Thanks Hook...good post as well...I totally agree and will take a look at this also. One factor I've never really been able to know for sure (though I went ahead and guessed) is the Cg location. If the CG lies above the Cl, then of course dihedral stability is diminished. Looking at the Cg location on the XP Baron...it might could be construed as too high. I'd describe it as about "at the belly button" Given fuel in the wings and engine mass....I think it reasonable this might be a bit lower and welcome folks "gut feeling" on this one. If I were to lower the Cg but 5-6 inches (at about seat surface height), then I'd expect to gain a bit more stability from the dihedral.

 

Tom K

This is a well worded description of the issue we seek to resolve.

 

http://ma3naido.blog...e-reaction.html

 

This supports my assertion that some form of asymmetrical lift has to be applied to adjust for engine torque in order to keep a non counter-rotating twin wings level at a given speed. The tools available to the real world designer are myriad. As long as lift is increased on one side, the effect can be neutralized, but only at a given speed. x-Plane has only a few tools to simulate this effect...the most prominent is "default aileron trim" and the method I choose to use in the absense of slipstream corkscrew effects or any other trim inducing device that Beech has employed that I am unaware of. This technique in x-plane deflects the aileron a default amount so that when your "trim wheel" is in the neutral position, the ailerons are still deflected a tiny bit. From Austin's perspective, it's just a roll force..whether it's from a trim tab or the aileron matters not. This setting has been calibrated for "reasonable" wings level at about 160 knots. By reasonable I mean I can fly a specific speed "hands off" and the plane will only roll very slowly. I am sorry, but as an engineer, I can't in good conscious say that a plane with the control yoke ridgidly locked would remain perfectly "roll free". The goal is to put slight pressure...but given flight sim hardware and it's spring centering....there's just no way to get the feel to that level.

 

Where I think many of us get caught up here is some feel this is a "cheat". I mean, no real trim is used i the plane, why is it used in x-plane. My response to that is simply that some method must be employed in reality...whether it's engine offset, bent trim tabs or whatever...in x-plane, the simplest and easiest is the default aileron trim. I am intersted in exploring other solutions designers may use though and ideally, it'd be nice to employ the same methods as the real beech baron.....whether it's some form of rigging, a trim tab, offset or canted engines I have no idea. Until then though, the default aileron trim tab, set to balance the plane at cruise is the method I'm using.

 

Tom K

 

Thanks for the answer-that explains the situation well.

I think there is a serious inconsistency here. The linked document says:

 

"Generally, the compensating factors are permanently set so that they compensate for this force at cruising speed, since most of the airplane’s operating lift is at that speed. However, aileron trim tabs permit further adjustment for other speeds."

 

On the other hand, Geoff you said:

 

in my Baron I never ever had to touch aileron trim-ever and the only time I touched rudder trim was went doing cut engines.

 

Only time I ever used rudder trim was in engine outs. Otherwise I never ever had to touch rudder/aileron trim (When this thread started I actually had to tax my brain to remember where the rudder/aileron trim were). A Baron is very stable and does not roll by itself in a matter of seconds to a 45 degree bank once trimmed for level flight. It does not need either rudder or aileron trim-unless of course it is misrigged which would be a one time adjustment.

 

So, if I understand correctly, the Baron doesn't have a significant tendency to roll, and hence no need for varying aileron trim, whatever the flight conditions: climb, cruise at different speeds, descent at idle. Can you confirm that Geoff? This is in contrast with what the document linked by Tkyler says.

 

Marco

You are correct Marco. Neither have I seen a tendency on the other small aircraft I have flown.

My debonair needed little right rudder in climb or descents as it had a built in rudder aileron connect. A maneuver like a chandelle did require full rudder in the end in the debonair-which I haven't found simulated well in any sim.

On the Baron I found only a very little rudder needed in the climb/ descent. Cut an engine though and you will get roll and need a good amount of rudder.The Diamond da40 I flew though needed quite a bit of rudder-but it did not have rudder/aileron trim like most small aircraft.

 

I have had the stability sliders all the way to the left so will try putting them to the right and see if that helps with the continual trim I have to do-since it now sounds like this is not a cheat but a necessity.

Strange though, from my recollection doing this on the Carenado's aircraft made them less stable while making the rest of the fleet more.

You are correct Marco. Neither have I seen a tendency on the other small aircraft I have flown.

My debonair needed little right rudder in climb or descents as it had a built in rudder aileron connect. A maneuver like a chandelle did require full rudder in the end in the debonair-which I haven't found simulated well in any sim.

On the Baron I found only a very little rudder needed in the climb/ descent. Cut an engine though and you will get roll and need a good amount of rudder.The Diamond da40 I flew though needed quite a bit of rudder-but it did not have rudder/aileron trim like most small aircraft.

 

Hi Geofa,

 

I'm trying to pin down the issue...

 

In a Baron with 260hp engines, 2500 rpm, full power, the total torque produced by props is around 1090 lbs*ft. This is about corresponding to 2 people of 440 lbs each (!), both sitting on the same side of the aircraft, 1.2 feet from centerline (e.g. co-pilot + passenger on the right side).

 

Now my question is:

 

1) Imagine the difference in the roll tendency between a full power climb, and an idle power descent.

 

2) Now, imagine the difference in the roll tendency between being solo in the aircraft, and having a 440lbs copilot + a 440lbs passenger on the right side.

 

According to your knowledge of the Baron flight dynamics (I guess you never actually had 2 * 440lbs people sitting with you on the right side :smile: ) should 2) be much greater than 1)?

 

If it is so, then it means that only the torque produced by props is somehow compensated. This in turn, also means that the compensation happens mainly because of surfaces directly hit and influenced by prop slipstream (wingspan downstream of the props, maybe elevator too?).

 

Marco

It is not only the Baron, but almost every aircraft I queried the pilots about (and, yes I recall my Cessna Awagon story...). A Cessna Caravan, Pilatus Turbo Porter, a B1900d, a B55, my glider tug fellow pilots and myself flying with them on glider towing flights, all confirm mainly yaw, to be compensated with rudder, or rudder trim, and absolutely no bank! In Xp if one tries to use rudder or rudder trim only we end up with the wings levelled but in a sideslip, with the ball asking for left rudder :-/ In the real, say, Robin DR-400, when we use the right foot the ball centers and the wings are levelled. This is how it is in RL, at least on these aircraft.

I believe your last sentence to be correct-but is not roll mainly taken care of by dihedral of the wing?

 

As for idle power descent-you would never do that (at least I wouldn't in a Baron or Bonanza). You pull 1" or so every once in a while and get down to eventually 17" in the summer and 15" in the winter as the final approach power setting and minimum. Same pulling back the power after takeoff-perhaps if you jerked it suddenly off 3-4" there would be a rolling moment but I never did that, and a pilot at least how I was trained pulls the power back so gradually and gently that a passenger should not even know it happened. My Deb had vernier controls that made it possible to make incredibly smooth gradual adjustments.

 

The only real difference in handling between a Baron, Bonanza, and a C172 is the Beech go faster, they are hard to slow down, they are more stable due to their higher gross weight, dutch roll can be a problem for the passengers in back,and if you let the nose drop at all they build up airspeed rapidly. As far as handling they are very docile (and the controls don't feel like beer cans... B) ).

I think there is a serious inconsistency here. The linked document says:

 

 

 

On the other hand, Geoff you said:

 

 

 

 

 

So, if I understand correctly, the Baron doesn't have a significant tendency to roll, and hence no need for varying aileron trim, whatever the flight conditions: climb, cruise at different speeds, descent at idle. Can you confirm that Geoff? This is in contrast with what the document linked by Tkyler says.

 

 

My RV6 had aileron trim. It's got short stubby wings, and there can be a noticeable difference with a passenger & fuel load, although I'd switch tanks every half hour to balance fuel. Many RVs don't use any aileron trim. I'd just adjust mine a slight bit, to keep every thing perfect.

 

During the takeoff run, the RV needed lot's of right rudder. Since the engine is quite powerful for the size of the airplane, and the fact that the constant speed prop allowed it run to full rpm...............the pull to the left is very noticeable. If doing a touch & go, with a quick application of throttle, or just a real quick application of throttle on a normal takeoff, you could feel the torque as it pushes down on the left landing gear. I'd be ready with some right aileron as soon as the plane leaves the ground. Sometimes, it even rolls a bit to the left, which is quickly countered with aileron. But...............once you're climbing out from the airport, that roll from torque............dissapears. I'm still using right rudder until airspeed picks up to counter left yaw, but I'm not actively using the stick to counter roll. And what I certainly don't do..............is constantly trim for roll, while either in the climb, cruise or descent. It's rudder only.

 

I have many takeoff & cruise pics looking out over the wing. My aileron tab will either be neutral with ailerons balanced in perfect trail, or the tab is slightly moved, and the ailerons are slightly offset. This is just a "balance" thing..........because it's a small plane with short wings. Most of the time, the ailerons are just straight with the flaps............including high speed climbs. In fact, for all I know...........the slight offsets may have been during a turn...

 

L.Adamson

I believe this post I just made is more related to the topic on this thread than on the one about "flying on rails"....

There were a few loose ends on my work and the Baron did not go out with all the new changes I've made per this thread...a few, but not all.....my goal is to have all my work refined before 10.20 final....which we are working towards currently.

 

TomK

Great news-thanks Tom!

I guess someone needs to go to the org. and tell them about this thread. I can't. Today's answer there, is that engine torque in cruise is normal, and that it's compensated in real life by varying incidence on the wings, adjusting ailerons, or built in tabs. It's another case of someone trying out X-Plane & finding that a rolling motion doesn't seem realistic.

Poor souls.... And what really irritates me is that they could at least listen to you, who most certainly better than many of them knows what is saying. After all you built your RV, or at least knew about it down to the pickiest details, so, you know there is no such asymmetric camber or incidence or thickness, or whatever...

 

But there are a few posts by me ( jcomm there too ) on this subject, and confirmation, among others from Brett, that it's a known X-Plane "bug", together with the ground friction....

 

I told I wouldn't post here again before X-Aviation's Saab got out... sorry... I couldn't resist...

 

This is a lost cause Adam, I believe, and one of the items in my list Austin said he didn't find relevant... The rw lighting, at least, will get a fix... So, I don't expect to see proper prop behaviour in X-Plane10... Maybe when XP11 get's announced (?)

 

It's nice to see this sort of flight dynamics "problem" dealt with correctly in both FG2.10 JSBsim-based models of teh best quality (there's a bit of everything among the myriad of available models just as with any simulator...), and in DCS World's p51 d too !!!

 

Reciprocating engine modelling in X-Plane10, specially at altitude, is another problem very few times mentioned.... Pick your preferred prop to an altitude where you know your engine would be unable to work, unless proper leaning is used, and you'll find it working beautifully... Well...

Sometimes, I just go crazy with what I read. Especially when I can't reply to another forum in which it's written...........the org. Actually the thread over there is getting a fair amount of attention, with the fact the "un-realistic" roll does exist within the X-Plane flight model. But then I see remarks such as this, which are second hand, and may not be exactly correct. I have a lot of time in RV9's. With my own time, and time flown with others in two RV9's, it's about 180 hrs.

 

Quote from other forum:

 

The larger (and therefore more effective) the vertical stabilizer is, the more the sideslip gets canceled and the *less* directionally stable the plane is! Gary, a guy I used to work with, built himself a Vans RV-9 - lovely little high performance kit plane. While he was building the real plane, I built him an X-Plane model. I found the model to be pretty unstable - it required frequent corrections to keep it flying straight. The reason was the large vertical stabilizer this plane has. And guess what? Gary has also found the real plane to require fairly frequent attention to keep it flying straight.

 

I can tell you from first hand experience, that the RV-9 is anything but unstable. It's very docile compared to my Van's RV6. I won't say it's as stable as a Cessna 182, but it's certainly very easy to fly, without making any constant corrective forces. Just like any other plane, it won't simply maintain course & altitude without pilot inputs.

 

Point is, some of this information is put on forums, then many will think this is exactly how it is. Sometimes it justify's the flight model, when it certainly should not. It's also the reason you'll see remarks from new users of X-Plane who think..........."WOW, for the first time, I find that airplanes require much more pilot input to the controls, than I ever found with FSX (the flying on rails sim). XP really does model the interaction of air over flight surfaces." Of course, thanks to X-Plane marketing..........they believe that the XP flight model is just like the real thing.

 

In this case, the flight model is WRONG. I only wish that I could convey my thoughts (on the same day the post is written), based on real world experience with these "exact" aircraft, that there is a problem. But I can't. I was censored at the org.

You take this totally out of context. That's dishonnest from your part.
This is in a post where Andy Goldstein explains the problem of stability in aviation, and how it works, which is not as straightforward as one would think (I've learnt a lot by this post alone). More importantly, he acknowledges and identifies precisely where X-plane falls short in this domain.
In the same thread, he and several people dissect the problem of excessive roll. Again, Andy is actively looking for a solution to this problem, which is far from simple. Sure, Austin won't be happy with just a set of parameters, that's not his style, but a precise description of what happens physically will go a long way to solving that long standing problem.