Degraded Su-27 aerodynamic lift - Page 22 - ED Forums
 


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Old 03-01-2018, 03:00 PM   #211
GGTharos
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I think you're misinterpreting some things - these aren't hard limiters like the FBW on the M2K. They're there to provide awareness. All pilots are fairly experienced by the time they drive a flanker and the exact utility of these devices is taught to them.

You can expect any flanker pilot to pull right through this the moment they want to rate, especially at lower airspeeds.

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Originally Posted by HWasp View Post
In my opinion the purpose was to enable experienced pilots to get that last little bit of performance out of the aircraft at the expense of safety.

I think what the authors mean by that statement is that generally it does not worth the risk to go beyond limits. But also I have never seen an aircraft manual, that says: yea just go disregard any limits, it will be good for you
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Old 03-01-2018, 03:01 PM   #212
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Thank you guys.

Quote:
Originally Posted by HWasp View Post
In one of my previous posts I have already given you the page number (14\269) where it clearly states the AoA limitations depending on Mach number. (Cannot upload from my tablet sorry)

Also, again I am aware of the basics.

I think that the purpose of a limiter should be to hold the limitations Also, since pulling through the limiter might be dangerous, I don't think that it was meant to be overriden by the average pilot all the time.
Looking forward to seeing what you have for us once you get back home. I'm here to learn, as I am not good at pointing out what's wrong with the FM or anything about aerodynamics. I find this discussion interesting and I'm very interested in seeing the DCS FM compared to the real thing.
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Old 03-01-2018, 03:02 PM   #213
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Quote:
Originally Posted by GGTharos View Post
The rule is to not use direct control (which some people use in dogfights! In a dogfight, realistically, you probably wouldn't be reaching for that switch anyway - and it isn't necessary either). The limiter can be pulled through by applying more force to the stick ... no need to turn it off RL.
I thought that was not something they do IRL

One day I have had a long, guns only dogfight session with a friend of mine flying the Su-27 and I have found out that the best way to win the game is to go direct control before take off and switch it on for the landing only (IF there is a landing)

The plane is extremely responsive in that config, but of course I would not even think about it in a real plane.

My observation is that the limiter is too restrictive and it holds the aicraft way too far from it's real capabilities. In my opinion this might have something to do with the constant 22 deg AoA limit...
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Old 03-01-2018, 03:04 PM   #214
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Correct Ironhand.

The speed on the stick deflection is something the limiter takes in count to activate the extra force needed. And is a sum of all this things, shaking, extra force-sttifening, and in the edge a force to the center that must be counter also.

More precisely i think is the speed in the amount of G or AoA increasing at any given moment.

Another thing is Direct Control. If by this you mean turning off the FBW ( the famous S key in DCS ) this is completly FORBIDDEN in the manual. Is extremly dangerous and you can crash the plane very easy.
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Old 03-01-2018, 03:10 PM   #215
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Quote:
Originally Posted by Esac_mirmidon View Post
...

Another thing is Direct Control. If by this you mean turning off the FBW ( the famous S key in DCS ) this is completly FORBIDDEN in the manual. Is extremly dangerous and you can crash the plane very easy.
I don't go anywhere near that switch except for demonstration purposes. It's a good way for the unwary to lose the aircraft.
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Old 03-01-2018, 03:11 PM   #216
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Quote:
Originally Posted by HWasp View Post
I think that the purpose of a limiter should be to hold the limitations Also, since pulling through the limiter might be dangerous, I don't think that it was meant to be overriden by the average pilot all the time.
AFAIK the F-15 doesn't really have one and in the MiG-29 there is no separate switch to turn it off - it is just stick pull through. In the Hornet there is a paddle switch on the stick that allows overriding the limiter by pulling it at stick position close to full aft.

Don't really see why overriding the AOA limiter should be less permissable in the Su-27 - aren't we confusing it with disabling the FCS as such(direct control)?

Edit: what Esac_mirmidon said
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Old 03-01-2018, 03:14 PM   #217
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Or your BFM is poor ...

Quote:
Originally Posted by HWasp View Post
My observation is that the limiter is too restrictive and it holds the aicraft way too far from it's real capabilities. In my opinion this might have something to do with the constant 22 deg AoA limit...
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Old 03-01-2018, 03:37 PM   #218
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Quote:
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Or your BFM is poor ...
That may well be

But still, back to the manuals.

1. The flight envelope on pg 20/269 shows that 8 g is available for the airframe at around M 0,46 (550kmh) at 21400 kg (this should be absolute max. with limiter override)

2. The other graph at 51/269 shows max 6g at 600 kmh and 8 g at 740 kmh (Much less, obviously)

In my opinion this means, that pg 20 shows the values without the limiter and pg 51 shows the operational values, with the limiter.

If that would be true, then the problem is that the plane does not reach the values according to the pg 51 graph.

In this case I can not understand why the limiter would not increase it's limit to 24 deg according to the Mach vs AoA limit on page 14 so that it could meet the performance data on page 51.
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Old 03-01-2018, 03:48 PM   #219
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Quote:
Originally Posted by Esac_mirmidon View Post
I´m not sure about your last statement.



In the Su-27SK manual also there are a explicit reference about "Turning Off the limiter during acrobatic maneuvers doesnt give any apreciable gain in maneuvrability and is possible to make the plane stall or exceed the load limits"
Having a huge margin would disagree with this statement from the manual.
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Old 03-01-2018, 03:50 PM   #220
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What margin are you talking about?

There are an AoA-G limit the pilot can bypass with brute force on the stick ( 17 Kg ). Turning off the limiter is not increasing the maneuvrability of the Su-27 in an appreciable marging and is making the flight more easy to enter a stall or spin or overstreesing the airframe. That all.

You can bypass the limit for extra AoA or G in some circunstances just pushing or pulling more on the stick, knowing the danger you are taking, but the benefits are marginal and the danger, big.

Also there is a big difference between the limiter logic in the former Su-27. and the newer Su-35 ( also i think the Su-27SM series). In the original versions the logic was some sort of a fixed value for a fixed weight, but in newer Su-27/Su-35 versions this limiter logic is much more "inteligent" and dynamic taking in count more parameters for beeing more precise at different weights, speeds, maneuvers, etc.
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