Sonex Longitude Trim

[skippydiesel]

I invite constructive comments on the following;

 

My Sonex is in its early test flying phase. 

 

• Flights are conducted with one 70Kg pilot, nil baggage  and up to full fuel in wing tanks (2 x 30L almost on the C of G) Note: the centre, in fuselage, over pilots legs, 40L tank, is empty at this stage.
• Flight surface tuning (trim?) for level flight is well under way.  An erly tendency towards heavy nose ,or if you would prefer, the need for excessive back stick, has been addressed, in part, by reflexing the flaps up and by adding a heavier, pilot adjustable, aft trim spring. 
• The elevator is slightly raised - about 10-20 mm, at all times in cruise (I need to take more measurements to be precise).
• The ailerons (adjusted to the best "book"  compromise), are about 10-15mm (trailing edge) below the flaps. 
• This strategy has worked well for air speeds between 100 & 120+knots.

 

With higher air speeds, I run out of aft trim adjustment at about 135 knots.  This would be okay if centre tank was full ie as fuel burns off so trim could be adjusted forward.

 

I feel the trim spring solution is pretty much done.

 

I could add a small fixed trim tab to the elevator trailing edge, to lighten stick forces but would rather avoided this course solution if I can.

 

My preferred option is: Aileron Adjustment

 

Small change of flight surface alignment with/to the induced wind, usually have significant impacts on flight characteristics. If I adjust my ailerons to match the flap settings, this may further lighten the "weight" on the aft stick  BUT likely change the UP: DOWN ratio of the aileron movement  - what might the changes to flight characteristics be?

 

Any other thoughts?

 

 

 

[skippydiesel]

Where have all the want to be aeronautical advisors gone, long time turning??

 

Surely some of my friends would like to munch on this little problem.

[Thruster88]

Reflexing the ailerons up should have minimal effect on the differential ratio. Any change in the differential ratio will depend on where the ratio is produced, at the bell crank or at the aileron connection. 

 

If the aileron pushrod connection and the aileron pivot are at 90° to the cord in the neutral position then no change to ratio.

 

One advantage of reflexing ailerons up and maybe even reducing flap up reflex could be better stall behaviour. By reflexing only flaps up you are effectively reducing the wing wash out.

 

I would seek the advice of the manufacturer.  

[skippydiesel]

2 hours ago, Thruster88 said:

Reflexing the ailerons up should have minimal effect on the differential ratio. Any change in the differential ratio will depend on where the ratio is produced, at the bell crank or at the aileron connection. 

 

If the aileron pushrod connection and the aileron pivot are at 90° to the cord in the neutral position then no change to ratio.

 

One advantage of reflexing ailerons up and maybe even reducing flap up reflex could be better stall behaviour. By reflexing only flaps up you are effectively reducing the wing wash out.

 

I would seek the advice of the manufacturer.  

Thanks Thruster88

 

I have tried getting help from Sonex (not on this topic) and found that when your project strays from the catechism, they get a bit evasive.

 

I have very limited exposure to aircraft  kit suppliers but within this, have found the Europeans flexible and the Americans rigid - litigation concerns??

[RFguy]

being a 19- experimental aircraft with you as the builder affords you a high degree of flexibility in ways to kill yourself of course. That is the big plus of 19-

 

changing the reflex / static pos of any of the control surfaces (aielerons) or high lift devices (flaps) will have a relatively big change to stall characteristics, all types of provoked stalls of course.

 

If you have plenty of altitude, I'd suggest you write up a  good barrage of repeatable stall testing . That thing has a big rudder and you wont load it tail heavy so recovery with correct technique and altitude is likely.

There WOULD BE a flight test regime from the manufacturer. Maybe test against that ?

 

 

[skippydiesel]

Yes Sonex have a test flight regime - very much focused on FAA modeling - I am slowly working through the RAA Flight Test, which may also  have its origins in the FAA.

 

I hope not to kill myself - hence the questions about the implication of any changes I might be contemplating.

 

At this early stage stalls are benign, without any tendency to wing drop.

 

Stall, without flap, is 40 knots, right on Sonex specifications. Stalls, with flap, are 37 knots (all stages) a bit higher than specification of 35 knots.

 

More complex stalls, at different weights & power, have yet to be conducted.

 

TO is exhilarating, climb out 1000ft/min @ 80 knots, landings messy (still lerning) as significantly higher approach speeds than Zephyr.

 

Multiple incremental adjustments to flight surfaces,  have resulted in a level cruise with the "ball" in the centre (no yaw). A shallow turn, without rudder input, will see the ball remain centered.

 

Also -I have not yet settled on flap/aileron/elevator setting - so stalls will have to be repeated for all adjustments,  which may result in some changes in above findings.

 

On the ailerons- the flaps have been adjusted to effectively counter a heavy forward stick (nose down). The aileron's are now trailing lower than the flaps. My thinking - this must appose (to some degree) the  effect of the flap adjustment. I may get more improvement, if I adjust the ailerons (by equal amounts) to the flap. With luck this improvement may be most pronounced at high speed cruise (where the excessive aft trim is currently needed). That is if I don't kill myself in the process.😆

 

[skippydiesel]

 

 

[RFguy]

Dont get too wound up about the exact  flapped stall speed, measuring airspeed accurately  at high AoAs is difficult ... (not to mention dependence of AUW weight, CoG location, ) 

Sounds good Skip, at least writing it out here can provoke your brain a bit as your write.  My observation is that flaps on some aircraft dont really change stall speed much ,  more used to increase decent rate and increase drag and tweak the attitude a bit. 

There are others here that can offer far more. Which way is the aft trim required at 'high speed cruise' ?

Edited March 2, 2023 by RFguy

[skippydiesel]

11 minutes ago, Arron25 said:

Don't know how Sonex varies to its older brother the Sonerai.. but my Soni lands tail first  ( like a 3point but tail first) and at near stall.. with stall warning (set just above stall) screaming in my ear.... too fast and it floats in ground effect until it slows to its happy speed

Cant realy comment - landings all over the shop. Haven't bent her (yet!) Done tail first, wheelers and the occasional three pointer - part of problem is grass runway, a tad uneven so can do a "greaser" and still bounce after landing (poor excuses).

 

Grappling with higher sink rate and twitchier aircraft, than  pervious 12 years of experience. At slow speeds my Zephyr was the most undemanding/forgiving of any aircraft I have flown - the Sonex requires a much higher degree of discipline.

 

Don't have a stall warning at this stage - fitted for Reserve Lift (AofA) needs to be commissioned.

Edited March 2, 2023 by skippydiesel

[facthunter]

Does the maker mention adjusting the rigger's AoA of the horizontal stabiliser?  IF you're flying with up elevator in cruise that might be a fix. Stall speed checks are done with  max rearward Cof G.  There's no reason for extra risks if you proceed logically and with caution.  Use extra height and be spin aware and capable.  Nev

[facthunter]

The above needs correction re the CofG which is in the MAX FORWARD position as then the "up" elevator applies a down load and that has to be added to what the wing carries and is the most adverse position. I posted too quickly as  a friend came to the door. RFGuy spotted it. Quickly on the ball as usual. The "rest' of you would have of course??  Nev

[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).
 

[Kiwi]

Is the thrust line of Rotax correct?

[Flightrite]

Id be sniffing around Sonex forums, not so much here. At the end of the day it’s just another plane. I own 4 diff types, (and drive high perf jets to bug smasher's) I simply adapt, pilots are meant to be be able to do that, don’t over think it!

[skippydiesel]

1 hour ago, Kiwi said:

Is the thrust line of Rotax correct?

 I have no reason to think there is any problem with the engine/prop thrust line. Consequently I have not checked (no idea).

[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 elevators 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.

 

[Thruster88]

144 ktas very impressive. Faster than those euro ones ay. What rpm and manifold pressure to get that speed?

[Blueadventures]

How do you measure elevator up 2 to 3 mm above Flap a neg 1*?

[skippydiesel]

3 hours ago, Thruster88 said:

144 ktas very impressive. Faster than those euro ones ay. What rpm and manifold pressure to get that speed?

5340 rpm @ 23.3 in - Indicated 127 Kn - Ground speed 131 Kn

 

That's what the Dynon says(CASA approved provider has verified accuracy within "acceptable limits") - who am I to question it

Edited March 5, 2023 by skippydiesel

[skippydiesel]

2 hours ago, Blueadventures said:

How do you measure elevator up 2 to 3 mm above Flap a neg 1*?

Mixed up my elevator with my ailerons.  Sorry

 

I believe the  elevator is still about 10mm above the horizontal stabiliser - need to check this out to be sure

 

 

[RFguy]

11 hours ago, skippydiesel said:

5340 rpm @ 23.3 in - Indicated 127 Kn - Ground speed 131 Kn

 

That's what the Dynon says(CASA approved provider has verified accuracy within "acceptable limits") - who am I to question it

ahh so that's wide open throttle then (IE manifold pressure is approx same as (static) air pressure) ?

 

or is that Manifold pressure gauge ? . 

[skippydiesel]

2 hours ago, RFguy said:

ahh so that's wide open throttle then (IE manifold pressure is approx same as (static) air pressure) ?

 

or is that Manifold pressure gauge ? . 

"or is that Manifold pressure gauge" - I don't follow.

[RFguy]

Well... you mentioned "23.3 in". was that manifold pressure , or just the pressure altitude  ?

[skippydiesel]

19 minutes ago, RFguy said:

Well... you mentioned "23.3 in". was that manifold pressure , or just the pressure altitude  ?

MAP - is the usual figures used when quoting power settings😃

[facthunter]

The density altitude will affect power and the QNH  affects manifold pressure.  Nev