Hello guys,
I am Karthick Ashwath. I want to build a solar aeroplane.I am now doing the background research for it. It is based on the Tern which is a flying wing designed by Holski77. Here is the link to it http://flitetest.com/articles/the-tern-60-flying-wing . I have finished the solar theoretical part of it (i have just completed the research, not built it) I want to find an electric motor which provides 700-900g of thrust at 3S and consumes LESS THAN 10A. Don,t mind about the kv or size, it is not important for the calculations. Could you please help me to find such a motor that costs less than or equal to Rs.2000, preferably from Indian sellers? If you want to calculate and find out the specs, you could try this link: http://ecalc.ch/motorcalc.php?ecalc&lang=en

Thanks in advance,
Karthick Ashwath.

@karthick ashwath,

Notes made during some testing last year show that my DT750s delivered 700gms static thrust using an 11x5.5 EMP prop, drawing 9amps/110watts on a 3s. May meet your requirements. Available online from Indian hobby shops for Rs1300-1500.

I presume your wing area is about 4sqft, and all up weight including 3s 2200mah lipo (but excluding solar panels) will be 500-600gms. That should give you a payload capacity of 500-700gms (depending on whether lipo retained or not) for the solar panels.

Curious about the area and weight of solar panels to provide say 8-10amps at 12-15volts.
Regards

Hello,
Thank you KK Iyer for your recommendations. But could you please recommend a motor with more thrust? This kind of just makes it.Also, it would be great if you could find a 5010 360kv motor that fits this specifications. This motor may or may not fit the specifications, but it was what RCTESTFLIGHT used in his solar plane prototype video, where he mentions that it pulled 7.3A. Here are more details about my solar setup:
Seperate cell details:
Area 6x6"
Amperage:8A
Voltage:0.5
Total no. of cells:20
20 cells in series gives me 10v. I have refined my calculations , just to find that every thing was wrong.I will get back to you with the right details.

@karthick ashwath,
1. What's the weight of the solar panels?
2. Are you planning to use the solar cells to power the motor directly, or via lipo?
3. How did you arrive at your thrust requirement? You may like to look at this:
http://www.rcindia.org/electric-planes/iyer's-tech-talk-how-much-power/
Regards

Edit:
Many of the RCI members apparently think that the (static) thrust must equal or exceed the weight. This is true only for helicopters!

Oh, thank you very much Mr.Iyer then definitely this DT750 is the motor for me. AS you said,I had thought that the static thrust must exceed the weight. Now I get it. It need not.
Ijust figured that my selection of the airframe is very bad and that the area is not enough to fit 40 cells. So now I am looking for a new airframe whose wing area(preferably flat) is greater than or equal to 1440 square inches.And also your motor tips are very good!
Since I am looking for a new airframe, I would have to do the theoretical part again.
I planned to use 40 cells which would give me 160watts(minimum) and I don't know the weight but it is very light and fragile.
I am going to use solar as main power supply and 4400mah 3S lipo as backup(2 2200s in parallel)
Thanks,
Karthick.

@karthick ashwath,
Are you planning to use solar power as a primary source, or as a charger for the battery?
2x2200 3s will weigh close to 400gms!
Regards.

Edit
Are you tracking Solar Impulse?

I was planning one such plane months ago and here are my suggestions,

>You can place a small 1000mah Lipo( Tiger power from rcsportz is lighter enough than most other brands and provide a backup for most applications and power the plane directly from solar panel(primary source)
>though your calculation are correct you do not need 1:1 power ratio and hence you can fly a plane with well below power ratio.
>i believe you are looking at this solar panel: http://www.ebay.in/itm/Flexible-Solar-Cell-High-Efficiency-10-Pieces-/111769715570?hash=item1a05fe8372
If not please do. they have better efficiency i have seen so far, do refer me a better one if you have on in mind.
>motor selection will depend on the AUW and hence is not a question now.
> i choose a flying wing instead of conventional plane. there are lot of flying wing plans in outerzone.co.uk and here is my selection: Windfreak-RCM-11-78
this one has lot of surface to place enough panels and balsa construction make it lighter enough and a flying wing is simple to build in balsa than a conventional plane and this is a simpler design with few good advantages.
>the extended nose on the front enables you to balance cg with minimum lead weight without a hefty battery.
>can be used in both tractor/pusher config with the same motor and prop config, no limitation of prop size by elevons however a pusher config needs a bit of modification.
>i prefer a tractor config and foldable prop for better efficiency, towline launch since the power should be just enough to fly the plane and not for a immediate takeoff.

these are my observation/study/research so far. i believe this is enough to get your project to jump start. let me know if you need any info.

@kk iyer
Yes, I like the Solar Impulse and I update myself about it on Facebook. Yes, I am planning to use 2 2200mah lipos only if they can be fit in the new airframe I am searching for. If not, I will settle for 1. Yes, I do plan to use solar as my primary power source.
Thank you sir,
Karthick Ashwath.

@v2eagle
I am actually looking at 6x6 inch square solar cell which actually perform better than these. It has a better area to wattage ratio. I am planning to use 40 of them.
Thanks,
Karthick Ashwath.

@karthick ashwath,
40 of 6x6 is going to need a wing of 10' span and 1' chord!
That's huge...

So, is it not possible to build an airframe like that that weighs <= 1400g using foam?
Or, we can half the no. of cells and reduce the area required and also reduce the size and power of the motor?
Eg.20 of 6x6 will give us 12 v at 7A and will have a power of 80W. So can we get a good motor that pulls <= 7A and have it power an airframe whose wing area is 720sq. inch? Can that motor power that airframe without stalling?
Thanks,
Karthick.

Difficult, but possible.
One important piece of data i don't have.
How much does each 6x6 cell weigh?
(I presume 12v, 300ma per cell, correct? And depreciated by the cosine of the angle of the sun away from vertical... )

What about a land vehicle?
Can't remember where it is, but about 20 years ago, a visiting American had presented my son a kit for a solar vehicle, with a 1cm x 2cm cell, and wheels about 4cm dia.
Today's paper says solar autorickshaws being introduced...

That apart, do tell me the weight of each cell, so that we can proceed with planning your aerial project.
Regards.

I tend to think along conventional/sailplane lines because that is my area of interest.

New projects, however, need out of the box thinking.

Take a look at something called 'Nutball' on flitetest site.
Not exactly a good aerodynamic solution, but a 4' span will give you enough surface for 40 cells.
(If they are not too heavy  )

May i ask you a question that i sometimes ask members of this forum:
What, Sir, is your objective?
Suitability of suggestions depends entirely on the answer...
Regards.

I dont have any data or calculations to share. But from what i read you are suggesting a plane similar to the impulse on a smaller scale that can fly all day and have enough juice stored in the batteries to fly all night and basically relative to pilot endurance on the ground flies forever.
first thing to consider is that it will cost a lot to build such a plane, secondly the building techniques have to be very refined and the design has to be very aerodynamic.
Why not try something similar to this: http://flitetest.com/articles/our-solarplane-dreamship-surprise

Even getting 2-3 hrs of flight with solar panels would be impressive. Long endurance planes and "UAV"s are easy to see in your head and on paper as a concept but making it work in the real world will require a lot of testing and refining with the materials and resources you have available.

All the best for this project

@rcneil21
First of al, I would like to make a few things clear.
1.My plane is going to be capable of flying 11 hrs per day(as long as the sun shines), not all day long.
2.The purpose of the battery is to provide a backup to return/land safely, not to fly for 14 hrs.
3.My battery will probably be a 2200mah 3S lipo, which can sustain the motor at full throttle for 24minutes.
4.And till date , it has not seemed too costly to acquire 40 cells.

Thanks in advance,
Karthick Ashwath.

@kkiyer
Sir could you please stop calling me sir? I am just 13 years old.The weight  of each solar cell is about 6 grams. So 40 cells means about 240 grams. Also sir, could you please explain wing loading(your favourite subject)? I don't think I quite understand it. And 40 cells looks a bit overkill for this project.20 cells would be enough. As each cell gives about 0.6 volts at 8A, if we connect them all together in series, we would get 12v at 8A.  I am building this plane, I would gladly elaborate:
1.No limit to the extent to which I can fly
2. No limit for the amount of time I can fly(every fpv pilot's dream)(I have loved the feeling of infinity since I was very small. Eg. I have played with toy planes in my dream world imagining that they have infinite fuel, infinite...)
3.(this reason is one of the minor reasons)Giving the world a correct and complete tutorial on how to make a solar plane
4.This has been my dream for a very long time.

@kkiyer
Sir are you sure that the DT750 consume only 9A?Could you give me the prop using which it pulled only 9A and gave 700g of static thrust?It is absolutely unbelievable!Also, does it pull 9A at optimal conditions or is this at full throttle?
Thanks,
Karthick Ashwath.

Data from my notes of last year:

Motor DT750, prop EMP 11x5.5, battery 3s 2200mah turnigy & Haiyin from kinetic hobbies.

Amps Watts Thrust gms
3.2     40      300
4.5     56      500
7.5     92      600
9.0    110     700
11.0   132     800
13.6   161     900
14.4   168     950

Useful?

@karthick ashwath,

The purpose of putting the @ is to ensure that the recepient gets an email notification of a new post.
For that the recepient's handle has to be correctly stated.
@kkiyer gives me no notification.
Try @k k iyer
Anyway, since your project interests me, i check RCI every day. So don't worry about wrong tag!
Regards

@karthick ashwath,
13 eh?
Not much difference. (Only about 50 years )
You are at the right age to dream of the future. Do continue.
At 13, I built my first model truck, with a reverse feature, that enabled me to get the Junior Science Talent Scholarship. At 16 I built my first wind tunnel, that helped me get the Senior Science Talent Scholarship.

But you have to be careful about your data.
You said each solar cell gives 8 amps at 0.6v!
Is this right? (see edit below)

And,
Remember my query about objectives?
1. Getting solar cells to power a motor adequately is one project
2. Building an airplane model that can fly reliably, is an altogether different project
3. Combining the two above is the third project...

Best wishes. Don't let a few obstacles stop you.
See this.
https://en.m.wikipedia.org/wiki/The_Spirit_of_Butts%27_Farm

Edit: 8amps could be correct from 6"x6".
The 3"x3" panels on the Solar Dreamship (flitetest) apparently give 2amps (@0.6v).

Sir, according to my calculations, using the formula P=VI, I found that:
Motor requirement 120W(9A+1A extra x 12V)
Solar cells required = 20(gives 12 v at 8A when in series)
120/8 = 15(total watts required/no. of amps produced)=no. of volts required
15-12=3
3/0.6=5
So if we have 25 cells in series we will get 15v at 8A(120W)
So if we use a simple DC-DC step down circuit, we can get around 115W with ease(approximate)
I chose this method of putting 25 cells in series and stepping it down as it is easier and lighter to add 5 cells instead of a greater number that would have been required.

According to RCTESTFLIGHT, who is building a solar airplane and is in his fifth attempt,
Power produced by solar cells is inversely proportional to temperature.
So, if we apply that here, we find out that when the plane is cruising, cool air will be rushing over it. The extra efficiency of cells will be balanced by the loss of efficiency due to the angle at which it is to wards the sun. So we can expect realllllly good results(I suppose so)

And, can anyone suggest a good airframe with at least 900 square inch wing area?And could I use a DT700 instead of a DT750? Many say that the DT750 vibrates a lot which may damage the solar cells. But the thing with the DT700 is that it gives lesser thrust at the same weight. So if anyone has any motor thrust test data for the DT700, please post it here. It will be very useful for me.Also, can anyone say who is the manufacturer of this motor? I do not know which manufacturer to select when I am using a thrust calculator.

Thanks in advance,
Karthick Ashwath.

All the calculations are good. One question is this your first RC plane build?
The manufacturer of DT700,DT750,DT900 and DT1000 is Hextronik a subsidiary of HobbyKing i think.

So with a 90" span and 10" chord and i am assuming a rectangle shaped wing and model weight of 1.5kg your looking at a wing loading of 26gm/sq.dm.
Which is a pretty good loading. If you get it to around 1kg AUW which is very hard for this size plane with the solar panels and battery it will be even better.
Also For stable flight characteristics you will have to use a polyhedral shape wing which will reduce the amount of wing area at optimal angle and also give less efficiency but you wont have to fight the plane and it will make your plane more easier to fly. There is a lot of planning to do Karthick, your very lucky to have Iyer sirs guidance something that rctestflight and another guy who attempted making a solar plane, mygeekshow didnt have.
So your success rate is definitely higher than either if you can execute everything well and Follow the guidance,advice,modifications and instructions of Iyer sir to a T

Wow.
Undeserved praise! Made me blush at the thought of Gusty sir and other old hands laughing. 
Remember that i'm only a self taught amateur, not a pro!

A few thought experiments to start with:

1. If 24 6x6 cells could be placed in a 2x12 grid on the wing, the minimum wing size is 1'x6'. But this will be possible only of the cells are flexible enough to go around the top of the airfoil.

2. If not, they will have to be placed on the rear 2/3rd or so of the chord in a 1x24 grid. This will need a wingspan of 12'! And chord of about 9". Aerodynamically good (with aspect ratio over 13), but not so easy to construct both strong enough and light.

So the first question is "are the cells flexible?"

No sir they are not flexible. But sir, I thought of building the solar panel array on a normal rectangular piece of foam and connect it to the motor, which I plan to leave out in the sun all day and find if the motor keeps running. Is it advisable to do such a thing?And I also plan to take periodic amp,volts and thrust values(record them/note them down). So, if this is successful, I think we could continue with this project.

Sir, I heard some people say that the DT750 sounds like a coffee grinder and they recommended to use a DT700. So what motor should I use? Or should we broaden our scope and look at DT 900 and 1000s?

And sir, don't you think it would be better if we use flying wings as our airframes?Also , it happens to be 25 cells, not 24.

Thanks in advance,
Karthick Ashwath.