Ракеты в DCS

[nighthawk2174]

4 hours ago, MA_VMF said:

the advantage of the lattice is that it can be made smaller than a monoplane wing, while maintaining the same torque as a monoplane fin

Yes however at the cost of drag especially in the M0.7-M2.5 region. Ultimantly thrust vectoring is a far more appealing solution without really any downsides apart from complexity.

 

3 hours ago, okopanja said:

Not sure why so much discussion on grid fines, especially in sub-sonic and transsionic range:

1. Launch platform can accelerate beyond transsonic range

2. majority of DCS missiles are between 2-3 Mach when they hit, which means the aircraft and missiles are most of the time in super sonic range.

Therefore what matters is actual performance in super sonic range. 

1 - It can but often at the cost of high fuel consumption.
2 - True but chocked flow still persist even past the transonic its not until the shocks are at a low enough angle they do not interact till well aft of the lattice that flow becomes unchocked.
3 - Even then you will generally still have more drag when comparing similarly sized fins, based on actual dimensions not reference area, due to higher area. Even at higher mach regimes their drag coefficients do leave something to be desired when compared to monoplane.

[okopanja]

35 minutes ago, nighthawk2174 said:

3 - Even then you will generally still have more drag when comparing similarly sized fins, based on actual dimensions not reference area, due to higher area. Even at higher mach regimes their drag coefficients do leave something to be desired when compared to monoplane.

Do you happen to have charts which demonstrate this difference?

Edit: or these charts from before were calculated or measured?

Edited July 4 by okopanja

[MA_VMF]

6 часов назад, nighthawk2174 сказал:

Yes however at the cost of drag especially in the M0.7-M2.5 region. Ultimantly thrust vectoring is a far more appealing solution without really any downsides apart from complexity.

it depends on the shape of the lattice, and the upper limit may be less than 1.5M

[tavarish palkovnik]

Tomorrow I could have some free time for one experimental work.

Rocket 9M79 has grid fins and for this rocket I have plenty of inputs for testing. Motor is fully known in all aspects so it’s work with gradual changing of altitude can be very precisely modeled. Trajectory to maximal distance is also known, how many seconds flight takes etc etc 

Only what is unknown is drag coefficient function to match max distance in exact time. 
 

At the moment, because I already made program base, to match it passive i58 should be 1,25 and tomorrow I will calculate what could be i58 for rocket without fins and for rocket with some classically shaped fins in reasonable size. I don’t expect some huge difference but we will see when results drop out 

[okopanja]

5 minutes ago, tavarish palkovnik said:

Rocket 9M79 has grid fins and for this rocket I have plenty of inputs for testing. Motor is fully known in all aspects so it’s work with gradual changing of altitude can be very precisely modeled. Trajectory to maximal distance is also known, how many seconds flight takes etc etc 

This might be too large and not very manouverable missile.

The paper nighthawk reference above is missing some important information, but most importantly makes some assumtpions on deflection angles.

Is it known what is the minimal deflection angle for e.g. minimal, medium and large corrections?

E.g. I would expect that deflection angles of traditional fins is larget than for grid fins, due to lower efficiency.

[tavarish palkovnik]

27 minutes ago, okopanja said:

E.g. I would expect that deflection angles of traditional fins is larget than for grid fins, due to lower efficiency.

And what larger fin deflection, larger possibility of air stream sliding over fins, larger angle of attack of rocket in general make as result in final dragging 

[nighthawk2174]

On 7/5/2025 at 11:04 AM, okopanja said:

This might be too large and not very manouverable missile.

The paper nighthawk reference above is missing some important information, but most importantly makes some assumtpions on deflection angles.

Is it known what is the minimal deflection angle for e.g. minimal, medium and large corrections?

E.g. I would expect that deflection angles of traditional fins is larget than for grid fins, due to lower efficiency.

ADA509444.pdf Is a publically availble doc that has data up to M5.0 with more information, its results agree with the one I posted and is a source of wind tunnel data used by other reports.
 

What assumptions on deflection angles did it make that you are questioning?

Traditional fins will need larger deflections but at the same time their far more efficent with those deflections and have less 0 aoa drag. The biggest thing is the reduction in hinge moment per unit of aoa you want to get too, that is where the lattice has its largest advantage over a planar fin.

Just as an example lets say the missile needs to generate 300 lbs of lift per fin at M2.5 for whatever manuver it will be doing at that moment (I assumed 1000ft at STP for aero values). This would be what i'd probably clasify a "light-medium" correction considering you'd get thousands of lbs of angular force from all 4 fins. Using the data in the first report to generate 300lbs of lift the lattice fin will be at ~0.7-1.1deg aoa and the planar at ~3.8-4.2deg. At those angles the gridfin will generate nearly 15x the drag (60lbs vs 805lbs) or a L/D of 5.0 vs 0.38. Keep in mind this is also with a very suboptimal planar fin design used in the study. This drag penatly is why these types of fins are not in use for A/A missiles anymore. They make a lot more sense on ballistic missiles or bombs. Where the low hinge moments are very usefull and the drag penalty not as big a concern. In the paper I listed newer shapes of the lattice that were tested can cut the drag from 25-40% depending on mach and exact shape but the R77's fins are not one of these and even then planar fins still have better L/D.

Edited July 7 by nighthawk2174

[okopanja]

9 minutes ago, nighthawk2174 said:

What assumptions on deflection angles did it make that you are questioning?

Mainly the deflection angles used for one vs other approach. Due to the greater efficiency the drag comparison should not occur for same angles, but rather those that match equivalent performance of control surfaces.

[MA_VMF]

53 минуты назад, nighthawk2174 сказал:

Keep in mind this is also with a very suboptimal planar fin design used in the study. This drag penatly is why these types of fins are not in use for A/A missiles anymore. They make a lot more sense on ballistic missiles or bombs. Where the low hinge moments are very usefull and the drag penalty not as big a concern. In the paper I listed newer shapes of the lattice that were tested can cut the drag from 25-40% depending on mach and exact shape but the R77's fins are not one of these and even then planar fins still have better L/D.

Complete nonsense

As we can see, the honeycomb design surpasses the monoplane fin to speeds of 2.5M.

L/D

null

Edited July 7 by MA_VMF

[nighthawk2174]

1 hour ago, MA_VMF said:

Complete nonsense

As we can see, the honeycomb design surpasses the monoplane fin to speeds of 2.5M.

L/D

null

Can you post the definition of Kmakc. 

Another study to prove my point; data is from the US army supersonic wind tunnel with the reference area being idential between the two fins. Appears to be a study of using GMLRS body as a base with a planar and grid fin design. Study utilized CFD and supersonic wind tunnel testing and data. DREV is data from the wind tunnel.

null

nullOnce again in this study a suboptimal design was used for the planar fin as it was just a rectangle with a double wedge chord shape. Not to mention it was extremly large.
nullNumerical Investigation of Aerodynamics of Canard-Controlled Missile Using Planar and Grid Tail Fins. Part 1. Supersonic Flow

[MA_VMF]

41 минуту назад, nighthawk2174 сказал:

Can you post the definition of Kmakc. 

Kmax=L/Dmin . This is the ratio at which the lifting force is greater than the drag at a certain angle of attack.

[nighthawk2174]

5 minutes ago, MA_VMF said:

Kmax=L/Dmin . This is the ratio at which the lifting force is greater than the drag at a certain angle of attack.

Do you have the page which defines this value what you say here is confusing. L/Dmin is a very atypical expression to be used to analyze L/D ratios. As minimum drag will occur at Cd_aoa=0 and even more so if you mean minimum Lift over drag? And per your description this would describe the point where L/D>1.0?

I should also note based on the studies i've listed peak L/D efficency for the planar fins occur in the 3-6deg range. While lattice's are much higher often double this.

[MA_VMF]

7 часов назад, nighthawk2174 сказал:

As minimum drag will occur at Cd_aoa=0

by Aoa=0 L=0;

7 часов назад, nighthawk2174 сказал:

I should also note based on the studies i've listed peak L/D efficency for the planar fins occur in the 3-6deg range. While lattice's are much higher often double this.

According to the presented work, AoA <= 1 degree

[nighthawk2174]

1 hour ago, MA_VMF said:

by Aoa=0 L=0;

According to the presented work, AoA <= 1 degree

Yes hence my confusion, your description of Kmax doesn't make much sense 

 

 

And as described above for a moderate lifting load aoa difference is a few degrees.

Edited July 8 by nighthawk2174

[MA_VMF]

2 часа назад, nighthawk2174 сказал:

Yes hence my confusion, your description of Kmax doesn't make much sense 

 

 

And as described above for a moderate lifting load aoa difference is a few degrees.

The research you're showing is complete nonsense

Edited July 8 by MA_VMF

[nighthawk2174]

5 hours ago, MA_VMF said:

The research you're showing is complete nonsense

Yeah right, its up to you to prove the supersonic wind tunnel data in the following reports, which align with the one with the charts, are nonsnese. Grid fins experience more drag per unit of lift across most of their range especially at lower angles making the L/D much worse. Yes they produce more lift per unit of aoa, with less hinge moment, but at the cost of substantially more drag across their entire range. Hence why their not everywhere on air-to-air missiles.


ADA509444.pdf

Numerical Investigation of Aerodynamics of Canard-Controlled Missile Using Planar and Grid Tail Fins. Part 1. Supersonic Flow

DTIC ADA426637: Aerodynamic Analysis of Lattice Grid Fins in Transonic Flow : Defense Technical Information Center : Free Download, Borrow, and Streaming : Internet Archive

[MA_VMF]

null

[MA_VMF]

AoA=20, L/D=2.5 

[nighthawk2174]

1 hour ago, MA_VMF said:

AoA=20, L/D=2.5 

Could you define a few of the other variables listed here such as t_bar/H_bar/m/n (where _bar just indicates it has a bar over it)

null

Yes and in the document I posted, the original one, they get ~2.4-2.5 L/D. The NAO wind tunnel paper with a slightly different gridfin design gets a hair over 3.3 L/D for M4.0 but for the fin only no body. 

[MA_VMF]

t_bar=relative grid pitch, t/b

H_bar= relative height of the grid H/L

n-The number of plans in the grid

[MA_VMF]

null

[okopanja]

19 minutes ago, nighthawk2174 said:

Could you define a few of the other variables listed here such as t_bar/H_bar/m/n (where _bar just indicates it has a bar over it)

null

Yes and in the document I posted, the original one, they get ~2.4-2.5 L/D. The NAO wind tunnel paper with a slightly different gridfin design gets a hair over 3.3 L/D for M4.0 but for the fin only no body. 

Still munching over the document you sent, but wanted to ask why were they so concerned about roll stability? E.g. how does it influence maneuverability and drag when it actually flies (no wind tunnel or simulation)?

E.g. the use cases for these missiles and guidance configuration look different, is the controlling function achieved with rear fins or canards in front?

[nighthawk2174]

2 hours ago, okopanja said:

Still munching over the document you sent, but wanted to ask why were they so concerned about roll stability? E.g. how does it influence maneuverability and drag when it actually flies (no wind tunnel or simulation)?

E.g. the use cases for these missiles and guidance configuration look different, is the controlling function achieved with rear fins or canards in front?

Roll stability is important in that while manuvering if you are unstable in roll small pertubations can induce roll oscilations which you have to counteract with your control system. You can get long term periodic oscilations which are highly undesirable such as dutch roll if you are lacking roll stability. This can increase miss distances or reduce the efficency of the control system in general. For the army study this would be critical for reducing miss distances of guided muntions like glmrs.


For the army document the point was more so to analize performance between nose control canards and tail control lattice fins. 

[MA_VMF]

Mach=2.5, AoA=5 

null L/D-4.5

Edited July 9 by MA_VMF

[nighthawk2174]

23 minutes ago, MA_VMF said:

Mach=2.5, AoA=5 

nullL/D-4.5

2D only flow?