Bob Llewellyn
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Everything posted by Bob Llewellyn
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Circular wing
Bob Llewellyn replied to gimballock's topic in Aircraft Building and Design Discussion
The aspect ratio is 1. At a lift coefficient of 1.4, the induced drag coefficient will be 0.637 (times the wing area). For a 300kg 95:10 machine, at a lift coefficient of 1.4 the induced drag will be 68.4 lbf (304N odd). This lift coefficient corresponds to 36 kts, making the induced drag power 7.6hp. By contrast, the mighty T-83 (Thruster) has an induced drag power at 36kts of 1.5hp. With a streamlined bump for the pilot, the disk wing would have a (minimum) total drag of ~78lb, plus ~2lb for the engine cooling (if cowled well) and ~9lb for the U/C as shown. The power for level flight would therefore be about 10hp, on a thrust hp of perhaps 20 (prop inefficiency eats the rest), giving a max ROC of 500fpm on a rotax 503. Funnily enough, my T-83 with a single-carb, points ignition 503 also gets 500fpm... -
...getting into a punch-up with that bloke...
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Indeed - so why not have recreational twins?
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Piper Apache 150?
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Crashworthiness costs - and light light aeroplanes have not much margin of useful load. Where does the cost/benefit cut off?
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If it was big enough to cushion the whole aeroplane! The instrument panel is outside the critical flail envelope. The weight of the units and the reinforced supports - they go off with a bang - would cost fuel. Leaving the tanks dry and making brmmm brmmm noises is very safe
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The Scion also had, from memory, a 10-seat configuration. The point I was trying to make is that twin engines increase safety, especially when flying over tiger country, provided the aeroplane isn't loaded so heavily that the engine-out handling is razor-edged.
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So, the 503s are definitely the cheaper solution - glad you agree! Hey, the Short Scion used a pair of Pobjoy Niagaras, and look at its load factor...
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Marm, ya shoulda used the boot, look you! Your majesty...
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Hi Maj. I was under the belief that 25rego. was not certified, but was registered as being approved for training. the 55rego. came out as the certified model and what is the difference between the two? Cheers Davo P.S. see you at Old Station 95:25 aircraft were issued with Certificates of Type Acceptance (or Approval, CASA used both wordings); so 95:25 aircraft are certified and approved (or accepted!). 101:55 aircraft ditto, but if a recognised standard such as JAR-VLA were used under 101:55, a Type Certificate could be issued. The difference is that a CTA is valid only in Australia; an Australian Type Certificate is acceptable in any ICAO country. This is good news for any international airline operating under RAAus...
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twice as much as a 914?
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The 503 on my Thruster is pretty retarded, and I start it with a string...
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Look you, reality has nothing to do with aviation - if CASA tell you it's unsafe, then it must be... The FAA declared their technical incompetence about a decade ago, and it was a CASA bloke who showed me the FAA video, and explained that CASA was following suit. The difference is, Keating made CASA a litlgation target, and they've been in arse-covering mode ever since.
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Lazairs, like Cri-Cris, were grandfathered - 95:10 does not limit the number of engines, tho' how the Cri-Cri fits into the 95:10 wing loading requirement...
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Sigh. From the Design Standards - and a little inside knowledge - a certain amount can be deduced: ANO 95:25, the original for two-seat trainers, limited them to 40 kts stall and 1,000lb (454kg) MTOW. The Lightwing was designed sensibly, so needed a light engine to meet this ill-conceived design pseudo-standard. Then the Calair Skyfox couldn't meet the stall speed of CAO 95:55, so a fudge was added. CAO 101.55 subsequently allowed 1,200lb (540 kg) MTOW (and an almost sane stall speed of 45kts), so it seems the Lightwing was pushed out to its then structural limit at 480kg*. Subsequently a tiny bit of bent tin (aluminium) was added, and the massive(?) weight of an 80hp 912, and the structure and performance then met the design standard at 540kg. The foward fuse & engine mount structure analyses were checked, and a 99hp 912 was stuck in at least one under an EO. Now LSA allows 600kg (and a piffling 300 fpm MROC), so AL know which airframes can safely go up to 600kg MTOW (probably with no other limits changed). The NEW LSA GR-912 is, like a Cherokee Arrow to a Cherokee 140, an evolutionary step. * This weight may have come from applying the Skyfox fudge to the Lightwing under 95:55.
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It'll be "in the interests of safety"...
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...ooof!' as he barged headlong into Rat, who had been scalping tickets for...
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err, from the TCDSs the old 81 hp was 1211cc, the 99hp was 1352cc... same stroke... thought the 914 was a blown 1352cc?
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gee, 2 x Rotax 503s cost so much... hey, a Lazair with 277s instead of 185s would do...
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Them there bolts are actually quite sophisticated - brittleness is the enemy of high-strength alloys, and various process stages - the original alloying, forging, forming, plating, and any straightening - can predispose a bolt to failure, or simply increase its sensitivity to over-torquing. I wonder how much the bolt size increased from the 80-hp 912 to the 914?
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yes, why don't we have twins? Oh, I forgot - twins are too complex for RA people to fly, no matter how qualified they are in other fields of aviation...
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It's actually quite a challenge to achieve a cruise speed of twice the stall speed, due to the induced drag going up as the 4th power of the speed coming down - that is, in order to have enough wing to be able to climb when close to stall speed, one has too much wing to go fast on low power. The limited speed range of fixed pitch propellors also challenges the top end...
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...pipe cleaning and saki stirling; the lumours of nose picking are entiley false!". At that point, Endo stepped out of...
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I was talking in terms of the multiplicity of recreational types - and some GA - with marginal or less VS, not saying this was a great step fowards for Lightwings ... Bill was guided by Bruhn, and Howie was - to some degree - guided by Bill, so all the HW Lightwings represent an intersection of engineering conservatism and practical useability. I am not so much a fan of the long nose, because in the balked landing case such a prop position has a significant deleterious effect on pitch stability - if an aeroplane has the tailfeathers to handle it, it's less efficient than it would be without the hose nose. By eye, and from my limited GR-912T flying, the Lightwing should handle it...
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Nice. touch of Auster, touch of Porter, touch of Maule. Very nice to see an adequate vertical stabiliser for a change... and like the Austers, it's a NACA 230XX airfoil, which should reduce the trim drag and improve the stall speed a tad.
