NACA data indicates that the BoS Yak Clmax is too high

[Holtzauge]

So while digging around I found some data on the Yak’s Clark YH wing profile in NACA TN 240 which actually contained measurements from the NACA variable density wind tunnel at a Reynolds number of 3.6 million for a finite wing of aspect ratio 6. The result indicated a Clmax of 1.3 for the Clark YH with no flap deflection under these conditions.

 

So maybe I should write a FM trouble report in the proper format so the devs can fix this ASAP since according to JtD’s measurements here The Yak in BoS now has a Clmax of 1.39 which is much higher than the 1.3 measured by NACA for an aspect ratio 6 wing meaning that the Clmax for the Yak needs to be dialed down even lower since it only has an aspect ratio of 5.8.

 

BTW: This new discovery will undoubtedly make Turban very happy seeing his deep commitment to historical accuracy for the Fw-190 which I’m sure also translates to a wish to see the Yak as historically accurate as possibly.

 

Edit: Updated the link to NACA TN 240

Edited April 24, 2016 by Holtzauge

[URUAker]

Hi Holtzauge, I enjoy reading your posts so I can learn something, also read with attention posts from others that seem to know what they are talking about, even if some of you disagree.

 

It will be great if you could send the reports of your findings to the Devs in the format they want. I´m not saying you are wrong or right, but I will be very grateful if you or others take the time to report any finding that can lead us to an even better sim.

 

S!

[Stig]

+1

[Holtzauge]

Well that is the plan if it turn out I'm on the right track. I think so, but really, before sending it to the devs it would be good to get some second opinions from the community and maybe dig around some more in the NACA archives. I did see another NACA report on the Clark YH (CYH) with the effects of flaps but I have not had a chance to look at that one yet and maybe there is more around. The NACA NTRS server has LOTS of goodies and there are probably more CYH reports waiting to be discovered there. So maybe we can find some more data and nail things down some more before deciding what to do.

[Dr_Molenbeek]

Unfortunately, i fear that devs will ignore this because "Russian datas for Russians and German datas for Germans".

 

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Edited April 25, 2016 by BlackSix

[JtD]

To add a couple of more cents:

 

In the TR 628 they give clmax of 1.48 for a 5x30 wing (aspect ratio therefore also 6) at a Reynolds number of 3.05 mio. It's figure 72 in the report, page 44 in the pdf. Might be corrected to 2D, I would have to read up on this. ClarkY, which I have chosen for my comparison test, is about 1.56 at RN 3.17 mio. figure 58, page 37. Hence my emphasis that my comparison was, if anything, conservative.

 

In TR 610 a similar study is carried out with the 23012 airfoil (figure 15, page 17), at an "effective" Reynolds number of 3.88 you're at clmax 1.5.

 

Or, if you check the tables in the end of both reports, there are clmax for high RN given,

ClarkY: 1.68@8.4

ClarkYH: 1.58@8.1

23012: 1.74@8.37

All theoretical data indicates that the airfoil used on the Fw have a significantly higher lift coefficient than the airfoil used on the Yak-1, and not even the built features like wing twist (washout) and varying profile thickness will negate that effect completely. Yet in game, the Yak-1 has a significantly higher lift coefficient.

[Holtzauge]

To add a couple of more cents:

 

In the TR 628 they give clmax of 1.48 for a 5x30 wing (aspect ratio therefore also 6) at a Reynolds number of 3.05 mio. It's figure 72 in the report, page 44 in the pdf. Might be corrected to 2D, I would have to read up on this. ClarkY, which I have chosen for my comparison test, is about 1.56 at RN 3.17 mio. figure 58, page 37. Hence my emphasis that my comparison was, if anything, conservative.

 

In TR 610 a similar study is carried out with the 23012 airfoil (figure 15, page 17), at an "effective" Reynolds number of 3.88 you're at clmax 1.5.

 

Or, if you check the tables in the end of both reports, there are clmax for high RN given,

ClarkY: 1.68@8.4

ClarkYH: 1.58@8.1

23012: 1.74@8.37

All theoretical data indicates that the airfoil used on the Fw have a significantly higher lift coefficient than the airfoil used on the Yak-1, and not even the built features like wing twist (washout) and varying profile thickness will negate that effect completely. Yet in game, the Yak-1 has a significantly higher lift coefficient.

 

 Will take a closer look tomorrow evening when I will have more time. Must say the values look high: 1.74 for the NACA 23012. IIRC then the NACA 23015 was 1.68 in another report and it would be good to check if this is corrected to the 2-D values as you say. As far as I could see the 1.3 was for the model as tested in TN 240 but it looks like all this definitely needs some more attention to figure out. Anyway good find!

[Holtzauge]

Unfortunately, i fear that devs will ignore this because "Russian datas for Russians and German datas for Germans".

 

Well let's hope they see it as neutral info since both the Germans and Russians were basing their designs on NACA research and data, i.e. the CYH on the Yak and the NACA 230 on the Fw-190. What a bunch of freeloaders!

[URUAker]

Well that is the plan if it turn out I'm on the right track. I think so, but really, before sending it to the devs it would be good to get some second opinions from the community and maybe dig around some more in the NACA archives. I did see another NACA report on the Clark YH (CYH) with the effects of flaps but I have not had a chance to look at that one yet and maybe there is more around. The NACA NTRS server has LOTS of goodies and there are probably more CYH reports waiting to be discovered there. So maybe we can find some more data and nail things down some more before deciding what to do.

       

[Original_Uwe]

Love where this is going.

[DD_Arthur]

So am I understanding this right?  Someone who does not own this game and has not flown it is preparing an FM bug report?

[MK_RED13]

Unfortunately, i fear that devs will ignore this because "Russian datas for Russians and German datas for Germans".

 

2. This forum is provided by 1C-777 Ltd. as a courtesy and its usage is a privilege and 1C-777 Ltd. reserves the right to ban any member temporarily or permanently for any reason at any time. Any penalties listed below for violations of the rules are guidelines only and forum administration may take additional action if they feel it is warranted. Use of the forum is not connected to usage of the game and access to this forum is not guaranteed to users as a consequence of purchasing the game.

 

17. Spreading false or harmful information about the product is prohibited and will be deleted by forum administration. Claiming ignorance of the subject to justify harmful or obviously untrue info will not be tolerated.

 

90 days ban on entry. If you continue to publish similar statements in the future you'll receive a permanent ban on entry.

 

 

[II./JG77_Manu*]

So am I understanding this right?  Someone who does not own this game and has not flown it is preparing an FM bug report?

If i were you, i would be thankful that there are (still) people around who have the technical knowledge to get the game more polished and inaccuracies fixed, and not troll around with childish smileys

[DD_Arthur]

Thankful?  For a couple of sad, internet egomaniacs who have pursued each other over various flight sim forums and have landed up here yet do not actually own the game?  You've gotta' be kidding.

 

If I had the power I'd kick 'em straight off these boards as a public menace.  

[Original_Uwe]

Well luckily you don't.

Anyone with actual aircraft design experience is valuable, far more so than the average layman that just happens to own the game.

[Holtzauge]

As I was saying, I do own BoS and I do fly it. It's to bad you have to put up with the above type of BS. But this is the internet and trolls will be trolls......How nice that work is waiting......

[Holtzauge]

BTW: Would be good if moderators cleaned this thread since some of us plan to post some actual info later on......

[DD_Arthur]

As I was saying, I do own BoS and I do fly it. It's to bad you have to put up with the above type of BS. But this is the internet and trolls will be trolls......How nice that work is waiting......

 

As you actually own BoS then I apologise to you unreservedly Holtzauge.  It's not a matter of shooting the messenger - I'm well aware that in the case of the '190 the devs have introduced some unfortunate characteristics into its latest FM - its more a case of weeding out the contribution of that certain fraudster who has taken to gracing us with his presence here after being banned from the DCS forums. 

Edited April 26, 2016 by DD_Arthur

[unreasonable]

Perhaps the forum needs some kind of ownership symbol under the name? If I have this right, the bars (ahem, buffs his with a clean cloth) signal only early access ownership, gold for the idiots like me who have bought the lot and silver for the cheapskates who have avoided the fun of skidding the Fw across the skies. If you buy BoM after early access you get no bars. Those who bought after early access should have had a better idea of what they are getting and deserve some kind of symbol under their avatar.  

 

No doubt someone will correct me if I am wrong - and [Edited] will correct me even if I am not.

 

Fun fact: if you google "symbol of stupidity" under images, the very first thing you get is this:

 

http://www.funnyjunk.com/funny_pictures/2775732/Symbol/

Edited April 26, 2016 by Bearcat
Personal

[Holtzauge]

As you own actually own BoS then I apologise to you unreservedly Holtzauge. It's not a matter of shooting the messenger - I'm well aware that in the case of the '190 the devs have introduced some unfortunate characteristics into its latest FM - its more a case of weeding out the contribution of that certain fraudster who has taken to gracing us with his presence here after being banned from the DCS forums.

Thanks, and apology accepted. A rare thing these days on the internet so kudos to you!

[Dakpilot]

Fun fact, silly personal digs do nothing to help threads stay on track

 

Cheers Dakpilot

 

Neither does responding to them.

Edited April 26, 2016 by Bearcat

[unreasonable]

Fun fact, silly personal digs do nothing to help threads stay on track

 

Cheers Dakpilot

 

[Edited]

Edited April 26, 2016 by Bearcat
Personal

[Dakpilot]

[Edited]

Edited April 26, 2016 by Bearcat
Personal

[Crump]

To add a couple of more cents:

 

In the TR 628 they give clmax of 1.48 for a 5x30 wing (aspect ratio therefore also 6) at a Reynolds number of 3.05 mio. It's figure 72 in the report, page 44 in the pdf. Might be corrected to 2D, I would have to read up on this. ClarkY, which I have chosen for my comparison test, is about 1.56 at RN 3.17 mio. figure 58, page 37. Hence my emphasis that my comparison was, if anything, conservative.

 

In TR 610 a similar study is carried out with the 23012 airfoil (figure 15, page 17), at an "effective" Reynolds number of 3.88 you're at clmax 1.5.

 

Or, if you check the tables in the end of both reports, there are clmax for high RN given,

ClarkY: 1.68@8.4

ClarkYH: 1.58@8.1

23012: 1.74@8.37

All theoretical data indicates that the airfoil used on the Fw have a significantly higher lift coefficient than the airfoil used on the Yak-1, and not even the built features like wing twist (washout) and varying profile thickness will negate that effect completely. Yet in game, the Yak-1 has a significantly higher lift coefficient.

 

I have not participated in this because I was being polite to both Holtzauge and JtD.  Holtzuage raises a good point and backs up what I determined.  It is the result of using indicated airspeed

 

However, JtD is simply proving the point I have been trying to make and he has been arguing vehemently against...;.

 

Focke Wulf says the CLmax of the wing design on the FW-190 is 1.58.  Do the Re math and you will see that is were it should be at the stall speeds of the FW-190!!!

 

2D data CLmax is the basis for any flap design.   Clean wing CLmax is also in standard use to calculate unstick speed, btw.  Guess what?  It works out.

 

 

If we run the math on the RN and ballpark the scale it to find the velocity the FW-190 would have to achieve to achieve the CLmax range of the 2D airfoil we find:

 

Velcoity = (8900000*.000156927)/2 = 698 fps or 475mph

 

At an RN of 8900000, our 24 inch airfoil has to be traveling at ~475mph to achieve a Clmax of 1.7.

 

The FW-190 with its wing chord of 5.95 ft would have to travel at 234 mph. That is well above stall speed. Wind tunnel corrections change that speed specific speed.

 

Will call that our high speed realm.

 

The next RN is 2600000 and delivers a CLmax of 1.5.

 

Velocity = (2600000*.000156927)/2 = 408 fps or 139 mph.

 

Our speeds work out to 139 mph for our 24 inch airfoil section and 46 mph for the FW-190 wing at an RN of 2600000.

 

Well, the FW-190 cannot fly at 46 mph so that is our low speed value.

 

So we can say with certainty the 2D airfoil could produce a CLmax ranging from 1.5 to 1.7 and the 1.5 lower end is not representative of the FW-190 wing's CL max. The CLmax in all probability lies somewhere in the middle!

 

 

Wow....

 

<edited to add in the correct NACA 23015 root airfoil and not the NACA 23012 which I am sure is a typo on JtD part.>

Edited April 26, 2016 by Crump

[JtD]

...

However, JtD is simply proving the point I have been trying to make and he has been arguing vehemently against...;.

...

If that's what you understand then clearly you have misunderstood. Because it was Focke Wulf who was contradicting you, not me. I was just the messenger. And, I just checked, Focke Wulf did not change their statement.

 

<edited to add in the correct NACA 23015 root airfoil and not the NACA 23012 which I am sure is a typo on JtD part.>

<Edited to point out 23012 is not a typo but fully intentional.>

 

---

Details for the data posted earlier: 1.5 is for AR6, 5*30 dural airfoil panel as tested at RN3.88, 1.74 is 2D. The panel at RN8.37 is given with Clmax~1.63. High RN figures for ClarkY and ClarkYH are 2D, low RN figures for the dural panel again.

Edited April 26, 2016 by JtD

[Holtzauge]

While I was typing this I saw that JtD already beat me to a few points so some of what follows below may be redundant but anyway here is some more input:

 

Beginning with NACA report 628: So far as I can tell while the tests to derive the section data were done with model wings of the size 5 x 30 inches the report comes with a table that lists the section (i.e. 2-D) Clmax figures for a number of section, including two of interest when it comes to the Yak:

 

Clark Y Clmax 1.68 at Reynolds number circa 8 Million

 

Clark YH Clmax 1.58  at Reynolds number circa 8 Million

 

That the Clmax is 0.1 units lower for the CYH is logical since the reflexed trailing edge, which differed it from the CY, can be thought of as a negative flap deflection that reduces the maximum lift potential.

 

While the CY and CYH comes in one flavour only, i.e. the thickness to chord ratio (t/c) is fixed the NACA 230-series comes in different t/c version. The book Theory of wing section by Abbot and von Doenhoff compiles a lot of NACA data and contains data for both the NACA23012 and 15, i.e. with 12 and 15% t/c respectively.

 

These have an impressive Clmax of 1.78 and 1.7 (at Reynolds number 6-8 Million) respectively which was also why they were so popular since they married a high Clmax with the low pitching moment characteristics (change of pressure center with changing lift as in speed changes) that the CY did not have and that were bought at a cost in the CYH at the cost of a reduction of the Clmax from 1.68 to 1.58.

 

In NACA 610 it is also made clear that the results are based on tests on rectangular wings with aspect ratio 6 at a reduced Reynolds number of around 3.8 Million for the Clmax tests and that this is then used as a base to derive the higher Reynolds number section (2-D) data that is listed above.

 

Now having taken a second look at NACA TN 240 I’m not as sure anymore that this can be used directly to compare with the Yak: While it looks like the base 1.3 Clmax data is based on an aspect ratio 6 wing it is as far as I can tell probably a rectangular wing since the report states that it was “tested in the usual manner” which AFAIK for the variable density tunnel was an aspect ratio 6 rectangular model so it is probably better to stay with the 2-D values for a comparison. So it looks like we are back to comparing with the 2-D values as JtD did before. Still, I can’t see any reason why the Yak should reach a higher percentage of its 2-D section lift potential than the Fw-190? In addition, the Fw-190 seems to have quite an advantage in 2-D Clmax potential as in 1.7-1.78 as compared to 1.58.

 

Finally, does someone know the Yak wings washout figures, i.e. what kind of twist is built into the wing? This would be very good to know. Does somebody know this or can find out?

 

As a footnote, a friend contacted me and noted that we should not forget that one also needs to reduce the Clmax due to trim effects since there is a download on the tail. However, this effect is there both on the Yak and the Fw-190 and for a fair comparison we can look at the first order effects as in the untrimmed Clmax to begin with but be aware that to get the actual “true” trimmed Clmax then one needs to also take this effect into account.

[Crump]

 

 

Because it was Focke Wulf who was contradicting you, not me.

 

No, Focke Wulf was not contradicting me....

 

You found 1.58 in a completely seperate document as the landing speed CLmax.

 

That checks out.....

 

An airplane at the same weight and airspeed requires the same coefficient of lift.

 

That is why the landing speed is equal to the 1G clean configuration stall speed, JtD.

 

Again, the 2D backs this up as you just found out:

 

 

All theoretical data indicates that the airfoil used on the Fw have a significantly higher lift coefficient than the airfoil used on the Yak-1, and not even the built features like wing twist (washout) and varying profile thickness will negate that effect completely. Yet in game, the Yak-1 has a significantly higher lift coefficient.

 

Wing twist has nothing to do with it and the wingtip airfoils do not determine the stall.  The twist and the root airfoil are there to improve stall characteristics.

[JtD]

Finally, does someone know the Yak wings washout figures, i.e. what kind of twist is built into the wing? This would be very good to know. Does somebody know this or can find out?

The technical description of both the Yak-9 and Yak-9u state the "angle of attack of the wing = 0°". No differentiation for root and tip. Since the wing geometry did not change between Yak-1, 7 and 9 it is safe to assume it's also the case for the Yak-1.

Edited April 26, 2016 by JtD

[Bearcat]

I have edited this thread..

 

Chillax.......

[JtD]

.... so it is probably better to stay with the 2-D values for a comparison...

Getting back to that now - on the one hand, it's a little unfortunate, but on the other, not unexpected. The primary reason I'm an advocate for correct relative performance in that regard over correct absolute performance is that absolute performance in real life varied a lot. Really a lot.

 

Now if you were to take the 230xx series as applied to the Fw190, take into account wing twist, varying profile thickness, wing root transition, leading edge protrusions and holes (guns), panels, control surface gaps, and and, and manufacture it to the aerodynamic smoothness standard used for the wind tunnel models that give the quoted clmax, you may end up at a clmax of around 1.5. However, the factories did not produce surfaces that smooth. In the field, particularly operating from improvised air strips in winter conditions, you'd be far, far away from that figure, and probably be lucky to achieve 1.2. If you just take a look at the 23015 data Crump's posted here, you have data for the smooth airfoil, and for standard roughness. According to NACA, this is (paraphrasing) "worse than manufacturing quality and service conditions but better than conditions in mud, snow or battle damage". It reduces clmax from 1.65 to 1.2, just to illustrate my point.

 

So, imho, the only correct way to properly model a large variety of aircraft correctly in their relative performance, is to settle for one common, standardized approach for all of them. Not to take various tests for various planes as various references. If I did it like that, I could prove to you that the Fw190A-3 outturns the Fw190A-3 by 10 seconds. It doesn't work.

[Kurfurst]

I am sure the developers have something better than unverifiable speculations of wildly varying accuracy based on theoretical US studies or non/near identical wing configurations - for example actual flight / wind tunnel trials  on the actual aircraft's real configuration, made and analysed by professional aircraft engineers of TsAGI / CAGI. 

 

I also do not get why the hairy one has trouble with "Russian datas for Russians and German datas for Germans" - to me it seems like a sound principle, for one it avoids one of the pitfalls with the testing often on poorly understood / serviced  and/or damaged captured aircraft.

[unreasonable]

I am sure the developers have something better than unverifiable speculations of wildly varying accuracy based on theoretical US studies or non/near identical wing configurations - for example actual flight / wind tunnel trials  on the actual aircraft's real configuration, made and analysed by professional aircraft engineers of TsAGI / CAGI. 

 

 

 

While I would certainly like to think that too, I cannot help wondering why, if that is true, we have had so many significantly different versions of the FM?

[Holtzauge]

Getting back to that now - on the one hand, it's a little unfortunate, but on the other, not unexpected. The primary reason I'm an advocate for correct relative performance in that regard over correct absolute performance is that absolute performance in real life varied a lot. Really a lot.

 

Now if you were to take the 230xx series as applied to the Fw190, take into account wing twist, varying profile thickness, wing root transition, leading edge protrusions and holes (guns), panels, control surface gaps, and and, and manufacture it to the aerodynamic smoothness standard used for the wind tunnel models that give the quoted clmax, you may end up at a clmax of around 1.5. However, the factories did not produce surfaces that smooth. In the field, particularly operating from improvised air strips in winter conditions, you'd be far, far away from that figure, and probably be lucky to achieve 1.2. If you just take a look at the 23015 data Crump's posted here, you have data for the smooth airfoil, and for standard roughness. According to NACA, this is (paraphrasing) "worse than manufacturing quality and service conditions but better than conditions in mud, snow or battle damage". It reduces clmax from 1.65 to 1.2, just to illustrate my point.

 

So, imho, the only correct way to properly model a large variety of aircraft correctly in their relative performance, is to settle for one common, standardized approach for all of them. Not to take various tests for various planes as various references. If I did it like that, I could prove to you that the Fw190A-3 outturns the Fw190A-3 by 10 seconds. It doesn't work.

 

Well I agree that it is difficult to do an exact analysis for the Clamx as we are trying to do here but that applies to all aircraft performance. You can say the same for climb, speed, turn performance etc: What was the aircraft's service condition? At what temperature was the data collected? What was the radiator flap setting? Were the cowling guns sealed? Were the wings "gespackelt und poliert"? Could the measurement be seen as a median value or an outlier? etc. etc. So whatever data you are trying to pin down you will have the same problem.

 

However, I agree that the most important thing to get right is the relative data: So, in BoS or any other sim, if the absolute values are a bit high or low is not that important as long as they are translated in the same direction for ALL aircraft. However, if this is not so and one is off on the high end and one on the low end then that is obviously a problem and right now my impression is that the BoS Fw-190 seems to be on the low end while a Clmax of 1.39 is a very high figure.

 

Generally, some people, me included, like to think of the Spitfire Clmax as around 1.36 and the Me-109 at around 1.4 based on the data available but by the same token as above this figure will vary with service condition and Reynolds number so we could say there as well that since this is difficult to determine and varies we just don’t know so why bother.

 

The wind tunnel data for both the CYH and NACA 230 was gathered by NACA career professionals in the same manner using the same methods and procedures so I think they are pretty good for comparisons. I'm not ready just yet to give up and say it's difficult so let's not even try and to be honest Clmax = 1.39 sound quite high for the Yak given that it has a CYH profile with the reflexed trailing edge. AFAIK the 2R1 profile used on the Me-109 is supposed to be quite close to the NACA 230 so I would be surprised if the Yak with its CYH profile was as good on this point.

 

Last but not least: Are you sure that the “0 deg” figure for the Yak refers to zero twist and not the profile angle of attack versus some datum line? If the Yak really did have no twist in the wing like the Me-109 then how did it manage to handle aileron control at stall? Because the Yak in game is fantastic in that regard and how was that possible without either twist or slats? If it turns out that the Yak designers actually manged to marry good handling with no twist and no slats then this I think would go some way to explain a high Clmax given that also the outer portions of the wing can contribute more since they will be at a higher angle of attack than if twist was present.

 

Finally, I have forwarded the question of the Yak Clmax and wing twist and some other interesting questions to someone I know who has access to a lot of aeronautical data and knowhow and who may be able to dig something up if he can spare the time.

[JtD]

Well, it is the profile angle of attack against the datum line, but you'd sometimes get this figure for both root and tip, if there's twist.

 

And what would be the point in choosing a profile with a flat bottom for ease of production and then built twist into it, so that it's not easy to produce any more?

 

But it's good if you forwarded this, because the only definitive I have at the moment is that statement from the manuals.

 

As for the rest, I think we're pretty much on the same page.

[Crump]

Standard roughness generally is used to represent the lift characteristics of an airfoil after a moderate icing event. It is defined as .0011 sand grains on a 24 inch chord airfoil applied to the leading edge of the airfoil to 8% chord covering. Depending on the chord...that 5% to 10% of airfoil surface.

 

 

The NACA further defined a series of numbered roughness standards that represent everything from bugs to minor surface manufacturing defects.

 

Those are not standard roughness.

[Crump]

Well, it is the profile angle of attack against the datum line, but you'd sometimes get this figure for both root and tip, if there's twist.And what would be the point in choosing a profile with a flat bottom for ease of production and then built twist into it, so that it's not easy to produce any more?But it's good if you forwarded this, because the only definitive I have at the moment is that statement from the manuals.As for the rest, I think we're pretty much on the same page.

Camber and airfoil characteristics can be used to mitagate the stall without wing twist.

 

The Clark Y series is unique in the fact it has several scaling methods. The Yak -1 used the Clark YH 14% root and Clark YH 10% tip.

[Crump]

 

 

If you just take a look at the 23015 data Crump's posted here, you have data for the smooth airfoil, and for standard roughness. According to NACA, this is (paraphrasing) "worse than manufacturing quality and service conditions but better than conditions in mud, snow or battle damage". It reduces clmax from 1.65 to 1.2, just to illustrate my point.

 

 

 

Standard roughness generally is used to represent the lift characteristics of an airfoil after a moderate icing event. It is defined as .0011 sand grains on a 24 inch chord airfoil applied to the leading edge of the airfoil to 8% chord covering. Depending on the chord...that 5% to 10% of airfoil surface. 

 

Standard roughness is not representative of manufacturing quality, service conditions, or any kind of normal aircraft operation.  

 

Although all icing events are bad, Snow and frost is actually worse than moderate icing events because of the amount of area it covers.  There are no tolerance for any snow or frost on the critical surfaces of an airplane.  You simply cannot safely fly the aircraft.  You can see from the 2D polars the differences in lift characteristics and generation an airfoil exhibits.


The NACA further defined a series of numbered roughness standards that represent everything from bugs to minor surface manufacturing defects.

Those are not standard roughness. 

[Crump]

 

 

So we can say with certainty the 2D airfoil could produce a CLmax ranging from 1.5 to 1.7

 

That is the take away from examining the wing design, construction, and airfoil selection Focke Wulf used.  Anything that does not fall within that range is simply incorrect.  A complete measured polar of the aircraft will produce an airplane CLmax of ~.2 less than the 2D data. 

 

Hint:

 

If you do the Re math for the NACA 23015 airfoil at speeds the FW-190 could fly.......

 

It comes out to 1.6.  1.6 - .2 = 1.58

 

Craziness, huh?

You can do the same thing to the Yak-1 wing design and see what the CLmax for the wing MUST deliver.  If it does not, then it is not a Yak-1 wing.

[Crump]

BTW,

 

That data must be used with subsonic incompressible flow theory and used correctly in order to predict aircraft performance.  The reason subsonic Incompressible flow theory has been in use for over 100 years to determine the performance and behaviors of high aspect ratio winged aircraft at velocities below ~1.2 mach is the fact it is accurate.

 

More complicated math theory does not deliver increased accuracy.  In fact, it can do the exact opposite because increased complexity means increased assumptions.  That is why there is such a huge variation in compressible flow theory predictions.

 

AAIA determined for an established design, the margin of error between the 6DOF equations of motion and subsonic incompressible flow theory for a maneuvering aircraft is about 1.5%...

 

It simply comes down to Newtons basic law of F=Ma which all aircraft performance math is derived from.......l

[JtD]

That is the take away from examining the wing design, construction, and airfoil selection Focke Wulf used.  Anything that does not fall within that range is simply incorrect.  A complete measured polar of the aircraft will produce an airplane CLmax of ~.2 less than the 2D data.

Pretty much what I'd be expecting, too.

 

Hint: 

If you do the Re math for the NACA 23015 airfoil at speeds the FW-190 could fly....... 

It comes out to 1.6.  1.6 - .2 = 1.58

Craziness, huh?

1.6 - 0.2 = 1.4

 

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Holtzauge, any news from your contact regarding (no) wing twist on the Yak-1?