Help,

I have extended the ailerons, rudder & elevator on my plane, now its like trying to fly a ball bearing in a plate.
The cg is good (I think)

I have sudden wing tipping at any speed which is difficult to recover from, and it’s generally unstable with erratic behavior.

Any suggestions please.

It sounds like you made it sprially unstable by adding too much vertical area to the tail. If it won't track straight and keeps trying to fall off to one side or the other into a spiral dive then that's what you did. Or if it's a close thing and you go into a turn the model will try to tighten into a spiral so that you bank into the turn and then have to hold some constant "top" aileron to prevent the turn tightening. That's a milder form of the problem. Try cutting off the extra you added to the rudder at least. If that fixes the problem then what you need to do if you want more rudder area is to move the hinge line rather than adding area. Pretty much means making a new fin and rudder.

I am confused, how would it be unstable in the vertical axis with respect to yaw when there is an increased in vertical stab area? Wouldnt increasing the area make it more stable and be able to track better? Is the prop wash making this unstable condition?

One would think so but in reality it's the other way around. Make a fin too small and you get dutch roll where the model won't track well in level flight and often will have sort of a swinging oscillation from side to side. In really bad cases it'll swing so hard it'll induce a snap roll and spin. Marginally small shows up in the turns with a model that seems to want to hang nose high and shows signs of adverse yaw when using ailerons.

On the other hand if you make it too large the model actually becomes unstable the other way and wants to drop off a wing on either side and it becomes hard to control just as Stratman is finding. The size of the vertical fin really does fall into a smallish range of acceptable size for any particular design.

Factors influencing the size are side area in the fuselage, tail moment arm length, dihedral in the wing and center of gravity location.

A few years back I tried all this on a hack 2 meter aileron glider. I was dismayed at the control response of some of the sailplanes I'd had a chance to test fly and wanted to get a handle on all the factors. So I made a nice big all sheet fin and rudder for this model and went out with my TX and hobby saw in hand. I found that with the oversized vertical and a foward CG it was sort of controllable but showed some tendency to drop a wing in the turns. I move the CG back for the next flight and it was like trying to balance a broom handle end on. CONSTANT input was needed to keep it level. Out came the saw and off came about 10% of the vertical area. Next flight was about the same as the first with the CG forward. So off came another 5-8% and now I had a model that flew great in level flight and grooved very nicely in the turns up to about 50 or 60 degree banks at which point it wanted to try and steepen up again. A few more flights fine tuned the CG back a little and worsened the spiral dive bit so off came another two bits of fin on two flights. About 5% each time. The first made the model fly beautifully, the second made it start to show signs of adverse yaw despite the use of coupled ailerons and rudder. So on went the last piece taken off, a trim cap of monokote and I called it finished.

All of which goes to show that the vertical tail area is very important to how a model flies. There seems to be a "happy" range of about 10 % area between nasty on either side.

Thanks you guys for the comeback, my first thought was like what Cappio said, that more rudder would help, but after reading what Bmathews has written I can see the logic in that.
Unfortunately after flying it yesterday the plane is now dust, went in full throttle taking my new ish Irvine 53 with it (cracked the crank case). Total loss of radio contact, just had to watch as it went in.

I now have more questions, any thoughts would be appreciated.
The low down on this plane is that I got second hand virtually free, it was an old pattern ship. I put my sanwa radio set in it, and flew it. I liked it so much because it was so stable and predictable; I gave it a new engine and covering job.
But while I was at it, I doubled the rudder size rearwards (no height), ½” to elevator and the ailerons were 1” strips that I increased to 2” at the root tapering out to 1” at the tips. When I flew it on Wednesday it knife edged so easy, but like I said in my earlier post “tippy and unstable”. On Wednesdays flight my first thought as it took off was that I did not have total radio control, but after a while I found I could control it to a fashion, it was slow to respond and would do odd flicks like someone else was flying it.

I went to the field Friday after posting here, but I had pulled out all of the radio gear and installed the JR receiver from my extra and new futaba servos. This was to eliminate the radio as possible problems. I also added a couple of degrees of right thrust as I noticed the plane had a tiny bit of left thrust. She took off much the same and was erratic until I gained height and then she smoothed out and was flyable for a while. I did a few laps inverted with just a touch of down. I think it was calm weather up there but as I brought her down where it was probably more turbulent due to the trees, she was tippy and erratic again. If the rudder was to too big I suppose it would make sense that it would fly rough in spots of the field where it was more windy.???

Took off for another flight, gained height real quick with power on then lost total radio contact, she flipped over went in full bore inverted.

When I was sweeping up the wreckage I noticed the crystal was out of the receiver, so I pushed it back in, it’s a good tight fit so was baffled as to how it had come out.
When I showed the wreck to a guy at the field, he was concerned as to how I had mounted the receiver by sticking it to the inside fus wall with a couple of layers of double sided sponge tape. His issue was with vibration that can occur. Does anyone think this can cause loss of signal, is this sort of practice a definite no no?
I know my radio gear to be spot on as it has well over 200 flight in my Extra and I am now worried about putting it back in the Extra for fears of repercussion.

We range checked the radio gear on the ground after the crash and no problems were detected.
I am thinking now with regards to the sanwa gear that was previously in the plane, could I of had radio interference there too as the receiver was mounted the same way, or is there two issues here. I am confused to say the least.



Any feedback would be greatly appreciated.

Stratman, when you say erratic flight does it mean erratic behavior on every axis or just one? If your crystal was loose you probably were getting intermittent control as soon as the engine vibrations acted on the receiver. This is a more logical explanation than an increase in tail area. I have played with tail area many times and all I found was more sensitivity to operator input but no instability as long as the center of lift is recalculated. I remember a friend found an ugly stick in the trash and we rebuilt it with a ridiculous extra large circular vertical stab with a happy face. It flew normal with no bad tendencies until one use the rudder, where it will start a spin in a split second. But as soon as you let go of the rudder it center itself and continue flying. Thats why it was so strange that it would work against a stabilizing condition.
As far as the receiver mounted on the side of the fuse that would be "ok?" on gliders since there is no vibration but still I wouldnt recommended. In the even of a crash you want some cushion for your electronics. Now, as far as power flight.....ALWAYS isolate your receiver from the rest of the airframe as much as you can....thats why the common practice of wrapping it on foam cushion. Sorry about your crash bro.

I too am sorry to hear about that. I've always been a believer in a full foam jacket for batteries and receivers but then I come from the old school that took this sort of stuff seriously because they really had to with the old state of electronics. But some things never go passe. Proper vibration and crash protection for expensive and sensitive electronics is never a waste of effort.

I guess we'll never know about that increased rudder size now. Too bad all around.

Next model please.......

I have sort of accepted that the cause of the crash was the crystal vibrating out, that seems to be the most logical explanation as I found it in the grass at the crash site. I feel better for believing it was my fault for having an airhead moment when I installed the receiver, instead of thinking it was caused by an unknown event. I have learnt a lesson by this and I will have to be more thoughtful in the future. I have always wrapped radio gear in foam on my other planes so I don’t know why I thought it was acceptable not to do it on this one.

As for the flight behaviour, I am sure it was caused by the increased rudder.

From the info you guys have provided, It has brought up an interesting point as to why my Somethin’ Extra also has ideas of its own whilst in the air. I have found that it is not a good idea to use the ailerons when using the rudder because it snaps. If I am prop hanging and try to use the ailerons it flicks out quick and the nose nearly always ends up pointing south. I searched RCU prior to buying the SE and most of the guys said they extended the rudder to help with Knife edge so this is what I did with mine at the building stage.
It looks like I over enlarged it, as the turns do tend to tighten in to spiral if I’m not careful and it weather veins quite bad in a breeze. If I fly a down wind leg slowly it will do a flat turn and line itself up into the wind virtually hands off. Interesting to watch but annoying when trying to do other stuff.

When I think about it, because the SE was my first aerobatic plane and I just thought I had to get use to the constant wing tipping when flying in a breeze and assumed this type of plane flew like this. It can be a constant battle to keep the wings from tucking under when breezy. On a calm day it is an amazing aeroplane, and you wonder how it stays up at such a slow speed and it lands like a heli most of the time.
I am going to cut down the rudder to a more acceptable size as it was never any good at real knife edge anyway.

Can anyone shed some light on the characteristics of the rudder ? Is the height of the rudder more of a problem than the length? Should the rudder be short in height if it is long out the back and tall if short out the back?

Any info appreciated.

"Erratic Flight Behaviour" doesn't sound to me like too big a fin or rudder.
Sounds more like the CG too far aft or radio problems, or something is loose or flexing.
A bit of structure or a control surface or pushrod cracked and moving about would be my guess.
Shame it is too late to find out and sorry to hear about the damage. Trashing an Irvine 53 is a tragedy.