F1B C of G

[Anonymous]

I am repositioning the pylon on my Vivchar F1B.Should the C of G be at 55% wing chord. I need a ball park starting point rather than specific knowledge of this model.The model is a few years old and was my first in this class, so I am having an improvement session with it. The original position I set it in was 60%.which I suspect was a little too rearward.

[Roger Morrell]

On that model 60 is too far back. 55 to 58. Probably 56

On Vivchar models it is easy to experiment with the CG by making weights out of brass that look like oversize wheel collars. These fit in the back of the hub over the bearing housing. Just like a wheel collar you use a set screw to hold them on. You can make a weight of up to 10 grams that will fit in the model and not foul anything.

This will let you experiment before you move the pylon as moving the pylon is quite drastic and can damage the motor tube so you want to get it right.

For the model to climb well you need at least 3.5 degrees of decalage.

I use weights like this to move the CG forward for thermal, very windy or wet conditions.

Roger

[Anonymous]

Thanks Roger
It is now 56 degrees.
The next question is,what angle of incidence should the wing be?The decalage seems as you indicated by eyeballing it.I don’t have a meter with me at present.The glide is pretty good which would confirm the decalage is about right.
There is no adjustment screw for down or side thrust ,so the thrust line is zero.At the moment it seems to steam forward rather than climb on the last 15 seconds of the motor run.I wondered if this could be due to too high a wing incidence causing relative down thrust.The wing angle of attack is positive relative to the fuselage and thrustline, and the stabiliser is about equally negative.
I wondered about fitting 4 grub screws to the front end to make the thrust line adjustable.Altering the wing incidence would mean moving the wing joiner or the rear location pin/hole.The wiggler pin is not adjustable in the relaxed position.
Many thanks for your advice.
Jim

[Roger Morrell]

On a Vvchar front end you set the side and down thrust – and you need some with a tapered shim. Normally you get a set with the front end.

The come as a ring – you cut the ring at the narroest point so it sides over the hub.

Roger

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