I guess at 35% (66mm) it should be just slightly nose heavy. At 20% (39mm) it should balance perfectly. Gusty please elucidate..................I'm following the same thumb rule for the Avispad.

As per what i have read..... we should have CG at the place where wings are thickest & we should have aerofoil shape such that the thickest part is at 35% of chord.

That is the place we have lift force acting so balancing cg at this point keeps plane horizontal.

@ VC - Unless done you will not know is the plane nose heavy or tail heavy.... You need to fix the CG point then add/ remove weight to make it nose / tail heavy.

Lets hear from Gusty ( rather learn from him) what he has to say.... Sir....

I beg to differ here. All models can't have a CG fixed at 35% from the L.E. It depends on the flying characteristics of the model. The faster the model is designed to fly, more forward will be the CG. Gliders can have a CG as far back as 35 - 50%. Warbirds as far ahead as 20%. It also, therefore, depends on the wing aerofoil shape.

Sundaram, stop reading and start participating!

Yes i accept that difference of flying characteristics......

But this plane is more of a glider ( am i wrong or right)

To begin with I always go for CG at <= 30% Chord for maiden of a straight wing without any sweep forward or back to have it slightly Nose heavy to have it manageble to fly it. other wise it will pitch up moment you open throttle, sink tail and stall on throttle cut, will not glide down easy for land and it will have to be flown in forced down to land it, even then it will be difficult to manage.

Once established flight characteristics I push CG back based on performance.

PS : VC Stop prowling On Me

I agree on your last post. I believe CG <=20% is too far ahead for RC unless it is a very high performance wing aerofoil or canard models, forward swept wing.

I am a fast learner Sandy. I have some brilliant teachers based in Meghalaya.

  Thats to you VC.

I am signing Off to witness birth of Lord Krishna. Adieu

God bless. Good night.

20% is based n the pic umesh posted, critical aspect is who will maiden it, without the required skill set she will go down in flames

Gusty I believe you have miss-spelt as nose heavy at 35% I suppose .  If you are able to balance CG at 35% or more you have actually managed a tail heavy characteristic plane. You have to add/shift  weight forward to balance CG ahead at lesser percentages of Chord to have a nose heavy plane.

Thanks a lot Saurabh Boss for sparing time and posting.
How do you know so much about jaipur... have you been living here... how often do you visit ... may be you can help me with maiden flight. Would you ??
After this I have dropped the idea of flying this plane at all and planning to build a primary trainer instead.
I am definitely worried about the strength of the frame and finding ways to strengthen it.
Can I apply a coat of epoxy on the expense of adding some weight
I do have spars upto about 8 inches ... should I add one more along the length...

regards

Thanks a lot vc boss, sundaram boss, rcpilot boss for the knowledge...
Now with a lot of feed backs pouring in I know I am not a lone builder ..

I have atleast understood that CG is more complex than what I thought it was !!!
And it has to be between 20% and 35% .. 

Actually I am also worried about the tires tripping into something while takeoff and breaking prop, if its nose heavy... is my worry legitimate..   

thanks

That would depend on a few factors. Where are you taking off, how strong are your wheel supports / legs, how big are your wheels.

Your wheels look the right size, however, I can't make out the main undercarriage assembly from your pictures. How have you bolted it to the fuselage?

The tail wheel looks a little too big (same dia as the main wheel?) and the spring assembly is good. What you want to do is to brace the pink foam with light ply / balsa (where the spoke enters the fuselage) from both sides.

Sorry I misread the above post. I thought you were worried about the wheels getting ripped off during take off / landing. If you are concerned about prop breakage, use a prop saver.

you tailwheel rubber has the tendency to come off, needs a little CA(foamsafe) there

Your plane is to big to suggest fevicol & tissue coat etc etc..... such a plane is basically made on 3mm Ply or Balsa wood frame.
At the max try getting wooden sticks get then 2-3 mm thickness and embed along the fuse and wing base.try making a frame at the cockpit for strength.

Thanks VC boss .. noted your suggestion for re-enforcement..
now Can someone help me the Dihedral..
currently its around 6-7 degrees. Now I have to fix the struts and planning to freeze them at 5 degrees... will it be OK... I dont know how to calculate the angle and I am confused with the resource available on the net ...

thanks

I found something
http://adamone.rchomepage.com/cg_calc.htm

Hi all,
after the unsuccessful  maiden of my Big Beaver and crashing it for thirteen times I have given up on it and spared the little thing until my new scratch built blue baby is ready for flying..

Hi Umeshk,
I had also started the route you have taken. I built and crashed 3 models before good sense prevailed and I got hold of someone ( Divay Puri in our field) who helped me with basics.

Try to get hold of a local guru

regards
Pankaj

Aaahmm.....not a guru.....but yes enough to put u on a fast track....
By the I was in Jaipur for last 6 days

But all the same... Has any one compared this pink foam to depron? Would like to understand how they stack up

pankaj

thanks saurabh and pankaj,
ill definitely need your help saurabh... for the last few weeks i was stuck up with business and all ... was working overtime burning midnight oil to complete Blue baby by tony65x55 from rcgroups. now its almost ready will try it out ..
Pankaj I may be i was lucky enough or its the pink foam that despite my dumbthumb my beaver managed to survive... Its the only material I could manage to source here in jaipur.. would love to work with depron too..

Likewise Umesh, I work primarily with depron (aka biofoam) would love to get hold of pink foam.

Depron is not biofoam at all.  Haven't seen depron locally much.  Biofoam/foamboard is an entirely different animal.

Anwar.
This is possibly the first time i have been told that biofoam and depron are two different things. However as per my understanding. Sunboard is pvc materials and altogether different.