Flight Characteristics of Excessive Nose Weight

[Michael Massey]

I just rebuilt a fuselage a great flying airplane.  In that process, I converted it to electric from gas.  All of the critical dimensions are the same and all of the incidences are at zero.  On the test flights at the field, the plane now hunts and will not lock in to a stable level flight.  Following the convention of adding nose weight to help stabilize the plane did not help.  When I got home and did a careful CG measurement and fount the plane was very nose heavy.  The CG was about 1/2" forward of the design CG. 

To the question, tail heavy planes can hunt, is the same true of significantly nose heavy planes?  Thanks in advance for your thoughtful comments.

Mike

[Mark Scarborough]

yes,, as can lead out position, ANY friction or drag in controls,, any incidence variance ( which with a rebuilt airframe I would suspect)

[Larry Fernandez]

Mike, Give me a call

Larry, Buttafucco Stunt Team

[Brett Buck]

To the question, tail heavy planes can hunt, is the same true of significantly nose heavy planes?  Thanks in advance for your thoughtful comments.

  Hunting is almost never caused by being tail-heavy, and it is almost never cured by adding nose weight. Hunting is almost always caused by something in the controls binding somewhere. Back in the good old days, various people decided nose weight was the solution to every problem. Nose weight increases the stability, but hunting isn't caused by instability, or at least not classic instability.
   As you note, sometimes nose weigh causes hunting by binding up the controls. The more nose weight you put in (with no other changes)  the more load there is on the leadouts at the guide. Sometimes that causes the leadouts to bind a bit.

    Brett

[Air Ministry .]

it'll ' understeer , noseheavy - and turn OUT of the corner strongly , easing controls . This is with it ' way ' noseheavy .

Blunter Airfoils seem less prone than sharp ones to be useless , noseheavy .

[Trostle]

When a model is "excessively" nose heavy, it will be very sluggish on the controls.  Because it is nose heavy, the nose will tend to drop with neutral elevator.  To correct with up elevator, the model will not immediately respond until a lot of up elevator is applied and then the nose will start to rise, but the response will be slow.  Then when the nose rises, the model will start to climb and neutral elevator will not necessarily stop the climb, it will take a noticeable amount of down elevator to get the nose to rotate and the response will be slow.  You end up having to add elevator control almost 1/2 a lap before you see the response in either situation.  The model will look like it is on a roller coaster.  Then when there is any wind say approaching more than 7 or 8 mph, the situation is exacerbated as it goes around the circle.  (Don't ask me how I know.)  If the model becomes more and more nose heavy (as in carrying more fuel forward of the CG), the elevators will not be able to lift the nose and essentially becomes uncontrollable.

So, when a model is really really excessively nose heavy (a new term for all of you aerodynamicists), the elevators will not have enough authority to lift the nose.  That is a factor in the determination of the most forward CG on full size aircraft.

Keith

[Michael Massey]

Thank you all for sharing your expertise.  I will take a good look at each of the suggestions you gave.

I will have to say that this sport is one of the few sports where most everyone involved shares their expertise and are always willing to help.

Tx.

Mike