Nose "heavy"

[GraemeSmith]

I've just re-read the whole thread.

An OPINION:

At almost the outset it was stated:

Full disclosure; This Sonex has had its wing/horizontal stabiliser, angle of attack increased by 1.6 degrees from factory/plans specifications.

Engine thrust line is defined by Sonex (factory) engine frame, with latest Sonex/Rotax "bed" adapter - I would hope that this would be well within design parameters.

IMO There is the problem right there. The intended consequence of moving the 1.6 degrees has NOT had the desired effect. No amount of klutzing around this has fixed it satisfactorily. I suspect that if the 1.6 degrees was removed - all would be well. Till then it's test piloting at its extreme.

[Skippydiesel]

At last some debate - even if its hardly positive.

First; a correction - I miss quoted the change to the wing angle of attack its 1.5 degrees (not 1.6) which probably doesn't change the negative opinions but facts are better than errors.

Second; I hade this airframe inspected by a professional aircraft engineer (I paid for his input because he has the qualifications/experience) prior to purchasing. In his opinion the changes (primarily 1.5 & wing tanks) would have little impact on the aircrafts performance & handling and may achieve the builders goal which was to correct, his perceived, error in the Sonex level flight attitude.

Third; this is an experimental aircraft - those brave soles who advocate strict adherence to doctrine/design, miss the point of this class of aircraft. Presumably they have not in any small way "personalised" their creation - in my opinion they are the poorer for it.

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.

As a neophyte in the world of aeronautical engineering/aerodynamics I try to get some opinion on any changes I am contemplating - I ask you.

This is a completed aircraft, fundamental changes to its construction are, in my opinion, not to be contemplated ie a waste of breath.

My idea to adjust the position of the ailerons, to that of the flaps, is logical - flaps have been adjusted to trim the aircraft, at the moment ailerons are apposing/countering that adjustment. I ask your advise on the possible ramifications, not permission or approval to proceed.

[GraemeSmith]

The Wing Tanks are close enough to on CG that I don't think anyone thinks that's a problem.

I have no idea what you paid a "professional aircraft engineer" for their services - but it's not a trival exercise to do a complete analysis of the original design, come up with what changes may entail and then sign the aircraft off as "probably" going to be OK.

And as you then rightly point out - it's an EXPERIMENTAL. But with EXPERIMENTAL comes a responsibility to not endanger the General Public while experimenting.

Now let's be clear - I'm NOT accusing you of that. You have come to a body of knowledge to seek some solutions. This is good. But I wonder if you have approached the designer/factory for their input. While to some extent you might get a "liability" type "we don't recommend you do that". But you might also get a "we tried that and it xxxxxx........"

Proceed all you want. But don't kill an innocent member of the public. Enough of them think we are crazy enough as it is!! :-)

[Scott Todd]

The first few flights on my Biplane (2005) took lots of forward stick to keep it level. I extended the nose during the build about 8 inches to make room for the AeroVee. I did the math and extended the aft fuselage to account for the weight shift. Here is the fixed trim tab. The other elevator has has a movable tab but I didn't get a picture. Also you can see where I changed the stab incidence after the first few flights. None of these were enough to get it in trim. Finally after talking to some other Biplane pilots, we thought the upper wing was creating a down wash on the stab. I went flying and stuck my hand up in the airstream and it made a HUGE difference. Just breaking up the air hitting the stab worked. So I added this small tab to the upper wing. Problem solved. It looks a little goofy but it flies well,is trimable in all speed ranges, and stalls benign.

I have an adjustable tab on my Onex. Same as I had on my Sonex. It works well and I like it a lot. I forgot to get a picture but this link should get you to one.

viewtopic.php?f=5&t=6667&p=50596#p50596

You can see a fixed tab under the right aileron. My Onex was started by someone else and apparently a wingtip was installed slightly warped. I discovered it after careful analysis after noticing the hard roll after first flights. Instead of taking it apart and rebuilding it, I choose the tab for now. One day I may fix it but I got it flying straight and I'm happy with it. It tends to consistently drop that wing first in a stall which is totally understandable.

Its not going to spontaneously explode. The wings are not going to fly off. The extra downthrust is an annoyance but it can be trimmed out. Add a trim tab and enjoy your new airplane :)

[sonex892.]

I think the extra incidence is an interesting idea. Done correctly it would definitely improve the visibility in cruise and also get it closer to the stall for 3 point landings. I previously built a sonerai and always thought if I was to build another I would consider increasing the incidence. Per the plans the sonerai wings were set at 0 deg incidence, the stall angle on these like the sonex is also way higher than the 3 point stance.

I dont get your thought, that the elevator pushing down is creating more drag on the wing. I'm no aeronautical engineer but or a given weight and speed the wing the be at a given angle of attack regardless, wouldn't it?. The only time the elevator wont be pushing down when flying in a normal condition is with a c of g that is dangerously too far aft. I too would not be messing with reflexing flaps and ailerons, apart from the previous comments on reflexing the ailerons, the aileron up travel may be restricted by the counterweight.

I would think your problem is the thrust line pulling the nose down and you just dont have enough tension either on the fixed spring or on the trim spring to overcome it.

I would check the thrust line by climbing high then whilst level hold a constant speed check the elevator position. Then go to idle and glide at the same speed to see if the stick is in the same or similar position. If the stick position is alarmingly different address the thrust line of the engine. My 3300 also pulls down but I dont have an issue with that as the trim has enough authority to be set at any c of g and speed higher that 70 kts. I only ever run out of back trim when slowed to about 70 kts.

Personally I would just add an adjustable trim tab as per the plans and move on, it is very effective.
Steve

[Murray Parr]

I installed the dial a trim to my Waiex B and followed the instructions precisely and found the adjustable spring wasn't anywhere near strong enough to put the elevator in the desired position so I added a much stronger spring which acheived the specified position. I haven't flown it yet (soon:-) but I expect to need an aditional spring for this. I wouldn't be too worried about adding a heavier spring while stil utilising your inner spring (Bunnings has a great assortment to choose from).

I think you will struggle to get much experienced advice with your question as you are likely the pioneering test subject for this. Maybe reach out to Sonex tech support and see if they have any insite to add. I would just go ahead and adjust your ailerons in small increments and test to see if any improvements or declines in performance are made. can always adjust back if necessary.

If you have the conventional tail instead of Waiex, you could just convert to the lever operated adjustable trim tab which would give more range is another potential solution. I also don't think your 10mm elevator position above the stabiliser is an issue, a lot of the 10mm would probably dissapear with dynamic forces that don't show while parked, have you thought of that?

[Skippydiesel]

Scott Todd you are a gentleman and generous with your experience, and advice - Many thanks.

I adjusted my ailerons today - one full turn of the ball end, on each short aileron rod, has brought them exactly level with the flap trailing edges. I was going to fly but the combination of dehydration/low blood sugar (hadn't eaten/drunk in about 8 hrs) and a gusting cross wind changed my mind.

Will fly at the next opportunity and post a report.

[Skippydiesel]

Hi Steve,
".........that the elevator pushing down is creating more drag on the wing........."

Okay, in essence I am a retired farmer, not an engineer or fluid dynamists, so will just mumble in the hope of being mistaken for intelligent -

The horizontal stabiliser is sized and oriented (angle of attack)
So as to counter any tendency of the aircraft to stall tail first i.e the stabiliser will still be generating lift after the main wing stalls, so when the wing stalls the aircraft will drop nose down, gain speed & the wing achieve lift/out of stall.
To accommodate varying load conditions/locations.
The attached Elevator is a pilot controlled movable aerofoil that can modify the amount of stabiliser lift required for a given load/distribution and air speed.

If the stabiliser is too effective (generating more lift than necessary) the elevator must be employed to counter this lift. The rotational force generated acts on the main lifting surface (wing) as if additional load is being added which may result in a less than optimum angle of attack, reducing efficiency/speed, requiring more energy to stay aloft.
In addition the Elevator, being deployed into the slip stream, will create additional drag.

Could all be BS!

[Skippydiesel]

I installed the dial a trim to my Waiex B and followed the instructions precisely and found the adjustable spring wasn't anywhere near strong enough to put the elevator in the desired position so I added a much stronger spring which acheived the specified position. I haven't flown it yet (soon:-) but I expect to need an aditional spring for this. I wouldn't be too worried about adding a heavier spring while stil utilising your inner spring (Bunnings has a great assortment to choose from).

I think you will struggle to get much experienced advice with your question as you are likely the pioneering test subject for this. Maybe reach out to Sonex tech support and see if they have any insite to add. I would just go ahead and adjust your ailerons in small increments and test to see if any improvements or declines in performance are made. can always adjust back if necessary.

If you have the conventional tail instead of Waiex, you could just convert to the lever operated adjustable trim tab which would give more range is another potential solution. I also don't think your 10mm elevator position above the stabiliser is an issue, a lot of the 10mm would probably dissapear with dynamic forces that don't show while parked, have you thought of that?

Gudday Murray,

"............followed the instructions precisely and found the adjustable spring wasn't anywhere near strong enough .........."

I am perversely pleased, that there is one more Sonex pilot that has found the Sonex adjustable trim spring to be not strong enough. Like you, I sourced my additional spring (goes inside the Sonex one) from Bunnings Aerospace :)

"............a lot of the 10mm would probably disappear with dynamic forces that don't show while parked, have you thought of that?......"

In short yes. In flight, I employ a very expensive highly accurate piece of plywood, to measure the stick position, relative to the bottom of the instrument panel. When on ground, I can move the stick to the position I have marked on the ply, look back and see the position of Elevator as it was in flight.

It will be interesting to see if the Elevator position changes, after the ailerons have been adjusted to the Flap position - will let you know.

I have yet to fill my fuselage tank, about 29Kg over the pilot/passenger legs - fwd of CofG. As is, I have no aft trim left at 135 knots. (I do have plenty of stick movement) If the aileron adjustment doesn't lighten the stick loads sufficiently, I will have consider an Elevator trim tab of some description, so that I can fill this tank.

[Skippydiesel]

I would think your problem is the thrust line pulling the nose down and you just dont have enough tension either on the fixed spring or on the trim spring to overcome it.

I would check the thrust line by climbing high then whilst level hold a constant speed check the elevator position. Then go to idle and glide at the same speed to see if the stick is in the same or similar position. If the stick position is alarmingly different address the thrust line of the engine. My 3300 also pulls down but I dont have an issue with that as the trim has enough authority to be set at any c of g and speed higher that 70 kts. I only ever run out of back trim when slowed to about 70 kts.

Personally I would just add an adjustable trim tab as per the plans and move on, it is very effective.
Steve

Sorry Steve, did no fully respond to your suggestions/observations.

I will certainly try your suggestion for determining engine/prop thrust influence.

I don't have any adjustable spring trim issues below 120 knots or at landing pattern speeds.

Before you added the Elevator trim tab, did you find that you required more aft trim as your speed increased?