High transition length NLF body

I was looking Parson’s high transition length body in a book and thought that maybe if I modify my body shape also so that the nose becomes sharper. By sacrificing some interior space, the flow acceleration can be kept for high transition length according the book I was reading this. My modified body looks like this.

Despite the QFLR5 algorithm is not maybe designed for simulating NLF bodies (it is designed for simulating wings), the pressure distribution looks like the same as the wind tunnel data for the Parson’s body which makes me think that it might not be that much wrong.

    • Exo Cruiser
    • May 21st, 2009

    Well, the body outer shape is not all, you still have to fit everything in it. I have hard time fitting everything in my fuselage shapes.. i have to enlarge the shape 10-20% time to time. The shape is nice but there starts to be too much space in some areas when other areas finally fit.

    • Thad Beier
    • May 22nd, 2009

    My favorite low-drag airframe was the AR-5 — just amazing. And 16 years old now!


    • Karoliina Salminen
    • May 26th, 2009

    Exo Cruiser:
    Yes, the internal space is a problem.
    However, there is not that much to fit. I think fitting three persons inside would be meeting the concept initial requirements. The equipment (which I was thinking fully integrated EFIS system) does not take much space. Control stick (either center or side stick) does not occupy much space. I was thinking all switches etc. not all the time needed things should go away from instrument panel and should be located for example on a overhead panel. Backup instruments could be where they fit, it is emergency anyway if backup instruments are needed and it is not a question then how ergonomically laid out they are.

    Fitting people inside just would require enough diameter for the pressure vessel. I plan to measure that in practice with some mock-up.

    Thad Beier:
    The AR-5 has turbulent body with low wetted area and low frontal area and it also has low interference drag. It is not a laminar body and it neither benefits from laminar flow much (if at all possible behind the prop). The wings on the AR-5 are NACA 6-series, but the fuselage is pretty traditional minimum size turbulent body. However, there is no magic. It is just small and the drag is low because of that, not that much because of the shape.

    The AR-6 is more impressive than the AR-5, but that too has tractor propeller and has turbulent flow over the body and associated drag penalties from that.

    In my concept, I am trying to optimize the shape to achieve the minimum profile and minimum or non-existent interference drag on that. Zero interference drag is possible with blended wing body configuration.

    It is very hard to predict at this point if the quest for lower drag will work out better by optimizing the shape and surface quality instead of the size (which is larger than minimum size).

    • Dennis Gearon
    • September 16th, 2009

    From what I've seen, the 25 year old Piaggio Avanti is the best exercise in airframe design out there. If one reads the design criteria, everything had a reason, and the reasons added up to the most efficent, cheapest, and fastest turpoprop in its class – And second in speed only to jets in its class.

    Looking at the bottom view of it pretty much says – I go fast, far.

    Also, look at 'hydrodynamic creatures' who have to move though water continuously, sharks, for more inspiration. I believe that sharks have been shown to have 'dynamically modululated' microscopic turbulators, (not something that will be on airplanes for a while 🙂

    • Dennis Gearon
    • October 5th, 2009

    One other thing about the AR-5. Sure, it had low roughness on its surface. And it had all the other things Karolin talks about above. But it also had VERY low waviness – something that does not get much coverage in press. Really fast, turbulent designs do quite well with a low waviness.

    This is had by paying attention to two different things. One, the original finish – use very long, shaped, sanding blocks for sanding. Use a different, conforming shape for each area. Make sure the paint follows the curve of the body underneath.

    Two, make sure the structure does not 'oil can' or distort the surface material in flight conditions, under load. This is one reason why the modern 'Spam cans' now use a type of sandwich construction. I'm not sure what it is, but they bond or machine a stiffening structure across the entire inner-structure face (like nomex honeycomb and another sandwich layer on the other side of that). It does not provide structure for carrying the load, intentionally that is. But it stiffens the skin and prevents load induced waviness.

  1. I really cannot see how could one use that for measuring fuselage drag…but you just did ! Thanks for the hint.

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