Wing Can Expand To Fly Really Slow For Short Take-Off And Landing

[Mike Patey] had made a name for himself by building high-performance experimental aircraft. In his latest project, he added a transforming wing that can extend its chord by up to 16 inches for low speed and high angle of attack performance.

The aircraft in question, a bush plane named Scrappy, has been attracting attention long before [Mike] even started building the wings. Designed for extremely short take-off and landing (STOL) performance, only some sections of the fuselage frame remain from the original Carbon Cub kit. The wings are custom designed and feature double slats on the leading edge, combined with large flaps and drooping ailerons on the trailing edge. The slats form an almost seamless part of the wing for normal flying, but can expand using a series of linkages integrated into each precision machine wing rib. Making extensive use of CFD simulations, the slats were designed to keep the center-of-lift close to the center of the wing, even with 50 degrees of flaps. Without the slats, the pilot would need to use almost all the elevator authority to counteract the flaps and keep the aircraft’s nose up.

Leading-edge slats have been around since before WW2, but you don’t see them used in pairs like this. Aircraft like Scrappy will never be commercially viable, but innovation by people like [Mike] drives aviation forward. [Mike]’s previous project plane, Draco, was a large turboprop bush plane built around a PZL-104 Wilga. Sadly it was destroyed during an ill-considered take-off in 2019, but [Mike] is already planning its successor, Draco-X.

56 thoughts on “Wing Can Expand To Fly Really Slow For Short Take-Off And Landing

  1. Those whole people being water balloons in a flying hunk of metal seems dangerous enough. Building your own flying contraption just seems like tempting fate. Physics is not kind to us water balloons; we pop.

    1. In the 1980’s there were five times as many homebuilt aircraft registered per year as commercial aircraft in the USA.
      Now that companies like Cessna are selling lots of light aircraft again, the numbers aren’t as skewed: there are more homebuilts registered per year than any commercial aircraft company sells, but the total number of aircraft built by Cessna et al is greater than the number of homebuilts, barely.
      There are a _lot_ of homebuilt aircraft in the sky and the vast majority of them do very well.

      1. Cessna and Piper are not selling a lot of light aircraft. I will bet that more new homebuilts are flying every year than manufactured aircraft. I think you will find that average age of manufactured light aircraft is getting higher all the time. at least in the piston market.

      1. It’s depressing how many very talented designers and builders end up dead when their aircraft come apart because they made mistakes.
        I’m thinking specifically of Steve Wittman here, who was one of the most experienced designers and pilots in history.

        1. its not really my place to tell people what risks they should and shouldn’t take. i don’t like it when people tell me i shouldn’t do something because its risky. best i can do is tell them what i think the risks are and let them make up their own mind.

          as for those aircraft designers, they don’t exist to be your personal idol, they live to build aircraft. if they die doing what they love then thats a good death. its unfortunate, especially when all that was needed was a second set of eyes to tell them that something wasn’t right with the aircraft. i suppose they could play it safe and die in obscurity doing something they dont much care for with their lives. or worse, delegate the risks to others. let the bold be bold.

          1. I think Mike uses the videos he puts out as a second set of eyes to watch over his work. He wants people to ask questions as a way to cover different angles of looking at the plane he is building. In answering those questions he is also looking over what the person sees and then checks it again and again. Pretty thorough all in all.

    1. Now just consider what the world would look like if more or most people had the resources to explore what interested them. It’s a shame we’ve been convinced that the resources of the world should be concentrated into the hands of the greedy and unimaginative and the masses should be held perpetually on the brink.

  2. This is really cool. Double slotted flaps are pretty common, especially on large aircraft, but double slats are unusual.
    For a time, a lot of designers were building aircraft with auto slats that popped out as a result of air pressure when the angle of attack was high enough that flow separation was starting, but that had issues when one opened and the other didn’t because of slight differences in lift (particularly exciting in low speed turns during landing) and the resulting asymmetric lift was Very Exciting.
    Since then, people have spent a fair amount of design time trying to ensure lift augmentation devices deploy and behave in a symmetric manner, and the higher the lift augmentation, the more important that symmetry becomes.
    My STOL friends concentrated on more power and wingtip extensions. This is a far cooler and more ambitious route of development.

    1. From my reading (theory of wing sections, Perkins&Perkins, a couple other less rigorous books, all referencing NACA studies), it seems like slats don’t add anywhere near as much to absolute lift as slotted/fowler flaps do, but help a ton in delaying separation. I can’t watch the full video now, but I’m interested to hear what Mike expects to gain from the slats, I doubt it’ll give an absolute lift increase as extending chord by the equivalent amount would, but it could enable a wing with a longer chord to hold onto lift down into STOL speed regimes and AoA a lot better.

    1. Because the power to weight ratio of a scaled down RC plane is vastly different, and the Reynold’s number is not scale invariant, so the aerodynamics behaves differently.

    2. neither the mechanical nor aerodynamic factors really scale directly. you learn about as much from your RC model as you do from knowing that a boeing passenger jet also has leading edge slats. it’s not nothing but it’s not a direct validation of your engineering.

      i don’t say this because i think it’s reasonable to test it on a crewed airplane…rather the opposite. testing this enough to have decent confidence in its mechanical characteristics, let alone its aerodynamic ones, is a real beast of a problem!

    3. RC planes can let you get away with murder. It’s more or less possible to hot glue a receiver, brushless motor, and some servos to a sheet of foam core and expect that it will actually fly, if poorly.

      1. “poorly”.

        Not even. I’ve done just this with a flying wing and it flies very well without a foil section. It works better for small (~400 mm wing span) designs otherwise the foam board can fold during high gees aerobatics. AoA is far more important than traditional lift through foil design for small R/C craft.

    4. Despite the comments – NASA does this frequently. The Reynolds number effects are typically for the transition from laminar to turbulent flow and scales linearly with size and velocity for constant density and viscosity. Building a 1/2 scale R/C plane is certainly within reason and the difference in Reynolds number is not significant. The tougher part is matching the airspeed and AoA as the weight of the scale model will decrease by a factor of 8 while the wing area decreases by a factor of 4.

      OTOH – one can apply the exact same simulations for the 1/2 size plane and use the 1/2 size plane to determine any deficiencies in the simulation so that those can be corrected and improve the chances the simulation for the full size plane will be representative.

      The reason they aren’t doing this is that they aren’t going to instrument the full sized plane or any other test article because doing that is very expensive – a factor that NASA, doing basic research has to do. There’s little point to making a model if there’s no data coming from it. At best they might determine a useful CG range.

  3. This guy does have so much knowledge and so much money – yet he can`t afford to buy a simple clip-on mic? I find it really hard to understand what he is saying because of the acoustic properties of his hangar… come on. But also: THIS IS SOOO COOL! I have been watching several DRACO vids in the past, what he (and presumably, his team) achieves on a regular basis is astonishing!

      1. You’d be dumping all the lift you created to equal out the forces. Instead, he equals them out by adding MORE lift instead of decreasing it. If you watch the video, he explains it clearly :-)

        1. Also, fuel is in the wings, so shifting the entire wing would require a lot more force when moving it forward against the drag by the air and the weight of all that fuel.

          1. You also have to transfer all the lift forces through whatever mechanism you’d design, which would inevitably lead to a relatively heavy mechanism.

    1. This isn’t to change the CoL, it’s to increase maximum lift. Swivelling the wing will increase AoA, essential to generating lift, similar to pitching the whole plane up. This has its place (see Vought F-8), but a cub-a-like isn’t it, as their taildragger orientation is well suited to forcing high AoA on takeoff and landing, and the mechanism and load paths to tilt or swivel the entire wing would weigh a lot, which has a huge effect in a plane as light as this. You can be sure that he will design appropriate landing gear geometry so he can pull all the lift out of the wing that it will give.

  4. Very smart, but I look at the wing and one thing goes through my head “complexity is the enemy of safety”. Yes day one this thing will work exactly as expected, but how about after a year or two years of wear what are the failure modes and are they all safe. I have no idea how many are planned but I’m guessing about ten of fifteen of these devices per wing with at least eight to ten moving parts in each so that would be about 160 to 300 moving parts.

    On the flip side if this works very well I could see it being fully embraced by commercial plane manufactures, because wings then become a replaceable part (¥¥¥/€€€/£££/£££), that needs to be inspected and serviced before failure.

    1. I watched the followup video and he appears to be using two on each side of the wing for four in total, which is less moving parts than I would have expected. But I guess these would only be used during takeoff and landing that there would be minimal shear force on the eight aluminium bars because no turning is involved.

      I typoed above it should have been (¥¥¥/€€€/$$$/£££)

  5. This is great stuff and I watch all his videos.

    It is not likely that this wing has laminar flow all the way to the end of the flap. The flow stays attached but that does not mean it is laminar, where focus is on low drag for high speed rather than high lift at low speed. Most wings are turbulent flow designs, since even bug splatters on the leading edge can trigger transition from laminar to turbulent flow.

  6. It’s all fun and games until the wing flaps/slats on one side jam halfway through the cycle in a remote area where you only have a short field and have to land slow and steep, or (worse) one is stuck all the way out and the other all the way in (CF the DC 2 1/2 variant: I’d hope there is a “partial deployment” option to balance things out.

      1. If you watch Mike’s more recent videos on YouTube he explains how the system is designed using a torque tuge with flexible joints and everything controlled by a single linear actuator. There is no real possibility of an asymmetric deployment.

    1. You always budget additional fuel to get to an alternate runway. If your flaps get stuck you land long, pilots train for these things in good conditions so they know what to do in an emergency.

  7. Mike Patey has built enough record setting airplanes to make me feel totally comfortable with this added complexity.
    He knows what he is doing, and takes no unnecesary risks in his construction.
    If you on the other hand want to see a shitshow of an airplane build, there is another dude on youtube (he has stopped posting now) that builds an “airplane” where he makes a new compromise in every step, he has flown, but blown an engine because “it was hard to get a retainer ring into place, so I skipped it, and the seal that the ring was supposed to hold blew out during flight”
    He even contacted professional test pilotes to take it up for him, but they didn’t want to do it due to many reasons, so he did it himself.

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