Enclosing an Evans Volksplane VP-2

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by cluttonfred, Oct 26, 2014.

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  1. Oct 28, 2014 #21

    FritzW

    FritzW

    FritzW

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    Hi Ron,

    I don't know if you've flown a VP, but control harmony between the stabilator and ailerons is not as good as it could be. The stab is light, crisp and solid but the ailerons are a little heavy and the roll rate is a little slow and sluggish. History has proven that this isn't a problem, just an area that could be improved.

    It's safe to say the aspect ratio of the VP's ailerons is probably too low. It's even out of the "Approximate Proportions for Best Results" range in Bud Evan's Evans Lightplane Designer's Hanbook. ...it's way out in fact. The "fattest" ailerons recommended are 20% of the wing chord and 48% of the simispan. The VP-1's ailerons are 31% of the chord and 39% of the simispan. But it's probably the simplest way to do ailerons and simplicity was what he was after.

    By widening the ailerons one bay and shortening the chord by 5" you'd get an aileron that was about 21% of the wing chord and 50% of the simispan, just off the high AR end of the "recommended" chart.
     
  2. Oct 28, 2014 #22

    cluttonfred

    cluttonfred

    cluttonfred

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    Another option that I would consider for the VP is rerigging the ailerons for up-only or extreme differential operation with the existing proportions and attachment to the rear spar. See https://www.homebuiltairplanes.com/...cs-new-technology/14732-up-only-ailerons.html

    I'd also be interested in learning if anyone has tried moving the hinge line of the stock ailerons as TF suggested and how that worked out.
     
  3. Oct 28, 2014 #23

    FritzW

    FritzW

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    Moving the hinge aft (and widening the span to keep the area the same) is what #12 is all about.
     
  4. Oct 28, 2014 #24

    cluttonfred

    cluttonfred

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    Sorry, maybe I misunderstood, but I thought that TF was suggesting maintaining the aileron dimensions and proportions as per the original design but moving the hinge further back to create a balanced aileron surface, either symmetrical ailerons on cantilever hinges or maybe Frise ailerons.

    cantihinge5.gif bgjbrok-albums-constructies-picture165590-frise-aileron.jpg

    Either would require changing the aileron hinge design, however. I think you could make cantilever ailerons by reversing the eyebolts in the ailerons, lengthening the eyebolt in the rear spar and passing it through a hole in the aileron spar to move the axis of rotation back, but then the pins would be inside the aileron and hard to inspect.

    49.jpg

    Alternatively, if going with up-only aileron rigging, maybe something like this would work to relieve the stick forces, as I mused in that up-only aileron thread.

    22211d1359459015-up-only-ailerons-sketch.jpg

    Perhaps the simplest solution would be to add some sort of aileron spade to a reinforced aileron center rib, which could also serve to mount the mass balance in order to clean up the wingtips.

    P1020088.JPG
     
  5. Oct 28, 2014 #25

    FritzW

    FritzW

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  6. Oct 28, 2014 #26

    cluttonfred

    cluttonfred

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    Yup, saw that one, wasn't too sure about the elephant ear approach, wingtips can be unpredictable places. I wonder if anyone has any design guidelines for aileron spades? That said, I'd rather have a less drastic solution, likely some variation of a Frise aileron within the stock aileron cutouts. I'd love some suggestions on an easy way to do that, ideally something from an aircraft of similar characteristics.
     
  7. Oct 28, 2014 #27

    Turd Ferguson

    Turd Ferguson

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    Correct. Same ailerons, different hinge location. Aerobatic guys do this to lighten up aileron forces and it works are well as spades.
     
  8. Oct 28, 2014 #28

    Riggerrob

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    Sleekest canopy I ever saw on a VP-1 was a NACA pattern similar to a Turner T-40 single-seater. The big advantage of the NACA pattern is that all the clear parts are flat-wrapped.
     
  9. Oct 28, 2014 #29

    Riggerrob

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    There a two advantages to bulged canopy: smoother airflow over the tail surfaces and more room for crew.
    Chief advantage of a bulged canopy is more elbow room ... like the aluminum elbow bulges on the Bolkow Junior. But you want most of the bulge down at elbow level, more like a Feischler Storche.
     
  10. Oct 28, 2014 #30

    Riggerrob

    Riggerrob

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    I like the idea of Frise ailerons.
    Does anyone know how to attach piano hinges to a stick and fabric wing?
     
  11. Oct 28, 2014 #31

    cluttonfred

    cluttonfred

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    With a false spar like Fritz's narrow chord aileron in post #16?
     
  12. Oct 28, 2014 #32

    Turd Ferguson

    Turd Ferguson

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    Fritz's concept drawing is dead on and would probably make for a nice handling airplane. The only downside is it would have to be done during build or major rebuild. I would think an existing airplane could be modified with different hinges and get some improvement but I could be completely wrong about that. That rear spar may not like longer hinges twisting on it.
     
  13. Oct 29, 2014 #33

    cluttonfred

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    Looking at the relevant plans page below, I does seem that it would be possible to make lighter ailerons as follows:


    • Use about a 2” longer eye bolt in the rear wing spar, 1” extending from the wing to move the aileron hinge point aft the same amount and 1” projecting back into the wing through a flat-topped triangular bracing block to give more “bury” to the bolt.

    • Shorten the aileron ribs one inch with same flat bottom profile and a slightly steeper upper surface to the trailing edge.

    • Add as large-radiused a quarter round fairing to the forward upper face of the aileron spar as aileron movement will allow, effectively creating a thickened aileron as is sometimes used to energize the boundary layer and increase control surface responsiveness on RC models and full-size aircraft.

    • Add a matching fairing to the rear face of the rear wing spar.

    • Do the same to the lower face of the aileron spar and drill the eyebolts in that spar slightly higher to allow aileron to project slightly below the wing profile for the same boundary layer effect;

    OR

    Attach as long an aluminum angle to the lower face of the aileron spar as aileron movement will allow to act as an aerodynamic Frise balance.

    • With both of these, it might be possible to move the aileron balance weight to the front of the fairing or angle in the form of a spanwise thin lead rod or bar to eliminate the overhanging mass balance altogether and go will full-chord wingtips.​
     

    Attached Files:

  14. Oct 29, 2014 #34

    FritzW

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    Do you have a "flat-topped triangular bracing block" on the rear face of the wing spar also? ...something to go under the head of the eyebolt.
     
  15. Oct 29, 2014 #35

    cluttonfred

    cluttonfred

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    I didn't but probably should have. I was trying not to have too many or too wide gaps in the aileron leading edge fairings. Of course, all this speculation on modifications is great fun, but at this rate only my grandkids would get to fly it.

    I should probably take my own advice about "sticking to the original bare-bones, open-cockpit design and rejecting any modification that would add rather than subtract weight." In that case I should just build it exactly as designed except for cutting weight (Oratex fabric, Nikasil cylinders, lighter wheels, drilling lightening holes wherever I can safely get away with it) and just go flying, heavy ailerons and all! ;-)
     
  16. Oct 29, 2014 #36

    Tiger Tim

    Tiger Tim

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    Yes, do that. If you start flying it and decide you want to keep the wind out, just build a giant canopy for it and look like Roger Ramjet...
    [​IMG]

    -Tim
     
  17. Oct 29, 2014 #37

    FritzW

    FritzW

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    ...oh great, now I've got the Roger Ramjet theme song stuck in my head
     
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  18. Nov 16, 2014 #38

    FritzW

    FritzW

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    I just re-read this thread after following the "VP-2 Kit" thread. I must have missed your comment here. Which changes make you nervous?

    In some of the renderings I posted above some of the plywood was set to transparent so the giblets would show. I just looked at the firewall rendering in the top image and the fact that what you see is only the inner core isn't obvious.

    As far as I can tell none of the changes I suggested would lower the design limits.
     
  19. Nov 16, 2014 #39

    cluttonfred

    cluttonfred

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    Don't take it personally, Fritz, I just don't have the engineering knowledge or math to know whether or not cutting away so much of the firewall core or reducing plywood skin thicknesses here and there would have a significant impact on strength, ditto the move to a wooden anti-servo tab without reengineeering the whole stabilator. Lightening the seat and seat support, going with the lightest possible covering, maybe using a fiberglass tailwheel spring, things like that I am confident will not have an impact on anything critical. For my own VP-2 project (so far only in my head) I would probably dream about lots of mods and changes and in the end mostly save weight by omission and/or spending money for the lightest plywood, using spruce where pine would do (but not replacing douglas fir, which is there for strentgh), etc.
     
  20. Nov 16, 2014 #40

    FritzW

    FritzW

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    It's nothing like that. I was just filling in information that my poor choice of images might have left out.
     

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