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most efficent rc plane

quorneng

Well-known member
#3
You will have to specify what you are trying to achieve with your "efficient" plane.
The obvious target for an electric powered plane is to make it fly for as long as possible.
Is that what you mean?
 

clolsonus

Active member
#5
My 2 cents: The key observation is the slower you run your motor, the longer your battery will last.

The heavier your plane becomes, the more power is required to keep it aloft. Also the faster you fly, the more drag you have to overcome and the more power is required.

So as bracesport suggests, you want an airplane that is as light as possible and designed to fly as slowly as possible.

I think for many of our model airplanes you can substantially increase flight times simply by installing a little bit bigger battery (to a point, there will be diminishing returns as weight increases) and then trim the airplane to fly just a bit above stall speed ... just above the speed where everything starts to get mushy and you start falling behind the power curve. Then just slowly steer it around the sky with very a very gentle touch never banking more than 10-20 degrees for the next hour or two. It's not for everyone. :)

I have an X-UAV Talon (1900mm wing span) that has flown 77 minutes on an 8000mah 4 cell battery. I have a classic telemaster (8' wing span, all wood) that has flown 50 minutes on an 8000 mah 5 cell battery. I have an old skywalker (pusher prop, sort of fat foamy glider with a T tail) that I've flown close to an hour on a single charge. These long flights are all under autopilot control. I wouldn't have the patience or focus to carefully fly them just above stall speed for an hour under pure manual control.

For what it's worth some aerodynamic efficiencies probably come into play with airfoils and such, but those are not the most important things to focus on at the start. There are some fun things to think though in terms of size and structure and battery and motor/prop. Everything is a tradeoff.

But at the end of the day, your airplane is going to have an "n" amp draw to fly level at "x" speed. You can change the motor and prop and number of battery cells all day long, but you haven't changed the drag of the airplane so you'll still need an "n" amp draw to fly. You might bump up or down on a motor/prop efficiency curve a bit, but you won't see that much difference in overall flight times.

Disclaimer, I am not a real aerospace engineer, but I try to fake it...

Curt.
 

Ranger_107

Well-known member
#6
thanks curt,
do you have any Idea what size the prop should be for it to fly slower?
I think I am going to do a wing, and maybe try to have solar sheets on it.
my scetch of what it might look like has it at a 3' wingspan.
Any reccomendations for what to do?
 

Tench745

Well-known member
#7
You really need to define your goals of effiency better.
This is probably the most efficient plane I know of.

But it's not RC, it's not electric powered, it doesn't' fly outside, it's not made of foam board, and it's incredibly fragile.
Maybe that's important to you, maybe it's not. Without defining exactly what it is you want, we may be ignoring solutions that would work for you, or giving your things that won't work at all.
 
#8
thanks curt,
do you have any Idea what size the prop should be for it to fly slower?
I think I am going to do a wing, and maybe try to have solar sheets on it.
my scetch of what it might look like has it at a 3' wingspan.
Any reccomendations for what to do?

I don't do any long range flying so there are probably people here that know more details and nuances but I hope this leads you in the right direction.

I went with a 10x6 slow fly prop for my 40-60 inch diy planes and they have served me well. The bigger propellers tend to be a bit more efficient and lower pitches have more grunt at the cost of top speed. I have used APC 10x4.7 slow fly props but they are a tad bit more expensive than orange eBay 10x6 slowfly props. The APCs are great though, just be careful not to break it. Whichever decision you end up making, i recommend trying Ecalc / Prop Calc. The free version doesn't have every motor available, but there is plenty enough to help you with amp draw and such to get you in the ballpark. If you have some motors in mind already, check the spec sheets if they are available to find out these amp loads, voltages, and acceptable prop sizes before you buy.

For my designs a 10x6 with a 1200 or so kv motor on 7.4 is just powerful enough and doesn't draw too many amps (around 12). If you want a bit more power and wish to stick with 7.4, bump up the KV or Increase the prop size. If you wanted to go with more volts on the same motor you might end up needing to drop to a 9 or even an 8. However, if you ran a bigger 800 or 900KV motor on say, 3s 11.1v then the 10x6 (or even 11" prop, it depends) should work. Note that higher voltages, higher prop sizes, and higher KVs increase amp draw.

There is a bit of trial and error involved but make sure to keep temps in check and use a watt meter to stay safe.
 
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Merv

Well-known member
#9
If you have never flown before, I’d recommend you start with a known design like the Tiny Trainer. The TT has a lot of the characteristics you are looking for. It’s also easy to build and repair. Most people will destroy 2-3 planes learning to fly. After you learn to fly, then build your dream plane.

You will want a plane with a high aspect ratio 8-10:1 (wing length/width). Motors that will turn a larger prop slowly are more efficient, 10 grams of thrust per watt is not difficult to achieve 20+ g/w are possible.

Here is a plane that will just about fly all day.

 

clolsonus

Active member
#10
thanks curt,
do you have any Idea what size the prop should be for it to fly slower?
I think I am going to do a wing, and maybe try to have solar sheets on it.
my sketch of what it might look like has it at a 3' wingspan.
Any recommendations for what to do?
I think your project will be the most satisfying if you do things the way you want. A forum is a great place to get advice (and there are lots of people here way smarter than me) but if you ask 20 people on a forum, you will get 100 different suggestions to sort through and you might never get anything started. There is value to planning ahead and there is value to making build/flight progress. You need to find a comfortable balance between those two opposing forces. Many great projects never get out of the designer's head because they just tried to do too many things at once. The design became too difficult to manage. Many funky builds never truly fly because the concept was ill conceived and hacked together too hastily. So aim for something in the middle of that. Come up with an initial plan, and then take the jump and make it work! And be flexible along the way: A project like this is kind of like walking through a crowd ... you have to adjust your path and sometimes your destination as you go to fit what the situation gives you. There's too many variables to plan it all out ahead of time, but some plan or strategy can help.

I don't know your level of experience, but be careful not to bite off too much at once. I really like the idea of building a simple prototype that you can fly successfully. Then iterate on that. For each new version, focus on a thing or two you really want to improve on or add.

So for example, build a simple 3' flying wing and get it to fly reliably. Maybe add battery capacity until it becomes too hard to manage reliable launches and landings. At this point you probably have a 100 things you want to improve structurally, or size wise, or flight characteristics you didn't like, etc. So pick a few of those things and make informed design changes. Now you know what you are improving and why and how to go about it. After a few iterations, you could have a pretty sweet design if you are thoughtful at each step of the way.

All that said, for an endurance plane, I would not recommend a flying wing. Fun wings are super light wing loading, way over powered, and fly great. Endurance wings are way overloaded with battery, way under powered for efficiency, and get extremely tricky and frustrating to launch and land.

Typically the larger the aircraft, the more relative weight it can carry (google cubed wing loading.) So generally, the larger your design, the easier it will be to make it fly a long time ... but with that said, there is still a lot you can do with a smaller design if you keep it light enough.

As you increase size and speed, then real aerodynamics become more important ... things like wing aspect ratio, airfoils, and drag do start to make a difference.

But don't forget, in the end it boils down to the simple observation that the slower you run your motor, the longer your batteries will last. So think about how you design an airplane that stays aloft with the least amount of power possible.