How to Fly (Better) Entry #2 - Straight and Level (part 2)
Understanding and Predicting Trim Changes
One important thing to remember about trim tabs is that they are applying aerodynamic forces to your control surfaces to hold them in a particular place. This means that when the aerodynamic forces acting on your aircraft change, the forces applied by the trim tabs change as well, and suddenly, you are no longer trimmed for straight and level flight. Fortunately, these can be anticipated by the pilot. The primary factors are airspeed, engine power, and angle of attack. Other secondary factors are flap position and landing gear position. In addition, features unique to the type of aircraft you are flying such as dive brakes, spoilers, oil cooler flaps, or radiator flaps, may also have an effect on trim. For instance, opening the radiator shutter on early Spitfires up to the Mk.VI, causes a tendancy to roll to the left. Aircraft weight also has an effect, as you will notice when you drop 2,000lbs of bombs all at once. I won't get into all the aerodynamic reasons for all of this here, I just don't feel like typing that much! But let's look at how to predict some of these things and how to use them to our advantage. When you trim your aircraft to fly straight and level hands free, you are trimming it for the specific configuration of all of those factors you are in at that moment, at the airspeed you are currently flying at.
Airspeed changes are the most foundational of the factors listed above. Suppose you are trimmed for straight and level flight, and your airspeed decreases. The nose of your aircraft will tend to drop and you will start to descend. The reverse is true if airspeed increases. The pilot, if trying to hold the nose level, will have to pull or push increasingly hard on the controls to do so. The control forces required can actually easily exceed the pilot's strength to maintain even on fairly small aircraft. Elevator trim is used to relieve the pressure. So, you retrim your elevator for the new airspeed, and adjust ailerons and rudder trim as well as required. Now you are back to hands free straight and level.
In most aircraft, engine power is going to have an effect on trim. In the vast majority of cases, increased power will cause the nose to go up, and decreased power will cause it to drop. This couples nicely with the effect of airspeed on trim, so both the increased engine power and the resulting increase in airspeed will be working together. This keeps things nice and predictable. An exception to this rule in CFS3 is Ted's PBY. Because the engines are mounted so far above the fuselage, they exert leverage on the aircraft such that increased power will initially cause the nose to pitch down. However, as the increased power causes airspeed to increase, the increased airspeed will eventually overpower this effect and the nose will start to rise once more. The reverse of course being true with reducing power. Try the PBY and compare it to another plane and you will indeed see this happening in CFS3 (nice FM work, Ted.)
On propeller driven aircraft, aerodynamic effects caused by the rotation of the propeller will have an effect on rudder and aileron trim as well. The more power your engine is producing, the stronger the effect. Clockwise turning engines (as viewed from the pilot's seat) will pull to the left. Counterclockwise turning engines will pull to the right. Counteract this with your rudder and then trim out the pressure. You are aiming to center the ball of the slip indicator, or in British aircraft, it is the top arrow of the turn and slip indicator that you want to center. If you have counter rotating propellers, like in a P-38, the effects from one engine cancel out the effects of the other engine, provided they are running at the same power settings.
Angle of attack (an aerodynamic term referring to the angle between the wing and the oncoming wind), will tend to exaggerate the effects of engine torque in trim. The higher the angle of attack (such as in a climb) the stronger the effect.
All of the other factors are related to the effect of flaps, landing gear, various cooling flaps, etc have on your aircraft when their position is changed. The effect they have will be unique to that aircraft type, so you will need to learn them for whatever aircraft you are flying.
Why Understanding Trim Will Help
The point here is to be aware of the different things that are going to affect your trim. Being aware of these factors allows you to anticipate the change and reminds you to be ready to divert some focus to trimming your aircraft any time there is a change to one of them. Stability and, especially, predictability are the basis for everything else you will do with an airplane. You want to be able to fly with stability, and if you are not, whether intentionally not not, you want to know how to return to that state. Crucially, you want to be able to do this without thinking too hard about it, because other things on your mission are going to be demanding your attention.
You might object to putting this kind of effort into stability and predictability, on the basis that in a combat environment, those things might aid your enemy considerably in his attempts to kill you. This is true. However, if your aircraft is predictable to you, and you know how to return easily to a stable state, you are now in full control of your aircraft, which gives you what you need to be as unpredictable as possible to your enemy.
Now, since you probably want to be able to do something other than fly straight and level, in the next section we're going to start putting all of this together into a coherent method of flying that you can take with you into any airplane in CFS3. Meanwhile, pick an aircraft to get familiar with over the course of the next entries. It will be helpful as you try different techniques, to try them on the same aircraft. You will get to know what to expect from that particular aircraft and thus be able to apply the techniques consistently. Try flying the aircraft and pay attention to how changes in airspeed, flap setting, landing gear configuration, etc affect the trim on this aircraft.
IIRC most serious flight sims expect one to do a bit more than CFS3 does, with the exception of your ac. Of course my remark is a bit hypocritical, as I seldom fly in CFS3 for fun these days; just checking Ted and Co's great work or my missions. Your daytime single engine fighter aircraft are a whole new level though.
