The other day I was flying from LDVA to LJBL with constant light to moderate turbulence caused by strong northwestern wind. The beginning was benign due to low hills in Croatia but entering Slovenia the effect became stronger although the wind was weaker. Unfortunately I had to fly between Ljubljana CTR and mountains without option to move a bit farther to find less turbulent air. The picture below shows ground speed fluctuations but I remember IAS going up and down pretty much consistently with throttle up to maintain the altitude or down to remain within green arc. Once I download flight log data, I’ll submit IAS graph.
Flying in the mountains and there is some wind, I often go with the flow (constant IAS) rather than sticking to one set altitude, within reasons of course. More comfortable and less work (without autopilot 
)
Is this a question or a report? I had thermals of up to 10 m/s in gliders, that’s 20 knots. If you approach the thermals the angle of attack changes and the speed against air too. So in turbulence a variation of up to 20 knots might be regarded as normal.
It’s mountain wave. Flying across Provence the other day in winds of up to 50 knots (yes really) I was seeing airspeed variation between 110 and 150, depending on whether I was in an updraft or a downdraft. That was hand flying.
Years ago I was flying south into the LA area on autopilot and I noticed similar airspeed variations. Then I hit a rotor on the lee side of the ridge. That was more than exciting and I hope never to encounter it again. Lost 2000 feet in about 10 seconds, then everything which had hit the ceiling crashed down again.
As I assumed, IAS was more-less consistent with GS.
UdoR wrote:
Is this a question or a report? I had thermals of up to 10 m/s in gliders, that’s 20 knots. If you approach the thermals the angle of attack changes and the speed against air too. So in turbulence a variation of up to 20 knots might be regarded as normal.
It’s just reminder to my old glider days when flying in turbulent air was the only flying I was doing
LeSving wrote:
I often go with the flow (constant IAS) rather than sticking to one set altitude
In this case it wasn’t possible due to ATC requirements and I couldn’t tell that I wasn’t able to comply – it wasn’t that hard
I had 30KNTS across the Pyrenees, across and had airspeed variation loss of 30-35knts. Flying at a higher power setting, then reducing as the IAS/TAS/GS increased seemed to help. Was pretty annoying rather than rough at FL100.
One just needs to be careful not to go into the yellow arc in such situations. It’s easy to do, especially as you descend trying to maintain altitude.
Not a problem obviously if the air is smooth, but often these waves are the result of rough air (as in this case).
Lots of fair weather flyer forget about this as they don’t fly that much in anything but nice calm days and have long forgotten about rough air speeds.
Lots of fair weather flyer forget about this as they don’t fly that much in anything but nice calm days and have long forgotten about rough air speeds.
They should move down here (Provence / Cote d’Azur). They’d soon learn about flying in seriously windy weather.
dublinpilot wrote:
One just needs to be careful not to go into the yellow arc in such situations.
Don’t you mean Va, maneuvering speed?
One of the characteristics of flight training, is that 99% is conducted around 1G. This is compounded with 95% of theory knowledge (eg ATP) is for un accelerated flight, again, steady state 1 G given some small variations in climb and descent.
The V-g envelope might deserve some more study. Our GA fleet, the gust envelope is 30 fps, or approximately 15 knots wind shear. This is around the mid to upper end of moderate turbulence.
Pretty universal that the Va for negative G is significantly lower than Va for positive G. In the vicinity of moderate turbulence might it not be more sensible to use negative G Va? You hear of pilots hitting their heads in moderate turbulence, that is a negative G event. How do you find negative g Va. Well it is not published typically for GA, but perhaps around 10-15% below published positive G Va?
You then need to factor in the effect of weight on Va, effectively Va is a function of the square root of the proportion aircraft mass to the Max all up Mass.
Then Va only protects on one axis, rolling and pitching simultaneously means Va protection is lost.
You also have pilots applying wing vortex generators to their wing, which in turn reduces the aircraft stall speed, and ceteris paribus, you got it, this reduces Va.
I have a Va of 134 KIAS and a Vno of 167 KIAS, but my SOP for moderate turbulence is 120 KIAS. I also treat severe turbulence and MTW SIGMETs as no go items.
