Dafydd Llewellyn

True enough for headphones. Also, headphone jacks pass milliamps, not amps. However, many car and aircraft systems use currents that will cause considerable heating due to contact resistance, so the oxidation rate at the contacts increases exponentially. Whilst aircraft wiring uses (or should use) tinned copper wiring in non-PVC jacketing - thus escaping the corrosion that one finds on bare copper in PVC jackets, the issue of corrosion in crimped terminals, and at mechanical contacts, is a reliability issue - and can be a fire hazard. The use of 24 volt systems greatly reduces this, but you don't find them in either cars or recreational aircraft. PVC insulation produces hydrogen chloride when it gets hot, and that's not good to breathe, either. OK, OK, I'm getting off-topic - maybe this should be in a thread on aircraft wiring practices.

Yeah, the cooking-grade stuff is good for about ten years under most conditions - longer in favourable circumstances. That suits the "whitegoods" mentality quite well - and ensures they buy a new one well inside that time. However, if you want things to last longer than that, contact resistance starts to become a nuisance. I tend to want my machinery to still work a bit longer than that. I drove from QLD to Adelaide & back a week ago, to collect a glider canopy; the only vehicle to hand with a long enough suitably-protected load space was a Peugeot 505 7-seat wagon. It ran well and efficiently - but every couple of days, the heater went full hot - due to contact resistance in a blade-type fuse holder. The car was mechanically fine, but the electrical system was dieing due to oxidation in lousy two-bob bits of the electrical system. This is common in a lot of machinery that is around 20 years old; the electrical bits die first. So I'd like the next step up in component quality.

Provided you know what you're doing, yes.

But gold is the least affected by oxidation of the contact surfaces, which is the critical issue.

What CASA is doing, is protecting its liability under S8.2 of the Civil Aviation Act 1988. Unlike the FAA (and all other National Airworthiness Authorities of which I am aware), CASA can be sued; S8.2 of the Act says so in words of one syllable. So CASA is seeking to reduce its vicarious liability for the design approvals made by Authorised Persons in the industry, by eliminating them. The first step was to close CAR 35 and replace it with CASR 21.M, which limits the scope of these people to minor modifications, and vastly increases the paperwork involved - and hence the cost. It also increased the liability exposure of the APs; so naturally the cost of an approval went up by almost an order of magnitude. It will get worse; within about three years, CASR 21.M individuals will have to become CASR 21.J Design Organisations (this is the EASA model). These changes are also a consequence of the policy of "following World's best practice" - which means, in effect, avoiding any necessity to think about what works best for Australia. The CAR 35 system was unique to Australia; but the "Cringe Australia" policy has prevailed yet again. So, if you want to tinker with the thing, starting with an LSA aircraft is about the worst choice; and a certificated aircraft is getting to be the next worst choice - tho it was not always so. Starting with a certificated aircraft is by far the safest choice, however. If you start with a -19 aircraft, you are starting from something that has not been proven to comply with ANY safety standard whatsoever. Caveat Emptor.

I don't see why anybody should consider that post funny; it's dead right. For the benefit of the deadheads on this Forum, and for about the fifth time, you can discover which Jabiru models are Type certificated by CASA (and look up the serial numbers) by looking up Australian Type Certificates on the CASA website, www.casa.gov.au. ALL jabiru models up to the J 160 C were Type Certificated. This information is in the public domain, so there's no excuse for guessing about it. The difference between a J160 C and a J 160 D is that the former is manufactured under CASR Part 21 subpart G (i.e. a Production Certificate) for which a TC is a prerequisite; and as such it's eligible for a normal Certificate of Airworthiness (if VH registered) - which means its C of A is recognised in any ICAO signatory country; whereas the J160D is manufactured under the LSA rules, so it does not have a TC, the "certification" is from the manufacturer only, not from CASA, and as such it's only eligible for a "special" C of A (i.e. valid only in Australia). The 160D can only be modified with Jabiru's permission. The 160C does not require Jabiru's permission.

That's pretty much the reality of it. However, practical experience (on the Seabird Seeker) shows that a suitable configuration of VGs can increase the maximum lift coefficient by about 13% - which would take the Jabiru value from 2.2 to just under 2.5 - which would result in a stall speed reduction of about 2.5 knots - PROVIDED there was sufficient elevator power to allow the necessary increase in the angle of attack. Also, PROVIDED the design of the VG layout is correct - and most of them that I've seen are not - this can be achieved with very good stall handling behaviour. What Seabird did to achieve that is their proprietory information. It's a hazardous area for experimentation.

In the real World, the original Jabiru achieved a maximum lift coefficient for the whole aircraft (i.e., Cn max, not Cl max) 0f 2.2 with its single-slot flap at 33 degrees deflection. That's about as much flap as it can carry and still be able to climb in a baulked-landing situation. The practical reality is that a "balanced" LSA design with the normal sort of power and wing loadings, won't be able to use much more than this.

Yep; as far as the KR2 goes, my view is similar to that of the farmer who was asked for directions to Bungledoo - he scratched his head, looked up and down the road, and then said "If I wanted to get there, I wouldn't start from here."

Yes, if you look only at the potential gain in the maximum lift coefficient, there appear to be some startling possibilities. There are, however, several major disadvantages in these extreme possibilities: Firstly, if you look at the effect of such a powerful flap system on the airfoil pitching moment, Abbott & Von Doenhoff show, for example, that the common 26% chord 2h slotted flap at 30 degrees deflection, increases the nose-down pitching moment of 23012 from around -0.02 to around -0.36 - i.e. eighteen times the zero-flap value, for a maximum lift increase of about 90%. So the download on the tail increases much more than the lift on the wing. This effect reduces the potential gain in lift, because the wing must carry the additional download. In practice, this effect reduces the potential benefit of the flaps to around half what the lift coefficient gain suggests it possible. Further, the increased tailplane size necessary adds to the cruise drag. You also need a larger vertical tail, to maintain directional stability - and increased dihedral to offset the spiral instability due to the larger vertical tail. Secondly, the induced drag increases in proportion to the square of the lift coefficient - and there's an addition to the simple induced drag due to the variation of the drag from the flaps; this results in the minimum drag speed being increased; so the tendency towards speed instability ("on the back side of the drag curve") is markedly increased; extreme STOL aircraft are noted for tending to fall out of the air due to this; the Helio Courier etc were notorious for it. Thirdly, the lateral stability is adversely affected because of the effect of the asymmetric slipstream interacting with a powerful flap system, in the crossed-control case required by the certification testing. Fourthly, the behaviour of such aircraft in an aborted landing can be rather startling - in the case of the Helio Stallion, approaching lethal. Generally, the more powerful the flap system, the more powerful needs to be the engine - and the combination often produces a violent pitch-up tendency when power is applied to go around; there are limits set in FAR 23 to the stick force necessary to control this - they are there as a result of the Helio Stallion, which needed both hands on the wheel, so you could not re-trim the thing, because it lacked an electric trim capability. It's all "designing into a corner". All these things can be catered for in the original design - the Twin Otter is a prime example - but there's a price for it. STOL was fashionable in the 1960s, with aircraft like the Helio Courier, turbo Beaver, Pilatus turbo-porter, Caribou, etc, which can show startling performance; however they did not make much market penetration except where special circumstances gave them an advantage. Ansett, for example, found to his cost that a Caribou, when operated under normal civil rules for balanced field length, could not lift as much freight as a DC-3, on identical engines & propellers. (It became known as the Caribou boo). In military use, which ignores the risk of engine failure on takeoff, the Caribou was remarkable. It either works, or you're dead. Cessna found it advisable to remove the fourth flap notch from the 182, because the average pilot was barely able to contend with the side effects of the increased performance. The latest C172 has reduced flap deflection, so it's difficult to make a steep power-off approach in it. I can only assume this is a result of the cost of product liability insurance, but this is the way things are going.

I studied a canard layout as my graduation design project. Even built a wind-tunnel model and tested it. The principal problem with a canard is that longitudinal stability of an aircraft having two lifting surfaces one behind the other, requires that the front lifting surface must always operate at a higher lift coefficient than the rear one. This applies whether the layout is conventional (larger surface in front) or Canard (larger surface to the rear) or tandem-wing (equal size surfaces). The result, for a canard, is that the foreplane has to work harder than the wing; you can't generally put high-lift devices on the wing, they have to go onto the foreplane. So for a given combined area of the two lifting surfaces, the canard uses them less effectively than does a conventional layout. So in general, the maximum lift coefficient for a canard has to be lower than for an equivalent conventional layout - i.e. for the same weight and stall speed, the canard needs a larger total area. The second big problem with a canard is that the larger lifting surface - which provides the volume for fuel - is not close to the centre of gravity; the CG usually needs to be well forward of the wing. So you cannot put the fuel in the wings, if they are unswept. The Vari-Eze's swept wing is there so the front corners of it can be close enough to the CG to provide fuel stowage. The more one studies the Canard layout, the more the three-surface layout makes sense - especially if the front surface is a free-floating pitch-trim device, but does not contribute to longitudinal stability - e.g. the Piaggio Avanti. Canards also make sense as pitch-trim devices for supersonic flight. However, they are getting to be very complex devices - and the best place for a propeller is NOT behind something that can shed ice. All this is interesting - but rather off-topic.

Can't help being curious where the 'roos get their ASIC cards . . .

Yes, it's a bit discouraging to have to force the tail down - thus increasing the load the wing has to carry - in order to increase the wing lift. This thought leads one to a canard layout. However, that has its own set of disadvantages; overall, the conventional layout works best, unless some special consideration prevails. The harder you try to get a high maximum lift coefficient for the aircraft as a whole, the more the secondary factors make it difficult. The Westland Lysander was quite a good example of that, and so is the Fiesler Storch. This is why, if one wants to design an aircraft, one needs to understand both the longitudinal stability equation and the longitudinal balance equation - and also know how to take account of the downwash field of the lifting surfaces. Any fool can come up with something that flies - but to get something that flies really well, requires some depth of knowledge. To get a really good result, you have to get into the "flute music". That puts it out of the scope of this website, I believe. A good starting point is Stinton, "The design of The Aeroplane".

Normally aircraft control cables are 7 x 19 stainless to Mil-C-18375. Minimum size 1/8 inch for primary controls. Look up FAA AC 43.13-1 Chapter 7. Available from Skyshop (Aircraft Spruce)

The Skyfox, Jabiru, and Seabird Seeker all use commercial grade extrusion, usually 6061-T6 or 6351 T5 or similar; but they proof-test EVERY lift strut to 1.5 times the limit load tension as the means of qualifying both the material and the assembly.

I'm not familiar with the Savannah setup; but fuel tank venting is a more complex problem than most people realise. If you face the vent forward, to get some ram pressure on it (the amount you get at 100 knots is actually around 1/10 of a psi, which is pretty piffling given the minimum fuel pressure required by a Bing carbie), it's liable to get plugged by an insect - (or ice, if you were fool enough to get into icing conditions) unless you locate it behind something; take a look at the tank vents on a typical high-wing Cessna; they face forward, but they're located in the lee of the lift strut. Also, it's prudent to have more than a single vent; the Cessna setup has a vent on each wing, connected to the corresponding tank; but the tank airspaces are interconnected, to prevent siphoning if one vent has less pressure than the other - so one vent blocking will not spoil your day - that's cheap insurance, in my book. The vent system gets very complex - if it is to meet all the relevant requirements - if the engine can draw fuel from more than one tank at a time. The vent system plumbing needs to be arranged so it has no low spots in which water could freeze. It's worth while looking up FAR 23 on the subject.

That effect is a clear indication that the aircraft is elevator-limited; the effect of a couple of hundred revs is mainly to increase the velocity over the tailplane (unless it's a T-tail, of course). The downside is increased landing float. We also used that trick on the Skyfox, to get it through. All these fine-tuning tricks can gain is quite limited; about 2 ~ 3% at best. Maybe that would suffice for the KR-2 in question. In a certification scenario, one has to take into account a whole lot of aspects, and find the best trade-off for all of them. The "stickiness" of the Skyfox ailerons when drooped, would have prevented the aircraft from passing the lateral stability requirement - which is that it must tend to raise the low wing when the ailerons are released from a full crossed-control situation, at any available power and speed and centre of gravity (including assymetric fuel). Aircraft design is a complicated juggling act, and the textbooks only discuss one aspect at a time. This is where the "theoreticians" - at least, the amateur ones - tend to come unstuck. In the real World, one has to take account of all of them. Going to extremes in any one area will invariably produce a problem somewhere else.

Yes, they did try the drooping flailerons - the initial configuration of the Skyfox when I first flew it, was a Kitfox 3 with an aeropower engine; it had, like the K3, the drooping ailerons, operated by what is now the trim lever. They were completely ineffective in reducing the stall speed, because the aircraft was elevator-limited - i.e. at forward CG, one hit the up-elevator stop before the wing stalled; so increasing the lifting capability of the wings was actually counter-productive, because in doing so, the droop increased the nose-down pitching moment of the wing, which further exacerbated the inadequacy of the tail. That could not be fixed by increased elevator travel, because the "flat-plate" tail surfaces were already at the limits of their capability, due to the limited tailplane span necessary to allow the aircraft to be road-towed with its wings folded. We made the greatest improvement (one knot) in stall speed by gap-sealing the elevators, and that was just sufficient to meet the 40 KCAS requirement of CAO 101.55. Further, putting the "flaps" down loaded-up the aileron circuit so that it required considerable effort to turn onto final - and the movement of the flailerons in so doing caused the droop to return to zero. The mechanism was obviously in need of complete re-design if that feature was to function properly. So the decision was made to delete the droop function and use the lever for the elevator trim instead.

OR take a break and go fly a glider for a few hours; that will teach you how to handle flying close to the stall; gliders fly in that condition whenever they are thermalling, and you get the feel of it. However, you do NOT fly close to the stall in the circuit; gliders fly at around 1.5 times the real stall speed, on their landing approach. The normal minimum approach speed for landing a powered aircraft (which does not have dive brakes) is 1.3 times the REAL stall speed - and most people add about half the gust velocity to that (so if the wind is, say, 15 knots gusting to 25 knots, add five knots).

I would assume he meant the Pawnee with the 235 HP low-compression 0-540; that's the version most commonly used as a glider tug.

Since most aeroplanes are elevator-limited at their most forward centre of gravity, modifications that are aimed at increasing the wing lift are generally ineffective in reducing the stall speed. Further, anything that increases the nose-down pitching moment of the wing will increase the download at the tail, so if the aircraft is - as is normally the case - elevator limited, increasing the span of the flaps (or anything else that increases their power) will generally act to INCREASE the stall speed. Jabiru tried this way back in their early days, with exactly that result. Message: The stall speed is a consequence of the design of the whole aeroplane, not just the wing or the flaps.

What seems to be being overlooked here, is the effect of metal fatigue from repeated rapid cooling. Glider tugs commonly do up to about 12 tows per hour - that's about 2.5 minutes at full power, at climb speed (around 60 knots) followed by 2.5 minutes of descent. That's 12,000 thermal cycles per 1000 engine hours. The various hot parts do not all heat up and cool down at the same rate, and there have to be temperature gradients in order to move the heat from inside to the fins. A cowboy in a glider tug can do thousands of dollars worth of damage in the form of cylinder head cracking, cylinder barrel cracking etc. The issue is NOT overplayed; but it's more severe in the larger barrels on Lycomings etc than on the smaller ones on RAA aircraft

For the methods used to measure stall speed, see http://www.casa.gov.au/wcmswr/_assets/main/rules/1998casr/021/021c40.pdf The stall speed that is relevant to aircraft registration category limits is generally the result of the methods described in the AC, at maximum take-off weight and most froward CG - so determining it required accurate weight & balance. Most aircraft are elevator-limited at forward CG, usually as a means of improving the stall handling. If you increase the elevator power, to the point where it becomes capable of stalling the wing at the forward CG limit, the stalling behaviour is very likely to become considerably less benign. VGs, if intelligently applied, can give about 6% reduction in the REAL stall speed; but unless you know what you are doing with them, they can make the stall extremely vicious. Any change in stall behaviour normally requires spin testing - and that's NOT something to get involved in unless you have extensive knowledge in that area. Generally, if you need a significant reduction in stall speed, it's cheaper to sell the aircraft and buy one that has the stall speed you need.

Yes, it will take at least a decade - and I won't be flying by then. But if one is setting up an aircraft, it's stupid not to make provision for it; so I'll be putting a transponder in the Blanik - probably a mode C; I doubt it warrants mode S. AND FLARM, since it's a glider.

I once had the enlivening experience - flying into Sydney late one afternoon via George's River, for the old 05/23 runway - of being told to follow the 727 about 3 miles on my left. Naturally that led to some urgent scanning, to try to see the thing; but as it happened to be dead up-sun from me, a small point that the approach controller had overlooked, I could not see it no matter how hard I tried. I was flying a Bonanza, so the 727 was naturally overhauling me, and at about my 9 O'clock position at that moment. An ADSB overlay would have allowed me to be aware of it long before the controller called, and would have prevented about 20 seconds of frantic scanning and radio calls - which does not aid one's general situational awareness of other matters. The Mk 1 eyeball is an essential part of the apparatus, but it is far from being the complete answer. If you have ever watched for gliders approaching the finish line at a gliding competition - especially in the days before the lower altitude limit was raised for finishes - it's an education in the limits of the Mk 1 eyeball; you know exactly where to look, but look as you may, the gliders are invisible until they are about 200 metres away, because they are coming straight at you and so present a very small cross-section area. They suddenly blossom into view exactly where you were looking, just above the horizon, and whistle overhead a couple of seconds later. The implications for a mid-air are quite terrifying. I had a somewhat similar experience on a cruise-descent into Sydney in the Bonanza; I was doing about 3 miles a minute and glanced down to check the EGT - as one has to do about every minute, on a descent - and when I glanced up again, a Victa Airtourer was coming at me, backwards, at about 100 knots closing speed. I was approaching him from dead astern, and the same phenomenon as for the gliders, had prevented me from spotting him against the Sydney smog. The resulting manoeuvre was fairly lively; nowadays it would have warranted an incident report. I doubt the occupants of the Victa were aware of my proximity; they were turning gently to the left, so I passed outside their field of view. I'll be putting strobes on our Blanik, pointing aft and forwards; but all they can do is give another couple of seconds warning, if you happen to see them. A properly-designed traffic overlay should show the position of the relevant traffic AND a line extending forward of the target, showing where it's likely to be in 30 seconds. You can see where to look for it in an instant; so it does NOT act to keep your eyes inside. However it is NOT affected by whether the target is directly up-sun, or just below the horizon, or in cloud, or approaching from behind or below. Roll on, ADSB; the sooner it becomes affordable, the better.