High Airspeed Flap Deployment BUG

[philstyle]

At high airspeed (above around 280 mph IAS) the flaps will (correctly) not deploy. However, using the flap level in the cockpit causes the nose to "trim down" as though the flaps have been delpoyed, even though they actually remain in the up position until the airspeed is reduced.

 

 

This is obviously a bug, and also gives away the fact that the nose-down trim effect is not acually an aerodynamic or CoP change in DCS, but just a scripted change in the air-craft's trim (which is a little bit disappointing).

 

 

Here is video of what I am talkign about. The whole video contains content from another sim, so please IGNORE that from a bug-reporting perspective (I do not intend to break any forum rules here, but I do not want to upload a seperate video just for this - so I am being explicit about what section of the video contains the relevant content).

 

 

 

The content specific to this bug report is at 14:44 in the video, or at the exact timestamp in the link below.

 

 

 

Edited July 8, 2019 by philstyle

[grafspee]

At high airspeed (above around 280 mph IAS) the flaps will (correctly) not deploy. However, using the flap level in the cockpit causes the nose to "trim down" as though the flaps have been delpoyed, even though they actually remain in the up position until the airspeed is reduced.

 

 

This is obviously a bug, and also gives away the fact that the nose-down trim effect is not acually an aerodynamic or CoG change in DCS, but just a scripted change in the air-craft's trim (which is a little bit disappointing).

 

 

Here is video of what I am talkign about. The whole video contains content from another sim, so please IGNORE that from a bug-reporting perspective (I do not intend to break any forum rules here, but I do not want to upload a seperate video just for this - so I am being explicit about what section of the video contains the relevant content).

 

 

 

The content specific to this bug report is at 14:44 in the video, or at the exact timestamp in the link below.

 

 

 

 

are you sure that flaps didnt extend a little bit ??

how you expect to change CoG with deployment of flaps, i can see that they move a little but weight of flaps are low dont change a lot i think.

Pneumatic flaps will not exted fully at high speed but they will extend partialy and at high speed you dont need full extention of flaps to get same result in plane behavior as it happen at low speed

Edited July 8, 2019 by grafspee

[DefaultFace]

Phil is referring to a change in pitching moment, and not an CG change.

[philstyle]

are you sure that flaps didnt extend a little bit ??

I am sure watch the video . . .

 

 

 

 

How you expect to change CoG with deployment of flaps, i can see that they move a little but weight of flaps are low dont change a lot i think.

 

 

Typo. Should be "CoP", changed now.

 

 

 

 

Pneumatic flaps will not exted fully at high speed but they will extend partialy and at high speed you dont need full extention of flaps to get same result in plane behavior as it happen at low speed

 

 

I don't think you follow the bug report I am making.

[Yo-Yo]

At high airspeed (above around 280 mph IAS) the flaps will (correctly) not deploy. However, using the flap level in the cockpit causes the nose to "trim down" as though the flaps have been delpoyed, even though they actually remain in the up position until the airspeed is reduced.

 

 

This is probably a bug, and also gives away the fact that the nose-down trim effect is not acually an aerodynamic or CoG change in DCS, but just a scripted change in the air-craft's trim (which is a little bit disappointing).

 

 

Here is video of what I am talkign about. The whole video contains content from another sim, so please IGNORE that from a bug-reporting perspective (I do not intend to break any forum rules here, but I do not want to upload a seperate video just for this - so I am being explicit about what section of the video contains the relevant content).

 

 

 

The content specific to this bug report is at 14:44 in the video, or at the exact timestamp in the link below.

 

 

 

 

I think, you probably find a bug. I will explain: the flaps itself in the FM gives their pitching effect naturally. It's very easy to find if you compare AoA at the same speed with and w/o flaps. But, and it is very distinctive, the flaps works regarding pitch in FM correctly FOR FIXED STICK.

Flaps deploying generally changes elevator hinge moment due to downwash changes. In RL very often it causes UNCONTROLLED stick movement that aggravated this pitch down effect. This effect is recorded at least one time, and I saw it himself in Yak-52.

So, we had to implement it as a momentarily shift of a stick as in RL.

The effect you saw - it's the added effect to control. The bug is that probably the signal for it is taken not from the flaps position but, as it was more convenient for the programmer, from the pneumo cylinder pressure, for example.

 

But there is a second reason - it's not a bug and the effect is taken, as it must be, form the lift changes due to flaps, and this added pitch down effect is very pronounced even at 20-30 degrees deflection.

Edited July 8, 2019 by Yo-Yo

[grafspee]

i will try to deploy flaps at 280IAS.

Hmm you are trying to say that plane is getting pitch down tendency after activating flaps but becouse of high speed plane is getting this pitch down tendency even flaps remain closed am i understand it right ??

[philstyle]

i will try to deploy flaps at 280IAS.

Hmm you are trying to say that plane is getting pitch down tendency after activating flaps but becouse of high speed plane is getting this pitch down tendency even flaps remain closed am i understand it right ??

 

 

This is the "bug": At 280mph+ the flaps do not deploy, but the nose still pitches down.

[philstyle]

So, we had to implement it as a momentarily shift of a stick as in RL.

The effect you saw - it's the added effect to control. The bug is that probably the signal for it is taken not from the flaps position but, as it was more convenient for the programmer, from the pneumo cylinder pressure, for example.

 

 

I *think* I understand what you are saying. The flaps are trying to deploy, but the air-pressure on the flap (which is alos holding the flap in the "up" position") is going back up the control rods/wires and is pushging the stick around int he pilot's hands. . .

 

That sort-of makes sense, however, so long as gthe flaps are fully up, the flaps themselvs are being prevented from further moving up - becasue the wing is blocking them. There should not be any tension going back up the controls, because the wing is taking the forces.

 

 

 

But there is a second reason - it's not a bug and the effect is taken, as it must be, form the lift changes due to flaps, and this added pitch down effect is very pronounced even at 20-30 degrees deflection.

 

 

I am reporting pitching changes at 0 degrees defelction. I would not report a bug if there was "some" deflection in the flap (even 1 or 2 degrees). But I see full attitude changes before any defelection has started.

[Yo-Yo]

I *think* I understand what you are saying. The flaps are trying to deploy, but the air-pressure on the flap (which is alos holding the flap in the "up" position") is going back up the control rods/wires and is pushging the stick around int he pilot's hands. . .

 

That sort-of makes sense, however, so long as gthe flaps are fully up, the flaps themselvs are being prevented from further moving up - becasue the wing is blocking them. There should not be any tension going back up the controls, because the wing is taking the forces.

 

 

No, the effect on elevator is due to wing downwash - the wind direction over stabilisator and elevator depends on downwash depending on wing lift. So, if the elevator is trimmed w/o flaps, the trim will change as flaps are down.

 

So, if it's a bug it will be fixed.

[DefaultFace]

As long as the profile of the wing hasn’t changed (ie the flaps don’t deploy) there shouldn’t be a change in downwash at the tail anyway, which means this is still a bug.

 

What yo yo is saying is that the pitch moment of the wing resulting directly from the change in lift distribution is simulated as it should be, but that the downwash that the wing induces at the tail is scripted, and at least the part which sompensates fer flap deflection may be linked to the actuator pressure (which could change regardless of whether the flaps move or not).

[philstyle]

No, the effect on elevator is due to wing downwash - the wind direction over stabilisator and elevator depends on downwash depending on wing lift. So, if the elevator is trimmed w/o flaps, the trim will change as flaps are down.

So, if it's a bug it will be fixed.

 

 

 

 

Ok thanks.

I will leave it with you and the team to look further. :)

[grafspee]

hmm i though that extended flaps would simply create drag which would simply rotate plane nose down and you would have to counter this with aditional trim on elevator to maintain level flight so pitch down tendency comes from this tail stab downwash alone ??

[DefaultFace]

It is both due to an increase in induced downwash and changes in the lift distribution & Cl of the wing. And the Drag.

[Terry Dactil]

Isn't this discussion irrelevant?

You should not be in this situation anyway.

Warning

Flaps MUST NOT be down or lowered at speeds above 160 mph.

Why are you ignoring an operating limitation then complaining that it is not perfectly modeled?

 

It seems like getting all upset if the wings are falling off at 495 kts instead of 500kts. Just don't go there and it is not a problem.

 

 

Sorry: That comes across a bit snarky. Just trying to say that if you operate within the limits you will never see that bug.

Edited July 8, 2019 by Terry Dactil

[Yo-Yo]

Ok thanks.

I will leave it with you and the team to look further. :)

 

We just investigated the effect... I have to say that in your test the angle WAS NOT ZERO. So, the hinge moment was really calculated and was exactly the same 2degrees deflection must give. Regarding the high speed and high ptch sensitivity you can see the effect. Iw it was FULL DEFLECTION at this speed, the effect would be much greater.

 

So, NOT A BUG. Just feature. So, my second version was right.

[philstyle]

Sorry: That comes across a bit snarky. Just trying to say that if you operate within the limits you will never see that bug.

 

 

1. There are no negative consequences to operating outside of the limits. To be honest, I was actually hoping that something would "break" at the high speeds, and then I'd be able to say "well, the flaps broke away due to the high speeds", but they didn't (in both of the sims I tested), so the absence of mechanical failure led to to the next observation which was, what is going on then? This is how I test, I set up a scenario to see what happens, if something unexpected happens I observe it and note it.

 

2. Context, context, context - which would require watchgin the entire video and being familiar with the series

[philstyle]

We just investigated the effect... I have to say that in your test the angle WAS NOT ZERO. So, the hinge moment was really calculated and was exactly the same 2degrees deflection must give. Regarding the high speed and high ptch sensitivity you can see the effect. Iw it was FULL DEFLECTION at this speed, the effect would be much greater.

So, NOT A BUG. Just feature. So, my second version was right.

 

Well, well, well!

I will definitely comment on this and correct my conclusion in the next video!

Thanks.

I am surprised.. but have learned something.

 

 

This thread can be marked "NO BUG" now :)

Edited July 8, 2019 by philstyle

[Magic Zach]

This reminds me of the elevator trim and prop wash effect I see on the Mustang (haven't tried other aircraft, just something I noticed). Trim the elevators down in the Mustang, leave your stick neutral, and increase throttle, and you can see the in-game stick pitch forward with the thrust increase. Just goes to show how detailed these modules are.

[hazzer]

This reminds me of the elevator trim and prop wash effect I see on the Mustang (haven't tried other aircraft, just something I noticed). Trim the elevators down in the Mustang, leave your stick neutral, and increase throttle, and you can see the in-game stick pitch forward with the thrust increase. Just goes to show how detailed these modules are.

 

That isn't correct the elevator and thrust prop authority is weak and hardly existent. It is easily confused with the air speed. But the propwash effect over the control surfaces isn't high enough

[Magic Zach]

That isn't correct the elevator and thrust prop authority is weak and hardly existent. It is easily confused with the air speed. But the propwash effect over the control surfaces isn't high enough

To clarify, I'm in the ground, so as far as I can tell, it is correct.

[grafspee]

That isn't correct the elevator and thrust prop authority is weak and hardly existent. It is easily confused with the air speed. But the propwash effect over the control surfaces isn't high enough

 

prop wash is weak thats new

i actualy been in propwash stream of 120hp engine i cant immagine how would it be in 1500hp engine case :P

Edited July 8, 2019 by grafspee

[mkiii]

I too have spent many an unhappy hour behind a much lower power engine, getting blatted by the prop wash while fettling engine timing etc. (Chipmunk), but powerful as it will be on a Spit, I'm guessing that it is still less significant than the airflow over the controls caused by airspeed. Bear in mind that only a proportion of the propwash is hitting the tailplane at any given angle, but just about all the airflow does. Think about how rudder authority is minimal until airspeed rises to near takeoff speed - isn't the prowash already high at that point?

[grafspee]

I too have spent many an unhappy hour behind a much lower power engine, getting blatted by the prop wash while fettling engine timing etc. (Chipmunk), but powerful as it will be on a Spit, I'm guessing that it is still less significant than the airflow over the controls caused by airspeed. Bear in mind that only a proportion of the propwash is hitting the tailplane at any given angle, but just about all the airflow does. Think about how rudder authority is minimal until airspeed rises to near takeoff speed - isn't the prowash already high at that point?

 

prop wash is enought to actualy move control surfaces that is what i ment i didnt say that air flow is weaker

[Yo-Yo]

I too have spent many an unhappy hour behind a much lower power engine, getting blatted by the prop wash while fettling engine timing etc. (Chipmunk), but powerful as it will be on a Spit, I'm guessing that it is still less significant than the airflow over the controls caused by airspeed. Bear in mind that only a proportion of the propwash is hitting the tailplane at any given angle, but just about all the airflow does. Think about how rudder authority is minimal until airspeed rises to near takeoff speed - isn't the prowash already high at that point?

 

The aerodynamic force is about 1/2 of the force at takeoff speed, significant enough to avoid or perform nose to the ground flip.

[grafspee]

The aerodynamic force is about 1/2 of the force at takeoff speed, significant enough to avoid or perform nose to the ground flip.

 

yo-yo i tried it in spitfire and past some boost level controls are not suficient to prevent nose tip to the ground i think someone need to hold tail to perform full power ground run up, but hell no it wont be me :P