Squawk7700
Why scrap arguably some of the worlds best airframes when they could simply be re-engined if it came to that?
Absolutely spot on. My choice for a personal transport machine is a J200 fitted with a Rotax 914 Turbo. Its been done by a guy in Tumut with excellent results.
One of the benefits of an LSA and kit manufacturer is self-certification so they "simply" sign-off the new install or kit builders simply fit an engine of their choice
A double edged sword. It can reduce costs and red tape in implementing engineering fixes and updates but can be manipulated by manufacturers for commercial reasons, such as excluding other parts manufacturers or to introduce changes that have not been tested comprehensively, something Jabiru is well known for.
Aussie Bob
Sorry Oracle, I disagree, casa as usual got it wrong and overreacted. A disgusting restriction on an Australian manufacturer who has succeeded despite all odds.
I respect your opinion on this and I myself made phone calls in support to Truss's office, leaving the electoral officer in no doubt as to the ramifications of a CASA execution. I think in the prelude CASA's behaviour and release of documents was atrocious. My personal opinion is that CASA has been muzzled on this one, once the politicians realized the **** fight that would occur. Either that or CASA are trying to make us grateful that we only got two of the best not six. Threatening the owners (who can afford to have up to ninety grand lying around) of what is essentially a non commercially viable toy could quickly result in a messy class action and may still do. Flying schools conducting commercial training out of Bankstown, Moorabbin and Archerfield fall squarely within CASA's perceived turf, are not able to threaten CASA, and will be crushed. I support Jabiru and they have achieved miracles but one can never rest on your laurels. It is Rod Stiff's business and he can run it how he pleases, but eventually rising outside pressure must be acknowledged.
Thorn Bird
Oracle, I guess then the best thing would be to sell the rights to china,or the Indians. Let them make them and buy the engines from them.
Rest assured Stiff has already flirted with Chinese manufacturing. It was tried with the Drifter as well until cables started snapping while taxiing. Chinese manufacturing doesn't have the quality control quite yet but they have bought companies such as Mooney and Continental, be assured they will be reverse engineering until they can eliminate the West. Buy or steal, 250 years of engineering know how has been handed over on a platter by greedy plutocrats intent on making a cheap buck on the slave labour margin, leaving Western youth unproductive and aimless.
Finally and of the greatest interest,
Rutan Around,
I 'heard' that the flexible nature of a wooden prop acts as a quill shaft or as a torsional balance . If you use a fairly inflexible composite or worse a metal prop things will break inside the engine. I'm sure you would have knowledge pertaining to this and will be able to clarify the situation.
I thank you for this compliment but unfortunately, thanks to a misspent youth and mathematical ineptitude, I am but a glorified mechanic. However, unlike many of my fellows, I am obsessed with flying all things small and I have made concerted efforts to both understand and control the theoretical risks from a practical viewpoint. The conversation I had with one CAR35 engineer regarding the Jab engine and pertaining harmonics was many moons ago and I have long since lost interest in the engine. From memory the problem wasn't prop related, but don't quote me on that. If you wish to delve further I have PM'ed you the contact details of said gentleman, who is well known for his interest and charity in facilitating flying for the masses. I highly recommend his three DVD set on aircraft design which is presented in layman's terms, is highly informative and worth every penny.
Regarding wooden props,
Wooden props are well known for fatigue resistance and damping harmonic resonance due to the flexible nature of the material. (Just like a tree blowing in the wind, still many things we cant beat nature at). They have weaknesses as well such as structural integrity and swelling with humidity but composite sheathing and metal leading edges have begun to address some of the problems. Wood has become a material of choice in some highly advanced composite propellers such as MT, who's expertise is unquestioned. Wood is also lighter and has less momentum. Metal props have a tendency to propagate certain frequencies, when certain frequencies coincide amplification occurs and the energy has to be absorbed somewhere in the aircraft. Jabirus reasons for the choice of wooden prop include the properties mentioned but they also have commercial imperatives, including cost of manufacturing and testing. The wooden prop is also desirable (given the amount of low time pilots) in the event of a prop strike as the ends just shear off. Jabiru was testing a two blade composite prop with a swept foil. They had great success in the performance area but they found that the carbon fibre version was simply too stiff and they reverted to fibreglass. I don't know what came of this. Others have designed and fitted composite props to Jabiru engines, no one has died yet, but it is unknown whether this is by accident or design. I stress that no definitive answer can be reached on harmonics and the nodes at which it is present unless you hook up vibration sensors, collect data in multiple operating regimes, and have someone available who is able to interpret the results. I would like to know if Jabiru has conducted this exercise.
In conclusion harmonics is a little understood (by the unwashed masses) and highly dangerous phenomena which can destroy integral structures rapidly and with no warning. One example that comes to mind that completely dodged the brightest minds was the whirl mode on the Lockheed Electra, an aircraft that went on to give good service in specific roles, for a simplified explanation see here,
Lockheed L-188 Electra - Wikipedia, the free encyclopedia
Harmonics needs to be examined with the whole aircraft in mind. Early research into harmonics in GA aircraft caused some big surprises. The example that sticks in my mind was the testing of a certain engine and prop combination in an aluminium airframe. The combination promptly destroyed itself in testing, catching the engineers completely by surprise. The engine and prop combination was then tested in a different airframe with absolutely no problems. Then the original airframe was tested with another different engine and prop combination again no problem. Go figure, everything has a resonant frequency?