MANUVERING SPEEDS

[EDMO 1078]

Nobody ever said that "Old pilot are smart pilots": Maybe old pilots sometimes cannot comprihend things that the young pilots are taught, like Va, Vb, Vc, and all those alphabet things that we older pilots have to say in longhand American.

I just read Barnaby's article in the new Sport Aviation mag, and I totally don't understand how a manuver or wind gust can overstress a plane at a lower weight and not at a higher weight. I follow all of his articles with intense interest, but am lost on this one. Looks like to me that if you are at max gross, then any strain on the wings could put you in danger faster than if you are lighter.

Can someone smarter than me explain this to where I can understand it?

Ed in MO

[horsepower 24]

Nobody ever said that "Old pilot are smart pilots": Maybe old pilots sometimes cannot comprihend things that the young pilots are taught, like Va, Vb, Vc, and all those alphabet things that we older pilots have to say in longhand American.

I just read Barnaby's article in the new Sport Aviation mag, and I totally don't understand how a manuver or wind gust can overstress a plane at a lower weight and not at a higher weight. I follow all of his articles with intense interest, but am lost on this one. Looks like to me that if you are at max gross, then any strain on the wings could put you in danger faster than if you are lighter.

Can someone smarter than me explain this to where I can understand it?

Ed in MO

The manuvering speed changes with different condtions such as weight and turbulence,dont really know how to determine manuvering speed on a light weight homebuilt but if your wings fall off I guess it was overstressed.I was taught that a fully loaded airplane had a reduced manuvering speed when in turbulent air as opposed to a lighter loaded plane.I may be wrong,wouldnt be the first time.Randy

[HuDuGuru 0]

Maneuvering speed most definitely decreases with decreased weight. I’ll take a stab at explaining it without any math formulas.

These numbers are just made up to illustrate a point.

Airplane X= 1000 pounds, flying angle of attack=10 degrees.

Airplane Y=1500 pounds, flying angle of attack =15 degrees.

Both airplanes are flying at the same speed.

Critical angle of attack will be the same for both planes, say 20 degrees. Once critical AOA is exceeded the loads are dramatically reduced for both planes.

G forces are directly related to the amount of time an aircraft has to accelerate. Airplane X will have to move 10 degrees before reaching critical AOA, airplane Y has to move only 5 degrees. Since it takes more time to move 10 degrees compared to 5, airplane X will spend more time accelerating therefore developing greater G forces.

By reducing your flying speed, you are also INCREASING your angle of attack, which puts you closer to the critical AOA, which in turn gives the plane less time to accelerate before reaching critical AOA.

I hope this helps, I understand the physics behind it, but I usually suck at explaining things.

EDIT: to avoid some confusion, when I use the word “accelerate†I don’t mean increasing your airspeed. I meant gravitational acceleration, which is what happens every time you pull the stick back.

Edited 1 May 2012 by HuDuGuru

[EDMO 1078]

The manuvering speed changes with different condtions such as weight and turbulence,dont really know how to determine manuvering speed on a light weight homebuilt but if your wings fall off I guess it was overstressed.I was taught that a fully loaded airplane had a reduced manuvering speed when in turbulent air as opposed to a lighter loaded plane.I may be wrong,wouldnt be the first time.Randy

That was what I thought I had been taught too. Barnaby says it is just the opposite: Lighter means more reduced manuvering speed than heavier ones.

Guess we all need to increase our weights (maybe eat more?) to go faster and pull up to avoid the trees!!!

Ed in MO

[EDMO 1078]

Maneuvering speed most definitely decreases with decreased weight. I’ll take a stab at explaining it without any math formulas.

These numbers are just made up to illustrate a point.

Airplane X= 1000 pounds, flying angle of attack=10 degrees.

Airplane Y=1500 pounds, flying angle of attack =15 degrees.

Both airplanes are flying at the same speed.

Critical angle of attack will be the same for both planes, say 20 degrees. Once critical AOA is exceeded the loads are dramatically reduced for both planes.

G forces are directly related to the amount of time an aircraft has to accelerate. Airplane X will have to move 10 degrees before reaching critical AOA, airplane Y has to move only 5 degrees. Since it takes more time to move 10 degrees compared to 5, airplane X will spend more time accelerating therefore developing greater G forces.

By reducing your flying speed, you are also INCREASING your angle of attack, which puts you closer to the critical AOA, which in turn gives the plane less time to accelerate before reaching critical AOA.

I hope this helps, I understand the physics behind it, but I usually suck at explaining things.

EDIT: to avoid some confusion, when I use the word “accelerate†I don’t mean increasing your airspeed. I meant gravitational acceleration, which is what happens every time you pull the stick back.

I need a while - maybe a long while - to digest all of this. I've heard that ultralights are more critical in turbulance, and guess this is the reason. Well, maybe everyone needs to think about this for a while.

Ed in MO

[HuDuGuru 0]

Ed, I wouldn’t worry about it too much. Once you’re up in the air you don’t have the option of making the airplane heavier or lighter, but you do have the option of slowing down. The only thing you have to remember is to slow down if your flight turns into a roller coaster ride.

There are no published figures for maneuvering speed for Avids and Kitfoxes, so I’m not sure how much to slow down. What I do know is other general aviation aircraft (Cessnas and Pipers) have published maneuvering speeds approximately 10-20% below normal cruise speed.

[EDMO 1078]

Ed, I wouldn’t worry about it too much. Once you’re up in the air you don’t have the option of making the airplane heavier or lighter, but you do have the option of slowing down. The only thing you have to remember is to slow down if your flight turns into a roller coaster ride.

There are no published figures for maneuvering speed for Avids and Kitfoxes, so I’m not sure how much to slow down. What I do know is other general aviation aircraft (Cessnas and Pipers) have published maneuvering speeds approximately 10-20% below normal cruise speed.

I believe that the manuvering speeds for Kitfoxes is published. am thinking it was 80 to 88 mph depending on the model - will have to check the book on them, because that sounds fast - thats cruise for some of them. Isn't manuvering speed indicated on the markings on the Airspeed Indicator for each plane?

I could be wrong on the indicator, but think that this is where the yellow mark starts between the green arc and red line?

Ed in MO

Edited 2 May 2012 by Ed In Missouri

[dholly 718]

Maneuvering Speeds from my Kitfox POH:

Classic 4 (1050 lb Gross Weight) w/ Rotax 503 = 96mph

Classic 4 (1200 lb Gross Weight) w/ Rotax 912 = 102mph

Model 4-1200 (1200 lb Gross Weight) w/ Rotax 912 = 102mph

Speedster (1200 lb Gross Weight) w/ Rotax 912 = 106mph

[HuDuGuru 0]

I phoned the kitfox factory a number of years back asking a few questions about some of the performance numbers, I was told there were no published figures for maneuvering speed on a model 3. I guess I just assumed this applied to later models… you learn something new every day.

[EDMO 1078]

Maneuvering Speeds from my Kitfox POH:

Classic 4 (1050 lb Gross Weight) w/ Rotax 503 = 96mph

Classic 4 (1200 lb Gross Weight) w/ Rotax 912 = 102mph

Model 4-1200 (1200 lb Gross Weight) w/ Rotax 912 = 102mph

Speedster (1200 lb Gross Weight) w/ Rotax 912 = 106mph

Quoting from "KITFOX PILOT'S GUIDE" by Ed Downs, it looks like the "lighter is slower" holds true here.

Kitfox Lite = 62 mph Manuvering Speed

Model 1-532 = 75

Model 2-582 = 76 Model 3-582 = 76 Model XL-503 = 76

Model 4-1050-582 = 82 Lite Squared-503 =82

Classic 4-618 = 85 Lite Squared 912 = 85 912S = 85

Series 5/1400-912 =88

Series 5/1400-912S = 92 Series 5/6-0-200 = 92 Series 5/6-0-235 = 92 Series 5/6-IO240B =92

All Series 7 = 92

Guess you can compare each of these to the Avid / Airdale?

Don't have a clue why Doug's POH says different. Maybe ask Kitfox?

Ed in MO

Edited 2 May 2012 by Ed In Missouri

[dholly 718]

Don't have a clue why Doug's POH says different. Maybe ask Kitfox?

Ed-

I also have the KF Pilot's Guide rev. 2004-1. My best guess for the disparities is because my KF 4-1200 POH rev. 7/19/94 was published by Skystar Aircraft Corporation while the KF Pilot's Guide is published by Kitfox Aircraft LLC.

Isn't manuvering speed indicated on the markings on the Airspeed Indicator for each plane?

I could be wrong on the indicator, but think that this is where the yellow mark starts between the green arc and red line?

Yes, I believe that is correct Ed.

Ex., in the 'Required Placards and markings - Airspeed indicator range markings' section of my Aerotrek SLSA POH, it shows the Green Arc 50-109 mph (IAS) and defines it as: "Normal operation range. The lower limit is the maximum-weight zero thrust stall speed with flaps retracted, and the upper limit is maneuvering speed." The Yellow arc 109-143 mph (IAS) and defines it as: "Caution range - operation must be conducted with extreme caution and only in smooth air." The Red line, or V_NE for all operation, is 143 mph (IAS).

However, the POH is confusing (at least to me) about this. In the 'Overview of speed limits' section, it specifically states that "Maneuvering speed (V_A)" is 109 mph (IAS), which does coincide with the airspeed indicator markings. Elsewhere, in the 'Operating Limitations' section, it states "Maximum maneuvering speed (V_A)" is 85 mph (IAS). Further, in the 'Emergency Procedures - Extreme turbulence encounter' section, it states "When an area of extreme turbulence is encountered, reduce airspeed to approximately 85 mph. Do not reduce the airspeed to lower values to prevent the aircraft from stalling due to turbulence." For reference, stall speeds at M.TO.W. of 1232 lbs. at zero angle of bank is 43 mph (IAS) Flaps down (V_SO) and 49 mph (IAS) Flaps up (V_S).

Is this confusing to anyone else or am I missing something?

[EDMO 1078]

Ed-

I also have the KF Pilot's Guide rev. 2004-1. My best guess for the disparities is because my KF 4-1200 POH rev. 7/19/94 was published by Skystar Aircraft Corporation while the KF Pilot's Guide is published by Kitfox Aircraft LLC.

Yes, I believe that is correct Ed.

Ex., in the 'Required Placards and markings - Airspeed indicator range markings' section of my Aerotrek SLSA POH, it shows the Green Arc 50-109 mph (IAS) and defines it as: "Normal operation range. The lower limit is the maximum-weight zero thrust stall speed with flaps retracted, and the upper limit is maneuvering speed." The Yellow arc 109-143 mph (IAS) and defines it as: "Caution range - operation must be conducted with extreme caution and only in smooth air." The Red line, or V_NE for all operation, is 143 mph (IAS).

However, the POH is confusing (at least to me) about this. In the 'Overview of speed limits' section, it specifically states that "Maneuvering speed (V_A)" is 109 mph (IAS), which does coincide with the airspeed indicator markings. Elsewhere, in the 'Operating Limitations' section, it states "Maximum maneuvering speed (V_A)" is 85 mph (IAS). Further, in the 'Emergency Procedures - Extreme turbulence encounter' section, it states "When an area of extreme turbulence is encountered, reduce airspeed to approximately 85 mph. Do not reduce the airspeed to lower values to prevent the aircraft from stalling due to turbulence." For reference, stall speeds at M.TO.W. of 1232 lbs. at zero angle of bank is 43 mph (IAS) Flaps down (V_SO) and 49 mph (IAS) Flaps up (V_S).

Is this confusing to anyone else or am I missing something?

Don't take much to confuse me. I am going with caution, and mark my ASI with the lower numbers for the yellow arc.

I think I would lean toward Ed Downs' numbers.

ED in MO

[dholly 718]

Don't take much to confuse me. I am going with caution, and mark my ASI with the lower numbers for the yellow arc.

I think I would lean toward Ed Downs' numbers.

ED in MO

Yes, I agree regarding the Kitfox(s). But I am confused about the seemingly conflicting info in my Aerotrek POH.

[EDMO 1078]

Yes, I agree regarding the Kitfox(s). But I am confused about the seemingly conflicting info in my Aerotrek POH.

I wouldn't worry about it. Just slow down for manuvers and turbulance to the lower speed. 85 is nowhere near your stall speed.

Ed in MO

P.S. I don't think any of us will be doing aerobatics in this type of plane anyway. I went up with a WW2 instructor in a T-34 some years ago, and decided quickly that I was not capable of being a fighter pilot. After only about 3 minutes of twists, turns, etc, I asked him to please fly level back to the airport and let me get out and try to walk, or just sit down and watch the world spin by!

Edited 3 May 2012 by Ed In Missouri

[High Country 69]

Ok so I'm going to take a crack at this. I just finished up my private cert last June so its all still pretty fresh in my mind. The yellow mark on the airspeed indicator is NOT maneuvering speed it is for fastest cruise and only to be used during calm stable air. Maneuvering speed is NEVER indicated on an ASI because it changes with weight, reason being (going back to the beginning of this post) if you are flying a light aircraft you have to increase AOA a lot before the wing looses lift (critical AOA) and stalls giving you a lot of time to increase stress and load factors that may tear your aircraft apart, If you are flying a heavier aircraft you are already at such a high AOA that it doesn't take much increase in AOA to stall the wing, thus less time to break something. If your wing is stalled it is no longer creating lift thus it doesn't have stress on it and is completely safe as long as you recover from the stall which we should all be able to do with no problems right!!!

Hope this helps

-Robert-

[EDMO 1078]

Ok so I'm going to take a crack at this. I just finished up my private cert last June so its all still pretty fresh in my mind. The yellow mark on the airspeed indicator is NOT maneuvering speed it is for fastest cruise and only to be used during calm stable air. Maneuvering speed is NEVER indicated on an ASI because it changes with weight, reason being (going back to the beginning of this post) if you are flying a light aircraft you have to increase AOA a lot before the wing looses lift (critical AOA) and stalls giving you a lot of time to increase stress and load factors that may tear your aircraft apart, If you are flying a heavier aircraft you are already at such a high AOA that it doesn't take much increase in AOA to stall the wing, thus less time to break something. If your wing is stalled it is no longer creating lift thus it doesn't have stress on it and is completely safe as long as you recover from the stall which we should all be able to do with no problems right!!!

Hope this helps

-Robert-

Not disagreeing with you on the yellow arc - that is correct. However, lets say the top of the green mark is the manuvering speed, or maximum cruise speed in turbulant air (at gross weight, I think), so the start of the yellow is still the manuvering speed.

Ed in MO

Edited 5 May 2012 by Ed In Missouri

[John_L_Seagull 0]

Hi

The start of the yellow Arc

would be the end of normal operating Range of Speed and the start of the caution Range of Speed

Green Arc: Normal Operating Range

The green arc shows the normal operating range of the airplane.

The speed at the bottom of the green arc, abbreviated Vs1, is the stall speed with the flaps and landing gear retracted, power at idle,

and the airplane at maximum gross weight.

The top of the green arc shows the high end of the normal operating range,

the maximum structural cruising speed, abbreviated Vno.

Yellow Arc: Caution Range

The yellow arc represents the caution range—speeds appropriate only in smooth air.

The top of the yellow arc coincides with Vne, the never-exceed speed of the airplane.

Red Line: Never-Exceed Speed

A red line near the top of the airspeed range marks Vne.

Exceeding this speed even in smooth air could damage the airplane structure.

White Arc: Flap Operating Range

The white arc shows the range of speeds in which it's safe to extend full flaps.

The upper limit of the white arc is called Vfe, maximum flap extended speed.

Extending the flaps at higher speeds could cause structural damage.

The lower limit of the white arc, abbreviated Vso,

is the stalling speed or minimum steady flight speed at maximum gross weight with the flaps and landing gear in the landing position.

PS: Here's a pic to show the Range of speeds

Edited 6 May 2012 by John_L_Seagull

[EDMO 1078]

Good photo and description. I will go check my factory KF2 ASI and see how they marked it to compare with Maneuvering speed listed.

When I mark my new ASI, the yellow will start at 80 - my conservative estimate of a "slow-down and don't break it" speed for my plane.

Ed in MO

Edited 6 May 2012 by Ed In Missouri

[dholly 718]

Your normal and caution speed arcs are looking a little goofy to me.

[John_L_Seagull 0]

Your normal and caution speed arcs are looking a little goofy to me.

Glad you noticed that lol

old pic from when I bought the plane,and it was late when posting

[dholly 718]

Yeah, it was late when I saw that, and I had to rub my eyes a couple times before my brain went that ain't right!

Now, I want to know what the red and blue lines within the White Arc on the other pic above represent...

[EDMO 1078]

Yeah, it was late when I saw that, and I had to rub my eyes a couple times before my brain went that ain't right!

Now, I want to know what the red and blue lines within the White Arc on the other pic above represent...

I had to take a second look at that too Doug.

The Red line at the lower airspeed is in the wrong place. It should be below the green arc, and should indicate the stall speed. Some pilots put a short yellow arc between the red line and the lower end of the green arc to represent a safety factor before sure flying speed is reached, or to indicate being close to stall speed espedially when winds are gusty.

The BLUE LINE - I never heard of it and dont have a clue, unless it could have something to do with one engine operation on a twin,

But really dont think that is the answer. Got to dig out my AMT books again!!!

Ed in MO

Edited 10 May 2012 by Ed In Missouri

[John_L_Seagull 0]

Multi-engine aircraft , have two additional airspeed markings

(except really large aircraft)

A red line near the lower limit of the airspeed range indicates minimum controllable airspeed, Vmc

This is the lowest speed at which the airplane is controllable when one engine is inoperative and the other engine is operating at full power

A blue line on the airspeed indicator marks best single-engine rate of climb airspeed Vyse

This speed delivers the best rate of climb with one engine inoperative.

ps:

Airspeed indicators on large aircraft, like the Boeing 737-400

don't have these markings because the speeds they represent vary considerably depending on aircraft weight, power settings, and other factors

Pilots calculate these speeds before each takeoff and use markers called "bugs" on the airspeed indicator as reminders of those speeds under current conditions.

Edited 10 May 2012 by John_L_Seagull

[EDMO 1078]

Multi-engine aircraft , have two additional airspeed markings

(except really large aircraft)

A red line near the lower limit of the airspeed range indicates minimum controllable airspeed, Vmc

This is the lowest speed at which the airplane is controllable when one engine is inoperative and the other engine is operating at full power

A blue line on the airspeed indicator marks best single-engine rate of climb airspeed Vyse

This speed delivers the best rate of climb with one engine inoperative.

ps:

Airspeed indicators on large aircraft, like the Boeing 737-400

don't have these markings because the speeds they represent vary considerably depending on aircraft weight, power settings, and other factors

Pilots calculate these speeds before each takeoff and use markers called "bugs" on the airspeed indicator as reminders of those speeds under current conditions.

Figured it was something like that. Will remark mine if I put twin Soobs on it! Been too long since I flew twins.

For the single-engine, the red line should still be at stall speed, I think. I never look at it when landing - from flare to touchdown, too busy trying to fly - or not fly!!!

Ed in MO

Edited 10 May 2012 by Ed In Missouri

[John_L_Seagull 0]

Twin Soob's....cool

I'm the same,keep a stable approach speed

then flare is all out the window