Sapphire relaunch?

[Dafydd Llewellyn]

Or buy (wisely) a second hand aircraft; why does it have to be new.There are plenty of second hand Drifters out there usually around $15k ... Thrusters even Sapphires. Hell you can even buy a good ol Auster for $30 to 35K. C150s to 172s from $25K to $35K. But if you are hell bent on new, you will pay the premium. These days even with new it is 'buyer beware'. Sometimes old established brands have good predictability and with the right inspections you can limit the risk.

It doesn't, of course. So this is the way most people will enter recreational flying. This should have been, but was not, recognised by those who wrote the original rules; as a result, the cheap, second-hand aircraft will not be as good as they should have been. Therefore, it's not a good place for impulse buying; get a really thorough inspection of the aircraft by somebody you can trust.

 

 

[facthunter]

It is pretty hard to determine airframe life. Incidents may not have been reported that affect the airframe integrity, and you can't expect many thousands of airframe hours realistically, from a lot of these structures. They cannot be inspected properly in many cases. How long does wood last? Nev

 

 

[David Isaac]

Good points Nev. I have often wondered whether I would rather have a laminated timber spar or a metal spar. Of the two choices rightly or wrongly my instinct goes with the laminated timber.

 

 

[Chird65]

It is pretty hard to determine airframe life. ...They cannot be inspected properly in many cases. How long does wood last? Nev

How long is a piece of string. According to the FAA if treated well (Don't add water) then a long time . They give examples of 1930's planes still in service. Wood has a better fatigue life than metal and if it can be inspected is relatively easy to tell if it has a problem. Access issues aside, the repair is normally straight forward. Quality is also an issue and availability of the more common aircraft grade timbers, continues to be an issue.

 

I'm probably telling you something you already know. but for those interested download "http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_Ch06.pdf" for repairing and inspecting wooded airframes.

 

 

[bexrbetter]

For production, it needs good tooling -

There are a number of planes (and cars and boats) and kits constructed with no fancy tooling at all, Morgan's technique is but one example known to many here.

 

My current kit car tooling uses a total of one 300 x 600 x 5mm rectangular steel sheet, a couple of "5 minute whipped up" hand tools/alignment jigs and a couple of fibreglass moulds. Some go to the horrid expense of getting build tables milled flat, I just built a table with adjustable slats ...

 

 

For a kit-marketing exercise, the RV matched-hole technique is very clever; but of course the software for the NC machinery necessary to cut, form and drill the sheets is a substantial development cost.

$50K for a CNC laser, much cheaper for a plasma or router, isn't a "substantial devlopment cost" at the relative level but you don't need that anyway until you get to a level where it's cost effective.

 

Some years ago I did a small run of products that needed matched holes, I drilled holes through matching 3mm sheets of steel which became my sandwich jigs, bolted them together either side of my 1mm sheet and punch marked all the holes and fold lines. There was once a World without computers and match holing was around before Vans was born.

 

Sorry, but that's the truth of it.

No, it's merely your opinion.

 

There are many ways to achieve results, there is no "You have to do it this way" in my book. Follow mainstream thinking and you'll probably end up one of the 90%+ of business failures - who follow mainstream thinking.

 

 

[Oscar]

There are a number of planes (and cars and boats) and kits constructed with no fancy tooling at all, Morgan's technique is but one example known to many here.There are many ways to achieve results, there is no "You have to do it this way" in my book. Follow mainstream thinking and you'll probably end up one of the 90%+ of business failures - who follow mainstream thinking.

All very flippant and glib. However, if you have to meet accepted standards, then you have to either use accepted design criteria, materials and processes or be prepared to provide the proof of 'alternative compliance' required by the authorising authority. You can build an aircraft from string and vaseline if you wish, but pretending it is equivalent to something that has demonstrated compliance with all the relevant standards (and the operational word here is 'relevant', which depends on the requirements for operation) unless you have the necessary approval/s, is a con job.

 

 

[Dafydd Llewellyn]

I don't want to try to write a condensed book on aircraft structural fatigue; and no, wood does not fatigue; the principal issue with wood is the reliability of the glue - but if there are metal fittings in the critical load path areas, that's another story. Aluminium alloys fatigue. Most other materials have some sort of "fatigue limit" - either a stress value or a strain value - below which, for practical purposes, they can be assumed to not fatigue. Welded steel structures need to be treated with some caution in areas such as the lift-strut carry-through, where they were not designed by buckling. Brazing, silver soldering or bronze "welding" of aircraft steel structures is a well-known cause of fatigue problems.

 

If you look at most conventional aircraft structures carefully, the likely fatigue spots are generally not too difficult to at least make an intelligent guess at; aluminium-alloy lift-strut end fittings, for example, and undercarriage attachment bolts, and control-system parts that are subject to reversing bending loads, or cyclic loads.

 

Against that, it is all too easy to come up with a form of structure whose fatigue properties are impossible to analyse - and which is likely to be extremely variable in its structural reliability. Such structures attract requirements to prove their long-term integrity, in design standards such as FAR Part 23; but FAR 23 is not used for recreational aircraft, so potentially unreliable forms of structure can creep in.

 

For aircraft aluminium structures, the methods for estimating the safe life are quite thoroughly documented; see FAA AC 23.13A . However, the life can be severely reduced by poor detail design or poor installation practices or by corrosion or weathering. Why do people persist in building aircraft from aluminium alloys? Because they are predictable, to a greater degree than many others.

 

The fact remains that almost all small GA and recreational aircraft are single-load-path structures in the critical areas - so turning a blind eye to fatigue issues is fundamentally stupid.

 

 

[facthunter]

The "wood" was an aside question. The glue is the worry and how to carry through into metal fittings, otherwise no original faults (shakes) and don't share a hangar with someone who bashes stuff into it.. Wood might be good for a wing spar but I would look into a composite designed properly with a good manufacture process

 

A triangular pyramid is good for the rear fuselage and the cabin cell has to be a compromise but room for good individual design on most examples without using myriad small pieces and a lot of welds.(These are only my ideas). As far as the carry through at the bottom Just make it BLOODY strong. You should utilise the engine mount area for other things if possible. because it is there already and has to be fairly strong and then there is the seat belt attach points to consider carefully and seat supports. If they collapse onto your controls , things get hairy. I'm a high wing taildragging person so some version of a Supercub is Ok by me . Probably without flaps. Keep two doors Tandem seats. 90 knots Lycoming 115 hp. Nev

 

 

[Dafydd Llewellyn]

Hmmm. We seem to be drifting away from the Sapphire, onto "how to design a minimim-cost ultralight". I'm not going to go there, but there's one comment I'd like to make:

 

A tandem seating layout, in an aircraft of 540 Kg MTOW, usually demands a larger CG range than a side-by-side layout, unless it's designed to be like a Tiger Moth, i.e. solo from the rear seat. Such an increased CG range necessitates considerably more sophisticated aerodynamic design, especially of the control system, in order to provide acceptable handling at the aft CG limit. It therefore becomes a certification risk item. If you're talking about PA18 MTOWs, it becomes feasible, but the cockpit layout may still be a bit too cramped to meet FAR 23.562 head-strike criteria. There's a reason why all the littlies are side-by-side.

 

 

[facthunter]

A tandem seat layout does raise Cof G limit possibilities, which is evident on a Drifter for example requiring all kinds of actions to cope . Regardless I'm not aware of too many CofG caused incidents with those aircraft. (Surprisingly)

 

I prefer the Tandem for visibility, and it is usually not cramped. To make a small side by side big enough it has to look like a CT, which has an unusual (but effective) design.

 

We as a group are a bit ignorant of the dangers of Cof G movement and should be required (by training) to be aware of it more. It flew OK past time is not good enough, particularly with some critical designs.

 

A fail safe situation is where major loads are IN the allowable Cof G range. Could be done in theory. (in something simple)

 

Getting the Cof G in the optimum place for efficiency is having it rearward, but don't overdo it. Nev

 

 

[Dafydd Llewellyn]

The usable CG range of a simple aircraft is usually around 12% or so of the mean aerodynamic chord of the wing. The MAC of , say, an early Jabiru, is around 1 metre, so the CG range is of the order of 120mm. If the fuel is in the wing and the seating is side by side, the variable load items can be kept inside this range. An Auster J5G has an unusually large CG range, around 9 inches (229 mm) if my memory serves me correctly, but it has a much larger chord.

 

There's no earthly way to keep the major variable loads inside such a range, with a tandem layout, but you can put the optional occupant on the CG and use the essential occupant as a balance mass for the engine etc - which is what De Havilland did for the Moth series.

 

However, that gives the pilot a very poor forward view, except in a glider, where he can be in front, so not popular.

 

 

[dj_rex]

I had a tandem design envisioned for the future, however the re-power needs to come first. I am loving the discussion this has generated for this lovely little plane. Hopefully the numbers stack up, and we can get her airborne again.

 

 

[Guest Andys@coffs]

Actually, rag and tube (rag and bone, as George Markey called it) is very labour-intensive. It's a good way for a one-off amateur-builder, because it requires little in the way of tooling; but it's a mistake to try to go that way for a bottom-end production aircraft.For production, it needs good tooling - and the tooling has to be designed to achieve a balance between the cost of production man-hours and the cost of the tooling itself. As a production exercise, the Jabiru is a brilliant balance between these two. The investment in tooling is considerable.

 

For a kit-marketing exercise, the RV matched-hole technique is very clever; but of course the software for the NC machinery necessary to cut, form and drill the sheets is a substantial development cost.

 

So, unless people are prepared to clear out a shed and roll up their sleeves, the bottom line - for a new aircraft - is at this level. If $25K is your limit, and you can't DIY, then go look at sailing dinghies.

 

Sorry, but that's the truth of it.

And yet Airborne trikes have survived the ages and the wing was and still is rag and tube and airborne survives and propsers (I think I read that the owner recently bought the old pelican airport at Belmont Newcastle with Matt Hall and another......) so somehow they have bucked your generalization.... That said its my personal view that the cost of a new trike is crazy high for what they do, perhaps its more a fact that they are firmly entrenched in much of the world as "The trike manufacturer" and don't have the same apples vs oranges competition that is the reality in the fixed 3 axis aircraft

 

Andy

 

 

[Dafydd Llewellyn]

You're correct about apples & oranges; a sailcloth wing is a very different proposition to covering a conventional airframe with Ceconite, with rib-stitching. I wasn't talking about trikes; they're another world. There is a place for all forms of construction; it's hard to beat welded steel tube for the cockpit "crash cell"; weld is the fastest-setting glue of them all. Sheet metal is best for energy-absorbing structure, and where fatigue is not an issue, usually lighter than composite, if they are designed to the same code, because composite has to have an ultimate safety factor about 50 % larger than metal. The article in the latest RAA magazine on carbon fibre adds a new constraint to its use.

 

Composites are best where complex curvature is an advantage (rather than a styling feature). But all generalisations will inevitably have exceptions.

 

 

[dj_rex]

interesting to see my idea is not an original. In the latest "Sport Pilot" magazine Ligetti is looking to re-engineer the Stratos. Also a single seat. They have more resources and are further along their path. I wish them all the best. Have a look at their website.

 

http://www.lgtaerospace.com/index.php/home

 

 

[Oscar]

The Stratos is not a genuine contender because it has serious fundamental aerodynamic problems. The website promoting it is another piece of hopeful bovine fertiliser foisted on the public. Websites and bovine fertiliser are cheap tricks. A genuine, safe, cheap and good-performing aircraft is not a cheap trick.

 

A re-vamped Sapphire is a contender - if there is a genuine market for a single-place touring aircraft.

 

 

[bexrbetter]

Sheet metal is best for energy-absorbing structure, and where fatigue is not an issue, usually lighter than composite, if they are designed to the same code, because composite has to have an ultimate safety factor about 50 % larger than metal. The article in the latest RAA magazine on carbon fibre adds a new constraint to its use.Composites are best where complex curvature is an advantage (rather than a styling feature). But all generalisations will inevitably have exceptions.

Carbon Fibre long ago took over from aluminium in motor racing where weight, strength and safety are everything. Simple flat sided and 2 dimensional shapes are being referred to here, not fancy 3D curves..

 

A number of motor racing teams and composite manufacturers now advise the aviation industry, a complete 180 degree turnaround over the last 30 years or so.

 

 

[Oscar]

Complete horse manure in regard to aircraft design. The only primary structure c/f motor racing vehicles are F1 cars, and they have to meet destructive test requirements that cost- literally - millions of $$ for compliance.

 

This is just another example of the self-serving disinformation that you spread to a hoped-for market. Or, in short form - a con-job. But of course, there are people who know your past in that regard.

 

 

[bexrbetter]

Complete horse manure in regard to aircraft design. The only primary structure c/f motor racing vehicles are F1 cars, and they have to meet destructive test requirements that cost- literally - millions of $$ for compliance.This is just another example of the self-serving disinformation that you spread to a hoped-for market. Or, in short form - a con-job. But of course, there are people who know your past in that regard.

Having another bad day Oscar? Actually you are on my ignore list but read this while not logged in.

 

F1 was using carbon fibre tubs, starting with Lotus and McLaren around 1983, long before they introduced crash testing. Lotus used a flat fold up bonded with kevlar system while McLaren baked them one piece in an autoclave.

 

http://en.wikipedia.org/wiki/McLaren_MP4/1

 

There are many car race classes using carbon fibre structures as well as motorcycle racing and even snowmobiles are getting into the act. Williams and McLaren and a number of others now do a lot of development work with composites for the aircraft industry, not sure why that upsets you.

 

I have no interest in developing or selling carbon fiber anything, aluminium and rivets is what I intend to use but I can't change the simple fact that CF is lighter and stronger.

 

 

[Downunder]

I know there are eastern european companies that make c/f racing car parts that are now moving into aircraft parts.......

 

 

[bexrbetter]

I know there are eastern european companies that make c/f racing car parts that are now moving into aircraft parts.......

When F1 got very serious in terms of aerodynamic downforce and carbon fiber during the 80's, it turned heavily to the aerospace industries naturally and started buying up all the top guns engineers in those fields.

 

Not long after F1 exploded with budgets getting to a reputed billion a year and having the very best in computers, wind tunnels and aerospace engineers, it was only natural that some of the teams started outsourcing their talents back to the aerospace industry. It's not rocket science, oh wait, it is!

 

Actually Colin Chapman, the famous founder of Lotus cars, had all but given up motor racing (the running it si and was developing into the aircraft industry when he died.

 

 

[Dafydd Llewellyn]

Generalisations again! The use of composites - including carbon fibre - in aircraft, started with missiles and gliders, where it was used primarily to increase the structural stiffness to weight ratio; NB stiffness and strength are NOT the same thing. The Pik-20-C was, I think, the first glider to use it, in the main wing spar caps (glider wings are designed more by stiffness than by strength). At that time, there was very little knowledge about its fatigue behaviour, whereas there was a great deal of knowledge about the fatigue behaviour of aluminium alloys. The fatigue life of an airliner structure is a major issue; whereas it is of very little consequence for a missile or a racing car - and in that regard, Oscar is, I think, quite correct; F1 experience has little relevance to an aircraft designer. Gliders were used, to a degree, to obtain some practical experience in its fatigue behaviour in a real-world structure; however by the time a glider wing had sufficient stiffness to avoid aeroelastic problems, it generally had considerable excess strength. That's not the case for short wings on recreational aeroplanes.

 

Its use in recreational aircraft has been facilitated by the guidance material in appendices to the design standard, JAR-VLA (now CS-VLA), which allowed fatigue life testing to be sidestepped provided specified limit-load stress values were not exceeded. However, this basis is not considered to be valid by some fatigue experts, for a number of reasons, not the least being that the standard does not make it clear whether the stress value applies to the laminate as a whole, or to the actual fibres within the laminate. A far more plausible basis is the limit load strain value. (I should perhaps explain - stress is the force per unit of cross-section area of the material; whereas strain is the elongation per unit length of the material that results from the applied stress). A commonly used rule of thumb is that the limit load strain should not exceed 0.003 inches per inch length of the material (3000 microstrain) - that's for E-glass; the corresponding rule of thumb for CF I do not know. The strain relates to the actual fibre stress, not the bulk stress on the laminate as a whole. So, one can consider that recreational aircraft made from CF are in fact still serving as test articles. Not altogether a comforting thought. Alan Kerr did quite a bit of fatigue testing on critical parts of the Jabiru J160 structure, BTW, despite this not being required by the design standard; it contains no CF.

 

The use of a limit-load value for an aircraft relates closely to the flight load envelope. However, the design criterion for an F1 shell, so far as I am aware, is related primarily to impact protection of the driver - and that's largely due to the use of carbon/kevlar mixture, not to straight CF, which tends to disintegrate into lethal shards on impact. This being the case, there is no real correlation between the two.

 

Composite aircraft structure, if designed to keep the limit load strain below 3000 microstrain, does NOT compare particularly favourably with metal structure in regard to its weight; and in any case, the additional safety factor required for composite aircraft structure to cope with its inherent variability, also tends to negate its weight advantage. When fatigue can be ignored, and variability can be dealt with by batch-sampling, as in a missile, CF offers a considerable advantage.

 

Obviously, the major aircraft manufacturers have a great deal of proprietory information on the behaviour of CF composites; and there is some data in Mil-handbook-17, for specific materials, but it is far from being a general cook-book for designing carbon-fibre aircraft structures. The increasing use of it by Boeing etc, presumably reflects more recent knowledge on its fatigue properties - but that ain't in the public domain yet, to my knowledge.

 

The Goulburn STING crash showed just how little occupant protection was provided by the CF structure.

 

 

[bexrbetter]

Since you seem to like reading here's some reading for you

 

http://speautomotive.com/SPEA_CD/SPEA2008/pdf/k/K3.pdf

 

F1 is an extremely competitive field where they spend millions in research and testing 24/7, year round to find an edge in the competition and they have been doing it since 1980 when CF parts first started appearing.

 

F1 progressed from chrome moly (Renolds 531) tube aircraft structures to riveted aluminium monocoque aircraft structures to aluminium honeycomb aircraft structures to hybrid aluminium honeycomb carbon fiber structures and now they lead the world in everything carbon fiber long surpassing any other discipline in the real world use of the material.

 

I only see the first 2, being tube and riveted structures around here, not that that's a bad thing by any means, don't get me wrong, does the job well but doesn't make many around here qualified to comment on CF.

 

Composite aircraft structure, if designed to keep the limit load strain below 3000 microstrain, does NOT compare particularly favourably with metal structure in regard to its weight; and in any case, the additional safety factor required for composite aircraft structure to cope with its inherent variability, also tends to negate its weight advantage.

Gliders make a mockery of that statement but I would agree it's not for homebuilders on the same level as wood or metal or even fiberglass is.

 

However, the design criterion for an F1 shell, so far as I am aware, is related primarily to impact protection of the driver

Nope, stiffness and strength to weight ratio was the number one reason, the mandatory safety testing stuff didn't come along until 12 years later in a great panic after 1994 when Ratzenburger and Senna got killed and Barrichello almost all on the same weekend.

 

The Goulburn STING crash showed just how little occupant protection was provided by the CF structure.

Ironically you started your post out with "Generalisations!!" .....

 

 

You really should get used to Carbon Fiber because it's coming right now in many big ways into most people's lives, don't be afraid.

 

But anyway, going back to topic somewhat, here is a carbon fiber competitor to the Sapphire ...

 

http://www.acla.eu/sirocco-ng/

 

 

[Dafydd Llewellyn]

As I said, if people ignore the 3000 microstrain at limit load rule of thumb, carbon fibre does offer considerable weight advantage. From what I see, most modern gliders ignore this; they have restricted fatigue lives accordingly. CF is the darling of the throw-away whitegoods era. The Sirocco, I see, claims compliance with BCAR S - which is one of the design standards that completely ignores fatigue considerations. So, what's its safe life? It may well be a considerable improvement on the original Sapphire, which also ignored fatigue life.

 

The Mk II Ultrabat was almost entirely made from carbon pre-preg; I'm fairly familiar with CF, but I'm NOT into designing throw-way whitegoods. CF can be used - but not in the way you describe - to produce a form of fail-safe structure; I'm using it that way, to comply with FAR 23.573 - but also NOT in the way used in the Beech Starship, which example is rather more relevant than the ones you cite.

 

 

[Head in the clouds]

But anyway, going back to topic somewhat, here is a carbon fiber competitor to the Sapphire ...http://www.acla.eu/sirocco-ng/

I flew about 4-5 hours in one of the early production models of the Sirocco in southern France in 1984. It was just after they changed to the Rotax 377, it originally had a JPX engine (like one of the twin engines used on the Lazair at one time) but was underpowered so they changed to the Rotax. I was looking at them with a view to establishing a distributorship. There was a lot of hype about the Sirocco at the time, being quite cute looking, but the performance didn't live up to the manufacturer's claims. At the time they were spruiking a cruise as well as max straight and level speed of 63mph which was their and USA's legal limit. I wasn't able to get it that fast in level flight and realistic cruise was only about 45mph. And the spoiler roll control was less than exciting.

 

The reason for the low speed was the very large amount of drag from the upper and lower wire bracing and probably also because it used a very high lift airfoil section developed by Paul McReady for man-powered flight IIRC. It certainly wasn't in the class of the Sapphire or even the Hummer, nor the Drifter which came along later.

 

I gave up all ideas of distributing them and instead built my own version. Below is what I think is the only surviving photo of it during a move from the garden shed to my first 'real' factory. I had intended making it a strut braced version to try and improve the performance envelope but ended up having a lot of trouble getting it into the 115kg weight restriction that was becoming more closely policed than in previous years, so it too ended up wire braced. It flew acceptably well but, like the Aviasud Sirocco was just a bit too slow to interest many people.

 

The current Sirocco has been re-engineered by autoreply from HBA (some folks here will know who I mean) and makes extensive use of CF to get the weight down even lower than previously and now has a MTOW of 250kg but still has a relatively massive 130+ sq ft/12+ sq m of wing area allowing it to comply with the European, British and US ultralight regulations but which mean that it will realistically be restricted to dawn and dusk flight unless you're happy to keep your speed right down and still have your teeth and eyes rattled out in the least bit of turbulence.

 

Contrary to gliders making a mockery of the weight/strength issue, gliders are deliberately built heavy for performance reasons as well as strain mitigation. As Dafydd mentioned, the only reason for use of CF in gliders is to stiffen the wings even though it makes for a harder ride in turbulence. As I understand it the stiffening is mainly to prevent control lock-up when the wings flex excessively and cause misalignment of the control surface hinging. There's no reason not to build gliders heavy, since the wings are additionally filled with water ballast to assist penetration speed. Similarly, for its diminutive size the Sapphire is not a particularly light aircraft, which is why it ended up needing to be built under 95.25 rather than 95.10, and is also why it flies so comfortably and relatively fast. There's probably no reason to use CF in a Sapphire unless you wanted to reduce its wing area as well as its weight so as to still keep the stall speed within LSA limits.