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Old Mar 15, 2011, 05:41 PM
Zach
Illinois
Joined Feb 2004
806 Posts
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Originally Posted by knlever View Post
That's a lovely boat. How on earth do you waterproof it? Waterproofing needs to be done for model planes as well in case of wet weather etc.
A lot of paint. I learned early on that you want to apply the paint in thin coats and allow each one 4 hours to dry before applying the next coat. Otherwise the cardboard would soak up the water in the paint like a sponge.

I also used water based latex paint because it is still a little flexible after it dries and cardboard is a flexible material. I was also told to avoid using oil based paint because the oil would soak into the cardboard and never dry.

I found the best tape to use was the brown packing tape that has water activated adhesive on the back. Also know as gummed tape. It's not the easiest thing to use but it is strong and takes paint well.
http://www.staples.com/Staples-Stand...?cmArea=SEARCH

You're pretty good with that 3D CAD software. That takes a while to learn.

Zach
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Old Mar 15, 2011, 09:59 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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Originally Posted by Tail Spin1 View Post
A..... I was also told to avoid using oil based paint because the oil would soak into the cardboard and never dry. ....
Then you were told wrong and swallowed someone's idea that had no idea hook line and sinker. You would have been better off doing your own testing on the numerous scraps that were left behind.

Latex paint remains pourous. Which is one reason why the better exterior latex paints are idea for coating wood since it's both flexible and breaths. Oil based varnish or oil paints would form a far more water resistant film and would have been idea for your paper boat. But all is not lost since a good grade of polyurethane varnish could be applied over the well dried latex paint and serve as an excellent water sealing finish. I'd suggest two or three coats of Flecto brand Varathane in the original oil formula. The stuff is amazing and tough as nails whenever I've used it over the years. In one case I painted a coat on a carboard box I used for transporting indoor models something like 40 years ago. I still have the box and the models inside. It withstood rain on frequent occasions while moving it from the car or truck to the flying hall. Granted that wasn't a boat but the point is that the oil based varnish dried just fine and in a normal amount of time.
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Old Mar 16, 2011, 07:28 PM
Just shut up and build!
Sri Lanka
Joined Mar 2010
652 Posts
Quote:
You're pretty good with that 3D CAD software. That takes a while to learn.
Zach, thanks for the compliment. I was going to say it's no big deal but actually I started 2D modeling in 2007 using VRML. Since then I have been using Wings 3D - it is really easy to use once you get the mouse set up. It took me about two years to do a reasonable model, but it is fun.

I never get tired of looking at the 3D models in Turbo Squid and on the RC groups CAD gallery. Have you done any 3d models of your own?
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Old Mar 24, 2011, 07:36 PM
Just shut up and build!
Sri Lanka
Joined Mar 2010
652 Posts
First Construction Pix

Pictures of the 180. I have been working on the model - here are the first pictures. The material used is bristol board, except for the tail plane which is paper and bamboo. The tube you see down the middle is the rubber motor tube. The model balances around 50% of chord so that is a good start. The tail section is not stiff at all, building it up should fix this. Alignment of the parts is not quite correct, hope to fix this on the next model. I have learned much: what materials to use, how to build the model and how to attach the parts together. The sequence of assembly is important.
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Old Mar 25, 2011, 04:43 AM
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Yak 52's Avatar
UK
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Good stuff! Jon
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Old Mar 25, 2011, 09:01 AM
Just shut up and build!
Sri Lanka
Joined Mar 2010
652 Posts
Thanks Yak 52. I knew I could count on you. Nice work on the Redwing
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Old Mar 29, 2011, 06:33 PM
Just shut up and build!
Sri Lanka
Joined Mar 2010
652 Posts
More construction pic.

The plane flies in this condition , just barely maintaining height. It is very stable in its flight, and balanced without any nose weight, a bit nose heavy. Adding the rear panels has changed all this.

I have several options: add more power, which I have done I added another rubber band for more power and to decrease weight, the wing is the main candidate for improvement weighing maybe 10 g or more. The other option is to change the construction material to paper, with proper reinforcing.

Weigh is 35 g wingspan is 42 cm or about 16 inches
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Old Apr 03, 2011, 06:43 PM
Just shut up and build!
Sri Lanka
Joined Mar 2010
652 Posts
In Flight Pix

Made several flights on 100 - 130 turns on the rubber motor.

(The photos have been edited, by the way, to remove unwanted objects in the background)

To recap: the model is a 45 cm ( 17 inch) span Cessna 180 model weighing around 40g. The propeller is a Guillows 15 cm just (under 6 inch) propeller. Two loops of rubber bands are used in parallel, rubber bands are of thickness 3mm or so. Construction is out of Bristol Board and paper, the yellow and white areas on the model respectively.

The model is very stable, flying straight and level when launched correctly on all flights. It does not really climb but certainly flies like a powered model.
An earlier crash bent the wing out of place, it would do a snap roll after launch : I glued an extra bamboo skewer underneath the wing and it is fine now. At present the main limitation is motor duration, but for short spaces , this is fine. I have learned much from building and flying this model, thanks for all the advice I got saying 'build many models'.

What next? Well the landing gear came off, I have yet to find a good way of attaching a landing gear with rolling wheels. That is the next priority. Painting and finishing is the next thing.

The model flies quite fast, due to its relatively high RPM on the prop, but I feel it needs to fly this fast to maintain level flight. With a good electric motor it should fly, definitely, but I am not sure I want such a heavy model. Next step is to build another model with more paper used to lower the weight, and one strand of rubber for a slower revolving prop.

I can get only abut 180 turns max on the lubricated, not stretch wound/ stretched motor- will better rubber solve this problem? Contest rubber?

Appreciate comments. I think anyone could build a flying model like this - no need to use balsa.
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Old Apr 03, 2011, 10:14 PM
Registered User
Joined Oct 2005
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Quote:
Originally Posted by knlever View Post
Made several flights on 100 - 130 turns on the rubber motor.

The model is very stable, flying straight and level when launched correctly on all flights. It does not really climb but certainly flies like a powered model.

At present the main limitation is motor duration, but for short spaces , this is fine. I have learned much from building and flying this model, thanks for all the advice I got saying 'build many models'.

What next? Well the landing gear came off, I have yet to find a good way of attaching a landing gear with rolling wheels. That is the next priority. Painting and finishing is the next thing.

The model flies quite fast, due to its relatively high RPM on the prop, but I feel it needs to fly this fast to maintain level flight. With a good electric motor it should fly, definitely, but I am not sure I want such a heavy model. Next step is to build another model with more paper used to lower the weight, and one strand of rubber for a slower revolving prop.

I can get only abut 180 turns max on the lubricated, not stretch wound/ stretched motor- will better rubber solve this problem? Contest rubber?

Appreciate comments. I think anyone could build a flying model like this - no need to use balsa.
KNLEVER,

A good attempt.

Powered models can climb.

The main limitation is that you do not have enough power to sustain level flight or climb. Not duration. You need to address the power/lift issue first. Landing gear, painting etc. are WAY down on the list of priorities. First the model must sustain flight. Since the model is not climbing, it is too heavy for the wing area/ lift produced. You are essentially falling under power. Better rubber, lubricated and stretch wound will help A LOT! (more power per gram, better power release)

So what to do??

Build you next model with 20% larger wing and tail area. You really need to have some form of rudimentary airfoil/ undercambered section to provide more lift. You also might consider lengthening the fuselage ahead and behind the CofG to permit more rubber without affecting the CofG. A stronger motor tube will withstand more force. Remember, you want to slow down the rpm's so the motor run will last longer. Try more pitch and/or a bit more diameter. Try to coat the tube with a coat of dope or shellac, or varnish. Alternatively (and perhaps more likely to succeed) would be to use a bamboo skewer to serve as a motor stick (instead of the pape tube). Build it up like it was an indoor model using thin wire for a prop bearing.

Kim.
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Old Apr 04, 2011, 02:48 AM
Just shut up and build!
Sri Lanka
Joined Mar 2010
652 Posts
Kim

Thanks for the comments. I see you were one of the posters in the 'increasing rubber powered flight times' thread.

Well the model does sustain flight. Of course it is heavy: the point was to experiment with cardboard and see how far I would get. At the moment I am very pleased with the result. The model could be made lighter through redesigning and changing some cardboard to paper. Also, the run times on the 6 inch rubber I am getting with a 5.5 inch or so prop is in the range of 10 seconds total, which is too little.

Better rubber is an option, but I prefer to leave out stretch winding at the moment. I can increase the lenght of rubber to run the entire length of the fuselage instead of halfway or so.

What to do? Well I have tried to go the other way - build a smaller but lighter model, with a simpler setup, using paper mostly. This time it will be a long nosed model with retracted undercarriage such as a Pilatus PC 9.

As for an undercambered airfoil do you mean a curved airfoil as in the world war 1 planes?

Any suitable from this list? http://en.wikipedia.org/wiki/Airfoil
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Old Apr 04, 2011, 03:28 AM
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UK
Joined Jan 2009
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A good start Knlever...

First, a 17" span model at 40 grams will need a lot of power... make it again at 30 grams and you will see a big difference. My latest rubber model is 20" span at 20 grams.

Second - you can improve the motor run significantly. I would suggest you try adding another loop of rubber bands: more rubber crossection gives more power. Then make it as long as you can - as you said. The prop needs to be bigger (7-8" maybe) to reduce revs and increase run time. Experiment with different types of rubber bands too. I would imagine the flat ones are better than the square section ones?

The other thing you can try is increasing the tail incidence (to give up elevator effect) this should make the glide slower... BUT because the model is heavy you may not be able to slow it down without stalling...

A proper airfoil will also help but reducing weight is the way to see real gains...

So to recap:
- Lighten the plane
- Increase the amount of rubber
- Lengthen the motor
- Increase the prop diameter
- Improve the airfoil
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Old Apr 04, 2011, 04:04 AM
Just shut up and build!
Sri Lanka
Joined Mar 2010
652 Posts
Thanks. This should be fun!
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Old Apr 05, 2011, 02:01 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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I'll echo the suggestion to work on cutting down the weight. And at the same time bump up the size a little to around 22 inch span. Then work with the same thickness of materials. The added wing area will carry some weight with more ease. But you still need to work on lightening the model up.

I've never had much luck with models where the prop is more than 1/3 of the wing span. The trimming just seems to get too tricky due to torque effects from the prop and rubber.

Also keep in mind that adding loops makes the rubber more powerful but it also reduces the run time due to accepting less turns and the added torque spinning the prop faster so it runds down sooner. Lengthening it allows for more turns but does not add any torque. So finding the best cross section and length involves some trial and error.

None of those airfoils on that page will work with your card stock wing construction. I'd suggest you play with something more like this folded "side and a half" style of airfoil made from card stock similar to that used for greeting cards. It works with the strengths of the material while avoiding a lot of the weaknesses. And best of all it's pretty simple to do it this way
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Old Apr 06, 2011, 08:20 PM
Just shut up and build!
Sri Lanka
Joined Mar 2010
652 Posts
Quote:
First, a 17" span model at 40 grams will need a lot of power... make it again at 30 grams and you will see a big difference. My latest rubber model is 20" span at 20 grams.
What is your latest model - any pictures? I would love to see it in flight.

I agree about the weight - there are lots of ways to reduced the weight, the most obvious is to build a long nosed model that does not require nose weight.

It occured to be that stretching the rubber inside the fuselage, that is, the installation where the rubber is stretched, actually decreases the cross section of the rubber and increases flight times! So that is why the stick plane model flies so nicely.

Lets see the suggestions:


- Lighten the plane -OK
- Increase the amount of rubber - OK
- Lengthen the motor - OK
- Increase the prop diameter- Not possible at the moment, - where can I get mail order good props?
- Improve the airfoil - OK. A curve substantially increases lift - see foilsim


Right now weight is confirmed at 40 g +/- 5 g



Quote:
I'd suggest you play with something more like this folded "side and a half" style of airfoil made from card stock similar to that used for greeting cards

Thanks Bruce, will have to go with the curved airfoil and see.


What about launch technique? I used to launch it by giving a quick push, but decided that it would be better to move the model at flying speed and let go suddenly, without twisting or grabbing on to the model. How do you launch your models?
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Old Apr 07, 2011, 04:47 AM
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Yak 52's Avatar
UK
Joined Jan 2009
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Quote:
Originally Posted by knlever View Post
What is your latest model - any pictures? I would love to see it in flight.
It's a Keil Kraft Playboy, pics are in the 'Post your FF model Pics' thread, page 94, post #1410. It's not outstandingly light for a free flight model but it will do a minute... hopefully more when I have it fully sorted.


Quote:
Originally Posted by knlever View Post
I agree about the weight - there are lots of ways to reduced the weight, the most obvious is to build a long nosed model that does not require nose weight.
That's one of the reasons why scale is harder to do than a non-scale 'sport' model.

More important is to reduce structure to a minimum for strength. Especially in the tail of the plane.

You need to start thinking in terms of wingloading, not just weight. Bruce's suggestion of a bigger model is a good one because larger models can support a higher wingloading.

My Playboy has a wing area of 49 square inches (0.34sq.feet). The all up weight (including rubber) is about 23g (0.81oz).

So the wing loading is 0.47 grams per square inch or 2.4oz per square foot. (I can explain how to work this out more fully if it helps...)

So build something a little bigger and aim for 0.5 grams per square inch or 2.5oz per square foot... then you'll have a good flyer.


Quote:
Originally Posted by knlever View Post
It occured to be that stretching the rubber inside the fuselage, that is, the installation where the rubber is stretched, actually decreases the cross section of the rubber and increases flight times! So that is why the stick plane model flies so nicely.
Er... No. The motor is stretched when winding but when unwound is totally slack. You can increase the length of the (slack, unwound) motor up to 2 times the length of the 'prop hook to rear peg' distance. The longer the motor the more turns it will take, hence a longer motor run.


Quote:
Originally Posted by knlever View Post
...
- Increase the prop diameter- Not possible at the moment, - where can I get mail order good props?...
You can make pretty decent props from a plastic yoghurt pot...


Quote:
Originally Posted by knlever View Post
...What about launch technique? I used to launch it by giving a quick push, but decided that it would be better to move the model at flying speed and let go suddenly, without twisting or grabbing on to the model. How do you launch your models?
If you can decrease the weight, the stall speed (and therefore launch speed) gets slower. If your model is nice and light a small push will have it flying and climbing away out of your hand.

A heavy (or highly loaded) model will require a faster launch, so as you say, it gets a bit tricky to let go without disturbing the flight path. If you don't give it sufficient flight speed the model will stall or drop the nose until it reaches sufficient speed... but that obviously means a loss of height.


Jon
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