Greg,

Please see comments below:

The increased thrust component from gravity will offset the increase
in drag due to forward c.g. The trimmed speed should not change.

I'm not talking about drag.

This is a stability/control issue. By moving the CG, you are changing
the speed for which the aircraft is trimmed.

Alright, so to sum up the situation (please correct me if I am wrong)

1. If you have a forward shift in c.g. without touching the controls,
you'll have an imbalance in pitching moment that translates into a
pitch-down attitude. Your angle of attack is reduced, and the
airplane will speed up. If you're in the front of the power curve,
your drag will also increase with the higher airspeed. The angle of
descent will be such that the thrust provided by gravity will offset
the drag increase.

2. In a previous post, you wrote "If you move the CG forward, and want
to keep the same airspeed, you will have to increase the tail down
force, i.e., nose up trim. In this scenario, you will have the same
airspeed, but slightly higher drag and will incur a slight descent.".

My question is this: When you increase the downforce, lift must also
be increased for the balance of forces in the "vertical direction".
Since neither your angle of attack nor airspeed are changing, how do
you maintain Lift = Weight in this case? Unless your nose-up trim
change upped the angle of attack...


My understanding is that hang gliders use this technique by shifting
their bodies forward and aft. I've never flown one, so I can't say
from personal experience.

I've never noticed that leaning forward and back changed attitude or
airspeed.

Well, either go try it, or trust me. g Probably takes a small
plane before the effect is noticable. I've only done it in a 152. I
will occasionally demonstrate to a student how they can climb,
descend, and turn using only body shifts and opening and closing the
doors.

Thanks for pointing that out. I definitely will try it next time. Do
you use the door trick to induce more drag and increase your descent
path as if you're you're adding more flaps?

Alex