Choosing a length for the canard

[Spodman]

Lengthy cut'n'paste from an old CP (from when there were about 20 Varieze flying) which leads me to understand something I didn't before - a heavier motor and a longer canard are both ways toward an aft c of g:

 

"Those of you who do have the heavier engines and alternators are

finding that the nose weight needed to get the cg forward is cutting

into your useful load, already reduced with the heavy engine. If this

were a conventional airplane there wouldn't be much you could do, short

of moving the engine or wing. But, since the VariEze has two widely

separated, lifting wings, the allowable cg range can be shifted by

shortening or lengthening the canard. Thus a "tailheavy" airplane can

be made to fly "nose-heavy" merely by sawing off canard span, making no

change to actual cg! This can be done only up to a point, where

directional stability is lost as cg is moved aft. We have tested the

flying qualities and confirmed that the canard/elevator is free from

flutter at two canard spans - 150" as shown in the plans and 142" which

is obtained by sawing 4" off each tip. If 4" is sawed off each canard

tip (142" span) you can move the allowable cg range aft 1.2 inches.

This is equal to adding 15-lb weight in the nose at F.S. 5.

Let's look at a couple of examples to see what this canard trim can do

for you. Assume you weigh 170 lb and you are using an 0-200 with

alternator and a small battery. When you do your weight and balance

you find you will need 30-lb ballast in the nose to get to the nose

heavy condition (preferred for low pitch sensitivity) for first flight.

Then later you can remove 1/2 the ballast, but will have to carry 15 lb

of lead in the nose for the life of the airplane. If you trim the

canard you will find that you only need 15-lb ballast to get to the

forward cg you need for first flight. Then, when you are comfortable

with the stick forces you can remove all ballast and have the best

useful load and a mid to aft cg. Thus, trimming the canard has

increased your useful load by 15 lb!"

 

Also showing more tolerance toward modification then, probably until the death toll mounted...