Does moving C.G. back make a plane 'snap' less?

[rosco]

Thanks for reading.
I have a plane with a nasty snap if you get it flying too slow.
Will moving the C.G. back make it less likely to snap? I am thinking this because moving your C.G. back will decrease your landing speed.
cheers
rosco

[JetPlaneFlyer]

Moving the CG back wont make any significant change to low slowly the model can fly. And if by 'snap' you mean tip stall then movng the CG wont help that either.

Minimum flying speed is to a large extent down to wing loading. So to decrease the stall speed the most effective way is more wing area or a lighter model, or both.
The best way to prevent tip stall is to build in some 'washout' this is a twist in the wing so that at the tip operates at a lower angle of attack than the wing root. When building a wing this would usually be achieved by packing up the trailing edge at the tip. Depending on the wing construction of your model it may be possible to twist some washout in.

Steve

[Andrew McGregor]

Does it always snap the one way? If so, you might need your lateral balance fixed, and perhaps the rudder trim as well. Won't change the stall speed, but might well improve the plane's manners when it does stall.

Best way to fix up rudder trim is to attach about a meter of string to each wingtip and then trim the rudder so the tail flies centered between the strings at cruise throttle. For even more accurate trim, find out where it has to be at idle and full as well, then set up a mix that will keep the rudder trim set at all throttle settings. This is a great idea on scale models, as fullsize the pilot would be dealing with rudder trim in this way too.

[vintage1]

washout or lower wingloading is the only solution.

[Texas Buzzard]

Thanks for reading.
I have a plane with a nasty snap if you get it flying too slow.
Will moving the C.G. back make it less likely to snap? I am thinking this because moving your C.G. back will decrease your landing speed.
cheers
rosco
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If the only change you make is to move the C of G back towards the tail then the ship should become more sensitive to elevator input.

When flying as in the landing pattern ( at a slower speed ) a slight stall can induce "tip stall" which results in a "snap-roll" of some sort. At higher wing loadings as in WarBirds tip stalls can "eat your lunch".

[rosco]

Thankyou for your input gents.
The plane is a Jaeger...it is a hotliner here is Australia. There is not many around.
I will dial a bit of wash-out into the ailerons.
I still may move the C.G. back. The problem is, that unlike its prototypes, its tail has been built heavier and just to get the C.G. near the prescribed position, I have had to add 42grams of lead up at the nose. This is with a 220gram motor and speedie and batteries pushed right up behind the motor.
A person(who has been very helpful) suggested that adding even more lead or a heavier motor has helped another one of these planes. Although like yourselves, I am not to easy with increasing the wing loading.

I am actually wanting to move the C.G. back mainly for the reason of removing the lead and hence reducing the wing loading. We will see.
cheers
rosco

[JetPlaneFlyer]

I will dial a bit of wash-out into the ailerons.

Moving the ailerons up wont work the same as 'proper' washout. All it will do is decrease the lift that the wing can produce and therefore increase the stall speed... not good!

[rosco]

Thanks again for the input.
I think we have solved it...
We moved the C.G. back by removing 1 piece of lead at a time. I am happy that we have lost 42 grams from the airframe.
The elevator is still fine, not too touchy.
But I think the thing which has stopped the nasty tip stall is that we removed the aileron to flap mixing. The flaps were getting about 1/4 of the aileron.
Now the plane is a piece of cake.
Thanks again.
cheers
rosco