1
$\begingroup$

In a recent question it was proposed that adding excess power to an aircraft in a level 45 degree banked turn would cause it to pitch up into a rolling climb.

This case was compared with level flight using a positive static stability (CG forward-tail down force) model.

In level flight, adding excess power will initially cause an increase in speed, followed by increase in tail downforce, followed by a pitch up, followed by speed stabilization and climb. Pitch controls speed, power controls altitude.

Roll 45 degrees and do a level coordinated turn around a point. Add in power. What I am seeing is a turn around a barber pole with no change in roll, an ascending spiral.

If we added more pitch, leaving the throttle, rudder and ailerons where they were, a slower upward spiral with steeper barber stripes?

The plane does not seem to roll, the wing is always pointed to the same pole.
Is there any rolling motion WRT aircraft performing these manuvers?

$\endgroup$
  • 1
    $\begingroup$ Well you have torque and slipstream effects, which are both causing yaw and reducing trim speed, complicating things. In flight you will be making subtle changes to control inputs to hold the bank angle almost unconsciously, and if you don't it'll wander off on its own soon enough. $\endgroup$ – John K Jun 6 '19 at 16:55
  • $\begingroup$ "But the plane never rolls, the wing is always pointed to the same pole.." if your nose is really high, say 60 degree climb angle, and your left wing always points to the barber pole, you will be rolling a lot. $\endgroup$ – MikeY Jun 6 '19 at 17:00
  • $\begingroup$ @Mike Y Let's call it orbiting. I believe there is a roll effect see answer below. $\endgroup$ – Robert DiGiovanni Jun 6 '19 at 19:59
  • $\begingroup$ Well. If you add power, the first thing that happens is the aircraft gains speed. This widens the turn. Then it pitches up (meaning up and inward, as aerodynamic “up” is rotated 45°). So now - are we still coordinated here? $\endgroup$ – Cpt Reynolds Jun 7 '19 at 11:48
  • $\begingroup$ @Cpt Reynolds "The radius widens" yes. Then it pitches up (speed decreases, radius decreases). "are we coordinated" if rudder and aileron are unchanged, and airspeed remains the same, Yes? (But now we are in a climbing spiral). $\endgroup$ – Robert DiGiovanni Jun 7 '19 at 17:46
1
$\begingroup$

The key is that you qualified the turn as coordinated. If the turn continues coordinated after the application of more power, then the aircraft will climb due to increased energy being converted to altitude. Unless you decide to "lower the nose" and turn at a faster airspeed.

$\endgroup$
  • $\begingroup$ I did not address rolling. There are many aspects of your questions, and I thought I would address perhaps the most important first. $\endgroup$ – mongo Jun 7 '19 at 1:46
  • 2
    $\begingroup$ Learning the physics might be accomplished in a different manner. A starting book on practical aerodynamics which I send primary students to, as well as CFI candidates, is by John Denker, av8n.com/how Take a look at that. If you are motivated, just start at the beginning and work your way through the book. $\endgroup$ – mongo Jun 7 '19 at 3:18
  • $\begingroup$ From my perspective there are several interrelated questions, for which an effective answer would either require prerequisite knowledge and understanding, or a tutorial, which is beyond the scope of comments. So I suggested the source so that you could increase your knowledge base. In any engineering/scientific inquiry there are different thought models which can be used to explain things, and the referenced book answers most of your questions in one or more of those models. That is why I suggested it. In general, a single question may get a better answer, but you might have to bound it. $\endgroup$ – mongo Jun 7 '19 at 13:24
  • $\begingroup$ I will rephrase the question. $\endgroup$ – Robert DiGiovanni Jun 7 '19 at 17:17
0
$\begingroup$

Could not see a roll in an orbiting aircraft, but so many experienced people said there is a difference in roll force in an ascending or descending turn. Outside wing has greater angle of attack?

After running the simulation in my mind many times, it occurred to me that vertical velocity ascending vs descending will create an opposite effect on the TAIL, more specifically, the vertical stabilizer. If it is canted over to 45 degrees, an increase in vertical velocity (say from 0 feet/sec to 5 feet/sec) will create a rolling force!

Another source of roll in a pitch up would be the aileron input required to overcome dihedral stability effect, which is strongest when the plane is in horizontal flight. As it pitches up, the lift differential caused by rolling is less and less. One would have to "roll toward the high wing" to compensate. But the effect would be same in a dive, not opposite. However, it would not be transient, and would increase as pitch increases.

These effects may be part the mystery. An orbiting plane does not roll in a constant turn around the point, but if it changes pitch rolling forces may be created.

$\endgroup$
  • $\begingroup$ I think it’s kind of important to define which effects you want to consider and which not. Is thrust assumed to be a point vector? Do you consider propeller slipstream? What about rudder effects to counter prop torque? Once these all are considered, it becomes an aircraft-by-aircraft question, not a theoretical generic exercise in flight mechanics... $\endgroup$ – Cpt Reynolds Jun 7 '19 at 6:34
  • $\begingroup$ I’m not sure I get what you mean... are we considering prop effects and the likes, or is thrust balanced in pitch, roll and yaw in our assumptions? $\endgroup$ – Cpt Reynolds Jun 7 '19 at 11:50
  • $\begingroup$ @Cpt Reynolds I was actually modelling with an F16 to try to eliminate these factors and stick to the maneuver itself. There is agreement that a turn around a point has no roll. I was (laughing a bit) as to what would happen is you applied full thrust. Wound up worrying about G forces. $\endgroup$ – Robert DiGiovanni Jun 7 '19 at 11:55
  • $\begingroup$ Huh? I second the Cpt., I have trouble following the line of thought you are trying to convey here. $\endgroup$ – AEhere supports Monica Jun 7 '19 at 11:58
  • $\begingroup$ @RobertDiGiovanni -- re "Could not see a roll in an orbiting aircraft, but so many experienced people said there is a difference in roll force in an ascending or descending turn."-- you are confusing the geometrical fact of a non-zero roll rate, with a statement about roll torque. They are not the same. $\endgroup$ – quiet flyer Jun 7 '19 at 12:30
0
$\begingroup$

What I am seeing is a turn around a barber pole with no change in roll, an ascending spiral.

Here’s a way to see that in an ascending spiral, you must have some roll, along with some pitch and yaw.

Take your model airplane by the wingtips and hold in an angle of bank with some nose up, so it is in the position of an ascending spiral. Now give it a wee little bit of yaw, which will drop the nose. Give it enough rotation about the wingtips (pitch) to return the nose to the set angle above the horizon. Keep repeating this, being careful not to add in any roll. You are simulating a simultaneous yaw and pitch without roll.

Watch what the angle of bank does.

$\endgroup$
  • $\begingroup$ In order to simulate simultaneous rotations about two or three axes, you need to do it in small, little increments. Like, a degree or two at a time. A little yaw, a little pitch. Try it. $\endgroup$ – MikeY Jun 8 '19 at 14:09
  • $\begingroup$ Thank you so much for staying with it! A plane sets its roll and "turns" around a circle with its wing! The maximum roll component of an orbit is...1 roll per orbit if the same wing points to the "pole". The plane would have to be flying with its nose almost straight up (using some of its thrust to continue the circle like a helicopter) and the plane slowly rolling to stay pointed. An average GA plane would orbit a 0.5 mile radius in around 1.5 minutes, giving a roll rate at around 90 degrees pitch of 0.66 rolls per minute. $\endgroup$ – Robert DiGiovanni Jun 8 '19 at 18:03
  • $\begingroup$ The key is to keep the radius of the circle constant. Modelling an ever tightening circle confuses the roll component of orbiting object with other factors. In reality, it is real, but relatively insignificant. I realized that thinking how the moon keeps the same side towards the earth. It "rolls" every 30 days! But it is real, and thanks for making me more aware of it. $\endgroup$ – Robert DiGiovanni Jun 8 '19 at 18:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for?Browse other questions tagged or ask your own question.