DCS P-51 Propwash Effects Video

[Smokin Hole]

That's probably true. Non pilots like to use the term "seat of the pants" to describe how really good, natural pilots fly. But really there is no such thing. This would be the exception. Any time you are in a tailwheel and it is moving you must stop undesired yaw very early before it accelerates past your ability to limit it. It's a little like hovering a helicopter. But there is a difference that separates planes from the bike analogy. Tracking a conventional gear plane is a visual process. That is how its taught: find landmarks on either side of the nose and use those marks to sense yaw. Also, in light wind, the P-51 should, to my inexperienced mind, track fairly straight once the tail rises at 60-80. That vertical stab is very big. The wheel base is wider than practically anything else flying relative to size.

[Yo-Yo]

That's probably true. Non pilots like to use the term "seat of the pants" to describe how really good, natural pilots fly. But really there is no such thing. This would be the exception. Any time you are in a tailwheel and it is moving you must stop undesired yaw very early before it accelerates past your ability to limit it. It's a little like hovering a helicopter. But there is a difference that separates planes from the bike analogy. Tracking a conventional gear plane is a visual process. That is how its taught: find landmarks on either side of the nose and use those marks to sense yaw. Also, in light wind, the P-51 should, to my inexperienced mind, track fairly straight once the tail rises at 60-80. That vertical stab is very big. The wheel base is wider than practically anything else flying relative to size.

 

THe wider is the base the more stable is nose-wheel plane and more UNSTABLE is a taildragger. And this is the main common feature of bicycle and taildragger - they are bank(bicycle)/yaw(taildragger) unstable. So the earlier you avoid bank/yaw deviation the more you are safe.

[Smokin Hole]

Well, I used to teach this stuff and I myself was taught by some very experience old salts. We may have had it wrong but what we were taught was this: The instability of conventional gear planes is mainly due to the CG location aft of the mains. This makes any drift tend to accelerate until corrected by the pilot. As a rough guide, that drift can be stopped with rudder, brakes or both until the CG passes laterally beyond the wheelbase. After that, again roughly, things have progressed too far for a recovery. If you throw brakes into the equation the wide wheelbase becomes an obvious advantage.

Edited May 11, 2012 by Smokin Hole

[Yo-Yo]

Well, I used to teach this stuff and I myself was taught by some very experience old salts. We may have had it wrong but what we were taught was this: The instability of conventional gear planes is mainly due to the CG location aft of the mains. This makes any drift tend to accelerate until corrected by the pilot. As a rough guide, that drift can be stopped with rudder, brakes or both until the CG passes laterally beyond the wheelbase. After that, again roughly, things have progressed too far for a recovery. If you throw brakes into the equation the wide wheelbase becomes an obvious advantage.

 

You are absolutely right and the point is that the earlier you begin to counteract starting yaw the more chances that there will be no ground-loop. In sim you have to wait to estimate the tendency. When I begin to TO in DCS Mustang the model had mistakes in main wheels position - they were shifted forward - and the plane was extremely unstable, I used clouds as a reference to see any small yaw... it helped. :) And thiis was a crutch for the acceleration feeling.

[Smokin Hole]

Yo-Yo. So I've noticed that my takeoffs are straight as an arrow regardless of how I do them. I don't feel as if I am doing anything different than I did at day one (when they were much uglier) but it is, as you say, an issue of recieving and processing yaw cues. Whether its a visual thing or a sensation of acceleration is not as relevant as teaching your virtual feet to react to inches of movement instead of meters of movement. Here's the hard part: admitting that my initial problems were attributable to bad technique and not a faulty FM.

[effte]

THe wider is the base the more stable is nose-wheel plane and more UNSTABLE is a taildragger. And this is the main common feature of bicycle and taildragger - they are bank(bicycle)/yaw(taildragger) unstable. So the earlier you avoid bank/yaw deviation the more you are safe.

 

Talking about two different things here, I think. You are talking about wheel base - distance between tail wheel and mains - while we're talking about the stability provided by the large track width - the distance between the two mains.

 

Tail wheel locked, wheel base doesn't matter a whole lot for stability as long as the tail wheel isn't skidding. Tail wheel unlocked - still doesn't matter, obviously. :)

 

Tail length, empennage/fin area and - first and foremost - distance mains to center of gravity is what does it. Wider track width means increased roll stability and far less chance of damaging something when being ham-fisted in the aircraft.

 

I'll chime in with Smokin' on the process of yaw control on takeoff being almost entirely done visually. The seat of your pants, so useful during smooth flying, is all but useless on the ground roll due to all the "noise" vibrations and bumps caused by rolling down the runway. No real difference between sim and real life there, apart from the little help you get by being rocked back and forth in your harness. On the other hand, that happens due to bumps in the runway as well. By the time you're getting definitive sensory feedback, you're already in an established yaw/turn well on your way into a full-on ground loop. Way too late.

 

FWIW, I've never really had any trouble keeping her straight. My first takeoff wasn't worth posting in the first-takeoff thread, as it wasn't very amusing at all. There's always some drift back and forth across the runway which I definitely don't see even in videos of low-time pilots in poor conditions. Definitely enough, and difficult enough to control, to rule out any thought of formation takeoffs. However, it is conceivable that formation takeoffs are/were never done at full power settings, so I'm giving it the benefit of the doubt for now while exploring the limited-power takeoff - always been the full 61" for me*.

 

Another factor is the fact that we're taking off from concrete runways. Conventional gear pilots, especially of warbirds with more interesting ground handling qualities, shy away from concrete runways preferring grass if given the option - especially with a crosswind. The lower friction offered by the grass makes it a lot easier - that I know from own experience. This leads me to another suspect in the Great Stability Debate - are the tyre slip angles modelled as of yet? If not, it will have a huge impact on stability on the ground.

 

Right now, I don't perceive any differences in ground handling taking off and landing "off field".

 

As I've said before, I'm not ready to call foul on the yaw stability on the takeoff roll. What I do find difficult to believe is the difficulty of catching incipient yaw deviations. Once it starts going, it pretty much is going no matter what you do. To save myself from retyping too much, I'll quote myself from another thread:

 

The difficulty of keeping things straight on take-off and landing is plausible to me. However, the difficulty to get things back under control once you allow it all to go pear-shaped is probably WIP. If it was really this easy to wreck aircraft on the ground, the pilot's manuals would have page upon page with warnings and advice and there'd be no end to the journal footage and written accounts of aircraft going off the runways.

 

The Mustang was considered benign as compared to the narrow-track Spit and Bf109, so imagine what they'd be in a crosswind relative to what we are seeing? I've never seen landing accidents listed as a serious cause of attrition in the war-time Mustang fleet - unlike for the aforementioned two aircraft - and pilots were sent to crud weather in Europe with relatively few hours on-type.

 

...

 

I reiterate - I consider this to be WIP and expect to see things change back and forth as the beta period progresses, so I try to take it at face value and not get too upset as of yet.

 

(The lack of difficulty experienced I attribute to learning to fly dancing on the pedals, and keeping the skill alive through other simulators during recent more boring tricycle gear flying.)

 

*) Remember the list of the most useless things in aviation - altitude above you, runway behind you, etc etc

Edited May 17, 2012 by effte

[Smokin Hole]

I find that I can keep a track within a couple of feet if I turn TrackIR off. Doing so greatly improves sensing yaw early. Once the tail comes up there is a definite lack of what should be a natural tendency to track into the relative wind. There is a section in the bugs/flight dynamics thread that discusses yaw stability at low speed. One post by Weta suggests that the current (not yet released) beta build exhibits different characteristics. So this may very well solve itself on the next update. Oh, and the other thing that ha helped was to keep the rudder trim neutral. This simplifies things by concentrating most control inputs predictably to one foot.

Edited May 17, 2012 by Smokin Hole

[effte]

Yeah, I figure we're way too early in the open beta to start getting our... ahem... socks in knots over this. We can, probably should and certainly will discuss it, but I'm not going to worry much about it for now. Wags' signature is a good one. :)

 

Just right on the TIR. I have my TIR enabled at all times, but the G head movement was on very briefly as it darn near did me in!

[cichlidfan]

I find that I can keep a track within a couple of feet if I turn TrackIR off. Doing so greatly improves sensing yaw early.

...

 

Oh, and the other thing that ha helped was to keep the rudder trim neutral. This simplifies things by concentrating most control inputs predictably to one foot.

 

Pausing TIR definately helps you see the drift, that alone makes a big difference.

 

Will have to try the 'no trim' idea, the back and forth is part of what is killing me.:thumbup:

[Elnocho3]

For those who are interested, the TrackIR-off effect is just Gibson's optical flow in action.

 

Motion is perceived most efficiently and accurately via visual information when the fixation point remains constant (in this case the orientation of the viewpoint in the simulator). This gives a consistent optic flow pattern (to imagine optic flow, think of when ships go into hyperspeed in starwars!), which is easier to translate into perceived motion than when the fixation point changes.

 

So basically......zoom out, and stop swiveling your head around!

[Anatoli-Kagari9]

http://www.youtube.com/watch?feature=player_embedded&v=Wd5cg77mA48

 

Listen to the after flight comments from the pilot...