Simviation Forum - Centre of Gravity...

Sep 25^th, 2011 at 4:45am

Fozzer Offline
Colonel
An elderly FS 2004 addict!
Hereford. England. EGBS.

Posts: 24861

FS 2004: Cessna 150 Aerobat. C150_v2.

Hello all...
As you can see, the centre of gravity of my little Cessna 150 Aerobat makes the aircraft extremely nose-heavy, making it "unusual" to trim correctly, for take-off, flight, and landing!
This is the setting with just me aboard (154Lbs), and wing tanks half full of fuel (13 Galls).

Whereabouts in the settings, in the Aircraft file, to adjust the C of G more centrally, where it should be, in the Aircraft?
(Its not possible to drag the C of G Icon).

Many thanks...

...!

Paul... Cool

...!

P.S...I've suddenly noticed that whilst supping a few glasses of California's best Red Vino whilst preparing Sunday Dins, that my own personal centre of gravity has also shifted slightly to the left!
...HIC!... Embarrassed

...

...!

« Last Edit: Sep 25^th, 2011 at 5:54am by Fozzer »

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Reply #1 - Sep 25^th, 2011 at 10:10am

Strategic Retreat Offline
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idiotic as an average

Posts: 603

I fear you must search for another C152. The center of gravity specified in the .AIR file, and the corrections inside the Aircreft.CFG only use it as a reference point for the rest of the various parameters. Undecided

Usually, this kind of out-of-whack gravity happen in planes coming from another version of FS, in this case I believe from FS2002. Try finding a FS9 native C152 (I have and desultorily use the F1 one, so can't really suggest you one).

If you can't or don't want to find another C152, try in the Aircraft.CFG playing around with the parameters reference_datum_position= and empty_weight_CG_position= under the [WEIGHT AND BALANCE] section, changing values and then loading the plane into FS to check the new CG point. But KNOW since now and before starting mucking with it that is never a sure deal. It may work if the .AIR files allows it, it may NOT work, or it may even backfire, needing you to shift other Aircraft.CFG parameters around to make that 152 flyable again with the new CG position. Tongue

Before starting to muck around, remember to make a backup copy of the Aircraft.CFG, for immediate rollback purposes, should your tweaks not sort the desired effects out. Wink

Fozzer wrote on Sep 25^th, 2011 at 4:45am:

P.S...I've suddenly noticed that whilst supping a few glasses of California's best Red Vino whilst preparing Sunday Dins, that my own personal centre of gravity has also shifted slightly to the left!
...HIC!... Embarrassed

...

...!

Ah... never checked that wine out, since my land (Italy) is wine land par excellence. I simply suggest that if normally one is used to drink beer while dining and desires to step up to wine, one has to keep in mind that the fermented grapes juice has an average stronger alcoholic content than beer, and this one must go easy on it on first until some resistance up can be built. Wink

There is no such a thing as overkill. Only unworthy targets.

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Reply #2 - Sep 25^th, 2011 at 3:10pm

garryrussell Offline
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Why not just some weight in the rear most position

Just like they use ballast weight in real life

You could also remove your pilot weight

It doesn't really matter what figures are in there as long as it gives you what you want. It's an easy fix and adjustable

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Reply #3 - Sep 25^th, 2011 at 3:29pm

Fozzer Offline
Colonel
An elderly FS 2004 addict!
Hereford. England. EGBS.

Posts: 24861

garryrussell wrote on Sep 25^th, 2011 at 3:10pm:

Why not just some weight in the rear most position

Just like they use ballast weight in real life

You could also remove your pilot weight

It doesn't really matter what figures are in there as long as it gives you what you want. It's an easy fix and adjustable

Garry...

I fear that if I remove myself from the Aircraft, to conserve/shift weight, there will be no-one left to fly my little Cessna 150 Aerobat... Wink

...!

As has been suggested, the "Problem", (for me), may be related to the actual design of the aircraft...the original "Air" file...which only the designer has access to!
It is a FS 2004 aircraft, which may have originated from FS 2002....slight incompatibility?

It does require some strange "trimming" to get her airborne!... Grin

...!

Paul...Trimming...Short back and sides... Cool

...!

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Reply #4 - Sep 27^th, 2011 at 8:02pm

microlight Offline
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It's a bird...
Southern UK

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Posts: 2236

Greetings, Paul.

Which version of the FDE are you using? Mine is dated April 2007 in the aircraft.cfg header. I just reset the loading figures to match yours (I'm a little heavier than you!) and the CoG is still exactly where it should be.

You can indeed modify this yourself from the aircraft.cfg quite easily; look for this line in the [airplane_geometry] section.

wing_pos_apex_lon = 2.23

Maybe you can confirm what value your line is set at? Increasing the positive figure moves the CoG backwards towards the tail, so try increasing in increments of 0.1 until it's where it needs to be. This is a quick-and-dirty method (it amends where the position of the wing apex is along the plane body) without having to look into what the rest of the FDE is doing, but any errors that this particular change induces aren't noticeable (to me, anyway). I think I must have done this myself when I got the plane as with this setting, not only is the CoG where it should be, she takes off at full throttle, no flap at 80kts at centre trim with just a gentle pull back on the yoke, just as you'd expect.

Let me know how you get on.

Wink

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Reply #5 - Sep 28^th, 2011 at 6:21pm

Capt.Propwash Offline
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Let's get a little mud
on the tires!
KCHS, Charleston, SC, USA

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go on the main website, and search for AIR EDITOR. it is the 5th one down that you want.

FSX/FS2004 AirEd Revised (Category: FSX > Utilities)
Zip file preview
0.21Mb (2809 downloads)
AirEd - Fligh Dynamics Editor. This is a good copy of AirEd by William M. Roth. I have noticed that other versions of this utility are missing things. Like in primary aerodynamics under lift, there should be 8 records, not 6. This upload is for anyone who is trying to tweak the flight dynamics of FS 9 or FSX aircraft and might have been having a problem. Unzip to a folder of your choice. replace what you have been using, or if this is your first time with AirEd; just copy the AirEd folder where you want it. Open AirEd by double clicking on the aired.exe file, and click the special menu; then click on Set AirEd for Air files. You should now be able to double click any air file and have it open with AirEd. This upload is done because I think there are people out there who are trying to make money from the simulator community who have used their knowledge to make it harder for the average person to produce an aircraft that flys well. They do this in part by corrupting the original work of the AirEd author. Bob Chicilo.
Posted Aug 6, 2009 10:26 by Bob Chicilo

Now you have Access to the .air file to make changes just as a developer would.

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Reply #6 - Sep 28^th, 2011 at 7:33pm

microlight Offline
Colonel
It's a bird...
Southern UK

Gender:
Posts: 2236

I'd advise caution when fiddling about with .air files, for two reasons.

First is that even with AirED (which I also use), many of the .air file functions are to this day unknown outside Microsoft - and represented as ???s in the appropriate AirED fields - so unless you know exactly what you are doing, you can do more harm than good.

Second is the fact that in the main, the more common settings in the .air file are directly modified by the .cfg file during loading. FS9 loads the .air file first and then modifies its settings with the equivalent settings in the .cfg file, so that modifying the .air file in FS9 (and even in FS2002/FS8) becomes largely redundant in these cases - which practically speaking is most of the time. I've proved this by creating a L1011 trijet FDE using the default unmodified 747 .air file, and the resulting L1011 operates as it should. Same with a 727 using the default 737 .air file.

So while programs like AirED are great for modifying the parameters that the .cfg file doesn't touch - and of course there are some - developers indeed know which these are, which to stay away from and which are modified by the .cfg file, so that they don't waste time and effort.

Wink

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Reply #7 - Sep 29^th, 2011 at 3:44am

Fozzer Offline
Colonel
An elderly FS 2004 addict!
Hereford. England. EGBS.

Posts: 24861

microlight wrote on Sep 27^th, 2011 at 8:02pm:

Greetings, Paul.

Which version of the FDE are you using? Mine is dated April 2007 in the aircraft.cfg header. I just reset the loading figures to match yours (I'm a little heavier than you!) and the CoG is still exactly where it should be.

You can indeed modify this yourself from the aircraft.cfg quite easily; look for this line in the [airplane_geometry] section.

wing_pos_apex_lon = 2.23

Maybe you can confirm what value your line is set at? Increasing the positive figure moves the CoG backwards towards the tail, so try increasing in increments of 0.1 until it's where it needs to be. This is a quick-and-dirty method (it amends where the position of the wing apex is along the plane body) without having to look into what the rest of the FDE is doing, but any errors that this particular change induces aren't noticeable (to me, anyway). I think I must have done this myself when I got the plane as with this setting, not only is the CoG where it should be, she takes off at full throttle, no flap at 80kts at centre trim with just a gentle pull back on the yoke, just as you'd expect.

Let me know how you get on.

Wink

Hello Micro...

..!

Ta for the response!

This is my default setting in the C 150 Aircraft file...>>>

"wing_pos_apex_lon = -2.40 //Feet, longitudinal distance from reference"

I'll have a go at altering the setting...

...see wot 'appens.. Wink

...!

(I'll have a go at deleting/omitting the "minus" sign?)

Paul....

...!

This is the source of my little delight...>>>

http://www.flightsim.com/file.php?cm=SEARCH1&fsec=0&fname=C150_V2.ZIP

http://simviation.com/1/search?submit=1&keywords=C150_v2&categoryId=

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Reply #8 - Sep 29^th, 2011 at 4:22am

Fozzer Offline
Colonel
An elderly FS 2004 addict!
Hereford. England. EGBS.

Posts: 24861

...PS....

Wonderful stuff, Micro!... Cheesy

...!

Just omitting the "Minus" sign positioned me back in the ~~Pillocks~~ Pilots seat again, aft of the engine.

"wing_pos_apex_lon = 2.40 //Feet, longitudinal distance from reference"

Excellent....Ta Micro!

The Trim Wheel acts as it should do now!

Paul.... Cool

...!

Fozzer wrote on Sep 25^th, 2011 at 4:45am:

P.S...I've suddenly noticed that whilst supping a few glasses of California's best Red Vino whilst preparing Sunday Dins, that my own personal centre of gravity has also shifted slightly to the left!
...HIC!... Embarrassed

...

...!

P.P.S...
..also cured that little problem. I just load up my right-hand pocket with lead weights... Wink

...!

Dell Dimension 5000 BTX Tower. Win7 Home Edition, 32 Bit. Intel Pentium 4, dual 2.8 GHz. 2.5GB RAM, nVidia GF 9500GT 1GB. SATA 500GB + 80GB. Philips 17" LCD Monitor. Micronet ADSL Modem only. Saitek Cyborg Evo Force. FS 2004 + FSX. Briggs and Stratton Petrol Lawn Mower...Motor Bikes. Gas Cooker... and lots of musical instruments!.... ...!
Yamaha MO6,MM6,DX7,DX11,DX21,DX100,MK100,EMT10,PSR400,PSS780,Roland GW-8L v2,TR505,Casio MT-205,Korg CX3v2 dual manual,+ Leslie 760,M-Audio Prokeys88,KeyRig,Cubase,Keyfax4,Guitars,Orchestral,Baroque,Renaissance,Medieval Instruments.

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Reply #9 - Sep 29^th, 2011 at 8:04pm

microlight Offline
Colonel
It's a bird...
Southern UK

Gender:
Posts: 2236

Paul,

Glad your problem's fixed - happy to be of service!

Cheers,
Martyn
Wink

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