RC India

RC Models => Electric Planes => Topic started by: Siddhant_Sangai on June 14, 2014, 12:37:41 PM



Title: What should be the ideal thrust to weight ratio ?
Post by: Siddhant_Sangai on June 14, 2014, 12:37:41 PM

Hi, I am new to Rc

Just bulit a 530gm foamy. Was wondering what should be the thrust to weight ratio to make it fly.
i am getting a thrust close to 610 gm.

Plz help guyz...!!


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: manojswizera on June 14, 2014, 01:13:30 PM
thrust you are getting is more than 1:1, its more than sufficient for your plane.
Be gentle on the throttle.


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: Siddhant_Sangai on June 14, 2014, 01:16:49 PM
ThankYou.
I feel the same hopefully it should fly.
good to see rc lovers in regions near nasik


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: K K Iyer on June 14, 2014, 01:46:18 PM
@siddhant_sangai
Thumb rules for thrust:
Trainer with low wing loading - 100watts/kg or 50% thrust/wt
Mild aerobatics - 200watts/kg or 1:1 thrust/wt
Fully aerobatic - 300watts/kg or thrust=wt x 1.5

But that is not all - you need an appropriate prop.
A large dia with small pitch (eg, 10x4) will give lot of thrust but low forward speed.
At 9000rpm, or 150 revs/sec, a 4" pitch prop cannot exceed 50ft/sec, or 55kmph.

Whether this is safely above the stalling speed or not depends on the type of model and its wing loading.
A glider type will fly with low power, low rpm, low pitch.
A jet type will need high power and high rpm and/or high pitch.

For a more specific answer you need to post a picture of the model and give details of the motor, prop, ESC, battery, wing area and all up weight.
Best of luck.



Title: Re: What should be the ideal thrust to weight ratio ?
Post by: Siddhant_Sangai on June 14, 2014, 01:51:34 PM
@KK Iyer

Sir, I have used an avionic 2836(1120KV) motor ordered from Rcbazzar.
I calculated its thrust on a somewhat test bench.
Prop is 9x4.7E
battery is Zippy 1300Mah 20c 3 cell lipo.
Esc is turnigy multistar 45 amp.

Since my budget is low i m going for mild aerobatic. its my first flight just want it to see flying.... ;D ;D


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: Siddhant_Sangai on June 14, 2014, 01:53:07 PM
The flying weight is around 530 gm.
i have no idea about its wing area.
the thrust i have calculated is around 610 gm on my not so scientific test bench.


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: Siddhant_Sangai on June 14, 2014, 02:06:39 PM
here are some pics...


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: K K Iyer on June 14, 2014, 02:40:52 PM
@siddhant_sangai
Did you not look at the specs for your motor on the RC Bazaar site?
It says:
PROP 9x4.7E
● Get 1100gms Thrust

So you are not going to be short of thrust!

Hope you have build the model from a proven design so that you know the suggested position of the centre of gravity, the neutral position of the control surfaces and the recommended control throws.

May not be suitable as a first model. What is needed for the first flight is not aerobatics but STABILITY (ability to fly by itself on releasing the controls)


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: Siddhant_Sangai on June 14, 2014, 02:48:17 PM
Sir, I did view the specs and that's why i did buy that motor.
But i wanted to test it myself so that i could confirm it.
Yes i have built the model from a proven design.
Thank you for correcting me now i ill focus on stability.


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: K K Iyer on June 14, 2014, 03:01:56 PM
Best of luck for maiden flight.
Pl recheck CG position. May presently be too nose heavy.


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: Prashant_G on June 14, 2014, 11:30:11 PM
Hi Siddhant
   i am also from Nashik, i think that the model you have built is very nice  :goodjob: but difficult to fly for beginners,it will be very fast, you'll need lot of practice on simulator... here is my attempt of making rc plane completely from scratch, my be helpful for you...  http://www.rcindia.org/electric-planes/home-made-plane-%27ice-cream-sandwitch%27/msg167095/#msg167095 (http://www.rcindia.org/electric-planes/home-made-plane-%27ice-cream-sandwitch%27/msg167095/#msg167095)


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: Siddhant_Sangai on June 15, 2014, 08:45:54 AM
@Prashanth_G

Thank you....
looking forward for help frm you.


Title: Re: What should be the ideal thrust to weight ratio ?
Post by: Prashant_G on June 15, 2014, 02:53:01 PM
If there is any RC activity, i'll definitely call you, i hope that we'll meet soon. :)