Turbulence penetration question
Moderator: Moderators
-
- Post Take off checks
- Posts: 226
- Joined: Tue Jul 31, 2018 7:13 pm
- Closest Airfield: YBAF
- Location: Head in sand
- Has liked: 57 times
- Been liked: 91 times
Turbulence penetration question
Hi all
So far I have encountered 2 schools of thought on what speed to fly in heavy turbulence.
1.Fly at the halfway point between Vs and Vne
2. Fly Va
What do you guys think?
Edit: for aircraft without a published speed for this
So far I have encountered 2 schools of thought on what speed to fly in heavy turbulence.
1.Fly at the halfway point between Vs and Vne
2. Fly Va
What do you guys think?
Edit: for aircraft without a published speed for this
Last edited by Slam and Go on Fri Feb 14, 2020 4:24 pm, edited 1 time in total.
GR III C210 B1900 YDKWYDK
-
- Too Tousand
- Posts: 2037
- Joined: Tue Apr 21, 2009 12:39 pm
- Closest Airfield: FAOR
- Location: Kempton Park
- Has liked: 252 times
- Been liked: 405 times
Re: Turbulence penetration question
Fairly straight forward according to my flight Manual and herewith the following operating speed (IAS) limitations :-
Max permitted speed - VNE - 135 knots
Max speed landing flap - VFE - 86 knots
Max speed rough air - VRA - 102 knots
Max Maneuvering speed - VA - 102 knots
Max permitted speed - VNE - 135 knots
Max speed landing flap - VFE - 86 knots
Max speed rough air - VRA - 102 knots
Max Maneuvering speed - VA - 102 knots
-
- Post Take off checks
- Posts: 226
- Joined: Tue Jul 31, 2018 7:13 pm
- Closest Airfield: YBAF
- Location: Head in sand
- Has liked: 57 times
- Been liked: 91 times
Re: Turbulence penetration question
Thanks for the info.
Now we all think of Va applying one control input abruptly. In heavy turbulence there is often rolling and pitching going on.
I see the logic to fly below Va in this case.
Now we all think of Va applying one control input abruptly. In heavy turbulence there is often rolling and pitching going on.
I see the logic to fly below Va in this case.
- These users liked the author Slam and Go for the post:
- Flooi
GR III C210 B1900 YDKWYDK
-
- 1k poster
- Posts: 1454
- Joined: Mon Jul 03, 2006 8:57 am
- Closest Airfield: Cab
- Location: The Matrix
- Has liked: 66 times
- Been liked: 187 times
Re: Turbulence penetration question
My first response would be something along the lines of "what does your POH / AFM suggest?"
Part 25 aircraft and some Part 23 have a defined rough air penetration speed that should be published in the data available to the pilot. The wording on the previous version of Part 23 was:
"FAR 23.1585(a)(3) A recommended speed for flight in rough air. This speed must be chosen to protect against the occurrence, as a result of gusts, of structural damage to the airplane and loss of control (for example, stalling);"
Older Part 23 aircraft may not have a defined rough air speed in their manuals. In the absence of a defined speed, an airspeed less than VA, but greater than Vs by a margin seems reasonable.
Part 25 aircraft and some Part 23 have a defined rough air penetration speed that should be published in the data available to the pilot. The wording on the previous version of Part 23 was:
"FAR 23.1585(a)(3) A recommended speed for flight in rough air. This speed must be chosen to protect against the occurrence, as a result of gusts, of structural damage to the airplane and loss of control (for example, stalling);"
Older Part 23 aircraft may not have a defined rough air speed in their manuals. In the absence of a defined speed, an airspeed less than VA, but greater than Vs by a margin seems reasonable.
The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair.
- Douglas Adams
- Douglas Adams
-
- 10000 and still climbing
- Posts: 17253
- Joined: Thu Jun 19, 2008 7:46 am
- Closest Airfield: FAGG
- Location: Wilderness
- Has liked: 1133 times
- Been liked: 1449 times
Re: Turbulence penetration question
Stressors, am I correct in thinking it gets less when the aircraft is light?StressMerchant wrote: ↑Mon Feb 10, 2020 1:30 pmMy first response would be something along the lines of "what does your POH / AFM suggest?"
Part 25 aircraft and some Part 23 have a defined rough air penetration speed that should be published in the data available to the pilot. The wording on the previous version of Part 23 was:
"FAR 23.1585(a)(3) A recommended speed for flight in rough air. This speed must be chosen to protect against the occurrence, as a result of gusts, of structural damage to the airplane and loss of control (for example, stalling);"
Older Part 23 aircraft may not have a defined rough air speed in their manuals. In the absence of a defined speed, an airspeed less than VA, but greater than Vs by a margin seems reasonable.
jim
"PPL Manual"
"Flight Tests"
"So Others May Live"
"Flying in Africa" Vol 1
"Flying in Africa" Vol 2
Look inside these books, or buy them at: www.jimdavis.co.za.
"Flight Tests"
"So Others May Live"
"Flying in Africa" Vol 1
"Flying in Africa" Vol 2
Look inside these books, or buy them at: www.jimdavis.co.za.
-
- 1k poster
- Posts: 1087
- Joined: Fri Apr 20, 2012 10:29 am
- Closest Airfield: Fahg
- Location: Nigel
- Has liked: 161 times
- Been liked: 108 times
Re: Turbulence penetration question
LSA with light wing loading.... as slow as safely possible.... keeping in mind that in turbulence, the aircraft may unexpectantly find itself below stall speed. Also maintain safe altitude.
-
- Niner Tousand
- Posts: 9199
- Joined: Wed Nov 16, 2005 10:49 pm
- Closest Airfield: FAJS
- Location: JHB INTL/Kpt Park/Rand Apt
- Has liked: 37 times
- Been liked: 281 times
Re: Turbulence penetration question
I was taught:
1) Below Va - full abrupt control surface application, the control surface will encounter aerodynamic stall before becoming overstressed
2) Above Va - full abrupt control surface application, the control surface, the attachment point, or further internal structures can experience structural damage
1) Below Va - full abrupt control surface application, the control surface will encounter aerodynamic stall before becoming overstressed
2) Above Va - full abrupt control surface application, the control surface, the attachment point, or further internal structures can experience structural damage
sometimes we suffer a bit from C.R.A.F.T. sickness..Can't Remember A F@#%ing Thing
https://www.facebook.com/ralf.t.schulz
https://www.facebook.com/ralf.t.schulz
-
- Tree Tousand
- Posts: 3594
- Joined: Tue Mar 02, 2010 10:10 pm
- Closest Airfield: FASX
- Location: Barrydale Western Cape
- Has liked: 526 times
- Been liked: 202 times
Re: Turbulence penetration question
Myself flying mostly LSA aircraft albeit with a PPL, my self made rule has always been in very rough turbulence to fly at Vy. And I am still here to tell the tale 

Cubby Aircraft Factory
Suppliers of Nitrate, Butyrate, Adhesive, Fabric.
New front seat solo Cubby Renegade
Cell : 072 6716 240
SACAA Approved Person 402
Email: cubbyaircraftfactory@gmail.com
Suppliers of Nitrate, Butyrate, Adhesive, Fabric.
New front seat solo Cubby Renegade
Cell : 072 6716 240
SACAA Approved Person 402
Email: cubbyaircraftfactory@gmail.com
-
- 1k poster
- Posts: 1087
- Joined: Fri Apr 20, 2012 10:29 am
- Closest Airfield: Fahg
- Location: Nigel
- Has liked: 161 times
- Been liked: 108 times
Re: Turbulence penetration question
Agreed.... my POH gives Vy at 68knts IAS. If turbulence is high, 55 knts IAS mushes with more comfort. Maybe the high aspect wing ratio makes the difference. Not sure.....Jean Crous wrote: ↑Mon Feb 10, 2020 6:18 pmMyself flying mostly LSA aircraft albeit with a PPL, my self made rule has always been in very rough turbulence to fly at Vy. And I am still here to tell the tale![]()
-
- Take off Clearance
- Posts: 126
- Joined: Wed Jan 21, 2015 8:38 am
- Closest Airfield: FAOR
- Location: Gaborone
- Has liked: 1 time
- Been liked: 6 times
Re: Turbulence penetration question
I once did a license conversion in Namibia with a gentlemen called Leon and was asked about Va and what it means. To cut the long story short, I was told that it's not my fault that I didn't know, but he blamed the person who taught me. After reading parts of this thread, I'm now more inclined to agree with him about this aspect not being taught well.
To fully understand this concept of Va, one has to look at the reason why it reduces with weight, like Oom Jim said, or vice versa. You also have to know what the G load limit of your aerie is. This has to do with the load factor as the angle of attack is increased. (YouTube has very nice explanations of you search for why Va decreases with a decrease in weight)
In basic terms, Va speed will ensure that your wing stalls before exceeding the g limit which acts as a relief on the structural strength. So, if your aircraft does not have a stipulated turbulent penetration speed, fly at VA.
To fully understand this concept of Va, one has to look at the reason why it reduces with weight, like Oom Jim said, or vice versa. You also have to know what the G load limit of your aerie is. This has to do with the load factor as the angle of attack is increased. (YouTube has very nice explanations of you search for why Va decreases with a decrease in weight)
In basic terms, Va speed will ensure that your wing stalls before exceeding the g limit which acts as a relief on the structural strength. So, if your aircraft does not have a stipulated turbulent penetration speed, fly at VA.
To know Him
-
- Too Tousand
- Posts: 2782
- Joined: Sat Jul 31, 2010 2:47 pm
- Has liked: 895 times
- Been liked: 265 times
Re: Turbulence penetration question
better to avoid turbulent air - might mean you fly a few extra miles.
(e.g. flying down the West coast at midday will be bumpy - we all know that! so fly early in the morning, or fly over the sea, within glide of the land.)
i.e. better planning
(e.g. flying down the West coast at midday will be bumpy - we all know that! so fly early in the morning, or fly over the sea, within glide of the land.)
i.e. better planning
- These users liked the author rare bird for the post:
- Duff
-
- Six Tousand
- Posts: 6391
- Joined: Mon Sep 19, 2005 3:45 pm
- Closest Airfield: Rhino Park
- Location: Pretoria
- Has liked: 44 times
- Been liked: 432 times
Re: Turbulence penetration question
There seems to be a lot of confusion about V speeds...
First, some definitions:
Va = maneuvering speed (safely apply full control deflection without structural failure).
Vno = maximum structural cruising speed (only go faster is still air).
Vb = design speed for max gust intensity.
Vra = rough air penetration speed (max safe speed in severe turbulence).
Vno and Vb are fairly similar (IIRC Vno assumes max 30fps gust and Vb max 45fps gust). No idea how Vra differs from Vb. I have not seen any light aircraft manuals that specify Vb or Vra though...
Secondly, these are book numbers, and DO NOT CHANGE. (Some books do give different numbers for different weights - but the V speed is the number given in the book for the weight.)
Theoretically, you could safely maneuver a little faster than Va in a heavy aircraft, but do you really want to be a test pilot.
As for the other speeds, all bets are off... Are you in part of the envelope where stall determines the limit (higher weight = faster), or part of the envelope where structural loads determine the limit (higher weight = slower)? Do you really want to try find out?
Rather fly the numbers as they are in the book.
Justin Schoeman
ZU-FSR (Raven)
ZU-FSR (Raven)
-
- Too Tousand
- Posts: 2782
- Joined: Sat Jul 31, 2010 2:47 pm
- Has liked: 895 times
- Been liked: 265 times
Re: Turbulence penetration question
certainly keep within the numbers, however do remember it is a 3D envelope
You do not have the required permissions to view the files attached to this post.
-
- Frequent AvComer
- Posts: 945
- Joined: Mon Feb 07, 2005 7:15 am
- Closest Airfield: FARA
- Location: Petit (FARA)
- Has liked: 22 times
- Been liked: 94 times
Re: Turbulence penetration question
Just a correction, Va is the speed at which you can apply full deflection of any ONE flight control without overs stressing the airframe. So you cannot go do a roll at Va like some think you can. You do get away with it for a while but like Justin said "do you really want to be a test pilot"
- These users liked the author stefan for the post:
- Pete
-
- 1k poster
- Posts: 1454
- Joined: Mon Jul 03, 2006 8:57 am
- Closest Airfield: Cab
- Location: The Matrix
- Has liked: 66 times
- Been liked: 187 times
Re: Turbulence penetration question
Rough air penetration speeds and manoeuvre speeds have similar issues regarding definitions and applications. You’ll find differences in approach between older aircraft and newer aircraft, between single engine and multi-engine, and between Part 23 and Part 25. So a degree of confusion is understandable.
Design vs Operating: The engineers design the aircraft to withstand manoeuvre and gust loads defined in Subpart C (Structures). The pilots operate the aircraft in accordance with information specified in Subpart G (Operating Information and Limitations / Flightcrew Interface and Other Information). In some cases the distinction between the two is not clear. And it doesn't help that in big companies they are implemented by different teams.
Looking at Subpart C:
Old Part 23: Aircraft is designed for static loads as follows:
VC: Gusts up to 50 ft/s
VD: Gusts up to 25 ft/s
In addition, for multi-engine aircraft certified after 1987:
VB: Gusts up to 66 ft/s
For new Part 23 aircraft, the regulation requires that:
“The applicant must determine the structural design loads resulting from the following flight conditions: (a) Atmospheric gusts where the magnitude and gradient of these gusts are based on measured gust statistics.”
For Part 25 aircraft, the requirements are:
VB to VC: 56 ft/s
VD: 50% of the value at Vc
(all sea level values, reductions are specified for increasing altitudes)
Subpart G requires that the designer include speeds in the Airplane Flight Manual, but these speeds do not need to be the same as the Subpart C speeds. Logically they would not be higher than the Subpart C speeds, but they may be lower for reasons for crew comfort, handling characteristics, or airframe fatigue considerations.
Part 23: Up to 1993, Part 23 aircraft were not required to specify a recommended rough air speed. For Part 23 aircraft certified after 1993:
(a) For all airplanes, information ….. must be furnished, including-- (3) A recommended speed for flight in rough air. This speed must be chosen to protect against the occurrence, as a result of gusts, of structural damage to the airplane and loss of control (for example, stalling);
The new Part 23 requirement is:
“(a) The Airplane Flight Manual must contain the following information— (1) Airplane operating limitations; (2) Airplane operating procedures; (5) Other information that is necessary for safe operation because of design, operating, or handling characteristics.”
Part 25 requires furnishing of a Rough Air Speed, VRA. This is a recommended turbulence penetration speed, and is established relative to Vmo. The relationship between VRA and VB is indirect.
Design vs Operating: The engineers design the aircraft to withstand manoeuvre and gust loads defined in Subpart C (Structures). The pilots operate the aircraft in accordance with information specified in Subpart G (Operating Information and Limitations / Flightcrew Interface and Other Information). In some cases the distinction between the two is not clear. And it doesn't help that in big companies they are implemented by different teams.
Looking at Subpart C:
Old Part 23: Aircraft is designed for static loads as follows:
VC: Gusts up to 50 ft/s
VD: Gusts up to 25 ft/s
In addition, for multi-engine aircraft certified after 1987:
VB: Gusts up to 66 ft/s
For new Part 23 aircraft, the regulation requires that:
“The applicant must determine the structural design loads resulting from the following flight conditions: (a) Atmospheric gusts where the magnitude and gradient of these gusts are based on measured gust statistics.”
For Part 25 aircraft, the requirements are:
VB to VC: 56 ft/s
VD: 50% of the value at Vc
(all sea level values, reductions are specified for increasing altitudes)
Subpart G requires that the designer include speeds in the Airplane Flight Manual, but these speeds do not need to be the same as the Subpart C speeds. Logically they would not be higher than the Subpart C speeds, but they may be lower for reasons for crew comfort, handling characteristics, or airframe fatigue considerations.
Part 23: Up to 1993, Part 23 aircraft were not required to specify a recommended rough air speed. For Part 23 aircraft certified after 1993:
(a) For all airplanes, information ….. must be furnished, including-- (3) A recommended speed for flight in rough air. This speed must be chosen to protect against the occurrence, as a result of gusts, of structural damage to the airplane and loss of control (for example, stalling);
The new Part 23 requirement is:
“(a) The Airplane Flight Manual must contain the following information— (1) Airplane operating limitations; (2) Airplane operating procedures; (5) Other information that is necessary for safe operation because of design, operating, or handling characteristics.”
Part 25 requires furnishing of a Rough Air Speed, VRA. This is a recommended turbulence penetration speed, and is established relative to Vmo. The relationship between VRA and VB is indirect.
- These users liked the author StressMerchant for the post:
- Robbied
The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair.
- Douglas Adams
- Douglas Adams