i was just thinkin, a lot of sport/fun flys you never really use rudder, i just flew my gp dazzler and i was just bankin' and yankin' when i wanted to turn (you know, slam the ailerons over then pull back on elevator) never once did i touch the rudder - only on the ground for steering,

soooo...... the question is what would happen if you design a plane that didnt have a rudder? more importantly a vertical fin

just a wing and horiz. stab and elevator

??what would happen?

I have a 25 sized plane with only ailerons and elevator.

A vertical stab helps the plane track straight and provides yaw stability.

Would one fly without? Yes. But it would be a terrible pattern plane, and a terrible 3D plane where you often use lots of rudder.

Vertical stabs also help a lot in spin recovery. But look at flying wings, most don't have vert stabs. But a lot of them do for yaw stability.

Anything will fly with a big enough engine.

mmm, interesting, yeah i forgrot about flying wings

now what about a little ultralight pusher plane?

i have my kadet senior left over wings with barndoor ailerons on them and would like to build a fuse with a pusher engine in the back and a sq. alum. tube out the back and just put on the horiz stab and elev. no vert. fin/rudder

would it be a squirrly thing?

SWEPT and HIGHLY TAPERED flying wings can get away with it because the sweep and taper puts the center of drag behind the center of gravity. The old Klingberg wing and the Northrop bombers are expamples of this. However it's a touchy thing. The Klingbergs were well known for acting like they had a hinge in the middle and would oscillate in yaw under various circumstances. The Northrop bombers used the "fin" effect of the prop discs and propellor extension housings to provide the vertical fin effect. Note how when they went to the jet design they had to add little fins to compensate for the missing props and housings.

So it's not correct to say you do not NEED a vertical stabilizer. You DO but there are some options depending on your planform.

For conventional models you can't get away without one. It has to be there or the model just will not fly for more than a brief and exciting show of nutiness. However I fully agree that you do not need to use a rudder. But if you do not have one forget about ground based takeoffs and switch to handlaunching. The only way you can take off the ground without a rudder safely and predictably in varying wind directions is with a rudder. Ailerons are not usable until the wheels leave the ground. I know a few deltas and others have used nose wheel steering via coupling to the ailerons but I'll bet there are some anxious moments during sidewind takeoffs.

yeah, ill just put on the vert fin and rudder and be done with it

"I have my kadet senior left over wings with barndoor ailerons on them and would like to build a fuse with a pusher engine in the back and a sq. alum. tube out the back and just put on the horiz stab and elev. no vert. fin/rudder

would it be a squirrly thing?"
.

It won't be squirrelly at all, about 25 feet into the takeoff run. Then it will turn itself into junk at 26'.
YES, a vertical surface is needed, for the configuation specified.

NO. Try the Spratt Control Wing Concept. no rudder, no horizontal tail. has been around since 1907, some say he preceeded the Wright Brothers. have modified a 80" Playboy and it works. (rudder and hort tail still there, nonfunctional). havn't gotten the courage to try one without them,yet. dick

here are photos of my control wing, wing...dick

The control wing is essentially the same idea as a flying stab.... except its doing sort of like elevons or flaperons.

Pivot the entire surface at the 25% chord line and the whole wing acts as the aileron with a relatively low load on the servo.

The control wing system doesn't change the need for a vertical stab, so its a good thing you left it on. Other things have to change to maintain stability. The same goes for the horizontal stab.

You COULD design a control wing aircraft that was a flying wing. Elevator control would be by variable CG (which would be really "interresting"[:-]) and with proper design you could have no vertical. I wouldn't want to be the guy test-flying in the thing if it were full scale.[X(] Learning to use the control system would be a bit odd.

If I remember correctly... there have been some "scale" RC birds which used what adds up to the control wing at the wingtips with fixed main lifting area. they were getting very close to the control-wing flying-wing there.

Pulled my old Hustler delta out after sitting many yrs. took off. flew a couple of mins. One of the fins fell off, The Ambroid let go. Coming around to land it. At obout 75 ft lte other one fell off. Went into an immediate very fast flat spin. Decent rate was very slow so not much damage, just a few holes in the silkspan. As Bruce said, has the steerable nosewheel connected to the aileron servo.

my Playboy was a conveint way to start. have learned enough, that I can proceed with a model of Bill Wolfe's full scale seaplane. there are no horizontal or vertical control surfaces, 2 small 45 degree fixed stub fins. its an interesting subject and will continue to pursue it along with the conventional aircraft. dick

.
Is that ALL there is?
What is the pitch control?

the complete wing rotates about the pivot point, sliding tray does the job. still experimenting-- but it flys. dick

This Spratt wing is basically a wingeron type model like the Ninja sailplane. OK yeah, I know the Spratt came first. But the point is that the Spratt moves the control functions to the wing while still retaining the stabilizing effect of the tail surfaces. That flying boat uses the tail surfaces as the vertical stabilizer and a mix of the surfaces and pendulum effect to provide pitch stability for the fuselage as the wing finds it's own flying angles above on it's pivot.

Dick, I know you don't use moving tail surfaces but the model still requires them. The vertical area stabilizes the whole model in yaw while the horizontal stabilizes the fuselage provided you figured out how to let the wing free pivot on it's own but still mix in some pitch control through the servos. If you just joined the servos directly to the wing then all you have is wingeron control to replace the tail controls. To be a true Spratt as I read it the wing has to be free to find it's own pitch angle based on the power to the aircraft.

In any event the point is that if you removed the vertical tail on your Playboy I don't think you'll find that it flies very well.

PS: I've moved this to Aerodynamics as it has nothing to do with building. But it's an excellent discussion. Keep those cards and letters coming folks!

no problem. will foreward your responses to my Spratt expert, who flies a full sized Spratt Wing and see if he wants to get involved. I am not a aerodynamist. just a retired old man, building and flying models since middle 1930's. dick

FYI I had a Tiger 60, During the maiden flight I lost the rudder/fin, and she flew pretty darn well

Hey Briansommers,

Are you getting all of this?

Geeze, now I can't even figure out why rain falls down

no, but thats ok, im just going to put my rudder on and be done with it

All wing aircraft with bell shaped lift distributions that have washout in the proper areas have no need for a rudder a good place for you to look is TWITT "The wing is the thing". It explanes why you do not need a rudder
The all wings that have the right design architecture will not need a rudder..
Birds do not have rudders becaue it is not needed....

when you say bell shaped lift, do you mean a reflexed airfoil?

and birds, dont they shift there CG around when they fly?

There's a difference between a rudder and a vertical stabilizer.
I believe the subject here is the latter, exclusively.
I have found that with sufficient airspeed, a vertical surface isn't required, but it surely IS when the airspeed drops below a particular value..

And as CHanson found out the fuselage also had a contributing effect. In fact if you put a large enough kite tail on the model it would act sort of like a fin. Draggy as blazes though.

I fly the ruddder and what a diff it makes in many maneuvers from procedural turn to rolling circles and loops ! 3D without rudder is impossible

am backing out of the discusion, getting too deep for this old man. main thing is to KEEP Building the Model Airplanes., and helping the newcomers. dick

Here, here. And keep up the good work Dick. [8D]