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FSXA Helicopter questions?

mhlarsen

mhlarsen

Messages
176
Country
denmark
Ok, I am a total newbie at this.

I have a heavy-lift helicopter that I want to adjust the flight dynamics to better match realworld performance. This helicopter seems to be based on the default EH-101.

I have a performance mark like this:
68% torque at 60 kts should give a climb of 3000-3500 fpm.

I have tried the 'direct' approach by giving more thrust.
I changed inflow_vel_reference from 56.0 to 73.0.
This gives me the performance mark above.

But now the helicopter on ground seem to rotate ever so slightly to the right even when parking brake is on.

How can I correct this?

I have also changed the number of blades from 5 to 6.
Would this increase inertia so much that I will have to modify weight_to_moi_factor?

I also changed the radius of both rotors to +20%, as to match realworld dimensions.


Michael
 
Hi Michael,

I have only very recently entered the world of FSX after a long time away from it. However, in 1999 (!) I did a lot with FS helo .air files and plan to get back up to speed eventually.

In the meantime, here are some ideas from an old document I wrote:

HELICOPTER FDE EDITING

Here are a few ideas on how to go about editing these sections of a helicopter .air and .cfg files (= FDE for short).

(1) As with any FDE file, you should start by setting your helicopter's physical properties with real-world values. These include: stablizer surface areas, fuselage surface areas, number of rotor blades, rotor blade length, rotor blade circle area, etc.

(2) After setting the fuselage surface areas, you will want to fine tune the drag coefficients for each surface area. This value tells FS how "sticky" or "draggy" each surface area is. For example, if the helo frontal surface is sloped and smooth like the Bell 206B, it will have a lower drag value. If the helo is an older model with a blocky shape or with spotlights or topedoes hanging off the sides, the drag coefficient will be higher.

(3) Next you will have to do some guesswork on the lift and drag coefficients and angle of incidence for both stabilizers. Both the vertical (VStab) and horizontal (HStab) stabilizers take effect when the helicopter has reached about 25 knots in forward airspeed.

(4) Finally you will want to adjust the drag coefficient and both effectiveness values for the main and tail rotors. These allow you to tell the simulator how powerful and "draggy" these rotors are. Use only small changes of value here!

(5) Some values in these sections should probably not be changed. For example, the friction values in sections 1402 and 1403 which have effects on the engine should stay the same.
Click to expand...

In your case, your new engine and added rotor blade are throwing off the "yaw" balance of the helo on the ground. Have you adjusted the tail rotor to compensate?

Best,

Steve
 
Hello,

maybe I can help with this.

Unfortunately ALL suggestions by Steve DO NOT have any effect on your helicopter - not a single one. The reason for that is that the eh-101 model uses a completely different/new airfile. It uses different parameters and cannot interpret the old ones anymore. Almost all fde relevant params are now in the aircraft.cfg file.

(I guess you found it out already as the airfile is almost empty, correct?!)

Now to your prob:

The crux is increasing rotor diameter. Can you confirm this by just trying your old diameter setting? The spinning should stop then.

The eh-101 fde model brings some really nice and realistic features, but it also has a few disadvantages. On this point it's really low ground friction of the gear/skid in relation to the torque. By increasing the rotor diameter you increased the rotor moi a lot and therefore more torque is applied. -> The gear/skids cannot longer counteract that torque and that' s why the helo spins.

Solutions:

- decrease rotor diameter
(you should only need to edit this for a realistic feeling of the rotor disk e.g. in descent or sharp higher speed manouveres -> so the bigger the disk the more you float up when you raise the nose above the horizon when you are decelerating)
( the lift should always be regulated by inflow_reference setting and the heavier feel of the rotor disk should be included in the pitch_moi and bank_moi setting)

- decrease torque_scalar
(only do that if all other fails as this is primary to get the "torque-induced-yaw" right) (the higher this scalar is the more pedal input you have to apply to counteract the rotor torque)

- decrease the weight_to_moi_factor
(this directly decreases the rotor moi and so its torque) (CAUTION: this and the first solution also have effect on the autorotation time available until rotor drops too and on the start up duration)

----------
I know getting all this settings into the "perfect" balance is really hard work, but it generally pays off!

Hope this was of any help for your problem.

Have a nice flight,
Steven
 
SierraB said:
Hello,

maybe I can help with this.

Unfortunately ALL suggestions by Steve DO NOT have any effect on your helicopter - not a single one. The reason for that is that the eh-101 model uses a completely different/new airfile. It uses different parameters and cannot interpret the old ones anymore. Almost all fde relevant params are now in the aircraft.cfg file.

(I guess you found it out already as the airfile is almost empty, correct?!)

Now to your prob:

The crux is increasing rotor diameter. Can you confirm this by just trying your old diameter setting? The spinning should stop then.

The eh-101 fde model brings some really nice and realistic features, but it also has a few disadvantages. On this point it's really low ground friction of the gear/skid in relation to the torque. By increasing the rotor diameter you increased the rotor moi a lot and therefore more torque is applied. -> The gear/skids cannot longer counteract that torque and that' s why the helo spins.

Solutions:

- decrease rotor diameter
(you should only need to edit this for a realistic feeling of the rotor disk e.g. in descent or sharp higher speed manouveres -> so the bigger the disk the more you float up when you raise the nose above the horizon when you are decelerating)
( the lift should always be regulated by inflow_reference setting and the heavier feel of the rotor disk should be included in the pitch_moi and bank_moi setting)

- decrease torque_scalar
(only do that if all other fails as this is primary to get the "torque-induced-yaw" right) (the higher this scalar is the more pedal input you have to apply to counteract the rotor torque)

- decrease the weight_to_moi_factor
(this directly decreases the rotor moi and so its torque) (CAUTION: this and the first solution also have effect on the autorotation time available until rotor drops too and on the start up duration)

----------
I know getting all this settings into the "perfect" balance is really hard work, but it generally pays off!

Hope this was of any help for your problem.

Have a nice flight,
Steven
Click to expand...

Hi Steven

Yes, when I return to the old rotor radius the slow spin stops.

I will try to begin reducing weight_to_moi_factor from 0.577 to 0.555 and then begin testing.

The problem is really that this payware heavylifter based on EH-101 has not been changed at all in the aircraft cfg settings, although it is 8000 lbs heavier in gross weight and 4000 lbs heavier in empty weight.

Another odd thing, which was present from the start with this heavy-lifter is, that despite parking brake being on, I can rotate the helicopter on ground with the rudder alone.
This can not be done with the default FSX EH-101.


Thanks
Michael
 
Last edited:
Michael,

you say the aircraft.cfg is exactly the same like the one of the eh-101.
So the values of weight, pedal_control_scalar and tail rotor section are also the same?
Btw, THAT'S CALLED PAYWARE???? :eek:

Is it a taildragger?


Steven
 
SierraB said:
Michael,

you say the aircraft.cfg is exactly the same like the one of the eh-101.
So the values of weight, pedal_control_scalar and tail rotor section are also the same?
Btw, THAT'S CALLED PAYWARE???? :eek:

Is it a taildragger?


Steven
Click to expand...

Almost exactly yes, some companies take shortcuts i guess :rolleyes:

Taildragger? No it's a heavy-lifter.


Michael
 
Sorry with taildragger I meant something like the Seaking that has a tail wheel;)

Well, the only params that can affect this are in the tail rotor section or the pedal control scalar.

Also take a look at toe_brakes_scale in the [brakes] section. Eh-101 default is 0.7.
This one affects the parking brake as well.

Steven
 
SierraB said:
Sorry with taildragger I meant something like the Seaking that has a tail wheel;)

Well, the only params that can affect this are in the tail rotor section or the pedal control scalar.

Also take a look at toe_brakes_scale in the [brakes] section. Eh-101 default is 0.7.
This one affects the parking brake as well.

Steven
Click to expand...

Hi Steven,

I actually set toe_brakes_scale to 2.0 to get better control, but not much.

To compare with EH-101 and this Heavy-lifter:

From EH-101 [Helicopter] section:

reference_length = 74.1
reference_frontal_area = 125.0
reference_side_area = 308

From Heavy-lifter [Helicopter] section:

reference_length = 74.1
reference_frontal_area = 125.0
reference_side_area = 308

Now this could be a problem I think if I compare the physical dimensions of wheel to wheel width together with height:

EH-101:
Width 3.82 m (12.53 ft)
Height 6.62 m (21.71 ft)

Heavy-lifter:
Width 7.90 m (25.91 ft)
Height 5.67 m (18.60 ft)

This should give the Heavy-lifter better stability for ground handling, but I do not now how to change the parameters to reflect that.


Michael
 
The wheel positions are defined in the [contact_points] section.
Code: 
[contact_points]
;gear
point.0=1,  -14.10,   0.00, -4.60, 2100, 0, 0.5187,75.0, 0.50, 1.7, 0.6, 3.0, 3.0, 7.0, 0.0, 0.0
point.1=1,  -37.70,  [COLOR="Red"]-6.37[/COLOR], -4.40, 3500, 1, 0.5187, 0.0, 0.900, 1.2, 0.6, 3.3, 3.3, 7.0, 0.0, 0.0
point.2=1,  -37.70,   [COLOR="red"]6.37[/COLOR], -4.40, 3500, 2, 0.5187, 0.0, 0.900, 1.2, 0.6, 3.8, 3.8, 7.0, 0.0, 0.0

The red numbers define the lateral position of the main gear. By default they're set for 6.37 + 6.37 = 12.74 feet. Change them to 13 (don't know the exact gear configuration of your heavy-lifter) and it will be a lot more stable on ground.
But IMHO this does not affect the rudder problem.

Steven
 
SierraB said:
Sorry with taildragger I meant something like the Seaking that has a tail wheel;)

Well, the only params that can affect this are in the tail rotor section or the pedal control scalar.

Also take a look at toe_brakes_scale in the [brakes] section. Eh-101 default is 0.7.
This one affects the parking brake as well.

Steven
Click to expand...

Hi Steven,

The pedal_control_scalar for this Heavy-lifter is default at 0.6 and for EH-101 it is 0.4.


Michael
 
SierraB said:
The wheel positions are defined in the [contact_points] section.
Code: 
[contact_points]
;gear
point.0=1,  -14.10,   0.00, -4.60, 2100, 0, 0.5187,75.0, 0.50, 1.7, 0.6, 3.0, 3.0, 7.0, 0.0, 0.0
point.1=1,  -37.70,  [COLOR="Red"]-6.37[/COLOR], -4.40, 3500, 1, 0.5187, 0.0, 0.900, 1.2, 0.6, 3.3, 3.3, 7.0, 0.0, 0.0
point.2=1,  -37.70,   [COLOR="red"]6.37[/COLOR], -4.40, 3500, 2, 0.5187, 0.0, 0.900, 1.2, 0.6, 3.8, 3.8, 7.0, 0.0, 0.0

The red numbers define the lateral position of the main gear. By default they're set for 6.37 + 6.37 = 12.74 feet. Change them to 13 (don't know the exact gear configuration of your heavy-lifter) and it will be a lot more stable on ground.
But IMHO this does not affect the rudder problem.

Steven
Click to expand...

Hi Steven,


The Heavy-lifter has these values at 9.54, but I will set it at 13.


Thanks
Michael
 
So this could be the reason .

Unfortunately almost every parameter is responsible for MULIPLE things. For example lowering pedal_control_scalar will solve your ground problem, but you will have less (maybe unrealistic) tail rotor authority in flight.

It's all about a good compromise ;)
 
SierraB said:
So this could be the reason .

Unfortunately almost every parameter is responsible for MULIPLE things. For example lowering pedal_control_scalar will solve your ground problem, but you will have less (maybe unrealistic) tail rotor authority in flight.

It's all about a good compromise ;)
Click to expand...

I agree, its like adjusting a wobbly chair by correcting one leg at a time :D

Should I set pedal_control_scalar lower than EH-101, now that this Heavy-lifter has more power?


Michael
 
True words :)

Well, more power does not always mean high tail rotor authority...
Generally I would :

1. set my main rotor params to reflect lift and inertia behaviour correctly

2. adjust torque_scalar to reflect a realistic feeling of yaw-induced-torque

3. adjust pedal_control_scalar to give satisfying yaw control in flight (maybe you have some real world data like maximum yaw rate or sth like that)

... or you rather want the helo to behave realistically on the ground. Then you might go with the lower pedal setting.
 
SierraB said:
True words :)

Well, more power does not always mean high tail rotor authority...
Generally I would :

1. set my main rotor params to reflect lift and inertia behaviour correctly

2. adjust torque_scalar to reflect a realistic feeling of yaw-induced-torque

3. adjust pedal_control_scalar to give satisfying yaw control in flight (maybe you have some real world data like maximum yaw rate or sth like that)

... or you rather want the helo to behave realistically on the ground. Then you might go with the lower pedal setting.
Click to expand...

Well, i guess flight dynamics when airborne must be of highest priority.
Although this Heavy-lifter can and do taxi to/from runway, its not really necessary.
I have tried though to make the rudder less sensitive in the air as well, but I am having a hard time doing it.
I have tried calibrating and setting up FSUIPC, which helped about 10%, so maybe it has to be done through the aircraft.cfg.

Torque_scalar is 20.0 for both helicopters.

I will dance around with the parameters you mention to find some kind of a sweet spot :)


Michael
 
Last edited:
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