Replies

  • Great points mentioned here, JB, what's your currently most efficient setup? 

    JB said:

    My pleasure Christian.

    With the props I think one of the main issues will be that the best one for forward flight will be a steeper pitch, whereas the lift propeller should be much shallower pitch. With our quadplane this was quite revealing in that we used a much higher pitch, and smaller prop for forward flight then we did without having the ability to VTOL using the quad for takeoff. The reason is that there is no requirement for low speed static thrust on the forward motor with a quadplane, as it can takeoff from the ground using the quad motors, and then gradually accelerate to forward flight using a high pitch prop, even if that prop is actually stalling because it hasn't reached cruise speed yet.

    My point is that fixed pitch props are typically optimised, as a compromise between takeoff thrust and cruise speed thrust. However, with a quadplane (or similar platform) it is possible to optimise the forward motor and prop only for forward cruise speed thrust and flight. As such the efficiency is much greater and the forward motor can be dimensioned accordingly, and setup to spin a optimised prop at exactly the drag thrust required to propel the plane at cruise. (For example the same normal non-QP airframe requires a 300W motor to takeoff and fly, whereas the QP only needs a 60W motor to achieve the same cruise speed - however it would not be able to takeoff with such a small motor)

    In your proposed design you will not be able to do this, and will have to compromise with the prop/motor combination in that:

    1) Both motors need to be high peak performance motors to lift the aircraft vertically - they will be underutilised in forward flight

    2) The prop pitch for lift will be significantly less for VTOL than for forward flight - the propeller and motor design are critical when developing a high performance aircraft - using a variable pitch prop will likely be the only solution to make it flyable and will not necessarily improve efficiency

    3) The above is both true for combustion engines as well as electric motor propulsion 

    The hybridisation can assist further in gaining efficiency, however, aerodynamically it would be wise to design the aircraft from the propeller backwards. 

    Flight strategies can also assist pending the mission/flight profile required. At a minimum a VTOL platform is typically required to takeoff and land in the smallest possible space and travel long distances at high cruise. That sort of flight profile could be as little as 20-60 seconds of hover, and hours of forward flight. Some electric motors can be run at higher peak loads for shorter periods that can be of benefit, but overall a certain measure of redundancy should be incorporated into the design. This in turn is completely dependant on the mission profile. For example: Does it need to operate around humans? If so then safety and redundancy leads to considerably more robust design specification, which in turn adds cost and typically weight etc. etc.

    In the end the design is the result of addressing all the variables, in the effort to achieve a specific goal. I always like to specify the goal first, then design the tool to meet it. ;-)

    What is the intended market/use?

     

  • My pleasure Christian.

    With the props I think one of the main issues will be that the best one for forward flight will be a steeper pitch, whereas the lift propeller should be much shallower pitch. With our quadplane this was quite revealing in that we used a much higher pitch, and smaller prop for forward flight then we did without having the ability to VTOL using the quad for takeoff. The reason is that there is no requirement for low speed static thrust on the forward motor with a quadplane, as it can takeoff from the ground using the quad motors, and then gradually accelerate to forward flight using a high pitch prop, even if that prop is actually stalling because it hasn't reached cruise speed yet.

    My point is that fixed pitch props are typically optimised, as a compromise between takeoff thrust and cruise speed thrust. However, with a quadplane (or similar platform) it is possible to optimise the forward motor and prop only for forward cruise speed thrust and flight. As such the efficiency is much greater and the forward motor can be dimensioned accordingly, and setup to spin a optimised prop at exactly the drag thrust required to propel the plane at cruise. (For example the same normal non-QP airframe requires a 300W motor to takeoff and fly, whereas the QP only needs a 60W motor to achieve the same cruise speed - however it would not be able to takeoff with such a small motor)

    In your proposed design you will not be able to do this, and will have to compromise with the prop/motor combination in that:

    1) Both motors need to be high peak performance motors to lift the aircraft vertically - they will be underutilised in forward flight

    2) The prop pitch for lift will be significantly less for VTOL than for forward flight - the propeller and motor design are critical when developing a high performance aircraft - using a variable pitch prop will likely be the only solution to make it flyable and will not necessarily improve efficiency

    3) The above is both true for combustion engines as well as electric motor propulsion 

    The hybridisation can assist further in gaining efficiency, however, aerodynamically it would be wise to design the aircraft from the propeller backwards. 

    Flight strategies can also assist pending the mission/flight profile required. At a minimum a VTOL platform is typically required to takeoff and land in the smallest possible space and travel long distances at high cruise. That sort of flight profile could be as little as 20-60 seconds of hover, and hours of forward flight. Some electric motors can be run at higher peak loads for shorter periods that can be of benefit, but overall a certain measure of redundancy should be incorporated into the design. This in turn is completely dependant on the mission profile. For example: Does it need to operate around humans? If so then safety and redundancy leads to considerably more robust design specification, which in turn adds cost and typically weight etc. etc.

    In the end the design is the result of addressing all the variables, in the effort to achieve a specific goal. I always like to specify the goal first, then design the tool to meet it. ;-)

    What is the intended market/use?

     

  • Thank you JB for your contribution!

    I completely agree with you in terms of raising wing loading in favour of cruise flight efficiency and the concept is already (roughly) dimensioned to harvest that effect. Although the first fully functioning prototype will serve as a test-bed to reach a sweet spot regarding rotor disc loading, wing area and transition strategy (we are currently working on CFD - optimization cycles and simulation).

    Hans's point is indeed valid, but that is one of the reasons for locating the rotors inside the wing: Due to the aerodynamic barrier caused by the wing during hover, there is no risk for the formation of a vortex ring, therefore they can be optimized for cruise rather than hover flight performance in terms of disc loading and/or blade twist without the risk of losing lift when it is needed most.. -> btw. the V-22 Osprey I think has killed a few people due to that problem.

    The trade off however is higher energy consumption during hover states, which can be met by mathematically optimized take-off-transition-routines, effectively limiting the duration of such unfavourable states to absolutely necessary minima.

    The cruise missile you suggested is definitely the way to go in terms of wing loading - but bear in mind that in order to reach such high speeds [more or less] efficiently we will have to rely on the help of expanding/hot gases for some time to come... ;-)

    As development of this project comes along some compromises need to be taken, but I'm convinced that with an electric or hybrid-electric power-train present efficiency and therefore range/endurance boundaries can be pushed a great deal.

    That and the ability to take off and land vertically make this project worth while.

    To answer your question: yes we have tested the prototype in wind - and it performs great with the additional attitude - authority! :-)

  • Christian maybe you should have led with your other video that shows the model actually flying, instead of the CAD drawing?

    https://www.youtube.com/watch?v=DkdD65DvgCA&feature=youtu.be

    Which I must say is much more impressive! ;-)

    Have you managed to do any tests in wind yet? 

    (No need to get defensive if some members are critical because they lack the understanding to verify the principles)

    YouTube
  • If you want to do a radical design, get rid of most of the wing area and substitute it with a wing body fuselage instead. 

    Being able to "transition" to forward flight from VTOL, also means that a compromise can be made in favour of a high stall speed, which means one can neglect most of the wing for forward lift, especially at high velocities. There is simply no reason to have such a large wing area, which also hinders VTOL ops.

    As Hans rightly pointed out, there is an issue with the propeller design and pitch, if it needs to be used for lift and fast efficient forward flight. Much easier to simply use a third motor for forward propulsion and CoG balancing attitude control, and the other two for VTOL lift.

    BTW a quadplane need not transition between flight states, they can also use the props to auto rotate for lift, and using monoprops gives even more options for airframe configuration, that do not necessitate mounting them inside the wing area.

    Add a dose of morphing wings and some folding geometry to replace the sliding CoG mechanism and you should be set. ;-)  

    This s all the wing you need if you have a unlimited runway in the sky:

    300px-Tomahawk_Block_IV_cruise_missile_-crop.jpg?width=300

  • @ Greg Covey: You can use my discussion to market your product all you like - this is not aimed at folks who's needs can be satisfied with just another multi-rotor-foam-wing-hermaphrodite. ;-)

    Don't get me wrong, I respect everyone who has reached a great level of functionality with their concept and yours is definitely a few steps ahead in its development.

    When the decision was made to open up this discussion, we where hoping to address some like-minded people with the ability to perceive the level of our achievements.

    Instead we received mainly negative responds mostly based on aeronautical half-knowledge... Thanks!

    We thought this forum was all about thinking-outside-of-the-box.

  • Not public just yet - sorry! 

  • I would like to know the patent number if you have it.

  • Design: Make wing big and "hide" the propellers inside the wing.

    Is there anyone who have got this type of VTOL work?

    The problem is that there is a contradiction in itself:
    Efficient flight as "drone" = large propellers, low pitch.
    Efficient flight as "aircraft" = small propellers, big pitch.

    Sure, you can fly like a 'drone' with smaller propeller and large pitch, it will however be very inefficient with a strong limitation in the lift capacity.

  • Designing a concept is one thing, building it successfully for a reasonable cost is another. I still prefer the simplicity and reliability of a chain drive transition system like in the FireFLY6 or a software mode transition system like a QuadPlane.

    FireFLY6 Simple Autonomous Flight from Gregory Covey on Vimeo.

    Bix3 QuadPlane Autonomous Mission 2 from Gregory Covey on Vimeo.

This reply was deleted.

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