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Some Basic Flight Model Questions - Final Approach

scottb613

scottb613

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unitedstates
Hi Folks,

While I've dabbled in the arcane art of FDE mods - I'm a novice... I've used Air Wrench, AirEd, and AirUpdate so I have some familiarity with the process... I'm just looking for some basic guidance on how to proceed...

I've got some real world time in light twins but most is in single engines - so I have some frame reference for what it should fly like...

I have an aircraft - twin engine Baron - that has some good flight dynamics and is pretty enjoyable to fly... It feels realistic in most flight regimes...

The problem is getting this aircraft on a stable approach - it's approach speed should be around 95 knots... When flying at this speed with full flaps/gear the aircraft is sitting back on its haunches as it were flying behind the power curve... It should be flying at a slight down angle maybe around 3 degrees with around an 800 ft/min decent... If I fly the correct sight picture - I seem to be able to maintain my airspeed however the decent rate is off the charts at 2000 ft/min or greater... I noticed that dropping the gear and increasing the flaps has no notable effect on pitch and it should... In section 1101 there are parameters for flaps lift, flaps drag, and flaps pitch - - - would you think these are the parameter I should be playing with ??? Could it be more just a center of balance issue With the existing FDE ? Is the wing just not generating enough lift ? (I've played around quite a bit with the flap lift, pitch and drag values and I haven't found anything that really works - I also realize that the aircraft.cfg contains some flap values)

Any thoughts or guidance ?

Thanks...

Regards,
Scott


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Last edited:
If you're a bit into the whole equations thing, check Yves Guillaume's documentation of the FSX flight model (fs_flight_dynamics_v1.0.zip). Might provide more insight into what shouold be tweaked where.
 
Hi...

Thanks - I have that document somewhere but I haven't looked at in years - let me poke around and read it again...

Regards,
Scott



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Depending on the accuracy of the CG point (and I have no knowledge of where you would acquire said accurate measure) I would say that moving it would solve your issue for approaches, although you would probably get some weird effects during normal flight. A better idea is adjusting the scalars you noticed. The only way I have found to make these work correctly is to change them "on-the-fly" by tweaking one or the other (NEVER more than one at a time) and then reloading the flight. They are immensely powerful, as back in the day people used them to make semi-VTOL aircraft. Small changes . . . anyway, that should be where you are focusing your attention.
 
Hi...

Thanks for your thoughts - I'll continue to play with this and see if I can get some reasonable performance out of it...

Regards,
Scott


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I would suggest a structured approach to the problem. Random tweaking will only achieve a solution by accident.
First, before doing anything to the air file check what "Flight Tuning" scalars are active in the aircraft.cfg, if any, and I would recommend setting scalar values to 1.0.
There are pitch lift and drag scalars in the flaps section of the aircraft.cfg and you should put them to 1.0 also

Years ago I had a CPL Instrument Rating and Type rating for Piper Aztec and Navaho, but I never flew a Beech airplane.
My source of data on the Baron is just the FSX beech_baron_58_ref.htm. It states that the stall speed at maximum weight is 84 KIAS. It also states that the stalling speed in landing configuration is 75KIAS. Typically approach speed is 1.3 times the stall speed and 75 * 1.3 is 97.5, Close enough to 95.
Since you have AirWrench check what it says for clean stall speed on the air foils page. Use the max gross weight value on the Weight page and insert that over the zero fuel basic value in the air foils calculator. For the stock Baron that gives 75 kts and that is about the clean stall speed in the air. With gear and full flap the stock Baron stalls at 60 KIAS. That would make the correct approach speed 78 KIAS.

So your second step should be to do a test flight at about 1000 ft in the landing configuration with your airplane and note the stall speed. Fly level (zero climb rate) and gradually reduce your airspeed until you can no longer keep the nose up to stay level. Note the stall speed. If it is about 60 kts like the stock airplane you will have to decide if you want to continue with that or make changes to give a more representative speed. The FSX documentation and the FSX Baron performance are different. The stock airspeed gauge has the bottom of the green arc, clean stall speed, at 84 KIAS, so the documentation may be correct.

Now that you have data you can decide what you want to achieve.
From what you say the nose appears to be too high. I assume you are referring to the 3D cockpit/panel because the 2D panel gives zero forward view.
To get the flaps and gear to drop the nose when extended you can adjust their pitch coefficients in the air file. They are in 1101 under Pitch
Flaps is Cm_df and gear is Cmg. Positive numbers give nose down in the sim. Something like 0.1 would be a good start.

Try these things, take data and post your results. Then I can help point you in the right direction.
Roy
 
Hi Roy,

Thanks so much for the very detailed response... Let me digest this a bit as it sounds like a good plan... I'd truly like to get to the point where I can do this well... I've only got time in a Duchess for twins which is quite a bit lighter and way less powered than a Baron... It's a B55 Baron I'm working on - and - I've done a bunch of research finding specs (which vary a bit) and watched almost every landing video I could find on YouTube... I've also compared it to the old Dreamfleet B58 that was well received when it came out and Lou had a bit of a reputation of an almost anal attention to detail on his planes... I truly miss Dreamfleet... So the 95 knots might even be a bit high according to the 1.3 VS0 rule - which means the plane might be pitching up even more - I have found some checklists that did mention 95 knots though... Again - I'll check this all out in greater detail over the weekend - if the Northeast USA blizzard leaves me some time... I'll follow up here - and - - - thank you...

Regards,
Scott
 
Agree with Roy, especially: "I would suggest a structured approach to the problem. Random tweaking will only achieve a solution by accident."

The previous suggestion to adjust CG is a random one.

Be sure to set stall speed in Airplane_Geometry section to ZERO. FS uses that number to trigger an 'on/off' stall and that won't get you what you need. The certified stall speed is defined as the speed which an airplane can no longer maintain level flight. After turning off that silly trigger, you can fly the plane and see what the aerodynamics are doing.
 
Hi Folks,

I'm still working on this model - usually just on the weekends... While I realize it's probably not what the pros use - Jerry's Air Wrench is doing the bulk of the work (his new F1 release includes a tool that just changes specific values - similar to AirEd without adjusting the entire flight model)... The original FDE is payware - so it probably wouldn't be right for me to post it here... I've done quite a bit of legwork gathering real world specifications and making changes that have improved the model... I think I'm making good progress...

Anyone familiar with AirWrench ? I've got a question on the various flap modifications... There are three different places to tweak flap values - the Systems Basic Flaps drag and pitch sliders - the Systems Advanced Flaps for lift, pitch, and drag - the Coefficients tab (new) where it has lift, pitch, and drag for flaps...

I recall Jerry mentioning the Systems Advanced Flaps was really intended for jets with complex flaps and spoilers - however it seemed to provide lift which the Systems Basic Flaps doesn't... I believe the coefficients screen is new to his F1 release...

Anyone know how these three different screens interrelate with each other... If I put a value in the Systems Advanced Flaps does it override any changes to the Systems Basic Flaps settings and vice versa ? How does the Systems Basic Flaps determine lift - from the size of the control surfaces ? Should I leave the values as 0.0 or 1.0 in the Systems Advanced Flaps lift, pitch, and drag settings ?

As always - any help appreciated...

Regards,
Scott


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Scott,
You really need to ask Jerry for clarification of details on his new AirWrench version. I have read the new users manual and it is not clear to me either. Jerry has always been very helpful to me and most of what I know came from him.
However, the coefficients page must give final values after any other modifications, so any changes you make there would be preserved.
Roy
 
Hi Roy,

Thanks so much - understand - similar experience with Jerry as well - will do... Yeah - I've read the manuals/tutorials and I still have much to learn...

Regards,
Scott



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