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Author Topic: Trimming  (Read 2034 times)
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Swarthog
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« Reply #25 on: July 20, 2013, 11:55:12 PM »

P.S. Anyone ever tried carnuba wax as a balsa finish? Works pretty well on hard woods, though it needs to be renewed from time to time.

Gleaned this from the 1941 Vart plan page "When the
glider is completely dry the completed model may be
waxed for a super-smooth finish. "

So the world record holder went for every little extra edge he could get.
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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #26 on: July 21, 2013, 07:33:58 PM »

Yes, Swarthog, I have used wax on my indoor HLGs, back when my arm was good and I set some IHLG records, partly due to the great Champion
Joe Foster mentoring me with such advice. He recommended Glaswax or Mirarub(sic?)which was available then(50s, 60s)and was basically pumice
suspended in liquid wax. The wing was coated first with several(3-4)coats of sanding sealer(Testors, in those days)and sanded after each coat.
By the time the 4th was fine sanded, grain was really filled, so the Glaswax was then applied and rubbed out.
All I can say is I broke the 'Magic Minute Mark' (did 67 sec on first rollout flight) with first glider I made after Joe's advice, then set Sr record on
next official flight of 1:11.6.
The waxed finish was one major factor toward my successful indoor HLG career, as it seems it was for Leo Vartanian as well.
It still amazes me that those Chicago Aeronut IHLG fliers knew so much about what worked best, all those years ago!
His fine 12" glider is flown succesfully to this day as an Outdoor CLG, for the most part, and against all comers, not just Oldtimer events!
 
Lee
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Leeper
Swarthog
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« Reply #27 on: July 22, 2013, 08:41:53 PM »

Thanks for the reply! I really appreciate all the help and advice.  The Catago (14"ws) made it's final flights today and made many nice flights before self destructing.  I'll keep working on that one. I got a new printer now and can print out these plans. I'll make some Varts, Thermic 18, Frog Wasp, and a Vega or two. For free flight rubber guys it makes sense to have these gliders around for lots of reasons. I learn a lot about gliders, which all rubber jobs are after the power runs out.  It provides "instant" fun for when something does go wrong with your other planes. You can hand one to a kid and really not worry if they lose or break it. The smiles of "would you look at that thing go" are priceless!  For around $20 you can make at least a dozen, which might be the most fun for the $ you can get these days.

I can use some of my furniture finishing skills here I see. What it looks like you are trying to achieve is a very smooth "closed pore" finish. Sounds like French Polish to me. Which I'm sure many of you know is an old very time consuming method of getting a mirror shine on fine furniture. After sanding you fill the grain with pumice (sounds familiar) and then build up very thin layers of shellac. You make the "cut" pretty thin I would bet. Shellac flakes can be had at Rocklers. After a good shellacking, waxing would improve things just a bit more. Since the gliders are so small, compared to an armoire, even a time intensive task like French Polish can be completed before your brain melts into mush, which is why everyone uses lacquer now days Smiley     


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Tmat
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« Reply #28 on: July 23, 2013, 04:22:44 PM »

You don't need to do such an elaborate finish with catapult gliders (outdoor gliders) these days Swarthog. We just rub on a coat of Minwax Spar urethane, then wipe it all away and allow to dry. Sand with 400 grit and repeat. No need to fill the pores (heavy) or use shellac or lacquer based products (smelly and brittle and prone to warpage on thin balsa surfaces). Keep it simple and copy what the "big boys" are doing like Leeper, Stan B, etc.

Tmat
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F1B guy...
But don't hold that against me!
Ministick7
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« Reply #29 on: March 11, 2018, 12:22:43 PM »

Hi, Thank you for your good advice. I will try your methods and go to launch as soon as a reasonable glide is achieved, with slight nose up when hand launched straight ahead. A finishing question, please: I have Minwax urethane spar varnish, semi-gloss. How do I apply it lightly using paper towels? Can't wait for snow and wind to go away to start flying these new gliders! I will try to attach a picture of some of the squadron. Thanks again.
Bob
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OZPAF
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« Reply #30 on: March 12, 2018, 03:13:28 AM »

Quote
How do I apply it lightly using paper towels?

You need 2 paper towels or more. Use one to dip into the varnish, wipe over the surface rubbing it in gently. I wet one wing panel - top and bottom and then immediately wipe it off with a dry paper towel leaving just a dull sheen.

The idea is to just get some into the balsa and then wipe it off so that it only has a very light coat.

I find it can take a few days before the surface of the balsa is completely dry. Don't try to sand it if it still feels tacky and as TMAT mentions fine sand it with 400 and that's all that's needed.

John
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sweepettelee
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Simplicate & add more lightness. Keep sanding!



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« Reply #31 on: March 14, 2018, 01:35:54 PM »

To expand somewhat on Tmat's reply(July 23, 2013) and Ministick7's query(13 Mar, 2018), Minwax can be applied with cheap foam disposable brushes.
I recommend using the blue paper shop towels, since they seem lint-free, which most other paper towels will leave small shards of lint, hence adding some roughness to be sanded away.  Gloss Minwax works equally well, IMO. Grin
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Leeper
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« Reply #32 on: March 27, 2018, 07:17:26 PM »

Prerequisite 1.  Make sure you have at least a bit of decalage to start.  Decalage is the difference in angle at which the wing and stab see the air.  I.e. the air should hit the underside of the wing a bit more than the stab.  This should be small; about 1/2 degree is a good start; more is OK initially, but not a lot.

Prerequisite 2.  Make sure the glider balances where shown on the plans, or slightly aft to start with.  If the plans don't show a CG (center of gravity), start at about 60%-70% of the wing chord back from the leading edge.

I really wish I'd *read and understood* #1 prior to spending an hour this morning building a 0-0 cradle.


I have been playing with some of the planes that call for an airfoil on the fin instead of angling to induce a turn.  Have you looked into airfoiling the bottom of the stab rather than negative declage?
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OZPAF
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« Reply #33 on: March 28, 2018, 06:34:18 PM »

Quote
really wish I'd *read and understood* #1 prior to spending an hour this morning building a 0-0 cradle.

My personal preference is to start as close to zero - zero as possible. The amount of positive decalage required is usually very small and it is much easier to add it rather than take it out.

Quote
I have been playing with some of the planes that call for an airfoil on the fin instead of angling to induce a turn.  Have you looked into airfoiling the bottom of the stab rather than negative declage?

I doubt whether airfoiling the stab has very much effect and only then possibly at high speed. I do taper and airfoil the stab but it's mainly done for strength and to keep it light. I also use an air foiled fin but still need to angle it for turn.

John
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xptical
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« Reply #34 on: March 28, 2018, 07:29:56 PM »

I just finished a few small 0-0 CLGs.  They fire straight up then come straight down.

This is a 12" v-tail I just made tonight.  It started with -0.5 degrees as per Rewinged's suggestion.

I shot her up at maybe 45-degrees and she flew a ballistic arc.  I had to tweak the stab tips maybe 1/8" up to see a good transition.  Then maybe a smidge more blue-tac to get her back on the glideslope.

I wish I could do more trimming, but I really need a field for anything bigger than 8".
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OZPAF
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« Reply #35 on: March 29, 2018, 08:45:15 PM »

The fuselage may be bending downwards at speed and reducing the necessary decalage. I would try stiffening up the fuselage and see how that works. I use 1/8 spruce for the tail boom on my 12" WS CLG's.

John
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Hepcat
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« Reply #36 on: March 29, 2018, 09:20:57 PM »

If you find trimming a catapult glider to perfection is challenging (and most people do) I would have thought the last thing to mess with would be a 'V' tail. Indeed, is there ever a reason to use a 'V' tail, except to be different? Smiley
John
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OZPAF
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« Reply #37 on: March 29, 2018, 10:54:36 PM »

I was actually thinking much the same thing John. I would think that they would be annoying to trim as you are adding elevator and rudder inputs with each trim movement. Also I think the adjustment for say elevator would need to be a fair bit more than you would need on a conventional tail for the same effect, due to their lower effeciency.
However I have built one - Mick Paige's butterfly 2. It had built in adjustments and I don't think I made any alterations when trimming it before I gave it to the young fellow I built it for. It did however have what is now called a Y Tail as used on the latest tip launched gliders with a rudder under the V tail, and this would have simplified rudder adjustments.
John
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