c o g

[Evan Pimm]

Or, with this wing shape, measure 1/2 way from root to tip and that is the Mean Chord. Place the balance point at the suggested 25 to 30% on this chord. Flavour to taste after flying it there and getting a bit of trimming done. Simple enough, and works for any straight taper (unswept) wing.

Evan.

[Martin Harris - Moderator]

If I understand the post above correctly I'm not sure this is good advice.  The swept forward trailing edge will move the mean chord inboard with the result that the correct C of G point will be further forward at the root. in percentage terms.

[Evan Pimm]

It might, Martin, but so long as the taper isn't gross, when you do the drawing, it makes very little difference and with my usual 'slightly forward' balance advice (25~30%) the balance is nicely conservative and unlikely to be a worry during those first trimming flights. Simple too, which was the point of the thing.

Evan. 

[Martin Harris - Moderator]

I accept that this particular wing shape will not give a very erroneous result this way but I think it might confuse people if they are told the MAC is at half span on this or any other tapered wing. Perhaps  you might have said that half span should be "near enough" with a slightly tapered wing?

Edited By Martin Harris on 25/08/2010 08:52:37

[Evan Pimm]

If you read what I initially wrote Martin, 'With this wing shape...'

Evan.

[Martin Harris - Moderator]

Isn't that what I said in the previous post? 

Quote "I accept that this particular wing shape will not give a very erroneous result this way".

 

My point was "I think it might confuse people if they are told the MAC is at half span on this or any other tapered wing"

 

However small the movement is in this case, the one place the MAC won't be on a tapered wing is at half span.

 

I would add that all these "rule of thumb" methods assume that the aircraft has an average conventional layout and don't take tailplane effectiveness into account like the "proper" calculations and most of the online calculators do.

Edited By Martin Harris on 26/08/2010 10:15:51