Turbulence and maneuvering speed

[xftrplt]

Cumulus clouds can be just "puffies" and are often unavoidable.  Now a Cumulonimbus is something else.  A kitten :: a tiger, dude. 

[Steve Dawson]

Without getting my slide rule out while I'm traveling through turbulence, would someone describe what a 30 ft/sec or a 50/sec would be as in a reference to an example?

Ie: a 30 would lift you off your seat (as in 1 g) and a 50 would peg you against the ceiling.

I was at 12,000 ft at an IAS of around 135 kph and ran into some clear air turbulence (would describe it as moderate). I immediately slowed the aircraft however I'd like some reference points to turbulence.

Thanks,

[Piloto]

Quote

: allsmiles

 

.........I have 4 very pretty assistants!

More like white jacketed asylum attendants 

LOL!!!! Love it. They probably help with his weekly enema ritual 

[AndyFromCB]

What does Newton's law have to do with flying airplanes. We all know that what keeps an airplane in the air and in one piece is stacks of greenbacks.

[1964-M20E]

So I take both proportionally related and inversly proportionally related to both mean that they are directly related to the independent variable in question, and I am taking the phrase indirectly related to mean that there is an implicit function in the relationship.  Really implicitly related is the technical work and indirectly is a weaker and slightly ambigious synonym for the same.

See we have lots of fun at university.  :-)

[Hank]

If two things are directly related, it means that changing one will also change the other. If they change in the same direction, they are proportionaly related [yoke position to elevator position]; if they change in opposite direction, they are inversely proportional [altitude to blood oxygen level]. If changing one will make some sort of undefined change in the other, then it is an indirect relationship. This is my take after too much Engineering Math in college and years of non-academic experience. It may be "not fully true" in the way that drives my Math Professor cousin crazy, but that's her problem.

 

Without getting my slide rule out while I'm traveling through turbulence, would someone describe what a 30 ft/sec or a 50/sec would be as in a reference to an example?
Ie: a 30 would lift you off your seat (as in 1 g) and a 50 would peg you against the ceiling.
I was at 12,000 ft at an IAS of around 135 kph and ran into some clear air turbulence (would describe it as moderate). I immediately slowed the aircraft however I'd like some reference points to turbulence.

Thanks,

 

As for flying through turbulence, I once read a good description of the various amounts. From memory:

 

-light turbulence will make you spill your coffee

-moderate turbulence will make the stewardess spill your coffee

-severe turbulence will spill the stewardess

 

Applied to my Mooney, if it's much rougher than driving my car down a dirt road, I'll slow down some. If things are shifting around inside, if my wife is bouncing off the ceiling, if the wings are flexing an amount that I don't like, I'll pull back below Va [for my C, 132 mph at gross, going down an undefined amount with weight reduction]. So far, I've managed to avoid turbulence severe enough that reading the gages or GPS is difficult, and I've not bounced the wife very many times.

 

For scale,

60 mph = 88 feet per second = 5280 feet per minute [fpm on your VSI]

500 fpm = 5.7 mph [approx. 100 fpm = 1 mph vertically]

 

But speed alone won't bump you into the ceiling, that takes acceleration. How fast is your speed changing by 30 or 50 fps? Zero to 30 fps in ½ second is quite a different feeling than level flight to 1500+ fpm in two seconds inside a cloud. "Acceleration" is a measure of how fast your speed is changing, conveniently measured in g's, while 30 feet per second is just a speed.

 

Happy flying, and try to avoid clear air turbulence. For what it's worth, I descend with MP and EGT at cruise values all the way down unless it gets rough; then I level off to bleed speed, reduce throttle and descend at a lower IAS so the bumps aren't as harsh.

[Steve Dawson]

Time to start looking for a stewardess then, this may be expensive,

[TTaylor]

Without getting my slide rule out while I'm traveling through turbulence, would someone describe what a 30 ft/sec or a 50/sec would be as in a reference to an example?

Ie: a 30 would lift you off your seat (as in 1 g) and a 50 would peg you against the ceiling.

I was at 12,000 ft at an IAS of around 135 kph and ran into some clear air turbulence (would describe it as moderate). I immediately slowed the aircraft however I'd like some reference points to turbulence.

Thanks,

 

jetdriven said it best: "So, recap. Outside of severe turbulence, Keep it out of the red. Don't make large abrupt control deflections above Va."   Driving around in the green arc is overkill in most cases especially in the older C models with such a low yellow arc.  I could never keep the C out of the yellow letting down.  Just don't overreact and pull hard or slam the ailerons.  I tend to pull back gently when impacting the first turbulence and and try to be smooth on the controls.

 

Can't resist posting this one for fun.  The first hit at about 15 to 30 seconds was fun, I was in the lead glider. Felt like it compressed my spine even with flexible wings and 20 gallons of water in the wings.

 

[aviatoreb]

Hi xftrplt, yes I was a bit abrupt.  So not to be a math prof but I was brief and now I will fix my guilt about being specific.  Anyway, the use of mathematical language incorrectly in a mathematical or engrineering setting is not correct even in high school.  Even if high school teachers may do it.  On the other hand, use of the same language in other settings doesn't bother me.  So I will clarify just becaue I apologize for being brief before, and feel free to skip folks.

Here is the sharp use of the mathematical language.

y is proportional to x means y is a dependent variable on the independent variable x, AND furthermore the functional relationship is simply the multaplicative statement, y=k*x for some constant x.

y is inversly proportional to x means y is a dependent variable on the independent variable x, AND furthermore the functional relationship is proportional in terms of multaplicative inverse y=k/x for some constant x.

y is indirectly proportional to x means y is a dependent variable on the independent variable x, but the actual functional relationship is not specified, but rather it is implicit.  For example, consider in the rocket equation, F=ma, but unlike most system where m is assumed constant, a rocket is essentially an empty tube and so during its flight it looses most of its mass.  It does so in many rockets  by a means of constant flow where m changes proportionally to time.  Long story short, impluse is change of velocity and delta V=Ve ln(M_0/M_F) where M_0 is initial mass and M_F is final mass.  So delta V is logarithmically related to M_F.  And M_F is related to how the fuel is burned, which changes proportionally to burn time.  It would be fair to say that delta V is indirectly (meaning implicitly) related to burn time. So stated functionally, delta V(M_F) and and since M_F is a function of time t, then M_F(t)  (that is called the implicit function) and then delta V(M_F(t)).  But delta V is not proportional to M_F or to t and yet delta V is indirectly depependant on t.

So I take both proportionally related and inversly proportionally related to both mean that they are directly related to the independent variable in question, and I am taking the phrase indirectly related to mean that there is an implicit function in the relationship.  Really implicitly related is the technical work and indirectly is a weaker and slightly ambigious synonym for the same.

See we have lots of fun at university.  :-)

[aviatoreb]

So I take both proportionally related and inversly proportionally related to both mean that they are directly related to the independent variable in question, and I am taking the phrase indirectly related to mean that there is an implicit function in the relationship.  Really implicitly related is the technical work and indirectly is a weaker and slightly ambigious synonym for the same.

See we have lots of fun at university.  :-)

 

No wonder I hated math in college. :0

[aviatoreb]

Did any one here mention in this long thread where Va comes from - in severe turbulence you don't want to have such high g-loads that the airplane can be torn apart, so Va is the aerodynamic speed at which the airplane will stall instead of of reaching a acceleration incurring a force high enough to damage the airplane.  So while it was mentioned in several responses here that it is all about newton's law F=ma, that is not the whole story - it is related to a stall speed as well.

[aviatoreb]

 

Taking it further.

Turboprop aircraft have no yellow arc.  The Beech 1900D, for example, has a 249 KIAS VNE, and it must withstand a 50 FPS gust loading at that speed (FAR 23 certification).  It also has a Va of 184 KIAS.   The former is gust tolerance. The latter is pilot induced overload. 

So, recap. Outside of severe turbulence, Keep it out of the red. Don't make large abrupt control deflectons above Va.

 

I understand what you are saying Byron that a turbo prop is spec'ed differently for higher gust loading, so they do not have a yellow - but that's different from a piston that is not spec'ed the same isn't it?  I am confused.

[M016576]

Did any one here mention in this long thread where Va comes from - in severe turbulence you don't want to have such high g-loads that the airplane can be torn apart, so Va is the aerodynamic speed at which the airplane will stall instead of of reaching a acceleration incurring a force high enough to damage the airplane.  So while it was mentioned in several responses here that it is all about newton's law F=ma, that is not the whole story - it is related to a stall speed as well.

Yep. Maneuvering speed (Va) is the intersection of the lift and load limit lines on an EM diagram. Above that speed, full control deflection WILL over-G the aircraft. Below that speed, your wing will stall prior to the point at which you could over-G the aircraft.

Realize that altitude, weight and configuration all change your maneuvering speed... No "one number" will work for all cases... Although across our relatively small weight margins you could probably use a "rule of thumb" at the lower end of the spectrum safely. Seems like that is the common practice in GA, as we don't have the instrumentation available to really tell where we're operating... And it really isn't required as our typical flight profile is benign (more heart of the envelope rather than at the edges) (IMHO)

[FloridaMan]

I usually slow to maneuvering speed just because the ride is rough. A couple saturdays ago in FL there was a front coming through and it was just miserable. 

 

As for turbulence definitions. 

 

Light is bumps

Moderate is *really* bumpy, but you can maintain control. That Saturday it was moderate as hell. 

Severe is when you're out of control of the airplane at times. I experienced severe clear air turbulence in my Mooney in New Mexico. It was 15 seconds of pure terror. The flight was so calm and boring at 11,000ft, that I was messing with my phone, listening to music, just letting the time pass. All of a sudden I am completely out of control. I was pulling a good 4Gs of acceleration in what was more like a smooth roller coaster ride than bumpy turbulence. 

[Alan Fox]

Hey Allsmiles...is this you?

 

(Flame on!!)

Inversely he also knows everything..... As far as the video , what type or Girdle springs do the pretty assistants wear...

[Steve Dawson]

Not to get between math majors and the grammar police but is there an app that would measure G loads? That may at least give an idea on what the turbulence had been before you slowed to Va.

[carusoam]

Interesting idea....

-a-

[carusoam]

I looked g meter up in the I store. There are at least two apps of interest. One for driving in 2D, including braking and acceleration.

And another, simple aviation g meter gage with a needle indicating positive or negative g forces.

In the same search I also found the sound meter. Decibel Pro.

Most of the apps are $1.

Interesting if you can get it to run in the background collecting and graphing data.

See how smooth your landings are...

G sensors are used with gps to give some level of accuracy.

Probably works best with an iphone5...

Best regards,

-a-

[aviatoreb]

Inversely he also knows everything..... 

 

This time its conversely.  

 

>Not to get between math majors and the grammar police but is there an app that would measure G loads? That may at least give an idea on what the turbulence had been before you slowed to Va.

 

I know - ain't we stinkers?

 

[aviatoreb]

Happy flying, and try to avoid clear air turbulence. For what it's worth, I descend with MP and EGT at cruise values all the way down unless it gets rough; then I level off to bleed speed, reduce throttle and descend at a lower IAS so the bumps aren't as harsh.

 

That's pretty much what the AOPA safety review of the Mooney said a number of years ago:

 

"Mooneys suffer very few in-flight breakups, even when the pilot doesn't maintain control. The result is sadly the same as with other aircraft; it's just that all the Mooney's pieces are found in one spot. I also have a theory that perhaps some other Mooney pilots will confirm or deny. The M20E that I used to fly was exceptionally stiff in turbulence; when it got bumpy, the only way to avoid becoming bruised was to slow down, thus relieving the stress on the airframe. (The bruises also may have had something to do with worn seat cushions.)"

 

from http://www.aopa.org/asf/asfarticles/sp9510.html

[Alan Fox]

This time its conversely.  

 

>Not to get between math majors and the grammar police but is there an app that would measure G loads? That may at least give an idea on what the turbulence had been before you slowed to Va.

 

I know - ain't we stinkers?

 

[Steve Dawson]

Not to get between math majors and the grammar police but is there an app that would measure G loads? That may at least give an idea on what the turbulence had been before you slowed to Va.

And out of work comedians,

[FloridaMan]

I know of one Mooney pilot who claimed his aircraft ended up with hail damage all over the underside of it following flying through a thunderstorm. 

[Hank]

Reb the Rocket Man--

 

Interesting article about flying the short body, but my seats are comfortable. My wife has only bounced off the ceiling once, apparently her seatbelt wasn't properly tightened for a 15-minute breakfast run.

 

[Yeah, I know, upstate New York ain't very rebel-ish, but that's just how I keep track of you.]

 

So far, I've only throttled back for turbulence in cruise twice, once in eastern Wyoming when it was forecast, and once in the NC mountains going past AVL, unforecast but the westerly winds were quite strong [my passenger later said it was the worst he'd ever flown through; it would definitely have spilled coffee if we'd had any]. I'm pickier on descent, when my normal profile puts me almost to the yellow arc, and in it if I don't pay attention and go past 500 fpm for very long. Bumps get harder as you move faster, so if it starts getting bumpy on descent, I'll moderate speed a little to ease the thumps.

[jetdriven]

Xavion has g meter functionality.  I haven't had the opportunity yet to test it, though.

 

Jim

 

Unless it's bolted to the airframe, it wont accurately measure peak G-loads. Your leg, arm, or seat cushion will skew the results.  IIRC the Insight G-series engine monitors will measure G loads.