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  1. S

    I've gone soft - need help on some aero

    It is difficult to think of any analysis invoking unspecified magic as other than rough order / sensitivity. (Not a criticism of what Marc is doing here, which is a good example of the kind of rough order sanity check that simple models are good at.)
  2. S

    I've gone soft - need help on some aero

    I think what I have in there is technically correct, just less clear than what you suggest. I snuck the "one over" into a negative exponent on the right hand side out of laziness. It checks out dimensionally, and when I run it...unless I've made a compensating error in my test code. Regardless...
  3. S

    I've gone soft - need help on some aero

    Arg, got "best L/D" speed in my brain as your query. Continuing here rather than additional edits. At best L/D speed: Writing the ratio of the L/D between the two aircraft: Pulling in our previously calculated CL for best L/D: Probably easier to just plug things in now, but since I'm on a...
  4. S

    I've gone soft - need help on some aero

    At best L/D speed the parasite and induced drag are equal and lift equals weight so: Power is drag times velocity so: We can do a similar expansion for the lift coefficient: Hold power constant for each aircraft and we can set this equal: Conveniently, all of the aircraft parameters...
  5. S

    Anyone know Ros Briegleb sailplane field in Nv ?

    Perhaps this: http://www.airfields-freeman.com/NV/Airfields_NV_S.htm#hidden https://maps.app.goo.gl/64ERoqGXV2MUgfQ19
  6. S

    Rethinking Propellers?

    I think that speculation about the merits of blade counts, disc loading philosophy, and blade warping or discussing propeller "specifications" like blade pitch and static thrust are missing the forest for the trees here. Before we rethink propellers as a whole, we should probably start by...
  7. S

    Now, GPS can tell you which seat you're in. And even which direction you might be leaning.

    There are several paths to using GNSS aiding for quite good attitude solutions. As addaon says, the errors are very correlated over aircraft scales so basic differential works surprisingly well, especially with a decent baseline size. Most RTK systems can be put into a moving baseline mode...
  8. S

    Concordia

    He placed 7th in the 2012 World Gliding Championships in it. It was very impressive to watch and instantly recognizable in the air (I suspect it would blend in a bit more with the Binder's now though). https://www.soaringspot.com/en_gb/32nd-fai-world-gliding-championships-2012/results/open He's...
  9. S

    Craigslist

    There are some pretty heavy composite touring motorgliders out there, but the newer versions have shown significant improvement. I have help put wings on a Phoenix, and removed the wings from a pure glider L-13 ( :'( ). The Phoenix wings were lighter... Specifications on the L-13 SE / Vivat are...
  10. S

    Schrenk approximation

    The original description of Schrenk's method also describes how to address this (albeit with a few places where the terminology and definitions could be a bit more explicit): https://ntrs.nasa.gov/api/citations/19930094469/downloads/19930094469.pdf That said, recall that Schrenk's method was...
  11. S

    Tailless, but with a small hat?

    This is a potentially clever idea but I can't think of a good way to address it quantitatively for homebuilder-reasonable amounts of time and money. Separation (even of the "2d" variety) is an inherently three dimensional, time-varying, and viscous phenomenon. In short, it ruins all of our good...
  12. S

    Winches, Motorgliders, and Soaring, Oh My!

    This exactly. So much so that in general any L/D above 30:1 gets turned into speed until you are back down to about 30:1 (unless you are flying an EB29R or similar). In most of the world on a reasonable soaring day 30:1 seems to be about the magic number that reliably lets you get to the next...
  13. S

    SGS 1-26 redesign as an ultralight motor glider

    Coincidentally 5 years or so ago the contest id "RV" started popping up occasionally at soaring contests attached to a self-launching Arcus motorglider...
  14. S

    The difference between winglets and higher a/r

    I understand the desire to create simple equivalencies between options, but these simply do not exist in a general way. Even were there a nice aerodynamic equivalency, this is only helpful in setting an initial guess what you should do because mission performance is what actually matters in...
  15. S

    Struts on a Glider

    Off the top of my head I think it is partly cultural and partly technical. (I've never designed a micro-lift sailplane, done market research for one, etc. apply a suitable number and size of salt grains to this opinion) Cultural: Sure, some of it is probably that "modern gliders don't have...
  16. S

    Trailer Design - Resources?

    I don't have any design resources, but I've had the misfortune to deal with a variety of home built sailplane trailers and fortune to deal with a number of name brand ones. Regardless I rig and derig almost every time I fly (now from a "homebuilt" Jiran half-clamshell which is the best of the...
  17. S

    Dynamic Soaring Blows My Mind

    Lord Rayleigh's observations of albatrosses "The Soaring of Birds" from 1883 is generally thought to be the earliest study of dynamic soaring. His analysis was largely qualitative but clearly lays out the basic ideas of dynamic soaring. As you show, the early literature of soaring is mostly in...
  18. S

    Using only GPS as your EFIS inputs??? Why u do dat?

    What do you mean by "EFIS" and "useful?" Any system which has attitude requires sensors other than GPS, and anything with a PFD requires pitot-static data. If any system is displaying a PFD based on inertial data I think we would agree that is not an appropriate thing to do. Focusing on...
  19. S

    Using only GPS as your EFIS inputs??? Why u do dat?

    The point I was trying to get at is that AHRS is improved by GPS. Adding GPS to a silicon MEMS system reduces attitude error by roughly a factor of 10 (even more for heading). That is the why. It is possible that some EFIS does this poorly but that is a mark against a particular implementation...
  20. S

    Using only GPS as your EFIS inputs??? Why u do dat?

    The solid state "gyroscopes" in these electronic AHRS systems are not gyroscopes in the traditional sense. They indicate angular rates, not attitude. To get attitude from them you could start from a known attitude and add up the angular rate over a series of small steps in time. Unfortunately...
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