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Guest iholrf

Solving a heavy nose

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So one of the things I have been trying to fix is a tendency for the plane to drop the nose a little to dramatically when cutting power. I require about 15% trim ( a huge amount) when taking off, or the plane is very difficult to hold steady as it goes through the speeds, and only a little less trim on landing, or when it hits about 100k it require way to much stick to keep the nose up and of course any let up in pressure results in the dramatic drop. Now all of this can be tuned out with trim settings and at normal cruising speed trim is almost neutral when fully loaded, a little less than neutral when completely empty, and nutral when loaded with passengers, but low on fuel. The behavior is desireable. As we all remember from flight training, your good old Cessna has much the same tendency to drop its nose (which is a designed in safety feature to help cope with stalls). The problem here is not what its doing but the rate its doing it at. I have played with the cg-positions, remeasured the reference data point, moved the placement of passengers and fuel tanks, and the nose is still way too heavy (though it will not flip on hard breaking -- not sure why - probably my aft limit) and the empty weight CG as displayed in the fuel and payload graphic is way to far back, yet the AC is still nose heavy. The other trend is the plane is nearly impossible to stall (neither the control surfaces nor the aircraft). This of course bothers me.So now I am remeasuring the various points such as contact, engine placement, wing placement and so on. I have a few questions that need clearing up.What does the following do (no reference found in SDKs)?:empty_weight_coupled_MOI = 0.0 CG_forward_limit= 0.000CG_aft_limit= -1.000What is the static pitch as it relates to FS? (it seems to be different than real world)Does the sim take engine weight into consideration and its placement (and if so why is there no setting for it or is it in the airfile only?). When measuring for engine plaement, is this point to be taken from the HUB or from the center of the engine proper?Are there other things to check that I have not listed here?TIAShad

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The two lines:static_pitch = 0.3 //degrees, pitch when at rest on the ground (+=Up, -=Dn)static_cg_height = 5.800 //feet, altitude of CG when at rest on the grounddo not have the right description. What these values actually set are the aircraft pitch and height WHEN YOU PRESS THE SLEW KEY. Obviously it is best to set these as close as possible to the pitch and height of the aircraft when sitting on the ground so that repeated pressing of the slew key shows little change in the aircraft.Some designs don't get these values right and that is why you will see aircraft dropping onto the ground when coming out of slew.

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>Are there other things to check that I have not listed here?Yes, these are other influencial factors:1. wing_pos_apex_lon / wing_root_chord / wing sweep(these three are interrelated wrt CoG position)2. Center of Lift (CoL) shift wrt CoG (airfile, rec 1204)Put CoG at ref_datum first. Do the same with the payload (everything at ref_datum). Set up wing geometry according to real specs (pt. 1). Set CoL at CoG (pt. 2). Now, adjust the CoG position wrt ref_datum to get it where it should be (I usually try +- 25 % behind the leading edge). For more info go to www.avhistory.org's Airfile Decode forum. Ron Freimuth has some excellent tips on this topic over there.Good luckAdam

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Hi guys,Thanks for your reply. I decided to try some experiments when the forums were down, and re-made the ac.cfg from scratch, using as close to the real values as possible.Then I ran fsedit as per the SDK instructions ("at least once") and tested the plane. While all the reference datum were correct and all placements accurate the net result was an unflyable AC that flys like the tail is 80000 lbs (the tail never lifts .... yet it still flies... albeit at a virtical angle (and not for long as it can not keep the speed up).I went and read every flight dynamic posting I could fine, downloaded three seperate airfile edit programs, and noticed that the contents of the airfile were total greek to me.So now I need to find resources that describe the internals and how to translate the real world values to the needs of the sim.A couple of more questions.When setting the apex for wings and tail, one thing that I had to guess at was what to do for a twin tailed plane like the Beech. The settings seem to acccomodate only planes with a single, fuselage mounted v. stab. I considered doubling the value of a single v.stab, and then moving the hight up buy the corrisponding amount the v stab should fall below the h. stab.This is ugly and not right if the sim uses these heights to apply physical forces. The plane will never behave properly as the forces would be upon surfaces not actually present in the real plane.Are there airfile fixes for this?How important is the taildragger setting, its off, but the planes is a tail dragger.CheersShad

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Well, after much playing I have restored the plane to flying condition. It dawned on me that I had gotten a new joy at the same time I was working on getting the plane to fly the first time - I have not actually flown much else since then.I decided to take the King Air and Mako for a spin and realized that they had similar issues (KA drops the nose, Mako had overly twitchy behavior), so I am going to blame the nose sensitivity and twitchiness on my new joystick. (Saitek Cyborg Evo).CheersShad

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