Jabiru skin thickness?

[turboplanner]

that he thought it would be more than sufficient for the fuse skin also.

Yeah, that's one method of design

 

 

[Dafydd Llewellyn]

Yeah, that's one method of design

Y'know, people don't try to be surgeons or dentists without proper training; beats me why some of them think they can be engineers without it. Yes, it's fun to create your own design; but a composite aircraft structure, without some knowledge of the fundamentals? I assume our friend is in that situation, because he would surely not ask that question otherwise. Look at Scott Winton . . . or Charles Ligetti . . . or Gordon Bedson . . . Lots of luck, Pal, I suspect you're going to need it.

 

 

[facthunter]

Just a general comment on that phenomenon no reference to the current person on this thread. Commonly people do a short course in welding or machining for say 1 night a week for six months or so and they think they are a fitter and turner or a welder. or mechanic or whatever. I've been working on engines since I was 10 and I'm still learning. The level of technology we use you cannot be an expert in many things. Today is an era of specialisation. There has never been so much knowledge out there , in a general sense. Some of the information is misleading and erroneous. We may have forgotten some essential things and lost some skills. Coopering wheelwrights wooden shipbuilding etc

 

Sometimes we try to re-invent the wheel. That is doing it the hard way nev

 

 

[rtfm]

Good grief. What a self-rightous bunch you are turning out to be. For goodness' sake - chill guys... This finger pointing and tut-tutting is unnecessary.

 

Duncan

 

 

[Dafydd Llewellyn]

Good grief. What a self-rightous bunch you are turning out to be. For goodness' sake - chill guys... This finger pointing and tut-tutting is unnecessary.Duncan

FFS, at least get yourself Bill Whitney's CD on how to work out the loads and proof test your aircraft.

 

 

[turboplanner]

You've been given very sound advice by several very knowledgeable people for free, you've asked a question which indicates a serious deficiency, you've backchatted people who tried to help you, so what do you expect.

 

 

[Head in the clouds]

I think this is a very unfortunate outcome and rather typical of the know-all attitude of certain people here.

 

I've known Duncan for a good while now and I'm sorry to say that some of you have assumed a bit too much and probably solely based on Duncan's rather poorly worded original question. Let me assure you that Duncan is no fool, and whilst not being an engineer he does have a remarkably good understanding of the engineering requirements for designing and building his plane, and the math knowledge and skills to conduct the calcs for any part of his structure.

 

Duncan is a very active member of another site which is more oriented to homebuilding and amateur design than RecFlying is, but I asked him to come and post here so that the Aussies could all enjoy his build experiences as others elsewhere have been doing.

 

For the benefit of those of you who don't know as much as some here obviously do, the calcs associated with composite structures are very complex and the results of the calcs are very rarely realised in real-life, especially where amateur construction in uncontrolled environments is concerned - that was admitted by Rutan as being the major weakness with his line of kits and plans, and hence all Rutan designs are way heavier than need to be if the construction of them could be guaranteed to be consistent from one builder to another. With that in mind Duncan has, over some years now, conducted representative experiment with a large number of lay-up possibilities and tests those pieces to destruction to further his knowledge and product development based on real componentry rather than theoreticals, with a view to improving on the dumbed-down product.

 

Quite unlike Daffydd's examples of Scott Winton, Charles Ligetti and Gordon Bedson, all of whom I knew very well, Duncan is one who is always willing to listen to informed opinion, and is also one to experiment to advantage.

 

All Duncan wanted to know was the thickness of the foam used in the sandwich on the Jabiru fuselage and he thought someone might be kind enough to measure theirs. 32 posts, two weeks and a vault of unsolicited advice and criticism has been forthcoming but not one person out of the dozens who own a Jabiru, has actually been kind enough to offer whether theirs has foam in the region of 10mm thick or 3mm thick. For the benefit of those who don't profess to be experts, and who might have had an interest in what Duncan was sharing with the forum, below are pictures of an uncoated Jab fuse showing the (white) regions where foam is used to stiffen the structure.

 

Duncan emailed me last evening and mentioned that he does not at this stage intend to return to the site which is a shame, his build story has been fascinating and there aren't many committed amateur experimenter/designers in Australia any more, in the 1970s/1980s we led the world and now we've been left way behind, in part, IMHO, due to the knocker mentality of some.

 

 

 

 

[turboplanner]

All Duncan wanted to know was the thickness of the foam used in the sandwich on the Jabiru fuselage and he thought someone might be kind enough to measure theirs.

If that is what he had asked, and he had also given a location, he may well have received a dimension in the very next post.

 

 

[Dafydd Llewellyn]

I think this is a very unfortunate outcome and rather typical of the know-all attitude of certain people here.I've known Duncan for a good while now and I'm sorry to say that some of you have assumed a bit too much and probably solely based on Duncan's rather poorly worded original question. Let me assure you that Duncan is no fool, and whilst not being an engineer he does have a remarkably good understanding of the engineering requirements for designing and building his plane, and the math knowledge and skills to conduct the calcs for any part of his structure.

 

Duncan is a very active member of another site which is more oriented to homebuilding and amateur design than RecFlying is, but I asked him to come and post here so that the Aussies could all enjoy his build experiences as others elsewhere have been doing.

 

For the benefit of those of you who don't know as much as some here obviously do, the calcs associated with composite structures are very complex and the results of the calcs are very rarely realised in real-life, especially where amateur construction in uncontrolled environments is concerned - that was admitted by Rutan as being the major weakness with his line of kits and plans, and hence all Rutan designs are way heavier than need to be if the construction of them could be guaranteed to be consistent from one builder to another. With that in mind Duncan has, over some years now, conducted representative experiment with a large number of lay-up possibilities and tests those pieces to destruction to further his knowledge and product development based on real componentry rather than theoreticals, with a view to improving on the dumbed-down product.

 

Quite unlike Daffydd's examples of Scott Winton, Charles Ligetti and Gordon Bedson, all of whom I knew very well, Duncan is one who is always willing to listen to informed opinion, and is also one to experiment to advantage.

 

All Duncan wanted to know was the thickness of the foam used in the sandwich on the Jabiru fuselage and he thought someone might be kind enough to measure theirs. 32 posts, two weeks and a vault of unsolicited advice and criticism has been forthcoming but not one person out of the dozens who own a Jabiru, has actually been kind enough to offer whether theirs has foam in the region of 10mm thick or 3mm thick. For the benefit of those who don't profess to be experts, and who might have had an interest in what Duncan was sharing with the forum, below are pictures of an uncoated Jab fuse showing the (white) regions where foam is used to stiffen the structure.

 

Duncan emailed me last evening and mentioned that he does not at this stage intend to return to the site which is a shame, his build story has been fascinating and there aren't many committed amateur experimenter/designers in Australia any more, in the 1970s/1980s we led the world and now we've been left way behind, in part, IMHO, due to the knocker mentality of some.

 

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Well, that's a relief to know. Duncan's original question was pretty much identical to some I've had asked of me in the past, and several of those askers ended up dead. The people who responded were, as far as I could see, concerned that this was another tradgedy in the making, as was I.

I hope his investigations have taken into account stress diffusion aspects at concentrated load points; carbon fibre is not forgiving of local stress concentrations. Coupon testing won't answer those issues. The photos you supplied of the early Jabiru proof testing are most apposite; that's the sort of thing that is involved in proving a composite structure - but that's just the test for point A on the manoeuvre envelope, for the wings and the primary lift truss. A typical basic loads report for a simple aeroplane will contain around 64 cases for the manoeuvre encelope and 32 or so for the gust envelope, from which one selects four or five of the most critical combinations of wing and tail load. In the process, one must verify that the controls do not lock up due to the structural deflections at limit load. Then there are a whole raft of control system load tests; and the undercarriage drop tests.

 

It is prudent to use a relevant design standard as a guide, even if you have no intention whatever to proceed to certification. Those standards are written in blood, and it's just plain dumb to ignore them.

 

 

[Old Koreelah]

Thanks for your explanation, HITC. Your last post helped us understand where rtfm was coming from. We need people like him, so I hope he doesn't stay away. It's a shame this thread ended up badly. Many pioneers started with a pretty fresh slate and ended up with very innovative designs; many others, as Dafydd points out, paid a high price for ignoring expert advice. I can see both perspectives: those who have built their qualifications through decades of hard work, and those (like me) who have had to postpone building a plane till later life, and haven't the time or ability to develop the full skill set.

 

I hope rtfm can take on the good advice offered here. I was once in a similar situation to him. I spent a couple of years trotting my design around Australia's best aircraft designers and engineers. Each one, including Bill Whitney, gladly gave hours of priceless advice FOR FREE. Dafydd gave me a whole day.

 

 

[turboplanner]

http://rtfmaero.wordpress.com/library/1-airfoils/