C of G position

[baronbeeza]

One of the questions I would often put to a pilot to get them thinking is to point out the C of G point on the aircraft.
Some try and guess using figures from the loading charts and datum etc.
I think they should have an appreciation of what it looks like. Where it is relation to the seats, to the fuel tank (centre) and obviously for the cargo areas.

I saw this pic and my guess would be behind the wheels, which it obviously can't be. I have to assume there is very little weight on the nose gear.
We can't see his legs and I suspect they hold the key.




Some very good pics on the site so if this thread takes off Dave may have to relocate it.

www.aviationwa.org.au/aircraft-photos-movements/2015-2/sabc-annual-fly-in-serpentine-airfield-27-sept-2015/

[Bruce]

Generally the C of G will be somewhere between 1/3 to 1/2 Wing chord. On the Cris cris the wing chord is pretty small! Its an interesting discussion when you look at something this small, and where a human beings C of G would actually be. On this aircraft, the base of the seat is essentially right over the undercarriage attachment. The pilots legs extend out flatish along the fuselage, which puts the pilots C of G actually in the thigh somewhere. The fuel tank sits under the pilots knees, and all the instrument panel weight is forward of that again. I would visualise the Cof G being about where the tie-down ring on the wing sits. Most Cris Cris (especially the Jet variants) have a lead brick mounted in the nose to fine tune the Cof G after construction. The structure of this thing is incredibly light - much of the internal framing is polystyrene foam - I think the pilot's breakfast becomes an issue!

[baronbeeza]

Thanks Bruce, I knew you would be up with it. I am used to telling my story about with the Tomahawk and how it all happens under the pilot's bum, - the C of G being under the bum which is about the middle of the fuel tank also. I was just surprised to see how, visually at least, this pilot appeared so far back. Optical illusion stuff.
It will be a good pic for my discussion in future so thanks for the gen.

[craig]

Interesting... Relationship between the CoG and Centre of Pressure, (Which is what occurs during flight) and CoG vs main landing gear on the ground. Clearly on a trike the CoG must be ahead of the mains and vice versa (behind the mains) for a tail wheel.
On a Cessna 206 it is possible to take off (possibly not legally) with the aircraft nicely sitting on all 3 wheels. However after some hours of flight and fuel burn on shut down the aircraft settles down onto its tail (not a good look at all!) This is due to the fuel tanks being slightly ahead of the mains, allowing the CoG to move aft of the mains due to fuel burn. The opposite may be an issue for Tail wheel aircraft where most of the consumable load sits aft of the main wheels. In this case the aircraft may be considerably more nose heavy on landing and hence at greater risk of nose over (though certainly not to the same degree as the trike eg above)