Maneuvering speed

[shumway76]

Refering to C172N POH, the higher your aircraft weight, the higher is your maneuvering speed.

eg. 2300lbs, max maneuvering speed 97kts, 1900lbs, max maneuvering speed 85kts etc

Why is the max maneuvering speed higher when weight is higher?

[Morrisman1]

cos when you are lighter you can reach the max load factor of the aircraft at a slower speed. If you produce X amount of lift on a plane weighing 2000lb, then produce the same X amount of lift on the same aircraft but this time only weighing 1750lb then the loading of the airframe will be greater. Because Va normally relates to a maximum loading, then in order to not exceed this loading for the lighter aircraft they limit the airspeed, and hence the maximum amount of lift it produces and keeps the airframe within loading limits

[foxmoth]

Because the wing loading is higher and therefore the stall AoA is lower (remember - THERE IS NO SUCH THING AS STALL SPEED!).

Not sure about any of this statement - IIRC the stall AoA is actually the same no matter what the weight is. With a higher wing loading due to higher mass the 1G (and for that matter that at any other set G) stall will occur at a higher speed.

There is such a thing as a stall speed, but it does need to be defined!

[NzCaptainAndrew]

Va is the speed in which above it, it is possible to damage the aircraft structure before a positive stall is achieved with positive loading.
You can find this on a V-G diagram.

**
Two identical aircraft are flying at the same speed.

The heavier aircraft must maintain a higher AoA to maintain its straight and level flight path, compared to the lighter aircraft, which has a lower AoA

Hence for the lighter aircraft to reach the critical AoA (same for both aircraft) you need to pull harder to achieve the stall, in which some cases, you may exceed the maximum allowable positive G-Load factor for the airframe.

Simply put, a heavier aircraft is easier to stall than a lighter one.

I'm sure if you search the forums there are multiple threads on this topic, and many different forms of explainations

[Dg800]

Because the wing loading is higher and therefore the stall AoA is lower (remember - THERE IS NO SUCH THING AS STALL SPEED!).

But there is such a thing as a maneuvering speed, which is what the OP is all about. Actually reading the question before answering is a useful exercise. Add to that the fact that such a statement is utter bollocks, the stall AoA is constant for a given profile, irrespective of wing loading.

As for the original question, it's just like Captain Andrew said. With a higher wing loading you reach stall before you overstress the plane from a higher (i.e. greater speed) starting point than at a lower wing loading, exactly because critical AoA is constant but airspeed for a given AoA is proportional to the square root of current wing loading.

Ciao,

Dg800

[bravobravo74]

Because Va normally relates to a maximum loading

Va is the highest speed at which the abrupt application of full nose-up elevator will cause the aircraft to stall before the limiting load factor is exceeded.

Or so I read.

[Shaggy Sheep Driver]

Yes of course, I must have been asleep when I posted that, Stall AoA is a constant and I knew that, but the speed at which you reach it depends on loading. So there is still no such thing as stall speed. Or there are an infinate number of stall speeds - take your pick.

[Dg800]

I personally prefer the expression: "For a given wing loading, the stall speed is constant." This takes into the account both the static wing loading and the momentary load factor, which indirectly influences stall speed by changing the actual wing loading (actual_wing_loading = static_wing_loading X load_factor).

Ciao,

Dg800

[Shaggy Sheep Driver]

Dg - do you fly aeros? IAS is relatively unimportant when the 'G' loads are changing rapidly. AoA rules, you fly angle of attack, and as I've said before I'd gladly throw out a handful of the (not many) instruments in the Chippy for an AoA indicator!

[Dg800]

Dg - do you fly aeros? IAS is relatively unimportant when the 'G' loads are changing rapidly. AoA rules, you fly angle of attack, and as I've said before I'd gladly throw out a handful of the (not many) instruments in the Chippy for an AoA indicator!

Spiraling in tight thermals might qualify as aeros to some pilots (definitely to those I have taken along for a ride and who ended up barfing their lunch ), and I do that a lot as you can surmise from my forum handle. I usually don't turn with 2Gs but still I have experienced incipient stall at a significantly higher speed than that for level flight, exactly because of the higher apparent wing loading, while trying to maintain a low speed (< 100 kmh) at too high an angle of bank.
As I have no AoA indicator I still have to estimate stall speed for a given bank angle if I want to keep on not crashing into the mountainside every time.

Ciao,

Dg800

[Another St Ivian]

If you're painfully curious and want to know the textbook answer, most of the aircraft we fly are certified originally to an FAA Part 23 basis, for which the definition of the design speeds can be found here: 14 CFR 23.335.

The long and short of it is that at V_A, you should be able to apply full deflection in any singular control axis and not damage the aircraft. The weight dependancy simply comes from rearranging F=ma to a = F/m; As you decrease the aircraft's mass, you will have a greater accelaration. Since you want a constant accel (say, 6G), you reduce the speed such that you stall first.

Key thing to note is that V_A says nothing about cyclic application of controls - If you swing the rudder from stop to stop with abandon, even below V_A, don't be surprised if the tail falls off!

[Dg800]

Key thing to note is that V_A says nothing about cyclic application of controls - If you swing the rudder from stop to stop with abandon, even below V_A, don't be surprised if the tail falls off!

Further to that, design requirements actually specify that below Va you can apply full deflection in one axis only without compromising structural integrity. Pulling the yoke back to the stops while at the same time pushing it left or right to the stops will induce extreme torsional loads on the wing structure and you might not like the final result of such a maneuver. This applies obviously to utility type aircraft, full aerobatic capable aircraft have different design specifications as there are several aerobatic maneuvers that require you to do exactly that.

Ciao,

Dg800

[Another St Ivian]

Originally Posted by Dg800

you can apply full deflection in one axis only

Quite right - Thank you for picking that up. A swift edit has been made!

[Shaggy Sheep Driver]

If you're applying the 'G' gradually as in pulling into a steep turn, you can 'pull to the buffet' if your aeroplane is gentlemanly enough (like the Chippy) to afford you such a warning. In aeros, however, the 'G' is often pulled on quite sharply and it's dead easy to go straight through buffet (even if there is some) into departure.

Also, some aeroplanes (the Yak 52 comes to mind from my experience, though I've heard the Harvard and others do it too) will readily flick out of a manouvre with no warning if the aeroplane is even a bit out of balance when stall AoA is exceeded.