How a weight change influenced flight characteristics

[Peter Germann]

Remembering earlier work published by Ted Fancher and David Fitzgerald, I have today made a similar flight test using my current F2B airplane:
Citation Two, 45 qdm (702 sq. in) electric, equipped with an active power control system by Igor Burger. To find the influence of added weight on basic flight characteristics I have added 120 Gr. or 4.2 oz on the C.G and then did back-to-back flying with no setup changes in between. Wheather was calm at 25°C.
Here are my first impression findings when adding 120 Gr. or 4.2 oz on the C.G:

a. No weight added
Citation Two T/O wt:  1’803 Grams (63.6 oz) 
Wing Loading: 39.8 Gr/qdm (13 oz/ft^2) 
Speed: 5.0 sec / lap
Target throttle: 145
Sensitivity: 55
Pull in 3rd. corner of hr. glass: sufficient 
Corners: tight
Tracking: sufficient 

b. 120 Gr (4.2 oz) added on CG
Citation Two T/O wt.1’923 Grams (67.8 oz) 
Wing Loading: 42.5 Gr/qdm (13.9 oz/ft^2) 
Speed: 5.0 sec / lap
Target throttle: same as above
Sensitivity: same as above
Pull in 3rd. corner of hr. glass: Good
Corners: a touch wider
Tracking: perhaps a very little bit better

From this test I conclude that the flight characteristics of this particular aircraft would have remained more or less the same even if I had built it 120 Grams or 4.2 oz heavier.

[kevin king]

Good. Now we can build with readily available 12 lbs RC  balsa.😃

[Paul Walker]

You should redo those tests in a 8 to 9 m/s wind befire concluding the extra weight is acceptable.

[frank williams]

Paul,

8-9 m/s might be a bit high

I think a back to back in a 4-5 m/s wind would be a worthwhile test

I know its hard to believe for me, but I did build a model that was too light.  Teds experiment of adding weight to the cg did make it flyable.

At the extremes, we face a conundrum of line tension for control versus wing loading for flight performance.