Degraded Su-27 aerodynamic lift - Page 15 - ED Forums
 


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Old 02-25-2018, 12:53 AM   #141
Maverick Su-35S
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Quote:
Originally Posted by Esac_mirmidon View Post
...
I don't know what was the reason for this reply as I was saying the same thing. I admit I didn't also tell that the effective AoA decreases (defined by the affected chord line), thus lift coefficient decreases, so I only focused on it's primary role: increasing the critical AoA only (not moving the slope as flaps do) and logically, of course (maybe this I also forgot to say) the maximum lift by prolonging the lift slope.

But..., for what reason do you guys still like or want to call the droops as flaps? Because they act like plain flaps mounted on the leading edge? Seriously, it's not the first time when someone invents a new terminology which is not normally recognized and creates a lot of confusion and later contradictions. I know it's not you guys here who named the droops as leading edge flaps, but someone did that and it's wrong. There is only ONE leading edge device for which the name leading edge flaps came out... and those are the kruegers, nothing else.

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Originally Posted by Esac_mirmidon View Post
LE flaps are usually found at the outboard portion of the wing.
It's not a general rule where they are placed along the wing. They may be placed anywhere along the wing.
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Last edited by Maverick Su-35S; 02-25-2018 at 12:56 AM.
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Old 02-25-2018, 12:56 AM   #142
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In mobile so keeping it short.

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Originally Posted by Maverick Su-35S View Post
the Eagle has a higher STR than the Flanker at any airspeed for similar fuel percentage,
This is correct.

Quote:
which is utterly wrong and this is what I'm trying to point out more than everything,
And this is not, which is exactly why I keep saying that the only valid comparison is that of the aircrafts data to itself.

To make the point, you opinion on the relative performance here is irrelevant. The performance of the aircraft is what it is, period. You don't judge it by another aircraft's performance.

Quote:
How can the F-15 with no lerx, no droops (not slats) have such a great roll control even at 25 to 30 AoA,
Because the Eagle has a very effective ARI, huge rudders and a lighter airframe.

Eagle AoA capability is available from NASA studies and was used to tune the FM.

Quote:
while the Flanker's roll control (which should be enhanced in comparison to the Eagle) is badly degraded above 17..18 AoA for the same amount of beta (sideslip angle).
While the FLANKER has more inertia, may or may not have an effective ARI, longer wings and so on.

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For me, it's case not closed until the truth wins!

Regards!
No, the case IS closed. While you may want to satisfy your curiosity as to how and why these things are, the performance simply is what it is. The Eagle matches its own data and so does the flanker.

If you want to prove something is wrong, price that the data doesn't match.

I'll reiterate again that opinions of who should be outturning who are invalid for pretty much everything FM related.
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Old 02-25-2018, 12:59 AM   #143
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There are a lot of publications naming that Leading Edge Flaps but if the exact term is Leading Edge Droops or simply Droops is ok for me.

But there are multiple sources calling that Leading Edge Flaps. Books, internet pages and several publications. Is not me, is just hundreds of references around internet using that terminology.

Why this name is used so often is out of my knowledge but is a fact that LEF is used a lot.
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Old 02-25-2018, 01:53 AM   #144
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Quote:
Originally Posted by Bushmanni View Post
The OP's argument that F-15 turns better than Su-27 in DCS is just plain wrong. I don't know where he has gotten this idea and anyone who knows how to BFM can see it themselves by tryin it out (assuming both have realistic combat fuel load that gives similar endurance). I haven't done any accurate measurement if the FM has changed very recently but I cant feel any major difference in it.
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Originally Posted by Maverick Su-35S View Post
Well, then you talk without knowing what's going on in DCS atm. Test, then come back!
I did a very quick test with "competitive" BFM fuel setting (71% for F-15 and 55% for Su-27) which gives them same endurance on full AB at 5000m (things might have slightly changed since these settings were tested last time) and 2 heat seeking missiles. F-15 could sustain ~18deg/s at ~460KCAS and Su-27 could sustain same ~18deg/s but at ~325KCAS so Flanker could turn as fast as Eagle while doing it inside Eagle's turn circle. If that's not an turning advantage for Su-27 then i don't know what is.
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Old 02-25-2018, 08:03 PM   #145
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Originally Posted by bbrz View Post
Yes, I'm talking about the F-15C and that buffeting/flow separation starts at 8deg is a fact, straight from NASA/MCD data.
Then tell ED to implement it! In DCS the F-15 finds a constant CL increase up to 35 AoA. How is that compared to the very low critical AoA you suggest? Like I said, you only know 2D aerodynamics!

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Originally Posted by bbrz View Post
...your knowledge about aerodynamics and performance is surprisingly limited (despite your signature)and you are apparently trying to prove something by referring to tables and links you don't even understand, like e.g. the wrong statement that Krueger flaps are the only type of LE flaps and how the various LE devices actually work.
I guess you are the one who's limited in aerodynamics knowledge by what you wrote all along, and I'm not the only one contradicting you on things. I do have a background for more than 10 years in this domain and I didn't waste time on just one direction, you only have words so far and regarding the leading edge flaps, I have never head of (although it wouldn't matter much) anything else than kruegers. The droops are normally not regarded as leading edge flaps, but non-slotted slats if I may call them this way (because slats are of only one type = with gap).

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Originally Posted by bbrz View Post
This has become a jungle of endless quotes and replies from your side and most likely your next reply will consist of even more quotes and replies. Way too time consuming for me.
For me it's not time consuming as long as good things can also come up.

Regards!
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Old 02-25-2018, 08:10 PM   #146
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Quote:
Originally Posted by bbrz View Post
This link contains one of the rather bad descriptions for LE flaps/droops and I agree with Mr.Kämpf who wrote: Your graph shows an exceptionally poor representation of a typical LE device.
If they would work as described they could really be used on the outboard section of the wing, but since they actually don't (noticable) increase the critical AoA they are usually used only on the inner section of the wing e.g. 747, A380.
The droops don't increase the critical AoA...! You are very none sense my friend! Sorry, but that graph is correct! The droops reduce your effective AoA (thus the null AoA lift drops or becomes negative) and increase the critical one. Exactly what you told me (regarding aerodynamics knowledge) matches you in fact...!
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Old 02-25-2018, 08:13 PM   #147
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Quote:
Originally Posted by Maverick Su-35S View Post
Then tell ED to implement it! In DCS the F-15 finds a constant CL increase up to 35 AoA. How is that compared to the very low critical AoA you suggest? Like I said, you only know 2D aerodynamics!


CL should increase up to 40deg AoA.

Last edited by SinusoidDelta; 02-25-2018 at 08:21 PM.
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Old 02-25-2018, 08:43 PM   #148
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Quote:
Originally Posted by GGTharos View Post
In mobile so keeping it short.
To make the point, you opinion on the relative performance here is irrelevant. The performance of the aircraft is what it is, period.
I only wish you were right, but I can't agree that the DCS F-15C respects the real plane's wing lift performance cause in the end this is what mostly affects a plane's turning ability (besides T to Drag ratio and wing loading).

Quote:
Originally Posted by GGTharos View Post
You don't judge it by another aircraft's performance.
Why not? I'm forced to use other references such as the F-16C if I haven't seen a chart of the F-15's performance from ED which matches our plane in DCS and which totally differs from what I see on the internet (the charts that we can find).

The best F-16C (GE powered) can't do a 360 in less than 14 seconds, but our Eagle with no LE devices, no lerx is much better than the best, by doing it about +13 at 25% fuel. I trust the true F-15C's performance only so far, not what I see in DCS at the moment, which I find deliberately exaggerated and I believe that someone at ED wanted/liked it this way.

Quote:
Originally Posted by GGTharos View Post
Because the Eagle has a very effective ARI, huge rudders and a lighter airframe.
I was talking about roll rate? There is a basic knowledge problem here if you say that weight affects roll rate. The Flanker doesn't have ARI? The Flanker has even bigger rudders if this is what you're looking at, but that's not what matters for a rolling acceleration and rate to gain a specific value. What matters is the ratio between the resultant aerodynamic moment to rolling inertia moment.

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Originally Posted by GGTharos View Post
Eagle AoA capability is available from NASA studies and was used to tune the FM.
At the moment, I do not trust that the way it was tuned reflects the same values found by NASA as I do not believe that what I see in DCS reflects the real plane, sorry!

Quote:
Originally Posted by GGTharos View Post
While the FLANKER has more inertia, may or may not have an effective ARI, longer wings and so on.
Again, I was talking about roll rates, not moments and yes, the wing span and the relative aileron area to that of the wing, the relative aileron span to that of the wing and it's position along the wing affect the resultant roll rate, but the general sense tells that if the F-15 has very much lower aileron span and area to wing ratios than that of the Su-27 and if the Su-27's flight controls and aerodynamics are correctly modeled in this area, the F-15's achievable rolling rate should by logic be lower for the same AoA not higher.
[/QUOTE]
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Old 02-25-2018, 08:44 PM   #149
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Quote:
Originally Posted by SinusoidDelta View Post


CL should increase up to 40deg AoA.
Ok, but is this extracted from DCS's FM or is a NASA result?

Regards!
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Old 02-25-2018, 08:47 PM   #150
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Quote:
Originally Posted by Maverick Su-35S View Post
Ok, but is this extracted from DCS's FM or is a NASA result?

Regards!
NASA’s test data
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