Smoothie Trim Question

[Kim Mortimore]

I'm currently flying a Smoothie, the first plane I've had a plane with a lot of wing asymmetry.   The wing looks level upright, but I'm seeing the bottom of the wing inverted.  Someone said the outboard wing drops noticeably when the engine quits, and suggested I reduce tip weight.  The tip weight box is empty.  Any Smoothie veterans out there with suggestions?

Thanks,
Kim Mortimore

[Busby]

As strange as it sounds it may require some tip weight on the inboard wing.
Stranger things have happened.
Busby
 

[John Miller]

I'm currently flying a Smoothie, the first plane I've had a plane with a lot of wing asymmetry.   The wing looks level upright, but I'm seeing the bottom of the wing inverted.   Someone said the outboard wing drops noticeably when the engine quits, and suggested I reduce tip weight.  The tip weight box is empty.  Any Smoothie veterans out there with suggestions?

Thanks,
Kim Mortimore

Two items to consider. One is a warp, though unlikely the cause, and the other is needing some tip weight.

[John Sunderland]

 Check for warps but, as designed it has to much asymmetry. Could be the culprit?

  John

[Dennis Adamisin]

Its warped.  Tweak the flaps ( or twist & heat the wing) and try again.  THEN adjust the tip weight.

[Ted Fancher]

Its warped.  Tweak the flaps ( or twist & heat the wing) and try again.  THEN adjust the tip weight.

This Denny guy is really sharp!  Where'd he come from? Juuuuust kidding.     

I'd also bet that the ship is a little light on the lines when inverted and doing outsides.  What you've got is a warp which rolls the airplane to the right (right wing down when upright, up when inverted) but inadequate tip weight.  If the tip weight were correct the warp would result in the right wing being down upright and up inverted.

You will almost certainly end up tweaking the outboard flap "down" a bit and adding a bit of tip weight.

I'd do a little of both to start with because only tweaking the flap will result in the outboard wing being up both upright and inverted.  Adding a half oz of tip weight while doing the flap tweaking is a good safety gimmick, especially if you're flying in less than ideal wind conditions, etc.

One final note, the best solution to the twisted wing/flap condition is to very carefully examine them to find the warp and then remove the warp.  It's a technically superior fix to tweaking the flaps although I doubt anyone could tell the difference if the warp is modest.  View the wing from the tail toward the trailing edge of the wing.  Check first for twisted or warped flaps (very common with the thin, 1/8" flaps of the era) and straighten any twist.  While you're at it, double check that both are "neutral" at the same time.  It's not at all uncommon for a bit of differential to show up if the horn arms or the holes they go into aren't parallel. Once any obvious flap problems are resolved recheck the wing focusing beyond the flap to the hingline.  Based on your description what you might expect to see is the trailing edge of the right wing warped up a little bit toward the tip and/or the trailing edge of the left wing warped down a tad.  If you or a flying buddy have an incidence meter it can help identify such problems although it is important to remember that the accuracy of the hinging and the shaping of the flap can distort readings when the meter is attached to the leading edge of the wing and the trailing edge of the flap.

Ted Fancher

[Brett Buck]

This Denny guy is really sharp!  Where'd he come from? Juuuuust kidding.     

I'd also bet that the ship is a little light on the lines when inverted and doing outsides.  What you've got is a warp which rolls the airplane to the right (right wing down when upright, up when inverted) but inadequate tip weight.  If the tip weight were correct the warp would result in the right wing being down upright and up inverted.

You will almost certainly end up tweaking the outboard flap "down" a bit and adding a bit of tip weight.

I'd do a little of both to start with because only tweaking the flap will result in the outboard wing being up both upright and inverted.  Adding a half oz of tip weight while doing the flap tweaking is a good safety gimmick, especially if you're flying in less than ideal wind conditions, etc.

One final note, the best solution to the twisted wing/flap condition is to very carefully examine them to find the warp and then remove the warp.  It's a technically superior fix to tweaking the flaps although I doubt anyone could tell the difference if the warp is modest.  View the wing from the tail toward the trailing edge of the wing.  Check first for twisted or warped flaps (very common with the thin, 1/8" flaps of the era) and straighten any twist.  While you're at it, double check that both are "neutral" at the same time.  It's not at all uncommon for a bit of differential to show up if the horn arms or the holes they go into aren't parallel. Once any obvious flap problems are resolved recheck the wing focusing beyond the flap to the hingline.  Based on your description what you might expect to see is the trailing edge of the right wing warped up a little bit toward the tip and/or the trailing edge of the left wing warped down a tad.  If you or a flying buddy have an incidence meter it can help identify such problems although it is important to remember that the accuracy of the hinging and the shaping of the flap can distort readings when the meter is attached to the leading edge of the wing and the trailing edge of the flap.

Ted Fancher

   And I would be willing to wager that it either needs a tab on the outboard flap. With a normal design, the "needs different tipweight for different conditions" can frequently be traced to excess rudder offset. But in this case, I would guess that the excess asymmetry is the cause of the wingtip dropping in maneuvers. So if you get enough tipweight in to keep the wing level in level flight, it will roll strongly out in maneuvers. A larger outboard flap (or adding asymmetry to the stabilizer, which is probably the root cause) might be necessary.

    Brett

[peabody]

Tom Hampshire introduced me to an "area tab" on my Smoothie....made it a thoroughly satisfying flier! We have since added them to several other Smoothies...I used clear celluloid/plastic with four square inches of area......

[Kim Mortimore]

OK, let's see.....Dennis, Ted, Brett.  Now if I could just get some guys who REALLY know what the heck they're talking about to reply, then I might get somewhere.         Stunt forums are "the bomb", as the kids say these days.   

   And I would be willing to wager that it either needs a tab on the outboard flap. With a normal design, the "needs different tipweight for different conditions" can frequently be traced to excess rudder offset. But in this case, I would guess that the excess asymmetry is the cause of the wingtip dropping in maneuvers. So if you get enough tipweight in to keep the wing level in level flight, it will roll strongly out in maneuvers. A larger outboard flap (or adding asymmetry to the stabilizer, which is probably the root cause) might be necessary.

    Brett

Brett,
I think my original message was poorly worded.  I'm seeing the bottom of the wing in level flight inverted. The wingtip drop happens when the engine quits, according to an observer.  As for roll attitude during maneuvers, I'm so used to some degree of positive roll during some maneuvers on many of the planes I've flown that I have tended not to worry about it unless it's extreme.  Rudder offset is very slight.  Also, I'm flying at a fast enough clip to maintain the really solid overhead line tension I like, ~4.5, that the probably inevitable variation in line tension between in and outside maneuvers Ted mentioned is not noticeable to my less than expert hand. 

I followed everything Ted said (for a change!) and then what you said up to "...(or adding asymmetry to the stabilizer, which is probably the root cause)..."  I suspect I'm not the only SH reader who could use some tutoring on stabilizer asymmetry, so if you have time at some point to say a bit more about this, or refer us to previous posts or other resources, I would certainly appreciate it.

 

Tom Hampshire introduced me to an "area tab" on my Smoothie....made it a thoroughly satisfying flier! We have since added them to several other Smoothies...I used clear celluloid/plastic with four square inches of area......

Rich,
The area tab goes on the outboard flap, or beyond the flap?  4 sq in is a pretty hefty tab.  Just looking at the wing it's easy to see how that much could be needed.  It's good that clear plastic doesn't change the wing's appearance much.

Sincere thanks to all of you for taking time to reply.  Us stunt grunts never had it so good!   

Thanks,
Kim

[Brett Buck]

OK, let's see.....Dennis, Ted, Brett.  Now if I could just get some guys who REALLY know what the heck they're talking about to reply, then I might get somewhere. 

  No kidding! Bring it out on Sunday, you might also get a World Champion.


     Brett

[tom hampshire]

Hi Kim - The tab goes on the outboard flap, to equalize the flap area on each panel in spite of the huge 2" panel offset.  Works exactly like making the outboard flap 1/8 wider at the outboard tip with a conventional (3/4") panel offset.  Try splitting the flap at the TE, and inserting a tab of stiff celluloid or other similar packaging material with PFM or Goop glue to hold the tab in place.  Tom H.

[scott bolton]

  Hi guys, Just thinking about the load of information on the trim issues for the smoothie. I've never had to use trim tabs in my short time of control line flying.If someone could please post some pictures of a wingflap that has a trimtab installed to show all us rookies exactly whats involved. I too have a smoothie (profile) with some slight wing highth issues. THANKS for all the help guys !!!!!!!   scottbolton

[Larry Fulwider]

. . . The wing looks level upright, but I'm seeing the bottom of the wing inverted. 
. . .

Thanks,
Kim Mortimore

Typically, a Smoothie has the vertical CG above the leadouts. That is, they fly like an Al Rabe design -- if you forget the dihedral.

Hang the Smoothie by the leadouts up close to a wall, gear just touching the wall. If the outboard tip is closer to the wall than the inboard tip, you have defined the problem.

If that is the problem, well, figure out a way to hang it by the leadouts so both tips are equidistant from the wall. 

Larry Fulwider

[tom hampshire]

Here Y'are, Scott.

[Steve Fitton]

Good heavens Tom, what did you do to that muffler!!

[john e. holliday]

Hey Tom,  I love the color scheme of that Smoothie.  DOC Holliday

[Kim Mortimore]

I made the trim changes initially suggested, and went to the field.  Since Sunday was my last practice day before the NW Regionals, I chose the field that would allow me the most practice flights before the predicted near 100-degree heat melted me into a puddle of quivering biogoo, which was Gilroy (thanks anyway for the invite, Brett.  Probably next time).   

Within 3 flights I had the wing level upright and inverted.  However it was rock and roll city in maneuvers with the additional tip weight, especially insides, where I got a pretty detailed look at the bottom of the wing, even with a 4 square inch tab on the outboard flap.  The funny thing is, it felt great, at least in near dead calm.  Overhead line tension was very solid, even flying slower than previously.  All rolling was in a positive, line-tightening direction.  But....you just can't fly with that much roll.  It's hard for judges to write numbers when they're laughing.  Squares have to be very soft.  Rolling is sure to bite you in the wind.  And it looks stupid.  Also, lots of wake turbulence yesterday in the calm, which may have been made worse by the funky roll attitude.  Not sure.  At least the wing was sure nice and straight in level flight both ways!   

Typically, a Smoothie has the vertical CG above the leadouts. That is, they fly like an Al Rabe design -- if you forget the dihedral.

Hang the Smoothie by the leadouts up close to a wall, gear just touching the wall. If the outboard tip is closer to the wall than the inboard tip, you have defined the problem.

If that is the problem, well, figure out a way to hang it by the leadouts so both tips are equidistant from the wall. 

Larry Fulwider

Later I saw Larry's message and tried Al Rabe's wall-hanging test.  The outboard tip is 1-3/4" closer to the wall than the inboard.  Somebody who knows how to do the math might be able to convert 1-3/4" over 52" into degrees FWIW.  I am told that the cause is a combination of low wing, no dihedral, upright heavier modern engines (+ mufflers not used in 1952), and lighter wheels.  Even though it won't be possible to move the vertical CG all the way down to the leadouts, I am also told that a workable compromise can be reached (making this plane an especially instructive trim tutorial as a side benefit, IMHO, something I definitely want).  Or maybe I could follow Larry's final suggestion, locate a tilted wall, and redo the hang test.   

Before the contest I plan to reduce the tip weight to bring the roll under control.  After the contest, I will replace the heavy stock muffler with a lighter one.  A switch from an LA40 to an LA46 would help a little, but doesn't seem worth disrupting the very nice working relationship between this engine, tank and plane.  Anybody have any old, heavy 3" wheels they'd like to sell?  We fly in fairly long grass sometimes, and the larger wheels should help there also.  The guy who posted the topic about adding wheelpants to his Smoothie could bury some lead weights in them.  Lead in the pants. 

Kim