Engine thrust line

[Murray Parr]

Has anybody considered adding a degree or 2 of right thrust to the Rotax engine to help minimize out of trim conditions and if so, what methods would/have you used?

I am thinking the easiest way to adjust the thrust line would be to add a AN970 type of washer between where the gear mount attaches to the airframe. Any thoughts on this or other suggestions?

[Kai]

No- not really!

I´ve just finished my third taildragger season with this engine and close to 100 hrs in the air, after throwing in th towel with th Jab. My 120HP EP915ECI is rigged zero/zero degrees in the mount. True- initially after adding t/o power it pulls to the left like there is no tomorrow, which has to be sorted with a heavy foot on the right pedal. But once in the air everything evens out nicely. I´ve got the fixed rudder trim tab set so that it will cruise (120 kts) straight ahead without my feet on the pedals. Like all the others mine went left wing down when solo, but this was fixed by reflexing both flaps to the max, and gradually lower the left flap in small increments- with the huge barndoor flap it did not take much. The big surprise here was putting on the flap/fuselage angle: I recall it made a significant difference, and I had to fly all the tests again.

I also have installed a simple cockpit adjustable aileron trim that takes the effort out of any aileron imbalance. Initially rigged neutral during cruise, I now hardly bother to retrim when solo- but flying with a passenger requires a few turns on the trim wheel. Total time on the airframe thus rigged is now some 650 hrs.

I guess this did not help much…….

[Skippydiesel]

Kai - I have been thinking of fitting a pilot controlled aileron trim, (to counter effect of passenger) so would very much like to have details on how you have done this.

[Skippydiesel]

Has anybody considered adding a degree or 2 of right thrust to the Rotax engine to help minimize out of trim conditions and if so, what methods would/have you used?

I am thinking the easiest way to adjust the thrust line would be to add a AN970 type of washer between where the gear mount attaches to the airframe. Any thoughts on this or other suggestions?

Hi Murray,

I would go with Kai's experience ie application of boot on take - off/climb out.

I hope to have my Sonex back in the air in the next 10 days or so. Along with a lot of small & not so small modifications, I have packed the front engine mount with a 1 mm washer on each side, very slightly raising the thrust line, in the hope of reducing the need for up elevator at high speed - will report after next phase of test flight.

[13brv3]

The number one thing I'd do differently is to add some right thrust in the mount, or at least allow for shimming to the right. My radiator and oil cooler are attached to the mount, so if I shim the mount now it would misalign my cowl inlet alignment. If it was easy, I would have done it long ago.

I have a fixed trim tab for the rudder and ailerons. They work fine, and cruise is hands off. The torque makes coordinating rudder completely different for left vs right turns. If you increase and decrease throttle in cruise, there's a comical amount of tail wagging. On the Onex, I think it could have used a bit larger vertical stab anyway, since it's a little tail happy anyway. None of this is a real problem, but there's definitely room for improvement.

Rusty

[Kai]

Kai - I have been thinking of fitting a pilot controlled aileron trim, (to counter effect of passenger) so would very much like to have details on how you have done this.

Hmmmm.

While this system works fine for me and has been copied on one other Sonex A, I am sure there would be a lot of naysayers, as they would feel it could interfere with aileron control. If the rules Down Under are the same as here- if something is not specifically approved, it is absolutely forbidden! Anyhow, due to cracks in the aluminium sheet I need to take my seat pan out for replacement when winter sets in, I´ll then get a photo or two from the setup.

[Skippydiesel]

Kai - I have been thinking of fitting a pilot controlled aileron trim, (to counter effect of passenger) so would very much like to have details on how you have done this.

Hmmmm.

While this system works fine for me and has been copied on one other Sonex A, I am sure there would be a lot of naysayers, as they would feel it could interfere with aileron control. If the rules Down Under are the same as here- if something is not specifically approved, it is absolutely forbidden! Anyhow, due to cracks in the aluminium sheet I need to take my seat pan out for replacement when winter sets in, I´ll then get a photo or two from the setup.

I am no authority, however by my understanding, we have two basic small aircraft categories - Factory Built & Home Built (Experimental).

Factory Built - Can not legally be modified in any way, without the approval of the factory/manufacturer
Home Built (Experimental) - Do whatever you like

All Sonex aircraft in Australia are home built. Although you could install a V8 turbo diesel there might be problems getting the aircraft registered due to control issues.

In short, I can install or not, whatever trim system I so choose

[Murray Parr]

[/quote]Hi Murray,

I would go with Kai's experience ie application of boot on take - off/climb out.

I hope to have my Sonex back in the air in the next 10 days or so. Along with a lot of small & not so small modifications, I have packed the front engine mount with a 1 mm washer on each side, very slightly raising the thrust line, in the hope of reducing the need for up elevator at high speed - will report after next phase of test flight.[/quote]

Yes I expect to heavy foot the rudder pedal on climbs. I am more trying to get the cruise stage closer so it won't need as much of a fixed trim tab to fly hands off during the cruise stage and hopefully give up a little less speed loss as a result.

With your added washers to pitch up the thrust line, my guess is that will cause you to need more right rudder than before. Could you let us know if you actually find that to be the case once you test fly it please?

[Skippydiesel]

We will talk Murray.

Ball now centred (most of the time)

When last flying, had a small fixed trim on rudder to counter left yaw.

Got the flaps about right but will fine tune when back in the air - still has slight tendency to lift right wing & drift to the left.

It will be interesting to see if small engine alignment change has any noticeable effect - movement at prop tip about 6mm.

A smidgeon here - A smidgeon there - will eventually have a nice stable hands of cruiser (I hope)

[BRS]

Kai - I have been thinking of fitting a pilot controlled aileron trim, (to counter effect of passenger) so would very much like to have details on how you have done this.

Here is how I installed aileron (& elevator) electric trim.
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