Wing and C of G

[Chris Walby]

I'll start the build log on this at some point, but at the moment I am well and truly in a quandary.

Its a plan circa 1975 ish hence the some of the traditional way of doing things and I have now got around to putting all of the big bits together (some sheeting still to do), but all the main components are there.

So with gear up, my C of G is well forward of the mark which raised the question of the C of G mark being in the right place on the drawing. Yes okay its on the main spar, but that is angled backwards and its a straight LE, swept TE.

I thought there was a rule of thumb that said about 30% back from LE, but this is closer to 40%.

Please take a look and comment so I don't think the covering will move the C of G back much.

I can engineer the C of G into the "as published" position, but its far easier if its closer to the 30% area.

 

PS its tricycle UC and it all drops forwards

PPS - It all depends on where I take the TE of the wing as to if I get 40% or a lower figure, I suppose I could use some software to calculate it, but people normally know better!

Edited By Chris Walby on 23/03/2020 17:37:41

[flight1]

read here to get your c of g . very usefull info and how to calculate

 

and here is good read too

Edited By flight1 on 23/03/2020 17:50:42

[Denis Watkins]

Chris, Just my twopennerth based on flying and rotating at take off.

For a Trike U/C, the C of G goes just in front of the main year to rotate and lift off

Your proposal to go further forward, increases the leverage to lift it's nose and rotate

So bear this in mind

[eflightray]

Here's a CG calculator that also takes into account the tail area and the distance between the wing and tail --

**LINK**

.

[cymaz]

Posted by eflightray on 23/03/2020 18:58:11:

Here's a CG calculator that also takes into account the tail area and the distance between the wing and tail --

**LINK**

.

+1 . I have used it on several planes and it works.

[Cuban8]

Posted by cymaz on 23/03/2020 19:11:05:

Posted by eflightray on 23/03/2020 18:58:11:

Here's a CG calculator that also takes into account the tail area and the distance between the wing and tail --

**LINK**

.

+1 . I have used it on several planes and it works.

Yes it does indeed. Saved one model with a very tapered wing. I didn't like the look of the plan's CG and it turned out to be a good inch out of whack according to the calculator. Flew well right from the off. Zlin 526.

[Don Fry]

If you have a trike, if the balance point is too far in front of the main wheels the launch goes, accelerate, bit of left rudder, pull back, pull further back, more, nose rears up, stalls. Don't go there.

How far? Not much

[Chris Walby]

Cheers guys, I'll go take the measurements and input them and see what it says.

Thanks Denis about the point regarding moving the C of G forwards and rotation however from memory the U/C is very very close to the C of G anyway (might be using lots of down to taxi!) and that the plans incorporate a tail skid!

The original aircraft was a tail dragger but the pilots complained about very poor visibility so they fitted a nose wheel. There are some photos where its sitting with its tail almost on the deck, but you never know if there was a load of missing weight (armaments, radar, pilot/radar operator etc).

[Chris Walby]

Thanks again and I thought I would report back.

Measurements made and numbers crunched

Plan says 124mm

Cal says 119mm at 5% static margin

Cal says 92mm at 15% static margin

I think I'll try for 120, fill the tanks (well weight them as if full) and check it again an see what it come out like.

Oh just remembered the original had fixed UC so its only change in C of G would have been fuel, perhaps the 124 mm was empty?

Once again thanks