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Help! Help with RC plane design

#1
I am participating in an RC plane competition at my college. The goal is to build an RC plane weighing up to 1.5 kg, consist of a cargo section (5*1.5*1.5 inch L*W*H) and carry the maximum load. So please suggest a design and material for my RC plane.
 

clolsonus

Active member
#2
I wouldn't get too stuck on what other people have done, but it's probably worth looking at reports and designs from previous years. I would oversize the horizontal stab because presumably in a heavy lift competition you will get near the edge of a stall as your weight goes up and that might give you better pitch stability. I know it's difficult to have enough time for everything as a student, but if you can build and test a couple prototypes as part of your process I think your final result will have a much better chance of success. I've not participated in a competition like this myself, but it looks to me like people pick heavily cambered (high lift) airfoils for their wings (imagine smoothly curved flaps permanently deployed.) That might be hard to do well in foamboard. Foamboard is great for a lot of things, and it will probably be great for your quick early prototypes, but a competition design probably needs to be a bit more sophisticated. That said, I bet if you showed up with a well engineered foamboard design, did a good job with workmanship and all the details you could easily finish in the top half of the competition. A lot of teams overthink specific details that aren't maybe as important in the big picture, then make a big mistake on a small detail or two, have never prototyped their design, maybe never flown it completely successfully before the competition, (maybe never built/flown an RC plane before in their life), etc. I'm not being critical here, I get that students (especially aerospace juniors and seniors at big universities) are already close to maxed out on their time; not everyone has the same RC/DIY/hobby background, so it's easy to make some rookie mistakes, and easy for time to run out and not be able to do everything to the level you intended.
 

Merv

Well-known member
#3
Most of the contestants I’ve seen use the formula (Payload / Empty weight) which is a completely different contest than an heavy lift with no maximum payload.

Go with a lower Kv motor (900-1100). Use the largest diameter low pitch prop you can. Foam board is an ideal material, it’s cheap, lightweight and strong when formed.

I would start with a known plan and modify it to suit. Something like the FT Bushwhacker or Scorch OR the Experimental Airline Donkey
 
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quorneng

Well-known member
#4
nivin
Four points.
Are there any rules? Do you have any RC experience? How long have you got? and are you doing this alone?
The answers to these questions will rather determine your starting point.
With no RC experience and just yourself then you really have no alternative but to do as Merv suggests. Take an existing design FT design, build it and see what you can achieve.
An existing FT design will fly and it may be possible to modify it within the competition rules to improve its weight lifting capability.
Also never under estimate the benefit of just completing the required flight task as many of the potentially better but more extreme designs may simply fail.
Finally.
The competition rules will almost certainly be set to favour a particular approach. If you can work out what that is you will have a significant advantage.;)
 
#5
nivin
Four points.
Are there any rules? Do you have any RC experience? How long have you got? and are you doing this alone?
The answers to these questions will rather determine your starting point.
With no RC experience and just yourself then you really have no alternative but to do as Merv suggests. Take an existing design FT design, build it and see what you can achieve.
An existing FT design will fly and it may be possible to modify it within the competition rules to improve its weight lifting capability.
Also never under estimate the benefit of just completing the required flight task as many of the potentially better but more extreme designs may simply fail.
Finally.
The competition rules will almost certainly be set to favour a particular approach. If you can work out what that is you will have a significant advantage.;)
I am a mechanical engineering student and I have no experience with RC planes. So I am studying the basics of aeronautical from online journals and forums. The main rules are,
1. Draw design of RC plane and do analysis (CFD and Stress analysis) in any CAD software.
2. The plane should not weigh more than 1.5kg excluding cargo.
3. The plane should complete a 300ft semi-circle flight.
4. Highest payload fraction and lowest empty weight.
My team consists of 6 members and I got 1 month to submit the design report.
 
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quorneng

Well-known member
#6
nivin
Interesting but to put it mildly it is a very ambitious task for a 'first' plane.
Does this competition count towards your study or is it just for fun? If it counts towards your study your team may have to decide if 'method and reporting' is more valuable than simply winning the competition.

Is there any 'formula' for the ratio of cargo weight to the plane's all up weight or does it simply come down to the maximum cargo weight that can be carried within the 1.5 kg all up limit?
How is the plane to be powered? Are there any restrictions on the maximum power that can be used? Does it have to take off by itself?

The flight requirement is modest. If it can fly in a controlled manner at all then a 300ft semi circle should be no problem but from an engineering point of view the design will be a more onerous task.

You should bear in mind that the strength to weight of a structure improves with a reduction in scale, smaller is relatively stronger, but aerodynamic efficiency in particular declines with reducing scale hence size is factor. Finding the best compromise is not at all simple as it depends very much on the materials selected and how they are used.

In general there is no particular advantage with such a task in flying fast so 'big and light' will work better but to achieve this successfully does of course require detail engineering design, sound aerodynamic principles and appropriate material selection.

Does your "design report" have to cover an analysis of your actual chosen design or does it only have to cover the design principles to be used?
If the former then starting with an existing design may be the only practical option.

Just as an aside I do have a modest (0.7 kg all up) RC plane (I even flew it today) that includes a payload, actually a battery that is 10 times the size required for it to fly, so as a result the battery weight is equal to the planes bare weight. It did however take me several attempts to design and build before it flew successfully. ;)
 
#7
nivin
Interesting but to put it mildly it is a very ambitious task for a 'first' plane.
Does this competition count towards your study or is it just for fun? If it counts towards your study your team may have to decide if 'method and reporting' is more valuable than simply winning the competition.

Is there any 'formula' for the ratio of cargo weight to the plane's all up weight or does it simply come down to the maximum cargo weight that can be carried within the 1.5 kg all up limit?
How is the plane to be powered? Are there any restrictions on the maximum power that can be used? Does it have to take off by itself?

The flight requirement is modest. If it can fly in a controlled manner at all then a 300ft semi circle should be no problem but from an engineering point of view the design will be a more onerous task.

You should bear in mind that the strength to weight of a structure improves with a reduction in scale, smaller is relatively stronger, but aerodynamic efficiency in particular declines with reducing scale hence size is factor. Finding the best compromise is not at all simple as it depends very much on the materials selected and how they are used.

In general there is no particular advantage with such a task in flying fast so 'big and light' will work better but to achieve this successfully does of course require detail engineering design, sound aerodynamic principles and appropriate material selection.

Does your "design report" have to cover an analysis of your actual chosen design or does it only have to cover the design principles to be used?
If the former then starting with an existing design may be the only practical option.

Just as an aside I do have a modest (0.7 kg all up) RC plane (I even flew it today) that includes a payload, actually a battery that is 10 times the size required for it to fly, so as a result the battery weight is equal to the planes bare weight. It did however take me several attempts to design and build before it flew successfully. ;)
In the rule book, there is no mention of the formula for the ratio of cargo weight to the plane's all-up weight.
Design report comprises of design, analysis, predicated payload weight,type of material used and whats the advantages of the material used in plane compare to other material. Also the plane should be hand launching type.
I have no idea about the choice of an airfoil, swept wing/normal wing, the shape of the fuselage, front/back propeller and material type.
When I look through the different forums and databases there are hundreds of airfoil shapes. So I am confused about airfoil shape.
 
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Merv

Well-known member
#8
So I am confused about airfoil shape.
You will want a flat bottom wing, the Clark Y is hard to beat. The wing thickness should be about 15% of the cord.

Take a look at the Cabbie, it may be larger than your rules allow. My normal size FT planes weight in at 850g or less. Somewhere in between is your target size.

 

nivin

New member
#9
You will want a flat bottom wing, the Clark Y is hard to beat. The wing thickness should be about 15% of the cord.

Take a look at the Cabbie, it may be larger than your rules allow. My normal size FT planes weight in at 850g or less. Somewhere in between is your target size.

The plane parts should fit in 3 feet cuboid box.
 
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BATTLEAXE

Well-known member
#10
MIni Guinea. Any of the FT planes can be scaled down to fit your dimension requirements and it will definitely fit your cargo size dimensions. It is a great lifter due to the wing design, easy to fly, easy to build, a couple simple materials and the electronics. Search it up on YouTube and check it out
 
#11
I am participating in an RC plane competition at my college. The goal is to build an RC plane weighing up to 1.5 kg, consist of a cargo section (5*1.5*1.5 inch L*W*H) and carry the maximum load. So please suggest a design and material for my RC plane.
Readiboard is a great strength to weight ratio building material and I would opt for a simple design like the skyvan. Here’s a great FT article on the RC skyvan https://www.flitetest.com/articles/the-skyvan
 

Hai-Lee

Old and Bold RC PILOT
#13
I am participating in an RC plane competition at my college. The goal is to build an RC plane weighing up to 1.5 kg, consist of a cargo section (5*1.5*1.5 inch L*W*H) and carry the maximum load. So please suggest a design and material for my RC plane.
If still seeking a design to with or to use as a basis for your own design you could build on of these; https://www.flitetest.com/articles/reworking-an-old-favourite-das-ugly-foamie-stik

To make the 3ft box the wings could be make so that they join using a slide in CF spar and have the fuselage made in 2 pieces that you join together using skewers or the like.

By making the support wire longer the load could even be carried internally and dropped if that is a requirement. With the large wing area as well as very effective flaps the bird can / would carry a lot more than its own weight. You would need to swing the largest prop you can and a SF,(slow fly) prop at that.

Just a thought!

Have fun!
 

clolsonus

Active member
#16
For whatever it's worth, I've seen a number of student projects hyper-focus on airfoil optimization before they pay attention to any other details. Airfoil choice can have an affect on flight performance, but my advice to students is start with clarky or flat-bottom and work out everything else first. Once you have a flying model that you can compete with, and if you still have bonus time left over, then maybe spend a bit of time hunting for a slightly more optimal airfoil. Evidence: look at how wonderful any of the flite test airplanes fly ... with a trapezoid airfoil. You could find a slightly better airfoil and maybe the plane would perform 1% better, but if you spend 50% of your project time optimizing your airfoil choice, that would be a complete waste of effort when you can fly really well with almost no airfoil or something folded out of flat foam with creases in it.

There are a few competitions out there and I haven't paid much attention to the details of each one, but a lot of the highly successful teams compete every year and have large groups with faculty sponsorship/mentoring and continuity from each year to the next (so they aren't starting from scratch with a new group of students each year.)

In these competitions you probably get a lot of points for a good design report, so that is important. But (for myself) I would want to kick butt in the actual flying portion of the competition ... that's where I would have the most fun myself.

If you care about flying successfully in the competition, here's my best high level advice. You don't know what you don't know (true for all of us.) So SPRINT to a working prototype. Make lots of assumptions, cut corners, be a little sloppy, and get something flying ASAP -- like in a week (metaphorically.) Have a pilot on hand that can fly the airplane (or have someone practice practice practice and learn how to be a competent RC pilot.)

I have seen many projects that dutifully proceed through a careful design process; they cut out intricate laser cuts parts, they put together an extravagant and complicated build, and they finish at 3am the night before just in time to go to the competition. Usually it's the first RC airplane they have ever built, they've designed and built everything from from scratch, (they may fancy themselves designing the next breakthrough airplane innovation), and they probably show up at the competition with the airplane never even flown once. I'm not knocking that approach, it's fun, team building, and you still learn a lot ... but the real prize is seeing your design fly successfully.

There are so many details (that are obvious to long time RC hobbyists) that students often completely miss ... things like proper center of gravity, free moving control surfaces, zero slop in hinges and linkages, properly securing the battery or the wing, etc. If no prototypes are built and test flown, you can end up with crazy mistakes, wrongly sized tail or control surfaces, wildly wrong CG location, even things like control surfaces reversed, and you would never notice it until the plane crashes and everyone looks at each other confused and says, huh? what just happened?

I have horror stories I can tell ... I saw a student design with landing gear that wasn't long enough for prop clearance ... so they literally hacked off about 6" of a 2x4 (yes a real 2x4) and used that as a landing gear spacer. We had a student design project where the CG was several inches too far aft, but the team member who computed the CG claimed it was correct (obviously not, but he claimed he did the math.) We said *please* check your numbers and the answer should be about --> here <-- (picture us pointing 1/3 to 1/4 back from the leading edge), and in the end they tried to fly with the CG about 1" forward of the trailing edge of the wing and folks here probably can guess how that went. So also listen to your project mentors when they attempt to stress a point as important! Once we had a team who's lead I can only describe as casually arrogant. They ignored all the advice we tried to give them. As we were explaining the issues you could feel the disdain coming back, and again the final flight result was about what folks here would imagine.

I know that time is not your friend in these situations, but designing a successful airplane is an iterative process. Even the flite test guys who have designed dozens of really nice flying airplanes do iterations on their designs (and they are starting with a ton of real world experience with each new airplane.)

So decide how you want to approach the competition and where you want to invest your time and optimize points ... but if you hope to successfully complete a round of actual flying, you need to be flying your first prototypes now. And don't forget safety! If this is your first time working with lipo batteries, and sharp knives that spin at 1000's of rpm's 2 inches from your hands arms and face .... please be super careful. In our school we lock the props up and don't even let the students have them until the flight test day.

I know the information from all the posts here is a lot to digest, so that's why I am trying to stress that you should be flying prototypes now. That is how you will truly learn what suggestions here are important (and how important they are.) ;-)
 

Piotrsko

Well-known member
#17
The plane parts should fit in 3 feet cuboid box.
1.442 x1.442x1.442 or some other dimensions totaling 3 cubic foot? See I'm already thinking outside the box.

As above said there are multiple people who advocate a similar approach to success, and not because we are all old ex-instructors.
 

Merv

Well-known member
#19
Readiboard is not available in our area. Can you please suggest another materials?
Can I use balsa wood instead of Readiboard?
Yes balsa is a great material to build planes with. Relative to other materials, balsa is expensive and is labor intensive. It takes a long time to build balsa plane. Balsa is not very consistent, sometimes it’s heavy, sometimes it punky. You will need to be selective in the balsa sheets you choose.

Other materials, as others have said just about any thin foam, when covered, will work. Cover it with fiberglass, laminate film or paper, something like newspapers or brown paper sack. Before foam board, I made planes from cardboard, from used cardboard boxes, appliance boxes were the best.
 

BATTLEAXE

Well-known member
#20
Coroplast might be another option for building material. It's abundant and for the most part free. Promo signs, election signs, real-estate signs etc. The wire makes good landing gear struts too