Drag of flaps too high

[frumpy]

Hi guys,

as I read about getting the Yak out of Alpha (finally! ), I wonder if the issue with the flaps drag will be resovled?

The drag is much too high, as reported here:

It would be great if the Yak could be flown by the numbers.

Thanks, Olli

[Yo-Yo]

It does fly by the numbers. From the manufacturer.

[frumpy]

Thanks for the pic, but I am not sure how to test in the sim.

Do you have an explanation why the guy in the video says drag of flaps is much too high?

[Mogster]

They are just very simple split flaps aren’t they, not the sort you’d find on a modern aircraft. Lots of drag and not much lift, almost like an air brake.

[fapador]

@Yo-YoWhat exactly does this diagram tell us? I am sorry but I don't speak russian. For example what coefficient is CyMb and what Cx?

Edited February 24, 2022 by fapador

[Yo-Yo]

On 2/21/2022 at 4:38 PM, frumpy said:

Thanks for the pic, but I am not sure how to test in the sim.

Do you have an explanation why the guy in the video says drag of flaps is much too high?

The only explanation is that this guy did not measure anything. Feeling is not a term for FM tuning.

 

[fapador]

57 minutes ago, Yo-Yo said:

The only explanation is that this guy did not measure anything. Feeling is not a term for FM tuning.

 

 

Edited February 24, 2022 by fapador

[Callsign112]

He does mention in the video linked by the OP that his comments are based on his initial observations, so more or less his feelings of the DCS model compared to his own experience. Could some of the discrepancy he sees be related to differences in the way the stick/control surfaces feel in a real plane compared to the feedback you get in a computer simulation?

[Ramsay]

16 hours ago, Callsign112 said:

Could some of the discrepancy he sees be related to differences in the way the stick/control surfaces feel in a real plane compared to the feedback you get in a computer simulation?

Possibly but the linked RL Yak-52 pilot's comparison isn't the only one (there are another 2 owners of the real, that say similar things).

As a sim pilot, I've never flown a RL Yak-52, so find it's flight model "reasonable", however RL pilot's scan their controls and instruments and note throttle/rpm needed, etc. as more/less throttle, etc. than usual can be an indication of something wrong/missed i.e. gear/flaps not down, etc.

Flying in DCS, RL pilots have quickly noticed discrepancies between the Yak-52's real behaviour and DCS.

Paraphrasing what one Yak-52 owner/DCS player said, unlike a F-16, etc. with a "civil aircraft" there are a lot more DCS players who have flown the real and ED can't handwave flight model issues away and get a pass. He then praised the DCS Yak-52 for the bits it got right but had bought it mostly to support ED and encourage them to fix it's problems/make similar aircraft.

IMHO the DCS Yak-52 has never had the resources for it FM to be finished to a high quality and seems to be mostly running on systems ported from DCS's WWII warbirds, it may keep it cheap but from the comments of RL pilots of the Yak-52, it's been at the expense of accuracy.

[Callsign112]

On 2/25/2022 at 9:18 AM, Ramsay said:

Possibly but the linked RL Yak-52 pilot's comparison isn't the only one (there are another 2 owners of the real, that say similar things).

As a sim pilot, I've never flown a RL Yak-52, so find it's flight model "reasonable", however RL pilot's scan their controls and instruments and note throttle/rpm needed, etc. as more/less throttle, etc. than usual can be an indication of something wrong/missed i.e. gear/flaps not down, etc.

Flying in DCS, RL pilots have quickly noticed discrepancies between the Yak-52's real behaviour and DCS.

Paraphrasing what one Yak-52 owner/DCS player said, unlike a F-16, etc. with a "civil aircraft" there are a lot more DCS players who have flown the real and ED can't handwave flight model issues away and get a pass. He then praised the DCS Yak-52 for the bits it got right but had bought it mostly to support ED and encourage them to fix it's problems/make similar aircraft.

IMHO the DCS Yak-52 has never had the resources for it FM to be finished to a high quality and seems to be mostly running on systems ported from DCS's WWII warbirds, it may keep it cheap but from the comments of RL pilots of the Yak-52, it's been at the expense of accuracy.

Agreed, but I watched the video and can't say he gives many clues in terms of what he was referring to. At one point it sounded like he was referring to what others had said about the drag, but I was expecting to hear him talk more specifically about why he felt it was too high, but he didn't.

Regarding the Yak's FM, I wouldn't know how to go about modeling, or even tuning the FM of a plane, but I do have a limited experience using CFD software to model very complex fluid flows and I doubt very much that is how it works. I highly doubt anything was ported from another plane. Certainly the DCS Yak is different from any of the other props in DCS including the CEII as they all are.

Again, I am wondering if some of what is being translated here are the difference between a computer model and the way a human pilot feels feedback in real life.

[Ramsay]

5 hours ago, Callsign112 said:

Again, I am wondering if some of what is being translated here are the difference between a computer model and the way a human pilot feels feedback in real life.

What RL pilots report aren't subjective "feelings", rather they are objective "observations" - i.e. in RL they'll use 40% throttle (in DCS 60%) to taxi, in a dive DCS picks up too much speed, in a climb DCS bleeds too much speed, at speed "x" they - use left rudder, ball is centered, use right rudder, etc.

I forget all the details of the Yak's FM issues and would need to refer back to a none English video and run it's transcript though google again (IIRC he speculated engine torque was over-modelled), however going into such detail would be flogging a dead horse as AFAIK it was reported in both the English and Russian forums and the Yak just doesn't have sufficient priority.

There was some tuning done for flaps drag (a couple of years ago), so I'm not sure on it's current status.

For the general FM - the main issue I still see is rudder behaviour where with a fixed trim tab "tuned" for a set cruise speed i.e. 210 kph, we should be using left rudder for take off, centered pedals/ball at cruise speed and right rudder when faster but that's not what we see in DCS.

Perhaps one day the Yak's rudder trim adjustment will work in special options but I'm guessing that's the best we can hope for.

Edited February 27, 2022 by Ramsay

[Callsign112]

23 hours ago, Ramsay said:

What RL pilots report aren't subjective "feelings", rather they are objective "observations" - i.e. in RL they'll use 40% throttle (in DCS 60%) to taxi, in a dive DCS picks up too much speed, in a climb DCS bleeds too much speed, at speed "x" they - use left rudder, ball is centered, use right rudder, etc.

I forget all the details of the Yak's FM issues and would need to refer back to a none English video and run it's transcript though google again (IIRC he speculated engine torque was over-modelled), however going into such detail would be flogging a dead horse as AFAIK it was reported in both the English and Russian forums and the Yak just doesn't have sufficient priority.

There was some tuning done for flaps drag (a couple of years ago), so I'm not sure on it's current status.

For the general FM - the main issue I still see is rudder behaviour where with a fixed trim tab "tuned" for a set cruise speed i.e. 210 kph, we should be using left rudder for take off, centered pedals/ball at cruise speed and right rudder when faster but that's not what we see in DCS.

Perhaps one day the Yak's rudder trim adjustment will work in special options but I'm guessing that's the best we can hope for.

 

I never used the word "subjective", but since you brought it up, I think ED's response to this is spot on because the Yak pilot presents nothing objective in any of the 3 videos. So I think the comment regarding measurement, or the lack of, is valid.

I am certainly not questioning the pilots real-life experience in the Yak, but I think he could have offered so much more given his resources. What would be more valuable IMO would be to show the community what happens in real life when the flaps are applied. Then it would be easy for anyone interested to try and replicate it at home in DCS.

I did it just now myself using a power setting to maintain level flight at 180, and applying the flaps causes the speed to drop to about 140. So the question is what happens in real life? And what is totally unrealistic to a pilot, might not even be noticeable to a you and I.                     

[Ramsay]

12 hours ago, Callsign112 said:

I did it just now myself using a power setting to maintain level flight at 180, and applying the flaps causes the speed to drop to about 140. So the question is what happens in real life? And what is totally unrealistic to a pilot, might not even be noticeable to a you and I.

The video that says flap drag was to great is from Aug 2018.

As I said the flap drag in DCS was adjusted and looking back at AcroGimp's comments from Sept 2019 (after some more FM changes)  he said "The pitch moment and drag from flaps I would say is finally correct" however he still noted other outstanding issues.

In terms of providing data, not all pilots are setup to record themselves while flying/doing aerobatics but I'd say John Knolla has gone "above and beyond" what could be expected, recording several videos of himself flying various aerobatic manoeuvres in DCS and commenting on the differences he sees between DCS and RL.

This is the Russian video (from May 2020) I mentioned, you should be able to get most of his meaning regarding DCS's Yak-52 using youtube subtitles with youtube auto-translate.

However, given the limit resources available for DCS's Yak-52, while it's good to know the differences between DCS and *real life*, the module is best enjoyed for what it is.

Edited February 28, 2022 by Ramsay

[Ramsay]

On 2/21/2022 at 2:38 PM, frumpy said:

Do you have an explanation why the guy in the video says drag of flaps is much too high?

The video is from Aug 2018 when flap drag was higher, the FM was adjusted in 2019, and retested by AcroGimp in September of that year.

The adjusted FM was thought to better represent the pitch and drag changes seen in the *real* aircraft when deploying the flaps.

IIRC I didn't notice a huge change at the time, just that the initial FM's flap drag had been "toned down" and landings were "smoother"*. However I don't fly the Yak very much, so it's possible the changes were more extensive and I just didn't notice them.

* I know "toned down" and "smoother" are imprecise but as a sim pilot, I really don't know how the *real* flies beyond descriptions in the POH, etc.

Edited March 1, 2022 by Ramsay
Try to improve wording

[Callsign112]

@Ramsay, I have no idea how I missed him saying 130 at full throttle, so thanks for pointing that out. And yes, I really enjoyed watching all his YouTube Yak-52 stuff, and appreciate his willingness to share what he has.

And it seems to have been adjusted based on comments in the OP's linked video. The discussion was before my time here, but full throttle with flaps deployed in level flight is between 155 to 160 for me. 

 I'm can't say I know why you feel the Yak-52 is using a FM ported from another plane, but we can at least say that ED has done some fine tuning and that with the recent announcement of more tuning on its way, the Yak has not been abandoned.   

[Ramsay]

1 hour ago, Callsign112 said:

I'm can't say I know why you feel the Yak-52 is using a FM ported from another plane, but we can at least say that ED has done some fine tuning and that with the recent announcement of more tuning on its way, the Yak has not been abandoned.

It's not so much that the FM is ported, rather building the whole system model of an aircraft is very complex i.e. engine fuel burn, torque reaction, air/oil cooling, radiator sizes, etc., etc.

To speed up the development process it seems to me (as a consumer with no inside knowledge) that ED start with a system model from a "similar" type of airframe and then adjust/add features to account for differences. Given enough time/resources this *will* result in accurate system models but sometimes (due to time/resource constraints) "temporary" values become "good enough" values and wrong behaviours are untouched (i.e. pitch reaction for RH turning blades, is applied/inherited by a LH turning helicopter).

This may be confirmation bias but I see this confirmed by -
• bugs revealing internal variable names from a different aircraft i.e. spitfire_xxx
• bugs inherited across multiple modules i.e. remote magnetic compass not being gimbaled on tail draggers, so displaying magnetic dip (when stationary) until airborne /in level flight
• known early access bugs in the F/A-18C's radar also appearing in the first iteration of the F-16C's radar
• The LH turning Huey having some pitch/roll changes more appropriate to a RH turning helicopter when increasing/decreasing collective
• Early damage models using another modules 3D model(s)

This is not to criticise ED, as starting with a blank system model would mean being unable to prototype/test the basic of features until everything was built.

TBH the Yak felt "almost done" at release and only requiring a little more work/tuning to make it complete (FM tuning, damage model, ADF, LODs, Cold Start failures, more liveries), it just never got the resources/priority.

As to inherited bugs for the Yak - I guess the overcooled oil temperature and suspected excess engine torque are candidates.

One bug I can't explain is the Yak's none working rudder trim adjustment in Options>Special as the setting works for DCS's other WWII planes.

[Callsign112]

If you think about it, some of the things you mentioned like issues with magnetic compass and radar across multiple planes/jets actually makes sense. Considering the technical item in question is being used for the same purpose in multiple aircraft, if there is an implementation issue with the technology in  DCS, it would be reasonable to expect the same issues to crop up wherever the technology is used. 

And the fact that rudder trim works in other DCS planes suggests to me that ED really does treat each module as a separate entity. To me the most likely explanation for it not working in the Yak-52 is that it just simply hasn't been fully implemented yet.