Electric Wright Stuff B

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bernard
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Electric Wright Stuff B

Post by bernard »

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nepalinerd (May 15th, 2022, 9:55 pm)
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Re: Electric Wright Stuff B

Post by coachchuckaahs »

Welcome to Electric Wright Stuff!

The Nationals Free Flight Society (NFFS) now sponsors the flying events, and we are striving to be an ongoing resource center for flying excellence. We have just updated our Science Olympiad Website, including a resource links page. As new resources are developed, we will keep adding to these pages. You can find them at https://freeflight.org/join-learn-fly/science-olympiad/

If you have questions on building, trimming, etc., this forum is the best place to ask. Coach Brian, Coach Jeff, and I frequent this forum and answer pretty quickly. Asking and answering here ensure the responses benefit everybody in the flying community. In addition, digging thought the prior years' forums, posted by Bernard above, is a hugely valuable resource.

This year brings a new challenge: Capacitor electric flying! While some basic principles (construction, flight, trimming) remain the same as Wright Stuff, the motors, charging, and tuning are a new area for most of us. With no gearbox, the variables are probably more limited, which is good, but we will learn together what it takes to stay out of the rafters and yet fly a long time!

One important note if you build your own design: Electric motors are NOT all created equal! Different motors, for different purposes, have different speed characteristics. Due to the small motor size, they tend to be fairly high revving. However, "drone" motors in the interesting size range (5mm to 8mm diameter) tend to run at over 40,000 RPM on 3V, whereas some "pager" motors that look the same are rated for 10,000-12,000 RPM. So be sure to check the rated RPM before purchasing a motor. Lower is probably better, allowing you to carry a larger prop!

Good luck, and get building!
Coach Chuck
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Little-Acorn (October 23rd, 2021, 10:28 pm)
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2019 C WS Champion
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Re: Electric Wright Stuff B

Post by Little-Acorn »

I believe the "speed rating" for an electric motor in the sizes you described, is its rating at its max RPM with no load. No propeller, no gears, nuttin but a bare shaft. Correct?
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Re: Electric Wright Stuff B

Post by coachchuckaahs »

That is correct. And these props, small as they are, do load the motors more than I expected. However, for similar looking motors, the RPM with a given prop, static not flying, varied by a factor of more than 2, which means the power varied by well over a factor of 2. One of the motors would put the plane into the ceiling on a full charge with the smallest prop, while the other would not get to the ceiling at all with the largest prop tried.

Obviously, something in between would be best, as you would not want to reduce charge to avoid rafters.

The ratio for RPM (Read with my tachometer from R/C Airplane racing) between the motors was relatively consistent across prop sizes.

In addition to RPM, we measured current at 3.0V, which would be an indication of input power, again in static rather than unloaded condition.

Unfortunately, many available motors do not include data on the load vs RPM, or even the open shaft RPM.

Coach Chuck
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2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records
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Re: Electric Wright Stuff B

Post by BigZ »

If anyone is confused about this event, or needs a plane for their competitions, contact Joshua Finn at j&hareospace.com. (Yes, this is an advertisement since he is my supplier and helped me out a ton. So go check him out if you need help with this event at all.)
DM me if your life is oofed
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Re: Electric Wright Stuff B

Post by coachchuckaahs »

A very good tutorial on the type of motors we are using is here: https://www.didel.com/microkit/moteurs/Motors.html

While it is difficult to get RPM data in flight (or even current data), this information can help you understand the difference between motors.

Bottom line though, don't be afraid to try different props on your motor, both statically and in flight. Some results in flight were somewhat non-intuitive, possibly because we were over-loading the motor beyond the halfway point in RPM. Based on this we are acquiring a variety of motors to test.

Also, note form these charts that the POWER goes up as the SQUARE of the voltage (ignoring back-EMF). Therefore going form 2.5V charge to 3V charge results in a 44% increase in power! Your plane trim may change dramatically with that much change in power. Work your way up in voltage slowly!

Be sure to read the note at the bottom about not applying axial loads on the motor while inserting gears (or propellers in our case). We hold the shaft with pliers while installing or removing the prop. However, fixtures they highlight in the linked page may help ensure installation without damage. Further, it should be noted that if you have a bad flight (sharp stall, wall hit, etc.) that results in the plane going straight down, you may destroy the motor. Therefore it pays to have spare motors on hand.


Coach Chuck
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2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records
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Re: Electric Wright Stuff B

Post by jgrischow1 »

My kids are having trouble getting their planes to even close to the ceiling. They are landing with many, many, turns left, so it's not a charge issue. I knew little about WS but even less about EWS so I feel ill-equipped to help them. What should we try? Lighten the plane? More incidence? Higher launch angle?
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Re: Electric Wright Stuff B

Post by coachchuckaahs »

You have not given much information to resolve. Perhaps link a video would help.

What is the character of the flight? Is it fast and level, stalling, diving?

Did you work through trim? Set CG per plan (If a J&H, put CG at rear of wing). Then increase decalage (difference in incidence between wing and tail) until a slight stall in late flight, then reduce decalage until stall stops.

What motor are you using? (size, ohms, unloaded RPM) What prop? What pitch on the prop? Are you measuring the voltage after charging, before starting the motor? What voltage at launch?

How high is your ceiling?

What is the voltage after landing? The prop may turn a lot just holding it, but with no real thrust. Ideally you are at or below 1V on landing.

Lots of questions. Data is your friend! Answering these questions will help determine if it is a trim or powerplant issue.

Oh, and yes, your plane should be right at the 9.5g minimum weight. These are marginally powered, so any extra weight will really increase drag (lift creates drag) and overcome the available power. How heavy is the plane?

Coach Chuck
Coach, Albuquerque Area Home Schoolers Flying Events
Nationals Results:
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records
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Re: Electric Wright Stuff B

Post by jgrischow1 »

coachchuckaahs wrote: January 5th, 2022, 6:35 pm You have not given much information to resolve. Perhaps link a video would help.

What is the character of the flight? Is it fast and level, stalling, diving?

Did you work through trim? Set CG per plan (If a J&H, put CG at rear of wing). Then increase decalage (difference in incidence between wing and tail) until a slight stall in late flight, then reduce decalage until stall stops.

What motor are you using? (size, ohms, unloaded RPM) What prop? What pitch on the prop? Are you measuring the voltage after charging, before starting the motor? What voltage at launch?

How high is your ceiling?

What is the voltage after landing? The prop may turn a lot just holding it, but with no real thrust. Ideally you are at or below 1V on landing.

Lots of questions. Data is your friend! Answering these questions will help determine if it is a trim or powerplant issue.

Oh, and yes, your plane should be right at the 9.5g minimum weight. These are marginally powered, so any extra weight will really increase drag (lift creates drag) and overcome the available power. How heavy is the plane?

Coach Chuck
I will work on a video.

Flight is fairly fast and level.

Their CG is probably too far forward...seems to be about 1 inch in front of rear wing post.

Motor came with the JH kit. Not sure of its specs. Capacitor is 2.7 volt and 5 farad. Prop came with the kit. Not sure how to accurately measure pitch; ideas?

We have not measured voltage at launch or landing. We will try that next time.

Ceiling is about 26 ft. 22 ft to bottom of rafters.

One of their planes is about 10.95 g with no clay. We will try to figure out how to lighten it.
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Re: Electric Wright Stuff B

Post by coachchuckaahs »

Yeh, fast and level probably means a trim issue. Step through trimming process (J&H should have video on that). Basically increase decalage until it stalls late in flight, then back off. J&H planes like CG around rear of wing. SMALL changes to CG will radically change flight, so be sure to take copious notes in your log (Hint: CG location is an important parameter to record, as is decalage).

About 1.5g over is a lot, but should still climb some.

J&H earlier motors were about 2-ohm, and climbed strongly. More efficient motor recently, about 3 ohms, will not climb as sharply.

But it sounds like you have trim issues.

Coach Chuck
These users thanked the author coachchuckaahs for the post:
nepalinerd (May 15th, 2022, 9:56 pm)
Coach, Albuquerque Area Home Schoolers Flying Events
Nationals Results:
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records
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