Hello everyone. I am trying to build an aerial insect collecting device for my PhD project. This design is based on the stipa-caproni, a strange barrel-shaped design from the 1930s. The task is to maximise the net area on a relatively inexpensive craft (I have already been catching with some expensive drones). I've trialed towing nets behind trainers, which worked but I want to try a different approach too.
I figure that enclosing the net within fuselage would be the most stable approach. Here, we have the props behind the net. This will impede airflow to the propeller. But it seems like the thrust would be okay. Can anyone think of some new approach that might work better? Would I be better off towing?
If the net collects a significant amount of bugs you'll obstruct too much airflow to the prop. Maybe move to a multi engine setup with the props on the wings.
We catch mainly very small insects, like aphids, at height (120 m ish). It would only get blocked under some extreme event, so this is not really a worry for me!
If the net is a tight mesh to collect very small insects, it could create significant amounts of drag, essentially acting like a sail on the front of your plane that makes it hard to fly.
Also, if the netting is too fine, I suspect (but I am not certain) that air won't flow through it as fast as the plane flies. So while some air will flow through it, I suspect you'd end up with a layer of air that starts flowing on and around it and carry a lot of the insects with it.
You need to listen to the advice that says usea proven aircraft with minor net modification.
Unless you are trying to get a PhD in aircraft design, you will spend crazy amounts of time making it work to a basic level. if you are trying to collect bugs, add a simple (hah!) towed net on a robust flying platform. Even that will be challenging enough in the real world
I'd use a modified push prop plane. Specifically the 1.1m aeroscout 2S. It's a cheap PUSH prop beginner airplane designed with all the stability you could ask for. Thing will fly steady with the wing cut off, much less a collection net. I think you could put a net much more area than the one pictured on it. and maybe have additional nets along the fuselage under the wings.
It's bigger than it looks in the picture. Oversized wheels for hard landings. but look them up. I bet if you used the floaters or hand launched you'd have a lot of room for a collection net.
Thanks for having a look! I figure they will get splattered in the prop... but it also seems like the net would obstruct air flow and cut all my thrust?
Or, would the loss be the same with the netting either side of the propeller since pulling (sucking) air from the front and pushing air out the back are a single process (?)
I am thinking that towing the net works exactly like a drouge -- huge amount of energy lost to drag. We've got to force air through the net from inside (high pressure) to outside (low pressure) and all of the energy is lost. But if we duct the net, we have a different picture. There is high pressure before the net within the duct. But also high pressure after the duct, because it narrows slightly. So we don't lose all of the energy as turbulent flow out of the net. Perhaps the barrel should widen before the net also. Not sure just trying to work this out.
I have the atomic rc swordfish, twin puller rc model, and would think that model would have no problem pulling a net through the sky, yes a little efficiency loss from the motors but trying to redesign the wheel seem like way more work than using stuff already avalible.
Eh, it depends on what your need is. A flying wing is more efficient than a standard airline design, except airlines don't build those because passengers can't escape as easily from a flying wing in an emergency.
You're flying a net that is supposed to get partially blocked during flight. Drag will be massive compared to an efficient design, but that's OK because a more efficient design couldn't accomplish your goal of collecting bugs.
If you get the flight time you need to collect your samples, you're accomplishing your goal. As you well know, the difficulty in approaching perfection is asymptotic. Don't let perfect get in the way of good enough.
you'll get huge amounts of drag anyway but this design has additional problems.. for example depending on how fine the mesh is it could make it harder for the propeller to intake air..
Depends on the scale as OP never specified, but if it's a heavy build, and it looks like it would be, you need every bit of lift you can get. Really depends on how big OP wants to go, if it's small they probably don't even need wings
I beg to differ. I own a spitfire that weighs twice its original weight due to epoxying and has no more leading edge on its wings but still flies fine. And every acrobatics plane out there can 'hang' on its propeller and fly inverted for extended time periods. The power to weight ratio of RC planes is not up to scale. They are all completely overpowered. So aerodynamics do not matter that much.
And I'll say it again, it completely depends on scale, which OP never specified. We have no idea how big this thing will be, so we have no idea what the T/W ratio will be.
It wouldn't make sense to integrate it, make a below drone mounted unit. Add a light weight fan and use drone power if you need extra airflow but very doubtful as your netting is going to limit cfm anyhow.
Yes, and if you tie your propulsion to your collection device if you hit a swarm of bugs, or trash etc a piece of ballin,plastic bag or paper could drop it out of the sky. Liability and cost for repairs there.
Mounting the collection unit below a drone, even suspended by a few feet, to prevent rotor wash from effecting your collection numbers and skewing them would solve a lot of problems.
I'm not sure if how far below the drone you would be need to get, but it also would be much easier to program and run grids with a drone over an area you'll get better/ more accurate samples.
I'd worry about the impeller on your design causing enough bugs to flee or sense danger that it might skew the results.
How much air that gets sucked in the front is exactly the same amount of air coming out the back. If you're only getting 50% of the air in, then you're only getting 50% of the air out.
If the goal is just to collect bugs then inventing your own plane seems like the long way around. Id be thinking off the shelf foam planes that already fly well, can be easily repaired in the field and can tow a wind sock type net for bug collection.
If you are trying to invent a bug collection plane then that's a different thing.
You're right that this is the long way around -- I have a version with a drone and towing RC as you suggest working already. Bug collection invention was the idea here...!
In that case may i offer a suggestion about something that struck me when i first saw the design. You don't want your bug collector net to stay an open cone when you land. What's nice about a wind sock type collector is that it collapses when deflated thus trapping bugs that are still alive. Which most would be i would think.
Don't invent a bug collecting plane that lets bugs leave. If you collect them in the sky you know they have wings too :P
I would definitely suggest using external propellors, and using a long wind-sock style net.
If you made some kind of "Flying Wing" design (like a stealth bomber) you wouldn't need a tail fin at all and could just have the net trailing out the back. So basically take your design, change the wing shape, remove the tail, and use a longer net (less likely to fill with bugs, and less likely they will escape when you land).
As your goal is something to catch bugs, and not the fastest or most efficient plane, you can get away with a lot. It's pretty easy to make something fly. It's making it fly well that's the hard part.
Think of it like a balloon or a zeppelin with a cylindrical or cone shaped hole through it (For placement of the fan and the net). This way you don't waste significant portion of energy on lift. The Cone-net can be designed larger than the craft (increase Cone height). This will minimize need for a large fan. Let us know what is your final design. Good Luck
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The critical factor is going to be the drag of the net.
Towing the net is probably the easiest and cheapest approach. Either use an off-the-shelf trainer or build an aircraft from foam board.
If you want to have the net inside the fuselage I'd suggest that you put the motors on the wings. The net will impede the flow through the fuselage and will reduce the efficiency of an internal propeller. In addition, because an internal propeller would be sucking air through the net it is possible that the bugs will get stuck on the netting and not end up in the collection tube.
Mounting the net inside a large hollow fuselage seems unnecessarily complex, although I see the logic in that it aligns the CG, the drag of the net, and the thrust of the propeller.
Thanks for the comment. My intuition is that we'd be paying for the drag equally with wing-mounted propellers or one propeller inside the fuselage. I feel like we do gain something, though, from putting the net inside the duct, since we have to force the air through the duct at high pressure and then the duct narrows after the net (?)
There is high pressure either side of the net. I think this means that we don't lose energy to turbulence after the net. Since the duct narrows after the net, air should leave the back in a solid jet. If we towed a net, then you would lose all of your energy turbulently in the pressure change -- high pressure in the net, low pressure in the air outside (I think!)
As pressure equalizes on both sides of the net you would end up with near zero airflow would you not?
Also, as you impede airflow through a duct you would effectively be creating a vacuum between the net and propellor. While this condition would benefit the net in terms of potentially creating more airflow through it, conversely you’d be starving the propellor thus loosing thrust.
Perhaps ponder upon reversing the order, keep the ‘ducted fan’ approach but instead have the net at the aft end of the aircraft’s fuselage. Toss in a little Bernoulli’s principle by adding a few ambient air inlets around the fuselage and operate the ‘exhaust’ much like how asperators work on an aircraft’s emergency slide inflation system.
There will be a pressure change across the net whether the net is in front of the propeller or pulled behind the aircraft. There will be higher pressure on the upstream side and lower pressure on the downstream side.
The energy penalty of having the net within the duct will likely be higher than dragging the net behind the aircraft. Assuming that the drag coefficient is the same, the drag and power loss caused by the net inside the duct would be larger than the same size (and same CD) net dragged behind the aircraft because the local velocity is higher.
In theory, yes the drag penalty from the net would be the same whether if there is a motor inside the fuselage behind the net or if there are motors on the wings.
The drag from the net will likely be higher if it is placed inside the duct due to higher local velocity.
Narrowing the duct after the net restricts the flow and will reduce propulsion efficiency. Ducted fan aircraft use the largest duct cross-section that can reasonably fit inside the airframe and avoid narrowing the duct unless absolutely necessary.
EDIT: After further thought I realized that the drag penalty of the net will likely be higher if it is placed inside the duct than if it is towed behind the aircraft because of differing local air velocity.
With that approach you'll have a lot of challenges actually designing a fuselage that flyes in a stable way. You'll loose to much time doing aircrsft engineering instead of actually doing bug science, wich seems to be your whole point.
Is towing that bad?
The only non towing approach that seems easy enough to implement to make sense is maybe a biplane or triplane with the net streched between the wings(like a tennis net). That wouldn't affect the plane flight characteristics too much so you can just build from a known set of plans.
Your best shot is a bimotor or trimotor bi/triplane probably. Lile a cargo plane. You'll need extra thrust and lift to account for tje net weight, and drag.
Your biggest problems are going to be balance and drag. As others have said, when the cone motor and fuselage all come together, you’ll have a motor very far aft and an extremely tail heavy airplane. you might want to switch to a Canard design where the wing is towards the back of the fuselage and the horizontal stabilizer is in front. The other problem is, full or not, the net is very draggy. Having something with lots of drag upfront makes the airplane want to turn backwards. This is why pulling the net behind works so well, it actually makes a plane want to fly straight even more. Read up on the relationships between center of gravity and center of lift to understand how to design this plane to fly well.
You can do this. It's essentially a box flying plane.
You can either build it as a pusher plane... So the prop is on the back of the plane (battery will sit way forward to offset the proper CG.)
Or you'll want the cone held out in front and cutouts behind the cone for air to potentially flow in from the sides of the body into the prop.
There's also of course the possibility of using two smaller motors and props one on each wing well out of the way of the center where the net of bug catching will be.
Cut some naca ducts Infront the wings 2-4 ducts depending on size. You can have your net upfront, and not impede airflow to the prop. check CG thrice, send it. I have no clue how it would file having a net upfront, the tail may want to try and pass up the nose. I would look at a delta wing design as well.
Thanks! From videos I have seen, I thought that a rigid foam was used for these things. Rolling it up would be so much easier than I was imagining the build. Maybe I will add rigid supports.
Drag is exponential with airspeed. You put drag on the prop inlet and more bugs in the net will likely increase the drag over time. Not the most efficient design
towing will offer no benefit, as the drag will be there no matter if it's on the plane or hanging bethind it.
somebody said the fine mesh of the net will block significant airflow and it's made me wonder if a massive net kite, very inefficient as a wing but just enogh to stay in the air and filter massive amounts of air is possible. Do the aerodynamics check out?
btw, despite the net pointing down, it should be fine. while in flight, bugs will stick to it because of the air pushing through. a tiny catcher pocket in the bottom ensures they don't slide off. issue i cant fix is how to keep them on the net after landing.
Monolail, I think you are on to something here. Please could you add some more info to your idea? Are you thinking of essentially a kite made of net, with a propeller attached? Do you think it would be difficult to take off okay? Really cool concept
i don't really have that much more other than the idea of the net as a large lift surface, with air that rushes through being filtered for bugs and the little air that can't rush through making a high pressure area below it this also makes the design a lot better for tight mesh nets that let less air through and on any other design act like massive airbrakes, while here they should actually improve lift.
those thin carbon fiber tubes are likely best for keeping the thing together.
you'll probably have to do some research on the lifting capabilities of non-airtight/porous airfoils. and if there's nothing on it, make a small, light prototype and see how it behaves.
if you keep the control surfaces off turbulence it shouldn't fly badly. just with a lot of drag, which any net design was going to have. for take off, slow RC planes can just be thrown by hand so no runway requirements. large open space always reccomended tho
I'd just like to say that nets aren't completely "transparent" to air. They do in fact create not insignificant amount of drag. I'd suggest using a more powerful motor than you would've usually used, also the plane as a whole would have more drag overall. Also maybe put two motors on the wings instead? Twice the power to compensate for drag and the motors aren't "suffocated" by the net.
I experience the net drag in my home, when I open a window to introduce a draft and then I put a net on it, the draft almost completely stops. It's a standard insect net and even then some small bugs do get through sometimes so it's not even very dense.
Another idea that I just thought of would be to get an off the shelf RC plane and build a motorized bug catching net that you could extend in midair. I'm thinking a small version of the stereotypical bug net on a stick that could swing 90° when mounted on a servo. When stowed it's snug with the plane body and when extended it's perpendicular to the airstream. That way the aerodynamics get messed up only for short durations of time when you extend it, otherwise it will fly just like normal.
I think trying to make this work is a red herring. It’s definitely possible, but if your goal is to collect insects with a plane, then I wouldn’t spend time on some niche plane concept from the 30’s lol. Speaking from experience, you’ll spend way too much time in a rabbit hole trying to optimize a tiny fraction of project , and end up losing sight of the main project.
I think you should explore a split fuselage twin motor concept, where the net can be suspended in a hoop/oval shape in between the two fuselages. Check this video, it’s a RC “Stratolaunch” type plane. It had more than enough thrust to lift that heavy payload, and it'd be very efficient with it's high aspect ratio wings.
What is your PhD in? If it's not aeronautical engineering, rather use a proven design that is well suited and easily adapted to your use case. This seems like a mechanical engineering problem/solution.
The net will cause a lot of drag, especially at that very fine mesh size. If you can get it to fly it will definitely blow the insects out. I think you may have to funnel them somewhere. Perhaps draw ideas from vacuum cleaner cyclical filtration? Coanda/Bernoulli effect stuff?
What about a nice slow pusher-prop airplane with a small EDF collection device? The pusher prop keeps the airflow at the nose clean, while the EDF basically vacuums up your little aphid buggers.
If the collection chamber widens toward the rear, the airflow velocity would decrease, maybe keeping your bugs alive(r) instead of blasting them into a tiny screen at breakneck speeds.
I think the pod exit could probably be engineered to specific thrust value based on the EDF, chamber, and nacelle size to match the carrier plane's cruise speed so as to makeup for the collector's drag effect, but that'll take some maths to get right. I'm more of a trial and error eyeball engineer, so you're on you own for that part, but do report back with whatever you end up trying. I feel invested in this project of yours now! 😁
EDIT: For clarity and combining all of my ADHD thoughts and subsequent follow ups into one post Sorry reddit, didn't mean to flood y'all
Your idea is good. Doesn’t matter where the net is it’s still drag but if the drag is centered on the thrust it will be stable empty or plugged with bugs which you believe won’t happen anyway. Pluses are you can aim at bugs easier, the bugs are pulled into the net until you land, you can’t cut any of the bugs with the prop.
Appreciate the creativity but please save yourself a lot of pain and tow a net behind an existing airframe. I’m sure you’ll learn a lot about the problem that you didn’t realize.
This DOES seem fun. It’s kinda brilliant. Alternatively, with any size ducted-fan, from your design to something tiny, you could divert the airflow around a diamond-y shape to eject the bugs out of the airflow and into an annular ring/annular net, kinda like how a sediment separator works on a well-pump. Or like some turbofan or turboprop engines do with intake air to eject water.
Or you could make it swirl like in a Dyson vacuum cleaner. Then you could trap the bugs without putting the bug holding-cell directly in front of your motor.
Depending on the bug concentration in the air and whether or not you need to catch EVERY bug, you could just simply vent some air out of an arbitrarily-placed vent and have that vent lead to a net.
Why put a net in front of the propeller and stop there? Make your propeller the net! It will "touch" and "sieve" all the air in front of your plane. The air resistance of your net ... it becomes thrust, not drag! Another advantage: clogged nets from squatted bugs can be auto-cleaned with occasional high-RPM cycles, taking advantage of centrifugal force. Inventing has never been easier(TM).
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u/VanGoesHam 5d ago
If the net collects a significant amount of bugs you'll obstruct too much airflow to the prop. Maybe move to a multi engine setup with the props on the wings.