MYTH. I can fully deflect controls Below max Vno

[Ultralights]

MYTH: I CAN FULLY DEFLECT THE CONTROLS BELOW MANEUVERING SPEED!

 

The wing structure in light planes is usually certified to take +3.8 G's, -1.52 G's (plus a 50% safety factor). Put more load on the wing than that and you should consider yourself dead.

 

But here is the nice part: Below a certain speed, the wing simply cannot put out a full 3.8 G's of lift! It will STALL first! This speed is called "Maneuvering Speed". "Maneuvering Speed" is defined as the maximum speed the plane can be moving and still STALL before the WING BREAKS no matter how much you pull back on the stick.

 

If you are going slower than this and you pull all the way back on the stick, the wing will STALL WITHOUT PHYSICALLY BREAKING. If you are going faster than this and you pull all the way back on the stick, the wing can put out so much lift that it can be expected to break. So, as a result of the info above, people think they can deflect the stick as much as they like below maneuvering speed and stay alive. WRONG! The maneuvering speed is based on pulling BACK on the stick, NOT PUSHING FORWARDS!

 

Note what I said above: The "Maneuvering Speed" is defined as how fast you can go and not be able to put out more than 3.8 G's of lift... but the while the plane is certified for POSITIVE 3.8 G's, it is only certified for a NEGATIVE G-load of 1.52 G's!!!!! In other words, you can fail the wing in the NEGATIVE direction by pushing FORWARDS on the stick well BELOW the maneuvering speed!!!

 

Nobody know this. They just think they can fully-deflect the stick below Maneuvering Speed and live but THAT IS ONLY TRUE FOR PULLING THE STICK BACK AND BEING GUARANTEED 3.8 G's OF POSITIVE G-LOAD STRUCTURE, NOT PUSHING FORWARDS, WHERE THE WING CAN FAIL AT A MEASLY 1.52 G's!

 

Also, for airliners, certification requirements require that the rudder can be fully-deflected below maneuvering speed, BUT ONLY IF THE PLANE IS NOT IN A SIDESLIP OF ANY SORT! WHAT A LOAD CRAP! In a wonderfully-timed accident shortly after Sept 11 2001 that everybody thought might be terrorism, an Airbus pilot stomped the rudder in wake turbulence while the plane was in a considerable sideslip. The COMBINED loads of the sideslip and rudder deflection took the vertical stab to its critical load! A very simple numerical analysis based on the black box confirms this. The airplane lost its vertical stab in flight and you know the rest.

 

Also, if you are at your maximum allowable G-limit (say 3.8) and you put in some AILERON CONTROL, you are actually asking for MORE LIFT FROM ONE WING THAN THE ALLOWABLE LIMIT! SO COMBINED ELEVATOR AND AILERON CAN BREAK THE PLANE, EVEN IF THE ELEVATOR IS POSITIVE-ONLY!

 

 

[Guest Andys@coffs]

Just remeber though that 0 isnt the reference point, rather +1G is. As such using the example given the delta between normal and max +ve G is 2.8G similarly the delta between normal and max -ve G is 2.52G so while your correct, in the case you mentioned the difference is small... but not one to ignore.

 

Perhaps the most important factor that you havent covered is the non aerobatic trained pilot whose respective sustained G limits arent as good as the wings. In that case the wings will be fine while the plane finds its own way down.

 

Andy

 

 

[Guest pelorus32]

Also the use of Vno is wrong. The certification is for Va. That is the speed at which full control deflection will result in a stall before the load limit is reached. Va is usually substantially less than Vno.

 

Of further interest Va decreases as the mass of the aircraft decreases because the aircraft will stall at a lower speed with the lower mass.

 

Regards

 

Mike