how to correct twist in sheeted/glassed stab?
10-30-2009, 09:57 PM
#1
how to correct twist in sheeted/glassed stab?
I started a 65" WS Royal/Marutaka P-51 Sr. when I was young and relatively inexperienced as a builder, then put it aside for decades. About 10 months ago I decided to revive the project. In the course of construction or during the various moves and storage over 23+ years there appears to have developed a twist in the left horizontal stabilizer.
Unfortunately I didn't notice this prior to glassing it 23 years ago or during the recent finishing stages until I started checking(yes, late...I know) elevator alignment and decoulage. As you can see painting and detailing are also completed leaving me with a real conundrum.
Is it possible to correct the twist without damaging the finishing work that has already been completed? If this were a simple Iron-on covered area the solution would be equally as simple but I have never had this kind problem on this type of build/finish.
The construction is much the same as a typical main wing, LE, TE, and ribs but NO spar, then sheeted, epoxy glassed and painted. Wondering how this would respond to heat and opposite force or just long term, gentle opposite force bracing?
The pics are a bit "busy" with the checker pattern but you can see the negative LE washout at the tip in relation to the root. The elevator is neutral at the root, and is flat and true, so the relationship is pretty obvious at the tip; looks like down elevator.
The twist measures at @ -3 deg. at the tip. Is this enough to worry about? Should I just let it be? How much would this affect the flying characteristics?
Posting in aerodynamics and scale also.
Unfortunately I didn't notice this prior to glassing it 23 years ago or during the recent finishing stages until I started checking(yes, late...I know) elevator alignment and decoulage. As you can see painting and detailing are also completed leaving me with a real conundrum.
Is it possible to correct the twist without damaging the finishing work that has already been completed? If this were a simple Iron-on covered area the solution would be equally as simple but I have never had this kind problem on this type of build/finish.
The construction is much the same as a typical main wing, LE, TE, and ribs but NO spar, then sheeted, epoxy glassed and painted. Wondering how this would respond to heat and opposite force or just long term, gentle opposite force bracing?
The pics are a bit "busy" with the checker pattern but you can see the negative LE washout at the tip in relation to the root. The elevator is neutral at the root, and is flat and true, so the relationship is pretty obvious at the tip; looks like down elevator.
The twist measures at @ -3 deg. at the tip. Is this enough to worry about? Should I just let it be? How much would this affect the flying characteristics?
Posting in aerodynamics and scale also.
10-30-2009, 10:26 PM
#2
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RE: how to correct twist in sheeted/glassed stab?
Hi frets24,
My suggestion is to clamp a length of 1"x1/2" light pine or similar to the stab where it is distorted and apply weight in the opposite direction of the twist. Over time even light weight with a sufficient length of lever will twist it in the direction required. Keep checking and take it slightly past the zero moment before removing the weight.
Cheers,
Colin
My suggestion is to clamp a length of 1"x1/2" light pine or similar to the stab where it is distorted and apply weight in the opposite direction of the twist. Over time even light weight with a sufficient length of lever will twist it in the direction required. Keep checking and take it slightly past the zero moment before removing the weight.
Cheers,
Colin
10-31-2009, 05:51 PM
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RE: how to correct twist in sheeted/glassed stab?
A bit of heat on a glass surface will work .. but remember you have to move the wood underneath which has the twist and it is the hard part.You will need to mount the fin and put on some opposite twist and leave.
I have the same problem at the moment with my Zero ..One wing had 3 deg to much wash out after sitting for 19 years.I cut a section out of the bottom of the wing ,which took the wood stress out,made up a mounting jig and put the wing in with the correct twist and now ready to recover. My wing was all painted and glassed as well.
It can be done but needs a bit of work...cheers
I have the same problem at the moment with my Zero ..One wing had 3 deg to much wash out after sitting for 19 years.I cut a section out of the bottom of the wing ,which took the wood stress out,made up a mounting jig and put the wing in with the correct twist and now ready to recover. My wing was all painted and glassed as well.
It can be done but needs a bit of work...cheers
10-31-2009, 08:34 PM
#4
RE: how to correct twist in sheeted/glassed stab?
Had some tips from the guys over at the aerodynamics board saying much the same. I think I'm going to make up a jig to hold everything where I need it then wrap the stab in a small heating pad for a few hours before starting to apply opposite twist whilst maintaining the heat . If I have to leave it for 3-4 hours or 3-4 weeks I'm ok with it. No sense in rushing it now...it's only been 20+ years since starting on the project!
Hopefully the wood and resins will move enough and reset without resorting to cutting. Again, no hurry so that should help. Other airplane toy projects and "honey-do's" can keep me occupied so that will help against getting impatient.
Thanks for the input. Cheers!
added;
Which Zero is that? I've got the ESM/CMP clone in 70-72" 120 size so it's a treat to see what the guts of the wing structure are like. ( even if yours is a kit build or other mfg)
Hopefully the wood and resins will move enough and reset without resorting to cutting. Again, no hurry so that should help. Other airplane toy projects and "honey-do's" can keep me occupied so that will help against getting impatient.Thanks for the input. Cheers!
added;
Which Zero is that? I've got the ESM/CMP clone in 70-72" 120 size so it's a treat to see what the guts of the wing structure are like. ( even if yours is a kit build or other mfg)
11-01-2009, 02:25 AM
#5
RE: how to correct twist in sheeted/glassed stab?
This stab isn't really that substantial even though it is built up and sheeted, doesn't take a load of pressure with thumb and forefinger on opposite sides@ LE and TE to reverse twist it up to and a bit past true.
Just with messing arond with a 120* kitchen sink water heated gel pack and another refrigerator cooled pack alternately over a couple hours or so is showing very promising results...@ 80% done.
wrap it hot for @ 15 min and it seems to penetrate and get everything just a wee bit looser. hand hold it for 5 min w/heat still applied, remove the heat and hold it for 5 min, then 5 more held with with the cold wrap on. then let it sit unbraced for @20 min and it feels room temp on the surface anyway. have 4 reps on it now. Seems to move back to old memory twist less during each 20-30 min rest period.
I'll look at it again in the AM, see if the recent progress has held overnight.
Just with messing arond with a 120* kitchen sink water heated gel pack and another refrigerator cooled pack alternately over a couple hours or so is showing very promising results...@ 80% done.
wrap it hot for @ 15 min and it seems to penetrate and get everything just a wee bit looser. hand hold it for 5 min w/heat still applied, remove the heat and hold it for 5 min, then 5 more held with with the cold wrap on. then let it sit unbraced for @20 min and it feels room temp on the surface anyway. have 4 reps on it now. Seems to move back to old memory twist less during each 20-30 min rest period.
I'll look at it again in the AM, see if the recent progress has held overnight.
