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alnanarthur(at)sbcglobal.
Guest

Posted: Wed Mar 01, 2006 9:56 am Post subject: calculating Va

Michel,



Here is how I arrived at Va for my series 5.



Just above stall (45 mph) the aircraft is sustaining one g in level  

flight.



Lift goes up as V squared, therefore at 90 mph at increased angle of  

attack due

to turbulence the aircraft can be subjected to 4 g's.  The stress  

limit for standard

catagory aircraft is 3.8 g.   My Va  "rule of thumb" is twice stall.



At 135 mph, turbulence could subject the aircraft to 9 g's.  That  

could be serious.

I believe that the series 5 was designed for 6 g ultimate.



Also as the  aircraft is more lightly loaded.  Va should be reduced.

Allan Arthur

Kitfox 5, N40AA

Rotax 912s, Warpdrive 3 blade

Byron Airport (C83)  Hanger C8



 	  Quote: 	
		  

 For the Va speed, I understand that it is a matter of comfort and  

 that,

 when in turbulent air, Vne is quickly exceeded as both vertical and

 indicated speed needles move fast in all directions. But, I remember

 that I once sailed into a French harbour to hear French yachtsmen who

 had just arrived before me, talking about sailing in a storm ...  

 when I

 would have called it a moderate gale. It's all in the observator's  

 eye.

 As a novice pilot, any turbulence is a bit scary and I was wondering

 what is real bad stuff that needs to stay at Va to avoid structural

 damages. Do I have to loose my denture, wig and glass eye, to call it

 significant turbulence? So far, the worse I have experienced is a  

 short

 moment when I felt my feet lifted from the floor ... it must have been

 negative Gs. Is that "bad turbulence" or ... "moderate gale?"



 I also like Rod Machado's saying: "Turbulence are like waves at sea,

 only that you don't see them ... and that's what horror movies are  

 made

 of!"  



 Cheers,

 Michel



 do not archive

Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Wed Mar 01, 2006 12:12 pm Post subject: calculating Va

Thanks Jim and Allan,



Yes Jim, turbulence is much depending on the mass and speed of the 

aircraft. I usually explain to passengers that my Kitfox is like a 

small dinghy on the waves. While it may move more up and down, it is 

less of a structural strain than a larger vessel or aircraft.



Allan, my Va is from Denney (I have an old model 3) marked to be 70 

MPH, which is, indeed, the speed at which I will stall when Gs exceed 

what is structurally safe to fly. But ... I don't have a G-meter and 

while Jim gives the description of different turbulence reporting, I 

was actually wondering how it feels to have turbulence that needed to 

slow down to Va.



Since I understand this is more of a subjective notion, I'd ask then: 

How often, any of you has been in turbulence that they estimated to be 

structurally dangerous in a way that it requires Va? I know, it's very 

subjective but ... some of you may have a G-meter and recorded how it 

moved in severe turbulence.



BTW, at sea, I never use a wind speed indicator because, when sailing, 

there are only three wind speed: Not enough, enough and too much! And 

it's all very subjective, indeed! 



Cheers,

Michel



do not archive

_________________
Kitfox 3 - Jabiru 2200

smokey_bear_40220(at)yaho
Guest

Posted: Wed Mar 01, 2006 3:30 pm Post subject: calculating Va

Hi Michel,



We are lucky to have such a well built airplane to

play with.  The airplanes I fly every day are good

only to 2.5 G`s normally, or only 2 G`s with flaps

down.  We quite regularily have to reduce to VA in

turbulence.  It is more a subjective value to do it,

as you said.  When it scares you, slow down.



I am convinced that turbulence is brought on by having

to write something while flying, drinking coffee, or

the opposite, flying with a full bladder.  Weather has

nothing to do with it.  



In the Fox, I slow down when it scares me.  If the

turbulence is due to thermals, I get an extra 10 knots

at the same power setting, so I have to decide if I

need to go fast, or write something, etc.  If I want

comfort, I climb out of the bumps, or land.  If the

bumps are as hard as I land, I slow down too.  If it

is a G`loading bump, I worry a lot more than if it is

a wing rocking bump.  Straightening the wings is more

a nav problem than a structural problem.



And that is my simple plan for VA.



The calculations for VA that you were already given

are correct.  It is based upon stall speed.  But you

must remember to reduce VA when you are light.  You

can pull more G`s at the same speed if you weigh less.



Kurt S.  S-5



--- Michel Verheughe <michel(at)online.no> wrote:



 	  Quote: 	
		   Thanks Jim and Allan,

 

..............
	


 	  Quote: 	
		   I was actually wondering how it feels to have

 turbulence that needed to slow down to Va.

 

 Since I understand this is more of a subjective

 notion, I'd ask then: 

 How often, any of you has been in turbulence that

 they estimated to be 

 structurally dangerous in a way that it requires Va?

 I know, it's very 

 subjective but ... some of you may have a G-meter

 and recorded how it moved in severe turbulence.

 ..............

 Cheers,

 Michel

 

 do not archive

bmwebb(at)cox.net
Guest

Posted: Wed Mar 01, 2006 6:14 pm Post subject: calculating Va

Va, aka maneuvering speed, is not really subjective at all. By definition,

it is that speed at which full, abrupt control deflection will not exceed

the design load factor, (not the ultimate load factor). If a turbulent bump

causes the load factor to exceed the limit as if you applied full, ABRUPT

control input, you're toast. Below Va, you don't have enough control

authority to exceed those limits.



Va must be determined by the engineer who designed the plane. And frankly,

no one wants to find out what it really is. The Lockheed Electra (P-3 Orion)

was the first aircraft to be tested to that limit (failure), but the effort

to do so nearly bankrupt the company. I would imagine most production

aircraft are tested to failure, in an effort to validate the design, more

than increase safety. As builders, I guess we determine the design load

factor limits, but I doubt many of us are qualified to make that

determination. You just take it on faith that the engineer who drew all that

tubing you covered with fabric knew what he was doing.



Generally, the yellow arc is for smooth air, and below in the green is for

the rest of the time. How smooth is smooth? Up to you, buddy! As long as you

don't exceed the ultimate load factor, you're ok. But one good, hard bump in

the yellow is Russian Roulette. When and where that bump is is anybody's

guess. Likewise, if you exceed Vne, it doesn't necessarily mean you're going

to shed the wings at that moment. But you've exceeded the design limit (not

the ultimate limit).



I don't see how we are able to calculate it at all. Without testing in a lab

environment, all you can really do is go with Skystar's numbers and hope it

all works out.



It doesn't really matter if you're doing 40 or 400. Straight and level is

1G. At 40, there's not enough control authority available to stress the

airframe. But at 400, there's plenty enough to pretzel the fuselage and

fully articulate the wings. Load factor, again.



Bradley



--

smokey_bear_40220(at)yaho
Guest

Posted: Thu Mar 02, 2006 8:23 am Post subject: calculating Va

Hi Bradley,



You missed the point Michel brought up.  It is not VA,

but gauging turbulence without a G meter that makes

the degree of turbulence subjective.  VA is of course

well defined.  He just wanted to know when to apply

it.  



Kurt S.



--- Bradley M Webb <bmwebb(at)cox.net> wrote:



 	  Quote: 	
		   Va, aka maneuvering speed, is not really subjective

 at all...............

bmwebb(at)cox.net
Guest

Posted: Thu Mar 02, 2006 8:57 am Post subject: calculating Va

My understanding is that smooth is smooth, no bumps at all. Any bump

(thermals, mountain wave, clear-air turbulence) requires a reduction to Va.

I guess that is subjective, in that minor bumps can probably be ignored, but

if there's a big one lurking up there...



I do the same that most others do, I guess. I fly with my hand on the

throttle to keep the airspeed manageable. I'm usually not in a big hurry,

anyway. So reducing to 70mph is no big deal. An in-flight break-up is second

only to mid-airs on my list of worst ways to die.



By the time a G-meter tells you the info you're looking for, the wings will

be gone. Again, IF you've exceeded the ultimate load factor (failure). I

think that the reduction to Va is pre-emptive, to prevent the break-up

before it happens.



It's all about mitigating the risk.

Bradley



--

spaghettiohead(at)hotmail
Guest

Posted: Thu Mar 02, 2006 9:18 am Post subject: calculating Va

The possibility of exceeding the design limitations of the Kitfox airframe 

are very rare...You can be completely comfortable bombing through a bit of 

turbulence here and there at your normal cruise speed. A speed reduction to 

Va is completely unnecessary. When was the last time turbulence had you 

pulling well over 2G's?



Besides, Va is really only for haevy-pulling, maneuvering flight. If you are 

worried about stressing the airframe in turbulence, the speed you are 

interested in is Vno, or normal cruise speed. This is the speed at which, on 

GA aircraft, the ASI dial gets shaded yellow. It is also known as "turbulent 

air penetration speed." Just fly below Vno when in turbulence. No need to 

slow all the way down to Va!



Andrew

KF3 582

[quote]From: "Bradley M Webb" <bmwebb(at)cox.net>

Reply-To: kitfox-list(at)matronics.com

To: <kitfox-list(at)matronics.com>

Subject: RE: calculating Va

Date: Thu, 2 Mar 2006 11:56:32 -0500






My understanding is that smooth is smooth, no bumps at all. Any bump

(thermals, mountain wave, clear-air turbulence) requires a reduction to Va.

I guess that is subjective, in that minor bumps can probably be ignored, 

but

if there's a big one lurking up there...



I do the same that most others do, I guess. I fly with my hand on the

throttle to keep the airspeed manageable. I'm usually not in a big hurry,

anyway. So reducing to 70mph is no big deal. An in-flight break-up is 

second

only to mid-airs on my list of worst ways to die.



By the time a G-meter tells you the info you're looking for, the wings will

be gone. Again, IF you've exceeded the ultimate load factor (failure). I

think that the reduction to Va is pre-emptive, to prevent the break-up

before it happens.



It's all about mitigating the risk.

Bradley



--

jdmcbean(at)cableone.net
Guest

Posted: Thu Mar 02, 2006 10:01 am Post subject: calculating Va

Andrew,

	Yesterday... 2.3 just for the record...



The Yellow arc is for smooth air only and even then with caution... The

Green arc (Normal operating range) is from Stall clean (Vs1) to maximum

structural cruising speed. (this is not Va)



Fly Safe !!

John McBean

www.sportplanellc.com

"The Sky is not the Limit...  It's a Playground"



--

morid(at)northland.lib.mi
Guest

Posted: Thu Mar 02, 2006 10:35 am Post subject: calculating Va

To all, just for the record.  If there's anyone out there who doesn't know

what all these V speeds are, just go to the link below.

Deke

http://www.aviationboom.com/terms/vspeeds.shtml



---

Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Thu Mar 02, 2006 12:28 pm Post subject: calculating Va

Hello Kurt,



On Mar 2, 2006, at 12:29 AM, kurt schrader wrote:



 	  Quote: 	
		   In the Fox, I slow down when it scares me.


	


So do I! But I was hoping for a slightly more descriptive experience. 

It looks like I have opened a can of worms and that people have 

different meanings. But, first, I never fly without reading METARs and 

TAFs. If anything is above light turbulence, I don't fly. After all, 

and unlike you, I don't have to get into that mess to make a living.

Incidentally, the Rans S6 of my instructor had a G-meter and when we 

were practising landings, he used to say: Any landing that moves the 

needle to 2 Gs is a bad landing.



Anyway, thanks everyone for sharing your experience. It is always a 

pleasure to read you and learn, even if my question wasn't answered as 

accurately as I was hoping for.



Bradley, I also fly, most of the time, with my right hand on the 

throttle, especially when with a passenger, as my right tight is 

covered by the kneeboard. An old friend of mine, flying for the first 

time with me, asked me why I kept my hand on the throttle. I then moved 

it on his tight and asked: "Would you rather have it like this, 

darling?" We both had a big laugh!



Cheers,

Michel



do not archive

_________________
Kitfox 3 - Jabiru 2200

spaghettiohead(at)hotmail
Guest

Posted: Thu Mar 02, 2006 1:59 pm Post subject: calculating Va

2.3 G's...that's impressive 



And in my posting I was attempting to show how the two speeds were in fact 

different...



Andrew

[quote]From: "jdmcbean" <jdmcbean(at)cableone.net>

Reply-To: kitfox-list(at)matronics.com

To: <kitfox-list(at)matronics.com>

Subject: RE: calculating Va

Date: Thu, 2 Mar 2006 11:00:45 -0700






Andrew,

	Yesterday... 2.3 just for the record...



The Yellow arc is for smooth air only and even then with caution... The

Green arc (Normal operating range) is from Stall clean (Vs1) to maximum

structural cruising speed. (this is not Va)



Fly Safe !!

John McBean

www.sportplanellc.com

"The Sky is not the Limit...  It's a Playground"



--

bmwebb(at)cox.net
Guest

Posted: Thu Mar 02, 2006 2:13 pm Post subject: calculating Va

Michel, yeah a can of worms, but all in the name of education and safety. I,

for one, would like to know whether I am pushing my luck by doing something

I'm not supposed to do, maybe because I'd not thought of it, or read the

manual, or had no guidance on the proper procedure.



Either way, we're all a little more aware of the situation, whether you're

right or wrong.



Isn't that the real point of a forum such as this?



I only grab the thigh if she's real cute (like my better half)! My

rule-of-thumb, (applicable in almost all situations, BTW) is that if you've

got more hair on your legs than I do, leave it alone!



Bradley

--

AMuller589(at)aol.com
Guest

Posted: Thu Mar 02, 2006 2:26 pm Post subject: calculating Va

you are probably tired of it all by now but I would like to address Vno,  

something I haven't seen addressed yet. You would need more charts than the  

company make to find the Va. More important to a pilot is the Vno (maneuvering  

speed in turbulence). It is the speed you cannot exceed if you intend/need to  

use full deflection of any flight control surface. Not many documents address  

this but if you are in severe turbulence (especially the longer  period 

turbulence where you have time to react) you can use full aileron,  elevator, rudder 

deflection if you are at or below maneuvering speed. If the  turbulence is 

less than severe you must use proportionally less control movement  if your 

airspeed is higher than Vno. Attached is the pdf copy of the  definitions of 

turbulence and airspeeds. They are quite clearly defined.

 

I haven't found good references to these yet. I think they are in the  design 

guides.

alnanarthur(at)sbcglobal.
Guest

Posted: Thu Mar 02, 2006 4:35 pm Post subject: calculating Va

Dear AMuller,



I believe that you have Va and  Vno mixed up.



Rod Machado, page  B44 states:



"The design maneuvering speed (Va) is the  speed at which the  

airplane will stall  before exceeding its design  limit-load factor  

in turbulent conditions or when the flight controls are suddenly and  

fully deflected in flight".

My Kitfox Series 5  Pilot Operation  Handbook on  page  1-10:



"Va  Maneuvering Speed is the maximum speed at which application of  

full available aerodymamic control will not overstress the airplane.   

This is most  often used for turbulent air penetration and is not  

indicated  on  the airspeed indicator".



Also your pdf didn't come thru.  Maybe you could copy and paste it   

into the body  of the message.



I am going for my BFR soon and all this V speed stuff is good review.



Al  Arthur

On Mar 2, 2006, at 2:25 PM, AMuller589(at)aol.com wrote:



 	  Quote: 	
		   

 you are probably tired of it all by now but I would like to address  

 Vno,

 something I haven't seen addressed yet. You would need more charts  

 than the

 company make to find the Va. More important to a pilot is the Vno  

 (maneuvering

 speed in turbulence). It is the speed you cannot exceed if you  

 intend/need to

 use full deflection of any flight control surface. Not many  

 documents address

 this but if you are in severe turbulence (especially the longer   

 period

 turbulence where you have time to react) you can use full aileron,   

 elevator, rudder

 deflection if you are at or below maneuvering speed. If the   

 turbulence is

 less than severe you must use proportionally less control movement   

 if your

 airspeed is higher than Vno. Attached is the pdf copy of the   

 definitions of

 turbulence and airspeeds. They are quite clearly defined.



 I haven't found good references to these yet. I think they are in  

 the  design

 guides.

AMuller589(at)aol.com
Guest

Posted: Thu Mar 02, 2006 5:01 pm Post subject: calculating Va

I could have mixed these up working with so many files of definitions etc.  

My original didn't carry the cut/paste picture which was copied  from  

scan0001and pasted into  the original text.. I am sending two attachments  one is PDF 

with Turbulence levels defined and another with the Vxxx s defined  the second 

attachment is an expanded set of Vxxx s defined. It states the Va  cannot be 

shown as one number since it depends on weight etc.  I have  documents on all 

this and how aircraft are required to be designed with their  expected flight 

and mission environments defined somewhere but may take a while.  Also I 

haven't checked the age of the documents to see if one is older than the  

other.thanks for the reply Al Muller

Clem Nichols

Joined: 10 Jan 2006
Posts: 88
Location: Munfordville, Ky

Posted: Thu Mar 02, 2006 6:09 pm Post subject: calculating Va

I know I'm going to regret posting this as soon as I hit the send button because no one else seems puzzled by the fact that Va decreases as the load decreases.  To my non-engineering mind this seems counterintuitive.  It seems to me that for a given sized set of wings and support structures the force applied to them would be greater if they were supporting a heavy load and suddenly encountered a very strong updraft or downdraft than if they were supporting a lighter load.  As a very primative example, if I tie a one pound rock to a slack length of twine which is tied at the other end to a stationary object, and then throw the rock, it's obviously going to be less likely to break the twine than would a five pound rock similarly thrown.  The same thing would apply if I were swinging the rocks in circles above my head.  I'm going to be able to swing the small rock faster than the big rock before the string breaks.  What am I missing here???



Clem Nichols

Do Not Archive

wingsdown(at)comcast.net
Guest

Posted: Thu Mar 02, 2006 6:17 pm Post subject: calculating Va

The string stops being a string sooner with the heavy weight. 



Rick



--

jdmcbean(at)cableone.net
Guest

Posted: Thu Mar 02, 2006 7:02 pm Post subject: calculating Va

Clem,

	Lets see if we can help...



This will be very simplified:  We know that the wing stalls at a given angle

of attack not airspeed.



Is the wing at a higher or lower angle of attack at a higher weight ?

Higher the load the greater the angle of attack to maintain level flight.



So at cruise flight at gross weight, the wing is already at a higher angle

of attack to carry the heavier load and therefore closer to the critical

angle of attack.



Lightly loaded,  the angle of attack on the wing to maintain level flight

will be less due to the lighter load and therefore further away from the

critical angle of attack.



These are just numbers for reference: Lets say the critical angle is 18

degrees and Va is equal to 12 degrees.  To maintain level cruise flight, a

gross weight loaded aircraft needs to be at  8 degrees... as the load

decreases so does this angle to maintain the level cruise flight.  So lets

say the angle for a lightly loaded aircraft to maintain cruise level flight

is 4 degrees.



The heavier aircraft needs to fly faster to maintain the 12 degree angle at

Va. The lighter aircraft will need to fly slower to maintain the 12 degree

angle at Va.



Gravity is always there...   Hope this makes sense.  This is simplified and

it is much easier to explain in person.

Fly Safe !!

John McBean

www.sportplanellc.com

"The Sky is not the Limit...  It's a Playground"



--

alnanarthur(at)sbcglobal.
Guest

Posted: Thu Mar 02, 2006 7:09 pm Post subject: calculating Va

Clem,



You are quite  correct  the wings are stressed less at when the  

aircraft is lightly loaded but they can accelerate the lightly loaded  

aircraft more.  This puts more

stress on the engine mount (which is attempting to keep the engine  

from departing from the nose  of the  aircraft) the seat and the  

baggage compartment.



Hope this helps.  This was explained to me by the bright young  

aeronautical  engineer at Skystar when I asked him the same question.



Al Arthur

On Mar 2, 2006, at 6:19 PM, wingsdown wrote:



[quote] 



 The string stops being a string sooner with the heavy weight.



 Rick



 --

Clem Nichols

Joined: 10 Jan 2006
Posts: 88
Location: Munfordville, Ky

Posted: Thu Mar 02, 2006 7:40 pm Post subject: calculating Va

John:



Thanks for your reply.  I think I'm beginning to see the light.  Va is not 

an absolute speed, but the speed at which the plane will stall before 

structural damage occurs, and obviously the heavier plane will stall at a 

slower absolute speed than the lighter one.  It's apparently where one thing 

counteracts the other.  I had in mind a situation last winter when a farm 

hand of mine was feeding a 1500 pound roll of hay on a tractor-mounted 

hayfork.  The ground was frozen hard, and when he drove over a rut which had 

been created when the ground was muddy, the back wheels dropped down into 

the rut, and snapped the spear off the hayfork.  If he had been going more 

slowly, this would not have happened.  By the same token, if he had been 

carrying a 100 pound roll of hay at the same speed or if he had been 

carrying the heavy roll more slowly it wouldn't have happened.  What this 

thinking doesn't take into account, obviously, is the "stall speed" of the 

tractor.  



Clem Nichols

Do Not Archive

---

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