Do you have any EF planes?

Try doing tight figure 8s 4 feet off the ground without cutting into a roller with a 16x7.

E.g., I think people are adapting to the inconsistent effect on roll--inconsistent when turning to the left or the right in upright harrier--by going with it...but if you wanted to stay in an upright harrier either you've just got the musle memory built up with the 16x props, or you are having to consciously deal with it like I do.

All props have torque... So your going to have to correct with any prop, even a 15x8. With the 16x8 I have the authority to make quick small adjustments. I been doing figure 8s inverted and upright just fine, they take practice and all planes are different and require different inputs. You have to anticipate what the plane is going to do next.

16x7, for some, is not that much different than a 16x8, because torque and angular momentum doesn't really consider pitch. But the 16x7 is still better than even a 15x8 when it comes to HP and thrust at the same RPMs.

I also have never felt any adverse effect from angular momentum, which would be yaw, and not roll, as torque is. Since it is a force determined by moment size, RPMs, and mass, the only thing different that I can think if is if you are using a heavier prop than we are, or you are accelerating the prop more than it needs to. Maybe throttle curve or expo is the difference. Don't know.

As far as torque, it is different than angular momentum, and is relative to just the moment length and RPMs. So if you feel that controlling the roll in a harrier or hover is the issue, then the throttle curve may work here as well, but the 16 will produce more power and torque at the same RPMs.

Bottom line is that if you like the 15, use it, but I personally couldn't give them away to the guys at the field with EXPs. I've tried... and I know there are guys that feel the same about 15's. Maybe it's the lower air pressure in the hotter climate here in Florida, but the 15 inch prop is a really a dead prop for these planes here.

I'm using Xoars...the effect is the plane wants to roll when harriering to the right. I don't think it's torque...I think it's gyroscopic. It might be a roll induced by the rudder and elevator due to pitch effect...who knows. All I know, if I want to keep an constant upright alpha in a sharp turn around, it is harder with the 16" props.

It was windy yesterday, and I didn't do a lot on the 16x7 as far as upright harriers go, and I liked the 16x7 just fine.

Originally Posted by 7oneWo1f

Do you have any EF planes?

Nope.

I think I have felt what LW is talking about- it is exacerbated on a 3s setup with a 14x7 in my memory. I never have actually tried a 15" prop on any of my 60ish" airplanes.

I also put an additional washer of right thrust in my builds to help keep my up lines straight...that complicates the turn as LW describes it. I have definitely felt like I have to 'muscle' the plane around in harrier at times, depending on which way I want to go. I compensate by lifting the nose more....then I can point it in any direction I want, as tightly as I want to do so.

We have angular momentum (left yaw), P-factor (left yaw), slipstream (left yaw), torque (left roll).... if you are generating a force the causes you to roll to the right, I'd check your main wing incidence... pick the plane up from the tail and look down the fuse. From what you are saying, I'd expect to see the trailing edge of the right wing at the root to be slightly higher than the trailing edge of the left wing. Just the first thing I'd check.

Well, I will try to think a little more about why. I'm not as interested in the why behind the effect as the effect, but the why is often interesting. I do not think it is incidence because I've felt it on two different planes in the same way, and it goes away with the 15x props.

So I am thinking it is: gryoscopic precession.

Upright harrier to the left leading with rudder will result in a force that tries to change the pitch up, whereas to the right it will want to pitch down.

To the left, it will want to pitch up, and require less elevator and throttle to maintain alpha. To the right, it will want to pitch down, and will require more elevator and perhaps more throttle to maintain alpha and altitude.

To the right with a force trying to pitch down, and the combination of more elevator to counteract pitch, and more rudder to counteract other forces, will cause a roll to the right.

I'll have to go review some old videos I have when I was battling this on the 16x props and see.

The net effect was that the difference on what you needed to do when doing tight figure 8 upright harriers was greater for the 16x props than the 15x props, leading to a feeling of squirrelly and inconsistent behavior when doing upright figure 8 harriers. I'll check incidence because it is easy, but you would think if it were a wing issue the problem would not change with prop diameter, unless there is some twising right between the 15x and 16x prop wash cones.

P.S. I'm not a physics professor so feel free to correct my line of thinking.

Incidence issues at stall speeds will be compounded by a bigger prop, and that was why I mentioned it. I'm not a physics prof either but I knew more of them than I really wanted to.

I've never met a physics professor I didn't like

I took a picture of one of mine standing on his desk with a Slinky extended to the floor... it made it to the Yearbook. He didn't like that too much until I told him that it made him famous. He agreed, so we were cool. Now, with the Internet, a video of the lecture would have gone viral.

I once made a flier to restart the physics club, which had been defunct for a few years...with a cartoon of a cute young woman in a too short mini-skirt flirtatiously looking back over her shoulder, with a talk-buble that said "Physics students do it by reducing the coefficient of kinetic friction."

Surprisingly, over 80% of the students that showed up for the first meeting were women, and they were there to join the physics club, and were oblivious to the flier controversy that had ensued after in the campus newspaper regarding the "objectification of women." It didn't help that I posted the flier in front of the women's center, which was run by a man hating women's liberation social sciences type.

The physics prof who agreed to be the professor associated with the physics club wasn't too pleased about the wider controversy, but he forgave me eventually, especially when it turned out that most of the officers of the club, including the president, were women. It turned out that the flier helped attract more women than men.

Now THERE is a sociology research paper...!

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