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Drag caused by Flap position

falcon409

falcon409

Moderator
Staff member
In the aircraft.cfg file, would reducing the number for the Induced_drag_scalar, lessen the drag effect when the flaps are activated?
 
According to the FSX SDK the 'Induced_drag_scalar' forms part of the [Flight Tuning] section and it has this to say:

[h=5]Drag parameters[/h]Drag is the aerodynamic force that determines the aircraft speed and acceleration. There are two basic types of drag that the user can adjust here. Parasitic drag is composed of two basic elements: form drag, which results from the interference of streamlined airflow, and skin friction. Parasite drag increases as airspeed increases. Induced drag results from the production of lift. Induced drag increases as angle of attack increases.


The parasite_drag_scalar and induced_drag_scalar parameters are multipliers on the two respective drag coefficients. For example, a value of 1.1 increases the respective drag component by 10 percent. A value of 0.9 decreases the drag by 10 Percent. Negative values are not advised, as extremely unnatural flight characteristics will result. The default values are 1.0.
Click to expand...

The '[flaps.n] drag_scalar' is described as follows:

The percentage of total drag due to flap deflection that this flap set is responsible for at full deflection.
Click to expand...

If you are trying to reduce (or increase) the drag when the flaps are deployed then I would think it is the 'drag_scalar' that you need to adjust but remember that each [flaps.n] section has it's own 'drag_scalar' value.

Bear in mind too that initial flap positions induce lift rather than drag and the drag only comes into play as more flap is deployed.
 
"In the aircraft.cfg file, would reducing the number for the Induced_drag_scalar, lessen the drag effect when the flaps are activated?"


No, not necessarily.

Flap drag is addressed under the flap heading and also within the airfile.

Which aircraft?
 
mal998 said:
"In the aircraft.cfg file, would reducing the number for the Induced_drag_scalar, lessen the drag effect when the flaps are activated?"

No, not necessarily.
Flap drag is addressed under the flap heading and also within the airfile.

Which aircraft?
Click to expand...
The 310B. . . .on ILS approaches, setting one notch of flaps seems to cause the airplane to lose trim rapidly and unless you immediately add some major throttle input you'll lose the glideslope. I was hoping to lessen the abrupt effect of one notch of flaps and make it a bit more docile for this type of approach.
 
falcon409 said:
The 310B. . . .on ILS approaches, setting one notch of flaps seems to cause the airplane to lose trim rapidly and unless you immediately add some major throttle input you'll lose the glideslope. I was hoping to lessen the abrupt effect of one notch of flaps and make it a bit more docile for this type of approach.
Click to expand...

You must first determine if the effect is caused by rapid slowing (too much drag thereby quickly decreasing lift) or too much pitch change (or not enough).

Once determined, you can influence the appropriate actions through the flap lift/pitch/drag scalars.

EDIT: Also consider if flap deployment speeds are too fast or correct for the type, and 2) is your flap deployment speed correct or at the low end of the band. It is not unexpected to add throttle for flaps deployment for light aircraft but if deployed at max recommended flap speeds you should have more time to respond.

Ron Friemuth did an FM for the FSD? 310 back in 2003 roughly and we communicated a lot about that one. Not sure if that is still available for comparison.

EDIT2: Downloaded and flew; flap scalars seem to be pretty good to me; gear drag seems very high however causing quick loss of speed. May be correct, just surprised me.
 
You might also put it in context of part of the discussion in the last link of my post in the 310B thread:

"Then I inherited the cleanup of the analysis of the wind tunnel tests. One of the other selections for the configuration was a split flap, to be sure of drag when you needed it on this very clean configuration, such as during power-on approaches. This choice was a departure from flaps selected for other Cessna models of the era.

The tunnel test indicated not only that the split flap gave good incremental lift, but produced so much drag it was almost dangerous. Thus we limited the deflection of the flap from the 75 degrees tested in the tunnel to 60 degrees on the prototype and, based on flight confirmation, limited it further to 45 degrees on the initial production airplanes.

The other thing the tunnel showed was that the configuration didn’t have enough static longitudinal stability, which confirmed an analysis done earlier by some other aerodynamicist."

Thus it seems that the first notch should add lift and then significant drag for each increment past that. It sounds like it would be a bit abrupt ( or just really effective) and probably means that part of the cure is pilot technique - ie. pre-setting the trim in anticipation and holding attitude manually against it before lowering the flaps so that after the first stage is deployed it will naturally settle into a trimmed condition.
In development they increased the size of the horizontal stab. to meet the required stability criteria but 'only just enough' sounds like the description and it might be a bit unforgiving. I may have a chance to talk to a former 310 pilot tomorrow and if so, I'll ask.
 
Hi Ed,
the best way to adjust the lift/drag properties is by using a little program called “Aircraftairfilemanager”
Under the heading “Primary Aerodynamics” the entries “Drag coefficient-Flaps” (at the moment set at 0.1640625)
and “Lift-Flaps”( (0,2964583261472) why that's such a long number I have no idea.) are the numbers to play around with.
There are other values in that section affecting the final outcome so altering one will upset another, should you mess things up you can easily go back to the original.
I, like most of us here, am not a real world pilot and I’ve never been in a Cessna 310 so the flight dynamics are only my opinion based on what I've read.
The comments by srgalahad are very interesting, thanks for that.


RobR
 
Couple of things re the C310, flew the real thing for awhile, never liked it ruined by flying Beech Barons at the time, compared to the Baron always felt a bit like riding a greasy pig especially with a full load, ok empty.

Induced drag increases with AoA is correct. If you have a look at some basic aerodynamic texts you will see a steady increase in drag with AoA to the critical angle where the wings stalls. Putting out flap simply changes the curve profile of the overall wing camber with two desired effects, a nose pitch down and increased lift/drag. The initial pitch up experienced with flap deployment is the curve change increasing lift and for most aircraft there is a marginal decrease in speed and a minor drag increase. The drag only significantly rises as more flap is deployed to full flap stage. Flap changes always have to be accompanied by a elevator pitch down change and the addition of trim to hold the attitude. However a few types do pitch down with large flap activation.

Now the 310, as I recall the split flaps added little to drag until full flap was deployed. I once had a flap problem whereby the flaps failed to fully retract to the full up position and hence were trailing in the wind so to speak, their was no noticeable change in pitch and only a minor one or two knot decrease in speed but airframe buffet and low rumble from underneath was the give away that something was amiss turned out there was a problem with the tracks and the flaps were not retracting properly. You only got a significant decrease in speed and drag at full flap. I also recall that the aeroplane would squirrel, or yaw as the undercarriage went down and there was a small speed loss but not like other aircraft where putting the undercarriage down acts as a great speed brake.

Thats about all I can add. I think fiddling with the scalars will not change much and may do little in the end that correct technique to fly the ILS would do, in other words gear down only on intercepting the glideslope, set the attitude to get the rate of descent that is approximately half of the IAS (100 kts=500fpm ROD, 120kts=600 fpm, 180kts=900fpm etc.) and trim trim trim to hold the attitude and power to control the ROD is basically it. As speed decreases and flap is deployed trim trim trim and hold and attitude and power setting to get the speed/ROD matched as described.
 
BendyFlyer said:
Couple of things re the C310, flew the real thing for awhile, never liked it ruined by flying Beech Barons at the time, compared to the Baron always felt a bit like riding a greasy pig especially with a full load, ok empty.

Induced drag increases with AoA is correct. If you have a look at some basic aerodynamic texts you will see a steady increase in drag with AoA to the critical angle where the wings stalls. Putting out flap simply changes the curve profile of the overall wing camber with two desired effects, a nose pitch down and increased lift/drag. The initial pitch up experienced with flap deployment is the curve change increasing lift and for most aircraft there is a marginal decrease in speed and a minor drag increase. The drag only significantly rises as more flap is deployed to full flap stage. Flap changes always have to be accompanied by a elevator pitch down change and the addition of trim to hold the attitude. However a few types do pitch down with large flap activation.

Now the 310, as I recall the split flaps added little to drag until full flap was deployed. I once had a flap problem whereby the flaps failed to fully retract to the full up position and hence were trailing in the wind so to speak, their was no noticeable change in pitch and only a minor one or two knot decrease in speed but airframe buffet and low rumble from underneath was the give away that something was amiss turned out there was a problem with the tracks and the flaps were not retracting properly. You only got a significant decrease in speed and drag at full flap. I also recall that the aeroplane would squirrel, or yaw as the undercarriage went down and there was a small speed loss but not like other aircraft where putting the undercarriage down acts as a great speed brake.

Thats about all I can add. I think fiddling with the scalars will not change much and may do little in the end that correct technique to fly the ILS would do, in other words gear down only on intercepting the glideslope, set the attitude to get the rate of descent that is approximately half of the IAS (100 kts=500fpm ROD, 120kts=600 fpm, 180kts=900fpm etc.) and trim trim trim to hold the attitude and power to control the ROD is basically it. As speed decreases and flap is deployed trim trim trim and hold and attitude and power setting to get the speed/ROD matched as described.
Click to expand...
Great information and your last statement is basically what I have been using since the first instance of losing the glideslope. Trim and throttle makes for a successful ILS approach. Thanks to you and Rob for the insight.
 
Falcon, thanks glad to assist where possible. The whole split flap design concept is interesting and I think was generally adopted for ease of construction especially the wing area build. It was quite popular in early pre WWII and WWII aircraft, e.g DC-3, Spitfire. A lot of modern lighties had them too. They all were the same in terms of handling in one way little affect with initial flap deployment and then a lot of drag with full flap.

I always thought the early C310's were a really lovely aeroplane to look at but the long nose variety lost something for some reason. The Baron however was faster and stable as a rock in bad weather but those tips tanks on the 310 could have you rockin n rollin especially when full, in the pilots seat you sat a lot lower in the Baron as well so the forward visibility was not good, wasn't brilliant for either of them really with those engines nacelles sticking out there, same as the King Air, could see bugger all from the pilots seat. I think we tried em all for Coastguard work at one stage but give me a P3 or a Dash 8 any day.
 
I've tweaked the flight dynamics a bit and will make the files available to those who wish to have them provided I can get the author/s approval. If someone knows how to get in touch with Robert Richardson, please PM me with the info.
 
As far as I can tell flap drag is related to the lift values and resultant induced drag generated either in a linear or polynomial function imbedded in the sim. We are not provided an adjustable curve to bend this parameter, however one can use the leading edge flap parameter to tune drag and lift at a differing extension angle which can approximate some adjustment capability. For the module types it is also possible to tune spoiler drag in there.

I have not done this but using the AFSD utility one could plot flap drag and lift vrs various parameters such as the aircraft lift and induced drag, flap extension angle etc to see just what the MS idea for deriving this parameter were.

Cheers. Tom
 
^ I think PMDG do this with their flaps setups.

They have multiple flaps sections. Some with lift scalar or drag scalar or pitch scalar set to zero.

This is all to compensate for the inherent linearity in the FSX flaps behaviour.

Like this in their 737NGX. Note how the second and third entries are used to tweak the flaps behaviour.

Code: 
[Flaps.0]
type=1                                   // ** FLAPS **
extending-time=39                        // Total seconds
span-outboard=0.69                         // 0.0 .. 1.0
flaps-position.0= 0.000                  // pseudo-degrees
flaps-position.1= 8.888                  // 1
flaps-position.2=18.333                  // 2
flaps-position.3=25.000                  // 5
flaps-position.4=31.111                  // 10
flaps-position.5=33.333                  // 15
flaps-position.6=35.000                  // 25
flaps-position.7=36.666                  // 30
flaps-position.8=40.000                  // 40
lift_scalar = 1.0
drag_scalar = 1.0
pitch_scalar= 1.0
system_type = 1

[Flaps.1]
type=2                                   // ** CORRECT LIFT**
extending-time=14                        // Total seconds
span-outboard=0.30                       // 0.0 .. 1.0
flaps-position.0= 0.000000               // pseudo-degrees
flaps-position.1= 2.653105               // 1
flaps-position.2= 8.209540               // 2
flaps-position.3= 12.35437               // 5
flaps-position.4= 14.48548               // 10
flaps-position.5= 15.34695               // 15
flaps-position.6= 10.25102               // 25
flaps-position.7= 9.560591               // 30
flaps-position.8= 1.32156                // 40
lift_scalar =-1.000
drag_scalar = 0.000
pitch_scalar=-0.5

[Flaps.2]
type=2                                   // ** CORRECT DRAG **
extending-time=20                        // Total seconds
span-outboard=0.30                       // 0.0 .. 1.0
flaps-position.0= 0.000000               // pseudo-degrees
flaps-position.1= 7.8893473              // 1
flaps-position.2= 15.257930              // 2
flaps-position.3= 20.006734              // 5
flaps-position.4= 19.763003              // 10
flaps-position.5= 18.353201              // 15
flaps-position.6= 17.344649              // 25
flaps-position.7= 15.968918              // 30
flaps-position.8= 0.000000               // 40
lift_scalar = 0.000
drag_scalar =-1.000
pitch_scalar= 0.0
 
One must also remember that the real aircraft that PMDG modeled have multi slatted fowler flaps, leading edge slats and leading edge Kruger Flaps, all of which deploy in a programmed sequence, not all at once or linearly. The above sequence in the .cfg file is indeed what I was referring to as a way to wiggle the lift vrs drag curve. Note that the PMDG aircraft as well as the Milviz 737-200 (which I did the dynamics for) use a program module to work around many of the sims simplifications to achieve a more realistic result.

For the Boeing aircraft the operations manual for flight with unreliable airspeed gives us about the only generally available data we can use in a bend to fit, paint to match (reverse engineering) effort to closely duplicate the models performance to the real world aircraft.

Regards. Tom
 
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