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7 Answers

FORWARD CG VS AFT CG- WHICH IS BETTER and WHY?

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Commercial Pilot, Flight Instructor, General Aviation, Private Pilot, Student Pilot

Oral Question:

What are the handling Characteristics of an airplane with a Foward CG? 

     Generally more stable

     Fly at a slower Airspeed due to more drag

     Stall at a higher indicated stall speed

What are the handling Characteristics of an airplane with an AFT CG? 

     Generally unstable aircraft

     Fly at a higher airspeed

     May be impossible to recover from a stall or spin

Yes, we want the CG to be within the CG Range of the aircraft, but which is better a Foward CG or an AFT CG? 

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7 Answers



  1. Mike on Feb 07, 2012

    Well, I think the answer to that is not as easy as pick one or the other.  A lot will depend on what you are doing and potentially where you will be flying.
    A transatlantic jumbo jet will obviously want the higher speed/less drag configuration as the chances of worrying about a stall or spin are very low.
    If I am flying bush plane in Alaska I would be more inclined to go with a forward CG as the plane will handle the elements better and there is a higher chance for a stall to occur, which if it does, I want the best chance to recover.
    So, I don’t think there is a best, but simply one is more suited for different applications.

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  2. Brian on Feb 07, 2012

    Being at the aft CG limit will almost always be the better of the two choices. First, aft CG doesn’t make the airplane unstable in pitch, design won’t let that happen because it’s unsafe. Furthermore, CG within the pitch range has a negligable effect on roll or yaw stability.
     
    The key to realize is that while an aft CG is less stable than a forward CG it is also more controllable. In fact, forward CG is set by the minimum allowable control in ground effect. In other words, when you land is when you’re most succeptible to run out of control in a forward CG condition. Get a strong down gust feet off the runway, you’ll be in a better position to handle it with an aft CG than a forward one.
     
    Long story short, aft CG gives better cruise speeds and better controllability to the pilot. So for all normal conditions it would prove more useful. The only time forward CG may prove better is during spins. Though, keep in mind, when you fly aerobatics you load to the aft limit specifically to have more control. Aft limit, by design, still has a safety margin above unstable built in. 19 percent MAC in a 172 loaded to the normal aft limit. 😉

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  3. Derek Schwalenberg on Feb 08, 2012

    Certain maneuvers like spins may require [depending on the airplane] that you are in the utility category. (typically more foward CG). Although an aft CG can be a bit more stable, [possibly more nose ‘heavy’ feel in the flare] but more comfortable for passengers. As long you stay within the weight and balance limits though this: http://www.youtube.com/watch?v=VTnW2TXOacY is less likely to happen to you.

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  4. John D. Collins on Feb 10, 2012

    The key point with CG is to remain within the limits for the aircraft.  If you are at the forward CG limit, you will find the nose heavy, particularly when landing. Forward of the limit, you may end up without sufficient control authority to flare and land.  At the aft CG limit, controls are lighter and stability is reduced.  It is easier to overload the airframe with excessive G forces with the controls with a CG at the aft limit. Beyond the aft limit, the aircraft moves towards becoming neutrally stable in pitch which means that a displacement of the controls will not result in a tendency to return to the trim attitude. Trim can be difficult to achieve.  If you are trying to set a world distance record, loading close to the aft CG will give you the best range, but short of that, most loading within the CG limits will not have a major effect.  Some aircraft have the fuel located forward of the empty CG location and as you burn fuel, the CG shifts aft.  It is possible to take off within the CG limits and end up outside the aft limit before you land.  On aircraft that have this characteristic, one normally calculates CG at takeoff and at landing and determines what the minimum fuel that must remain at landing to remain within the aft CG limits.  There are several factors that the pilot has available to adjust the CG location including: where passengers are seated; where the seats are adjusted to; sometimes the location of the seats (A36 allows forward or rear facing middle seats at pilot discretion); where the baggage is stored, where ballast is stored (in a nose heavy airplane such as most turbo aircraft, putting ballast in the rear makes it more controllable in the landing); and, how much and where fuel is stored and in what order it is consumed.

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  5. hasan on Mar 17, 2013

    Sir, I have forward CG limit from 2.40 to 2.46 And rearward CG limit 2.59.
    my question when I calculate the CG for my A/C it was 2.471 is this acceptable ? is the range of CG is between 2.46 and 2.59?
    thank you in advance.

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  6. Jack DeBiasi on Aug 22, 2013

    Personally I would want Forward CG since Aft CG makes it more difficult to recover from a stall. You here all these stories recently on these pilots that have difficulty recovering from stalls; as a result, the most logic answer would be to stay safe and comfortable since the aircraft won’t abruptly change pitch.

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  7. Svein Erik Aam on Apr 08, 2015

    When I was in college for my career as a professional pilot I preformed Weight and Balance for normally 8 to 10 flights for Continental airlines at Stapleton International airport. The fact that Denver is the Mile High city and when the temperature rose above 60 deg F, the amount of payload that each aircraft could take off with was greatly reduced. So the Capt would talk to the Dispatcher and they would find a way to decrease the Burn Off for the flight. Hence less required fuel. So the fuel loaded was decreased. So the pressure was on the crew to ask for Higher altitudes, direct headings, etc.. Any way to decrease the fuel burn. As a Load Planner I would plan and have the aircraft loded so that the CG was just forward of the aft CG limit. That reduces the drag caused by needing the Horizontal Stabilizer to create a large Tail down force. Decreasing the amount of Drag hence increasing the Nautical Miles per pound of fuel.

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