Dafydd Llewellyn

Much too expensive - no politician is worth it.

Point 1: The Jab LSA 55 is NOT unstable - provided you fly it within its certificated CG range. How do you know it's within the correct CG range? Oh, yes, you may not have valid information on the loading rules, because the RAA has only just realised that it's NOT exempt from the normal weight & balance requirements that apply to GA (and everything else.) However, if it's loaded behind its aft limit, it will tend to drop the tail on the ground when you get in - provided the undercarriage hasn't been damaged and incorrectly replaced. Point 2: The Jab LSA 55, like many other of its contemporaries, does not have the optimum control harmonisation - that's the relative response for a given effort, about the three axes - difficult to quantify, but often described as that the ratio of the relative effort needed to get an equivalent response should be something like 1:2:4 for the ailerons:elevators:rudder - in other words, the elevators should be twice as "heavy" as the ailerons, and the rudder twice as "heavy" as the elevators. The Jab is more like 4:2:1, which makes it not quite as pleasant to fly. There are quite a lot of aircraft like that, especially the older gliders. It does not make them "difficult" to fly; it's just something to get used to. You need to learn to "feel" sideslip on your backside, and use the rudder. That's a good thing; far too many "pilots" have "lazy feet". Point 3: I do wish that people who speak of "stability" or "instability" in an aircraft, would learn what the definitions of those terms actually are. Point 4: The trick with flying the LSA 55 is to rest your arm on the armrest and fly it with your wrist and fingers only - do NOT move your arm. If you do that you will find that it's a delight to fly. The same trick - except you rest your arm on your thigh - works in most single-seat gliders, and I am told, in some helicopters, and in things like Lancair IVs that have a side-stick. However, again like many of its contemporaries, the Jab's stick-free stability (ability to hold a trimmed speed) is very light with the flaps down - especially if you're making a dragged-in approach with a fair bit of power - so you do need to watch your speed on approach. But you MUST use your feet. The later Jab models had most of these quirks removed - so they are no doubt preferable ab-initio trainers, at least for the initial experience. But I find them a bit insipid, compared to the LSA 55. Things like Cessna 172s and Piper Cherokees are truck-like compared to the LSA 55. I came to the prototype Jab LSA as an experienced pilot, and had no problem with it at all, Rod Stiff and Phil Ainsworth bundled me in it, showed me where the throttle was, and stood back. I found myself quite at home by the time I'd lined up to take off. As a personal economical hack, it is hard to beat. And yes, it handles turbulence and crosswind surprisingly well if you know what you're doing.

True - but you do have eyes in the front that can warn you if you're flying towards an obstacle. Landing an aircraft without flaps used to assume you'd be able to see because you'd be flying it sideways.

Yes, I am. The field of view out of a high wing Cessna is like sitting in a letterbox, looking out the slot. OK, I've been spoiled by flying the Seabird Seeker, but the reality is that the top of the instrument panel coaming in the Cessna line is much higher than it needs to be; not sure why they did that, maybe to give it an "airliner" feel (in the DC 6 era). That's a "fashion" - quite a lot of aircraft layouts have "stylist" features that really do not make sense. It was even worse when the things had radial engines - at least straight ahead. The situation can be improved considerably by Fowler flaps, used at a "takeoff" setting, but it's dire with zero flap in an obstacle-clearance climb.

Also across Warragamba dam and Cataract dam - and a thousand other places. You will only see them (unless they have visibility balls) if they are silhouetted against the sky - this is the Ag pilot's trick - but look at the statistics for wire strike in Ag aircraft - and even then you will have only split seconds to take evasive action. Also, most Ag aircraft are designed to provide maximum survivability in the event of a wire-strike crash; no GA or recreational aircraft is set up that way; it won't balance. If you make a habit of flying down valleys, sooner or later you will hit one. Wires are always a concern if you're landing on other than a licenced aerodrome; there's a lot to be said for overhead circuit joining and making a habit of steep approaches; the dive brakes on gliders are very useful in this regard. Learn to side-slip. A dragged-in approach is asking for trouble.

If the pilot's field of view over the nose is such that he cannot see objects in his flight path when on an obstacle-clearance climb (i.e. climb at minimum airspeed), that says something pretty serious about the basic design on the aircraft.

The simple fact is: the catenary shape of a powerline NEVER hangs upwards from its supports. If you stay above the ridge tops, you won't hit one.

The general drag equation is (in its most basic form) Cd = Cdo + (Cl^2)/(Pi x Aspect ratio). Cd is the total drag coefficient; Cdo is the "fixed" part of the total drag coefficient (roughly, that due to friction and form drag) and the second term is the induced drag. Wing span extension or winglets increase the effective aspect ratio and thus reduce the induced drag; in effect one can think of the wing as being a device to hold the tip vortices apart - the further apart they are, the less the induced drag. However, when the aircraft is flying at something like twice its minimum drag speed, the induced drag term becomes very small; so if you have a lot of horsepower for the weight, you can fly sufficiently fast that a low aspect ratio has little effect on the overall drag in cruise; that's the basic philosophy of the RV series, amongst others. But if you need to fly as efficiently as possible, this means flying only just sufficiently above the minimum drag speed to avoid speed-instability; and then the induced drag contribution amounts to almost 50% of the total drag. This is the situation for airliners and sailplanes; and if there is a physical constraint on the actual wingspan (hangar width, taxiway clearance, or the FAI class restrictions for sailplanes, for example), then it's possible to gain a few percentage points by a "virtual" span increase from winglets. Generally speaking, the best form of GA wingtip for general use is probably the Dornier raked version of a Hoerner tip - i.e. it looks like a Hoerner tip from the front, but the maximum span is at the rear corner. However, "wingtip hot-ups" have been a popular gimmick, starting from the "conical camber" tips on the original Cessna 210 (which were actually there to slightly reduce the dihedral effect of the C182 wing, since the undercarriage was retracted; and there have been some pretty extreme examples. If you want to see some examples of extreme aspect ratio wings, look up Hurel-Dubois.

You're essentially crossing over Barrington Tops, from Quirindi to Taree, aren't you? I've travelled VFR north-south over that area many times; to avoid the Tamworth zone I tracked Armidale - Mt Sandon - Scone- Cessnock (or the reverse). That keeps you over landable country. You should be able to go Quirindi- Wallabadah - Mt. Sandon - Walcha (or pretty close to that) and thence to the coast without too much mountain wave effect. Bit of a dog-leg but not as dire as direct over-the-top. There's some tiger country East of Walcha; you need sufficient height to cross that, which would be the critical weather consideration. Mt. Sandon is a VOR site, you'll need to find it on an RNC, I expect; hard to spot visually, but it's right on the edge of the scarp, close to a small reservoir. You wouldn't need to pin-point it, but cut the corner to the south over the Walcha plains.

Yep. Practicality has to be addressed; and the aerodynamics usually have to adapt to that reality. The trick is, getting both to work to advantage. . .

Yep; that was one of the noticable things about Peugeots, from the 203 onwards; their steering was tight enough that you could do that and take pleasure in leaving dead straight wheel tracks on a wet road. Very few cars will do that themselves. The first one I found that would, was a Citroen CX. That's a car that doesn't even notice the blast from a B-double at 200 Kmh closing speed.

It's called "evolution in action" . . . . In nature, the penalty for stupidity is - death. No argument, no reprieve, no excuses - just sudden death. Human society disguises that sufficiently for idiots to survive long enough to become a nuisance. Their eventual demise should not rebound excessively on those who are more sensible - but we've yet to learn how to achieve a proper balance in that regard. In regard to the various arguments about over-regulation, insofar as that applies to aircraft design - my experience has always been that the aircraft design standards are written in blood - they represent the accumulated wisdom of a great many deaths. So I see them as not just something you have to comply with in order to get e piece of paper; but very convenient bottled wisdom. It's especially informative to dig into the Notice Of Proposed Rulemaking (NPRM) document that accompanies FAR Part 23 - because it goes into the reasons behind every change there has ever been to Part 23. Once you understand the history and reasoning behind each requirement, you can assess its relevance to your situation. The same principle applies to airmanship, in my view - but it's more difficult to find the reasons behind the rules (though it's often obvious). I find it very useful to write out a draft compliance statement for every aircraft modification I do; tedious, yes - but it draws to your attention the issues that need to be considered. Even after doing this for a living for damn near fifty years, I'm still picking up things. When you stop learning, it's time to quit.

I expect there are quite a few out there - there are certainly airflow software packages that use finite element analysis, which produce pretty pictures (that may or may not be real); since I don't use them, I'm not familiar with them. A web search should find lots of them; people have been trying to get the "black magic" element out of aerodynamics for almost two centuries. Bill Whitney has a CD on the subject - and if you give me an email address, I can send you a few ramblings - and Stinton's book was written to do just what you are asking. Unless you are planning to go GA experimental, your design will have to fit into one of the existing categories, which usually have some defined limitations (weight, stall speed, etc). The starting point for any aircraft design is, what disposable load must it carry, how far, and how fast. Those factors dictate how big and heavy it must be. The aerodynamic form of it follows from that, not the other way around. The issues that dictate the layout are very often entirely different from what a lay person would normally expect, and if you start from the wrong end, you'll end up with a camel, not a horse. I'll give you an example - what dictated the shark-like shape of the Me 262 fuselage?

All fixed-wing aircraft obey essentially the same basic physical principles; their performance is defined fundamentally by their wing loading, wing aspect ratio, equivalent flat-plate drag area, and power loading. Or if you prefer, span loading, flat-plate area and power loading. Without those numbers, it's not possible to predict the performance. So you need to make a better "first guess" than your description, before anybody will be able to come up with any numbers. A good starting point is the required stall speed; with this and the weight, the wing area can be estimated. Most aircraft with a power loading of 10 lbs per horsepower or slightly above, manage to cruise at about 2.5 times the flaps-retracted stall speed. A higher power to weight ratio will allow maybe 3 times the stall speed; this is about the practical achievable range. An extreme WW2 fighter type might get to a TAS of 4 times the sea-level stall speed, at its optimum altitude. Jet airliners get high true airspeeds by flying so high that they are cruising not much above their minimum drag speed. Polishing the thing and getting close to an "ideal" aerodynamic form does not change this speed relationship very much; but it can reduce the fuel consumption. So the "ultimate" sexy shape actually has less effect on performance than is popularly imagined. The drag breakdown analysis allows you to estimate the equivalent flat-plate drag area (the hypothetical area of a flat plate pushed into the air and subjected to the full dynamic pressure, 0.5 x the air density x the speed squared). Hoerner* is indeed the "bible" for this, but how to use the result to estimate performance needs a bit more; a useful guide to both realistic actual drag data and how to put it together to estimate various aspects of performance, is "The Design of The Aeroplane" Author Darrol Stinton, ISBN 0-632-01877-1; it's quite readable, even if you don't follow the mathematics. *you won't find Hoerner in your local library; it was published only by the author, so it's a very rare book. Aviation professionals and university libraries are likely sources. Below the critical Mach number (about M = 0.6), Drag can be represented by two parts, namely the "parasitic" drag, which increases in proportion to the square of the speed; and the "induced" drag, which is basically due to the fact that, because the wing pushes air downwards in order to support the aircraft, it is always flying somewhat "uphill". It decreases in proportion to the fourth power of the speed. At the speed for minimum drag, half the drag is parasitic, and half is "induced" drag. This normally occurs at around 1.2 to 1.4 times the flaps-retracted stall speed. This idealisation is varied a little by the fact that the parasitic drag of the wing can change somewhat erratically, if it experiences a significant amount of laminar flow over portion of its operating range; however the literature on "laminar airfoils" is not too realistic in the real world. All this is also affected by the propeller; firstly by the aerodynamic efficiency of the propeller, and also by the increase in drag of parts of the aircraft immersed in the slipstream. Most simple performance estimates make a fairly crude assumption about the likely propeller efficiency, and are often optimistic because of that. In an aircraft that cruises at less than 100 knots or so, the propeller efficiency can be surprisingly low. Again, Stinton gives some useful rules of thumb.

Yep.

Are you not confusing the MTOW with the category weight limit? Some aircraft categories have an allowance for floats; but that does NOT normally mean you can exceed the certificated MTOW for which the aircraft structure was proven.

I've often come across them when flying gliders; they'll often join a gaggle of thermalling gliders and show us all up. They consider themselves to be the rightful owners of the sky, and they'll compete with a thermalling glider, just to show who's the best. I've had one stay with me to cloudbase, at 7000 feet. I've only seen one attack a glider once - and that was because it came up behind him in a thermal and bumped him (at about 5 knots relative speed) - quite inadvertently, but the eagle was not amused.

Dead right! However, induced drag and wing root separation are two separate things.

I don't know for an RAA aircraft, but I would doubt 19 regos would be exempt. The RAA maintenance "system" has been very loose; I expect it's being tightened-up a bit. Is it such a problem to have an L2 look at the thing? Really? Even LAMEs have to get a duplicate inspection on anything that affects the control system. For an experimental glider under GFA, the same periodic inspection rules apply as for a certificated glider; and a GFA glider inspector has to sign and issue a Maintenance Release, much the same as a LAME. GFA ADs for things like tow release units, safety harness etc apply to ALL gliders.

Yep, that's a practical viewpoint - for those who have the knowledge to do their own maintenance. Why should a LAME have to accept the liability of signing-out an experimental aircraft? I'm doing exactly that with my powered Blanik conversion. If you do not want to go into controlled airspace or fly over built-up areas, this is a good way to go.

Some of the more crude low-wing GA designs omit fillets in order to get sufficient pre-stall buffet from the separated flow affecting the tailplane, in order to (or in an attempt to) avoid the necessity to fit a stall-warning device. Saves the cost of the fillets, too. That thinking, carried right through the design, gets a cheaper product on the showroom floor; the idea is that the customer only sees the initial cost, not the ongoing cost. This goes with the point of view that most people "only buy the paint" - if it has a snazzy paint job, a low aspect ratio, and lacks wing root fillets, you can make a pretty fair guess what the manufacturer's priority was. The costs, as Bob has pointed out, are some reductions in performance all round - higher lift-off and touch-down speeds, reduced climb rate, and increased cruise fuel consumption. The effects are not huge, but you only have to compare a Cessna 172 model that has a 150 HP Lycoming, and a Piper Cherokee 140 with the same engine power, to see the difference these things can make. However, the practicalities of owning and operating an aircraft often outweigh such considerations. Yes, the Cherokee 140 was a bit less lively than a comparable 172; but it had a big nosewheel, so you could land it in a paddock if necessary without too much risk of damage. It also did not blow over as easily when tied down outside. Its fuel tanks didn't hang on to water, and you did not need a ladder to refuel it. Pity that Piper's emphasis on low first cost was carried through to omitting proper corrosion-protection on things like the rear wing attachment, and floating pistons in the undercarriage oleos to keep the oil and the air apart. The reality is that all aircraft design is compromise, and the trick is to make the right choices in the compromises. For example, the British made a deliberate choice to omit de-icing provisions from their bombers. The Heinkel 177 was an attempt at higher aerodynamic efficiency than was the Lancaster. History shows that that was the wrong choice for Heinkel. When you look at an aircraft, try to see what the designer's choices of compromises were, because the way to find what is satisfactory to you, is to find a set of compromises that match you needs. A prime example, with recreational aircraft, is lift struts; the differences between a cantilever wing (no struts), a torsionally-stiff strut-braced wing (one strut per wing) and a torsionally flexible wing (two struts per wing) are profound. How many purchasers have the slightest idea of what these compromises imply for the utility of the aircraft? These things are worth some study, in my view.

Well, yes - it was designed for the Jab 3300, but I've been waiting for Ian Bent's developments. Still a lot of work to go. The criteria of a "successful" design vary greatly from one individual to another. I would like to achieve an aircraft that is a tool, rather than a toy. Because I suspect that the economic circumstances that have allowed the explosion of so many LSA "toys" will not last; but the need for small, durable aircraft to do a job of work, be it mustering, or any of the many uses people find for aircraft, if their certification category allows such use, will continue. So I'm aiming at a small aerial-work aircraft that is just above the maximum weight limit for a recreational aircraft. The Jab 230C is really in this class - or would be if its certification category allowed this. So in a sense, I'm using the infrastructure that has evolved from the recreational aircraft scene, to go one small step further. Such a step needs things you do not find in recreational aircraft, such as fail-safe structure in certain areas, and design to minimise the necessity for labour-intensive maintenance. I don't want to talk about it more until it's flying - and that's several years off.

No, I've always been called in to sort out the mess.

Because I've been too busy designing and certificating them for other people. My memory may be faulty, but I recall the Joey was fitted with a reed-valve conversion of a Victa 150 cc engine, when I saw it at Mangelore.

I was at Mangelore when the AUF was first started; walking around, the only ultralight aircraft there that did not have an obvious basic structural design deficiency, was Keith Jarvis's Joey glider, which had a hotted-up VICTA lawnmower motor on it, mounted on a piece of Cessna lift-strut above the wing centre-section. It also flew rings around every other ultralight there. They were all single-seaters and mostly barely capable of flying at all; let alone safe by any measure. The only argument that could be made for them was that they flew so slowly, and weighed so little, that if one fell on your roof, all it would do would be to break a few tiles. Shades of "Those magnificent Men" indeed. This "low momentum" argument originated from the original Skycraft Scout. Go look at the parking area at Temora to-day, and you will find two-seat aircraft capable of safely flying a thousand miles on a good day. The progression between then and now has been, in effect, a re-invention of General Aviation, but with limited weight capability so they did not compete with "real" GA aircraft. That restriction is a hang-over from the "low momentum" argument, but it's well past time it was recognised for the fallacious argument it really is, for anything beyond 95.10. This pattern - which starts from people saying "There really has to be a simpler way" - basically because they can't be bothered making the effort to understand whatever the existing way actually is - has been repeated at least four times within my memory. The cycle is just about to repeat itself yet again, to judge from the complaints. Plus ca change, plus ca meme