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Bob Llewellyn

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Everything posted by Bob Llewellyn

  1. Bob Llewellyn
    Makes good sense to me. Er, the downwash is a distributed ellipse, and your HW looks to have enough span to stick outside the region normally considered (by NACA) for the HS... you may end up with a tad more lift on the rear stablewinger than you expect. This is what prototypes are for, of course! :o) It's normal to call the smaller horizontal surface a stab, whether it lifts up or down... in high wing layouts, the rear surface may lift both ways in a normal flight. A lot of the 1930-1940's French load carriers used a large, high-aspect-ratio rear surface, often with endplate fins. They were pretty efficient, too... If you let me know the horizontal separation of the centres of lift of the wing and rear surface, and the CG possie (both vertical and horizontal), I can have a stab at a stability curve too, if you like.
  2. Bob Llewellyn
    Well, the curves show 110kts indicated on Prop #8, and bags of TO performance, so I'd say 120kts indicated is within reach of a 2-blader... if the diameter is reduced, 130kts may be possible, fixed pitch. At this end of town, it's all about drag; you've eliminated induced drag pretty well, but in my experience things like separation at control surface hinges, cooling drag, exhaust "plume" drag and wingroot-fuselage interference still have the potential to stuff things. From the sounds of your research, maybe you've got all that under control too... Note that 120kts indicated will, at 5,000ft on a warm day, get you over the ground at close to 135 kts...
  3. Bob Llewellyn
    Ok, here's a first shot at the probable performance. I've assumed spatted and faired U/C, no unwanted separation anywhere, Prop #8, and a 48lb load on the 34 sq. ft HS... looks like you'll get impressive TO and 110kt IAS cruise, which suggests we could stop working on the TO end of the prop performance, and try to improve the top end. Cheers! Rough Performance Estimates #1.pdf Rough Performance Estimates #1.pdf Rough Performance Estimates #1.pdf
  4. Bob Llewellyn
    Here's prop #7 with the outboard taper made a bit more abrupt (still 3" tip chord), and an extra 1% thickness. Prop #5-8.pdf Prop #5-8.pdf Prop #5-8.pdf
  5. Bob Llewellyn
    I think of it as marketting... or venting? Thanks to NATO, I too work in Imperious units!
  6. Bob Llewellyn
    and here's the previous one (Prop 6) with a 1% increase in thickness to chord ratio. Makes quite a difference... Prop #4-7.pdf Prop #4-7.pdf Prop #4-7.pdf
  7. Bob Llewellyn
    About a million years ago, I got some bargain extruded polystyrene from "Austech" at Eagle Farm... it's a dow corning product, gold in color, may be what the yanks call "pink foam"...
  8. Bob Llewellyn
    I use commercial aluminium, 2mm... never burned it!
  9. Bob Llewellyn
    Well, I've been studying props, it's nice to get a chance to use it... of course, when I've got it all working to my satisfaction, I plan to charge huge sums of money for advice...... or start making props! This lot use those donk specs; as you can see, the rising line of the aircraft drag will cross the descending line of the prop thrust; and when you push the thrust out to higher speeds, you lose takeoff performance. I'm also trying to make a point about how many variables are significant... the analytical technique I use is pretty accurate; so it should be able to let you work out what's the best you can expect from a fixed pitch prop. If you get a prop that won't deliver, you should then know to change the prop, not the aeroplane... ps When I get to the end, I hope to produce a less confusing summary for you (and me!). If you'd care to let me know your wing area, aspect ratio, tail areas, approx fuselage surface area, and wheel size, I can fold this prop data into a polar and give some estimated performance figures, including TOR / TOD, by the methods I've found to work. Cheers, Bob
  10. Bob Llewellyn
    ...but was cut off by Ben Tley: "How droll" he sneered, wishing he had lost his Chery years ago. "Oh, slut up you pommy dlongo!" exclaimed Hy Undai. "You're living in an invisible time walp!". Ben went very red, and reaching out with both hands...
  11. Bob Llewellyn
    My T-300 has a HUDS! Well, the engine instruments are on the roof (other than that, it's not much like a Super Connie...) Can we all get real? Fit all ultralights with 2.75" FFARs (missiles), and just blast illegally parked ferris wheels into the next dimension... so obvious...
  12. Bob Llewellyn
    Look you, that nose-high rubbish doesn't happen with a 172B... the O-300 is a safety feature from that, er, viewpoint. One steers around Ferris wheels...
  13. Bob Llewellyn
    the patch of grass behind the men's amenity block. Just then, a white Toyota Coaster drove onto the active runway...
  14. Bob Llewellyn
    ...and here's prop #5, with the twist on the outer half of the blade(s) fudged a little - not optimally, but in a more betterer direction. Note the ugly little dip around 40kts - that's due to a stall instability (a chunk of the blade is very close to stall, so a very small change in local inflow causes it to stall... and then unstall by 50kts). If you've ever had a prop that buzzed at a certain speed, or whined, or hummed, it was the same sort of thing. I could micro-twist that behaviour out of it, but there are bigger improvements to be had. Since the compressibility margin is good (it gets nowhere near sonic choking at any speed), increasing the section thickness outboard should improve the stalling characteristics, which should give the highest thrust yet at ~40kt, and may improve the sub-40kt curve... ps I've dropped the first coupla props, the graph was just getting too crowded... Prop #3-6.pdf Prop #3-6.pdf Prop #3-6.pdf
  15. Bob Llewellyn
    It takes training, and years of practice...
  16. Bob Llewellyn
    Shakespear had it right - in pursuit of universal amity, let's kill all the lawer. Once that's done, I'll point out that the F-16 is a "lightweight" fighter, which makes a FIAT G-91 or a Folland Gnat ultralight...
  17. Bob Llewellyn
    I know a bit about this! The standard "improves" the safety of a less-thoroughly-designed aeroplane, by setting requirements that aim at keeping the speed low enough that flutter won't be an issue, landing energy won't be anything like a Beech Baron in a thunderstorm at night, and a few other considerations. Now, sticking b-y great floats on an otherwise sleek Thruster reduces the cruise & top speeds - making it less likely to flutter - and gives a longer effective undercarriage stroke, reducing mean landing decelleration. SO - A Thruster with an extra 50kg (assuming the lift truss can handle it) and floats, SHOULD be slower enough that the rough air penetration speed is reduced less than the cruising speed is reduced, flutter is a non-event, and lands like fairy fluff (which they do anyway . Be a test pilot, it's exciting. PS the two-seat thruster lift truss was tested to 7.2G @ 400kg without yield, so it's one that could handle an extra 50kg, if all the paperwork were lined up. The T-500's big weakness is that a PT-6 just pushes it too fast...
  18. Bob Llewellyn
    "Kinetic Energy Kills" just doesn't have the same ring... "Stop the Speed!" has a truly prime ministerial ring to it; "stop the excess kinetic energy"... too many syllables...
  19. Bob Llewellyn
    Yes, Cessnas have big noses. Get a Thruster TODAY!!!
  20. Bob Llewellyn
    yes, it's got a big nose...
  21. Bob Llewellyn
    Look, M6, surely you realise that if you take personal responsibility for your person, you're doing a lawer out of a case? Shame on you!!!
  22. Bob Llewellyn
    HEY!!!!
  23. Bob Llewellyn
    smoke source on ground?
  24. Bob Llewellyn
    Indeed, that's why igloos are built of compressed snow, it's thermodynamics. The point of the Merlin butterfly is simply that, rather than raise the air above impact icing temperature before the carby, RR ensured a high heat flow per square inch on the butterfly; the point of that being, when supercooled water droplets are ricochetting off the butterfly before ice has formed, the heat flow out of the butterfly is much greater than either caused by cold air alone, or after the butterfly is insulated with a nice blanket of ice. If you're not using a RR scale heat flow, the blanket of ice better not get too thick before it's cooked off, or it can simply choke the cold manifold downstream of the carby... The Rotax electric carby mitten is challenged just by the airflow and evaporating fuel cooling; supercooled droplets lead to ice, which, yes, soon breaks off in slabs. This does not garauntee immunity from power interuptions, which Rotax themselves state.
  25. Bob Llewellyn
    CS-VLA 1093(a)(4)... there's no "Acceptable Means of Compliance" explaining which carbies will do; so obviously we need to ask at our local carby shop. ps I got the wording slightly wrong; it's "...a carburettor tending to prevent icing..." - does that means it protects the wing leading edges as well?
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