Engine thrust line

[Skippydiesel]

[
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.

[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.

[Skippydiesel]

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.

[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?

[Murray Parr]

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 :-)

[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

[Bryan Cotton]

Welcome back Jake! Glad to hear you are ok.

[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.

[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.

[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!