Hello everyone, I chose Solar Airplane as my B.tech final year project. Started working on it from January and have time until may 1st week. Basically I'm from mechanical background with utmost interest in airplanes. So i have joined a team(sept 2015) which make planes for SAE Competitions abroad. Absolutely loved working and learning new things and learned as much as i can from designing to flying(less than 2 hrs flying experience). With this 1.5 years of experience in light weight rc planes and some research on solar cells i came to a conclusion that solar airplane is not an easy task.
           
     So instead of making a model and trying to fit solar cells on it I'thought designing a plane to fit solar cells would be a better choice. I have gone through this entire forum and found only 4 topics related to solar plane among which "new college project from PVA MODELS by Pradeep" and "coro flying wing by sbajare" found to be more informative .  So with help of some rc experts like "K K Iyer Sir, Sbajare Sir, Anwar Sir, Pradeep Sir".......      i can make this project even more successful.   I want to make sure that I'm going in the correct way.

Thanks in advance,
Aneesh.

I would like to help you in this project please let me know how I can help.

Aneesh.p,
Welcome to the forum.

Take a look at the thread 'selection of motor for tern'
It is long, 9 pages, 203 posts, most of which are not directly related to a solar power plane.
But there are a few posts containing factual data and/or raising important issues involved.
You may find them of some use.

Best of luck.

Thanks for the respose!
  That's indeed the first topic i have gone through in this forum . I have selected the motor Emax Mt 3510 for this project using a 12X10 prop(is it ok to use small dia ,high pitch) and have done a thrust test .Regarding solar cells i have bought 30 sunpower C60 semi flexible solar cells (5000rs around) kept 26 untouched while done some testing and experiments on 4 of them, readings seems quiet reliable for small quantity but not sure about 24 put together. Chose an airfoil with minimum camber and sized the wing accordingly to accommodate 24 cells. thinking to finish this project in less than 30,000(team of three). Started manufacturing and its going good. Im not sure about how to connect solar cells to battery and motor ,and how to charge battery in flight

@aneesh.p
If you are open to comments, here are some observations.

Quote from: Aneesh.P on March 31, 2016, 09:41:16 PM
I have selected the motor Emax Mt 3510 for this project using a 12X10 prop(is it ok to use small dia ,high pitch)
prop range on emax site for this motor is 12-15"dia, 3.8-6" pitch for 3s-4s
12x10 could be gross overload. Pl check for overheating.
As per emax data, max thrust, 1780gms is at about 22amps x 14.8volts, say 330watts, using a 14x4.7,
or 20amps/300w using 15x6


and have done a thrust test.
kindly share the volts, amps, thrust, prop dia, pitch found by testing, as well as motor and Esc temp if monitored

i have bought 30 sunpower C60 semi flexible solar cells
5.5x5.5", 3.34watts?
Say 0.5v x 6amps per cell?
Or about 15v x 6amps, or 90watts?
That would give you 6-800gms thrust depending on prop (typically under 6" pitch)

Chose an airfoil with minimum camber (why?)
and sized the wing accordingly to accommodate 24 cells. (not 30?)
thinking to finish this project in less than 30,000(team of three).
Started manufacturing and its going good.
Im not sure about how to connect solar cells to battery and motor,
and how to charge battery in flight

More observations/comments only if desired!
Regards.

Sir thanks for the reply! I came to know about this forum recently so i was left alone while designing the plane initially. I have made lot of assumptions while designing (don't know anyone to ask). I will try to answer from last question, please correct me if there is any mistake

why not 30 cells?
getting required type of cells in a short span of time puzzled me initially. After finding a dealer in hyderabad i initially got 30 pieces and thought to order more if required(don't want to waste) and those were very delicate and not conventional as others.so started testing to see voltage(0.55), current(5.1amp) with transparent sheeting , to know its extreme conditions of failure wasted 3 of them and kept one(slightly damaged) for further testing. Hence was left with 26 perfect cells. If i use 26 cells that would be without any spare, if some thing happens in between i cant get new ones(cells went out of stock  ) so kept 2 as spare and designed for 24cells(enough to charge 3s battery).
  I'm using 3s battery (for takeoff ) and calculated the cells to get 12v
  so 24X.55v=13.2v @5.1amp  (Testing were done in mid-feb, can expect more in april-may)
  Can accommodate more if necessary

Chose an airfoil with minimum camber (why?)
each cell is 12.5cmx12.5cm sized (Considering 13cm with soldering gap), to fit 24 cells i need 24X13cm=312cm span with 15cm chord- manufacturing problem.
  So tried placing two cells chord wise ie two cells in a column giving 12 cells in a row so 12X13cm=156cm with 30cm chord. so gone for considerable minimum cambered foils to place two cells chord wise without flexing much(this is only one criteria in airfoil selection)
Added extra tapered sections to accommodate control surface,polyhedral and to improve performance

thrust test readings
since MT3510 is a multirotor motor its dynamic thrust has relatively less importance. After simulating (REAL FLIGHT 7 Simulator) a similar spec motor with different propellers i came to know that higher pitch propeller has relatively more dynamic thrust and was able to achieve a level flight at minimum watts. Hence decided to go for an higher pitch props and ordered 14x7,13x6.5,12x10
   14x7 -max 1158grms thrust -172W-14.4amp
  13x6.5-      930grms           -152W -12.7amp
   12x10-      1065grms          -169W-14A(found to be satisfactory)
   12x10-      500grms            -63.6W-5.1A(solar cells alone assuming)
   12x10-      400grms            -48.2  -3.9A
thrust test done with 2200mah3s,30amp esc and in pusher configuration,left at full throttle for a min and motor is slightly heated since it doesn't have any airflow
I'm designing this plane for good level flight performance where it will be charging the battery and powering the motor simultaneously, battery is used as a backup(takeoff,sudden clouds etc)

Is there anything wrong or did i miss any thing in my calculations?

maximum plane weight 2kg trying hard to get it to 1.5kg
have done cfd analysis for this model stall speed(4.1m/s expected)
at 8meters/sec(level flight)  lift=1.8kg   and drag=.120kg (not sure in real though).

Thanks in advance,
Aneesh.
 

     
 

@aneesh.p,
Hi,
I don't know the basis on which you made your initial choices, but prima facie it looks like these are very good starting points, giving your project a favourable chance of success.
Before i mention why i think so, can we have an estimate of the payload?
102 g motor
  25 g prop est
  50 g Esc est
  68 g 4x17g servos
  30 g extension cables est
200 g 3s 2200mah lipo
Total 475 gms so far.
How much does each solar cell weigh? Total for 26-30 cells?
How much will the connections between the cells weigh (as they will carry 5-15amps)?

Hence estimated total weight of payload (ie, excl bare airframe)?
Regards.

Just a noob question , which is a better choice a flying wing or a conventional plane ?

conventional.
Flying wings. unforgiving for beginners

@Tanmay.mathur
Well flying wing will obviously be a good choice due to its performance and lack of integration but stability is kind of a problem(i dont want any crashes)
since i have 1.5 years experience in conventional i went for it 

@prabal276
exactly said !

The answer lies in the answer to these two questions:

1. What percentage of full size and model airplanes are flying wings?
2. Why does the Solar Impulse 2 have a conventional tail?

Unless one is thinking of foot launched sailplanes, most of which seem to be tailless.

Also on what one means by 'better'.
For some specialised applications, a flying wing may be better, but perhaps not in general.

Quote from: Aneesh.P on April 01, 2016, 09:34:08 PM
@Tanmay.mathur
Well flying wing will obviously be a good choice due to its performance and lack of integration but stability is kind of a problem(i dont want any crashes)
since i have 1.5 years experience in conventional i went for it 

Lack of integration? 
Sorry i couldn't understand that 

@ K K Iyer Sir
motor+ xmount +prop+spinner+bullet connectors-close to 150 grms
esc-30 grms
using 6gram servo-rudder-t=1.2kg/cm
        9gm           -elevator-1.6kg/cm
        17gm         -ailerons-2.5kg/cm
control rods+linkage stoppers+screws=10 grms est
2200mah 3s-210grms
am using a separate circuit for rx and servos(in case some thing happens to main battery or ciruit)
1100 3s lipo-100grms
bec-15grms
reciever-10grms
extension wires-70 grms (need to find a way to get light duty wires)
solar cells 8g each so 24x8=192grms
tabbing wire 30grms(not sure about ratings but thats the same wire used in 100watt solar pannels so should work)
voltage regulator-40grms
sheeting-200 grms est
wings,tail manufacturing done-500grms around
fuse will finish by 3rd-less than 100 grms est
thats a total of 1.7kg est trying to get it to 1.5kg (a smaller battery ,ext wires,fuse)

will fly without cells first to see the throttle for level flight then with solar cells
Only problem so far is electronics circuit -how to manage charging while running motor simultaneously 



     

lack of integrations- i meant fuse-wing,fuse tail integrations ,attaching servo leads etc 

Do you mean you shall use a 3s lipo for rx and a bec too ?
Why not a 1s lipo + power bank circuit (step up regulator) to make 3.7v to 5v.

Would you use flaperons? Landing gear or belly land?
Curius bug.

@Tanmay.mathur
i dont have any 1s /2s and dont want to buy one just for one flight test  
there will be 2 batteries one for propulsion and other for control

Its hand launched and belly landing, flaperons will give a try theres an option in my teams 6-ch transmitter

I too was a curious bug thats what make us experiment things

@aneesh.p,
Everything looks about right so far!

Wing size. Big enough to accomodate cells, but not so big as to be difficult to construct.
Aspect ratio. Fairly good for efficiency, but not so high as to be difficult to construct.
AUW. 17-1800gms, or 60-63oz. Excellent target that i thought would be hard to achieve. But looks like you will achieve it.
Wing loading. 7oz/sqft. Excellent. (Just have to be careful in strong/gusty wind). Hence stall fairly slow at ~4m/s. You can consider a slightly higher cruise speed than 8m/s (30kmph) to cope with wind)
Airfoil. What airfoil have you used?
I estimate that cruise will be at CL of ~0.7, which seems a reasonable initial estimate.
Reynolds number. Probably around 150,000 (much better than sub50k i often work in!)

Only 3 things remain.
1. I suggest a stress test of say +-3g for the wing.
2. Reconsideration of prop size, espcially pitch. 8m/s or 320"/sec with 10" pitch needs 32 rps, or under 2000 rpm. Please check if you get power/weight ratio of at least 1:3, or 1:2 for safer launch/climbout. High pitch prop will provide slower initial acceleration...
3. Solar cell maxWatts may be only 70% of maxVolts x maxAmps, or only 50% in less sunlight.

Would like to see your airfoil section and wing construction.
And i assume you have provided adequate tail volume coefficients and static margin in CG position 

Excellent project. Solar issues can ba tackled after flight test on lipo.
Best of luck.

I could give a 1000 mah 1s or 2s if you need. U shall need a power bank circuit.
It could be very good setup (1s+step up)

Thanks tanmay
meanwhile i will look around in my collage for smaller batteries
thought its not must for initial flight test since i dont need to keep solar i will use only one battery

Ok let me know if you plan . Material for fuse and wings ?

@Tanmay.mathur
balsa and carbon fire entirely
ply for integrations

Balsa honeycomb ?
Is it expensive ?
Total airframe cost ?

@ K K Iyer sir
The data u mentioned is correct
cl-.69
reynolds num 143k at root and 95k at tip(i designed in such away that its near 1lakh)
included a -4 degree twist in end sections to improve efficiency and to increase stall angle(better stall characteristics)
Airfoil is we3.55(which u may not find in internet  -only mentioned in 2 journals so far-  its almost similar to s9000(9%) )
Tail volume coeff is .62+(considered losses in efficiency,manufac so kept a little high
Static margin is around 20%+(kept highly stable to compensate for gusts at low crusing speed)
Cg position can be changed have a lot of room in fuselage so thst sm could be brought to 10% if desired

about solar im not sure but im pretty confident on my design so it will be either solely solar powered or will charge the battery in glid(its a good glider)

seems we think a bit alike have done stress test in last week for 3kg point load and 3.3 kg uniformly distributed
Tail weighs 109grms
entire wing weighs 370