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Old Nov 29, 2012, 01:08 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
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Norm raises a good point that the very best low to medium height ceiling gliders are designed to suit the required launch height. When optimized to suit a given flying site the models are built down in weight and material sizes to where they are just a little bit away from being destroyed by the launch forces. Also the weight is only barely high enough to give them the momentum to reach the maximum useable launch hieght.

For example, that model I talked about above which was optimized for a 28 to 30 foot ceiling was taken down to a flying event in Seattle where I had around 45 feet of height to work with. I simply could not get the model to go much above 30 feet without resorting to a serious side arm launch where I know it would have peeled off the wings.

Unfortunetly learning how to build a model down to such a weight and still keep it strong enough is one of those things you need to do over time. It also basically comes down to a "make it lighter until it breaks" sort of deal. And if you're not flying often in this site then it's hard to spend enough time to go through that many models and building them down to the weights required with a suitable testing period.
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Old Nov 29, 2012, 10:11 PM
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Malaysia, Selangor, Serdang
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Quote:
I'm including a link to a very old, but excellent design for a 7+ meter ceiling. Note the wood dimensions, total weight and flight time. See: http://www.freewebs.com/halconesenel...eppette_16.jpg
Quote:
Norm raises a good point that the very best low to medium height ceiling gliders are designed to suit the required launch height. When optimized to suit a given flying site the models are built down in weight and material sizes to where they are just a little bit away from being destroyed by the launch forces. Also the weight is only barely high enough to give them the momentum to reach the maximum useable launch hieght.

For example, that model I talked about above which was optimized for a 28 to 30 foot ceiling was taken down to a flying event in Seattle where I had around 45 feet of height to work with. I simply could not get the model to go much above 30 feet without resorting to a serious side arm launch where I know it would have peeled off the wings.

Unfortunetly learning how to build a model down to such a weight and still keep it strong enough is one of those things you need to do over time. It also basically comes down to a "make it lighter until it breaks" sort of deal. And if you're not flying often in this site then it's hard to spend enough time to go through that many models and building them down to the weights required with a suitable testing period.
Yes, I realized it too after did the current model. For sure, I'm going to produce Sweppette as my next model. But, I would like to get some advice on building techniques with limited tools. Big problem that I'm facing is to sand the surfaces even especially when doing undercamber. Is there any techniques to produce almost same undercamber on both wings? And can I replace the balsa fuselage in the design with carbon fiber tube of same length, since I don't have balsa of 3/32"? The wing is located higher than horiz. stab. So, I would have to use pylon shaped wood over the CF tube. Or do you suggest any other models?

Thank you.

-Raj
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Old Nov 29, 2012, 11:54 PM
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Sweepette can be built with a minimum amount of tools. Sandpaper and a razor blade would be fine. I suspect a carbon tube would be too heavy. Note the total weight is 4 grams.

You might get away with laminating two pieces of wood and sanding to thickness. Apply glue very sparingly

The glider in my avatar is 12" in span and about 6 grams. Carbon tubes were considered, but way too heavy for a small glider.

The Sweepette wing is made from a flat sheet of 1/16 and the upper airfoil is sanded or razor planed to shape. The undercamber is formed by gently bending the in the shape. Once the dihedral is added, the wing will hold the undercambered shape.

Norm

Control of weight is very important. The Sweepette plan, like the Pelicatoo plan calls out the wood density before it is shaped.
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Old Nov 30, 2012, 12:24 AM
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Quote:
Originally Posted by Norm Furutani View Post
Sweepette can be built with a minimum amount of tools. Sandpaper and a razor blade would be fine. I suspect a carbon tube would be too heavy. Note the total weight is 4 grams.

You might get away with laminating two pieces of wood and sanding to thickness. Apply glue very sparingly.

The glider in my avatar is 12" in span and about 6 grams. Carbon tubes were considered, but way too heavy for a small glider.

The Sweepette wing is made from a flat sheet of 1/16 and the upper airfoil is sanded or razor planed to shape. The undercamber is formed by gently bending the in the shape. Once the dihedral is added, the wing will hold the undercambered shape.

Norm

Control of weight is very important. The Sweepette plan, like the Pelicatoo plan calls out the wood density before it is shaped.
Thank you, Mr.Norm. I'll do it as per suggested by you and will upload the pics here.
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Old Nov 30, 2012, 12:30 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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One option that folks with outdoor gliders have done is to sand down the wall thickness of the tube towards the tail. With axial style pultruded tube this requires a VERY light pressure as you get the tube down to a very thin wall.

The way to do it easily is with the tube in an electric hand drill and just fold the sandpaper around the tube and spin. Keep the sandpaper moving so as to ensure a reasonbaly consistent taper. Also in the end you'll want to varnish or lightly spread glue over the tube to re-lock the fiber ends.

The raised wing is nice to have but try it without the balsa pylon as well. You'll likely still want to glue a finger hold "shark's fin" under the wing so you have something more secure to hold onto. I would also wind a wrap of thread and glue around the nose of the tube so that the pultruded makeup doesn't try to split open due to nose impacts.
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Old Dec 05, 2012, 05:51 AM
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Sweepette 16 glider done

Hi! I've done the sweepette 16" glider. Started yesterday and finished today. I used medium C-grain 2mm balsa wood for the wings. Sanded it to 1.6mm to get the airfoil shown in the plan.

http://www.freewebs.com/halconesenel...eppette_16.jpg

Total weight of the model is 7g without noseweight added and nearly 10g when noseweight added to achieve 63% of CG as mentioned in plan. Exceeded the 4g as said in the model

Wing(glued dihedral): 4g
Both vert. hori. stabs : 1g
Fuselage: 2g
Ballast:3g

My weighing scale can measure up to 2kg with 1g sensitivity. Still haven't tested it yet for endurance. But, its gliding well

I did some modifications to the nose by adding heat shrink with some rubber(eraser) part stuffed into it. Later, I heated it slightly using lighter to make it shrink and hold tightly. It would function as damper or to protect the model from nose impacts


-Raj
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Old Dec 05, 2012, 07:48 AM
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The further forward you can put that nose weight, the less of it you'll need.
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Old Dec 05, 2012, 12:27 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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The read tubing and dome of clay makes it look like you tried to put a bird's head on the nose....

As you are finding it's not that easy to make an indoor model truly light. It calls for light contest grade wood for the wings and tail surfaces along with carefully selected medium hard wood to produce a light but resilient fuselage.

For best results the sheet stock first needs to be weighed to determine the density. For the wings and tail the closer you can get to 4 lb stock the better. From there I like to cut off a small test stick that is about 1/4 wide by 1 inch long and snap it. I'm looking for the long hard fiber content in the wood. The lighter stock typically does not have much fiber in it and it's not uncommon to see the break line straight across and so smooth that it's rather like you get when you snap a piece of glass. But when you find some wood which tends to snap with a jagged edge and has fibers sticking out which would interlock the joint you know you've got a good piece of wood.

For the fuselage I like to look for 12 to 15 lb stock then again test for the fiber content. The heavier wood will have more fibers than the light density stock but you can still compare test pieces from suitable sheets to find those which have a higher density of fiber in the wood. That's the stuff you want to use for the fuselage.

Also be sure that when you're cutting away the test pieces that you cut it from the same edge close to where you will cut the parts out. Often sheets tend to change charactaristics across the face. So it's important to test the part that you want to use.

Every little bit you can sand, thin or remove from the back will result in MUCH less nose weight being needed. It's also hard to avoid crashing the things too. And the typical damage was that the mass of the tail surfaces generally snapped the tail boom just in front of the tail area. When this happened instead of making the fuselage stick bigger I opted to sand the tail wood thinner and use lighter stock. The fin on these things can be almost paper thin without issue. And the stabilizer only needs a reasonable strength around the center area. I used to sand the wood down from the center out so that the center area was about .025 to .028 and it tapered out so the edges were about .010. The lighter surfaces results in less inertia during a "bad arrival" so the tail boom can flex instead of snap.

The fuselage stick was also sanded to remove excess wood. The 1/8 thick wood was sanded under the wing so it was more of a "V" shape with the belly being about 1/32 wide. The tail boom is also tapered as much as on can dare until they start snapping. Then the next model is built with the tai boom left a trifle more fat than the last one. Again it's all about saving those 10's of grams here and there where the wood isn't needed.

It would be nice if you can find access to a scale which resolves down to .1 or .2 grams. It's tough to work on such a model where 10's of grams are so important when the scale only resolves to the nearest gram.

The whole thing is that the lighter you make it the "stronger" it becomes. Well, not really. But the light weight reduces the dive speed and the light weight results in less harmful inertia when it does hit. In the end if it's light enough it needs less strength to survive.

You balance this with the need for strength and mass needed to reach the maximum useable height of the flying sight. It isn't any good to make a 4 gm model if it won't survive a full power launch. You won't win if you can't use the entire height provided.

Mating the model strength and weight to the flying site is a balance of all the factors you've seen up to now. I know it took me a good dozen or more models to find just the right combination for the 28 foot gym where I frequently flew. And that the resulting model was totally outclassed when I flew it in a 45 foot gym. Mind you I got lots of "ooooo's" and "ahhhh's" at the slow flying speed and low sink rate. But it simply wasn't even good enough to be in the running compared to the heavier models that used all the altitude they could get. So light is great but it's got to be just barely heavy and strong enough to still reach the highest point of the hall and still pull out neatly.
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Old Dec 06, 2012, 12:36 AM
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OK Raj- you're getting there!

Some observations from your pics. Looks like a your rudder is set for a lot of left turn. I think you could sand the surfaces more. Start with say, 180 grit to shape and taper the surfaces, then 320, 400, 600 grit. After 600, Lee would have flipped the 600 over and burnished the wood with the back of the sandpaper. Should be no fuzzies visible!

Some tips:
1. Check your progress by holding the part up to a light. It should be uniform along the edges.
2. Use a block with the sandpaper glued to it.
3. Sand away from the hand holding the part. If you sand towards the holding hand, you might crumple the part.
4. Cut the bottom of the rudder oversize so you have something to hang on to while sanding. Trim to size before gluing.

Trimming for flight: This glider was designed for a low ceiling, 30 feet. The flight pattern for a right hander is a slight left climb and left circling glide.

Did you offset the wing as per the plan? If no, try flying first.

If the rudder is actually straight, add a slight amount of left rudder to the bottom last 3/16 of the rudder. This is for launch trim!

For glide trim either add weight to the port tip or twist the fuselage so the port side of the stab is higher than starboard.

With a slight push, aiming for the floor across the room, you should get a gentle flat glide to the left.

If good, push a little harder with a slight left bank in your launch.

Report back with results!

- Norm
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Old Dec 06, 2012, 06:00 AM
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Hi! I've tested it today. Max time recorded was 19s for a short circle (since the hall is compact).

Actually I've modified the wing part shown in the plan. I've made 7.91" on the left and 8" on the right. I've made it to be right-right pattern because I'm more comfortable with it.

I launched it with full push & (slightly banked right),(10deg up) to a horizontal distance of 6 meters. It climbed up to 7 meters and started circling.

I tried the same launch technique for nearly 20 times and every time it made glide for 14-17 seconds consistently with initial radius approx: 5m and final radius: 2 or 3m.

The nose impact damper which I added to the glider, saved the glider when it bumped into walls and floor

Trims made:

1) lesser noseweight than shown in images. moved it to tip as adviced.
2) slightly right rudder
3) slightly warped up elevator

Thanks for your advices Will make a duplicate backup model of it.
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Old Dec 06, 2012, 09:14 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
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Quote:
Originally Posted by Norm Furutani View Post
.....Trimming for flight: This glider was designed for a low ceiling, 30 feet. The flight pattern for a right hander is a slight left climb and left circling glide......
I always saw low cieling gliders described as right-right for a right hand launch. And of course left-left for lefties. And certainly all my models did just fine with a right-right pattern from a right hand launch.

For 50 foot and higher I went back to right-left like an outdoor glider.

And then there's the difficulty in a right hander giving the model a left bank for the launch. So all in all I'd have to suggest that right turn and set it up for a more or less straight up or slight right bank and transition right wing low into a right hand glide.
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Old Dec 06, 2012, 10:11 PM
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Originally Posted by BMatthews View Post
I always saw low cieling gliders described as right-right for a right hand launch. And of course left-left for lefties. And certainly all my models did just fine with a right-right pattern from a right hand launch.

For 50 foot and higher I went back to right-left like an outdoor glider.

And then there's the difficulty in a right hander giving the model a left bank for the launch. So all in all I'd have to suggest that right turn and set it up for a more or less straight up or slight right bank and transition right wing low into a right hand glide.
Either direction is OK for a low ceiling launch, whatever is comfortable.

What we haven't discussed is the grip. The orig. low ceiling Sweepette was flown pinching the fuselage between the thumb and forefinger, left - left pattern.

Throwing to the left is easier for me, so much so that it's a problem I have with larger planes, I have a tendency to hook the launch to the left!

As you say, for higher ceilings the pattern became rt-lt, but the grip changed to a finger tab on the trailing edge and a right bank launch. Then there were right tab/left tab fliers.

- Norm
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Old Dec 07, 2012, 12:34 AM
B for Bruce
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Joined Oct 2002
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Pinching the fuselage is what I did with the low cieling stuff too. Including a couple of Sweepettes that I made. I still chose to go right-right though. Even though the launch for low cieling is an over the shoulder sort of thing rather than a side arm style like high cieling and outdoor.

I guess it really doesn't matter much if it's left-left or right-right as long as the model is setup with the offsets, angles and tilts needed for the turn pattern of choice.
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