Rudder in front?

[Laneman]

Building an RC canard from plans. Current design flies extremely well with a V-tail at rear of fuselage but no rudders. I was thinking of adding a single vertical stab on top front with a functioning rudder. I figure the elevator works fine up front, why not a rudder too? Any thoughts?

[dpaton]

That would be a rhino rudder, which is what the Long-EZ was originally designed with. The first Long also had significantly more sweep in the wings, and looked like an enlarged VariEZE. The changes Burt Rutan made before he released plans to the homebuilding community included rudders on the winglets and a completely new wing which fixed all of the poor handling characteristics of the plane.

 

If it's large enough, or if you make it fully pivoting instead of a control surface on a vertical stab. I think it'll be fine.

 

-dave

[Laneman]

What is the disadvantage of a standard rudder on a fixed tail vs. a fully pivoting rudder? My initial idea was to use a pivoting rudder, but I thought it would be hard to design a mount for it, so I then thought I would try a standard tail with rudder. It's good to hear it's been tried already. I was thinking things might end up bad on the test flight.

[dpaton]

Well, tried already is a misnomer...it was tried and discarded because on the real aircraft it was tried on, there were a lot of problems with aerodynamic performace.

 

The advantage to a fully pivoting control surfact is that it can provide more control authority for a given amount of deflection. For something way up on the nose, I'd want as much authority from as little deflection as possible, for visibility reasons. For your model, you can probably go either way.

 

Out of curiosity, can you post a pic of your model? I'm curious what kind of canard has a V tail, and why it would need more yaw control, as the canards we fly here need almost no rudder in most turns.

 

-dave

[Laneman]

The designer flies his with no rudders, I just like having another dimension to flight with the RC's (knife edge). I'd also like to see if I can make it hammerhead with a nose rudder. We do some extreme aerobatics with the RC's. Here's a link to a photo of his plane. Type in starliner in the search window when the page opens. http://www.gamarc.org/photos/

[Spodman]

Well, tried already is a misnomer...it was tried and discarded because on the real aircraft it was tried on, there were a lot of problems with aerodynamic performace.

 

Erm, not sure this is as per the actual history. The Vari-eze first appeared with 'normal' ez rudders on the winglets, but had no ailerons. Roll & pitch controlled by elevons on the canard. Spoilers were added because of crap handling, then the elevons & spoilers ditched in favour of elevators on the canard and ailerons on the wings. I had an email from Nat Puffer claiming to be the only home-builder to have installed all three! Long-Ez was the same as the definitive Vari, with the option of 'high performance' rudders (as in bigger and more rudder-looking) as per the Cozy plans version.

 

The Defiant was the only Rutan canard with the forward rudder, a small, all moving surface under the nose. Rather than correcting bad handling it was there to make the controls easier to build, (no moving parts on the winglets & shorter control runs), and taking advantage of a steerable oleo nosewheel that didn't have to retract to park. Versions have been flown with the rhino rudder and others with Long-Ez rudders, with no great change in performance.

I am not aware of the rhino ever being approved by Burt for the Vari or the Long, never heard of anybody trying it either. But you can probably see more canards at you local than have ever been built here in all of Oz:D

 

Adding a rhino to an existing design you would have to appreciate the de-stabilising effect of having a fin up front. Having no fixed part of the fin will minimise the effect. You may have to increase the size of your butterfly tail to compensate?

 

PS. I've had a look at the pikkie now those fins are already huge, maybe rudders on them would be more effective. Nice looking model.

[dpaton]

Erm, not sure this is as per the actual history......Long-Ez was the same as the definitive Vari, with the option of 'high performance' rudders (as in bigger and more rudder-looking) as per the Cozy plans version.

By the time the plans were released, that was true. When it was originally built, the Long had a rhino rudder and Vari like swept wings. After the initial flight testing there was poor control in all 3 axes, and the wings were completely rebuilt with the Long style attach (the original had Vari style wing attach points to go with the Vari-ish wings) system and with the new profile and sweep. Rudders were put on the winglets and the improvement was marked. The report appeared in CP23, page 2, 1/1980. Relevant portion below.

 

-dave

 

The original configuration of the Long-EZ used VariEze wings placed out on a centersection spar that was 4 ft longer than a VariEze. The wings were swept more than a VariEze to support the heavier engine. It had Rhino’ rudder on the nose and no control surfaces on the winglets. That aircraft 79RA, was built in four months in the spring of 79 and made its first flight on June 12, ‘79. It did not fly well. Directional stability was weak. Dihedral effect was excessive. Adverse yaw was high. Roll rate was sluggish. Early airflow separation on the wing caused pitch instability at low speeds. The stall speed was too high.

During the next five weeks, N79RA made 51 flights, testing the effects of over 30 different modifications. Modifications included many configurations of wing leading-edge cuffs, wing fences and vortex generators. The winglet "can't" angle was changed. The ailerons were rigged to various neutral positions. Some of the changes resulted in improvements in pitch stability and lateral-directional flying qualities.

However, we were unable to improve the stall speed, landing attitude and roll rate to a satisfactory level. By August we were convinced that to get the Long—EZ we really wanted, we would have to build an entire new aft wing.

The new aft wing, first flown in October 79, had the following improvements:

(1) Less sweep

(2) More area

(3) A new Eppler airfoil similar to that on the Defiant.

(4) Longer ailerons.

(5) Improved winglet juncture to eliminate airflow separation at wingtip.

(6) Overlap—type wing attachment to centersection spar, allowing incidence adjustment and eliminating the expensive fittings.

[dpaton]

The designer flies his with no rudders, I just like having another dimension to flight with the RC's (knife edge)

Looking at the size of that V-tail, a standard 2 servo mixer would mock elevator and rudder motion without any trouble for most things.

 

That said, knife edge with a V-tail will be tough no matter what. I had a .60 powered stick model that would do everything under the sun but that. I swapped the V tail for a T and it did knife edge too. Just my $0.02.

 

-dave

[Laneman]

Very interesting posts. Sometimes I think I should just build the plane per the plans because it flies better than anything at the field. I just don't want to give up rudders yet. The Starliner RC had fluttering in the rudders, so the designer removed them. He thought it was caused by the rudders being in the propwash. This is why I thought of adding a rhino rudder up front. My other idea is to move the tails out onto the wing about a third away from centerline and change them to vertical like this Santorin.

[Spodman]

It had Rhino’ rudder on the nose and no control surfaces on the winglets.

Fair enuf, guess I'm wrong again!

[dpaton]

Fair enuf, guess I'm wrong again!

No worries, I'm wrong at least 3 times a day, which is why I try and quote a specific source with every statement of important fact I make. Plus, it makes searching for posts easier ;-)

 

-dave

[Spodman]

I found a picture. Sadly the rudder itself is not clearly in view, anybody got a better one? Taken Oshkosh 1979.

[dpaton]

I can see the TE of the rudder...if that guy without his shirt on would just move, we'd be able to see the whole thing.

 

-dave