Parts deleted by me..

 

There is no continual left roll in any of these aircraft and why most of them do not have aileron trim. Contrary to much of the aerodynamic talk of engine canting above I believe there is a simpler explanation-if a wing drops dihedral takes control and thru a gentle number of Dutch rolls specified by the FAA (which xplane flunks) the plane comes back to its level state. Pipers are notoriously stable this way-my friend with an Arrow used to brag he did not need an autopilot and he was right-it was unbelievably stable.

 

That's it! Dihedral in the wing is what gives the plane a positive stability. And anytime there is dihedral, the plane will eventually bank and turn, if the yaw isn't counteracted with rudder. There is always going to be a left drift tendency, whenever power is applied with a clockwise turning prop from the cockpit view. This is offset with a built in offset in the vertical stab, or a fixed or adjustable rudder tab. Since the effects of the engine/propeller are amplified with more power, the engine "cant" automatically adds more "lift" to the vertical stab to compensate against left yaw. And getting to the nitty-gritty, I can still see where right engine cant could provide additional lift to the inboard right wing, as the nose would be blocking some airflow to the left wing. There are some nice drawings on the net, which explain loss of lift on inboard wing sections, when the plane yaws in a slip, just due to the nose/cowl area blocking the airflow.

 

What's NOT done these days, is changing the incidence of wings, to add some right roll. The same with (wing/aileron) tabs, unless the plane just won't fly halfway straight without them. This just causes additional drag. And with them, you half to compensate the opposite direction, when power is pulled back. That's more un-needed drag.

Contrary to much of the aerodynamic talk of engine canting above I believe there is a simpler explanation-if a wing drops dihedral takes control and thru a gentle number of Dutch rolls specified by the FAA (which xplane flunks) the plane comes back to its level state. Pipers are notoriously stable this way-my friend with an Arrow used to brag he did not need an autopilot and he was right-it was unbelievably stable.

 

As I said, the difference in torque between idle and max power (in a C172) is the same as being solo and having two 180lbs passenger on the right. Physics law does not make a distinction if the torque is caused by engine or by passengers, it's simply there.

 

So, if you need to re-trim ailerons between a solo flight and a flight with two 180lbs pax, but do not need to re-trim ailerons between idle and full power, it _necessarily_ means that the reason must be strictly linked to aerodynamic effects caused by the engine.

 

On the other hand, if aileron trimming is not needed when you're flying with two pax, then your explanation could be correct.

 

Do you need to re-trim ailerons when travelling with two pax on the right in a C172 class aircraft?

 

There are great things the blade element approach does-Dutch rolls from disturbing air, ground effect, the general landing process etc. I don't understand why it is so hard to admit there are areas that it doesn't do so well and hope for fixes in a never ending goal to have a better flight sim.

 

Mmm I think nobody denies that, and I'm the first to admit it. Surely X-Plane FM needs to be improved, even if already now, the best X-Plane add-ons developers are able to give excellent flight models for their products and get through many of its limitations.

 

What I think, is that a BET approach _can_ give better results than "lookup tables", and I'm not the only one to think so, since it seems to be confirmed by the fact that all the recent flight simulators giving FM top priority use a BET approach: Condor Soaring, Silent Wings, DCS, Rise Of Flight...

So, if you need to re-trim ailerons between a solo flight and a flight with two 180lbs, but do not need to re-trim ailerons between idle and full power, it _necessarily_ means that the reason must be strictly linked to aerodynamic effects caused by the engine.

 

Perfect!

 

 

 

Condor Soaring, Silent Wings, DCS, Rise Of Flight...

 

True, and IL2 Sturmovik Battle of Stalingrad will adopt the same "school" of aerodynamic modelling.

 

The triuth is that the implementation of this method in, for instance, the DCS P51d, is certainly much more refined than what we have in X-Plane.

 

I never bought a p51d model available at the org, because I guessed it would disapoint me with the overdone torque. But I did buy A2A's p51d, and DCS P51d. Well, the FSX model does a nice job, but, as A2A has recently commented, before the new C172, all of their models used the core p-factor and torque, and gyroscopic scalars to model props. So, you can expect that under most circumstances the model in FSX falls short of what you get in DCS.

 

In DCS, during takeoff or high power climbs, and assuming there is no load / fuel imbalance ( Murmur, your observation was EXCELLENT, because of course, any imbalance will easily be felt in the p51, and I believe that applies to the real thing to... hence the aileron trim ), you will have yaw to the left and roll to the left. Both are countered *** ONLY *** with rudder, and when you give rudder, you can level your wings and center your ball. In X-Plane, if you level your wings using right rudder, you're going to slip, and the ball will escape to the left ( inconsistently asking for left rudder !!! ).

 

Also, in the DCS model, as you gain speed / lower AoA, the rolling tendency, and the yaw, fade away, if you used rudder trim you'll have to cancel it, and sometimes, depending on your cruise speed, your weight ( and hence AoA ) you'll even have to use left rudder trim!

1) it would be impossible to do what you said above be because a large number of GA aircraft do not have aileron trim-it is not needed. The C172's that I flew did not not have aileron trim. My bonanza did but I only touched it once-never the Baron.

Why would I only touch it once and the day I bought the plane?. I bet Larry knows.....

I have seen pilots use rudder trim on takeoffs to ease the right rudder pressure needed

 

2) a plane does not continually roll to the left-regardless of the number of passengers.

Do you need to re-trim ailerons when travelling with two passengers on the right in a C172 class aircraft?

 

These small planes do not have aileron trim. The Cessna 172 has adjustments made at the factory for any tendency to roll right or left at cruise speed. It's done with adjustable cam bolts on the rear spar. In flight, you just compensate with the yoke, it the weight difference is that bad. Just tell the rear seat person to move to the left.

 

In my RV, I purposely installed anything that weighed enough.......in the right wing. Examples are the auto-pilot servo for ailerons, and my aileron trim tab servo. This was to help offset my left seat weight as pilot. I did install aileron trim, because I'm a trim perfectionist. I want the ability to completely let go of the stick, and see no forces present from the flying surfaces. This works very well for fuel & passenger adjustment. I'd also run the on the right wing tank first, although I swith back and forth. The Cessna will be running on both tanks. Of note, I once took a passenger in the right seat, that weighed 80 lbs. more than me. I may have compensated with some aileron trim. I don't remember. But what I do know, is those stubby short wings, created enough lift to hold us near level. I certainly didn't fight a roll. On the otherhand, a dry left wing tank, and a full right one, would do the same. Just about 80 lbs.

 

.and of course the dry wing would cause the wing to dip, then would be corrected by dihedral with Dutch rolls repeating itself and making especially your back passengers vomit. No decent pilot would do so, and I had a front seat passenger vomit once from motion sickness-not a pretty sight and something I would want to repeat....

Well, the guys flying the C172 at A2A, and a friend of mine who drives one at the airclube confirm having unbalanced passengers in the C172 R does cause a bank tendency and requires compensation, with yoke.

In my example, it's not important if the aileron trim is there or not, of course the important thing is if there is need to have constant deflected ailerons.

 

So, if you say that a C172/bonanza/etc. class aircraft does not need constant yoke deflection to the left if there are two pax on the right, then in this case, your reasoning could be correct.

Well, the guys flying the C172 at A2A, and a friend of mine who drives one at the airclube confirm having unbalanced passengers in the C172 R does cause a bank tendency and requires compensation, with yoke.

 

That's interesting info. :smile:

But!

 

Let's not forget that the bank caused by fuel imbalance or pax imbalance is a kind of bank that starts a slip, because it is not accompained by a coordinated input of rudder.

 

Just like in a low wing dihedral helps static lateral stability, in a high wing aircraft like a C172, it's not any sort of pendulum effect that acccounts for that stabiltiy, but rather the slip itself.

 

During a slip on a high wing aircraft, the airflow that flows laterally over / bellow the fuselage causes the AoA in the lower wing to increase, and also the one on the upper wing to decrease, so, a rolling moment opposing the one that started the slip tends to build up and restore the stability...

 

BTW Geofa: The oscillatory motion of a Dutch Roll is, simply put, a result of an aircraft design that causes the static lateral stability to be more effective than the static directional stability. Just that :-)

It's typical of wigh swept back wings, but non only... High fins can overcome the problem, but cause other problems to the construction of the aircraft, so, using smaller fins than what would be the ideal implies the use some artificial stability device, like the yaw damper... I know you know this, but in one of your posts above it was not related to what was being debated ;-)

Also, in the DCS model, as you gain speed / lower AoA, the rolling tendency, and the yaw, fade away, if you used rudder trim you'll have to cancel it, and sometimes, depending on your cruise speed, your weight ( and hence AoA ) you'll even have to use left rudder trim!

I don't have the DCS model, and don't have the A2A P-51 either. Do have the X-Plane P-51. It's the reason I'm not liked at the org. But never mind that...In the meantime, I do believe that all single engine planes with a clockwise rotating prop from the cockpit.......will need a continual form of right trim, when ever the engine is producing power. It's the reason so many planes have a built in vertical stab offset. I know, that until I taped on a temporary wedge on my RV's rudder..........that it would just yaw slightly to the left in cruise. And I left it that way for probably 10 hrs, until I got around to it. The forces to counter this yaw with the rudder pedal, are very strong. Yet, with just a little 1*6" wedge of about 5/8" deep, took care of it. I later installed a permanent rudder trim tab. My RV had no built in offset, but the engine is canted. These same offsets and tabs, are what causes a yaw to the right, when power is pulled back, as in a descent. Now it's left rudder or rudder trim to compensate.....if you have rudder trim.

In my example, it's not important if the aileron trim is there or not, of course the important thing is if there is need to have constant deflected ailerons.

 

No, there is not a continual need. If you do let completely go of the yoke, the plane with eventually start to drift off of course and altitude, no matter what. Unless it's on auto-pilot. You DO have to make those small corrections to keep on course and altitude. But it's not tiring (*see next paragraph). They're subtle and not continuous. If a sim is inducing too much of the force effects, then it becomes annoying. And that's what I do not see as a challange, as is expressed by some. You might have noticed, that I've called some sim planes annoying. A friend of mine could fly my plane for hours in cruise, and he's not a pilot. He too, would just make small corrections when needed.

 

*Okay, it's a bit tiring after hour after hour. It's the reason I installed a two axis auto-pilot. I loved it!

But!

 

Let's not forget that the bank caused by fuel imbalance or pax imbalance is a kind of bank that starts a slip, because it is not accompained by a coordinated input of rudder.

 

Just like in a low wing dihedral helps static lateral stability, in a high wing aircraft like a C172, it's not any sort of pendulum effect that acccounts for that stabiltiy, but rather the slip itself.

 

During a slip on a high wing aircraft, the airflow that flows laterally over / bellow the fuselage causes the AoA in the lower wing to increase, and also the one on the upper wing to decrease, so, a rolling moment opposing the one that started the slip tends to build up and restore the stability...

 

This explanation apparently seems to be consistent, but think of the example made by LAdamson: a single aileron of his RV6 had a slightly larger trailing edge radius, and this little asimmetry caused the aircraft to roll in one direction, so that he had to correct that.

 

Even in this case, if your explanation would hold true, the induced bank, not accompained by rudder input, would have induced a slip, that would have induced a restoring force... etc. But instead this wasn't happening, and the aircraft was wing heavy by LAdamson words.

Also depends on the aircraft. My friend with the arrow with anything but bad turbulence would let go of the yoke for minutes at a time. It used to drive me crazy because his altitude would be moving up and down very slowly +-100 ft. And the heading like wise a few degrees either direction but it always did come back to the " average by itself-thanks to that Hershey Bar wing.

 

Larry-only tiring cause you live in the mtns with all those disturbing air currents!

For me 64bit is meaningless if the areas I fly (mostly around cities) continue to look unrealistic.

That doesn't really makes sense. If you want realistic views, you have to set higher texture-resolutions for example or a higher object-density. This will need some more memory, that's why you will need the 64Bit version to experience this. Otherwise you would experience some frequent  memory-crashes ;-)

 

And sorry but: Xp looks unrealistic? I really don't think so, since it's one of the things that are very appreciated (Global scenery) and will still be improved (mesh HD2 etc.)

What's NOT done these days, is changing the incidence of wings, to add some right roll. The same with (wing/aileron) tabs, unless the plane just won't fly halfway straight without them. This just causes additional drag. And with them, you half to compensate the opposite direction, when power is pulled back. That's more un-needed drag.

 

Well, if wings with differential incidence or aileron tabs were used in the past, that means indeed that engine do cause roll torque, tending to bank the aircraft. It's just that this roll torque is compensated in some way: by using differential incidence or aileron tabs in the past; by using just canted engine nowadays.

 

Also depends on the aircraft. My friend with the arrow with anything but bad turbulence would let go of the yoke for minutes at a time. It used to drive me crazy because his altitude would be moving up and down very slowly +-100 ft. And the heading like wise a few degrees either direction but it always did come back to the " average by itself-thanks to that Hershey Bar wing.

 

Very stable! I never found an aircraft so stable in pitch and roll either in FSX or X-Plane. :smile:

No, there is not a continual need.

 

I was referring to the "two pax on the right seat" case, not to the engine torque.