Flaps

[Caldera]

Hey All,

 

There is a problem that I experience occasionally only when I am playing on a multi-player server.

 

My flaps will fully extend and I can not retract them normally.  I do not know exactly when this happens, but I do see them lower one notch when I extend them following start-up in preparation for take-off.  I would use my HOTAS to do that.  On the runway, when I am doing last checks, that is when I notice that they are fully extended.  I have not noticed when the "in between" part occurs.

 

If I move the Flap Control lever in cockpit, nothing happens.  I have checked both key board and HOTAS binds in ADJUST CONTROLS and both always work on the ADJUST CONTROLS screen, but not in the cock pit.  I have also checked that there are no blown fuses.  The only way to get the flaps to retract is by using the Emergency Retract switch in the cock pit.  However, once doing that the flaps will stay locked in the retracted position and can not be extended at any time.

 

Is this problem unique to my system?  Does anyone else have this problem?

 

Thanks in advance,

Caldera

[Caldera]

Hey All,

 

I am guessing that I am the lone wolf on this one...

 

But, I also wanted to get back to everyone who might have read the above.  Because, I managed to figure out what was going on.

 

I have flaps up and down mapped to my HOTAS using up and down on a 4-way switch.  I don't know why, but I also had Flap Emergency Retract (FER) mapped to the same switch as a press.  So, I was inadvertently pressing FER by mistake as I tested the flaps prior to take-off.

 

What I did not know is that if you activate FER while on the ground it does not retract the flaps instead it lowers them to full and they stay there.   FER functions like Flap Emergency Extend while on the ground.

 

Problem solved...

 

Caldera

[Yurgon]

I'd read your report when you posted it, but didn't know the solution. Glad you figured it out!

 

Here's some of what the manual says about the flaps emergency retract switch:

 

Quote

Flap Emergency Retract. Labeled FLAP EMER RETR, this is a two-position switch. When in the down position, flap control is governed by the flap control on the throttle. When in the up position, the flaps are closed using aerodynamic pressure.

 

And:

 

Quote

If the flaps lose hydraulic power, they will retain their current position unless the flap emergency retract switch is enabled. See Emergency Flight Control Panel chapter.

 

As I understand it, the flaps emergency retract switch allows the flaps to retract by using aerodynamic pressure when the hydraulics have failed. However, this switch does not actually retract the flaps, it merely allows them to retract using the force of the oncoming wind. Since said wind is usually absent on the ground, the flaps will then actually drop by the pull of gravity, so I guess in DCS at least the flaps emergency retract switch basically disconnects any and all locks from the flaps and allows them to act on any external forces rather than hydraulics and down/up locks.

Edited October 1, 2021 by Yurgon

[Caldera]

Yurgon,

 

Thanks!

 

I did a little testing as my curiosity was sparked. 

 

Most of this you probably already know.  Apologies...

 

Flaps general:

• MVR = 8%  +1 deg AOA
• DN = 20%   +3-5 deg AOA
• manual extend < 185 knots
• auto extend < 185 knots
• auto retract > 200 knots

FER activated on runway prior to take-off:

• 0 knots = 20%
• ~150 knots = 16%

FER activated in flight 150-185 knots from flap position:

• UP = 0%
• MVR = 0%
• DN = 16%

So from what I can determine, FER and aerodynamic pressure only fully retract the flaps from the maneuvering position, not from the full down position.  From the full down position the flaps will retract only 4% at all speeds.

 

The is for DCS and frankly not exactly what I had expected.  Kind of seems weird to me for RL.  As it seems that the aerodynamic pressure would be the greatest when fully extended, especially at higher speeds.  Then as speed was reduced the flaps would begin to extend slowly on their own (kind of like slow slats).  Maybe it is by intention in the design, no clue really.  I have very little knowledge mechanically how the flaps actually function.

 

Caldera

[Yurgon]

17 minutes ago, Caldera said:

From the full down position the flaps will retract only 4% at all speeds.

 

Interesting, I certainly didn't know that! And I agree, that's a bit unexpected. But I guess that's where actual pilots have to work for their money, knowing all this stuff in case of emergency.

[jaylw314]

13 hours ago, Caldera said:

 

FER activated in flight 150-185 knots from flap position:

• UP = 0%
• MVR = 0%
• DN = 16%

So from what I can determine, FER and aerodynamic pressure only fully retract the flaps from the maneuvering position, not from the full down position.  From the full down position the flaps will retract only 4% at all speeds.

 

The is for DCS and frankly not exactly what I had expected.  Kind of seems weird to me for RL.  As it seems that the aerodynamic pressure would be the greatest when fully extended, especially at higher speeds.  Then as speed was reduced the flaps would begin to extend slowly on their own (kind of like slow slats).  Maybe it is by intention in the design, no clue really.  I have very little knowledge mechanically how the flaps actually function.

 

Caldera

 

referring to TO 1A-10C-1, when at speed and flaps are in MVR, and FER is engaged, the flaps are driven all the way up to 0 degrees by aerodynamic pressure.  When flaps are in DN and FER is engaged, flaps are only driven up to 15 degrees by aerodynamic pressure.

 

It sort of makes sense if you look at the flaps, which are fowler flaps rather than simple flaps.  There is a hinge that angles them down, but they also slide on a track AFT.

 

In general, flaps cause more drag than lift as they're extended further.  Once they've they're fully down and slid aft, they cause so much drag they're pretty tough for the airstream to push them forwards.  In the MVR setting, they create more lift than drag and they have much less distance to travel forwards.

 

You should realize that with the flaps DN and FER engaged, the flaps essentially remain extended (you're only getting them up to 15 degrees).  That means technically your maximum airspeed is limited to 200 KIAS (flaps extended).  I don't think your crew chief will yell at you if people were shooting at you, though  

[silverdevil]

20 hours ago, Caldera said:

I did a little testing as my curiosity was sparked. 

 

Most of this you probably already know.  Apologies...

 

lol. i quite like the curiosity. i learn more from listening than talking (or typing). so at least i get something from your attention to detail. clear skies!

[Puma]

TO1A-10C does have the warning clause “Aerodynamic blowback may not fully retract the flaps”, so it seems fair that DCS chose to model partial blowback.  It likely should be a function of airspeed rather than initial flap position, but it can’t be said its “wrong” as it stands.  Fun bit of trivia to have discovered, thank you.

[jaylw314]

4 hours ago, Puma said:

TO1A-10C does have the warning clause “Aerodynamic blowback may not fully retract the flaps”, so it seems fair that DCS chose to model partial blowback.  It likely should be a function of airspeed rather than initial flap position, but it can’t be said its “wrong” as it stands.  Fun bit of trivia to have discovered, thank you.

My understanding with flaps in the DN position, the MAXIMUM it will lift with aerodynamic pressure is to 15 degrees, and in the MVR setting, the MAXIMUM it will lift is to 0 degrees.

[Caldera]

Jay (or anyone else knowledgable),

 

Would you mind taking a moment to explain how the flaps on the A-10 work to me.  There is a gap in my understanding and this has been bugging me.  I am not a RL pilot so please, forgive any misconceptions.

 

What I notice is that in DCS when flaps are deployed to MVR I get a 1 degree pitch up with some more drag.  When flaps are deployed to DN I get a 4-5 degree pitch up with quite a bit more drag.

 

For me that makes sense for the MVR position as this position is designed to optimize maneuvering at slower speeds.  Basically, making the wing wider from front to back and adding a bit more curvature to the airfoil (adding a little thickness).

 

The DN position I do not fully understand.  From what I have read, flaps fully extended should actually produce negative camber of the wing.  This is because of the large up force it creates on the trailing edge of the wing leveraging the leading edge of the wing downward.  I get how negative camber improves glide slope for landing, but I am missing something in between.

 

Shouldn't negative camber actually create a negative AOA not a positive AOA?

 

Thanks in advance,

Caldera

[Frederf]

AOA is a function of airflow and chord line, not mean camber. With flaps down the chord line changes because the trailing edge moves. It's still positive mean camber because most of the airfoil is above the chord line.

 

Pitch moment on flap extension can be various effects due to a few factors. In terms of CP and CG position if CP is forward of CG then more lift is a pitch up moment. Extending the flaps can move the CP aft of the CG which can cause the opposite. Flap extension can change airflow over the tail causing anything. In some planes you get one then the other.

[jaylw314]

2 hours ago, Caldera said:

Jay (or anyone else knowledgable),

 

Would you mind taking a moment to explain how the flaps on the A-10 work to me.  There is a gap in my understanding and this has been bugging me.  I am not a RL pilot so please, forgive any misconceptions.

 

What I notice is that in DCS when flaps are deployed to MVR I get a 1 degree pitch up with some more drag.  When flaps are deployed to DN I get a 4-5 degree pitch up with quite a bit more drag.

 

For me that makes sense for the MVR position as this position is designed to optimize maneuvering at slower speeds.  Basically, making the wing wider from front to back and adding a bit more curvature to the airfoil (adding a little thickness).

 

The DN position I do not fully understand.  From what I have read, flaps fully extended should actually produce negative camber of the wing.  This is because of the large up force it creates on the trailing edge of the wing leveraging the leading edge of the wing downward.  I get how negative camber improves glide slope for landing, but I am missing something in between.

 

Shouldn't negative camber actually create a negative AOA not a positive AOA?

 

Thanks in advance,

Caldera

 

I think you are misunderstanding "camber," and are instead talking about the aircraft's nose attitude.  Lowering flaps will indeed pitch the aircraft nose down (with some exceptions) with respect to the TVV or the direction of motion.  Watch the TVV when you deploy MVR flaps, you will see the TVV slide up about 3-4 degrees (alternatively, keeping the TVV steady requires pitching the nose down).  The plane can pitch up or down transiently and varies due to a number of design factors, but the aircraft will always pitch down compared to the TVV.

 

My favorite exception is the Cessna 172, which pitches nose up (and climbs) a lot when you extend flaps, because the downwash over the flaps hits the horizontal stabs.  If we had a HUD with a TVV and kept the TVV steady, though, we'd need a pitch down moment.

 

On approach to landing, the pitch down moment gives you a better view than if you're pointing excessively nose high, like the Concorde.  

 

The aircraft pitches nose down for 2 reasons.  AFAIK, #2 is more significant than #1

1. The wing chord angle changes.  When you drop flaps, the wing actually gains some AOA if you draw a line from the leading edge to the trailing edge, so to fly the same AOA requires the rest of the plan to pitch down by the same amount
2. The wing creates more lift, and more lift ALWAYS produces a nose down moment.  For this, it doesn't matter that the flaps are at the rear--leading edge slats that create more lift will also cause a nose down moment when deployed

When you drop the flaps to MVR, you increase lift more than drag.  When you drop the flaps to DN, you increase drag more than lift.  Hence, the pitch down moment is stronger dropping from UP to MVR than from MVR to DN.

 

FWIW, camber is a description of the shape of the wing's cross section.  Most wings have positive camber, and dropping flaps and/or slats actually increases camber.  Positive camber produces more lift and drag for a given AOA, but also decreases stall speed.

 

 

Edited October 12, 2021 by jaylw314