R-27 Control Surfaces

[Cmptohocah]

I was wondering if someone could help me understand this topic:

 

R-27 seems to have much larger relative control surfaces then some other A2A missiles like (AIM-7/9/120). Why is that so? What is the benefit/disadvantage of having such large surfaces compared to the other ones that don't?

[Airhunter]

Disadvantage is drag, advantage is lift and controlability at subsonic speeds. It's a fairly old design.

[Cmptohocah]

So it should then slow down more quickly and be more maneuverable relative to its NATO counter parts, right?

[Cmptohocah]

I just realized I have posted in the wrong sub-forum. This thread was meant to be started in "Flaming Cliffs 3.0" and not in "F-15".

[GGTharos]

So it should then slow down more quickly and be more maneuverable relative to its NATO counter parts, right?

 

No. It is basically the same control setup as the AIM-7, ie. mid-body movable wings as control surfaces. Both missiles can achieve ~25g. We might be able to see some differences once ED does their CFD analysis, which could be interesting. The R-27 is also HEAVY.

 

Differences from more modern MRMs - those are tail-controlled, allowing better control, higher AoA and more maneuverability while using less motive power for the fins.

 

A lot of SRMs were front-fin controlled as well, which have similar advantages but not quite the same. A lot of SRMs are switching to tail-control now.

[Airhunter]

27R/ER also has a target G limit of 8G's. It's not a turner by any means.

[GGTharos]

I believe that this is a non-nuanced view. Yes, 25g turning ability yields 8g for the target because the N in PN is ~3. In practice the amount of g you need to escape may be quite a bit more than this depending on intercept geometry and the target's own maneuver capability. It could also be less based on a bunch of factors.

 

If you turn in-plane with the missile don't be surprised if it ends up keeping up with a higher g turn.

[HWasp]

Correct me if I'm wrong, but Aim-7 is around 230 kg while R-27R is 250kg. Why do you consider it HEAVY with capital letters?

[Boogieman]

My guess is he is referring to the extended range variants (ET/ER) which are ~100kg heavier than the baseline iterations IIRC.

Edited June 24, 2020 by Boogieman

[FoxAlfa]

Also keep in mind that most of the weight difference is rocket fuel, and it tends to go outside of the missile pretty fast...

[GGTharos]

Yes, I was referring to the ER. The non E has ~60kg of fuel, and so does the AIM-7. Here the AIM-7 wins in fuel fraction, and overall is a lighter missile when the fuel is expended.

 

IIRC the ER has a whopping 130kg of fuel (don't quote me on it, it has been a long time since I saw the figures) and it will weigh some 220kg when that is expended.

[Cmptohocah]

...The non E has ~60kg of fuel, and so does the AIM-7. Here the AIM-7 wins in fuel fraction, and overall is a lighter missile when the fuel is expended.

 

I guess this would mean that R-27 should be more manoeuvrable is the fuel-burning stage, compared to AIM-7 in this case (similar weight, bigger control surfaces) and once the fuel has been expended they should manoeuvre the same or the AIM-7 should have the advantage and the R-27 should loose more speed 'cause of bigger drag.

[FoxAlfa]

I guess this would mean that R-27 should be more manoeuvrable is the fuel-burning stage, compared to AIM-7 in this case (similar weight, bigger control surfaces) and once the fuel has been expended they should manoeuvre the same or the AIM-7 should have the advantage and the R-27 should loose more speed 'cause of bigger drag.

 

The good thing is R-27 flight model is getting updated to the new standard now so we should see improvements in turning performance, hopeful it will make it in the next patch.

 

Currently the R-27 flight model is quite old and made to older standard so it is not a straight forward comparisons to the updated flight model of the Aim-7

[BlackPixxel]

If I understood it correctly R-27 (and R-77) will receive a drag change to their current FM next month, as a temporary "fix" until the complete overhaul is done.

 

I hope ED does not delay the proper CFD & autopilot update for the R-27 to much, but I am afraid they will.

[ZHeN]

looking at how lately ED reacts to red stuff, I wouldn't be surprised if the CFD update would actually nerf the missile, instead of buffing :D don't hold your breath boys, if you don't wanna be disappointed

[FoxAlfa]

looking at how lately ED reacts to red stuff, I wouldn't be surprised if the CFD update would actually nerf the missile, instead of buffing :D don't hold your breath boys, if you don't wanna be disappointed

 

I understand a 'lack of faith' since Red stuff was on back burner for awhile and got to a derelict state, and we might not agree with their focus but ED does good work.

 

And based on IASGATG and nighthawks work we should see improvements, not necessarily in straight line range, but for sure a millisecond notch or limited maneuver won't defeat the missile.

Edited June 25, 2020 by FoxAlfa

[Airhunter]

looking at how lately ED reacts to red stuff, I wouldn't be surprised if the CFD update would actually nerf the missile, instead of buffing :D don't hold your breath boys, if you don't wanna be disappointed

 

Doubt it, if anything we'll have a significant drag reduction in most areas and better, more energy conserving guidence, which in turns extends the maximum range and increases energy retention. The main goal of this CFD treatment is for the missile to be believable and not hit a brick wall at certain speeds or do irrational guidence corrections all the time. Don't expect it to be able to compete with AMRAAM's or Phoenixes but even a marginal increase in reliability would be very welcome. The biggest issue with it is the fact that we only have arcady and very simplified FC3 platforms to launch it from, which is some cases may be a good thing (fast target acquisition and reaction time) but sometimes can be a bad thing as well (losing lock too easy based on aspect or radar going for chaff).

 

It will for sure be interesting to see the results. I do hope we can all the main missiles reworked by the end of the year (R27, R77, all AIM-9's, AIM-54 and further improvements to the Sparrow and Amraam).