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 Post subject: Aileron tabs
PostPosted: Tue Feb 22, 2011 7:41 am 
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I know this is not LSA but the characteristics might be similar. When we purchased the Beech Skipper I liked how it flew except the ailerons had almost no centering. It felt like they would pull you into a turn instead of having some force feedback to center. Also in turbulence the airplane would dutch roll or yaw side to side terrible. Smooth air was fine. The yaw would happen even though I was holding the rudder pedals and yoke centered.

I was looking at the aileron linkage and noticed it has differential. More up than down. Then I looked at the GAW-1 airfoil Beech installed. The wing has a lot of cusp or undercamber at the trailing edge. The GAW is known to have a lot of pitching moment which makes it inefficient real world. What came to me is the aileron is being pushed up. It should balance against the other aileron but with the differential gearing the aileron going up has more leverage.

The Skipper has a small aluminum tab on the trailing edge of each aileron. I bent both up at about a 35-40 degree angle with wide jaw sheet metal vice grips.

Next flight it was totally different. The ailerons center and the ride in turbulence is much better. Since a lot of LSA designs have a undercambered airfoil with differential ailerons if you are having centering trouble this might help.

Why it helps the yaw I don't know because the yoke was held centered during the yaw. The only thing I can think of is the reflex tabs act like the tip elevon reflex on a flying wing.

The other thing I noticed is the Skipper aileron to tip fit is terrible. The aileron balance weights are at the tip and the only other design I know like this is a Mooney. Which also can yaw in turbulence. I'm thinking a small yaw makes air go through the tip weigh to wing tip gap and changes the tip votex. That increases drag on one tip and pulls the tip back till it sheds some of the vortex. Then it starts on the other side.

Thought it was all quite strange but it worked. Fixed with a bend of the tabs.

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 Post subject: Bends
PostPosted: Tue Feb 22, 2011 8:09 am 
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Location: Cartersville Georgia
Whatssup Cub?

About bending the tabs on your skipper... Great! There's a lot that takes place in aerodynamics that's not explainable. When something works that can't be explained, that's a good thing.

About differential throw on the ailerons... you may already know this. In its' simplest analysis, a downward deflected aileron creates more drag than one deflected upward, the same amount.

If they were set-up equally up vs. down, for example, if you are rolling into a right turn, (left aileron goes down) the plane would want to yaw left very strongly. THIS IS CALLED ADVERSE YAW, and is one reason aileron AND RUDDER is needed to do a coordinated a turn.

Aircraft manufacturers rig the ailerons so that up travel is much greater than down travel, in an attempt cancel out adverse yaw.

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Bryan Cobb
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Commercial Rotorcraft Helicopter
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 Post subject:
PostPosted: Tue Feb 22, 2011 8:18 am 
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I've got the adverse yaw, differential, rudder coordination down ok. What struck me as unusual in this case is the yaw problem was in level flight.

Holding rudder and aileron as rigid centered as I could it would yaw / dutch roll all over the place. Holding the controls centered gave me the most fixed fin area possible. No control surface float.

With the trim tabs bent it's much better. Still holding controls centered.

Sure it takes coordinated rudder in the turns but I did not like the ailerons getting sucked into the turn instead of pushing back towards center. Felt like the airplane was balanced on a knife edge. No roll stability. Now it has great aileron feel. You could probably vary the tab bend to tune the ailerons to the feel you want.

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"Perfection is finally attained not when there is no longer anything to add but when there is no longer anything to take away." Antoine de Saint Exupery


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 Post subject: Re: Aileron tabs
PostPosted: Tue Feb 22, 2011 9:10 am 
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Location: Lock Haven PA
Cub flyer wrote:
The Skipper has a small aluminum tab on the trailing edge of each aileron.


Curious that you have a tab on each aileron. All the planes I've flown had (at most) just one, on one side. You bent it down, or up, as necessary, to fly wings level with neutral control inputs.

Some planes of the same pedigree come out of the factory without the tab, so I made some inquires some years ago at the Beech factory. I was told the planes are built first without the tab, rigged, and test flown. If the plane flies wings level, they ship it. If not, they add a tab to one side, bend it, get the plane flying straight, and then ship the unit.

So, your Skipper came with two band-aids instead of one. Interesting!

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The opinions expressed in this post are those of one CFI, and do not necessarily represent the position of the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS
AvSport of Lock Haven
http://AvSport.org fly@AvSport.org


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 Post subject: Re: Aileron tabs
PostPosted: Tue Feb 22, 2011 9:16 am 
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Cub flyer wrote:
Also in turbulence the airplane would dutch roll or yaw side to side terrible.


This is a characteristic of all the short-coupled Beechcraft. It was very pronounced on the Model 35 Bonanza, and that plane's critics blamed it on the V-tail. But the Model 33 Debonaire (essentially a Bonanza with a straight tail) did the same thing, so that explanation didn't wash. The Musketeer line and its derivatives (Sport, Sundowner, Sierra) did the same thing. So too the Skipper. I don't know the aerodynamics of the matter, but since all these Beechcraft have different airfoils, it must be related to the short-coupled design that they all have in common. (As Microsoft would say, it's not a bug; it's a feature.)

Glad you found a solution, Charlie. You ought to post it to the Beech Aero Club forums and see how those guys respond.

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The opinions expressed in this post are those of one CFI, and do not necessarily represent the position of the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS
AvSport of Lock Haven
http://AvSport.org fly@AvSport.org


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 Post subject:
PostPosted: Tue Feb 22, 2011 9:25 am 
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I guess if you have two tabs on a system with differential you could also do the opposite and bend both down for less stick force.

I usually adjusted a flap slightly for wing heaviness on the Apache or Cherokee. I like looking out and seeing the controls all line up. Adjusting an aileron tab made the controls out of line in flight.

It's funny about the short coupled thing. The Piper Vagabond is VERY short with a fat fusleage and it is dead stable in yaw. So was the Pitts.

The Skipper was odd because it would roll and yaw sometimes. Looking out at the wingtip it would move backward then up and forward in a circle. Made me sick.

All gone now. I suspect the tabs just a band aid. The real problem is the fit of the aileron weights to the tips. I've been trying to think of another airplane with the tip weights/balance on the wing tips. Only other one I can come up with is the Mooney. I also was thinking back to free flight model days and it might be the Beech series has too much dihedral.

How is the SportStar in this situation? It has a flat wing and smaller tail


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 Post subject:
PostPosted: Tue Feb 22, 2011 9:35 am 
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Location: noble, IL USA
Every T-tailed airplane I've flown has been like that at least a little.


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 Post subject:
PostPosted: Tue Feb 22, 2011 10:47 am 
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With the T tail it probably has to do with the weight of the additional structure to carry the tail up high. Extra weight on the ends of the fuselage can't help much in turbulence. The Cessna Crusader had the mid fin horizontal tail and it yaws around also in the bumps. Luckily there's a yaw damper.

I thought the T tail or lack of fin area was the problem was at first. I was really surprised bending the tabs helped. I thought it would just affect the ailerons.


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 Post subject:
PostPosted: Tue Feb 22, 2011 1:59 pm 
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It may be that the T-tail contributes to the Dutch roll, but I don't think that's the dominant factor. After all, the V-tail and conventional tail Beechcraft all have the same characteristic.

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The opinions expressed in this post are those of one CFI, and do not necessarily represent the position of the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS
AvSport of Lock Haven
http://AvSport.org fly@AvSport.org


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 Post subject:
PostPosted: Wed Feb 23, 2011 2:53 am 
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Location: Bellevue, WA
Cub flyer wrote:
Looking out at the wingtip it would move backward then up and forward in a circle. Made me sick.


FWIW from what I remember from flight dynamics equations this is strictly speaking is suppposed to be an elliptic motion ;) Also how much the dutch roll is pronounced in aircraft depends on relative relationship of directional stability vs. lateral stability not any one one alone and is design charachteristic of an aircraft. With directional stability relatively weaker than lateral stability the dutch roll gets more pronounced. So, for example, "too much" dihedral for a given directional stability to lessen spiral mode could increase dutch roll tendencies. Maybe the fact that Skipper was certified for intentional spins has something to do with this.


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 Post subject:
PostPosted: Wed Feb 23, 2011 6:46 am 
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I think your right. The airplane has to be tricked into a spin with full opposite aileron just after stall breaks and you apply full rudder. otherwise it just won't spin

Also they have stall strips on both wing leading edges near the tips instead of the wing root.

The stall is gentle and no nasty habits like the Tomahawk. I'm guessing it was too gentle and it would not spin initially. They started with a low tail very similar to the Skycatcher but it might not have worked out well.

The dorsal fin is sharp edged on top to help directional stability but it's behind a fat fuselage and canopy area. I read a few pilot reports talking of the yaw in turbulence. Others never mention it. It might be the individual airplane. I'm still thinking the wingtip fit has something to do with it.

I can't find ANY other airplanes with the up angled Horner style tip and a aerodynamic/mass balance at the wingtip. Anyone know of one?

The air coming up the Horner is supposed to push the vortex out increasing effective span. The aileron weight gap is very strange. It's sculpted out on the inside and I think air is getting in there with a little yaw and dragging the tip back.

The wing tips are painted lexan and historically the weak point on a Skipper. A guy was going to make fiberglass units to replace them but I don't know the fit.

Only way to know is make a couple soft foam seals and bend the aileron tabs straight to see if the problem comes back.


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 Post subject:
PostPosted: Wed Feb 23, 2011 11:16 am 
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Cub flyer wrote:
The wing tips are painted lexan and historically the weak point on a Skipper. A guy was going to make fiberglass units to replace them but I don't know the fit.


I don't know for sure if these are the same as the tips on the Sport, Skipper, and Sierra, but if so, Beechcraft called the material "Royalite" (It probably is Lexan, or something similar, though). Cracking at the attach screws was always a problem. On the Sierra, I replaced mine decades ago with the Demers fiberglass droop tips (not sure if those are available for the Skipper, but along with the 3-bladed prop and VGs, gave me really good STOL performance). Only problem with that mod is the STC lowered the max gross wt by 135# - not an issue in the Sierra, but something you can't afford in a Skipper.

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The opinions expressed in this post are those of one CFI, and do not necessarily represent the position of the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS
AvSport of Lock Haven
http://AvSport.org fly@AvSport.org


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 Post subject:
PostPosted: Thu Feb 24, 2011 11:23 am 
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good news was yesterday I flew 1.6 hours and used 7 gallons


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