Worlds First R/C Airfoil Flairboat

this video is sponsored by brilliant more on them later this is the third video in a multi-part series where i play around with different ground effect vehicle designs and try to figure out if it's possible to actually make an aircraft that is entirely dependent on the ground effects to fly in other words it can't fly high like a normal plane in my opinion such a craft is kind of impractical but it's a very interesting engineering problem so i thought it would be fun to play around with the concept in the first video of this series i built a tandem wing model that was sort of inspired by the airfoil flare boat which was designed by gunter jurg in the 1970s my model really sucked because i screwed up a lot of the key details that i'll get into in a bit in the second video of this series i successfully built an aircraft that could take off from the water but could not fly more than a few feet high this was achieved by reducing the maximum motor power until i found the sweet spot where it could still get up off the water but just barely sustained flight although this worked really well it kind of felt like cheating i was still very curious as to whether an aircraft could be aerodynamically dependent on the ground effect not just underpowered to the point where it couldn't fly high that brings us back to the airfoil flare boat i found a few clips online that said it was aerodynamically stable in the ground effect and could not flip over like those hydroplane race boats do once the boat reaches a certain speed a delicate balance is struck between the weight of the craft and the lift generated by the ground effect this ensures it will never flip over everything else is taken care of by the aerodynamic stabilization on its own hearing this made me wonder what exactly was going on with the aerodynamics because my first version definitely had a tendency to flip up i also found some better pictures and video of the underbelly and airfoil profiles of the flare boat so i decided to revisit the design and build one that is more similar to the real thing i started by laying out the airfoil profiles and fuselage shape in cad and then cnc cutting them out of insulation foam with my stepcraft m1000 i tried to make the airfoils as similar as possible to the real ones but in hindsight it looks like the front airfoil on the rear flare boat had some negative camber whereas mine just has a flat bottom both on the front and back one of the interesting things about the design is that the rear airfoil is a lot thicker than the front one so after cnc cutting all my parts out i removed them from the stock and made an other side for the fuselage out of some six millimeter depron for this model i decided to add elevons it does not look like the real thing had any control surfaces other than of course the rudder i decided to add elevons just for trimming and so that i would have some control if it decided to flip up out of ground effect i completely covered the wings and packing tape so they would glide smoothly on the water and glued them into the fuselage i also put packing tape on the bottom of the fuselage to get the tape to stick better i even ironed it on this helps it adhere to the kind of fluffy foam that was left over from milling i then glued on some side rails and finished everything else here it is looks pretty cute i added an rc receiver that had a built-in rate gyro which doesn't actually do any attitude control it just kind of smooths out unwanted movements there are four channels so elevons rudder and throttle here it is compared to the old one it's a little smaller but also quite a bit lighter so before we try it out i'm going to talk about what's wrong with the old one so the biggest problem in my opinion was that the underside had too many flat spots these kind of stick to the water and cause too much drag all the planing surfaces really should be at a steeper angle so that when it's up on plane as little surface area as possible is touching the water like look at the bottom of my flying sled only these two edges here were actually contacting the water on plane the second problem was that the trailing edges of the wing were not low enough they really need to be on the water like at the same level as the planing surfaces of the hull thirdly i put my motors in the front so that they could be pivoted upwards and blow air under the wings to get it up off the water this worked great but the problem was that once they were pivoted back to their flat position the coaanda effect would pull all the prop wash over the front wing and under the second this would cause it to ride a nose wheelie at high speeds in the first video there were a lot of people saying that it was doing this because the motors were too high causing the thrust line to be above the center of gravity but this is incorrect because i always had the motors slightly angled up even in their lowest position so that the thrust line was not pulling the nose down the universal hovercraft's tw1 also has a tandem wing with motors in the front but it looks like they got around this coanda effect problem by just always having the motors angled up enough to also blow air under the front wing the fourth issue is more of just a theory but the extreme negative cambered airfoils i was using might not have been optimal because only the trailing edge is close to the water so the high pressure pocket that builds is narrower the real flare boat had relatively flat bottom airfoils so maybe this helps spread out the high pressure more so all these issues were addressed with my new model you can see how the underside is much more similar to the real airfoil flare boat the trailing edges of the wing are really as low as possible they're basically steps for the planing surface the first thing i noticed upon placing it in the water was that the leading edge of the wing was floating really low this made me nervous that it would not be able to get up on step the trailing edge is also submerged but that's fine because it comes up as you build speed luckily with a little up elevator the leading edge does not go underwater and it was able to build up enough speed to get up on plane and right as that happened it was clear that this thing was actually going to work i was still having some pitch oscillations at this point but apart from that it was doing really well the wind's blowing away from us so if it capsizes or something we're pretty screwed it's going to blow across [Music] oh yeah it's like right when i reduce the throttle that's when it kind of starts to just barely fly above the water just perfectly i think it kind of looks like it's hard to tell because even when it's not touching the water there's still a little bit awake from the air always so try it again [Music] the motor's kind of tilted down so it's pushing the aircraft down so when i reduce the throttle it starts to fly in hindsight i'm not actually sure if it needs more or less motor angle because on one hand the motor is above the center of gravity so more throttle equals more downwards pitching moment but on the other hand the motor already has some down tilt to it so it was just pushing the aircraft down a bit and reducing the throttle would essentially make it lighter either way when i would quickly reduce the throttle it would sometimes even completely flip up like the hydroplane boats but if i would just reduce the throttle smoothly it wasn't ever really a problem i continued to do more and more testing but then tragedy struck it flipped over no but luckily the air propeller became a water propeller and i was able to drive it back to shore upside down so after quite a bit more tuning and tweaking i figured out that this thing is extremely sensitive to cg and elevator trim changes even just a few clicks of trim is enough to completely screw it up so i'm glad i put in a lot of time just messing around with things because that's really what it took to get this figured out but after that look how great this thing works it's so incredible and to my knowledge it's the world's first functional rc airfoil flare boat at least the first one posted on the internet gunter jurg had a small scale model here but who knows if it actually flew that motor he has on there looks suspiciously small with the camera low to the water we can clearly see that it's just perfectly flying above the ground and the wake you see is entirely caused by the downwash from the wing not by any part of it actually contacting the water it's just so good but don't let this amazing video fool you because there's a pretty delicate balance being struck here if there was any amount of wind or chop in the water i don't think this model would work nearly as well it's pretty picky so this plane is super lightweight and i've heard some people say the ground effect works better with heavier aircraft i know aircraft can carry more payload in ground effect and have lower induced drag and all that but what i'm talking about is the actual negative feedback loop of the ground effect that is self stabilizing and that's what apparently is stronger with a heavier plane this intuitively makes sense but i have not yet had the opportunity to test it it's definitely something on my to-do list but unfortunately i'm not going to be able to test it with this plane because with any extra weight there's no chance it would be able to get up off the water the leading edge of the wing just sits too close to the water line and if having a lighter plane actually makes it harder to stay in ground effect then that makes this model all the more impressive because as you can see it works super well it's a very delicate balance but when the balance is met it's just so perfect i mean look at that thing it's beautiful here's my camera setup for the long low shots it's an old canon 400 millimeter lens right down next to the water so although this thing definitely still utilizes ground effects i feel like it would be more appropriate to call it a ram effect vehicle it kind of seems like it's almost more closely related to a hovercraft on an airplane it's just a hovercraft that gets pressure from forward airspeed instead of a dedicated lifting motor i think if you could figure out a way to do par thrust with this thing it would be even better but unfortunately that's difficult because the air gets pulled over the back of the front wing and underneath the rear wing which causes the pitch issues that was perfect [Music] drug daddy wants some milk brother headed to the lake buster r.c sliding on the water like a jet ski two airfoils looking sexy country design do not test me 3700 kv with no wake scare a couple geese as i fly by they looking at me with the evil eye whoa dude that was sick did you make that song i i did make it yes that was really good it was really made by uh uh metro boomin and offset maybe 21 savage but he doesn't actually do anything oh okay what's the original song title ric flair drip where can people find your full album oh uh soundcloud or no uh bandcamp there we go so this whole video series is about whether or not it's possible for an aircraft to only be able to operate in ground effect and not have the ability to fly high so the question then becomes can this one fly high like a normal plane the answer is most definitely yes or at least it can with angular rate stabilization on the pitch axis i didn't try it without that with enough airspeed and too much pitch trim the thing would just pitch up and start flying look at that fish wow must have been eating a bug pretty neat in the first two videos i was talking about how some poorly informed people were saying that it's not a real ground effect vehicle if it can exit ground effect so by their definition this is not a real ground effect vehicle and since this thing does not utilize par thrust i don't think it would be possible to make it a real ground effect vehicle by simply reducing the total power enough as to where it cannot flip up i've never tested this but i'm pretty sure that if you did reduce the total power enough for this thing to not be able to fly then it would also not be able to get up off the water or get up on plane so they said the real airfoil flare boat was self-stabilizing and it would not flip up so i'm wondering if this is just because they would quickly throttle back once it broke contact with the water or if there's some other sort of aerodynamic phenomenon going on not sure one thing is for certain and that is if the full-size airfoil flare boats indeed did not have any control surfaces then they would certainly not have been able to fly in any sort of controllable manner so there's no doubt that that counts as a real ground effects vehicle there we go [Music] you're stuck there we go it's so skillful okay i'm gonna gas it right when i start pointing straight there it goes on the topic of stability and preventing the whole aircraft from just flipping up i did realize one thing interesting when i was watching the video of the universal hovercraft's tw1 it looks like this aircraft is permanently using par thrust in the front i feel like doing this might allow them to move the cg really far forward so far forward that it would not be able to fly out of ground effect and preventing the flip up problem so this was similar to my first tandem wing driving around in what i called hovercraft mode with the motors angled up so that they would just blow air under the front and back wings evenly not really it just hit a stick in the water oh no oh me i'm dead in the water and i don't even have a kayak this time i guess i've gotta swim yet again the good old inflatable kayak comes to a rescue it blew over into the swamp over there so gotta go save it there's wood all over the place under the water here i'm getting straight i'm getting high centered on random logs here we are approaching the aircraft ah got it oh now i'm in the swamp dang we definitely messed up the nose that sucks oh and the wing damn this thing is just about out of commission it looks like that's the stick i hit right there wow just the tip of the iceberg look at this there's a beaver dam right next to the freeway they must not mind the road noise so after that i glued the front and back together and put some popsicle stick skids in the front to use on dry ground i brought it to the field and i was pretty surprised to find that i could not get it to work nearly as well as it did on water for one thing there's no par thrust so it could not even get going without me pushing it by hand to build up the cushion of air underneath once it was moving it would just not stay perfectly low to the ground like it would over water i think this could be because the air diffuses down into the grass more easily so having your trailing edge scraping across the top of the grass blades is just not as effective as when it's going over a smooth surface like the water to test this theory i tried it on the street given it wasn't a very smooth street but it still didn't work so maybe the geometries got screwed up or something in the crash or maybe the air just diffuses past the concrete more easily too i'm not really sure but maybe it really does only work on water for some reason weird if you want to build a similar model i've posted the cad files online there's a link in the description i did make one slight adjustment though i lowered the angle of incidence of the rear wing by one degree because i have a hunch that it will fly better like this since it needed quite a bit of up trim with my version that had both wings at the same angle so the design hasn't completely been tested but i think it will work even better so take it or leave it in the next ground effects video i built a really wacky idea that i've had for a vehicle that is designed to be entirely dependent on the ram air effects it's really interesting so stay tuned and don't forget 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Channel: rctestflight

Views: 779,343

Keywords: Ground Effect Vehicle, ekranoplan, airfoil flairboat, tandem, flairboat, rctestflight, WIG

Id: jQNWLDSTbok

Length: 17min 19sec (1039 seconds)

Published: Wed Jun 22 2022