Piper Comanche - Rudder

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TonyW
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Piper Comanche - Rudder

Post by TonyW »

Hi,

Just a couple of questions about the use of the rudder in the Comanche.

1 - When should rudder trim be used? From flying lessons I did a long time ago in a Cessna 152 I remember having to use right rudder to counteract yaw caused by prop wash. Am I correct to say that as speed increases that this yaw effect reduces? It seems counter intuitive but on the Comanche I seem to notice that once I'm cruising there is no yaw effect. I'd like to use right rudder trim on take off roll, but finding it difficult to know how much - around 20% seems OK, but is yaw going to be continually varying? Adjusting the rudder trim is difficult during take off roll because you've got to take your eyes off the runway.

2 - When I'm flying and turning I notice little or no movement on the ball, even though I have Auto Rudder turned off - why is this?

Regards,

Tony

Hook
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Re: Piper Comanche - Rudder

Post by Hook »

I don't remember the Cessna 150 needing any rudder during level flight. It required right rudder on takeoff and climb, left rudder on descent, and the usual rudder in turns to counteract adverse yaw.

The Comanche has differential ailerons which reduce the effects of adverse yaw. I believe this is explained in the manual.

Typically I don't use rudder trim except to balance an unbalanced load. If you are doing a long climb, just dial in enough right rudder to keep the plane stable. It's better to learn this setting by experience as your aircraft probably won't be loaded the same as other people's. It's going to be better to counteract yaw with the rudders and it will vary depending on crosswind and other factors.

Hook

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AKar
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Re: Piper Comanche - Rudder

Post by AKar »

As this is Flight Academy forum, let us extend this a little bit from single props solely towards more general speaking. :)

It is usually highly desirable to have a fairly strong (but of course not overly so) dihedral effect in an airplane. What this means in simple terms is that the airplane's side slip induces rolling moment. This effect can be achieved by wing dihedral, hence the name, but also by other factors such as, even more importantly in many cases, the wing sweep angle.

In airplanes with reasonably strong dihedral effect, the rudder trim alone can be used to relieve any banking tendencies due to unbalanced loading or other factors. A very good case of this comes up with the airliners: in there any banking tendency would be compensated by the autopilot usually, by roll input, but if the aerodynamic and/or weight imbalance causing the issue are fairly significant, the necessary roll input does cause the roll spoilers of the 'light wing' to come up some, causing a significant drag penalty. Hence, it is preferred to trim the airplane to near-zero aileron input using the rudder trim, while allowing for the residual side slip.

In the very latest airliners this is done instead by automatically extending the flaps asymmetrically just a tiny bit in cruise, so they also mitigate the drag penalty caused by the side slip.

Getting back to single props, I have only flown so few in reality, none of which either had nor in which I ever used the rudder trim, but keeping a slightly pressed foot tends to allow for hands-free on the yoke/stick. The same principle!

-Esa

TonyW
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Re: Piper Comanche - Rudder

Post by TonyW »

Thanks for the replies,

Yes, I remember in the Cessna having to use right rudder on t/o roll and climb but not on cruise. Up to now I've just used my rudder pedals (Saitek) so I found today for example when on the t/o roll around 15% meant less foot pressure, then as I climbed I gradually reduced it back to neutral. I generally fly the Comanche light - two lightweight passengers - a virtual me + virtual wife! plus baggage. In reality we both weigh around 60 Kg so I use that in the sim also plus 25 Kg baggage! I'll start off with all 4 tanks full but let the fuel go down to around 25% before refilling. Trying to get as real as possible!

I do know from a previous flight how important weight is. Months ago I accidently used a single tip tank instead of the main tank and I found it harder and harder to stop the plane banking as the tank emptied. It wasn't until I was back on the ground after a terrible landing that I saw my error.

Tony

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Scott - A2A
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Re: Piper Comanche - Rudder

Post by Scott - A2A »

Just to add / reiterate:
TonyW wrote: 02 Apr 2020, 09:261 - When should rudder trim be used?
Rudder trim is a convenience and not necessary since you have feet available at all times. Some people trim in a climb so they don't have to stay on the rudder, for me I only adjust rudder trim once settled in a cruise then leave it there. I recall being in training on final with an engine out and my instructor moved the rudder trim for me to make up for the imbalance between engines. I said "don't do that I'm fine" but he proceeded anyway. It ended up really messing me up on landing flare as when I pulled the power back the plane instead of becoming neutrally centered it was yawing. Personally I prefer to feel that engine out the entire time and when power is off, it's all off and balanced. But that's just me and other pilots may do this differently.

TonyW wrote: 02 Apr 2020, 09:262 - When I'm flying and turning I notice little or no movement on the ball, even though I have Auto Rudder turned off - why is this?
The ball is only really going to move a lot when you are using ailerons while entering or exiting a turn, but once established in a turn it should be become relatively normal.
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Hook
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Re: Piper Comanche - Rudder

Post by Hook »

Scott - A2A wrote: 06 Apr 2020, 06:18 The ball is only really going to move a lot when you are using ailerons while entering or exiting a turn, but once established in a turn it should be become relatively normal.
Wait, what? I thought the Comanche had differential ailerons and that was keeping the ball centered when banking into or out of a turn. I haven't flown the Comanche in a few weeks; is my memory faulty?

You scared me. I had to go check my options to make sure auto rudder wasn't checked. AutoCoord is false. Use Autorudder is unchecked.

Hook

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Scott - A2A
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Re: Piper Comanche - Rudder

Post by Scott - A2A »

Hook I may be wrong but I don't think differential ailerons alone are able to do that without some rudder.
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Hook
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Re: Piper Comanche - Rudder

Post by Hook »

Scott - A2A wrote: 06 Apr 2020, 13:30 Hook I may be wrong but I don't think differential ailerons alone are able to do that without some rudder.
You fly the real thing! Do you have to use much rudder when banking into a turn? I'm going to assume the A2A version flies as close to your real one as it is possible to get.

I typically do my banking very slowly so I may not be getting as much adverse yaw as people who are more aggressive with it.

Hook

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AKar
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Re: Piper Comanche - Rudder

Post by AKar »

For what it's worth, the ailerons in PA-24-250 move 19° up and 15° down, by the spec. This is a fair bit of differential, and it likely plays a notable part in reducing adverse yaw (though almost certainly not fully eliminating it, throwing in an educated guess). But I learned in gliders anyway, so most SEP airplanes feel like trains in yaw to me. :mrgreen:

-Esa

William Hughes
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Re: Piper Comanche - Rudder

Post by William Hughes »

I fly a 250 and I'll trim out a long climb and I'll trim out in cruise. Other than that it doesn't get touched much. A high power climb can put a lot of pressure on your feet for several minutes and it is very easy to let a wing droop. Plus it is really un comfortable after a short time. In cruise you need to trim that out, and I think I can pick up a couple of knots if everything is trimmed just right.

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DHenriques_
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Re: Piper Comanche - Rudder

Post by DHenriques_ »

Good instructors never get into complex explanations on the use of rudder in turns.
The RIGHT answer is in this case the simplest answer.
Since the need for rudder application will vary with airspeed when involved with turns the correct way to deal with rudder is simply to say,
"Use whatever rudder the aircraft is telling you to use or not use with the nose. Think of the nose as linked directly to your feet. This will work for ALL phases of flight" !!!
Dudley Henriques

GaryRR
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Re: Piper Comanche - Rudder

Post by GaryRR »

I suspect I would come to ground school armed with a lot of knowledge from reading this forum . People pay for that. VERY Interesting.

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