Increased Stall Speed with Forward C.G.

[turbojet28]

Could anyone help explain, or direct me to a website, how and why stall speeds increase as the C.G. moves forward? I have searched for a little bit on Google and have looked through past threads, but can't seem to find a good answer.

Aircraft are designed so that the C.G. is in front of the center of lift, giving the aircraft a nose-down tendancy. Therefore, the horizontal stabilizer is set at an angle of incidence that will produce negative lift, which holds the nose up. So, as the C.G. moves forward, more force will need to be exerted downward by the horizontal stabilizer to maintain the desired angle of attack. But why, then, does stall speed increase as the C.G. moves forward? Thank you very much for answering!

 

[Dazzler]

Think of it this way:

The more "nose-heavy" the aircraft, the more lift the wings have to produce to maintain a given airspeed at constant altitude. Therefore, if you pitch the nose up, the aircraft is going to reach its critical angle of attack "sooner" i.e. at a higher airspeed. Therefore the stall speed is higher.

 

[cime_sp]

To add to the previous post a little.....

If you are nose heavy, you need to have an equal amount of tail down force for the aircraft to remain balanced in flight, correct? Well, the issue here is that the wings now need to lift this "extra" down force as well as the weight of the airplane. In order to create the extra lift needed the wing needs to be at a higher angle of attack for a given speed.

Example (numbers are made up but illustrate the point):

In "normal" balanced flight at 100 knots you need to mantain 2 degrees nose up in order to maintain level flight. Now, in a nose heavy situation, you may need to maintain 4-5 degrees nose up to keep level flight at 100kts. You are now closer to the critical angle of attack.If you work your way down the speed scale towards the critical angle of attack, with a nose-heavy aircraft, you will exced the critical angle at a higher airspeed.