adjusting elevator

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adjusting elevator

Postby kenryan » Sat May 17, 2014 1:20 pm

The spec for elevator deflection is 28 up and 28 down, plus or minus 2. Is this measured relative to the head rack or relative to the horizontal stabilizer, which is down 1.6 ?
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Re: adjusting elevator

Postby danerazz » Sat May 17, 2014 2:23 pm

That should be relative to "streamlined" with the horizontal stab.
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Re: adjusting elevator

Postby levyland » Sat May 17, 2014 4:53 pm

If you are building a Super Stol you should devise a way to make the horizontal stabiliser adjustable. I have been doing a lot of testing and there are issues as to the incidence of the wing and the stabiliser. Part of the problem is that you will need to build flap seals as the air stays attached aft of the leading edge and creates a downward pressure on the flaps and the tail is dragging in the air. t's not unsafe but annoying as the elevator is unable to get in trim with the HS.
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Re: adjusting elevator

Postby Familyflyer » Sun May 18, 2014 9:07 am

From the pictures I have saw, the airplane is deffinately not in trim while in cruise. Trim tab is really working hard. I asked the factory about this before I covered. They said it wasnt an incidence problem but an issue the long gear with the big tires is creating. The tires are so far below the center line, it is basically pulling the nose down when the speed comes up. They also said when loaded up with an aft CG the problem goes away. Hopefully levyland can comment on that wing the case or not?
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Re: adjusting elevator

Postby kenryan » Sun May 18, 2014 2:07 pm

Familyflyer wrote:The tires are so far below the center line, it is basically pulling the nose down when the speed comes up.


This may be another good argument for the 26 inch rather than 29 inch tires. The other is the 10 pound weight savings.
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Re: adjusting elevator

Postby levyland » Sun May 18, 2014 4:41 pm

I call it "the itch" and there is nothing worse than an airplane out of trim. Be it pitch or roll.
In level flight the airplane is flying in a nose high attitude, however the elevator and trim tab are in a nose down attitude.
I talked at length with Steve Henry, Steve Dentz, Troy and Jim Pekola. Steve Henry had the same issue and developed the flap seals which really helped, but did not completely solve the problem. It also added about 7 knots to the airplane. Steve also suggested flying "in cruise" with 10 degrees of flaps which surprisingly "brings the tail up" but does not create a speed penalty.
It helped but the elevator still has a wee bit of down in it. But heaps better.
The next "port of call" was to make "gurney" flaps ( suggestion from Jim) for the ailerons in an attempt to get the tail flying higher. But that made the ailerons super heaver, and they came off muy pronto. Steve Henry has been experimenting with them on both the ailerons and flaps, and seems to like them. I am currently making an aluminium gear and down strut fairings as Steve Henry, and I noticed Familyflyer have done with covering, and I would highly recommend that ALL builders follow suit.I talked to Troy and he feels as Familyflyer pointed out that with the landing gear "dropping down" it is pulling the CG forward. He said the green machine with the 31" tires is more pronounced than the red one is with the 29". So the argument for the 26" tires possible has some merit possibly in making the airplane go faster which is another subject. My airplane cruises at only 65 knots. Steve Dentz may weigh in on this one as I know he has done a few "costume changes" with his tires. Anyway, regardless of why it's happening, it is happening and if you have not covered and painted your horizontal stab attachment point I would highly recommend that you make a provision for doing so. I would not go to an elaborate screw jack assembly but rather a simple shim system that will allow the leading edge of the horizontal stab to adjust up or down. You might have to put in turnbuckles in the forward flying wires, or possibly the different bolt holes in the tangs will suffice. Im off to work in California for a few weeks so I will not be able to experiment but I will keep you posted once I get back.. Hope that helps sport fans. Levyland
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Re: adjusting elevator

Postby kenryan » Sun May 18, 2014 8:09 pm

levyland wrote:In level flight the airplane is flying in a nose high attitude, however the elevator and trim tab are in a nose down attitude.


Familyflyer wrote:The tires are so far below the center line, it is basically pulling the nose down when the speed comes up.


I'm confused (nothing new with that). Levyland seems to be saying that the airplane is naturally out of trim with a nose high attitude, caused by incorrect incidence of the horizontal stabilizer, combined with air pressure caused by a lack of flap seals. On the other hand, Familyflyer seems to be saying the airplane is naturally out of trim with a nose down attitude, caused by the drag of the large landing gear hanging well below the aircraft.

Have I understood both of you guys correctly? Are we all talking about the same airplane (SuperSTOL)?
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Re: adjusting elevator

Postby levyland » Mon May 19, 2014 5:00 am

Here are some pictures to better explain the situation. The airplane has always flown in a tail low attitude. The elevator has always been in a pitched up position or applying downward pressure as if the airplane is tail heavy.

This requires forward stick to compensate to try and get the elevator and HS neutral in straight and level flight.

If I move the elevator trim tab to the neutral positing it requires a tremendous amount of forward stick pressure to keep the airplane flying straight and level.

As mentioned the flap seals made a huge difference in picking the tail up and getting the elevator better aligned with the HS.

If I add 10 degrees of flaps the elevator and HS become better aligned without any significant difference in ground speed.

I hope this explains it a wee bit better.

Cheers,

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Attachments
IMG_2464.jpg
Gurney flaps attached to the ailerons not pretty but Steve Henry likes them
GOPR0221.jpg
Climbing out note elevator position in relation to horizontal stab
GOPR0212.jpg
In straight and level flight note elevator position in relationship to HS
IMG_2422.jpg
WIth the flap seals taped to the bottom of the wing. Notice pink tell tail
IMG_2404.jpg
View of Dynon. Notice trim position in level flight in far left
IMG_2092-e1390962642431-400x202.jpg
airplane in level flight. This is before I installed the flap seals
IMG_2092-e1390962642431-400x202.jpg (40.91 KiB) Viewed 3252 times
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Re: adjusting elevator

Postby Familyflyer » Mon May 19, 2014 10:20 am

I personally do not think it matters what you do with the elevator incidence location. Sure you could change its angle to take the load off the elevator (Which s how it should be) but that is not going to change the angle that the wing is flying at. Modes to the wing like the seals will help the most or fly with some flaps in. A properly angled elevator will still give you a high angle of attack in cruise. I personally think the main wing is at the wrong angle to the fuse too. Clearly the wings flying angle is different to what they thought. The wing attach points to the fuse needs to be higher at the front spar. This wing does not fly like the highlander wing. That will also mean a totally different fuse and strut jigs from the Highlander. Dought it will happen. However the rib design would allow the angle change, there is room to move the bottom rib up on the front spar. I hope I am wrong but that is what I see right now. You could prove that by putting on wee little tires and test that I guess.
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Re: adjusting elevator

Postby Familyflyer » Mon May 19, 2014 10:22 am

kenryan wrote:
levyland wrote:In level flight the airplane is flying in a nose high attitude, however the elevator and trim tab are in a nose down attitude.


Familyflyer wrote:The tires are so far below the center line, it is basically pulling the nose down when the speed comes up.


I'm confused (nothing new with that). Levyland seems to be saying that the airplane is naturally out of trim with a nose high attitude, caused by incorrect incidence of the horizontal stabilizer, combined with air pressure caused by a lack of flap seals. On the other hand, Familyflyer seems to be saying the airplane is naturally out of trim with a nose down attitude, caused by the drag of the large landing gear hanging well below the aircraft.

Have I understood both of you guys correctly? Are we all talking about the same airplane (SuperSTOL)?



What I am saying is that the tires are so far below the center of gravity that you have to pull the nose up above the horizon to maintain level flight from the wheel pulling the nose down. Hope that makes more sense?
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Re: adjusting elevator

Postby kenryan » Mon May 19, 2014 10:48 am

Thanks for the input. I'll probably just build it the way it's designed and take it from there.
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Re: adjusting elevator

Postby Gil T » Mon May 19, 2014 11:43 am

Wow!! All this tech stuff and theory and ideas is making my head spin. All I can say is I'm happy with my S/N 28 which started out as a Escapade, then was modified with a Highlander tail, longer wings with Escapade wing struts (18 ins farther in than a Highlander wing). With the flap gap seal added (didn't notice much difference), VG's (noticeable difference-nose 1.5 degrees lower, +6kts), Grove gear, I can make 110+ @5500. You guys keep up the good work. That's what "Experimental" is all about.

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Re: adjusting elevator

Postby scubarider2 » Mon May 19, 2014 12:24 pm

Gil, so when you added the VG kit you got another 6kts in cruise? I have the Escapade with the Highlander wings. Would be glad to add the VG's if I could get a faster cruise and a better stall. I am cruising right at 105mph at 5500rpms and that is with wheel pants.
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Re: adjusting elevator

Postby levyland » Mon May 19, 2014 3:34 pm

I agree with Troy, I think the wing incidence in relationship to the fuselage water line is incorrect. That would be in the "way too hard box". The easiest "fix" is an adjustable HS.
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Re: adjusting elevator

Postby av8rps » Mon May 19, 2014 10:04 pm

I think the horizontal stabilizer needs the leading edge to go up (about an inch??). Main wing incidence would be very difficult to change, but stab shouldn't be. The up elevator needed currently is compensating for too much negative incidence on the stab. Of course problems like this can be very confusing to resolve. It would be cool to get a Super STOL on a computer where one could prove my theory before having to do the real thing.

Not sure I buy the idea about too much drag on gear and tires as that if anything should cause tail to go higher, not too low.

I have a Lake Amphibian and it has a HUGE amount of drag from the engine pylon along with a large wide chord hartzell constant speed prop causing a large braking effect, along with very significant throttle-induced pitch changes. Plus Lakes are very sensitive to weight and balance issues due to everything being loaded forward of aircraft CG. But yet in spite of these issues, it will fly pretty much flat (not tail high or low), unlike what I see with the Super Stol...
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