How much turbulence

[usafhaynes1]

I've been reading NTSB accident reports (almost overwhelming how many per month are listed) and one caught my eye about turbulence. 

 

http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20120531X02455&key=1

 

My recent turbulence example:

I've got speed mods on my M20C and in smooth air, it cruises at 160mph in the yellow arc (getting 150-170kts groundspeeds!).  On a recent trip from VA to NY, I was at 6500', light clouds and just after passing east of DC, the turbulence kicked in enough for me to pull MP down to get into the green arc.  Amazingly, I had to pull MP down significantly to slow down into the green arc.  To me, this turbulence was consistently bouncing the plane around but not enough to cause any altitude changes.  Since I'm still a "new" pilot, I immediately pulled power to slow the plane down for the bouncy ride, which lasted all the way into PA. 

 

Here is my question, other than extreme thunderstorm turbulence the plane experienced from the NTSB report, which was a fatal choice, how much turbulence does anyone fly through before slowing down?  Does any sustained turbulence, no matter how mild qualify as a reason to pull power and slow down (into green arc) or do some pilots only pull power if unable to maintain consistent altitude (turbulence causing more than 10' altitude variations)?

 

 

 

[mooniac58]

I have a g-force meter in my aircraft...with a high/low memory feature.  The most extreme turbulence I have ever seen register was 2.7Gs...and that was some miserable stuff on a hot summer day over Arizona - I was at high altitude (11,500) so IAS was already low enough I did not feel a need to slow all the way to Va speed.  I have never flown into TX clouds to see what that must be like - and I hope to never know!

 

Someone might need to correct me here but I think I heard before that certified normal category aircraft need to withstand ~5G at max gross weight.  Speed and the magnitude of the turbulence should determine the G forces felt on the aircraft.

[bnicolette]

From my POH (M20J):

 

Yellow arc (176 - 198 KIAS) - Operations must be conducted with caution and ONLY in smooth air.

[Joe Zuffoletto]

I fly in light to moderate chop about 75% of the time here in Colorado. The plane can withstand far more than my passengers, and sometimes me as well. Once I enter turbulence and determine that it's likely to remain continuous, I drop into the green.

[Awful_Charlie]

I rarely fly in the yellow at all!  One of the advantages of going high is that you can keep the TAS without the IAS, and it is normally smoother higher too - albeit the view may not be as good.

 

If turbulence means I bang my head on the ceiling, or my kneeboard doesn't stay in my lap due to gravity alone, then I drop to Va or below - it makes the bumps a lot more gentle on box the aircraft and the occupants, and I wouldn't want to spill my gin & tonic

[John Pleisse]

While the Appalachians aren’t the Rockies, I have developed a 6^th sense of knowing when a smooth air decent is about to produce a jolt. I have stopped yellow arc decents all together. Likewise, anything that rocks the wings more than 2 feet a side or shear that wags the tail more than 2 or 3 feet makes me pull back to 20”MP. Severe vertical gusts (continuous moderate or worse), immediately to Va. Eckelbar’s Bonanza books give great mathematical definition of vertical gusting vs. airspeed and why Va is so critical.

 

We are blessed to have several aeronautical and structural engineers on Mooneyspace. I’d value their analysis of what a 30 year old airframe should withstand. (Norm? KS Mooniac?) I always bought into young CFI’s saying these planes can take “anything” and I flew like rodeo rider for many years. Not anymore.

[bd32322]

My POH says 0 negative G with flaps extended, otherwise its normal category limits.

[jetdriven]

V_NO, top of the green arc, is the speed at which the airplane can withstand an instantaneous 30 FPS sharp edged vertical gust (1,800 FPM).  V_A is the speed at which maximum control deflections can cause structural damage or failure.   They are two different things.  One, the turbulence breaks the airplane. The other, the pilot breaks the airplane.

[Steve Dawson]

There is a thread somewhere here covering this and trying to find out how to describe the limits of turbulence. Personally I pull back when I am strained against the seatbelts in either a up or down draft or mild to severe turbulance. I believe the J is limited to 3.8+ and 1.58- Gs

[NotarPilot]

I fly in light to moderate chop about 75% of the time here in Colorado. The plane can withstand far more than my passengers, and sometimes me as well. Once I enter turbulence and determine that it's likely to remain continuous, I drop into the green.

 

I wish I had that problem...  My J model only goes in the yellow while I'm in a powered decent.

[201er]

If turbulence means I bang my head on the ceiling, or my kneeboard doesn't stay in my lap due to gravity alone, then I drop to Va or below - it makes the bumps a lot more gentle on box the aircraft and the occupants, and I wouldn't want to spill my gin & tonic

The downside of slowing down for turbulence (in relation to comfort and not structural strength) is that you then have to spend more time in it and endure it longer.

[PTK]

... how much turbulence does anyone fly through before slowing down? Does any sustained turbulence, no matter how mild qualify as a reason to pull power and slow down (into green arc) ...

Is there a good and sane reason you'd want to exceed Vno, especially with ANY hint of turbulence? That's Maximum STRUCTURAL Cruising Speed!

As for g's and Va consult Newton's second law. Here's some good reading.

http://www.meretrix.com/~harry/flying/notes/va.html

[usafhaynes1]

I appreciate all the inputs.  I'll continue the practice of pulling MP back into the green arc at the sign of any continued turbulence, no matter how slight.  A bump or two here and there is not enough to be bothersome, sustained turbulence and I'll dial it back quickly.

[carusoam]

It seems that M20Cs have a low yellow arc on their ASIs compared to newer models using the same wing. The C is capable, in this case, of cruising in the yellow arc and descending easily near the red line.

With great power comes great responsibility...

There is not a lot of chance you will see the turbulence before you hit it.

You want to be going slow before the lap based iPads go floating by...

never spill Charley's G&T without being safely below the weight dependent speed limit...

Peter,

Nice article, what was the source?

Best regards,

-a-

[usafhaynes1]

luckily my iPad mini is yoke mounted!  But I get your point.  The article comes from NTSB website.  I've been pouring over accident reports, analyzing trends (students wreck lots of cessna's by improper rudder control!) and trying to see how I can learn from the accidents to ensure I prevent my own.

[PTK]

Peter,

Nice article, what was the source?

Best regards,

-a-

Hi Anthony. It's written by Harry Mantakos. He is a software engineer by profession in the Baltimore area and also a pilot and an acquaintance.

[jetdriven]

In the absence of an emergency, I can't imagine needing to descend at greater than my J model's 201 MPH Vno. The C model that I fly occasionally, though, is a whole other thing entirely.

Jim

I usually leave 2500 RPM, LOP, full throttle power set for the entire descent until about 3 miles out for landing.  Even so, to get 200 MPH IAS takes a 1000 FPM or greater descent. Its a real sleigh ride.  My friend's E model, however, thats his redline. It will handily wind up to that number in the same descent.

[Sabremech]

Very interesting topic,

 Let me relate what happened to my C model prior to me purchasing it the best I can. 2652W has a bunch of speed mods and cruises in the yellow arc all the time. It was during a descent if I remember correctly, that the previous owner encountered heavy turbulence. The next flight he noticed something odd with the airplane seeming to wag the tail while flying. After landing it was found that the horizontal stabilizer could be deflected well beyond the limits of play allowed. Both of the tail pivot bolts were found bent and the left side fitting rivets pulled away from the skin.

 I inspect the tail before every flight and pull the MP back to get the airplane into the green arc if mild to heavy turbulence is encountered. Those bolts and fittings are amazingly small considering what they hold!!!

 David Staffeldt

[Z W]

You can often cruise in a C model in the yellow, below about 7k feet.  I always kept mine in the green in anything other than totally smooth air.  If it's bumpy and I'm in the yellow, I climb until WOT cruise produces speeds in the green, around 8-10k.  Usually gets you out of the bumps anyways.

 

It is actually fairly challenging to keep it out of the yellow while descending in a C without dropping the gear.  Slow down before you go down.

[Super Dave]

As was pointed out earlier, the airplane will be within the gust envelope when encountering a 30fps sharp edged gust all the way to the top of the green arc. Further, we are still within the gust envelope with a 15fps gust all the way up to redline. With these limits in mind, I think it is overly cautious to say that we should never be in the yellow arc in anything other than perfectly smooth air. Especially considering the fairly low yellow arcs on some of the earlier Mooneys. But since we have no practical way of knowing if we are encountering or are about to encounter a 30fps or 15 fps sharp edged gust; how do we decide, as the OP wonders, when to stay out of the yellow arc?

I found some excellent guidance regarding the yellow arc in the NORMAL PROCEDURES section of the Operators Manual for my 76 F model.

"When flying at lower altitudes, it is possible to cruise at airspeeds above 175MPH (152 Knots) in the yellow arc. The yellow arc indicates the range of airspeeds in which you must exercise caution when flying in rough air or gusts. Rough air is defined as flight in turbulence of a degree that is uncomfortable to the pilot and passengers."

So, Mooney says that we can operate in the yellow arc as long as the turbulence does not make the pilot and passengers uncomfortable. Since 30fps gusts at the bottom of the yellow arc, or 15fps gusts at red line would provide one hell of knocking about, Mooneys guidance seems conservative but practical.

[carusoam]

Back to the iPhone g-meter discussion to collect data???

Best regards,

-a-

[carusoam]

Jim,

Seems like two interesting functions that Xavion provides. Gs and gliding opportunities...

Now, back to how to mount the iPhone to get reliable g data...

Best regards,

-a-

[fantom]

....after I install your old Tempest fine wire plugs. 

 

So that's where they went

 

You probably only need them on the bottom, Jim, and then send the other four to me

[jetdriven]

You guys could probably get away with the fine wires on the bottom. Fantom, being a typical "mooney guy" only wanted to buy them one at a time, at each annual when his plugs wear out. 

 

Jim, hit the injectors with an ultrasonic cleaner and run the GAMI test on them, you can swap them out, and I have a set on loan I thinkI can send your way and you have a few spares to swap around.

 

Unfortunately my A3B6 refused to run LOP worth a hoot on the stock injectors, and we installed a set of GAMI injectors in it. Much improved now.

[fantom]

You guys could probably get away with the fine wires on the bottom. Fantom, being a typical "mooney guy" only wanted to buy them one at a time, at each annual when his plugs wear out. 

 

 

 

Well, yeah