Flying 3D-Printed Kingfisher! - Transonic RC Aircraft Testbed

Follow us along in this video to see us flying our 3D-printed Kingfisher prototype as we prepare to maiden fly the full-scale aircraft.
Special thanks to Chris Szabo for piloting the aircraft.
Visit www.themachinitiative.com for more.
Search for The Mach Initiative on Linkedin and KZbin.
Edited by DS
Music from Uppbeat
License code: LBRARFJUW37ZCG3N
#aviation #worldrecord #rc

[@TheMachInitiative]

*You may be thinking "all this wind tunnel testing and you still got the CG wrong?"* Our wind tunnel studies predicted that the Kingfisher **may** be stable at static margins of 5%, but might experience some nasty neutral point movements and control reversal at high angles of attack, we knew that at 8% static margin the Kingfisher would be flyable. However, increasing the static margin increases the amount of ballast/ weight, and increases trim losses. So, we wanted to find the minimum static margin we could get away with. Hence, the plan was to always start with 5% and slowly increase. As we found, a 7% static margin was necessary to be flyable. For reference, the static margin is a measure of how far the CG is ahead of the neutral point. The neutral point is sort of like the centre of pressure, but is defined as the point where the pitching moment is constant for small (sub 10 degree) angle of attack changes. *3DP SPECS:* We sized the 3DP to match the wing cube loading of the full-size Kingfisher, which is a good indicator of how an aircraft handles because it also takes into account the size. Length = 0.8m (60% scale) Weight = 2 kg Wing loading = ~130 g/dm^2 Wing cube loading = 37 g/dm^3 (vs 39 for the full-size Kingfisher) Powerplant = 70mm 6S EDF Thrust to weight ratio > 1 To maximise TWR and wing loading at the same time (to be as representative of the Kingfisher as possible), the EDF is basically the same size as the fuselage. We had to saw off the front of the EDF to get it to fit inside such a tight package. It looked super clean once integrated!

[@Megs2022]

You might want to consider a net to catch it on landing XD

[@brucebaxter6923]

@@TheMachInitiative Yep. That cg vs stability vs efficiency is a real bitch. Glad you got an estimate in the wind tunnel. Looks like your estimates were pretty close. I’m sure you have already looked into the cp change as it goes transonic. I can’t help you there apart from the obvious of sacrifice sub sonic lift for supersonic stability. Ie, symmetrical shape and airfoil. As always, I’m very impressed with how you kids are going to

[@Project-Air]

Wow congrats!!! Looked amazing in the air. What a great silhouette. Congrats to the entire team on your successful flight!

[@TheMachInitiative]

Thanks James - we’ll have to get you to the field soon!

[@steveobhave]

I wonder if your pitch stability issues are due to the shape of the nose. It's like a big paddle when it changes angle of attack and I'd imagine you get some airflow coming unstuck leading to messy airflow (flow separation) over the wings and also odd spanwise flow. I reckon I'd be looking at perhaps some stabilisation gyros to dampen the pitch issues as really the shape is about how slippery it is at high speed and not how well it turns... right up until you need to bring her around for another run.

[@thegps7197]

That's amazing progress. Hopefully with the log files you can see why it was so twitchy in the air and dial it in. You can easily have a few different profiles setup on a toggle switch to flick between modes that allow you to have minimal input and the fc does most of the work and then slowly swop it so you have all the control. Nice work

[@stonestm4197]

Looking forward to see how the Kingfisher will eventually handle, great job :)

[@EinhanderSn0m4n]

Any chance of an FPV version? Maybe mod the intake to a divertorless design and put a camera window in the bump? EDIT: Saw your other response about full scale version having analog FPV. Awesome!

[@ohiorc5586]

Fellas I think you may need to do slightly more research on the rc hobby side. First off… You had it tailheavy beyond flying, You MUST ALWAYS center your surfaces before you fly, And you need lower rates for higher speeds. This is a cool project wouldn’t wanna see it crash

[@TheMachInitiative]

Thanks for your support of the project and advice - to address some of these points: The change in CG between flights 1 and 3 was only 1cm - wind tunnel tests had shown we may be unstable with the initial cg depending on the margin of error of the experiment, but we wanted to see what we could get away with, as we want to minimise how much ballast we have to put in the big one. The first two flights cemented that we needed a more ballast than we hoped for! Offsetting the elevons was a conscious decision - the delta wing needs 15-20 deg of upward elevon to trim on takeoff/ landing and stop it from rotating. For higher speed flights we’ll defo level them or have a transmitter mode to switch from trimmed low speed deflections, to levelled high speed deflections. Strongly agree on point 3 - we’re going to have multiple transmitter modes to alter the throws at different speeds. The full-size aircraft has split elevons so we’ll only control using the inboard elevons at high-speed for better sensitivity.

[@Darrylx444]

Nice! Idea: add contrasting color/pattern to wing surfaces to more easily distinguish top/bottom. For pilot and video observers.

[@profile5]

Looks awesome! I’ve been following for a little while now and think this is great progress

[@dhouse-d5l]

U fellas are inspirational...l;ove the enthusiasm.

[@richardm.newlands2417]

Congratulations Guys, you got it airborne! Here's my quids-worth: too low a static margin also lowers the dynamic margin, which can make it wobbly with inertial coupling between pitch and roll oscillations. Also, high alpha's on slender delta configurations like yours (struggled with this myself!) can produce a weird short-period roll oscillation caused by the wing vortices literally battling it out over the upper fuselage forebody - this won't show up in wind tunnel testing as you need freedom in both roll and yaw. I christened this 'wibble' (induced wobble) and at first I mistakenly thought it was some sort of 'Dutch roll' oscillation, which it's tempting to combat using yaw damping. But that could make the 'wibble' worse! Add some roll-rate damping into your flight controller, but only that. Much later into the flight-test programme you can add more functionality. Every 5 degrees of leading-edge sweepback has the same effect as 1 degree of wing dihedral, ergo zero dihedral is over-stable! I've found that combatting this with notable negative wing dihedral ('an-hedral') really helps, even though it feels counter-intuitive. Most manned deltas have anhedral. P.S. we've got a very long launch-rail!

[@rcbinchicken]

Yooo unrelated thanks for this! I build a lot of slender deltas and I've always wondered why their high-AoA wing rock was so much more pronounced... In your experience, would making a slender delta that was a low-wing affect this at all, e.g. the fuselage acting like a bit of a fence to keep the vortices separate? Or am I picturing it wrong?

[@Abdullah_Al_Saud]

6 hrs ago upload and youtube recommended to me...

[@Cosimo-yi9jl]

Great progress guys, Love it!! For the 1/1 scale you intend to “catapult” launch it (bungee cord)? Since it’s going to be very heavy for it’s dimentions, maybe you could try taking it into air with a bigger Rc model; some what the idea with the space shuttle. At least you’ll already have some airspeed and altitude Keep it up guys!! 💪💪💪🔥🔥🔥🔥

[@felixm.8910]

I like your thinking of giving the aircraft more static airspeed from the get-go. My initial thought was that it further complicates getting the kingfisher into the air. Requiring additional engineering, fabrication and testing time. And also money. I think making the slingshot/catapult longer for the full-scale model would give the aircraft a longer range to accelerate and maybe also make the acceleration more gradient, reducing the forces upon launch. These are just my 2 cents. I would love to hear other peoples thoughts on this!

[@rcbinchicken]

The dimensionless wing-cube-loading works out to ~34 just for the EDF demonstrator, that's insane... Respect to your pilot that he was able to keep it in the air and nurse it to a - well, a "gentle crash"! 😁 The fact that it literally started backflipping with the CG "ahead" of the calculated neutral point, even by a few percentage points, makes me wonder if something about the fuselage aerodynamics etc. is throwing off the CG calculation. I've flown a LOT of intentionally-tail-heavy deltas and personally have always found I had to be well into the negative static margin to get such uhhhh... "gleefully" divergent behaviour (admittedly, none of mine have been anywhere near this high WCL!) You mentioned in the pinned comment that the static margin was derived from wind tunnel testing - did you work it out by any other means as a comparison? If yes, did they agree well with the wind tunnel results?

[@08ryanalollipop]

Top tip: if you have really windy audio there are lots of AI solutions to remove it. The voice can end up sounding a tiny bit odd but it's a lot nicer to listen to!

[@TheMachInitiative]

We tried putting the pilot interview through an AI tool but it sounded really weird - next time when talking on the field we’re going to makesure to wear a microphone instead of relying on the camera audio!

[@brucebaxter6923]

Awesome work. Still looked tail heavy but I want there. Worried the autopilot (cheap simple version) was not installed to retrieve flight data. (I do that with my toys) Excellent to see this going so well

[@crezzlin]

Drop it from a drone so you don't smash it lol and don't stand so close with radio on takeoff.. Probably failsafe.. 👌👌 Cool project..

[@cosmo2002]

1st. Congrats 2nd.I told u before and tell you now...its too small. Not matter the cience before the concept, the pilot NEED to see it. More import if the plane is fast.

[@jaqummh]

Winky wonky but I am sure you’ll get hang of it 💪

[@YensR]

Great stuff! How does the EDF wing loading compare to the full scale jet powered one?

[@TheMachInitiative]

The wing loading on the 3D print is slightly lower - landing speed is about 40 mph vs 50 mph for the jet-powered one

[@YensR]

@@TheMachInitiative that sounds like a good approximation for these flights! Good luck for the big one!

[@TheMachInitiative]

@@YensR Its worth noting that Wing Cube Loading (mass/area^1.5) is a much better indicator of how an aircraft handles. We tried to match this as closely as possible, so the 3DP has a WCL of 370 g/dm^3 vs 390 g/dm^3 for the full-size aircraft

[@YensR]

@@TheMachInitiative thank you, that's very interesting, I had not heard of that variant!

[@spencer963]

Excellent work, can't wait to see you shatter the record!

[@AndyFromBeaverton]

3:00 That plastic sheet really fought against the plane since it wanted to attach to the wings.

[@TheMachInitiative]

Good spot - we need to makesure to pin the sheet down better, or use a more rigid surface

[@sortaspicey9278]

OMG OMG OMG NEW VIDEO 🎉🎉🎉🎉

[@MarkxTube]

Great looking aircraft! Was it on purpose that you let it stick to the ground while launching? Maybe a detachable undercarrage or sled would do wonders. For landing maybe thin extendable skids? Carry on the great work! Will your 3d files be available?

[@TheMachInitiative]

The launch and landing procedure is something we’re ironing out - clearly for the full-scale flight we’ll need some kind of release mechanism. Ideally we’d run the aircraft along a rail to keep it straight but we’ll see how practical that is to implement. Stopping it from flipping on landing is another challenge we’re working through - extendable skids would add a lot of complexity, we’re hoping the skid shaped fuselage will do the trick. The full-size Kingfisher has sacrificial 3D-printed wingtips which can easily be replaced

[@MarkxTube]

@@TheMachInitiative The skids could just consist of a metal strip on a hinge, a spring and a small servo to unlock. After activation they pop out and would just dampen the landing so the nose can't dig in. For the rail you could go with a simple double rail and just slide along with your bungee or a tube with a roller cart. Are you planning on fpv for controlling? At those speeds it will be very hard to see in the sky and from the ground.

[@MarkxTube]

You could also just use a big net and fly into it.

[@bobjoatmon1993]

From my experience in RC i think you were still needing to move more weight forward. I wouldn't add weight, just shift things. And yes, i saw how the height decreases in the nose, perhaps a compromise of "perfect" aerodynamics might be necessary and do a mod. Back to the old form follows function and pushing the 'guts' forward requires some form thickening. Also, when the time comes, you might consider something ive had good success with on launching large RC models by attaching a launch rack to the roof of a car, driving up to flight speed and doing a release. Ive launched some 4.5 meter wingspan craft that way. (Note that i also used the roof rack first with a pivot without releasing tge bird to check CG and control response tuning. Much better to do than launch with hope then collect pieces into a garbage can)

[@I_like_rc13]

I think you should add FPV analog system that will help flying on bigger altitudes and have less drag

[@TheMachInitiative]

We probably won’t be flying at higher altitude due to legal/ practical limitations, but we do have an analogue fpv system on the full-size aircraft :)

[@I_like_rc13]

In Poland we have max altitude of 120m and it’s hard to see the drone so FPV is good for this

[@I_like_rc13]

And the analogue has a low delay

[@emotodude]

I do hope you're aware the current RC speed record is 548mph and held by a GLIDER doing Dynamic Soaring. If you're scared of piloting your machine, imagine doing it in a 50g corner in 60mph winds, just a few meters off the ground ;) kzbin.info/www/bejne/Zp_cipSCZcl6d6M

[@cabanford]

Dynamic Soaring already at 550 mph with no engine. Mind blowing

[@knowledgebyte]

Congrats guys. Keep up the good work.

[@jarrettporst4799]

I've been curious why I've not seen a plane with golfball type dimples on the entire top of the air craft? Thoughts?

[@maxjones811]

They do exist - they're called Turbulators, but they aren't common for a number of reasons. 1 - Aircraft fly a lot faster than golf balls, so the flow is normally turbulent without needing any help. 2 - While turbulent flow reduces wake drag, it increases skin friction drag. Streamlined bodies like aircraft tend to have more skin friction drag than wake drag - so turbulent flow usually makes more overall drag on a plane. In fact in a few cases (like the p51 Mustang) special effort is put in to keep the flow laminar, not turbulence, and that helped with that aircraft's particularly long range. Hope that clears things up! -Max

[@frasersteen]

Do one with a pusher and release the stls!

[@dante9192]

Tail heavy, check your CG

[@JackRoseTravels]

Have you accounted for scale speed? If the plane is flying over 500mph in true speed, then the scale will surely be Mach 3 or something right? Either way, that design isn't suitable. That inlet seems to be acting as an airbrake at the wrong angle of attack.

[@TheMachInitiative]

We’re targeting 570 mph true speed, there is obvs a lot to do before we get there!

[@JackRoseTravels]

I think it's definitely doable but I'm wondering if it would be better to curve the inlet around the body more. And have it directly pass over top of the engine for cooling. ​@@TheMachInitiative

[@ianturpin9180]

500+mph already achieved by a RC glider. Achieved by dynamic soaring. So your powered plane is quite slow. Oh and their glider was not weighed in ounces but kilos.

[@arl6565]

congratulations... they can go in a circle fast. whatever. being able to travel from one location to another is far more interesting.

[@ianturpin9180]

@@arl6565 the gliders can keep this speed up for hours. Something this small jet cannot do. The duration of its flight will be measured in minutes, NOT HOURS.

[@kolbevilla]

The gliders can go for hours, as long as they’re on the right slope of a mountain with perfect wind conditions. And they can’t leave the mountain with any meaningful speed. Let these guys have their moment

[@profile5]

@@ianturpin9180there’s a huge difference between self powered flight vs unpowered flight, we can have both

[@mikhailjairnisbett441]

@@ianturpin9180 Do you have anything positive to say?