Ok, imagine this – You are flying your low winger with a very small amount of dihedral on a normal wide turn banking left and all of a sudden the rudder clevis lets go so the rudder is free as the breeze, What do you think would happen to the plane in the turn?

1. Would the pressure from the spiralling prop wash pushing on the left side of the fin now have more authority and cause the plane to yaw to the left and induce a left spiral dive because the rudder is not holding the aircraft straight.

2. Would the left side pressure also push the rudder to the right, holding up the nose in the turn.

3. Or would the rudder just flap frantically in the breeze fishtailing the aircraft and making it hard to control.

4. Or have you got your own theory.

Any input please.

you probably loose a bit of stability causing the nose to pitch down as in 1, but it's not propwash, it's the pressure differences on each side caused by the turn, however it'd probably just flap about until you land, that is if you level out and slow down in time.
depends on how big the rudder is i guess and your speed at the time.
The rudder is only one part of the stability, you still have the fin and the rudder will want to follow that all be it with a bit of wobble, it's unlikely that vibration would be enough to make much difference to the planes heading.
so lets here what happened next

If nothing "locks" the freed surface, it will streamline with the air goind past it, and there will no major effect from the surface.
The plane might respond as if part of the vertical vanished, which in essence it has.
Probably unnoticeable until after the landing, if you don't use rudder in flight.

I think Tall Paul is right. (not much will happen) You can take your feet off the rudder peddles in a small airplane that has nothing more than pull-pull cables going from the pedals to the rudder.

having had similar happen (broke off control horn on rudder in flight):


1) This is speed dependant and fuselage design dependant. (also thrust angle.. too many variables) If You get the rudder flutter... this point will never come up.

2) See #1, as this is really the other side of the same question.

3) the flutter issue is airspeed and rudder design dependant. At high speed 9when it broke) the rudder was buzzing like crazy. Slowed down and it quit. While the rudder fluttered the plane wanted to dance all over the place.

4) (sort of...) Depending on the model, you may be able to have good enough control to land it.
Rule #1 on a failure that leads ot a control surface flapping: SLOW DOWN. You want the model to be below the speed where the surface flutters.
You need to verify good control before attempting landing. If the plane doesn't have good control... plant it in a tree or in the dirt as far from people as possible.

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I have had the rudder come loose as described in the original scenario, and was able to save it. I have seen the rudder come off of a model and it be saved. (with the rudder hanging by the clevice!)

I have had an aileron clevce break in flight... the model was controllable only AT stall speed. I landed that one out in the weeds about 50 ft further than the runway. (lost both wingtips in a mid-air playing R/C combat... and was missing 1/4 of one wing.)

I have had a plane seem to explode in flght... lost one FULL wing due to overstress, and I put the plane into knife edge to get it pointed away from the pits. That one I planted in the trees and totaled the rest of the airframe.


Whatever the failure... DON'T PANIC. Do your best to regain control and put the plane down safely. (as in not hitting anyone.. to heck with the model.)

as someone whos flown home safely a funfly inverted with no tailplane using throttle for pitch control, and also a club trainer with a snapped wing brace during a students roll, wings at 40 degrees and a huge urge to turn, full aileron and rudder to fly straight!. Seen a scale Mustang fly home with NO fin or rudder.
so don't panic, use all your controls, keep it slow but fast enough for control, if you've lost a wing for example fly the fuz home and use what controls you have to first get it away from crowds etc then try to induce a spin or some form of control to lessen the impact

I have had this happen on a cap 232...and as several people have mentioned it doesnt affect the plane at all....i didnt even notice it had come undone till i started to try to hover. I went ahead and flew the plane around for a few more minutes and really couldnt tell the rudder was unhooked until i landed in a fairly strong crosswind.

Ok, Thanks for the replies. It looks like most are agreed that it would not effect the flight too badly.

I was trying rule out some possible causes of a crash. My mate was flying as described in the first post the other day and he said whilst turning the plane it flipped on its back quickly but despite holding in right aileron the plane went out of control and no input seemed to make any difference. He shouted my name and as I looked up I just saw it go in. It trashed the plane but we checked every thing was working before we picked up the bits.

It range checked ok, battery is still good, but I noticed the clevis was out of the horn for the rudder. But it does now seem this happened in the crash considering every thing that has been said here.

I remember hearing him shut the throttle before it hit so we are probably looking at a short radio hit or some turbulence caught him out, tipped it over and possibly stalled the wing which he could not get out of. He did say that the plane slowed up before tumbling to the ground as he described it.

Really... what happens with one model is not guaranteed to happen with another on loss of rudder. The rest of the aircraft design makes a difference.

A minor warp in the fuselage which was trimmed for with rudder could be a disaster if the rudder clevice breaks.

Most 4-channel aircraft, if you get in a spin and don't have rudder control... its game over.

To aid in evaluating why a model crashed we really needed to know more of what was going on with the model that crashed... not be speculating about which result could happen from one clevice breaking.

It is VERY possible that your clevice popped free and that it caused the crash.
A) the plane did respond to throttle command before the crash, so the radio was working.
B) clevices rarely pop free in crashes... more often the control horn is ripped out of the rudder or the pushrod bends. (or breaks)
C) a short radio hit would almost certainly allow reganing control before it hit if he had time to regain throttle control.
D) a short durration rudder flutter can pull the fin and stab off of some aircraft. (game over)

It is impossible to transfer a torque across a hinge.
Unless something keeps the loose rudder from flopping freely, the worst can do is flutter itself off.
If the pushrod keeps the rudder in contact with the rest of the plane, then what happens to the airplane can be "odd".
Attached:
A sloper with ZERO, 2 and 3 vertical surfaces. As long as the speed is kept up, the version with NO vertical flies well.
Let the speed drop, and it can fly sideways and backwards..
The Kadet vertical was hit by another plane.. Kept the speed up, and landed straight ahead.

Fluttering control surfaces can transfer energy to the fixed surface very easilly... The rudder moves right, the rudder-fin are now airfoiled "lifting" left... then the rudder waves over to the left and they are lifting right. The sudden change in direction of force can be an immense shock load. (not to mention the dynamics of that rudder's mass swinging back and forth) You can litterally rip the fuselage in half this way.

Never underestimate the power of Flutter. It can break ANYTHING.

Who said it was a torque being passed across the hinge? BTW you CAN you can twist a hinge 90 deg to the direction it is meant to move... you will transfer a LOT of torque via the hinge.

Never said a plane DESIGNED to fly with no rudder wouldn't fly without it. Plenty of 2-channel aileron-elevator slope gliders do it all the time. But you rip the empanage off a conventional aircraft in flight (OFF, not held by the covering as with the Kadet pictured) and I defy you to keep it in the air.

BTW.. if that Kadet's fin wasn't held in line with the airflow by the covering on the right side... it wouldn't have had a snowball's chance in hell of getting down intact. (and I note the rudder pushrod is still attached...)

You sure about that?

If the vertical stab is infinitely stiff, then with no linkage, the rudder will fair into the relative wind.

For flutter to occur (in the modes I am familiar with) there must be an "energy" coupling between the fin and the rudder. These forces would transfer between the flexible vertical stab and the rudder through the hinge. It seems that the force on the rudder will act at the hinge point and create a torque through the CG of the rudder.

This is why we balance rudders at the hinge line, so that any force on the hinge will NOT generate a torque and move the rudder. If the CG and the hinge are coincident, then the moment arm is zero, and no torque is generated.

When they are not balanced on the hinge line, any movement of the fin (from flexibility, a gust, whatever) will cause a torquing moment, between the hinge and the CG of the rudder

Sorry if I messed this up, I thought it ws how it worked

Who's this "we"?
Never have balanced a rudder.
If the surface (not limited to rudders) can bind against what is supporting it, then what happens to it can affect the plane.
Every one that's come loose on the planes I fly has faired itself. It's a rare event in any place.
A sufficiently heavy surface.. rudder, elevator, aileron, -can- go into flutter and affect the rest of the plane, but mostly it will fair and exert no influence on the plane.
Surface flutter is frequently created by an overly heavy surface, restrained or not.
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Witness some early pre-WWI biplanes with the ailerons dangling when the plane is sitting still on the ground.
As speed increases during the takeoff run, the aileron will rise, attempting to fair itself. The control cable, which pulls the surface down only, restrains the upward motion at some designed angle.. then the surface acts as an aileron is expected to.
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Flying contact combat on the slope, losing the control horn on an aileron merely inactivates that surface. As long as the aileron on the other side was still operational the combat can continue.
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Losing an elevator horn, or having the pushrod snap, is not a benign situation though. It's as if half the horizontal vanishes, and the plane seeks a new trim position, which is generally some feet underground.
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This one lost the entire right side horizontal in flight.. the pushrod was on the left half. The plane was landed without incident

Having never seen a lose control surface flutter... you are VERY lucky.

The best example I had was a mid-air taking off a section of wing, and snapping that wing's aileron clevice pin. Anything faster than right on stall speed, the aileron fluttered and the plane was very unstable. At stall speed it was easilly controlled. ( I still have the airplane... havn't gotten around to fixing it either.)

I had a coroplast airplane develop aileron flutter (clevice stayed attached) that split the hinge for 6 inches before I got the plane slowed down enough to stop the flutter.

I had another coroplast plane flutter the vertical stab (no rudder) right off the plane. (didn't keep that one in the air..) I heard and saw the signs of flutter and before I could move the throttle... the tail had parted company with the fuselage. (ripped part of the fuselage and some of the horizontal stab's skin off with it, so it wasn't a bad glue joint... ALL of the glue held.)

OK I thought we were talking theory here I guess not. You could line up a hundred planes that do not need rudder linkages to fly at 70 mph with no flutter, does not address the underlying theories.


You have never heard of balanced surfaces to prevent flutter? If the surfaces are not balanced, and 'unbinded" rudder and fin can transfer energy back and forth,. That is what causes fludder in the first place.


My last fast jet did about 282 mph, so I have heard of it.

Everyone is assuming that this guy was flying a straight plane to begin with, he could have been flying a" potato chip" that needed 15% of rudder trim[initially] to stay airborne. I have flown low wingers with no dihedral that were as solid as a rock. Most" unexplainable" crashes are from a too heavy a plane, slowing down just enough, on a down wind turn, and the pilot's initial reaction is to say that he did nothing wrong, because that's the way it seems at the time. The more crooked a plane is, the easier it is to recreate this scenario.

Yep.. straight, properly balanced aircraft with adequate airspeed for flight were in my base assumptions. and we all know what happens when we ASSuME something... [X(]

All the people I've had to tell that they were STALLING at the top of a loop (doing 90 mph and still stalling...) I should have thought of a stall-spin+dumb-thumb combination.

I've had any number of planes flutter. I had an ANABAT slope combat which I induce aileron flutter at will. And stop it.
I DO fly these things.

guy here flys the correx buzz bomb, any fast pass has a flutter to it, does no dammage. as with a sport plane i had, it was strong enough to survive the high frequency low movement flutter. i've flown flunflys with flapping ailerons with not much trouble.
a loose surface in wind will want to move tho, thats why buildings sway and what starts flutter. if you slown down to below this natural point you wont get flutter and it'll just hang at the back doing nothing.
Having flown a 130Mph delta through a 60mph Ganster head on, left my wing tip in his foam wing then took out the entire left side of his tailplane i can say anyplane that still has at least half a working elevator can land with no troubles as we both did, my damage was the wingtip only so my elevons were fine. now loose elevons, thats trouble!!!!! but i've seen a Rapier land with one elevon only!!!!! the other controled roll until it's glide path brought it to ground.

continuing to fly with flutter is about as bright as dousing the plane with gasoline and droppng a match on it.

Flutter (even that small movement high frequency tye you think is benign) can rip the gears out of your servos. It can snap the control horn off of the control surface. it can rip the hinges apart... it can shatter the entire aircraft if nothing else breaks first.

my plane only fluttered on the fastst of passes and checks showed even after months of this no damage, i have also seen the milisecond buzz bang happen.
anytime i hear flutter i yank the throttle back and hard up at the same time, this dumps speed quicker than anything else. however if the plane can take it a little buzz every now and again winds up the old guys who start moaning
the buzz bomb however gets cheers for longer and longer flutters ( as it's pretty slow and takes a lot to start it off lol )