RC India

Hi, my low wing plane is no taking off. :( It runs around 100metres and climbs slightly after full elevator and then falls.Specification
30inch wingspan, 1000mah 3 cell lipo, 800grams thrust motor, Planes weight with electronics-500grams

Do I need a bigger motor?

Check wing & motor shaft incidence

As you are an intermediate flier I presume that all other points are OK

Everything is ok.

@kiran rc,
Please do the following to enable members to give you help:
1. Attach pics of top view, side view and front view of your model
2. Attach a pic of the plan, or free hand drawing, with all dimensions marked
3. Weigh the model with battery etc, and indicate actual weight (not estimate)
4. Check where the CG is and post distance from leading edge
5. Make, model and Kv of motor
6. Dia/pitch of current prop

Prima facie i suspect that a 30" span model weighing 500gms with 800gms thrust would be extremely hard to fly, definitely not in the trainer category.
We have no idea about your flying experience. We do not even know whether your model is a high or low winger, whether it is a monoplane or bipe, or whether it has dihedral, or how many channels you are using.

If you provide the above data, i am sure you'll get dozens of replies.
Unless of course, like Rai saheb says,
Best of luck.

Iyer sir

He has mentioned it is a low winger. He also has mentioned he is an intermediate flier.

Is it a flat wing or profiled? 30" for 500gm as Iyer Sir pointed out is a bit too high!

The model name is 3dx from foamyfactory.com
The cg is ok
Current prop-10x4.7sf
The wing is flat.No dihedral

kiran - post a pic of your plane

in fact two or three - a plan view and a side profile shot...
then we can try and help

your use of the term " falls down" seems to indicate a beginner

have you tried hand launching ?  a 30" plane should be easy to throw

Will a larger motor solve the problem of being heavy? But it would fly fast. :-\

Did not try hand launch.I always have practice taking off the ground ;D

You seem determined to use a bigger motor, totally contradictory to what the description of your problem seems to imply.

Why don't you just do it then? Do let us know the result

ok - after doing some googling I found your plane ...

the 3dx (mini) from foamy factory is supposed to have a weight of 230 gms.. yours is
nearly twice heavier.  and you wonder why it does not fly ?

putting a larger motor will require a larger esc and (and maybe a larger battery ) which
will in turn increase weight ... leading to an even larger motor .... and so on.

try and reduce weight ..

@ sanjay sir,I dont have a large motor right now.I was just doubting the thrust ratios.Here are a few pictures.

Another one.

please have a look at the pics.It is 3d.Not the same mini 3dx.

Please describe 'climbs slightly after full elevator'
Does it gets into almost Nose up attitude at that stage and then stalls?

@kiran rc,
I apologise if i offended you with my response.
But the fact is that an RC pilot of 'intermediate' level building a 3D model,
And asking a question like 'my plane is no(t) taking off'
Is a self contradiction.
Sir,
If nothing else, at least indicate your CG position.
If possible also your motor and prop details.
Only trying to help.
Pm me if you don't like my inputs and i'll stop!

Edit: sorry, careless of me as pointed out by sanjayrai55.

no sir not at all

no, not nose up.The cg is balanced.

@Iyer sir, cg is around 30% from leading edge,  motor ishttp://www.rcbazaar.com/products/1483-odin-2210-kv1200-thrust-810-gms.aspx
Propeller is already described.10x4.7sf

@kiran rc,
Battery down. Will revert tomorrow.
Meanwhile you could perhaps try a 9x6 prop?
Will share details of a friend's retired Rare Bear that i repaired and test flew (successfully!) today.
Similar specs to yours. And a handful!

Well, I wasn't referring to CG there. I was referring to your comment about 'Full Throttle' which makes perfectly balanced planes stall (mostly for beginners though)

@kiran _rc u call this a low winger.... this is a mid winger dude
@Sanjay rai sir kyun le rahe ho ???

Kiran:

Theoretically your motor prop combination is fine for your model. For a 3D model you want less speed (read KV) and more torque (read thrust)

However, a certain minimum airspeed is always required to create lift. You may achieve this by using a 9*6 prop, but the reduced thrust will affect the 3D ability.

IMHO you are not achieving adequate airspeed (provided all other factors including incidence are correct)

If you have a tachometer, or can get access to one, you will get the story clear. You should be able to clock 14-15000 RPM at full throttle. Less means the motor does not have enough power to handle the 10*47 SF prop.

With the same motor you could also try a 9*47 SF prop. Although in theory it will give less thrust, the RPM drop under load (which I suspect is significant) will be less. Or, if you could do a trial with a more powerful motor it would be instructive.

For the 10*47 (which I feel is a good choice of prop) you would ideally be using a 1000 KV or thereabouts motor capable of 250 W. This will give you good 3D performance. A 2836-1100 KV from RCB or RCD will give you this.

Do check the incidence nonetheless. If you have an Android phone you could download the "Clinometer" app. Check the wing and motor thrust line w.r.t. the horizontal stab.

@kiran rc
From the pictures the chord looks like about 6", giving a wing area of about 180sqin, or 1.25sqft.
With AUW of 500g (17-18 oz), your model has:
Wing loading of over 14oz/sqft,
Wing cubic loading of over 12.
These are in 'Warbird' range. Ie, models which fly fast and have small control surfaces and small control throws
It seems to me that your model:
1. Is too heavy
2. Has inadequate power reserve for its high wing loading
3. Relative to 1 and 2 above, the control surfaces are grossly oversized

I saw that most Foamy Factory models of 30-33" span using 10" props of 3.8-4.7" pitch (ie, low and hence meant for slow flight) weigh under 200 gms!

(Did you use coro instead of depron and make a box fuselage instead of a profile one?)

Since it may not be possible to reduce the weight now, i suggest:
1. Check if your motor, Esc and battery can support full throttle on a 10x6 without overheating. Current draw may exceed 20 amps
2. Reduce throws on ailerons and elevator drastically to about 3mm each side.
3. Hand launch and be prepared to fly relatively fast, say above 60kmph (ie much faster than you would with a foamy 3D model)

The Rare Bear is 34" span, has 222 sqin wing area, has a symetrical aerofoil (not flat plate), weighs 490gms, has small control surfaces/ throws, uses a 10x6 on an Emax 2822 1200kv with a 1000mah 3s and flies more than twice as fast as my wife's 54" e-trainer. It's WL is 11.25 and WCL 9. Your model's WL is 14 and WCL 12.6. So it needs to fly even faster to remain airborne!

Best of luck. Have some fast flying fun and build another in depron for 3D.

Iyer sir, a 10*6 prop turning at 13,000 rpm will develop 2.06 Kg thrust, fly at 118 Kmph, and need 659 Watts of power.

From the pictures his model appears to be Depron

An 8 degree downthrust, or a 5 degree negative incidence will cause the exact effect he is observing

Kiran, is this model from a readymade kit or a scratch build?

I think originally it had an X-Frame fuse. And used a 110 W Himax motor. The AUW with a 3S 900 mah Lipo was 8.5 oz, or 241 grams.

Here's the build log:  http://www.rcgroups.com/forums/showthread.php?t=411019 (http://www.rcgroups.com/forums/showthread.php?t=411019)

The motor:  http://www.maxxprod.com/pdf/HC2808-xxxx.pdf (http://www.maxxprod.com/pdf/HC2808-xxxx.pdf)

And yes, Iyer sir (aye aye sir)  :giggle:; the original WL was 4.9 oz/sq ft  ;D

Thankyou Iyer and Sanjay sir :hatsoff:

Sir it is scratch built.