Sustained level turning with flaps down

[JtD]

First of, a little bit on the physics of sustained turning - it's essentially a very simple thing. The aircraft needs to have the necessary lift to get through a turn and needs to have the necessary thrust to not lose speed or altitude. To provide the necessary lift is the problem at low speeds, and providing the necessary thrust is the problem at high speed. If you look at typical turn time charts (like the first attachment), you will see more or less these two factors as the borders of the envelope - the lift limit (stall line) and thrust limit (level flight line). You can't fly left of the lift limit, because you're stalling out. But as the speed increases, so does the possible g-load in the turn. You can fly right of the lift limit, and depending on how much you pull the stick, you'll either have more power than necessary, less power than necessary or enough power to maintain altitude and speed. If you lose or gain altitude or speed, you're not flying a sustained level turn. So you'll be following the thrust limit to do that.

 

As can be seen, the best turn times are achieved (roughly) at the highest stalling speed where you still have enough thrust to maintain speed and altitude.

 

Now flaps have two major effects on turning performance - 1, they increase drag, 2, they increase lift. I've attached a couple of charts to illustrate the effects:

 

1st - a chart where only drag is increased, as can be seen, the thrust limit moves up as the additional drag caused by the flaps makes it impossible to fly as fast at the same power. The best sustained turn time increases, in my example by about 1.5s.

2nd - a chart where only lift is increased, as can be seen, the lift limit moves left as the additional lift created by the flaps makes it possible to fly the same g's at a lower speed. The best sustained turn time increases, in my example by about 2s, but only at low speed.

3rd - a chart that shows the combined effect. Obviously, due to the extra drag the flaps up configuration turns better at any speed above stall speed - the extra lift provided by the flaps does not have any advantage here. However, when the flaps up configuration stalls out, the flaps down configuration can still turn, making up for deficiencies lacking at higher speed. In my example the best turn time for flaps down is about half a second better than the time for flaps up. In real life, this would vary.

 

And now there have been endless debates about the effects of the flaps of the in game Yak-1 on turning performance. So I've done a couple of turning tests in game, standard conditions, standard loadout, 200m altitude, at four different speeds each. I came up with what is shown in the latest attachment, I've added some theoretical lines to better illustrate the trend. Results:

a) The Yak-1 has a better best sustained turn time with flaps down by about 1.5s.

b) It only turns better with flaps down below the stall speed of the flaps up configuration.

c) While pretty much at the stall limit at 250 flaps up and 210 flaps down, 210 flaps down was much easier to control. Probably due to much reduced angle of attack.

d) The relation of the maximum lift coefficients is realistic.

e) In order to get my calculation close to the in game relation, I only about doubled the drag for flaps down, which is low and less than tested by me in level flight for fully extended flaps (tripled here). It is possibly due to the partially retracting flaps at higher speeds.

f) Low speed thrust limits of the propeller were not considered in my calculation and seem to be no limiting factor in game.

 

Overall, the Yak-1 flaps down turning performance and the turning performance as such are not fundamentally wrong and may require a little fine tuning at best.

Issues I see with the Yak-1 flaps down behaviour still are the auto retract feature and the ease of handling at high angles of attack.

[unreasonable]

Nice clear charts!

 

So keep the speed up to 250 kph and there is no turn speed advantage to dropping flaps. (Not that I ever do in a fight anyway - keep forgetting which button I have them mapped onto )

[coconut]

I think I'll need to read that again a couple of times before I understand it all  Excellent work! Exactly the kind of post I want to see in FM discussions.

[coconut]

I think there might be a typo in there. Let me see if I got you right:

 

 

 

2nd - a chart where only lift is increased, as can be seen, the lift limit moves left as the additional lift created by the flaps makes it possible to fly the same g's at a lower speed. The best sustained turn time increasesdecreases, in my example by about 2s, but only at low speed.

 

Question: How did you get the charts 2 and 3?

 

 

Edit: Removed a question. I had misread "flaps up" as "flaps down".

Edited October 24, 2015 by coconut

[JtD]

Yes, sustained turn time decreases, improves. Turn rate increases. Blimey.

 

I did the charts with a spreadsheet I made for comparative purposes some years ago, for chart 2 I increased the drag coefficient for zero lift (cd0) by a factor of about 3 and for chart 3 I increased the maximum lift coefficient by ~30% or ~0.5. The spreadsheet did the rest.

 

Thanks for the positive feedback!

Edited October 24, 2015 by JtD

[303_Kwiatek]

What about other planes full flaps down sustained turn rate?

 

If even turn time will decrase with flaps full down still plane with flaps up would have advetnage casue it wouldn't be loose altitude in turns as much as plane with full flaps down -  so after few circles plane with clean config would be higher and with more energy so it would eat plane with flaps down.  In BOS it wont work in that way.

[JtD]

So keep the speed up to 250 kph and there is no turn speed advantage to dropping flaps.

Well, the other guy may drop flaps and turn inside you, he'll be flying slower on a smaller radius with a higher rate of turn - he'll not only catch up to you, he'll also be inside you in a firing position. Given that you're at a higher speed, your E is better and you may use that to your advantage, but in a simple turn contest, the guy with flaps down wins.

 

I have flaps down on "f". Whenever I wasn't sure how to lower flaps, I started my trial&error with pressing f like flaps.

[JtD]

What about other planes full flaps down sustained turn rate?

Feel free to test, I didn't take the time.

 

If even turn time will decrase with flaps full down still plane with flaps up would have advetnage casue it wouldn't be loose altitude in turns as much as plane with full flaps down -  so after few circles plane with clean config would be higher and with more energy so it would eat plane with flaps down.  In BOS it wont work in that way.

As I have explained in the OP, the premise is sustained level turn. No plane loses altitude, no plane changes speed. Hence we have the thrust limit, which is how fast a plane can go without the necessity to dive or to slow down. If you look again at chart 5, you can see that if the Yak-1 with flaps down wanted to turn with the flaps up configuration at speeds above 250km/h, it would indeed need to descend to keep up in the turn. But this is not the case for the best sustained level turn, where flaps down is better at 210 than flaps up at 250. One reason for this is also that the drag caused by the flaps gets mitigated as the speed decreases.

[Dakpilot]

What about other planes full flaps down sustained turn rate?

 

If even turn time will decrase with flaps full down still plane with flaps up would have advetnage casue it wouldn't be loose altitude in turns as much as plane with full flaps down -  so after few circles plane with clean config would be higher and with more energy so it would eat plane with flaps down.  In BOS it wont work in that way.

 

show evidence

 

Cheers Dakpilot

[unreasonable]

Have people done an in-flight test fight of a flaps down Yak against a flaps up Yak?

 

I always find the videos people post of Yak vs 109s a bit unconvincing since there are so many degrees of difference between the two: but if it is just the flaps at issue surely the only way to see if there is anything wrong is a) Individual tests as per JtD's graphs, and/or 2) a trial fight between two aircraft identical except for the variable under consideration.

 

So can someone produce a Yak-Yak trial with two competent pilots where the use of flaps can be shown to give an advantage: perhaps of the sort that Kwiatek asserts?

[303_Kwiatek]

I did such test and Yak-1 with flaps down always win with Yak-1 clean config even if was trying to use energy adventage which i should got with clean confing.

 

Similar test was done with Fw 190 and A-3 with full flaps down after few circles ended without speed and energy and A-3 with flaps up win.

 

http://forum.il2sturmovik.com/topic/15470-yak-1-flaps-down-arcadish-behaviour/page-2

 

Post from 58

show evidence

 

Cheers Dakpilot

 

Spitfire turn charts with flaps down and up posted on these forum (dont remember where now).  Spitfire with full flaps down even if got better sustained turn time it loses altitude where clean config dont. So plane with clean config could used energy for outclimb plane with flaps down in turns which after few circles would end with plane clean confing victory.

 

It work with other planes in BOS as it should but in Yak-1 case not.

 

Another funny things is used by Yak-1 pilots flaps in vertical manouvers -   IRL plane would risk flaps damage but also would create a lot of drag and plane destabilisation thats why it would be absurd to do it ,  in BOS it is freqently used to get firing solution.

Edited October 24, 2015 by 303_Kwiatek

[Willy__]

I really dont give a damn about Yak pilots using flaps for sustained turns, any german turning with a Yak should lose. The problem is that some people uses the flap to "helicopter"/prop hang. Picture the scenario: you're dogfighting with a yak and you are in a advantage position/with more E than him, and theres the chance of doing a hammerhead, so you decide to do the hammerhead. What the Yak pilot does ? He goes straight up into you, but instead of stalling, he deploys the flaps right before stall and prop hangs the shit out of it, and sometimes, more often than not, hes able to get a gun solution on you because of that. Anyways, thats just my 2c....

Edited October 24, 2015 by istruba

[JtD]

Have people done an in-flight test fight of a flaps down Yak against a flaps up Yak?

 

I always find the videos people post of Yak vs 109s a bit unconvincing since there are so many degrees of difference between the two: but if it is just the flaps at issue surely the only way to see if there is anything wrong is a) Individual tests as per JtD's graphs, and/or 2) a trial fight between two aircraft identical except for the variable under consideration.

 

So can someone produce a Yak-Yak trial with two competent pilots where the use of flaps can be shown to give an advantage: perhaps of the sort that Kwiatek asserts?

Would be nice to see - have one guy drop the flaps and when he's on the six of the other guy after a couple of turns, have him raise flaps and the other guy drop them and see how things go from there...

Spitfire turn charts with flaps down and up posted on these forum (dont remember where now).  Spitfire with full flaps down even if got better sustained turn time it loses altitude where clean config dont...

Actually that's how you interpreted it, same way you interpreted my above information, and it is again not correct. The Spitfire data showed pretty much the same behaviour my fictional example shows. In a sustained level turn the Spitfire flaps down would have outturned the flaps up configuration, but would have done that at a lower speed.

[Dakpilot]

I did such test and Yak-1 with flaps down always win with Yak-1 clean config even if was trying to use energy adventage which i should got with clean confing.

 

Similar test was done with Fw 190 and A-3 with full flaps down after few circles ended without speed and energy and A-3 with flaps up win.

 

http://forum.il2sturmovik.com/topic/15470-yak-1-flaps-down-arcadish-behaviour/page-2

 

Post from 58

 

Spitfire turn charts with flaps down and up posted on these forum (dont remember where now).  Spitfire with full flaps down even if got better sustained turn time it loses altitude where clean config dont. So plane with clean config could used energy for outclimb plane with flaps down in turns which after few circles would end with plane clean confing victory.

 

It work with other planes in BOS as it should but in Yak-1 case not.

 

Another funny things is used by Yak-1 pilots flaps in vertical manouvers -   IRL plane would risk flaps damage but also would create a lot of drag and plane destabilisation thats why it would be absurd to do it ,  in BOS it is freqently used to get firing solution.

 

If anything that thread does more to suggest there are no problems....rather a lot of reading and irritating with the usual off topic posts and eventually closed by the usual suspects...

 

Don't get me wrong I have never said there is nothing wrong with Yak, but why would vertical manoeuvres near stall speed damage flaps? be they Yak or 109

 

Cheers Dakpilot