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Old 08-03-2018, 04:50 PM   #1
AcroGimp
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Default Flight model and other early impressions

First off my qualifications:

FAA licensed commercial pilot, ~700 hrs total time, 350 in Yak-52 which I have owned for 3 and half years. I am a member of the Red Star Pilot's Association, I hold a Formation Wingman Card and am working on upgrading to Lead. I fly weekly, formation, aerobatics, I lead a casual 3-ship formation aerobatic team, and I even take her out for the occasional $200 hamburger or very short trip.

Initial observations as follows from a 10-15 minute free flight:
- Airplane does not start like my Yak, my start procedure is simple, straightforward and based on DOSAAF training, I was unable to start Yak on multiple attempts
- Start sounds are completely wrong, the pneumatic starter has a very unique and easily recorded sound - this is an instant immersion breaker
- Engine rotation on start unrealistically slow
- Energy retention in vertical upline maneuvers is incorrect, bleeds off too fast - this shows in quarter clover up, vanilla loop, cuban eight with entry speeds to 400 kph, I know that I can loop the Yak down to 210 kph entry speeds (it is very small edge of stall loop but still - thanks Gennady!)
- Engine power seemed off, should have no trouble developing ~750-800 mmHg manifold pressure at 1000m wide open with RPM 82% and it was down around 600
- There is something VERY off for rudder/yaw modeling - aircraft should require an increasing amount of right rudder when speed increases, the model requires left rudder which is literally the exact opposite of real life
- Aircraft should require more left rudder over the top when slow
- All 3 axes feel WAY too light but I will try curves to tame that
- Roll rate 'felt' fast but that could be result of no curves - I'll time it and see how it compares to real world
- My Yak has NEVER thrown a wingtip vortex, not once, ever, under any conditions or load - the prop on the other hands throws a beautifully wicked spiral vortex under heavy load in the right conditions

It's not all bad news though:
Cockpit and exterior models are fantastic, very true to life - in VR it is exactly like sitting in my Yak.

In-cockpit sounds when flying are pretty good.

The snap/snatch is very well modeled, this is a unique characteristic of the Yak that catches new Yak pilots by surprise and it is exactly as I experience in my Yak when I ask too much.

The post stall/ballistic behavior is also very well modeled and matches my experience.

Happy to discuss these observations further if requested. As I said, initial impressions based on a short free flight since I could not get the plane started - some may be addressed with control curves but there seem to be some foundational and critical errors in the flight model that I hope can be fixed - I want to enjoy this model.

'Gimp (DISCO vVMFA-122)
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Last edited by AcroGimp; 08-03-2018 at 09:12 PM.
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Old 08-03-2018, 05:02 PM   #2
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Thanx for the great insight. Can you maybe take a quick glance at this question? https://forums.eagle.ru/showthread.php?t=217347
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Old 08-03-2018, 05:54 PM   #3
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OK, flew it again, still unable to get it started with my real world procedure.

Curves at 15 for all 3 axes, no deadzone feels close.

Roll rate is maybe 10% optimistic, should be 160 deg/sec as I recall.

Taxi, takeoff and climbout, stall and spin behavior are all close, incipient spin is too nose down and initial rate of rotation too high but pops out with proper spin recovery - power off upright explored, will check advanced spins when I get back home on Sunday (power on, aggravated and flat, both upright and inverted).

Verified that the speed/yaw behavior is BACKWARDS, I have a screengrab which is feet on floor at nearly 350 kph, that should require ~2 inches of right foot to counteract, it indicates it needs left rudder on both slip/skid balls.

Fix that and start sounds/behavior and it will be a good start.

'Gimp (DISCO vVMFA-122)
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Old 08-03-2018, 06:18 PM   #4
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Regarding the roll rate at least:
https://forums.eagle.ru/showthread.php?t=203148

Regarding left rudder while speed increases: generally the plane has trim tab set for the certain speed to feel pedals neutral. As far as I remeber DCS Yak is not pre-trimmed. And as far as I just have found trim tabs setting does not work for Yak-52 yet... sorry, early access .

Wingtip vortex is a bit overmodelled now... waits for the future humidity implementation to the atmosphere model.

About the MP at 1000 m: there is no problem to get 730mm at 100 m ASL ISA - a bit less than it should (750). I have an only idea about 600 mm - Nevada?

About energy retention... due to its nature Yak is very sensitive to the AoA/G-load during the maneuver... stop, sorry - Nevada?
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

Last edited by Yo-Yo; 08-03-2018 at 06:34 PM.
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Old 08-03-2018, 06:33 PM   #5
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Quote:
Originally Posted by Yo-Yo View Post
Regarding the roll rate at least:
https://forums.eagle.ru/showthread.php?t=203148

Regarding left rudder while speed increases: generally the plane has trim tab set for the certain speed to feel pedals neutral. As far as I remeber DCS Yak is not pre-trimmed. And as far as I just have found trim tabs setting does not work for Yak-52 yet... sorry, yearly access .

Wingtip vortex is a bit overmodelled now... waits for the future humidity implementation to the atmosphere model.

About the MP at 1000 m: there is no problem to get 730mm at 100 m ASL ISA - a bit less than it should (750). I have an only idea about 600 mm - Nevada?

About energy retention... due to its nature Yak is very sensitive to the AoA/G-load during the maneuver... stop, sorry - Nevada?
Yo-Yo, the issue with speed vs Yaw is that no Yak I have flown, and in addition to mine I have flown at least 7 others, plus Nanchang CJ-6's which are 'somewhat' similar ALL require lots of left rudder on takeoff, and the DCS Yak does seem to have that correct, but as speed increases, usually past about 250 kph (~125 kts) in mine, it starts to require right rudder to remain in coordinated flight, but especially at any speed at or beyond 300 kph such as you see on essentially any downline for an aerobatic figure it requires a substantial amount of right rudder - this would be left rudder in the other aerobatic planes I have flown like the Citabria, Christen Eagle, Great Lakes Biplane or the Extra 300L but that is because their engines rotate clockwise, opposite the Vedenyev in the Yak.

This behavior is totally incorrect and seems to be outside the laws of physics.

Given the reported origin of this project I simply cannot believe this behavior is present because anyone who has flown the Yak in real life would notice it about 5 minutes after takeoff.

I did figure out the start issue as ED has the ignition switch in the rear cockpit set OFF as default, that switch is safety-wired ON in my aircraft since I cannot control people in the back seat.

Start behavior is correct, the sound is still all wrong.

'Gimp (DISCO vVMFA-122)
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Last edited by AcroGimp; 08-03-2018 at 09:13 PM.
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Old 08-03-2018, 06:36 PM   #6
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Quote:
Originally Posted by AcroGimp View Post
Yo-Yo, the issue with speed vs Yaw is that no Yak I have flown, and in addition to mine I have flown at least 7 others, plus Nanchang CJ-6's which are 'somewhat' similar ALL require lots of left rudder on takeoff, and the DCS Yak does seem to have that correct, but as speed increases, usually past about 250 kph (~125 kts) in mine, it starts to require right rudder to remain in coordinated flight, but especially at any speed at or beyond 300 kph such as you see on essentially any downline for an aerobatic figure it requires a substantial amount of right rudder - this would be left rudder in the other aerobatic planes I have flown like the Citabria, Christen Eagle, Great Lakes Biplane or the Extra 300L but that is because their engines rotate clockwise, opposite the Vedenyev in the Yak.

This behavior is totally incorrect and seems to be outside the laws of physics.

Given the reported origin of this project I simply cannot believe this behavior is present because anyone who has flown the Yak in real life would notice it about 5 minutes after takeoff.

I did figure out the start issue as ED has the ignition switch in the rear cockpit set OFF as default, that switch is wired ON ni my aircraft since I cannot control people in the back seat.

Start behavior is correct, the sound is still all wrong.

'Gimp (DISCO vVMA-122)
You are testing DCS Yak in Nevada, right?
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 08-03-2018, 06:40 PM   #7
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Question @AcroGimp

How do you manage the oil temperature?
In the free flight Mission (winter time) my oil temperature drops near zero and pressure rises to max, even with radiator closed, cyl.head temp. in green. Tried different rpm settings...
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Old 08-03-2018, 06:50 PM   #8
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Quote:
Originally Posted by Yo-Yo View Post
You are testing DCS Yak in Nevada, right?
Yes, to be similar to my real world environment near San Diego I took off from Henderson (KHND) in NTTR.

I think the engine is running about 75 mmHg low on available power which is substantial as well, and my engine is tired at 1400 hrs TT.

@Beta Sokoi, the Yak oil temp is tough to manage in extreme cold, typically there is an actual blocking plate for the oil cooler to restrict air flow in.

Best approach, and keep in mind all of my Yak time is in SoCal so I don't have cold temp issues - best approach is warm engine up (gills closed) with oil cooler door fully closed as well, but I think the Caucasus missions will always suffer from cold oil temp in winter conditions.

In SoCal I see oil temps of 55-80 usually, able to safely runup after 5 minutes usually.

CHT and oil temp do seem to be behaving accurately in the DCS Yak Module.

Heading out for Big Bear Lake, will be back on later.

Again, I am offering this up as hopefully constructive criticism, I want to like this module and I want to get my Yak's paint scheme skinned on it.

'Gimp (DISCO vVMFA-122)
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Last edited by AcroGimp; 08-03-2018 at 09:13 PM.
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Old 08-03-2018, 06:55 PM   #9
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Henderson elevation is 760 m ASL, San-Diego - ?

So, we need to have all input parameters equal to have correct results.
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 08-03-2018, 07:07 PM   #10
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5m for San Diego
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