adjusting elevator

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Re: adjusting elevator

Postby R Rinker » Tue May 20, 2014 12:14 pm

Levyland...I see you put tank drains in your wing tanks..I understand the tanks don't have an actual sump (beveled out low spot) so what did you do?.........Rodger
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Re: adjusting elevator

Postby av8rps » Tue May 20, 2014 3:00 pm

av8rps wrote:(snip)... 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.


Oh,and after thinking about all this I have one last comment about the gear and wheel drag causing this issue; If that were true, how in the world would any airplane be able to handle a huge set of heavy floats hanging down below it? Remember, floats hang well past the nose of the aircraft (typically by a couple of feet), and most of the bulk of the floats are forward of the aircraft center of gravity. And ironic to this discussion, aircraft some times will actually handle better when adding floats due to lowering the center of gravity, making the aircraft more stable. And even though my 650 lb Kitfox has a set of 260 lb amphib floats haning under it, it flies nice and flat, neither nose or tail high. So while the gear might sound logical as the likely culprit, I just can't believe that can be causing this problem. And even if it were, it should be easily offset by adjusting the incidence angle of the tail.

But in thinking how to actually determine a fix for nose high Super Stols, maybe it would be worth doing a simple test like I did with models when I was a kid;

When young and learning about basic aircraft design and flight characteristics through models, I used to test concepts and ideas by holding a crude model out the passenger side window while my someone drove the car. My "poor mans wind tunnel" taught me a lot about aircraft, including how incidence of the wing and tail work together. I'm certainly no genius aeronautical engineer, but testing and learning through sinmple but practical testing procedures has many times helped me to solve some serious issues with undesirable flight characteristics with my models when I was young, and later in life with the real thing.

Of course a really high tech person might put this into a computer that allows one to "test fly" changes made before actually doing the changes to the real thing. But you obviously need to have the contacts and/or the software to do this.
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Re: adjusting elevator

Postby smiley » Tue May 20, 2014 10:52 pm

I noticed this question before I purchased my Superstol. I questioned putting and adjustable jack shaft on the front of the horizontal stabilizer. No one at the time seemed to think it was necessary. I am still working on a simple ground adjustable screw that will test this problem. It is simply a piece of square tubing on the F-1029 front attach bracket that slides up and down on the post with a 3/8" threaded bolt to adjust it. It will require turnbuckles on the flying wires. But will not be to complicated to adjust. I originally wanted a flight adjustable system but do not feel the framework is stiff enough on the stabilizer. Will post a picture when I get it complete.

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Re: adjusting elevator

Postby Familyflyer » Tue May 20, 2014 10:54 pm

I think you got the moving of the elevator opposite. The front of the horizontal stab needs to go down more to trim the elevator out. The elevator is in the up position to fly in trim, so the front of the horizontal stab needs to go down more to compensate. Trouble is the bolt would end up inside the fuselage fabric if it gets lowered much more. The nut on mine is digging into the fabric already.
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Re: adjusting elevator

Postby bluemax » Wed May 21, 2014 10:37 am

The comments on this issue is very interesting, but I was especially relieved when I learned this is only an issue with the super stol, and not the basic Highlander. I wondered whether I would regret my decision to not upgrade my Highlander kit to a super stol, but I'm feeling a little better about it now. I'm sure that with trial and error someone will come up with a fix that everyone can use.
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Re: adjusting elevator

Postby Familyflyer » Wed May 21, 2014 10:56 am

bluemax wrote:The comments on this issue is very interesting, but I was especially relieved when I learned this is only an issue with the super stol, and not the basic Highlander. I wondered whether I would regret my decision to not upgrade my Highlander kit to a super stol, but I'm feeling a little better about it now. I'm sure that with trial and error someone will come up with a fix that everyone can use.


I am regretting my decision. You work so hard to build the airplane the best you can and find there is a major problem with the design that is being ignored. No airplane should have an elevator that far out of trim in cruise flight. I asked the question to the factory before I covered because I was concerned that their angle was wrong of 1.6 down. They insisted it was correct and blamed the tires. I do not know what to think.
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Re: adjusting elevator

Postby kenryan » Wed May 21, 2014 12:35 pm

Regardless of the position of the elevator during cruise, it seems to me that being able to fly in the low 20s to the upper 90s is pretty darn good.
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Re: adjusting elevator

Postby av8rps » Wed May 21, 2014 1:56 pm

kenryan wrote:Regardless of the position of the elevator during cruise, it seems to me that being able to fly in the low 20s to the upper 90s is pretty darn good.

I agree. The Super Stol is an exceptional aircraft even with this little glitch. And personally, I'm convinced as this is discussed further, someone will solve the problem.

I read an article a long time ago about the Helio Courier. And while it went on and on about how capable the Helio was, the overall description of the handling characteristics was that it was one of the most difficult aircraft the writer had ever flown (and he had flown many). He ended the article by saying he felt flying qualities had been traded off for capability. So what is the Helio known for? It's capabilities. In all the years I've heard people talking about Helio's, I've never heard anyone until that article talk bad about the Helio's handling, as they were more focused on it's outstanding capabilities.

So even if the Super Stol never gets this issue resolved, it will always be recognized for its exceptional capabilities. And last I knew, it essentially has nothing in its class that can compete with it. Plus it has a huge bonus, the Super Stol flies well, and IS NOT hard to fly. So if comparing it to the world famous Super Stol Helio, the Just Aircraft Super Stol more than holds its own. And that says a lot!

Now if anyone doesn't like their Super Stol, just let me know. I'll trade you even up for my Highlander :wink:
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Re: adjusting elevator

Postby av8rps » Wed May 21, 2014 2:06 pm

Familyflyer wrote:I think you got the moving of the elevator opposite. The front of the horizontal stab needs to go down more to trim the elevator out. The elevator is in the up position to fly in trim, so the front of the horizontal stab needs to go down more to compensate. Trouble is the bolt would end up inside the fuselage fabric if it gets lowered much more. The nut on mine is digging into the fabric already.

I suppose I could have it backwards, but I don't think so. Just visualize removing the elevator and moving the horizontal stabilizer into a position that would cause the aircraft to fly level. I believe that would require moving the leading edge of the stab up. By raising the leading edge, it will lift the tail.

At least that's my logic. But of course I could be wrong? (did I really say that? :roll: ). I haven't tried a mock up model out of the car window yet...
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Re: adjusting elevator

Postby dkshow » Wed May 21, 2014 3:06 pm

Hey guys, I don't know how much difference this makes but I thought I had seen some video of the prototype somewhere in (close to cruise) speed. I found a couple seconds in one of the early Swingle videos that makes the elevator look like it's trimmed pretty well. Makes me curious what changes there have been since that air frame and wing combo. Here's the link if anyone is interested. https://vimeo.com/49725088 (go to the 00:47 - 00:50 mark)
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Re: adjusting elevator

Postby Familyflyer » Wed May 21, 2014 3:53 pm

dkshow wrote:Hey guys, I don't know how much difference this makes but I thought I had seen some video of the prototype somewhere in (close to cruise) speed. I found a couple seconds in one of the early Swingle videos that makes the elevator look like it's trimmed pretty well. Makes me curious what changes there have been since that air frame and wing combo. Here's the link if anyone is interested. https://vimeo.com/49725088 (go to the 00:47 - 00:50 mark)


Great eye. You are absolutely right. Does all the new SuperSTOLs have this issue or is it just random? Or like you said, what changed?
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Re: adjusting elevator

Postby FlyerChief » Wed May 21, 2014 7:44 pm

Hey guys, I don't know how much difference this makes but I thought I had seen some video of the prototype somewhere in (close to cruise) speed. I found a couple seconds in one of the early Swingle videos that makes the elevator look like it's trimmed pretty well. Makes me curious what changes there have been since that air frame and wing combo. Here's the link if anyone is interested. https://vimeo.com/49725088 (go to the 00:47 - 00:50 mark)


I have a Highlander so maybe I shouldn't even be weighing in on this, but if it's so well trimmed, shouldn't we be looking back at the horizon ...not the ground??? Correct me if I'm wrong, but it seems to me that the plane must be fairly nose high to get this view.

SS.jpg

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Re: adjusting elevator

Postby danerazz » Wed May 21, 2014 11:30 pm

av8rps wrote:I suppose I could have it backwards, but I don't think so. Just visualize removing the elevator and moving the horizontal stabilizer into a position that would cause the aircraft to fly level. I believe that would require moving the leading edge of the stab up. By raising the leading edge, it will lift the tail.

At least that's my logic. But of course I could be wrong? (did I really say that? :roll: ). I haven't tried a mock up model out of the car window yet...


The issue is the wing needs a higher angle of attack for level flight, but you have a nose-down pitching moment suggesting a center of lift that is aft on the airfoil. To give the wing the angle required to maintain level flight you need UP elevator, or DOWN stab to overcome the nose-down moment. It is not an issue of just raising the tail to level the pitch, it is FIGHTING the tail raising forces the wing is producing or you won't be able to maintain level flight (altitude, not attitude).

I don't have a superstol, but I see two options (without any serious scientific analysis):

1. Put more of a down angle on the stab to take load off the elevator in cruise flight, accepting the fact that the fuselage will have a somewhat draggy nose high attitude in cruise

2. Raise the leading edge/lower the trailing edge of the wing to give it a more level fuselage in cruise

The issue with both of these, especially #2, is this is a high lift airfoil, even with slats retracted. You will have pitching moment changes throughout the speed range. If you make any changes to correct cruise, you might take a hit on control authority or performance on the bottom end. An adjustable stab may be the best, if not most simple, way to go. The most simple is to accept the fact that it does still perform well on both ends, and there are compromises made to make it really good at one end.
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Re: adjusting elevator

Postby danerazz » Wed May 21, 2014 11:57 pm

Other thoughts:

As a cambered airfoil decreases angle of attack (i.e. you lower the nose from climb to cruise) the center of pressure moves aft, and the more asymmetric camber you have the more it moves (as opposed to a symmetrical airfoil, in which it does not move). Also, the pitching moment coefficient is proportional to the square of the airspeed, so the faster you go the more it pitches. These factors are what try to pull the nose down in cruise: you decrease angle of attack and increase speed= need lots of up elevator power to keep the nose up.

The SS being optimized for SLOW flight is probably nice and neutral in pitch on the bottom of the ASI. So to achieve that you are going to give something up at the top.

As for using a notch of flaps, this changes the total angle of attack of the wing, effectively raising it and creating more lift at a given airspeed, so you can let the tail come up a bit and decrease AOA to maintain altitude at a lower fuselage angle.

Also (last time), if you raised the leading edge of the wing, you might be able to touch down flatter, but the wing might block airflow to the tail and decrease elevator and/or rudder effectiveness at low speeds (when you really need it).

Or I could be talking out my @$$ and completely wrong on all counts.
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Re: adjusting elevator

Postby taildrgfun » Thu May 22, 2014 12:01 am

I was pretty loaded down on my Alaska trip and my elevator was directly in line with the hor stab. When I'm flying it light, it is always a little up elevator but not much. The very best thing that I have done to my SS was making some aluminum pieces that bring the flat bottom of the wing all the way back to the front of the flap. It brought the tail up and the nose down a good 3 degrees. I am positive that it made the flaps create a lot more lift in cruise flight and it moved the center of lift back, making it fly more level and making it carry a load much better. I also covered my gear legs, made aero covers for those big shocks and filled in the area between the flaps and the turtle deck which reduced the drag and increased my speed.

I know that quite a few of you noticed that I was strangely silent for awhile after I started flying my SS. I always really liked landing it but I was disappointed in the slow, nose high attitude that it cruised at. It really bothered my after being so used to the low nose attitude that my Highlanders always flew. I didn't care for the way it felt with a load in it the most. As I said above, filling in the front of the flap cove flat out to the flap made all the difference in the world for me. When I did that I was SO MUCH happier with the way it flys. I think that space where the cove was gently rounding up was causing turbulance that was ruining the lift of the flaps in cruise flight. I always flew it with a notch of flaps make it fly more level before, but that created some more drag that I did not want.

When I said I burned less than 5 gph on this trip I had missed a fill up. I actually got 5.2 gph flying 90 to 100 mph for a few thousand miles. I think Gary got 5 gph in his 100 hp Highlander with a constant speed Airmaster prop. Because I have more power I would back off a little for him flying wide open. If I had a 100 hp like him then he would no doubt have had to back off some for me to keep up.

I really am happy with my SS at this point and I am probably more demanding of my airplane than most. I'm not super picky about the looks but I'm very picky about the way it performs and flys.
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