Returning to this forum after a long time  

Didn't know about sweepstakes, so forgot to put the newspaper . So this may not be eligible for sweepstakes.

Built an Avispad from 5mm Depron, hence the name AviFoamie

Armin wing construction shown in the pics. Refer experimental airlines video on youtube for details.

Used a Balsa Dowel as spar.

url=https://postimg.org/image/fsezwg0bz/][/url]

Ready for maiden, tomorrow morning.

Another avispad was made by my friends, but with coro

It's ready to fly!

I had a strange problem today while flying. The motor rpm wasn't increasing after 60% throttle. It was actually decreasing. I tried with two different ways. Same thing was happening.
My motor was RCTimer 1120kv motor. 1250mAH Wolfpack LiPo, Turning 25A ESC, some other 30A ESC ( I don't remember the brand). I even tried removing the prop and then giving full throttle. Nothing worked. Any reason as to why this is happening? Tomorrow I'll borrow a friend's motor to test it.

Nice build 

Try recalibrating the ESC

I wish I had known that before. I tried to launch it 5 times, all the times crashed. The Nose is damaged. I saw a few videos. That is exactly my problem. Anyway, I'll repair and fly!!

@topalle,
Hi Srinivas,
Since the problem remains even with prop removed, probably throttle calibration is reqd.
Needed when ESC is changed.
You probably know how to do this, but just in case...

Usual method is:
Switch on tx, move throttle to full.
Switch on onboard power.
You should hear a long beep (usually) indicating that ESC has noted full throttle position.
Move throttle to idle.
You should hear another beep indicating ESC has noted low throttle position.

Then you are ready to go when you get the cell count beeps!

Incidentally, when you say you have an 1120kv motor, it doesn't convey enough information.
It could be a 120watt motor drawing 10amps,
Or a 500watt motor needing 40-50amps!

You have to specify the max amps or watts rating, if you have the data.
Otherwise at least the weight of the motor.

If your motor weighs about 70gms, it is probably RCTimer's 2836/7 1120kv motor.
This motor is rated for 336watts max on 3s, or say about 30 amps.

How much you actually draw depends on the prop. The recommendation on the site is 11x7 for 2s and 7x3 on 4s. So say 9x5 on 3s. Does this agree with what you are using?

This week i tested my DYS2836/7 1120kv that looks just like the RCTimer one!
With a 10x5 EMP prop and 3s 2200 lipo, i got:
1000gms thrust at 8800rpm using 220watts (20amps x 11volts).

So the possibilities are:
1. Throttle not calibrated
2. Over propped
3. 1250 lipo not able to cope
4. All of the above  

Btw, the motor i tested, is able to pull my 700gm Magic straight up, after rolls on takeoff!
Don't know how heavy your model is, but a trainer like yours should easily fly on thrust of 50% of weight, or about 100-150watts per kg of weight.

Hope this helps.
Regards

Mine is just 600Grams.
9x6E Prop.
Yes it is the exact same motor.

I am about to recalibrate the ESC. I am sure that is the only problem. I checked the battery voltage, it barely dropped 1 volt after trying to fly it for 10 mins.

And one more question. I want to have a thrust to weight ratio of 0.75, Please suggest a motor for 9x6E prop. I want to buy another one as it is a crieteria for the IIT Aeromodelling competition I am building this for.

Thank You Sanjay sir and KK Iyer sir for helping me out!

@topalle,
This motor will easily give over 900gms thrust!
If you want only 450gms thrust, or a bit less, then you need an EMax CF2805
Not the 2800kv, but the lower one (about 1600 I think)
I have one in my 450gm Sunbird, and i never need more than 50% throttle! with a 6x4 prop on 3s.

You said 'please suggest a motor for a 9x6 prop'

Why 9x6 only?

Would you like to share the task requirements?
You can PM, email, sms, phone me 
Regards.

Turns out it was a faulty motor. I got to know that after using a friend's motor. Ordering a new motor. By evening I'll post a video.

@topalle,
Hi Srinivas,
Saw your PM that you are considering an Avionics 2822 1400kv.
RC Bazaar data says that to stay under 450gms thrust, (75% of your est AUW) you'll need a 6x5prop.

A 1400kv will do 16800rpm at 12v
Or say 12600 at 75% efficiency.
That is 210rps.
At 5" pitch, that is a speed of 1050/12~ 90fps or ~100kmph!
Probably too fast for your model.

You'll have to check what the thrust is on say 8x4, 7x3.5, 6x4, 6x3 props..
Better I think to opt for a smaller & lower kv motor if you can, if your model is in 600gm range.
Else you can build a larger model!
(That option may be worth exploring if you have time)
Regards

My model will be shredded to pieces at that speed

I'll search for lower kv motors then, with lower thrust.

Avionic PRO C2822 KV1200 brushless motor
● Get 500gms Thrust
PROP – 8x4E
Lipo – 3cell 11.1V
ESC - 30 amp

Specification:
● Stator Diameter: 22.0 mm(0.866 in)
● Stator Thickness: 6.0 mm(0.236 in)
● No. of Stator Arms: 12
● No. of Magnet Poles: 14
● Motor Wind: 11 Turn Y
● Motor Kv: 1200 RPM / Volt
● No-Load Current (Io): 0.5 Amps @ 10 volts
● Max Continuous Current: 12 Amps
● Max Continuous Power: 150 Watts
● Weight: 41 Grams(1.446oz)
● Outside Diameter: 27.8 mm(1.094 in)
● Shaft Diameter: 4.0 mm(0.157 in)
● Body Length: 22.0 mm(0.866 in)
● Overall Shaft Length: 36.5 mm(1.437 in)
● Max LiPo Cell: 3-4 S
● Motor Timing: 5°
● Drive Frequency: 8kHz


How is this combo?

Can you post the weight of your model with servos and ESC, but without lipo and motor?
Also span and chord of wing?

Weight without motor and LiPo is just over 450 grams.

Wingspan 1200mm
Chord including ailerons is 200mm, aileron width is 1.5 inch or 38mm

So about 48"x8"
Or say 2.67 sqft
Assuming 200gms or 7oz for lipo, 100gms or 3.5oz for motor&prop.
And 16oz for airframe and servos
All told say 27oz for 2.7sqft wing area, or 10oz/sqft loading.
That is quite good for this task!

At that wing loading, you should be able to fly easily at 20-25fps (about 2-2.5 x stall speed)

That is 1200-1500fpm
Or about 5-6000 rpm on a 4" pitch prop..

On a 48"span, you may need a 12" prop.

But 10inch is the max propeller dia in the rules. And 120 grams is the maximum weight of batteries

Quote from: K K Iyer on December 05, 2016, 09:15:50 PM

A 1400kv will do 16800rpm at 12v
Or say 12600 at 75% efficiency.
That is 210rps.
At 5" pitch, that is a speed of 1050/12~ 90fps or ~100kmph!

From this calculation, I am getting a speed of 60 fps or 66kmph for 1200kv motor with 4inch pitch prop.

Another Calculation on MotoCalc gave me the result saying that I should use ~700kv motor with ~9-10 inch dia prop having ~5-6 inch pitch.

The nearest match I'm getting to that spec is
Avionic 3506 - 850KV pancake quad motor
http://rcbazaar.com/product.aspx?productid=4746

I'm thinking 3S battery with 8*4 prop should give proper thrust, and proper speed also.

or

Avionic C2830 KV850 QUAD brushless motor with long wires
http://rcbazaar.com/product.aspx?productid=4625

with 3S battery and 8*4 again.

Please check and tell

We need less power, not more, due to restriction on thrust.

You can consider RC Bazaar Avionic C2822 1200kv.
On 2S lipo, its thrust is listed as 425gms on a 9x6, 475gms on a 10x5.

I have ordered a Emax cf2822 1200kv from vibrant hobbies. I'll check the prop and batteries required for that.

Good choice. Excellent value for money.
Will exceed 800gms with a 10x5 at about 7700rpm.
So may be around 500gms on 2s.
Best of luck.

I got the motors, then I realized shaft dia was 3mm and all the prop adapters I have are of 4mm dia. Then I went to RCBazaar( because it's nearby) and picked up a 3mm prop adapter. Now the problem is that there is not enough of the adapter length to fasten the prop properly (:p).
I have attached pictures.