FF kit being stubborn...

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Re: FF kit being stubborn...

Post by pumptato-cat »

I looked through the forums-should gluing a patch of mylar with super 77 fix the tears?

The Duco cement will not dissolve with acetone, how do you all apply acetone? I think I'm doing something wrong(I use a q-tip)
Last edited by pumptato-cat on November 24th, 2022, 12:56 pm, edited 4 times in total.
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Re: FF kit being stubborn...

Post by bjt4888 »

pumptato-cat wrote: November 24th, 2022, 8:26 am I looked through the forums-should gluing a patch of mylar with super 77 fix the tears?

The Duco cement will not dissolve with acetone, how do you all apply acetone? I think I'm doing something wrong(I use a q-tip)
Cat,

We use a glass eye dropper to flow the acetone over the length of a Duco joint. You don’t need to squeeze the eye dropper bulb usually, this might apply too much to quickly. For a joint the size of the stabilizer to fuselage connection, Just touch the eye dropper to the joint with about 2-3 ml of acetone in it and run along the joint. Acetone is so thin, this touching to the joint will probably cause the acetone to flow. If not, then touch the eye dropper to the joint and very gently squeeze the bulb while running along the joint. Then allow a couple minutes for the acetone to start dissolving the glue and very slowly try to pry the joint apart with a dull single edge blade. You may get the joint partly separated and need to apply the acetone one more time.

Brian T
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Re: FF kit being stubborn...

Post by bjt4888 »

pumptato-cat wrote: November 24th, 2022, 7:59 am I somehow managed to tear the mylar on the stab... Might have to just rebuild at this point. It's a small v-shaped tear near the center rib.
Duco cement just refuses to dissolve with acetone, so I had to cut the stab off. ARGHH.
Cat,

Spray a one quick spritz of 3M77 in a medium sized bottle cap (like a Gatorade bottle cap) and (this is the trick) thin it with about 3 ml of Naphtha. Acetone will basically dissolve 3 M77 to nothing and Naphtha will thin it without completely breaking it down. Then use a small paint brush (we use a 000 brush; cheap hobby brush) to brush the thin glue on the flying surface about 1/8” all around the tear. Go ahead and let this thin glued dry for a few minutes. (Next trick) sandwich a 4”x4” piece of the covering film (wrinkled is good, but unwrinkled is ok too) and use a very sharp blade to cut through the paper/Mylar/paper sandwich to cut the patch to size (maybe 1/4” bigger than the tear in all directions). Then slide one newspaper layer away slowly and discard. Now you have a perfectly cut patch and the remaining newspaper layer provides a handy way to carry the patch without it becoming a static cling ball in your fingers. Hover the patch/newspaper over the repair area and slide the Mylar off the paper and on to the repair area perfectly covering the tear. Next dip the brunch in the thin glue and paint around the patch gently. Don’t touch the brush to the patch. Paint around the patch very close to the patch. You’ll see the thin glue painted next to the patch wick under the patch. Now leave the patched area alone overnight.

It takes longer to describe the patching process than it does to do it.

Enjoy,

Brian T
Last edited by bjt4888 on November 24th, 2022, 5:18 pm, edited 1 time in total.
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Re: FF kit being stubborn...

Post by bjt4888 »

bjt4888 wrote: November 24th, 2022, 4:23 pm
pumptato-cat wrote: November 24th, 2022, 7:59 am I somehow managed to tear the mylar on the stab... Might have to just rebuild at this point. It's a small v-shaped tear near the center rib.
Duco cement just refuses to dissolve with acetone, so I had to cut the stab off. ARGHH.
Cat,

Spray a one quick spritz of 3M77 in a medium sized bottle cap (like a Gatorade bottle cap) and (this is the trick) thin it with about 3 ml of Naphtha. Acetone will basically dissolve 3 M77 to nothing and Naphtha will thin it without completely breaking it down.

Then use a small paint brush (we use a 000 brush; cheap hobby brush) to brush the thin glue on the flying surface about 1/8” all around the tear. Go ahead and let this thin glued dry for a few minutes.

(Next trick) sandwich a 4”x4” piece of the covering film (wrinkled is good, but unwrinkled is ok too) and use a very sharp blade to cut through the paper/Mylar/paper sandwich to cut the patch to size (maybe 1/4” bigger than the tear in all directions). Then slide one newspaper layer away slowly and discard.

Now you have a perfectly cut patch and the remaining newspaper layer provides a handy way to carry the patch without it becoming a static cling ball in your fingers. Hover the patch/newspaper over the repair area and slide the Mylar off the paper and on to the repair area perfectly covering the tear. Next dip the brush in the thin glue and paint around the patch gently. Don’t touch the brush to the patch. Paint around the patch very close to the patch.

You’ll see the thin glue painted next to the patch wick under the patch. Now leave the patched area alone to dry overnight.

Clean the brush in straight Naphtha several times, wiping on paper towel between each cleaning.

It takes longer to describe the patching process than it does to do it.

Enjoy,

Brian T
Last edited by bjt4888 on November 24th, 2022, 4:26 pm, edited 1 time in total.
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Re: FF kit being stubborn...

Post by bjt4888 »

bjt4888 wrote: November 24th, 2022, 4:24 pm
bjt4888 wrote: November 24th, 2022, 4:23 pm
pumptato-cat wrote: November 24th, 2022, 7:59 am I somehow managed to tear the mylar on the stab... Might have to just rebuild at this point. It's a small v-shaped tear near the center rib.
Duco cement just refuses to dissolve with acetone, so I had to cut the stab off. ARGHH.
Cat,

Spray a one quick spritz of 3M77 in a medium sized bottle cap (like a Gatorade bottle cap) and (this is the trick) thin it with about 3 ml of Naphtha. Acetone will basically dissolve 3 M77 to nothing and Naphtha will thin it without completely breaking it down.

Then use a small paint brush (we use a 000 brush; cheap hobby brush) to brush the thin glue on the flying surface about 1/4” all around the tear. Go ahead and let this thin glued dry for a few minutes.

(Next trick) sandwich a 4”x4” piece of the covering film (wrinkled is good, but unwrinkled is ok too) between two layers of single sheets of newspaper and use a very sharp blade to cut through the paper/Mylar/paper sandwich to cut the patch to size from an edge of the 4x4 piece (maybe 1/4” bigger than the tear in all directions). The rest of the 4x4 paper/Mylar/paper sandwich is saved for the next repair job. Then slide one newspaper layer slowly away from the patch and discard.

Now you have a perfectly cut patch and the remaining newspaper layer the patch rests on (and is clinging to) provides a handy way to carry the patch without it becoming a static cling ball in your fingers. Hover the patch/newspaper over the repair area and slide the Mylar off the paper and on to the repair area perfectly covering the tear (1/4" extra patch material on all sides of the tear). Next dip the brush in the thin glue and paint around the patch gently. Don’t touch the brush to the patch. Paint around the patch very close to the patch.

You’ll see the thin glue painted next to the patch wick under the patch. Now leave the patched area alone to dry overnight.

Clean the brush in straight Naphtha several times, wiping on paper towel between each cleaning.

It takes longer to describe the patching process than it does to do it.

Enjoy,

Brian T
Last edited by bjt4888 on November 24th, 2022, 5:17 pm, edited 2 times in total.
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Re: FF kit being stubborn...

Post by bjt4888 »

Not sure how this posted three times. Only the last version has all the edits. Maybe the moderator can delete the previous two.
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Re: FF kit being stubborn...

Post by Maxout »

bjt4888 wrote: November 24th, 2022, 7:59 amJeff,

3/4” is a lot of washin. As this years rules created an airplane with marginal roll stability (and marginal pitch stability), this is how much washin is required. The FF kit recommendations are for this much and my teams have 14 Div C airplanes flying great and all have this much washin too. Without this washin amount (and we tested, of course) they attempt to roll and dive and barely climb.

Side note, this washin amount is for the winglet style wing. The tip dihedral prototype wing we tested takes about 1/4”, which is more typical.

Also, the Freedom Flight kit this year doesn’t have a tailboom. Fuselage/tailboom is a single piece of 3/16” x 3/8” x 15.375” wood with the rear rubber hook at the TE of the Stabilizer.

Brian T
Holy crap that's a ton of washin! I've built several Div C planes this year and the most I've used is 1/8", and that was on the ill-fated Guru plane. How tight are y’all trying to turn? Is the FF plane just weird on trim this time around (I've not seen the Div C in person and haven't built out my kit yet).
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Re: FF kit being stubborn...

Post by bjt4888 »

Might be be able to reduce washin after playing with CG, turn settings and propeller pitch a little more. We’re getting pretty good overall duration, but flight profile needs work (too quick initial climb, very good later climb and cruise and landing with very few turns remaining; thinner rubber with this trim results in poor climb). Circle size is around 20-25 ft.
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Re: FF kit being stubborn...

Post by bjt4888 »

pumptato-cat wrote: November 23rd, 2022, 11:38 am Sorry, I've had more technical issues and I thought I posted this but I guess something went wrong?
bjt4888, thanks for posting my trim measurements. I will reset to FF default and do some test flights this Friday(am unable to fly today or tomorrow :c)
I would send flight times and updates but the entire stab attachment is messed up, so I need to cut some new pieces from scrap balsa and redo the TB.
I'll PM you a video of my plane if that helps, coachchuckaahs.
Thanks for the replies, and sorry for the late response... I should have a new computer soon, but the current one refuses to turn on occasionally and is unresponsive half the time :(

EDIT: here is a picture of my stabilizer. I'm not sure what I did to get 5 degrees 😅
calculations were: 5.5mm for distance from ruler to left edge of stab, and 4mm from center of stab to ruler, 13.8cm for the horizontal distance between tip and center. calculation was : sin^-1(1.5/138) = 0.6227 (*10 for mm to cm)
I think I somehow confused myself... not sure now whether this tilt is enough or should be increased.
How do you all adjust rudder offset if your stab is glued to the plane? I've tried using DUCO Cement and it refuses to dissolve(I had to tear it off in the end...)
Cat,

Yes, the rudder offset measure calculation above looks pretty good and shows 0.622 degrees. I would still use the stabilizer center rib angle as it is easier to measure than the angle of the TE for half of the stabilizer. This is enough rudder offset for now. If after reattaching your stabilizer and correcting the tilt the rudder offset is between 1-3 degrees, you’re fine.

Brian T
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Re: FF kit being stubborn...

Post by pumptato-cat »

I will post more details later but currently, my plane stubbornly refuses to fly stably... The flight circle is TINY(like 8-10 feet, sometimes less) and it's sometimes stable, sometimes shaky. I have tried decreasing stab tilt by 2-3deg to help the circle widen out, but no change at all. The plane still stalls and drops frequently- I have set everything except incidence to FF kit defaults..(initially tried default incidence but it was stalling badly) moved CG forward by adding ballast on the nose, experimented with pretty much every cg+incidence+washin combo and nothing's helping. Any ideas? 😞
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