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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, I think it's worth examining some of your objections to small engines. I don't see that you have a clear, well-reasoned argument based on fundamental physics or some other very basic objection like the properties of air or the strength of materials. I don't claim that small...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, Your comments and criticisms are always appreciated. I will attempt to respond as rigorously as possible. I'm really trying to understand why the industry does not opt for small engines, and what you say is relevant. The issue about nullifying lift-induced drag is a matter of...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, It was basically by considering low-speed aircraft that I was led to question propellers. In one of my earlier posts I posed that question. What exactly is it, as we increase the airspeed from zero, that causes us to change from ducted fans to propellers? I don't see where we run...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, Your remarks are thought-provoking. It is of course difficult to prove that the combination of techniques I am considering, including the aerodynamic integration of the wing and propulsion system, small engines, separate engine classes, thermal efficiency improvements for the...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, That's interesting. Your reasoning suggests that it would be more efficient if we used a centrifugal approach at high speed and an axial approach at low speed. Up until I read your post, I would have said that for high speed, say, Mach 0.7, it wouldn't matter much, but at low...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, Your argument about thrust to weight ratio works differently for the takeoff problem and the cruise problem. Takeoff is a low-altitude, low-speed, high-thrust problem. Cruise is a high-altitude, high-speed, low-thrust problem. People who believe in the large-engine paradigm try...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, OK, maybe the comparisons to digital cameras, personal computers and styrofoam coffee cups are a bit strained, but I'm trying to push the debate into a mode where we don't consider the engine to be so precious that we start making economic arguments based on its supposedly...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, We seem to be worshiping at two different churches. In my religion, complexity costs nothing because I assume an entirely robotic assembly line. The only reason to be careful about introducing thermal or mechanical complexity is that we do not want to compromise safety. My...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, OK, I admit it. I cannot make the claim that a small engine could have just as good a thermal efficiency if I restrict my design to just a rescaling, even if I choose different scale factors for the different spatial directions. However, the direction parallel to the flow in a...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, I don't agree with your argument about engine scaling. You seem to hold this opinion quite strongly, so it may be an area where you and I would have to agree to disagree. Even so, I think we agree that if the smaller engines do indeed have reduced thermal efficiency, we could...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, There are a number of good ideas in your post. I'll focus on three of them: (a) the scaling argument that suggests an increase in drag, as a percentage of total power, in small engines, (b) the use of heat exchangers and other methods to enhance cycle efficiency, and (c) the...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Hi Gordon, You raise some interesting points. I will respond first by reiterating and amplifying the arguments in favour of small engines, and then I’ll try to see if there is some common ground in the way you and I approach the surrounding issues. What I am contemplating is the...
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    Centrifugal Impellor in place of Axial Ducted Fan

    Dave: I too am interested in finding an answer to your question about efficiency. The context is: I am trying to determine whether it makes sense, in any aircraft design, to use a large number of small engines, instead of a small number of large engines. Arguments in favour of the use of...
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