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Author Topic: Beginners attempt at Scale Rubber Power, Guillows 17" Chipmunk  (Read 2986 times)
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Dan Snow
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« Reply #50 on: August 11, 2018, 10:08:39 AM »

Thanks Konrad, that is exactly what I'm going to do.  I know will likely need nose weight to compensate but I can live with that!!
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Konrad
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« Reply #51 on: August 11, 2018, 12:20:14 PM »

Thanks Konrad, that is exactly what I'm going to do.  I know will likely need nose weight to compensate but I can live with that!!
Not likely as the gear is already close to the CofG. But as always do take your time with the flight trimming. Have you read up on how to trim a low wing rubber band powered FF model? To some (myself) it was counter intuitive on how to use the stall and motor torque to control the climb.

Don Ross's Rubber Powered Model Airplanes (ISBN 0-87938-325-9) taught me everything I know about Rubber Powered Airplanes. Well, everything that works. I think you can still find a copy. If you can get it!
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Dan Snow
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« Reply #52 on: August 11, 2018, 04:40:17 PM »

I have the book on  order, should have it mid-week.
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Dan Snow
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« Reply #53 on: August 12, 2018, 10:03:16 AM »

Everything is covered and shrunk!

Will start assembly soon. Unfortunately my shop has no AC so I;m limited to early morning for 3-4 hours during the summer.
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Konrad
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« Reply #54 on: August 12, 2018, 11:39:44 AM »

Do swamp coolers work in the Sacramento valley? I know I cherish the FOG that comes down the valleys here in San Francisco.
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Dan Snow
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« Reply #55 on: August 12, 2018, 12:23:26 PM »

They do, Konrad, but I have a lot of wood working tools and would rather not have to oil everything to fight rust. I had thought about a portable AC unit, but don't have any windows that open so I would have to punch a hole in a wall to vent the hot exhaust,. I'm up early every morning so I get a few hours each day before the heat gets too much.
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Dan Snow
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« Reply #56 on: August 12, 2018, 04:25:40 PM »

The assembly of the Chipmunk is 90% complete. Wings and tail feathers attached and I think reasonably straight. I figure the first test glide will show me how straight they really are!! Smiley Smiley I still need to attach the canopy, install the rear motor mount tube and get the nose block and prop hook squared away.

As the first photo shows total weight without sealing or any ballast that might be needed for CG, it came in at 23 grams.

For now I'm counting this as a learning effort to knock of the rust and fire up the desire to see something I built take to the air.
Important lessons learned so far:
1. Never, ever, ever buy a Guillows Die-Squashed kit again. (They are not worth the frustration of mangled parts.)
2. Read the directions and building instructions, TWICE!! At Least Twice. (Don't ask me how I learned this!)
3. Good Lord these suckers are FRAGILE!!  Many repairs caused by fumble fingers.
4. CA adhesives and glue sticks have made these teensy things a lot easier to build. (Except when you glue the part to a finger instead of the model!)

P.S. I just noticed the camera angle and background for the 2nd photo makes the stab look a bit like it has a propeller twist in it, which I can attest it does Not have! Smiley
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Konrad
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« Reply #57 on: August 12, 2018, 05:40:08 PM »

She looks fantastic!  I'd be hard pressed to get a model looking that good!

A lesson I've learned is not to use CA as a primary adhesive. CA is hard to sand and the joints are brittle. I like Titebond as I can force dry the small parts in a microwave (almost as fast as CA), it sands well and isn't brittle. This last property makes flight trimming easier.

All the best,
Konrad
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« Reply #58 on: August 12, 2018, 08:20:30 PM »

What a nice first effort - it looks like the rust has been removed Smiley. With the same care used in trimming the model - you will have a good flying model. Next one will be easier!

I agree with Konrad re CA. I use PVA or Aliphatic glues - double gluing with end grain joints particularly. Used sparingly it is light and very strong without being brittle. Mistakes can be remedied by softening the joint with water. it takes a fair amount of soaking to do this by the way, so the joints don't fall apart when you water shrink for example.

Glue sticks certainly help the covering but I would follow the advice to seal the edges/overlaps with some PVA to help stop the edges creeping.

John
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Dan Snow
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« Reply #59 on: August 12, 2018, 10:03:57 PM »

Thank you folks.

I'll admit CA has it issues, but I've been using it for a lot of years and models and I'm comfortable with it. Plus I have respiratory issues with some of the more volatile adhesives and the odorless CA doesn't give me any problems.

Being a part time worker, maker of wooden toys, I use a lot of Titebond and other wood glues where I can clamp and allow it to dry for at least a few hours, never thought to try it on balsa.
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Konrad
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« Reply #60 on: August 12, 2018, 10:21:34 PM »

Original Titebond and a microwave oven are made for each other. Ok, a toy builder that shows in your build.
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MKelly
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« Reply #61 on: August 12, 2018, 10:59:00 PM »

Been using Titebond II for my last 10 or so stick and tissue models - love it.  I put it in a school-size Elmer's glue bottle (the kind with the orange twist lid) and use it straight from the bottle, no pre- or double-gluing.  Light, sands well, and as others have said doesn't get brittle like CA does.

Your Chipmunk is looking good!

Mike
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kittyfritters
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« Reply #62 on: August 12, 2018, 11:37:56 PM »

Original Titebond and a microwave oven are made for each other. Ok, a toy builder that shows in your build.

I've used the Titebond II/microwave oven trick ever since I worked in a professional wood shop.  However. do not ever, EVER, EVER forget to take all the pins out before putting a part of the model in the microwave to cure the glue!  (You might also consider keeping a CO2 fire extinguisher near the microwave.)  Putting a model in the oven at 200 degrees (F) for a half hour also cures aliphatic glues. Don't go any hotter, if the water in the glue boils it will push the joints apart.

When I use CA I always use kicker immediately, sets the glue and kills the smell.  I use a dribble bottle with a 0.010 nozzle to drip it on, never spray the stuff.

KF
« Last Edit: August 12, 2018, 11:48:19 PM by kittyfritters » Logged

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Andrew Darby
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« Reply #63 on: August 13, 2018, 04:56:35 AM »

Hey KF.

Do you know if Guillows are going to laser this series of kits?

Nice work Dan, looks like a flyer...

Andrew
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« Reply #64 on: August 13, 2018, 06:44:05 AM »

Yes, looks very neat and tidy, and “true”.  Should fly well.  Don’t get fed up trying to trim it. One of the appeals of this kind of modelling is the challenge of trimming.  Some models can be very cantankerous and obtuse.  Enjoyable topic so far thank you.

PS Konrad - has anyone really sprayed CA?. 
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Dan Snow
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« Reply #65 on: August 13, 2018, 08:42:02 AM »

I have a couple more questions, I guess looking for an answer from folks here in the USA. 

1.)The picture shows the three lacquer choices available to me. There used to be a 4th, Valspar from Lowes, but for some reason they have chosen to drop the Valspar in favor of Rustoleum. I don't know why, as the Rustoleum is a lot slower drying than the Valspar.

So I'm looking for recommendations on what to use the seal the Chipmunk. And of course I realize there is always Nitrate dope. I'm very nervous about warping.  I would imagine I need to use very light misting coats and do the whole model at once for even shrinkage?

2.) I just looked over the plans very carefully, and NO WHERE on the plans do they show the recommended CG position. Any one out there that has built this particular model? I'm going to start maybe 1/16" forward of the main spar.   Can't believe that they wouldn't show this very critical dimension.
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Konrad
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« Reply #66 on: August 13, 2018, 11:08:02 AM »

I use non-taunting Nitrate Dope ( I think this is Randolph's dope marketed by Sig). This has been good on some of my models for 15 to 20 years.
I've tried Future Floor Polish (from the grocery store) and it did not destroy my model.

Needing a secret decoder ring was typical of many of the kits of old. It really hampered us kids in trying to get our creations to fly.
I start with the center of gravity placed at the 25% point of the MAC (Mean Aerodynamic Chord). Flying wings or models with too small a stabilizer I'd try 20%. I think there is a bold black arrow pointing to the wing tip that is too designate the CofG.

Dave- I've been accused of spraying a lot of stuff  Roll Eyes but CA isn't one of them.


All the best,
Konrad
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billdennis747
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« Reply #67 on: August 13, 2018, 11:37:33 AM »

Steam shrink, non-shrink dope diluted, pin down only if necessary, no problem. Dope has been used forever; if it destroyed models, I guess people would have stopped using it by now.
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Konrad
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« Reply #68 on: August 13, 2018, 12:04:58 PM »

Original Titebond and a microwave oven are made for each other. Ok, a toy builder that shows in your build.

I've used the Titebond II/microwave oven trick ever since I worked in a professional wood shop.  However. do not ever, EVER, EVER forget to take all the pins out before putting a part of the model in the microwave to cure the glue!  (You might also consider keeping a CO2 fire extinguisher near the microwave.)  Putting a model in the oven at 200 degrees (F) for a half hour also cures aliphatic glues. Don't go any hotter, if the water in the glue boils it will push the joints apart.

When I use CA I always use kicker immediately, sets the glue and kills the smell.  I use a dribble bottle with a 0.010 nozzle to drip it on, never spray the stuff.

KF
Yep, those pins make real nice radiating antenna! I use masking take to hold parts together while in the microwave. I also only use 15 second heating cycles (depends on the power of your oven). 3 to 4 heat cycles and the Titebond is dry. Hint: If you find a warp heating the glue joints (the whole structure) and then hold the part straight until is cools. This really has saved a lot of my bannaned fuselages from the trash can (recycling bin here in California)

All the best,
Konrad
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Dan Snow
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« Reply #69 on: August 13, 2018, 12:23:29 PM »

Just for the heck of it I googled "Where is the CG on the Guillows Model 903 DH Chipmunk?" and actually got a hit!  Fellow said he contacted Guillows and they told him to balance on the 1/16" top wing stringer. That seemed awfully far forward, and would require I add 5 grams of weight to the nose!! And even if I had installed the main landing gear, I still would have need at least a couple grams of nose weight. I'll attribute this partially to the 1/2" x  3/4" x 1/16" balsa reinforcement I added to each side of the fuselage to strengthen them for the rear motor anchor tube.

I then calculated the MAC and at 25% it still puts the CG only 1/16" aft of the top wing stringer.  Well darn, there goes my sub 30 gram weight!!

BTW- I didn't mean to infer that dope was bad, I've used a lot of it.  I was just thinking that if I could save a trip to the Hobby Store that would be good.
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Konrad
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« Reply #70 on: August 13, 2018, 01:45:18 PM »

Its not you. Its a scale model, and as such the nose is too short! You might have noticed that all sport rubber models have much longer noses. Also this is a simple build that uses sheet sides. Guillow tried to minimize this issue with the use of 1/20 sheet.

All the best,
Konrad
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kittyfritters
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« Reply #71 on: August 13, 2018, 01:59:41 PM »


PS Konrad - has anyone really sprayed CA?.  

Not the CA the kicker!

Hey KF.

Do you know if Guillows are going to laser this series of kits?

Nice work Dan, looks like a flyer...

Andrew

As to this series being laser cut, Guillow has all the series redrawn and test built for laser cutting.  They have to buy more laser cutters to have the capacity.  The scale models are not their only revenue stream, in fact not their largest, so they have to balance all their tooling purchases among all their product lines.  Have patience, it will come.


KF
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Dan Snow
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« Reply #72 on: August 13, 2018, 02:24:42 PM »

I decided to call Guillows and ask them directly. I received a voicemail from a nice fellow named Mark K and he explained that the CG should be about 1 1/8" back from the leading edge at the root. This puts it about 1/4" forward of the main spar. That sounds a lot more reasonable then the other information I saw and means a lot less noseweight. I'll start there and let folks know how it goes.
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Indoorflyer
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« Reply #73 on: August 13, 2018, 02:32:20 PM »

This thread is in the Indoor FF Forum. You don't need to seal the model with dope if it will be flown exclusively indoors. A light misting of clear
acrylic from a rattle can will work, if you do fly outside. Easy to go overboard with decorating, which does nothing to enhance flight performance.
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Konrad
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« Reply #74 on: August 13, 2018, 03:02:18 PM »

I decided to call Guillows and ask them directly. I received a voicemail from a nice fellow named Mark K and he explained that the CG should be about 1 1/8" back from the leading edge at the root. This puts it about 1/4" forward of the main spar. That sounds a lot more reasonable then the other information I saw and means a lot less noseweight. I'll start there and let folks know how it goes.
Dug out some of my series 900 plans. They all show the Center of Gravity with a common pin in the wing tip. (Sorry I don’t have a set of plans for the Chipmunk) Under “Adjusting and Flying Model” in the first sentence it states “After model is completed, place straight pin in wing tips carefully at exact location indicated on plans”. This location looks forward a 1/4 inch of the bottom spar and 1/16 aft of the first top spar. Like I said I’d start at 25% MAC (that looks like the pin location) and move aft as the flight trimming dictates.

All the best,
Konrad
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