Hello guys!!! I am new here...i wanted to know the best propeller and motor combination for a rc plane of  total takeoff mass of 5kg. How to know which motor to use and what is the procedure to determine it? Any reply would be greatly appreciated.

@sr_1000
Welcome to the forum.

Since you’re talking of a 5kg airplane, I presume you have experience of RC airplanes.
Hope this is not your first RC plane!

You might get some ideas from one of my old threads (though some data needs updating)
http://www.rcindia.org/electric-power/iyer's-tech-talk-how-much-power/msg196376/#msg196376

Besides the AUW, you have to consider the type of airplane, the wing loading, the airspeed and mission profile (that’s just a fancy term for how you expect to fly the airplane  )

More later if desired...
Regards

 @ K K IYER
 Thankyou sir for your reply!! The fact is i am new in this hobby with no past experience with rc planes and i need the plane  for SAE aeromodelling ( regular class aircraft with maximum weight of 5kg). Now i am finding it extremely difficult in approaching to choose the right motor and prop. I will surely go through the link you gave but still if you can help me out in any other way it will be very helpful to me.  Thank you once again

Is this what you are attempting?

https://www.saeaerodesign.com/cdsweb/gen/DownloadDocument.aspx?DocumentID=79ea00a0-d2d6-4ea8-8c29-e28f05e18b12

@ K K IYER
 Yes sir. You got that spot on. Sir can you help me out for this one. I am in the propulsion unit in our team. So use of correct electronics is completely upon me. Thank you sir!!

@sr_1000,
So you have to do a circuit and landing carrying minimum 2.85kg (10 passengers of say 60gms each, with luggage of say 225gms each) on max 1000 watts power. Correct?

Could you share the following data about the winner, and the lowest qualifier last year?
1. Payload
2. All up weight
3. Wing area or wing loading
4. Airfoil
5. With or without flaps

This will help in estimating the size and empty weight of earlier successful attempts...

You stated a target AUW of 5 kg. Basis?
Assuming 750-1000gms for the electronics and propulsion system, you are thinking of a bare airframe weight of 1-1.25kg to carry about 4kg of electronics and payload.

What size of model and construction materials are you thinking of to meet these requirements?

FRP is not allowed, but are Carbon Fibre and Fibreglass allowed? Is depron allowed?

If you can build a model light enough (below say 1.5kg bare airframe) strong enough for 4 kg load, and large enough to have a reasonable wing loading, then the power loading shouldn’t be a problem.

With the max power limited to 1kw, and an initial AUW target of say 11lbs, you potentially have a power loading of say 90watts/lb. You can easily fly at half that power loading, and take off without an excessive ground run, provided the wing loading is low enough.

What size of airframe do you think you can build in 1-1.5kg bare weight?
10’ span x 1’ chord?

That’s why we need to look at previous attempts.
Good luck and keep me updated
Regards

After that long lecture, if you are still interested, I could tell you why I think power is not the limiting factor for this excercise...

Iyer sir ! That was awesome ! I am standing on the side walk of this post but loving the discourse. Pity I am not building the 5kg plane.

2018 Sae East results
1. Winning (Univ of Manitoba) model of 5.5kg carried 17kg of payload. Wow!
2. 14 of the 34 entries had zero score for flight
3. Including all 4 Indian entries.

I remember having mentioned in a similar thread last year what a judge considered the most important success factor- RELIABILITY

This can only be achieved by doing enough testing and practice flying with the prototype (and a back up), initially empty, then with gradually increasing payloads, to establish what result can be achieved consistently.

Hope you have enough time. When and where is the competition?

This is true only for a 5kg AUW model as you mentioned, with 1000 watts available.

But the successful models are not in this weight range. They are ~20kg!
With 1000w input and say 800w output, you have under 20w/lb.
That’s about the power loading of my Sunbird that has 5ft wingspan, and weighs under 0.5kg!

So are you considering a model weighing 5kg with or without payload?

it gets better ....... 20 kg , wow , i can imagine a splendid wingspan, rather than go for electronics, now i think an engine would be better

Aah, guess no one is interested...
Even OP, offline last 5 days, no response to even email

All I know is that in SAE EAST 2018, none of the 4 Indian entries recorded even a single flight!

Pity, no?

i Guess they are all busy , i am interested but, no way for any way to compete