F5E RC Solar Powered Aeroplanes - RC Groups
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Feb 09, 2017, 03:10 PM
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F5E RC Solar Powered Aeroplanes


Hi all,

today while checking the 2017 F5 Sporting Code (yes, in F5B it is now 3points deduction for each second of motor in duration...#every second counts!) I noticed that the class F5E was completely revised:
It is no longer a distance, duration and landing task, but the distance task is changed to be maximum distance flown as recorded by a GPS logger, followed by a spot landing. Thus no more legs flown between base A and B. The 30minutes working time must not be exceeded. There seems to be no limit on motor running time so I understand that the motor is on for the entire flight, and high score is achieved by flying as fast as possible for half an hour while powered only by solar cells, and then landing on the spot.

This sounds really interesting to me...as no negative molds models are permitted it should allow for innovative airframe construction, and the maximum solar cell area of 0.25m2 will keep model size moderate and hopefully keep cost in check also.

The FAI sporting code is found here: link

Is anybody working on developing a plane for this competition? I think ill run some numbers over the weekend...


Cheers, Andy
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Feb 14, 2017, 12:41 PM
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gotboostedvr6's Avatar
Looks like a fun class
Feb 14, 2017, 04:58 PM
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Considering the goal of the competition, it seems the requirements demand a plane with somewhat opposing design points be developed.

Case A: Perfect weather: blue sky, little wind, high sun irradiation: In this set of conditions the solar cells will allow for comparatively high power output. Here the best score is achieved by flying as fast as possible, clocking up as many kilometers as possible during the 30minutes. Thus the model should have lowest drag possible at the highest possible design speed, while still be launchable and landable on the spot.

Case B: Intermittent clouds, possibly some wind, high sun irradiation: Here it may happen that the sun is blocked out by clouds, so to overcome periods of no power the model should be able to glide well, possibly use thermals. In periods of sunshine it should not fly fast but use the power to climb in order to store some potential to glide down in power out times.

Case C: Low sun irradiation: Use all power available to stay aloft. Best lift to drag ratio needed.

We know airfoils that have good lift to drag ratio as well as low drag: Hand launch gliders and hotliner airfoils. However, all of these modern airfoils make use of flaps to adjust camber to either reduce drag in cruise or have the best L/D in thermals. But including flaps in a solar array wing makes the design very difficult: If the cells are only included on the fixed part of the wing, wing surface needs to be large to accomodate the flaps behind the cells.

When looking at existing solar powered airframes, as solar impulse, they all have very high aspect ratios (long slender wings) in order to have very low induced drag and very good L/D ratios. But none of the long endurace planes were made to fly fast, and high speed will pose a problem to slender wings in terms of flutter or divergence. Solar planes that fly fast are usually deltas or low AR flying wings which offer a lot of surface, but which usually have real bad L/D so when the sun is out they come down soon.

It would appear that a wing of moderate aspect ratio with flaps would best fit the bill.

Next question is: conventional or flying wing?

To be continued..

Andy
Last edited by Dotcom; Feb 14, 2017 at 05:07 PM.
Feb 14, 2017, 09:34 PM
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I'm curious, is anyone flying these models presently? Any links?

I didn't read the rules thoroughly but they say "Same rules as F5B, except":
- max area of solar generator: 25 dm2 (F5B total area is 26.66 dm2 so similar flying surfaces)
- only monocrystaline cells may be used

How much energy can one yield from 25 dm2 via monocrystaline cells ? That's only 0.25 m2. This link suggests 150-200W/m2 in good sunlight. Does that sound right? I'm guessing must be pretty anemic flying. Well.... relative to F5B with 1750 W*min limiter.
http://www.theecoexperts.co.uk/how-m...e-solar-panels
Feb 15, 2017, 01:09 AM
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200 Watts sounds way too optimistic:
Assuming: Solar cell efficiency of 20% (monocrystalline cells), 0.25m2 cell area, 1000W/m2 irradiation yields:
Pc = 0.2 x 0.25m2 x 1000W/m2 = 50Watts! delivered by the cells.

This needs to pass through ESC, motor, gearbox and propeller. Assuming all these together have an efficiency of 70%, which is quite optimistic, then
Pm = 50W x 0.7 = 35W is available as mechanical power to the airframe.

Further assuming a airframe mass of 1kg and a L/D ratio of 30, and airspeed of 10m/s, the airframe requires
dU/dt = 1kg x 9.81 x 10m/s /30 = 3.3W to maintain altitude.

The remaining 35W - 3.3W = 31.7W can be used to climb:
v_climb = 31.7W/ (1kg * 9.81) = 3.2m/s

Note that this is in optimal conditions, ie the wing perpendicular to the sun rays to achieve the 1000W/m2. If you fly at an angle or the sun is low, power is significantly reduced and even staying aloft will become challenging already!
Feb 15, 2017, 06:06 AM
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If you want to learn more about solar planes you might want to look here:
https://www.youtube.com/results?sear...-+RCTESTFLIGHT
Feb 16, 2017, 05:06 PM
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I also found this example:
RC SOLAR AIRCRAFT WITHOUT ACCU THAT´S GREAT AND AMAZING DEMO FLIGHT / Bad Wünnenberg Germany 2016 (3 min 37 sec)


In the video he says he is not even using a receiver battery. It looks to be kinda challenging to keep it in the air in these prevailing winds.
Feb 16, 2017, 05:21 PM
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Lenny970's Avatar
Quote:
Originally Posted by Dotcom
I also found this example:
https://www.youtube.com/watch?v=aCeMHfzxDH8

In the video he says he is not even using a receiver battery. It looks to be kinda challenging to keep it in the air in these prevailing winds.

Very cool!
That reminds me of the challenging early days of electric flight with woefully over weight, under powered models.
Any successful flight was cause for celebration. Ahhh, the good old days!

Lenny
Feb 17, 2017, 05:34 PM
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This class looks awesome, and might be my first foray into the competition world. That said, I had an idea to maintain consistent RX power that I think might be beneficial, but may also be illegal.

The plan is to use a brushed motor spinning a flywheel to maintain power for the receiver in spots with very low sunlight. It might not work well, but seems like it could help, and sound interesting.

Edit: I had not realized a receiver battery was allowed. This may still be applicable to propulsion, but is far less important or useful.
Last edited by Remzak; Feb 17, 2017 at 05:39 PM.
Feb 20, 2017, 04:30 PM
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I think they allow an RX battery to be used for safety reasons, and frankly I would feel much safer with such a brittle aircraft at least being able so maintain controlled gliding flight after loss of motor power due to clouds.

The RX circuit must be separated from the propulsion circuit, I presume just removing the positive lead from RX to ESC should satisfy that requirement.

If you go by the letter of the class description, the only kind of energy storage forbidden is batteries and capacitors. With batteries I take it means any sort of chemical batteries as we know it (LiPo, NiCd, NiMH, Pb, etc) but as I read it it would allow a flywheel in the propulsion circuit.

Note that you would need to use a set of diodes to convert the alternating current from the flywheel motor/generator to direct current to supply the RX, and possibly some sort of voltage controller or BEC.

-Andy
Feb 22, 2017, 12:45 PM
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Hi,
you have the best batterie allways with . Klimb as high as you can ,it's pure Energy . And for the rx the solarcells will delifer enough power when the motor is shut of . The biggest cloud will not slow down the rx and servos. Here in the German rc-network is the solarflyer tread with Holger Lambertus . http://www.rc-network.de/forum/showt...flieger/page11 . It's in German but if you have a question try to aske there or you can aske here and i will forward your quest. Page 11 is a good start .

Happy Amps Christian
Feb 27, 2017, 04:08 PM
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Thank you Christian for the link to the German forum, there is a ton of useful info to be found...

It seems the cell type to go is the Sunpower C60. It is a bit flexible and can thus conform to the wing surface. 16 cells will just squeeze into the 0.25m2 limit.

I will see if I can get my hands on some to start testing...
Jun 05, 2017, 10:48 AM
Registered User
Some update on this: System sketch

The following figure shows the proposed system layout.
Essential for solar powered flight is the use of a Maximum Power Point Tracker (MPPT). This is a controller which adjusts the throttle such that the solar cells are loaded at their maximum output point at all times. As the output of the cells varies constantly during flight due to change in angle to the sun (due to manoevering), due to clouds etc, the throttle is to be adjusted by the MPPT such that the maximum power (voltage multiplied by current) is obtained.

In a first shot it will be attempted to use the telemetry signal from the Unilog2 as the control input for the MPPT. This avoids carrying additional sensors next to the Unilog stuff. External input will be the throttle signal from the receiver (on-off only). Output will be the throttle signal to the ESC, so modified that the maximum power point is tracked. Make sense?

The rest of the system is straight forward: RX, GPS logger, motor with gear and propeller.

Andy
Jun 05, 2017, 10:57 AM
Registered User
Airframe layout

Here a first shot at the proposed airframe layout and weights.
Fairly conventional: Hotliner with four flaps to allow for cambering. Wing with ribs and a carbon tube spar. Fuselage with balsa pod and carbon conical tailboom. Balsa V-tail with single elevator servo.

Span: Just over 2m to accomodate 16x the Sunpower C60 cells (125x125mm each).
Length: ca 1.3m
AUW: ca. 800g

For all my plane designs a mass and balance sheet is prepared to record component mass and position with respect to CoG to help with proper balancing and positioning of the components. In total the resulting mass moment should be zero or positive (nose-heavy).

I named the thing Aereon, after the elemental featured in the Riddick movie.

Andy
Jun 05, 2017, 11:31 AM
Registered User
Quote:
Originally Posted by Dotcom
Airframe layout

Here a first shot at the proposed airframe layout and weights.
Fairly conventional: Hotliner with four flaps to allow for cambering. Wing with ribs and a carbon tube spar. Fuselage with balsa pod and carbon conical tailboom. Balsa V-tail with single elevator servo.

Span: Just over 2m to accomodate 16x the Sunpower C60 cells (125x125mm each).
Length: ca 1.3m
AUW: ca. 800g

For all my plane designs a mass and balance sheet is prepared to record component mass and position with respect to CoG to help with proper balancing and positioning of the components. In total the resulting mass moment should be zero or positive (nose-heavy).

I named the thing Aereon, after the elemental featured in the Riddick movie.

Andy
The calculation sheet is a great idea. The fact that you don't need a battery (or are required not to have one) really lowers the total weight!


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