http://www.rcindia.org/electric-power/understanding-electric-power-systems/msg104023/#msg104023

this is definitely going to help us.....Go through this link.

Quote from: swizera on May 31, 2012, 08:07:38 AM
Vikalp we can cut down a little weight from motor. as Motors like Cf2822 has wt less than 50gm and thrust of nearly 750 gm. for more thrust we can go for turnigy motor with wt of around 80gm and thrust of 1000gm.
Motor mount wt weight can also be reduced by 40 gm.
In total 80 to 100 gms can be reduced from electronics. which can be adjusted to make the frame more tough by reinforcement.

I agree with that, but those figures are rough. & i wanted to show what all is considered in rough estimation of weight. Once we have that we will proceed with finding critical parameters, like thrust, power....once we have our thrust requirement we can always chose a motor with least weight & cost. A better weight estimate will be carried out later.
We shall keep note about the motor you mentioned.

Now since we have our max. weight estimated, we can proceed to the next step, which is estimation of critical performance parameters. they are : Cl(max), L/D, W/S & T/W. These are governed by our own set requirements of : takeoff & landing distances, stall speed, max. speed, rate of climb.
Please note that we yet have not fixed our requirement of stall speed, max. speed and rate of climb. So before proceeding any further we need to finalize these 3 points. Need everyone's opinion.

I suggest the following requirements:
Max Weight: 800gms
take off and landing distance: 20ft each
Max Velocity: 20km/hr
Rate of Climb: 2ft/sec
Stall Velocity: 8km/hr

Please guide me on this. Need others opinion & contributions too.

This project has stalled.....no participation???

Sorry I was out.....

I think the "Rate of Climb" needs to be greater that 2ft/sec. I mean flying with this low rate of climb will be difficult even for advanced flyers...It will be too difficult to maintain altitude then. Lets just increase it up to around >10~15ft/sec atleast...

Well, Max weight is OK, But Would the plane of this weight can have stall speed and Max velocity so low like 8kph and 20kph resp.? Can we imagine a plane of this size to fly very little faster than average human walking on the street(An average young human being has walking speed of ~6kph)...I am not saying it is impossible but I mean that would need a lot of wing area while we have already set the Wing Span to 50 inches. So, We can only move the numbers around Wing chord. Having the chord too large will aerodynamically need bigger Control surfaces, specially Bigger Elevator surface, for even gradual climbs. So, With the weight 800gms we have to put the stall speed and max velocity little higher. or we have another option, We can expect less AUW but it will then require less Wing area to be aerodynamically what we want it to be.

I have a suggestion from my side. That is, With a wing span of 50", AUW around 800gms, Airfoil type KFM3, and Wing Area 500sq.inch, Our plane will have around 22kph Stall Speed while its max static pitch speed should be 2.5 to 3 times of Stall speed. That means we should look for ~60kph max with our power system. This result is obtained by Motocalc application.

Well I can understand your point of view with your suggestion that Low speed plane will be more easier to fly. But to achieve 8kph as stall speed on a 800gms plane and with a wing span of 50", We would need the Wing area to be around 1400sq.inch (Again Motocalc Data). That means we would need the wing chord to be 28inch Which is less practical for a trainer plane...

And I don't think 22kph Stall speed is fast for a plane of this size.

Waiting for others suggestions.
Thanks.

Hi Sumeet, thx for the information!
Could you please tell me what is the density and Coefficient of lift that you used for calculating stall speed of 22km/h?

Coefficient of density or of drag...?

Here are the lift coefficients of Airfoil(KFM3) I used....

CL = 0.52
CLmax = 1.20
CLopt = 0.64

It is 12% thick, 3.5% Cambered with 2.5% Angle of attack.

Please confirm, Was it Density or drag that you wanted to know.....

Quote from: vikalp11 on June 03, 2012, 10:19:15 PM
This project has stalled.....no participation???

Count me in  ...though I am a noob but probably can help you guys in making design sheet etc.

Great. I am glad to see you participating...........

I hope you enjoy this project..........

Hey Sumeet, thx for that information.
I meant just density, which I have took as 1.225kg/cu.m.
My idea is to keep Vstall as low as possible & Vmax as high as possible.
So, Keeping the area as 500sq.in, if I consider Vstall of 8km/hr & Vmax of 60km/hr then I need Clmax of 0.87 and Clmin of 0.02. (I converted all units to: kg/metre/second.)
So to achieve that range of Cl we need to play with camber,chord & thickness of the airfoil. Now I am thinking how to vary these three parameters so that the mentioned range is achievable.
My objective was to see the plane fly so slowly too....thats it.

You can try it....

Motocalc 8.0

Above application with which I calculated doesn't needs Air density but Sea-Level Air Pressure. And the value I fed is 29.92 inHG and Altitude which was set to 1700ft (As I live in Indore which is situated on top of a plateau called "Malwa Plateau"). Just calculate again in Motocalc. It can tell us better what we have to do.... 

Thanks.

Meanwhile I calculate, we can continue with the values that you have suggested.
Lets not pause this project....

As most of the parameters are set. Let's talk about design. How it would look...?

Any suggestions...?

So the design requirements have been set to:
1. Max. weight - 800gm
2. Takeoff Distance - 20ft
3. Vstall - 22km/hr
4. Vmax - 60km/hr
5. Rate of Climb - 10ft/sec
6. Landing Distance - 20ft.

I am a complete noob. Built a trainer out of coro which did not fly. So I have started designing a complete coro pusher on my own from the experience I have gathered. Please correct me if I am wrong:
A wingspan of 50" using coro will flex quite a bit. Since we are keeping the costs low (I have to ) I am not considering CF rods or depron. So is it possible to decrease the aspect ratio and still retain good glide characteristics?
An AUW of 850gms seems right to me!