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LSA IN TURBULENCE


Guest Bruit2
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I find that the LSA can be frighteningly difficult to handle in turbulence. The reason I'm posting is to ascertain whether this is normal or not. I fly frequently across the hay plain.

 

Cheers Rob.

 

 

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Guest Graham Lea

In summer, when I fly out west I do so before 11.00 am if possible and high (like >5000). After around 11 I go to as high as possible. Dubbo - Lightning Ridge or Bourke I use 7500 for safety reasons. Winter is fine for going low. All or most a/c have this problem out west.

 

 

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I am not trying to be facetious but maybe you should think about doing a gliding course.

 

Most pilots could probably add 5 knots to their average cruise speeds in a lot of the above country if they knew how to use the rough [?] thermals and thermal streets or cloud streets and avoid the worst of the heavy sink areas that really slow you down as you try to maintain altitude.

 

Although if you are below 3 thousand or perhaps below 5 or 6 thousand feet on a very hot day in those areas, you may be flying in a super adiabatic layer and that is bloody rough, hot and horrible and that is in a glider let alone a power aircraft barrelling along in an attempt to maintain a fixed course.

 

 

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Yes, I can assure you that this IS normal. The higher the better in summer / hot days will get you above the thermal activity. The LSA can be a REAL handful in turbulence, especially when landing on a bumpy day, you really have to chase the controls all over the stop as they say.

 

On some of the hottest days in Vic you would need to be over 6,000ft to get out of it and the more you go north or inland the more this altitude increases for a smooth ride.

 

Soon when we get aproval to go above 5,000ft for non-operational reasons this can smooth out a cross-country trip for you significantly.

 

 

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Technically no, i don't think it qualifies, you have to be flying over terrain that you believe wouldn't provide you with a safe landing yadda yadda yadda... personally, if im not flying over an airstrip, i consider ALL terrain to unsuitable.. ;)

 

 

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Returned from USA via Los Angeles in 2000 on the last day of the Sydney Olympics in a Kangaroo 747 and about 140 miles East of Sydney the cloud tops were at about 55,000 AMSL if my memory is correct.

 

I had wondered why we still seemed to be at normal cruise power and so high at the time until I saw the bright flashes in the solid clouds below us. It must have been an awesome sight from the flight deck. I think we were not very far from Sydney when they eventually reduced power for the descent into Kingsford Smith International to touch down at about 9:32 pm local time according to my watch.

 

It is not that unusual to see fair weather cumulus cloud bases over 10,000 feet around Leeton in the middle of summer although the average bases are probably less than that.

 

If you fly under fair weather cumulus clouds with good vertical development in summer here it is possible but not likely that you could experience rising air maybe as strong or stronger than 2,000 feet per minute up (approximately 20 knots up) but probably more likely in the range of 800 to 1200 feet per minute.

 

I have had at least one flight in a glider where I saw the vario hard up against the stop which was at 2,000 feet per minute up. There is a real strong risk of being sucked up into the base of a cumulus cloud as you get nearer to it because the released latent heat from the moisture condensation can dramatically increase the strength of the thermal in and near the base of the cloud.

 

As a very general rule if you fly under near the edges of cumulus clouds or in between them you will usually be flying in sinking air maybe as much as 2,000 feet per minute down! The sink rate will probably be less than the corresponding rising air that caused it.

 

Of course there are often in the summer many hours of the day before the rising thermals get high enough to get cold enough to condense and form clouds. So it is handy to know the dew point temperature and the lapse rate and then you can work out the potential cloud base AMSL or even if there is going to be a cloud base. If you want to know more about this stuff ask a gliding instructor as I have forgotten more than I ever knew about it.

 

In general if you fly through a big high pressure system you will be flying in a sinking air mass which does not do much for your fuel consumption or average ground speed particularly if you are on the wrong side of the high for the direction of your flight where in addition (or should I say subtraction) you would cop a head wind or X-wind instead of a tail wind.

 

 

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Coming back to the original question, I did my initial training in a J160. I found it very twitchy, partcularly in the lee of the ranges. I transfered to a Tecnam Echo and found it much more stable. The Pioneer is more stable again. Even so, we recently flew into Alice Springs about mid day. Higher up it was smooth but below 5000 was most uncomfortable. Around 3000 and lower was the worst that I have experienced and it was a good thing I wasn't PIC because I was GREEN!

 

Answer may be .. different aircraft react differently in low to moderate turbulance but all get thrown around in more severe conditions. What aircraft were you flying?

 

 

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Guest Flyer40

Interesting that no one has mentioned wing loading. Compare the Lightning and the Zodiac 650. They are similar aircraft, both two-seaters with a Jab 3300 and with a MTOW in the 600 to 650 kg range. I haven't flown either, however one has a wing loading of 76 kg/m2 and the other 48. Surely the Lightning gives a better ride in turbulence?

 

 

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Broadly, in turbulance the faster the TAS the rougher it feels and the lighter the wing loading the worse it feels. As the 45 Kn stall limit applies flaps down in Australia it might be possible to have a high loaded wing flaps up with large triple slotted fowler type flaps to meet the stall limit. Don't hold your breath waiting for an aircraft from Europe or the USA; their stall limit is flaps up!

 

 

  • Caution 1
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Don't forget the effects of the different wing section profiles as well as wing loadings.

 

As a couple of glider manufacturers and their customers found out the expensive way, some wing profile sections can perform very well in smooth air but the performance just fall to pieces in turbulent air.

 

I suspect that significant wing section profile differences could be the reason when aircraft with similar wing loadings per square metre give completely different rides and performances in rough and turbulent air.

 

Even the description "rough" and "turbulent" describe different types of air masses and the ride you will experience in either.

 

Rough air just plain bounces one around.

 

In Turbulent air the aircraft just constantly jiggles and twitches and pitches and rolls often all at the same time.

 

It is quite nasty and very unpleasant when flying for long periods in turbulent conditions.

 

 

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turbulance is my nemisis!! I agree with the advice of flying early or late in the afternoon in summer. In my area it is like the thermals 'wake up' pretty much right on 10am. My prefernece of late has been to fly in the afternoons as the air is great and the changing light can make local flying very nice.

 

I am finding the different performance between aircraft quite interesting. I fly a tecnam sierra, a certified 503 drifter and a fisher sport. The fisher is 100 kg lighter than the certified, has no dehidral and a symetrical airfoil. In the normal bubbly turbulance I find it just 'hops' accross where the certified seems to get mushed around a bit. In quite serious turbulance, ie crossing the boarder range, it is like riding a body board in 3m surf:sad:. The tecnam is ok, though being tall I have been put into the canopy a few times. From flying the drifter I now find it intuative as to when I am going to get hammered. Flying with a gliding pilot/instructor will really educate you on this.

 

On a recent flight out west in the certified I was terrified. I made the decision as PIC that it was definatly a safety call to exceed 5000ft. Unfortunatly it was also freezing in the open cockpit so I had to find a balance between freezing and being terrified! In hindsight going higher was not be the answer as at some point I had to come down and it was getting latter in the day and resultantly more turbulant. Same situation again; i'd divert to nearby clifton and enjoy the company of the club there for a few hours. There is always the afternoon to finish the flight.

 

 

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I fly a 200 accross NSW E to W every other week, Mildura to Narromine. Afternoons in summer regularly have to go up to avoid turbulance. Sometimes to no advantage

 

Friday arvos it can get rough but not that much worse than I remember flying in GA AC in the same conditions.?

 

JR

 

 

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Height to fly.

 

Flying up the centre, where the temps would be the highest, (bar the kimberly's) the lowest height that you could obtain a smooth ride was above what we referred to as the inversion layer. This is where the lapse rate shows a sharp change and sometimes it can be noticed as a line where the dust and smoke flattens out and doesn't continue to rise. This particular surface rises during the day, probably reaching its max height at about 3 or 4 in tha afternoon. From memory, you may have to go well above 10 or 12 thousand feet to get above it, (more on days where high surface temps are reached).

 

Get up early and do your flying before mid-day. Nev.

 

 

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  • 1 month later...

Basically comes down to wing loading. The lower the wing loading, the more effect bumps and grinds will have on a plane. Hence, when a transport or fighter jet reports light to moderate turbulence, you may experience severe turb in your Jabiru or Cessna 150.

 

 

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wing loading -absolutely!!

 

Flyer40 and skip D are absolutely right with the wing loading factor in turbulent conditions, Bruit2 asked about the brutal beating he gets riding in a LSA on a hot day and wing loading is a factor so will the ride you are going to get...For instance flying a skyfox or lightwing in these conditions would be akin to riding on the back of a butterfly (all over the place) Jab a little better than that. In fact anything with a wing loading of less than say 15lbs per sq inch. regardless of the wing loading though, turbulance will be felt in all aircraft in these conditions it is only the degree of discomfort really...Rom takes advantage of this discomfort by riding on high aspect wings and converts this bubbling energy into lift etc..As he says if you know a little about gliding, anyone can take advantage of this and use thermal and cloud streets to get a little more speed out of their aircraft and by using a lower power setting at the same time SAVE fuel. ;)

 

 

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Wing loading, speed and possibly high/low wing influence it mostly. My flying has been in mostly Jab 160 and Lightwing Speed. The Speed has a higher wing loading, low wing, and higher speed but is much less effected.

 

PIC has discression now in height flown regarding 5000ft while the new 103 did not restate the 5000ft "limit" (see also Presidents Report Oct RAA mag).

 

I personally beleave that height not only can reduce potentally dangerous turbulance but is the best friend you can have if the unthinkable happens (as it has to me) and it becomes VERY quiet up there!

 

 

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PIC has discression now in height flown regarding 5000ft while the new 103 did not restate the 5000ft "limit" (see also Presidents Report Oct RAA mag).

Doesn't Eugene's report talk about this "in the near future" ? Surely the existing rules apply until the CAO are changed.

 

John

 

 

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Guest pelorus32
Doesn't Eugene's report talk about this "in the near future" ? Surely the existing rules apply until the CAO are changed.John

I think you're right John. Here's the CASA proposal:

 

Project OS 08/13 - Early implementation of certain proposed CASR Part 103 standards via CAO

 

Nothing to suggest that it has been implemented yet.

 

Regards

 

Mike

 

 

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What I said was:

 

1. Pilot in command NOW has discression on height flown,

 

2. I IMPLIED that that the current CAO which has the reference to 5000ft will be replaced in the fullness of political time with the new 103 in which it is omitted.

 

3. My reference to RA-Aus President's Report would, for any one reading it, see it is listed under a sub heading "The Future". What was clear in my in my mind was the current requirements, and what the (hopefully soon) requirements would be. I am sorry some could not understand what I was saying.

 

 

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  • 1 month later...
Guest check-in

On the subject of turbulence in hot weather, it seems that at even 10,000 feet you will still cop a beating over some areas. And aircraft size may not help either. I well remember flying a Cessna 404 Titan on charter work in W.A. many years ago - this is quite a substantial twin and about as stable and controllable as one could wish for in that type of aeroplane. To avoid having passengers throw up all over the place, it was routine for us to 'cheat' by flying at 10,500 or even 11,000 feet - outside CTA of course. We would duck back down to 10,000 to make a position report every hour or so (so we were not telling porkies on the radio), then sneak back up to get out of the bumps. Yes, before anyone berates me, I do know it's technically illegal to a) fly in the transition layer and b) fly at that level without crew oxygen. At the time we regarded it as about as dangerous as being being 10km/hr over the road speed limit - most people do this routinely and it is probably not all that serious under most circumstances.

 

Flying RAA aircraft OCTA and above 5000 to avoid over-stressing the airframe when turbulence so warrants could be argued to come into a clear 'safety of flight' category. The previous point someone made about being as high as possible when there are no good forced landing fields is also relevant.

 

As with many rules in aviation, there are lots of arbitrary numbers - 5,000 feet has long been symbolic in Australia as the separation between application of quadrantal rules, VMC criteria etc. In other parts of the world similar arbitrary boundaries could be established at 18000 feet or 3500 feet. In Australia's case, where summer turbulence is acknowledged as being potentially very severe, it does seem that OCTA there would be no harm in allowing RAA aircraft to go to whatever VFR altitudes were within the aircraft's performance capability. In many cases that would seem to peak at about 7500 feet anyway when either the pilot gets too cold or the engine starts gasping for air, so we are unlikely to have too many hyopxic RAA pilots.

 

 

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Rom. I don't wish to sound like a know it all, but for those interested adiabatic is a noun that pertains to heat change in a body of air for instance where by it cools without the actual transfer of heat ie. no convection etc. Where it expands and cools as work is done by this expansion. It get more complicated but this gives the jist.

 

Michael

 

 

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No worries Michael.

 

My casual use of glider slang needed explaining although not many glider pilots fully know what a super adiabatic lapse rate is either.

 

Usually super adiabatics only extend for a few hundred feet up on those stinking hot days and before the thermals get organised and strong turbulence as in being bounced, juddered and generally thrown around are their hall marks.

 

Sometimes they go to several thousand feet as over a lot of deserts around the world.

 

I experienced a day like that at Horsham where it took over an hour to climb above 6000 feet and it was sickening turbulence all the way with no definite lift or any organisation of the lift, just crash, bang the whole time.

 

Once I managed to break through the top of the super adiabatic layer, I hit well over the 1000 FPM smooth thermals right through to 14,000 feet.

 

Didn't stay up there long but made damn sure I did not get below about 7,000 feet for the rest of the day.

 

 

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