http://forums.x-plane.org/index.php?app=downloads&showfile=19813

 

Available for X-Plane 10.

 

I didn't fly it yet, but will try to ASAP !!! ;-)

I'd be interested to hear your opinions about the flight model (especially with the engine stowed.)

With your gliding knowledge just how good is XP's rendition of of glider flight dynamics: control response, inertia, drag, stall spin behaviour, reponse to crosswind etc. With a standard joystick/ rudder combination what XP controller setting do you prefer.

Well, thepitts, I'll try this one and then I'll ellaborate a bit on my oppinion regarding the way X-Plane 10 "renders" gliders.

 

The default AS-K21, if the hidden flaps are deployed, performs more realistically :-), and looking at the airflois in airfoil-maker reveals that some editing was performed for fine-tuning. Based on my RL experience in the type, it is not bad, but spins more easily than the real thing - the real AS-k21 is difficult to get into a proper spin, unless you get your CoG way behind... and that's not good...  but the spin in the x-plane 10 model reproduces the pitch oscillations of the real glider.

 

There is way too much rudder authority in the X-Plane 10 model too. In RL it' true that you can easily run out of rudder authority during a sideslip, but the yaw rate and moments when full rudder deflection is used are way overdone in the X-plane 10 model...

I was surprised some time ago, to discover how much the spin characteristics are influenced by the ratios between the different radii of gyration (as in RL, by the way).

 

The real Aermacchi MB339 can spin (and even do Lomcevaks), but the X-Plane one (from Paolo Matricardi) could not at all. I then just put custom RoG's (close to the ones of the real aircraft) in Plane Maker, and voilà, it could be spun and do Lomcevaks! Probably its behaviour could be improved with further tuning.

 

 

Compare with the real deal:

 

 

Also, I strongly suspect (although I don't have hard data) that the effectiveness of flight controls in the post stall region is exaggerated in X-Plane. I'm not referring to blanking due to fuselage, etc., I'm referring precisely to the effectiveness of the control surface when the wing/stab on which it resides is stalled. This could be the reason why ailerons/rudders etc. remain too effective during a spin, and allow unrealistic control response during deep stalls/spins.

 

I think the only way to change this is via a plug-in, albeit it would be not too difficult to write.

Murmur,

 

your observations seem correct to me, specially regarding way to much control authority beyond and approaching stall...

 

Where did you get the RoGs for the Aermachi from? Many books include MOIs, but converting to RoGs is a painfull task...

I don't remember with 100% certainty, but probably I took the adimensional RoGs provided in Roskam book for various jet trainers and re-calculated them for the MB339 based on its specific lenght and wing span. It can be done very quickly and the results should not be far from real values. Certainly much better than X-Plane guesses. :smile:

Interesting information.

It seems to me that the construction of a high fidelity aerobatic glider model including correct reponses upto and through the stall (including spin) would be an excelllent test of the potential of the basic X-plane software without the complication of engines, especially propellor engines.

I suspect that even in this pure flight model task  the software would need tweeking with plugins. Definately one to compensate for the responses that an average computer joystick / rudder controller combination can achieve compared with those in an actual glider.

If achieved eventually the lessons learned could be applied to a single prop aerobatic plane to give a high fidelity desktop simulation..........do you think my scheming is too transparent :rolleyes:

thepitts,

 

I've been long trying to prove myself the superiority of X-Plane's FDM.

 

I believe that after a series of cycles, I am back in the right course. I do believe in it's potential, I also understand some of it's limitations, I have used a few aircraft that are an excellent proof for me, at least, that a carefully designed aircraft can achieve a very plausible behaviour.

 

I will have to test the Nimbus more carefully, but the first impression wasn't very good :-/... I feel I'll have to tweak the trim efficiency for a start...

 

I'll report back ;-)

 

Most aircraft add-ons for X-plane 10 and FSX don't stall any near realistically. They can be stalled, you can keep the manch pulled all the way back, and after a while they recover :-/ and even start climbing again.

 

In FSX RealAir, A2A and a few other have managed to create realistic stall behaviour, and the same is true about some good aircraft models for X-plane 10. It's actually very easy to edit an airfoil with AirfoilMaker and start tweaking it in order to get a more credible stall behaviour.

 

Just as Murmur pointed out, "!playing" with the RoGs is another good tweaking exercise, although I believe the default calculations are probably very acceptable...

 

Some aircraft really puzzle me. A good example is the Felis IL-14 I am now flying again in X-Plane 10 thanks to an updated sasl plugin.

 

This aircraft is incredably "realistic" ( I never flew the real thing, but have consumed a lot of texts and movies... and even pilot reports... ); yet, when you open it im PM you notice that no art-stab, no edited RoGs, just plain aircraft data was used. The airfoils also perform beautifully near and post-stall IMO.... Is this the proof that, just as some have long been saying, a well designed aircraft is all that is required for X-plane's FDM to show it's true potential???

It seems to me that the construction of a high fidelity aerobatic glider model including correct reponses upto and through the stall (including spin) would be an excelllent test of the potential of the basic X-plane software without the complication of engines, especially propellor engines.

I suspect that even in this pure flight model task  the software would need tweeking with plugins. Definately one to compensate for the responses that an average computer joystick / rudder controller combination can achieve compared with those in an actual glider.

If achieved eventually the lessons learned could be applied to a single prop aerobatic plane to give a high fidelity desktop simulation..........do you think my scheming is too transparent :rolleyes:

 

That's exactly what I'd try to do, but the problem is, I know I'd end up spending too much of time on it and I can't afford that. In theory, a plugin would only be needed to override flight control effectiveness. All the rest (RoG's, post-stall airfoil behaviour, trim, etc. can be tuned).

 

Just as Murmur pointed out, "!playing" with the RoGs is another good tweaking exercise, although I believe the default calculations are probably very acceptable...

 

X-Plane tends to significantly underestimate RoGs, and also their respective ratio is not generally precise. This is one of the reasons (not th only one I suspect, i.e. also flight control effectiveness etc.) causing poor stall behaviour.

Regarding the sluggishness of the controls near the stall region, I've been using the "Control Phase-Out" with "reverse" semantics :-)

 

By sacrificing the overdone authority at high speeds, and trying to use just small control inputs at higher speeds (as it is after all supposed to be done IRL...), I set, say for the default C172, the low-speed threshold to 30 KIAS and 0.09 effectivity, and then I set the 1.00 effectivity for the red mark...

 

It's probably not the best way to tune aileron responsiveness near stall, but I'm far from starting to build plugins :-/

 

P.S.: Murmur, in the copy of Roskam I have I only get MOIs and no ROGs... I know it can be converted, but it's not an easy task :-(

 

Also, for most aircraft ( also in FSX ) there are cross-moments, but there is no cross-ROGs ... and I couldn't figure out how to properly translate those cross-moments of inertia into X-Plane's ROGs...

P.S.: Murmur, in the copy of Roskam I have I only get MOIs and no ROGs... I know it can be converted, but it's not an easy task :-(

 

Also, for most aircraft ( also in FSX ) there are cross-moments, but there is no cross-ROGs ... and I couldn't figure out how to properly translate those cross-moments of inertia into X-Plane's ROGs...

 

Uhm, my "Airplane Design" text has "Non-dimensional Radii of Gyration" for a lot of aircrafts in the appendix B of volume 5.

 

Looks like there are not cross-moments implemented in X-Plane, but they are usually very little and of little importance, unless the aircraft has a peculiar shape.

Is it possible in x-plane to divorce the visible model (the "art") from the flight model (the "science" ). Surely an approach would be to set up a simplified flight model (like a simple balsa wood plane) use some reverse endineering to get it to perform as expected and finally cloth it in artwork.

 

 

Is it possible in x-plane to divorce the visible model (the "art") from the flight model (the "science" ).

 

They are separated, although most think they aren't... All that counts are really the lift / drag generation surfaces that you declare in Plane-Maker as wings, etc... and some coeficients, used pretty much like in FSX... The big difference is that X-Plane takes the info from all of those sources to calculate the resultant aerodynamic forces.

 

If it took into consideration the design / blueprint, we wouldn't have to force a pitching down moment on some aircraft that raise their "nose" when you add flaps, or the way around, etc...

 

So yes, I believe that tallented designers can even directly manipulate the datarefs to tweak their models ( ? )

 

I really have to start trying SASL, or Gizmo, or both :-)