Selected Stall Speeds

[Stoney]

Just wanted to make sure load factor didn't impact the formula differently.

[hitech]

Stoney, Load factor, or more accurately AOA would effect the numbers slightly do to the definitions of lift being perpendicular to Vel vector. And as you rotate the plane, the moment arms of tail and wing change in respect to the CG. I.E. (extreme example) when you are straight up, and your vel vector is parallel to the ground. You CL is now below the CG. Now drag is creating the torques and lift is not creating any. The same effects are happing at any AOA. But this is a very small effect and can be estimated by simply multiplying the additional lift with the cosine of the AOA.

HiTech

[Soulyss]

I do enjoy these threads even if I can only wrap my head around about half of it and even that small portion gives me a headache.

[Stoney]

Stoney, Load factor, or more accurately AOA would effect the numbers slightly do to the definitions of lift being perpendicular to Vel vector. And as you rotate the plane, the moment arms of tail and wing change in respect to the CG. I.E. (extreme example) when you are straight up, and your vel vector is parallel to the ground. You CL is now below the CG. Now drag is creating the torques and lift is not creating any. The same effects are happing at any AOA. But this is a very small effect and can be estimated by simply multiplying the additional lift with the cosine of the AOA.

HiTech

So, using your example earlier:  A 10,000lb plane in unaccelerated flight with the CL 6 inches behind the CG and tail at 15 feet would have lift = to 10,000*1.0333.  Assuming the plane stalled at 15 degree AoA, lift would equal 10,333*cos(15) = 9980?  If that same aircraft stalled during a 3g sustained turn, lift at the stall would be = to 9980*3?  Or, would it simply be better to assume the 1g lift number to determine Clmax and then use that to plug into the Clmax during the 3g turn?  I'm assuming the latter.

Ultimately, I don't have any weight and balance data for these aircraft, so I assume I'll just have to add a disclaimer.

[hitech]

Stoney


((CG - CL) / TailLengthFromCG * Cos(AOA)  + 1) * Weight;


HiTech

[hitech]

Or in your example

10000 + (333 * cos(16)) - (Thrust * sin(AOA - IncidenceFromThurstLine)) is Required lift;

HiTech

[Ardy123]

The spinning of the prop creates a spiraling/corkscrew airflow behind the prop correct? wouldn't this affect the AoA on the wing roots where the prop-wash would hit the wing? Is this impact negligible?

[Krusty]

It's not negligable. You notice it in left/right turns.

EDIT: I mean right turns as compared to left turns, and vice versa.

[Ardy123]

Oh I thought the pull to the left or right was the engine torque? or is the thing I mentioned above not modeled.

[Krusty]

Well, there's the torque, but I thought it also had to do with which wing had more airflow over it because of the prop direction..

Now that you mention it, I could be totally wrong.

[FLS]

Oh I thought the pull to the left or right was the engine torque? or is the thing I mentioned above not modeled.

The engine torque is negligible compared to the spiral slipstream. IIRC both are modeled.

[Charge]

"10000 + (333 * cos(16)) - (Thrust * sin(AOA - IncidenceFromThurstLine)) is Required lift;"

Errr, so even with a trim change the total weight of the aircraft does not "increase" because it is absolute. Dynamically it "increases" if you use it as a function to e.g. available thrust but I'm not sure if I understand it that way.

The FWD heavy trim difference would cause a need for a change in elevator trim that would turn into drag and into a need for more thrust if the same speed is to be maintained. With this logic you could extend the CoG a certain distance ahead from CoL until the tail would run out of either aerodynamic elevator authority, or leverage, or the a/c would run out of thrust to maintain level flight. Well, dynamically it resembles the situation where the plane suddenly got "heavier" but only as a function to control authority and that way to drag and again that way to available thrust?

But if the CoG is aft of the CoL the aircraft is not "lighter" but the elevator drag increase for correction is almost the same as is the need for additional thrust to make up for the difference or the speed will again decrease.

Am I even close?

-C+

[FLS]

No one said the weight increases. The weight is a load on the wing and the load on the wing increases because you're adding the downforce on the tailplane needed for level flight.

[hitech]

Charge to think about it, take a stick and hold it up with a finger under each end. as long as each hand does not cross center , the sum of the weight on each hand is = to the weight of the stick. This is the case where both tail and wing are lifting.

Now take the stick and move your left hand underneath the stick 1/4 of way from the right and your right hand on top of the stick on the right end.


Your left hand is now holding the weight of the stick, plus how much your right hand is pushing down on the stick to keep it level. This is force we are speaking of.

HiTech

[OOZ662]

Not sure if this would help in this discussion, but NASA has a few Java applets that demonstrate airfoil effects, such as this one.