Canard configuration and very flexible tapered wand that is able to be parallel to the waters surface at the tip when in contact, for minimal drag and high frequency ripple damping
I love it that Daniel is equally happy to talk about the options which "do not fly", as well as those that do. Humans learn by doing that - and over time we get better. Lesson there for all of us!!
Coming from a moth sailor the wands are very sensitive. They are carbon with a lot of flex and usually a paddle on the bottom. They’re moved as far forward as possible to have the cleanest water to skim. They also have gearing mechanisms, usually a barrel adjuster that changes the sensitivity between the wand and control surface. We’re constantly adjusting these for different speeds. They act as our tuning to prevent bucking and maintain ride height.
Having the wand as far forward as possible also probably increases the phase delay margin of the system. That's probably what caused the oscillations here. Also being able to adjust the gain almost definitely helps with that as well.
I thought having a way to adjust the sensitivity on the fly might be a good thing, but accomplishing that in such a small platform, especially on a retrofit would be a challenge.
I hope people understand just how much amazing content has been dropped on this channel throughout the years. when I see an rctestflight video in my feed, I know it's an instant hood classic.
i really hope daniel spends like 75% of his time just out there testing his vehicles and having fun. He seems to have so much fun just playing with them and testing them and learning more.
I think in the original iteration of the wand control, the overturned feedback you were getting (about 2:27) was due to too much nose down elevator thow that was only commanded at higher speeds. If the elevons' throw could be mechanically limited to maybe half (or less) of the original throw, that might help. Great videos... Keep at it!
You can see that when the wands lose contact with the water, the the elevator throws all the way down, causing the nose to drop quickly. Maybe just locking the elevators so they can't go down at all would help.
I was about to write a comment to exactly same effect. You can clearly see that when the wands break contact with the surface the rubber band causes the elevons to go full tilt down, causing the oscillation. Limiting the throw so the control surface does not bottom out in negative pitch input will definitely eliminate the undesired effect.
Greatest GE action I've ever seen! No roll or pitch control and perfect flight IGE!! Man o man this is perfection! This version of the Bixel Wig has to be the holy grail of All WIGs!!
This video induced nostalgia from my freeflight & control line days. Mechanical feedback is so awesome I love me some PID tunability but mechanical is just beautiful
For the last experiment, have you thought about making the bows of each catamaran hull like that of the bow of a boat or a ship? It might push air around it and under the wing area instead of under it to the hull area. Playing around with the shape of each bow would also possibly allow you to choose how much air is directed where.
Good Sir, I shit you not: over the last two+ years I've been going through some horrible times and your videos [waypoint tug boat, snow cat, ground fx, the lot] have helped me through some of the worst of it. I cannot thank you enough. 🤙🤙
Hey rctestflight, another idea: what if you could release air from underneath the body of the craft to control height? Not by adjusting the angle of the craft or and flaps, but literally one or several holes in the center of a craft that are getting more or less covered using a servo. This with e.g. lidar should give you great altitude control without disturbing the pitch axis or anything else
@@DerKrawallkeks It was something one of the teams did a number of years ago, that made use of a very clever loophole in the rules. They added a duct that scooped up air from the front, and sent it back to the wing to stall the airflow over it, but only when the driver blocked a small hole in his cockpit, otherwise the air just went around. So when the driver put his thumb in the hole, the car got less drag on the straights and could reach a higher max speed
10/10 Would like to see more mechanical stabilisation, its so cool how changing the height, angle, leverage, flexibility, etc. changes the parameters like electronic stabilisation.
I noticed that the commercial wands you showed at the beginning were more flexible over their length than your shorter wire one. Perhaps that flexibility affects the amount of throw at any given angle to provide a damped input at higher speed?
YOOOOOOOOOOOOO BEST RC CHANEL IN YOUTUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUBEEEEEEEEEEEEEEEEEEEEEEEEEEE (i love you man, make more endurance solar powered rc planes or boats and stuff, love those)
I remember back when I was a kid we had these race cars. You threaded a "T" shaped, geared handle in to a slot, whipped it back out and an inertia wheel powered the car. You were meant to crash them in to each other or a wall and all the pieces would fly off. You had to re-assemble the car to race again. That's what this scene reminded me of. I'm old.
You may wanna try to add dampers to that motor angle control ski. It seems like it's bouncing quite a lot and causing a really quick feedback loop. I'm sure some small pneumatic pistons with maybe some length of capped off tubing to give the air more room to compress would slow down the bouncing and let the craft even out
bit of a thought on the last experiment you did - having the two pontoons on either side helps scoop and capture oncoming air, whereas having the massive monohull lets the oncoming air get shunted pretty badly out to either side. You probably lost a good bit of usable lift due to not having that captured cushion of air trapped directly underneath the craft anymore.
The reason you were getting oscillation is not due to positive feedback but because you had nearly zero damping of the control linkage. The reason why the hydrofoils didn't experience this is because the fins in the water provided the damping. Try Tightening the linkage pivot screw so that it resists change.
I just love your videos, @rctestflight! Really solid tests, explanation about your thought process, and sharing of both successes AND failures! Your test “lab” is outstanding too…just lmfao with the comic vignettes when wildlife wants to join in the testing! 😂😂Thanks for the thoughtful and humorous entertainment 👍👍
Given the relative density of the water, a wand is going to get a lot more activation at higher speeds proportionally. Higher speed also means that any deflection of the elevator is also going to be proportionally more aggressive, so you have two elements both disproportionally stronger at higher speeds, which probably can't work well.
That cool slo-mo footage at the end gave me an idea for a future series of yours: How to make an RC airplane fly as slowly and stably as possible, yet still easily controllable for smooth solid flight paths. To make it look and act more like a very large IRL airplane, and not some squirrelly twitchy toy. Related to how VERY large IRL aircraft always appear to be flying very slow compared to what our brain expects.
I wonder if the trouble you were having was due to where you were actually sampling from. On the full-sized ones it appears as though the wand samples the height of the very front of the vehicle and is then controlling the pitch at the rear. This means that pitch corrections occur in reaction to pitch rather than just reaction to altitude. When you're sampling from the middle of the vehicle by the time the wand is affected the pitch has already occurred and you're into the resultant altitude change. You were close in the beginning but the wand was really long so even though it was hinging toward the front it was still sampling the middle of the craft. I would be really curious to see what would happen if you put the wand out the front and head it actually sample the height of the very front of the craft so you would be getting corrections in response to pitch changes not just altitude changes.
I love the way you think, Daniel. I've been watching your ground effect experiments very closely, as it fascinates me but also I intend to build one this Spring (Which is Apr, for us). Idt my first one will work well, as I'm also working on an outrigger hydroplane and I had to build three prototypes of that one before finding the right balance vs buoyancy. Now that I have, the rig itself will have two counter-rotating EDFs, driven by 300amps and have an adjustable T-tail. I hope to shoot for a record or two, this year. This vid was especially useful. Thanks for making it longer and more informative. It was educational and yet I was so entertained by the calm way your ground effect flies, at times. You are lucky to have water recreation at this time of year. All of my lakes are frozen. Stupid water. ;_)
I used to see the HMCS Bras d'Or sitting on dry dock every day, and i have been to the Alexander Gram Bell Museum many times, his HD-4 was pretty impressive for being built around 1919.
Agree with all your conclusions, and would like to see you try a mechanically stabilised hydrofoil at this point to prove if that can work at model sizes.
I realize my comment isn't super clear. What I intended to describe was this: the wands, if shaped like "skis" at the tips, would present less drag as they were pulled up "nose first," so only the "heel" was still making contact with the surface.
I recommend the mid linkage control with front deflection surfaces. Front surfaces should be higher than main wing to gather more air under the wing. The body shape was an inverted airfoil and should be flat bottomed with bow incline. It should be like trying to fly a funnel or amphitheater. Gather lots of air, squeeze it under the craft. Wings are for steering or additional cargo weight. Maybe taper the floats to do the ski jumper thing and catch air wide up front and narrow out the stern.
May I suggest something regarding your safety? As mentioned under your battery endurence test I highly recommend waering a floating device - espacially in a kajak in cold conditions. Cold water (or water that feels cold) can highly impact your ability to swim. And wearing heavy warm clothes makes swimming much more harder - even one layer of cloth makes it much more difficult to swim and stay afloat. (I had to swim in one layer of cloth for a certificate once to twice a year)
This is so exciting as someone who wingfoils, as it could totally translate over. Wouldn't be surprised to see it show up on foilboards somewhere soon. If you ever wanted to, I bet you could get a job with any of the foiling companies.
5:24 Theory: The oscillations are most likely caused by the wands themselves and the amount of drag they create when confronted by the water, they seem to dig in a little bit, which causes drag and causes the nose to drop. Which could be why it works at higher speeds, when the extended angle is greater which causes the most drag. I do believe the positive feedback loop at the rear does exacerbate the situation some more though.
a note on the oscillations, its not a positive feedback loop (or at least that component is not the cause of the oscillations). the wand only provides P-term feedback, and the system is an n-th order (height adjusts control surface, which adjusts pitch rate, which adjusts pitch, which adjusts aoa, which adjusts g load, which adjusts height) theres pretty much a guarantee the system will be unstable with only height-derived P term input
Great engineering choice on isolating the oscillation, simplify. Set as many variables to zero as possible. Harry Larson Z80A, 1MHz, thats impressive in 2020. It strikes me as an outsider that the ground effect generates a higher pressure under the wing than free flight so could a barometric pressure sensor be used in the control loop. I dont know what loop you are running, 22mph is 10m/s so i would guess 1ms seems reasonable giving a reaction per cm but you no doubt know better. This reminds me of tuning a balancing robot where only after tens of hours watching it fail did I start to really understand the dynamics. The purely mechanical control is control in its purest form , well done. With gyro and accel stabelization the key was to add angular velocity into the control loop, not sure how that translates to pure mechanical control. Best of luck. Love the channel.
Coolsville! I think your experiments would be greatly aided by you building a scale wind tunnel. I've often wondered what exactly the airflow is doing around your designs. Vortices, turbulent, stall and starvation zones, etc. Could be a fun project, too.
You might want to consider some sort of finer-grained pitch control. You’re so close to the ground, and your vehicles are so small and light, that pitching up or down too quickly will rapidly take you into or out of your target ground effect zone. You should consider a mechanism that tries to control how quickly the pitch of your aircraft changes. Basically, you’ve been trying to stabilize your ground effect vehicle using only proportional control. “How far away is my vehicle from my target altitude”. That works fine at lower speeds because the entire system reacts slowly enough for everything to work. However, it stops working at higher speeds because your vehicle pitches up or down faster than your system can react. “How fast is my target vehicle changing altitude.” By the time your proportional control system is far enough away from your target altitude to work, your vehicle is ascending or descending too quickly for the system to compensate, so it either shoots into the sky or darts into the ground. I’d consider making a system that controls the rate at which your vehicle’s pitch changes. If your ground effect vehicle is only pitching up or down slowly, it’s not that big a deal. At lower speeds, your aircraft is stable enough passively, and it’s only at higher speeds where you’ve been having issues. However, if your aircraft begins changing pitch rapidly, as it does at higher speeds, your system should react more quickly, damping oscillations. Once you get that down, you can refine your vehicle’s design so it can be more passively stable at higher speeds, requiring less corrections from whatever electronic or mechanical system you design; or you can redesign your current altitude stabilization mechanisms and probably have better success with them at higher speeds.
The wands out front will anticipate the height of the craft, whereas further back they react to it, so more likely to cause oscillation. The sailboats you referenced have them out front and are stable. I think the out front wand on yours would have worked better coupled to the elevons rather than the canard.
The start of the oscillation happened when the craft reached height the wire wands were out of the water. So you're spot on about the positioning and further to add, the length of the wand and a flex in the wand can be incorporated to make that system work.
Being janky is what makes it cool. It's the quick and dirty prototypes that I love. Trial and error engineering at it's best. This is therapy for my OCD. I can now build quick and dirty planes and they are a blast to fly and crash. Ohhh jeez I just turned the comments section into a confessional and therapy session.
It seems that the oscillations are appearing when you get to the point where the rods got out of the water leading to a strong control input. Perhaps a longer paddle shape that's thin at the bottom and thick at the top would work better (inducing a gradual increase in control output depending on the height of the craft due to increased drag from the paddle)
One thing to note, at the beginning your wands were too short and were coming out of the water causing the nose to suddenly drop. If you made them longer there'd be more room for it to adjust back down gently. Another issue is that your control was linear, it had the same pitch down effect even as the pitch up motion started running away. You could solve this by adding a bit of curl to the ends of longer rods, that way as you start to pull away the rods have to rotate faster and faster to keep in contact. With enough bend you should find a balancing point where the pitch up of the nose and the pitch down from the controls balance for neutral flight without having either runaway ahead of the other's corrections. I believe you could get a similar effect by rotating the control arms some degrees out of phase from one another, but that's harder to adjust and plan, maybe something to do once you identify the correct input curve later.
For the wide monopontoon I was thinking you could install vertical guide plates on the sides to avoid spilling of the ground effect pressure sideways onto the wings. That way you could avoid turbulence hitting the wings, which reduced their lift and control. It would also help keeping the airflow under the monopontoon more homogenous across the whole width, increasing its effect and also helping to keep the airflow more laminar for the trailing edge.
Dashpots or shocky from the body to a short distance down the wand would mitigate sudden bounce movements in the wand from the water's uneven surface, minimising the sudden corrections as they'd be absorbed by the dashpot/shock absorber, tuning achieved by absorption and length on the wand at which its connected Short sudden irregular corrections disappear, but large average corrections are passed through to the ailerons
In certain instances your wand will have to be balanced like a real aircraft’s control surface. Otherwise it’s own inertia will cause it to add Input to the control loop.
Interesting course of study and your R&D is really interesting also. I have the exact same Boston whaler you have and found these vids also. Consider the Freeman boat Hull design, they use a catamaran hull to funnel lift but they stay in the water. You might be able to use a gull wing design to funnel each wing instead of the flat wing
The reason it was oscillating in the first half is either because 1. the gain is small and the ailerons react only when it's already too pitched up and/or 2. there is no damping in the aileron response. If there were damping (piston damping, etc.) then the positive feedback loop could be avoided. (I had the exact same problem for one of my projects.)
You know when you skim a rock over water it bounces, is this something that could explain some of the problems ? Maybe some kind dampener on the linkage from the water wands or change the weight or thickness of them ? Love watching you solve problems as they occur and the onsite fixes helping diagnose what's going on. Cheers for the videos.
I think boundary layer effects increase inversely with the size of the aircraft, so at some scale the boundary layer shear between the bottom of the aircraft and the surface of the water, even without turbulence, will dominate over the "go forward" force of the props for anything other than "just actually flying not near the water". That might contribute to some of your instability. The ground effect combined with boundary layer shear will probably cause the aircraft to pitch down uncontrollably whenever you actually start to "truly" fly in ground effect. Sort of similar to how a real helicopter needs more yaw input when its hovering in ground effect than hovering at altitude (though there are a lot more complicating factors with helicopters hovering in ground effect). I tried to think of a simple way to compensate for boundary layer shear but the best I could come up with off the top of my head is to use several (like 3 or more) high aspect ratio wings instead of one big wedge. It wouldn't look the same as a full sized ground effect vehicle, but it might work closer to the same. Its also a lot more effort.
The reason your flight starts to oscillate at high speeds: The reason your RC goes oscillating with the wand directly controlling the flaps depending on the relative altitude of the water: -The angle of flaps depend on the altitude of your RC -The altitude depends on the direction(yaw) of the RC, speed and time passed since previous position -The yaw is dependent on the angle of the flap,speed, and and yaw since previous position Even a simplified version of the problem is a second order differential equation - The solution of this has a harmonic component - meaning an oscillation of yaw/angle/speed Look for active and passive solutions to reduce resonance in mechanical systems.
2 parts your wands are creating a pitch forward moment and generating a bit of lift when in contact. Its not a lot but your plane doesn't weigh much. When your wands break the surface the lower stop is so far forward you destabilize the plane in pitch and roll causing this oscillation. It would be if every time you pitched up too much you kick the stick forward. You need a bit of a damper. try using a fine string as your paddle so that the disconnect is less sudden and it generates less lift from the surface. The more you lift up the less of it is in the water, the less drag and hence less torque. Also if you put the contact point of the string closer to your CG you can eliminate your pitch down tendency.
I was working on some unique hydrofoils inspired by my aeronautics training that employed semi flexible intersection joins (‘hydroelastic’) and winglet like devices for flow control - I had the backers drop out in prototyping stage but to this day no one has come close to my auto regulating, propulsive hydrofoils - li e your approach
Once again, lots of amazing fun! You have lots of oscillations going on obviously. The responses way too fast. And the rate of oscillation is perfectly in tune with the response of the whole apparatus and its control system. What you need is a dampener to slow down the rapid input. Friction is not a dampener. Something like a cylinder with a piston and a fluid. Not a tightly sealed piston, but something like a disc with lots of small holes in it. Doesn't have to be very big at all and there's plenty of water available to fill the cylinder. I'm sure you've heard of PIO, pilot induced oscillation. This is when the reaction speed of the pilot at the controls is pretty much the same as the oscillation rate of the aircraft. You have WIO, wand induced oscillations. Needs a dampener.
Re the sled changes at the end, Force = Pressure x Area, so if you concentrate all the lift in a small area then you need a greater pressure for the same force.
great work, one of the best I've seen in years. Few thoughts: have you calculated the aerodynamic center of your vehicle? It seems like there is an inherent dynamic instability. Also, the vortex that are blown out under, once the laminar flow is broken down cause a strong suction effect that I think is causing most of your crashes. Putting multiple smaller propellers in front + back and controlling the airflow under the belly can help fix that.
I think part of the problem is the relative position of the wand and the control surfaces. The canard configuration is obviously the way to go, but the way you built it, with the wand much farther back, it looked like it built in a sort of delay. Because the wand is closer to the center of mass, it's sensitive to both pitch and overall altitude, and I'm not sure that's optimal. Thinking about which control scheme is desirable, it occurs to me that the height these kinds of craft float above the water is significantly smaller than their length. That means that even with a constant height at the center of mass, the nose or tail could easily dip down to contact the water surface due to pitch variation, which introduces all kinds of forces that seem like they'd be basically uncontrollable. So I think instead I'd try moving the wand way forward to the nose. That way if the nose dips, it gets lifted, and if it gets too high, it gets pushed down. It might even be desirable to have an elevator at the back controlled by a separate wand. That would give you control over pitch with the front wand, absolute height to the water at both front and rear with either/or, and average height to the water with both at once. I also wonder if the paddle on the wand isn't too big? A smaller paddle, or even just the bare wire could likely be thought of as averaging out the control inputs to be less on/off in nature. Smaller/no paddles would also reduce the drag caused by the wands. It's a really interesting concept that I think has some promise, but I suspect it will be very difficult to tune. You're basically creating a purely mechanical PID controller, and since tuning those digitally is a pain in the butt, tuning a physical one can only be even harder, heh.
I think the first idea would work better if you some sort of limiter or dampener on it so that when it goes to high it will slowly correct and thus remove the bronco effect ? a car without shocks is a nightmare.
so close bro! the oscillations aren't causing a feedback loop, if anything they are too active. Motion smoothing is your answer. Whether shock absorbing or other flexible membrane to curve out the waves and water pressure difference on the lil wands.
Well done with your tests, fascinating stuff. Feedback systems can be prone to oscillation, like another commenter I had wondered about adding damping to the control.
Unbridge your front ramps (at the end of the video) and put one double-width ramp near the rear of the craft. Now you have a snowmobile arrangement, and those tend to hover quite well above the ground, with only the snow-effect holding them up. If it tries to fly at that point, then it's simply too light, which would imply that it would be useless as a real product anyway. Continuing with the snowmobile theme, your front ramp/skis can be shaped and hinged so that they have greater lift proportional to how much contact a local wand contacts the water, but also reducing deflection angle (lift) as velocity increases, to help prevent taking flight.
This is a very neat concept and video! It would be interesting to see what effect it would have if you could add some kind of damping to the wand's control linkage to smooth out the high-frequency movements. It might help stabilize some of the oscillation. You could probably accomplish this by mounting some RC car dampers/shocks (either ones with no springs or with the springs cut off) to the control horn pivot, then playing with the mounting angles like you did with the sensitivity of the rod itself.
Maybe adding some kind of damper on the wand might help? When the wand comes out the water, it's immediately snapping all the way forward, triggering an aggressive pitch down. If you could slow the wands return, it might reduce the oscillations.
i think this is something which works in "full scale" but is extreamly hard to recreate in a rc scale because of the light weight and therfore less play.
hey on the one large pontoon foil, to get rid of the air hugging the bottom of the craft and making it pitch up, maby you could add vortex generators so the air comes off of the first ram air scoop cleanly? or cleaner at least.
Daniel your Ground Effect Videos are awesome. You have found the true Ground Effect Vehicle that will not fly OUT of Ground Effect when you removed the Elevon link and how your Bixel happily flew about 10cm above the surface with no Roll or Pitch control! My Q is, how to balance it with a rear mounted pusher prop?
