Hello all, Hope everyone is having a great Christmas day.

Stek79,

Thanks for the respectful reply, and the challenge to my input. After all, discussion is why we are here. Good stuff. Please post the link to the engineering explanations to which you refer. I am interested. Meanwhile let me clarify my post.

2 points to begin with.

First is the overall design aim. There are 2 different directions involved here - optimizing for right side up flight only, and optimizing behavior while trying to preserve the same good behavior flying upright as well as inverted. Aerobatic designers vacillate between these. One argument is that although inverted maneuvers are performed, the majority of flight (takeoff and landing at the very least) follows the upright sense, so an upright design bias is better. Piloting is made easier for majority of maneuvers at the expense of more corrections required while inverted. If equal emphasis is placed on inverted handling, design elements tend toward only those that help upright and inverted equally. Piloting requires some corrections but piloting technique becomes the same each way. Also the sequences flown in different competition classes influence this. Classes have varying degrees of emphasis on inverted performance. In my above post I tried to differentiate between these design intents.

Secondly I did not say pattern planes use no R thrust. I said they typically use less than trainers or some sport planes. Basically due to the above reasoning. I think your example of 4 degrees does not represent the norm? Note Dick Hanson’s comment from his post above: “I elect to use very little offset and simply set rudder as needed…”

Now regarding P factor. I say right thrust does help to compensate for this. Paraphrasing my above: “for props spinning clockwise, at high AOA thrust is shifted right, yawing nose left. Right thrust line angle pulls nose back right.” Simple as that. Please explain how this is not correct?

Also note that “high AOA” means “towards the sky” whether upright or inverted. High AOA towards the ground, whether upright or inverted, reverses P effect. And (only while flying upright) down thrust helps compensate for (positive) P effect at high (towards the sky) AOA even more by zeroing out blade AOA differences. So this is part of why R and down thrust are common on trainers and such. Trainers are “trainers” because they incorporate design features, like R and down thrust and many others, which make them easy to fly right side up. Consequently trainers don’t fly as well inverted.

Regarding right thrust and spiraling slip stream for aerobatic designs. And here I mean a design that will fly as well inverted as right side up. Specifically from my post above: “A slight yaw is produced from the vertical fin because it only sticks out on the top side. A right rotating prop slip stream pushes top mounted fin right causing some left yaw. A small amount of right engine thrust can help with this, and works when flying inverted too. Thrust points the other way but vertical fin is inverted and getting pushed the other way too.” You stated that “It is well known why right thrust is introduced, in this is ONLY for spiraling slipstream and NOT for P-Factor!!!” I disagree. Explanation by example as follows:

Envision a perfectly symmetrical design. With a right hand rotating propeller set at Zero degrees R and down thrust angle. Thrust line, wing, and horizontal tail, all exactly on centerline. Fuselage and vertical fin mirror images above and below (emphasis on an equal size vertical fin below centerline also). CG at the neutral point.

Begin in level flight at cruise speed. The aircraft is of course pitched up slightly to produce the needed lift. Will the aircraft tend to yaw left slightly? If yes, then due to P effect or spiral slip stream?? Explain how??? (I say yes, and due to P effect as I noted above)

Now introduce some right thrust - for whatever reason. Then roll to inverted level flight at cruise speed. What is that right thrust doing now? This illustrates the problem with right thrust for “aerobatic” design.

Multiflyer