Full Scale Load Factor

[tommy321]

Alright...

So now, read the above, but instead of pulling back on the stick, imagine you get hit by a sudden gust of turbulence coming at you from below.

A gust from below will change the relative wind to increase the angle of attack... increase in angle of attack makes more lift, which increases the load factor, which gives you the kick in the pants you feel when flying through turbulence.

The absolute worst case scenario is that the gust of turbulence is strong enough to increase the angle of attack to the critical angle.... and we're back to the same argument as above. critical angle = maximum lift = maximum load factor at a given airspeed.

That's why maneuvering speed applies to moving the stick AND turbulence... they both do the same thing... increase angle of attack and cause the airframe to experience load factor.

There ya go... hope this helps.

Tom

[Mithrandir]

I seem to recall in FAR 23 the Maneuvering speed was the maximum speed at which full stick/Pedal deflections would not result in exceeding limit loads. The plane does not necessarilly need to be stalled. If there are automated systems limiting full stick deflections, this speed can be increased...

[Stainless Skills]

I think when you get into larger planes it begins to change like that but I still dont understand why VA increases when weight increases during turbulance.

[Imac Kiwi]

Again Load factor limits are based on the Max lift the wing can produce, which occurs just before the stall.

For a given externally applied acceleration force at a given airspeed and weight, you will get result (a). If you increase the weight, you will get less displacement for the same applied force.

[Stainless Skills]

Turbulance pushing on a light airplanes wings would move the airplane more causing more G's but would put a lesser force on the wings because of the lesser inertia from the lighter plane but a heavier airplane in turbulance whose wings are being pushed on by the wind has more inertia and so moves less than a lighter airplane in turbulance but has a greater force applied to its wings even though the G forces applied to the heavier plane are less. Am I getting this right? Is that what turbulance is about or not?

[OverTemp]

Same thing... turbulence can over-g an airplane if it becomes severe or extreme. Fly at a speed that's low enough and the plane will go into a temporary accelerated stalls before it over-Gs.

We have speeds to observe in our airplane that preserve the structure in varying conditions. For example, we have a max recommended speed that is good up to moderate turbulence. We have a design speed that is good in smooth air (this is actually based on shockwave induced drag). We also have a severe turbulence penetration airspeed which is the lesser of 180 knots or power-off-stall (determined by weight) plus 65 knots. In this last case the desire is the plane stalls before over-Ging.

One more thing... in faster aircraft, the faster the plane goes the firmer the air's grip on the wing. If you hit the same turbulence traveling at high vs. speed the shock loading on the wing is higher when travelling faster. If you were travelling at the slower speed the wing will have more of a tendancy to "mush" through the turbulence and the hits come at a slower pace. Kinda hard to grasp or explain, but you can really feel the difference when you hit a band of turbulence and you slow from 300 knots to 180 knots... you can feel the wings breath a sigh of relief

Cheers

[Stainless Skills]

Thats awesome, You could sort of imagine that when you think of a submarine in water but maybe even that doesn't work to well.

[jack01]

Stainless, to understand the shock loading, just think of it like the air is "harder" at higher speeds. Fall off a boat at 10mph, you get wet. Fall off at 50, and it hurts.

There is one thing about Va that I haven't seen anybody mention. VA is designed to protect the airframe against damage only when a single abrupt control input is given. In other words, it doesn't protect against rolling and pulling or rapid control reversals. For example, a Super Decathalon is rated for 6+, but only 4+ when you are rolling. Reason being, rolling in itself put a G load on part of the wing. Couple that with the G load from pitch changes, and you can overstress a wing. Another example is the airliner that blew the tail off during windshear. They were well below Va, but the co-pilot pumped the rudder back and forth about 4 times. That put the tail into what amounted to a sling-shot oscillation, where the tail flexed more and more each time, untill it broke.

[OverTemp]

The worst things you can do for a large airplane are :
1) rapid roll reversals
2) Applying full aileron is very short amounts of time
3) applying heavy assymetric G's (rolling while pulling).

It's broken wings off planes before. Unfortunately a lot of them were friends of friends.

[troposcuba]

fwiw, it's not much fun for us structural maintainers when a plane gets over G'd either! lots of work for us.

[jack01]

	Quote: Originally Posted by troposcuba
	fwiw, it's not much fun for us structural maintainers when a plane gets over G'd either! lots of work for us.

Lol! No kidding! I knew a guy who was a Crew Chief on F-14's. He used to just love it when new, arrogant pilots would brag about their flying abilities and then come back and report they over g'ed it.....

[3dav8r]

Over "G"ing make lead mechs very upset!!!!!