Rudder effectiveness

[Holbeach]

Something more concrete than

 

 

For example, level flight, no roll, 1000ft, 400knots CAS, full fuel, full rudder defection - 10 degrees per second turn rate.

 

I got, at 210 kts IAS, where the manual states, as you would expect, the rudder is most effective at directional control, around 0.1 deg per sec turn rate. (Tacview, same condition except for speed).

 

.

[iFoxRomeo]

Thanks, your post is very clear.

I think what is freaking me / us out is that BST is still waiting for data to see IF they are wrong or not.

But the point is that, despite what BST thinks that all airplanes fly differently, there are some things that are common to EVERY airplane.

 

It is widely accepted and proved that wings produce lift on ALL airplanes

It is widely accepted and proved that ailerons will make ALL airplanes roll

It is widely accepted and proved that elevators will make ALL airplanes change their pitch

 

and you guessed it...

It is widely accepted and proved that rudders will make ALL airplanes yaw and change their heading.

 

I mean, airplanes have been developed on these basic principles since 1903. If you're doubting that rudders work the way they work, then you're doubting basic principles of physics and as a FM developer that doesn't make you look too good.

 

I truly appreciate the fact that you want to model things based on real data, but if you don't have that data, you still have to do the best you can and calculate it yourself / get pilot input etc. But you can't leave the FM as it is and advertise it as high fidelity. It has to be fixed.

Bkthunder please don´t go this way. You won´t make BST change anything this way.

Calm down and relax. It is just a "game" and no reason to get grey hair from.

And "It is widely accepted and proved that..." is no argument.

 

 

 

Fox

[msalama]

around 0.1 deg per sec turn rate

 

So it _does_ flat turn after all? Note: cannot test until Xmas or thereabouts myself, away from the simming computer until then, still following this w/ interest however :)

[NineLine]

I truly appreciate the fact that you want to model things based on real data, but if you don't have that data, you still have to do the best you can and calculate it yourself / get pilot input etc. But you can't leave the FM as it is and advertise it as high fidelity. It has to be fixed.

 

Once again, you claim it has to be fixed, but you offer no proof that the F-86's rudder was not very effective at all. Now I have a feeling it was more effective in real life than it is now BUT the difference is I spent last night pouring over documents I could find to see if there was anything on the subject. I cant trust my feelings as I cant be sure that in the early stages of the jet age that things like this couldnt happen. If the F-86 was the perfect, shape, form and such, then we would still be flying them as front line fighters, I would imagine there was things about the F-86 that were beyond their knowledge back then, read about test flights of the 262, its similar... they simply didnt know what they were doing back then with certain aspect of jet design.

 

So this is how bug reporting works:

 

You state there is an issue (this has been done enough times)

You submit what is happening in the sim (this has been done)

You submit the correct action based on real life reports, data, etc (this hasnt been done AGAIN not saying that the rudder performance in the sim is correct, but they wont guess at it)

 

So unless you have anything else to add besides "It doesnt feel right based on my feelings" then you have nothing left to add, its been reported internally to be checked out, I sent one document to CC to see if there is anything worth while in it, gonna keep looking as well. Anything based on feelings, or claims that BST doesnt want to do the best possible job on the FM, or they dont listen or all the other blah blah blah that has been going on will be considered a violation of 1.10.

[wolle]

Can anybody explain to a non-pilot how to perform this test? Is the following procedure the correct one?

 

-fly level and straight.

-apply full rudder.

-apply opposite aileron until there is no deflection on the roll indicator

-pull back elevator and add power to compensate for increase in drag until plane does not sink or climb and maintains constant speed.

-observe if there is any change in heading with time.

 

I did some quick tests in the Sabre and the Dora. In neither case could I observe a significant change in heading, both planes simply side-slip. Am I doing it right?

[Zentaos]

I'm confused. Are we talking about heading, or vector? As soon as you input rudder deflection, heading changes. Vector may change very slowly depending on conditions.

 

I have very limited flight experience, less than 30 hours in C152 & R22, and 3 hours in an SF.260, but I never had an instructor have me turn the aircraft with the rudder by yawing.

 

In a C152, if you deflect the rudder, the aircraft will slowly roll towards the deflection changing the lift vector. Or the pilot can counter the roll with opposite aileron deflection and put the aircraft into a slip this causes a number of aerodynamic instabilities. The lift vector remains vertical, but the thrust vector is not constant with heading so the aircraft translates sideways. It also decreases lift on the leeward wing from the airflow being blocked by the fuselage which requires a power increase to maintain altitude. I have never performed a full 360 degree flat turn in an aircraft. So, as a STUDENT pilot, no it is not common knowledge to me that all aircraft will perform a flat turn, as I was never taught how, i was taught coordinated turns. I was taught slips, not for approach in crosswind, but as a method for bleeding off altitude on an approach vector. In crosswinds, you point the nose into the wind to achieve a constant track with the runway, ie. You fly into the wind, as you approach, the wind pushes you left of the runway, but your nose is pointed right so you track straight with the runway (also known as a crab) then you apply rudder just before touchdown to match heading (not vector, vector is already in line with the runway by flying into the wind) with the runway.

 

I have never flown a swept wing jet, but i have ridden in a lear 31. The pilot did not perform any flat turns. So I cannot assume that yawing should produce a 360 degree turn. As for rudder deflection and heading, i do remember in my first flight lesson that the instructor had me deflect the rudder then release to see how the aircraft would weather vane in relation to its vector. Which is why the rudder is separate from the vertical stabilizer.

[Iberian]

I'm confused. Are we talking about heading, or vector? As soon as you input rudder deflection, heading changes. Vector may change very slowly depending on conditions.

 

I have very limited flight experience, less than 30 hours in C152 & R22, and 3 hours in an SF.260, but I never had an instructor have me turn the aircraft with the rudder by yawing.

 

In a C152, if you deflect the rudder, the aircraft will slowly roll towards the deflection changing the lift vector. Or the pilot can counter the roll with opposite aileron deflection and put the aircraft into a slip this causes a number of aerodynamic instabilities. The lift vector remains vertical, but the thrust vector is not constant with heading so the aircraft translates sideways. It also decreases lift on the leeward wing from the airflow being blocked by the fuselage which requires a power increase to maintain altitude. I have never performed a full 360 degree flat turn in an aircraft. So, as a STUDENT pilot, no it is not common knowledge to me that all aircraft will perform a flat turn, as I was never taught how, i was taught coordinated turns. I was taught slips, not for approach in crosswind, but as a method for bleeding off altitude on an approach vector. In crosswinds, you point the nose into the wind to achieve a constant track with the runway, ie. You fly into the wind, as you approach, the wind pushes you left of the runway, but your nose is pointed right so you track straight with the runway (also known as a crab) then you apply rudder just before touchdown to match heading (not vector, vector is already in line with the runway by flying into the wind) with the runway.

 

I have never flown a swept wing jet, but i have ridden in a lear 31. The pilot did not perform any flat turns. So I cannot assume that yawing should produce a 360 degree turn. As for rudder deflection and heading, i do remember in my first flight lesson that the instructor had me deflect the rudder then release to see how the aircraft would weather vane in relation to its vector. Which is why the rudder is separate from the vertical stabilizer.

 

During instruction they won't teach you everything, just the basics to get you started. Eventually as you get more experience you learn some other tricks, like during long 9 hour cross country flying with a single prop you may just want to relax your hands, so you correct heading with the use of rudder and don't really touch the yoke...

 

Or some guys just land the airplane by the use of trim alone during the approach, no direct elevator inputs..

 

One that gets a lot of people confused is that control speed with pitch, and altitude with power. But over time people realize that...

 

Just a few examples of how there is different ways to control the aircraft.

[Cykyrios]

I have very limited flight experience, less than 30 hours in C152 & R22, and 3 hours in an SF.260, but I never had an instructor have me turn the aircraft with the rudder by yawing.

 

I have zero real world flight experience myself, but I believe the reason they do not teach you flat turns is that they are extremely inefficient. Coordinated turns are the way to go if you want to turn, flat turns require a large turn radius.

 

Now as I see it, the issue with the Sabre is that it is extremely inefficient. I have just tried performing flat turns with both the A-10C and the Sabre, and while their wing profiles are quite different, the difference was rather extreme indeed. Of course, rudder efficiency varies with speed, but even then, applying full rudder in the Sabre has little effect on the plane's heading (and even less on its velocity vector), while in the Hog, you get into a crab very quickly (and into a roll as well), and can perform a turn.

 

If only data about rudder will make BST change something, we may not see a "fix" to this, as I doubt flat turn performance is something that is worth writing down.

As many people said, though, it "feels" wrong, but there is no concrete data backing up that claim.

[Zentaos]

My point is, that if the aircraft performs correctly and is able to meet the numbers of the real aircraft's envelope, why are why concerned about a maneuver that would never be useful and has no real world data to back it because it is not useful?

[gavagai]

I know someone who has flown a Mig-15. Would you all be satisfied with his opinion? No, it's not an F-86, but it's very close. I will send an email to see what he says.

 

 

---------------------

 

Got a response!

 

What is your opinion of the F-86 yaw behavior in DCS? Some have pointed out that rudder will change the aircraft's heading, but not its vector. So when you release rudder input you are back at your same initial heading. Since you've flown a Mig-15, which is very close to a Sabre, I'm curious to know what you think.

 

and the reply:

 

That is fairly accurate for most aircraft. If you push and release, heading goes back to close to the original. If you hold in the rudder, your vector will change when some bank reorients your lift vector

 

When he says "most aircraft," most of his flying hours have been in single-seat military jets.

Edited November 30, 2014 by gavagai
added reply

[CoBlue]

My point is, that if the aircraft performs correctly and is able to meet the numbers of the real aircraft's envelope, why are why concerned about a maneuver that would never be useful and has no real world data to back it because it is not useful?

Because it effects the whole aerodynamic FM of the aircraft & has consequences during the whole flight envelope.

We don't want this for performing a 360 flat turn.

It's however a valid argument to prove that there is something wrong with the current PFM with regards to the rudder & we want it as real as possible.

And this technique does matter i.e close formation flying:thumbup:

[Flagrum]

I know someone who has flown a Mig-15. Would you all be satisfied with his opinion? No, it's not an F-86, but it's very close. I will send an email to see what he says.

 

 

---------------------

 

Got a response!

 

 

 

and the reply:

 

That is fairly accurate for most aircraft. If you push and release, heading goes back to close to the original. If you hold in the rudder, your vector will change when some bank reorients your lift vector

 

When he says "most aircraft," most of his flying hours have been in single-seat military jets.

I think, that reply does sadly not really help to answer the question.

 

"Push and immediately/soon-after release the rudder pedal": yes, ofc the nose will yaw back to the initial heading and the vector of the aircraft will not have changed. It just takes longer than a brief push of the pedals to have an significant effect.

 

"hold rudder and the vector will change when the aircraft banks": yes, ofc the aircraft's vector will change when banked.

 

But the real question remains still unanswered: what if the rudder is kept pushed and the automatic banking is then countered by applying aileron input - so that no banking occurs.

[gavagai]

No, what I think is important here is that we have someone who owns the DCS F-86 module and has stick time in a very similar aircraft, the Mig-15. If he doesn't find a problem with the F-86's yaw behavior in DCS then I have to be satisfied until I can ask someone who has better first-hand experience.

[Zentaos]

But the real question remains still unanswered: what if the rudder is kept pushed and the automatic banking is then countered by applying aileron input - so that no banking occurs.

 

 

Then you are slipping

[Flagrum]

No, what I think is important here is that we have someone who owns the DCS F-86 module and has stick time in a very similar aircraft, the Mig-15. If he doesn't find a problem with the F-86's yaw behavior in DCS then I have to be satisfied until I can ask someone who has better first-hand experience.

The point is, I think he did not yet understood what the real question was ... and therefore he can not say if there is a problem or not.

 

Then you are slipping

The question is, does the aircraft change it's flight vector?

 

If I am not mistaken, the term slipping would imply that the flight vector is changing, right? And while the slip indicator does show a corresponding behaviour (iirc), the aircraft's flight vector is in fact not changing significantly (i.e. less than what is probably caused by pilot induced banking errors).

 

Anyhow, I am not the right person to discuss or comment on the actual issue here - I am rather interested in what the MiG-15 pilot says. :o)

Edited December 1, 2014 by Flagrum

[gavagai]

I disagree, but how would you like me to rephrase the question? Do you have a certain procedure to follow?

[Flagrum]

Fwiw, I - as layman and non-engineer - found this somewhat enlightening in regards to the general effectiveness of the rudder, especially in flat turns:

 

Turn on flat surfaces

 

If the bank angle is zero, the surface is flat and the normal force is vertically upwards. The only force keeping the vehicle turning on its path is friction, or traction. This must be large enough to provide the centripetal force, a relationship which can be expressed as an inequality, assuming the car is driving in a circle of radius r:

(http://en.wikipedia.org/wiki/Banked_turn ... the rest of the article is also quite interesting.)

 

Keywords here: friction or traction to counter the centripetal foce

 

I would think, that the surface of the rudder would only provide a very tiny amount of traction/friction in our flat turn. It is probably like a car trying to drive in circles ... on a frozen lake of polished ice ...? :o)

[Flagrum]

I disagree, but how would you like me to rephrase the question? Do you have a certain procedure to follow?

He says that the aircraft will change it's flight vector when the rudder input is kept when the aircraft banks.

 

That sounds to me that he just describes the well known behaviour: you give rudder input, the aircraft starts to roll. And now it goes into a banked turn, resulting in a change of the flight vector.

 

But this change of the flight vector is not directly caused by the rudder deflection. It is caused by the changed lift vector of the now banked aircraft. I.e. this is not the "flat turn" that we are discussing here.

 

What we want to know is, will the aircraft's flight vector change if rudder input is given while (actively) maintaining a wings level attitude.

[gavagai]

Ok, I'll ask him to try it out more thoroughly in DCS. As for comparison to the Mig-15, it might be too late now for an apples to oranges comparison. Fwiw, the reason for the Mig-15 sorties was to experience a very pronounced dutch roll.

[Zentaos]

No, slipping does not change velocity vector. However, skidding does change velocity vector, but in order to keep from inducing a stall during a skidding turn, your turn rate would be so slow it might take more than ten minutes to perform a complete 360 degree turn. A standard turn rate is 3 deg. per second, or 2 minutes for a full 360 degree turn. Steeper bank angles with increased power and AoA can produce faster turn rates. I am off to perform a skidding turn in the F-86.

 

edit:

okay, I was able to get about 8 degrees of turn in 2 minutes using only rudder to skid while keeping the wings level at a speed of 350 KIAS. This would yield a full 360 deg turn in about 90 minutes, very poor turning performance indeed, but this is not conclusive to accuracy. Have errors been discovered in other areas of the flight envelope? Weather or not you feel this "may" affect other parts of the PFM, if normal maneuvering yields correct performance, it may not be affecting the overall performance of the PFM as we think. There may not be any published data because the skidding turn performance was so dismal, the Airforce mandated to never perform such a maneuver.

 

I just don't get the witch hunt here against BST. we got what we payed for, "the most accurate representation" of the real aircraft flight model to date on a PC, and it is still in beta. I do not feel that this is an accurate test to prove rudder effectiveness, I would instead, fly crosswinds at the edge of published limits to see if the performance is accurate. I feel, and this is my opinion, that efforts should be focused elsewhere as far as community testing and developer time is considered. I would rather have animated troops in my Huey than be fretting over flat turns that I never perform.

Edited December 1, 2014 by Zentaos

[wolle]

I just don't get the witch hunt here against BST. we got what we payed for, "the most accurate representation" of the real aircraft flight model to date on a PC, and it is still in beta. I do not feel that this is an accurate test to prove rudder effectiveness, I would instead, fly crosswinds at the edge of published limits to see if the performance is accurate. I feel, and this is my opinion, that efforts should be focused elsewhere as far as community testing and developer time is considered. I would rather have animated troops in my Huey than be fretting over flat turns that I never perform.

 

I appreciate your point, but I don't think the discussion is only about flat turns. Rudder performance factors into many maneuvers other than flat turns. For example, it is impossible for me to keep the Sabre going straight down the runway at 10m/s crosswind using rudder alone. With the addition of differential breaking, yes, but the rudder seems to be very ineffective during crosswind take-offs and landings. So, I really hope that BST will double check this aspect of their flight model. No witchhunt, just hope they will look into this.

[Zentaos]

Perfect, my point exactly. Focus on data that can be proven and/or measured. If there is a problem, I stand behind all wanting it corrected. A problem must be approached in a manner in which it can be solved. You don't test buoyancy by first sinking a hull and then trying to remove the water.

[Flamin_Squirrel]

No, slipping does not change velocity vector. However, skidding does change velocity vector...

 

Why would you think one does but the other doesn't?

[iFoxRomeo]

By accident I saw a strange behaviour of the rudder. When on the ground, the rudder moves through the complete range. But when airborne it moves to one end of the range (when full pedal is applied) and then reduces its deflection, though I keep the pedal pushed to the maximum. When flying fast the deflection is quickly reduced to nearly zero. At speeds below 200 it does not reduce so fast and not to zero.

You can also see this by watching down to the pedals.

 

I refer to DCS V1.2.14u1. This is a new behaviour, the "autoreduction" wasn´t there before v1.2.12. You can see it in my previously posted video here, that the rudder could be pushed completely to one end of its range and held there.

 

Watch the video in 1080p to see the joystick/rudder position indicator.

 

 

Fox

[NeilWillis]

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.

 

Rudder effect is however drastically reduced at higher speeds, because the aerodynamic forces acting upon the wings, the stabilising effect of the dihedral, and the lateral forces against the fuselage sides prevent the rudder from applying sufficient force to overcome all those factors.

 

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.

 

Do we have any first hand testimony from a real F-86 pilot?