Elevator Flutter

H

hawkeye52

Charter Member
I cannot remember the last time I encountered elevator flutter. Yesterday I installed Phoenix Designs' EE Canberra Pack 4/5 and :pop4:

Is there a "fix" for this in the CFG?

- H52
 
If you're talking about uncontrolled "gyrations" in a force-feedback controller, reduce the elevator area a little at a time until it stops.
 
I would leave the elevator settings alone in aircraft.cfg as the problem is in section 320 of the airfile and that is where it has to be fixed.
 
This could also be an issue of the Elevator Moment of Inertia (MOI) being too low. Increase the MOI until the flutter stops. This will also increase control pressure, so elevator effectiveness might need to be increased also.
Disclaimer- I'm no FS Guru, this is just my Humble Opinion from my Experiences modifying aircraft.CFG files. When in doubt, go with the Smart Guys:) Good Luck!!!
 
I followed Tom's advice and reduced the elevator area by 33% (from 60 to 40) and that got me another 145 knots before flutter onset. Of course, elevator authority is somewhat reduced, but I can live with it.

Nevertheless I'm going to try Sctybdy's MOI fix and then Rich's airfile and report back.

Thanks for your replies!

- H52
 
hawkeye52, I think if you open that airfile with notepad you will find it is for a B737, personally I would not use a reduced performance, the airfile Kevin did is specifically for the Canberra.
 
After being forced by circumstances to take time away from FS, I'm back to report.
===============================================================

As mentioned earlier, I was able to delay the onset of the elevator flutter by following Tom Clayton’s advice and reducing the area of the elevator. By reducing the original area of 60 sq.ft. to 40 sq.ft. I was able delay flutter from 285 KIAS to 430 KIAS. Nevertheless I wanted to try the other proposed solutions.

Sctybdy, I could find no spot in the CFG to modify the Elevator MOI, so I was unable to try that proposal.

Rich suggested I substitute Kevin Kelleher’s airfile from BNINMk8FDE files.zip. This I did (after restoring the elevator area to 60 sq.ft.) and it absolutely eliminated the flutter. Unfortunately, it also reduced maximum airspeed in level flight to barely 233 KIAS.

So I went back to the 40 sq.ft. elevator and all is fine in Canby Land.

Thanks to all for your assistance.

- H52
 
Hopefully this will explain your low max speed with Kevin's airfile, both aircraft.cfg's have the same engine thrust 7500 which is right for the Canberra but not B737.

Pd Aircraft.cfg [WEIGHT_AND_BALANCE]

[WEIGHT_AND_BALANCE]
max_gross_weight= 53000.000 <<<<<<<<<<<<
empty_weight= 23265.000 <<<<<<<<<<<<

reference_datum_position= 0.000, 0.000, 0.000
empty_weight_CG_position= 8.000, 0.000, 0.000

max_number_of_stations= 50

station_load.0= 22265.000, 0.000, 0.000, 0.000

;Moments of Inertia
empty_weight_pitch_MOI= 1272394.000
empty_weight_roll_MOI= 1272394.000
empty_weight_yaw_MOI= 2437024.000
empty_weight_coupled_MOI= 0.000
CG_forward_limit= 0.000
CG_aft_limit= 1.000

Kevin aircraft.cfg [WEIGHT_AND_BALANCE]

[WEIGHT_AND_BALANCE]
max_gross_weight = 46000 <<<<<<<<<<<<<<<
empty_weight = 22200 <<<<<<<<<<<<<<<

reference_datum_position = 0.0000, 0.0000, 0.0000 // (feet) distance from FlightSim Reference position: (1/4 chord, centerline, waterline)
empty_weight_CG_position = 0, 0, 0
CG_forward_limit = 0
CG_aft_limit = 1

max_number_of_stations = 3
station_load.0 = 200, 15, 0, 1, //Pilot
station_load.1 = 200, 17, 0, 0, //Navigator
station_load.2 = 0, 0, 0, 0, //Bomb bay Payload

empty_weight_pitch_MOI = 208000
empty_weight_roll_MOI = 99058
empty_weight_yaw_MOI = 252748
empty_weight_coupled_MOI = 0

Notice the differences in weight and the MOI's

PD aircraft.cfg [TurbineEngineData]

[TurbineEngineData]
fuel_flow_gain= 0.002
inlet_area= 12.000
rated_N2_rpm= 29920.000
static_thrust= 7500.000
afterburner_available= 0
reverser_available= 1

Kevin aircraft.cfg [TurbineEngineData]

[TurbineEngineData]
fuel_flow_gain = 0.002 //0.001
inlet_area = 4.0 //2.2169671888856
rated_N2_rpm = 7800
static_thrust = 7500
afterburner_available = 0
reverser_available = 0

Notice the inlet area this has a big effect on drag, only the thrust is the same.

PD aircraft.cfg [airplane_geometry]

[airplane_geometry]
wing_area= 1000.000 <<<<<<<<<<<<< BIG effect on drag
wing_span= 94.750 <<<<<<<<<<<<< Big effect on drag
wing_root_chord= 20.000 <<<<<<<<<<< Big effect on drag
wing_dihedral= 6.200
wing_incidence= -0.500
wing_twist= 0.000
oswald_efficiency_factor= 0.750
wing_winglets_flag= 0
wing_sweep= 10.000
wing_pos_apex_lon= 0.000
wing_pos_apex_vert= 0.000
htail_area= 750.000
htail_span= 28.000
htail_pos_lon= -33.000
htail_pos_vert= 0.000
htail_incidence= 2.100
htail_sweep= 30.000
vtail_area= 137.000
vtail_span= 7.000
vtail_sweep= 50.000
vtail_pos_lon= -31.000
vtail_pos_vert= 1.500
elevator_area= 112.900
aileron_area= 94.000
rudder_area= 56.200
elevator_up_limit= 22.500
elevator_down_limit= 19.500
aileron_up_limit= 30.000
aileron_down_limit= 30.000
rudder_limit= 26.000
elevator_trim_limit= 20.000
spoiler_limit= 60.000
spoilerons_available= 0
aileron_to_spoileron_gain= 3.000
min_ailerons_for_spoilerons= 10.000
min_flaps_for_spoilerons= 0.000

Horiz tail and vert tail area all to big and cause drag as does elevator and aileron area which is why you got such a low max speed


Kevin aircraft.cfg [airplane_geometry]

[airplane_geometry]
wing_area = 960.3 <<<<<<< What it should be, much less drag
wing_span = 63.96 <<<<<<< Likewise
wing_root_chord = 16.00 <<<<<<< Likewise
wing_dihedral = 5
wing_incidence = 1.0
wing_twist = -0.5
oswald_efficiency_factor = 0.90
wing_winglets_flag = 0
wing_sweep = 0
wing_pos_apex_lon = 4.0
wing_pos_apex_vert = 0
htail_area = 196.0
htail_span = 26.2
htail_pos_lon = -30.0
htail_pos_vert = 0
htail_incidence = 0
htail_sweep = 20
vtail_area = 70.0
vtail_span = 11.8
vtail_sweep = 0
vtail_pos_lon = -30.0
vtail_pos_vert = 6.0
elevator_area = 87.5
aileron_area = 69.1
rudder_area = 45.5
elevator_up_limit = 30
elevator_down_limit = 30
aileron_up_limit = 25
aileron_down_limit = 15
rudder_limit = 30
elevator_trim_limit = 20
spoiler_limit = 60
spoilerons_available = 0
aileron_to_spoileron_gain = 0
min_ailerons_for_spoilerons = 0
min_flaps_for_spoilerons = 0


PD aircraft.cfg [Reference Speeds]

[Reference Speeds]
flaps_up_stall_speed= 150.000
full_flaps_stall_speed= 120.000
cruise_speed= 490.000



Kevin aircraft.cfg [Reference Speeds]

[Reference Speeds]
flaps_up_stall_speed = 80.8
full_flaps_stall_speed = 65.2
cruise_speed = 380
max_indicated_speed = 565
max_mach = 0.8543

PD aircraft.cfg [Flaps.0]

[Flaps.0]
type= 1
span-outboard= 0.800
extending-time= 20.000
system_type= 1
damaging-speed= 250.000
blowout-speed= 300.000
lift_scalar= 1.000
drag_scalar= 1.500
pitch_scalar= 0.000
flaps-position.0= 0.000, 0.000
flaps-position.1= 1.000, 0.000
flaps-position.2= 2.000, 0.000
flaps-position.3= 5.000, 0.000
flaps-position.4= 10.000, 0.000
flaps-position.5= 15.000, 0.000
flaps-position.6= 25.000, 0.000
flaps-position.7= 30.000, 0.000
flaps-position.8= 40.000, 0.000

[Flaps.1]
type= 2<<<<<<<<<<<<<<<<<<<< Leading edge Slats
span-outboard= 0.800
extending-time= 2.000
system_type= 1
damaging-speed= 250.000
blowout-speed= 300.000
lift_scalar= 1.000
drag_scalar= 1.000
pitch_scalar= 0.000
flaps-position.0= 0.000, 0.000
flaps-position.1= 1.000, 0.000

[Flaps.2]
type= 2 <<<<<<<<< Leading edge slats
span-outboard= 0.800
extending-time= 3.000
system_type= 1
damaging-speed= 250.000
blowout-speed= 300.000
lift_scalar= 1.000
drag_scalar= 1.000
pitch_scalar= 0.000
flaps-position.0= 0.000, 0.000
flaps-position.1= 0.500, 0.000
flaps-position.2= 1.000, 0.000



Kevin aircraft.cfg [Flaps.0]

[flaps.0] //Trailing Edge Flaps
type = 1
span-outboard = 0.5
extending-time = 5
flaps-position.0 = 0
flaps-position.1 = 60, 159
damaging-speed = 175
blowout-speed = 192
system_type = 1
lift_scalar = 1
drag_scalar = 1
pitch_scalar = 1


A lot of difference between the 2, the aircraft.cfg that originally came with the download will fit a 737 as did the airfile, It was about 3 years ago Kevin did his flight dynamics and as he did not have a force feed back stick so I checked the FF bit for him removing a bit of flutter at high speed, ending up with a model that would fly a little faster than the max published speed with no flutter.

If you are happy with what you have ok but I would suggest you try both the airfile and the aircraft.cfg in Kevin's updated set where you will have a fairly accurate flight model
 
Standby on the above, I think the canberra download you have came off Classic British files not Flightsim.com where I downloaded it from they appear to be different so will disect the one of CBF tomorrow meanwhile try Kevins airfile and aicraft.cfg together and see how you get on.
 
hawkeye52, this is a fixed airfile for the Canberra you originally down loaded no flutter, add it and use your original aircraft.cfg as it was with the elevator area unaltered.

On the subject of speed this is from the RAF pilots notes for the Canberra

Red line airspeed 483kts (556Mph) .75 mach up to 15000 ft

So the speed I get 534 kts @ 1000 ft in level flight is way above that, I think there was a mix up of Kts and MPH so some juggling may be in order.

To delay the Overspeed warning to around the correct speed find and replace [Reference Speeds] with this

[Reference Speeds]
flaps_up_stall_speed= 105.0 //Knots True (KTAS)
full_flaps_stall_speed= 95.0 //Knots True (KTAS)
cruise_speed= 330.0 //Knots True (KTAS)
max_mach= 0.698
max_indicated_speed= 465.0 //Red line (KIAS)


Let me know how you get on with the airfile
 
Canb-750-F.zip

Hi, Rich --- Installed the airfile, made the [Reference Speed] changes and returned the elevator area to its original 60 sq.ft. in the CFG.

470 KIAS / M 0.69 @ 1,300' ASL
375 KIAS / M 0.71@ 14,800' ASL

Close to the RAF pilots' notes values at Sea Level, but not at altitude. Wikipedia lists max speed as 504 Kts / M 0.88 @ FL400.

The 750-F.air is for the model with tip tanks, which is what I used. I went to CBF looking for a 750.air (no tip tanks) but could not find any.

- H52
 
hawkeye52, there was only 1 fits all airfile, you need 2 separate aircraft folders as a lot of stuff is controlled by the aircraft.cfg so 2 different ones needed, if you check Kevins update he has 2 airfiles and 2 aircraft.cfg 1 for clean and 1 for tanks you may want to try that
 
CORRECTION to Post # 13 of June 18th

hawkeye52 said:
This is what I recorded:
470 KIAS / M 0.69 @ 1,300' ASL
375 KIAS / M 0.71@ 14,800' ASL

Close to the RAF pilots' notes values at Sea Level, but not at altitude. Wikipedia lists max speed as 504 Kts / M 0.88 @ FL400.

- H52
Click to expand...

Should've noted that 375 KIAS is approx. 487 KTAS @ 14,800' ASL and is not far from the listed 504 Kts.

- H52
 
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