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Bob Llewellyn

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Everything posted by Bob Llewellyn

  1. Bob Llewellyn
    ok, ya got me...
  2. Bob Llewellyn
    I'll bite: The adverse pressure gradient becoming sufficiently large to nullify the mean rearward velocity of the boundary layer (the layer in which the continuity equations no longer match Bernoulli's total energy sum) on the suction surface of the lifting plane. As an immediate consequence, the boundary layer becomes vastly thicker, disrupting the free stream flow - or "separating".
  3. Bob Llewellyn
    By fatality rate, GA in Aus should be a tad ahead of RAAus at the present time. Where is the evidence that GA maintenance defects are mainly caused by maintenance? Where is ANY requirement that RAAus aeroplanes possess physical endurance?
  4. Bob Llewellyn
    A couple of observations from a purely aerodynamic aspect: 1) The mass of a "conventional" aeroplane can only be moved (effectively) by its wing. In order to accelerate the mass sideways - which is what a turn is, in a particle physics sense - a lateral force must be applied (and sustained) through the centre of mass. This is achieved by tilting the wing - lowering one end and lifting the other - so that a part of the wing normal force vector acts in the horizontal plane. Ailerons do this directly. There are some aeroplanes which, when yawed, develop a bit of side force from the fuselage acting as a vertical wing; but except for the Transavia Airtruck, the effect is generally very small. 2) A sideslip increases the drag to lift ratio - by increasing drag; an increase in parasitic drag from the yawed fuselage is intuitive, but the increase in induced drag caused by reducing the effective aspect ratio - remember, the load factor remains 1 - becomes the more powerful factor as soon as the sideslip bank reaches 15~30 degrees typically (depending upon the aeroplane...). Opinion - fly the aeroplane, don't just ride in it!
  5. Bob Llewellyn
    In the days of single-channel R/C, you just put the aeroplane into a spiral dive; when fast enough, straighten up and it loops! Or - for non-models - if you yank the stick hard back then boot the rudder, a flick roll! But ultralights aren't R/C OR aerobatic (sob, sniff...). ps Peter, the prototype Thruster T-83 (single seater) BARELY rolled rudder-only - about a 2km turn radius in cruise - until I rebuilt it with a bit more dihedral
  6. Bob Llewellyn
    Ok, no worries - from the aspect of "What can be done", it's all about Certification, because that's the big - sometimes HUGE cost - of getting even a simple aircraft onto the market. The talk about re-creating the Thruster / Drifter, when 95:25 has officially self-destructed, makes no economic sense - those aeroplanes were designed / evolved purely for minimum manufacture cost on small production runs (i.e. minimal tooling, moderate labour). Dafydd was involved in the certification of the Drifter SB* (and has a few of my Thrusters in his hangar), and is all too aware of how the certification cost of such designs blows out once certification grows beyond a CAR 35 engineer declaring the design "airworthy" (which is what 95:25 is all about). LSA seems to be the beacon of hope for affordable aviation; the trouble is, it costs just as much to demonstrate compliance for a single-seat, minimum-profit entry-level aeroplane as it does a minature Mooney; and the profits on the Mooney are bigger. *And the Calair Skyfox, the Jabiru LSA (with 1600 donk), the J-160...
  7. Bob Llewellyn
    So - you are opposed to controlling the aeroplane? A sideslip final allows a higher kinetic energy be retained, with obvious advantage in situations involving mechanical turbulence and potential windshear. Why do you feel that this manouvre is too complex?
  8. Bob Llewellyn
    I agree, check your facts. RAAus does not Certify aeroplanes against design standards, CASA does. I quote ANO 95:25, issue One, 1.2: "This Section of the Air Navigation Orders shall be cancelled when Air Navigation Orders Section 95:55, 100:55 and 101:55, issue 1, become effective." I had a discussion with Eugene Holzapfel on this head, whilst preparing some paperwork for Rob Thompson to get Drifter production back into gear. Eugene did not quibble over the "grandfathering" of 95:25, although CASA exercised its discretionary authority to give Rob the maximum support - once he cleared the hurdles - to get going. RAAus is still required to support airworthy 95:25 aeroplanes - called "old" 95;25 aeroplanes in 95:55 - but have stuff all to do with certification; they will not claim otherwise. As the regs are online and not long, please read them.
  9. Bob Llewellyn
    I agree with your philosophy, but query the commercial material penalty: Are you using "A"-basis (2.7 sigma) material properties, or just "S" basis? What about fatigue? For the bomding, how do you render the aluminium oxide film impervious? What happens to your bond when cycled beyond 1.7mStrain? These are what I have found to be the stoppers to using commercial material, esp bonded aluminium, in any airframe that has to meet a design standard. If you've got them solved, the whole picture changes...
  10. Bob Llewellyn
    How do you make a Drifter for $10k ~ $12k?
  11. Bob Llewellyn
    Wrong - 95:25 is expired. Thrusters and Drifters are as much shaped by 95:25 (CAP 482 as well), as by any other influence.
  12. Bob Llewellyn
    CAO 95:25 is expired. Unless you are proposing re-introducing 95:25 (supposing CASA would come to the party, and secondly, supposing you could find a 21M signatory willing to accept the liability), Thrusters and Drifters are historical relics. Note Well: I am committed to keeping all Thrusters operational for as long as possible; but I do not delude myself that regulations have not changed.
  13. Bob Llewellyn
    GFC / recession got anything to do with it?
  14. Bob Llewellyn
    Originally electrical, now mechanical; but CAR 35 work is aeronautical...
  15. Bob Llewellyn
    Of sorts - I was 7/8ths of the required experience for a CAR 35 when the regs changed. I've done a couple of years of uni - long ago - and am back there now.
  16. Bob Llewellyn
    They seem to have a remarkably high rough air penetration speed, considering the load factors and wing details. Has anyone cruised through a blue-air thermal or similar? How confortable was it?
  17. Bob Llewellyn
    monosyllabic analyses are of strictly limited value. All the words I use may be found in dictionaries. I would suggest that your above response exceeds the literary capacity of most five year olds.
  18. Bob Llewellyn
    I didn't know that this forum was populated by potential flyers - I thought this was a discussion between experienced recreational flyers about whether there is a sufficiently common perception of an acceptable "first ultralight", to be able to create a design that can benefit from economies of scale - i.e. that more than three people might buy...
  19. Bob Llewellyn
    To those of you not currently flying, an aeroplane is a flying machine that sustains itself by the reaction of the air on fixed surfaces (e.g. wings); an aircraft is anything that flies and is capable of bearing a human being. Something that can be described as an aeroplane is, ipso facto, of an aeroplane-like description.
  20. Bob Llewellyn
    ok, so if it can be done by one person in less than 5 minutes and then fits onto a trailer, it's a goer?
  21. Bob Llewellyn
    absolutely - but the Skyfox wing folding seemed to never get used, and then the ailerons went soggy and the aileron hangers (arse of ribs) went rotten. As a frustrated designer, I've long believed in folding wings, but after the 'fox experience, I thought nobody would use 'em.
  22. Bob Llewellyn
    One of the features of the noisy, smelly two stroke is that, to a fair degree, it self-inhibits. In the early days, one could blatt off for a weekend's flying, wipe its chin, and stick it in the shed / on the trailer, and forget about it for a month or two if other things came up - and then go flying, no rusty camshafts, no rusty cylinders... If grassroots cheap flying machines of an aeroplane-like description were made, should they in fact be 2-strokes?
  23. Bob Llewellyn
    sounds neat! market research here: Do you use the wing folding much?
  24. Bob Llewellyn
    If it's not a personal question, wottiz it? (the 95:10, this is not meant to be philosophical!)
  25. Bob Llewellyn
    All of them, to my understanding. The Tamworth office of the CAA/CASA kept visiting Australian Lightwing, and inspecting every single aeroplane against the design... I think Howie Hughes may have started implementing variations because he was so tired of the endless scrutiny, he figured he might as well get some use out of it. The result was he has a stack of individual "signings off" by CASA... your tax dollar at work! Howie still has - I think - all the records, they're happily building quite a respectable LSA low-wing package these days. They're probably willing to do a little work on the high-wing aircraft, if offered money:faint:
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