Turbulence and maneuvering speed

[NotarPilot]

Does anyone know if there is a correlation between maneuvering speed and turbulance or do you just need to keep the airspeed in the green arc in turbulant conditions?

[Jeff_S]

Whoah. This is a basic part of your PPL teaching so while I don't mean to denigrate your experience or knowledge, you may want to go back to the books a bit and get a refresher.

Maneuvering speed is a function of the current weight of the aircraft; the lighter the aircraft, the lower the indicated maneuvering speed. The whole point of Va is to keep the aircraft at a speed that will prevent major turbulence from exceeding the structural integrity of the frame...in other words, at the correct maneuvering speed, any major turbulence that causes aircraft upset will stall the wing before it rips it off.

Heavier planes are less impacted by turbulence which is why the Va starts higher and goes down as you burn off fuel.

Now, Mooney's are exceptionally strong airframes as everyone knows, so in practicality you could say "just keep it in the green" and unless you are caught in a T-Storm you might be okay. But I generally bring it back to at least the middle of the green arc if I'm in anything more than light turbulence, which has the added benefit of smoothing out the ride a bit.

Sorry, don't mean to lecture, but your question seemed to need some deeper explanation.

[Piloto]

I always slow down to 120kts IAS in turbulence or when penetraing cumulus. 110kts is my minimum otherwise the stall alarm will start beeping at times. When starting a descent (in clear air) I throttle back and keep speed to 140kts IAS. Turbulence is more prevalent at the lower altitudes thus avoid high speed on descent or you may get unexpected jolts. Although the airframe will tolerate turbulence very well such is not the case for the gyros. Flying routinely through turbulence accelerates the wear on the gyros and possible other components. To avoid turbulence fly early in the morning and above 3000ft AGL. Make sure all passengers have the their seat belt tight to avoid head bumping. Some will suggest to disconnect the autopilot to alleviate airframe loading but I found that most autopilots handle turbulence better than me. Keep it smooth.

José

 

[Jerry 5TJ]

There are quantitative suggestions in the later Mooney POH for maneuvering speed versus weight, for vintage Mooney aircraft see the MAPA guidelines.  One is on-line at

http://72.10.105.106/tms/misc/MAPAMooneyManual.pdf.

For the M20C the speed is 130 MPH indicated at gross weight of 2575 pounds.   That decreases to about 110 MPH near 2100 pounds.   As even the M20C generally cruises at 140+ MPH indicated you have to slow down a lot when the going gets turbulent, if you wish to remain in the recommended maneuvering speed range.

[jetdriven]

Quote: Jeff_S

Maneuvering speed is a function of the current weight of the aircraft; the lighter the aircraft, the lower the indicated maneuvering speed. The whole point of Va is to keep the aircraft at a speed that will prevent major turbulence from exceeding the structural integrity of the frame...in other words, at the correct maneuvering speed, any major turbulence that causes aircraft upset will stall the wing before it rips it off.

Heavier planes are less impacted by turbulence which is why the Va starts higher and goes down as you burn off fuel.

Now, Mooney's are exceptionally strong airframes as everyone knows, so in practicality you could say "just keep it in the green" and unless you are caught in a T-Storm you might be okay. But I generally bring it back to at least the middle of the green arc if I'm in anything more than light turbulence, which has the added benefit of smoothing out the ride a bit.

[PTK]

 

Quote: NotarPilot

Does anyone know if there is a correlation between maneuvering speed and turbulance or do you just need to keep the airspeed in the green arc in turbulant conditions?

[NotarPilot]

Quote: jetdriven

 

Now, green air-yellow arc. The top of your green arc is Vno.  Normal operation range. At the top of this arc, your aircraft can withstand a 30 FPS sharp-edged gust without damage.  That is 1,800 feet per minute.  Instantly.  This decreases linearly to 15 FPS gust tolerance at the redlline. Outside of a thunderstorm, a severe TCU, or a standing lenticular, I don't think you will ever see something like a 30 FPS gust load. The lack of airframe failures in clear air attests to that. A M20K experienced several +/- 10 G loads in rapid succession after it flew through a lenticular in Colorado, in cruise flight and landed.  The aircraft was condemned by Mooney as it was permanently deformed, but it attests to the strength of these aircraft. I know of one M20J that suffered an inflight negative overload of the wing and tail in a Level 6 thunderstorm.

 

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.

[xftrplt]

Quote: allsmiles

 

 

The relationship between Va and turbulence is defined by Newton's 2nd Law, F=ma or a=F/m. Acceleration, a, is indirectly proportional to mass, m. For a given force F a lighter object will accelerate faster than a heavier one. Recall that our airplanes' load characteristics are expressed in g's which is an acceleration quantity (aka acceleration due to gravity.) To be sure we don't exceed our airframe's g load acceleration we need to be sure that according to a=F/m, a (or g) remains within safe margins.

The only way we can control this is through airspeed! This is also due to F=ma because speed (velocity expressed as acceleration) is directly proportional to force F. Force F is thus a function of airspeed! The lighter airplane is unable to withstand the same maximum force F as the heavier one. Simply because the lighter one accelerates easier and will exceed its g loading.

This is why a lighter airplane needs to be flown slower in turbulence!

------------------

1.   Thanks, Bryan, for correctly defining the terms and getting this thread back on course.  

2.   Allsmiles makes several errors.

       a.  Acceleration is inversely (not "indirectly") proportional to mass. 

       b.  "Speed (velocity expressed as acceleration)" is a non sequitur.  One cannot/does not express velocity as acceleration--which is the rate of change of velocity.  But, maybe, he means higher IAS allows greater G available, which, of course, is true. 

       c.  "The lighter airplane is unable to withstand the same maximum force F as the heavier one."  Incorrect.  (And, in fact, the reverse is usually is true.)  Rather--for a given IAS and AOA--an aircraft achieves/experiences greater G when lighter.

[danb35]

Quote: allsmiles

Recall that our airplanes' load characteristics are expressed in g's which is an acceleration quantity (aka acceleration due to gravity.) 

[PTK]

Quote: xftrplt

[xftrplt]

Inversely and indirectly are synonymous.  I stand corrected.

[FlyDave]

Quote: xftrplt

Inversely and indirectly are synonymous.  I stand corrected.

[Piloto]

Quote: xftrplt

Inversely and indirectly are

[Piloto]

Quote: xftrplt

Inversely and indirectly are synonymous. I stand corrected.

[bnicolette]

Whoa!!  That's 10 minutes of my life I'm not getting back.  That reminded me of this:

http://mylifedock.com/how-a-usaf-missile-knows-where-it-is

Always an education though.  Thanks guys.

[aviatoreb]

Quote: allsmiles

[FlyDave]

Hey Allsmiles...is this you?

 

(Flame on!!)

[xftrplt]

 

Sorry, guys, I shouldn't have used the term "synonymous" in acceding that--in this precise context--the terms appear--at least on the high-school level--to be used interchangeably (according to several math sites, like wikianswers).  To me, however, it injects a unnecessary degree of imprecision, as José points out.  And I gladly respectfully defer to our resident math professor, who states they aren't interchangeable. 

[PTK]

Quote: FlyDave

Hey Allsmiles...is this you?

 

(Flame on!!)

[fantom]

Quote: allsmiles

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

[aviatoreb]

Quote: xftrplt

Sorry, guys, I shouldn't have used the term "synonymous" in acceding that--in this precise context--the terms appear--at least on the high-school level--to be used interchangeably (according to several math sites, like wikianswers).  To me, however, it injects a unnecessary degree of imprecision, as José points out.  And I gladly respectfully defer to our resident math professor, who states they aren't interchangeable. 

[John Pleisse]

Hey Notar...read "Flying the Beech Bonanza" by John Eckelbar. There is a chapter on turbulence and airframes. It is well supported by easily digestable mathematics and puts into perspective airspeed vs. turbulence. It is the best mainstream read on the subject and will leave you with no questions.

[fantom]

Back to the original question, yes, it's advisable to slow up in turbulence.

How much is a variable I'll leave to the academics ;-)

[PTK]

Taking Newton's second law as it relates to acceleration due to gravity one step further, W=mg or g=W/m we see that g is directly dependent on weight, W. As long as we remain on the ground the difference between weight and mass is more philosophical and the terms are used interchangeably. But they are different. Especially when our airplanes leave the ground and fly around in the air. Mass is the amount of matter contained in our airplane and is measured in kgs. Mass never changes. Weight is the pull of gravity on our airplane. A force. The weight of our airplane changes depending on where it is and how it is flying. Therefore g's will change according what W is at any given moment. This is the basis of Va and why we express loading characteristics in g's.

[FlyWalt]

Quote: Piloto

 or when penetraing cumulus.