Nose "heavy"

[Scott Todd]

The Aileron trim tab on my Onex is the second one. The first was smaller and I need a bit more. I sent Skippy a PM with a suggestion.

[dbdevkc]

But here we have a Sonex that was built with admitted changes that make the airplane unstable and possibly a danger to both pilot & passenger.

Why hasn't Sonex themselves raised their voice as to what is happening here?

I am a little surprised about that as well. I can see why people would be a bit concerned about putting an engine on the front that is over the weight limit set by the factory, for more than just W&B issues. Although I'm not quite as concerned as I have a 3.0 sitting on my coffee table waiting and ready to go - lol.

"Those that suggest this Sonex is somehow more dangerous because of the 1.5 degree change are blowing smoke out of their nether regions - the aircraft flies and well (TO, Stall, Slow Flight & Landing all good) BUT requires some fine tuning for high speed cruise."

Maybe. But maybe not. Has the factory given their opinion of the change and what they would recommend? Has the angle of thrust been changed such that it remains in alignment with the wing angle of attack? 1.5° does not seem like much of a change - but it does seem to be giving you fits trying to adjust flight characteristics for that change.

[Dave Wolfe]

Naah.. whats giving him fits is not using an aerodynamic fix for an elevator trim problem.

The waiex elev trim springs are a v tail bandaid because its difficult to rig up two elevator trim tabs. The adjustable standard sonex straight tail trim tab seems to work well by all accounts.

Im sure all the prop planes I flew had 1.5 degrees of engine mount sag.

[Scott Todd]

I don't mean to throw Murray under the bus but his observation the spring isn't strong enough may be invalid. He notes he hasn't flown it yet. The spring isn't intended to take the static weight of the elevator on the ground. Its meant to balance the aerodynamic loads.

Also, Skippy's 10mm up position is in flight. This much elevator deflection is required to offset the added down thrust. Its not a big deal but is definitely costing him speed. He could be losing an entire knot or two ;) A small fixed trim tab on the underside of the elevator will solve his stick force problems and he can get it adjusted so the Sonex spring system works as designed. It will still fly with the elevator trailing edge up slightly unless he monkeys with the aileron and flap positions more. Changing this rigging is not really advised as it deviates further from the original design and could have other consequences.

For review, and those who have not read the entire thread, his airplane was built with different wing and tail incidences. This resulted in added down thrust. He has been trying to find a solution to take the added stick forces out at higher speeds. Raising the flaps was suggested. He did that and it helped. Raising the ailerons was also suggested. He has done that but has yet to fly it again. Adding an elevator fixed trim tab was suggested. This requires some minor fabrication and installation and he has not tried that yet.

[Skippydiesel]

Flight Test Report;

Unfortunately low cloud base about 2500-3000ft - airfield 900ft & some rain showers around. Air, not what I would call turbulent, just a little lumpy (typical Sydney Basin weather).

Aileron adjustment has worked beyond my expectations, stick forces much lighter. Trim no longer all the way aback, at 135 knots indicated. May have picked up a knot or two, hard to say due to lumpy air.

Ailerons adjusted level with flap, on ground - During high speed cruise noticed ailerons still slightly down, probably due to air load on flap - have adjusted ailerons another 1/2 turn up (will report any change).

Tried Steve's suggestion for diagnosing thrust issues - didn't realy have sufficient altitude (balls) to dive steep enough/long enough to get the same air speed, as in cruise. The little I did did not seem to change the, already improved, stick forces - will try again another day, from above 5500ft.

[Skippydiesel]

...........................................................
For review, and those who have not read the entire thread, his airplane was built with different wing and tail incidences. This resulted in added down thrust. He has been trying to find a solution to take the added stick forces out at higher speeds. Raising the flaps was suggested. He did that and it helped. Raising the ailerons was also suggested. He has done that but has yet to fly it again. Adding an elevator fixed trim tab was suggested. This requires some minor fabrication and installation and he has not tried that yet.

Scott - I think you are leaping to a conclusion with this statement.
It is correct that the aircraft has been built with a deliberate 1.5 degree (up) change in flight surface angle of attack.
As for the consequences of that change - it is more likely that my attempt to adhere to the Sonex rigging instructions, designed for a standard aircraft, is where the heavy stick forces have their origin.
I had to start with the Sonex specifications (I had no other) which have clearly not resulted in the handling characteristics (especially at high speed) that most builders seem to experience from the first (?) flight.
The latest adjustments have put a huge smile on my face & spring in my step. I may be straying somewhat from doctrine but it seems the girl & I may be developing some simpatico.

[Scott Todd]

Its not leaping to conclusions. Its geometry. The engine now has 1.5 degrees more down thrust compared to the wing and stab center lines. This will require more nose-up trim and be exaggerated as speeds increase.

[Skippydiesel]

Its not leaping to conclusions. Its geometry. The engine now has 1.5 degrees more down thrust compared to the wing and stab center lines. This will require more nose-up trim and be exaggerated as speeds increase.

Fair comment!

[Skippydiesel]

Flight Test Report; .9 hrs, 6500ft, OAT 16C

Plus 1/2 additional turn (1 1/2 turns since start of adjustments) UP for both ailerons.

On ground, the ailerons are now 2-3mm above the flap position. In the air still slightly down, relative to the flap - I think I will leave it at that (for the moment)

In high speed cruise, 144 Kn TAS, Sonex is now very well behaved. Stick forces have lightened up considerably. Trim indicator has moved from full aft to about neutral. Couldn't be happier.

Now that I have a reasonably predictable aircraft, that I am no longer fighting with & engine temps are tolerable, I will focus on the RAA Test Flying Program.

After Test flying completed (& signed off) I plan to return the Sonex to the workshop to revise cowling/engine lay out, with a view to achieving better cooling.

My thank to one & all for your advice/observations - I hope I can call on you again, to "shoot the breeze" or solve a niggling aircraft problem.

[Bryan Cotton]

Nice! Glad you got it figured out.