trimming question

[Matt Colan]

On my Ares, the wing is down right-side up and way up inverted.  After maybe 5 flap tweaks both ways and an elevator tweak, it is still down right-side up and up inverted.  I noticed that the outboard wing has a warp in it maybe 1/16 or 3/32 something like that.  It isn't warped until maybe the last 4 or 5 full ribs in the wing. Is that warp enough that no matter which way I move the flaps it will still be down right-side up and up inverted?  I just can't seem to figure out why it is like that.

[Brett Buck]

On my Ares, the wing is down right-side up and way up inverted.  After maybe 5 flap tweaks both ways and an elevator tweak, it is still down right-side up and up inverted.  I noticed that the outboard wing has a warp in it maybe 1/16 or 3/32 something like that.  It isn't warped until maybe the last 4 or 5 full ribs in the wing. Is that warp enough that no matter which way I move the flaps it will still be down right-side up and up inverted?  I just can't seem to figure out why it is like that.

      Of course 3/32 is a pretty big warp, but eventually tweaking the flaps will get rid of it. And from your description, there is NO doubt that there is a warp that must be taken care of. I wouldn't suggest tweaking the elevator at all - just put it straight. It's very ineffective for countering wing warps.

    I am not sure I recall how it's covered, but if you have that much warp, it would probably be worth removing it with steam/towels+boiling water. Tweaking the flap horns is always an "iffy" proposition - you can break the horn and then you have a BIG problem that will involve Zona saws to fix. The wing should be very easy to tweak with heat or steam, they are pretty wimpy torsionally aside from the covering.

   Brett

[Howard Rush]

Dewarping should go pretty well with an I-beamer.  Trying to counter that big a warp with a flap tweak would give you a substandard airplane. 

Elevator tweaks might affect yaw trim.  And therein lies a tale.  When we were putting fly-by-wire flight controls on the 777, we were scheming up things we could do with the new capability.  I proposed using differential elevator to eliminate the need for a high-speed inboard aileron, making more trailing edge space available for flaps.  We didn't do it.  I forget why.  Gary Letzinger explained to me some years later that people had tried differential elevator, and it affected the flow over the vertical stabilizer, which makes sense when you think about it.  So if you need some right rudder and your rudder is fixed, tweak the elevators. 

[Randy Powell]

If you're sure you have a wing warp, then go with Brett's and Howard's advice. They are surely correct (and I ALWAYS listen to Brett on trimming issues). But your description sounds like you have too much tip weight (wing low upright and inverted). Especially if you tweaked the flaps and didn't have any effect on the problem.

[billbyles]

If you're sure you have a wing warp, then go with Brett's and Howard's advice. They are surely correct (and I ALWAYS listen to Brett on trimming issues). But your description sounds like you have too much tip weight (wing low upright and inverted). Especially if you tweaked the flaps and didn't have any effect on the problem.

Hi Randy,

If I read Matt's posting correctly he said that the wing was down when flying upright and up when flying inverted.  That sounds more like a wing warp than tip weight to me.  Now that I re-think this, does he mean, when flying inverted, "up" as away from the ground or "up" as toward the canopy?  Naahhh, I still think it sounds like he has a wing warp.

Bill

[john e. holliday]

Now if he will listen to the experts, he will dig out the old tea kettle.  If you don't have one ask Grandma for one.  The other alternative is a trim tab that can be adjusted.  Tweaking flaps is only a measure to see if the plane will fly.  Just think if you do lltweak flaps, when they move they are not in alignment will cause head aches.

Also if you draft Grandpa to help you the steaming is the only way to go.  DOC Holliday

[Brett Buck]

Now if he will listen to the experts, he will dig out the old tea kettle.  If you don't have one ask Grandma for one.

    And if you use a gas burner under it, be careful about setting the tissue on fire!  It has happened...

    I would be a little surprised if tea kettle steam will be enough to make the change permanent, but towels/boiling water might work TOO well on an Ares.

     Brett

[Bradley Walker]

On my Ares, the wing is down right-side up and way up inverted.  After maybe 5 flap tweaks both ways and an elevator tweak, it is still down right-side up and up inverted.  I noticed that the outboard wing has a warp in it maybe 1/16 or 3/32 something like that.  It isn't warped until maybe the last 4 or 5 full ribs in the wing. Is that warp enough that no matter which way I move the flaps it will still be down right-side up and up inverted?  I just can't seem to figure out why it is like that.

Tape a 1/4" stick to the bottom side outboard wingtip in line with the flap hinge line.  It basically works as a trim tab.

[Scott B. Riese]

Several years ago Brett or Howard wrote about using a hot wet towel to remove a warp. MAYBE one of them can relate back to our younger years and post that again. It's great reading.

Scott ( need a towel now) Riese 

[Matt Colan]

Dewarping should go pretty well with an I-beamer.  Trying to counter that big a warp with a flap tweak would give you a substandard airplane. 

Elevator tweaks might affect yaw trim.  And therein lies a tale.  When we were putting fly-by-wire flight controls on the 777, we were scheming up things we could do with the new capability.  I proposed using differential elevator to eliminate the need for a high-speed inboard aileron, making more trailing edge space available for flaps.  We didn't do it.  I forget why.  Gary Letzinger explained to me some years later that people had tried differential elevator, and it affected the flow over the vertical stabilizer, which makes sense when you think about it.  So if you need some right rudder and your rudder is fixed, tweak the elevators. 

I tweaked the elevators because they were off a little bit, and now they are straight.

[Matt Colan]

Now if he will listen to the experts, he will dig out the old tea kettle.  If you don't have one ask Grandma for one.  The other alternative is a trim tab that can be adjusted.  Tweaking flaps is only a measure to see if the plane will fly.  Just think if you do lltweak flaps, when they move they are not in alignment will cause head aches.

Also if you draft Grandpa to help you the steaming is the only way to go.  DOC Holliday

DOC, the flap tweaks gave me half a heart attack when we tweaked them once and the flap cracked.  Grandpa fixed it when I went away on vacation.  I asked him about steaming and he said it would take a LOT of steam to dewarp the wing.

[scott bolton]

 Hey guys, just my two cents worth on tweeking flaps. Old school fliers have always told me that if you need to tweek flaps something is NOT straight! But if a slight tweek is required use small blocks of wood on the top and bottom of the flaps to keep from busting the control horn out of the flaps. Best of luck with the trim issue.           

[Brett Buck]

DOC, the flap tweaks gave me half a heart attack when we tweaked them once and the flap cracked.  Grandpa fixed it when I went away on vacation.  I asked him about steaming and he said it would take a LOT of steam to dewarp the wing.

  Boiling water and towels will certainly do it. Maybe too well.

     Brett

[Garf]

I hope you didn't build the wing with white glue.

[Howard Rush]

Tape a 1/4" stick to the bottom side outboard wingtip in line with the flap hinge line.  It basically works as a trim tab.

This works, as do flap tweaks and trim tabs, but if you have a substantial warp and counter it with one of these prostheses rather than removing the warp, your airplane will suck.  The reason is that different parts of the wing will be operating at different angles of attack.  That's OK at low angles of attack, but when you push the wing beyond where lift is linear with angle of attack (and that place will start early for some parts of a warped wing), it will start to do perverted things.  Corners will not be nice.  

[Howard Rush]

  Boiling water and towels will certainly do it. Maybe too well.

To elaborate, pour boiling water on the wing while twisting it opposite the warp.  Use the towels to wipe up the water.

Back to you, Brett.
By the way, thanks, Brett, for your help with my engine today.

[Randy Powell]

>>If I read Matt's posting correctly he said that the wing was down when flying upright and up when flying inverted. <<

Yep, I misread it.

Good points. I've had to tweak flaps slightly, though it usually because they weren't quite straight to begin with. The tea kettle idea works. Last time I did this, I used gloves and soaked a hand towel in hot water, wrapped the wing to twist. Held it twisted in the correct direction and had my wife pour some addition hot water on. took maybe 5 minutes of holding it, but it worked. The finish got kinda cloudy, but once dry, it buffed back up pretty well. Try to keep the water out of the holes where the gear goes in, the flap horn and where the flaps meet the fairings. Not much fun if these swell up.

[Brett Buck]

To elaborate, pour boiling water on the wing while twisting it opposite the warp.  Use the towels to wipe up the water.

Back to you, Brett.
By the way, thanks, Brett, for your help with my engine today.

  Might want to hold off until you fly it!

    Brett

[Matt Colan]

I hope you didn't build the wing with white glue.

No, I used CA.  We built the wing on a straight table so I don't know why it got warped.  During the flying season when I had the basic airframe done, the plane was sitting by a heater.  That wouldn't make it warp would it?

[Howard Rush]

My guess would be that the torsional stiffness of that wing is pretty low, so that a little imbalance in covering shrinkage was able to twist the wing pretty far before reaching equilibrium.  Fire up that teakettle.

[Matt Colan]

My guess would be that the torsional stiffness of that wing is pretty low, so that a little imbalance in covering shrinkage was able to twist the wing pretty far before reaching equilibrium.  Fire up that teakettle.

We covered one wing panel at a time, top and bottom and in as quick a time as possible because we were afraid of the wing warping.  I think I'll post a picture of the warp at a later time.

[Matt Colan]

I looked at the Ares today for a closer inspection.  The outboard flap is wider than the inboard flap.  Also the outboard flap is tweaked down rather than what it should be up.  There is a 1/16 warp in the outboard wing.  How much would that affect the whole thing?

[Howard Rush]

If you take out the warp, the warp won't have any effect.  Get out the teakettle.

[Matt Colan]

Ok Howard.  If I steam the wing, do I hold it over the steam and twist the wing in the right direction?

[Howard Rush]

To elaborate, pour boiling water on the wing while twisting it opposite the warp.  Use the towels to wipe up the water.

[Howard Rush]

I can understand your reluctance to do anything drastic to your airplane.  I had a similar experience Tuesday.  My dentist has a new laser, which we discussed using to blast a mole thing off the inside of my cheek.  "What's the advantage in keeping it there?" she asked, as I contemplated the laser blowing a hole in my face.

[john e. holliday]

As quite a few people have stated on here  you need to get the elevators lined up.  Get the flaps lined up, that is the flaps and elevators should be on zero when you site them.  Then sight the wing and get it straight.  Then if it still is not flying level you  may need a trim tab.  If it flies high outboard wing both upright and inverted then you may need tip weight.  If the opposite direction you may have to remove weight.  Too bad we can't be there to watch your plane fly.  It would be so much easier to figure out the fix.  DOC Holliday

[Howard Rush]

I'd leave the flap control horns as they are until you fly. That's one fewer time you'd need to tweak them.  Dewarp the wing and flaps (if they're warped, too).  Then fly it and tweak flaps as needed.  You won't see that many trim tabs on Nats top 20 day.

[Matt Colan]

As quite a few people have stated on here  you need to get the elevators lined up.  Get the flaps lined up, that is the flaps and elevators should be on zero when you site them.  Then sight the wing and get it straight.  Then if it still is not flying level you  may need a trim tab.  If it flies high outboard wing both upright and inverted then you may need tip weight.  If the opposite direction you may have to remove weight.  Too bad we can't be there to watch your plane fly.  It would be so much easier to figure out the fix.  DOC Holliday

I know DOC, it would be alot easier to figure it out if it there were other people flying with us.  The only PAMPA members in Vermont are me and grandpa.  The elevators were a little off, but we tweaked them right.

[John Ashford]

Hey Guys,

We sometimes forget the material we are working with is WOOD.  Some woods are more stable than others and Balsa is pretty far down the stability list.  I occasionally build planes and regardless of how much wood matching, jigging and measuring I do and no matter how perfect the "bare bones" project is put together I still get warps during the finishing process about half the time. 

Brett and Howard have both given you very good advice but I want to emphasize a couple of points they just touched on in this post.

One:  "Tweaking" flaps or elevators is a really bad choice for NATs caliber planes. The misalignment this produces will certainly make the plane fly level both ways but will cause you more problems than you can imagine when you do the tricks.  How to correct that leads me to number two.

Two: Depending on the covering material used, you have to approach this in different ways.  Monocote and other plastic coverings are generally the easiest because you can bend the wing and apply heat.  With these coverings it won't last because these coverings will relax in heat or sun over time and go back to where it was. The answer for that is to check before contest day and reheat and bend.  Not a major problem just something you need to pay attention to.   Polyspan is just as easy to fix in the same manner as plastic but will hold its position for a long time.

Silkspan or Silk is a whole 'nother ball game.  A steam kettle is only going to burn your hands on a finished plane and won't solve the problem.  Best answer I've found means you're going to have to enlist the help of a friend or understanding spouse.  Get a kettle of boiling water and a small bath towel.  Wrap the offending member, be that wing or fuselage, in the towel and have helper pour the water on the towel enough to soak it. Let it set for about 30-45 seconds and then over-bend (slightly) the needed direction.  Hold until the towel cools and then take a look.  If needed, repeat but if it is straight when it cools then it will probably stay that way for a long time. Wearing oven mitts or some other form of heat protection is a really good idea.

Howard, I love you but pouring hot water over a plane and then mopping up with a towel is really not the way to go.

Later,  John

[Matt Colan]

Hey Guys,

We sometimes forget the material we are working with is WOOD.  Some woods are more stable than others and Balsa is pretty far down the stability list.  I occasionally build planes and regardless of how much wood matching, jigging and measuring I do and no matter how perfect the "bare bones" project is put together I still get warps during the finishing process about half the time. 

Brett and Howard have both given you very good advice but I want to emphasize a couple of points they just touched on in this post.

One:  "Tweaking" flaps or elevators is a really bad choice for NATs caliber planes. The misalignment this produces will certainly make the plane fly level both ways but will cause you more problems than you can imagine when you do the tricks.  How to correct that leads me to number two.

Two: Depending on the covering material used, you have to approach this in different ways.  Monocote and other plastic coverings are generally the easiest because you can bend the wing and apply heat.  With these coverings it won't last because these coverings will relax in heat or sun over time and go back to where it was. The answer for that is to check before contest day and reheat and bend.  Not a major problem just something you need to pay attention to.   Polyspan is just as easy to fix in the same manner as plastic but will hold its position for a long time.

Silkspan or Silk is a whole 'nother ball game.  A steam kettle is only going to burn your hands on a finished plane and won't solve the problem.  Best answer I've found means you're going to have to enlist the help of a friend or understanding spouse.  Get a kettle of boiling water and a small bath towel.  Wrap the offending member, be that wing or fuselage, in the towel and have helper pour the water on the towel enough to soak it. Let it set for about 30-45 seconds and then over-bend (slightly) the needed direction.  Hold until the towel cools and then take a look.  If needed, repeat but if it is straight when it cools then it will probably stay that way for a long time. Wearing oven mitts or some other form of heat protection is a really good idea.

Howard, I love you but pouring hot water over a plane and then mopping up with a towel is really not the way to go.

Later,  John

I really am wary of doing that, pouring boiling water on the wing, and bending it to get it right.  I covered the Ares wing with heavy silkspan and the fuselage was with 00 silkspan.  Next time we fly, I'm going to get a square 1 flight, and then if the wing level thing is not right, I'll make up a trim tab and put that on it.  If the wing is down in level flight and up inverted, I would put that trim tab on the top of the outboard wing right?  Also when I have the plane inverted, the wing is up so much I can easily see the trim, which I don't find normal

One thing I just remembered was when I do a wingover, I see the bottom of the wing.  I don't see that as normal, but then again I haven't had a plane that I've needed to do this much trimming with.  My smoothie was tip weight, handle adjustment and a slight flap tweak.  my profile I can't remember what trimming we did with it since it was so long ago (2 years ago).  Have I been spoiled 

[Howard Rush]

Matt, this boiling water is the sort of thing you'll want to try on somebody else's plane first to gain confidence.  Maybe borrow a plane with the excuse of taking some measurements. 

[Howard Rush]

"I'll make up a trim tab and put that on it.  If the wing is down in level flight and up inverted, I would put that trim tab on the top of the outboard wing right? "

Who cares?  Wherever you put it, the airplane will still suck . 

[minnesotamodeler]

Well, that's real helpful...

If the outboard wing is down in upright flight, it needs lift on the bottom, not the top.

But for what it's worth, Howard is right...the warp and the trim tab cancelling each other out will create bunches of drag out there too.  Can you spell "YAW?

I wouldn't be afraid of trhe hot water trick, your plane won't dissolve.  I think the towels are for wrapping the wing BEFORE you pour the hot water on, right guys?  Anyhow that's how I'd do it.

[Howard Rush]

"Wearing oven mitts or some other form of heat protection is a really good idea."  Better yet might be having a younger sibling hold the airplane with the oven mitts if the mitts are not waterproof.  

[Howard Rush]

Well, that's real helpful...

If the outboard wing is down in upright flight, it needs lift on the bottom, not the top.

But for what it's worth, Howard is right...the warp and the trim tab cancelling each other out will create bunches of drag out there too.  Can you spell "YAW?

I wouldn't be afraid of trhe hot water trick, your plane won't dissolve.  I think the towels are for wrapping the wing BEFORE you pour the hot water on, right guys?  Anyhow that's how I'd do it.

I have been teasing Brett about towels.  Towels might be needed on a beefier structure, but on silk-covered sheeted-leading-edge combat planes without a shear web closing the D tube, the water alone works a treat.  I'd think that you could dewarp an I-beamer just by spitting on it if you have reasonably warm spit.

[minnesotamodeler]

Didn't someone suggest using the exhaust of their car for a heat source?  Course you'd want to hold your breath I guess.

I use my heat gun, but then most of my wings are shrinkwrapped.

[Dennis Adamisin]

Matt: listen to Howard

If you KNOW there is a warp then the most direct solution is to remove that warp - everything else is just window dressing.  As he says, I-Beams are notoriously weak in torsion.  Put another way it almost DOES NOT MATTER if you build them straight, they WILL warp at the slightest provocation when you cover & paint.  This is one of the reasons I never built I-beams - until recently - and now I only cover them with monocote, because I can twist & reshrink so easily.

Someone suggested using a heat gun or iron - MIGHT work but is pretty easy to overheat and burn the paint if you are not careful.  Even boiling water will "only" be 212 degrees.

Way back when my brother had a Sting Ray based design that finsihed out with about a 1/2" (!!!) twist in one wing.  He got it out by blocking it up outdoors on the picnic table, twisting it straight and applying hot wet towels to it - outdoors on a hot sunny day.  Kept re-applying towels every half hour or so but in a few hours the twist was gone.

if you are afraid to try pouring boilng water on the wing directly, then I suggest putting a wet towel folded a couple times soe it fits the wing, then gently pour the boiling water onto the towel, distributing the water so the get the heat all over the surface.  The towel will also keep it from running off so fast..

However, fix the PROBLEM furst and do not rely just on the band-aids (tabs) to do the job...