS event (if SO has one for middle schools next year). All the kids on the team were 6th and 7th graders, no 8th graders for some reason. So all are eligible to come back. We'll see.
 
I saw the (Div. C) trial event EWS at State after our Div. B WS event was over, and was astounded at how little most of the teams (students and coaches both) knew about electric motors, capacitors etc., as well as airframes and flying. Since I spent most of my misbegotten youth building and flying model planes, and trained in college on Aerospace and Electrical engineering, I knew something about them, so decided to learn all I could about EWS-type planes and drive systems, just so I wouldn't wind up looking cross-eyed as often as I did last season.

Designed the test set so that (a) Any future team where I was a coach or parent, could do useful tests and learn some of the things I lacked, and (b) so that it could eventually become a wind tunnel, both for motor/propeller systems, and for complete full-size airframes at their normal flying speeds, something I wish I had had last season with my WS team.

Presently I don't know how likely it is for SO to have either a WS or EWS event next season. Their summer workshop schedule had mentioned EWS, but that was quietly changed to WS for Div. C only. I hope they change their minds, but we'll see. A wind tunnel would be VERY useful for both WS and EWS events.

The SO summer workshop schedule can be found here. It hasn't changed since March 2018 that I know of. But I hope it does change soon, to accommodate EWS as well as WS.

https://www.soinc.org/sites/default/files/uploaded_files/2018_Schedule_032618.pdf
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JasperKota
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« Reply #51 on: May 21, 2018, 10:08:57 PM »

I am almost completely sure that EWS/WS will be a Division C event only, as they always do 2-year rotations, and this year was the 2nd year that WS was division B, and the 2nd for Helicopters in Div. C, but again everything is tentative as of now. If the high school in your area starts with 9th grade though, your kids will likely have a chance to participate in WS again.

Personally I'm hoping for regular Wright Stuff, and it seems like the committee leaning towards that but hopefully anyone who goes to the coach's meeting can give us more information then. I do wonder if it will be more competitive next year, considering many of the Division B kids who previously competed in WS will likely be in Division C next year (myself included  Smiley). I don't know the reasoning behind the committee's decision to remove ELG from the rotation, as I think that probably evened the playing field since it would be more likely for everyone to be inexperienced.
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Little-Acorn
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« Reply #52 on: May 22, 2018, 06:28:48 PM »

JasperKota, personally I'm favoring EWS. But maybe that's because I've never been in it. The novelty is fun, and an electric-powered plane sounds elegant, regardless of wide tolerances in capacitors.

My son will by in 7th grade next season, but is not interested in flying things. In sharp contrast to myself, I couldn't get enough of them when I was his age. If Div. B has neither WS nor EWS, I might volunteer to coach at the local high school, if they have either one, and don't mind an old fat man hanging around.
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Little-Acorn
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« Reply #53 on: May 22, 2018, 06:43:34 PM »

When you build a test set, you just have to start playing with it.  Grin  At least I do.

Tested three different configurations.

First one is called "Vapor", has a Vapor prop, mini-Vapor motor, and Ember gearbox. See the "Data" image below for details.
Second one is called "Mini-Vapor". Replaced the prop with a slightly smaller and flatter Mini Vapor prop, all else is the same.
Third one is called "Quad". Used a motor and direct-drive propeller from a fairly small, cheap, dead quadcopter.

Ran the same tests on all three, measuring current, thrust, and voltage at the motor while a long, skinny 5F 3V AVX capacitor discharged from 3V into them.

Eventually I want to such measurements on a LOT of different motor/gearbox/propeller combinations, for comparative purposes so I can start judging which combo is better for which plane etc.

Still trying to figure out what data collection is most useful for figuring out flying characteristics. I spent 4 years in college as an Aerospace Engineering student, would hate to think I wasted it all.

Eventually I also want to put the test set in a shroud, with a big but slow fan and a flow straightener at one end, to make a wind tunnel. Hopefully big enough to put an entire WS plane into, to test it at its normal flying speed.
Attached files Thumbnail(s):
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
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Little-Acorn
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« Reply #54 on: May 22, 2018, 07:20:44 PM »

Rebuilt the test set, put it on a narrower board and mounted the motor/prop on a pivoting arm on a scale (resolution: 0.01 grams) so it can measure thrust. Top scale measures thrust/drag, the scale beneath it will measure lift/weight when it becomes a wind tunnel with a plane mounted on it.

All three meters now have independent power supplies (three 9V batteries on the right).

Moved the controls to the front. Right switch lights up the LEDs in the meters, left switch controls the motor. At the upper right is the capacitor that's discharging into the motor. At upper middle is the 0.1 Ohm resistor that measures current. At bottom are (another) quadcopter motor and prop, the Vapor propeller, and the Mini Vapor propeller-gearbox-motor. Bottom right is the "clothespin" and two D cells to charge the capacitors. The scraggly wires on the far right are for a variable-voltage 5A regulated power supply, not built yet, for steady-state testing.

Here the quadcopter motor/prop is still mounted on the arm, it's running, capacitor is half discharged, and the test set is doing its thing.
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Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
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Little-Acorn
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« Reply #55 on: May 30, 2018, 04:25:36 PM »

Possibly the most useful info to come from this test set. I tested eight different combinations of propeller, gearbox, and motor; and measured the thrust (in still air) from each. Powered by a capacitor typical of those that might be used in a competition: Marked 5F, 3V. But tests showed its actual capacitance was 5.11F. It was capacitor #00 in previous tests.

The capacitor's voltage drops as it discharges, of course. So the propeller slows down and the thrust drops too. I recharged the cap to 3.1V before each run. As soon as I hit the switch, the cap started discharging, prop began spinning up, and voltage dropping. After a few seconds, it reached (mostly) steady state, and I started recording data, shown on the graph.

Question I wanted to answer was, which combination would be best for an EWS competition plane?
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SyLa-20871
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« Reply #56 on: June 04, 2018, 02:11:13 PM »

Little Acorn,

That is an interesting set of data.  Scientific data always seems to ask another question to further drive the experimentation.  At what "thrust" level is the plane no longer flying?  Once that is answered, some combinations can be eliminated.  Alternatively, the answer can be answered by brute force.  Determine which combination keeps the plane flying the longest.  You will need a good time keeper to start/stop the time when you push GO.  After a few trials, it may(?) become apparent where the lower end of flyable thrust is.

A second question:  Does an initial high thrust overcome the early (faster) depletion of charge thus dropping below the flyable thrust threshold to maintain a longer flight?

Regards,
Lee
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Little-Acorn
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« Reply #57 on: June 04, 2018, 02:52:17 PM »

Quote
At what "thrust" level is the plane no longer flying?
Actually not so hard to get a pretty close answer to. Weigh the plane, then glide it. Measure how far forward it went, and how much altitude it lost before touching down in a flat, smooth glide. Multiply the weight by the altitude lost, and then divide it by the distance forward. The result is the amount of thrust it would take to make the plane fly straight and level at that speed and configuration.

You might do this with the propeller mounted and not turning. Then do it again with the propeller removed and a small weight installed in its place, so the balance and weight don't change.

Hard to tell if the prop blades dragging in the air, would produce extra drag that the flying (powered) plane wouldn't have. So try it with and without.

As for quick climbs with more powerful motors that run the capacitor down sooner, a quick climb might simply bonk it into the ceiling sooner, so the higher altitude you might have gotten is wasted.

With my (rubber-powered) Wright Stuff team, the question always was, what was the skinniest (i.e. longest-running) rubber motor we could use that would bring the plane up to just below the ceiling, and then let it fly level the longest and then glide the shallowest?

Sounds like time for experimentation to me!  Grin  
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Little-Acorn
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« Reply #58 on: March 15, 2019, 01:54:48 AM »

I just found out that Electric Wright Stuff will be a Trial Event at the southern Calif State Science Olympiad tournament at Caltech in Pasadena CA, to be held on April 6, 2019.

Yep, some 3 weeks from now.

It will be Div. B this year (Middle Schools). Last year's EWS Trial Event was for Div. C (High Schools). Rules can be found at http://socalscioly.org/downloads/Electric%20Wright%20Stuff%20B%202019.pdf if the link works.

Min weight = 7 grams including motor, prop. gearbox in any, and capacitor.
Max wing size = 40cm x 10cm
Max stabilizer size = 20cm x 7cm
Max propeller diameter = 14cm
Max capacitor values = 5F, 3V. I assume this means labeled values. I've measures some of these, actual values often come out higher. Data sheets for these capacitors often list capacitance tolerances up to 30% higher.

Sorry Wright Stuff flyers, you can't just pop a motor and capacitor onto this season's Ziegler plane.

I'm very happy to see the re-introduction of EWS, though I'm appalled at the (relatively) tiny amount of time teams would have to design, build, and test fly capacitor-powered planes.

Time to dig out those AVX capacitors from last May, dust off the test set, and replace the batteries. And maybe borrow a wing and tail from my (rubber-powered Wright Stuff) Coach's plane from last year.

I'm sure this will re-ignite the complaints about the wide tolerances of capacitors, for example a capacitor labeled as 5F could actually deliver 6.5F and still be within spec.
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Little-Acorn
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« Reply #59 on: March 15, 2019, 02:42:32 AM »

Just had a look at the datasheet for the AVX 5F 3V caps. Digi-key is selling them, as they were last year.

Biggest surprise here is that, while the tolerances for the ones Digi-key was selling last year were -10% to +30%, now the tolerances for this year's batch are 0% to +100%.

Holy shiite. Means that if you buy a cap labeled 5F 3V, you might get one that has a capacitance of 10F, and still be within the manufacturer's spec!

They seem to be available in the same physical sizes as last year. I wonder if the short, fat ones are the ones with the incredible capacitances (or lousy QC standards)?
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frash
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« Reply #60 on: March 15, 2019, 11:11:55 AM »

The original capacitor powered plane for Science Olympiad by Chuck Markos is posted in the Plans Section. This original SO proposal permitted the use of a 10-farad capacitor.

This design is still quite good and I flew my Markos plane only for recreational flights on Wed, 3/13/2019 for five consecutive flights for times of 2:05-2:15. Disclaimer, East Tennessee State U was on spring break and the Johnson City, TN Mini-Dome was almost empty. I was also lucky not to hang up on speakers and other high objects that I hit.

These flights in a large site with 10-F caps are not representative of typical SO situations. I have heard nothing to indicate that the TN State SO will have this trial event.

In the HPA Plans Section:

Capacitor-Powered FF and Science Olympiad (frash)
Miscellaneous Articles

Date added: 04.19.2017 19:56
Comments: 1
Downloads: 221
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SoCal-SciOly-Dad
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« Reply #61 on: March 18, 2019, 01:12:44 AM »

Little-Acorn,

Thank you for your excellent contributions to the community with this thread.  We recently were informed by the ScyOly head coaches of our middle school about this trial event at the SoCal State competition on April 6.  This is a tight timeline!  We are working on locating an existing plane from last year that we can help our two sixth graders convert to electric drive.  Your posts will be helpful.  We plan to share what we learn on this thread as well.

Best regards,
SoCal-SciOly-Dad
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Little-Acorn
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« Reply #62 on: March 20, 2019, 11:36:53 PM »

A couple pics of the vanilla airframe we cobbled together in the last few days for the EWS Trial Event at Caltech (SoCal State Science Olympiad tourament) on April 6.

At first made it a pusher, with the propeller just behind the trailing edge of the wing, 21" long fuselage (3/16" x 3/16", 7PCF balsa), capacitor an inch forward of the leading edge. It was astonishingly tailheavy. Moved the capacitor all the way forward to just behind the front stabilizer, it was STILL tailheavy. And weighed 10.6 grams, without the long wires needed to connect the capacitor to the motor. With 2-1/2 weeks before the tournament, made an executive decision to abandon the pusher configuration and make it a tractor.

Started the tractor with the wing and capacitor about an inch behind where you see them here. It was a little noseheavy. Glided in a nose-down attitude. Moved the wing and cap forward about an inch, the result is what you see here. It glides flat and smooth, not bad at all. Most parts are presently held on with rubber bands, including motor and capacitor, that will change when we start powering it. This was just for glide tests. Nice to know we have a viable airplane. Fuselage of the tractor is 1/8" x 3/16", plane weighs in at 9.8 grams.

We'll have to try hard not to hit any walls (or floors in a vertical attitude), those will trash the gearbox and maybe motor.

* Ember gearbox, 0.58 grams
* Vapor motor, 1.94 grams with short leads and single-plug-lead pigtails
* 140mm prop. I think from Vapor, 1.14 grams
* Capacitor is AVX SCCS20E505SRB 5F 3V, -10% +30%, 2.19 grams
* Wing is 40cm x 10cm, 1.47 grams
* Stab is 20cm x 7cm, 0.70 grams
* Fin is 0.32 grams
* Fuselage is (now) 1/8" x 3/16" x 20.5" balsa, 0.97 grams
* Covering is produce bag from nearby grocery store, 0.549 grams/sq.ft., tougher than a nickel steak

With the motor, gbox, prop, and capacitor alone weighing in at 5.85 grams (without an airplane attached), bringing the all-up flying weight of the plane in at 7 grams or below, is something I don't know how to do. Present tractor plane weighs in at 9.8 grams, will probably get to 10 before we're done. Hmm. Maybe use a Mini Vapor motor and prop? Would that have enough power to fly? Can't reduce the capacitor, it's the fuel tank, wrong move in an endurance contest.

Just got in some AVX caps (5F, 3V) with tolerances (datasheet) of -0% to +100%(!!) Will test them for actual measured capacitance. Should be a roller coaster ride.

Using the produce bag because we don't have the time to keep repairing Ultrafilm (0.204 grams/sq.ft.). The produce bag is tough as nails and still very light.

Note to self: Put some shrink tubing on those motor wires before they start a fire.

First powered tests this week or weekend. Fingers crossed.
Attached files Thumbnail(s):
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
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calgoddard
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« Reply #63 on: March 21, 2019, 12:08:03 AM »

Little-Acorn -

Nice report.

Keep us posted on how she flies.

Perhaps you could post a link to a YouTube video of one of your test flights.

Thanks.
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SyLa-20871
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« Reply #64 on: March 21, 2019, 12:31:38 PM »

Little-Acorn,

That is a nice looking plane.  Thanks for sharing and good luck!  As calgoddard mentioned, I would love to see a video of your flights.

Best,
Lee
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strat-o
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« Reply #65 on: March 21, 2019, 04:19:57 PM »

Little-Acorn, I'm learning how to make super-capacitors.  When you make them yourself you can pick and choose which materials to use for weight suitability and also sizing.  I believe it's feasible to create a super capacitor with about 10F with only 2 sq cm in the typical paired layer format (flat, not rolled).  You can probably make one having 7F for maybe 0.5 g.  It's not going to have the fancy aluminum canister unless you decide to do it that way.  It will be more of a flexible flat package with two leads coming out.  Making them does involve some study but the cool thing is the materials are non-hazardous.  Mainly variations of carbons, graphites and graphenes and relatively safe salt-based electrolytes.

Strat-O
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Little-Acorn
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« Reply #66 on: March 22, 2019, 09:11:01 AM »

Wow, Strat-o, I've never even considered making my own supercap. I know nothing about the chemistry and geometry that goes into them, but assumed (there's that word again) that it involved microscopic dimensions and really tight rolling of the layers, or something. Since they've only been around the last dozen years or so, I figured they were exotic somehow.

Good luck, let us know how it goes!
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« Reply #67 on: March 22, 2019, 11:19:03 AM »

Well there are microscopic dimensions but that is actually inherent in the starting material.  For example, a good starting material is activated carbon commonly used for filtration in fish tanks.  This material has an incredible amount of surface area which makes it quite suitable for super capacitors.  You simply grind it up, make an ink out of it, and coat it on a foil electrode.

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Little-Acorn
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« Reply #68 on: March 26, 2019, 03:16:29 PM »

Well, the plane flew, nice to see, but not as well as I hoped. Never climbed more than about 15 ft. above the floor, max endurance was maybe 20 sec. Sorry, didn't get any movies. I suspect the plane's 10-gram weight was holding it back. I have yet to cherry-pick capacitors.

So did some mods, now the weight is exactly 1 gram less at 9.02g. I hope that's good enough.

* Skinnier fuselage, 1/8" x 1/8", 20" long, 7 PCF density. Might make it shorter soon.
* Same wing, different mount so I could put diagonal braces on it and wedges to control wing warping. Note the wooden wedge at the back of the wing, doing just that.
* Lighter tail, covered in Ultrafilm, left over from last year.

Hope it flies.

Still has the Vapor prop and motor, Ember gearbox, nominally 5F 3V AVX capacitor. I'm wondering about the Vapor prop, very flat pitch, 140mm x 40mm pitch. Would a slightly higher pitch help? I have some Champ props, smaller diameter, higher pitch, but the hole in the middle is slightly too big. Would need to be glued to the gearbox shaft, would hate to do that except in extremis.

See photos attached, of the new 1-gram-lighter prototype. First flights tonight I hope.
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Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
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« Reply #69 on: March 29, 2019, 03:02:20 PM »

So far so good. Several good flights (plus some not-so-good ones). Three trips to the ceiling of our 25-foot gym, wonderful climb. I guess the Vapor motor and prop, plus the Ember gearbox, do have enough power to do the job, if the plane is set up right (a big IF). One 38-second flight, which included bouncing off one wall, recovering without hitting the floor, then hitting another wall and sliding down to the floor. If we can get this plane to straighten up and fly right, we might have something worth taking to State at Caltech.
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« Reply #70 on: March 30, 2019, 02:08:40 AM »

Finally had a chance to get out the camera, tonight (Friday March 29). One student crunched a wing, so built a new wing at tonight's practice and it flew right off the building board. Another student had some fuselage problems, so built a new fuselage and got that one flying with its original wing, all today after dinnertime.

42 second flight: https://youtu.be/itnBQn7OZ0s
Shorter flight that hit a wall: https://youtu.be/ldzN_VG1DZg

Changes and adjustments proceed apace. Eight days until tournament time!
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« Reply #71 on: March 30, 2019, 01:38:49 PM »

Can you slow the climb, and therefore the energy draw, by going to less pitch? This is opposite of what we do with rubber power. Rubber is "constant torque" (ok, it is declining torque, but the torque at any point of the flight is given, and the prop spins at a rate to absorb that torque) while electric motor is "constant rpm" (instantaneous for a given voltage). Therefore, the electric motor will develop whatever torque needed to get that RPM (with limits, of course), and so higher pitch will require (and get) higher power from the motor. Therefore, I think if you went to lower pitch or otherwise reduce the load, you will not climb as fast, and you will preserve some energy for later in the flight.

Not that I have tried EWS, just my observation.

Chuck
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Little-Acorn
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« Reply #72 on: March 30, 2019, 02:25:28 PM »

Ceandra, electric motors may indeed be constant-torque for a given voltage. But these EWS planes are powered by a capacitor, not a battery, and the voltage of the capacitor declines at a measured rate is current is drained from it. It may start at 3V, but within a few seconds it is down to 2.5V, then soon 2.0V etc.

Good news is, your suggestion of reducing the current draw is a good one nonetheless. It just needs to be done differently. The Vapor prop I am using is already a pretty flat pitch, 140mm x 40mm or so. One of our planes has a habit of pointing up at a 45 degree angle or more, and just hanging on its propeller without stalling - something it could not do with a more "normal" pitch like, say, 140x70.

The Vapor plane is that company's "standard" small indoor RC plane. They also make a "Vapor Lite", whose motor is physically shorter but is the same diameter as the standard motor. Also has the same pinion gear. That plane is powered by a smaller propeller, somewhere around 126x35 or thereabouts (still very flat pitch). I'm considering trying that motor and prop, to reduce current consumption. Climb will suffer, of course, but right now the planes are climbing too much. So a reduction in climb capability, along with a reduction in current consumption, could be a good thing. Of course, this "Lite" motor and prop might simply have too little power to keep the plane airborne and climb at all, we'll see.
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« Reply #73 on: March 30, 2019, 03:51:44 PM »

I understand that the cap, like a battery, drops in voltage. But, at a given instance, the motor will try to run at an RPM related to the voltage available (not a fixed torque for a given voltage, but a fixed RPM), and will draw enough current to get there. Of course, then there are resistive and other losses, so the effective voltage in the coils is lower. But, nonetheless, I believe in the interest of conserving energy for later in the flight, the point is that a lower pitch will reduce the power draw, which is backwards from rubber thinking. I agree, it is climbing too much initially. Saving some of that energy may result in longer reserves for later in the flight, albeit the reduced voltage may then drop the power too much to stay aloft. As in all things, experiment will best determine the right prop combo.

Chuck
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« Reply #74 on: April 05, 2019, 10:14:58 PM »

This is related to Indoor Science Olympiad Capacitor Electric FF planes but is OUTDOOR FF.

The latest Free Flight Quarterly FFQ71.pdf from Australia has a 3-page article describing an OUTDOOR 20-in span Starduster powered by a 3-volt, 10-farad capacitor. This is like an outdoor E-20 except that the 10-F capacitor without timer is used instead of a 1S LiPo cell with a timed, limited motor run. The author, Alexandre Cruz suggests the name C-20.

Some of you will already be subscribers to FFQ. It is highly recommended.

Fred Rash
 
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