Hi everyone,
After a long time, I am back to the RC hobby. I would like to design an RC plane that can lift the maximum payload, like a cargo airplane.
The problem is after a lot of research I am confused at what should i start my design process with. For eg will under-cambered airfoils give me maximum lift or a fully symmetrical airfoil? I would like to limit the wingspan to less than 1.3-1.5m for logistic's sake. Weight probably around 1kg to 1.5kg without payload. Would Bi-planes with a single motor be the best or monoplanes with 2 or more motors on the wing?
Any suggestions or free plans are appreciated. Thanks!

bump

Quote from: tiluji on May 19, 2022, 10:57:47 PM
Hi everyone,
After a long time, I am back to the RC hobby. I would like to design an RC plane that can lift the maximum payload, like a cargo airplane.
The problem is after a lot of research I am confused at what should i start my design process with. For eg will under-cambered airfoils give me maximum lift or a fully symmetrical airfoil? I would like to limit the wingspan to less than 1.3-1.5m for logistic's sake. Weight probably around 1kg to 1.5kg without payload. Would Bi-planes with a single motor be the best or monoplanes with 2 or more motors on the wing?
Any suggestions or free plans are appreciated. Thanks!

Before anyone can respond meaningfully, perhaps they need to know your experience level.
For example:
-What have you built and flown successfully so far
-What have you designed, built and flown successfully so far
Regards

Hi,
So I have made quite a few airplanes, the latest being a coro slow fly, with an undercambered airfoil but due to incorrect motor alignment I faced thrust line issues while flying. Fixed it later but the overall lift capacity left a lot to be desired.
I looked up a few NACA airfoils but I am not sure if they would scale well to RC.
Basically I have two questions,
1) Biplanes vs monoplanes - if max payload is the criteria
2) UnderCambered vs Fully Symmetrical airfoils for the same
Thanks

When you design any airplane, you would need to be certain of these things:
MTOW- Maximum Take-off Weight (weight of aircraft + payload)
Aspect Ratio desired
Wing Loading pre-defined as a structural constraint (you can find similar wing loading of aircraft after you define your MTOW) where wing loading = weight/surface area
This will help you get surface area(S) of wing, which you can use to find chord length as you already constrained wingspan.
and all these numbers will help you find lift required for selecting an airfoil shape.

And symmetrical airfoils are used for 3D planes only. For simple cruising aircraft like cargo ones, you need cambered airfoils like NACA 4415

@tiluji,

If you are even THINKING of symmetrical airfoils, you are Way over your head.

Lets look at a typical 40" span model.
Say 7" chord, or 2 sqft of wing area.
What do you think its wing loading is?

Let's start from here before we go to high lift airfoils.
It's worth exploring.
But only step by step!

@tiluji,

This may be of some help...

https://www.instructables.com/DIY-Heavy-Lift-Fixed-Wing-RC-Aircraft/

Best wishes for your project.
Regards
Iyer

Thanks a lot for your inputs yash and iyer ji. I read a lot about the technicalities of a good wing design, and what I've understood is symmetrical airfoils are a no-no for my application. Speaking of wing loading, I read about it and it says its the total mass of the airplane divided by the area of the wing. That being said, does it mean that the lower I keep my wing loading, the higher the payload carrying potential?
As yash ji mentioned since my wingspan and mass of aircraft is constrained, all I have to do is find the aspect ratio for my application.
Like gliders, should I go with long but narrow rectangular wings? Or in a bid to increase wing area i should make my chord length as big as possible?

@tiluji,

See this video.



There's a lot that can be learnt by watching it and by extrapolation.
I'll explain in my next post.

That plane flies so smooth
Looks like they're using a pretty simple airfoil, with 4 motors that would give it a ton of power.
Plus the wings are having a relatively high aspect ratio too.
Anything else that I am missing KK sir?

Quote from: tiluji on May 29, 2022, 08:55:36 PM
That plane flies so smooth
Looks like they're using a pretty simple airfoil, with 4 motors that would give it a ton of power.
Plus the wings are having a relatively high aspect ratio too.
Anything else that I am missing KK sir?

Missing anything?
Yes. Lots of stuff.
The aspect ratio is NOT high. It's fairly low, about 5.

Let's see what we can learn from that video.

Wing span about 48"
Chord about 10"
Wing area about 4.5sqft
Weight ready to fly (without payload) about 60 oz, say 1.75 kg
So wing loading about 14 oz/sqft

(A 40 size trainer of about 56" span, 11" chord (about 4.5 sqft) typically weighs around 2.5kg, or 88 oz, so has a wing loading of 20-21 oz/sqft)

The model in the video carried 3lbs, (48 oz, 1.35kg)
AUW say 108 oz (~3kg)
Or a wing loading of 24oz/sqft on a crude airfoil

You can do much better with a simple approximation of a flat bottom Clark Y airfoil.

As you will see in the next video I'll post a bit later, after tackling another issue.

How much power did the model in the video have?
It's possible to make a reasonable guess by looking through the entire video.

That's the homework for tonight.
Back later with more...
Goodnight

Geez, that's a lot of stuff I overlooked...
I dug around to find if he has put up a build video of the cargo condor. Found a 3 part video here :

So from the video I learned that the motors are HobbyKing bluewonder 1300kv motors, 14oz, or 400g of thrust each. So thats 1600g of max thrust, he was probably cruising at around half throttle. Also apparently the wing is 70inches, much bigger than it looked

hello sir,
I had the same idea sometime back to make a cargo plane .
I would suggest you to make the ft gunnyPig thats a good plane with quite a lot of space inside .
I hope my sugestion will help .
Regards

@tiluji,

Homework was fun, no?

The model in the video I posted might be a smaller version of the one in the video you posted.
The reason I think so is this:
If it's 70" span, say 12" chord, or say 6 sqft wing area, and carries 6-6.5lbs incl payload, the wing loading is only 16-17 oz/sqft.

That makes it a FLOATER, not a load carrier!

See the specs of my Goldberg Anniversary Cub in the attached pic.

If you wish, we can discuss the power requirements...

Regards

Edit:
Meanwhile please see this...

Wow that thing is hauling a lot of weight!
Looks like I have a decent idea now of what to do. Will post an update about the plane soon hopefully!
Thank you KK sir and everyone else on this thread!