Tail Damage - Opening can of worms...

[mtnman]

When rudder input is given, it doesn't cause a roll.  It causes a yaw.  The yaw is what leads to the roll- in many planes, anyway.

That's actually pretty easy to see in RC planes that have no dihedral.  Or, at least that's probably the easiest way for many of us to see that effect.  You see that rudder-input "wags the tail", but doesn't directly lead to roll, and especially on aerobatic planes will lead to very little roll at all.  Actually, in aerobatic planes the effect of rudder leading to roll, or aileron input leading to yaw, or elevator input leading to either roll or yaw  (or both) is undesirable, and pains are taken to minimize those effects (through design).

When the yaw is induced, more lift is generated by the wing that "moves forward" faster, while at the same time the other wing generates less lift.  This alone will cause some roll.  On planes with dihedral or polyhedral, even more roll will be generated because the wing that moves forward will have its bottom presented to the slipstream, which will deflect it upward.  It leads to a roll, but it's a "dirty" roll.  It is, however enough of a roll to control 2-channel RC planes via rudder and aileron as long as enough dihedral or polyhedral is present.  An airplane with too little dihedral or polyhedral doesn't generate enough roll through rudder input to be controllable.  And if "extra" rudder is given in an effort to achieve that roll, things get ugly.

Keep in mind that while the rudder swings the nose to one side, it doesn't alter the flight direction to the same extreme.  This results in a a slip or "crab".

So in effect, it isn't the rudder that causes the roll, it's the design and orientation of the wing...  And due to those, left rudder leads to a left roll...

Now, to make things confusing, think about what you guys are arguing with the "rudder-induced roll" idea, and how you think that should translate to an "elevator-induced roll"...

If what you're claiming were true, then an input of left rudder would cause a roll to the right.  That's not what happens though, is it?

Kind of intriguing, huh?

[Chalenge]

The same way it works on F-14s or any other plane with elevons. Sorry but the way it works right now is just wrong.

EDIT: UNLESS like I said the representation of the surface being missing is one of simplifying graphics and yes Im hoping the new damage system will take care of that.

[mtnman]

The same way it works on F-14s or any other plane with elevons. Sorry but the way it works right now is just wrong.

EDIT: UNLESS like I said the representation of the surface being missing is one of simplifying graphics and yes Im hoping the new damage system will take care of that.

Not really "apples to apples"...  I'm not arguing that the tail damage here is correct either, I can't prove it one way or the other.  And really, I like these threads, because I can learn something from them.

However, it appears that people are jumping to gut conclusions without thinking things through entirely.

In the F14 example, you have a specially designed airplane specifically designed to roll due to elevon control (aided by wing-mounted spoilers and rudders).  The entire wing design is also completely different.  To think that a WWII fighter would "accidentally" roll "the same way" with only 1/2 of its elevator, as an F14 with two fully functioning elevons, and spoilers, and two rudders seems kind of far-fetched.  If a damaged WWII plane could do it (without those benefits), and 1/2 of it's it looks like the F14 wasn't designed very efficiently.  

In the end, we're looking at a damaged or missing elevator, not a set of elevons.  I'm not "buying" the theory...      yet...

[Chalenge]

No. Sorry. Spoilers on the F14 do not help it roll. It doesnt take a full flying elevon to make an airplane roll either. If a single stab+elevator combination could not cause an airplane to roll then two of them could not cause an airplane to loop.

Its that simple.

[mtnman]

No. Sorry. Spoilers on the F14 do not help it roll. It doesnt take a full flying elevon to make an airplane roll either. If a single stab+elevator combination could not cause an airplane to roll then two of them could not cause an airplane to loop.

Its that simple.

No need to apologize...  I think you're the sailplane pilot, right?  Don't confuse those spoilers with the ones the F14 uses.  It isn't that simple.  I'm an RC sailplane buff, and understand the use of spoilers on those type of planes.  Different application.

In here-

http://www.globalsecurity.org/military/systems/aircraft/f-14-design.htm

Notice-
"The design of the F-14B allows for incredible pitch authority as well as good roll control to produce an extremely agile fighter. Rolling maneuvers are accomplished through the use of differential horizontal stabilator and 8 spoilers located on top of the wings. Its general arrangement consists of a long nacelle containing the large nose radar and 2 crew positions extending well forward and above the widely spaced engines. The engines are parallel to a central structure that flattens towards the tail; butterfly-shaped airbrakes are located between the fins on the upper and lower surfaces. Altogether, the fuselage forms more than half of the total aerodynamic lifting surface. With the wings in the 20 degree position most of the lifting force comes from the wings, in the 68 degree position over 60% of the lift is generated from the fuselage itself".

"Lateral control is achieved by long-span spoilers, ahead of flaps, and tailerons. Automatic leading-edge slats assist maneuvering, and strakes emerge from the wing glove leading-edge at high airspeeds. The automatic wing sweep has manual override, with automatic scheduling of control with airspeed and autostabilisation and angle of attack protection provided by the autopilot and automatic carrier landing system (ALCS). Airbrake panels are located above and below tail, between the twin fins and rudders. For roll control below 57 deg (this is referring to wing-sweep, not degree of bank), the F-14 uses spoilers located along the upper wing near the trailing edge in conjunction with its all-moving, swept tailplanes, which are operated differentially; above 57-deg sweep, the tailplanes operate alone. For unswept, low-speed combat maneuvering, the outer 2 sections of trailing edge flaps can be deployed at 10 deg and the nearly full-span leading-edge slats are drooped to 8.5 deg. At speeds above Mach 1.0, the glove vanes in the leading edge of the fixed portion of the wing extend to move the aerodynamic center forward and reduce loads on the tailplane".

"The tail control surfaces on F-14s are known as "rolling tails", in that the aircraft does not have ailerons on the wings to control roll. Roll control is instead provided at low speeds by wing-mounted spoilers and at high speeds by differential horizontal stabilizer deflection. This configuration also produces side force, or yaw, which contributed to the inadvertent spin entries. This large tail configuration is to aid in takeoff from aircraft carriers, by providing more pitch moment".

Also, for more detail look here (if nothing else, read the first paragraph in the Introduction)-
http://www.seas.ucla.edu/~mcloskey/PDF/jgcd98.pdf

So, I'm still of the opinion that 1/2 of an elevator doesn't equate to an elevon, stabilitator, or "rolling tail" system.  

I'd love to see an aero-engineer step in and give us some clarity, but I think a huge part of the equation here is that so much of the F14's lift is generated by its fuselage, where that isn't the case with conventional WWII planes.  Having the lift located so close to the center of the roll axis is what makes the flying tail possible.  Even at that, it isn't "really" adequate until the wings are swept, which centralizes the lift even more-so.  In effect, the F14 is rolling like an arrow spins with helical fletching.  "Normal" planes don't do that, and in its more conventional (un-swept) configuration, the F14 doesn't even do that without help from its wing-mounted control surfaces...

In reality, I think we might see some roll effect from a WWII plane with only one elevator.  But which way would it roll?  If the right elevator were removed, we'd probably argue that up-deflection would give a left roll, and down-deflection would give a right roll...  But would that really be the case?

Deflecting the elevator would cause asymmetrical drag on the left side of the plane, and it would occur for either up or down elevator.  Ever stick you hand out of the cockpit of an airplane in flight?  The few times I've done it, the plane yawed to that side, due to the asymmetrical drag.  Enough so that the pilot (I was in back) immediately looked back to see what was going on.  And I only stuck my hand out part-way, and just for a second...

So, if that were to have any effect on the WWII plane, deflecting the left elevator would cause a left yaw, resulting in a left roll (regardless of whether the deflection were up or down).  Now, would that be the end result?  Or is it an effect that would lead to another, or be cancelled out by another (like adverse yaw from aileron deflection, which is overcome by rudder?).

It's not simple.

[mtnman]

And again, I'm not arguing that the tail damage model is correct, since I don't know for a fact one way of the other... 

I'm just playing devil's advocate here, and pointing out potential flaws I see in the argument.  The F14 info took me all of 30 seconds to locate, which is more time than I've accumulated researching them in my entire life.  I have less interest in jets than I do in my septic tank.

As a result, I could easily be wrong...

[Stoney]

And again, I'm not arguing that the tail damage model is correct, since I don't know for a fact one way of the other... 

I'm just playing devil's advocate here, and pointing out potential flaws I see in the argument.  The F14 info took me all of 30 seconds to locate, which is more time than I've accumulated researching them in my entire life.  I have less interest in jets than I do in my septic tank.

As a result, I could easily be wrong...

You might be wrong, but the 30 seconds of effort you used to look this information up is a stab at providing some evidence to support your argument, versus what some folks in this forum do by firing an opinion downrange with nothing more than their occluded intuition to guide them.

Comparing the flight dynamics and control system of the F-14 to a Spitfire, for example, is most definitely apples to oranges.

[Chalenge]

Sitting behind a desk you will never experience the chance that can come upon you when things like midair collisions occur to your radio control aircraft. If you accept the nature of a video game over reality then all you are is a funnel for bad information.

Stoney have you sat down and played with the formulas?

[Stoney]

Sitting behind a desk you will never experience the chance that can come upon you when things like midair collisions occur to your radio control aircraft. If you accept the nature of a video game over reality then all you are is a funnel for bad information.

Stoney have you sat down and played with the formulas?

I'm actually having trouble figuring out which ones to use for this.  Most of the stability equations I have assume uniform pitch inputs from the elevator, so they won't really have any merit here. 

[mtnman]

Sitting behind a desk you will never experience the chance that can come upon you when things like midair collisions occur to your radio control aircraft. If you accept the nature of a video game over reality then all you are is a funnel for bad information.

Stoney have you sat down and played with the formulas?

I'm confused as to what your point is, and/or if it's directed towards me?

I've been flying RC planes for 25 years or more.  I've built (mostly scratch-building, with my own self-drawn plans, but also a bunch of kit-planes) and flown sailplanes (thermal and slope), high and low-wing "sport" planes, semi-scale (civilian as well as WWI and WWII fighters), float planes, combat-streamer planes, and aerobatic biplanes (Ultimates and Pitts).  Throw in some RC "bird-type" gliders as well, and even some of the modern "simplistic" helicopters.  

I've experienced all sorts of mid-air mishaps (even a lost elevator, believe it or not, with a safe, uneventful-but-stressful landing).  Flutter (aileron, which led to a disintegrated wing at high speed and low altitude, an engine-mount failure (again, a safe landing, with the engine hanging by the throttle-servo push-rod) flap failure on one wing (flap stuck down on one side), a $10,000 mishap with a hospital window, and others...

If by chance you're referring to me with "sitting behind a desk" and the "funneling bad info", feel free to post some evidence of your own.

[Chalenge]

I wasnt talking of or to anyone in particular but since you say you have so much radio control experience you should be aware that the trimming procedure for elevators involves looping the airplane and 'trimming out' any rolling tendency. This is why the majority of precision aerobatic planes like the Sukhoi series have dual elevator horns and the difference of 1/2 clevis turn can make a very large difference which is why the even larger scale aircraft tend to have finer adjustments.

Its just as important in full size aircraft.

By the way my model aircraft flying extends back to the 1960s and controllers that just barely qualified as radios. These days I fly larger and slower planes to compensate for age reflexes and eyesight.

[mtnman]

I wasnt talking of or to anyone in particular but since you say you have so much radio control experience you should be aware that the trimming procedure for elevators involves looping the airplane and 'trimming out' any rolling tendency. This is why the majority of precision aerobatic planes like the Sukhoi series have dual elevator horns and the difference of 1/2 clevis turn can make a very large difference which is why the even larger scale aircraft tend to have finer adjustments.

Its just as important in full size aircraft.

By the way my model aircraft flying extends back to the 1960s and controllers that just barely qualified as radios. These days I fly larger and slower planes to compensate for age reflexes and eyesight.

Hehe, I'm amazed at how fast my planes seem to be flying these days too!  I'm finding that I'm having difficulty keeping up with them, and am transitioning back into slower, more docile planes myself.  I'm flying an el-cheapo ASH-26 right now, and am actually tempted to shelve it for a floater.

I've never flown single-wing aerobatic planes, and have also never noticed a very pronounced rolling tendency with elevator trim.  Some, maybe, but nothing extreme, and I sure couldn't peg it as being elevator-related anyway (it could have been any of a multitude of other factors).  The plane that lost an elevator was one of my scratch-built Ultimate Bipes, and I don't recall any roll issues when I brought it in.  I wasn't really watching for it though, and it's been years since it happened.  It's the only plane I've flown that had separate elevator servos.

Having a flap jam down (on an F4U) was a much more traumatic experience.  I was able to get that plane down by dropping my other flaps, but it was scary.  There was nothing like that much of a roll effect when I lost the elevator; I'm sure I'd have remembered it.  Those Ultimates rolled like mad anyway though, so maybe I just didn't associate it with the elevator?  That plane landed pretty "normally".  It felt like I had "bragging rights", but in truth it wasn't that hard.

If it was a "huge" issue, you'd think we'd need a vertical stab and rudder under the fuselage too.  Otherwise we'd have "huge" issues with roll being associated with rudder input, and it would be opposite of rudder deflection...  Right rudder would create left roll.  The only reason it doesn't is because of the wing...

Flying aerobatic planes, I'm sure you're familiar with the fact that planes without dihedral sure don't roll well/quickly/immediately with rudder input, do they?  Which again makes me wonder...  If right rudder creates right roll due to the dihedral of the wing, why does removing the dihedral not result in a right rudder/left roll effect?

[Chalenge]

It depends on the design of the plane. Rudder will in some cases cause a stall of a portion of the wing due to the fuselage nose disturbing the smooth flow of air over the wing center and with the unequal lift comes roll. I suspect you have just forgotten how the loss of one elevator effected flight or your experience took over and you didnt have difficulty in making changes to land the plane or since the ailerons are so over-whelming on the Ultimate it was easy to retrim. I have flown planes with the elevator control reversed without difficulty but I brought it down immediately and reversed the throw.

Im not sure what has you thinking right rudder would cause left roll? I have never experienced that. I have flown a straight wing (zero dihedral) Ugly Stick and yes it rolled on rudder. It was more of a barrel roll but it rolled.

[Mace2004]

I have less interest in jets than I do in my septic tank.

HERESY!!!!
I shall have you burned and darn you to heck!   

[mtnman]

It depends on the design of the plane. Rudder will in some cases cause a stall of a portion of the wing due to the fuselage nose disturbing the smooth flow of air over the wing center and with the unequal lift comes roll. I suspect you have just forgotten how the loss of one elevator effected flight or your experience took over and you didnt have difficulty in making changes to land the plane or since the ailerons are so over-whelming on the Ultimate it was easy to retrim. I have flown planes with the elevator control reversed without difficulty but I brought it down immediately and reversed the throw.

Im not sure what has you thinking right rudder would cause left roll? I have never experienced that. I have flown a straight wing (zero dihedral) Ugly Stick and yes it rolled on rudder. It was more of a barrel roll but it rolled.

Without wings (just a fuselage and tail), right rudder would cause the fuselage to twist/rotate to the left.  Just like helical twist fletch's would do to an arrow shaft.  The fuselage would "spin" opposite of the rudder deflection (if we ignore torgue, etc).  It's an easy experiment actually, if you're having trouble visualizing it.  Take a soda straw, cut 1" slits in one end and insert a paper elevator and rudder.  Put a paper clip on the other end.  Bend in some right rudder.  Toss it, it rolls left.

You can't/don't see that effect with wings, because wings reverse that effect.  Even with no dihedral, one wing moves forward faster than the other, generates enough excess lift to raise a bit, and exposes its underside to the slipstream (the plane will be in a bit of a skid- uncoordinated), and initiates a roll.  With wings, left rudder gives left roll.  Without wings, left rudder gives right roll.

Back to the (eeeew) F14...  Ever have or seen a spoiler on a sailplane malfunction?  (If not, buy a CMPro glider, mine are now packing-taped "closed", and the servo removed).  The effect is that one wing loses lift (the one with the good spoiler), and one heck of a roll ensues.  It isn't really a roll though, just one wing dropping fast.  I imagine that in slome variety is how they get the F14 to roll with spoilers when the wings are "out".  The wing without the spoiler must still be generating lift (and it's going faster) so a spiral dive eventually results with a glider.  I wonder if that lift is enough to get the full roll out of the F14?  Otherwise it seems like it should get "stuck" when it reaches a 90 degree bank?

FWIW, I just lost my (F4U) right elevator in a fight.  With some difficulty, I was able to kill the guy.  The horizontal stab remained intact.  Left elevator remained.

Down elevator results in the nose dropping, and right roll...  Up elevator results in the nose lifting, and left roll.  That was without auto-trim.  Maybe auto-trim dampens the effect?

Think about that for a minute...  If down (left)elevator gives me a right roll, what happens when I reach 90 degrees right bank, and the elevator is vertical?  It's now "kind of" like a rudder...  And it's effectively deflected left, but I'm rolling right...

Ailerons too...  They create a roll/movement opposite of the deflection (except for the adverse yaw effect).  Why would the rudder create movement toward the deflection?