Rudder effectiveness

[iFoxRomeo]

Yawing when the rudder is applied should result in the outside wing rising due to the effects of dihederal, and the fact that the outside wing will present a larger frontal section due to the sweep of the wings.

 

It should therefore raise that wing, and the plane should enter a turn due to the bank angle inducing a velocity vector.

 

Maybe you missed it, but people here are not talking about a banked turn.

The flat turn is the problem. The DCS Sabre cannot do a flat turn. That is what makes the people here scrach their heads. Every other jet and prop aircraft in the DCS World can perform flat turns.

 

...

 

Try using the rudder at low speeds, and see if it is more effective. At higher speeds, it should have no effect at all as far as I understand things. The Rudder is very small in the F-86 anyway, so the chances are that it is very ineffective in comparison with other aircraft.

The second part of my video is at 150-160Kts. The DCS Sabre´s ruddereffectiveness is not dependent on the airspeed. It is simply not there at any speed, when trying to perform a flat turn.

 

...

Watch the video again. I point to a strange behaviour of the rudder itself. Ignore the yawing and banking for a moment.

To make it clear: In that video I do only make "digital" inputs to the rudder. Either full rudder or no rudder. But despite my "digital" input the rudder varies in its position.

 

Fox

[wolle]

Watch the video again. I point to a strange behaviour of the rudder itself. Ignore the yawing and banking for a moment.

To make it clear: In that video I do only make "digital" inputs to the rudder. Either full rudder or no rudder. But despite my "digital" input the rudder varies in its position.

 

Fox

 

Interesting observation, Fox!

[julian265]

I presume its because (good) simulations interpret stick/rudder input as a certain amount of force, rather than travel (at least for directly controlled surfaces like in WW2 aircraft).

 

This means that full computer pedal deflection equals full pilot force on the simulated pedal. Higher airspeed makes the simulated control surface harder to deflect, and hence full computer pedal deflection may not result in full simulated rudder deflection.

[NeilWillis]

Indeed, and also, have you tried deploying the airbrakes on the A-10C when it is not flying slowly - they don't fully deploy either - do you consider that to be a bug?

 

And can i ask you a very basic, pertinent question...

 

Why would you even try to carry out a flat turn in a Sabre? Why would you use the rudder at all other than to co-ordinate turns? I would equate that to complaining because your gear box explodes in a car travelling at 80 MPH if you try to engage first gear! It happens, but why would you want to do it other than to show you can't?

[aaron886]

Why would you even try to carry out a flat turn in a Sabre? Why would you use the rudder at all other than to co-ordinate turns? I would equate that to complaining because your gear box explodes in a car travelling at 80 MPH if you try to engage first gear! It happens, but why would you want to do it other than to show you can't?

 

Because this is a simulation. A good racing simulator these days models the exact damage you described. If you wanted to question the viability of his concern, best to do it directly, not by dismissing it.

[NeilWillis]

My suggestion was that you wouldn't CHOOSE to select first gear under those circumstances, disregarding the fact that the majority of racing cars these days have sequential gearboxes anyway, and nor would you choose to turn the aircraft with the rudder.

 

I'm not dismissing it, I am just pointing out that as bugs go, it is a little out there. I have also noticed that the Bf-109 won't accelerate through the sound barrier in a vertical climb. But hey, that's not supposed to happen either!

[f86enthusiast]

Indeed, and also, have you tried deploying the airbrakes on the A-10C when it is not flying slowly - they don't fully deploy either - do you consider that to be a bug?

 

And can i ask you a very basic, pertinent question...

 

Why would you even try to carry out a flat turn in a Sabre? Why would you use the rudder at all other than to co-ordinate turns? I would equate that to complaining because your gear box explodes in a car travelling at 80 MPH if you try to engage first gear! It happens, but why would you want to do it other than to show you can't?

 

Both you ailerons were just shot off or severed leaving only your elevators and rudder to get the bird home. How do you control your longitudinal axis at this point? By use of rudders. Without rudders Neil you are missing a considerable portion of the experience.

[Invisibull]

I personally find the rudder invaluable for kicking over the top of a loop at slightly over stall speed.

[King_Hrothgar]

I noticed this issue the first time I flew it after picking it up in the flash sale. I was strafing trucks and tried to make some minor corrections with the rudder. This is normal for me, it works in every other plane in every CFS I've ever played. But with the sabre here, the rudder did nothing. It would sideslip the plane ever so slightly but that's it. I could not walk the guns onto the target without rolling/pitching. The rudder is so ineffective, it might as well not be present. I wasn't going absurdly fast either, maybe 350kts at most.

[NeilWillis]

I said much earlier that I'd like to hear what the real F-86 rudder response at high speed was.

 

I take it we have no input from pilots that actually flew them? What you can do in other simulators is frankly irrelevant if you want realism, and the F-86 is accurately modelled.

 

So, can anyone actually shed real light on the matter instead of just wild speculations? Kicking a rudder in at the top of a loop is feasible. Kicking a rudder in at Mach 0.8 in a Sabre, given that it has flying elevators due to the reduced effects at high speeds - do you think the rudder would actually do anything? Assuming of course you could actually get it to move given the high aerodynamic forces involved.

 

So, ailerons being shot off might actually mean the only viable option is to punch out anyway. Or is reality not an issue for you arcade types?

 

So, instead of this pointless back and forth about how bad the rudder effects are, shall we try and establish what really happens when you kick in some rudder in a Sabre at high speeds, and not just jump to obvious, but probably erroneous conclusions without knowing what the designers had in mind, or what is actually feasible?

[Zentaos]

:)

[f86enthusiast]

I said much earlier that I'd like to hear what the real F-86 rudder response at high speed was.

 

I take it we have no input from pilots that actually flew them? What you can do in other simulators is frankly irrelevant if you want realism, and the F-86 is accurately modelled.

 

So, can anyone actually shed real light on the matter instead of just wild speculations? Kicking a rudder in at the top of a loop is feasible. Kicking a rudder in at Mach 0.8 in a Sabre, given that it has flying elevators due to the reduced effects at high speeds - do you think the rudder would actually do anything? Assuming of course you could actually get it to move given the high aerodynamic forces involved.

 

So, ailerons being shot off might actually mean the only viable option is to punch out anyway. Or is reality not an issue for you arcade types?

 

So, instead of this pointless back and forth about how bad the rudder effects are, shall we try and establish what really happens when you kick in some rudder in a Sabre at high speeds, and not just jump to obvious, but probably erroneous conclusions without knowing what the designers had in mind, or what is actually feasible?

 

I'll bite Neil, is the person who nurses back a jet with severed control cables or missing ailerons the arcade hero, or is the person who thinks a tactical aircraft cant make it back with rudder and elevator alone? Its called survival instinct Neil pass it on.

[Filament]

Y'know what? I'll add my 2 cents. More than that, did I vote with my wallet for this excellent-in-most-respects aircraft.

 

The rudder is wrong.

 

I don't care by how much, at what speeds, in what configuration, under what loads/wing-loading...blah, blah blah.

 

No 'real' aircraft would do that - especially in low-speed regimes. NO aircraft. Turbine or prop or glider. I don't care if a 'bunch' of rudder is added, so that we can tune our controller axis to dial it out! At least cross-wind landings, etc. are more 'believable.'

 

We can argue about 'how much' should be present at what speeds, etc....LATER.

Fix it.

Now.

It's wrong.

[NeilWillis]

 

We can argue about 'how much' should be present at what speeds, etc....LATER.

Fix it.

Now.

It's wrong.

 

 

I have already asked the question - how do you KNOW it is wrong? Ever flown a real Sabre?

 

Until we get someone here with hands on stick time, we are all just speculating according to our past experiences and I'll guarantee that none of these so-called experts have a clue how the real Sabre rudder behaved.

 

I'm still waiting for some empirical evidence that suggests the rudder is indeed buggy, and until anyone comes up with any substantive evidence, I remain utterly unconvinced. It does work, but it is simply very ineffective, and looking at the size of it, I'm frankly not surprised.

 

So no matter how many of you are adamant that it is wrong, you're wasting your pixels. Where is the evidence guys?

[Wolf_ofthe_North]

For 1950 standards it was cutting edge technology, introducing the all-flying tail, that was critically important at keeping the jet stable beyond red-line speeds.

 

 

Also in development since November 1949 was a major improvement to enhance controllability at and beyond critical Mach number. Called the “all-flying tail” or

“stabilator” (combination horizontal stabilizer and elevator), it was introduced on the NA-170/F-86E. Fully hydraulically powered and complete with an “artificial feel” system for tactile control force feedback to the pilot, the “all-flying tail” was relatively simple and very effective, permitting full control beyond “red line”. Impressed, the USAF ordered 111 F-86Es in January 1950.

 

"...aerodynamically, the Sabre was a very “slick” (low drag) design enabling excellent acceleration downhill, even with a Flight Manual imposed “Limit Mach” (later known as Velocity Never Exceed [V

Sabres v. MiGs, 1950-1953 Korea Dildey and Thompson © Osprey Publishing •

www.ospreypublishing.com 2013, p. 14

NE]) of 0.95M. It remained stable beyond “red-line”, although flight control was “touchy” in that regime. While control reversal was felt by pilots when above VNE, the F-86A’s hydraulically-boosted elevators – and later the F-86E’s “irreversible, all-flying” stabilator – minimized its effects to such an extent that it was fully controllable even on the other side of “red line.”

Id. p 21

So considering it had full control beyond .95 Mach, yeah I'd say we can conclude the rudder was an integral part of a pretty effective piece of technology, the All-Flying tail. Something it's counterpart, the MiG-15bis, did not have.

[f86enthusiast]

I have already asked the question - how do you KNOW it is wrong? Ever flown a real Sabre?

 

Until we get someone here with hands on stick time, we are all just speculating according to our past experiences and I'll guarantee that none of these so-called experts have a clue how the real Sabre rudder behaved.

 

I'm still waiting for some empirical evidence that suggests the rudder is indeed buggy, and until anyone comes up with any substantive evidence, I remain utterly unconvinced. It does work, but it is simply very ineffective, and looking at the size of it, I'm frankly not surprised.

 

So no matter how many of you are adamant that it is wrong, you're wasting your pixels. Where is the evidence guys?

 

Since you wont listen to plenty of people with knowledge in this area look in the F86F Flt manual Chapter 6 Flight Characteristics. Amazingly it doesn't say there are any adverse rudder handling techniques. It states (due to being a turbojet vice prop) that very little rudder is required for coordinated turns(duh!).

 

Look at your rudders as they move side to side while on ground at idle. Look at the full control deflection in degrees, they look normal to what I'd expect. Get airborne and they only can travel about 1/3 of that distance either way. There is a good possibility they've modeled the rudders to become less effective with more airflow due to the increased forces the pilot would have to input at higher speeds. I believe they might have modeled this in the beta just a little too aggressively.

 

It also notates that with asymmetrical loading due to uneven stores that the rudder should be used to fly coordinated meaning it should have some effectiveness. This also means that when I'm level and input rudder the aircraft should initially yaw towards the input then follow with a roll in that direction.<-------that's aerodynamics Neil not 0's and 1's regardless of aircraft you've flown. With that being said why do I fly level and input full rudder, get the rudder to deflect 1/3 of the way, which is all it'll do and get no yawing at all? That's not correct unless you know how to bend the rules of physics. Go try it in external view first, then go to the cockpit and see if you pipper moves at all left or right regardless of airspeed. When in real life does a control input in the airflow not make any change, it doesn't.

 

If you need to get a hold of the manual you can find it on this forum or my forum in my sig.

Edited January 9, 2015 by f86enthusiast

[Curly]

The issue with the F-86’s rudder comes down to 2 points, can the rudder be effectively displaced by the pilot throughout the flight envelope, and does the rudder generate enough force to create yaw and sideforce.

 

First, lets look at rudder displacement. From Fox’s video and testing it appears that the full range of the rudder deflection is not available thorough the flight envelope. I was able to track down the hinge moment coefficient and calculate the rudder pedal forces on the actual F-86.

http://www.dtic.mil/get-tr-doc/pdf?AD=AD0069271

 

At the highest hinge moment coefficients and large dynamic pressures, the pilot is still able to exert enough force to deflect the rudder and keep the rudder deflected much further than in game. And at much greater yaw angles than is possible in the current flight model.

While forces may be high, they are within the realm of forces that a pilot is capable of generating. As defined by the NACA and Airforce reports. IE forces up 300-410 lbs

http://www.dtic.mil/dtic/tr/fulltext/u2/639028.pdf

 

A later modification program of Sabers, which provided a hydraulically boosted rudder, found that the craft behaved and felt similar to the original when the equivalent max force of 300lbs of was transmitted through the pedals via the boost system. Thus in the sim we should be able to hold rudder deflections and yaw angles that require up to and above 300 lbs of pedal actuation force. As was the case by the men who piloted the Sabre.

http://www.dtic.mil/dtic/tr/fulltext/u2/106019.pdf

Below are the hinge moment calculations.

 

 

Chr = rudder hinge moment coefficient.

CHr= H/q SfCav

 

 

 

H = Hinge Moment

 

q = dynamic pressure

Sf = Contronl Surface Area 33.44 Ft (that is the Tail size) (Rudder is 8.12 ft^2)

 

Cav = Average Control Surface Chord 55.99 inches = 4.665 feet

 

 

Calculations For Rudder with area size (8.12 ft)

Based on 6 inches of Rudder Pedal Travel

(Gear Ratio 6/27.5) = .21 inch/ Degree =12.4962095 inch / radian

 

Sea Level Mach 4.0, KTAS 264.591

Ch=.23 = H / 237.0163 * 8.12* 4.65

Ch= .23 = 2058.33/237.0163 * 8.12 * 4.65

12.49*x=2058.33

x= 164.79 Lbs of force to applied to the rudder pedals to hold -25 Degrees with no yaw angle

 

 

 

Sea level at Mach .4 KTAS 264.591

 

Ch = .24 = h/ q *8.12*4.65

q= 237.0163

Ch = .24 = h/ 237.0163*8.12*4.65

Ch= .24= 2147.82/ 237.0163*8.12*4.65

 

12.49*x=2147.82

x=178.985

178.985 lbs of pedal force for rudder displacment < -25 degrees with no yaw angle

 

 

Sea Level at Mach .8 KTAS 529.1829

Ch = .24 = H / 948.065 *8.12*4.65

Ch = .24 = 8591.29/948.065*8.12*4.65

12.49*x=8591.29

x=687.853

687.853 lobs of pedal force at Rudder angle < -.12 degrees. and no yaw

 

 

20,000 feet at Mach .8 KTAS 491.491

Ch = .24 = h / 436.02* 8.12*4.65

Ch = .24 = 3951.18 / 436.02*8.12*4.65

12.49*x=3951.18

x=316.347 lbs of pedal force with a rudder angle <-15

 

Lower Ch

Sea Level at Mach .8 KTAS 529.1829

 

Ch=.08 = h / 948.065 * 8.12*4.65

Ch = .08 = 2863.76 * 8.12* 4.65

12.49*x=2863.76

x = 229.284 lbs of pedal force at Chr .08 which should be more than -10 degrees of rudder.

Ch = -.03= h/(237.0163*8.12*4.65)

Ch = -.03= -268.478/(237.0163*8.12*4.65)

12.49*x=-268.478

x= -21.495; Rudder lbs of pedal force to keep 5 degrees rudder at zero yaw angle.

 

Ch = -.04=h/237.0163*8.12*4.65

Ch= -.04 = -357.97 / 237.0163* 8.12 * 4.65

12.49*x= -357.97

x=-28.66 lbs of rudder pedal to maintain a 5 degree rudder delfectionwith a 3 degree yaw3

On the issue of rudder effectiveness, The F-86 flight manual states that the rudder is effective for a crabbed approach up to 25 knots. If the rudder has enough power to crab in a 25 kt crosswind, then those forces will be enough to cause changes of it's flight path vector without a crosswind component. Also, as velocity increases, for a given rudder displacement, the rudder actually generates more lift and greater side forces and yaw moments. Furthermore the rudder is well sized for the vertical tail. With a rudder area to tail area ratio of .242 it’s similar in proportions to large passenger craft.

 

http://faculty.dwc.edu/sadraey/Rudder%20Design.pdf

 

http://www.dept.aoe.vt.edu/~lutze/AOE3134/YawMoment.pdf

 

https://courses.cit.cornell.edu/mae5070/Caughey_2011_04.pdf

 

http://www.dept.aoe.vt.edu/~mason/Mason_f/LDstabdoc.pdf

 

Personal accounts also indicate that it was possible to turn the Sabre 180 degrees using the rudder only.

https://books.google.com/books?id=aDNVY4lgOAQC&lpg=PA15&ots=aSy4pWoLqK&dq=f%2086%20sabre%20hydraulics%20out%20%20rudder%20cable%20turn&pg=PA15#v=onepage&q&f=false

 

 

While not Yaw moment or force reports for the f-86, it seems that the modeling of the rudder forces, either due to lack of rudder displacement or incorrect modeling of forces prevents the DCS exhibiting accurate rudder forces. If access to reports listed below is made available. It would be possible to more accurately make an assessment of the rudder performance of the F-86:

December 1950: Johnston, E. W. F-86E Characteristics for Lateral Directional Dynamic Stability Studies. North American Aviation, Inc. Report NA-52-286 March 1952

NA 50 928 Aerodynamic Dimensional Data F86E.

NA 50 1277

NA 47 1043, NAAL 99

NA 49 467, NAAL 99

 

 

From observing the behavior of the craft In game I’m not sure what Belsimtik is attempting to model with the current rudder behavior. I could speculate and say they took the hinge moment coefficients, and interpreted these as the ranges for the rudder at various speeds and normal forces displaced by the rudder. Which would be easy to do, because the report is poorly formatted and labeled. Thus making it seems like the entire range of motion isn’t available, because the report’s author was trying to fit a lot of data onto 2 pages. Though this is just speculation, thus it would be nice if the Developers would discuss their source material and how they arrived at the current behavior of the rudder.

 

F-86 maintenance manual, shows rudder system layout: http://www.avialogs.com/viewer/avialogs-documentviewer.php?id=15729

Edited January 20, 2015 by Curly

[Charly_Owl]

VERY nice post, Curly! :)

[Foul Ole Ron]

Great post Curly. Looks to be exactly what Belsimtek were asking for before they would take a look at the rudder behaviour of the Sabre. Hopefully they'll decide to take another look now and make a correction so the rudder behaves, well, more like a rudder.

[NeilWillis]

Well stated, and well sourced. NOW we're getting somewhere!

 

This is a far far more convincing argument - thanks for that guys. I am with you, having seen some empirical data finally.

[OnlyforDCS]

Great post Curly!

[iFoxRomeo]

Thx Curly!

+rep

 

Fox

[Moggster]

I was looking for some F-86 stuff when I stumbled across an instructional\familiarization video for the Naval\Marine version of the F-86 E&F, the FJ2 Fury. In it pilots are warned to go easy on the rudder during firing to avoid skidding off the target and that the aircraft requires very little rudder. They start to talk about the rudder at about 8:09 in the video.

 

 

Apologies if this has already been posted.

[Outlaw24]

Outstanding research job Curly!

[Filament]

All I want to add, is:

 

:thumbup: Curly! Splendid job!