Turbulence and Safe Speeds to Adopt

[rrogerramjet]

Having just flown yesterday for some xwind practice in and very gusty (approx 290 to 330 from 10 to 30kts) was thinking same. Even in circuit at 100kts there are significant forces applied in such conditions. I wondered 'how much of this will an aircraft take' as I was being thrown about often jolted to 30-45 off wings level, in an instant.

 

So for many, who actually does the maths? How does one judge when your aircraft is being overstressed (which has no engineering relationship to the pilot being overstressed for the conditions)

 

Refer my other thread about becoming PPL and having to do the sums rather than a 'wet finger in the air' approach to managing your aircraft. This thread has given me a whole new line of learning to do!

 

FWIW I back off in bumpy conditions so I'm 30kts below Vno - just over 100kts in the 172, and my 'wet finger' rule is if my bum is separated from the seat and/or I can't hold within 50ft I turn around and go home.

 

Fly Safe

 

Ramjet

 

 

[poteroo]

FWIW I back off in bumpy conditions so I'm 30kts below Vno - just over 100kts in the 172, and my 'wet finger' rule is if my bum is separated from the seat and/or I can't hold within 50ft I turn around and go home.

Va for a C172 varies with weight - as does Vs. The range is from approx. 103kts @ full gross wt down to 88kts @ wt with jockey + minimum fuel. Quite surprising.

 

happy days,

 

 

[rrogerramjet]

Va for a C172 varies with weight - as does Vs. The range is from approx. 103kts @ full gross wt down to 88kts @ wt with jockey + minimum fuel. Quite surprising.happy days,

Exactly my point. Thanks for that.

Why one needs to do the maths, not just estimate.

 

So my estimation with full fuel and 3pax turns out to be about right.

 

I will do the sums, to satisfy my own asurance.

 

 

[Peter Anson]

Just when you think you have it all covered, not flying in the lee of mountains, avoiding storm clouds, flying below the structural cruise speed etc. here's my experience flying my Sonex with a friend near Mount Gambier early last year:

 

It was a warm summer day and the sun had been heating the ground up but cloud had moved in from the sea forcing us down to about 2000 ft AGL, so we were bumping along copping both turbulence from the clouds as well as thermals off the ground. Speed was backed off to under 110 knots when we passed over a pine plantation, much darker than the surrounding country, and hit a "wall". There was quite a loud thump and we were thrown up against the seat belts, head-sets dislodged and ipad hit the canopy followed by relative calm and an uneventful landing, although I was pretty careful to avoid other pine plantations. Maximums recorded on the G-meter were +6.9, -0.5

 

The relevant figures for the Sonex are:

 

Flight load at MAUW: +4.4g, -2.2g Vne 171 knots Va 109 knots Vc 118 knots

 

And that's how easy it was to exceed the allowable flight load by 57%.

 

 

[Jabiru7252]

I was flying my Jab on a hot day, only light winds, but found myself banked 45° and pointing 45° off the runway just as I started the flare. Landed heavily with the wing tip inches off the ground. Fought to keep from spearing off into the grass. Terrible experience, I suspect I was caught by a dust devil. I no longer fly in hot weather (> 30C°), too old to put up with that shite any more.

 

 

[turboplanner]

Just when you think you have it all covered, not flying in the lee of mountains, avoiding storm clouds, flying below the structural cruise speed etc. here's my experience flying my Sonex with a friend near Mount Gambier early last year:It was a warm summer day and the sun had been heating the ground up but cloud had moved in from the sea forcing us down to about 2000 ft AGL, so we were bumping along copping both turbulence from the clouds as well as thermals off the ground. Speed was backed off to under 110 knots when we passed over a pine plantation, much darker than the surrounding country, and hit a "wall". There was quite a loud thump and we were thrown up against the seat belts, head-sets dislodged and ipad hit the canopy followed by relative calm and an uneventful landing, although I was pretty careful to avoid other pine plantations. Maximums recorded on the G-meter were +6.9, -0.5

 

The relevant figures for the Sonex are:

 

Flight load at MAUW: +4.4g, -2.2g Vne 171 knots Va 109 knots Vc 118 knots

 

And that's how easy it was to exceed the allowable flight load by 57%.

Frightening experience Peter; wonder if we should be taught about these risks as part of Met. The subject always has seemed unfinished to me.

 

 

[kaz3g]

I was flying my Jab on a hot day, only light winds, but found myself banked 45° and pointing 45° off the runway just as I started the flare. Landed heavily with the wing tip inches off the ground. Fought to keep from spearing off into the grass. Terrible experience, I suspect I was caught by a dust devil. I no longer fly in hot weather (> 30C°), too old to put up with that shite any more.

I remember complaining to my instructor at Benalla many years ago about the strength of the windshear on short final for 17 over the old Highway. It was a real washing machine job. I was flying a Warrior and his response was "Why didn't you go around?"

 

I was still gliding then and pushing on with the landing was my reflex action. I've often reflected on it since.

 

Kaz

 

 

[JerzyGeorge]

Yes it is very interesting, I did read all answers and found them very useful. Perhaps more time should be spent during initial training on turbulence.

 

I developed my own technique to deal with turbulence. Never fly in yellow arc in rough weather, I always slow down before flying into turbulence , developed skills to predict rough ride,

 

I look for hills and valleys and wind direction, also thermal activities in summer time. I never stress airframe with big movement of the controls , quite often I do not resist or fight turbulence I let the a/c to fly with the turbulence and then gentle bring it back to my original course. Some times it does not look right for others but my control surfaces are not stressed and the whole airframe does not take punishment.

 

Of course this is when I can afford it i.e. with plenty AGL. Generally speaking I keep distance ( horizontal and vertical ) from turbulence generators and fly slower than in nice weather. If I could not follow these rules I treat my control movements under control ( gentle) and do not cause unnecessary airframe stress. The only exception is landing in rough air , I keep my speed higher then usual to be fully in control with small movements of control surfaces and take advantage of good engine power if I need. of course build your own method of dealing with turbulence suited to your skills and A/C you fly.

 

George

 

 

[facthunter]

Yes a more stabilised approach is available with power being used, In rough air.

 

Loosely maintain an attitude that lets the airspeed fluctuate about your selected turbulence penetration speed. Sometimes the airspeed fluctuations (without attitude or power being altered) will be quite large. I've had 50 knots in a C-150 so you are clearly going under and over what you want as ideal but you shouldn't chase the airspeed in these circumstances .Make minor corrections to attitude to raise or lower the MEAN airspeed without using large control movements and you will minimise airframe loads. In some circumstances consider changing level to get better air, but this adds to your workload so whatever you do, don't lose the airplane. and don't change trim. If you are trimmed for the right speed the feel of the controls assists you. If you are out of trim you are stacking the odds against yourself. Nev

 

 

[Old Koreelah]

I was flying my Jab on a hot day, only light winds, but found myself banked 45° and pointing 45° off the runway just as I started the flare. Landed heavily with the wing tip inches off the ground. Fought to keep from spearing off into the grass. Terrible experience, I suspect I was caught by a dust devil. I no longer fly in hot weather (> 30C°), too old to put up with that shite any more.

Dust devils deserve more discussion. If you're unlucky enough to encounter one on landing, it may only be visible in a dusty locality. What's the best reaction? What are your chances of applying full power and going around it?

How wide is the turbulent area?

 

 

[Garfly]

Regarding G-Meters, I see that Kanardia have just added that functionality to their round Horis instrument.

 

(As a full screen display switchable from the PFD / DI screen options.)

 

In light of what's been said above I'm hoping I can get the feature working on my own unit with a firmware upgrade.

 

Horis - Kanardia

 

News - Kanardia

 

 

 

 

[Old Koreelah]

A G meter that keeps a permanent record of max readings might be appreciated by pilots renting aircraft.

 

 

[djpacro]

Regarding G-Meters, I see that Kanardia have just added that functionality to their round Horis instrument.

It doesn't go far enough positive or negative.

A G meter that keeps a permanent record of max readings might be appreciated by pilots renting aircraft.

Even more so for owners renting their airplanes, as I do.

[Garfly]

About the Kanardia scale, I'm wondering if the range is adjustable in software.

 

I'd assume the coloured zones are a user setting (as they are for the Airspeed tape).

 

And/or maybe the max. value digits do record over scale values.

 

Something to research.

 

 

[poteroo]

Thread Resurrection

 

Thought it timely to talk about turbulence and managing its' effect on airframes after the 2 recent Cessna 210 fatal accidents - one near Darwin and the most recent near Albany WA.

 

It would appear from the reports to date that both aircraft broke up in flight.

 

The Darwin accident involved a strutless C210 which was negotiating its' way around significant thunderstorms. There is a possibility that it encountered extreme turbulence in normal cruise - as we don't know whether it was operating at reduced speed or not. The ATSB findings may determine whether there were other contributing factors, eg making a turn which increased wing loading, or had flaps extended at close to the book Va, and others. It was also apparently lightly loaded - a factor which reduces Va, and increases risk in rough air.

 

The Albany accident, (a mid 60's C210 with struts), occurred in clear skies with no known meteorological influences. It seems unlikely that this accident was due to any operational factor as the pilot was a highly experienced aggie and would be all too aware of airframe limitations. The loud 'bang' heard by the only witness, (to date), before he observed the aircraft spiralling almost vertically, and the 4 hectare spread of debris, - would appear to point to some unknown catastrophic event in cruise. The fact of there being no recorded Mayday would indicate the event was sudden in the extreme.

 

All pilots need to heed the airframe limits on their aircraft. Read the POH - understand what Va is, what flap does to airframe limits, what turning does to airframe limits, and more. With summer so close - please keep away from storms, slow down when it gets rough, and avoid coarse control inputs. Fly early AM and avoid the rough stuff. If you are flying a very much older airframe - be aware that it could have been stressed many times in the past by unknowing or caring pilots - treat it with care and respect.

 

safe flying and happy days,

 

 

[facthunter]

Agree with all the above. Plus If you see or hear of someone performing aeros in aircraft not certified for it do your best to track it down and take appropriate action. The irresponsible pilot should be dealt with and also the plane requires extra inspection. Similar if there is a heavy landing or hangar rash type incidents,

 

Application of aileron at speed may impose extra twisting loads on a wing also. Some aircraft are cruised at speeds very close to the turbulence limits. Watch your descent speed at altitude. In rough air, limit your control applications and you might have to let the plane have a bit of leeway rather than pin it precisely on a set level.

 

Slow up is the first thing and a significant power reduction is the best way, but don't overdo the action and get slow either as control problems can occur as a result of slow speed as well.

 

Watch your flap extension speeds. In gusts it's easy to exceed them and some aircraft have fairly restrictive Vfe speeds. The manufacturer means it when those limit speeds are stated.

 

Look after your airframe and have it inspected if you are in doubt. Loading it up in a steep turn and saying "she's OK, the wing's still on" isn't appropriate. Nev

 

 

[poteroo]

Va is calculated for a reason - to save you shedding airframe parts. Simply x your clean stall speed x 2 and you'll be very close to it.