Bergfalke II 55. 1/4. Plan C Williams

[cw]

Harold, I would suggest that you keep the CG at 40mm from the LE and try the next flight in a good wind. There is no such thing as a 'correct' CG, as it's position depends on what the pilot prefers. Some like the centre of gravity further back to enhance thermalling ability, I prefer it further forward for better stability in pitch. (If you put the model in a dive, it will recover by itself, very useful if you lose sight of it at a high altitude!)

2.5 degrees decalage will be OK

I have a very simple and un-scientific method for finding the CG with swept forward wings. I simply draw a line from one wing tip LE to the other and imagine that this now the LE of a new wing. Where the line joins at the centre, that is the new LE of the root wing rib. The starting point for the CG is then 25% of the new chord. The 40mm point on my Bergfalke was determined by a lot flight trials...

[de Schaetzen Harold]

Dear Chris,

After some further discussions with friends (thanks Vincent and Pierre) and calculations with the help of Tracfoil, http://tracfoil.free.fr/tracfoil/accueil.htm, I discover think that the CG is +/- at 58 mm rear of the LE. Calculation based on a reasonable CG position at 30% of the main chord.

The sweep distance, which depends of the swept angle, is an important factor is this calculation. I am measuring 60 mm on my wings.

As soon everything is repaired and settled, I hope to make new tests.

Regards.

Harold