How long until RAA get a weight increase approved?

[jetjr]

I dont need to do anything, its a point of view with a little experience. I have no details on scratch built aircaft, however most would be from kit suppliers. Until recently RAA saw no difference between builders and subsequent owners. Both can modify.

 

Kits will require support from manufacturer and you wont get that without them having done testing.

 

RAA adds complexity with capability for aircraft to have capcity beyond the MTOW of the catagory

 

I think thats why Jabiru wont support upgrades to earlier models as they werent tested to those weights originally.

 

Ther are plenty who have altered mtow after construction and not the builder. MARAP process should facilitate this at the worst, a minor mod to reduce stall speed may not even need that.

 

 

[Head in the clouds]

I dont need to do anything, its a point of view with a little experience. I have no details on scratch built aircaft, however most would be from kit suppliers. Until recently RAA saw no difference between builders and subsequent owners. Both can modify.Kits will require support from manufacturer and you wont get that without them having done testing.

RAA adds complexity with capability for aircraft to have capcity beyond the MTOW of the catagory

 

I think thats why Jabiru wont support upgrades to earlier models as they werent tested to those weights originally.

 

Ther are plenty who have altered mtow after construction and not the builder. MARAP process should facilitate this at the worst, a minor mod to reduce stall speed may not even need that.

Your self admitted "point of view with little experience" is exactly what we don't need! There's no difference between scratch-built and kit-built.

 

Your statement - "Until recently RAA saw no difference between builders and subsequent owners. Both can modify." -

 

Rubbish. Nothing has changed in that respect since I joined AUF in 1983! The builder can modify at will until it's registered, years ago they could change it after registration. Subsequent owners with an L1 (or L2, L3 or L4) cannot design ANY modifications, it's expressly prohibited, they can only repair and/or replace - as I said, it's in the Tech Manual ... I guess you don't have even an L1? You'd know if you did ...

 

Please get your facts together before you continue with your unsubstantiated nonsense. This forum is intended to be about promulgating valid information, not your kind of "I would have thought" and " A point of view with little experience" ...

 

 

[jetjr]

Sorry but you can modify, the process was strongly debated, some felt its introduction cut back their ability to modify at will.

 

Minor modifications are listed, they require notification only. Major ones require RAA backing and theres a process called MARAP. Theres even a new registration class for modified LSA

 

To retain training ability aircraft must remain approved by manufacturer ie LSA or certificated

 

Reckon you should research it, your getting pretty personal by the way, its a forum, open to everyone and their point of view. You never know they might be correct

 

 

[jetjr]

Section 6 on the tech manual might interest you, around 10 pages somehow you must have missed.

 

Until this version was released owners were able to conduct major modifications just the same as original builders, now the must have L4 review.

 

 

[Head in the clouds]

Section 6 on the tech manual might interest you, around 10 pages somehow you must have missed.Until this version was released owners were able to conduct major modifications just the same as original builders, now the must have L4 review.

Sorry if you felt my comments were getting personal, I didn't intend that, nor to offend you or anyone else. We do get a lot of 'unfounded opinion' on this forum which is frustrating when the documentation is there for all to consult and get the facts right instead of adopting a position which one feels 'should be the case'.

 

Thank you for the reference though I am well versed in the current Tech Manual including Section 6, the MARAP process etc, as well as the previous versions of the Tech Manual.

 

Just to be sure we're not talking at cross-purposes, 95.10 and 101.28/101.18 aircraft, and their owners were treated differently from each other in the past. Going back to TM Issue 2 (1996) and TM Issue 3 (2007) 95.10 owners could design and implement modifications and repairs at will if they were the owner and had 4 TM(2) paragraphs worth of knowledge in the Design (accurate knowledge of the forces involved, strength of materials, manufacturing processes), Manufacture and Installation (Good planning, workmanship, correct tools) Operation (fully tested and documented) Advice (contract qualified, experienced assistance where required).

 

However, I was referring to the 25, 55 and most specifically 28 reg. series, where you have NOT, historically, been able to modify at will. At least as far back as 1996 modifications have had to be approved by a person holding a CASA Instrument of Appointment under CAR 35.

 

See image -

 

 

The 19 and the E24 registrations seem to be a can of worms in the TM(3) and I concede I have probably missed the point there. Section 3.5.3 does discuss where modifications have been made to kit or factory-built aircraft, though it doesn't discuss by whom, so I imagine anyone might have done so, including a subsequent owner, as you mentioned. However - although that subsequent owner might have conducted the modification 'at will' they still needed to be issued with an Experimental or Special Certificate of Airworthiness by an 'Approved Person'.

 

That's all very well, and I think we all know those Certificates were being handed out quite freely at one time which resulted in a big mess for some people later on ... BUT (from para 3.a) that Special Certificate of Airworthiness "stops having effect if the aircraft is modified outside of the approval given by the manufacturer ..." (in which case see Section 7.5.4) which then makes it an E24 reg (private ops only) provided it still meets the LSA category regulations. Many of the kit/homebuilts wouldn't have met LSA category in the first place, so where would that leave them?

 

 

[spacesailor]

"In some cases those earlier designs might have originally been +6, -3g designs that are working nearer to +4, -2g already (at 600kg). So someone just declaring a new weight of, say, 750kg and not severely limiting the Vne and Va, might be risking losing their wings on a turbulent day ... I'm concerned even more for the unsuspecting second owner who comes along a few years down the track."

 

So, how can casa's limited "wing loading" make a Safer aircraft ?.

 

spacesailor

 

 

[Head in the clouds]

"So, how can casa's limited "wing loading" make a Safer aircraft ?.[ATTACH=full]62223[/ATTACH]

 

spacesailor

Theoretically it keeps the landing crash speed lower ...

 

 

[Bruce Tuncks]

About 1990, there was an increase in stall speed in the landing configuration that applied to the Jabiru SK among others.

 

The increase was from 40 to 45 knots. ( I think, feel free to correct me if you know more ).

 

Now weight corresponds to stall speed squared, so the allowable weight of the SK was therefore increased ( on stall speed considerations ) from 430kg to 544kg.

 

What about the structure? There is more than ample evidence, from comparisons with other aircraft to operational history over 20 years, to demonstrate that this increase is quite safe. I bet that detailed analysis of the structure would also agree, but I for one have not done this myself. As has been stated, who would be qualified to understand such calculations?

 

Anyway, many SK Jabirus have had the weight increase approved.

 

 

[Head in the clouds]

About 1990, there was an increase in stall speed in the landing configuration that applied to the Jabiru SK among others.The increase was from 40 to 45 knots. ( I think, feel free to correct me if you know more ).

Now weight corresponds to stall speed squared, so the allowable weight of the SK was therefore increased ( on stall speed considerations ) from 430kg to 544kg.

 

What about the structure? There is more than ample evidence, from comparisons with other aircraft to operational history over 20 years, to demonstrate that this increase is quite safe. I bet that detailed analysis of the structure would also agree, but I for one have not done this myself. As has been stated, who would be qualified to understand such calculations?

 

Anyway, many SK Jabirus have had the weight increase approved.

Interesting - I had no idea that was the basis for choosing the 544kg weight. (45²/40²) x 430kg = (2025/1600) x 430kg = 1.2656 x 430kg = 544kg. Simples!

 

But as you say the structural calcs are/would be another matter. Being composite structure, Jabiru tended to do most of their proving by load testing rather than rely purely on calcs though, some of their jigs and rigs are very impressive. I was at the very first load test they ever performed, at Caloundra in the Skyfox hangar around 1988/89 where they sandbagged the wings, amazing how high the sandbags were stacked and how much the deflections were. They had to stop at about +4.5g IIRC, the wings were still hanging on OK but the cabin roof structure and the jig were starting to fail due to the massive weight they had to support. It was enough to get them through that stage of the certification which was via BCAR S I think.

 

 

[Jim McDowall]

Maybe 544kg = 1200lbs

 

 

[Bruce Tuncks]

Here's an example of calculations.. the bolts in the Jabiru struts.

 

The strut-bolts are AN4 =1692kg ultimate in single shear. At the Jabiru strut angle, this gives 813.6kg upwards ultimate force times 4 (for 2 struts each in double shear.)

 

This gives 3254 kg or 6 G at 544kg. ( actually 5.98 G) The next step is the mainspar assembly with the wing skin contribution. I would bet that the extra contributed by the wing skins was ignored at the design calculation stage on account of how it would complicate the calculations.

 

There is no doubt that the Jabiru has plenty of strength.

 

Another reason is that fiberglass is a variable material and so the design strength is well below the actual due to conservative assumptions. One example I have already told of is when a Jabiru collapsed onto a wing when a u/c leg failed. Almost that same week, a Technam had a very similar collapse.

 

The result? No damage to the Jabiru, but a new wing needed for the Technam.

 

I am not saying the Technam is badly designed, on the contrary, it is accurately designed and the Jabiru is over-designed.

 

 

[Head in the clouds]

Here's an example of calculations.. the bolts in the Jabiru struts.The strut-bolts are AN4 =1692kg ultimate in single shear. At the Jabiru strut angle, this gives 813.6kg upwards ultimate force times 4 (for 2 struts each in double shear.)

This gives 3254 kg or 6 G at 544kg. ( actually 5.98 G) The next step is the mainspar assembly with the wing skin contribution. I would bet that the extra contributed by the wing skins was ignored at the design calculation stage on account of how it would complicate the calculations.

 

There is no doubt that the Jabiru has plenty of strength.

 

Another reason is that fiberglass is a variable material and so the design strength is well below the actual due to conservative assumptions. One example I have already told of is when a Jabiru collapsed onto a wing when a u/c leg failed. Almost that same week, a Technam had a very similar collapse.

 

The result? No damage to the Jabiru, but a new wing needed for the Technam.

 

I am not saying the Technam is badly designed, on the contrary, it is accurately designed and the Jabiru is over-designed.

Hey Bruce, I'd agree, spot on with the first half but when we get into composites there are too many variables within the manufacturing and ageing (UV, moisture, conductivity where CF is involved, and most of all, mould that gives off gases and breaks down the resin/fibre bond and/or matrix, environment that supports the development of osmosis, internal heat build-up in tropical climates causing degradation and much more), that it becomes necessary for composite manufacturers to over-build their products when new to ensure they will be serviceable at an age when they might reasonably expect to still be so. Given that composites supposedly don't fatigue in the traditional sense, some customers might expect their Jabiru (or similar) to still be 'perfect' when 50yrs old. But I ask you - would a Jab kept in a hangar in inland SA for 50yrs be the same as a Jab kept in the open, coastal, in north Qld for 50yrs?

 

Some may say 50yrs is asking a bit much, but hey, some Jabs are 30yrs old and more already and I don't see any of those owners respectfully wanting to drop their plane off at the local tip just quite yet.

 

Plenty of Sander Veenstra's aly/semi composite monocoque SV series planes still survive and are flying despite the aly components (spars etc) being subject to fatigue considerations - which he took well into account. It was his proudest statement that his planes would still be eminently serviceable in 50yrs if kept in hangars or trailers when not in use.

 

As far as pranging a wing into the ground - well you have to compare apples with apples instead of oranges ... my point being that if you take any aly rod of equal ultimate strength to a glassfibre rod and poke a tree with it, the aly rod will bend and remain bent, but the glass rod will deflect and spring back to shape. Under load in the air the two of them behave very differently also. The glass wing will give you a far more gentle ride in rough air by flexing the wing (more so with cantilever wings like gliders - did you ever see Ingo at race starts with wingtips near vertical?) but the stiff aly wing will get you out of trouble much more quickly if you need to pull up sharply for some reason, much like a monohull or cat in sailing, the mono spills wind by heeling, the cat not so much, so it responds much more quickly.

 

 

[coljones]

????????95.55

7.3

 

(a) states aeroplane limitations

 

(b) states engine limitations

 

These limits apply to all CTA & restricted areas not just over built up areas.

Bugger.

 

 

[Bruce Tuncks]

Good comments HIC. What happens is that the conservative assumptions add up with glass and the final structure is greatly over strength, so the only way out is to test-load. And yes, I agree about flexibility effects. This flexibility is what gives fibreglass its toughness as measured by the energy required to fracture.

 

Remember the Janus fatigue project? They had to double the applied loadings to get anything to happen. Gosh in 50 years of flying, I never saw wingtips deflected so much and this machine was doing it every few seconds, all day and week after week.

 

What happened was that the fatigue machine broke. Then they did some deliberately poor-quality repairs. Finally they got some action in that the metal embedded fittings began to come loose.

 

Fatigue in fibreglass is a furphy disseminated by those who have something to gain by frightening the scientifically challenged.

 

 

[turboplanner]

Fatigue in fibreglass is a furphy disseminated by those who have something to gain by frightening the scientifically challenged.

It wouldn't surprise me if this thread informs the CASA decision on whether to accept any change in the status quo.

Many people who own a boat don't need to be scientifically challenged when they find the floor or transom rotted out within a few years.

 

People who work in the FRP industry repairing FRP accident damage are not scientifically challenged when they cut out what appears to the owner to be perfectly good fibreglass panel.

 

The people who are scientifically challenged are these who have no idea of the equivalent to the difference between a horse and a blowfly.

 

Fibreglass is the product of melting marbles of glass and stretching them out into long and very fine strands almost hairs, which become flexible.

 

The fibres aren't much use floating around in the breeze by themselves, but will flex for ages.

 

"Fibreglass" is a name used by the scientifically challenged for a composite product called Fibreglass Reinforced Plastic, or Glass Reinforced Plastic.

 

To make this composite the fibreglass (the fine glass fibres) is laid on a surface and impregnated with a thermo-setting plastic resin to form a "laminate".

 

In this process, the fibreglass (the fine glass fibres) can take the form of strands (long length of fibres), chopped strand mat (fibres chopped into short lengths and matted together with an adhesive, rovings, a form of strands, woven rovings, which look like a piece of woven material, and a number of other forms.

 

The strength and flexibility is decided by the type of fibres used, the type of resin used, the method of laminating, the skill of laminating and the number of laminates.

 

The life cycle of FRP varies primarily with the type and quality of the resin, the laminating skill, and the force on the laminate thickness used.

 

While there are examples of highly flexible fishing rods and glider wings which may have lasted for many years, and vehicle bodies and some boats which have lasted for over 50 years, that life can be shortened down to as little as five years when a scientifically unchallenged academic gets his hands on some cheap resin and a ten dollar laminating kit.

 

 

[Bruce Tuncks]

Wow turbs, you have seen ROTTED fibreglass? That might be a world first.

 

Maybe you mean water ingress between laminations in a poorly made layup.

 

Please try to be clearer and more polite in your postings.

 

 

[djpacro]

Hey Bruce, I'd agree, spot on with the first half ......

Dunno about that. Strut generally doesn't carry the full vertical load from the wing - some vertical shear can be taken by the inboard spar attachments. Plus, a fitting factor is generally applied to bolted connections. Perhaps a good illustration but not "spot on".

 

Maybe 544kg = 1200lbs

Probably.

 

At least as far back as 1996 modifications have had to be approved by a person holding a CASA Instrument of Appointment under CAR 35.See image -

 

[ATTACH]62222[/ATTACH]

I did some CAR 35 work back then and I saw some silly attempts at showing compliance to BCAR Section S so I guess similar silly things going on with the self-certified LSAs but no-one is vetting it appropriately.

[Head in the clouds]

Dunno about that. Strut generally doesn't carry the full vertical load from the wing - some vertical shear can be taken by the inboard spar attachments. Plus, a fitting factor is generally applied to bolted connections. Perhaps a good illustration but not "spot on"........

Alright I shouldn't have said first 'half' - I was referring specifically to Bruce's figure for an AN4 bolt in single shear and the multiplication of that in double shear and for two struts, and if his assessment of the strut attach position and angle were correct then his numbers looked pretty close to the mark.

 

I couldn't verify it absolutely because I'm not privy to the actual strut angle, but based on online images it looks like about 55°. And the strut attach point looks somewhere close to the 45% half span which is quite close in compared to many designs, and obviously increases the load on the strut and reduces it on the fuselage spar attach points (I guess the % half span position might vary on the long-wing and short-wing versions), then allowing for say 10% tip loss, the strut might well be carrying most of the vertical wing load.

 

As you said, the strut doesn't 'generally' carry the full vertical wing load but then struts are often attached closer to the 60% half-span position. If that were the case, and with the same allowance for tip loss, then the strut would carry more like 2/3 of the total load and the fuselage attach points about 1/3.

 

 

[turboplanner]

Wow turbs, you have seen ROTTED fibreglass? That might be a world first.

Collins English Dictionary; synonyms for rot: "decay, break down, spoil, corrupt"

 

Maybe you mean water ingress between laminations in a poorly made layup.

No, I wasn't referring to that; the major cause is the resin used.

 

 

[Bruce Tuncks]

Good point djpacro. The strut would have to be placed just right for there to be zero up or down on the wing attach points. Just far enough inboard of 50% to allow for tip effects to balance out.

 

If I were designing a strut wing, I would like for the wing attach points to be carrying a bit of upload, mind you this would make the strut longer which is not good...

 

And Turbs, being scientific is not at all the same as being academic. The Wright bros were good scientists, better than professor Langley.

 

There are some good scientists posting on this forum who have not been to any academies.

 

I reckon this is the best site by far to get good technical comments on my ideas and proposals.

 

 

[dsam]

Remember the Janus fatigue project? They had to double the applied loadings to get anything to happen. Gosh in 50 years of flying, I never saw wingtips deflected so much and this machine was doing it every few seconds, all day and week after week.What happened was that the fatigue machine broke. Then they did some deliberately poor-quality repairs. Finally they got some action in that the metal embedded fittings began to come loose.

Bruce, I remember that Janus wing test-rig very well. I was in a technical media unit at RMIT filming that test-rig over many weeks. Your account matches my recollections too. We did a video called “Beyond 3000 Hours” as I recall... (probably still available at the RMIT library). We included some air to air footage (at Benalla) of another Janus doing loops to show natural flex, compared to the hydraulic test-rig. The airborne flex was similar, but less extreme compared to the test-rig load program.

 

 

[facthunter]

Your shear figures depend on the fit of the holes, and any gap between the structural elements Once there is some reverse barreling or a gapthe pin starts to get bent and the figures go to imaginary or your guess is as good as mine. Flexible structures need to be flexible over large % of the whole. distribute strain. Your strut concentrates (bending) load in one section of the spar which should be reinforced. It also has to work in reverse (negative "G") which gets complex, because it's a long thin column.. A strut makes a lighter structure but is triangulated and won't flex much. People don't like to see wings flexing but they pretty much have to. unless its a wire braced Bi plane. Nev

 

 

[Bruce Tuncks]

I have wondered about the negative G capacity of the Jabiru struts. There is a story ( I can't vouch for its truthfulness) about a guy ( south of Adelaide) who began doing loops in a Jabiru. Then he got a bit bored and started to do a bit of inverted at the top of the loop.

 

Inverted flight in a strut plane is something I never would contemplate, but if the story is true, then he got away with it.

 

Of course you can design compression struts, the Pawnee being an example. But those struts are a lot fatter than the Jabiru struts.

 

 

[facthunter]

You can get some high negative "G" in turbulence, without doing anything wrong.

 

. "Flimsy" struts have jury struts about 1/2 way along them to help prevent buckling in compression.. You have a few things to consider going negative. Porting of the fuel feed, engine oil going places you don't want. The Rotax will vent oil from the tank. Your carby bowls empty. IF your seatbelts aren't tight you hang in the straps with your bum not touching the seat and all the dirt floats up at you from the floor. You are way outside the envelope you should be operating in. you also may lose control and pull a lot of"G" recovering and overstress the plane. Think of the next person who may fly it as well. Nev

 

 

[Bruce Tuncks]

good points Nev. Yes, the Jabiru has an oil system which can't go negative. Nor can the carby.