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Author Topic: Ship floats going into wind - what trim change?  (Read 776 times)
Dennis Toth
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« on: May 06, 2012, 11:22:42 AM »

Guys,
I have been flying a Still Stuka that has one annoying characteristic, as the wind comes up it wants to float up. Balance is at the 18% point ready to fly. Some have suggested that I need to adjust the elevator to flap relationship by adding a 1/2 turn of down trim. What trim adjustment will improve the tracking?

Best,    DennisT
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john e. holliday
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« Reply #1 on: May 06, 2012, 11:44:56 AM »

Is everything in zero trim???   Also you might check your handle setting. Hoff
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Randy Cuberly
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« Reply #2 on: May 06, 2012, 12:28:19 PM »

Guys,
I have been flying a Still Stuka that has one annoying characteristic, as the wind comes up it wants to float up. Balance is at the 18% point ready to fly. Some have suggested that I need to adjust the elevator to flap relationship by adding a 1/2 turn of down trim. What trim adjustment will improve the tracking?

Best,    DennisT

Dennis,
If this is just a sight tendency to rise into the wind I think that is fairly normal even on a well trimmed stunter.  We (the nut on the handle) tends to more or less automatically compensate for that dendency.  Now the rub...if the controls are not completely free and smooth around neutral there is a light hesitation in that compensation for very small inputs of the type that this requires to maintain level flight.  So...question...are your control very free around neutral?

There is some validity in what Doc said also...if you are being forced to conciously hold some down (slight) in your handle setting to maintain level flight at 5 ft then the rise that occurs going into the wind will be more obvious because your response for correction will be slower.

In the event that your controls are very free then you might try adding a little down thrust in the engine or tweeking a little down into the elevator relative to the flaps.  This may however introduce an uneven turn rate between inside and outside maneuvers.  Since I've mentioned that are they even presently?  More handle sensitivity in one direction than the other can cause a tendency toward the problem you mentiond also.

Randy Cuberly
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Randy Cuberly
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Dennis Toth
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« Reply #3 on: May 06, 2012, 02:09:48 PM »

Guys,
This ship has been around about 15 years and has won it share but has always been one of those ships that you have to fly for the whole flight.  One thought that the comments sparked is to check the leadouts. This ship has solid leadouts and I wonder if they are more sensitive to the rake angle? The leads go through a nylon adjustable leadout. The rake has the leadouts about 1/2" behind the CG so it is in the normal range but I think I might try moving them back 1/16" and see what it feels like - if better I'll keep moving 1/16" at a time until it doesn't improve. If it doesn't improve going back I'll try the same thing going forward.

One other thing is the CG location, where have those that have the Stuka's been setting the balance point?

Best,            DennisT
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Ted Fancher
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« Reply #4 on: May 06, 2012, 02:10:46 PM »

Guys,
I have been flying a Still Stuka that has one annoying characteristic, as the wind comes up it wants to float up. Balance is at the 18% point ready to fly. Some have suggested that I need to adjust the elevator to flap relationship by adding a 1/2 turn of down trim. What trim adjustment will improve the tracking?

Best,    DennisT

Dennis,

Add 1/4 to 1/2 oz of nose weight and widen the spacing on your handle a small amount to get your desired corner back.  One of the first places I look to determine if a plane has a too far aft CG is the tension in the glide and ability to whip it into and through the wind.  If you're getting just a touch of float it shouldn't take much to bring it into the "right on" category.

Most classic era designs didn't have a large enough tail to allow a CG much beyond the 15 to 18% range without getting light in the glide.  Not sure how the Still fits into my little equation that I use as a rule of thumb.  I divide the area of the tail by the area of the wing (including flaps) and end up with a fraction usually between 15 and 25% or so.  I then initially set my CG at a point on the MAC equal to that same percentage aft of the leading edge (average chord is close enough) Most of the early designs never got beyond 20% and the vast majority were closer to 15.

I'd be interested to hear what the tail area/wing area relationship is on the Still.

Ted
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PJ Rowland
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« Reply #5 on: May 06, 2012, 08:20:47 PM »

My inital thought was to add a little nose weight also Ted.

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« Reply #6 on: May 08, 2012, 08:57:04 AM »

Ted has forgotten more about trimming airplanes then I will ever know, so I offer this alternate point of view with caution.

Learned this lesson flying RC sailplanes, if you want to penetrate in the wind you move the CG AFT.  Reason is with CG forward in glide you must hold a tick of up elevator, with CG farther forward you need more up - hence it balloons.  Move the CG aft and penetration improves - even old floaters like the Olympic can be improved this way.

I only recently encountered similar behavior in a CL model.  An somewhat extreme case, my new Joker OTS bird with power on balloons coming into the wind when the CG is forward.  With CG aft it does not.  I need to measure the tail area & specific CG locations and plug it into Ted's excellent ROT for CG's.  My guess is that een the aft CG is forward of what Ted's ROT would suggest.


Does your Stuka exhibit any other habits that could be attributed to CG being out of place?  Does it favor turning in one direction versus the other? - that might hint at the elevator adjustment...
 

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Denny Adamisin
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