FMS Olympus CofG help

[Robert Armstrong 2]

I recently decided that I must extend my aerobatic repertoire, as loop, roll and cuban is about it. Being a sucker for new toys, I was captured by the review of the FMS Olympus in the December 2014 issue.

Annette settled on a cofg 170 cm back from the leading edge, rather than the CML recommendation of 180 -190. I have balanced mine at 170, which looks an awfully long way back to me, never mind the recommended 180 - 190. I have a 5s 3700mah battery installed, though not yet functional (waiting for a new soldering iron to attach connectors).

Perhaps what I am looking for is reassurance . Anyone else had any experience of this model? I am sure that it is clear from the first sentence that I am not a 3D flyer, so I need a well balanced model rather than max agility.

[Colin Carpenter]

Robert . R C Groups has a short thread on this model. Useful info on there . Colin

[Denis Watkins]

I would balance it along the main spar Robert, just for preliminary flying until you get the urge to shake it down

[simon barr]

I've just looked it up, and it states the C of G at between 150mm and 160mm ....

[Peter Jenkins]

Robert, measure the root chord and tip chord. Add together and divide by two to give you a rough mean aerodynamic chord (MAC). Then at the mid span position measure back 25% of the MAC and mark that position on the root - do this by drawing a 90 deg to fuselage line from the fuselage to the 25% MAC point. This will give you a safe CG position. After that, it's a matter of moving the CG aft so that the aircraft is comfortably stable but does not require a lot of down elevator to fly level inverted. Move the CG aft in small steps. There is no need to measure it as you can feel the effect as you move the CG. I only ever use a measured CG as a starting point for trimming.

The lady who flew the Olympus has set her CG position where it feels comfortable for her. The CML recommended position may or may not be correct as some manufacturers can provide some duff information on CG position. The other way to determine CG position is to get a precision aerobatic pilot (not a 3D pilot who tend to opt for a more aft CG for 3D manoeuvres) to fly your aircraft and give you their views on the CG.

[Robert Armstrong 2]

Thanks for the feedback folks. Various comments, where all measurements are given from leading edge at root.:

The Olympus has a foam wing with two identical carbon spars, so I don't think using the forward spar (which is quite well forward - only 10cm from leading edge at root). Half way between gives about 15cm back.

FMS and parent CML seem to have given various positions over time. Evidently when Annette reviewed the model the enclosed instructions gave 150mm (interestingly, about the 'half way between spars position' ), but the CML website had 180 - 190.

The current enclosed instructions say 185mm (though the leaflet actually says 'forward of the leading edge - wouldn't even stand up as that is well in front of the u/c). The box lid just says 185 from leading edge.

Using the 'root chord and tip chord' (I have taken the tip measurement at the point that the curve of the wing tip starts) gives approximately 160mm at the root using 25%. (I have also seen 30% quoted with this approximation which would give nearly 185mm) These numbers are quite reassuring Thanks. I must remember the tapered wing formula for any future such models.

Edited By Robert Armstrong 2 on 01/09/2016 11:39:03

Edited By Robert Armstrong 2 on 01/09/2016 11:39:42