Dafydd Llewellyn

FFS - The MTOW is what the aeroplane was designed and certificated for. The LSA rule allows the applicant to design for a higher MTOW if the aircraft has floats. Strictly, the MTOW is the least of: (1) The maximum weight at which the aircraft was proven to meet the structural requirements; (2) The maximum weight at which the aircraft was proven to meet the stability and handling requirements; (3) The maximum weight at which the aircraft was proven to meet the performance requirements. An applicant can thus design for whatever weight he chooses. However, the rules designate a number of aircraft categories; for example if the aircraft is to be self-certificated by the manufacturer under the LSA rule, its MTOW will also be limited by whatever that rule allows. NOTE THE WORD ALSO . If the manufacturer anticipates selling the aircraft with a float capability, he may elect to justify it for any higher weight that happens to be allowed by the category. So it has nothing whatever to do with whether floats add lift; it's what the rules permit (and don't ask me how people worked out those rules - they don't make sense to me, either) and how the manufacturer / designer chooses to work within those rules. Unless an increased weight is allowed by the aircraft's certification, you CANNOT increase the MTOW by adding floats.

It does if you are using them - e.g. in a Bellanca Scout - for glider towing.

Yep, I know that trick too. However it's not really necessary with a bypass-type setup, I suspect.

Yes, I'm familiar with the principle. But I'm not dealing with a standard installation, here; the motor is in a pod at the top of a streamlined pylon, and the radiators are inside the pylon, with doors that are opened by the process of turning on the fuel. There's a limit to the number of control cables I can run up the pylon. I'll be testing the whole installation in an instrumented test cell, so I'll find out whether the thermostat will do the job.

Sounds like a reason to put a temperature sender in the engine water intake hose & see what's going on, then. I do prefer the bypass style of installation. I doubt what Rotax put on the 582 is that style, which means I'll be modifying it and adding a manual override valve to it.

No, because the thermostat always opens gradually; have you never tested one in a saucepan of water, on the stove?

Well, the man didn't say it was a four stroke - and as I've just purchased a 582, I'm interested in what might emerge on this thread. I'd assumed that the thermostat would suffice - and I'm looking at air restarts after periods of gliding. Yes, I'll be closing cowl intakes & outlets when the engine is shut down, and the restart procedure will have to include a warm-up at idle, to the thermostat cracking temperature. The early Gypsies, with bronze cylinder heads, were fairly immune to shock cooling - but you had to be a bit more careful with the later versions, which had aluminium alloy heads. I put a thermostat on a 912 in one of the first Murphy Renegades, because the heads were experiencing what I considered far to great a variation in temperature between climb and descent. The thermostat improved that greatly. However, I also included a manual thermostat bypass valve, in case the thermostat failed shut - and in fact that saved the engine (and possibly the aircraft) a couple of hundred hours later.

Erhm - the 582 has water-cooled barrels and heads, so the original question of the thread is apposite. Apart from cold start-up, will the thermostat not prevent a sudden circulation of cold water from the radiators?

Do you have a thermostat in the cooling water circuit?

See CAR 206(a)(i): 206 Commercial purposes (Act, s 27(9)) (1)For the purposes of subsection 27(9) of the Act, the following commercial purposes are prescribed: (a) aerial work purposes, being purposes of the following kinds (except when carried out by means of a UAV): (i) aerial surveying; (ii) aerial spotting; (iii) agricultural operations; (iv) aerial photography; (v) advertising; (vi) flying training, other than conversion training or training carried out under an experimental certificate issued under regulation 21.195A of CASR or under a permission to fly in force under subregulation 317(1); (vii) ambulance functions; (viii) carriage, for the purposes of trade, of goods being the property of the pilot, the owner or the hirer of the aircraft (not being a carriage of goods in accordance with fixed schedules to and from fixed terminals); (ix) any other purpose that is substantially similar to any of those specified in subparagraphs (i) to (vii) (inclusive);

No, don't think I flew KBY; this is in an old log book and I'd have to excavate my archives to find it. The Bathurst club had two J1Bs, one of which was ex-Dubbo, VH-KCJ; they re-engined it with a Gipsy 10 Mk 1 and fitted an oil cooler, and I organised a propeller from Barrie Bishton - and it performed surprisingly well. However, I'm fairly deaf nowadays as a result of flying them.

All POH speeds are given in IAS - that's a requirement. We used to tow gliders in the Auster at 42 KIAS - which indicated 50 in the Blanik, which has a particularly accurate ASI system. My first landing in my Mk III Auster (using the placarded approach speed) floated the full length of the Bankstown -29 runway. That's what started me digging into the Position Error. The Mk III did not have a POH, but there was a military AOP that gave the figures. They all had the same pitot-static head, so they all have much the same ASI system error. 13 knots slow at stall, and about 8 knots high at cruise.

Don't kid yourself - the cable brakes were quite capable of grabbing the first time they were applied from dead cold.

I hope you're right - but the fact remains that these aircraft were not designed to meet any fatigue requirements whatever. The scenario you envisage requires what is referred to as "Damage-tolerant structure" - and the certification criteria for that are given in FAR 23.573. So what is needed is a jump from no fatigue considerations whatsoever, to something that is a step beyond what virtually ANY current GA aircraft has. You cannot count on slowly-propagating cracks in locations that can be readily inspected. The Blanik demonstrated that very clearly. I take your point about farmers being much more mechanically savvy than your average city dweller; that's always been my experience. But I'd like to step over what I forsee as a painful learning phase.

Yes; and the airframe standards of recreational aircraft also reflect the expected usage of a private LSA owner or a flying school. They do NOT cater for the sort of usage that consumes a 912 every other year. Sooner of later, we'll see a repeat of what happened with agricultural usage of R22s; a few of these aircraft will lose wings, and the authorities will pull their heads out of the sand, and it will all change again. Re the speed illusion thing - when I was towing gliders at Bathurst, in an Auster J1B, we thought nothing of avoiding the problem of taxiing it crosswind* in a westerly, to get to the fuel shed, by landing it alongside the shed - after all, with a 25 knot stall speed, you can do that kind of thing, right? It was some years later that I discovered that the full-flap stall speed is actually 39 knots CAS. Didn't stop us landing in what was essentially a parking lot, filling the tank, and flying out of there again. *Austers are a complete pain to taxi crosswind with their original cable-operated drum brakes, which fade completely after about 100 yards, so the thing keeps rounding-up into wind. Most of them by now have Cleveland wheels and hydraulic disc brakes.

None of those designs get within a bull's roar of meeting FAR 23 certification criteria - and even those are minimal. David Isaac is correct, they need a larger weight limit in order to do so, and the large wing area necessary to get to the speeds SQUDI considers necessary*, limits the proportion of useful load to gross weight, so the MTOW has to increase disproportionately. The whole business of using aircraft built to watered-down airworthiness standards, for what amounts to aerial work, via the loophole of private usage over your own land, is not something a manufacturer can countenance from a liability point of view; it can only be done by the relevant authorities "holding the telescope to a blind eye". How long that will continue to be tolerated is not something I'd gamble on. * I wonder what the airspeed system error of these aircraft really is; putting leading-edge slats or VGs is likely to increase the available angle of attack sufficiently to cause considerable pitot error - a normal pitot is accurate only to about 12 degrees angle from directly into the airflow. Manufacturers have been taking advantage of that to get unrealistic indicated stall speeds, for at least the last seventy years; for example, an Auster ASI reads 13 knots low at stall speed. FAR 23 put something of a stop to that, in the late '60s - but none of the aircraft mentioned meet FAR 23, least of all the Hornet, so the ASI error can be anything the designer wants. Are you all fooling yourselves?

Well, I did point out that the realistic maximum speed benefit is about 6% of your original stall speed; if that was, say, 45 kts CAS, the best you are likely to see would be about 42.3 knots CAS. Where you WILL make a gain, is in the ability to use the lower part of the aircraft's speed range without it being quite so liable to try to spin if you do more than a very gentle manoeuvre. If you are not seeing a couple of knots reduction, you probably have the stall strips set a trifle too high on the leading edge. Whether you will be able to lower them to get that small improvement, and still avoid the assymetric stalling problem, is something you will have to find by test. Flying squares and averaging the GPS reading will give a rough idea of the airspeed system error, at cruise speed. It's useless around the stall speed. Also, to get any sort of accurate comparison, your tests all need to be done at the same centre of gravity position. The definition of Vso is, the speed in level flight at which the aircraft pitches uncontrollably nose-down, or the minimum steady flight speed with the stick on the up-elevator stop, in the landing configuration with zero power, at the maximum takeoff weight, and the most adverse centre of gravity position, when the speed is reducing at one knot per second during the approach to the stall. To measure this, in certification testing, it is normal practice to use a video camera to record both the test ASI instrument and a stopwatch and a light that shows when the stick is on the up-stop, and to perform perhaps a dozen stalls with differing rates of deceleration, (measured from 1.1 times the lowest speed recorded to the point at which the stick hits the stop). The results are then plotted on graph paper, to show the stall speed versus the deceleration rate, and a line of best fit drawn through the data, and where that line crosses one kt/sec is the Vso stall speed. One knot per second is a very slow approach to the stall, and surprisingly difficult to achieve in some aircraft; but when you are getting down to one or two knots difference, this level of effort is necessary to get an accurate result.

Mostly, vertical; however, I simply use a rod-end as my pivot, so it can accommodate either; it has about plus/minus 12 degrees of self-align capability, which is sufficient for most purposes. The version shown in the attachment is a bit more complex than a simple pitot, but the basic construction form is the same; it's mass-balanced about the pivot. The example shown comprises a shrouded pitot tube (which has high angle capability) co-axial with a form of venturi that has large-angle capability; I call it a "2-Q" head because in principle it should read double the dynamic pressure (this one reads almost three times the dynamic pressure). It makes it easy to do really accurate stall-speed testing, because you do not need a trailing-cone static with this setup; but the calibration factor has to be measured, either in a wind tunnel or by cross-reference against a simple weathercock pitot plus a trailing-cone static. A simple weathercock pitot plus a trailing-cone static is just about 100% accurate PROVIDED YOU ARE NEITHER CLIMBING NOR DESCENDING. If you are changing height with that sort of setup, there is an error due to the change in static pressure.

In case you have trouble discovering what a "swivelling-vane" pitot is, the terminology is imprecise - I mean, a pitot head mounted on a weathercock device, so it always points directly into the local flow direction.

OK, first question: How are you measuring your stall speed? If you are using the original aircraft's airspeed system, you are likely to be seeing an exaggerated effect; just as the marketing of VG kits tends to rely on the increasing error on the pitot head at higher angles of attack, giving an exaggerated reduction in stall speed, the same effect gives an exaggerated idea of the penalty for removing the VGs inboard of the fences. To get a more accurate idea of what is happening, I would normally use the sort of airspeed measuring system that is used for a certification exercise; i.e. at the very least, a swivelling-vane pitot, mounted one wing chord ahead of the wing leading edge, and a trailing-cone static. Accurate measurement of stall speed is one of the most difficult pieces of flight testing. Re the wing fences, I simply aligned them parallel with the aircraft's fore & aft axis. The form I use is what is termed a "short fence" in that wikipaedia article. It will develop the chordwise vortex when the inboard portion of the wing is forced to stall by the stall strips. Skewing them I assume means setting them at an angle, as one does with VGs; but that generates a vortex at all angles of attack, which is not what you need.

It would have to offer things that the J230 does not provide. I'm not going to go into that at this stage; I don't believe in telegraphing my punches.

The prototype is roughly half built; the problem is getting the right engine for it. Essentially, the CAMit equivalent to the Jab 3300. I have a quite extensive workshop, and enjoy working with my hands.

Thanks for that - it puts it all into perspective. Very useful. I have been thinking, for quite a while, that there might be a niche for an aircraft that one might describe as "half a Cessna 180" - i.e. a two-seater, built to be durable, with sufficient power to be able to take off in less distance than it lands, with a full-flap stall speed just under 45 KCAS, and the docile sort of handling exhibited by the Seabird Seeker - but with a cruise speed around 130 KCAS. It needs to be readily adaptable to whatever use its operator desires, which means it has to have versatility designed into it. It needs to be certificated in a category that allows aerial work in VMC by day.

I guess it depends upon how highly you rate low stall speed in your criteria. There are a damn sight more Cessna 180 / 185 in use for rural operations, than ultra-STOL devices. I suspect that's because they are more useful, all round. They carry a decent load out of a short strip, and they are not slow by comparison with other aircraft of generally comparable format. I've had a Cessna 180 operating out of my 350 metre strip. I rather suspect super-STOL is more a gimmick than a practical general workhorse type characteristic. I'd put more emphasis on taming the stall handling so one could make full use of the available speed range, rather than adding acres of wing area and fragile high-lift systems. The Storch had quite a powerful engine for its size and weight; but it was a reliable engine, which is very critical for a rural workhorse type aeroplane.

I can't comment on the Hornet; I've no real knowledge of it. It looks like an honest attempt to produce a workhorse style of aircraft; but how good it is depends very much on the detail - and that's not something one can pick up from a website. A serious main undercarriage generally weighs at least 5% of the aircraft MTOW, and that's for one designed for FAR 23 type loads (around 10 ft/sec limit impact velocity). Most of the spring-legs on recreational-type aeroplanes try to keep the weight down by setting the main legs at a fairly steep angle; but that makes them very vulnerable to side-drift landings, because if the resultant of the vertical and the side load passes close to the outer clamp of the undercarriage, it has very little "give" and the consequent loading generally snaps the leg (or damages it so it snaps one or two landings later). It's very difficult to beat a properly-designed steel spring-leg for durability and cost, but there's no getting away from the weight of it; and yes, damping is a problem for which there is no really satisfactory answer. Almost all recreational aircraft undercarriages are really under-designed in one way or another, in order to meet the category weight limits. It's an eye-opener to look at the structure of a Beech Skipper, especially the main gear. That aircraft is essentially an undercarriage with not much aeroplane wrapped around it. It contrasts hugely with a typical LSA aircraft; and to my mind this says the very tight weight limits on recreational aircraft are the result of unsound thinking. I was under the impression that Ole originally made the Hornet an experimental VH kit because he realised that making it sufficiently frail to stay within the CAO 95.55 limits was self-defeating - but perhaps I am wrong in that notion.