Jabiru experience

[Nobody]

here are the speed numbers from the POH for both the J-160 and J-170. Note the fairly significant difference between the two with regard to both maneuvering and stall speed. Also not that the J-160 number are for its MTOW of 540kg. The stall speed will increase by approx 5.5% in going from 540kg to 600kg.

 

 

 

[Guest Andys@coffs]

know a chap that reports loading his 160 to 600+, said the only difference to flight was longer take off, slower rate of climb, nothing else changed. Jab figures quoted must be conservative, erring on the side of caution.Interesting to note tho........600 in a 160, quite doable. ( but illegal )...........so's 65 in a 60 zone, and we've all done that.

Hmm Test Pilot territory........ Nothing changes right up until the point it does......of course whether he will survive that transition is in the hands of God.....bit like being bitten by a taipan and concluding after a minute that these snakes aren't apparently dangerous..........

 

60kg above stated MTOW doesn't sound like much but when aerodynamic loads of +4G are applied that of course turns into a load equivalent to 240kg on the ground.....not insignificant.... Jabiru on their website say the structure has been ground tested to +7G but only air tested to 3.8G...... If you add 60kg then ignoring the legal aspects that testing effectively reduces to 3.4G..... So what is an acceptable point of reduction???

 

 

[Russ]

lastly.........know another chap, built several jabs, has the ear of jab........stated " load em up" if the wheels get off the ground, then it will fly ok. This guy goes back many many yrs, almost to the birth of jab.

 

 

[DrZoos]

Im guessing its too late, once you find the actual point of failure, or stall, or lack of runway to tell anyone about it..... so dont be the first

 

 

[fly_tornado]

lastly.........know another chap, built several jabs, has the ear of jab........stated " load em up" if the wheels get off the ground, then it will fly ok. This guy goes back many many yrs, almost to the birth of jab.

Are you saying the Jabiru factory was unofficially encouraging pilots to fly over the MTOW?

 

 

[jetjr]

Read it again FT, it wasnt jabiru who stated it but a guy who had built a couple

 

 

[Russ]

FT.........

 

Not at all........not even alluding to that.

 

just 2 reports of heavier weights and their outcomes. Just what happins if over weight and in challenging conditions / etc etc............i have no answers. Pilot skill etc, would be another factor to factor.

 

maybe..................weight limitations were set by casa, regardless of crafts abilities.........maybe ???

 

 

[Geoff13]

This conversation won't do much to help the increase in MTOW argument.

 

The problem with this is if someone is willing to break one regulation no matter what the reasoning behind it then they are likely under the right circumstances to break others.

 

A couple of the posts above scream cowboy to me. 10% overweight. Hell I wouldn't drive a semi that was 10% over.

 

 

[fly_tornado]

FT.........Not at all........not even alluding to that.

 

just 2 reports of heavier weights and their outcomes. Just what happins if over weight and in challenging conditions / etc etc............i have no answers. Pilot skill etc, would be another factor to factor.

 

maybe..................weight limitations were set by casa, regardless of crafts abilities.........maybe ???

I am totally ok with jabiru giving a wink and nod to MTOW limits, how does the engines cope with the extra work load? Bet they must go through a few exhaust valves

 

 

[facthunter]

Stay on the medication ft. That has to be one of your most inspirational posts. Nev

 

 

[jetjr]

Overweight operation is a significant issue in RAA, small GA and the surprisingly the trucking industry.........

 

Like self maintenance it doesnt seem to itself be the cause of many problems unlike HF, dopey acts and fuel problems.

 

Not suggesting at all that it is OK to fly heavy but getting weights perfect then running out of fuel isnt a good outcome and more prevalent than structural failure from overloading.

 

Understand the 544kg and 600kg are not aircraft structural limits but catagory limits to meet stall speed. Hence the debate for higher MTOW and stall speeds.

 

Consider the similar aircraft - J430 is certified for 4 seats and 750kg MTOW elsewhere in the world with almost no changes

 

 

[fly_tornado]

Consider the similar aircraft - J430 is certified for 4 seats and 750kg MTOW elsewhere in the world with almost no changes

a wink and a nod is all you need

 

 

[jetjr]

What?

 

Many certified in RSA, more than Cessna.

 

 

[Nobody]

In many ways I think that this thread explains some of the engine issues that Jabiru have had. For some reason many of the owners of them feel that the weight limits in the POH don't apply. I wonder if people apply the same logic to the CHT limits?

 

I am sure Jabiru would have increased the weight limit of the 160 to 600kg if they could.

 

 

[Geoff13]

Consider the similar aircraft - J430 is certified for 4 seats and 750kg MTOW elsewhere in the world with almost no changes

What changes? And how do those changes affect safety of the aircraft at those increased limits?

 

 

[Ada Elle]

Jabiru certified the 160C under CS-VLA which has a 750kg class maximum limit, but the aircraft itself only has 540kg. So, in VH guise, the J160C is still limited to 540kg (under VA515 - I don't know if there is a later certification). This is not a CASA requirement - Jabiru themselves have elected to use the 540kg MTOW, for their own reasons (which I can hazard a guess at).

 

Also, be wary - CAR 235 prescribes 50 penalty units for flying overweight, but I'm not sure if flying overweight violates CAO 95.55 (in which case it would be up to 2yrs in prison for flying an RAAus rego plane overweight).

 

 

[jetjr]

Who said weight limits dont apply and whats that got to do with engine management? Im sure its illegal and a fool to do it.

 

Id suggest running a full suite of flight tests for a few VH reg C models (are there any?) wouldnt be worth the effort. Remember the max limit in all of RAA at the time of certification was 544kg

 

The joyful reality of certification means full restart to process to upgrade or change anything.

 

They cant raise MTOW anyway under RAA due to maximum stall speed of the wing.

 

Crossing back to larger airframe - Changes for 750kg include larger wing bolts....now an SB for all Jab aircraft at certain life.

 

 

[Geoff13]

just about says it all doesn't it.

 

 

[Ada Elle]

They ran the flight tests - how else do you think they were certified to CS-VLA?

 

The 160C is certified in the Primary Category, which allows for up to 61kt stall speed, and 1225kg. That Jabiru did not elect to increase the MTOW despite the certification category allowing for it is telling.

 

(Again, there are reasons for this that I can hazard a guess at.)

 

 

[Oscar]

They ran the flight tests - how else do you think they were certified to CS-VLA?The 160C is certified in the Primary Category, which allows for up to 61kt stall speed, and 1225kg. That Jabiru did not elect to increase the MTOW despite the certification category allowing for it is telling.

 

(Again, there are reasons for this that I can hazard a guess at.)

The J 160 C is certificated (TCDS VA515), not certified. The continual misuse of the two terms is not a matter of semantics, it goes to the root of responsibility for the airworthiness of the aircraft and unless the difference is recognised, then assumptions of all sorts that are incorrect will continue to proliferate. Misuse of the two terms indicates a fundamental lack of knowledge of the certification / certifying regime.

 

That TCDS was issued under CS-VLA which requires VSo of 45 kts. and an MTOW maximum of 750 kgs. Primary Category is NOT a standard of itself, but an operating regime dependent on the basis of the certification. You have taken the MTOW allowable in FAR 23.49 as the 'standard'; what you have ignored or not understood is that certification under different standards ( CS-VLA, BCAR-S, FAR 23) are not 'pick-n-use', but only ONE standard is allowed to be used for certification.

 

The stall speed limiting factor for the J160 is elevator power (and in fact, the MTOW for Jabs. back to the LSA55 has been mostly a function of elevator authority, not structural limitations.). The J160 has an elevator span of 2350, the J170D has an elevator span of 2660, hence a greater area and therefore greater elevator authority.

 

I would find it useful if you would indicate the 'reasons for this that I can hazard a guess at'. Prima facie, in the context you envisaged ( incorrectly), that is a statement of conviction that Jabiru has an 'issue'/'issues' which have impacted on its 'election' to increase the MTOW 'despite the certification category allowing for it, which is telling' (a nonsense statement, but one that I believe you, in fairness to Jabiru, should substantiate).

 

Perhaps you have information/insight that was not available to the qualified aero-engineers and test pilot responsible for the certification of the J160C, and the manufacturer. Please, share this with the members of this site.

 

 

[Oscar]

Who said weight limits dont apply and whats that got to do with engine management? Im sure its illegal and a fool to do it.Id suggest running a full suite of flight tests for a few VH reg C models (are there any?) wouldnt be worth the effort. Remember the max limit in all of RAA at the time of certification was 544kg

 

The joyful reality of certification means full restart to process to upgrade or change anything.

 

They cant raise MTOW anyway under RAA due to maximum stall speed of the wing.

 

Crossing back to larger airframe - Changes for 750kg include larger wing bolts....now an SB for all Jab aircraft at certain life.

JJ - I believe the change to the 5/16" wing bolts is a fatigue life limit (you can stay with 1/4", but they have to be replaced at 2000 hours); did I miss something that suggested that by changing to 5/16 you could increase the MTOW? The lift-strut end fittings are likely to be found to be the fatigue-life-critical elements ( I believe Alan Kerr is working on this at the moment).

 

The limiting factor for stall speed - depending on configuration and weight - for Jabs. usually comes down to elevator authority, though it's a juggling act there: to get into the Euro 'UL' category, Jabiru had to both extend the wing area and the elevator moment arm and authority ( the 'UL' or for the USA, the 'Calypso' model). The universal acceptance of the ASTM VLA standard has gotten around the disparate standards world-wide, but it's not without its problems.

 

 

[Ada Elle]

My guess is that Jabiru management saw the available standards, picked whichever one was easiest and cheapest to get to market in the most markets available, and went for it. The second guess would be that, even if Jabiru could meet the stall speed etc standards of FAR23, that meeting the rest of the standard would have been Too Hard.

 

I don't know if CASA ever went through with having a full set of CASR Part 26 standards - the CASR are fairly lacking in that section. I've taken the MTOW and stall speed from 21.024 as the Primary Category limits.

 

If elevator authority limits the steady state level flight speed of Jabirus, why not re-test them at a higher MTOW and restricted CoG range? (with a loading chart to represent the allowable CoG and weight limits).

 

 

[jetjr]

No you didnt miss anything, cant raise MTOW, as you said its the stall speed which limits. it not a structural limit.

 

I was indicating (poorly) that this is the extent of changes to run 150kg more weight. Only ever talking about larger fuse models where there is a experimental rated to higher weight to compare.

 

I believe all big factory Jabirus now run bigger bolts, mine were upgraded just because they were out a couple of years ago.

 

The point here is that the MTOW limitation is not structural but related to stall speed and therefore has little to do with safety as being implied.

 

Without doubt its the rules we operate under and breaking them is illegal. Thats a different debate to it being unsafe.

 

The details discussed provides basis for the push for altering stall/MTOW limitation currently in place to something more appropriate.

 

Retesting costs money (lots) and they probably dont sell any 160 to VH market and would be investing in a old model. All this was done before 170 was even developed.

 

 

[Oscar]

My guess is that Jabiru management saw the available standards, picked whichever one was easiest and cheapest to get to market in the most markets available, and went for it. The second guess would be that, even if Jabiru could meet the stall speed etc standards of FAR23, that meeting the rest of the standard would have been Too Hard.I don't know if CASA ever went through with having a full set of CASR Part 26 standards - the CASR are fairly lacking in that section. I've taken the MTOW and stall speed from 21.024 as the Primary Category limits.

Yes, they are the LIMITS. However, if you apply intelligent deduction to an examination of 21.024 (b) (i) you would realise that the CS-VLA MTOW is ' the applicable airworthiness requirements', since that is the basis of the J160 TCDS.

 

 

[DrZoos]

dont forget the stall speed is there for a very good reason...it helps improve survivability in aircraft that traditionally had little if any occupant protection...

 

My how things have changed...Im not arguing for or against a change in stall speed, but I would suggest the Jabiru offers SUBSTANTIAL occupant safety to when they 45 knot stall speed was chosen for the reasons it was..

 

At some point in the future airbags or airbag seatbelts will make it into our category and possibly even occupant safety cells, and ballistic chutes will become cheaper and more common..at which point surely the 45 knot speed limit would need to be reviewed upwards for some aircraft.

 

Whether we like it or not new materials, increases in living standards and incomes are adding higher end aircraft into our category. This will continue on mass as the older generation are gradually replaced by Gen X and Y who many lack the ability or desire to homebuild and would prefer or need to buy factory built .