SaCal72's question:
Can anyone explain thrust angles to me and how they are used and affect a plane and how they can be changed when you have an engine mounted to an engine mount and firewall. Thanks in advance for everyone's help!.
the first answer from 2slow2matter:
Thrust angles are used to offset things such as engine torque, and the tendency of a plane to climb excessively under power (especially trainers). So, trainers usually have a bit of down thrust built in, and right thrust built in (down to couteract the high lift of the wing, and right to counteract the torque of the engine, which tries to pull the nose of the plane to the left). Thrust angles can be either built into the firewall when built, or can be added by adding washers between the mount and firewall, either on the top two bolts (for down thrust) or the left to bolts (for right thrust).
Which is an absolutely great answer. Unlike most of us posting here on RCU he actually answered all of the points of the question. (That is a complement, not sarcasm.) Most folks on this list type a lot but never get around to answering the original question.
Then khodges went on with :
Thrust angles are used to counter a plane's tendency to climb, dive, or pull to the left due to torque reaction. What you add in terms of up, down, or side thrust will vary from plane to plane. Most kits and ARF's will have the firewall canted for what that plane needs. If you need more due to modifications, you can place washers (different #'s of, or thicknesses) behind the engine mount at the appropriate corner(s) to change the thrust angle. Sometimes the different mfg's take different approaches to correcting flight tendencies.
And John W expanded on this with:
Right Thrust…Beyond torque, prop wash on a single engine, single prop plane is asymmetrical. On a standard rotating engine, the wash swirls down the fuse, pushing harder on the left side of the rudder and fuse than the right. This causes a left yaw. There is a correlation between thrust and left yaw. By adding right thrust, the engine will counteract the left yaw. Again, nothing is perfect and right thrust can really only be set perfectly for one given speed, engine RPM and prop. The idea is to minimize the left law effect across the flight envelope. Like down thrust, changing prop will change right thrust.
OK, my short chain kicked in when I saw in all three posts a direct or inferred statement that right thrust has something to do with correcting the effects of engine torque on an airplane. As JohnW pointed out in this post:
Torque and P Factor
To the pilot, !QUOT!torque!QUOT! (the left turning tendency of the airplane) is made up of four elements which cause or produce a twisting or rotating motion around at least one of the airplane's three axes. These four elements are:
1. Torque Reaction from Engine and Propeller
2. Corkscrewing Effect of the Slipstream
3. Gyroscopic Action of the Propeller
4. Asymmetric Loading of the Propeller (P Factor )
Aircraft stability is a VERY complex issue. Many of these items cannot be studied independently of one another. Some are sequentially related. For example the way an airplane turns due to torque, and due to propeller thrust forces are completely different with respect to the sequence in which they happen. (please note I'm using the system of reference as if you are the pilot sitting in the cabin)
For torque, the engine turns the prop clockwise and the fuselage reacts by trying to roll counter clock wise. This results in a roll to the left. Now the wing is in a bank and its lift is directed to the left so the airplane begins to turn left. Note the sequence is torque, bank, turn. Bending the axis of the torque from the engine by adding right thrust has virtually no effect on this sequence.
For propeller effects. There is asymmetric airflow over the fuselage and vertical fin, causing the airplane to yaw to the left. Due to the uncoordinated yaw the left wing is now producing slightly less lift than the right wing and the airplane begins to roll to the left. And just as above it begins to turn to the left due to the banked wing. Note this sequence is; asymmetric thrust, yaw, bank, turn. Right thrust moves the asymmetric thrust from the right side of the fuselage to more closely pointing at the center of gravity of the airplane, and eliminates the forces that caused the yaw in the first place.
Take the reference to torque out of all of your answers and they are perfect with respect to the question: what do thrust lines do.
Thrust angles are used to offset things such as PROPELLER AIRFLOW EFFECTS, and the tendency of a plane to climb excessively under power (especially trainers). So, trainers usually have a bit of down thrust built in, and right thrust built in (down to couteract the high lift of the wing, and right to counteract the PROPELLER AIRFLOW EFFECTS, which tries to pull the nose of the plane to the left). Thrust angles can be either built into the firewall when built, or can be added by adding washers between the mount and firewall, either on the top two bolts (for down thrust) or the left to bolts (for right thrust).
BREAK, other issues next post so my verbosity doesn't run out of room.