Vapor Lock
Well-Known Member
Got bored so I skilled ahead a little bit but P-factor would also be a factor...just slightly
Steep Turns
- Thread starter Fly_Unity
- Start date
:yeahthat: With one caveat, the airplane isn't wings level so the force you explained (rotation about the vertical) isn't being applied directly to the left or right of the prop. Leaving the end result more involved than a simple nose down or up.
To expand, the force will be applied, say in a 45 left bank, to the bottom right side of the propeller. Rotate that force 90 degrees right and you put it on the bottom left (all relative to the pilot). In other words, the resulting GP in this case is a slight left yaw and slight nose down.
That's neither here nor there since the force applied is so small, and most propellers on trainer aircraft are also small (small arm), that the resulting GP force could be assumed negligible. GP is barely even notable with aggressive pitch up/down in trainers. Still can't figure out why we even mention it to people not flying tail wheel or aerobatics. :insane:
Site Picture: That's what I was taught (and shown). Wish I still had the pictures. Tape a camera to the glare shield, using pop-sickle sticks/coins/folded paper/etc to get it pointed where the pilots eyes should be. Establish in a trimmed steep turn both left and right and take pictures. Compare, the results will be a bit of an eye opener.
Without pictures the simple way to put it is (from the right seat), a turn left will give you a great deal of ground to look at when compared with a right turn. What do you think is the intuitive reaction? Pull up more, see less ground. To the right...push down more, see less sky. In other words, our brains say that it makes sense to have a similar appearance of both sky and ground when going left or right. So we try to match them. Hence why most pilots will either climb turning left or descend turning right, not both. Because they find one right way in one direction and try to match that view in the other direction. Clear as mud?
Swingwing111
Well-Known Member
I am a bit confused here. This discussion on gyroscopic precession peaked my interest so I dusted off my copy of "Stick and Rudder" and researched more info. on the subject and it all suggested that discounting other forces ie, "P" factor and torque, with GP in a steep turn to the right will cause the nose to fall and the tail to rise and just the opposite is true for a steep turn to the left. I may be misinterpreting what others on this thread have said but it seems to me others have intimated that "it will require slightly more elevator-back pressure in a left turn and slightly less elevator back pressure in a right to maintain the level turning pitch attitude. What am I missing?
Thanks
Thanks
First, ignore my paragraph two from my first post. The analysis is correct, except the results I explained were backwards to reality. Ooops
Now that that is cleared up, there is one way you can help wrap your head around this. The materials you will need are a pencil and one of those little model airplanes.
- Hold the aircraft so you are looking at the tail and put it in a 45 degree left bank.
- Put the pencil in front of the aircraft to simulate a propeller and hold the pencil parallel to the ground.
- To get a visual feel for the force rotate the pencil (keeping it parallel to the ground) so that the left side is pulled in towards you and the right side is twisted out away from you. Almost like you just stepped on the left rudder.
- Now, keeping the pencil in this awkward tilt (still parallel to the ground) we are seeing the initial application of this force that will be our GP.
- Finally, rotate the pencil (keeping that awkward tilt) clockwise like the propeller rotates. Rotate until it is perpendicular to the ground, I.E. you've rotated 90 degrees by this point.
The answer you should come up with is a combination of some back pressure and some right rudder. The combination of these actions would cause the nose to rise (in a left bank). And that is what GP is doing, just as the author from stick and rudder says.
BREAK!!!
HOWEVER, IMO this entire discussion is moot as the force discussed here is going to be so small I'm not even sure the best pilot in the world would recognize its existence. In a high performance war bird of the author of stick and rudder's day, with their massive propellers, the arm (distance from root of prop to tip) for this GP force to be applied was great. So the resultant moment force was great. Today airplanes are designed with much smaller propellers, because we know prop efficiency plummets if the tips break the sound barrier.
Anyway, that aside the magnitude of the force applied will be directly related to the aircraft rate of change. In this case rate of turn. If anyone here has been in an aerobatic aircraft they know that it isn't uncommon to do >25 degrees/sec pitch changes. In those cases, even with small propeller, GP is predominant. In the case of a tail dragger raising its nose for takeoff, that changes is ~20-25 degrees in just a seconds time. Again, GP is predominant.
A 45 degree turn at 100 knots is ~11 degrees per second. A resulting force that's half of the above examples. Further, the force strength is split in half AGAIN. Half of the force will be towards pitch and the other half will be towards yaw. (Assuming a perfect 45 degree bank.)
In other words, while GP sure does exist in the topic discussions scenario. I would argue that it's impact is to small to bother worrying about. I would tell my student to make it look and feel right and put my focus on understanding what they are supposed to perceive. Especially noting what I said in my previous post regarding the 'site picture.'
Hope that clears up any confusion. Apologies for the misinformation that first post.
Krieger
Well-Known Member
I'm glad we have so many knowledgeable members willing to give excellent explanations. But as some here already hinted, your CFI applicant's time would be better managed studying required content. Possibly on his weaker subjects. He seems able to "apply" and "correlate" gyroscopic precession in an acceptable manner.
good read though
good read though
drunkenbeagle
Gang Member
My University Physics classes say otherwise. Rotational inertia of the prop and crankshaft will have a gyroscopic effect, dependent on the mass/CG/and velocity of the spinning parts.
The effect was huge with older rotary engines in WWI aircraft - they effectively could only turn in one direction. They were also slow, with a high angle of attack and very massive engine, all of which was rotating.
In a modern light aircraft, the mass of the prop is minimal and airspeed is higher, so the effect is much smaller - but still does exist.
All of the left turning tendencies are more pronounced at high angle of attack/low airspeed/high power settings. This generally would occur during....takeoffs and steep turns.
(emphasis added)
Airspeed should be constant. Angle of attack does not impact GP. High power setting, sure 100-200 RPM. Not sure it is enough to matter, but it would make GP more pronounced. I still say the topic isn't worth worrying about while flying and is a bit beyond the scope for a CFI candidate, but still interesting information imo.
Site picture and how VISUAL cues can be used to perform a maneuver matter. How false perception of the sight picture present us with distorted, or false, visual cues matters. That's what I believe a new CFI candidate, and current CFI's need to start looking for. There is so much fun stuff outside, stop reading the VSI to tell me we are in level flight...DAMMIT! (can I say dammit here? I can't remember.)
Swingwing111
Well-Known Member
shdw; Thanks for the clarification..that was an excellent explanation of the effects and causes of GP and no apologies are necessary.. While I agree with Krieger and others that a CFI applicant's time should be spent studying "required content", the fact remains Gp is an aerodynamic force that must be dealt with, at least on some level. Therefore, IMO, a CFI should have at least a rudimentary understanding of Gp. Especially if he is doing instruction in tail draggers.
Thank you. I too agree the CFI should have an understanding of the concept. My contention with this topic is to what end their understanding is applied. We don't discuss the effect of air density on control pressures because it's too small for any human to recognize. We still require an understanding of air densities impact on engine power, however. We do that because it has a notable impact.
In other words, IMO, the CFI should learn what GP is and where to apply it. Steep turns is not a place GP requires application. Unless of course you need a good excuse for losing 150 feet. Then superb GP knowledge is mandatory!
R
Roger, Roger
Guest
Sure, it exists...but enough to require a measurable, flyable difference in pitch attitude for a right vs. A left steep turn? I doubt it. Not in any airplane I've flown anyway.