Engine thrust line
Posted: Thu Oct 12, 2023 1:51 am
by 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?
Re: Engine thrust line
Posted: Fri Oct 13, 2023 1:39 am
by 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…….
Re: Engine thrust line
Posted: Fri Oct 13, 2023 4:16 am
by 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.
Re: Engine thrust line
Posted: Fri Oct 13, 2023 4:22 am
by Skippydiesel
Murray Parr wrote: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.
Re: Engine thrust line
Posted: Fri Oct 13, 2023 10:12 am
by 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
Re: Engine thrust line
Posted: Fri Oct 13, 2023 3:10 pm
by Kai
Skippydiesel wrote: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.
Re: Engine thrust line
Posted: Fri Oct 13, 2023 5:30 pm
by Skippydiesel
Kai wrote:
Skippydiesel wrote: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
Re: Engine thrust line
Posted: Fri Oct 13, 2023 7:11 pm
by 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?
Re: Engine thrust line
Posted: Sat Oct 14, 2023 5:06 am
by 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)
Re: Engine thrust line
Posted: Sat Oct 14, 2023 11:45 pm
by BRS
Skippydiesel wrote: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.
viewtopic.php?f=3&t=6075&start=10#p45849
Re: Engine thrust line
Posted: Sun Oct 15, 2023 3:20 am
by Skippydiesel
BRS wrote:[
Here is how I installed aileron (& elevator) electric trim.
viewtopic.php?f=3&t=6075&start=10#p45849
Thanks BRS - I don’t think I need an external trim tab, even an electrically operated one.
My challenge is to “balance” my aircraft in flight, when;
I have a passenger
When transferring fuel from my 2 x 30L wing tanks to my central 40L header (located in the usual Sonex fuel tank position).
The fuel is not such an issue as , with care, I can take the same amount out of each wing tank, keeping the aircraft “in trim”.
However a passenger (of any weight) results in extra work for me.
My Sonex has been trimmed for just me in the left seat. This makes sense as I don’t often have the pleasure of having a passenger.
My last aircraft had a simple bungee & sailing cleat set up to work on the right aileron rod - the weight of a passenger could be easily compensated for by a few tugs on the bungee resulted in hands free level flight.
I would like a similar system in the Sonex but for the life of me cant figure out how to fit it.
Re: Engine thrust line
Posted: Sun Oct 15, 2023 10:54 am
by BRS
The same rayallen servo I used on the wing could be used under the seat to pull the bungee. There is probably a simpler way but what come to mind is…
one bungee pulling left (balancing bungee) and another pulling right but connected to the servo.
I just went with the aileron trim tab (before ever flying the plane or any sonex) during the rebuild because that is what I have in the Sportsman and am used to it.
Re: Engine thrust line
Posted: Sun Oct 15, 2023 8:52 pm
by Skippydiesel
BRS wrote:The same rayallen servo I used on the wing could be used under the seat to pull the bungee. There is probably a simpler way but what come to mind is…
one bungee pulling left (balancing bungee) and another pulling right but connected to the servo.I just went with the aileron trim tab (before ever flying the plane or any sonex) during the rebuild because that is what I have in the Sportsman and am used to it.
Great minds think alike - If I continue with the bungee concept, it will have to be using a linear move actuator (or step motor) to achieve the in flight adjustments, as there does not seem to be a “path” from under the seat, to the pilot, for a simple mechanical system like I had before.
Have figured out the linear actuator will have to be attached to the control stick mechanism below the seat - this means that the whole system will move back & forth with the elevator movement.
Fixing the system to the airframe/floor would result in changes to aileron trim with pilot activated elevator movements.
I had moveable external trim tabs on the GA aircraft I flew - that’s okay they belonged to someone else. For my last & current aircraft, I like to see a nice clean control system, so would only use external tabs if all else fails.
Re: Engine thrust line
Posted: Mon Oct 23, 2023 1:15 am
by CaseyCooper
Murray,
I have thought about it, and I have shimmed for it and it makes a bit of a difference! Your plane looks wonderful. I hope you’re having great success building time in it. I had made considerations for that when designing my cowl. The engine had a tendency to pull down and left under load. If using a ring mount it would be less pronounced but I’m using the bed mount.
Did you use the Sonex mount or make your own?
Re: Engine thrust line
Posted: Mon Oct 23, 2023 4:08 pm
by Murray Parr
Herraripower wrote:Murray,
I have thought about it, and I have shimmed for it and it makes a bit of a difference! Your plane looks wonderful. I hope you’re having great success building time in it. I had made considerations for that when designing my cowl. The engine had a tendency to pull down and left under load. If using a ring mount it would be less pronounced but I’m using the bed mount.
Did you use the Sonex mount or make your own?
Here’s a link to what helped a lot with this: viewtopic.php?f=58&t=7309&start=10#p56148
I have the Sonex bed mounts. Given they only suit the Rotax, I would suggest that Sonex might be wise to explore making them with an appropriate amount of right thrust. Probably doesn’t need much but I think getting it a bit better would add to the efficiency and wouldn’t cost much other than a bit of testing.
I ordered a new E-Prop so I will have to modify the cowl for that and will probably add a washer behind the left mounting points where the mount attaches to the firewall at that time. When you shimmed for it, where did you put the shims and how much did you use?
I now have 20 hours in this awesome aircraft and loving every minute of it 
Re: Engine thrust line
Posted: Wed Jul 24, 2024 5:19 pm
by SonexN76ET
I have been absent from this forum for an almost a year. I had an aggressive form of prostate cancer, different treatments, and eventually surgery. Healed up now. So getting back into things aviation once again.
I finally flew my Sonex after swapping out the Aerovee and installing Rotax 912 ULS. I made two flights and it flew horribly! I had to use almost full right rudder to keep it flying straight. I removed the early Sonex Supplied engine mount with the tiny AN4 bolts, fabricated new lower attach bars from steel, bolted them and welded them to the engine mount. I then welded on an extension to the mounting pads on the left side of the engine mount and drilled new holes to can’t the engine 2.5 degrees to the right. The original mount was canted about 4 degrees to the left. Probably whoever did the early mounts for Sonex must have gotten confused and thought a Rotax turned the same as an Aerovee.
I plan on flying it with the modified mount within the week and will have a report soon after for you.
A bit of caution for those going the Rotax direction. It is very expensive, is a much more complex installation than an Aerovee, requires precise maintenance, and you don’t have a complete factory firewall forward plan or support. You have to figure everything out for yourself. I was one of the first to start the Rotax installation using the Sonex engine mount, but it took me four years to do the conversion and I estimate 1200 hours to include fabrication of a custom cowling.
Jake
Re: Engine thrust line
Posted: Wed Jul 24, 2024 7:23 pm
by Bryan Cotton
Welcome back Jake! Glad to hear you are ok.
Re: Engine thrust line
Posted: Wed Jul 24, 2024 7:39 pm
by Skippydiesel
My Legacy/Rotax 912ULS only needs directional “boot” on take off/climb out. She flies straight (very small fixed trim tab on rudder)
My problem was having to use too much up elevator, one pair of fender washers (approximately 2mm thick), added to the front mounts, to raise the thrust line, has made a big difference.
Re: Engine thrust line
Posted: Wed Jul 24, 2024 8:48 pm
by sonex892.
I’m currently doing a rotax firewall fwd on a Sonerai I’m building. I made my own mount including the ring.
I set the engine 2 deg to the right, and 1 deg pitch up. I’ll be interested to see your results Jake.
Re: Engine thrust line
Posted: Thu Jul 25, 2024 2:07 am
by Kai
I fly a Legacy TD with an Edgeperformance EP 915 ECI- it´s basically a R912 with efi and slightly increased cubic capacity, giving 123 HP at 5800 rpm, and turning the same way as the Jabs. It drives a Sensenich fp two blade prop- the thing looks scary. Flat out upstairs I get 5800 rpm at 3500 ft amsl, wot during t/o is 5000 rpm. Right engine offset (if any) is the same as Sonex makes for their Jab 33A mount.
Upstairs the thing flies beautifully straight and level at all power settings, even with my feet off the pedals for a short while (small fixed trim tab on the rudder). Full throttle takeoff from my fairly uneven grass field is something else as soon as the tail wheel is off the ground. The paddle blade up front makes it turn briskly to the left. Bumps during t/o could lift the mains off the ground, causing so much left pull that the rudder won´t stop it. Any attempt to get off the ground with the slightest crosswind from the left is a no-no, as the plane continues drifting to the left. A hefty right bank at this airspeed and low altitude makes me cringe, but is the only thing that gets things in line again.
So what can I do? Off course avoid any crosswind from the left? Carefull with the throttle during the first 300 feet or so? Get a smaller diameter 3-blade prop? Get a checkout ride in a P51?
All suggestions welcome!