The 3DRCForums -Discuss Anything Thread-

[Decal Dennis]

Nice Dennis! Looks great!

Thanks Mike

 

[Aeroplayin]

Interesting to see how thick the AJ Laser wing is.....

So how does a plane like this perform a slow roll without any input other than aileron? What keeps the nose up as you roll to KE?

Design.

I'll give you a hint... when they were designing the P-51 at North American, they did something. My IMAC plane had that same something designed into it. :flyer:

 

[Aeroplayin]

I guess I should also mention that some of the physical forces of the rotating prop has a little to do with it too. Consider precession, throttle management, and how yaw affects the roll. So although no other control surface input is needed, throttle management is involved and the rotational direction used to initiate the maneuver.

 

[YellowJacketsRC]

Laminar airflow wings?
Lofted Fuselage?
Side exiting exhaust?

Precession should only come into play if you are using the elevator or the rudder. Rolling a plane should not cause any precession?? Maybe if you roll left you could bump the throttle at 90 degrees so as to gain a little upward pull of the nose from the fact that the motor is angled to the right?

 

[Aeroplayin]

Laminar airflow wings?
Lofted Fuselage?
Side exiting exhaust?

Good guess about laminar flow with the P-51, but no.
No.
No.

Precession should only come into play if you are using the elevator or the rudder. Rolling a plane should not cause any precession?? Maybe if you roll left you could bump the throttle at 90 degrees so as to gain a little upward pull of the nose from the fact that the motor is angled to the right?

Very warm, but unless you look at the declassified design plans for the P-51 documents online, you may not be able to guess. But increasing the precession on the first 1/4 roll to 90 degrees KE while rolling to the right first, is the first part of it. :clap:

 

[YellowJacketsRC]

Please explain how rolling causes any precession at all. I get that if you had precession occurring while rolling right, you could then goose the throttle a bit to increase the precession. But I don't get how your going to induce any precession without adding rudder or elevator?

As far as the design, I know the fuse was relatively tall and narrow, creating a flat side.

 

[AKfreak]

You can induce procession by adding throttle. Hell taking off with a P-51 will flip the plane over almost if you firewalled the throttle at a dead stop. Lots of right Ritter to go straight down the runway. I have first hand knowledge of this in a D model at K-84 airport.

 

[Aeroplayin]

Please explain how rolling causes any precession at all. I get that if you had precession occurring while rolling right, you could then goose the throttle a bit to increase the precession. But I don't get how your going to induce any precession without adding rudder or elevator?

As far as the design, I know the fuse was relatively tall and narrow, creating a flat side.

Okay, here it is. Precession is induced with RPMs. So if you start your roll to the right, and control throttle through the first 1/4 roll, you don't need rudder unless the plane can't roll axially at all, and there are some ARFs that fit into this category. If the plane is set up neutrally, you don't need input during level or inverted flight. This leaves the KE portion with the left wing down. Obviously, backing off the throttle here will eliminate left yaw from precession and slipstream, so the design only needs to compensate successfully for this part of the roll. The P-51 had a one degree left offset in the vertical stab to help counter left yaw from both precession and slipstream. This can also act as a slight right trim at times like the half second you are in that position during a slow roll. Taking the time to think about this, and incorporating it into the plane's design, is the advantage of a kit built airplane. I would never think about building my own plane from a kit without incorporating this offset. I would never build a kit for pattern sequences that did not have a wing with the Reynolds numbers needed to avoid separation too early when increasing AoA.

 

[YellowJacketsRC]

I hesitate to challenge you on this because you know your stuff. But my understanding or precession is that when a when is spinning and you apply a force to the axle in an effort to change the plane that the wheel is spinning in, the wheel does change the plane it is spinning in, but it does it at 1/4 intervals ahead of the actual force being input.

Nothing like that happens in a plane that is moving straight ahead. The only thing that causes a plane to yaw left on take off or in a slow roll (sans rudder and elevator input) is the slip stream.

 

[Aeroplayin]

No. A rapidly spinning object of any kind, whether it be cambered and pitched like a propeller, or not, will "precess" in a direction determined by the torque exerted by its weight. This is a bit different than P-factor. P-factor is induced as a pitched lifting body (like a cambered and pitched propeller) moves to a varying AoA relative to the oncoming air velocity.

So we also have vector properties of "rotational quantities" that has nothing to do with a camber and pitch. As ANY rotating mass spins, there is a force induced in a direction perpendicular to the angular momentum. The circular motion is called precession, and any spinning object will precess in a perpendicular direction. But a propeller will also induce other forces as it moves to an angle greater than the oncoming air. So we're talking about two things here.

Angular momentum... https://www.youtube.com/watch?v=NeXIV-wMVUk

P-Factor.... https://www.youtube.com/watch?v=5ByMx3muH-c