Remain or accelerate

[wileydog3]

Friend of mine posted this question..

You are droning along at 270kts saving fuel, enjoying life and pondering whatever. You encounter moderate turbulence. You instantly remember the Va for your JetBag 2300 is 290kts.

Do you remain at the bumpy 270kts or accelerate to the book answer Va of 290ts.

Either way, explain your choice.

Thanks.

(FWIW, we are using the definitions of moderate turbulence and not a subjective one)

[Genghis the Engineer]

Va is a structural maximum, you are below it, no problem.

I suspect that you may be referring to Vb / Vra (rough air speed). In that case, I'd either stay where I was because gust response is (approximately) proportional to airspeed so the aircraft should be safe at a lower speed; or, alternatively, because turbulence tends to reduce groundspeed at a fixed EAS, I might slightly increase airspeed to maintain groundspeed and stay on schedule - depending upon how critical that was.

G

[Matthew Parsons]

I don't have a reference, just a memory from flight school. I'm sure if I'm close that someone here will be able to provide a ref.

I recall that the turbulent air penetration speed was defined as the fastest speed at which you cannot exceed positive or negative 'g' limits (a plot of airspeed versus normal acceleration that shows stalling speeds, maximum airspeed and g limits would be really useful).

If you went faster than it then a severe gust could cause exceedance of a g limit, whereas at the turbulent air penetration speed that same gust would either cause the aircraft to meet a 'g' limit or cause the aircraft would stall.

If you went slower than the turbulent air penetration speed, then the concern is that you are more likely to stall due to a strong gust, and that you will spend more time in turbulent air.

If the speed you are talking about is derived the same as the turbulent air penetration speed that I remember from flight school, then the textbook answer would be, "it depends". If you were concerned that the turbulence could lead to stalling or structural damage, then that speed is your best bet, so by all means, speed up. If you weren't so concerned about losing control, but were instead concerned with comfort, etc. then the only benefit to speeding up is to minimize time in turbulent air, so...your call.

The funny thing is that even though this all works on paper, when you get into turbulence so severe that the above limits are a concern, your ASI will be all over the place, and the best you can do is to maintain the attitude you think would give you that speed.

Any other thoughts?
Matthew.

[Super Galeb G4]

Definitely look at the flight manual and check out the V-N diagram, you have a very well defined speeds for turbulent weather there and you must respect those limitations, otherwise wings will depart the aircraft. Cant give better answer until I check that out.

G4

[Wind Up Turn]

Matthew Parsons, please check your PM's
WUT:)