The International Cessna^® 170 Association

Excerpt:

"Many pilots believe that as long as the airplane is at or below this maneuvering speed, they can make any control inputs they desire without any risk of harm to the airplane. This is not true.

The design maneuvering speed (VA) is the speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane.

Even though the accident discussed above is a part 25 airplane, VA is applicable to part 23, CAR 3, and LSA airplanes."

Full Bulletin:

Another interesting point about Va is that it decreases as gross weight decreases. That is because at a given airspeed, a given force (full control deflection) will cause a lighter airplane to undergo more acceleration (g's). In the case of full up elevator application, the maximum lift load on the wings will be the same (more g's but at a lighter weight), but loads on things like engine mount, occupied seats, and cabin and baggage compartment floors will increase.

Using the math from the referenced bulletin, an airplane with a Va of 115 mph at 2200lb (170B, per the AFM) will have a Va of only 104 at 1800lb.

Since that time, a second Airbus has lost a fixed flight control in flight..with all passengers and crew lost.

Green Bean wrote:Since that time, a second Airbus has lost a fixed flight control in flight..with all passengers and crew lost.

There are two airplanes in airline use that I have been known to completely change travel plans because they were the assigned equipment. DC-10/Airbus. I simply won't ride in them. (Other aircraft include MU2, early Lear, OV-103...)
I have had no qualms about V-tail Bonanzas or DeHavilland Comets...but I won't get in those others mentioned.

Good Choices ,, Your up late tonight George.. Waiting out the storm, somewhere?

I'm home. Made the mistake of downloading an accident investigation report and got side-tracked reading related stuff.
It got down to 8-degrees F. (Finally got to bed at 5 AM and Jamie awoke me at 6 AM to tell me the electricity apparently failed after I went to bed... which shut down the recirculation pump and our hot water lines are frozen)

Another interesting fact about maneuvering speed is that air density affects it. True airspeed increases as air density decreases. At high altitudes it becomes possible, during a dive or long descent, to inadvertantly exceed manuvering speed while the airspeed indicator suggests the aircraft speed is safely above it.

Robert Eilers wrote:Another interesting fact about maneuvering speed is that air density affects it. True airspeed increases as air density decreases. At high altitudes it becomes possible, during a dive or long descent, to inadvertantly exceed manuvering speed while the airspeed indicator suggests the aircraft speed is safely above it.

Isn't Va a calibrated airspeed, just like stall speeds? And did you mean "safely below it"?

The same is true about VnE.

Va is a calibrated airspeed and yes I meant safely below it.

Robert Eilers wrote:Va is a calibrated airspeed and yes I meant safely below it.

Then I don't understand your point about air density affecting it, unless you meant that Va happens at different true airspeeds depending on air density. But Va on your airspeed indicator is the same, regardless of air density. I believe the same is true for all the V-speeds, isn't it?

jrenwick wrote:

Robert Eilers wrote:Va is a calibrated airspeed and yes I meant safely below it.

Then I don't understand your point about air density affecting it, unless you meant that Va happens at different true airspeeds depending on air density. But Va on your airspeed indicator is the same, regardless of air density. I believe the same is true for all the V-speeds, isn't it?

According to this article, flutter is a true airspeed phenomenon. Flutter, however, is not the only downside to exceeding Vne. Things like gust overload, or blowing out a windshield are dynamic pressure phenomena and thus are related to indicated (actually calibrated) airpseed. The 170B AFM states Vne at 160mph "True Indicated Airspeed" which I think is 1940's and 1950's language for what we now call calibrated airspeed, which makes me believe that a 170 is going to start shedding parts due to dynamic pressure overload before flutter sets in.

jrenwick wrote:...But Va on your airspeed indicator is the same, regardless of air density. I believe the same is true for all the V-speeds, isn't it?

Va isnt marked on your airspeed indicator. It's based on your weight and density altitude.

VnE is marked on your airspeed but is also dependent on density altitude...for the flutter part at least. Flutter happens when air molecules pass by the airplane at a certain velocity. That particular velocity of particles causes the plane to resonate...break apart.

Your airspeed indicator measures air pressure, not speed. This works fine for most places our tiny engines can take us represents V-Speeds rather well.

Vs is based on Air Pressure. So, the thinner the air, the faster you have to move thru it ( to get the same pressure) to keep from stalling. The ASI shows the same 'speed' because it's really pressure. High Density altitude requires higher air speeds to maintain air pressure to not stall.

At really really high density altitudes, air pressure is very low when air speed is very high.

At some point, the two (Vs and VnE) actually pass each other on the graph and you'd have to fly past VnE to avoid stalling...if you had a big enough engine.

Best example of this is the U2 spy plane. At 70,000 feet there was only a 10knot spread from Vne to Vs.

But us low altitude folks don't normally have this problem....unless you're a high performance sailplane.

...that's officially my longest post.

bagarre wrote:

jrenwick wrote:...But Va on your airspeed indicator is the same, regardless of air density. I believe the same is true for all the V-speeds, isn't it?

Imagine the ultimate stress placed upon the airframe in LIFT:

The max lift attainable at any airspeed occurs when the airplane is at CL-max.
Since maximum lift must be equal to the weight at the stall speed...if the airplane is flying twice the stall speed and the AOA is increased to obtain CL-max, a factor of 4 will result. At 3 times the stall speed, 9 G's will result, etc etc. Therefore any airplane which has high speed performance must have high manuevering load factors.

In the case of the 170, the gross-weight ultimate load factors are reached at 115 CAS and are reached at lower CAS at lighter weights (because at lighter weights stall speeds and man. speed also decreases.) However, for practical purposes in this airplane, IAS can be substituted for CAS and Density Altitude has negligible effect on stall or manuevering speeds and may be disregarded.

Anyone curious about where I got these ideas can consult Aerodynamics for Naval Aviators -"Aircraft Loads and Operating Limitations", pg 331.

gahorn wrote:

Green Bean wrote:Since that time, a second Airbus has lost a fixed flight control in flight..with all passengers and crew lost.

There are two airplanes in airline use that I have been known to completely change travel plans because they were the assigned equipment. DC-10/Airbus. I simply won't ride in them. (Other aircraft include MU2, early Lear, OV-103...)
I have had no qualms about V-tail Bonanzas or DeHavilland Comets...but I won't get in those others mentioned.

My limitation includes ALL PLASTIC airplanes. That's why I fly Alaska and Southwest, no plastic.