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  1. D

    Reduction of interference drag on a laminar airframe; pylon wing?

    A very good study on this subject is here: http://drum.lib.umd.edu/bitstream/handle/1903/8141/umi-umd-5315.pdf?sequence=1&isAllowed=y
  2. D

    21st century Volksplane?

    MB-04 is designed for 60HP engine and 450kg TOW. The power load is therefore 7.5 kg/hp, what is close to such plane as C-172. A motorglider with span load G/L^2 less than 3kg/m^2 and L/D >20 really can work with far less power to weight, say 10-11kg/hp to get the similar climb rate (about...
  3. D

    21st century Volksplane?

    I'm thinking seriously about a minimalist 2-seat motorglider for which a 30-35HP engine would be enough. Indeed the powerplant weight here is strictly limited. A converted Visa engine as well as large industrial V - twins (B&S, Kohler) may be suitable options along with the VW/2.
  4. D

    question about windmilling propellers

    Some data on this subject is given in the NACA reports #464 and #641 http://naca.central.cranfield.ac.uk/reports/1934/naca-report-464.pdf http://naca.central.cranfield.ac.uk/reports/1938/naca-report-641.pdf
  5. D

    question about windmilling propellers

    It is a complex matter. The drag of stopped and windmilling prop depends on pitch, blade shape and twist, and interaction between the prop and the airframe. The coarse pitched props of small size, high twist and narrow tips, installed in front of a blunt cowling generate minimal drag if stopped...
  6. D

    Prop Math and Design

    Jan, This yellow prop immediately catches my attention. it is very similar to what I see for my (still rethought) Kitten-Piglet motorglider project. I expect that such blade shape can provide a remarkable balance between the efficiency at climb and cruise as well as minimizing the stopped prop...
  7. D

    21st century Volksplane?

    Perhaps only if the grass is very high and wet, the ground is very soft and the wheel is very small. Normally a conventional taildragger plane with properly sized mail wheels will take off of almost any surface with a static thrust of just 20-25% of its TOW. The more important is the sufficent...
  8. D

    Wing strut question ?

    One may use much thicker symmetrical section, say 0030 in the struts and still have the friction Cd value similar to that of the complete plane referred to its wetted area, but this thicker strut will obviously have better strength to weight ratio and will provide only a miniscule contribution...
  9. D

    Is it possible to make fast 4 seater out of wood ?

    Wittman Tailwind has struts, its EFPA=2.03sqft with a 84sgft wing area, fixed taildragger gear and a tube&fabric fuselage, which possibly has room for four.
  10. D

    What can we learn from Pelicans?

    And all known birds are high-wing monoplanes.
  11. D

    Is it possible to make fast 4 seater out of wood ?

    Sorry, I did the typo. The equivalent drag area in my above example is 0.28 sq.m =3.04 sq.ft. It is slightly more than that specified for Hollmann Super Stallion (2.8 sqft), but I expect it is quite possible for an airframe of mixed structure, similar to Wittman Tailwind.
  12. D

    Is it possible to make fast 4 seater out of wood ?

    I've estimated the preformance of a conventional high-wing monoplane with such specs: Span 14m Wing area 12.8 sq.m Airfoil 4412 E=0.83 EFPA=0.8sq.m MTOW=750kg, Limbach L2000 engine. I've got the follwing SL performance numbers; Clean stall 47kt Climb gradient 1:11 at 56kt, maximal climb rate...
  13. D

    Staggerd seats in a Cub

    A small forward luggage space in this configuration is naturally arranged at the right side behind the firewall. It is accessible from inside the cabin. As the rear (now right) seat is moved forward by approximately a feet in respect to its original location, the CG of a crew of two equal weight...
  14. D

    Analternate aviation efficiency theory !

    A drooped wingtip may serve just one good purpose. In a long span motorglider it is a convenient place to install a side supporting wheel, which is used in inline landing gear configurations. It is the long wing that does the job together with small EFPA.
  15. D

    Strut braced vs. cantilever wings

    The drag of struts should be analysed together with other drag components. A strut itself is very small portion of the total wetted surface and also equivalent drag area. It is usually a symmetruical airfoil-shaped body with friction drag coefficient quite comparable with that for the whole...
  16. D

    8-10 place designs

    Star Jar, I have still more doubts on the merit of the X-foil simulation of a previously unknown and untested aircraft. A traditional analysis based on experimental data and basic aerodynamic laws says much more. Later I'll show my calculations and background behind them. Again, as I've...
  17. D

    8-10 place designs

    Some major faults are expected in this in X-plane simulation. Also the 4424 airfoil is not suitable for this application and will perform poorly. The 4412 is best, maybe one can try 4415, but not thicker. Also the 230-250HP engine will work for 3800-4000lbs MTOW with 46-47ft span, the minimal...
  18. D

    What would you change on the ch-701?

    The CH-701, 801 and 750 have so many engineering faults, that I'd abandon them completely. Possibly one can install a prefect wing without lE slot , providing gereater L/D an speed range. The tail earm in 701 is long enough to accomodate the wing of greater span and area, which is essential for...
  19. D

    8-10 place designs

    It depends on the boundary conditions. A simple non-supported uniform lift strut is an example of an ideal column pinned at both ends. It buckles according to the basic sine mode, when the maximal deviation from the axis is started at the middle, its effective length is equal to the geometrical...
  20. D

    8-10 place designs

    Yes, I've rechecked my numbers and it appears that the correct spar compression force is about 90kN. This is the total load compressing both spars, abnd this is well under the buckling limit. The combination of buckling and bending here is safe for the following reasons: 1. The bending moment...
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