"Tadpole" vs. "Delta"?

Aptera Community Aptera Discussions "Tadpole" vs. "Delta"?

Aptera Community Aptera Discussions "Tadpole" vs. "Delta"?

  • "Tadpole" vs. "Delta"?

     Ray Holan updated 1 month ago 6 Members · 17 Posts
  • Volker Schöch

    Member
    October 29, 2021 at 12:09 am

    The TWIKE is a European (Swiss-German) project that is remotely similar to the Aptera, in that it is an extremely efficient vehicle for two passengers that covers some of the use cases of a conventional car, but has some very unconventional properties. Also, the development timeline and delivery schedule for the TWIKE 5/6 is head-to-head with Aptera’s.

    Like the Aptera, the TWIKE is also a three wheeler — obviously, because three wheels are more efficient than four. However, the setup is different: The TWIKE is based on a Delta layout (single wheel in front) while the Aptera is based on a Tadpole layout (single wheel in the rear). TWIKE makes an effort to explain the rationale for their design in a short blog article:

    https://twike.com/en/detail/news/twike-5-delta-oder-tadpole-trike0/

    The original article is in German, but Google does a fair job translating it to English:

    https://twike-com.translate.goog/en/detail/news/twike-5-delta-oder-tadpole-trike0/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=nui

    I’d love to see a similar discussion of Aptera’s decision to go with a Tadpole layout! Mind you: I love Aptera’s approach and design, and I’ll happily drive it as soon as I can get hold of one. I’m just interested in the engineering, driving dynamics, aero dynamics or other aspects that were driving Aptera’s decision.

  • Ray Holan

    Member
    October 29, 2021 at 5:25 am

    Intriguing topic, Volker. I’m in the US. I had a chance to see a Twike several years ago and it is an elegant solution for short trips in an urban environment. It falls nicely into a continuum of vehicles: upright traditional bicycle, recumbent bike (I had several), electric bike or recumbent, Twike (enclosed combination of recumbent bike and electric propulsion), Aptera (enclosed SEV – solar electric vehicle).

    There have certainly been a number of delta configured three-wheeled vehicles. There’s the delta racer: https://grassrootsmotorsports.com/articles/death-deltawing/

    and Craig Breedlove’s original LSR Spirit of America: https://landspeedrecord.org/spirit-of-america-craig-breedlove/

    It seems the majority of three-wheelers have been tadpole designs. There’s the Polaris slingshot (mentioned repeatedly in posts on this site). The Morgan three-wheeler and the vehicle of my teenage dreaming: building my own XR3 Created by Robert Q. Riley Enterprises. The latter was merely a set of plans for building your own three wheeler.

    Community members with engineering backgrounds I’m sure will weigh in on this question of why tadpole vs. delta.

    Offhand, a single steerable front wheel simplifies the steering mechanism but presumes traction is available for that wheel. Under slippery conditions, having two wheels involved in steering is a good deal safer than just one.

  • Ken Kobayashi

    Member
    October 29, 2021 at 1:36 pm

    Everything else being equal, the tadpole configuration is more stable for cornering, for two reasons. First, the centrifugal force of cornering is not directly perpendicular to the car, but somewhat towards the front. (The force is away from the center of turn; that point is roughly where the wheel axes point to while cornering.) Second, cars tend to decelerate into the corner, and that deceleration causes a forward force. So it’s better to have wide track at the front to counteract these forces.

    I’ve owned pedal-powered recumbent trikes in both configurations and tadpoles tend to be more nimble and maneuverable. However, deltas can be made fairly stable. In fact my current trike is a delta (Hase Kettweisel) and it is almost as stable as a tadpole, thanks to the wide track and very rear-heavy weight distribution. (It’s so rear-heavy that I have to be careful not to accelerate too hard from a stop – otherwise the front wheel jumps up into the air.)

    The other big advantage of the tadpole configuration is that it’s a closer match to the teardrop shape which is ideal for streamlining. A delta configuration means the vehicle is widest at the rear end, which isn’t good for aerodynamics. Although the Aptera doesn’t really take advantage of this – in act, if you’re going to have outboard wheels, it’s probably better to have them in the back to allow a wider gap between the body and the wheel pods. Ideally the Aptera should have looked more like the Dymaxion Car, with a smooth aerodynamic shape extending to and covering the front wheels.

    • John Malcom

      Member
      October 29, 2021 at 6:52 pm

      Certainly won’t speak for Aptera Engineers, but will speak as a past aeronautical/space systems engineer for Lockheed-Martin. Aptera developed and refined the aerodynamic shape using the same tools we use in space systems design, rigorous physics/fluid dynamics based simulation with iterative refinement. With all of the resources at an aerospace company, I would be hard pressed to create a design any better.

      • Ken Kobayashi

        Member
        October 29, 2021 at 7:38 pm

        As a systems engineer, I’m sure you are aware that the tool is only as good as the people who use it. An optimization tool can improve a design you give it, but it’s always a local optimum, not a global one. The solution is only as good as the constraints and starting point you choose.

        • John Malcom

          Member
          October 29, 2021 at 11:31 pm

          Don’t disagree. Look at the qualifications of their chief engineer. Also they have hired young engineers with a variety of experience applicable to this discipline. Result drag coefficient of .13.

          In my experience we don’t do much optimization anymore. Too many Infeasible solutions. Local or global. Now more “Satisficing” approaches where we do not try to optimize an objective equation, but satisfy as much of each objective as possible or use more qualitative approaches like MADM or AHP.

          The last time I did any practical work in this area the team used a Goal Programming approach In conjunction with a Monte Carlo simulation.

          We had an integrated product team much like Aptera has and a process that the software people now call Agile.

          This,will date me. We programmed the operational system in APL if you know what that is.

    • Ray Holan

      Member
      October 30, 2021 at 5:35 am

      Thanks Ken and John for the informed commentary on the delta vs. tadpole question. Ken’s points about the distribution of cornering forces and the matching with a teardrop shape were particularly relevant.

  • Volker Schöch

    Member
    October 30, 2021 at 10:41 am

    These are great replies to my question! Thank you so much. Thoughtful, respectful, based on personal experience, that’s how I like my discussions. 🙂 The Aptera community seems to be a likable crowd. ❤️

    • Ray Holan

      Member
      October 30, 2021 at 11:12 am

      Welcome, Volker. Thanks for your positive comment.

  • GLENN ZAJIC

    Member
    October 30, 2021 at 11:22 am

    I think torque vectoring helps to address some of these issues associated with the tadpole design.

  • Curtis Cibinel

    Member
    October 30, 2021 at 11:38 am

    That steering system is bloody weird – two levers; most people are trying to decide if a yoke is too weird for them. The design could definitely be efficiency but obviously they have a lot less information out their than Aptera.

    • Volker Schöch

      Member
      October 30, 2021 at 12:22 pm

      That’s right, the steering is certainly unconventional. It‘s a tribute to the pedaling option, which is the TWIKE‘s signature feature. Pedaling requires some additional leg room, which a steering wheel doesn’t provide. Even more importantly: When you use your feet for pedaling, you cannot use them for acceleration or deceleration/recuperation. The „levers“, as you call them, are a consequence. Personally, I can really see myself getting used to them.

      Here are some more details, translation curtesy of Google:

      https://twike-com.translate.goog/en/detail/news/everything-in-good-hands-1/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=nui

      • Curtis Cibinel

        Member
        October 30, 2021 at 12:40 pm

        Its definitely an interesting vehicle. Drag is ~0.24 and frontal area is just over 18 feet (likely 3-4 smaller than aptera). It definitely can get around but isn’t trying to be all things with a far more modest battery capacity. It could be a good primarily around town vehicle.

        Can you explain a little better how each level / pedal works – I’m a bit confused. I figured it would be like bumper boats with full forward to full reverse on each half based on the lever. This could be a big safety issue if the driver was bumped so I’m now thinking I’m probably wrong. What do the pedals do?

        Edit: Nevermind found it. They can peddle to help charge the car. Unfortunately this is orders of magnitude from being practical as ~1 hour of peddling at 100 watts (sustainable for someone reasonably fit without sweating) would only be 100 wh (~1 mile). Unless your stopped in traffic peddling a ton it just wont add much; human power is just not very efficient.

        • Volker Schöch

          Member
          October 30, 2021 at 12:56 pm

          Right. This is how it started almost 40 years ago: As a covered bike for two riders side-by-side. Next version had electric support, like a pedelec or e-bike today. The version that is under development now, and that is (in some aspects) comparable to the Aptera, is fully electric — but it still has pedals so you can do your workout during your commute, and add some range to the battery while doing so.

          Here are some more details about the integration of pedals into the vehicle:

          https://twike-com.translate.goog/en/detail/news/human-machine-interface/?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=nui

          Mind you: The pedals are not meant as your primary source of energy. 😉 That’s a welcome side-effect and certainly offers some additional motivation for your workout, and it connects to the original versions of the TWIKE, which still have their fans.

    • Ken Kobayashi

      Member
      October 30, 2021 at 8:52 pm

      If you are referring to the handlebars on the Twike, having two sidestick handlebars is very common for pedal-powered recumbent trikes. It allows a lot more leverage than a steering wheel or yoke, and is quite comfortable – basically the same posture as sitting on a couch with your arms on armrests. The two handlebars are linked, so you can just steer with one hand if you prefer. In fact, I believe Greenspeed makes (or made) a racing trike with just one handlebar on one side.

      The problem is, they aren’t legal for cars or autocycles in the US. Otherwise I think someone would have tried it on cars by now. Most modern aircraft with fly-by-wire systems use sidestick controls (a small joystick to the side rather than a big yoke), including all current Airbus airliners and modern fighter jets.

      • Ray Holan

        Member
        October 31, 2021 at 6:41 am

        Ken, I owned one of these EV’s in the past. It did have two lever steering like a heavy duty riding lawn mower;) Driving it was strange at first, but I got used to it. It ran on AGM lead acid batteries and never set the market on fire. The website below is crude by today’s website standards, so I’m not sure they’re still in business.

        https://www.nevco-ev.com/index2.html

  • Volker Schöch

    Member
    October 30, 2021 at 12:55 pm

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