In an airplane with an extremely aft CG, very light back elevator control forces may lead to inadvertent stall entries and if a spin is entered, the balance of forces on the airplane may result in a flat spin. If the cg is behind the wing centre of pressure then the tailplane must always be producing an up force to balance it. An airplane has been loaded in such a manner, that the CG is located aft of the aft CG limit. When the CG in an airplane is located at or rear of the aft CG limit, the airplane a. Anatomy of a Stall • Idle thrust, wings level, 1-g deceleration • As airplane slows down – 1-g, Lift = Weight – Decrease in velocity – Increase in angle of attack (α) and therefore C L • Eventually αand therefore C L reach the maximum that the wing can produce • Flow separates, lift decreases, n decreases 2) Lower cruise speed ( wings at kept at higher angle inorder to get higher lift and compensate for downward pull at tail end. ) As the CG moves aft, it reaches a point where the stick force per knot drops to zero, then reverses. I tested stall speed at forward and aft CG, in this case no difference, although usually there is about a one knot difference (slower at aft CG). place the forward CG limit as far rearward as possible to aid pilots in avoiding damage when landing. How CG Affects Aircraft Performance is essential in understanding how your aircraft reacts to various loading situations. Aft CG • Benefits: – Lower fuel burn – Faster cruise speed – Higher stall speed • Drawbacks: – Airplane is not as stable – Harder to recover from stalls, spins • Overall, better for cross country flights • Benefits: – Lower fuel burn – Faster cruise speed – Higher stall speed • Drawbacks: – Airplane is not as stable – Harder to recover from stalls As the CG moves aft, the aircraft becomes less and less stable at all speeds. Whether a CG is more aft or more forward makes all the difference in the world! Aerodynamics 101. A CG that is too far aft or rearward can inhibit the natural tendency of the aircraft’s nose to fall during a stall—an aerodynamic tendency that aids in stall recovery. For a statically stable airplane the required column force, as speed varies from the trimmed condition, is less at an aft CG than it is at a forward CG. All these \olve closing speeds of 1,400 mph gadgets cost in weight, and the and cover miles of sky. In this paper, the control scheme of a distributed high-speed generator system with a total amount of 12 generators and nominal generator speed of 7000 min⁻¹ is studied. If we're just talking stalling speed then an aft cg reduces stall speed. 2. Just as when it’s aft, a forward CG presents important aerodynamic issues, which can adversely affect rate of climb, cruise airspeed, stall speed, fuel burn rate and airplane handling characteristics. as the first case the airplane won't stall. 1) Decreased longitudinal stability. We used ballast weight and a passenger (Colby Wallick) to move the weight and balance to this edge of the envelope. Swept wing jets often have rather bad stall manners so we would only practice recovery from a heavy buffet. Stall speed increases so both takeoff and landing distances increase. Aircraft stability? A. Forward CG. But I'm unclear in determining a maximum aft CG position for stall or near static conditions with stall/spin recovery my primary concern. A. Stalls occur not only at slow airspeed, but at any speed when the wings exceed their critical angle of attack. The stall originates at the stall strips, which are about 30 inches outboard from the fuselage. Indeed, the most critical CG violation would occur when operating with a CG that exceeds the rear limit. (Cons) Higher stall speed – stalling AOA is reached at a higher speed due to increased wing loading. Less drag = higher cruise speed, lower fuel consumption and more range. Desirable Stalls. A forward CG location will often cause the stalling angle of attack to be reached at a higher airspeed. In the benchmark model, the aerodynamic torque is estimated using (1), that is a nonlinear function of rotor speed (v r ), blade pitch angle (b), and wind speed (v w ) (Odgaard et al., , 2013. As a result, you can burn less fuel to maintain the same speed (or increase your speed for no additional fuel burn) compared to a forward CG. The minimum average gradient allowed by U.S. Federal Aviation Administration FAR Part 25 is one pound for each six knots. = 68.7" aft of datum Rearward limit 30% Wing chord 17.4" from L.E. Any further aft on the cg and it would have been uncontrollable. This video covers the build-up to as well as the heavy aft flight test of the airplane. What will happen to stall speed? Difficulty in recovering from a stalled condition * C. Stalling at higher-than-normal speed. In this video we look at the benefits of loading with an AFT center of gravity. herding, housework, stable and stall clearing, nursing children, feeding cattle, running errands and what whatever ever whatever else the master may require them to do. 4. This condition may necessitate a forced nose-down attitude to recover. If the CG moves either forward or aft of this range then interesting things happen. Forward vs. Aft CG. But why are lift and CG location related? 2.4.6 The icing and the pollution of the wing When the leading edge accumulates ice, for the same angle of attack, the lift decreases. Loading an aircraft to the most aft CG (center of gravity) or beyond is a very dangerous practice. FacebookTwitterGoogle+ Let’s face it, understanding how an aircraft’s center of gravity position effects things like stall speed or cruise performance is tough. In addition to decreased static and dynamic longitudinal stability, other undesirable effects caused by a CG location aft of the allowable range may include extreme control difficulty, violent stall characteristics, and very light control forces In level flight, approaching the stall in this case, the moment produced by the wing lift about the cg must be balanced by the up or down force from the tail. So to stall an airfoil the plane may be going at a slow speed, or a very high speed; this would be called an accelerated stall. A longer takeoff run. These characteristics are determined at the aft CG when stall speed is at its slowest. In fact, if you push both front seats in a 172 all the way aft (causing a more aft CG) you'll see about a 5kt speed increase if you re-trim the airplance for cruise. Follow along with me as I … Everything about a canard is more critical. It can go to the case one angle of attack and a higher load factor will result before stall as a result. The horizontal tail can not provide the pitching authority needed to support the wing loading (tail stall) 3. 1) Increased longitudinal stability. Becomes less stable at all airspeeds., and c. Could be difficult to flare for landing. This is particularly important in spin recovery, as there is a point in rearward loading of any aircraft at which a “flat” spin develops. This airplane has very benign stall characteristics, less than 5 deg of roll, and very little aileron input is needed to keep the wings level. Page 27, Subunit 1.11, New item 3.g.1): This update expands our discussion of … To stall a wing at a slow speed is accomplished by trying to maintain altitude with up elevator while continuing to slow down till the wing exceeds the critical AoA. At that CG loading a stall could only be made to break with some acceleration by snapping the yoke aft the last little bit. There are, of course, some safety concerns. Aerobatic Gross weight. This explains a very small increase of the stall speed at forward CG. Failure in stall recovery can lead to spin. One undesirable flight characteristic a pilot might experience with this airplane would be _____. If the aircraft were to stall, an aft CG makes it more difficult to lower the nose to get the wing flying again and recover from the stall. At the same given speed, etc. As long as you ensure you remain within your aircraft's CG envelope, you can test this out by having a passenger shift their seat aft while in cruise. reduced compared to aft CG. On the other hand, the angle of attack for stalling is lower with an iced profile (refer to drawing). A "stall" occurs as a result of one of two events: 1. With aft CG 27.5% 1375 lbs Of cord or (15.9” aft of leading edge) Maximum baggage (Subject to Weight & Balance) 100 lbs 2.06 Center of Gravity Limits Design CG range is: Forward limit 15% Wing chord 8.7" from L.E. To understand the stability imagine the tail down force and main wing lift force are fighting each other; similar to a group of people playing tug of war. If a stall with an aft CG is allowed to progress to a spin, it may be unrecoverable, even in an airplane certified for spins. When you create more lift, you create more induced drag, and your performance goes down. The opposite is true for aft. Develops an inability to recover from stall conditions and, b. Loading an airplane to the most aft CG will cause the airplane to be _____. The CG (Centre of Gravity) for an aircraft usually has a specific permissible range within which the stability of the aircraft is unaffected. Landing Distance- increased landing distance and speed needed to avoid a more probable stall with the aft CG. Cruise speed? After the fact I learned that minor variations in how they are built can show up in the stability/CG department. stall speeds - mph cas angle of bank condition 0° 20° 40° 60° 2300 lbs flaps up 57 59 65 81 gross flaps 10° 52 54 59 74 weight flaps 40° 49 51 56 69 power off -- aft cg. An aft CG location, while lowering an aircraft’s stall speed, is the most dangerous because with extreme aft CG positions it may be impossible to pitch down to reduce the angle of attack to recover from the stall. Recovery from a flat spin is often impossible. A full stall could take many thousands of feet, if available. Stall speed is increased when the wing surfaces are contaminated with ice or frost creating a rougher surface, and heavier airframe due to ice accumulation. The recovery from a stall in any aircraft becomes progressively more difficult as its CG moves aft. Since the tail load with an aft CG is up on the airplane the wing will need to decrease the angle of attack to try to keep the same 1 g load factor as in the first case. "Landing Distance- increased landing distance and speed needed to avoid a more probable stall with the aft CG." Heavier or more aft CG it would easily break into a classic stall and nose drop. It was very unstable. = 77.4" aft of datum I found that just 1/2 inch of cg change can make a very noticeable difference in flying qualities. 3) Higher stall speed ( easier to recover from a stall but increased drag ) 4) Low fuel efficiency ( due to drag ) Aft CG. CG: Your Airplane's Balancing Act. The relationship between your aircraft's performance and CG location is simple: by moving your CG forward and aft, you change the amount of tail down force and lift you need for stable flight. The recovery from a stall in any aircraft becomes progressively more difficult as its CG moves aft. B. The wings can not support the load of the weight being carried.