Rudder trim issue on my Drifter

[Guest Maj Millard]

Thrust does not come straight back from a propellor, it rotates. For instance on a tractor it can rotate around the fuselage until it strikes the tail completely opposite to what you would expect. The air hitting the tail of a Drifter is not going to be straight or parallel with the flight path either, it'll hit one side more than the other especially at full power.

 

The Caravan amphib float-planes that I work on (as an example) will have three times the corrosion problems in the left wing, compared to the right wing. It is because the rotational air coming off the prop, sends more spray onto the left wing than the right, at takeoff on water...I have done a lot of deadstick time and landings in Drifters, and they fly lovely, and straight as a die with no power .........................................................................Maj

 

 

[farri]

Rudder Trim.

 

Hi Justin, My opinion only and others may disagree. There is no short answer to your question, the answer is more complex than just putting a trim tab on the rudder.

 

I`ve had my Austflight WB Drifter for twenty seven years, instructed in it for twelve years...have thousands of hours flying time and I don`t have a rudder trim, nor will I ever have one and I`ve never needed one in the numerous other aircraft I have flown.

 

Primary effect of rudder is yaw, secondary effect is roll. Primary effect of ailerons is roll, secondary effect is Yaw.

 

If the aircraft doesn`t have any structural defects, a rudder trim is not required . I use the rudder in coordination with the ailerons, when taking-off and landing or when manoeuvring and doing turns. I don`t use the rudder in straight and level flight other than in severe turbulence. It doesn`t concern me if the nose of the aircraft isn`t pointing directly on track, in any case, with a cross wind, we need to hold off drift, so the nose of the AC won`t be pointing directly in line with the track.

 

When on the ground, you can`t stear the aircraft in a straight line, simply by fitting a trim tab and then turning the trim tab to the left or right. Running in a straight line, when taking-off and landing requires the correct amount of accurate foot work.

 

Depending on how we use the controls, once in the air, when manoeuvring, by using the rudder and ailerons in coordination, we reduce or overcome adverse yaw, secondly, the aircraft will respond twice as fast to the controll inputs, You can snap out of a turn and if done correctly, the nose of the aircraft should be pointing exactly at your reference point. In turbulence, you can pick up a wing accurately and twice as fast.

 

I don`t know if I`ve helped you much, but as I`ve said above, the aircraft doesn`t need a trim tab. I want to fly the aircraft, not have the aircraft fly me.

 

Frank.

 

 

[facthunter]

It is possible in theory to have a plane set up that doesn't have much control load both when you are climbing and when you are gliding, but I don't know how you would achieve it without engine offset where you only have one propeller. You usually require some engine offset and some fin offset as well

 

You don't ever fly a plane on trim except when there is a failure of a primary control or you are demonstrating or practicing how it can be done. You put the plane where you want it and if there is a load on any control you MAY want to reduce it with trim, depending on your situation.

 

ie if it is a back stick force in a steep turn you would not do it, unless you were flying something that had hydraulic controls and you had lost hydraulic power, where it could be absolutely necessary.

 

The "fixed" tab is a means of correcting some irregularity with the aircraft's rigging rather than do something more basic to cure the problem. Small adjustments may be acceptable, but larger ones really are not, as it is masking a bigger problem, giving your plane more drag and less control authority and adding to airframe loads. Nev

 

 

[Justin Hawkins]

Farri,

 

I understand the aerodynamics and forces involved, which is why I brought this up. Having a trim tab is generally not a bad thing, however all aircraft of the same type and equipment should require a similar trim tab. IE: If one Drifter SB582 should have one, all of them operated the same way should have them also. At least in a perfect world. That said, we all know that individual aircraft have their own quirks. But having a huge tab on mine and no tab on another seems excessive, indicating something is amiss.

 

I've been inspecting mine and measuring things to make sure it's straight. I've found a few things that concern me:

 

My sails are worn, so I'm replacing them. This might be a small factor as the tail sails are a little loose. The Right inboard batten has poked through in the front, reshaping the wing a tiny bit.

 

Inside the rudder, one of the lower ribs (made of styrofoam) was broken. I fixed this and I think it helped a bit.

 

I measured the wires from the mid trailing edge of the wings to the tail where they tie into the tail bracing wires. The left wire is 1/4" longer than the right. They're both semi-snug without being to tight. I'd say there's 2-3" of movement in the middle if that makes sense.

 

I'm not sure what the offset angle of the engine should be, or if there's any way to change it.

 

My main tube is straight and has no cracks. Inspected it with a digital inspection camera.

 

 

[skyfox1]

Hi Justin also check the ailerons to see if they are set even l have fixed to drifters that flew terrible because the ailerons were set with to much camber you always had to have heaps of forward stick pressure to fly level.

 

 

[Justin Hawkins]

Skyfox, What do you mean by camber ? Both ailerons were to high ? To low ? My drifter has flaps. Seems like pitch trim and control on my bird is great.

 

 

[skyfox1]

Hi Justin the ailerons were set with to much down throw creating heaps of lift and produing to much drag in level flight .

 

There is a standed for setting up of the ailerons yours might be different becuase you have flaps not familiar with your set up..

 

 

[Justin Hawkins]

Just in case anyone is curious, it appears that my rudder trim issue is solved. After fitting new sails from Wayne Fisher, the trim tab was left off of the rudder, and it now flies straight.

 

I believe the thing that fixed it was reshaping the wing battens, mine were pretty far out of spec.

 

 

[Tex]

Always curious when it comes to Drifters, thanks for the update Justin!

 

 

[Patrick Normoyle]

It is my understanding that the trim tab is used to counteract the uneven displacement of thrust air from the prop to one side more so than the other and the rotational torque force from the engine, my fisher Mk1 has one, every drifter I have flown has had one, 503, 582SB AND 582SB on floats.. I agree that the rear cables from the trailing edge of the wing spar that run to the main tube bolt should be taught, to make the installation / removal easier I have installed adjustable turnbuckles to each wire, they are then adjusted to be taught and equal in length, this should make the leading edge of the wing at 90deg angles to the main tube.. They should never be slack as these cables translate the rotational forces from the running engine into the airframe and as you can see above they can be caught by a spinning prop.. Another possibility, is your verticle stab really verticle or a little to one side, I'd hav a look here also, the cables can be adjusted by as you and others have mentioned, twisting the cables by a maximum of 5turns, remember one direction will shorten, the other will start to unravel the cable.. Good luck.

 

 

[Patrick Normoyle]

Just read the update, Justin that is great news, happy flying.