Flying jab's over 40 degrees

[slartibartfast]

The Good Oil

 

I spoke to Rod at Jabiru.

 

He assures me that the load testing was done at 54 degrees Celcius, and he has no problem with people flying their planes at that temperature.

 

The 38C was a hang-over from the certification process.

 

He points out that in Australia, people have to be able to fly at over 38C. In many places, there wouldn't be many days you could go flying otherwise.

 

See how we can get to the bottom of a question without vitriol?

 

Rod was also concerned about forums in general, because he says anyone with a beef can start or perpetuate a myth, and it is a hot-bed of misinformation (paraphrased).

 

We try to be very careful about accuracy, and we have a lot of very experienced people in many fields to help that objective.

 

However, you, the reader, also have to check information for yourself where possible.

 

We now return you to your regularly scheduled reality.

 

Ross

 

 

[Guest ozzie]

We now return you to your regularly scheduled reality.

Ross

Aww crap! i was hoping for a day of fantasy

 

 

[Matt]

Interesting comments Ross regarding Rod's comments. As a pilot, the flight manual is the bible for safely operating the aircraft within prescribed limits. Operating the aircraft outside the prescribed limits exposes you to risks you are no longer aware of, trained to manage etc.

 

Someone above mentioned insurance, I'd hazard a guess and suggest that any incident occuring where the ambient temperature was above 38 degrees (the flight manual stated operating limit...and apparently the certified limit) would result in a negative response from an insurance company...regardless of what the aircraft may be "capable of", what's important is what it's approved and certified for.

 

 

[slartibartfast]

That's true Matt.

 

Maybe we aren't at the bottom of the question yet?

 

I'd hate to have that argument with the insurance company.

 

Rod said some more about where the 38C figure came from, but I couldn't trust myself to report it accurately, so I won't.

 

It does leave you with a plane (eg. 160,170 or 230) where the manual says 38C but the factory says 54C.

 

The J120 manual doesn't have anything to say about ambient temperature.

 

He did say that if the wings start to droop, fly inverted until they look right again.

 

PS - no he didn't

 

 

[Guest brentc]

I'll stay on the ground if the temp is over 38. Not only because it will probably be an uncomfortable flight, but rather if I crash into someones house because my engine overheated I don't want fingers being pointed at my finances for those I care about that are left behind!

 

 

[Guest Baphomet]

So the long and short of it is, despite the way he framed his response, Steve was right. According to the manufacurer, the aircraft is safe to fly at 54 (however uncomfortable it may be). Re insurance companies, RAA aircraft don't have black box flight recorders to log temp, so proving the OAT was or wasn't a nominal figure is going to be problematic/impossible. (this means of course, that Jab owners are going to have to fit their aircraft with certified calibrated temp probes and data loggers to satisfy the needs of their insurance company!)

 

 

[Barefootpilot]

Do the J-120 have take off and landing charts? And if so what is the max temp that they go to? Thats the way we are limited in most GA aircraft I have flown. If you don't have performance figures you are in no mans land and I would suggest as others have that the insurance company would treat you as a test pilot and wish you the best of luck. But hey if its your aircraft and your life go for it just don't complain to anyone when you come back and the wings have a new sweeping look.

 

 

[Guest Ken deVos]

Data logging

 

Dynon EFIS fitted to most Jabs can now log data...

 

NEW INTERNAL DATA LOGGING Also included in version 5.0 release is the addition of EFIS Internal Data Logging, which stores readings for all primary flight instruments for later flight analysis. Data readings can be configured in 1-, 3-, 5-, 10-, 30-, and 60-second intervals. Data logging storage limit is at least ½-hours at the 1-second interval and up to 40 hours at the 60-second interval.

 

 

 

 

 

 

 

 

[slartibartfast]

So the long and short of it is, despite the way he framed his response, Steve was right.

Yep - but accidentally.

 

His argument that it wasn't in his manual didn't quite address the fact that it is in all the other manuals and they are all made the same way with the same composites.

 

It made me want to check with the manufacturer, and I don't even fly them very often.

 

Great question Bruit2

 

 

[slartibartfast]

Do the J-120 have take off and landing charts?

No Adam. The Take Off and Landing Distance Chart, and the operational restrictions sections are entirely missing from the manual for the J120.

 

They appear (and state 38C) in the J160, J170 and J230 manuals. Possibly the others but these are the only ones I checked.

 

Ian reports that Steve Bell (RAAus Tech Manager) states that it is illegal to fly a Jabiru other than a J120 at higher than 38C ambient temp because that's what they were certified at and that's what's in the POH.

 

I just tried to confirm, but Steve has gone home early today.

 

The thot plickens.

 

 

[Admin]

it is illegal to fly a Jabiru other than a J120 at higher than 38C ambient temp because that's what they were certified at and that's what's in the POH.

Ross, my apologies as perhaps I should have said:It is "technically" illegal to fly the Jab (non 120) at >38deg OAT as that is what it was certified at and is stated in the POH which is part of the aircraft's legal documentation.

 

 

[Admin]

This is how an insurance company will catch you out:

 

Because they are cold-blooded animals, crickets' metabolic rates are closely linked to the temperature of their surroundings. An interesting side-effect of this is that you can calculate air temperature based on the number of times a cricket chirps per minute: just divide by 4 and then add 40 to get the temperature in Fahrenheit. So 120 chirps per minute translates to 70 degrees F.

 

 

 

[BLA82]

I'll stay on the ground if the temp is over 38. Not only because it will probably be an uncomfortable flight, but rather if I crash into someones house because my engine overheated I don't want fingers being pointed at my finances for those I care about that are left behind!

Excellent point Brett:thumb_up:

 

 

[Tomo]

This is how an insurance company will catch you out:Because they are cold-blooded animals, crickets' metabolic rates are closely linked to the temperature of their surroundings. An interesting side-effect of this is that you can calculate air temperature based on the number of times a cricket chirps per minute: just divide by 4 and then add 40 to get the temperature in Fahrenheit. So 120 chirps per minute translates to 70 degrees F.

 

The only serious problem with that analogy is... I never hear the crickets during the day....i_dunno and who cares what the OAT is at night because your not flying then...

 

:ah_oh:

 

 

[BLA82]

and who cares what the OAT is at night because your not flying then...:ah_oh:

Oh can't I Tomo, my manual doesn't say I can't:laugh:

 

PS Just kidden

 

 

[Tomo]

Now on a more serious note...:big_grin:

 

What if the acft is sitting out side in the middle of the day with the sun bearing straight onto it, then the surface of the wing is going to a lot lot more than 38degs...?

 

on our exposed deck which is painted (:yuk: < thats the colour!! a tad darker actually) on a 35 degree day can get up to 75-80 degrees with the sun straight on it... so what we really need is surface temperature gauges so we know the temp of the surface:big_grin: rather than looking at the OAT and saying oh it's only 35degrees lets go flying, when really the top of the wing you could cook bacon and eggs on....??

 

I could be doubling up a bit on things, but that's my understanding...:big_grin:

 

 

[BLA82]

Now on a more serious note...:big_grin:What if the acft is sitting out side in the middle of the day with the sun bearing straight onto it, then the surface of the wing is going to a lot lot more than 38degs...?

 

on our exposed deck which is painted (:yuk: < thats the colour!! a tad darker actually) on a 35 degree day can get up to 75-80 degrees with the sun straight on it... so what we really need is surface temperature gauges so we know the temp of the surface:big_grin: rather than looking at the OAT and saying oh it's only 35degrees lets go flying, when really the top of the wing you could cook bacon and eggs on....??

 

I could be doubling up a bit on things, but that's my understanding...:big_grin:

To true Tomo,

 

I know on the last boat I built I had to send two test panels of a hull and deck sample to the certifier. One painted and the other not. I was terribly surprised at the difference. With light concentrated on it the unpainted had a surface temp of 7deg higher than OAT but the painted came back at 18deg above OAT. In fact the certifier made us change the paint colour and brand otherwse the resin manufacturer (WEST EPOXY SYSTEM) would void their material data, therefore voiding the certification of the boat.

 

 

[Guest brentc]

Ross, my apologies as perhaps I should have said:It is "technically" illegal to fly the Jab (non 120) at >38deg OAT as that is what it was certified at and is stated in the POH which is part of the aircraft's legal documentation.

Ian not to be personal in any way however there's really no technicality about it. It's outside the certification so you would be flying illegally, voiding insurance and the privelages of your licence! For those that think it would be hard to prove, the forecast and large number of BOM weather stations out there would say otherwise!

 

Think of this example.

 

When I did my PPL test the ATO asked how much flap to use in the 172 on takeoff. I said 10 degrees. The ATO then asked for me to find the appropriate reference in the POH to the 10 degree setting. It's not there. Everyone knows that the 172 takes off shorter with 10 degrees and most of us do it, but it's not in the POH (or atleast not for this model).

 

He then said 'under whose authority would I use 10 degrees?' I had no answer so he explained that I would be liable if I crashed on takeoff and injured or killed my passengers. He was 100% right and as Matt says the POH is the bible!

 

 

[Guest Baphomet]

Another observation: Burt Rutan, the man with more composite manufacturing experience than most of us will see in several lifetimes, has his operation based in the Mojave desert!! (In May the temperature will begin to climb in excess of 100°F and continue into October). He obviously considers those temps to be a real problem;)

 

 

 

[Guest Andys@coffs]

your missing the point..again

 

Its nothing to do with whether the composite are or arent going to cope at a particular place, at a particular altitude and particular temperature...... Its all to do with working within the documented limitations that are clearly published in all but the J120 POH. If we can ignore the MAX OAT temp limitation then why cant I also ignore the icing one, or the one that says I should have fuel reserves..... Each of those other limitations are sacrosanct and anyone would rightly call me an idiot for exceeding them. So why is the published Max temp any different? In reality there are many published maximums that I, for whatever reason dont agree with. For example 50kmph in my street is too slow Im better than average, in my humble and uninformed opinion and as such I should be able to ignore that limit....

 

With regards as to why the published max temp is what it is..... Again irrelevant if the manufacturer wants to up issue and revise or remove that limitation then let them do that and in turn I'll comply with the new max temp, or if its removed altogether then the engine operating temps will become the new determiner of when I can effectively fly.

 

So whether someone is working with composites in the desert or not is just BS in the context of this discussion. BTW perhaps their in the desert working composites not because of the temp but because of humidity.... anyway whatever!

 

Andy

 

 

[Yenn]

Where does this temperature come from? I assume you are referring to the temp. used by the met office, which is shade temperature.

 

I don't know wbout anyone else, but I can't fly in the shade on a sunny day, and 40 deg would be cool here on the ground in summer. Maybe we should all fly only at 5000' where it would be cooler, but fuel may be a problem.

 

 

[bushpilot]

Do the J-120 have take off and landing charts? And if so what is the max temp that they go to? Thats the way we are limited in most GA aircraft I have flown. If you don't have performance figures you are in no mans land and I would suggest as others have that the insurance company would treat you as a test pilot and wish you the best of luck. But hey if its your aircraft and your life go for it just don't complain to anyone when you come back and the wings have a new sweeping look.

I agree 100% with this observation. If the charts dont cover a higher temp. bracket, then surely the assumption is: 'dont operate in that range.'

 

 

[kevinfrost]

I have viewed this thread on the risk of flying the Jabiru in high temperatures with great interest. I"ve flown the Jabiru from the KFM powered onwards. I"ve flown & seen the early Jabs flown overloaded and in temperatures in excess of 40 degs on many occasions. Those same A/C have amassed around 5 to 6 thousand Hrs in less than ideal conditions ( training ). I know of none that have failed structurally in the air.

 

We are aware that fibre reinforced plastics and the like will reduce in strength with increase in temperature, how much depends on type of resins, fibre, vacuum, pressure, etc. I operated a crash and fibreglass repair business during the advent of the fibreglass gliders. At first it was a life of 2000 Hrs then 3000 then 4000 and so on. Those gliders are still flying after spending many Hrs above 40 deg on the deck.

 

On very hot days we launched taking it easy not to over load pick up a little alt, a

 

short while later it was back to max stength. If you"re flying an A/C that has only been max tested to 4 Gs you could be in deep S---t, 7 or 8 and you'.ve got a better safety margin. Some manufacturers don't like to talk about it. The design will have a lot to do with it, The 160, 170 and 200 series of Jabs with the rib wing design I would think would have less strength than the foam core of the 120, the internal heat of the wing would be considerably less on the foam core design. And the type of paint, that's another story.

 

Imagine what is trying to happen to a wing on the metal A/C we fly in RA,To keep in the weight range the metal is thin and you will see some that look like they've got a bad case of cellulite on very hot days. I wonder what is happening to the laminar flow on take off. You can hear some of them tin canning in the sun. It's no wonder some of the maufactured RA A/c are having to have rivets replaced in some skin areas after a relatively short time in service.

 

I'm not bagging any A/C in particular, I love any A/C I can get my bum in, after calculating the risk that is.

 

If you're not sure or it scares you, keep out of it or at least talk to somebody who has had experience in it. I do not suggest you fly overloaded A/C or take the risks mentioned above. It's good to see we have the extra weight now compared to earlier days, much safer. The heat! well, commonsense.:thumb_up:

 

 

[Alan]

Heating or soaking composites

 

I would go with Brentc on this; to go outside the conditions in the POH is I believe operating illegally, even if demonstrated and indicated safe verbally by the manufacturer it is still a "no go" area. I think the only way out of this dilemma is to obey the POH or get Jabiru to issue an amended POH.

 

I ask a similar operating question about my J230 seat loading being limited in the POH to 85Kg and the ramifications of exceeding this relatively low limit.

 

Just a quick point on composite materials and heat. We exposure test aircraft composite materials and structures here in FNQ (Not commercially, so I am not advertising). and yes strength is lost with temperature increase, but not linearly, there is a transition point that depends on the resin system, weave, direction of loading etc. It is more realistic to think of the composite having a recoverable loss of modulus (stiffness) with temperature increase. Interestingly many composites actually increase in strength with heating and time as any left over monomer in the resin cross link.

 

Moisture absorption also effects the modulus of many plastics. Hence being in Innisfail for this testing!

 

Alan

 

 

[Guest Brett Campany]

When I was flying for Surveillance Australia out of Broome, we had a temp limitation of 38 degrees C for the BN2B Islander (the Bongo). We were refuelling at Karratha and the temp read 42 degrees.

 

Now the operating manual for the Bongo stated that an engine failure during take off at a temp above 38 C would result in the other engine not being able to take the load of the aircraft....therefore we'd crash.

 

That was good enough for me.

 

The other reasons were that there's no aircon in the Bongo on the ground and the cabin reaches a balmy 45 - 50 degrees C and if we're stuck on the ground for a period of time waiting for other aircraft then we'd all melt like the wicked witch of the west.

 

So we waited it out till we could fly home.

 

Thos are pretty good reasons as to why you don't fly ANY aircraft, composite or metal, above the recommended temperature ranges.