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VGs and Manuvering Speed

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gliderx5

Joined: 30 Jun 2008
Posts: 203

Posted: Sun Sep 13, 2009 4:24 pm Post subject: VGs and Manuvering Speed

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Okay guys, hereâ€™s a question about vortex generators that I have not yet seen asked.  Will the addition of vortex generators lower my maneuvering speed?  From what I remember about maneuvering speed it is the highest speed at which it is safe to give abrupt, full control deflection.  While traveling slower than this speed the wing will stall before the G load reaches the max allowed for the wing.  If going faster than maneuvering speed the G loads on the wing could exceed the max allowed before stall occurs and unloads the wing.  So, since VGs delay the stall, would they allow excessive G loads at maneuvering speed?  Should we lower maneuvering speed when equipped with VGs.  Any thoughts?  

   

Malcolm Morrison

MKII

  

 [quote][b]

ces308

Joined: 03 Nov 2008
Posts: 317
Location: houghton lake ,mi

Posted: Sun Sep 13, 2009 4:54 pm Post subject: Re: VGs and Manuvering Speed

I don't believe it changes....the maneuvering speed on my 172 is 120 mph....that is the speed you can still use full travel on the controls....it is what it is....VG's only help you go slow.Your minimum controllable speed will change of course...



chris ambrose

m3x/jab

gliderx5

Joined: 30 Jun 2008
Posts: 203

Posted: Sun Sep 13, 2009 5:51 pm Post subject: VGs and Manuvering Speed

I believe that maneuvering speed listed in the POH is at max gross.  Any weight less than max gross will lower maneuvering speed, stall speed, Vx, Vy, best glide, etc.  I guess the question is "why is maneuvering speed 120 mph?".  I believe it is related to wing stall at high G (max G load).



Malcolm Morrison

MKII

---

ces308

Joined: 03 Nov 2008
Posts: 317
Location: houghton lake ,mi

Posted: Sun Sep 13, 2009 6:08 pm Post subject: Re: VGs and Manuvering Speed

I don't believe it has anything to do with the stall....it does ,however have to do with when the airplane could start coming apart or at least start bending something....



chris ambrose

m3x/jab

ces308

Joined: 03 Nov 2008
Posts: 317
Location: houghton lake ,mi

Posted: Sun Sep 13, 2009 6:38 pm Post subject: Re: VGs and Manuvering Speed

Malcolm,



Remember ,this is for my Cessna Skyhawk it is stated in the POH that any aerobatic maneuvers are to be done in the utility category,which is 2000 lbs gross wieght,which is 300 lbs less than actual gross wieght. I says nothing about any stall speeds at all. I'm not sure what the maneuvering speed is in the M3X and will NEVER fly this airplane like I would the 172.The book also says higher speeds can be used for the maneuvers as long as there is a slow deceleration as to not brake the airplane...



chris ambrose

ces308

Joined: 03 Nov 2008
Posts: 317
Location: houghton lake ,mi

Posted: Sun Sep 13, 2009 6:39 pm Post subject: Re: VGs and Manuvering Speed

...am I making any sense  at all???   lol



chris ambrose

m3x/jab

beauford

Joined: 25 Apr 2007
Posts: 127
Location: Brandon, FL

Posted: Sun Sep 13, 2009 6:41 pm Post subject: VGs and Manuvering Speed

Gents:

 Betcha if you dig, or if one of the aeronautrikal  perfessors on the List signs in and explains it in algebra,  you will find  that the maneuvering speed is derived by applying a formula to the power off  stall speed...(power off stall speed times the square root of the design load  limit of the airframe in G's)  Whatever you have specified as the design  load limit of your particular E-LSA Kolb (I use 3.5G on my toy) will drive the  outcome of your particular Kolb maneuvering speed computation. 

  

 Regardless of what you computed for maneuvering speed,  If you then lower the power off stall speed by adding  VG's , you  will necessarily also lower the maneuvering speed because you lowered the  number you used in the computation formula....but in our little machines,   don't really think it will amount to a hill of beans in practical  application...unless one is inclined to drill rifle companies (or angels) on the  head of a pin... when the air gets rough enough to be looking for maneuvering  speed in a Kolb, you'll likely be lucky to keep the needle bounce within 5 mph  anyway...

  

 my opinion...worth what ye paid fer it...

  

 beauford

 FF-076

 Brandon FL

  

  ---

aslsa.rng(at)gmail.com
Guest

Posted: Sun Sep 13, 2009 6:44 pm Post subject: VGs and Manuvering Speed

The maneuvering speed of a 172P loaded to gross is 99 kts IAS. As the airplane gets lighter the maneuvering speed goes down, not up. At 2000 lb. it is 92 IAS, at 1600 lb. it is 82. This is from the POH Section 2, Limitations, Figure 2-1, Airspeed Limitations. 



Rick Girard

do not archive



On Sun, Sep 13, 2009 at 9:08 PM, ces308 <ces308(at)ldaco.com (ces308(at)ldaco.com)> wrote:

[quote] --> Kolb-List message posted by: "ces308" <ces308(at)ldaco.com (ces308(at)ldaco.com)>

 

 I don't believe it has anything to do with the stall....it does ,however have to do with when the airplane could start coming apart or at least start bending something....

 

 chris ambrose

 m3x/jab

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=262863#262863

 

 

 

 

 

 

 

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mdnanwelch7(at)hotmail.co
Guest

Posted: Sun Sep 13, 2009 6:54 pm Post subject: VGs and Manuvering Speed

Malcolm C

 

  I believe Chris is correct9about Manuevering speed affecting stall speed).  "Manuevering speed" is the speed at which you can make (moderately) abrupt control inputs C and not bend your airplane.  It must also be pointed out that these abrupt inputs are limited to mild to moderate turbulence C if I recall correctly.

  A "high G loading" is suggesting an absolute maximum an airplane MAY NOT recover from C if you have to make a rapid control movement.

  (I haven't reached for my latest copy of the Airmen Information Manual C so don't make a federal case C if I got a detail or two wrong)

 

  From what I have heard C read C researched C etc. VG's augment the slow end of the flying spectrum.  They don't do much C if anything C for the upper end.  The VGs act on the wing's surface in a similar way the dimples on a golf ball allow it to go MUCH further than a golf ball without dimples.  They C the VGs or dimples C affect the boundary air going past the surface.

 

  On a separate note C some pilots have said they don't want VGs on their plane.  Period!!!  Why is this so hard for some others to accept?  

  For some purists C they do NOT want an airplane with whiskers C regardless of what the whiskers may do.  They aren't interested in any of the benefits C real or imagined C brought on by the addition of VGs.

  I don't recall hearing from any of these pilots that VGs don't work as advertised C they have simply said "No C thank you for me."

  It seems C for some inexplicable reason C there are those that simply won't rest until everyone has VGs.

 

  Personally  C I DO plan on adding VGs C when I get back to work on my plane in about two months.  I DO see their value C and am not worried about having the annoying sharp edges on the wings.  But I certainly respect another guy's decision to NOT use them!

  The science behind VGs is clear.  Their value is not in question when added properly on "some" wings.  But C not everyone wants them.

 

Mike Welch

MkIII CX

 



 

 	  Quote: 	
		   Subject: Re: VGs and Manuvering Speed

 From: ces308(at)ldaco.com

 Date: Sun C 13 Sep 2009 19:08:09 -0700

 To: kolb-list(at)matronics.com

 

 --> Kolb-List message posted by: "ces308" <ces308(at)ldaco.com>

 

 I don't believe it has anything to do with the stall....it does  Chowever have to do with when the airplane could start coming apart or at least start bending something....

 

 chris ambrose

 m3x/jab

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=262863#262863

 

 

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mdnanwelch7(at)hotmail.co
Guest

Posted: Sun Sep 13, 2009 7:08 pm Post subject: VGs and Manuvering Speed

Group C

  

   Rick G. is correct.  The following article explains why the Va (manuevering speed) goes DOWN with a lighter airplane.  (It's a little lengthy C but interesting.)

  

  Maneuvering Speed As private pilot students C we learn that maneuvering speed C or Va C gets lower as the plane's weight goes down. This sometimes seems unintuitive C our brains want turbulence to be a bigger problem for heavy planes C as that fits in with our notion of the wings "straining" to carry the load. So needing to slow down further when the plane is light doesn't seem to make sense. Why would it work that way? 

 Most explanations of this phenomenon provided in print are very vague and full of analogies C to help shield the reader from very basic simple high school physics. You'll hear things about being "closer to the stall" C which might be enough to help you remember the answer C but doesn't really provide a satisfying demonstration. This is my attempt to lay out the answer.  

Lift is a function of airspeed and angle of attack. Increase airspeed and you increase lift. Increase angle of attack and you increase lift C until your angle of attack hits the "critical angle of attack" C at which point lift begins to decrease again and the wing eventually stalls.  

When you're flying straight and level C the wings are always generating exactly enough lift to hold the weight of the plane. So "L = W" here. You're typically not at the critical angle of attack C so increasing angle of attack can increase lift C making "L > W". When you do this C the forces no longer balance C there's now a net force upwards C and any time there's a net force C the plane will accelerate in that direction. We'll see the plane's VSI jump and our track will become more vertical C eventually the VSI will stabilize at some rate of climb and we'll be in balance again. (The plane is only accelerating upwards when the VSI needle is "in motion" C once the VSI settles into a particular position C i.e. we're established in a climb or descent or just level C the forces are in balance again and there's no acceleration. Imagine a "perfect" VSI here C ignoring the VSI lag C etc.)  

If you put the wing at the angle of attack that maximizes lift C the amount of lift generated depends on airspeed C it will be greater at 120 kts than at 90 kts. If we were straight and level C and then suddenly put the wing at the angle of attack that generated the most lift C creating a net vertical force (and thus a vertical acceleration) C that vertical lift force would be greater at 120kts than at 90kts. So if we jerked back on the yoke at 120kts C we're going to create a greater upwards force C and thus a greater upwards acceleration C than if we do that same exercise at 90kts.  

So C clearly C we can induce higher levels of vertical acceleration at higher airspeeds C as we can creater higher maximum lift forces. But what else does acceleration depend on? Newton says "F = ma" C force equals mass times acceleration C which can be re-written as "a = F / m". This tells us that for a given force F C the acceleration that results will depend on the mass of the object. Apply the same force F to two objects C and the lighter one will accelerate more than the heavier one.  

This is the key to Va's variation with the plane's weight (which correlates directly with its mass). Take two identical planes (same wing C etc.) C one loaded lightly C one loaded heavily C and fly them both at the same airspeed C say 100kts. When you suddenly put the wings of those planes at max angle of attack C either by jerking back on the stick C or by hitting some turbulence that changes the direction that the air meets the wing C each wing will generate the exact same maximum lift force F C as the variables in the lift equation are the same for both planes (same wing C same angle of attack C same airspeed). But due to its lower mass C the lighter plane will see a greater acceleration result from this force.  

Now think of how our planes specify their load limits C it's not a particular force C it's a particular acceleration. We say our plane's load limit is "3.8 positive Gs" C that's a maximum acceleration. For our two planes above C if the lighter one has half the mass of the heavier one C when both planes see the same lift force C that can result in the heavy plane accelerating at 2 Gs while the lighter plane will accelerate at 4Gs.  

How do we protect a plane from exceeding it's load limit acceleration? The only way is to ensure that we're flying at an airspeed that's slow enough that the lift produced by the wing C when suddenly put at max angle of attack C is small enough that the resulting vertical acceleration is no greater than our load limit. In other words C we have to ensure that the wings can't generate an "F" great enough that our "a = F/m" is more than C say C 3.8g for our current mass 'm'. How can we limit that max lift force "F"? The max lift force will be a function of airspeed; if you slow the wing down C the max force it is capable of generating is lower C so you can ensure the wing isn't capable of generating a force great enough to create an acceleration that exceeds our load limit by limiting our airspeed.  

Our heavy and light planes are both flying with the same wings C and so both can see that max lift force if the wing's suddenly put at max angle of attack C but the lighter one can't sustain the same wing forces as the heavier one C as it's easier to accelerate. So we have to limit the max lift force on our lighter plane even more than our heavier plane C and we do this by limiting our airspeed in that lighter plane even more than our heavier plane C i.e. by setting Va even lower on the lighter plane.    harry(at)meretrix.com (harry(at)meretrix.com)   Mike Welch MkIII CX 



 

  Date: Sun C 13 Sep 2009 21:43:47 -0500

Subject: Re: Re: VGs and Manuvering Speed

From: aslsa.rng(at)gmail.com

To: kolb-list(at)matronics.com



The maneuvering speed of a 172P loaded to gross is 99 kts IAS. As the airplane gets lighter the maneuvering speed goes down C not up. At 2000 lb. it is 92 IAS C at 1600 lb. it is 82. This is from the POH Section 2 C Limitations C Figure 2-1 C Airspeed Limitations. 



 Rick Girard

 do not archive



 On Sun C Sep 13 C 2009 at 9:08 PM C ces308 <ces308(at)ldaco.com (ces308(at)ldaco.com)> wrote:

  	  Quote: 	
		  --> Kolb-List message posted by: "ces308" <ces308(at)ldaco.com (ces308(at)ldaco.com)>



I don't believe it has anything to do with the stall....it does  Chowever have to do with when the airplane could start coming apart or at least start bending something....



chris ambrose

m3x/jab





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gliderx5

Joined: 30 Jun 2008
Posts: 203

Posted: Sun Sep 13, 2009 7:09 pm Post subject: VGs and Manuvering Speed

Thanks Beauford



That's what I suspected.  I guess it was more of an academic question anyway.  If you are correct, then maneuvering speed would drop proportional to the drop in stall speed.  Therefore, a 15% drop in stall speed would result in a 15% drop in maneuvering speed.  At 50 mph we're only talking about 7 mph, no big deal in reality I suppose.



Malcolm Morrison

MKII



---

gliderx5

Joined: 30 Jun 2008
Posts: 203

Posted: Sun Sep 13, 2009 7:37 pm Post subject: VGs and Manuvering Speed

Hi Mike



I think VGs actually help out at high angles of attack.  The speed at which you reach high angles of attack depends on wing loading (weight, bank angle, etc).  In general we talk about VGs helping at slow speeds, but it is the high G, high wing loading arena that prompted my initial question.  I had not seen this discussed but I knew the group would have opinions.  Anything to do with VGs is always interesting.  BTW, I just removed my homemade VGs from my MKII tonight.  I made them the same as Jack Hart, but I never liked the way I mounted them.  The double sided tape caused them to stick up off he wing, so I'm making new ones that I will glue on.  I like the VGs and look forward to installing the new ones.



Malcolm Morrison

MKII

---

zeprep251(at)aol.com
Guest

Posted: Mon Sep 14, 2009 7:19 am Post subject: VGs and Manuvering Speed

Mike , They certainly are a giant pain when you clean your aircraft.

      G.Aman

 

   

 

   

 

 --

mdnanwelch7(at)hotmail.co
Guest

Posted: Mon Sep 14, 2009 7:35 am Post subject: VGs and Manuvering Speed

Gary C

  

   I'm expecting that I'll use my big fluffy car brush C you know C the kind that your garden hose attaches to.

  

   That C or hire some teenager.  LOL

  

 Mike Welch

 

  To: kolb-list(at)matronics.com

Subject: Re: Re: VGs and Manuvering Speed

Date: Mon C 14 Sep 2009 11:18:38 -0400

From: zeprep251(at)aol.com



 Mike  C They certainly are a giant pain when you clean your aircraft.

     G.Aman



 



 



--

zeprep251(at)aol.com
Guest

Posted: Mon Sep 14, 2009 8:04 am Post subject: VGs and Manuvering Speed

Mike, 

  No water available at the hanger so I use a trigger spray bottle and a towel to clean .The towel thing is the pain.

   G.Aman

 

   

 

   

 

 --

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Mon Sep 14, 2009 11:42 am Post subject: VGs and Manuvering Speed

Beauford/Gang:

  

 Took the words right out of my mouth.

  

 When the air gets rough enough to be uncomfortable  in my mkIII, I automatically reduce power and airspeed to compensate.  I  have a maneuver speed arc on my ASI, but don't need to look at it.   

  

 john h

 mkIII

 Rock House, Oregon

  

  

  

  

 [quote]   ---

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

by0ung(at)brigham.net
Guest

Posted: Mon Sep 14, 2009 11:42 am Post subject: VGs and Manuvering Speed

when the air gets rough enough to be looking for maneuvering speed in a Kolb, you'll likely be lucky to keep the needle bounce within 5 mph anyway...  

   

my opinion...worth what ye paid fer it...  

   

beauford  

FF-076  

Brandon FL  

   

 	  Quote: 	
		  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>   

   
	


The time I needed maneuvering speed this spring….  The air speed indicator  was bouncing back and forth  between 40 and 90  several times before we got out of the rough air.    I was too busy flying,,,  but I honestly thing that the gps would have shown very little change.   I don’t want to experience that again to find out.  

   

Boyd Young  

   

       [quote][b]

David Lucas

Joined: 10 Jan 2006
Posts: 79
Location: Europe. based Amsterdam NL

Posted: Wed Sep 16, 2009 12:22 am Post subject: Re: VGs and Manuvering Speed

 	  Quote: 	
		  Will the addition of vortex generators lower my maneuvering speed? 	




I read an article about this some time back. It was an AvWeb article back in 1997 that I'd saved to a 'safe place'. So safe it's taken me until now to find it   



Here's the reference; http://www.avweb.com/news/reviews/182564-1.html



About three quarters of the way down the article it covers this point starting with; . . . . "Another question that has come up frequently is whether the addition of vortex generators has an adverse effect on Design Maneuvering Speed (Va). " . . . .  and the next 4 paragraphs go on to discuss the issue. It's a good read.



Basically, and referring to certified aircraft, Va (maneuvering speed) is a formula derived figure based on Vs (stall  speed). It is a theoretical figure and is not flight tested or verified for certification. But if the stall speed goes down then the maneuvering speed also goes down too. However, from a certification viewpoint, there is no requirement to revise the Va figure downwards after the installation of VG's . . . . So they don't.



So the answer to your question is;  Yes . . . .Sort of !



David.

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