Flying jab's over 40 degrees

[Guest brentc]

Alan has a good point about the strength loss not being linear.

 

Remember that if your car is left out (with the dog or kids in it) in temps around 30-40 degrees, the actual temp in the car can reach closer to 70-80 degrees.

 

If the temp in the cabin is not linear, then another 10 degrees outside, could equal another 30 inside. Perhaps this could contribute to the limitation.

 

 

[jetjr]

J200 sect 2.7.3

 

"maximum air temperature for operations, 40 deg C for maximum takeoff @ gross weight"

 

That is 544kg

 

J400 (identical Aircraft w/4 seats and VH reg) sect 2.7.3

 

"maximun air temperature for operations, 40 deg C for maximum takeoff @ gross weight"

 

That is 700kg

 

From this info seems the RAA rego and Raa pilots fail at 40 deg, not the aircraft

 

Seriously though when its 40 deg

 

1. Engine temps can go up but its manageable

 

2. Its rough and turbulent

 

3. Gliders love these conditions and are all up flying

 

Three good reasons to stay on the ground

 

JR

 

 

[Guest Baphomet]

I didn't miss your 'points' I simply chose not to acknowledge them. Didn't see the smilie? my post was intended as humor (and to fan the flames). I know I'm a very bad man .. completely irresponsible.

 

 

[Chird65]

Ok I have some statements:

 

From my understanding epoxies get stronger after heating (So long as they are held in position they will not be damaged.

 

It is only after 350 F / 180 C that they show signs of failure.

 

if this is so then the curring at above 38 54 celcius would make them stronger.

 

does anyone here (Pylon 500 maybe) have knowlege about this?

 

thanks

 

Chris

 

Some of this is answered above but is still valid to the original post as i goes to explain why the limitation.

 

 

[Alan]

Chris.

 

Most resin systems continue to cure for a fairly long time after the recommended time. A simple analogy is lots of little short molecules are present in the liquid resin, adding a catalyst causes these to cross link to form bigger networks of molecules and form a solid. Like musical chairs not all the monomer (little molecules) can find partners or a nich to bond onto, so these slowly diffuse through the solid until they meet up with an active site or another monomer. Heating increases the reaction rate and the diffusion rate so a higher temperature will help the cure. But go too high and the heat becomes destructive to the resin system.

 

The strength of a composite comes almost all from the fibres, the matric (resin) holds the fibres together and provides form and stiffness.

 

Alan

 

 

[Guest pelorus32]

Ok I have some statements:From my understanding epoxies get stronger after heating (So long as they are held in position they will not be damaged.

It is only after 350 F / 180 C that they show signs of failure.

 

if this is so then the curring at above 38 54 celcius would make them stronger.

 

does anyone here (Pylon 500 maybe) have knowlege about this?

 

thanks

 

Chris

 

Some of this is answered above but is still valid to the original post as i goes to explain why the limitation.

G'day Chris,

 

just a comment on your temperatures above. Talking to some of the composite engineers around here they make the point that the resin manufacturers have varying temperature ratings on their resins. These ratings also mean that other characteristics of the resin may change.

 

So for instance some resins have the kind of high temperature rating you talk about but are most useful in places like train carriages where fire may be an issue and are not so structurally strong in other circumstances.

 

I think therefore that it's important that we not second guess or specify arbitrary temperature capacity as we don't know what went into a particular aircraft and what circumstances it was tested in.

 

Bottom line is as so many others have said: the manufacturer's directions.

 

Regards

 

Mike

 

 

[BLA82]

Just for info

 

This is a link to the West System which is probably the best Resin sytem that gets used in composite boat building (I know not aircraft). It is a comparison chart and shows the different properties. Take a look at the differences between types as this shows what everyone has been saying that there is no standard answers for composites. And as Pelorus and others have said, Stick to the manual

 

WEST SYSTEM | Epoxy Resins and Hardeners - Physical Properties

 

 

[bushpilot]

J200 sect 2.7.3 "maximum air temperature for operations, 40 deg C for maximum takeoff @ gross weight"

That is 544kg

 

J400 (identical Aircraft w/4 seats and VH reg) sect 2.7.3

 

"maximun air temperature for operations, 40 deg C for maximum takeoff @ gross weight"

 

That is 700kg

 

From this info seems the RAA rego and Raa pilots fail at 40 deg, not the aircraft

 

Seriously though when its 40 deg

 

1. Engine temps can go up but its manageable

 

2. Its rough and turbulent

 

3. Gliders love these conditions and are all up flying

 

Three good reasons to stay on the ground

 

JR

Seems to me that a blanket "maximum air temperature for operations" alone is a bit weird. Should it not be a operations chart showing temps and altitude at the point of take-off? That is, 40oC at 2,800' (my strip) is going to have a different affect than 40oc at sea-level...

 

 

[slartibartfast]

That reminds me Chris - I checked your strip last Saturday. It looks great!

 

Did you catch my pass?

 

I'll have to drop in sometime soon.

 

Back to topic

 

 

[bushpilot]

Still off topic..

 

That reminds me Chris - I checked your strip last Saturday. It looks great!Did you catch my pass?

I'll have to drop in sometime soon.

 

Back to topic

Didnt spot you - but wife said a white a/c with green and yellow highlights did a couple of low passes.. But that is not yours....

 

 

[nong]

Hi Brentc. A C172 (145 horsepower) might get off shorter using flap when LIGHTLY LOADED. Please don't try this off a short strip at max. AUW or with an overload. At the higher lift off speed required, the flaps will likely create just enough extra drag to kill any meagre amount of performance that might have otherwise been available.

 

The C180 uses a similar airframe but with 230 horsepower and will happily drag flaps through the air to gain a shorter take-off roll even when overloaded, just ask any old ag pilot. Guess you need a bit of spare grunt to drag flaps on take-off.

 

Cheers

 

P.S. I hope that angry poster with no language skills drops the attitude before taking his family members and friends aloft in his Jab.....whether above or below 40 deg. c.

 

 

[motzartmerv]

Sorry, ive been away and havn't revisited this thread..

 

Seeing as it was a statement from me that that started a small war i'll explain where i got it from..

 

I was talking to a student of mine who is an engineer and physacist( spelling), we were discussing the design limitations of acft and the 38 max temp in the flight manual for the 160.. He told me that composites start to loose strength above 40 deg (depending on many factors.).. now, i inturpreted that (wrongly) that the max operating temp of the jab was related directly to this problem.. So i appolagise for "inferring" that this is the case..

 

That being said......

 

The flight manual states a max temp..

 

the takeoff/ landing charts go to 38 deg

 

Anyone who calls themself an aviator should stick to the flight manual..END OF STORY.. The flight manual isn't just some book you throw in the plane to impress pax.. Design limitations aren't imposed to be "interpreted" by so called aviators.. And if your in the habbit of ignoring the rules and operating outside of tolerances then you have no business in an aircraft..

 

I know a guy who was in a jab during testing and they pulled in exess of 6 g's... So does that mean its rated to 6 g's??...hell no...

 

So all you guys who got your backhairs up and want to fly at 50 deg... go for it..

 

But you ARE operating illegally.. Just remeber that..

 

cheers

 

 

[facthunter]

Angry.

 

Nong, (which you aren't) the guy feels threatened. OUR defence (if we need one) is that we are trying to get at the facts here, and NOTHING should stand in the way of that.

 

A lot of posters take things very personally, and I would suggest to them that they stand back a short distance and try to see the big picture.

 

All take off charts cover a temp. range with an upper limit. IF the chart stops at 38 or 42 degrees that is the end of the matter LEGALLY. Doesn't matter whether you are flying a Jab or an A-380, That's it. I read somewhere that Jabiru's are white for a good reason. If you painted them a dark colour the heat absorbtion would be much greater, and the problem (structural) would be more pronounced.

 

You have 2 major considerations here, the performance one, and a structural one (due to the materials characteristics) Since australia is a pretty hot place, it could be argued that a more realistic "upper temp limit" might be appropriate. Not just for Jabiru).. Nev

 

 

[Vev]

I thought this paper by the ATSB may be of some interest to Jab owners (and others) as it offers some insight into composite materials that are used in aircraft.

 

http://www.atsb.gov.au/publications/2008/pdf/AR2007021.pdf

 

Best regards

 

Jack

 

 

[bushpilot]

Only distantly related: Is there such a thing as a generic chart that shows the impact on a/c performance, or more simply, air density, of different (airfield) elevations and ambient tempuratures? That is, I'm interested in the offset affect of generally lower temps at higher elevations.. and whether that can be simply estimated without deferring to a particular a/c's performance charts..

 

 

[Guest pelorus32]

Only distantly related: Is there such a thing as a generic chart that shows the impact on a/c performance, or more simply, air density, of different (airfield) elevations and ambient tempuratures? That is, I'm interested in the offset affect of generally lower temps at higher elevations.. and whether that can be simply estimated without deferring to a particular a/c's performance charts..

G'day Chris,

 

this is an interesting question. There are a number of comments to make (most of which will be no news to you...I'm going somewhere so repeat the obvious stuff to make the story clear):

 

1. The accepted measure of "air density" is ISA - the International Standard Atmosphere - and ISA is 1013.2 hPa and 15 degrees celsius at seal level - leave aside humidity for a moment. That tells us how dense air is as a "standard";
    
    
   
2. There is a standard lapse rate of 2 degrees C per 1000' accepted as ISA. So ISA for 2000 feet is 11 degrees C;
    
    
   
3. To calculate density altitude you calculate pressure altitude and temperature and see how it differs from ISA;
    
    
   
4. Most a/c POHs have a table in them which gives performance for a given range of conditions - usually a range of pressure altitude and temperature pairs - a short cut to density altitude;
    
    
   
5. The data that is used to build up these tables is based on a single set of tests which are then extrapolated using a series of factors. In other words take off distance for a known set of conditions is factored to other conditions which aren't necessarily tested.
    
    
   
6. Each aircraft may behave differently at different density altitudes but the trends will be the same.
    
    
   

 

 

 

What that means is that you need the density altitude - or PA and temp - in order to enter the tables which your manufacturer has supplied. If they haven't supplied them then I'm not sure you can just use some set of factors and be sure that it's OK _for your aircraft type_.

 

Long winded sorry.

 

Regards

 

Mike

 

 

[djpacro]

... and the higher the altitude the closer to the aircraft ceiling so any variation with temperature can differ markedly from one aeroplane to another. i.e. if, say, the rate of climb is 500 fpm at altitude the effect is much less than if the rate of climb is only 100 fpm. There are generic methods for doing the fairly straightforward sums but I have seen so-called experts get it wrong.

 

Regardless, the simple rule is not to extrapolate performance figures in the flight manual.

 

 

[Yenn]

It looks as if the temp. we are talking about here is air temp. If Jabiru's cannot be flown above an air temp. of 40 degrees I fail to see how Jabiru can fly them from Bundaberg in Summer. The average shade temp in Bundy would be 32 degrees in Summer and the air temp much higher.

 

As the density of air changes in accordance with Boyle's law it shoulld be easy to work out density for different temps and even if the POH doesn't go to the temp you want to fly at you can get a density height and if you have enough runway it should be OK to fly, bearing in mind that the plane may think it is at 8000' even though it is at sea level.

 

 

[Guest pelorus32]

It looks as if the temp. we are talking about here is air temp. If Jabiru's cannot be flown above an air temp. of 40 degrees I fail to see how Jabiru can fly them from Bundaberg in Summer. The average shade temp in Bundy would be 32 degrees in Summer and the air temp much higher.As the density of air changes in accordance with Boyle's law it shoulld be easy to work out density for different temps and even if the POH doesn't go to the temp you want to fly at you can get a density height and if you have enough runway it should be OK to fly, bearing in mind that the plane may think it is at 8000' even though it is at sea level.

Not sure I agree Ian. I think that it's wise to heed Dave's words - You may end up with and a/c without the ability to climb at all - at high DAs.

 

Regards

 

Mike

 

PS as an aside the "shade" temperature refers to the apparatus that the thermometer sits in - looks like a little white painted house with wooden louvres around the outside and a little roof. If you hear a temperature reported or predicted it's a "shade" temperature.

 

M

 

 

[LEJ]

Hi All, all comments makes very interesting read. My question is, if the temperature is say 40 degrees, the ground (if it is tar) plus cabin temperature would be a lot higher.

 

Anyone could comment on the safety of the fuselage and electronic component should the aircraft remain outside? An example if I may start, in the RAAus mag last year, there was a great story on how to maintain your Rotax engine and sometimes, to a newbie like myself, high tension cable without insulation might be touching the Rotax engine which in turn might cause wear and tear at a great rate, without me noticing it. Is there something that we should be checking on the Jab with such high temps?

 

 

[jcamp]

Only distantly related: Is there such a thing as a generic chart that shows the impact on a/c performance, or more simply, air density, of different (airfield) elevations and ambient tempuratures? .

Pre FAR, CASA, RAA nice POH etc there was the Koch Chart (actually nomogram) eg

 

NAPPF Density Altitude

 

at result 1 of 408

 

 

[bushpilot]

Pre FAR, CASA, RAA nice POH etc there was the Koch Chart (actually nomogram) egNAPPF Density Altitude

 

at result 1 of 408

Some real interesting tips in that link... For instance, I wonder why: "If high humidity does exist, it would be wise to add 10% to your computed takeoff distance and anticipate a reduced climb rate."...

 

And that 'Koch chart' is very telling... From that, off my 2,800' elevation strip last Sunday, with 85oF temp., my t/o roll would have increased by about 50% and climb rate would have been down by 30%..

 

Also, Mike, thanks for your "long winded answer"; it's responses like yours that make these forums so valuable...

 

Cheers,

 

Chris

 

 

[jcamp]

I wonder why: "If high humidity does exist, it would be wise to add 10% to your computed takeoff distance and anticipate a reduced climb rate."...

 

 

Humidity is (crudely) when 18 gm of H2O replaces 29gm of N2+O2 in a certain volume, all this gets a bit complex but what counts is absolute humidity which is a function of relative humidity (what BOM report)and temperature (the temp bits comes from higher temp=higher vapour pressure of H2O, roughly doubles every 10C reaching 1013mb @ 100C)

 

 

 

For airframe

 

Higher absolute humidly=lower density of air=less lift

 

 

 

For engine

 

Higher absolute humidly=lower charge mass+less O2=less power

 

 

[djpacro]

.. there was the Koch Chart (actually nomogram) ..

Thanks, I'd forgotten about that (must be 40 years since I last saw that). As it says:

This chart indicates typical representative values for "personal" airplanes.

One obvious assumption is the ceiling of around 14,000 ft (i.e. where rate of climb is zero) so at that density altitude the percent increase in take-off distance would be infinity. It should work pretty well around this part of the world for those types which fit the assumptions (notwithstanding my earlier comment about the rule of not extrapolating AFM data and I haven't checked any figures with POH data). Some years ago I used to fly a 172 at 85 deg F and 7000 ft elevation - from memory, the figures are in the ballpark.

 

From that, off my 2,800' elevation strip last Sunday, with 85oF temp., my t/o roll would have increased by about 50% and climb rate would have been down by 30%..

I wonder if my monitor is distorting the chart - I got about 70% increase in take-off distance and about 45% reduction in rate of climb.

[Guest pelorus32]

Thanks, I'd forgotten about that (must be 40 years since I last saw that).

Entirely off topic: The last time I saw it was in the car park of La Sciampagna Restaurant (in the countryside of southern Italy) after a very full lunch in early January. One of the guys had just come back from a tour of duty in Afghanistan and they were discussing the DA for Kabul in the summer. It was on a little laminated card.

 

I wasn't much worried about the DA on this particular day - much more concerned about the effects of the lunch and its beverages as they all made their way to the little airstrip half a kilometre up the road to fly!!

 

As an aside, the technical guys present were pretty cautious about using it in any situation which was critically limited.

 

Regards

 

Mike