RC India

Dear all
i have made a profile su-27 plane, wing span 28" length 40"  with thermocol reinforced with tape.
Power = Motor -turnigy 2836-2350 (bought it due to user reviews)
            http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7993
            Battery- zippy 2100 mha 3s 35c
            propeller- 6*5, 7*6, 6*4(not yet used)

total plane weight around 500gms
           
Now the problem is that when i use a 7*6 propeller it will stay in air for 20-30 seconds at a height from which it was thrown. At even full throttle it will just not go up.Esc and motor will get very hot.(as it comes down nose heavy so i have to raise aileron up wards so it will just do "high alpha" stunt with constantly degrading height )

and with a 6*5 propeller it will just come down floating (with help of aileron) and will not go up a little with even full throttle.
i just don't understand the problem.
first i thought it was nose heavy so i shifted battery toward tail no effect.
Is it non sanded wings,or motor is not powerful enough.
 please guys suggest me a solution.

i dont have the video now but uploading pictures.
             

hi,

chk cg.

+1
also 6x5 is too much prop for that motor, try a 5x4.

@sbajare help me find cg. can you please tell me how or where to align cg.how will cg effect a planes performence
should i sand the wings or it will have no effect
@sunlikestar
with 7*6 it maintain flight when thrown from some height.(fore some time with high ailerons in high alfa mode)
it doesn't even do that with 6*5
now advice me if i should throw it with a 6*4 or will i be just crashing my plane.
(for using 7*6 reviews of motor are responsible)
or the thermocol is responsible
please advice
 

I've just read all reviews and some guys who tried 7x5 say it draws 43A with that prop, that's way to much for your 40A esc. 6x4 is the max you should go or better get a 5x5. Get you CG right and it should be fine, you can find where the CG is from the plans you used to build it.

also i don't see any reinforcement in the wing and they seem to be "twisted". there is definitely some work required in the plane also but i'd wait for some other members experienced in building jets to comment on that.

your battery position at the back is the issue...!! ( will shift cg back making tail heavy... it will not fly ) try moving it in the front..

http://adamone.rchomepage.com/cg_calc.htm

calculate the CG using the above link with static margin 10-13%

are you sure your RC skills are INTERMEDIATE....?? doesnot look from what question you have asked.!!

also you have connected your alirons to the elevator..?? what were you thinking??

in that case when the elevator is down both the alirons go down..! it will act as a fully extended flap and a down elevator...!
moreover in case of rolling it will be a disaster...! this thing will never fly with this configuration.. if you are trying to save on servos, by using only two then my friend you will have to buy two more or only one for elevator..!( this is a expensive hobby you have to hurt you pocket )

+1

@ R/c vish  thanks for comment on my rc skills but they  will reach there in no time and we are both here to see that.
now my plan don't have cg mentioned.and if somehow i find it should i place my powering materials on the plane to keep cg where it is there. how do i test it after placing my materials. and will making from 10mm thermocol instead of 6mm depron effect cg.
about joining alirons and elevators" i have seen about all jet makers do that" i dont have any experience so i just followed videos and pictures.
so vish if you could help me it would be highly appreciated

@sunlikestar thanks
wings are twisted because of lots of crash landings thermocol is reinforced by covering it with tape so it will not break and acts like epp.
i don't have cg mentioned on plan.
as i mentioned earlier 7*6 keeps it in air for some time with both aileron and elevators may be because of nose heaviness though i have tried to make it tail heavy by keeping all stuff in tale side " as pictures suggest".
On a 6*5 it will just come when thrown from a 30 foot building even with full throttle and ailerons and elevators both upwards( to avoid nose striking ground) down .
should i try with 6*4 what are your suggestions

You have used 2 servos for the controls! Ok, so how have you connected them so that they can achieve the purpose for both an elevator and an aileron? And does your radio support mixing?

yes my radio support mixing
i have joined elevators and aileron on each sides.as pictures suggest.

Can you please post a small video of your working elevon + aileron, all up, down, left and right movements because I think the solution of your problem lies there and try and fly your plane by just having the servos controlling the elevons, the rear control surface and not the aileron, fix the aileron with clear tape and fly it with the elevons with proper CG, i think it will work.

@rohit
will try your suggestion tomorrow morning but my question is why do all other jet makers bind elevators and ailerons together. see any f22 vdeo on youtube or try tomhe su27 video 

Hi Anoop,

The there is nothing wrong in the way you have connected both your aileron and elevator in parallel in elevon mixing as elevectron. All my fighter profile models are connected exactly like that. Unlike the real aircraft where the aileron/ flap is marginally pulled down when elevator is pulled up, here in this configuration all four surfaces move up and down as elevator and opposite direction on both sides for aileron in elevon mixing. This configuration gives extreme response and high maneuverability. In fact we operate in -50% expo in this configuration.

Now about the CG your plane is way too tail heavy by the way you have placed the battery and components. This Plan is as such a tail heavy plan unlike other fighter plans of Tomhe. We use nose weight of plus 50 gms inspite of the fact that the battery 2200mah is placed as far up as possible below the battery compartment flap.

In your case the battery is placed parallel to the motor. Please move the battery as far up ahead as possible in the battery compartment. Depending upon how you want to fly it, your CG should be between 2" to 3" behind the place where the wing root leading edge is joining to fuse. I would say from where the canard is finishing and wing root is starting. Your model does not have a canard so from wing root leading edge.

About the prop part, your motor is firstly way too powerful for this plane since it is capable of folding up your wing in high 'G' maneuvers since I do not see any reinforcement on the thermocol. Ideal prop for your plane was 5 x 5 or 4.5 x 4.5. If you use any thing more than 5 Inches it will heat up the motor and ESC badly. secondly take care that the motor can is not touching any part of the foam and the motor and the prop is freely rotating. I hope you are sure about the AUW being less than 500 gms with thermocol and tape?

If possible change your plan to Depron or EPP if available.

It also appears to me from the photos that you have mounted prop "Ulta" as if in a puller configuration and rotating the prop clockwise. You should mount the prop for pusher configuration and rotate clockwise again

Just flip over the prop in the prop adapter but do not change the direction of rotation

Refer the sketch please

@sundaramvelar thank you
I placed the battery exactly at the same place as shown in your drawing but it was just too nose heavy to even glide when i threw it from a 15 feet height so it just crashed by nose, even while both ailerons and elevators were full upwards.test was done without throttle.
what was wrong at this time
Now can i try with 6*4 propeller , i could not find depron locally so i did it with thermocol can i use coro for same plan.
and if you could explain what were you saying about mounting propellers.

I believe you have mounted the prop for puller configuration and rotating in the direction clockwise as you see from the nose of the motor to achieve a pusher (since the direction of the motor nose is now facing rear)

Just flip the prop over in the prop adapter but do not change the direction of rotation of the motor in the present configuration (i.e the prop will be in the same orientation as if it were mounted on a motor nose facing forward, only the direction of rotation of the motor is changed when its nose is now facing rear, therefore the prop is still facing and rotating in same direction as if it were mounted in the nose. Only difference is that it is pushing instead of pulling since it is in tail now). You have now mounted the prop as if the tail is its nose and it has to pull in the direction of tail but pushing by reversing the direction of motor.

To say it in other words I believe the prop in your motor mounted for puller configuration at nose, you have flipped the motor in same configuration with Prop fitted in same orientation and mounted now so that the motor nose is facing rear and reversed the direction of rotation to achieve a pusher. making the prop very inefficient. What you should done is you should have flipped the prop over in prop adapter when making the motor to face rear to keep the orientation and direction of rotation of prop same with respect to the model.

Please charge the 3S Lipo to full capacity before test flying. I hope you are using a good balance charger for charging it to full 12.6 Volts 100% capacity.

You know why I am saying this because one of my friend thought a 3S 11.1 Lipo should be charged to only Max 11.1V and was switching off the charger when it reached 11.1V and was saying his model has no thrust and has very less flight time. At 11.1V you Lipo has only 30% Power.

Sunder Sir..a million thanks for the valuable advices.. :hatsoff:

Thanks Rupesh. You are welcome anytime.

since both elevator and aileron connected togather this plane is very responsive...so use little throw in control surfaces ... the motor ur using is pretty powerfull one and is of 2200+ kv, it will take no larger than 6x4 prop!!!!!!! other wise will heat up badly...

when it does unexpected high alpha... it is tail heavy...as sundar sir suggested it is very imp to get CG and then try it...of course check orientation of prop, if it is, as mentioned above, ULTA then trust me its efficiency will come down drastically and u will not get desired thrust....

all the best

Ashish

Anoop gave me a call saying he has flipped the prop over to correct orientation and now the efficiency of the prop has been restored and has good thrust with 6x4 Prop and is flying very well after the CG has been corrected by placing the Lipo ahead.

Good luck to you Anoop and happy flying. I hope you will graduate to Depron/ EPP after you are done with this model.